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Acknowledgement

An academic project is a golden opportunity for learning and self-development. I consider

myself very lucky and honoured to have so many wonderful people lead me through in

completion of this project.

I am highly grateful to Swami Shastrajnananda, Principal of Ramakrishna Mission

Vidyamandira for helping me to get the opportunity of carrying out thesis work at CSIR-

CGCRI.

I wish to express my gratitude and special thanks to Mr. Kamal Dasgupta, Director CGCRI for

him kind permission to carry out the project in this institute and to use the facilities available

in the institute.

I would like to express my deep sense of gratitude and indebtedness to my guide Dr. Swapan

Kumar Das, Chief Scientist and Mr Surajit Gupta, Senior Principal Scientist for their invaluable

encouragement, suggestions and support from an early stage of this research and providing me

extraordinary experiences throughout the work. Above all, their priceless and meticulous

supervision at each and every phase of work inspired me in innumerable ways. The

involvement of my guide with originality has triggered and nourished my intellectual maturity

that will help me for a long time to come. I am proud to record that I had the opportunity to

work with an exceptionally experienced scientists like them.

I am thankful to XRD, SEM and refractory testing division for their support. A special thanks

to all technical staff of CGCRI for their help during my work.

Arkaprava Mandal

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Contents

Subject Page Number

Objective and Plan of Work 2

Chapter 1: Literature review 3

Chapter 2: Experimental methods 24

Chapter 3: Results and Discussion 28

Conclusion 36

List of References 37

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Objective of the present study and plan of of work:

Although commonly used Glass Corrosion resistance refractory such as AZS ( Alumina-

Zirconia – Silica ) and Alumina based refractories are presently practised in glass

manufacturing processes , but new developments are necessary to protect highly corrosive glass

corrosion for many application particularly for high technical end application . In view of this

CSIR – CGCRI is carrying out research activities in the area of newer refractory crucible for

melting of high corrosive glasses . In my proposed work two compositions with two different

particle grading will be studied with respect to their slip casting behaviour , casting ability in

plaster mold , and related physico mechanical properties after firing at a particular temperature

with different schedule ( Reaction Kinetic Study ) .The work will consisting of ---

1. Collection of raw materials and its chemical analysis.

2. Selection of batch composition and its preparation

3. Sample preparation by slip cast technique and their testing with respect to shrinkage and

green density.

4. Fringing of sample at 1370oC with different heating schedule.

5. Determination of fired characteristics

% of linear shrinkage.

Bulk density.

% of Water absorption.

Flexural Strength.

Phase identification by X-ray diffraction technique.

Scanning Electron Microscopic studies.

EDAX analysis.

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Chaptar 1 : Literature Review :-

Introduction :

Refractories are heat resistant materials used in almost all processes involving high

temperatures and corrosive environment. These are typically used to insulate and protect

industrial furnaces and vessels due to their excellent resistance to heat, chemical attack and

mechanical damage. Any failure of refractory could result in a great loss of production time,

equipment, and sometimes the product itself. The various types of refractories also influence

the safe operation, energy consumption and product quality; therefore, obtaining refractories

best suited to each application is of supreme importance.

Researches in refractory materials frequently are necessitated by metallurgical and glass

researches at elevated temperatures, particularly when treatment of molten metal or glass of

high purity is involved. The material from which crucibles are made must be chemically inert

to the molten object, free from impurities that may be transferred to the metal or glass, and

must not melt or soften in use. The containers for this type of research must be of the desired

shape, size, and capacity, sufficiently strong and resistant to thermal and mechanical shock,

and resistant to the erosive action of the molten metal or glass.

A brief history of Refractory :

The history of refractory materials starts in the days when humanity just discovered fire.

Millennial learning and improvement of refractory materials allowed them to become the basis

of furnaces, such as - blast, glass, steel smelting, cement and brick, copper and others that are

currently in use in various industries.

After the blast furnaces appeared in Russia about the middle of the XVII century, people began

to produce refractory bricks from refractory clay and kaolin. A significant number of refractory

bricks was made of clay near Moscow. The development of refractory materials in the first half

of XIX century accounted for mainly in the steel mills as a supplement to the general direction

of the branch. Because of the agricultural orientation of the country, the problem of bi-

directional production existed for a long time and its had detrimental effect on the development

of industrial potential. So, at the same time, Europe, after the industrial revolution, had fully

working refractory plants that were put into operation during the Napoleonic Wars. The first

specialized production of refractory materials was founded in 1810 in Germany. The first steps

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of creating a specialized production of refractory industry in the Russian Empire had a dramatic

development of industry and promotion of the bourgeois class in the decisive political and

social roles. So, in 1893, there was founded the first refractory plant "Belokamensk" in

Bryantsevka (now Soledar). In 1897, there was founded a refractory plant in Latioy. The

refractory industry is only available in 35 countries from more than 212. More than half of the

production of refractories accountsfor the CIS and the USA. So, at the moment the presence of

the refractory industry and the quality of refractories in a country is characterized by its degree

ofindustrialization.

What is refractory ?

A material can be described as ‘Refractory’ if it can stand upto the action of corrosive

solids,liquids and gases at high temperature (>1650 oC) . Important characteristics which are

required of a Refractory are

i) High fusion temperature.

ii) Mechanical strength at high temperature.

iii) Resistance to thermal shock

iv) High insulation property &low thermal conductivity.

Classification:

Refractories can be classified on the basis of chemical composition and the methods

of manufacture or physical form.

Classification Based on Chemical Composition

Refractories are typically classified on the basis of their chemical behaviour, i.e. their reaction

to the type of slags. Accordingly the refractory materials are of three classes - Acid, Basic &

Neutral.

Acid Refractories : Acid refractories are those which are attacked by alkalis (basic slags). These

are used in areas where slag and atmosphere are acidic. Examples of acid refractories are:

1) Silica (SiO2),

2) Zirconia (ZrO2), and

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Neutral Refractories : Neutral Refractories are chemically stable to both acids and bases and

are used in areas where slag and atmosphere are either acidic or basic. The common examples

of these materials are:

1) Carbon graphite (most inert)

2) Chromites (Cr2O3)

3) Alumina

Out of these graphite is the least reactive and is extensively used in metallurgical furnaces

where the process of oxidation can be controlled.

Basic Refractories : Basic refractories are those which are attacked by acid slags but stable to

alkaline slags, dusts and fumes at elevated temperatures. Since they do not react with alkaline

slags, these refractories are of considerable importance for furnace linings where the

environment is alkaline; for example non-ferrous metallurgical operations. The most important

basic raw materials are:

1) Magnesia (MgO) - caustic, sintered and fused magnesia

2) Dolomite (CaO*MgO) - sintered and fused dolomite

3) Chromite -main part of chrome ore

Chemical characteristics of the furnace process usually determine the type of refractory

required. Theoretically, acid refractories should not be used in contact with basic slags, gases

and fumes whereas basic refractories can be best used in alkaline environment. Actually, for

various reasons, these rules are often violated.

