microstructure and mechanical … and mechanical properties of epox ... labouratory using hounsfield...
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1
MICROSTRUCTURE AND MECHANICAL
PROPERTIES OF EPOXY – RICE HUSK ASH
COMPOSITE
BY
NNAJI, NDUBUISI BENNERTH
REG NO:PG/M.ENG/08/49185
DEPARTMENT OF MECHANICAL
ENGINEERING
UNIVERSITY OF NIGERIA, NSUKKA
SEPTEMBER, 2012.
i
TITLE PAGE
MICROSTRUCTURE AND MECHANICAL PROPERTIES OF EPOX
Y- RICE HUSK ASH COMPOSITE
BY
NNAJI, NDUBUISI BENNERTH.
REG NO:PG/M.ENG/08/49185
A PROJECT REPORT SUBMITTED TO THE DEPARTMENT OF
MECHANICAL ENGINEERING, FACULTY OF ENGINEERING,
UNIVERSITY OF NIGERIA, NSUKKA IN PARTIAL FULFILMENT
OF THE REQUIREMENTS FOR THE AWARD OF MASTER OF
ENGINEERING (M.ENG) DEGREE IN MECHANICAL
ENGINEERING WITH SPECIALIZATION IN MATERIALS
TECHNOLOGY AND MECHANICS.
SEPTEMBER, 2012.
ii
APPROVAL PAGE
This project report has been approved as meeting the requirements for
the award of Master of Engineering (M.Eng) Degree in Mechanical
Engineering with Specialization in Materials Technology and Mechanics,
University Of Nigeria, Nsukka.
By
. . . . . . . . .. . . . . . . . .. . . . . . .. . ….
Engr. Prof. D.O.N. Obikwelu Date
(Supervisor)
. . . . . . . . . . . . . . . . . . . . . . . . …..
Date
(Head of Department)
. . . . . . . . . . . . . . . . . . . . .
Dean of Faculty Date
. . . . . . . . . . . . . . . . . . . . . . . . ….
External Examiner Date
iii
CERTIFICATION
This is to certify that this project is an original work carried out by
Nnaji, Ndubuisi Bennerth with Registration No: PG/M.ENG/08/49185 in
partial fulfillment of the requirements for the award of Master of
Engineering degree in Mechanical Engineering with specialization in
Materials Technology and Mechanics.
………………………………
Engr. Prof. D.O.N Obikwelu
Project Supervisor
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DEDICATION
This project is dedicated to my late father.
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ACKNOWLEDGMENT
My profound gratitude is expressed to the Almighty God for giving me life,
knowledge and resources to complete this study.
I express my unalloyed regards, indebtedness and deep appreciation to my
project supervisor and all the lecturers in Mechanical Engineering Department
University of Nigeria Nsukka, for scholarly criticisms, meticulous teachings and
sagacious advice throughout the study.
The fervent support of my mother, brothers, sister and brother-in-law is
highly appreciated.
Thanks to the management of the following establishments; Sheda Science
and Technology Complex, Abuja; Standards Organization of Nigeria, Enugu;
National Root Crops Research Institute, Umudike; Strength of Materials
Laboratory, University of Nigeria, Nsukka and Polymer and Textile Engineering
Laboratory, Federal University of Technology, Owerri. The technical staff of the
establishments listed above provided the professional advice and characterization
machines that helped me to finish this research. I acknowledge the assistance
rendered to me by my friends and course mates.
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ABSTRACT
This study is about the production and characterization of epoxy-rice husk
ash composite. Composites were produced at 10%,20%,30%,40% and 50%
volume fraction of Rice Husk Ash(RHA) fillers and the epoxy was cast neat at
0%RHA which served as the control .The microstructure of the composites were
studied with Scanning Electron Microscopy(SEM) and Energy Dispersive X-ray
Spectroscopy(EDX).Mechanical properties of the composites such as tensile
properties(tensile stress, tensile strain, Young’s modulus, tensile strength and
percentage elongation at fracture),compressive strength, toughness, flexural
strength and hardness were experimentally determined in the engineering
labouratory using hounsfield (monsanto) tensometer, charpy v-notch impact
testing machine, flexural testing machine and Rockwell hardness testing machine.
The Scanning Electron Microscopy (SEM) analysis showed that interfacial
interactions existed between the rice husk ash particles and the epoxy matrix.
Energy Dispersive X-ray Spectroscopy (EDX) analysis indicated that interfacial
reactions existed between the epoxy matrix and the rice husk ash particles
because the composites did not contain homogenous elements. However each of
the composites contained C,O,Si and Cl while the cast neat epoxy(control)
contained C,O and Cl. Results of the mechanical property tests showed low gain
in hardness, toughness, flexural strength and Young’s modulus. The tensile
properties showed: that at 40%RHA the highest tensile strength of 37.006MPa was
obtained, the cast neat epoxy (control 0%RHA) had the best Young’s modulus of
356.538MPa and percentage elongation at fracture improved from 1.3% to 2.0%
as volume fraction of rice husk ash increased from 0% to 10%,20%,30%,40% and
50%.Increasing the volume fraction of rice husk ash from 0% to 10%,
20%,30%,40% and 50% led to decrease of these mechanical properties: toughness
from 2.0J to 0.3J,hardness from 344hardness value to 144 hardness value and
flexural strength from 6.0Mpa to 1.50Mpa.There was significant improvement in
the compressive strength of the composites from 15.75MPa to 18.75MPa as the
volume fraction of rice husk ash increased from 0% to 10%,20%,30%,40% and
50%.It was deduced from the study that epoxy-rice husk ash composite is
suitable for engineering applications subjected to compression. Surface coating of
rice husk ash could be used to improve its adhesion to the epoxy matrix in order
to enhance the mechanical properties of the composites for other engineering
applications.
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TABLE OF CONTENTS
Title Page - - - - - - - - - - i
Approval Page- - - - - - - - - ii
Certification - - - - - - - - - iii
Dedication - - - - - - - - - - iv
Acknowledgement - - - - - - - - - v
Abstract - - - - - - - - - vi
Table of Content - - - - - - - - vii
List of Figures - - - - - - - - x
List of Tables - - - - - - - - xiii
List of Plates - - - - - - - - - xv
CHAPTER ONE: INTRODUCTION
1.1 Background Information - - - - - - 1
1.2 Statement of the Problem - - - - - - 5
1.3 Objectives of the Study - - - - - - 6
1.4 Justification of the Study - - - - - - 7
1.5 Scope and Limitations of the Study - - - - - 7
CHAPTER TWO: LITERATURE REVIEW
2.1 Overview of Composites - - - - - - 9
2.2 Rice Husk Ash - - - - - - - - 14
2. 2.1 Industrial Applications of Rice Husk Ash - - - - 15
2.3 Epoxy - - - - - - - - - 16
2.3.1 Curing of Epoxy Resins - - - - - - 17
2.5.2 Engineering Applications of Epoxy - - - - 17
2.4 Compressive Strength - - - - - - 18
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2.5 Toughness - - - - - - - - 19
2.6 Flexural Strength - - - - - - - 19
2.7 Hardness - - - - - - - - 19
2.8 Tensile Properties - - - - - - - 20
2.8.1 Stress - - - - - - - - - 20
2.8.2 Strain - - - - - - - - - 20
2.8.3 Tensile Strength - - - - - - - 21
2.8.4 Young’s Modulus - - - - - - - 22
2.8.5 Elongation at Fracture - - - - - - 22
2.9 Scanning Electron Microscopy - - - - - 23
2.9.1 Components of a Scanning Electron Microscope - - 25
2.10 Energy Dispersive X-Ray Spectroscopy - - - - 26
2.10.1 Applications of Scanning Electron Microscopy – Energy Dispersive
X-Ray Spectroscopy Analysis - - - - - 29
2.11 Microstructure - - - - - - - - 30
2.12 Adhesion and Cohesion - - - - - - 31
2.13 Calculation of Fiber Volume Fraction - - - - 32
CHAPTER THREE: MATERIALS AND METHODS
3.1 Materials - - - - - - - - - 33
3.1.1 Matrix Material - - - - - - - 33
3.1.2 Filler Material - - - - - - - - 33
3.2.0 Methods - - - - - - - - 34
3.2.1 Preparation of Composite Mould - - - - - 34
3.2.2 Composite Fabrication - - - - - - 35
3.3 Mechanical Property Tests - - - - - - 37
3.3.1 Tensile Testing of Composite Samples - - - - 37
3.3.2 Compressive Strength Test - - - - - - 38
3.3.3 Toughness Test - - - - - - - 38
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3.3.4 Hardness Test - - - - - - - - 39
3.3.5 Flexural Strength Test - - - - - - 39
3.4 Scanning Electron Microscopy and Energy Dispersive X- Ray
Spectroscopy Analysis - - - - - 40
CHAPTER FOUR: RESULTS AND DISCUSSION
4.1 Results - - - - - - - - - 42
4.1a Results for Mechanical Properties - - - - - 43
4.1b Results of Scanning Electron Microscopy Analysis - - 53
4.1c Results of the Energy Dispersive X-Ray Spectroscopy Analysis 61
4.2 Discussion of Results - - - - - - - 70
4.2.1 Mechanical Properties - - - - - - 70
4.2.1a Tensile Properties - - - - - - - 70
4.2.1b Toughness - - - - - - -- - 72
4.2.1c Hardness - - - - - - - - 73
4.2.1d Flexural Strength - - - - - - - 73
4.2.1e Compressive Strength - - - - - - 73
4.2.2 Scanning Electron Microscopy Analysis - - - - 74
4.2.3 Energy Dispersive X-Ray Spectroscopy Analysis - - 76
CHAPTER FIVE: CONCLUSION AND RECOMMENDATIONS
5.1 Conclusion - - - - - - - 78
5.2 Recommendations - - - - - - - 79
References - - - - - - - - - 80
Appendix I- - - - - - - - - - 85
Appendix II - - - - - - - - - 86
Appendix III - - - - - - - - - 87
Appendix IV - - - - - - - - - 88
Appendix V - - - - - - - - - - 91
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LIST OF FIGURES
Figure 2.1: Reaction and structure of a typical epoxy resin - - 17
Figure. 2.2 Stress and strain curve - - - - - 21
Figure 2.3: SEM column and specimen chamber - - - 25
Figure 2.4: EDS spectrum of the mineral crust of Rimicaris exoculta 28
Figure 2.5: Energy transitions during EDX analysis - - - 28
Figure 3.1 Mold - - - - - - - - 34
Figure 4.1 Stress- strain graph for cast neat epoxy - - - 48
Figure 4.2 Stress-strain graph for epoxy – rice
husk ash composite (90%epoxy 10%rice husk ash) - - - 48
Figure 4.3 Stress-strain graph for epoxy-rice husk ash composite
(80%epoxy 20%rice husk ash) - - - - - 49
Figure 4.4 Stress-strain graph for epoxy – rice husk ash composite
(70%epoxy 30% rice husk ash) - - - - - 49
Figure 4.5 Stress-strain graph for epoxy- rice husk ash composite
(60%epoxy 40% rice husk ash) - - - - - 50
Figure 4.6 Stress-strain graph for epoxy- rice husk ash composite
(50% epoxy 50% rice husk ash) - - - - - 50
Figure 4.7 Tensile strength - %RHA graph - - - - 50
Figure 4.8 Young’s modulus - %RHA graph - - - - 51
Figure 4.9 Elongation at fracture - %RHA graph - - - 51
Figure 4.10 Energy absorbed (toughness) - %RHA graph - - 51
Figure 4.11 Hardness value - %RHA graph - - - - 52
Figure 4. 12 Flexural strength - %RHA graph - - - - 52
Figure 4.13 Compressive strength - %RHA graph - - - 52
Figure 4.14 Scanning electron micrograph of Adani rice husk ash at
200x magnification - - - - - - - 53
Figure 4.15 Scanning electron micrograph of Adani rice husk ash at
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2000x magnification - - - - - - 54
Figure 4.16 Scanning electron micrograph of cast neat epoxy at 200x
magnification - - - - - - - 54
Figure 4.17 Scanning electron micrograph of cast neat epoxy at
2000x magnification - - - - - - - 55
Figure 4.18 Scanning electron micrograph of epoxy –rice husk ash composite
containing 10% rice husk ash at 200x magnification - - - 55
Figure 4.19 Scanning electron micrograph of epoxy- rice husk ash composite
