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Chapter 1
Int roduction
Chapter first of this thesis gives us the genral introduction of whole
thesis. This chapter provides us the structural chemistry of borophosphate
glass. The basic principles of the borophosphate glass was get understood by
the structural chemistry, which was put forwarded by many experiment in
recent years. Chapter also discusses the history of glass, synthesis & structural
development of glass and application of borophosphate glass. It also includes
the recycling of glass & finally the aim of the work is summarized.
We are going to discuss the following points----
1.1. Natural glass
1.2. History of artificial glass
1.3. Definitions of glass
1.4. Story of glass formation Myth and legend
1.5. Current Historical Knowledge of glass formation
1.6. Types of glass
1.7. Preparation methods of glass
1.8. Melt quench technique
1.9. Borophosphate glass
1.10. Importance & Applications
1.11. Recycling of glass
1.12. Aim of the Work
1.1 NATURAL GLASS
It is seems to be considered that glass exist from the beginning of time.
Glass is a result of high temperature. It is formed when certain types of rocks
melts. This is aimpact of meteorites, volcanic eruption & lightning strikes can
trigger this effect.Natural form of glass also found on moon. Sample of moon
rock was brought to earth by Appollo-14.
Fig 1.1 Sample of moon rock
Natural glass which made by volcanic eruption is also known as obsidian. It is
belived that this obsidian is used by the Stone Age man for cutting tools or
spearheads.
1.2 HISTORY OF ARTIFICIAL GLASS
Pliny the ancient Roman historian describes the history of glass
formation. Glass was discovered accidentally. Some Phoenician merchants
transporting stones, in the region of Syria one time they land on a shore for the
coocking purpose. They placed pot on a nitrate block. Because of the intense
heat of fire nitrate blocks started melting and it mix with beach sand. It forms
an opaque liquid, which is known as glass.
Origin of the glass was found to be describing by different
civilizations. Civilizations like Egypt, Eastern Mesopotamia etc. give the
evidences of glass making activities. Ancient glass was also made by the
people in Mycenae (Greece), China, and North Tyrol. They have their
evidences of natural glass and artificial glass.
1.3 DEFINITIONS OF GLASS
This section was composed to give an overview of glass science,
including what a glass is and the popular parameters used to characterize it.
Glasses have been defined a number of ways by Many authors, its definition
by Shelby seems to be the most appropriate: " Glass is an amorphous solid
completely lacking in long range, periodic atomic structure. And it exhibiting
a region of glass transformation behavior"(1)
Definitions of glass which are older one are describe below. But these
definitions are incomplete one. We are describing here the definitions and how
it is incomplete one.
1) First definition: “Glass is an inorganic product of fusion that has cooled to
a rigid condition without crystallization.”(2) This definition is accurate for
soda lime, silica etc. commercial materials. But totally ignores the H-
bonded, organic and metallic materials. Definition also ignores the
alternate processing routes like CVD, n-bombardment, sol gel etc.
2) Second definition: “Glass is an amorphous solid.” (3) But not all amorphous
solids are glasses. Like thin film oxides, wood, cement etc. These are
amorphous solids but do not show glass transition.
3) Third definition: “Glass is an under cooled liquid.” All types of glasses
exhibit solid properties. They do not flow at room temperature.
4) Fourth definition: “Glass is a solid that possesses no long range of atomic
order and upon heating gradually softens to the molten state.” This
definition not for the non-crystalline structure and glass transformation
behavior.
5) Fifth definition: “Glass is conventionally cooled oxide melts.”
Neither definition appears to be ideal. Thus, glasses can now be
prepared by methods other than by cooling from the liquid state, for instance
by the drying of aqueous gels of by vapor deposition.
Few things are required to be clarified for defining the glass. Since
number of inorganic glasses without silica as the main constituent can be
formed, therefore having silica is not the requisite of a glass. Melting is not a
mandatory requirement for glass as glasses can be prepared by sol-gel,
chemical nature of the material can’t be used to define the glass.
According to moray (4), 'Glass is analogues to liquid state an in a'
condition which is continuous, change of formation of a glass is reversible
change in viscosity during cooling has attained so high agree of viscosity as to
be for all practical purposes.
Tammann (5) who was anew of the pioneers of glass research has
defined the tern glass as In the glassy state, there are solid, uncrystallized
materials, These definitions however are too general. American Society for
Testing and Material (6) in 1945 has defined glass as ‘Glass is aproduct of
without crystallization of inorganic material. In which inorganic product has
been cooled to a rigid condition.
Thus, the definition given by the Shelby is considered to be complete
one according to him glass can be defined as, “Glass is an amorphous solid
completely lacking in long range periodic atomic structure and exhibiting a
region of glass transformation behavior.”
1.4 STORY OF GLASS FORMATION MYTH AND LEGEND
Where and when glass production began is uncertain, It is thought by
some that the first glass was probably developed in the Mitanni an or Harridan
region of Mesopotamia, possibly as an extension of the production of glazed
(5000 BCE) (7) around this same time a new material called faience was
developed, which was produced by utilizing a variety of techniques to create a
glaze layer over a silica core (8,9). It involved sintering (fusion below the
melting point ) rather than the complete melting of the silica mixture 910). As
such faience can be thought of as an intermediate material between a glaze and
glass.(10) Although this material was used to craft beads during the third and
fourth millennia BCE, it involved sintering (fusion below the melting point),
rather than the complete melting of the silica mixture.(10) As such, faience can
be thought of as an intermediate material between a glaze and glass(10). Glass
as an independent material is not thought. To predate 3000 BCE with the first
glass.
Objects including beads, plaques inlays and eventually small vessels (7,11-13)
Glass objects dated back to 2500 BCE have been found in Syria, and by 2450
BCE, glass were plentiful in Mesopotamia (10). Glass came later in Egypt,
with its manufacture appearing as major industry around 1500 BCE (10,14-17).
The oldest glass of undisputed date found in Egypt dates from 2200 BCE
(18).Many legends have attempted to explain the discovery of glassmaking. The
most famous of these was recorded by the first century historian Pliny the
Elder 1 in his Naturalism Historian (Natural History) (19).
1.5 CURRENT HISTORICAL KNOWLEDGE OF GLASS
FORMATION
While the accounts discussed so far make entertaining stories they are
not commonly accepted as historically accurate and currently scholars believe
that glass was discovered either as byproduct of metallurgy or from an
evolutionary sequence in the development of ceramic materials (20). These two
hypothetical origins are deemed plausible as both early technologies had
procedures that could be considered precursors of glass (10). Considering the
possibility that glass arose from metallurgical operations, a brief discussion of
the history of metallurgy is required it is known that the salting of copper
began as early as 6000 BCE in Anatolia (modern Turkey) (10). Others however,
credit the Sumerians in southern Mesopotamia with the organ of copper
smelting By 3700 BCE, copper was being produced in the Sinai Peninsula and
a litter later (3000 BCE) on Cyprus from which the word copper is derived (21).
