VYSOKÁ ŠKOLA BÁŇSKÁ – TECHNICKÁ UNIVERZITA OSTRAVA
FAKULTA METALURGIE A MATERIÁLOVÉHO INŽENÝRSTVÍ
Ceramic materials in metallurgy
Study Support
Jozef Vlček
Hana Ovčačíková
Ostrava
2015
Title: Ceramic materials in metallurgy
Code:
Author: doc. Ing. Jozef Vlček, Ph.D, Ing. Hana Ovčačíková, Ph.D
Edition: first, 2015
Number of pages: 39
Academic materials for the Metallurgy engineering study programme at the Faculty
of Metallurgy and Materials Engineering.
Proofreading has not been performed.
Execution: VŠB - Technical University of Ostrava
1
OBSAH
1. BASIC TERMS ............................................................................ 4
1.1
1.2
1.3
1.4
Ceramics ...................................................................................................................................... 4
Dividing of ceramic materials by their purpose of use................................................................ 4
Abbreviations used in ceramics................................................................................................... 4
Chemical and phase composition of ceramic materials .............................................................. 5
2. MATERIAL FOR THE PRODUCTION OF CERAMICS ....................... 7
2.1. Silicon dioxide SiO2 ...................................................................................................................... 7
2.2. Zirconium dioxide ZrO2 ................................................................................................................ 9
2.3. Aluminium oxide Al2O3 .............................................................................................................. 10
2.4. Clay materials and compound SiO2 – Al2O3 ............................................................................... 11
2.5. feldspars .................................................................................................................................... 14
2.6. Magnesium silicite ..................................................................................................................... 14
2.7. Forsterite ................................................................................................................................... 15
3. RAW MATERIAL FOR THE PRODUCTION OF CERAMICS ............. 16
3.1
3.2
3.3
3.4
Preparation of mixtures for forming ......................................................................................... 17
Forming of ceramic materials .................................................................................................... 17
drying of ceramics ..................................................................................................................... 20
firing of ceramics ....................................................................................................................... 21
4. FIRE-RESTISTANT CERAMIC MATERIALS ................................... 24
5. FIRE-RESISTANT CERAMIC MATERIALS ..................................... 28
5.1
5.2
5.3
5.4
5.5
silicic materials .......................................................................................................................... 28
ganister ...................................................................................................................................... 28
aluminosilicate materials .......................................................................................................... 29
high-alumina materials .............................................................................................................. 30
Not-formed aluminosilicate materials ...................................................................................... 31
6. ALKALINE FIRE-RESISTANT MATERIALS .................................... 34
Tab. 6 Basic types of alkaline fire-resistant materials ...................................................................... 34
6.1 Magnesite materials .................................................................................................................. 35
6.2 Magnesite - carbonaceous materials ........................................................................................ 35
6.3 Magnesite – dolomite products ................................................................................................ 36
6.4 Magnesite – chrome products .................................................................................................. 36
7. LITERATURE ............................................................................ 38
2
INSTRUCTIONS FOR STUDYING
You have received study materials for extramural studies for the subject Ceramic materials in
metallurgy of 2nd semester of following master’s study field.
PREREQUISITES
There are no prerequisites set for the studies of this subject.
AIM OF SUBJECT AND OUTPUTS OF STUDIES
Aim of the subject is to give students primal theoretical knowledge from the field of ceramic
materials in range from defining of basic input material and methods of their adjustment, technology
of production of ceramic materials to presentation of their basic characteristics and rules of their use
in practical conditions.
AFTER STUDYING OF THIS SUBJECT, STUDENT SHOULD BE ABLE TO:
Outputs of knowledge:
•
Student will be able to recognize ceramic material
•
Student will be able to characterize ceramic material
•
Student will be able to orientate in group of ceramic materials
Outputs of skills: for example
•
Student will be able to analyze classification signs of ceramics
•
Student will be able to divide ceramic materials according to their characteristics
•
Student will be able to decide about application of ceramic materials in practice
•
Student will be able to apply obtained information in the processes of technology of
production
WE RECOMMEND THIS PROCEDURE DURING STUDYING OF EACH CHAPTER:
To understand stated text, to look for further information in recommended literature and to study
stated problematic.
WAY OF COMMUNICATION WITH EDUCATORS:
Educator will give assignment of semester project for given topic from the area of economics and
management at the beginning of the semester. Project will be checked by educators within two
weeks after handover and results will be sent to students by email through the IS EDISON.
CONSULTATIONS WILL BE WITH GUARANTEE OF THE SUBJECT OR WITH LECTURER
Guarantee of subject: doc. Ing. Jozef Vlček, Ph.D.
Lecturer: doc. Ing. Jozef Vlček, Ph.D.
Contacts: [email protected]
3
BASIC TERMS
1.
Time for studying
3 hours
Aim

To define ceramic materials

To describe difference between chemical and phase composition

To apply shortened form of chemical compounds applied in the area of ceramic materials
Definition
1.1 CERAMICS
-
Non-metallic inorganic matter characterized by heterogenic structure, usually created by
crystal and glass phase and voids. These materials are under normal circumstances insoluble
in water in real time.
1.2 DIVIDING OF CERAMIC MATERIALS BY THEIR PURPOSE OF USE
-
Utility ceramics (ceramics for food or decoration – porcelain, earthenware, stoneware);
building ceramics (brick products, facing elements); fire-resistant ceramics; technical and
special ceramics (carbides, nitrides, borides, silicides); glass; glass ceramics; inorganic binding
materials (gypsum, lime, cement)
1.3 ABBREVIATIONS USED IN CERAMICS
CaO – C
SiO2 – S
Al2O3 – A
Fe2O3 – F
Na2O – N
K2O – K
MgO – M
B2O3 – B
H2O – H
-
For example shortened formulation of compound of metakaolinite: AS2H2 = Al2O3.2 SiO2.2
H2O
Raw material for the production of ceramics is widely accessible and easy to process for many
ceramic materials. That is why ceramic materials are found as one of the oldest products of human
hands. At the same time ceramics, because it is common archaeological finding proves that it is very
durable material.
4
1.4 CHEMICAL AND PHASE COMPOSITION OF CERAMIC MATERIALS
Characteristics of ceramic materials depend on many factors. Composition of ceramic materials can
be taken as the main factor. This is possible to express in chemical or phase way.
Chemical composition:
-
(or compounds) are basic chemical components, which are always in the material (they do
not change their composition because of activity of exterior forces). Many ceramic materials
are made of oxides that is why chemical composition of these materials is seen as
representation of oxides.
Phase:
-
are homogeneous parts of material, which are divided from one another by areas and these
phases can be mutually, mechanically separated from one to another. Characteristics of each
phase (density, hardness, thermal conductivity and so on) are different from one to another.
Most of ceramic materials contain more than one phase and we label these as multiphase
materials and at the same time are these materials labelled as heterogenic.
Difference between chemical and phase composition is easily understandable on next example,
which expresses composition of cement:
-
chemical composition
CaO, SiO2, Al2O3, Fe2O3
-
phase composition
C3S, C2S, C4AF, C3A
It is obvious from the stated information that mere mixture of compounds CaO, SiO2, Al2O3,
Fe2O3 does not, in any case, secure expected behaviour of cement. This means that mixture
of stated compounds mixed with water solidifies and hardens only under presumption that
compounds are parts of stated minerals and so they form required phases.
Summary of terms
ceramics
chemical composition of ceramics
phase composition of ceramics
5
Questions
Define term ceramics.
Describe basic differences between chemical and phase composition.
6
2.
MATERIAL FOR THE PRODUCTION OF CERAMICS
Time for studying
10 hours
Aim