containing 10% rice husk ash at 2000x magnification. - - - 56
Figure 4.20 Scanning electron micrograph of epoxy – rice husk ash composite
containing 20% rice husk ash at 200x magnification - - - 56
Figure 4.21 Scanning electron micrograph of epoxy – rice husk ash composite
containing 20% rice husk ash at 2000x magnification - - - 57
Figure 4.22 Scanning electron micrograph of epoxy – rice husk ash composite
containing 30% rice husk ash at 200x magnification - - - 57
Figure 4.23 Scanning electron micrograph of epoxy – rice husk ash composite
containing 30% rice husk ash at 2000x magnification - - 58
Figure 4.24 Scanning electron micrograph of epoxy-rice husk ash composite
containing 40% rice husk ash at 200x magnification - - - 58
Figure 4.25 Scanning electron micrograph of epoxy-rice husk ash composite
containing 40% rice husk ash composite at 2000x magnification - 59
Figure 4.26 Scanning electron micrograph of epoxy –rice husk ash composite
containing 50% rice husk ash at 200x magnification. - - - 59
Figure 4.27 Scanning electron micrograph of epoxy- rice husk ash composite
containing 50% rice husk ash at 2000x magnification. - - - 60
Figure 4.28 EDX spectrum of cast neat epoxy - - - - 61
Fig 4.29 Quantitative results for cast neat epoxy - - - 62
Figure 4.30 EDX spectrum of epoxy- rice husk ash composite (90% Epoxy,
10% RHA) - - - - - - - - 63
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Figure 4.31 Quantitative results for epoxy – rice husk ash composite
(90% Epoxy 10% RHA) - - - - - - - 64
Figure 4.32 EDX spectrum of epoxy- rice husk ash composite
(80% Epoxy, 20% RHA) - - - - - - - 64
Figure 4.33 Quantitative results for epoxy – rice husk ash composite
(80%Epoxy 20%RHA) - - - - - - - 65
Figure 4.34 EDX spectrum of epoxy – rice husk ash composite (70%
Epoxy, 30% RHA) - - - - - - - - 66
Figure 4.35 Quantitative results for epoxy –rice husk ash composite
(70%Epoxy 30%RHA) - - - - - - - 67
Figure 4.36 EDX spectrum of epoxy rice husk ash composite
(60% Epoxy, 40% RHA) - - - - - - - 67
Figure 4.37 Quantitative results of epoxy –rice husk ash composite
(60%Epoxy 40%RHA) - - - - - - - 68
Figure 4.38 EDX spectrum of epoxy- rice husk ash composite (50% Epoxy,
50% RHA) - - - - - - - - - 69
Figure 4.39 Quantitative results for epoxy – rice husk ash composite
(50%Epoxy 50%RHA) - - - - - - - 70
xiii
LIST OF TABLES
Table 3.1a Chemical com position of the rice husk ash used for the study. 34
Table 3.1b Composition of the composites - - - 36
Table 3.1c Dimensions of specimen for different mechanical property
tests - - - - - - - - - 36
Table 4.1: Load, Extension, Stress, Strain Values For Cast Neat Epoxy
(100% Epoxy 0% RHA,) - - - - - - 43
Table 4.2: Load, Extension, Stress, Strain Values For
Epoxy-Rice Husk Ash Composite (90% Epoxy 10% RHA) - - 43
Table 4.3: Load, Extension, Stress, Strain Values For
Epoxy-Rice Husk Ash Composite (80% Epoxy 20% RHA ) - - 44
Table 4.4: Load, Extension, Stress, Strain Values For
Epoxy-Rice Husk Ash Composite (70% Epoxy 30% RHA) - 44
Table 4.5: Load, Extension, Stress, Strain Values For
Epoxy-Rice Husk Ash Composite ( 60% Epoxy 40% RHA) - - 45
Table 4.6: Load, Extension, Stress, Strain Values For
Epoxy-Rice Husk Ash Composite (50% Epoxy 50% RHA) - - 45
Table 4.7 Tensile Strength - - - - - - 45
Table 4.8: Young’s Modulus - - - - - - 46
Table 4.9: % Elongation at Fracture - - - - - 46
Table 4.10: Toughness Test Result - - - - - 46
Table 4.11: Hardness Test Result (Rockwell) - - - - 46
Table 4.12: Flexural Strength Test Result - - - - 47
Table 4.13: Compressive Strength Test Result - - - - 47
Table 4.14 Elemental composition of cast neat epoxy - - - 61
Table 4.15 Elemental composition of epoxy- rice husk ash composite
(90% epoxy 10% RHA) - - - - - - - 63
Table 4.16 Elemental composition epoxy-rice husk ash composite
(80%Epoxy 20%RHA) - - - - - - - 65
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Table 4.17: Elemental composition of epoxy –rice husk ash
composite (70%Epoxy30% RHA) - - - - - 66
Table 4.18 Elemental composition of epoxy –rice husk ash composite
(60%Epoxy 30%RHA) - - - - - - - 68
Table 4.19 Elemental composition of epoxy – rice husk ash composite
(50%Epoxy 50%RHA) - - - - - - - 69
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LIST OF PLATES
Plate 1: Rice husks piles being burnt in rice Mills - - - 87
Plate 2: Close-up of burning rice husk - - - - - 87
Plate 3: Rice husk ash - - - - - - - 87
Plate 4 Mixing of the epoxy - - - - - - 88
Plate 5: Curing of the composites- - - - - - 88
Plate 6: Hardness test specimen - - - - - - 89
Plate 7 Tensile test specimen - - - - - - 89
Plate 8: Cast composites. - - - - - - - 90
Plate 9: Compressive test specimen - - - - - 90
Plate 10: Hounsfield Tensometer - - - - - - 91
Plate11: Charpy impact testing machine - - - - - 92
Plate 12: Rockwell hardness tester - - - - - - 94
Plate 13: Flexural testing machine - - - - - 94
Plate 14: Carl Zee’s Scanning electron microscope - - - 95
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1
CHAPTER ONE
INTRODUCTION
1.1 Background Information
Most times engineers are faced with the task of developing a new material that
has light weight, low cost and good mechanical properties. A promising option to
this task is to use a low density particulate material like rice husk ash in a polymer
matrix to form a polymer composite. Rice husk ash is a by-product of combustion
of rice husk at rice mills (Zemke and Woods, 2008). Researchers are currently
investigating the use of ash for composite production since ash is an abundant
agricultural waste, is renewable and has low bulk density. Rice husk ash had
been applied in other areas like manufacturing insulating powder, production of
refractory bricks, cement production and sandcrete block production. However
there are limited applications of rice husk ash in composite production.
A composite material is a microscopic or macroscopic combination of two
or more distinct materials with a recognizable interface between them. In a
composite material the constituents do not dissolve or merge completely in one
another. Normally the components in a composite material can be physically
identified and they exhibit interface between one another. A particulate composite
consists of a matrix reinforced with a dispersed phase in form of particles. Soft
particles like coir dust, rice husk flour, baggase ash, sawdust and rice husk ash can
be dispersed in a harder matrix to improve machinability and reduce coefficient of
friction (Lake,2002;Jiquao et al, 2010)
1
2
One advantage of a composite is that two or more materials could be combined to
take advantage of the good characteristics of each of them.
Composites are gaining a wide range of applications in engineering because of the
following advantages: weight savings, corrosion resistance, easy manufacturing,
low temperature processing, possibility of producing novel shapes, reduced parts
and long fatigue life (Nowosielki et al, 2006;Ranganathatiah,2010).
Composites can be made of two or more components, the matrix and the
dispersed phase. The properties of a composite material depend on the following :
properties of the matrix; properties and distribution of reinforcement, nature of
bonding at the interface and volume fractions occupied by the constituents (Lake,
2002).
A matrix is a material in which the reinforcements or other components of a
composite system are embedded. It can be made of metal, ceramic or polymer
(Askeland, 1994). The purpose of the matrix is to bind the reinforcements together
by virtue of its cohesive and adhesive characteristics, to transfer load to and
between the reinforcements and to protect the reinforcements from environment
and handling. The matrix is often the weak link in a composite when viewed from
a structural perspective. Chemical treatment of reinforcement materials or filler
increase interfacial adhesion between the matrix and fillers leading to better
mechanical properties of the composites (Gauthier et al, 1998). It is in view of
these expected roles of matrix materials that epoxy resin was used in this study.
3
A polymer matrix composite is a composite formed by the combination of a
polymer (resin) matrix and a fibrous reinforcing phase (Ezuanmustapha et al,
2005). Polymer composites are gaining importance as substitute for metals in
applications in the aerospace, automotive, marine, sporting goods and electronics
industries due to their light weight and corrosion resistance. Polymer matrix can
be classified as thermoplastics and thermo set. Thermoplastics include low density
polyethylene, high density polyethylene, nylon, polypropylene and polyester while
epoxy resin is an example of a thermo set.
Epoxy resin is currently of much research interest due to its superior properties
over polyester resin. Some of the properties of the epoxy resin identified by
researchers are low cure shrinkage, better resistance to moisture, better
mechanical properties, processing flexibility and better handling.
Epoxy resins are presently used more than all other matrices in advanced
composite materials for structural applications in the United States of
America(USA) Air Force and Navy. The dispersed phase of a composite refers to
the reinforcement or fillers added in the matrix and the role of reinforcement in
a composite material is to increase the mechanical properties of the neat resin
system (Askeland, 1994).
Filler materials are generally the inert materials which are used in composite
materials to reduce cost, absorb thermal stresses, improve mechanical properties
to some extent and in some cases to improve processing (Singla and Chawla,
2010). Fillers which increase bulk volume and hence reduce cost are known as
4
extender fillers while those that improve mechanical properties particularly tensile
strength are termed reinforcing fillers (Igwe and Onuegbu, 2010).
Many researchers like Suwanprateeb and Hathapamit(2002), Zemke and
Woods(2009) are optimistic to find out whether rice husk ash is a reinforcing
filler or an extender filler. The current challenge is to make composite production
cost effective and this has resulted to high filler loadings. An interface is the
boundary between the individual, physically distinguishable constituents of a
composite. It is the bonding surface or zone where discontinuity occurs. Interface
must be large and exhibit strong adhesion between the fibers and the matrix.
Wetting occurs at the interface and its failure at the interface is called debonding
which may or may not be desirable. Interfacial bonding is a bonding type in
which the surfaces of two bodies in contact with one another are held together by
intermolecular forces like covalent, ionic, vanderwaals and hydrogen bonds.
Interfaces have been identified as zones where compositional, structural and
mechanical properties are altered in composites. Mechanical properties are
properties of a material that are associated with elastic and inelastic reaction when
force is applied or the properties involving relationship between stress and
strain(Royalance, 2008).