The smelting of copper consisted of heating the ore malachite (Cu2CO2(OH)2)
in the presence of charcoal at temperatures of 12000C(22). The incomplete
combustion of the charcoal would result in a strong reducing atmosphere of
carbon monoxide, which would reduce the Cu (II) of the ore to metallic
copper. At the temperatures employed the metallic copper produced would
become molten (Cu mp=10840C) and could e isolated and cooled to generate
pure copper cakes(23) of course a complication in this process is that in
collecting the ore, a good deal of rock was unavoidably collected as well.
Common rock is comprised of various silicates and aluminosilicates which do
not easily melt at the temperatures applied of r the smelting of copper. Thus
their presence would result in the isolation of a solid heterogeneous mixture of
rock and raw metal which would then have to be broken up and the metal
removed, making its isolation cumbersome (23). To overcome this complication
a flux would be added to assist with the melting of the residual silicate and
aluminosilicate species early common flux would be added to assist with the
melting of the residual silicate and aluminosilicate species. Early common
fluxes confirming
types of species u
metal ores, also
salts. Known ex
(K2CO4) saltpete
flux would then re
rock and flux comm
miscible, they wou
furnace. The two
called liquation, i
time (Fig.1.2).
ng such iron ores as flux in copper smelting (21-23).
utilized as fluxes were quite diverse and in additi
included a number of simple carbonate, sulfa
xamples of such fluxes include soda (Na2
er (KNO3) and vitriol (meal sulfates)(24). Appli
result in a combination of molten metal and a fus
mmonly referred to as the slag. As the motel and
y would form two separate molten layers within
wo layers could be separated form one another v
in which the layers were poured of drained off
. However the
ition to various
ate and nitrate
2CO3) potash
li cation of the
sed mixture of
nd slag were not
n the smelting
r via a process
one layer at a
Fig 1.2 Smelting
furnace and fired
and slag (b); the
fore hearth (c)
When the
solid similar to obs
siliceous slogs (var(17, 25). Support for
fact that many ear
Glazes and glass
However, the most
glassmaking and
Egyptian site of Q
both the preparati
site. Thus, this p
taking place at
generated (25). Add
of second millenn
the presence of tin
The presence of
corrosion product
relationships have
blue New Kingdom
of New kingdom
g process: ore, flux and charcoal are mixed in
d (a); heating produces immiscible layers of
tap-hole is removed, Allowing the slag to drai
molten slag was allowed to cool, it produced a
obsidian. It is easy to imagine that experimentati
ariation in types and source of rock, vitreous s
or this proposed origin for glassmaking has also
arly
sses were colored blue by the addition of c
ost significant evidence for a relationship bet
metallurgy comes from archaeological finds. The
Qatar (late second millennium BCE), contains
tion of red opaque glass ingots and bronze casti
provides a clear example of the production of
the very site where metallurgical byproduct
Additional support for this connection comes from
nnium BCE light blue opaque Makita glasses, wh
n oxide (25). As these glasses are colored with copp
of tin indicates the potential use of bronze dr
ts as the source of copper (II) ions to color the
ve also been observed between the copper and ti
dom glasses the ratio which is compatible with the
boozed. It has also been Pointed out that slogs
n the smelting
molten metal
in off into the
d a rigid, glassy
tion with such
ous silicate objects
so included the
copper (17, 25).
tween ancient
The Rapeseed
ns evidence for
ting in a single
colored glass
ts were being
om the analysis
which revealed
copper species,
ross, scale of
he glass Similar
tin contents of
he composition
s from copper
smelting actually contain only a little copper and much richer in iron than
ether the either the early glazes of glasses (22). It must be remembered however
that only very small amounts of Copper would be needed to provide the blue
color. In addition the high amount of iron is not surprising considering the
common flux for copper was iron pyrites. The move to another flux via
experimentation could easily have resulted in early blue glass with low iron
content. The second possible origin for the discovery of glass is thought trod
be due to an evolutionary development of a family of highly siliceous
ceramics coated with alkali glazes originating in either Sumerian or Egypt (8,
17, 22). The immediate predecessor of glass in this developmental sequence is
the material known as faience (17,22) Faience was used mostly to make small
objects such as bands and is found in profusion at archaeological sites in
Egypt and elsewhere (10,22). It is produced utilizing a variety of techniques to
create a glaze layer over a silica core(8,9). The resulting surface of faience is a
transparent glass, usually blue or green encapsulating a body (21).
Unfortunately, the time period for the introduction of such glassy
faience is not well documented and thus it is not certain that it was made
before the invention of glass itself (22). An inconsistency that should also be
considered with this theoretical path is that while the full development of
faience was accomplished in Egypt (and thus commonly referred to as
Egyptian faience) (8) glass is tough to have originated in Mesopotamia and
Syria, with its spread to Egypt at a later date (7-12-16) As the more advanced and
significant faience production occurred in Egypt, it would be logical that the
transition from faience to glass would also take place among these Egyptian
artisans. Of course, this does not eliminate the possibility that the less
advanced faience artisans of Mesopotamia accomplished the more significant
advance to glass, while the Egyptian craftsman continued to perfect the
production of faience without the transition to the new material. In attempting
to explain the delay of more than 2000 years between the productions of
faience and of glass it has been suggested that an important factor was that the
production of faience involved only cold-working and reduced temperature
sintering of the raw materials(26). In contrast the routine production of glass
vessels and other objects involved the manipulation of hot, viscous fluids a
process that was more akin to metal working, Therefore, although the
production of essentially identical raw materials, the change from cold-
working for glazes and faience to hot-working for glass may not have been a
logical progression of an easy transition (26). Such a transition would most
likely have required input from metal workers who were more familiar with
such high temperature manipulations. Thus it can be argued that the discovery
of the techniques necessary ofr hot-working glass was the result of interaction
between the workers of glazed stone and faience and metal workers. Further, it
is possible that such interactions were a result of the changing control over and
organization of artisans following the political upheavals occurring in Egypt
and the Near East during the sixteenth century BCE.
As a result, artisans skilled in different crafts could have been brought
into close proximity in workshops and production centers. In such an
environment the transfer of technologies between crafts would have been
facilitated paving the way for the eventual discovery of glass production (26).
