Refractory Technology MCQs : This section focuses on the "Refractory Technology". These Multiple Choice Questions (MCQs) should be practiced to improve the Refractory Technology skills required for various interviews (campus interview, walk-in interview, company interview), placement, entrance exam and other competitive examinations.
Question 1
A steel member used in the furnace construction to take the thrust of the brickwork is called
A. buckstay
B. breast wall
C. armouring
D. baffle
Question 2
An indication of degree of firing in silica brick is its
A. specific gravity
B. fusion point
C. RUL
D. none of these
Question 3
An insulating refractory brick should have high porosity and low thermal conductivity. Which of the following is not used for inducing porosity in the insulating refractory bricks during its manufacture ?
A. Cork
B. Saw dust
C. Sand
D. Chemically prepared foam
Question 4
Beryllia (which is used in making crucibles for melting uranium & thorium) is superior to alumina in all respects for high temperature (> 1900°C ) use, except
A. cost
B. electrical conductivity
C. thermal conductivity
D. fusion point
Question 5
Capacity of a refractory brick to withstand-sudden changes in temperature is denoted by the property called
A. spalling resistance.
B. refractoriness.
C. refractoriness under load (RUL).
D. none of these.
Question 6
Cermets are combination of ceramic and metallic materials due to which they have high strength & resistance to high temperature. Cermets are used in the
A. hearth of the blast furnace.
B. nuclear reactors, missiles & space crafts.
C. insulation of high temperature furnaces.
D. roof of electric furnaces.
Question 7
Chemically, mullite refractories is
A. 3Al2O3.2SiO2
B. Al2O3
C. ZrSO4
D. ThO2
Question 8
Chromite refractories
A. are bonded with lime and clay.
B. (free from silica) have better thermal fatigue resistance than silica and magnesite refractories.
C. are resistant to basic slag.
D. all (a), (b) and (c).
Question 9
Fireclay bricks are not used in the
A. beehive coke oven.
B. by-product coke oven walls.
C. combustion chamber of B.F. stoves.
D. coke oven regenerators.
Question 10
Fireclay bricks are used in the
A. coke ovens regenerator.
B. outer lining of L.D. converter.
C. hearth bottom of blast furnace.
D. coke oven walls.
Question 11
Firing of refractory brick is done to
A. dehydrate the dried refractory.
B. develop stable mineral forms in them.
C. form ceramic bonds necessary for development of high crushing strength in the finished product.
D. all (a), (b) and (c).
Question 12
Firing temperature is minimum (1250-1400 °C) for __________ bricks.
A. fireclay
B. direct bonded basic
C. silica
D. magnesite
Question 13
Firing temperature of magnesite bricks is about __________ °C.
A. 800-1000
B. 1000-1200
C. 1600-1800
D. 2400-2600
Question 14
Fusion point of a basic refractory material is
A. reduced by the addition of acid oxides.
B. increased by the addition of acid oxides.
C. not affected by the addition of acid oxides.
D. always less than 1000°C.
Question 15
Grog
A. contains both alumina and silica.
B. iscrushed firebrick.
C. is a non-plastic material.
D. all (a), (b) and (c).
Question 16
High porosity refractory bricks have
A. poor resistance to the peneration of molten slag, metal & flue gases.
B. poor heat conductivity & low strength.
C. better thermal spalling resistance.
D. all (a), (b) and (c).
Question 17
Hollow refractory bricks are made by
A. slip casting
B. hand moulding
C. pressing/machine moulding
D. extrusion
Question 18
Hot metal runner in blast furnace are lined with __________ bricks.
A. silica
B. carborundum
C. fireclay
D. magnesite
Question 19
Magnesite bricks are used in those parts of furnaces, which are
A. subjected to temperature fluctuation.
B. required to resist corrosive basic slag.
C. subjected to high load.
D. none of these.
Question 20
Magnesite refractories are used for the construction of those furnaces, which are
A. not required to resist the corrosive action of basic slag.
B. not subjected to fluctuation in temperature.
C. used for raising & maintaining high temperature.
D. both (b) and (c)
Question 21
Maximum alumina content in high alumina refractory can be as high as __________ percent.
A. 30
B. 50
C. 70
D. 90
Question 22
Outer combustion chamber of blast furnace stove is lined with __________ bricks.
A. fireclay
B. silica
C. chrome magnesite
D. zirconia
Question 23
Panel test determines the __________ of refractories.
A. fusion point
B. spalling resistance
C. slag penetration resistance
D. refractoriness under load (RUL)
Question 24
Pyrometric cone equivalent (PCE) value (Segar cone) of 'superduty refractories' is more than 33 which corresponds to a temperature of __________ °C.
A. 1520
B. 1630
C. 1670
D. 1730
Question 25
Quartz is
A. stable form of silica upto 870°C.
B. converted to tridymite on firing between 870 to 1470°C.
C. transformed to crystoballite on heating above 1470°C.
D. all (a), (b) and (c).
Question 26
Refractories are dried in the
A. rotary kilns
B. tunnel kilns
C. sun
D. none of these
Question 27
Refractoriness of a typical silica brick corresponds to Segar cone number, '32', which is equivalent to a temperature of __________ °C.
A. 1380
B. 1520
C. 1710
D. 1915
Question 28
Refractoriness/fusion points of 'superduty' refractories is __________ °C.