Microstructure is the microscopic description of individual constituents of
a material. Microstructure studies of composites show what happens at the atomic
and microscopic levels of the interface.
5
Electron microscopy analysis is used to characterize the microstructure of
composites. Scanning electron microscopy shows the morphology and topography
of the composites while compositional analysis is conducted using energy
dispersive x-ray spectroscopy. Energy dispersive x-ray spectroscopy is a chemical
microanalytical technique used in conjunction with scanning electron microscopy
to determine the elements in the microstructure of a material.
1.2 Statement of the Problem
Most developing countries like Nigeria are not yet properly utilizing
agricultural wastes such as rice husk ash for gainful engineering production. Rice
husk ash constitutes environmental pollution and causes health hazards like
silicosis, cancer, tuberculosis, chronic cough and sight disorder in areas where it is
dumped. Therefore there is need to develop more ways of reducing the amount of
the waste in the environment. One of the easiest ways of solving the problem is to
rice husk ash as filler in epoxy matrix to form epoxy-rice husk ash composite.
Epoxy based composites can be used in producing sole of shoes, side stools ,slabs,
industrial flooring and other components for electrical and industrial engineering.
Material engineers are facing the problem of developing materials that have
low cost, light weight and enhanced mechanical properties for executing
construction works. Metals which have good strength are insidiously affected by
corrosion and heavy weight making the search for alternative materials like epoxy
based composites that can be substituted for metals in some engineering
6
applications inevitable. Particle filled composites are gaining wide research
interest due to the problem of delamination and fiber pullout associated with
fibrous composites. The behavior of epoxy resins have not been fully understood
by researchers especially its slow curing character. Microstructural study of the
effect of interfacial adhesions between particle and matrix is fundamental in
understanding mechanical behavior of polymer composites.
1.3 Objectives of the Study
The general objective of this project is to characterize composite materials
produced from different compositions of epoxy and rice husk ash. The specific
objectives of the study are:
1. To produce epoxy-rice husk ash composite using rice husk ash considered as
an agricultural waste as a filler.
2. To conduct scanning electron microscopy and energy dispersive x-ray
spectroscopy analysis on epoxy –rice husk ash composite and study the
effect of variation of rice husk ash volume fractions on the microstructure.
3. To carry out scanning electron microscopy on Adani Rice husk ash.
4. To examine the effect of rice husk ash volume fraction on some mechanical
properties of epoxy- rice husk ash composite and ascertain the suitability of
the composite for engineering applications.
1.4 Justification of the Study
7
This study is valuable in understanding the potentials of rice husk ash as
filler in composite production and the behavior of Epoxy resins. The study is
useful to engineers and researchers in the composite industry because it will help
to suggest ways of improving the mechanical properties of the epoxy-rice husk ash
composite. Composite production can offer employment opportunity to
unemployed youths due to low energy and machinery requirements for
production. The knowledge of microstructure and mechanical properties of
particle filled composites is vital in describing the behaviours at the interface and
the effect of forces on the composites. Proper understanding of the microstructure
and mechanical properties of composites will help to ascertain the engineering
application of composite in structures, industries, electronics, oil and gas, and
other industrial production.
1.5 Scope and Limitations of the Study
Experimental approach was used in this study involving composite
production, microstructural analysis using scanning electron microscopy and
energy dispersive x-ray spectroscopy as well as the determination of the
mechanical properties of the composite material. The composites were produced at
0%, 10%, 20%, 30% 40% and 50% volume fraction of rice husk ash fillers. The
rice husk used in the study was sourced from Adani rice mill, Enugu State,
Nigeria. Apart from production of the amorphous rice husk ash at 550oC
all other
experiments were done at room temperature. In order to adequately view the
8
particle and matrix interfacial interactions two magnifications of 200x and 2000x
were used for the scanning electron microscopy analysis. Lack of accessibility to
transmission electron microscope hindered possibility of investigating other
microstructural features. Other limitations faced in the research were sourcing the
epoxy resin and getting the characterization equipment.
9
CHAPTER TWO
LITERATURE REVIEW
2.1 Overview of Composites
The encyclopedia of life support defined composite material as a
multiphase material in which the phase distribution and geometry have been
controlled in order to optimize one or more properties. The intention of producing
a composite material is to make a material that combines the best properties of the
components whilst eliminating any poor properties. Composites are also materials
that comprise strong load carrying materials known as reinforcement embedded in
a weaker material known as matrix (Askeland, 1994).
Reinforcement provides strength and rigidity, helping to support structural
load. The matrix or binder (organic or inorganic) maintains the position and
orientation of the reinforcement.
The use of composites started many centuries ago. The Book of Exodus in
the Christian Bible recorded that straws were used to produce rigidity and strength
in mud walls. Historical examples include the use of bamboos as a reinforcing
material in mud walls in houses by Egyptians (15000BC) and laminated metals in
the forging of swords (1800AD). In the 20th
century, modern composites were
used in the 1930’s, where glass fibers reinforced resins. Boats and aircrafts were
built out of these glass composites commonly called fiberglass (wikipedia.org.
composite materials).
9
10
Since the 1970’s the application of composite materials has widely
increased due to development of new fibers such as carbon, boron and aramids and
new composite systems with matrices made of metal and ceramics.
Singla and Chawla (2010) produced epoxy-fly ash composites at high filler
loading using fly wheel ash particles. They found that as the Fly wheel ash
particles loading increased the compressive strength of the composites increased
while the impact strength reduced. Kulkurni and Krishore (2003) studied the
mechanical properties of fiber epoxy composites. The result of the study showed
that the addition of fly ash particles to epoxy matrix led to reduction of the density
and increase in the modulus of the composites. According to Cattaleeya et al
(2008) rice husk ash is not considered good reinforcing filler in rubber composites
due to the large particle size and low reactive functional group at the filler surface.
The reinforcing effect of rice husk ash is not as good as silica and carbon black,
but is only comparable to calcium carbonate (CaCO3). Cattaleeya et al were of the
view that chemical surface treatment of rice husk ash prepared under special
condition is effective in reinforcement only at low filler loading.
Hathapamit (2003) compared the suitability of silica particles and rice husk
ash particles for embedding composites in electronic devices. In his study he
found that silica filled epoxy composites had better tensile strength than the rice
husk ash filled epoxy composites but the mixing viscosity, water absorption and
coefficient of thermal expansion were better than the silica filled composites.
Osureminda and Abode (2010) reinforced rubber products with baggase ash fillers
11
and succeeded in improving the tensile strength, abrasion resistance and hardness
of rubber composites with increasing filler loading while the elongation at break
and compressive strength decreased.
According to Hanseung et al (2008) rice husk floor is not good reinforcing
filler for polymer composites but can be utilized as biodegradable filler in
polymeric materials to minimize environmental pollution. They found from the
study of mechanical properties of polypropylene composites that addition of rice
husk flour decreased the mechanical properties of the composites due to poor
interfacial bonding between the matrix and the filler and holes formed in the
microstructures because of pulling of filler particles in the matrix.
Ahmadi et al (2007) found that replacement of cement with rice husk ash
up to 20% volume in the matrix will improve the mechanical properties of the
concrete. The researchers posited that using pozzolans like rice husk ash will
reduce the utilization of cement and lower the cost of buildings.
Yunfu et al (2008) were of the view that particle size, particle matrix
interface adhesion and particle loading affect mechanical properties of
composites. They found that introduction of rigid fillers like Al2O3, glass, CaCo3
into epoxy matrix normally result to decrease in mechanical properties. Yunfu et
al further stated that coupling agents should be used in filler composites to
improve adhesion and that tensile modulus is not affected by adhesion but by
filler loading. The researchers found that using nano fillers increased the stiffness
of composites.
12
The findings of Sapuan et al (2005) showed that fiber treatment improved
interfacial bonding between fiber and epoxy matrix and led to better mechanical
properties of the spathe-fibre reinforced composite laminates.
Arukalam and Madufor (2011) studied the effect of filler loading on some
mechanical properties of calcite-filled low density polyethylene composite. They
found that as the filler loading increased tensile strength, tensile modulus and
elongation at break (ductility) of the composites reduced. There were gains in
hardness of the composites because calcite obtained from snail shell is harder than
the low density polyethylene matrix. Srinavasa and Bharath (2011) investigated
the hardness and impact properties of Areca fiber epoxy-reinforced composites.
They treated areca fibers extracted from areca husk with potassium hydroxide to
get better interfacial bonding between the fiber and the epoxy matrix. Mechanical
properties of the composites increased as the fiber volume fraction and composite
post curing time increased. They concluded that mechanical properties of fiber
reinforced composites depend on the nature of matrix material, the distribution and
orientation of reinforcing fibers and the nature of the fiber matrix interfaces and
interphase region.
According to Srinavasa and Bharath, Arecafiber – epoxy reinforced
composite is a good material in fabrication of lightweight materials used in
automobile body building, office furniture, packaging industry and partition panel.
Egwaikhade et al (2007) developed rubber composites using palm kernel
shell husk. The study proved that palm kernel husk is a potential filler for natural
13
rubber compounds because addition of palm kernel shell husk fillers improved
some mechanical properties.
Due to the continuous decrease of mechanical properties at higher filler
loadings associated with untreated fibers and fillers most researchers have
advocated the coating of fillers with coupling agents. According to the report from
handbook of USA Department of Defense (2002) coupling agents are substances
that are used in small quantities to treat a surface so that bonding occurs between it
and other surfaces. Coupling agents include bonding agents and surfactants
(surface reactive agents), compatibilizers and dispersing agents. Organic coupling
agents produce stronger adhesion and include isocyanides, anhydrides, silanes
and anhydride modified co-polymers.
Gauthier et al (1998) reported that adhesion can be improved using
coupling agents like maleic anhydride to incorporate hydroxyl groups on the
matrix through hydrophilization and consequently enhancing wetting effect of the
resin on the fillers.
Ranganathatiah(2010) did a comparative study of mechanical properties of
composites formed from epoxy matrix modified with amine containing silicone
and unmodified epoxy matrix using fly ash and calcium aluminosilicate as fillers.
He discovered that the fillers interacted favorably with the modified matrix and
mechanical properties were improved at higher loads.
Ezuanmustapha et al (2005) incorporated 4wt% of a coupling agent matrix
anhydride modified polypropylene into composites prepared with rice husk and
14
polypropylene matrix. It was observed that the addition of MAPP coupling agent
increased the flexural strength of the composites but decreased the flexural
modulus and impact strength. Razman etal(2003) studied the effect of chemical
modification of rice husk and reports that with chemical modification the
reinforcing effect can be increased to an acceptable limit.
2.2 Rice Husk Ash
Rice husk is an agricultural by product from the rice mill. It constitutes
about 20% of the weight of rice. Rice husk contains about 50% cellulose, 25%-30
lignin and 15-20% silica (Abubaker et al, 2010). Rice husk ash is the general term
used to describe all the types of ash produced from burning rice husk (Zemke,
2009). If the burning process is incomplete carbonized rice husk is produced. At a
burning temperature range of 550oC to 800
oC armorphous ash that is black in
colour is produced while at higher temperatures crystalline ash having grey to
white colour is produced (Bronzeoak limited, 2003). The nature and composition
of the ash produced by burning rice husk depend on the burning temperature, the
soil chemistry, paddy variety, climatic conditions and the type of fertilizer used in
growing the rice (Bronzeoak, 2003: Abubaker et al, 2010). The properties of rice
husk ash are low bulk density, porous morphology, good insulator, high meeting
point, light weight and high pozzolannic activity (Basha et al, 2005; Della et al,
2002). Major compounds from rice husk ash are silica and cellulose which yield
carbon when thermally decomposed (Omatora et al, 2009). Rice husk ash has
15
constituted serious environmental pollution in growing countries like India,
Thailand, Malaysia, Argentina (Bronzeoak, 2003).