While arguments can be made for either of the two commonly proposed
pathways to the origin of glass it is clear that either path is not completely
independent of the other. In the first case metallurgy is thought to originate in
the Pottery kilns, potentially as a consequence of using metal ores in glazes. In
the second case the high temperatures required for the production and working
of glass is thought to have required input from metal workers. As such it is
quite reservation between the two groups of craftsmen resulted in the
discovery of glass with origins in bother metallurgy and siliceous glazes.
Glass Formation
Any material, inorganic, organic or metallic formed by any technique,
which exhibits glass transformation behavior can be termed as a glass. During
the glass transition the amorphous phase exhibits gradual changes in its
derivative, thermodynamic properties such as heat capacity thermal expansion
etc. and many of properties change from crystalline to liquid like values with
increase in temperature (27). Glass transformation behavior can be discussed on
the basis of changes in either enthalpy or volume with the temperature. When
liquid is cooled to the temperature below Tm without crystallization, but with
increase in the vi
1.3.
Figure 1.3 the effec
The crysta
volume at the me
gradual change i
change occurs is
the tangents drawn
known as glass tra
region.
The pheno
theories have bee
characterize the g
iscosity. These changes are schematically repre
effect of temperature on the enthalpy (or volum
forming melt.
allization process is manifested by a sudden c
lting point, where as the glass transition is charac
in the slope. The temperature range over wh
called the glass transition range the point of i
wn on both solid and liquid side of the curve
ransition is continuous as the slope gradually cha
nomenon of glass transition is to thoroughly under
en suggested based on a single property / para
glass. However, these theories have been success
esented in fig
me) of a glass
change in the
aracterized by a
which the slope
intersection of
ve (Fig 1.3) is
anges over the
erstand. Many
arameter, which
ssful only to a
limited extent as the glass. Transition is a function by many parameters like
heat capacity bulk compressibility thermal conductivity melting temperature,
cooling/ quenching rat etc. for a particular glass. Normally differential thermal
analysis (DTA) dialtometric measurements etc. are used for measuring the
glass transition temperatures.
Conditions for glass formation
To understand why certain melts on cooling get converted to glassy
phase and the others do not requires the knowledge of both kinetics and
thermodynamics of nucleation and crystal growth involved, when a particular
melt is subjected to cooling. As these parameters are difficult to evaluate,
many authors have tied to obtain the information regarding the glass formation
from the known physical properties of its constituents.
Thermodynamics of glass formation:
There are two main types of pathway that a liquid may follow on
cooling, either it may crystallize at or below the melting temperature Tm, or it
may under cool sufficiently, without crystallization to form a glass. The
volume-temperature characteristics for a liquid that follows either of these two
pathways are shown in Fig1.3. The behavior of most non-glass-forming
liquids is similar to the changes represented by curves abcd. Crystallization
occurs, bc, at temperature Tm ,although for kinetic reasons, the liquid may
under cool somewhat before freezing actually occurs. The difference in slope
of regions ab and cd indicates that the coefficient of thermal expansion of
liquids is usually greater than that of solids.(28)
The behavior of glass-forming liquids on cooling is similar to
the changes represented by curves abief (or obgh). In region be the liquid is
under cooled but does not freeze. At each temperature in this region, the liquid
rapidly reaches a state of internal equilibrium following a temperature change
but is, nevertheless, thermodynamically met stable relative to the crystalline
state. With decreasing temperature, however, the liquid viscosity gradually
increases until a stage are reached at which the liquid can no longer maintain
itself in internal equilibrium. The atomic arrangement that is present in this
under cooled liquid then becomes effectively ‘frozen in’ and on further
cooling, the material acquires the rigid elastic properties of a crystalline solid
but without the regular three-dimensional periodicity of a crystal structure.
This change in properties or behavior, from an under cooled liquid to a glass
takes place at a temperature of range of temperatures called the glass transition
temperature, Tg.
For any given composition it is generally possible to prepare glasses
with different degrees of stabilization; i.e. with somewhat different Tg. values.
With a slow rate of cooling, and provided that crystallization does not occur
the under cooled liquid may be able to maintain itself in internal equilibrium
until a somewhat lower temperature that it would if it had been rapidly cooled.
Consequently, Tg is lowered somewhat (compare points e and g of fig 18.2).
The glass transition effectively represents the crossover of two timescales: the
timescale to measure some property such as viscosity (value~1013P<Tg) and
the timescale for internal is of the order of a few minutes at Tg and in practice
it is not possible to extend the dashed curve e.g. very far since progressively
longer times are required for the liquid to contract and attain internal
equilibrium.
Kinetics of crystallization and glass formation
In order for a glass to form the Rae of crystallization of the under
cooled liquid must be sufficiently slow that crystallization does not occur
during cooling . It is possible therefore to treat glass formation in glass
formation in terms of kinetic criteria as well as the structural and
thermodynamic criteria referred to above. Crystallization of an under cooled
liquid is a two-stage process that involves (a) the formation of crystal nuclei
followed by (b) their subsequent growth. A kinetic condition for glass
formation is that the rate of nucleation and /or the rate of crystal growth should
be slow. In some under cooled liquids, nucleation is easy because there are
plenty of nucleation sites available: foreign particles container surfaces, etc.
The rate of crystallization is then largely controlled by the rate of growth
which varies with temperature. The rate is zero at the melting point increases
to a maximum at a certain degree of under cooling and then falls to zero again
at still lower temperatures.
Glass structure Theory
A simple theory on glass structure reposed by Goldschmidt, stated that
glasses of the formula Room form most easily when the ionic radius ration of
the action to the oxygen atom were between 0.2-0.4, reference taken from
Shelby,1997 (1). Since these rations tend to produce tetrahedral coordinated
captions, I was proposed that any these structures can from glasses.
Later work by Zacharias, proposed that glass formation may occur if
an open network of exigent tetrahedral or triangles with sufficient bonding to
produce a continuous network structure exists (Zarthariasen1932). (29)
Additions of alkaline or earth alkaline captions were placed in the hallow
space within the
Structure without forming any chemical phase. According to this theory, any
metal or non metal oxide should form a glass however; the non existence of
TIO2 of Al2O3 could not be explained with this theory.
A refinement of the theory was proposed, focusing on the cooling
process (Hagg, 1935) (30) It was stated that glasses consist f chains or two
dimensional nets. The symmetry and bulkiness of the glass forming unit above
the melting temperature wearer thought to be responsible for the glass forming
capacity. This theory explained why species like SiO2 formed a glass TiO2 and
Al2O3, did not Bond strength has also even used in an attempt to predict the
ease of glass
Formation. Ire was argued that stung bonds prevent the reorganization of the
melt structure into a crystalline structure during cooling, promoting glass
formation (31).
Raw materials for Manufacture
Glass is generally composed of different oxides playing different roles.