Classification Based on Method of Manufacture

The refractories can be manufactured in either of the following methods:

a) Dry Press Process

b) Fused Cast

c) Hand Moulded

d) Formed (Normal, Fired or chemical bonded)

e) Unformed (Monolithic – Plastics, Ramming mass, Gunning, Cast able, Spraying

Classification Based on Physical Form

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Refractories are classified according to their physical form. These are the shaped and Unshaped

refractories. The former is commonly known as refractory bricks and the latter as “monolithic”

refractories.

Shaped Refractories:

Shaped refractories are those which have fixed shaped when delivered to the user. These are

what we call bricks. Brick shapes maybe divided into two: standard shapes and special shapes.

Standards shapes have dimension that are conformed to by most refractory manufacturers and

are generally applicable to kilns and furnaces of the same type. Special shapes are specifically

made for particular kilns and furnaces. This may not be applicable to another furnaces or kiln

of the same type. Shaped refractories are almost always machine-pressed, thus, high uniformity

in properties are expected. Special shapes are most often hand-molded and are expected to

exhibit slight variations in properties.

Unshaped Refractories :

Monolithic refractory, the name generally given to all unshaped refractory products, are

materials installed as some form of suspension that ultimately harden to form a solid mass.

Most monolithic formulations consist of large refractory particulates (an aggregate), fine filler

materials (which fill the interparticle voids) and a binder phase (that gels the particulates

together in the green state). Monolithic refractories are replacing the conventional type fired

refractories at a much faster rate in many applications including those of industrial furnaces.

The main advantages being:

1) It eliminates joints which is an inherent weakness

2) Method of application is faster and skilled measures in large number are not required

3) Properties can be better than pressed bricks

4) Transportation and handling are simple

5) Offers considerable scope to reduce inventory and eliminate special shapes

6) Has better spalling resistance and volume stability

7) Ability to install in “Hot Standby” mode

These are categorized as

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Insulating Castables : Insulating castables are specialised monolithic refractories that are used

on the cold face of applications. There are made from lightweight aggregate materials such as

vermiculite, perlite, extend-o-spheres, bubble alumina and expanded clay. Their main function

is to provide thermal insulation. They are typically of low density and low thermal conductivity.

Insulating refractories have inferior mechanical strength to that of conventional castables.

Plastic refractories : Plastic refractory is mixtures that is prepared in stiff plastic condition

and are delivered in blocks wrapped in polyethylene. During application, the blocks are sliced

into pieces and without further preparation, are rammed or poured into place with pneumatic

rammer. Plastic are easily rammed to any shape or contour.

Ramming mixes : Ramming refractory materials are very similar to plastic refractories but are

much stiffer. The particle sizes are carefullygraded and the final product is usually delivered

dry and then mixed with a little amount of water just before application. Other ramming mixes

are delivered in wet form and are ready for use immediately upon opening. Application is done

with pneumatic rammer.

Castables :‘Castable’ by name implies a material of hydraulic setting in nature. These are the

materials that contain cement binder usually aluminate cement, which imparts hydraulic setting

properties when mixed with water. Following the heat-up of the material the binder either

transforms or volatilises facilitating the formation of a ceramic bond. The most common binder

used in castables is HAC (high alumina cement). Other binders that are often used include

Hydratable aluminas and colloidal silica. These materials are installed by casting and are also

known as refractory concretes.

Gunning mixes : Gunning mixes are granular refractory materials sprayed on application area

using a variety of air placement guns. These are heat setting and are used for patching and

maintenance works for kilns and furnaces.

Fettling mixes : Fetting mixes are also granular refractory materials, similar to gunning mix

function, but are applied by shoveling into the furnace needing patching.

Mortars : Mortars are generally neither classified under refractory brick nor monolithic

refractories. These are finely ground refractory materials, which become plastic when mixed

with water. These are used to bond the brickwork into solid unit, to provide cushion between

the slightly irregular surfaces of the brick, to fill up spaces created by a deformed shell, and to

make a wall gas-tight to prevent penetration of slag into the joints.

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Properties of refractory :

The quality of a refractory and its suitability for a particular application is depends on the

physical , chemical and mineralogical properties it may be possible to assess the quality of

refractory on the basis of single property or group of properties . The most common properties

are

1. Apparent Porosity

2. Bulk Density

3. Modulus of Rupture ( MOR)

4. Hot Modulus of Rupture ( HMOR)

5. Cold Crushing Strength

6. Pyrometric Cone Equivalent (PCE)

7. Thermal Expansion

These properties are often among those which are used as ‘control points’ in the manufacturing

and quality control process. The chemical composition serves as a basic for classification of

refractories and the density, porosity and strength is influenced by many other factors. Among

these are type and quality of the raw materials, the size and fit of the particles, moisture content

at the time of pressing, pressure at mould, temperature, duration of firing and the rate of

cooling.

What is Kaolinitic clay ?

Since Kaolinitic clay is one of the main component in the present study. The structural and

others features are discussed below.

The outermost layer of our planet, the crust, contains the accessible mineral wealth of the

planet. The eight most abundant elements in the crust make up 98.5% of the mass of the crust

.The most common metal, silicon, is never found in its elemental form in nature. Instead, silicon

is combined in silicate minerals, which make up more than 90% of the mass of the Earth’s

crust. Depending on the composition and formation conditions, silicate minerals have

structures that range from individual clusters (ortho silicates) to three-dimensional networks

(tecto silicates) . These minerals can be contained in relatively pure single mineral deposits or,

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more commonly, in rocks such as granite that are made up of one or more mineral species .The

term clay refers to fine-grained alumina silicates that have a platy habit and become plastic

when mixed with water .Dozens of minerals fall under the classification of clays and a single

clay deposit can contain a variety of individual clay minerals along with impurities. Clay

minerals are classified as phyllo silicates because of their layered structure.. The most common

clay mineral is kaolinite, although others such as talc, montmorillonite, and vermiculite are also

abundant. Each of the clay minerals is composed of a unique combination of layers that are

made up of either tetrahedral or octahedral structural units that form sheets .Tetrahedral sheets

are made up of oriented corner-shared Si–O tetrahedra . Each tetrahedron shares three of its

corners with three adjacent tetrahedran, resulting in a structural formula of (Si2O5)n for the sheet

. Likewise, octahedral sheets are composed of Al bonded to O or OH anions, resulting in an

effective chemical formula of AlO(OH)2 The simplest clay mineral, kaolinite, is produced

when each of the Si–O tetrahedra in the tetrahedral sheet shares an oxygen with an Al–O/OH

octahedron from the octahedral sheet. The repeat unit or layer in the resulting structure is

A single e Si–O tetrahedron and the structure of the tetrahedral sheet

A single Al–O octrahedron and the structure of the octahedral sheet

Perspective drawing of the kaolinite structure

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Effect of heat on Kaolinitic Clay

When heated, kaolinite undergoes a complex series of chemical and physical changes that

transform the layered mineral to a combination of crystalline mullite and an amorphous

siliceous phase. Though simple conceptually, the study of this reaction sequence continues to

draw interest from the materials research community due to on-going controversies related to

the composition and structure of the intermediate phases. Notable studies of the reaction of

clays during heating have been conducted by LeChatelier , Brindley , and MacKenzie . In an

interesting parallel to the connection between the processing of clay-based ceramics and

advanced processing methods, the characterization protocols used in modern ceramic science

draw heavily on the work of these authors who were among the first in the field of materials to

apply characterization techniques that are now considered routine. LeChatelier used thermal

analysis, Brindley employed a combination of transmission electron microscopy and

diffraction, and MacKenzie made use of nuclear magnetic resonance spectroscopy.