A. 1520-1630
B. 1630-1670
C. > 1730
D. > 2000
Question 29
Resistance to slag attack of a refractory
A. depends on the nature of slag & refractory.
B. decreases at higher temperature.
C. decreases, if defective joints & cracks exist in the refractory.
D. all (a), (b) and (c).
Question 30
Roof of a basic electric furnace is made of __________ bricks.
A. superduty fireclay
B. silica
C. chromite
D. none of these
Question 31
RUL of refractories depends on the
A. chemical composition.
B. physical structure.
C. presence of impurities like iron & alkali.
D. all (a), (b) and (c).
Question 32
Skull is not formed on the carbon blocks in the hearth of a blast furnace, when it becomes cold, becaus of its
A. non-wetting characteristic.
B. high thermal conductivity.
C. high crushing strength.
D. none of these.
Question 33
Spalling of silica bricks occurs due to abrupt volume changes, when it is cooled below a temperature of __________ °C.
A. 770
B. 570
C. 270
D. 70
Question 34
Spray test determines the __________ of refractories.
A. resistance to slag penetration
B. resistance to CO attack
C. RUL
D. permanent linear change
Question 35
Test piece for determination of RUL of a refractory is heated in a/an
A. oxidising atmosphere
B. reducing atmosphere
C. electric furnace
D. neutral atmosphere
Question 36
Thermal diffusivity of a refractory brick is high, when its __________ is high.
A. density
B. specific heat
C. thermal conductivity
D. none of these
Question 37
Thoria
A. has high fusion temperature (> 3000°C) but poor resistance to thermal shock.
B. has high resistance to basic slags.
C. which is expensive & radioactive, is used in crucibles for melting high purity metals.
D. all (a), (b) and (c).
Question 38
Thoria is an expensive refractory material and is radioactive in nature. Thorium oxide is used in the manufacture of
A. segar cones.
B. muffles for muffle furnaces.
C. insulating bricks.
D. crucibles used for melting of high purity metals.
Question 39
Vacuum steel degassing units are lined with
A. silica bricks
B. low duty firebricks
C. high alumina bricks
D. graphite blocks
Question 40
Walls, roofs & combustion chambers of annealing furnaces are made of __________ bricks.
A. high duty fireclay
B. silica
C. mullite
D. carborundum
Question 41
Water content in ground refractory material to be shaped into bricks by hand moulding is about __________ percent.
A. 5
B. 20
C. 40
D. 55
Question 42
Which is not a basic refractory ?
A. Chrome magnesite
B. Magnesite
C. Dolomite
D. Silicon carbide
Question 43
Which is the stable form of silica below 870°C ?
A. Tridymite
B. Cristobalite
C. Quartz
D. None of these
Question 44
Which is the stable form of silica between 1470°C and the melting point 1713°C ?
A. Cristobalite
B. Tridymite
C. Quartz
D. None of these
Question 45
Which one expands on heating ?
A. Silica bricks
B. Fireclay bricks
C. Both (a) & (b)
D. Neither (a) nor (b)
Question 46
Which property of refractories is the most important for top section of the blast furnace?
A. Resistance to abrasion.
B. Resistance to slag peneration.
C. Stability of volume at high temperature.
D. Resistance to corrosion by slag.
Question 47
With increase in the alumina content, the refractoriness of high alumina refractories
A. increases
B. decreases
C. remains same
D. may increase or decrease
Question 48
With increase in the porosity, thermal spalling resistance of fireclay brick
A. increases
B. decreases
C. remains same
D. may increase or decrease
Question 49
Dry mix hydraulic compositions of refractory aggregates with suitable bonding materials are called refractory
A. Mortars
B. Cements
C. Castables
D. None of these
Question 50
Insulating refractories should have
A. High porosity
B. Low thermal conductivity
C. Both A & B
D. Neither A nor B
Question 51
Cermets are combination of ceramic and metallic materials due to which they have high strength & resistance to high temperature. Cermets are used in the
A. Hearth of the blast furnace
B. Nuclear reactors, missiles & space crafts
C. Insulation of high temperature furnaces
D. Roof of electric furnaces
Question 52
Basic bricks are not made of
A. Fireclay
B. Magnesite
C. Foresterite
D. Chromite
Question 53
Alumina-graphite bricks are used for lining the
A. Slide gate in teeming laddies
B. Continuous casting systems
C. Both A & B
D. Neither A nor B
Question 54
Maximum safe working temperature for fireclay bricks is about __________ °C.
A. 1150
B. 1300
C. 1450
D. 1550
Question 55
Chemically, mullite refractories is
A. 3Al2O₃.2SiO₂
B. Al2O₃
C. ZrSO₄
D. ThO₂
Question 56
Carbon refractories
A. Do not burn/oxidise, when exposed to air on heating
B. Are not attacked by slags, as they are not wetted by melts
C. Do not resist temperature fluctuations
D. Have extremely low thermal & electrical conductivities
Question 57
Carbon refractory blocks
A. Are wetted by molten iron
B. Are used in the hearth of blast furnace
C. Are acidic in nature
D. All of the above
Question 58
Conversion of silica mineral to cristobalite is accompanied by reduction in its
A. Volume
B. Specific gravity
C. Both A & B
D. Neither A nor B
Question 59
Cermets are
A. Composite material containing both ceramic & metallic constituents
B. Having high strength & resistance to high temperature
C. Used in space vehicles, missiles & nuclear energy plants
D. All of the above
Question 60
Which is not a basic refractory?