to describe raw material for production of ceramic materials

to distinguish types of ceramic materials according to their use
Definition
Raw material can be divided from several aspects.
Source:
-
natural material:
o processed
o not processed
-
synthetic material
-
secondary material
2.1. SILICON DIOXIDE SIO2
- common in nature  it is used almost solely as natural material for production of ceramics
- siliceous gangue – from washing in acids volume SiO2 > 99,95 % - for production of silica
glass
- sands, sandstone and quartzite – most common
- infusorial earth – porous raw material for production of thermal – isolation materials
- flint – not common use
- SiO2 is known in many polymorph forms (modifications).
7
Fig. 1 Modification changes SiO2 (Hlaváč, J.: Základy technologie silikátů. SNTL Praha, 516 s., 1988)
Horizontal changes – reconstruction are energetically demanding and process slowly. These
forms can be cooled under the temperature of change.
Vertical changes – displacive are energetically undiscerning, they process into directions
quickly.
Change  silica   cristobalite at temperature of 1025° C happens, if SiO2 is pure. In the
case of content of contamination  tridymite is produced at the temperature of 870° C.
Changes of modifications of SiO2 are connected to value changes. These are significant and
unfavourably come up during production of products with content of original silica. Volume stability
of final products is, as result of returnable changes, during cyclic changes of temperature also
endangered. Densities of each modifications of SiO2 are in the table.
Tab. 1 Characteristics of modifications of SiO2 (Hlaváč, J.: Základy technologie silikátů. SNTL Praha,
516 s., 1988)
Modification
Crystal system
Density (g.cm-1)
-silica
trigonal
2,65 (20 °C)
-silica
hexagonal
2,53 (600°C)
-tridymite
rhombic
2,26 (20 °C)
- tridymite
orthorhombic
- tridymite
pseudohexagonal
2,22 (200 °C)
- cristobalite
tetragonal
2,32 (20 °C)
- cristobalite
cubic
2,20 (500 °C)
---
-
Fact that reconstruction changes are energetically and timely demanding, causes that in fired
products is still silica present. For example in ganister, each modification of SiO2 changes
during almost all period of use of products.
8
-
Creation of tridymite and its stabilisation is supported by so called agents of mineralization,
for example alkaline oxides. It is a fact that there are other atoms than Si and O always
present in tridymite.
Volume changes during polymorph changes of SiO2:
 silica

 silica
0,82%
 silica

 tridymite
16,0%
 silica

 cristobalite 15,4%
 tridymite

 tridymite
0,5%
 cristobalite
2,8%
 cristobalite 
Besides stated forms of SiO2, there are also known other which demand special conditions
(for example high temperatures and pressures): keatite, coesite stishovite.
Crystal structure SiO2
Structure of glass SiO2
Fig. 2 structure SiO2
2.2.
ZIRCONIUM DIOXIDE ZRO2
It is produced from the mineral zircon ZrSiO4. Content of ZrO2 in products is 75 – 99 %. Pure
ZrO2 comes through polymorph changes (reversible changes) during heating, more in fig 3.
9
Fig. 3 Single-component diagram ZrO2 (Hlaváč, J.: Základy technologie silikátů. SNTL Praha, 516 s.,
1988)
Tab. 2 Parameters of modifications ZrO2:
Characteristic
monoclinic
tetragonal
cubic
Density (g.cm3
)
5,56
6,10
6,27
T. melting
(°C)
-
-
2710
Stability (°C)
up to 1 100
1 100 - 2 300
2 300 - 2710
Changes are connected to volume change up to 9 %. There is large mechanical stress  there
is danger of destruction of products. Reversibility of changes depends on the conditions; existence of
metastable forms is possible (outside the usual range of temperatures.) Stabilisation of cubic form
happens with addition of CaO or Y2O3. Modified product contains 70 – 80 % of cubic form and shows
low predisposition for further changes.
2.3.
ALUMINIUM OXIDE AL2O3
It has temperature of melting 2054°C. It is in nature in pure form as corundum  Al2O3.
Precious stone Al2O3
-
ruby containing Cr3+
-
sapphire containing Ti4+ a Fe2
Al2O3 a Al(OH)3 is used in ceramic industry.
10
Chemical preparation is most commonly from bauxites in so called Bayer’s process. Bauxite –
hydrated Al2O3 s containing mixture SiO2, Fe2O3 a TiO2.
Bayer’s process:
-
bauxite is extracted during higher pressure and temperature with mixture of NaOH
-
incurred solution Al(OH)4- gets rid by filtration of undissolved SiO2, Fe2O3 a TiO2
-
after cooling emerges  Al(OH)3
-
by calcination (1200 °C) emerges  Al2O3
-
various qualities dependent on purity (usually 99,5 %) and size of grain
-
main contamination – rests of Na2O
Cinter, ash and aluminosilicate soil are used for production in limited way.
Calcination:
-
 Al(OH)3 (hydrargillite) emerges by bayer’s process
-
by partial calcination (at lower temperatures)  Al2O3 is created
-
at temperatures above 1100° C  Al2O3, is created, this form is stabile until the temperature
of melting (2054° C)
Advantage  during use of material containing Al2O3 in changing temperatures does not
come to major volume changes.
By some types of raw material is form  gained by calcination at temperatures 1700° C. At
temperature 2000° C so called tabular corundum is created (tabular crystals).
Density 3,94 – 4,00 g.cm-3 and measurable area 15 – 4 m2.g-1 depend on the temperature of
calcination (values are valid for the range of temperatures of 1100 – 1500° C). Temperature of
calcination can be lowered with the addition of F.
Melted corundum
This is prepared by electric-melting; product during cooling is polycrystalline  Al2O3. Product
is modified by grinding onto required granulometry. Use in fire-resistant ceramics. During production
of melted corundum there can be created  Al2O3 (risk of emerging during presence of alkali). Its
creation is unwanted, it has lower solidity.
2.4.
CLAY MATERIALS AND COMPOUND SIO2 – AL2O3
Basic ceramic raw material (clay soil, kaolin, clays, soil).
Clay
-
Is mixed natural raw material primarily composed from fine grain minerals. With appropriate
volume of water it is plastic and during drying process and firing there comes to the growth
of hardness.
-
Plasticity
11
-
The ability to produce with water formable body. It depends on the fineness of grain
and mineral composition. The highest plasticity is in montmorillonite clays, further
kaolin. Plasticity is increased by interchange of ions Ca2+ a Mg2+ za Na+ a K+.
-
Components of clays are:
-
phyllosilicates – silicates with stratified structure
-
organic components
-
modification SiO2
-
feldspars, zeolites, oxides and hydroxides
Not all components of clay are clay minerals
-
clay minerals
-
phyllosilicates – minerals containing periodical nets of tetrahedrons connected with
nets of octahedrons
-
oxides, hydroxides of aluminium and iron – clay minerals which are not part of group
of phyllosilicates
-
supporting minerals
Structure of clay minerals
Clay minerals (phyllosilicates) feature stratified structure, where there are layers of
tetrahedrons and octahedrons changed
Fig. 4 Structure of kaolinite (left) and montmorillonite (right)
Tetrahedrons SiO4
cation Si4+ can be replaced by Al3+, Fe3+, Ge4+
Octahedrons AlO6
cation Al3+ can be replaced by Fe3+, Fe2+, Mg2+, Mn2+, Ca2+, Li+
Anion octahedrons
can be besides O2-, also OH-
Purity of clays
-
controlling instrument is content of Al2O3, its theoretical content in kaolinite is 39,5 %
-
increased content of SiO2 above stoichometric share incriminates contamination by silica
12
-
content of alkali incriminates presence of feldspars, which together with Fe2O3 decrease fireresistance and support emergence of melt at lower temperatures
-
content of organic matters  it burns during firing, influence the colour of shatter and its
mechanical characteristics
Thermal processing of clays
Clay minerals subject to phase changes during thermal process. Process of thermal process is
explained on kaolinite.
Al2O3.2SiO2.2H2O

