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Refractory Technology
Quiz 7
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Q.1
SiO₂ percentage in firebrick is about
35-40
55-60
80-85
>94
Q.2
High porosity refractory bricks have
Poor resistance to the peneration of molten slag, metal & flue gases
Poor heat conductivity & low strength
Better thermal spalling resistance
All of the above
Q.3
Which is not a high alumina refractory?
Mullite
Corrundum
Bauxite
Dolomite
Q.4
Carbon refractories have very high
Wetting characteristics
Refractoriness
Thermal conductivity
Both B and C
Q.5
Pick out the wrong statement.
Sand & coke is the main raw material for the manufacture of silicon carbide
Carbon refractories can not be used in the furnaces operating under reducing conditions
Mullite can be obtained by the heating of alusite, kyanite or silimanite
Silica occurs in nature in all cellular, amorphous or crystalline form
Q.6
RUL of refractories depends on the
Chemical composition
Physical structure
Presence of impurities like iron & alkali
All of the above
Q.7
Firing of refractory brick is done to
Dehydrate the dried refractory
Develop stable mineral forms in them
Form ceramic bonds necessary for development of high crushing strength in the finished product
All of the above
Q.8
The linear thermal expansion of __________ bricks upto 1000 °C is very low of the order of ≤ 0.5 percent.
Fireclay
Silica
Magnesite
Corundum
Q.9
__________ of carbon blocks in the hearth of blast furnace helps in avoiding skull formation, when it becomes cold.
High thermal conductivity
Low porosity
Non-wetting characteristics
High density
Q.10
Bottom of basic open hearth furnace are constructed of
Dead burnt magnesite ramming mass
Porous fireclay bricks
Semi-silica bricks
Silicon carbide bricks
Q.11
Magnesite refractories are used for the construction of those furnaces, which are
Not required to resist the corrosive action of basic slag
Not subjected to fluctuation in temperature
Used for raising & maintaining high temperature
Both (b) and ©
Q.12
Natural silica
Mainly contains quartz
Is not stable at high temperature
Transforms to other allotropic forms i.e tridymite and cristoballite involving very high volume changes
All of the above
Q.13
Pick out the wrong statement.
Insulating refractories used in place of regular refractory bricks are usually called light weight refractories, and they have similar composition as heavy bricks
Graphite refractories are also called plumbago refractories
Superduty fireclay bricks correspond to a pyrometric cone equivalent of 26-28
Calcined magnesite is also called dead burnt magnesite
Q.14
Fireclay bricks are not used in the
Beehive coke oven
By-product coke oven walls
Combustion chamber of B.F. stoves
Coke oven regenerators
Q.15
Ramming masses are used for
Obtaining monolithic working faces
Repairing construction of various furnace parts
Both A & B
Neither A nor B
Q.16
Graphite or carbon refractories
Exihibit wetting characteristics
Should be used in neutral or reducing atmosphere
Exhibit high shrinkage on thermal treatment
Are not resistant to corrosion by slag
Q.17
Refractories are dried in the
Rotary kilns
Tunnel kilns
Sun
None of these
Q.18
Refractoriness/fusion points of 'superduty' refractories is __________ °C.
1520-1630
1630-1670
> 1730
> 2000
Q.19
Which of the following has the lowest electrical resistivity?
Graphite
Fireclay
Alumina
Zircon
Q.20
Periclase is
Crystalline form of MgO
MgCO₃
ZrSO₄
Amorphous magnesite
Q.21
Pick out the wrong statement.
Refractories used in muffle furnace should have low thermal conductivity
The electrical resistivity of refractories drops rapidly with rise in temperature
For reducing spalling tendency, the refractory should be well fired and its porosity should be more
Refractoriness under load (RUL) of a refractory is always less than its refractoriness
Q.22
Fireclay bricks are not used in the
Blast furnace
Hot blast stove
Cupola
Wall of coke oven
Q.23
With decrease in porosity, the __________ of the refractories decreases.
Strength
Thermal conductivity
Spalling resistance
None of these
Q.24
Which refractory must have controlled atmosphere (temperature and humidity) for its safe storage?
Tar bonded dolomite bricks
Fireclay bricks
Mullite bricks
Magnesite bricks
Q.25
Pure oxide refractories are generally monocrystaliine in nature and are self bonded __________ bricks are generally used as moderator in nuclear reactors.
Beryllia
Carborundum
Corundum
Thoria
Q.26
Which furnace consumes maximum refractory annually in an integrated steel plant?
Soaking pit
Blastfurnace
L.D. converter
Coke ovens
Q.27
Because of its very high refractoriness of the order of __________ °C, silicon carbide refractories are used in zinc smelting furnace, muffle furnace and for supporting the wares in tunnel kilns.
1800
2200
2400
2700
Q.28
Carborundum used for making crucibles for melting non-ferrous metals is chemically
Silicon carbide
Silicon nitride
Crystalline magnesia
Zirconium sulphate
Q.29
Which one contains minimum percentage of SiO₂?
Firebrick
Sillimanite
Semi-silica
Aluminous firebrick
Q.30
Spalling of a refractory means its
Softening
Fracture due to uneven expansion at high temperature
Resistancce to compressive loads
Resistance to chemical action of gases and molten fluxes
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