Refractory Technology MCQ

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• Which is a basic refractory?
  ক

  Fireclay

  খ

  Silica

  গ

  Chrome magnesite

  ঘ

  None of these
• A steel member used in the furnace construction to take the thrust of the brickwork is called
  ক

  Buckstay

  খ

  Breast wall

  গ

  Armouring

  ঘ

  Baffle
• Porosity is induced in insulating refractories by adding
  ক

  Powdered naphthalene

  খ

  Ammonium chloride/sulphate

  গ

  Calcium phosphate

  ঘ

  All of the above
• Silica refractories
  ক

  Crack when subjected to sudden change of temperature

  খ

  Can not be used in the dome of hot blast stoves

  গ

  Have lower thermal conductivity than fireclay bricks

  ঘ

  All of the above
• Crushing strength of a refractory
  ক

  Increases with rise in service temperature

  খ

  Decreases with rise in service temperature

  গ

  Is unaffected with change in service temperature

  ঘ

  Decreases with increase in porosity
• Which of the following bricks should not be used, if the furnace is to be used intermit-tantly?
  ক

  Firebricks

  খ

  Silica bricks

  গ

  Silicon carbide bricks

  ঘ

  Sillimanite
• With increase in the alumina content, the refractoriness of high alumina refractories
  ক

  Increases

  খ

  Decreases

  গ

  Remains same

  ঘ

  May increase or decrease
• Spalling tendency of refractories is reduced by increasing its
  ক

  Porosity

  খ

  Specific gravity

  গ

  Thermal conductivity

  ঘ

  Strength
• Maximum apparent porosity of magnesite bricks is about __________ percent.
  ক

  8

  খ

  24

  গ

  44

  ঘ

  58
• High refractorinness of refractory bricks means, that it has a
  ক

  High spalling resistance

  খ

  Low spalling resistance

  গ

  High resistance to fusion

  ঘ

  Low porosity
• Bottom of basic open hearth furnace are constructed of
  ক

  Dead burnt magnesite ramming mass

  খ

  Porous fireclay bricks

  গ

  Semi-silica bricks

  ঘ

  Silicon carbide bricks
• __________ of carbon blocks in the hearth of blast furnace helps in avoiding skull formation, when it becomes cold.
  ক

  High thermal conductivity

  খ

  Low porosity

  গ

  Non-wetting characteristics

  ঘ

  High density
• Rate of slag attack on refractories increases with rise in temperature due to the
  ক

  Decreased viscosity of slag

  খ

  Increased thermal conductivity of brick

  গ

  Oxidising condition in the furnace

  ঘ

  None of these
• Which of the following does not occur during firing/burning of refractories?
  ক

  Removal of water of hydration

  খ

  Vitrification

  গ

  Decrease in crushing strength

  ঘ

  Development of stable mineral form
• 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?
  ক

  Cork

  খ

  Saw dust

  গ

  Sand

  ঘ

  Chemically prepared foam
• Refractoriness/fusion points of 'superduty' refractories is __________ °C.
  ক

  1520-1630

  খ

  1630-1670

  গ

  > 1730

  ঘ

  > 2000
• Refractories are dried in the
  ক

  Rotary kilns

  খ

  Tunnel kilns

  গ

  Sun

  ঘ

  None of these
• Graphite or carbon refractories
  ক

  Exihibit wetting characteristics

  খ

  Should be used in neutral or reducing atmosphere

  গ

  Exhibit high shrinkage on thermal treatment

  ঘ

  Are not resistant to corrosion by slag
• Ramming masses are used for
  ক

  Obtaining monolithic working faces

  খ

  Repairing construction of various furnace parts

  গ

  Both A & B

  ঘ

  Neither A nor B
• Refractory castables are used for
  ক

  Producing monolithic linings

  খ

  Patch work

  গ

  Minimising the number of joints in the structure

  ঘ

  All of the above
• Quartz is
  ক

  Stable form of silica upto 870°C

  খ

  Converted to tridymite on firing between 870 to 1470°C

  গ

  Transformed to crystoballite on heating above 1470°C

  ঘ

  All of the above
• Periclase is
  ক

  Crystalline form of MgO

  খ

  MgCO₃

  গ

  ZrSO₄

  ঘ

  Amorphous magnesite
• Which of the following has the lowest electrical resistivity?
  ক

  Graphite

  খ

  Fireclay

  গ

  Alumina

  ঘ

  Zircon
• Which is not a high alumina refractory?
  ক

  Mullite

  খ

  Corrundum

  গ

  Bauxite

  ঘ

  Dolomite
• High porosity refractory bricks have
  ক

  Poor resistance to the peneration of molten slag, metal & flue gases

  খ

  Poor heat conductivity & low strength

  গ

  Better thermal spalling resistance

  ঘ

  All of the above
• Carbon refractories have very high
  ক

  Wetting characteristics

  খ

  Refractoriness

  গ

  Thermal conductivity

  ঘ

  Both B and C
• Chromite refractories are used in
  ক

  Bottom of soaking pits

  খ

  Between acid & basic linings in basic open hearth furnaces to prevent their chemical action with each other

  গ

  Both A & B

  ঘ

  Neither A nor B
• Tar dolomite bricks are used in the
  ক

  Basic Bessemer converter

  খ

  Basic open hearth furnace

  গ

  Electric furnaces

  ঘ

  All of the above
• With decrease in porosity, the __________ of the refractories decreases.
  ক

  Strength

  খ

  Thermal conductivity

  গ

  Spalling resistance

  ঘ

  None of these
• Firing of refractory brick is done to
  ক

  Dehydrate the dried refractory

  খ

  Develop stable mineral forms in them

  গ

  Form ceramic bonds necessary for development of high crushing strength in the finished product

  ঘ

  All of the above