2(Al2O3.2SiO2) 
2Al2O3.3SiO2 + SiO2 (amorph.)
925 – 1050 °C
3(2Al2O3.3SiO2) 
2(3Al2O3.2SiO2) + 5 SiO2
> 1100 °C
SiO2(cristobalit)
> 1200 °C
SiO2(amorph.)

Al2O3.2SiO2 + H2O
Al2O3.2SiO2

metakaolinite
2Al2O3.3SiO2

defective spinel
3Al2O3.2SiO2

mullite
500 – 600 °C
Metakaolinite: shows little crystal structure  it is used in, for example, production of
inorganic bonding material. Stated scheme represents simplified process; in practical conditions
these products have often non-stoichometric composition.
Fig. 5 Balanced phase diagram SiO2 – Al2O3
Mullite
The only stabile compound (solid solution) in the A – S system
-
high temperature of melting
13
-
chemical resistibility
-
high solidity
-
it does not succumb to polymorph changes
-
low thermal expandability
-
high share of mullite is demanded in ceramic products
-
theoretical composition: 71,8 hm% A
There are many solid solutions with non-stoichometric composition in reality in given area,
but with similar characteristics as mullite  whole area is called area of mullite.
Other raw material needed for preparation of mullite:
-
natural minerals from the group sillimanite (andalusite, kyanite, sillimanite)
-
they have composition SiO2.Al2O3
-
they are not presented in the A – S phase diagram, because they emerged at high pressure
and at temperatures above 1300° C they are changed into mullite and S
-
with regards to major volume changes it is necessary to calcine kyanite before using
Further it is possible to prepare also synthetic mullite, which is prepared with the mixture of
clay and bauxite.
2.5.
FELDSPARS
-
Orthoclase K2O.Al2O3.6SiO2, Tt 1150 °C
-
Albite Na2O.Al2O3.6SiO2, Tt 1118 °C
-
Anorthite CaO. Al2O3.2SiO2, Tt 1552 °C
Feldspars make among one another, sometimes, in given areas mixture of solid solutions.
Feldspars are part of most crystal stones, however they do not occur in pure form (they
always contain silica, glimmer etc., these stones are called feldspar pegmatites). They are purposely
used in ceramics as melting agents (porcelain, earthenware, glazing, content up to 50 %), or as a
source of Al2O3 and alkali (glass industry). Often they are unwanted  they decrease temperature of
use in materials.
Melt of feldspars is easily cooled into glass and it is difficult (even impossible) to reach its recrystal abilities.
2.6.
MAGNESIUM SILICITE
Talc 3MgO.4SiO2.H2O
-
density 2,6 – 2,8 g.cm-3
14
-
it has laminar structure
-
shows specific plasticity even in dryness
-
forming is possible without addition of water
-
tendency for directional orientation of flakes  unequal shrinking during drying (anisotropy)
Characteristic is negated by possible calcination of material.
It is present in nature with presence of Fe2O3, magnesite, alkali, not wanted are iron and CaO.
It is used for production of electrotechnical ceramics, sometimes tiles.
Talc loses water during heating at temperatures of 700 – 900° C, and during further
increasing of temperatures there is MgO.SiO2.
2.7.
FORSTERITE
-
2MgO.SiO2
-
it is not commonly present in nature
It is produced by calcination from olivine  solid solution of forsterite and fayalite 2FeO.SiO2.
FeO oxides and there is created Fe2O3.MgO which is in balance with forsterite. Use in fire-restistant
ceramics.
Summary of terms
raw material:
plastic material – binders – allow forming
–
kaolin, clays and earth
non-plastic material – grog – they decrease shrinking and forming
–
silica, corundum, fired clay (shale)
non-plastic materials – melting agents – during firing secure emergence of melt
–
feldspars
Questions
Draw and describe binary diagram S-A
Describe and draw change of SiO2
Draw and describe diagram for polymorph changeover ZrO2
15
3.
RAW MATERIAL FOR THE PRODUCTION OF CERAMICS
Time for studying
10 hours
Aim

