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Refractory Technology
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Q.1
Resistance to slag attack of a refractory
Depends on the nature of slag & refractory
Decreases at higher temperature
Decreases, if defective joints & cracks exist in the refractory
All of the above
Q.2
Zircon refractories have
Low co-efficient of expansion
High RUL (1600°C) and refractoriness (> 2000°C)
High spalling resistance
All of the above
Q.3
Which form of silica has the highest specific gravity?
Quartz
Cristobalite
Tridymite
All of the above
Q.4
What is Thoria?
Thoria Has high fusion temperature (> 3000°C) but poor resistance to thermal shock
Thoria Has high resistance to basic slags
Which is expensive & radioactive, is used in crucibles for melting high purity metals
All of the above
Q.5
Zirconia refractory
Does not react with basic slags
Is produced from baddeleyite
Can not be used as an insulator
Has poor electrical conductivity at high temperature
Q.6
Porosity is induced in insulating refractories by adding
Powdered naphthalene
Ammonium chloride/sulphate
Calcium phosphate
All of the above
Q.7
A steel member used in the furnace construction to take the thrust of the brickwork is called
Buckstay
Breast wall
Armouring
Baffle
Q.8
Pick out the wrong statement.
A ceramic material which becomes fluid upon heating and can be moulded in liquid/viscous state is termed s glass
Ceramic materials do not undergo vitrification on heating
Ceramic materials are brittle in nature
Non-oxide ceramic materials generally act as a semi-conductor
Q.9
10 to 30% magnesite is added to chromite to produce chrome-magnesite refractories. Magnesite addition is mainly done to improve the __________ of chromite.
Spalling resistance
Refractoriness
Crushing strength
Resistance to slag
Q.10
Which is a basic refractory?
Fireclay
Silica
Chrome magnesite
None of these
Q.11
Which one expands on heating?
Silica bricks
Fireclay bricks
Both A & B
Neither A nor B
Q.12
Fireclay bricks are never used in the
Beehive oven
Coke oven walls
Zinc roaster
Lead blast furnace
Q.13
High density refractory bricks have lower
Spalling resistance
Thermal conductivity
Fusion point
Slag penetration resistance
Q.14
Which of the following impurities reduces the refractoriness of magnesite bricks?
Al2O₃
CaO
SiO₂
All of the above
Q.15
Silica bricks have low spalling resistance below 600°C, due to its
Very high thermal conductivity
High co-efficient of expansion upto this temperature
High thermal diffusivity
Low refractoriness
Q.16
With increase in the density of silica refractories, its
Resistance to slag attack increases
Spalling resistance reduces
Both A & B
Neither A nor B
Q.17
Spalling tendency of refractories is reduced by increasing its
Porosity
Specific gravity
Thermal conductivity
Strength
Q.18
With increasing alumina content, the fusion point of high alumina refractories
Increases
Decreases
Remains constant
May increase or decrease ; depends on its alumina content
Q.19
Addition of grog in fireclay brick during its manufacture is advantageous, because it results in
Less shrinkage in heating, decreased apparent porosity & increased specific gravity
High strength & thermal spalling resistance
Less addition of water to get a workable plasticity & lesser time required for drying the raw refractories and hence increased rate of production
All of the above
Q.20
Tar bonded dolomite bricks
Are stored under controlled temperature & humidity to avoid hydration
Are used in outer lining of L.D. converters
Have poorer hydration resistance than pitch bonded bricks
All of the above
Q.21
With increase in the alumina content, the refractoriness of high alumina refractories
Increases
Decreases
Remains same
May increase or decrease
Q.22
Which of the following bricks should not be used, if the furnace is to be used intermit-tantly?
Firebricks
Silica bricks
Silicon carbide bricks
Sillimanite
Q.23
Crushing strength of a refractory
Increases with rise in service temperature
Decreases with rise in service temperature
Is unaffected with change in service temperature
Decreases with increase in porosity
Q.24
Sillimanite is a __________ refractory.
Basic
Neutral
High alumina
Insulating
Q.25
Silica refractories
Crack when subjected to sudden change of temperature
Can not be used in the dome of hot blast stoves
Have lower thermal conductivity than fireclay bricks
All of the above
Q.26
silicon carbide refractories have very low
Refractoriness (< 1700°C)
Thermal conductivity
Resistance to thermal shock
None of these
Q.27
Fusion temperature of pure silica (SiO₂) is __________ °C.
1350
1715
2570
2800
Q.28
Spray test determines the __________ of refractories.
Resistance to slag penetration
Resistance to CO attack
RUL
Permanent linear change
Q.29
The main raw material for manufacture of silicon carbide refractories is
Corrundum
Carborundum
Bauxite
Periclase
Q.30
Which is a neutral refractory?
Graphite
Magnesite chrome
Silica
Magnesia
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