2. 2.1 Industrial Applications of Rice Husk Ash
1. Rice husk ash is used as a suitable additive in foundry sands for mold
production and as a binder due to its high melting point and good compressive
strength (Aigbodion et al, 2005).
2. Idenyi and Ani (2005) found that Abakaliki rice husk ash is suitable for
making cement and as an additive in clays for refractory bricks production.
3. Rice husk ash can is used for making low sandcrete blocks applied in building
houses (Oyetola and Abdullahi, 2010).
4. The Indian space research organization has successfully developed a
technology for producing high purity precipitated silica from rice husk ash and
this has a potential use in the computer industry (Omatora and Onoja, 2009).
Many American and British scientists have also developed ways to extract and
purify silicon from rice husk ash with the aim of using it in semi conductor
manufacture (Omatora and Onojah, 2009).
The silica from rice husk ash can is used for silicon chip manufacture used
in electronics (Bronzeoak, 2003).
5. Other useful applications of rice husk ash are: as a filler in rubber industry,
cleansing agent in toothpaste, building materials, in stabilization of soil for
farming, controlling insects and pest in farm, in steel industry, as an oil spill
absorbent, in making activated carbon used for water purification and in
16
improving corrosion resistance of steel pipes and concrete (Basha et al, 2005;
Bronzeoak, 2003 and Zemke, 2009).
2.3 Epoxy
Epoxy is also known as polyepoxide. It is a thermosetting polymer formed
from the reaction of an epoxide resin with a polyamine hardener. Epoxy is a
copolymer because it is formed from two different chemicals referred to as resin
and hardener (wikipedia.org.epoxy).
An epoxy resin contains oxirane or ethoxyline groups. Epoxy resins are
mostly produced by the reaction between bisphenol A with epichlorohydrin in the
presence of a basic catalyst (Sunilbhangle.tripod.com).
Examples of commercial epoxy resins are diglycidylether of bisphenol A
(DGEBA),glycidylethers of novolac resins and phenoxy epoxy resin. Properties of
epoxy resins are: low viscousity, low shrinkage, low glass transition temperature,
low shrinkage ,good adhesion to other materials ,good chemical and
environmental resistance, good insulating properties, ability to be processed under
variety conditions and good mechanical properties(May ,1988;Singla and
Chawla;2010 and Turner,2007). The structure and reaction of a typical epoxy
resin is shown in figure 2.1.
17
Figure 2.1: Reaction and structure of a typical epoxy resin diglycidylether of
bisphenol A, n is the degree of polymerization and ranges from 0 to 25.
2.3.1 Curing of Epoxy Resins
Curing process is a chemical reaction in which the epoxide groups in epoxy
resins react with curing hardener in order to convert epoxy resin into a hard,
infusible and rigid material (sunizbhangle.tripod.com).
Curing process normally involves an exothermic reaction. Epoxy resin cure
quickly and easily at practically any temperature from 5 – 150oC depending on the
choice of curing agent. Curing agents are amines, polyamides, phenolic resins,
anhydrides and isocyanates (pascault and Williams, 2010).
2.3.2 Engineering Applications of Epoxy
Epoxy resins were first commercialized in 1946 and are widely used in
industry in the following areas:
1) Protective coatings: Epoxy resins can be applied in corrosion protection of
steel pipes and fittings used in oil and gas industry (wikipedia.org.Epoxy).
18
2) Structural applications: Epoxy has been applied in the production of
composites, molds, industrial tools, laminates, casings, fixtures, automobile
bumper and other industrial production aids (wikipedia.org.Epoxy).
3) Electrical systems and electronics: Epoxy has excellent insulating abilities
that protect electrical components from short circuiting, dust and moisture.
This has resulted to usage in motors, generators, transformers, switch gear
and insulators. It is equally used in making integrated circuits, hybrid
circuits and printed circuit boards (wikipedia.org.Epoxy).
4) Singla and Chawla (2009) reported that epoxy can be applied in production
of military aircraft and commercial aircraft.
5) Consumer and Marine Applications: Epoxy is suitable for production of
shoe, furniture, boats and ship component. (wikipedia.org.Epoxy).
6) Adhesives: Epoxy adhesives are used for construction of aircrafts, bicycles,
golf clubs, snow board and other applications were high strength bond is
required (sunilbhangle tripod.com: wikipedia.org.Epoxy).
2.4 Compressive Strength (MPa)
Compressive strength is the capacity of a material or structure to withstand
axially directed pushing forces (wikipedia.org.compressive strength).
Compressive test determines the behaviour of materials under crushing loads.
When the limit of compressive strength is reached the materials fail completely. In
19
compression the molecules of atoms are forced together. Brittle materials are
stronger in compression than in tension (Onwuka, 2001).
Maximum Compressive Force (2.1)
Area
2.5 Toughness (J)
According to Roylance (2008), toughness is the ability of a material to
absorb energy before actual failure or fracture occurs. The higher the energy
absorbed by a material the higher the toughness of the material. Toughness can be
determined by performing an impact test with Charpy or Izod impact testing
machine or calculating the area under the stress/strain curve. Toughness indicates
how much energy a material can absorb before rupturing.
2.6 Flexural Strength (MPa)
Flexural strength is the ability of an engineering material to resist bending
or twisting under load (wikipedia.org.flexural strength). It is known as modulus of
rupture, bend strength or fracture strength.
Flexural strength is a mechanical parameter for brittle materials. Flexural
strength represents the highest stress experienced within the material at its moment
of rupture (Hogkinson, 2000).
2.7 Hardness
Hardness is the resistance of a material to localized plastic deformation; it
indicates wear resistance and resistance to scratching, abrasion and indentation
Compressive strength =
20
(Askeland, 1994). Hardness testing can be done with Rockwell, Vickers, Brinell
sclerescope, durometer, rebound and barcol hardness tester.
2.8 Tensile Properties
According to Liu (1999) tensile properties indicate how materials will react
to forces applied on tension. Tensile properties are determined by performing a
tensile test. Tensile test is a simple uniaxial test that consists of slowly pulling a
sample of material in tension until it breaks. These properties can be found from a
tensile test: modulus of elasticity, elongation at break, tensile strength, tensile
stress and tensile strain.
2.8.1 Stress (MPa)
Tensile stress of the material is defined as the force per unit area as the
material is stretched (Liu, 1999). The area used in finding tensile stress is the
original under formed cross sectional area because the cross sectional area of a
material may change if the material deforms on stretching.
Tensile stress (δ) = A
P=
Area nalcrossectio Original
forceor Load (2.2)
2.8.2 Strain
According to Onwuka (2001) Strain is the non dimensional measure of
deformation of a material with respect to a given length dimension of that
material. Tensile strain or engineering strain is the change in length of a sample of
material divided by the original length or gauge length of the sample. Strain can be
represented thus,
21
Strain = lengthGuage
lengthinChange
lengthOriginal
lengthinChange=
= 000
0
65.5 A
L
A
L
L
LLf ∆=
∆=
− (2.3)
Were L0 = Original length
∆ L = Axial deformation or change in length, Lf = final length, A . = Original
cross sectional area
2.8.3 Tensile Strength (MPa)
According to Askeland (1994) Tensile strength or ultimate strength is the
maximum amount of tensile stress that a material can absorb before breaking. It is
the maximum tensile stress reached on a stress-strain diagram. Tensile strength of
a material is affected by the preparation of the test specimen, the presence of
surface defects (voids, porosity and inclusions), the temperature of the test
environment and the nature of the material.
Tensile strength = Area. nalCrossectio Original
Applied Force Tensile Maximum (2.4)
Figure 2.2: Stress- strain curve
22
2.8.4 Young’s Modulus (MPa)
Young’s modulus or modulus of elasticity (E) is the slope of the stress-
strain curve (Askeland, 1994). According to Hooke’s law it is a measure of the
stiffness of the material. Stiffness is the property of a material to resist
deformation in the elastic range or within the proportional limit. Young’s modulus
(E) = Strain
Stress (2.5)
2.8.5 Elongation at Fracture (%)
Elongation at fracture is the strain on a sample when it fractures. It is
usually expressed in percentage and is a measure of the ductility of the material
.Elongation at fracture is the amount of uniaxial strain at fracture and is depicted
as strain. Elongation at fracture is mostly calculated by removing fractured
specimen from the grips, fitting the broken ends together and measuring the
distance between gauge marks. % Elongation at fracture = 1000
0×
−
L
LL f
Or 100length Original
Extension × (2.6)
Lf = final length of tensile test specimen at rupture. L0 = initial length of test
specimen.
23
2.9 Scanning Electron Microscopy
Scanning electron microscope is a microscope that uses electrons rather
than light to form an image. (Dunlap and Adaskareg, 2000). Since the
development of scanning electron microscope in the early 1950’s, new areas of
study in the medical and physical science communities have been developed.
Scanning electron microscope has allowed researchers to examine much bigger
variety of specimens because of the large depth of field which allows large
particle of the sample to be in focus at one time (Boyde, 1994). Scanning electron
microscope also produces images of high resolution which means that closely
spaced features can be examined at a higher magnification
(wikipedia.org.scanning electron microscopy). Preparation of sample is easy in
scanning electron microscopy and most scanning electron microscopes require the
sample to be conductive. These properties have made the scanning electron
microscope inevitable in the study of morphology of materials by researchers.
Sivasprasad and Krishnia (2011) analyzed the microstructure of A356.21 RHA
composite using scanning electron microscope. Their microstructure analysis
showed uniform distribution of rice husk ash particles in the aluminum alloy and
good retention of rice husk ash particles in the matrix.
Rajendran et al (2010) used scanning electron microscope to study the
topography of zinc oxide particles used for the production of antimicrobial textiles
and found that zinc oxide particles were embedded in the treated fabrics.
24
Nowosielski et al (2006) characterized the microstructure of composite materials
with powders of barium ferrite with x-ray diffractometer and scanning electron
microscopy. The result of the scanning electron microscopy analysis made it
possible to understand that the distribution of powders of barium ferrite in the
polymer matrix was irregular and the powder particles had irregular shapes and
dimensions.
Singla and Chawla (2010) applied scanning electron microscopy in the
study of mechanical properties of epoxy-fly ash composites. The scanning electron
microscope observations showed uniform distribution of fly ash in the matrix and
good adhesion.
Castejon (1998) used scanning electron microscope to study the cerebella
golgi cells of mouse, telecast fish, primate and human species and the scanning
electron microscopy analysis showed three dimensional neuronal geometry and
smooth outer surfaces of the organisms. The University of Tennessee equally
reported in 2000 that scanning electron microscope can be used in the following
areas:
1) Analysis of the surface features of materials,
2) Obtaining the crystallographic information of the materials,
3) Analysis of the microstructural features of materials, that is, grain size, grain
shapes, distribution of various phase and defects such as cracks and voids.
3) To determine the chemical composition of materials when used in
conjunction with energy dispersive x-ray spectrophotometry
25
2.9.1 Components of a Scanning Electron Microscope (SEM)
Figure 2.3 below shows the major components of a scanning electron.
microscope.(Dunlap and Adaskareg 2000).
