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Quiz 3
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Q.1
Which is the most stable crystalline form of silica at room temperature?
Quartz
Cristobalite
Tridymite
None of these
Q.2
Fireclay refractories
Are not resistant to the action of basic slags
Combine with salts (e.g. chlorides sulphates etc.) & bases (e.g. lime, magnesia etc.) forming fusible aluminates silicates etc
Shrink during firing
All of the above
Q.3
Refractoriness under loads (RUL) is quite close to the fusion temperature (PCE) for __________ bricks.
Fireclay
Silica
Dolomite
Very low alumina
Q.4
Which is the stable form of silica below 870°C ?
Tridymite
Cristobalite
Quartz
None of these
Q.5
Porosity of fireclay refractories is __________ percent.
5-10
10-25
25-35
35-50
Q.6
Cold crushing strength of a refractory does not depend upon its
Shape
Composition
Firing temperature
Texture
Q.7
Refractory bricks having lower porosity have
High insulating properties
Low heat capacity
Low thermal conductivity
Greater strength
Q.8
Fireclay bricks is not used for lining the
Cupola
Gas producer
Bottom of hot metal mixer
Roof of open hearth furnace
Q.9
Chrome magnesite is not used in the
Inner lining of L.D. converter
Aluminium melting furnaces
Wear out lining of steel melting furnaces
All of the above
Q.10
Magnesite bricks are used in those parts of furnaces, which are
Subjected to temperature fluctuation
Required to resist corrosive basic slag
Subjected to high load
None of these
Q.11
Carbon refractories are exclusively used in the
Hearth of blast furnace
Walls of coke oven
Regenerators of coke oven
Side wall of soaking pits
Q.12
Fireclay refractories have
Low co-efficient of thermal expansion
Poor thermal spalling resistance
Tendency to expand unduly high during firing
Very high cost
Q.13
Conversion of silica mineral to cristobalite is accompanied by reduction in its
Volume
Specific gravity
Both A & B
Neither A nor B
Q.14
Cermets are
Composite material containing both ceramic & metallic constituents
Having high strength & resistance to high temperature
Used in space vehicles, missiles & nuclear energy plants
All of the above
Q.15
Which is the stable form of silica upto 1470°C ?
Quartz
Cristobalite
Tridymite
None of these
Q.16
Firing temperature of magnesite bricks is about __________ °C.
800-1000
1000-1200
1600-1800
2400-2600
Q.17
Maximum safe working temperature for fireclay bricks is about __________ °C.
1150
1300
1450
1550
Q.18
Vacuum steel degassing units are lined with
Silica bricks
Low duty firebricks
High alumina bricks
Graphite blocks
Q.19
Capacity of a refractory brick to withstand-sudden changes in temperature is denoted by the property called
Spalling resistance
Refractoriness
Refractoriness under load (RUL)
None of these
Q.20
Colour of fireclay bricks is
Light buff to reddish buff
Yellow
Black
None of these
Q.21
Semi-silica bricks compared to silica bricks have
Less fusion point
Better spalling resistance
Both A & B
Neither A nor B
Q.22
Silicon carbide refractories are used in the
Muffle furnace
Zinc smelting furnace
Ceramic recuperators
All of the above
Q.23
Dry mix hydraulic compositions of refractory aggregates with suitable bonding materials are called refractory
Mortars
Cements
Castables
None of these
Q.24
Insulating refractories should have
High porosity
Low thermal conductivity
Both A & B
Neither A nor B
Q.25
Which is not a basic refractory?
Chrome magnesite
Magnesite
Dolomite
Silicon carbide
Q.26
Chrome magnesite bricks are
Acidic in nature
Neutral in nature
Having higher RUL than silica bricks
Made by mixing 30% chromite and 70% periclase
Q.27
Chemically, mullite refractories is
3Al2O₃.2SiO₂
Al2O₃
ZrSO₄
ThO₂
Q.28
Carbon refractories
Do not burn/oxidise, when exposed to air on heating
Are not attacked by slags, as they are not wetted by melts
Do not resist temperature fluctuations
Have extremely low thermal & electrical conductivities
Q.29
Which property is important for bricks used in the combustion chamber & dome of blast furnace stoves?
High refractoriness
High resistance to spalling
High strength and density
All of the above
Q.30
Magnesite refractories have low resistance to
Attack by basic slag
Abrasion
Disintegration on sudden change of temperature
Both B and C
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