Loss of Adsorbed Water

At temperatures below 150°C, water that is physically attached to clays evaporates. Physically

attached water can be present as water adsorbed onto the surface of particles or between the

layers of the clay structure. The loss of water is endothermic and results in measurable weight

loss. For kaolinite, the weight loss is usually minor, on the order of a percent or less. However,

other clays, particularly those that swell when exposed to water such as bentonite can have

considerable weight loss in this temperature regime (4–8 wt%) . For kaolinite, the changes due

to loss of physical water do not alter the structure as determined by X-ray diffraction.

Metakaolin

Around 450°C, the chemically combined water in clays is released, resulting in the formation

of metakaolin. As with the loss of physically adsorbed water, the loss of the chemical water is

an endothermic process that is accompanied by weight loss . The magnitude of the weight loss

depends on the amount of chemically combined water in the clay. For

kaolinite,Al2O3•2SiO2•2H2O, the weight loss due to chemically. combined water should be

13.9 wt%, which is similar to reported water contents for high-purity secondary kaolins . After

dehydration, metakaolin appears amorphous on X-ray diffraction, but the short range ordering

of the cations within the sheets that make up the kaolinite structure is retained . Brindley has

speculated that disruption of the order perpendicular to the sheets causes the change in the X-

ray diffraction pattern . Thus,metakaolin is a homogeneous molecular-level mixture of

noncrystalline alumina and silica. Metakaolin does not spontaneously rehydrate when it is

exposed to water and it remains stable up to approximately 980°C.

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Spinel

As metakaolin is heated, it undergoes a structural transformation around 980°C, a temperature

of significant interest in the synthesis of Mullite ceramics . Brindley, among others, has

observed the formation of spinel, an amorphous siliceous phase, and a small amount of nano

crystalline Mullite at 980°C . This process is exothermic with no accompanying weight loss.

The observed heat of reaction comes mainly from spinel formation . Investigators are in general

agreement that the spinel phase is similar in structure to the cubic transitional alumina γ-

Al2O3and that it contains most of the alumina from the original kaolin. The amorphous phase

is mainly silica, but it also contains a small amount of alumina plus most of the impurities from

the original clay. The mullite phase makes up only a small volume fraction of the total

volume after heating to 980°C and is composed of submicrometer needle-like mullite grains.

Questions remain regarding the composition of the spinel phase, with proposed compositions

ranging from pure γ-Al2O3t2Al2O3.3SiO2, which includes the mullite composition,

3Al2O3.2SiO2. It seems unlikely that spinel is pure γ-Al2O3, since mixtures of γ-Al2O3and silica

prepared from colloidal particles form α-Al2O3 and amorphous silica around 1200°C prior to

mullite formation at higher temperatures . It also seems unlikely that spinel is poorly crystalline

mullite, at least after heating to 980°C, since a second mullite crystallization event is recorded

at higher temperatures . Recent studies using nuclear magnetic resonance spectroscopy indicate

that the spinel phase formed at 980°C may contain just a few weight percent silica . Logically,

the composition of the spinel phase probably lies between that of metakaolin (Al2O3.2SiO2)

and mullite (3Al2O3.2SiO2) and is part a phase separation process that leads to the eventual

formation of mullite and an amorphous silica-rich phase.

Mullitization

As kaolinite is heated beyond 980°C, the small fraction of mullite crystals that formed at 980°C

continue to grow, albeit at a slow rate. Mullite growth is accompanied by the disappearance of

the spinel phase, although the amount of mullite formed is lower than expected based on the

spinel loss . Mullite formation does not approach completion until a second exothermic event

occurs at approximately 1200°C, as recorded by differential thermal analysis . When formed

by solid-state reaction, mullite has a composition of 3Al2O3.2SiO2, approximately 72 wt%

alumina and 28 wt% silica . According to Brindley, the mullite formed by heating to 1200°C

contains all of the alumina from the original clay, while the silica is distributed between the

mullite phase and an amorphous phase .Further heating alters the size of the needle-like mullite

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grains and can result in crystallization of the silica to crystobalite .Heating to 1200°C is

generally sufficient to fully densify clay-based ceramic bodies.

The SiO2–Al2O3 phase diagram :

Commercially, the silica–alumina system is an important one because the principal constituents

of many ceramic refractories are these two materials. shows the SiO2–Al2O3 phase diagram.

The polymorphic form of silica that is stableat these temperatures is termed cristobalite, the

unit cell for which is shown in Silica and alumina are not mutually soluble in one another,

which is evidenced by the absence of terminal solid solutions at both extremities of the phase

diagram.Also, it may be noted that the intermediate compound mullite,3Al2O3–2SiO2,exists,

which is represented as a narrow phase field in Figure 12.27; furthermore, mullite melts

incongruently at 1890oC (3435F). A single eutectic exists at 1587oC(2890F) and 7.7 wt%

Al2O3. refractory ceramic materials, the primeconstituents for which are silica and alumina, are

discussed.

15

Slip Casting

Slipcasting is a technique for the mass-production of pottery, especially for shapes not easily

made on a wheel. A liquid clay body slip (usually mixed in a blunger) is poured into plaster of

Paris moulds and allowed to form a layer, the cast, on the inside cavity of the mould. In a solid

cast mould, ceramic objects such as handles and platters are surrounded by plaster on all sides

with a reservoir for slip, and are removed when the solid piece is held within. For a hollow cast

mould, once the plaster has absorbed most of the liquid from the outside layer of clay the

remaining slip is poured off for later use. The cast piece is removed from the mould, "fettled"

(trimmed neatly) and allowed to dry. This produces a greenware piece which is then dried

before firing, with or without decoration and glaze. This process is used to prepare crucible.

This type of crucible is mainly used for melting glass and metal .

Advantages of Slip Casting

Low capital investment has to be made for the products to be produced.

Highly homogeneous slurries can be produced.

A wide variety of complex shapes can be produced that could not be produced using

other conventional methods.

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Review of past work related to present study :

Corrosion resistant castable refractory mix -Richard G. La Bar

A corrosion resistant Castable refractory mix is provided comprising a particulate mixture

capable of mixture with water to form a castable refractory having enhanced corrosion

resistance to molten aluminium. The mixture consists essentially of 20-34 parts by weight

calcium aluminate, 6-10 parts by weight of a zinc borosilicate frit, and 60-70 parts by weight

fused silica. The zinc borosilicate frit consists essentially of 50-60% by weight zinc oxide,

2040% by weight boron oxide, 8-12% by weight silicon oxide, and 0-10% by weight

aluminium oxide with less than 0.5% by weight of other impurities. The refractory mix contains

not greater than 1% by weight impurities [1].

Characterization and testing of refractories for glass tank meltes

M.Velez,M.Karakus,M.R.Reidmeyer,W.D.Headrick,R.E.Moore University of Missouri-Rolla,

Ceramic Engineering Dept.