Figure 2.3: SEM column and specimen chamber
Some of the components of SEM are the vacuum, beam generation, beam
manipulation, beam interaction, detection, signal processing, and display and
recording units.
These systems function together to determine the results and qualities of a
micrograph such as magnification, resolution, depth of field, contrast and
brightness. The functions are as follows: vacuum system: This system is required
26
when using an electron beam because electrons will quickly disperse or scatter due
to collision with other particles.
Electron beam generation system: This system is found at the top of the
microscope column. It generates the illuminating beam of electrons known as
primary electrons.
Electron beam manipulation system: This system consist of electromagnetic
lenses and coils located in the microscope column and control the size, shape and
position of the electron beam on the specimen surface.
Beam specimen interaction system: This system involves the interaction of the
electron beam with the specimen and the types of signals that can be detected.
Detection System: This system can consist of several different detectors each
sensitive to different energy/particle emission that occurs in the sample.
Signal processing system: This system is an electronic system that processes the
signal generated by the detection system and allows additional electronic
manipulation of the image.
Display and recording system: This system allows visualization of an electronic
signal using cathode ray tube and permits recording of the results using
photographic or magnetic media.
2.10 Energy Dispersive X-Ray Spectroscopy
Energy dispersive x-ray spectroscopy (EDS or EDX) is an analytical
technique used for elemental analysis or chemical characterization of a sample
27
(wikipedia.org.energy dispersive x-ray spectroscopy). Since the 1960’s EDS is
attached to scanning electron microscope. (SEM – EDX)
During energy dispersive X-ray spectroscopy analysis, a sample is exposed
to an electron beam inside a scanning electron microscope (SEM). The electrons
collide with the electrons within the sample causing some of them to be knocked
out of their orbits. The vacated positions are filled by higher energy electrons
which emit x-rays in the process. By analyzing the emitted x-rays the elemental
composition of the sample can be determined. Energy dispersive x-ray
spectroscopy is a powerful tool for micro analysis of elemental constituents.
(Ronjenkins, 2011). Accuracy of energy dispersive X-ray spectrum can be affected
by many factors namely
1) Windows in front of the detector can absorb low energy X-rays (EDS
detectors cannot detect elements with atomic number less than 4 that is H,
He, L)
2) Nature of samples, there is reduced accuracy in homogenous and rough
samples.
3) Elements that have overlapping peak.
Figure 2.4 shows the EDS spectrum of the mineral crust of Rimicaris exoculta.The
elements identified are C,Ca,Cl,S,Mg,Fe,P and O.
The energy transitions during EDS analysis is also shown in figure 2.5.
28
Figure 2.4
EDS spectrum of the mineral crust of Rimicaris exoculta (source
wikipedia.org.energy dispersive x-ray spectroscopy)
Figure 2.5 Energy transitions during EDX analysis
29
2.10.1 Applications of Scanning Electron Microscopy – Energy Dispersive X-
Ray Analysis (SEM-EDX)
Areekijsere (2009) used SEM-EDX to study the structure Spectroscopy
and elemental composition of soils from different agricultural areas in the western
region of Thailand. The SEM result showed that the soils were spherical in shape
while the EDX analysis revealed that the soils contained oxygen, magnesium,
aluminum, potassium, silicon, calcium, titanium and iron.
According to Andrews (2007) EDX can be used in electron beam analysis
of metallurgical samples in the areas of pyrometallurgy, mineral processing,
hydrometallurgy, physical metallurgy, corrosion and forensic analysis. Andrews
further opined that limitations of EDX are poor spectral resolution and high
detection limits while it has the advantage of speed especially for quick phase
transformations.
Atuanya et al (2011) studied the microstructure of wood composites using
SEM-EDX. It was found that there were no chemical interfacial reactions between
the wood particles and the recycled low density polyethylene matrix (LDPE). This
was because the EDX analysis gave carbon and oxygen as the major elements in
wood composites. Observations from the SEM analysis showed uniform
distribution of wood particles in the LDPE.
Asaka et al (2004) analyzed resin composites with EDX and SEM and
discovered that the main element in the resin composite was silicon. The SEM
30
observations showed three different types of filler morphology:- splintered,
splintered and prepolymerized and spherical.
2.11 Microstructure
Microstructure is defined as the structure of a prepared surface of thin foil
of a material as revealed by a microscope above 25x magnification
(wikipedia.org.microstructure).
According to Slouf( 2010) microstructures are structures of dimension 1um
to 1000um.The microstructure of a material can be analyzed with the optical
microscope, scanning electron microscope, X-ray diffractometer and scanning
transmission electron microscope (wikipedia.org.electron microscope). According
to the report from Lancaster State University handout (2010) microstructure is the
microscopic description of the individual constituents of a material. Microstructure
is equally the study of the crystal structure of a material, its size, chemical
composition, phases, defects, orientation and interaction and their effect on the
macroscopic behaviour in terms of physical properties and mechanical properties
such as strength, toughness, ductility, hardness, corrosion resistance, low and high
temperature behaviour, wearability and so on. These properties govern the
application of materials in industry. The basis of materials science involves
relating the desired properties to the structure of atoms and phases.
31
2.12 Adhesion and Cohesion
Adhesion is an attraction process between dissimilar molecular species
which have been brought into direct contact such that the adhesive (binder or
matrix) binds to the applied surface.
Cohesion is an attraction process that occurs between similar molecules,
primarily as the result of chemical bonds that have been formed between the
individual components of the adhesive or bonding agent for example curing of cast
neat epoxy.
Cohesion may be defined as the internal strength of an adhesive due to
various interactions within that adhesive or binder that binds the mass together
whereas adhesion is the bonding of one material to another namely an adhesive to
a substrate, due to a number of different possible interactions at the adhesive
substrate interface. The strength of adhesion between two materials depends on the
interactions between the two materials and the surface area which the materials are
in contact. (Fraunhofer, 2010). Adhesion is necessary for achieving high level of
mechanical properties.
The various types of adhesion are:
chemical adhesion: It is a type of adhesion in which the cohesive strength of a
matrix material is determined by chemical bonds within the matrix material,
chemical bonds due to cross linking of polymer(s) within a resin based material,
inter molecular interactions between adhesive (binder) molecules and mechanical
bonds and interactions between the molecules in the adhesive (resin, binder).
32
Wetting is the ability of a liquid to form an interface with a solid surface
(Fraunhofer, 2011). The two materials form a compound at the interface by Ionic
or covalent bonds that results in strong bond between them. Such bonds are
usually brittle except with nano particles.
Dispersive adhesion: This type of adhesion involves holding the surfaces of two
materials together by Vander walls forces.
Diffusive adhesion involves merging or intermingling of the materials at
the bonding interface by diffusion typically when the molecules of both materials
are mobile and soluble. Example includes sintering of ceramics or powder
metallurgy.
The types of adhesion explained above are the ones that affect mechanical
properties of composites. Interfacial region is known as the adhesion region.
2.13 Calculation of Fiber Volume Fraction
The fiber volume fraction is mostly calculated using this formula
Vf = fmmf
fm
WPWP
WP
+ (2.7)
Where Vf = volume fraction of fibers.
Wf = weight of fibers
Wm = weight of matrix
Pf = density of fibers
Pm = density of matrix
33
CHAPTER THREE
MATERIALS AND METHODS
3.1 Materials
3.1.1 Matrix Material
A standard epoxy resin of grade 3554A, chemically belonging to the
epoxide family and curing hardener of grade 3554B were used as the matrix
material. The resin and hardener were supplied by De Paragon Chuks Ventures
(NIG) LTD, 195 Faulks Rd, chemical Zone Ariaria, Aba, Abia State. The epoxy
resin has a density of 1.15g/cm3.
3.1.2 Filler Material
Rice husk ash
The filler material used in this study is rice husk ash which was produced
from rice husk waste sourced from Adani Rice Mill, Enugu State. The finely
milled rice husk fillers were collected in large quantity and washed with water to
remove impurities like dust, small rice particles and fine sand particles. After
washing, drying followed in the oven at a temperature of 70oC
for 24 hours in
order to remove moisture from it. The dried rice husk was taken to the Soil
Science Laboratory, National Root Crops Research Institute Umudike where it
was burnt in a furnace at 550oC
for 6 hours to produce the rice husk ash used for
the study. The rice husk ash was characterized using Atomic Absorption
Spectrophotometer (AAS) and the chemical compositions of the major compounds
33
34
were determined. Table 3.1(a) shows the chemical composition. Trace elements
and unburnt carbon (LOI) were not determined.
Table 3.1 (a) Chemical composition of the rice husk ash used for the study.
3.2.0 Methods
3.2.1 Preparation of Composite Mould
Mild steel sheets were cut and formed into different sizes that served as molds for
the test samples. The testing techniques for the composite required that five sets of
pattern (tensile, compressive, hardness, flexural and toughness) should be
produced. The patterns were made according to the required dimensions of the test
samples. Flat wooden bars were used and served as mould control volume for
other test piece samples. The molds were constructed to within ± Imm to give
allowance for machining, and the surfaces were rubbed with wax releaser to
ensure easy removal of the composite. Figure 3.I below shows the mold used for
composite production.
Chemical
compound 32OAl 2SiO MgO ONa2 ZnO K20 MnO4 PO4 Fe2O3 CaO
Composition
(%)
13.5 26.5 4.8 8.9 3.07 9.4 4.2 10.3 2.9 8.0
35
3.2.2 Composite Fabrication
The composites were produced using facilities at the Centre for Composite
Research and Development, Juneng Nigeria Limited, Nsukka. Manual mixing
method and hand lay up technique were used for the composite production. The
composites were prepared using 10%, 20%, 30%, 40% and 50% volume fraction
of rice husk ash.
The matrix material (epoxy resin, grade 3554A and hardener grade 3554B)
were prepared in the ratio of 2 parts of epoxy resin to 1 part of hardener (2:1). The
measured volume of resin and hardener were mixed in a container and stirred at
low speed for 10 minutes until the mixture became uniform, tacky and exothermic
reaction occurred. The mixture of the matrix material was poured into the mold.
Rice husk ash fillers were uniformly and evenly spread in the mold and adequately
impregnated into the matrix and allowed to cure. For the cast neat epoxy samples,
the epoxy resin and hardener were poured into the mold and allowed to cure. The
Figure 3.1: Mold
36
curing time was 24 hours at room temperature. Finally the composite plates were
demolded and cut into different dimensions for mechanical property tests.
Tables 3.1 (b) and 3. 1 (c) give the composition of the composites and dimensions
for different mechanical property test.
Table 3.1. (b) Composition of the composites.
S/NO Volume of RHA
filler (VF)
Volume of epoxy
matrix (VM)
Sample 1 0% 100%
Sample 2 10% 90%
Sample 3 20% 80%
Sample 4 30% 70%
Sample 5 40% 60%
Sample 6 50% 50%
VF = 100 - VM (3.1)
VC = VF +VM (3.2)
where VC is the volume of composite
Table 3.1 (c) Dimensions of specimen for different mechanical property tests
S/NO Test Length (mm) Breadth (mm) Thickness (mm)
1 Hardness 40 40 40
2 Tensile 300 19 3.2
3 Compressive 20 20 20
4 Toughness 55 10 10
5 Flexural 240 40 40
37
3.3 Mechanical Property Tests
3.3.1 Tensile Testing of Composite Samples
Tensile testing of the samples was done at the Strength of Materials
Laboratory, University of Nigeria, Nsukka.
Hounsfield (Monsanto) tensometer was used in performing the tensile test.