A. Chrome magnesite
B. Magnesite
C. Dolomite
D. Silicon carbide
Question 61
Chrome magnesite bricks are
A. Acidic in nature
B. Neutral in nature
C. Having higher RUL than silica bricks
D. Made by mixing 30% chromite and 70% periclase
Question 62
Chromite refractories are
A. Acidic refractory
B. Neutral refractory
C. Basic refractory
D. Fired at a temperature of 600°C only
Question 63
Refractory bricks having lower porosity have
A. High insulating properties
B. Low heat capacity
C. Low thermal conductivity
D. Greater strength
Question 64
Fireclay bricks is not used for lining the
A. Cupola
B. Gas producer
C. Bottom of hot metal mixer
D. Roof of open hearth furnace
Question 65
Colour of fireclay bricks is
A. Light buff to reddish buff
B. Yellow
C. Black
D. None of these
Question 66
Semi-silica bricks compared to silica bricks have
A. Less fusion point
B. Better spalling resistance
C. Both A & B
D. Neither A nor B
Question 67
Magnesite refractories have low resistance to
A. Attack by basic slag
B. Abrasion
C. Disintegration on sudden change of temperature
D. Both B and C
Question 68
Porosity of fireclay refractories is __________ percent.
A. 5-10
B. 10-25
C. 25-35
D. 35-50
Question 69
Cold crushing strength of a refractory does not depend upon its
A. Shape
B. Composition
C. Firing temperature
D. Texture
Question 70
Capacity of a refractory brick to withstand-sudden changes in temperature is denoted by the property called
A. Spalling resistance
B. Refractoriness
C. Refractoriness under load (RUL)
D. None of these
Question 71
Which property is important for bricks used in the combustion chamber & dome of blast furnace stoves?
A. High refractoriness
B. High resistance to spalling
C. High strength and density
D. All of the above
Question 72
Thermal conductivity of refractory bricks
A. Increases with decrease in porosity
B. Decreases with decreases in porosity
C. Is independent of its porosity and is maximum for insulating bricks
D. Increases with the amount of air entrapped in pores
Question 73
Thermal spalling mainly occurs during __________ of furnaces.
A. Cooling down
B. Warming up
C. Both A & B
D. Neither A nor B
Question 74
Refractoriness under loads (RUL) is quite close to the fusion temperature (PCE) for __________ bricks.
A. Fireclay
B. Silica
C. Dolomite
D. Very low alumina
Question 75
Which is the stable form of silica upto 1470°C ?
A. Quartz
B. Cristobalite
C. Tridymite
D. None of these
Question 76
Dolomite bricks have good resistance to attack by
A. Molten steel
B. Iron oxide
C. Lime slag
D. None of these
Question 77
Mullite is chemically represented by
A. Al2O₃ . 2SiO₂
B. 3Al2O₃ . 2SiO₂
C. Al2O₃ . SiO₂
D. 2Al2O₃ . 3SiO₂
Question 78
Chrome magnesite is not used in the
A. Inner lining of L.D. converter
B. Aluminium melting furnaces
C. Wear out lining of steel melting furnaces
D. All of the above
Question 79
Magnesite bricks are used in those parts of furnaces, which are
A. Subjected to temperature fluctuation
B. Required to resist corrosive basic slag
C. Subjected to high load
D. None of these
Question 80
Silicon carbide refractories are used in the
A. Muffle furnace
B. Zinc smelting furnace
C. Ceramic recuperators
D. All of the above
Question 81
Refractories subjected to alternate cycles of heating & cooling are liable to loose their resistance to
A. Thermal spalling
B. Slag attack
C. Fusion under load
D. CO attack
Question 82
To resist spalling tendency, a refractory should have
A. Greater diffusivity
B. Low specific heat
C. Low thermal co-efficient of expansion
D. All of the above
Question 83
Refractory materials are never used in the construction of
A. Segar cones
B. Orton cones
C. Pressure vessels
D. Ovens & retorts
Question 84
Refractoriness under load (RUL) is the most important property for the refractory bricks
A. At the hearth bottom of the furnace on which stock is placed
B. Used for furnace insulation
C. Used in the roof of the furnace
D. None of these
Question 85
Carbon refractories are exclusively used in the
A. Hearth of blast furnace
B. Walls of coke oven
C. Regenerators of coke oven
D. Side wall of soaking pits
Question 86
The largest consumer of refractories is the __________ industry.
A. Cement
B. Metallurgical
C. Fertiliser
D. Power
Question 87
Refractoriness under load (RUL) of fireclay bricks (under a load of 2 kg/cm² ) is __________ °C.
A. 500
B. 1000
C. >1350
D. >2000
Question 88
Which is the most stable crystalline form of silica at room temperature?
A. Quartz
B. Cristobalite
C. Tridymite
D. None of these
Question 89
Fireclay refractories
A. Are not resistant to the action of basic slags
B. Combine with salts (e.g. chlorides sulphates etc.) & bases (e.g. lime, magnesia etc.) forming fusible aluminates silicates etc
C. Shrink during firing
D. All of the above
Question 90
Fireclay refractories have
A. Low co-efficient of thermal expansion
B. Poor thermal spalling resistance
C. Tendency to expand unduly high during firing
D. Very high cost
Question 91
Super refractories' are made from pure
A. Carbides
B. Oxides
C. Borides
D. Nitrides
Question 92
Pyrometric cone equivalent (PCE) of a refractory is the measure of its
A. Spalling resistance
B. Fusion point
C. Resistance to slag penetration
D. Resistance to carbon monoxide attack
Question 93
Grog addition in fireclay during brick manufacture is done to
A. Reduce its shrinkage on heating
B. Impart greater spalling resistance
C. Enhance the strength of fired refractories
D. All of the above
Question 94
The maximum linear expansion of silica bricks during firing is about __________ percent.
