Refractory manufcturing,properties

Refractory manufacturing
Refractory testing
and
Refractory properties
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What is refractory ?
Is it a material which should withstand high temperature only ?
The right definition is that it should withstand high temperature,resistance to
thermal and thermo chemical load, posses high volume stability, resistant to
erosion and abrasion, be tough , and resistant to chemical corrosion
etc. Or otherwise it should have high RUL, high PCE, low conductivity , high
hot MOR, high creep resistance and optimum CCS etc
Overall it is a compromise with all the above properties.
Choice of refractories depend on the operating and mechanical
conditions of the kiln.
There is no refractory material which posses all the above
properties 100 %
In general any material which in service > 600 deg C is called refractory

Refractories
Shaped refractories Unshaped refractories or
monolithics
Acid refractories Basic refractories Neutral refractories
Silica based
refractories, fire clay
bricks
Magnesia, Magnesia
Chromium , Magnesia
Alumina , Dolomite
Alumino silicates
Alumina bricks,Zirconia
based refractories,
like zirconal, zircon, etc

Fire Clay
bricks
refractory clays Kaolins extended with
chamotte or non plastic argillacious matter
unwetted by water Al2O3 content = 30 to 45 %
High alumina
bricks
1)Cyanite,andalusite,and siliminite
2) natural hydrated
alumina(hydrargillite,bohemite,and disapore
contained in bauxite)
3)Artificial calcined hydrated alumina, and
natural and electro fused alumina
( Alpha -alumina or
Class A =45 - 60 % Al2O3
Class B = 60 - 70 % Al2O3
Class C = > 75 %Al2O3
Silica bricks Dinas
Magnesia
bricks
Magnesit ( MgCO3), Dolomite
( MgCO3.CaCO3), Mg(OH)2,Mgo Obtained from
dolomite,saline water and sea water
Spinel bricks
MgO and Al2O3 together sintered or fused
MgO from sea water and alumina from
alumina industries ,alpha alumina etc)
Raw materials used for manufacturing of bricks

Acidic Basic
neutral
Raw material user

ZrO2 Cr2O3
CaOSiO2
ZrS
Zircon silicate
1775 O C
A3S2
mullite 1840 O C
Important mineral phases in refractories
M2S
Forstrite
1890 O C
MCr
Picro chromite
C2S
Bredigit 2130 O C
CA6
Hibonite
1850 O C
MA-spinel
2135 O C
MgOAl2O3
2180 O C

Melting point of pure refractory oxide
1200
1400
1600
2000
2200
2400
3000
2800
2600
SiO2 Al2O3 Cr2O3 CaO ZrO2 MgO
1702
2050
2275
2600
2700
2800
Deg c

Classification of refractories regarding melting point and alkalinity
1234567891011121314
3000
2750
2500
2250
2000
1750
1500
melting point
Deg c
pH value
Cao
MgO
Al2O3
ZrO2
Cr2O3
SiO2
basic neutral acidic

Process flow chart for manufacturing
Comminution
preparation
classification
mixing
shaping
drying
firing

SIC crystals ( Silicon carbide)

ZrSiO4
Zircon crystals ,ZrSiO4

Refractory manufacturing process
Tunnel kiln Tunnel dryer
Tunnel cars
Finished product storage
Brick press
machines
Coarse
crusher
Fines
crusher
Ball mill
storage
elevator
Vibrating screen
Storage silos
classifier
Clay crusher
Clay mill
Drying tower / classifier Binder & liquids
Liquid dosage

Refractory manufacturing process
Schematic diagram of refractory manufacturing
Rough
crushing
Raw
material
middle
crushing distribution
fine
crushing
Storage by
Grain size
Measuring
quantity
mixing moulding
drying
firing
inspection packing
shipping

Refractory clay mine
Opencast mining
Under ground mining

Cone crusher

Hydraulic press

Iso static press machine

Tunnel dryer

Tunnel kiln

Important refractories used in
cement industry
Magnesia containing bricks _ mag chrome, mag spinel,
dolomite,hercynite, galaxite
based,
zirconia based
High alumina bricks - 60 - 70 % Al2O3
Fire clay bricks - 30 % Al2O3
Light weight insulating bricks
Unshaped refractories or castables - conventional,
low cement castable,
ultra low cement castables,
insulation castables