to define process for production of ceramics

to describe technology of production of ceramic materials
Definition
Production of ceramics includes these operations (not all operations are used during
production of particular product, glass production and inorganic binding agents are produced by
different processes):
•
preparation of raw material
–
synthesis of highly pure raw material (sol-gel method and condensation in gas phase,
pyrolysis of organometalllic precursors etc)
•
•
•
–
adjustment of granulometry
–
homogenisation
forming
–
common and isostatic pressing
–
heat pressing
–
forming by casting
–
extrusion
–
injection moulding, pressing
thermal processing
–
drying
–
firing
–
special proceedings (e.g. pressure sintering, reaction compacting etc.)
finishing operation
–
cutting, sharping and polishing
–
surface treatment (glazing)
16
3.1 PREPARATION OF MIXTURES FOR FORMING
The aim is homogenisation and adjustment of granulometry.
Grinding:
Most common is wet grinding in drum mills. Mainly non-plastic raw material is ground
and has around 10% content of clay component (clay slows down sedimentation of ground
matter). Grinding drum and grinding bodies must not contaminate ground raw material.
Dewatering of suspension
Dewatering with filter presses:
-
Dewatering of suspensions through cloth filter
-
Force of pressing 0,5 - 1,5 MPa  emergence of filtration cake
Sometimes (pressing from plastic batter) there has to be equated the moisture in filter press
cake by letting it be, further the mixture can be homogenised thanks to the press.
Spray drying:
Quick drying of sprayed drop of suspension in flow of heated air (500 – 800°C). Dried
ceramic matter is not heated above the temperature of 100° C, which is given by the speed of
flowing. It is possible to regulate the size of emergent granulate and its moisture.
3.2 FORMING OF CERAMIC MATERIALS
-
Casting from liquid suspensions:
-
with dispersive agent is 25 – 40 % of water, it is casted into cast forms
-
with dispersive agent is non-polar liquid (organic dissolvent), casted into non-porous
form
-
-
-
Plastic forming:
-
from batters containing 17 – 27 % water
-
with mixture containing 1 – 10 % non-water dissolver
Pressing:
-
from wet mixtures containing 17 – 27 % of water and organic additives
-
from semi-dry mixtures containing 8 – 15% of water and organic additives
-
from dry mixtures containing below 8% of water and/or organic bonding agents
Forming at high temperatures:
-
Injection casting, below temperature of 150° C
17
-
fire pressing at temperatures above 1000° C
Casting from liquid suspensions
Suspension (ceramic slurry) has to show low or zero limit of flowing and high liquidity by low
content of water. Suspension should be near to Newton’s liquid. Particles in suspension must not
agglomerate (coagulate), suspension must be perfectly peptised (made into liquid).
Lyophilic dispersion scheme is thermodynamically stable and does not need additive
stabilisation.
Lyophobic dispersion scheme is thermodynamically unstable and needs stabilisation, without
it there comes to coalescence of particles.
Liquefying of suspension:
By adding according electrolyte (peptide agent, liquefier) surface potential of particle 0 can
be increased.
Liquefying prevents coagulation of particles and allows increasing content of solid phase in
suspension. Surface potential is increased by substitution of ion fixed onto the surface of particle
(Ca2+, Mg2+) for ion with lower oxidizing number (Li+, K+, Na+).
Warning: multivalent cations are bonded to the surface of particle stronger than cations
univalent.
Solution: use of liquefiers supporting production of little soluble compositions in water to
bond unsuitable Ca2+.
Effect of addition of sodium carbonate:
Ca-kaoliniet+Na2CO32(Na-kaolinite)+CaCO3
Addition of liquefier increases potential of  and decreases viscosity at the same time.
Excessive addition of liquefier has opposite effect. Usual liquefiers for clays: Na2CO3, silicate, sodium
hexametaphosphate Na6P6O18.
Fig. 6 Change of viscosity in dependence on concentration was liquefying and change of
gradient of deformation dependent on liquefying of matter; 1 – not-liquefied matter, 2 – coagulated
matter, 3 – liquefied matter (HANYKÝŘ, V., KUTZENDÖRFER, J. Technologie keramiky. Praha:
18
Silikátový svaz, 2000, 287 s., ISBN 80-900860-6-3)
Plastic forming
Condition for successful production is balanced moisture and degassing of matter. Example
of use of plastic forming is belt press for production of brick products.
Fig. 7 Scheme of belt press (Hlaváč, J.: Základy technologie silikátů. SNTL Praha, 516 s., 1988)
Continuous belt comes from belt press, which is cut on desired lengths. Products of final
form and size (brickmaking products), or semi-products, which then are pressed (fire-resistant
bricks), or are dried and mechanically processed – lathed (electrical isolators). Speed of movement of
matter in press is not steady (it lowers towards the walls), which causes different orientation of
grains after cut of product  anisotropy of characteristics.
Pressing of dry mixtures
Content of water is lowered up to 0%. Ordering of particles and their deformation happens
during pressing. By monodisperse particles there is around 70% of form filled, by polydisperse up to
90% (process is very demanding).
Effects of pressing force:
-
one-sided, causes unequal concretion of presswork
-
both-sided
-
isostatic, mixture is filled into rubber form, this is then put into pressure tank. There
is difference between dry pressing (pressure in tank is made by pressed air) or wet
pressing (pressure in tank is made by pressed liquid). Pressure affects whole surface
of rubber form. Method is used both for quality and for slim walled products.
Extrusion (compression forming)
Suitable for shapes, where the length significantly overreaches diameter. Forming of clay raw
material, rheology is adjusted by addition of water. Method is also suitable for forming of non-plastic
mixtures with high content of Al2O3 and with addition of viscose liquid (polyvinyl alcohol) and water.
19
3.3 DRYING OF CERAMICS
The aim is to eliminate free water from formed ceramic product. It needs to be looked for
optimal process of drying. Drying of product produces stress in the product, which can cause its
destruction.
Process of drying
A) water makes continuous layers, which divide solid particles from one another
B) grains of matter touch each other, water fills the space between grains (pores)
C) water is not even in pores (there are only thin water covers – bond to surface of
solid particles in adsorption way)
State b represents critical value of moisture. If the moisture of the body is higher, drying of
material is accompanied by its shrinking. If the initial moisture of material is lower than critical value
of moisture, the material does not shrink during drying. Critical value of moisture is set by for
example Bigot curve.
Fig. 8 Bigot curve Wc - initial moisture, Wk critical moisture
(vlhkost – moisture, smrštění – shrinking)
Modes of drying
a) drying at low temperature and high moisture
b) drying at low temperature and low moisture
c) drying at increased temperature and increased moisture
20
Fig. 9 Distribution of moisture in the product in relation to the mode of drying
I – initial content of water; B – content of water after finished shrinking
Surface moisture
Moisture in the centre of the
product
(Hlaváč, J.: Základy technologie silikátů. SNTL Praha, 516 s., 1988)
Shrinking of the product depends mainly on the initial content of water. By clay products
formed from plastic batter it reaches values of 0,5 – 12 %. Fine grained system shows higher
shrinking than system coarse-grained (higher number of water covers). Shrinking becomes dangerous
in the case that it does not happen equally in the whole extent of the product.
Solidity of dried products is made through Van der Waals force. Fine grained mixtures have
higher solidity than mixtures coarse-grained. Solidity of dried clay products is about 0,5 – 10 MPa.
Product has to have so called manipulation solidity. Final content of water after process of drying is 1
– 2 %.
3.4 FIRING OF CERAMICS
Final fixation of form and solidity of product is gained by so called sintering – emergence of
solid accretions between grains. During firing of ceramics there usually comes to densification of
product.
Formation of further final characteristics of product
Action is connected with the process of physical and chemical reactions:
-
Evaporation of physically bound water
-
Dehydroxylation
-
Burning of organic components
-
Making of glass phase
-
Modification changeovers
-
Nucleation and crystallization of new phases
-
Sintering
21
-
Dissolution of phases in the melt
Sintering
•
Final phase of process of firing
–
creation of final characteristics of the product
–
accretion of solid particles
•
without presence of liquid phase (at temperatures 0,8 – 0,9 temperatures of
melting)
•
in presence of liquid phase
Driving force is decreasing of surface energy of particles.
Besides evaporating and condensation is defining action of the process is sintering of
diffusion. Mechanisms of diffusion are done through flow of vacancies. Vacancies diffuse from the
area of high concentration into areas with low concentration. Curved surface of particles is a place
with high concentration of vacancies. In upstream of vacancies there is a flow of matter
Stages of sintering (without presence of melt):
•
1. stage
–
creation of neck between grains, area of accretion is circa 20 % from the area of cut
of grains, grains do not change their number, size or structure
•
2. stage
–
there is linear shrinking (circa 6%), neck grows, area of accretion equals to area of cut
of grain, decreasing of porosity (up to level above 50% from original porosity),
process of additional growth of grains begins and canal pores are created, stage ends
by the creation of closed pores
•
3. stage
–
there comes to further production of closed pores, these pores gradually belittle,
speed of growth of grains increases, further there can be these variants, with the
growth of grains there comes to almost complete deletion of porosity, volume
weight gets close to density
–
or
•
some grains grow so quickly that pores grow into these grains
•
pores inside grains cannot be disposed of the material
•
volume weight of material is lower than density
Sintering by the presence of liquid phase:
Option is very common, more component ceramics contains at sintering temperatures
certain share of melt. Problematic of grain growth gets into background. Main problem is
22
amount of melt and its distribution in the matter. Surface stress decides on the distribution of
melt in the matter. If melt covers grains, solidity of product is given by its gluing effect.
Summary of terms
forming of ceramics
Bigot curve
modes of drying
sintering
Questions
What are the stages of sintering of ceramics?
Draw and describe Bigot curve.
What basic forming techniques of ceramics are there?
23
4.
FIRE-RESTISTANT CERAMIC MATERIALS
Time for studying
4 hours
Aim