A. 0.5
B. 1
C. 2
D. 3.5
Question 95
The highest melting pure oxide (m.p. > 3000°C) is
A. Thoria
B. Alumina
C. Beryllia
D. Zirconia
Question 96
Use of higher percentage of lime for bonding silica bricks, reduces their
A. Strength
B. Abrasion resistance
C. Both A & B
D. Neither A nor B
Question 97
Ganister is a source of the
A. Silica
B. Periclase
C. Lime
D. None of these
Question 98
Faster rate of drying of moulded refractories results in high __________ of refractories.
A. Green strength
B. Voids
C. Shrinkage
D. Both B and C
Question 99
Chrome magnesite bricks are used in the
A. Side walls of soaking pits and arc furnaces
B. Copper melting furnaces & converters
C. Burner block of glass tanks
D. All of the above
Question 100
Grog
A. Contains both alumina and silica
B. Iscrushed firebrick
C. Is a non-plastic material
D. All of the above
Question 101
Refractories used in/for __________ should have low thermal conductivity.
A. Coke ovens
B. Insulation
C. Regenerators
D. Muffle furnaces
Question 102
Machine moulding of dry mixture of refractories requires a pressure of the order of __________ kg/cm².
A. 10
B. 100
C. 500
D. 1000
Question 103
Si percentage in silica refractories used in the walls of coke oven is about
A. 45
B. 60
C. 80
D. 95
Question 104
Which is a neutral refractory?
A. Graphite
B. Magnesite chrome
C. Silica
D. Magnesia
Question 105
Which is an acidic refractory?
A. Magnesite
B. Dolomite
C. Fireclay
D. Chrome magnesite
Question 106
Ferromagnetic ceramic material is not used in the
A. Thermal insulation
B. Transformers
C. Magnetic switches
D. Television sets
Question 107
Electrical resistor bars are made of
A. Silicon carbide
B. Alumina
C. Zirconia
D. Graphite
Question 108
Chrome magnesite brick is not used for lining the
A. Hearth of soaking pits
B. Bottom hearth of reheating furnace
C. Coke oven regenerator
D. Burning zone of limestone rotary kilns
Question 109
silicon carbide refractories have very low
A. Refractoriness (< 1700°C)
B. Thermal conductivity
C. Resistance to thermal shock
D. None of these
Question 110
Fusion temperature of pure silica (SiO₂) is __________ °C.
A. 1350
B. 1715
C. 2570
D. 2800
Question 111
The main raw material for manufacture of silicon carbide refractories is
A. Corrundum
B. Carborundum
C. Bauxite
D. Periclase
Question 112
Which of the following consumes the maximum tonnage of refractories annually in an integrated steel plant?
A. Soaking pits
B. Ceheating furnace
C. L.D. converter
D. Rotary lime kiln
Question 113
Highest melting (m.p = 3070°C) oxide refractory is
A. Alumina
B. Thoria
C. Zirconia
D. Magnesia
Question 114
Fusion point of an acidic refractory material is
A. Increased by the addition of basic oxides
B. Reduced by the addition of basic oxides
C. Not affected by the addition of basic oxides
D. Not affected by the addition of basic oxides
Question 115
Which of the following is not a high alumina refractory material?
A. Kyanite
B. Sillimanite
C. Diaspore
D. Periclase
Question 116
Magnesite refractories are generally not used in the
A. Electric furnace walls
B. Steel melting furnace
C. Open hearth furnace
D. Burning zone of cement kilns
Question 117
Silica bricks are never used for lining the
A. Beehive coke ovens
B. By-product coke ovens
C. Dome of blast furnace stoves
D. Roof of open hearth furnace
Question 118
Cold crushing strength of ordinary fireclay brick is about 950 kg/cm² . On exposure to a temperature of about 1500°C, its crushing strength may come down to as low as __________ kg/cm² .
A. 450
B. 250
C. 150
D. 65
Question 119
Magnesite chrome bricks are used in the
A. Roof lining of basic open hearth & other basic furnaces
B. Reheating furnaces
C. Soaking pits
D. All of the above
Question 120
Which of the following bricks has the most close values of RUL and PCE?
A. Silica bricks
B. Fireclay bricks
C. High alumina bricks
D. Tar dolomite bricks
Question 121
__________ is the measure of the strength of refractory under the combined effect of temperature & load.
A. Porosity
B. RUL
C. Specific gravity
D. Thermal conductivity
Question 122
Hot face insulating linings of high purity alumina fused mullite are used, where
A. Very high temperatures are involved
B. Highly reducing conditions are involved
C. Presence of iron or silica is harmful
D. All of the above
Question 123
With increase in the alumina content in firebricks, its fusion point (refractoriness)
A. Decreases linearly
B. Remains unchanged
C. Increases
D. Decreases
Question 124
Which is required in an insulating refractory?
A. High thermal conductivity
B. Low porosity
C. Both A & B
D. Neither A nor B
Question 125
Mixing of ground refractory material and water is done in a __________ mill.