The main glass forming oxides are SiO2, B2O3, GeO2 & P2O5 , all of which
come from a certain area of the periodic table (see Fig : 1.3). They are oxides
of elements with intermediate electro negativity: these elements are not
sufficiently electropositive to form ionic structures, such as as NaCl, MgO
etc. but also are not sufficiently electro negative to form covalently bonded,
small molecular structures such as CO2 Instead bonding is usually a mixture
of ionic and covalent and the structures are best regarded as three-dimensional
polymeric structures.
Oxides of other elements around this group in the periodic able also
show a tendency to glass formation. Some such as As2O3, and Sb2O3 form
glasses if cooled very rapidly, Other such as Al2O3, Ga2O3, Bi2O3, Bi2O3,SeO2
and TeO2 are conditionals glass formers i.e. they do not form glasses alone,
but may do so in the presence of certain other non-glass forming oxides.
Fig 1.4 Elements whose oxides form glasses readily
Silicon oxide the primary glass former, But to its high melting point
(17500C) oxides of other elements are added to reduce its temperature in the
melting range and enhance the properties of glass as needed. Broadly, These
oxides which form the major constituents of a glass are as follows-
a) Glass former oxides or network formers
These oxides are capable of forming glassy network independently e.g.
SiO2, B2O3, P2O5 etc. it is the most essential comport in glass and each glass
and each has glass e.g. if silica content is more, then it is called as silicate
glass. If boric oxide is in equal amounts with silica then it is called as
borosilicate glass. Different compositions of these materials can be used to
form the glass. The examples of the glass formers are- silica (SiO2), Boric
oxide (B2O3) phosphorous oxide (P2O3) and under certain circumstances
GeO2, Bi2O3, As2O3, As2O3, Sb2O3, Ga2O3,V2O5,BeF2,ZrF4 etc. Thaw choice
of the base glass is very important to achieve the desired properties which in
turn depend on the glass former used for making the glass. Table1.2 represents
the properties of few pure glass formers. (32)
b) Flux
Flues are used to reduce the processing temperature of the glasses for
stability and for the improvement in the glass formation. Fluxes like soda ash,
potash, one pros aced, calcium fluoride etc. which induce rapid chemical
activity causing the batch to melt together and form glass. The examples of the
fluxes are- Na2O, K2O. B2O3, CaF2, PbO, Li2O etc.
c) Network modifier
These oxides do not form glass network of their own, but they modify
network, f glass and change properties of glass drastically hence these oxides
are also called property modifiers. The addition of fluxes degrades the glass
properties and hence to counteract their degradation the property modifiers are
added in glass. The examples of modifiers are- the alkali oxides (Na2O, K2O,
Li 2O etc)_ alkaline earth oxides (CaO, BaO, etc.) transition metal oxides,
alumina(Al2O3).
Fig 1.5 Elements whose oxides used as a flux and network modifier in reaction
d) Colorants
There are used to control color of final glass. Certain oxides or metallic
Salts of transition elements such as those of Ti, V, Cr, Mn, Fe, Co, Ni and Cu
are added to the fused glass to produce colored glass. See Table-1.3.
Due to presence of coloring matter, coloring matter, constitutional
change occurs and lass turns to be colored. Colored glass possessed technical,
scientific and decorative distinctions over the colorless glass and hence it has
specific applications.
Colored glasses are used for scientific, scientific, technocal & decoration
purposes. Therefore, coored glasses are used in the manufacture of tancy
articles window panels, artificial gems, files sun goggles, color filters, sighal
lights, globes etc.
Table 1.1 Colures and coloring materials
Sr. No. Colour Colouring Material
1
2
3
4
5
6
7
8
Blue Ruby Red
Milky white
Green
Yellow and Yellow
Brown Violet or purple
Pink
Black (unknown),
Dark Violet,
Dark Brown or Dark
Blue
Cupric oxide, cobalt oxide Cuprous oxide, Gold
Tin oxide, Calcium phosphate, cryolite
Chromium oxide
Cadmium sulphide sodium urinates, Antimony
trisulphide, charcoal etc.
Manganese dioxide Selenium or Tellurium Salts
Oxides of cobalt, Nickel, Iron or Manganese.
Fig 1.6 Part of periodic table shows transition metal used in reactionFining Agents
These are added in the glass batches to promote the removal of air
bubbles from the melt. The examples of fining agents are Ag2O3, Sb2O3,
KNO3, NaNO3, NaCl, CaF2, NaF, Na3AlF6 and number of sulphates (whose
quantity is < 1%)
1.6 Types of Glasses:
Depending on the network former used, glasses can be classified as
silicate, borosilicate, alumina silicate, borate, phosphate glasses, chalcogenid
glasses etc. and depending on its end used as optical glasses social application
glasses etc.
Large varieties of glass are obtained by varying the composition of the
batch. Based on the composition the different types of glasses have been
disused as follows.
1. Soda time Glass : (Soda glass or normal Glass or Soft Glass)
Soda lime of lime glasses are mode by fusing together appropriate
quantities of sand, lime or lime stone and soda ash. The approximate
composition of soda glass is Na2O, CaO, 6SiO2, Thus lime glass is a mixture
of sodium and calcium silicates, It is frequently called ‘soft glass’ as it fuses
very easily. As the raw materials are very cheap and as it requires very low
temperature for melting, soda glass backs, plate glass very cheap.
This glass is used in making glass tubes, bottle glass, glass bricks, plate
glass, ordinary chemical apparatus like test tubes, beakers, tubing, glass bends,
window glass, jars electric lamps, eye lenses etc.
2. Phosphate Glasses :
There is relatively poor chemical durability, which often limits their
usefulness in various applications (33) Durability can be improved by the
addition of Bi2O3, Al2O3, Fe2O3 etc.(33) These types of glasses have
considerable potential applications. (35) These glasses have wide technological
interest due to their unique physical properties such as low glass transition
temperature (Tg), lower melting temperature, high thermal expansion
coefficient high ionic conductivity & bio compatibility. (36)
The optical properties of phosphate glasses show many favorable
features for use in optical devices because of their excellent transparency and
good mechanical and thermal stability.
Important commercial applications of phosphate glasses do exists as in
the construction of secondary electron multipliers. As the absorption bands of
iron oxide in phosphate glasses are sharper in UV and IR region than in
silicate glasses, these glasses are nearly transparent to visible light. Phosphate
glasses containing Ion oxide are used as a heat absorbing glasses.
