Multiple Choice Questions and Answers on Refractory Technology
Question 1 : Maximum alumina content in high alumina refractory can be as high as __________ percent.
- 30
- 50
- 70
- 90
Answer : 4
Question 2 : Refractories are dried in the
- rotary kilns
- tunnel kilns
- sun
- none of these
Answer : 2
Question 3 : 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.
Answer : 2
Question 4 : Hot metal runner in blast furnace are lined with __________ bricks.
- silica
- carborundum
- fireclay
- magnesite
Answer : 3
Question 5 : Spray test determines the __________ of refractories.
- resistance to slag penetration
- resistance to CO attack
- RUL
- permanent linear change
Answer : 1
Question 6 : With increase in the alumina content, the refractoriness of high alumina refractories
- increases
- decreases
- remains same
- may increase or decrease
Answer : 1
Question 7 : A steel member used in the furnace construction to take the thrust of the brickwork is called
- buckstay
- breast wall
- armouring
- baffle
Answer : 1
Question 8 : With increase in the porosity, thermal spalling resistance of fireclay brick
- increases
- decreases
- remains same
- may increase or decrease
Answer : 1
Question 9 : Thoria is an expensive refractory material and is radioactive in nature. Thorium oxide is used in the manufacture of
- segar cones.
- muffles for muffle furnaces.
- insulating bricks.
- crucibles used for melting of high purity metals.
Answer : 4
Question 10 : Walls, roofs & combustion chambers of annealing furnaces are made of __________ bricks.
- high duty fireclay
- silica
- mullite
- carborundum
Answer : 1
Question 11 : Fireclay bricks are used in the
- coke ovens regenerator.
- outer lining of L.D. converter.
- hearth bottom of blast furnace.
- coke oven walls.
Answer : 1
Question 12 : Water content in ground refractory material to be shaped into bricks by hand moulding is about __________ percent.
- 5
- 20
- 40
- 55
Answer : 2
Question 13 : Chromite refractories
- are bonded with lime and clay.
- (free from silica) have better thermal fatigue resistance than silica and magnesite refractories.
- are resistant to basic slag.
- all (1), (2) and (3).
Answer : 4
Question 14 : Firing temperature is minimum (1250-1400 °C) for __________ bricks.
- fireclay
- direct bonded basic
- silica
- magnesite
Answer : 1
Question 15 : Which one expands on heating ?
- Silica bricks
- Fireclay bricks
- Both (1) & (2)
- Neither (1) nor (2)
Answer : 1
Question 16 : Refractoriness/fusion points of ‘superduty’ refractories is __________ °C.
- 1520-1630
- 1630-1670
- > 1730
- > 2000
Answer : 3
Question 17 : Outer combustion chamber of blast furnace stove is lined with __________ bricks.
- fireclay
- silica
- chrome magnesite
- zirconia
Answer : 1
Question 18 : Presence of MgO in alumino-silicate refractories __________ its refractoriness.
- increases
- lowers
- does not affect
- either (1) or (2); depends on its quantity
Answer : 2
Question 19 : Spalling of silica bricks occurs due to abrupt volume changes, when it is cooled below a temperature of __________ °C.
- 770
- 570
- 270
- 70
Answer : 3
Question 20 : Thermal diffusivity of a refractory brick is high, when its __________ is high.
- density
- specific heat
- thermal conductivity
- none of these
Answer : 3
Question 21 : 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 (1), (2) and (3).
Answer : 4
Question 22 : Vacuum steel degassing units are lined with
- silica bricks
- low duty firebricks
- high alumina bricks
- graphite blocks
Answer : 3
Question 23 : 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
Answer : 4
Question 24 : Which is the stable form of silica below 870°C ?
- Tridymite
- Cristobalite
- Quartz
- None of these
Answer : 3
Question 25 : Refractoriness of a typical silica brick corresponds to Segar cone number, ’32’, which is equivalent to a temperature of __________ °C.
- 1380
- 1520
- 1710
- 1915
Answer : 3
Question 26 : 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
- cost
- electrical conductivity
- thermal conductivity
- fusion point
Answer : 1
Question 27 : 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 ?
- Cork
- Saw dust
- Sand
- Chemically prepared foam
Answer : 3
Question 28 : 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 (1), (2) and (3).
Answer : 4
Question 29 : Chemically, mullite refractories is
- 3Al2O3.2SiO2
- Al2O3
- ZrSO4
- ThO2
Answer : 1
Question 30 : 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.
Answer : 1
Question 31 : 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.
Answer : 2
Question 32 : Which is not a basic refractory ?
- Chrome magnesite
- Magnesite
- Dolomite
- Silicon carbide
Answer : 4
Question 33 : Thoria
- has high fusion temperature (> 3000°C) but poor resistance to thermal shock.
- has high resistance to basic slags.
- which is expensive & radioactive, is used in crucibles for melting high purity metals.
- all (1), (2) and (3).
Answer : 4
Question 34 : Which property of refractories is the most important for top section of the blast furnace?
- Resistance to abrasion.
- Resistance to slag peneration.
- Stability of volume at high temperature.
- Resistance to corrosion by slag.
Answer : 1
Question 35 : 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 (1), (2) and (3).
Answer : 4
Question 36 : Grog
- contains both alumina and silica.
- iscrushed firebrick.
- is a non-plastic material.
- all (1), (2) and (3).
Answer : 4
Question 37 : Test piece for determination of RUL of a refractory is heated in a/an
- oxidising atmosphere
- reducing atmosphere
- electric furnace
- neutral atmosphere
Answer : 3
Question 38 : 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 (2) and (3)
Answer : 4
Question 39 : Roof of a basic electric furnace is made of __________ bricks.
- superduty fireclay
- silica
- chromite
- none of these
Answer : 2
Question 40 : Panel test determines the __________ of refractories.
- fusion point
- spalling resistance
- slag penetration resistance
- refractoriness under load (RUL)
Answer : 2
Question 41 : Fireclay bricks are not used in the
- beehive coke oven.
- by-product coke oven walls.
- combustion chamber of B.F. stoves.
- coke oven regenerators.
Answer : 2
Question 42 : 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.
Answer : 1
Question 43 : RUL of refractories depends on the
- chemical composition.
- physical structure.
- presence of impurities like iron & alkali.
- all (1), (2) and (3).
Answer : 4
Question 44 : Which is the stable form of silica between 1470°C and the melting point 1713°C ?
- Cristobalite
- Tridymite
- Quartz
- None of these
Answer : 1
Question 45 : Skull is not formed on the carbon blocks in the hearth of a blast furnace, when it becomes cold, becaus of its
- non-wetting characteristic.
- high thermal conductivity.
- high crushing strength.
- none of these.
Answer : 1
Question 46 : Firing temperature of magnesite bricks is about __________ °C.
- 800-1000
- 1000-1200
- 1600-1800
- 2400-2600
Answer : 3
Question 47 : Hollow refractory bricks are made by
- slip casting
- hand moulding
- pressing/machine moulding
- extrusion
Answer : 1
Question 48 : Quartz is
- stable form of silica upto 870°C.
- converted to tridymite on firing between 870 to 1470°C.
- transformed to crystoballite on heating above 1470°C.
- all (1), (2) and (3).
Answer : 4
Question 49 : An indication of degree of firing in silica brick is its
- specific gravity
- fusion point
- RUL
- none of these
Answer : 1