A. Pug
B. Ball
C. Tube
D. Rod
Question 126
Which of the following is not a neutral refractory?
A. Silicon carbide
B. Magnesite
C. Chromite
D. Graphite
Question 127
Which is not an acidic refractory?
A. Silica
B. Fireclay
C. High alumina refractory
D. Carbon black
Question 128
Thoria is an expensive refractory material and is radioactive in nature. Thorium oxide is used in the manufacture of
A. Segar cones
B. Muffles for muffle furnaces
C. Insulating bricks
D. Crucibles used for melting of high purity metals
Question 129
Hot blast main (carrying air at 1000°C) in blast furnace are lined with __________ bricks.
A. Silica
B. Fireclay
C. Magnesite
D. Zirconia
Question 130
Slide gates in teeming laddie used for steel pouring in ingot moulds is lined with __________ bricks.
A. Bakelite impregnated or fused periclase
B. Silica
C. Semi-silica
D. Fireclay
Question 131
Roof of a basic open hearth furnace is lined with __________ bricks.
A. Silica
B. Fireclay
C. Dolomite
D. Magnesite
Question 132
Bauxite calcining rotary kilns are lined with __________ bricks.
A. Fireclay
B. Carbon
C. 85% alumina
D. Corundum
Question 133
Lower part of hot metal mixer are lined with __________ bricks.
A. Superduty fireclay
B. High alumina
C. Silica
D. Carborundum
Question 134
Except __________ , all other refractories are bad conductors of electricity (i.e, have low electrical conductivity).
A. Fireclay
B. Carborundum
C. Graphite
D. Chromite
Question 135
Rotary kilns meant for calcination of limestone are lined with chrome magnesite in __________ zone.
A. Preheating
B. Cooling
C. Burning
D. All of the above
Question 136
Which one contains maximum percentage of Al2O₃ ?
A. Firebrick
B. Sillimanite
C. Magnesite
D. Aluminous firebrick
Question 137
Which brick undergoes maximum shrinkage on drying?
A. Tar bonded dolomite bricks
B. Fireclay bricks
C. Magnesite bricks
D. Chromite bricks
Question 138
__________ is not a single oxiderefractory.
A. Zirconia
B. Silicon carbide
C. Magnesia
D. None of these
Question 139
Carbon bricks are not used in the lining of the
A. Combustion chamber of blast furnace stoves
B. Electric furnaces
C. Highly chemical resistant equipments
D. Blast furnace hearth
Question 140
Permeability of bricks is a measure of the
A. Refractoriness
B. Melting point
C. Rate at which a fluid will pass through the pores
D. Expansion during heating
Question 141
Ceramic recuperators used for waste heat recovery from high temperature flue gas going out of the furnace is made of
A. Fireclay
B. Silicon carbide
C. Corrundum
D. Siliceous fireclay
Question 142
Cold crushing strength of refractories depends upon its
A. Composition
B. Texture
C. Firing temperature
D. All of the above
Question 143
Addition of zircon to silica refractory brick improves its
A. Crushing strength
B. Resistance to slag attack
C. Neither A nor B
D. Neither A nor B
Question 144
Which property of refractories is the most important for top section of the blast furnace?
A. Resistance to abrasion
B. Resistance to slag peneration
C. Stability of volume at high temperature
D. Resistance to corrosion by slag
Question 145
Silica bricks are attacked by basic slags at high temperature. Which of the following is not used solely as a binding material?
A. Aluminium phosphate
B. Water
C. Lime
D. Plaster of paris
Question 146
Which of the following is not an acidic refractory?
A. Silica bricks
B. Fireclay bricks
C. Bauxite bricks
D. Magnesia bricks
Question 147
Refractoriness of a typical silica brick corresponds to Segar cone number, '32', which is equivalent to a temperature of __________ °C.
A. 1380
B. 1520
C. 1710
D. 1915
Question 148
PCE value (Segar cone) of superduty refractories is more than 33, which is equivalent to a temperature of __________ °C.
A. 1520
B. 1630
C. 1670
D. 1730
Question 149
Magnesite bricks have poor resistance to attack by __________ slag.
A. Lime
B. Basic
C. Acid
D. None of these
Question 150
__________ bricks should not be used in oxidising atmosphere.
A. Tar dolomite
B. Carbon
C. Silica
D. Fireclay
Question 151
__________ bricks are used in the burning zone of a cement rotary kiln.
A. High alumina
B. Fireclay
C. Thoria
D. Silicon carbide
Question 152
High thermal conductivity of a refractory material is not important, when it is to be used in the
A. Coke oven regenarators
B. Muffle furnace
C. Blast furnace
D. Recuperators
Question 153
Upper portion of hot metal mixer are lined with mullite bricks, which helps in resisting the
A. Washing action of metal
B. Corrosion by layer of slag
C. Both A & B
D. Neither A nor B
Question 154
Most Cermets, which normally have high thermal conductivity and high thermal shock resistance, comprises of ceramic & metallic components of __________ percent respectively.
A. 80 and 20
B. 20 and 80
C. 50 and 50
D. 60 and 40
Question 155
Fusion point of a basic refractory material is
A. Reduced by the addition of acid oxides
B. Increased by the addition of acid oxides
C. Not affected by the addition of acid oxides
D. Always less than 1000°C
Question 156
Which is not a natural insulating material?