The tensometer was manually operated. The cured epoxy-rice husk ash composite
and the cast neat epoxy were cut into tensile test samples in accordance with the
ASTM standard D638. The cut tensile test samples were of dimension 300mm
long by 19mm by 3.2mm.Prior to the test the cross sectional area of the samples
was calculated. The steps followed before carrying out the test were: loading the
correct beam in the hounsfield, attaching the movable and fixed jaws, setting the
mercury indicator, attaching a graph paper to the rotating drum and ensuring that
the ends of the test piece were fitted into the grip of the tensometer. Tensile forces
were applied gradually by turning the hand wheel of the rotating drum. Turning of
the hand wheel of the rotating drum pulled the samples until fracture occurred.
The deformations were obtained from the load-extension curve. The traced load-
extension curve was converted to stress-strain values. Other tensile properties like
elongation at fracture, tensile strength and young modulus were determined from
this stress- strain curve.
38
3.3.2 Compressive Strength Test
The compressive strength test was done at strength of materials engineering
laboratory, University of Nigeria, Nsukka. Hounsfield (Monsanto) tensometer
universal testing machine was used in carrying out the test.
A compressive test rig was used for the compressive test. Compressive test
specimen of dimension 20mm by 20mm by 20mm were loaded to fracture by
applying uniaxial compressive force. The maximum compressive force that
crushed the specimen were read from graph paper attached to the tensometer. The
compressive strength was calculated using equation 2.1 which is:
Compressive strength = Maximum Compressive Force
Area
3.3.3 Toughness Test
The toughness test was performed at Engineering Laboratory, Standards
Organization of Nigeria, Emene Enugu. The test was carried out according to the
recommended standard charpy V- notched method. Impact specimen 55mm by
10mm by 10mm were notched at the middle to a depth of 2mm to create an area of
stress concentration for initiating fracture. Each of them were fixed on a charpy
impact testing machine to receive a blow from the fast moving hammer released
from a fixed height on the machine. The reading on a dial gauge on the machine
showed the energy absorbed (toughness) by the respective specimen.
39
3.3.4 Hardness Test
The hardness test was done at the Engineering Laboratory, Standards
Organization of Nigeria, Emene Enugu. An automatic electric powered Rockwell
hardness testing machine was used to determine the hardness value of the cast neat
epoxy and the composites. The procedure followed in performing the test were:
switching on the machine, selecting the desired
load of 30kgf, placing the surface of the specimen to be tested on the anvil of the
machine and releasing the indenter of the machine from the lever until it touched
the specimen making a green to be shown to indicate test zone specimen. The
next thing done was pressing the test button and there was automatic indentation
of the specimen by the conical shaped indenter of the Rockwell tester. At the end
of the indentation a red light showed “read” and instantly reading was directly
done from the dial indicator. The value was reported as Rockwell hardness value
{689HRD30}.
3.3.5 Flexural Strength Test
The flexural strength test was done at Engineering Laboratory of Standards
Organization of Nigeria, Emene Enugu. Each specimen of dimension 240mm by
40mm by 40mm was placed in the flexural testing machine. The three point
flexing and loading arrangement was used in which fracture occured at the middle.
40
The specimen was flexed and flexural force that fractured the specimen at the
middle was read from the scale of the machine. The flexural strength was
calculated using equation 3.3.
Fs = 2
bd
FL (3.3)
Where F= flexural force (KN)
L = length in (mm)
B = breadth (mm)
D = thickness (mm)
Fs = flexural strength.
3.4 Scanning Electron Microscopy and Energy Dispersive X-Ray
Spectroscopy Analysis.
The SEM & EDX analysis was done at the Advanced Physics Laboratory,
Sheda Science and Technology Complex, (SHETSCO) Abuja. The Carle Zees
scanning electron microscope with an attached INCA energy dispersive x-ray
microanalysis system was used for the analysis. The scanning electron microscope
has the microscope column, specimen chamber and vacuum system on the left
with the computer monitor and many other instrument controls on the right. The
energy dispersive x- ray spectrophotometer attached to the scanning electron
microscope has four set ups which are: the beam source, the x- ray detector made
of lithium drifted silicon, the pulse processor and the analyzer. The five composite
samples of different composition of rice husk ash particle, the cast neat epoxy and
41
the sample of rice husk ash were loaded in the specimen chamber. Conductive
double sided carbon tape was used to hold the specimens in order to make them
conductive. The cathode and magnetic lenses in the scanning electron microscope
created and focused a beam of electrons on each of the specimen. The
bombardment of the specimen with scanning beam of electrons generated
backscattered electrons and secondary electrons due to beam specimen interaction.
The backscattered electrons and secondary electrons were collected, amplified and
displayed on a cathode ray tube. The backscattered electrons and cathode ray tube
scanned synchronously to produce an image of the surface of the specimen
formed. The analytical lithium drifted silicon detector in the energy dispersive X-
ray spectrophotometer meter converted x- ray energy into voltage signals which
measure the signal and passed them onto the analyzer for elemental analysis and
data display. The morphology and elemental composition of the samples were
displayed on the computer screen sequentially with the help of the software.
42
CHAPTER FOUR
RESULTS AND DISCUSSION
4.1 Results
The results of the study are presented in three main headings, namely
mechanical properties, scanning electron microscopy and energy dispersive x-ray
spectroscopy analyses. Result of mechanical properties shows the behaviour of the
composites and cast neat epoxy to different kinds of forces. Scanning electron
photomicrographs showed the microstructure of the composites, the rice husk ash
and cast neat epoxy. The photomicrographs are shown in figures
4.14,4.15,4.16,4.17,4.18,4.19,4.20,4.21,4.22,4.23,4.24,4.25,4.26 and 4.27. The
energy dispersive X-ray spectroscopy results were presented with the EDX
spectrum in figures 4.28,4.30,4.32,4.34,4.36 and 4.38 and tables
4.14,4.15,4.16,4.17,4.18 and 4.19 showing elemental composition and
concentration of elements in the microstructure of the composites and statistical
bar charts in figures 4.29,4.31,4.33,4.35,4.37 and 4.39 illustrating the quantitative
results of each element.
42
43
4.1a Results for Mechanical Properties are shown as Follows:
Tensile properties are shown in tables 4.1 to 4.9
Table 4.1: Load, Extension, Stress, Strain values for Cast neat Epoxy (100% Epoxy
0% RHA,)
S/N Load (N) Extension
(mm)
Strain (ε) Stress (MPa)
1 0 0.0000 0.0000 0.0000
2 200 0.5000 0.0114 3.2894
3 400 0.8125 0.0184 6.1678
4 550 1.1250 0.0255 9.0460
5 1050 2.0000 0.0454 17.2697
6 1250 2.5000 0.0568 20.5592
7 1600 3.0000 0.0681 26.3158
8 2000 4.0000 0.0908 32.89471
Table 4.2: Load, Extension, Stress, Strain Values for Epoxy-Rice Husk Ash
Composite (90% Epoxy 10% RHA)
S/N Load (N) Extension
(mm) Strain (ε) Stress (MPa)
1 0 0.0000 0.0000 0.0000
2 250 0.5000 0.0114 4.1118
3 350 1.1250 0.0255 5.7566
4 550 1.7500 0.0397 9.0462
5 740 2.3750 0.0539 12.1710
6 970 2.7500 0.0624 15.9539
7 1150 3.5000 0.0795 18.9145
44
Table 4.3: Load, Extension, Stress, Strain Values for Epoxy-Rice Husk Ash
Composite (80% Epoxy 20% RHA)
S/N Load (N) Extension
(mm) Strain (ε) Stress (MPa)
1 0 0.0000 0.0000 0.0000
2 200 0.7500 0.0170 3.2895
3 400 2.0000 0.0454 6.5789
4 650 3.2500 0.0738 10.6908
5 750 3.5000 0.0795 12.3355
6 900 4.2500 0.0965 14.8026
7 1100 4.7500 0.1078 18.0921
8 1500 6.0000 0.1362 24.6710
Table 4.4: Load, Extension, Stress, Strain Values for Epoxy-Rice Husk Ash
Composite (70% Epoxy 30% RHA)
S/N Load (N) Extension
(mm) Strain (ε) Stress (MPa)
1 0 0.0000 0.0000 0.0000
2 300 1.2500 0.0284 4.9342
3 500 2.0000 0.0454 8.2236
4 850 2.5000 0.0568 13.9803
5 950 2.6250 0.0596 15.6250
6 1050 3.2500 0.0738 17.2697
7 1500 4.2500 0.0965 24.6710
8 1600 4.7500 0.1078 26.3157
45
Table 4.5: Load, Extension, Stress, Strain Values for Epoxy-Rice Husk Ash
Composite (60% Epoxy 40% RHA)
S/N Load (N) Extension
(mm) Strain (ε) Stress (MPa)
1 0 0.0000 0.0000 0.0000
2 150 1.0000 0.0227 2.4672
3 450 1.7500 0.0397 7.4013
4 800 2.7500 0.0624 13.1578
5 1000 3.2500 0.0738 16.4473
6 1250 3.7500 0.8510 20.5592
7 1650 4.5000 0.1022 27.1381
8 1850 5.0000 0.1135 30.4276
9 2000 5.5000 0.1249 32.8940
10 2250 6.0000 0.1362 37.0065
Table 4.6: Load, Extension, Stress, Strain Values for Epoxy-Rice Husk Ash
Composite (50% Epoxy 50% RHA)
S/N Load (N) Extension
(mm) Strain (ε) Stress (MPa)
1 0 0.0000 0.0000 0.0000
2 150 0.7500 0.0170 2.4671
3 300 1.2500 0.0284 4.9342
4 500 2.0000 0.0454 8.2237
5 800 2.8750 0.0653 13.1579
6 1000 3.3750 0.0766 16.4474
7 1300 3.7500 0.0851 21.3815
8 1500 4.2500 0.0965 23.8488.
Table 4.7: Tensile Strength
S/N Material Tensile Strength (MPa)
1 100% Epoxy 0% RHA 32.894
2 90% Epoxy 10% RHA 18.915
3 80% Epoxy 20% RHA 24.671
4 70% Epoxy 30% RHA 26.317
5 60% Epoxy 40% RHA 37.006
6 50% Epoxy 50% RHA 23.848
46
Table 4.8: Young’s Modulus
S/N Material Young’s modulus (MPa)
1 100% Epoxy 0% RHA 356.5380
2 90% Epoxy 10% RHA 234.9442
3 80% Epoxy 20% RHA 167.8115
4 70% Epoxy 30% RHA 245.4050
5 60% Epoxy 40% RHA 276.9320
6 50% Epoxy 50% RHA 285.729
Table 4.9: % Elongation at Fracture
S/N Material Elongation at fracture (%)
1 100% Epoxy 0% RHA 1.30
2 90% Epoxy 10% RHA 1.36
3 80% Epoxy 20% RHA 1.40
4 70% Epoxy 30% RHA 1.58
5 60% Epoxy 40% RHA 2.00
6 50% Epoxy 50% RHA 2.00
S/N Material Energy Absorbed (J)
1 100% Epoxy 0% RHA 2.0
2 90% Epoxy 10% RHA 1.6
3 80% Epoxy 20% RHA 0.9
4 70% Epoxy 30% RHA 0.7
5 60% Epoxy 40% RHA 0.5
6 50% Epoxy 50% RHA 0.3
Table 4.11: Hardness Test Result (Rockwell)
S/N Material Hardness value
1 100% Epoxy 0% RHA 344
2 90% Epoxy 10% RHA 219
3 80% Epoxy 20% RHA 202
4 70% Epoxy 30% RHA 190
5 60% Epoxy 40% RHA 150
6 50% Epoxy 50% RHA 144
Table 4.10: Toughness Test Result
47
Table 4.12: Flexural Strength Test Result
S/N Material Flexural
force(KN)
Flexural strength (MPa)
1 100% Epoxy 0% RHA 1.600 6.00
2 90% Epoxy 10% RHA 1.200 4.50
3 80% Epoxy 20% RHA 0.800 3.00
4 70% Epoxy 30% RHA 0.600 2.25
5 60% Epoxy 40% RHA 0.500 1.88
6 50% Epoxy 50% RHA 0.400 1.50
Table 4.13: Compressive Strength Test Result
S/N Material Maximum
compressive force
(N)
Compressive
strength (MPa)
1 100% Epoxy 0% RHA 6300 15.75
2 90% Epoxy 10% RHA 6400 16.00
3 80% Epoxy 20% RHA 6800 17.00
4 70% Epoxy 30% RHA 7100 17.75
5 60% Epoxy 40% RHA 7450 18.63
6 50% Epoxy 50% RHA
7500 18.75
48
Figure 4.1 Stress - Strain relationship for cast neat epoxy.