Several approaches have been taken to minimize corrosion in glass tank melters: improved

construction techniques, new crown designs, and use of new materials (for instance alumina-

based compositions in oxyfuel-fired furnaces where silica brick has failed, as well as AZS, and

spinel based compositions). Other approaches are based on understanding the corrosion

mechanisms and the modeling of the combustion space, linked to the melting of the glass and

operation of the furnaces. The degradation of refractories used in glass tank melters can

normally be assessed after a campaign when the furnace is partially or totally disassembled .

Corrosion tests to predict degradation usually employ small specimens exposed to accelerated

working conditions that might not be simulative of actual industrial conditions. The current

study covers three sections: post mortem refractory characterization, initial testing using

current techniques, and representative test development.

Crown Refractories. Silica is the preferred material for crown construction, in terms of cost and

of defect potential, among the possible choices for oxyfuel combustion . The typical chemical

and mineral composition of a Type A silica brickz is: 96% SiO2, 0.2-0.4% Al2O3, 2.5-3% CaO,

0.02-0.06 Na2O+K2O, 0.2-0.8 Fe2O3+TiO2+MgO; 45% cristobalite, 50% tridymite, <1%

17

residual quartz and <3% glassy Ca-silicate phase . During furnace operation, the chemical and

mineral composition, and therefore the properties of the brick change. The original SiO2

transforms to either cristobalite or tridymite, depending on local temperatures and presence of

alkalis. Corrosion studies of different superstructure materials have been performed . A

qualitative corrosion model has been proposed for the corrosion of silica under oxyfuel

conditions : deposition of alkali on silica surface, penetration/diffusion of alkali into the silica,

reaction between alkali and silica and formation of low-melting glassy phases, and dripping

of the glassy phases from the crown. Under oxy-fuel conditions stable Na-silicate glass phases

are formed in the higher temperature, near-surface zones of the silica bricks. Thermodynamic

calculations indicate a higher driving force for NaOH(g) to react with silica refractories under

oxy-fuel conditions .

Glass-Contact Refractories. The chemical reactions on the surface of refractories take place

between molten glass, fluxing agents, and/or volatile components. Erosion can follow; washing

away refractory grains after the original bond has dissolved. Corrosion studies are based on

operating and reaction temperatures, reaction rates, and the formation of any product coatings

on the refractory surface. The corrosion tests have been reviewed having in mind that they must

show good reproducibility. Different tests are compared regarding reproducibility, trying to

establish the most useful test for each particular case (dynamic finger test, rotating cylinder

face method, small rotating furnace test, crucible test, static finger, and static plate corrosion

test) [2] .

Ceramic crucibles: a new alternative for melting of PbO–BiO–GaO glasses

Maria Garcia dos Santos ,Rafael Carlos Martins Moreira ,AntoonioGouveia de Souza,Ronan

Lebullenger,Antonio Carlos Hernandes Edson Roberto Leite ,Carlos Alberto Paskocimas

,Elson Longo

PbO–Bi2O3–Ga2O3glasses present interesting properties such as good transmission in the mid-

infrared region, high magnetic Verdet constant and non-linear properties. The processing of

these heavy-metal-oxide (HMO) glasses is limited by the high corrosive nature of the melt,

even in relation to noble metal crucibles. In this work, three kinds of ceramic crucibles

(alumina, tin oxide and zirconia) were tested for melting HMO glasses. The main physical

properties of the prepared glasses, such as the characteristic temperatures, optical transmission

were studied in function of the crucible nature, time/temperature melting parameters. The

incorporation of crucible material in the glasses was determined by ICP and atomic absorption

.The maximum glass contamination from the crucible was 2.9,

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1.6 and 3.6 mole % for Al2O3,SnO2 and ZrO2crucibles, respectively, when melting was done at

900C/240 min, for zirconia crucibles and at 1000 C/60 min, for the other two crucibles. The

evolution of the physical properties was discussed as a function of contamination degree [3].

Corrosion of electro cast AZS refractories by CAS glass–ceramics melting

Hong Li*, Jinshu Cheng, Liying Tang

Extensive corrosion experiments on electro cast alumina–zirconia–silica (AZS) refractories by

molten CaO–Al2O3–SiO2(CAS) and Na2O–CaO–SiO2(NCS) glasses were carried out at

various temperatures under static condition. The features and mechanism of the corrosion were

compared and analysed. The changes of microstructure and phase composition of refractories

in the course of the melt corrosion were also studied. X-ray diffraction (XRD), scanning

electron microscope (SEM) and chemical analysis were used to characterize the corroded

refractory materials and reacted melts. The reasons of alumina–zirconia–silica bricks corroded

are the meltdown of their own composition, penetration or permeation of alkali oxide in the

glass melt and scouring of the glass melt. The results show that the refractories resistance

against corrosion of the oxides like Na2O, K2O or CaO is weak, and that the corrosion

mechanism of NCS/AZS is different from that of CAS/AZS. In a static condition, CaO–Al2O3–

SiO2melts corroded alumina–zirconia–silica brick more severely than Na2O–CaO–SiO2. The

result provides useful reference to a prospective selection of refractory materials in glass and

glass–ceramics manufacture [4].

The microstructural features of an alumina–mullite–zirconia refractory material

corroded by molten glass -Cemail Aksel

An alumina-mullite-zirconia refractory penetrated by a standard soda-lime-silica glass was

statically tested at 1370o C for 72 h. Microstructural features and EDAX analysis of the

compositions in the corroded region were examined by SEM. During penetration, alumina

particles started dissolving in the glassy-phase; and thus randomly oriented needle-like alumina

crystals were formed and began growing up in the penetrated region. On the other hand,

zirconia made an effective barrier in the corroded zone, and therefore the formation of needle

like alumina crystals disappeared steadily towards to the end of the penetration region, with a

low solubility rate of SiO2 Na2O and CaO, leading to a high corrosion resistance of the

refractory [5] .

Phase composition of alumina–mullite–zirconia refractory materials

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C.Zanelli,M. Dondi,M. Raimondo, G. Guarini

Refractories in the Al2O3–SiO2–ZrO2 system are widely used in many applications, for ceramic

rollers in particular, and are characterized by high mechanical strength, excellent thermal shock

resistance, resistance to corrosion by alkaline compounds and low creep at high temperature.

Their performances greatly depend on the amount and chemical composition of crystalline and

glassy phases, which were investigated by quantitative XRPD (RIR–Rietveld) and XRF in

order to assess the effect of various Al2O3/SiO2 ratios of starting batches and different alumina

particle size distributions. Refractories consist of mullite, corundum, zirconia polymorphs and

a vitreous phase in largely variable amounts. The mullite percentage, unit cell parameters and

composition vary with sintering temperature, being mostly influenced by the Al2O3/SiO2 ratio

of the batch. Its orthorhombic unit cell increased its volume from 1400 to 1500 °C, while its

stoichiometry became more aluminous. The corundum stability during firing is strongly

affected by the Al2O3/SiO2 ratio, but not by the particle size distribution of alumina raw

materials. Zirconia raw materials are involved in the high temperature reactions and about one

third of the available ZrO2 is dissolved in the glassy phase, ensuring excellent resistance to

alkali corrosion, mainly depending on the fraction of coarse alumina. The phase composition

of the vitreous phase increased with sintering temperature, being over 20% when the fractions

of coarse alumina in the starting batch are between 0.2 and 0.5 [6].