3. Borosilicate Glasses:
It has good chemical durability and thermal shock resistance, In
borosilicate glass part of silica is replaced by boric acid which confirms some
desirable properties to glass such as thermal shock electrical shock and high
stability. The glass is used in the manufacture of kitchenware, glass pipelines
in factories, high tension insulators; it is mainly used as heat resisting were
like oven were and laboratory glass were (37). The special types of glass called
Pyrex, Jena, corning etc. are manufactured from borosilicate glass; It is widely
used in laser technology (38).
4. Alumina silicate glasses:
When part of the silica in glass composition is by alumina (Al2O3),
Aluminosilicate glass gates formed.(39) Aluminosilicate glasses are used
commercially because they are chemically stable and withstand at high
temperatures. Thus application include combustion tubes, gauge glasses for
high-pressure steam boilers and in halogen-tungsten lamps capable of
operating temperature as high as 7500C.(40) Tungsten ions are well known due
to their unusual influence on the optical and electro chemical properties of the
glasses for the simple reason that the oxides of tungsten participate in the glass
network.(41)
5. Telluride Glasses:
Telluride glasses were prepared and studied by Starwort in 1952.(42)
The important properties of these glasses are refractive index up to 2.3 bad
high thermal expansion coefficient ~25.0 x 10-0c, TeO2 based glasses have
also been used in preparation of transparent glass ceramics, Most of the
telluride glasses have got good stability under ambient conditions.
6. Van date Glasses:
Pure V2O5 melts at around 6600C and forms glass only when it is
cooled rapidly. Glass formation between V2O5 and a number of oxides like
P2O5, TeO2, B2O3,GeO2, BaO, ZnO, CdO, MgO etc. has been investigated by
various authors and the regions of glass formation and the quenching rate
required for the glass have been reported.(43)
7. Chalcogenide glasses
Amorphous Chalcogenide materials can be prepared by a variety of
methods some methods for forming glasses are- Slow cooling (malt
quenching), moderate quenching, rapid quenching or splat cooling roller
quenching or melt spinning laser glazing , condensation from the gas phase,
sol-gel.(44) Melt quench technique is used to make this type of glasses.(45)
1.7 Preparation methods of glass
Different techniques have been used to prepare amorphous glassy
materials in various forms like bulk sheet, powder, thin films, etc.
Most of the traditional glasses are inorganic and non metallic, but
currently large number of organic glasses is in front line and they need
different preparation techniques. Metallic glasses are also becoming very
common with every passing year, Besides the conventional melt-quenched
technique, glasses are also prepared by other methods such as physical vapor
deposition, sol-gel method, applying intense intense shock waves mechanical
alloying etc.(22) Some of these described in brief in the following section.
1. Thermal evaporation,
2. Sputtering,
3. Glow discharge decomposition,
4. Chemical vapor deposition,
5. Electrolytic decomposition,
6. Chemical reaction,
7. Reaction amorphisation,
8. Inrradiation,
9. Melt quenching
10. Sol gel technique
11. Physical vapor deposition, etc.
Among the above, melt quench technique is the simple and widely used
for the preparation of glassy materials are very easy.
1. Glass preparation and handing are very easy
2. Speedy preparations of innumerable compositions of the glasses are
possible.
3. Ability to produce wide variety of new oxide glasses.
4. Bulk glasses can be prepared and comparisons can be made with
pulverized glasses.
5. Simultaneously, both amorphous and crystalline nature can be obtained in
the same molt, etc.
Hence, melt quench technique is used to prepare different
compositions of SAT. SPT and SVT glassy compounds.
Methods for preparation of glasses
Most of the traditional glasses are inorganic and non-metallic, but
currently large number of organic glasses is in front line and they need
different preparation techniques. Metallic glasses are also becoming very
common with every passing year, besides the conventional melt-deposition,
thermal evaporation, sputtering glow discharge, chemical vapor depositional
melt-supposition thermal evaporation, sputtering glow discharge, chemical
vapor deposition sol-gel method applying intense shock waves mechanical
alloying etc. (46) some of these are described in brief in the following section.
1) Thermal evaporation
This is one of the most widely used methods for producing amorphous
thin films (47) in this method the material in the form of grains, turnings or
powder is evaporated in vacuum~1 x10-6 Torr. A substrate is placed at a
suitable distance. The temperature of the substrate is kept at lower
temperature, The evaporation trial, placed in a boat (For high melting
materials). Due to the lower temperature of the substrate, the mobility o the
atoms reaching the surface of the substrate randomly, is frozen resulting in the
formation of an amorphous thin film. Thin amorphous films of amorphous
semiconductors like Si, Ga, As, Chalcogenide compounds like As2S3, As2Se3
etc. are prepared by this method. The main disadvantage of this method is the
differential evaporation of the individual constituent form compound : te
component, which is having lower melting point of higher vapor pressure
evaporates preferentially, thereby depleting the source and creating
compositional inhomogentiety in the film.
2 Sputtering
Sputtering method involves the bombardment of a source by energetic
ions obtained from low-pressure plasma resulting in the removal of atoms or
slitter of atom from the source material and its subsequent deposition a actins
film on the substrate. deposition as a this film on the substrate. Sputtering
method is more flexible compared to the thermal evaporation method
reasonably homogeneous and uniformly thick deposits can be produced by this
method (26, 46). The main disadvantage of the method is that it requires ration of
partial pressure of reactive gas to inert gas, power applied to target, bies
voltage of target of substrate etc.
3. R F Glows charge
Glow discharge method is similar to sputtering process. In this process,
instead of plasma ejecting the material from the target, chemical reaction is
initiated in the gas phase by creating in r.f. glow discharge of the reactant
glasses, leading to the deposition of a martial on the substrate placed inside a
chamber(47). The discharge can be produced It is either in the pure reactant
fast or in a mixture of reactant gases and a scarier as like argon. By using a
combination of reactant gases, films of different materials can be prepared. It
is difficult to control parameters precisely in this method as compared to
methods mentioned earlier.
4. Chemical vapor deposition
Chemical vapor deposition method, In principle, is similar to glow
discharge method bit the decomposition of the reactant gas is achieved b
thermal energy (pyrolytically), for which temperature of the order of 1000 K,
is commonly used. Amorphous hydrogenated Si (a-Si:H) as well as B and P
doped samples of amorphous Si have been prepared by this technique(40)
5. Melt-quenching
Melt-quenching is the oldest methods being used for the preparation of
glass. An essential pre-requisite for the glass formation from a melt is that, the
cooling has to be sufficiently fast to prevent nucleation and crystal growth tees
of cooling required for glassy phase formation are different for different
materials. For example certain glass formers such as B2O3, P2O5 etc. will from
glassy phase even under conditions of slow cooling (like 1K/s) Most of the
glasses with B2O3, SiO2 and P2O5 etc. as network rates of the order of 107 K/s
is required which require special techniques like melt spinning melt extraction
etc.