Raw materials for Magnesia bricks are
• Natural magnesite , MgCO3 , Coarse crystalline ,
fine crystalline
• Synthetic magnesia,sea water magnesia , salt brine
• The principal constituent determining the characteristic
properties of magnesia refractories is periclase
Properties of periclase
0 Melting point = 2800 deg . C
0 Thermal conductivity = 3 - 4 w / mk
0 Thermal expansion = 1.4 %
Refractory products for the cement kiln

• Magnesia bricks, MgO, > 80 %
• Magnesia spinel bricks, MgO , 80 - 90 %
• Magnesia hercynite bricks, MgO, 80 - 96 %
• Magnesia Zirconia bricks MgO, 85 - 96 %
• Magnesia chromite MgO, 55 - 80 %
• Chromite bricks Cr2 O3=25%
MgO = 25 %
• Forsterite MgO and SiO2
• Dolomite MgO = 60 % and CaO=40 %
• Magnesia, galaxite bricks Mgo=91% ,and MnO=2.6%
Basic bricks used in the cement industry

Mineral Formula Abbreviation Fusiontemp ,Deg C
Periclase MgO M 2800 deg C
Forsterite 2 MgO.SiO2 M2S 1890
Monticellite CaO.MgO.SiO2 CMS 1495
Merwinite 3 CaO.MgO.2SiO2 C3MS2 1575
Dicalcium silicate 2CaO.SiO2 C2S 2130
Magnesium ferrite MgO.Fe2O3 MF 1750
Dicalcium ferrite 2 CaO.Fe2O3 C2F 1435
Tri calcium silicate 3CaO.SiO2 C3S 1900
Brown mellarite 4CaO.Al2O3.Fe2O3 C4AF 1395
Dolomite CaO.MgO CM 2450
Andalusite Al2O3.SiO2 AS
Mullite 3Al2O3.2SiO2 1840
Siliminite Al2O3.SiO2 AS 1545
Important refractory minerals used in refractories

Andalusite Al2O3.SiO2 AS
Mullite 3Al2O3.2SiO2 1840
Siliminite Al2O3.SiO2 AS 1545
Corundum 2050
Hercynite FeO.Al2O3 FA 1760
Galaxite Mno.Al2O3 mA
Magnesia aluminaSpinel MgO.Al2O3 MA 2135
Gehelinite 2CaO.Al2O3.SiO2 C2AS 1590
Calciumaluminate CaO,Al2O3 CA 1600
Anorthite CaO.Al2O3.2SiO2 CAS2 1550
Dicalciumferrite 2CaO.Fe2O3 C2F 1450
Myenite 12CaO.7Al2O3 C12A7 1455
Gehelinite 2CaO.Al2O3.SiO2 C2AS 1590
Calciumaluminate CaO,Al2O3 CA 1600
Anorthite CaO.Al2O3.2SiO2 CAS2 1550
Dicalciumferrite 2CaO.Fe2O3 C2F 1450
Myenite 12CaO.7Al2O3 C12A7 1455
Important refractory materials used in refractories

Major refractory bricks used in cement industries
70 % Alumina bricks
Cooling zone ,burning zone,
transition zone
60 % Alumina bricks transition zone,calcining zone, t.a.duct
,calciner, cooler area
40-50 %Alumina bricks calcining zone, t.a.duct
,calciner, cooler area
30 % Alumina bricks t.a.duct, ,calciner, cooler area,pre-heater
cyclones
Magnesia chrome bricks
Dolomite bricks Burning zone
Magesia spinel bricks
cooling zone,burning zone ,transition zone
Hercynite ,nochrome
Galaxite no chrome transition zone
Location where it is usedType of brick

Refractory properties
Physical properties
1)Bulk density g / cm3
2)Apparent porosity %
3)Cold crushing strength N/ mm2
Thermal properties
1)Refractoriness under load (RUL)
OC
ta
te
2) PCE ( pyrometric cone equivalent)
SK (Arton cone in ASTM standard)
3)Thermal expansion ,lin % (PLC)
at 4000c
8000c
12000c

4)Thermal shock resistance (TSR)
at 9500 c in air
or
Water quenching cycles
5) Thermal conductivity at
3000c
7000c
10000c
Chemical analysis
MgO
Al2O3
Cr2O3
Fe2O3
CaO
SiO2
ZrO2
MnO2 etc