A. Diatomaceous earth/kieselgur
B. Asbestos
C. Vermiculite
D. None of these
Question 157
Zirconia refractories are not used in
A. Making sheaths for thermocouple
B. Lining high temperature ceramic kilns
C. Furnaces subjected to fluctuating temperature
D. High frequency induction furnaces in the form of inductors
Question 158
Silica refractories are not used in
A. Coke oven walls
B. Beehive coke ovens
C. Dome and upper portion of B.F. stoves
D. Open hearth furnace roof
Question 159
High alumina refractories are used in the
A. Dome of blast furnace stoves
B. Electric arc furnace roof
C. Glass melting furnaces
D. All of the above
Question 160
Lower wall courses of soaking pits are made of __________ bricks to avoid the action of molten slag & scale.
A. Chrome or magnesite
B. Silicon carbide
C. Silica
D. Lowduty fireclay
Question 161
Spalling resistance of a refractory can not be increased by
A. Increasing its porosity
B. Using a coarser grog during its manufacture
C. Decreasing its thermal co-efficient of expansion
D. Making it denser
Question 162
An ideal refractory should have high
A. Spalling rate
B. Fusion point
C. Shrinkage ability
D. None of these
Question 163
Furnace atmosphere for softening temperature determination of refractories (in which segar cones are placed) should be
A. Oxidising
B. Neutral
C. Either A or B
D. Neither A nor B
Question 164
Porosity of silica bricks varies from __________ percent.
A. 5 to 10
B. 20 to 30
C. 45 to 60
D. 60 to 75
Question 165
Maximum water percentage in refractory mix meant for hand moulding may be as high as __________ percent.
A. 2-3
B. 5-7
C. 7-12
D. 14-20
Question 166
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.
A. 55
B. 70
C. 80
D. 90
Question 167
Maximum shrinkage in volume occurring during burning/firing of dried refractories may be as high as __________ percent.
A. 10
B. 15
C. 20
D. 30
Question 168
Periclase refractory contains mainly
A. CaO
B. MgO
C. Al2O₃
D. SiO₂
Question 169
In panel test for spalling resistance, the average face temperature of panel assembly is maintained at __________ °C for 24 hours.
A. 700
B. 1000
C. 1600
D. 2000
Question 170
Porosity is induced in insulating refractories by adding
A. Powdered naphthalene
B. Ammonium chloride/sulphate
C. Calcium phosphate
D. All of the above
Question 171
Pick out the wrong statement.
A. A ceramic material which becomes fluid upon heating and can be moulded in liquid/viscous state is termed s glass
B. Ceramic materials do not undergo vitrification on heating
C. Ceramic materials are brittle in nature
D. Non-oxide ceramic materials generally act as a semi-conductor
Question 172
10 to 30% magnesite is added to chromite to produce chrome-magnesite refractories. Magnesite addition is mainly done to improve the __________ of chromite.
A. Spalling resistance
B. Refractoriness
C. Crushing strength
D. Resistance to slag
Question 173
Which is a basic refractory?
A. Fireclay
B. Silica
C. Chrome magnesite
D. None of these
Question 174
Which one expands on heating?
A. Silica bricks
B. Fireclay bricks
C. Both A & B
D. Neither A nor B
Question 175
Fireclay bricks are never used in the
A. Beehive oven
B. Coke oven walls
C. Zinc roaster
D. Lead blast furnace
Question 176
High density refractory bricks have lower
A. Spalling resistance
B. Thermal conductivity
C. Fusion point
D. Slag penetration resistance
Question 177
Zircon refractories have
A. Low co-efficient of expansion
B. High RUL (1600°C) and refractoriness (> 2000°C)
C. High spalling resistance
D. All of the above
Question 178
Zirconia refractory
A. Does not react with basic slags
B. Is produced from baddeleyite
C. Can not be used as an insulator
D. Has poor electrical conductivity at high temperature
Question 179
Which furnace consumes maximum refractory annually in an integrated steel plant?
A. Soaking pit
B. Blastfurnace
C. L.D. converter
D. Coke ovens
Question 180
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.
A. 1800
B. 2200
C. 2400
D. 2700
Question 181
Fireclay bricks are used in the
A. Furnaces allowed to cool frequently
B. Flues
C. Chimney linings
D. All of the above
Question 182
Skull is not formed on the carbon blocks in the hearth of a blast furnace, when it becomes cold, becaus of its
A. Non-wetting characteristic
B. High thermal conductivity
C. High crushing strength
D. None of these
Question 183
Spinel', a refractory mineral is chemically represented as
A. MgAl2O₄
B. MgAl2O₃
C. MgSO₄
D. MgAl2O₃.2H₂O
Question 184
Pick out the wrong statement.
A. Insulating refractories used in place of regular refractory bricks are usually called light weight refractories, and they have similar composition as heavy bricks
B. Graphite refractories are also called plumbago refractories
C. Superduty fireclay bricks correspond to a pyrometric cone equivalent of 26-28
D. Calcined magnesite is also called dead burnt magnesite
Question 185
Fireclay bricks are not used in the
A. Beehive coke oven
B. By-product coke oven walls
C. Combustion chamber of B.F. stoves
D. Coke oven regenerators
Question 186
Spalling of a refractory means its
A. Softening
B. Fracture due to uneven expansion at high temperature
C. Resistancce to compressive loads
D. Resistance to chemical action of gases and molten fluxes
Question 187
Magnesite chrome refractories
A. Have better spalling resistance than chrome magnesite refractories
B. Have very low thermal co-efficient of expansion
C. Are not at all resistant to the corrosive action of iron oxide
D. Have very low (50 kg/cm² ) cold crushing strength (C.C.S.), and can not be used in metalcase form
Question 188
Refractory bricks with lower permeability is produced by using
A. Higher firing temperature
B. Higher moulding pressure
C. Finer grog size
D. All of the above
Question 189
Which refractory must have controlled atmosphere (temperature and humidity) for its safe storage?