6. Sol-Gel method
Gel is an elastic solid matter produced abruptly form a viscous liquid
by a process involving continuous polymerization, Gel, which is amorphous
and homogeneous, is heated to remove voltaic components and produce an
initial densification, followed by a final process of sintering at appropriate
temperature to produce amorphous solid for example amorphous SiO2 can be
prepared from alloy silences, like Si(OCH2)4 or SI(OC2H5)4. These lakesides
undergo polycondensation and hydrolysis. Enrich on heating lead to
progressive formation of metal oxide. The reaction can be schematic
represented as
M (OR)n + n H2O M (OH)n + n R(OH) ………..(1.1)
P M (OH)n p Mon/2 + p n/2 H2O …………(1.2)
Where M is Si, Al, Ti, and Zr etc. the resulting metal oxide is in the
from extremely fine particles (~2nm).
Advantage of sol-gel technique is that many refractory materials can be
prepared homogeneously at a relatively lower temperature, especially below
the melting point. In addition, the purity of the materials can be improved as
the starting materials can be purified to the desired extent by various
techniques. (48) Even though the process appears to be simple, the reactions are
very sensitive to the external conditions like temperature, concentration of
solutions, reaction time etc. the main disadvantage of this process is to get
proper organometalic precursors for cations.
7. Electrolytic deposition
Amorphous layers of a metal oxide can be grown on the metallic
surface by using it as an anode in an electrolytic cell having a variety of
aqueous electrolytes. When DC voltage is applied between the electrodes the
captions migrate towards the cathode and the anions which include O2-
migrate towards the anode. At the anode under sufficient over voltage, O2-
reacts with the metal producing the glassy layer of the oxide having thickness
up to several thousands of angstroms. It has been demonstrated that glassy
films of oxides of Al, Zr, Nb, Ta etc, can be easily prepared by this method (59)
In addition to this any other methods have been reported to produce
amorphous materials which are specific for certain system, such as high
pressure shock waves, slow mechanical grinding, explosive compaction,
radiation damage etc. It has also been reported that amorphous intermetallic
compounds can be made by hydrogen absorption (50-52).
1.8 PREPARATION OF GLASS: MELT-QUENCHING TECHN IQUE
Glass is prepared by cooling the molten liquid form of the compound
sufficiently quickly. The cooling must be sufficiently fast to preclude crystal
nucleation and growth. The crystallization rate of an under cooled liquid
depends on the rate of crystal nucleation and on the speed with which the
crystal-liquid interface moves. These are strongly dependent on the reduced
temperature T,=T/T and the under cooling AT,=(T,-T)IT,. High values of
viscosity reduce the crystallization front velocity and hence, the crystallization
rate. Cooling rate is a critical factor in determining glass formation. Generally,
the quenching rate is from 10” to 10’ KS-‘depends upon the preparation
method and type of materials, Various types of materials can be prepared in
amorphous/glassy from using melt quench technique. Fig 2.1 shows types of
melt quench techniques used to prepare glasses. There are various techniques
used for creation different cooling to produce various types of glasses.
Preparation of glass by melt-quench technique involves four steps viz. Batch
calculations, batch melting, fining and homogenization.
1) Batch calculation
The batch calculation may be simple or complex as par the complexity
of the glass compositions and raw materials used.
Glass batch calculation or glass batching is used to determine the
correct mix of raw materials (Batch) for a glass melt.
Glass batch only consist the respective oxides in the state given as in
glass formula. However, if any of the components is present in one or more
forms of raw materials it requires much more complicated calculations. All the
calculation follow similar steps. Determination of the weight fraction of each
component required for desired molar composition.
Example Calculation
An example batch calculation may be demonstrated here.
The desired glass composition by wt% is-
5CaO – 30Na2O – 27.5 B2O3 – 27.5 P2O5 -10Al2O3 and as raw materials are
used sodium nitrate, Calcium oxide, Boric Acid, Diammonium hydrogen
phosphate and Aluminum trioxide. The formation and molar masses of the
glass and batch components are listed in the following table.
Table:1.2 The formation and molar masses of the glass and batch
components are listed
Formula of
Glass
component
Wt% of
component
Molar
mass of
glass
component
g/mol
Wt%
w.r .t.
molar
mass of
glass
com.
For
30gm of
sample
Batch
component
formula
Molar of
batch
component
g/mol
Net wt of
taken
batch
componen
t taken gm
Na2O 30 62 18.6 6.215 Na2CO3 105.99 10.624
CaO 05 56.08 2.804 0.937 CaCO3 100.08 1.672
B2O3 27.5 69.62 19.145 6.397 H3BO3 123.68 11.36
P2O5 27.5 141.94 39.03 13.042 (NH4)2HP
O4
264.16 24.272
Al2O3 10 101.96 10.196 3.407 Al(NO3)
9H2O
750.38 25.07
Batch
2) Batch melting
The batch melting comprises the following steps-
a) Release of glass
Initial heading of the batch releases the moisture present as absorbed
by particles, water of hydration, and hydroxyl group; generally, most of the
glass components are hygroscopic. The temperature of release of moisture
depends on the nature of bonds i.e. chemical or physical and the strength of
the bond.
Decomposition of carbonates nitrates. Sulphates, ammonium
phosphates yields the glasses like CO2, SO2, NO2, NH3 which results in the
expansion of volume of batch than the initial volume.
Alumina
crucible
Fig. 1.7 Photograph of Release of gases during heating in furnace.
This problem has to be dealt with roper stirring and mixing, Due to
stirring the bubbles are pushed towards the surface, A bubble of size 1 mm
diameter per m3 glass is the serious imperfection in any type of the glass.
b) Formation of liquid phases
Liquid phases are formed by direct melting of batch components,
Eutectic mixture is formed by meting the batch components Time needed t
melt original batch completely is called batch free time. The various factors
which influence the batch free time include temperature, composition,
components, batch homogeneity, grain size of reacting components, grain size
and amount of cullet added.
c) Melting accelerants
Various methods are used to decrease the batch free time and most
important one is the changes in read materials e.g. replacement of small
fraction of sodium carbonates by sodium sulphate speeds up the dissolution of
sand by forming additional lower melting additional lower melting eutectic
mixtures.
Components which force the water to enter the melt are especially
effective in accelerating melting processes water efficiently reduces the
viscosity of the melt. Mechanical methods which increase contact between
particles of raw materials are also very useful e.g. making brick, pellet and
granules of reactants.
d) Volatilization of component from melts
Loss of components which are volatile of higher temperatures can
significantly after the composition of glass obtained after prolonged melting as
compared to shorter melting time. These losses are significant for alkali oxide,
lead, boron, phosphorus, halides which have high vapor pressure at higher
temperature.