1. Bulk density
Density of all refractories is an indirect measure of their
capacity to store heat
.
2. Apparent porosity
The porosity of a refractory is a measure of % pores to the
( summation of open and closed pores)total weight of
a brick. This property is significant to decide
upon its resistance to penetration by slags and fluxes ,its
permeability to gases and its thermal conductivity
Porosity is controlled by the following
1) by controlling the texture of the bricks
2) by controlling the size of the particles
3) by method of making
4) by controlling the firing temperature
Physical properties

Porosity affects
• the strength of the
brick
• porous bricks are
mechanically weak
• lower porosity gives
better resistance to
slag attack
• thermal conductivity
pc
po
po
po
po
po
Po –open pores
Pc –closed pores
po
pc
Pc

3. Cold crushing strength ( CCS )
Cold crushing strength of a refractory material represents its
strength .In other words it tells us how much load it can bear
in cold condition
The mechanical strength (CCS) of refractory brick is governed
largely by the amount and the character of the matrix material
between the larger grains. Good tool to provide for evaluating
the degree of bond formation during production. It indicates the
ability of the brick to withstand abrasion and impact in low
temperature application.

CCS testing machine

Cold crushing equipment and CCS values
Brick grade CCS ( N / mm2)
Silica 15 -20
Fire clay 12 - 70
Corundum 35 - 80
Magnesia 50 - 110
Magnesia chromite 30 - 70
Magnesia spinel > 40
Insulating Brick 3 - 20

Density Coefficient of thermal
conductivity
Thermal
shock
resistance
Cold crushing
strength
Porosity
Correlation between the physical properties

Thermal properties
1.Refractoriness( fusion temperature or softening temp)
Transition of a solid material into the liquid form under
the influence of heat. A true melting point is temperature
at which the solid and liquid phase of the composition
co-exist in equilibrium.
It is the ability of a refractory to remain rigid at a given
temperature. It is an indirect indication of the amount
and the viscosity of any liquid which it may contain.
The reference samples are called seger cones in
DIN standards and Norton cones in ASTM standards.
Or PCE (pyrometric cone equivalent)

Test sample
Standard samples
1
2 3
4
5
PCE test(pyro-metric cone
equivalent)
Plaque
25 mm
82 O
8 mm

Seger cones before and after firing

Seger cone and reference temperature

Determination of the softening behaviour
under temperature and load
The three methods evolved are
• Determination of the refractoriness under load
• Determination of the refractoriness load ( diifferential)
• Determination of the thermal expansion under load ( creep)

Determination of refractoriness under load (RUL)
Characteristic temperatures are Brick grade t a / O c
t a : 0.3 mm compression from the Fire clay 1300 -1550
temperature the temperature of Corundum 1600 - 1750
highest expansion Silica > 1660
( 0.6 % compression of test sample) Magnesia chromite > 1550
t e : 10 mm compression from the Magnesia-hercynite 1600
temperature of highest expansion Dolomite 1700
(20 % compression of test sample) Magnesia spinel > 1700
t b : temperature of breaking sample: Carbon brick non-
softening

Curve example of refractoriness under load
Determination of the refractoriness under load (differential)

Determination of the thermal expansion under
load ( creep)
Curve example of Creep under load

Creep test equipments

Refractoriness under load
This is a measure of the resistance of a refractory body
to the combined effects of heats of load.This test helps
to study the behavior of a refractory product when
subjected to a constant load under conditions of
progressively rising temperature.
The ground mass / matrix helps to bond the entire mass of
a refractory brick strongly together. The amount and the
strength of the glass is fixed by the alumina - silica ratio,
fluxing oxide content and the temperature of firing.
It is an important parameter to decide upon the safer limit
of service temperature in a given situation.
Contributing factors to the increased resistance to the
pressure are
a) More thorough distribution of liquid throughout the brick
b) The growth of crystals through the influence of heat
c) Crystallization of a portion of the liquid during cooling.

