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Quiz 4
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Q.1
Cermets are combination of ceramic and metallic materials due to which they have high strength & resistance to high temperature. Cermets are used in the
Hearth of the blast furnace
Nuclear reactors, missiles & space crafts
Insulation of high temperature furnaces
Roof of electric furnaces
Q.2
Basic bricks are not made of
Fireclay
Magnesite
Foresterite
Chromite
Q.3
Chromite refractories are
Acidic refractory
Neutral refractory
Basic refractory
Fired at a temperature of 600°C only
Q.4
Carbon refractory blocks
Are wetted by molten iron
Are used in the hearth of blast furnace
Are acidic in nature
All of the above
Q.5
Which of the following is not an acidic refractory?
Silica bricks
Fireclay bricks
Bauxite bricks
Magnesia bricks
Q.6
Alumina-graphite bricks are used for lining the
Slide gate in teeming laddies
Continuous casting systems
Both A & B
Neither A nor B
Q.7
Maximum water percentage in refractory mix meant for hand moulding may be as high as __________ percent.
2-3
5-7
7-12
14-20
Q.8
An ideal refractory should have high
Spalling rate
Fusion point
Shrinkage ability
None of these
Q.9
Which is the stable form of silica between 1470°C and the melting point 1713°C ?
Cristobalite
Tridymite
Quartz
None of these
Q.10
__________ bricks should not be used in oxidising atmosphere.
Tar dolomite
Carbon
Silica
Fireclay
Q.11
__________ bricks are used in the burning zone of a cement rotary kiln.
High alumina
Fireclay
Thoria
Silicon carbide
Q.12
Silica refractories are not used in
Coke oven walls
Beehive coke ovens
Dome and upper portion of B.F. stoves
Open hearth furnace roof
Q.13
High alumina refractories are used in the
Dome of blast furnace stoves
Electric arc furnace roof
Glass melting furnaces
All of the above
Q.14
Most Cermets, which normally have high thermal conductivity and high thermal shock resistance, comprises of ceramic & metallic components of __________ percent respectively.
80 and 20
20 and 80
50 and 50
60 and 40
Q.15
Presence of MgO in alumino-silicate refractories __________ its refractoriness.
Increases
Lowers
Does not affect
Either A or B; depends on its quantity
Q.16
Pure bauxite is the best raw material for the manufacture of high alumina refractories, in which maximum alumina content can be as high as __________ percent.
55
70
80
90
Q.17
Maximum shrinkage in volume occurring during burning/firing of dried refractories may be as high as __________ percent.
10
15
20
30
Q.18
Furnace atmosphere for softening temperature determination of refractories (in which segar cones are placed) should be
Oxidising
Neutral
Either A or B
Neither A nor B
Q.19
Porosity of silica bricks varies from __________ percent.
5 to 10
20 to 30
45 to 60
60 to 75
Q.20
Maximum alumina content in high alumina refractory can be as high as __________ percent.
30
50
70
90
Q.21
High thermal conductivity of a refractory material is not important, when it is to be used in the
Coke oven regenarators
Muffle furnace
Blast furnace
Recuperators
Q.22
Thermal diffusivity of a refractory brick is high, when its __________ is high.
Density
Specific heat
Thermal conductivity
None of these
Q.23
Test piece for determination of RUL of a refractory is heated in a/an
Oxidising atmosphere
Reducing atmosphere
Electric furnace
Neutral atmosphere
Q.24
Lower wall courses of soaking pits are made of __________ bricks to avoid the action of molten slag & scale.
Chrome or magnesite
Silicon carbide
Silica
Lowduty fireclay
Q.25
Fusion point of a basic refractory material is
Reduced by the addition of acid oxides
Increased by the addition of acid oxides
Not affected by the addition of acid oxides
Always less than 1000°C
Q.26
Which is not a natural insulating material?
Diatomaceous earth/kieselgur
Asbestos
Vermiculite
None of these
Q.27
Periclase refractory contains mainly
CaO
MgO
Al2O₃
SiO₂
Q.28
In panel test for spalling resistance, the average face temperature of panel assembly is maintained at __________ °C for 24 hours.
700
1000
1600
2000
Q.29
Pyrometric cone equivalent (PCE) value (Segar cone) of 'superduty refractories' is more than 33 which corresponds to a temperature of __________ °C.
1520
1630
1670
1730
Q.30
Spalling of silica bricks occurs due to abrupt volume changes, when it is cooled below a temperature of __________ °C.
770
570
270
70
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