A. Tar bonded dolomite bricks
B. Fireclay bricks
C. Mullite bricks
D. Magnesite bricks
Question 190
Pure oxide refractories are generally monocrystaliine in nature and are self bonded __________ bricks are generally used as moderator in nuclear reactors.
A. Beryllia
B. Carborundum
C. Corundum
D. Thoria
Question 191
High alumina refractory compared to fireclay bricks have
A. Less load bearing capacity
B. Less resistance to slag attack
C. Low refractoriness
D. High resistance to thermal shock and creep
Question 192
Which is not an alumino-silicate refractory?
A. Fireclay bricks
B. Mullite bricks
C. Tar dolomite bricks
D. High alumina bricks
Question 193
__________ nozzles are used in continuous casting of steel,
A. Zircon
B. Thoria
C. Carborundum
D. Beryllia
Question 194
Magnesite refractories are used for the construction of those furnaces, which are
A. Not required to resist the corrosive action of basic slag
B. Not subjected to fluctuation in temperature
C. Used for raising & maintaining high temperature
D. Both (b) and ©
Question 195
Natural silica
A. Mainly contains quartz
B. Is not stable at high temperature
C. Transforms to other allotropic forms i.e tridymite and cristoballite involving very high volume changes
D. All of the above
Question 196
Carborundum used for making crucibles for melting non-ferrous metals is chemically
A. Silicon carbide
B. Silicon nitride
C. Crystalline magnesia
D. Zirconium sulphate
Question 197
Which one contains minimum percentage of SiO₂?
A. Firebrick
B. Sillimanite
C. Semi-silica
D. Aluminous firebrick
Question 198
Dilatometer is used for the determination of __________ of refractories.
A. Modulus of rupture
B. Permanent linear change
C. Resistance to CO attack
D. RUL
Question 199
Segar cones are used for the determination of __________ of refractories.
A. Softening temperature
B. Spalling resistance
C. Electrical conductivity
D. Resistance to slag attack
Question 200
RUL of refractories depends on the
A. Chemical composition
B. Physical structure
C. Presence of impurities like iron & alkali
D. All of the above
Question 201
Firing of refractory brick is done to
A. Dehydrate the dried refractory
B. Develop stable mineral forms in them
C. Form ceramic bonds necessary for development of high crushing strength in the finished product
D. All of the above
Question 202
The linear thermal expansion of __________ bricks upto 1000 °C is very low of the order of ≤ 0.5 percent.
A. Fireclay
B. Silica
C. Magnesite
D. Corundum
Question 203
With decrease in porosity, the __________ of the refractories decreases.
A. Strength
B. Thermal conductivity
C. Spalling resistance
D. None of these
Question 204
Tar dolomite bricks are used in the
A. Basic Bessemer converter
B. Basic open hearth furnace
C. Electric furnaces
D. All of the above
Question 205
Chromite refractories are used in
A. Bottom of soaking pits
B. Between acid & basic linings in basic open hearth furnaces to prevent their chemical action with each other
C. Both A & B
D. Neither A nor B
Question 206
Carbon refractories have very high
A. Wetting characteristics
B. Refractoriness
C. Thermal conductivity
D. Both B and C
Question 207
Pick out the wrong statement.
A. Sand & coke is the main raw material for the manufacture of silicon carbide
B. Carbon refractories can not be used in the furnaces operating under reducing conditions
C. Mullite can be obtained by the heating of alusite, kyanite or silimanite
D. Silica occurs in nature in all cellular, amorphous or crystalline form
Question 208
Fireclay bricks are not used in the
A. Blast furnace
B. Hot blast stove
C. Cupola
D. Wall of coke oven
Question 209
High porosity refractory bricks have
A. Poor resistance to the peneration of molten slag, metal & flue gases
B. Poor heat conductivity & low strength
C. Better thermal spalling resistance
D. All of the above
Question 210
Which is not a high alumina refractory?
A. Mullite
B. Corrundum
C. Bauxite
D. Dolomite
Question 211
Which of the following has the lowest electrical resistivity?
A. Graphite
B. Fireclay
C. Alumina
D. Zircon
Question 212
Periclase is
A. Crystalline form of MgO
B. MgCO₃
C. ZrSO₄
D. Amorphous magnesite
Question 213
Pick out the wrong statement.
