Q.1

Permeability of bricks is a measure of the

  • refractoriness.
  • melting point.
  • rate at which a fluid will pass through the pores.
  • expansion during heating.
Q.2

Basic bricks are not made of

  • fireclay
  • magnesite
  • foresterite
  • chromite
Q.3

Lower wall courses of soaking pits are made of __________ bricks to avoid the action of molten slag & scale.

  • chrome or magnesite
  • silicon carbide
  • silica
  • lowduty fireclay
Q.4

Hot blast main (carrying air at 1000°C) in blast furnace are lined with __________ bricks.

  • silica
  • fireclay
  • magnesite
  • zirconia
Q.5

Which of the following does not occur during firing/burning of refractories ?

  • Removal of water of hydration.
  • Vitrification.
  • Decrease in crushing strength.
  • Development of stable mineral form.
Q.6

Spalling resistance of a refractory can not be increased by

  • increasing its porosity.
  • using a coarser grog during its manufacture.
  • decreasing its thermal co-efficient of expansion.
  • making it denser.
Q.7

'Super refractories' are made from pure

  • carbides
  • oxides
  • borides
  • nitrides
Q.8

Insulating refractories should have

  • high porosity
  • low thermal conductivity
  • both (a) and (b)
  • neither (a) not (b)
Q.9

Thermal conductivity of refractory bricks

  • increases with decrease in porosity.
  • decreases with decreases in porosity.
  • is independent of its porosity and is maximum for insulating bricks.
  • increases with the amount of air entrapped in pores.
Q.10

Thermal spalling mainly occurs during __________ of furnaces.

  • cooling down
  • warming up
  • both (a) & (b)
  • neither (a) nor (b)
Q.11

With increase in the density of silica refractories, its

  • resistance to slag attack increases.
  • spalling resistance reduces.
  • both (a) and (b).
  • neither (a) nor (b).
Q.12

With increase in the alumina content in firebricks, its fusion point (refractoriness)

  • decreases linearly
  • remains unchanged
  • increases
  • decreases
Q.13

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 (a), (b) and (c).
Q.14

High alumina refractory compared to fireclay bricks have

  • less load bearing capacity.
  • less resistance to slag attack.
  • low refractoriness.
  • high resistance to thermal shock and creep.
Q.15

Silicon carbide refractories are used in the

  • muffle furnace
  • zinc smelting furnace
  • ceramic recuperators
  • all (a), (b) and (c)
Q.16

Fireclay refractories have

  • low co-efficient of thermal expansion.
  • poor thermal spalling resistance.
  • tendency to expand unduly high during firing.
  • very high cost.
Q.17

Chromite refractories are

  • acidic refractory.
  • neutral refractory.
  • basic refractory.
  • fired at a temperature of 600°C only.
Q.18

Dolomite bricks have good resistance to attack by

  • molten steel
  • iron oxide
  • lime slag
  • none of these
Q.19

Magnesite chrome refractories

  • have better spalling resistance than chrome magnesite refractories.
  • have very low thermal co-efficient of expansion.
  • are not at all resistant to the corrosive action of iron oxide.
  • have very low (50 kg/cm2 ) cold crushing strength (C.C.S.), and can not be used in metalcase form.
Q.20

Slide gates in teeming laddie used for steel pouring in ingot moulds is lined with __________ bricks.

  • bakelite impregnated or fused periclase
  • silica
  • semi-silica
  • fireclay
Q.21

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 (a), (b) and (c)
Q.22

Refractory bricks with lower permeability is produced by using

  • higher firing temperature.
  • higher moulding pressure.
  • finer grog size.
  • all (a), (b) and (c).
Q.23

Refractory bricks having lower porosity have

  • high insulating properties
  • low heat capacity
  • low thermal conductivity
  • greater strength
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