Figure 4.2 Stress – Strain relationship for epoxy – rice husk ash composite
(90%epoxy 10%rice husk ash)
Stress
Stress 90% Epoxy 10% RHA
Stress 100% Epoxy 0% RHA
Stress 100% Epoxy 0% RHA
Str
ess
(MP
A)
Str
ess
(MP
A)
49
Figure 4.3 Stress- Strain relationship for epoxy-rice husk ash
Composite (80%epoxy 20%rice husk ash)
Figure 4.4 Stress – Strain relationship for epoxy – rice husk ash composite
(70%epoxy 30% rice husk ash)
Stress 80% Epoxy 20% RHA
Str
ess
(MP
A)
Strain
Stress 70% Epoxy 30%RHA
Str
ess
(MP
A)
50
Figure 4.5 Stress – Strain relationship for epoxy- rice husk ash composite
(60%epoxy 40% rice husk ash)
Figure 4.6 Stress – Strain relationship for epoxy- rice husk ash composite
(50% epoxy 50% rice husk ash)
Figure 4.7 Tensile strength - %RHA graph
Stress 60% Epoxy 40%RHA
Str
ess
(MP
A)
Stress 50% Epoxy 50%RHA
Str
ess
(MP
A)
51
Figure 4.8 Young’s modulus - %RHA graph
Figure 4.9 Elongation at fracture - %RHA graph
Figure 4.10 Energy absorbed (toughness) - %RHA graph
Yo
un
g’s
Mod
ulu
s
(MP
A)
Young’s Modulus
(MPa)
Elo
ng
atio
n a
t fr
actu
re (
%)
(MP
A) Elongation at
fracture (%)
52
Figure 4.11 Hardness value - %RHA graph
Figure 4. 12 Flexural strength - %RHA graph
Figure 4.13 Compressive strength - %RHA graph
53
Results of scanning electron microscopy are presented in figures 4.14 to 4.27.
Figure 4.14 Scanning electron micrograph of epoxy – rice of Adani rice husk
ash x200.
4.1b Results of Scanning Electron Microscopy (SEM).
54
Figure 4.15 Scanning electron micrograph of Adani rice husk ash x2000.
Figure 4.16 Scanning electron micrograph of cast neat epoxy x200.
55
Figure 4.17 Scanning electron micrograph of cast neat epoxy x2000.
Figure 4.18 Scanning electron micrograph of epoxy –rice husk ash composite
containing 10% rice husk ash x200.
56
Figure 4.19 Scanning electron micrograph of epoxy- rice husk ash composite
containing 10% rice husk ash x2000.
Figure 4.20 Scanning electron micrograph of epoxy – rice husk ash composite
containing 20% rice husk ash x200.
57
Figure 4.21 Scanning electron micrograph of epoxy – rice husk ash
composite containing 20% rice husk ash x2000.
Figure 4.22 Scanning electron micrograph of epoxy – rice husk ash composite
containing 30% rice husk ash x200.
58
Figure 4.23 Scanning electron micrograph of epoxy – rice husk ash composite
containing 30% rice husk ash x2000.
Figure 4.24 Scanning electron micrograph of epoxy-rice husk ash composite
containing 40% rice husk ash x200.
59
Figure 4.25 Scanning electron micrograph of epoxy-rice husk ash composite
containing 40% rice husk ash composite x2000.
Figure 4.26 Scanning electron micrograph of epoxy –rice husk ash composite
containing 50% rice husk ash x200.
60
Figure 4.27 Scanning electron micrograph of epoxy- rice husk ash composite
containing 50% rice husk ash x2000.
61
The results of energy dispersive x-ray spectroscopy are presented in figures
4.28 to 4.39 and on tables 4.14 to 4.19.
Element App Intensity Weight% Weight% Atomic%
Conc. Corrn. Sigma
C K 342.57 1.5885 81.35 0.39 85.46
O K 16.44 0.3395 18.27 0.39 14.41
Cl K 0.86 0.8356 0.39 0.04 0.14
Totals 100.00
Table 4.14: Elemental composition of cast neat epoxy.
Figure 4.28 EDX spectrum of cast neat epoxy
4.1c Results of the Energy Dispersive X-ray Spectroscopy Analysis (EDX).
62
Quantitative resultsW
eig
ht%
020406080
100
Fig 4.29 Quantitative results for cast neat epoxy showing
weight% of elements.
C O Cl
63
Element App Intensity Weight% Weight% Atomic%
Conc. Corrn. Sigma
C K 112.01 0.7330 64.95 0.72 75.96
O K 19.53 0.3915 21.21 0.57 18.62
Al K 1.08 0.8643 0.53 0.04 0.28
Si K 13.56 0.9253 6.23 0.14 3.12
P K 0.52 1.2301 0.18 0.05 0.08
Cl K 1.51 0.8015 0.80 0.06 0.32
K K 3.08 1.0299 1.27 0.07 0.46
Ca K 1.46 0.9646 0.64 0.06 0.22
Fe K 2.26 0.8001 1.20 0.12 0.30
Zn K 5.26 0.7465 2.99 0.23 0.64
Totals 100.00
Table 4.15 Elemental composition of epoxy- rice husk ash composite (90%
epoxy 10% RHA)
Figure 4.30 EDX spectrum of epoxy- rice husk ash composite (90%
Epoxy, 10% RHA)
64
Quantitative resultsW
eig
ht%
020406080
Figure 4.31 Quantitative results for epoxy – rice
husk ash composite (90% Epoxy 10% RHA)
showing weight % of elements.
C P Cl Ca O Al Si K Fe Zn
Figure 4.32 EDX spectrum of epoxy- rice husk ash composite
(80% Epoxy, 20% RHA)
65
Table 4.16: Elemental composition epoxy-rice husk ash composite(80%Epoxy
20%RHA)
Element App Intensity Weight% Weight% Atomic%
Conc. Corrn. Sigma
C K 226.60 1.2025 71.37 1.51 77.97
O K 25.90 0.3866 25.37 1.48 20.80
Si K 3.83 0.9459 1.53 0.16 0.72
Cl K 1.28 0.8261 0.59 0.14 0.22
K K 0.73 1.0381 0.27 0.13 0.09
Fe K 1.79 0.7767 0.88 0.26 0.21
Totals 100.00
Quantitative results
We
igh
t%
020406080
Figure 4.33 Quantitative results for epoxy – rice husk ash composite(80%Epoxy
20%RHA) showing weight% of elements.
C O Si Cl K Fe
66
Table 4.17: Elemental composition of epoxy –rice husk ash composite
(70%Epoxy30% RHA)
Element App Intensity Weight% Weight% Atomic%
Conc. Corrn. Sigma
C K 286.07 1.5090 80.07 0.41 84.57
O K 15.43 0.3442 18.93 0.40 15.01
Al K 0.75 0.9089 0.35 0.03 0.16
Si K 0.45 0.9585 0.20 0.03 0.09
Cl K 0.72 0.8334 0.37 0.04 0.13
K K 0.21 1.0399 0.09 0.03 0.03
Totals 100.00
Figure 4.34 EDX spectrum of epoxy – rice husk ash composite
(70% Epoxy, 30% RHA)
67
Quantitative results
We
igh
t%
020406080
100
Figure 4.35 Quantitative results for epoxy –rice husk ash composite
(70%Epoxy 30%RHA) showing weight % of elements.
Figure 4.36 EDX spectrum of epoxy rice husk ash composite (60% Epoxy, 40%
RHA)
C O Al Si Cl K
68
Table 4.18 Elemental composition of epoxy –rice husk ash
composite(60%Epoxy 30%RHA)
Element App Intensity Weight% Weight% Atomic%
Conc. Corrn. Sigma
C K 307.99 1.5354 78.77 0.29 83.37
O K 18.48 0.3519 20.63 0.29 16.39
Si K 0.76 0.9588 0.31 0.02 0.14
Cl K 0.51 0.8331 0.24 0.02 0.09
K K 0.13 1.0406 0.05 0.02 0.02
Totals 100.00
Quantitative results
We
igh
t%
020406080
Figure 4.37 Quantitative results of epoxy –rice husk ash composite
(60%Epoxy 40%RHA) showing weight % of elements.
C O Si Cl K
69
Table 4.19: Elemental composition of epoxy – rice husk ash composite (50%Epoxy
50%RHA)
Element App Intensity Weight% Weight% Atomic%
Conc. Corrn. Sigma
C K 291.96 1.5144 79.69 0.32 84.22
O K 16.29 0.3464 19.43 0.32 15.42
Al K 0.21 0.9071 0.09 0.02 0.04
Si K 1.03 0.9609 0.44 0.03 0.20
Cl K 0.57 0.8328 0.28 0.03 0.10
K K 0.17 1.0400 0.07 0.02 0.02
Totals 100.00
Figure 4.38 EDX spectrum of epoxy rice husk ash composite (50% Epoxy,
50% RHA)
70
Figure 4.39 Quantitative results for epoxy – rice husk ash
composite (50%Epoxy 50%RHA)
4.2 Discussion of results
4.2.1 Mechanical properties
The mechanical properties of the composites did not improve with
increasing filler content as expected. Based on observations from labouratory
tests conducted on the composites and the rice husk ash in Standards Organization
Of Nigeria and Sheda Science and Technology Complex, Abuja the decrease in
mechanical properties could be attributed to the non coating of the surface of the
rice husk ash fillers with coupling agents, manual mixing method used for
composite production and the porous structure of rice husk ash.
4.2.1a Tensile Properties
Tensile properties showed how the cast neat epoxy and the composites
reacted to tensile forces. Figures 4.1 to 4.6 showed stress versus strain graphs of
the materials. From these graphs it can be seen that the materials were brittle. The
reason for the brittleness is because the composites did not sustain large
C O Al Si Cl K
Quantitative results
We
igh
t%
020406080
71
deformations before fracture and the stress-strain diagrams had no yield point.
Figure 4.7 shows the tensile strengths of the composites. The tensile strengths of
the composites with 10%, 20%, 30% and 50% volume of RHA were lower than
the cast neat epoxy while the highest tensile strength of 37.006MPa was recorded
at 40% volume of RHA. The reasons for this result are: tensile strength are
affected by volume fractions, degree of adhesion between the filler and the matrix,
level of dispersion of the filler and matrix and surface related defects. Tensile
strength can decrease with increasing filler content if the filler matrix adhesion is
weak and this accounts for the reason why the tensile strength of 10%, 20%, 30%,
40% and 50% volume fraction of RHA were lower than the cast neat epoxy. The
increase in rice husk ash content led to greater possibility of weak locations in the
composites which caused easy debonding at the interface when tensile forces were
applied. However the reasons for the higher tensile strength of the 40% RHA
could be because there were strong interfacial adhesions between the rice husk ash
fillers and epoxy matrix or better stirring during the production process. The
swingling of the graph is because manual mixing was used which caused irregular
dispersion of the fillers on the matrix.