you will get overview about the definition of fire-resistant materials and basic terms,

you will find substantiation of use of chosen oxides for the production of fire-resistant materials,

you will get acquainted with classification of very large group of fire-resistant materials and
classification criteria.
Definition
Fire-resistant materials (FRM) are defined as inorganic non-metal materials; fire-resistance is
 1500 °C. FRM belong to coarse grain ceramics – microstructure is created by large grains, basic of
shatter is coarse grained grog interconnected by fine matter. FRM are materials which are mainly
used as walling materials for furnaces and thermal devices. Condition for their use in mass scale is
not only their sufficient fire-resistance, but also sufficient presence and availability of raw material
for considerate prices.
Main characteristics of FRM:

is the ability to resist high temperatures,

sufficiently isolate other parts of devices from effects of high temperatures,

melt can be present at this temperature only in such amount and has to have such viscosity
not to cause deformation,

major part of fire-resistant products is made from oxides and their combination,

anticipation is high melting point and thermodynamic stability at high temperatures.
The highest temperatures of melting among known compounds have carbides, nitrides,
borides and oxides. Because first three mentioned groups of matters are in oxidation atmosphere at
high temperatures unstable, most of industrial fire-resistant ceramics is based on oxides.
Temperatures of melting of chosen oxides with high melting point are stated in the table 3.
Important for industrial production of fire-resistant materials are from these oxides only these six:
Al2O3, CaO, MgO, SiO2, Cr2O3, ZrO2, and compounds among them, combinations of oxide components
with carbon, or with covalent compounds, especially with SiC.
24
Tab. 3 Temperatures of melting of chosen oxides
Oxide
Temperature of melting of oxides °C
MgO
2852
ZrO2
2700
CaO
2625
Cr2O3
2265
Al2O3
2054
SiO2
1726
Fire-resistant raw materials are usually multi-component systems, which besides basic
components – carriers of fire-resistant characteristics (for each products these are for example Al2O3,
MgO, ZrO2 etc.), contain in little amount other components, which support production of melts at
low temperature, and by this decrease the fire-resistant characteristics of products (for example
alkali). Function of each oxide in each system can be variable. For example in aluminosilicate
products are carriers of fire characteristics Al2O3 and SiO2, but CaO and MgO despite its high
temperatures of melting, belong to melting agents. Opposite that in magnesite building materials,
where MgO is carrier of firing characteristics, SiO2 can be melting agent, especially with the presence
of other oxides. Function of specific oxide can be found out from multi-component phase balance
diagrams.
(Fig – upper left corner – aluminosilicate products, main components; upper right corner – alkalic <
7% of residual C, main components Mgo, Cao…; lower left corner – Alkalic products 7% - 30% of
residual C, main components Mgo, C, CaO; lower right corner – Special products).
Dividing of fire-resistant materials can be briefly summarized like this:
According to character of elementary base:
25
 oxide → are mainly on base of oxides and their compounds, most important oxides are Al2O3,
CaO, MgO, SiO2, Cr2O3, ZrO2,
 non-oxide → carbon FRM and carbides, nitrides, borides, silicides. Sialons are in this group
also – sintered derivates of silicon nitride.
According to content of main components, it means according to the chemical
composition:
 acidic → as main isolated phase they contain SiO2 (ganister, acidic fire-clay),
 alkalic (basilar) → they contain as main phase CaO, MgO (magnesite, periclase, chromemagnesite, dolomite and others),
 neutral → do not contain as main phase SiO2 , CaO či MgO, but Al2O3, Al2O3 a SiO2, Cr2O3, C
(chamottes, corundum materials, mullite, carbonaceous).
Besides chemical composition there are other aspects by which fire-resistant materials are
divided:
 form products → unit products, which have specifically defined form (bricks, desks, blocks,
fittings, trigs,…),
 non-form products → fibred walling, mixtures, from which monolithic walling is made (liquid
mixtures, chippings).
Further possible division according to density (porosity):
 dense materials, which have real porosity below 45 %,
 isolation materials, with real porosity above 45 %.
According to fire-resistance:
 fire-resistant
1580 – 1770 °C
 highly fire-resistant
1770 – 2000 °C
 specially fire-resistant above 2000 °C
Tab 4 Basic characteristics of fire-resistant ceramic materials
26
Summary of terms
fire-resistant oxides,
fire-resistant material, fire-resistant product,
classification of fire-resistant materials, classification criteria,
aluminosilicate materials and products,
alkaline materials including materials with residing carbon,
special products,
division of fire-resistant materials according to various criteria.
Questions
Define term fire-resistant material.
What are the differences of fire-resistant materials compared to other kinds of ceramic
materials?
Give reason of use of chosen oxides from extensive group of high melting oxides for
production of fire-resistant ceramics.
27
5.
FIRE-RESISTANT CERAMIC MATERIALS
Time for studying
3 hours
Aim

to describe what are basic technological differences for classic and special ceramics

you will get an overview about definition of fire-resistant materials and basic terms, you will be
able to define basic technological steps and describe them closer
Definition
5.1 SILICIC MATERIALS
Aluminosilicate fire-resistant materials contain as basic Al2O3 and SiO2 in various ratio. Fireresistant materials with high content of SiO2 > 93 %, practically on base of technical SiO2, are
ganister. Basic fire-resistant oxide is silicon dioxide. Silicon dioxide is known in different polymorph
modifications – their mutual changeovers are accompanied by volume changes, which can adverse in
technology itself, but also in characteristics of products. SiO2 is present in raw material in the form of
silicae.
5.2 GANISTER
Ganister is fire-resistant material which contains more than 93 % SiO2. It is typical
representative of acidic fire-resistant. It is produced from natural silica containing around 96% SiO2
mostly in the form of silicae, which during firing changes by decreasing of density into cristobalite
and tridymite. It is fired at temperature providing polymorph changeover of silicae (SiO2 ) into
tridymite and cristobalite. This is besides rests unchanged silicae first crystal phases of product,
which is produced during volume expansion, or by growth of porosity during firing. By sintering there
are volume changes by modifications of SiO2 .
Raw materials:

basic: silicae, sands, ganister fractions, cobbles

helping raw materials: lime or lime hydrate (binder)

plastificators which enhance processability of production mixture, for example sulphite lye,

mineralisators for quickening of changeover of silicae into high-temperature modifications.
28
Typical characteristic of ganister is:

acidic character, resistance against acidic melt

besides fire-resistance it also has positive fire-technical characteristics – resistance against
deformation in heat, capacity in heat (also above 1680 0C),

high resistance against sudden changes of temperatures above 600 0C,

high volume stability or (at lower level of changeover) tendency for additional expansion by
high-temperature use (compared to further shrinkage which is common by other FRM).
Disadvantages:
Low resistance against changes of temperature above 6000 C, caused by volume changes by
modification of SiO2, lack of suitable raw materials and damaging effects on human organism during
its production (silicosis).
Use:
Combination of advantageous characteristics makes ganister a classic material for selfsupporting vaults of furnaces for high temperatures. While in steel furnaces was ganister in this
direction substituted by basilar materials, it is even today important material for vaults and some
parts of walling of glass melting furnaces. For walling of places of thermal aggregates which are very
stressed as are vaults ant walls of furnaces and glass furnaces, for walls of coke ovens, regenerators
(for example heaters of air for blast furnaces), electric arch furnaces and also for example in sintering
belt of rotation furnaces by production of cement.
5.3 ALUMINOSILICATE MATERIALS
Aluminosilicate FR materials contain SiO2 and Al2O3 as main particles in various ratio. The
only aluminosilicate composition stabile at high temperatures is mullite - 3Al2O3.2SiO2 – temperature
of melting 1828 o C.

Acidic chamotte has less than 30 % Al2O3 and lower fire-resistance.

Chamotte products (from 35 % to 45 % Al2O3) contain mullite, which positively influences fire
characteristics in chamotte. Fire-resistance grows with the content of Al2O3, from which
mullite mineral is created as the only crystal composition resisting high temperatures.
Raw material for chamotte production:

plastic binding component: clays and caolines with high content of mineral caolinite, which
besides plasticity gives demanded fire-resistance
29

grog: fire-resistant burnt soil (burnt shales) and chamotte gravel, which makes the core of
product. It is gained mainly by firing of fire-resistant clays and shales above the temperature
of 1200 0 C.

melting agents: they enhance density and mechanical solidity of product, they decrease fireresistance of product, they are used in certain cases and low dosages

lightening additives: they are used for production of lightened chamottes
There are two basic technological processes of production of dense fired aluminosilicate
building materials. These are plastic or crumbling: plastic way of production can provide higher
quality of product, exact size (low shrinking) by lower energy consumption. Pressing during forming
of aluminosilicate products of plastic mixtures is 5-10 Mpa. During drying of pressings formed from
plastic it is necessary to get rid of water in the amount of 16 – 20 % weight of pressings, whereas it
comes to shrinking, which depends on the amount of clay in the matter. Grog contained in plastic
mixtures is circa 50 – 65%. Opposite to it are pressings formed from semidry mixtures (crumblings)
practically do not change measurements during drying, content of water is 3-10%, pressing press 3050% and content of grog is about 50-75%. Firing is directly on the tunnel carriages. By present
technical level of firing aggregates there comes to firing in tunnel furnaces according to the
temperature of firing 1250 to 1400° C usually 40 to 80 hours. Cycle of firing in modern trolley
furnaces and cover furnaces is considerably shorter.
Besides fire-resistance, chamotte has also good solidity in fire, resistance against changes of
temperatures, thermal isolation ability. Usual chamotte is the most common product which has low
solidity in stress and high absorbability. It is used there where walling is not strained on abrasion and
is not in contact with the melt. Chamotte with higher content of Al2O3 is material with high resistance
against deformation in fire.
It has low resistance against alkaline aggressive matters, softening and deformation of
products in wide range of temperatures. They are used in all branches, which thermally process their
products and mainly there where are periodical (interrupted) thermal workings. It is used in walling
of rotation furnaces during production of lime and cement, in glass and ceramic production of noniron metals. Used for walling of thermal aggregates for production of heat.
5.4 HIGH-ALUMINA MATERIALS
In high-alumina materials (above 45 % Al2O3) with increasing content of Al2O3 content of
mullite is increasing and content of glass phase is decreasing. With content of Al2O3 higher than
corresponds to composition of mullite (theoretically above 72 weight %) coexist two crystal phases –
mullite and corundum (Al2O3). With decreasing amount of glass phase the temperature of creation of
first melt is increasing.
High-alumina raw material:

natural minerals sillimanite (up to 63 % Al2O3), andalusite, kyanite, bauxite (up to 52 % Al2O3),

artificial (industrially produced basic high-alumina raw materials) – main material is most
commonly calcinated alluminium oxide, which is sintered or melted:
30
o sintered (tabular) corundum contains more than 99,4 % Al2O3 and is produced from
calcinated alluminium oxide with low content of alkali.
o melted corundum is produced in electric vault furnaces and contains 99,5 % Al2O3.
Characteristics:

very good resistance against changes of temperatures,

resistance against alkaline dross,

resistance against deformation in fire,

wear resistance.
During production of high-alumina building materials are higher additions of clay unwanted,
because lower quality matrix reasonably lowers quality of product. On other hand, there is effort
that quality of matrix would be same as quality of grain fractions. This is reached by minimalization of
content of clay and by creation of matrix from fine ground high-alumina open materials. Clays shrink
during drying and especially during firing; it means that during firing there is interrupted connection
of shrinking clay structure and size fairly state grain grog. Porosity is increased, solidity is decreased
and conditions for obtaining form and size accuracy are lowered. In semidry matters is by lower
moisture suppressed plastication function of clay, which fills only function of fine fraction. Negative
effects of its shrinking during drying and firing are suppressed by decreasing of its content and its
addition in the mixture of fine ground open material. This decreases shrinking of matrix (clay and fine
grog). Material mixture has to have optimal granulometry of open material. Plastic mixture is mixed
in wheel mixer, in case of crumbling there are used fast compounders, backflow compounders.
Composition of material mixture: in case when the building materials are from plastic batter, mixture
contains 55-60% of open material, if it is crumbling content of open material is 80-95%. Forming is
mainly pressing into metal forms thanks to hydraulic presses. Pressure during forming of plastic
mixture is 5-10 MPa and in case of crumbling 50-100 MPa. Products are dried in chamber and canal
dryers. It is fired in tunnel or chamber furnace. Temperature of firing is 1400-1700° C. The period of
firing is 3-7 days.
Temperatures of firing are for each kind of aluminasilicate products usually in these values:




usual kinds of chamotte building materials
top kinds of chamotte building materials
mullite and multi-corundum products
corundum products
1250 to 1400°C
1400 to 1500°C
1500 to 1600°C
1600 to 1700°C
5.5 NOT-FORMED ALUMINOSILICATE MATERIALS
Not-formed FRM represent perspective kinds of products, which subsidize traditional walling
from item formed material. Even if the prices of materials for monolithic walling are in some cases
higher, longer durability of walling and quicker installation (and so shorter time of not use of device
from work) equals this deprival and eventually brings decreasing of costs.
31
Refractory concrete:







are kinds of concrete for temperature of use above 200° C, by which during longer working of
higher temperatures comes hydraulic structure (HV) → into ceramic structure (KV),
deprival of products is decrease of solidity by first heating, where it comes to decay of HV,
sintering of refractory concrete happens at higher temperatures and monolith gets character
of fired ceramic product, but at the same time comes to PTL,
we distinguish refractory concrete according to their limit temperature 350, 700, 1100, 1200,
1500 and above 1500° C (according to the content of Al2O3 and further according to the used
cement),
light refractory concrete has porous structure, lower coefficient of thermal conductibility and
thus higher isolation ability; it contains lightened open material (aggregate), for example
stamped foam chamotte, expanded perlite, globular corundum, etc. and unit weight;
isolation refractory concrete is known as refractory concrete with unit weight < 600 kg.m-3,
by fire monolith with chemical bonding agent does not come during heating to decreasing of
hardness in pressure as by refractory concrete; by growth of temperature comes chemical
structure into ceramic
Advantages and disadvantages:

forming happens directly during application,

fully or partially firing drops out, this happens directly in aggregate,

jointless monolith walling (it increases resistance of walling against for example corrosion),

energy consumption lowers as a result of dropping out of firing,

general costs are lowered as well

number of gaps is significantly lowered in the walling, which increases corrosion resistance,

longer drying and firing

necessity of following exact technological procedures.
Not-formed aluminosilicate materials are mixtures containing:

aggregate (grog) – all kinds of fired aluminosilicate raw materials,

hydraulic binders – fire cement,

micro-additives – the finest solid component, very small pure oxides,

liquefiers, regulator of congealment,

water.
Types of refractory concrete (C) :
- isolation
- dense - with chemical structure
- with hydraulic structure
-
common refractory concrete (without liquefier)
-
liquefied refractory concrete (contains micro-additives and liquefier)
32
- MCC (with middle content of cement)
- LCC
(with low content of cement)
- ULCC (with ultra low content of cement)
- NCC (non-cement)
Use of refractory concrete (RC):

materials for monolith walling (fire monoliths),

materials for repairs of walling (gunite mixtures),

connecting materials (mortars and cements)

isolation refractory concrete
Summary of terms
raw material for production of aluminosilicic materials, ganister, characteristics and use
dividing, classification and classification criteria of large group of aluminosilicic materials,
technology of production of these products: formed dense building material and not-formed
dense materials
Questions
What materials are used for production of silicious fire-resistant materials, their
characteristics.
Technology of production of formed silicious building materials.
Kinds of refractory concrete and their dividing.
33
6.
ALKALINE FIRE-RESISTANT MATERIALS
Time for studying
2 hours
Aim

to define dividing and classification of very broad group of material, which main fire-resistant
oxide is MgO,

to get acquainted with the technology of magnesium building materials, especially with content
of residual carbon below 7% and secondly with content from 7 to 30%, or more residual carbon
Definition
Basic fire-resistant materials are characterized by the fact that oxide which is their important
part creates hydroxide with water. Main representative of this group is magnesium oxide (MgO).
Main aim in innovation during production of fire-materials is increasing of utility of products.
Characteristic is use of pure basic materials with minimum content of supporting oxides, which
create by increasing of temperature melt.
Tab. 6 Basic types of alkaline fire-resistant materials
Chemical – mineralogical composition
Type
magnesium
magnesiumspinel
magnesiumlime
group
MgO
Cr2O3
CaO
periclase
 95
magnesite
 85
chrom-magnesite
60 – 85
 20
chrom-magnesite
40 – 60
 35
chromium
 40
 35
lime- dolomite
5 – 35
60 - 85
dolomite
35 – 50
45 – 60
magnesite-dolomite
50 – 60
35 – 45
dolomite-magnesite
60 - 85
10 – 35
34
6.1 MAGNESITE MATERIALS
Magnesium oxide – Periclase is only stabile modification of MgO. Fire-resistant products with
MgO resist acting of basic cinder and melts containing oxides of iron. This characteristic comes from
phase ratios in schemes MgO – FeO and MgO – Fe2O3. That is why the main use of these materials is
by production and processing of metals, especially steel. They are used for walling of furnaces and
containers where there is high temperature and iron cinder.
Main raw material is fired magnesite. Magnesite (MgCO3) contains theoretically 47,81 % MgO
and 52,18 % CO2. Originally was created in hydrothermal condition by adding of magnesium into
carbonate stone. Demands for content of supporting oxides in form building materials are stricter,
than what quarried raw material gives us. This means that quarried rock must be processed. It is
main form of magnesium oxide used in production of fire-resistant materials. Material for production
is MgCO3. We divide it into crystals, which are with additives (for example dolomite, silica) or into
integral, which is composed from very fine crystals. Decomposition of magnesite begins at the
temperature of 399° C, when there is equal partial pressure CO2 over MgCO3 101,3 kPa by zero value
of standard free energy of reaction. Firing can be done in two ways: below 1000° C caustic magnesite
is created, which is further used as binder. Above temperatures of 1500° C is sintered magnesite
created, so called Mg cinder. This cinder has better quality for production of magnesite building
materials.
Forming mixtures are composed of several input cinders for securing thermo-mechanic
characteristics. Mixture is prepared from 2-4 grain grades for optimising of density structure of
building materials. Chemical binders provide cohesion of presswork and together with other
additives prevent creation of breach cause by expansion of CaO. Sulphate and magnesium chloride
are used mainly. Powdery mixtures have moisture around 2-3%, pressing happens on hydraulic
presses of press up to 100 MPa. Firing happens mostly in tunnel furnace at temperature 1500-1700°
C. Firing cycle in tunnel furnaces takes 60 to 72 hours by persistence in sintering zone and by set
expansion of firing 6 to 9 hours. Densification and growth of grains of periclase continues during
firing of presswork. Leafing of layers is part of typical and unfavourable mechanism of wearing of
alkaline walling, which is their major disadvantage. Besides fired magnesium building materials there
are also prepared non-fired. As binders are put into mixtures chemical compounds which produce
chemical structure (for example sulphate, phosphate) .
6.2 MAGNESITE - CARBONACEOUS MATERIALS
It is key area in production of basic fire-resistant materials for metallurgic industry – area of
non-fired building material from magnesite fixed with organic binders, with content of carbon below
7% and building materials magnesite – carbonaceous with content of carbon 7-30%. As binders are in
production of formed building materials used black coal resin and synthetic feldspars. Non-fired MgO
building materials differ from other types of alkaline materials by use of organic binders (black coal
resin), which leave after carbonisation carbon residue, which covers particles of magnesite and
connects them. Important part of carbon component of building material is crystal flaky graphite.
Deformability of graphite, low inner attrition, also attrition on walls of form during forming
by pressing allows to produce presswork with low porosity than from any other basic matter, used
35
for production of FRM. Graphite is different from MgO mainly, because it has majorly higher thermal
conductibility and majorly lower thermal expandability. As binders, there where presence of water
during processes is impervious, are used synthetic feldspars: resols and novolacs.
For preparation of forming mixtures there are several processes:

preparation in cold – binder is resol, sometimes combined with novolac, when the
basic material of prepared mixtures is matter containing hydrated CaO, mixtures are
pressed in cold.