High temperature creep
In a brick held at constant temperature and pressure,
gradual solution of solid material up to the limits of its
solubility in the liquid may cause some increase in the
viscosity of the liquid. This increase is dependent on
the nature of ground mass, glass content. Higher
glass content will result higher deformation in this
situation. This property of refractoriness is called high
temperature creep. Lower deformation will ensure
rigidity under the service condition.
The creep is the measurement of deformation of a
refractory product as a function of time when it is
subjected to a constant load and heated at a specified
temperature.

RUL measuring equipment
Carbon or mullite rod
insulating brick lining
Corundum, magnesite
or mullite tube
Steel casing
Metal electrode
Coarse amorphous
carbon
Test specimen
View point

RUL testing machine and creep test machine

Creep curves

Softening under load
0 200 400 600 800 1000 1200 1400 1600 1800
Pressure/extension(%)
- 2
- 1
0
1
2
3
Temperature o C
magnesia zirconia
magnesia spinel
Magnesia
chromate
dolomite

Creep measurement of various high alumina refractories
under 25 psi load at 2600 O F for 0 - 100 hours
Linearsubsidence-percent
5
4
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
0 10 20 30 40 50 60 70 80 90 100
Time(hrs)
60 % alumina - low alkali
70 % alumina
50 % alumina
85 % alumina

Linear expansion (Permanent linear change)
High temperature reheat test may
be used to reveal
1) if a brick has been fired long enough
or at a high temperature
2) whether a brick has adequate
refractoriness and volume stability
It is expressed as a percentage ,
preferably by the ratio of the length
of the test piece after heating and
the original value of the length
Equipments used to
determine
Thermal expansion

20 deg c
1000 deg c
2000 deg c
L= 1000 mm
L= 1013 mm
L = 1026 mm
Magnesia : Thermal expansion = + 1.3 % at 1000 degc
Alumina oxide : Thermal expansion = + 0.8 % at 1000 degc
Fire clay Thermal expansion = + 0.5 % at 1000 degc
Thermal expansion or refractory materials

Thermal expansion curves

Thermal expansion is important in service , as the effect of expansion has
to be taken into account during refractory installation and construction of
large installations ( expansion joints). The expansion curves of most of
refractories is more or less linear with increasing temperature or reversible.

Thermal shock resistance( spalling resistance)
Thermal spalling results from stresses caused by
unequal rates of expansion and contraction in different
parts of brick and usually associated with rapid changes
of temperature.
In cement rotary kiln the brick lining needs to be
spalling resistant as the lining is subjected to
continuation variation of temperature because of
rotary motion of kiln.
TSR ( thermal shock resistance ) is given in cycles.
Quenching is done by air or water

Equipments for thermal
shock resistance test

Thermal conductivity
The coefficient of thermal conductivity is defined as the quantity of
heat that flows across unit area in unit time if the temperature
gradient across this area is unity.
Thermal conductivity K is given as
k ( T1 - T2 ) At Kcal / hr - m - O C or BTU / hr -sq.ft - O F
Q =
d Q = amount of heat
T1 = hot face temperature
T2 = cold face temperature
A = area cross section
t = time
d = thickness
Thermal conductivity of a refractory decreases with increase in porosity.
Increase and decrease of thermal conductivity at elevated temperature
also depends on amount of glass, liquid and crystallinity of the material.

1
2
3
46
5
7
8
9 10
11
12
13 14
200 400 600 800 1000 1200 deg c
2
4
6
8
10
(w/km) Thermal conductivity of
fired refractory bricks
1. Insulating refractory bricks
2. Zirconia
3. Dry- pressed fire clay
4. Fused silica
5. Forsterite
6. Chromite
7.Corundum 90 %
8. Magnesia- chrome
9.Zircon silicate.
10. Corundum 99 %
11. Carbon
12.Silicon carbide 40%
13. Magnesia
14. Silicon carbide

Thermal conductivity depends
on temperature , chemical
and mineralogical,
composition of the brick ,
porosity, pore size and brick
firing temperature
Material Thermal conductivity
at 1000 O C (W/(m.K)
Magnesia 4.4
Magnesia chromite 2.5
Magnesia –spinel 2.8
Magnesia hercynite 2.6
Alumina 3.0
Insulating brick 0.6
Iron 28.0
Thermal conductivity

The bending strength can be
calculated by means of the equation
σ bending = 3.F.l / (2.b.h2)
l = distance between blades
b = width of sample
h= height of sample
In order to determine the magnitude of the rupture stress of
refractoies , the resistance to deformation under bending load
is measured.
F
Pressure load
Tensile load
Determination of modulus of rupture
sample