Fig 4.8 shows the Young’s modulus of the composites at different composition of
rice husk ash. It can be seen that the cast neat epoxy had the highest tensile
modulus of 356.538MPa. The addition of rice husk ash fillers caused loss of
tensile modulus because the manual mixing method used in the composite
preparation caused some rice husk ash fillers to be poorly dispersed and this
72
poorly dispersed fillers formed agglomerates. These agglomerated fillers acted as
stress concentration sites due to their porous nature and weakened the composite
stiffness on tension.
Fig 4.9 shows the graph of elongation at fracture versus % RHA. There was
gain in elongation at fracture from 1.30% to 2.0% as the percentage of rice husk
ash fillers increased. The improvement in elongation at fracture of the composites
could be attributed to the interfacial interactions between the rice husk ash
particles and the epoxy matrix. These interfacial interactions induced lattice strains
in the composites that led to higher strains.
4.2.1b Toughness
Figure 4.10 showed that the toughness of the composites decreased from
2.0J to 0.3J as percentage of rice husk ash increased. This decrease could be
because of poor wettability of rice husk ash which led to poor interfacial adhesion
between the hydrophobic epoxy matrix and hydrophilic rice husk ash fillers. Poor
interfacial adhesion (bonding) led to formation voids in the composites. These
voids acted as sites for crack nucleation and propagation upon impact. Hence as
the percent of rice husk ash increased the number of voids in the composites
increased amounting to lower energy absorbed before fracture. Similar works by
Singla and Chawla (2010), Arukalam and Madufor (2011) and Onuegbu and Igwe
(2010) equally showed that increase in filler content led to decrease in toughness.
73
4.2.1c Hardness
The hardness value of the composites decreased from 344 to 144 with
increase in percentage of rice husk ash as can be seen in figure 4.11. This decrease
is due to the soft nature of the rice husk ash fillers. The softness and lightness of
the rice husk ash allowed quick penetration of the indenter on indentation. Soft
material embedded in a harder material most times result in reduction of hardness.
4.2.1d Flexural Strength
The graph of flexural strength versus %RHA in figure 4.12 shows that
flexural strength decreased from 6.0 MPa to 1.5MPa as the percentage of rice husk
ash increased. Flexural strength is the ability of material to resist bending, twisting
and deformation under load. The reasons for the decrease in flexural strength were
poor interfacial adhesion (bonding) between the rice husk ash and the epoxy
matrix, distortion in the microstructure caused by addition of rice husk ash and
porous morphology of the rice husk ash. These defects accounted for lower
resistance of epoxy-rice husk ash composites to flexural force leading to quick
rupture.
4.2.1e Compressive Strength
From the graph of compressive strength versus % RHA in figure 4.12, the
compressive strength of the composites increased from 15.75MPa to 18.75MPa as
the % RHA increased. The increased resistance of the composites to crushing
loads could be attributed to the hollowness of the rice husk ash particles as shown
in figure 4.15 and the strong interfacial energy between the rich husk ash particles
74
and the epoxy matrix. Brittle materials have better resistance to compression; since
the composites were brittle in tension it is expected that they will have improved
compressive strength.
Another reason for the increase in compressive strength is that during
compression the molecules of the composites were forced together and cracks are
closed up.
4.2.2 Scanning Electron Microscopy Analysis
Scanning Electron microscopy analyses was done to observe the
distribution and interaction of rice husk ash fillers in the epoxy matrix and to
determine the morphology of the cast neat epoxy and Adani rice husk ash. Two
magnifications of 200x and 2000x were used in order to adequately view the
specimens. The explanations of the scanning microscopy analysis are given thus:
Figures 4.14 and 4.15 show the photomicrographs of Adani rice husk ash at 200x
and 2000x magnifications. At 200x magnification the rice husk ash had a porous
structure with the particles looking a bit rough and dispersed. The increase in
magnification to 2000x gave a hollow structure of the rice husk ash.
Figures 4.16 and 4.17 showed that the cast neat epoxy had a rough surface and
there were poor cohesion between the hardener and the resin in some regions in
the microstructure. An observation of the composite with 10% RHA in figures
4.18 and 4.19 showed that the surface of the composite was rough and the rice
husk ash particles were fairly distributed in the matrix. The rice husk ash particles
were interacting at the interface.
75
Figures 4.20 and 4.21 showed the scanning electron microscopy analysis of the
composite containing 20%RHA. It can be deduced from the photomicrographs
that the composite had a smooth surface with the particles of rice husk ash evenly
distributed and there were interactions at the interface. However the particles did
not bond well with the matrix. Looking at the microstructure of the composite
containing 30% RHA in figures 4.22 and 4.23. It can be seen that interfacial
interactions existed between the rice husk ash particles and the epoxy matrix. At
2000x magnification the particles formed a cluster at the edge and the particles did
not bond well with the matrix. The microstructure appeared strained at 2000x
magnification while at 200x magnification a smooth surface was observed.
From figures 4.24 and 4.25 the composite containing 40% RHA had a smooth
surface at 200x and fairly strained surface at 2000x. The rice husk ash particles
were uniformly distributed. Figures 4.26 and 4 .27 showed the microstructure of
the composite containing 50% RHA. It was observed that the rice husk ash was
not well distributed in the matrix. At 200x magnification a smooth surface was
noticed with clusters of rice husk ash while at 2000x magnification the surface
looked a bit strained.
Conclusively it was observed in the scanning electron microscopy analyses
that interfacial interactions existed between rice husk ash particles and epoxy
matrix. Scanning electron microscopy analysis equally showed that there was poor
interfacial adhesion (bonding) between the rice husk ash particles and the epoxy
76
matrix in the microstructure and poor dispersion of rice husk ash particles in the
epoxy matrix.
4.2.3 Energy Dispersive X-Ray Spectroscopy Analysis
Energy dispersive x-ray spectroscopy analysis showed the elements in the
microstructure of the composites and the cast neat epoxy .The elements and their
composition were found from the EDX attached to the SEM with the help of a
software. The EDX results showed that interfacial reactions existed between the
rice husk ash particles and the epoxy matrix because the composites did not
contain homogenous elements in their microstructure. In an EDX result, the EDX
spectrum showed the elements and their peaks with corresponding energy on the
horizontal line of the spectrum. The elemental composition was shown in the
tables. The elemental composition was given in atomic%, weight%, approximate
concentration and intensity. The results of the energy dispersive x-ray
spectroscopy analysis for the cast neat epoxy and the composites are explained as
follows:
Table 4.14 and figure 4. 28 show the elemental composition and the EDX
spectrum of the cast neat epoxy respectively It showed that the cast neat epoxy
contained these elements C, O,Cl. Table 4.15 and figure.4.30 gave the elemental
composition of the composite with 10% RHA as C,O, Al, Si, P, Cl,K, Ca, Fe, Zn.
The surface of this composite allowed more reactions between the epoxy matrix
and rice husk ash particles which accounted for the highest elements in its
77
microstructure than other composites. Table 4.16 and figure 4.32 showed that the
composite with 20% RHA contained C, O, Si, Cl, K and Fe.
From table 4.17 and figure 4.34 the composite with 30% RHA was found to
contain C, O, Al, Si, Cl and K.
Table 4.18 and figure 4.36 showed that the elemental composition of the
composite with 40% RHA is C, O, Si, Cl and K.
Table 4.19 and figure 4.38 showed that the elements in the microstructure of the
composites with 50% RHA are C,O,Al, Si, Cl and K.
It became evident from the analysis that all the composites had C, O, Cl and Si in
their microstructure. All the composites had higher composition of carbon in them
and their peaks overlapped.
78
CHAPTER FIVE
CONCLUSION AND RECOMMENDATIONS
5.1 Conclusion
This study showed from the scanning electron microscopy and energy
dispersive x-ray spectroscopy microstructural analysis that the microstructure and
elemental composition of the composites varied at the interface of the epoxy
matrix and rice husk ash particles.
It was found from the study that porous structure of rice husk ash, poor
dispersion and poor interfacial adhesion (bonding) between the rice husk ash and
the epoxy matrix caused decrease in flexural strength, toughness and hardness as
percentage of rice husk ash fillers increased. Due to these findings rice husk ash
could be utilized for composite production in areas subjected to tension and
abrasion as an extender filler to reduce cost and minimize environmental pollution.
Rice husk ash is not a good reinforcement material
The only remarkable reinforcing effect of rice husk ash fillers were on
compression because the compressive strengths of the epoxy-rice husk ash
composites were higher than the cast neat epoxy. Hence epoxy-rice husk ash
composite could be used in engineering applications in areas where light weight
and resistance to compression are required such as in producing sole of shoes,
industrial floors, tiles, coating of pipelines, grain storage silos, tanks, tables and
slabs.
78
79
5.2 Recommendations
1. The government should assist engineering research in universities through
the provision of some characterization equipment like Atomic Absorption
Spectrophotometer, X-ray Diffractormeter, Scanning Electron Microscope,
Transmission Electron Microscope, Scanning Transmission Electron
microscope, Instron Universal Testing Machine and Durometer.
2. The use of low volume fractions of rice husk ash for composite production
should be investigated.
3. Coating of the surface of rice husk ash with coupling agents should be done
to improve interfacial adhesion.
4. The particle size of rice husk ash should be reduced to a nano particle to
improve the mechanical properties.
5. Mechanized stirring and dispersants should be used in the mixing of rice
husk ash and epoxy to improve dispersion and prevent agglomeration of
fillers.
6. In order to increase the hardness of the composite harder reinforcing
materials like snail shell, Iron fillings, carbon fibers, periwinkle shell and
palm kernel shell should be used together with rice husk ash.
7. The rheological properties of epoxy should be studied.
80
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85
APPENDIX I
EDX Analysis of Adani Rice Husk Ash
86
APPENDIX II
Structures of different types of composites
a. Random fiber (short fiber) reinforced composites
c. Particles as the reinforcement (Particulate composites):
d. Flat flakes as the reinforcement (Flake composites):
b. Continuous fiber (long fiber) reinforced composites
e. Fillers as the reinforcement (Filler composites):
87
APPENDIX III
Rice Husk Ash Production Process
Plate1 : Rice husks piles being burnt in rice mills: Plate 2: Close-up of burning rice husk
Plate 3: Adani rice husk and Adani rice husk ash
88
APPENDIX IV
Composite Fabrication Procedures
Plate 5: Curing of the composites
Plate 4: Mixing of the epoxy.
89
Plate 6: Hardness test specimen.
Plate 7: Tensile test specimen.
90
Plate 8: Cast composites.
Plate 9: Compressive test specimen
91
APPENDIX V
Testing of Composites
ASTM D638 Tensile test specimen size
Plate 10: Hounsfield Tensometer
92
:
Plate 11: Charpy impact testing machine
Test specimen size for compressive test
93
Unotched specimen
Notched test specimen for toughness test
Test specimen size for hardness test
94
.
Plate 12: Rockwell hardness tester
Test specimen size for Flexural strength test
Plate 13: Flexural testing machine
95
Plate 14: Carl Zees Scanning electron microscope