Effect of Al4SiC4 on the Al2O3single bond SiC single bondSiO2single bond C

refractory Castable performance

A.P. Luza, M.M. Migliolia, T.M. Souzaa, S. Hashimotob, S. Zhangc, V.C. Pandolfellia

Carbon-containing refractories are widely used in the steelmaking process due to their

outstanding properties and, in order to improve their oxidation resistance, the so-called

antioxidants have often been used. Al4SiC4 is pointed out as a novel additive that presents

suitable properties such as Al, but without its drawbacks. Therefore, the effect of Al4SiC4

addition to Al2O3single bond SiC single bondSiO2single bond C Castable designed for lining

blast furnace troughs was investigated in this work. Apparent porosity, oxidation, thermo

gravimetric, X-ray diffraction, hot elastic modulus tests and thermodynamic calculations were

carried out in order to better understand the antioxidant effects and reaction mechanisms.

Additionally, the collected results were compared with those from the compositions containing

other commonly used antioxidants (Si, B4C and sodium borosilicate glass). The performance

20

of the novel additive proved to be limited as most of the carbon source used reacted earlier than

the Al4SiC4 action. As a consequence, intense carbon oxidation, along with the thermal

expansion mismatch among the phases during the cooling step, intensified the deterioration of

the evaluated refractory material [7] .

Colloidal stability–slip casting behaviour relationship in slurry of mullite

synthesized by the USP method

Remzi Go¨ren ,Bahri Ersoy,Cem O¨zgu¨r, Talip Alp

This study presents the outcome of a research concerning the relationship between the

colloidal stability of mullite powders synthesized by the USP (ultrasonic spray pyrolysis)

method and its slip casting behaviour. The colloidal stability of mullite slurry has been

investigated under three different pH conditions (4.5, 8.9 and 10.9) derived from pH-

dependent zeta potential (ZP) curves. Employing these pH values, mullite slurries with

50 wt.% solid content were prepared and slip cast. The microstructures of dried and

sintered specimens were examined using SEM. It is concluded that the pH significantly

influences the stability and in turn the slip casting behaviour of the mullite slurry. In

order to prepare homogeneous and stable mullite slurry for efficient slip casting it is

preferable to utilize a basic rather than an acidic medium. High pH (i.e. 10.9) tends to

leads to more closely packed mullite particles resulting in a homogeneous microstructure

and greater structural integrity [8].

Microstructure and phase evolution of alumina–spinel self-flowing refractory

Castable containing nano-alumina particles

Sasan Otroj*, Arash Daghighi

The microstructure and phase composition of alumina–spinel self-flowing refractory Castable

added with nano-alumina particles at different temperatures are investigated. The physical and

mechanical properties of these refractory Castable are studied. The results show that the

addition of nano-alumina has a great effect on the physical and mechanical properties of these

refractory Castable. With the increase of nano-alumina content in the Castable composition,

the mechanical strength is considerably increased at various temperatures. It is shown that

21

nano-alumina particles can affect formed phases after firing. The platy crystals of CA6 are

detected inside the grain boundaries of tabular alumina and spinel grains in samples fired at

1500oC. CA6phase can be formed at lower temperatures (1300oC) with the addition of nano-

alumina particles. As a result of using nanometre-sized alumina particles with high surface

area, the solid phase sintering of the nano-sized particles and CA6 formation can occur at lower

temperatures [9].

Refractory glass–ceramics based on alkaline earth aluminosilicates

G.H. Beall

Glass–ceramics that can be used at temperatures of 1200–1500◦C are found in the alkaline earth

alumina silicate field, and are generally nucleated internally with titania. These glass–ceramics

have good strength (>100 MPa, abraded), can be tailored to produce high fracture toughness

(2–5 MPa m1/2), and have good dielectric properties. Coefficients of thermal expansion

(CTEs) are low to moderate ((25–45)×10−7◦C−1, from25 to 1000◦C).The major crystalline

phase in the glass–ceramics exhibiting the lowest CTEs is hexagonal cordierite (indianite),

while important toughening accessory phases are enstatite and acicular magnesium dititanate

.The most refractory glass–ceramics that are easily melted at 1650◦C, yet when crystallized do

not deform at 1450◦C, are based on strontium and barium monoclinic feldspars of the celsian

type. CTEs range from 35 to 45×10−7◦C−1. Acicular mullite is an important accessory phase

aiding fracture toughness in these materials .Mullite glass–ceramics which contain

considerable siliceous residual glass are probably the most refractory of these glass–ceramics,

but they require melting above 1700◦C. Nevertheless, they can be used at temperatures near

1600◦C.Potential applications for refractory glass–ceramics include improved radomes, engine

components, substrates for semiconductors and precision metallurgical moulds [10].

Phase constitution of kaolin-based refractory concrete castables containing spinel

or mullite (preformed and insitu) additives

Morsy M. Abou-Sekkina1,*, Salah A. Abo-El-Enein2, Nagy M. Khalil3and Osama A.Shalma

The present maniscrupt aimed to improve the castable refractory castable concretes.

Thus, kaolin-based refractory castables investigated were carefully prepared. They are

composed of 90 wt. % well-graded (coarse, medium, and fine) kaolin aggregate, 10 wt.

% binding matrix and adequate amount of distilled water. The binder mixture was calcium

22

aluminate cement (CAC) containing 80 % Alumina and magnesium-aluminate spinel (MA-

spinel) or mullite either preformed or insitu. The castable batches were cast into cubes (25 x

25 x 25 mm), cured for 7 days under water, and followed by drying at 110ºC for 24 hrs. The

samples were then subjected to firing at 1550°C for a soaking time of 1 hr. The phase

composition of the prepared castable samples were investigated by using X-Ray diffraction

(XRD) analysis, scanning electron microscopy (SEM), energy dispersive X-ray (EDX)

analysis, differential thermal analysis (DTA) and thermal gravimetric analysis (TGA).

Results of these investigations confirm each other [11].

Synthesis of high alumina refractories from lithomargic clay

Anthony Andrews, Elsie Nsiah-Baafi, Simon K.Y. Gawu, Peter.A. Olubambi

Lithomargic clay underlying Awaso bauxite deposits consists mainly of kaolinite and minor

fractions of gibbsite. Gibbsite, useful as a source of alumina, was separated from kaolinite.

Gibbsite was added to lithomargic clay in various amounts, using Mfensi clay as a binder,

andfired at1350oC for 2 h. Linearfiring shrinkage, density, porosity, water absorption and cold

crushing strength were used to characterize thefired bricks.The mineralogical compositions in

thefired bricks were analyzed by X-ray diffraction techniques. The results showed that

increasing the gibbsite amount up to 40 wt% increased thefiring shrinkage and density whilst

the apparent porosity and water absorption values decreased. Increasing the gibbsite amount

enhanced mullite and corundum formation whilst the formation of free-silica phases was

inhibited. The cold crushing strength increased linearly with increasing gibbsite content [12].

