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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