3) Fining of melts
The terms fining and refining refer to the removal of bubbies from the
melts. Though the bubbles are not detrimental to scientific studies the are
undesirable in commercial glasses. Fining o the melt begins during the melting
process but typically extends till the complete disappearance of residua notch.
Bubble formation an also be attributed to physical trapping of atmospheric gas
due to decomposition of components.
Bubble can be removed by physically rising to the surface of by
chemical dissolution of the glass into the surrounding of the melt. A chemical
method for removal of bubbles depends on the addition of batch components
called as fining agents.
4) Homogenization of melts
The fluid produced during the initial batch decomposition process is
highly heterogeneous. This heterogeneity is reduced by stirring the glass
during the fining process. Homogeneity is described in a negative manner as
the homogeneous melt which is free from significant heterogeneities.
Significance of the heterogeneity is different for the intended end use of the
glass. Defects like bubbles, seeds. Stones. (un melted particles), striate cord
and color in homogeneity are the causes of in homogeneity Homo genetic can
be achieved by proper miming reducing the grain size of the components
stirring of the melt of bubbling of gas into the melt. Homogeneity can also be
achieved by proper mixing as well as by ball milling of the composition. The
optical and chemical homogeneity is achieved by stirring the glass melt by
mechanical stirring of bubbling of the gas the melt.
Glass transition
When a liquid cooled, depending upon cooling rate, it may take one of
the two routes of either crystallization or super cooled liquid amorphous at the
melting point. The crystallization processes manifested by an abrupt change in
volume at melting point and the amorphous formation is characterized by a
gradual decrease in the volume. If there is change in the slope of the volume
with decrease of temperature, the temperature at which the change of slope
occurs is termed as the glass transition temperature. The glass transition
temperature depends on the rate of cooling of the super cooled liquid. It is
found that the low cooling rate lowers the glass transition temperature. The
actual value of the glass transition temperature may vary from I 0 to 20% for
varying cooling rates of glass transition temperature and T,-melting
temperature and b show the heat capacity versus temperature plots
respectively for crystalline and glass transition temperature. The observed
discontinuity of C, vs. temperature indicates the glass transition temperature.
1.9 BOROPHOSPHATE GLASS
Borophosphate glasses have interesting structural network due to the
presence of two glass formers B2O3 and P2O5 thus incorporating mixtures
borate phosphate and borophosphate units. A range of captions had previously
been studied in borophosphate to assess the structure and some glass
properties. This includes Li+, Na+ K, Ca2+, Ba2+, and Zn2+. The addition of
B2O3 modifies the properties of phosphate glasses by cross-linking phosphate
chains to improve chemical durability.(29) previous structural B(3) or
tetrahedral(4) sites within the borophosphate glass network depending on
composition. The possible borophosphate (53) [analogous to AlPO4 structure (54)] and borates units (55) present in borophosphate structural networks are
shown in fig 2.10 In the phosphate rich commission range, boron atoms are
mostly B(4) while in the borate rich range B(3) dominates. This change in the
co-ordination no. will affect the properties of the glasses. Similar to that
observed in aluminophosphate glasses as descried earlier shows the glass Tg
as a function of the B/(B+P) ratio for calcium borophosphate glasses, where
the maximum observed at B/(B+P)=0.3 denotes the transition from a B(4)
network to a B(3) network.
O
B
O O O O
B O B
B B O O
O O O
O O O
O B O P O B O
O O O
O P O B O P O
O O O
Fig: 1.8 The incorporation of B(4) sites results in the formation of (B-O-P) bridges
cross linking neighboring phosphate chains.
The incorporation of B (4) sites results in the formation of (B-O-P) bodegas
cross linking neighboring phosphate chains leading to increased structural
cross land density. This causes an increase in the glass properties namely
density and glass transition temperature further increases in B2O3 result in
structural change from a disordered borophosphate network as the boron co
ordination no. changes B(4) to B(3). This covalent cross link density and
weakens the glass network.
1.10 IMPORTANCE AND APPLICATIONS
In all commercially important glasses B2O3 is used as a most common glass former
and is also used as a dielectric glass former material. Over a wide range of modifier
concentration borate glasses can be formed at relatively lower melting temperature. (56) B2O3 is a basic glass former in borate glasses because it has higher heat of fusion
and lower cation size. The most important point of borate glas formation is the
structural investigations of boron and related doped system. B3+ ions are triangularly
co-ordinated by oxygen atoms in borate glasses and triangle units are corner bonded
in a random configuration. In identifying several borate groups IR studies and 11B
MAS NMR investigation were important. (57-58) Borates group consists of boron
oxygen triangle and tetrahedral which forms the glass network at various
modifications levels. (59-61) Up to 33.3% of Na2O is found in alkali modified borate
glasses. Where there is continuous formation of BO3 - BO4 units and further
increase in alkali which leads to the reconversion of BO4 - BO3 with non bridging
oxygen. Other oxides can enter the glass network as a network former and also as a
network modifier. (62) Because of this structure of glass is expected to be different
from that of alkali borate glasses. (58, 63) in this study we report the synthesis and
structural studies of borophosphate glass.
Phosphate and borophosphate glasses present an important group of glass materials
having several commercial applications. Their research is still continuing and new
materials based on these glasses have neon prepared. Therefore studies of their
structure and properties are reported on international conferences on glasses
worldwide. Special phosphate glasses show promising usefulness as fast ion
conductors, waveguides, special switches, fibers, etc. Nevertheless the applications of
these glasses are offer hampered by their low chemical durability. The addition of
trivalent oxides together with substitution of alkali oxides by divalent oxides can
improve their chemical durability. Our studies in reent years were aimed at the
stabilization of phosphate glasses with B2O3 combined with ZnO of PbO. Such
materials offer better chemical durability than alkali phosphate or borophosphate
glasses. Several studies were also devoted to mixed MO-Me2O borophosphate glasses
with M= Pb and Zn and Me=Li, Na and K. We studied also the modification of zinc
phosphate and borophosphate glasses with higher-valiant oxides, e.g. Sb2O3, Bi2O3 or
TeO2 and transition metal oxides TiO2, NbO5, MoO3 and WO3, For structural studies
we applied Raman and infrared spectroscopy combined with 31P and 11B MAS NME
spectroscopy. The aim of these studies is to identify basic structural units in these
glasses and to investigate structural changes with changing glass composition and to
relate structural changes with changes in the properties of glasses.