The influence of zircon in a model aluminosilicate glass tank forehearth refractory

Cemail Aksela,Marie Dexet, Nelly Logen, Frederic Port,Frank L. Riley, Franciszek Konieczny

Standard aluminosilicate forehearth refractories are normally fabricated with a small proportion

of zircon to improve their performance. To identify possible bases for the action of the zircon,

fine-grain aluminosilicate materials of similar compositions were prepared and tested, to model

the behaviour of the finer grain bond phase in the standard refractory. The reference materials

contained a range of proportions of zircon, and further sets of materials were prepared in which

the zircon was replaced by varying amounts of very fine alumina, silica or zirconia powders.

The alumina and zirconia powders increased the strength at room temperature of the base

aluminosilicate, with zirconia having the largest effect; silica had only a slight effect. It appears

that the zircon increases strength through three mechanisms: the reduction in porosity brought

about by improved efficiency of the particle packing, a faster rate of sintering of the fine grained

23

bond phase, and a transformation toughening of the bond phase, caused by tetragonal zirconia

formed in situ by high temperature dissociation of the zircon [13].

Thermodynamic Analysis of Alumina Refractory Corrosion by Sodium or

Potassium Hydroxide in Glass Melting Furnaces

Karl E. Spear and Mark D. Allendorf

In this paper the high-temperature corrosion of Al2O3 refractories by MOH(g)(M=Na, K) found

in the combustion atmospheres of typical air- and oxygen-fired glass-melting furnaces is

examined using thermodynamic equilibrium calculations. These hydroxide species are

considered to be the primary reactive alkali species since their partial pressures are significantly

larger than those of M(g), the next most abundant gas-phase alkali-containing species expected

in typical furnace atmospheres. Thermochemical simulations show that corrosion ofa-alumina

by NaOH(g) at typical furnace pNaOH(g) of around 200 ppm under oxy/fuel-fired conditions

is unlikely as long as the refractory temperature exceeds 1564 K. For KOH(g) at 200 ppm, the

temperature of the refractory must exceed 1515 K to avoid corrosion. Under air-fired

conditions, p NaOH(g) is considerably lower (40-80 ppm) ; at50 ppm, corrosion is

thermodynamically unfavourable at temperatures above 1504 K. For KOH(g) at furnace levels

of;50 ppm ,temperatures must be above 1458 K. The paper also presents a re-evaluation of the

thermodynamic and phase equilibrium properties of the Na2O-Al2O3 and K2O-Al2O3 binary

systems to develop accurate and self-consistent thermodynamic data. The data for MAl9O14(β-

alumina) and M2Al12O19 (β’’-alumina) are particularly critical since these phases are likely

products of the corrosion of alumina refractories by MOH vapours in glass melting furnaces

[14].

Silica Crown Refractory Corrosion in Glass Melting Furnaces

A. Balandis, D. Nizeviciene

The critical parameters of silica refractories ,such as compressive strength, bulk density,

quantity of silica, microstructure and porosity were evaluated of unused and used bricks to line

the crowns of glass furnaces, when the rate of corrosion of crowns were about 2 times greater.

The change of these parameters, the chemical composition and formation of the micro cracks

in the used silica refractories material were studied. It was established that the short time at

service of container glass furnace crown can be related to low quality of silica brick: high

quantity of CaO and impurities, low quantity of silica, low quantity of silica, transferred to

tridymite and cristobalite and formation of 5 -10 µm and more than 100 µm cracks in the crown

24

material. The main reason of corrosion high quality silica bricks used to line the crown of

electro vacuum glass furnace is the multiple cyclic change of crown temperature at 1405 – 1430

oC range in the initial zone of crown and at 1575 – 1605 oC range in the zone of highest

temperatures [15].

Mass-Produced Mullite Crucibles in Medieval Europe: Manufacture and Material

Properties

Marcos Martino Torres,Ian C. Freestone,Alice Hunt,and Thilo Rehren

All the unused Hessian crucibles analyzed have very similar characteristics, which indicates

that raw materials and manu-facturing techniques were kept standardized for centuries. The

ceramic matrices are composed of a relatively pure kaoliniticclay, with a mean Al2O3content

of 39.6% and very low levels of alkali and earth alkali oxides, their sum being just about 2%.

The most typical nonplastic addition consists of 20–40 vol% subrounded or spheroidal quartz

sand grains, moderately wellsorted in the medium to coarse sand range (+0.25–1 mm) .These

grains appear internally cracked and show dis-solution interfaces with the surrounding ceramic,

even in unused vessels, which indicates a firing temperature above 12001C9 Afew (5 vol%)

smaller inclusions were identified, namely monazite, humboldtine, rutile, and some concentric

ferruginous concretions—all of which are known to occur in Hesse. Somerelict structures of

molten potassium feldspars were also noted.Overall, the scarcity of mineral inclusions other

than the quartz sand suggests that the clays were levigated, i.e. size sorted by settling in flowing

water.

Porosity is about 20 vol% and manifest in three forms: (a) subrounded pores around quartz

grains; (b) long, subangular pores parallel to the wall surfaces; and (c) fine vitrification porosity

.The first type is because clay platelets tend to be aligned with their plane faces tangential to

the surface of the nonplastic particles, and the cavities are then enlarged due to the high

expansion/contraction coefficient of quartz grains during lattice inversion upon firing and

cooling.The long pores are due to the shrinkage of the ceramic matrix during firing, and their

alignment is a reflection of the overall clay orientation during the manufacture of the crucibles

on a rotating potter’ swheel. The closed micro porosity in thec eramic matrix results from the

25

development of glass during firing, with the subsequent filling of small pores and gas diffusion

into growing,larger ones.10–11

XRD of a powdered sample from an unused crucible showed the presence of mullite,

cristobalite,quartz, andhematite. The presence of hematiteis consistent with the generally

reddish color of the sefabrics ,inspite of the relatively low FeO concentrations (B2%), and

suggests that the crucibles were fired in an oxidizing atmosphere. It should be noted, however,

that a recent studyhas identified metallic iron with in the vitrified matrix of a Hessian crucible.

Most important here is the presence of a mullite phase ,most likely crystallized following

the decomposition of kaolinite under high temperatures ,and which we interpretas the

main secret behind the superior material properties of the vessels. The XRD results are

consistent with the SEM observations on etched specimens of unused crucibles. The

vitrified groundmass appears composed of cuboid, primary mullite .In are as of higher

flux content caused by molten feldspars, a network of interlocking needles(r120mm)of

secondary mullite is present.As noted by Iqbal and Leeand Lee and Iqbalin their study of

porcelains, primary mullite crystals formed in the pure viscous feldspar relict in

agreement with previous observation s o fthe possible transformation of primary into

secondary mullite. In addition ,the substantial growth of these crystalsis consistent with

its firing nano xidizing atmosphere. The presence of well-developed mullite indicates

firing temperaturesinexcessof1200oC,while the limited presence of bubbles and the lack

of mullite dissolution suggest thata temperature of

1400oCwasnotexceededduringfiring.Thus we estimate that the firing of Hessian crucibles

involved sustained temperatures in the 1300o–1400oC range, in agreement with a recent,

independent estimate.[16]

Chapter 2 :Experimental methods

Raw Materials : Different types of clays , alumina were collected from ceramic mineral

suppliers .Before formulation of the batch compositions ,the raw materials are chemically

analysed. SiO2and Al2O3 were analysed gravimetrically and Fe2O3,CaO and MgO were

estimated volumetrically [ 17 ].Alkalies are determined by flame photometry. The list of the

raw materials given below –

Calcined clay from Talbasta

Indian Plastic clay – Rajmahal and Chitorepur

Imported Plastic clay – Ukraine.