Determination of hot modulus of rupture (HMOR)
Structural configuration of the refractory material as well as the
amount and properties of occurring melts characterize the HMOR
HMOR (N /mm2)
Testing temperature (deg C) 1200 1400 1500
Magnesia , low iron content > 14 11 8
Magnesia , high iron content > 12 5 1
Magnesia – Chromite > 10 5 3
High alumina > 25 18 7
Zirconia > 25 > 25 > 18

Modulus of rupture
MOR test
The resistance to bending stress of refractory products provide
information on their deformation behavior at high temperature.

Hot MOR Test

Principle of wedge splitting test

Wedge splitting
machine
Grooved
split
The specific feature of
this method of testing is the
determination of fracture
mechanical parameters at
higher temperatures , up to
1200 deg C

Influence of of the aggregates on the secondary
load bearing capacity of the softening behavior

Chemical composition
By quantifying all the constituents present in refractory, it is
possible to assess the chemical properties and melting behavior
of a given refractory.As it is important to know the % Al2O3 in
high alumina brick, % MgO in magnesite brick , and % SiO2 in
silica brick etc.,the determination of minor constituents has
also been recognized as controlling factors in the performance
of many refractories. The chemical composition is of great
importance with respect to attack by slag , glass melts , flue
dusts and vapors. In general the principle applies that a brick is
more resistant the lower the rate of chemical reaction gradient
between the slag and brick is. Therefore, where the acid slag
is expected , acid bricks are preferably used , and basic bricks
where basic slag is expected.

According to the behavior during contact reaction ,
the following groups of bricks can be differentiated.
Acid group - fused (99% SiO2), Silicon carbide bricks,
Zircon crystobalite . Zircon silicate
Basic group - dolomite, magnesia, magnesia chrome,
chrome magnesia ,forsterite
Inert or neutral - carbon , high alumina chromite
group

Cup corrosion test
Alkali test of a high alumina brick
with K2CO3
Alkali test of a sic containing
high alumina brick with K2CO3

Mineralogical investigations by X-ray diffraction
Determination of the mineral phases composition of material
X-ray diffraction diagram of a used magnesia –spinel brick grade ,
salt infiltrated

Microscopically techniques ( micrologies)
• Light micoscopy ( transmitted light and reflected light
microscopy
• Microprobe analysis ( WDS, EDS)
• Scanning electron microscopy
Advantages of these micrlogies opposite other investigation
methods
• Diagnosis of mineral phases composition in raw materials ,
refractory products etc and their configuration
( textural/ structural criterions, pore shape and size etc

Mineralogical investigations
Reflected light microscopy
Pictures of magnesia - spinel brick grades with different raw
material composition

Microprobe Analysis
Chemical – mineralogical composition in m m
Boundary between slag and corundum brick
Polished section image
(reflected light microscope)
Back scattered electron image
(microprobe)

Mineralogical investigations
Scanning electron microscopy (SEM)
Hydration of Magnesia .
crack formation ,caused by
formation of
brucite(Mg(OH)2

Minerological investigations

Cont...
Refractory Bricks Properties
Chem. Comp.
Bulk
Density
App.
porosity
CCS PCE
Therm
exp.
Therm.
Condct.
TSR (air)
(%) (gm/cm3) (%) (N/mm2
)
ta
(°C)
tb
(°C)
s.c
at 1200
O
C %
(W/mK)
at 1000
O
C
(cycles
at 950
O
C)
Ankral S
65-(Mg
chrome)
M = 77- 80
Cr = 7 - 9
Al = 2 - 4
F= 7 - 10
C= 1 - 2
S= 0.4 - 1
3.00 < 21 35 >1650 >1700 > 42 1.04 2.1 > 150
Perilex -
83 (Mg
chrome)
M=80 - 85
Cr = 3 - 5
A= 1 - 3
F= 7 - 9
C =2.5
S = 1.5
2.9 - 3.05 17 - 19 55 1600 >1700 42 1.7 2.8 80
Bazal Z
extra
(Mg
chrome)
M = 77
Cr = 8
A= 3
F= 9.5
C =1.6
S = 0.6
3 19 55 1720 1.6 2.4 100
Rexal S
extra
(Spinel
bricks)
M = 87
Cr = 0
A= 11
F < 0.5
C < 1
S < 0.3
2.93 17 50 >1740 1.7 2.9 >120
RUL