Study of thermal properties of glasses is carried out using a variety of
thermoanalytical techniques (DTA, DSC, and dilatometric and heating microscopy
thermal analysis). The most important applications of these glasses present laser
glasses, glasses for the deposition of radioactive wastes and glass solders. Nd-doped
laser glasses used in high power systems are predominantly phosphate-based with
near metaphosphate composition. These glasses are characterized by large stored
energy, efficient energy extraction, resistance to laser-induced damage and mature
manufacturing technology. For the storage of radioactive wastes glasses containing
about 40% Fe2O3 a 60% P2O5 were proposed due to their high chemical durability and
the ability to include a high content of radioactive oxides like Na2O, Cs2O, SrO, UO2
or Bi2O3. Thee oxide dissolve in the glass melt without a significant effect on its
chemical durability. Zinc borophosphate glasses or SnO-ZnO-P2O5 glasses were
proposed for the application in solders replacing lead-based solders. Both glasses
reveal a sufficient chemical durability, low values of the glass transition temperature
and a low coefficient of thermal expansion (64).
For phosphate-rich glasses the presence of B2O3 tetrahedral, associated with the B-O-
P bridges formation, and induces a random ramification and a rise of compactness of
the borophosphate glass network. Consequently, the glass transition and
crystallization temperatures, the density and micro hardness increase, whereas the
solubility in water and the cut –off wavelength in the UV region decrease. The
maximum of the crystallization temperatures glass structure. For higher B2O3
concentrations depurate structure gradually substitutes for the rigid borophosphate
network. The properties trends, except for the micro hardness, are reversed. The
substitution of the sodium for calcium weakens the cross-links between oxygen atoms
and metal captions and enhances the disorder of the structure. As a result of this
substitution, the glass transition temperature and the micro hardness decrease,
whereas the solubility in water increases. The intensify of the crystallization peak
tends to vanish. These structural hypotheses are under active investigation using NMR
and Raman spectroscopic analyses. (65)
Alkali Borophosphate glasses are use as a ionic conductors, biomaterials and optical
materials. Chemical durability of glasses improves by the intermixing of borate and
phosphate networks. It also maintains low processing temperature. A main body of
research has been focused on structureproperties of lithium calcium borophosphate
glasses doped with transition metal ion. But when we study the borate rich
compositional regime we find properties such as ionic conductivity and dissolution
are expected to be quite different. Previous study shows the network modifying
behavior of the less studied heavier alkali cations such as Cs, K, Rb which appear to
have a different structural role than Na & Li. (66) Phosphate glasses have a
comparetivelly high transmission in the ultra violet region compared to borate and
silicate glasses. (67) Phosphate glasses have low melting temperature and low glass
transition temperature as compared to silicate glasses. (68) Applications of
phosphate glasses are: 1) These glasses are useful for application in bone
transplantation. 2) Phosphate glasses are used to glass to metal seals. 3) It is also used
as a containment of radioactive waste and fast ion conductors. 4) Also used as a laser
host materials. etc. (69) Chemical durability of phosphate glass improves by the
addition of Al3+, B3+ and Bi3+ etc. It is because the formation and relative stability of
M3+-O-P bond. (70) Thermodynamical and optical physical properties are modified due
to these ions. This is only because formation of cross linked bond which changes the
glass structure. When we study verious multicomponent glass system. Borophosphate
glasses have the improved durability and various interesting applications. For fast ion
conducting applications alkali and silver borophosphate glasses have been developed.
previous study of structure of borophosphate glass by NMR soectroscopy (70) shows
the BO3 and BO4 structural units are present in glass structure. Fraction of BO4 unit
found in this study is important parameter to improve the durability of glass structure.
1.11 RECYCLING OF GLASS
Recycling of any material is important. Because for the new material
requires less energy, less time and min. raw material. It is very interesting to know
that glass can be recycled millions of times. We should know that what type of glass
can be recycled. Any recycled glass used to produce jars and bottles. As we studied
earlier glass is made up of silica, limestone and sand. In Australia glass manufacturers
does not use 100% raw materials. They use waste or recycled glass for the
manufacturing new glass. They take all recycle material in furnace for heating.
Recycled material melts at 1500 0C. Melted liquid is dropped in to a mould. This
creates jars and bottles. Moulded jars and bottles cooled and ready to use.
Waste or recycled glasses crushed, this crushed called as cullet. This cullet is mixed
with virgin glass and produces new glass. (71) Making glass using cullet saves energy.
Because cullet need lower temperature than vergin raw materials. Over all process
requires less energy.
We can recycle:-
We can recycle glass jars of jams and spreads bottles. Clear brown or green bottles
which includes, juce, beer, wine, sauces, and soft drink bottles can be recycled.
We can not recycle:-
Broken drinking glasses, light globes, china, medical or laboratory glasses, mirrors,
windows glass can not be recycle. Before recycling the glass bottles it should be
rinsed and have lids removed.
Benefits of recycling:-
This is the process where waste materials are convertd to best material. Means new
useful products are produce by recycling process. Recycling process is social
advantage, economical advantage and mainly environment advantage. Following
advantages are some of them:-
1. Recycled material produces less air pollution, less water pollution than virgin
materials. It means recycled material prevent environment.
2. Glass can be recycling millions of time without loss of quality.
3. It conserves natural resources and raw materials used to produce new product.
4. It generates environment awareness and civic pride.
5. Producing same product from raw material reduces global warming, saves
energy and reduces the chances of acid rain.
6. Land fill space is conserved because raw materials used for making new
one.(72)
1.12 AIM OF THE WORK
To study the synthesis and characterization of lithium calcium borophophate
glass doped with TMI is the main aim of this work. This study focused on the
synthsis of borophosphate glass with unique concentration pattern. That is
melt quench technique. And resultant products are characterized with different
characterization technique. Following summarized points give the detail frame
work of thesis:-
1. Our study includes the synthesis of binary-ternary borophosphate glass
containing alkali oxides like; Na2O, K2O, Li2O etc. & various transition metal
ions like Cr, Co, Ni etc.
2. Research & development work include synthesizing glass that replaces
imported glass in many applications involving high voltage, nuclear reactor,
optical devices, chemical Industries telecommunication sector, & ultrahigh
vacuum technology. They have superior electrical insulation ultrahigh
vacuumed compatibility high thermal & chemical stability, low thermal
conductivity and good mechanical strength.
3 Synthesis and optimization of borophosphate glass system.
4. Optimization of boron, mixed alkali effect, transition metal ion (TMI),
concentration in the glass system.
5. To study the effect of doping element on the optimized glass properties.
6 To study the effect to additives & alkaline earth ion optical on the glass
properties.
7 To study the thermo physical, mechanical, structural and degradation
properties of borophosphate glasses.
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