Technical Alumina – SRM 30 grade of Indalco .

Deflocculant and dispersing agent

26

Preparation of batches and their characteristics: All the raw materials as per composition

provided in table 1 were loaded in the ball mill along with grinding medium and required

amount water and mix for a specific duration to obtain the slurry suitable for slip casting . Two

types of slurries were prepared from the similar composition, namely Coarse and Fine body.

Coarse body contains different fraction of calcined clay (-10 +20 , -20 +40 and +40 mesh BS

shieve) .The shieve analysis of Fine body is generally -200+300 mesh 20 % and -300 mesh 80

% both the slurry was tested for density and PH.

Table 1.Main composition of the batch ( wt % )

Constituents Old New

Calcined clay 66 66

Plastic clay(Indian)

Rajmahal

Chitorepur

17

9.5

--

9.5

Plastic clay(Ukraine) -- 17

Technical alumina (SRM 30) 7.5 7.5

The samples were prepares from coarse and fine body as per the flowsheet .

27

Measurement of Physico Mechanical Properties, Morphology and Phase Identification:

The fired samples were subjected to physical tests like flexuralStrength, % LS , % WA , BD .

FlexuralStrength Determination :-

A three-point loading scheme for measuring the stress–strain behaviour and flexural strength

of brittle ceramics, including expressions for computing stress for rectangular sections.

Formula used :-

Where F = Applied Load

L = Length of the sample

b = Breadth of sample

d = depth or width of sample

Formula used to calculate % of Linear Shrinkage:

(Length of bar sample at green condition – Length of bar sample after firing) × 100/ Length of

bar sample at green condition

Formula used to calculate % of water absorption:

(Weight of sample at dry condition – weight of sample after boiling) × 100 /weight of sample

at dry condition

28

Micro Structure analysis:

SEM

In the scanning electron microscope the electron gun at the top illuminates the specimen with

the beam angle controlled by the condenser lens. The lenses below the specimen are used to

magnify the image of the specimen which is viewed on the final screen at many thousand times.

If a second electron gun is placed below the fluorescent screen at the bottom of the column and

the electron beam is projected upwards through the same lenses this second electron source

will be reduced in size by the same amount that the specimen image is magnified. This effect

can be observed with both electron guns on at the same time and demonstrates the reversibility

of rays through electron lens systems. In this way the resolved point in the specimen image on

the fluorescent screen or on the photo- graphic plate is equal to the focused electron probe in

the plane of the specimen. In order to obtain a two-dimensional image it is then necessary to

move the probe over the specimen and collect the transmitted or reflected electrons as a time

varying signal. This similarity between the two types of instruments is useful in understanding

both the probe- forming system and in the image formation when the scanning microscope is

used in transmission. The scanning microscope alone needs only one electron gun, quite often

placed at the top of the column as in conventional transmission electron microscopy.

29

Phase study:

XRD

X-rays are passed through a crystalline material and the patterns produced give information of

size and shape of the unit cell X-rays passing through a crystal will be bent at various angles:

this process is called diffraction X-rays interact with electrons in matter, i.e. are scattered by

the electron clouds of atoms .The angles at which x-rays are diffracted depends on the distance

between adjacent layers of atoms or ions. X-rays that hit adjacent layers can add their energies

constructively when they are “in phase”. This produces dark dots on a detector plate

THE POWDER TECHNIQUE:An X-ray beam diffracted from a lattice plane can be detected

when the x-ray source, the sample and the detector are correctly oriented to give Bragg

diffraction. A powder or polycrystalline sample contains an enormous number of small

crystallites, which will adopt all possible orientations randomly. Thus for each possible

diffraction angle there are crystals oriented correctly for Bragg diffraction. Each set of planes

in a crystal will give rise to a cone of diffraction .Each cone consists of a set of closely spaced

dots each one of which represents a diffraction from a single crystal. Crystal phase of the

selected sample was determined by X-Diffraction analysis using a Philips PW-1730 with Cu-

Kα radiation and Ni filter at scanning rate (2θ).

Chapter 3 :Results and discussion:

The chemical analysis of all theraw materials are given below

Table 2.Chemical analysis

Major Chemical

Constituent ( wt % )

Rajmahal

Clay (plastic clay)

Ukraine Clay (Plastic clay)

Chitorepur ( Plastic Clay

)

Talbasta ( Calcined

Clay )

SiO2 55.90 65.26 58 55

Al2O3 30.28 21.96 30 42

Fe2O3 0.71 0.95 0.8 0.5

TiO2 0.86 1.29 1.1 0.8

CaO 0.13 0.25 0.3 0.3

MgO 0.07 0.49 0.4 0.4

K2O 0.25 2.46 0.1 0.1

Na2O 0.09 0.54 0.2 0.5

L.O.I 11.28 6.60 9.0 0.4

30

From the above table2it may be seen that Ukraine clay differs from Rajmahal clay mainly in

silica and alumina contains. One of the interesting feature of Ukraine clay is that it contains

K2O to the extent of 2.46 wt % and it’s presence may help better sintering. Calcined clay contain

42 % alumina and it is advantageous for refractory composition. Technical alumina used in the

composition contain > 99% Al2O3 and it’s average particle size is 6-8 mµ .

The density of both the coarse and fine body are presented in the Table 3. It may noted the

density of coarse body is higher than density of fine body. There is no major difference between

new and old body

Table 3.Density of slip of different batches

The green density and % dry shrinkage of the cast sample is given in the Table 4. It is observed

that old body shrinks slightly more than new body .No major density difference is found.

Table 4.Green density and % dry shrinkage of the cast sample

Types of slip Density ( g/cc)

New Coarse (NC)

1.90

New Fine ( NF ) 1.75

Old coarse ( OC ) 2.00

Old Fine ( OF )

1.80

Sample

Code

% of

Linear

Shrinkage

Density

( g/cc)

OC 2.58 2.14

NC 1.93 2.00

OF 3.22 2.08

31

The fired properties namely % shrinkage,density,water absorption of the cast sample heated at

1370oC for different hours of soaking time (2,4,6,8,10 hours ) are given in Table.5 and

illustrated in figure 1,2 and 3 respectively.

Table 5. Different fired properties at a glance

NF 2.586 2.00

32

% of Linear Shrinkage:-

Fig. 1. Variation in % linear shrinkage of coarse and fine

body samples in relation to soaking time.

The figure 1 revealed that both coarse and fine body of Ukraine clay containing samples(New

body) shown high shrinkage than old body. The figure also indicates that the shrinkage

increases with increase in soaking time.

Bulk Density:

33

Figure.2 Variation in bulk density of coarse and fine body samples in relation to soaking time.