Cont...
Chem. Comp.
Bulk
Densit
y
App.
porosity
CCS PCE
T herm
exp.
Therm.
Condct.
TSR (air)
(%) (gm/cm3) (%) (N/mm
2
)
ta
(°C)
ta
(°C)
s.c
at
1200
O
C %
(W/mK)
at 1000
O
C
(cycles
at 950
O
C)
Al mag -
85
(Spinel
bricks)
M = 85 - 89
Cr = 0
A= 9 - 12
F < 0.5
C < 1
S < 0.5
2.85 - 3 16 - 18 50 >1700 >1700 > 42 1.4 2.8 >100
Al mag -
85 SLC
(magnesi
a fused
spinel
bricks)
M = 85 - 90
C r = 0
A= 9 - 12
F < 0.5
C < 1.4
S < 0.9
0.9 17 55 >1700 >1700 42 1.4 2.7 100
Ankral R -
19
(Spinel
bricks)
M = 94
Cr = 0
A= 5
F = 0.2
C = 0.9
S = 0.2
3 16 40 >1700 >1750 42 1.5 3 >101
Ankral R -
17
(Spinel
bricks)
M = 86
Cr = 0
A= 12
F = 0.5
C = 0.7
S = 0.2
2.95 16 >40 >1700 >1750 >42 1.49 2.6 >100
RUL

Cont...
Chem. Comp.
Bulk
Density
App.
porosity
CCS PCE
Therm
exp.
Therm.
Condct.
TSR (air)
(%) (gm/cm3) (%) (N/mm
2
)
ta
(° C)
tb (° C) s.c
at
1200
O
C %
(W/mK)
at 1000
O
C
(cycles
at 950
O
C)
AS - 90
(Spinel
bricks)
M = 91- 94
Cr = 0
A= 5 - 7
F = 0.5
C = 0.8
S = 0.2
2.9 17 >40 1700 2.9 >100
Mag Pure
- 93
(Spinel
bricks)
M = 89-93
A= 5 - 8
Cr= 0
F = 0.5
C = 2
S = 1
2.9 16 - 18 50 >1700 >1700 >42 1.5 2.9 100
Mag Pure
- 95
(Spinel
bricks)
M = 93-96
A= 3 - 5
Cr= 0
F =0.5
C = 1
S < 0.7
2.9 17 - 18 50 >1700 >1700 >42 1.6 3 100
Refra
Mag -85
(Spinel
bricks)
M =84-89
A= 9 -12
Cr= 0
F =0.8
C = 1.4
S =0.9
2.9 17 -19 45 >1700 >1700 >42 1.4 2.7 100
RUL

Chem.
Comp.
Bulk
Density
App.
porosity
CCS PCE
Therm
exp.
Therm.
Condct.
TSR (air)
(%) (gm/cm3) (%) (N/mm2
)
ta
(° C)
tb
(° C)
s.c
at 1200
OC %
(W/mK)
at 1000
O
C
(cycles
at 950
O
C)
Ferro Mag
-90
(Magnesia-
hercynite)
(Spinel
bricks)
M =87 - 92
A= 4- 6
Cr= 0
F =3-5
C = 1.5
S =0.5
2.9 18 - 20 50 1600 >1600 42 1.5 2.6 100
R -63
(Magnesia-
hercynite)
(Spinel
bricks)
M =86
A= 2.5
Cr= 0
F =8.2
C = 1.8
S =0.9
3.1 17 > 50 >1600 >1700 42 1.5 2.7 > 100
Ankral X2
(Magnesia-
galaxite)
M =91
A= 3.5
Cr= 0
F =0.7
C = 0
MnO =2.6
2.98 15 90 > 1700 2.7 > 100
VRW-70
A = 70 %
Fe2O3 = 3.5
2.65 23 > 55 1460 37 2 1.9 30
VRW- Lofal
70
A = 70 %
Fe2O3 = 2.5
2.65 23 > 55 1500 36 2.5 1.9 30
RUL

Thank you
for your
Kind attention

Refractory manufcturing,properties

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