Q.1

Pick out the wrong statement.

  • Fluxing material like lime is added in clay to reduce the vitrification temperature.
  • Main constituents of clay are alumina and silica.
  • Addition of sand in ceramic materials makes it non-plastic, increases its fusion point and reduces its shrinkage on burning.
  • Vitrification of fireclay material is done to increase its porosity.
Q.2

SiO2 percentage in firebrick is about

  • 35-40
  • 55-60
  • 80-85
  • >94
Q.3

Spalling of a refractory means its

  • softening.
  • fracture due to uneven expansion at high temperature.
  • resistancce to compressive loads.
  • resistance to chemical action of gases and molten fluxes.
Q.4

Roof of a basic open hearth furnace is lined with __________ bricks.

  • silica
  • fireclay
  • dolomite
  • magnesite
Q.5

Chrome magnesite is not used in the

  • inner lining of L.D. converter.
  • aluminium melting furnaces.
  • wear out lining of steel melting furnaces.
  • all (a), and (b) and (c)
Q.6

Graphite or carbon refractories

  • exihibit wetting characteristics.
  • should be used in neutral or reducing atmosphere.
  • exhibit high shrinkage on thermal treatment.
  • are not resistant to corrosion by slag.
Q.7

Magnesite chrome bricks are used in the

  • roof lining of basic open hearth & other basic furnaces.
  • reheating furnaces.
  • soaking pits.
  • all (a), (b) and (c).
Q.8

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.

  • 1800
  • 2200
  • 2400
  • 2700
Q.9

Porosity is induced in insulating refractories by adding

  • powdered naphthalene.
  • ammonium chloride/sulphate.
  • calcium phosphate.
  • all (a), (b) and (c).
Q.10

High alumina refractories are used in the

  • dome of blast furnace stoves.
  • electric arc furnace roof.
  • glass melting furnaces.
  • all (a), (b) and (c).
Q.11

Which of the following bricks has the most close values of RUL and PCE ?

  • Silica bricks
  • Fireclay bricks
  • High alumina bricks
  • Tar dolomite bricks
Q.12

'Spinel', a refractory mineral is chemically represented as

  • MgAl2O4
  • MgAl2O3
  • MgSO4
  • MgAl2O3.2H2O
Q.13

Chrome magnesite bricks are

  • acidic in nature.
  • neutral in nature.
  • having higher RUL than silica bricks.
  • made by mixing 30% chromite and 70% periclase.
Q.14

Magnesite bricks have poor resistance to attack by __________ slag.

  • lime
  • basic
  • acid
  • none of these
Q.15

Refractoriness under load (RUL) of fireclay bricks (under a load of 2 kg/cm2 ) is __________ °C.

  • 500
  • 1000
  • >1350
  • >2000
Q.16

Zirconia refractories are not used in

  • making sheaths for thermocouple.
  • lining high temperature ceramic kilns.
  • furnaces subjected to fluctuating temperature.
  • high frequency induction furnaces in the form of inductors.
Q.17

Upper portion of hot metal mixer are lined with mullite bricks, which helps in resisting the

  • washing action of metal.
  • corrosion by layer of slag.
  • both (a) & (b).
  • neither (a) nor (b).
Q.18

Semi-silica bricks compared to silica bricks have

  • less fusion point.
  • better spalling resistance.
  • both (a) and (b).
  • neither (a) not (b).
Q.19

An ideal refractory should have high

  • spalling rate
  • fusion point
  • shrinkage ability
  • none of these
Q.20

Silica refractories are not used in

  • coke oven walls.
  • beehive coke ovens.
  • dome and upper portion of B.F. stoves.
  • open hearth furnace roof.
Q.21

Tar dolomite bricks are used in the

  • basic Bessemer converter
  • basic open hearth furnace
  • electric furnaces
  • all (a), (b) and (c)
Q.22

__________ of carbon blocks in the hearth of blast furnace helps in avoiding skull formation, when it becomes cold.

  • High thermal conductivity
  • Low porosity
  • Non-wetting characteristics
  • High density
Q.23

Bauxite calcining rotary kilns are lined with __________ bricks.

  • fireclay
  • carbon
  • 85% alumina
  • corundum
Q.24

Carbon refractories

  • do not burn/oxidise, when exposed to air on heating.
  • are not attacked by slags, as they are not wetted by melts.
  • do not resist temperature fluctuations.
  • have extremely low thermal & electrical conductivities.
Q.25

Pyrometric cone equivalent (PCE) of a refractory is the measure of its

  • spalling resistance.
  • fusion point.
  • resistance to slag penetration.
  • resistance to carbon monoxide attack.
Q.26

Mixing of ground refractory material and water is done in a __________ mill.

  • pug
  • ball
  • tube
  • rod
Q.27

Ganister is a source of the

  • silica
  • periclase
  • lime
  • none of these
Q.28

Refractory materials are never used in the construction of

  • segar cones
  • orton cones
  • pressure vessels
  • ovens & retorts
Q.29

Segar cones are used for the determination of __________ of refractories.

  • softening temperature
  • spalling resistance
  • electrical conductivity
  • resistance to slag attack
Q.30

Pick out the wrong statement.

  • Electrical conductivity of refractory is not important, when these are to be used in electrical furnaces.
  • Graphite and metals are the good electrical conductor among the refractories and others are all electrical insulators.
  • Refractories used for lining electrical furnaces should ordinarily have very low electrical conductivity.
  • Electrical conductivity of porous refractory material is low.
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