Refractory Technology

51. Except _________, all other refractories are bad conductors of electricity (i.e, have low electrical conductivity).

1. Fireclay
2. Carborundum
3. Graphite
4. Chromite

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52. Faster rate of drying of moulded refractories results in high _________ of refractories.

1. Green strength
2. Voids
3. Shrinkage
4. Both (B) and (C)

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53. Ferromagnetic ceramic material is not used in the

1. Thermal insulation
2. Transformers
3. Magnetic switches
4. Television sets

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54. Fireclay bricks are never used in the

1. Beehive oven
2. Coke oven walls
3. Zinc roaster
4. Lead blast furnace

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55. Fireclay bricks are not used in the

1. Beehive coke oven
2. By-product coke oven walls
3. Combustion chamber of B.F. stoves
4. Coke oven regenerators

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56. Fireclay bricks are used in the

1. Furnaces allowed to cool frequently
2. Flues
3. Chimney linings
4. All (A), (B) and (C)

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57. Fireclay bricks is not used for lining the

1. Cupola
2. Gas producer
3. Bottom of hot metal mixer
4. Roof of open hearth furnace

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58. Fireclay refractories

1. Are not resistant to the action of basic slags
2. Combine with salts (e.g. chlorides sulphates etc.) & bases (e.g. lime, magnesia etc.) forming fusible aluminates silicates etc
3. Shrink during firing
4. All (A), (B) and (C)

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59. Fireclay refractories have

1. Low co-efficient of thermal expansion
2. Poor thermal spalling resistance
3. Tendency to expand unduly high during firing
4. Very high cost

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60. Firing of refractory brick is done to

1. Dehydrate the dried refractory
2. Develop stable mineral forms in them
3. Form ceramic bonds necessary for development of high crushing strength in the finished product
4. All (A), (B) and (C)

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