A. Refractories used in muffle furnace should have low thermal conductivity
B. The electrical resistivity of refractories drops rapidly with rise in temperature
C. For reducing spalling tendency, the refractory should be well fired and its porosity should be more
D. Refractoriness under load (RUL) of a refractory is always less than its refractoriness
Question 214
Quartz is
A. Stable form of silica upto 870°C
B. Converted to tridymite on firing between 870 to 1470°C
C. Transformed to crystoballite on heating above 1470°C
D. All of the above
Question 215
Refractory castables are used for
A. Producing monolithic linings
B. Patch work
C. Minimising the number of joints in the structure
D. All of the above
Question 216
Silliminite (Al2O₃.SiO₂) refractory, which is a neutral refractory, is not used in
A. Pottery furnace
B. Glass melting furnace
C. Crucibles
D. Gas retorts
Question 217
Ramming masses are used for
A. Obtaining monolithic working faces
B. Repairing construction of various furnace parts
C. Both A & B
D. Neither A nor B
Question 218
Graphite or carbon refractories
A. Exihibit wetting characteristics
B. Should be used in neutral or reducing atmosphere
C. Exhibit high shrinkage on thermal treatment
D. Are not resistant to corrosion by slag
Question 219
SiO₂ percentage in firebrick is about
A. 35-40
B. 55-60
C. 80-85
D. >94
Question 220
An insulating refractory brick should have high porosity and low thermal conductivity. Which of the following is not used for inducing porosity in the insulating refractory bricks during its manufacture?
A. Cork
B. Saw dust
C. Sand
D. Chemically prepared foam
Question 221
Which of the following does not occur during firing/burning of refractories?
A. Removal of water of hydration
B. Vitrification
C. Decrease in crushing strength
D. Development of stable mineral form
Question 222
Rate of slag attack on refractories increases with rise in temperature due to the
A. Decreased viscosity of slag
B. Increased thermal conductivity of brick
C. Oxidising condition in the furnace
D. None of these
Question 223
__________ of carbon blocks in the hearth of blast furnace helps in avoiding skull formation, when it becomes cold.
A. High thermal conductivity
B. Low porosity
C. Non-wetting characteristics
D. High density
Question 224
Bottom of basic open hearth furnace are constructed of
A. Dead burnt magnesite ramming mass
B. Porous fireclay bricks
C. Semi-silica bricks
D. Silicon carbide bricks
Question 225
Pick out the wrong statement.
A. Electrical conductivity of refractory is not important, when these are to be used in electrical furnaces
B. Graphite and metals are the good electrical conductor among the refractories and others are all electrical insulators
C. Refractories used for lining electrical furnaces should ordinarily have very low electrical conductivity
D. Electrical conductivity of porous refractory material is low
Question 226
High refractorinness of refractory bricks means, that it has a
A. High spalling resistance
B. Low spalling resistance
C. High resistance to fusion
D. Low porosity
Question 227
Cold crushing strength of fireclay bricks is about __________ kgf/cm².
A. 50-100
B. 100-150
C. 200-400
D. 500-1000
Question 228
Maximum apparent porosity of magnesite bricks is about __________ percent.
A. 8
B. 24
C. 44
D. 58
Question 229
Pick out the wrong statement.
A. Fluxing material like lime is added in clay to reduce the vitrification temperature
B. Main constituents of clay are alumina and silica
C. Addition of sand in ceramic materials makes it non-plastic, increases its fusion point and reduces its shrinkage on burning
D. Vitrification of fireclay material is done to increase its porosity
Question 230
Spalling tendency of refractories is reduced by increasing its
A. Porosity
B. Specific gravity
C. Thermal conductivity
D. Strength
Question 231
Which of the following bricks should not be used, if the furnace is to be used intermit-tantly?
A. Firebricks
B. Silica bricks
C. Silicon carbide bricks
D. Sillimanite
Question 232
Crushing strength of a refractory
A. Increases with rise in service temperature
B. Decreases with rise in service temperature
C. Is unaffected with change in service temperature
D. Decreases with increase in porosity
Question 233
Silica refractories
A. Crack when subjected to sudden change of temperature
B. Can not be used in the dome of hot blast stoves
C. Have lower thermal conductivity than fireclay bricks
D. All of the above
Question 234
Silica bricks have low spalling resistance below 600°C, due to its
A. Very high thermal conductivity
B. High co-efficient of expansion upto this temperature
C. High thermal diffusivity
D. Low refractoriness
Question 235
Addition of grog in fireclay brick during its manufacture is advantageous, because it results in
A. Less shrinkage in heating, decreased apparent porosity & increased specific gravity
B. High strength & thermal spalling resistance
C. Less addition of water to get a workable plasticity & lesser time required for drying the raw refractories and hence increased rate of production
D. All of the above
Question 236
Tar bonded dolomite bricks
A. Are stored under controlled temperature & humidity to avoid hydration
B. Are used in outer lining of L.D. converters
C. Have poorer hydration resistance than pitch bonded bricks
D. All of the above
Question 237
Sillimanite is a __________ refractory.
A. Basic
B. Neutral
C. High alumina
D. Insulating
Question 238
Which form of silica has the highest specific gravity?
A. Quartz
B. Cristobalite
C. Tridymite
D. All of the above
Question 239
What is Thoria?
A. Thoria Has high fusion temperature (> 3000°C) but poor resistance to thermal shock
B. Thoria Has high resistance to basic slags
C. Which is expensive & radioactive, is used in crucibles for melting high purity metals
D. All of the above
Question 240
Resistance to slag attack of a refractory
A. Depends on the nature of slag & refractory
B. Decreases at higher temperature
C. Decreases, if defective joints & cracks exist in the refractory
D. All of the above
Question 241
Which of the following impurities reduces the refractoriness of magnesite bricks?
A. Al2O₃
B. CaO
C. SiO₂
D. All of the above
Question 242
With increase in the density of silica refractories, its
A. Resistance to slag attack increases
B. Spalling resistance reduces
C. Both A & B
D. Neither A nor B