It may be observed from fig. 2 that bulk density (BD) increases with increase with soaking time

in all the cases. Between 2 hours to 6 hours soaking time the rate of increase in BD is rather

slower than the rate seen in between 6 hours to 10 hours soaking time. AS expected, the BD is

maximum at 10 hour soaking time. The coarse body of old composition shown higher BD at

all soaking times.

% of Water Absorption:-

34

Fig.3Variation in % water absorption of coarse and fine body samples

in relation to soaking time.

The figure revealed that the water absorption decreases with increase in soaking time due to

enhanced densification. It is seen that old coarse body possesses less water absorption which

is contradictory to shrinkage value. This may be due to better compactness.

Flexural Strength:The modulus of rupture of the sample heated at 1370oc at 10 hour soaking

period give below

a b

Fig. 4.Variation in flexural strength of 1370oC, (a) 10 hour and (b) 4hour soaking time in

relation to coarse and fine body of old and new composition.

From figure 4.(a),(b) it is revealed that fine body possesses higher strength than coarse body

due to better sintering.Also, NF (new fine) body shown higher strength as it is contained

Ukraine clay. From figure 4.(b) it is observed that in the case of 4 hour soaking the strength of

old fine body drastically reduces with respect to 10 hour soaking time. It may be due to

generation of internal flaws. This needs further study .

35

Microstructure Study:-

NF 10H OF 10H

a b

Figure 5 SEMphotomicrography of (a) NF and (b) OF heated at 1370oC,10 hour soaking

The SEM photomicrograph of New and Of body fired at 1370oC,10 hour soaking are shown in

Fig 5 (a) and (b) respectively. Both the structures are compact and the grains are uniformly

distributed in the matrix. Pores are also seen in the structure. No major difference in

grainmorphology between old and new body were found. Presence of mullite crystals are seen

but not well developed.

EDAX analysis :

EDAX of NF

36

Figure 6.a

EDAX of OF

37

Figure 6.b

Figure 6.EDAX analysis of (a) NFand (b) OF heated at 1370o C, 10 hour soaking.

From Figure 6.(a),(b) the EDAX analysis shown the presence of Si and Al due to presence of

Kaolin and Alumina in composition

Phase Study:-

Fig 7XRD pattern of OF and NF heated at 1370oC,10 hour soaking

Thefigure 7 confirm the formation of mullite (3Al2O3, 2SiO2) as one of the major phase. The

free quartz present in the clay converted to cristoballite and this is advantageous due to its lower

thermal expansion than quartz.

Conclusion :

20 30 40 50 60 70 80 90

0

200

400

600

800

1000

1200

MMMMMMM

M

MMM

+C

M+CCCM

M+C

M

C

MM

M+

C

C

M

C

M

Inte

nsity

(in

Arb

t. U

nits

)

2(in Deg.)

20 30 40 50 60 70 80 90

0

200

400

600

800

1000

1200

1400

1600

1800

M

M: Mullite, C: cristobalite

Sample: OF10

Sample: NF10

MMMMMM

M

MMM

+C

M+CM

M+C

M

MM

M+

C

M

M

CCCC

C

38

Two new slip cast refractory crucible bodies were studied, one with all Indian plastic clay and

another with replacement of one plastic clay by imported Ukraine clay. The Ukraine clay

containing composition heated at 1370o C, 10 hour soaking shown higher flexural strength due

to its better densification. No major difference in microstructural features (SEM) was observed

between old and new body. The EDAX analysis confirm the presence of Si and Al as major

element. The XRD pattern confirm the presence of mullite ( 3Al2O3, 2 SiO2) and cristoballite

as major crystalline phases.

List of References –

1. U.S.Patent , May 9, 1978 ,4088502, CORROSION RESISTANT CASTABLE REFRACTORY

MIX, Richard G. La Bar, Export, Pa.

2. Cerâmica vol.47 no.302 São Paulo Apr./May/June 2001, M. Velez, M. Karakus, M. R.

Reidmeyer, W. D. Headrick, R. E. Moore University of Missouri-Rolla, Ceramic Engineering

Dept. Rolla, MO 65409-0330, USA

39

3. Journal of Non-Crystalline Solids 319 (2003) 304–310 Ceramic crucibles: a new alternative

for melting of PbO–BiO1:5–GaO1:5 glasses

Ieeda Maria Garcia dos Santosa,Rafael Carlos Martins Moreiraa, Antooniode Souzab, Ronan

Lebullenger, Antoonio Carlos Hernandes,Edson Roberto Leite, Carlos Alberto Paskocima,

Elson Longo

4. Journal of Non-Crystalline Solids 354 (2008) 1418–1423, Corrosion of electrocast AZS

refractories by CAS glass–ceramics melting .Hong Li*, Jinshu Cheng, Liying Tang.

5. Ceramics International 29 (2003) 305–309, The microstructural features of an alumina–

mullite–zirconia refractory material corroded by molten glass ,Cemail Aksel.

6. Journal of the European Ceramic Society,Volume 30, Issue 1, January 2010, Pages 29–35,

Phase composition of alumina–mullite–zirconia refractory materials, C. Zanelli, M. Dondi,

M. Raimondo, G. Guarini.

7. Ceramics International 38 (2012) 3791–3800 , Effect of Al4SiC4 on the Al2O3–SiC–SiO2–

C refractory castables performance.A.P. Luz , M.M. Migliolia , T.M. Souza, S. Hashimoto,

S. Zhang, V.C. Pandolfelli.

8. Ceramics International 38 (2012) 679–685, Colloidal stability–slip casting behavior

relationship in slurry of mullite synthesized by the USP method ,Remzi Go¨ren, Bahri

Ersoy, Cem O¨zgu¨r, Talip Alp.

9. Ceramics International 37 (2011) 1003–1009,Microstructure and phase evolution of

alumina–spinel self-flowing refractory castables containing nano-alumina particles.Sasan

Otroj, Arash Daghighi

10. Journal of the European Ceramic Society 29 (2009) 1211–1219, Refractory glass–ceramics

based on alkaline earth aluminosilicates G.H. Beall

11. Elixir App. Chem. 34 (2011) 2398-2403, Phase constitution of kaolin-based refractory

concrete castables containing spinel or mullite (preformed and insitu) additives . Morsy M.

Abou-Sekkina, Salah A. Abo-El-Enein, Nagy M. Khaliland Osama A.Shalma.

12. Ceramics International 40 (2014) 6071–6075, Synthesis of high alumina refractories from

lithomargic clay,Anthony Andrews, Elsie Nsiah-Baafi, Simon K.Y. Gawu, Peter.A. Olubambi.

13. Journal of the European Ceramic Society 23 (2003) 2083–2088, The influence of zircon in

a model aluminosilicate glass tank forehearth refractory .Cemail Aksela,, Marie Dexet, Nelly

Logen, Frederic Porte,Frank L. Riley, Franciszek Konieczny.

14. Journal of The Electrochemical Society, 149~12 B551-B559~2002. Thermodynamic

Analysis of Alumina Refractory Corrosion by Sodium or Potassium Hydroxide in Glass Melting

Furnaces.Karl E. Spear and Mark D. Allendorf .

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