preparation at higher temperature – binders are novolacs, or their fusions at
temperature 60 to 100° C, presswork is hardened after pressing at temperatures 80 –
200°C.
Antioxidants prohibit oxidation of carbon; prolong its stay in fire-resistant material. With
presence of CO they are unstable. CO is created by oxidation of carbon and is reduced into new –
secondary carbon, which hardens structure of building material. The most known antioxidant is
carbon. Major part of carbon building materials with content of carbon higher than 7% is natural
crystal graphite. Low inner attrition and attrition on walls of form during press forming allows
producing presswork with low porosity.
6.3 MAGNESITE – DOLOMITE PRODUCTS
Basic product is formed building material, produced from sintered fired dolomite. If we
increase content of MgO with help of magnesite, group of magnesite-dolomite products is created.
Dolomite, dual carbonate magnesite-lime Mg Ca (CO3)2, is rock creating mineral. It is present on
many places of Earth surface. Theoretically contains 30,41 % of CaO, 21,86 % MgO and 47,78 % CO2.
Dolomite is decomposed on two levels with annealing treatment. Crude crystal dolomite with low
content of supporting minerals can be fired into dense sintered product only at temperatures above
2000° C. In little crystal type there is enough the temperature about 1600° C.
Firing is done in same devices as by magnesite. Dolomite is processed mainly into products
non-fired, bound by black coal rosin containing residual carbon below 7%. In recent years is this
method subsidized by phenol bitumen mainly because of the hygiene of work. By fired products form
dolomite it is specific technology of precautions against hydration of CaO in presswork. Products
from dolomite and from magnesite-dolomite are used by production of steel for walling of pans and
containers of pan metallurgy. Other important user is cement industry, where are these products
used for walling of fire areas of rotation furnaces.
6.4 MAGNESITE – CHROME PRODUCTS
Magnesite and chrome ore are main materials during production of magnesite-chrome
products. Chrome ore as one of the basic materials is basically created by complex spinel. Sherd of
magnesite-chrome building material is produced from two composites with very different physical
characteristics. Very different is thermal expandability and change of volume by both materials.
Specialty of these products is increasing of volume of work layer of walling (so called swell) during
36
work in steel furnaces. Non-fired material with chemical structure (MgSO4, MgCl2 or alkali
polyphosphate) can be prepared, besides fired building materials. MC building materials can be
bound by oleoresin with tar. Building materials are used for walling of exposed parts of convertors
for argon-oxygen decarburisation (AOD), containers for degassing of steel in vacuum, RH, DH and
some other pan furnaces in ladle metallurgy, especially there, where have effect dross with ratio C/S
also bellow 2.
Summary of terms
magnesium oxide – periclase and its characteristics
magnesite cinder
antioxidants
Questions
What are sources of MgO and what are processes for preparation of magnesite cinder.
Describe and evaluate process of firing of magnesite and dolomite.
Meaning of antioxidants.
Describe technology of production of other alkaline fire-resistant materials, including raw
materials and characteristics of products.
37
7.
LITERATURE
[1]
HLAVÁČ, J. Základy technologie silikátů. 1. vyd. Praha: SNTL, 1981. 516 s. (Basics of
technology of silicates)
[2]
HANYKÝŘ, V., KUTZENDÖRFER, J. Technologie keramiky. Praha: Silikátový svaz, 2000. 287 s.
ISBN 80-900860-6-3. (Technology of ceramics)
[3]
CARTER, C., B., NORTON, M., G. Ceramic Materials Science and Engineering. New York:
Springer, 2007. 716 s. ISBN 0-387-4620-8.
[4]
SVOBODA, L., aj. Stavební hmoty. Bratislava: JAGA Group, 2007, ISBN 978-80-8076-057-1.
(Building matters)
[5]
HERAINOVÁ, M. Žárovzdorné materiály. Učebnice pro SOŠ: Technologie keramiky - část III.
Praha: Silikátový svaz, 2003.(Fire-resistant materials)
[6]
HLAVÁČ, J. Základy technologie silikátů. Praha: SNTL, 1981. 516 s.
[7]
KALOČ, M. Žárovzdorné materiály v koksárenství. Ostrava: ES VŠB, 1982. (Fire-resistant
materials in coke industry)
[8]
KUTZENDŐRFER, J. a MÁŠA, Z. Žárovzdorné tepelně izolační materiály. Praha: Informatorium,
1991. 268 s. (Fire-resistant thermal insulation materials)
[9]
KUTZENDÖRFER, J., TOMŠŮ, F. Žárovzdorné materiály, Díl. I. Praha: ČSVTS – silikátová
společnosti ČR, 2008. ISBN 978-80-02-02076-9 (Fire-resistant materials)
[10]
LANG, K. Žárovzdorné materiály, Díl. II. Praha: ČSVTS – silikátová společnosti ČR, 2010. ISBN
978-80-02-02244-2. (Fire-resistant materials)
[11]
PALČO, Š. Žárovzdorné materiály, Díl. III. Praha: ČSVTS – Silikátová společnosti ČR, 2010. ISBN
978-80-02-02245-9. (Fire-resistant materials)
[12]
TOMŠŮ, F., PALČO, Š., Žárovzdorné materiály, Díl. VI. Praha: ČSVTS–Silikátová společnost ČR,
2009. ISBN 978-80-02-02170-4. (Fire-resistant materials)
[13]
KUTZENDÖRFER, J., Žárovzdorné materiály, Díl. V. Praha: ČSVTS–Silikátová společnost ČR,
2009. ISBN 978-80-02135-3. (Fire-resistant materials)
[14]
KUTZENDÖRFER, J., Žárovzdorné materiály, Díl. VI. Praha: ČSVTS–Silikátová společnost ČR,
2007. ISBN 978-80-02-01981-7. (Fire-resistant materials)
[15]
KUTZENDŐRFER, J. Žárovzdorné materiály II. Praha: VŠCHT, 1995. 70 s. ISBN 80-7080-246-4.
(Fire-resistant materials)
[16]
LACH, V. Keramika II: Teoretické základy výroby pálených stavebních látek. 1. vyd. Brno: ES
VUT, 1988. (Theoretical basics of production of fired building matters)
[17]
LACH, V. Keramika. 3. vyd. Brno: ES VUT, 1992. (2. dopl. vyd. 1986). ISBN 80-214-0332-2.
(Ceramics)
[18]
ROUTSCHKA, G. Refractory Materials. Essen: Vulkan-Verlag, 1997. ISBN 3-8027-3147-6.
[19]
STAROŇ, J. a TOMŠŮ, F. Žiaruvzdurné materiály: Výroba, vlastnosti a použitie. Banská
Bystrica: MEDIA, 2000. Vyd. SLOVMAG Lubeník, SMZ Jelšava, KERAMIKA Košice. 445 s. (Fireresistant materials: Production, characterics and use)
[20]
Klasifikace žárovzdorných výrobků hutných. Část 1 až 4. ČSN EN 12475 – 1 až 4
38
(72 6014). Praha: Český normalizační institut, 1998. (Classification of fire-resistant dense
products)
[21]
Sborník přednášek Hutní keramika. 1997, 1999 až 2007, 2008-2012 Rožnov pod Radhoštěm.
Ostrava: Tanger.
(Compilation of presentations of Metallurgic ceramics)
39