Q.1

Electrical resistor bars are made of

  • silicon carbide
  • alumina
  • zirconia
  • graphite
Q.2

Which is a basic refractory ?

  • Fireclay
  • Silica
  • Chrome magnesite
  • None of these
Q.3

With increasing alumina content, the fusion point of high alumina refractories

  • increases.
  • decreases.
  • remains constant.
  • may increase or decrease ; depends on its alumina content.
Q.4

Chrome magnesite bricks are used in the

  • side walls of soaking pits and arc furnaces.
  • copper melting furnaces & converters.
  • burner block of glass tanks.
  • all (a), (b) and (c)
Q.5

High thermal conductivity of a refractory material is not important, when it is to be used in the

  • coke oven regenarators
  • muffle furnace
  • blast furnace
  • recuperators
Q.6

Ceramic recuperators used for waste heat recovery from high temperature flue gas going out of the furnace is made of

  • fireclay
  • silicon carbide
  • corrundum
  • siliceous fireclay
Q.7

tomagnesite is added to chromite to produce chrome-magnesite refractories. Magnesite addition is mainly done to improve the __________ of chromite.

  • spalling resistance
  • refractoriness
  • crushing strength
  • resistance to slag
Q.8

Silica bricks are never used for lining the

  • beehive coke ovens.
  • by-product coke ovens.
  • dome of blast furnace stoves.
  • roof of open hearth furnace.
Q.9

Pick out the wrong statement.

  • Refractories used in muffle furnace should have low thermal conductivity.
  • The electrical resistivity of refractories drops rapidly with rise in temperature.
  • For reducing spalling tendency, the refractory should be well fired and its porosity should be more.
  • Refractoriness under load (RUL) of a refractory is always less than its refractoriness.
Q.10

Pure oxide refractories are generally monocrystaliine in nature and are self bonded __________ bricks are generally used as moderator in nuclear reactors.

  • Beryllia
  • Carborundum
  • Corundum
  • Thoria
Q.11

Carbon refractory blocks

  • are wetted by molten iron.
  • are used in the hearth of blast furnace.
  • are acidic in nature.
  • all (a), (b) and (c).
Q.12

Which is not an alumino-silicate refractory?

  • Fireclay bricks.
  • Mullite bricks.
  • Tar dolomite bricks.
  • High alumina bricks.
Q.13

Cold crushing strength of a refractory does not depend upon its

  • shape
  • composition
  • firing temperature
  • texture
Q.14

Which is an acidic refractory ?

  • Magnesite
  • Dolomite
  • Fireclay
  • Chrome magnesite
Q.15

Machine moulding of dry mixture of refractories requires a pressure of the order of __________ kg/cm2.

  • 10
  • 100
  • 500
  • 1000
Q.16

Maximum safe working temperature for fireclay bricks is about __________ °C.

  • 1150
  • 1300
  • 1450
  • 1550
Q.17

__________ is the measure of the strength of refractory under the combined effect of temperature & load.

  • Porosity
  • RUL
  • Specific gravity
  • Thermal conductivity
Q.18

Which is not a natural insulating material?

  • Diatomaceous earth/kieselgur
  • Asbestos
  • Vermiculite
  • None of these
Q.19

__________ bricks should not be used in oxidising atmosphere.

  • Tar dolomite
  • Carbon
  • Silica
  • Fireclay
Q.20

Faster rate of drying of moulded refractories results in high __________ of refractories.

  • green strength
  • voids
  • shrinkage
  • both (b) and (c)
Q.21

Periclase refractory contains mainly

  • CaO
  • MgO
  • Al2O3
  • SiO2
Q.22

Refractoriness under load (RUL) is the most important property for the refractory bricks

  • at the hearth bottom of the furnace on which stock is placed.
  • used for furnace insulation.
  • used in the roof of the furnace.
  • none of these.
Q.23

Carborundum used for making crucibles for melting non-ferrous metals is chemically

  • silicon carbide
  • silicon nitride
  • crystalline magnesia
  • zirconium sulphate
Q.24

Ferromagnetic ceramic material is not used in the

  • thermal insulation
  • transformers
  • magnetic switches
  • television sets
Q.25

Fireclay bricks are not used in the

  • blast furnace
  • hot blast stove
  • cupola
  • wall of coke oven
Q.26

Magnesite refractories are generally not used in the

  • electric furnace walls.
  • steel melting furnace.
  • open hearth furnace.
  • burning zone of cement kilns.
Q.27

Pick out the wrong statement.

  • Insulating refractories used in place of regular refractory bricks are usually called light weight refractories, and they have similar composition as heavy bricks.
  • Graphite refractories are also called plumbago refractories.
  • Superduty fireclay bricks correspond to a pyrometric cone equivalent of 26-28.
  • Calcined magnesite is also called dead burnt magnesite.
Q.28

Rotary kilns meant for calcination of limestone are lined with chrome magnesite in __________ zone.

  • preheating
  • cooling
  • burning
  • all
Q.29

The highest melting pure oxide (m.p. > 3000°C)is

  • thoria
  • alumina
  • beryllia
  • zirconia
Q.30

Which of the following impurities reduces the refractoriness of magnesite bricks ?

  • Al2O3
  • CaO
  • SiO2
  • all (a), (b) & (c)
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