০০। 'Spinel', a refractory mineral is chemically represented as
ক) MgAl2O4
খ) MgAl2O3
গ) MgSO4
ঘ) MgAl2O3.2H2O
০১। 'Super refractories' are made from pure
ক) carbides
খ) oxides
গ) borides
ঘ) nitrides
০২। 10 to 30% magnesite is added to chromite to produce chrome-magnesite refractories. Magnesite addition is mainly done to improve the __________ of chromite.
ক) spalling resistance
খ) refractoriness
গ) crushing strength
ঘ) resistance to slag
০৩। 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
০৪। Addition of grog in fireclay brick during its manufacture is advantageous, because it results in
ক) less shrinkage in heating, decreased apparent porosity & increased specific gravity.
খ) high strength & thermal spalling resistance.
গ) less addition of water to get a workable plasticity & lesser time required for drying the raw refractories and hence increased rate of production.
ঘ) all (a), (b) and (c).
০৫। Addition of zircon to silica refractory brick improves its
ক) crushing strength
খ) resistance to slag attack
গ) both (a) and (b)
ঘ) neither (a) nor (b)
০৬। Alumina-graphite bricks are used for lining the
ক) slide gate in teeming laddies.
খ) continuous casting systems.
গ) both (a) and (b).
ঘ) neither (a) nor (b).
০৭। An ideal refractory should have high
ক) spalling rate
খ) fusion point
গ) shrinkage ability
ঘ) none of these
০৮। An indication of degree of firing in silica brick is its
ক) specific gravity
খ) fusion point
গ) RUL
ঘ) none of these
০৯। 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
১০। Basic bricks are not made of
ক) fireclay
খ) magnesite
গ) foresterite
ঘ) chromite
১১। Bauxite calcining rotary kilns are lined with __________ bricks.
ক) fireclay
খ) carbon
গ) 85% alumina
ঘ) corundum
১২। 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.
ক) 1800
খ) 2200
গ) 2400
ঘ) 2700
১৩। Beryllia (which is used in making crucibles for melting uranium & thorium) is superior to alumina in all respects for high temperature (> 1900°C ) use, except
ক) cost
খ) electrical conductivity
গ) thermal conductivity
ঘ) fusion point
১৪। 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.
১৫। Capacity of a refractory brick to withstand-sudden changes in temperature is denoted by the property called
ক) spalling resistance.
খ) refractoriness.
গ) refractoriness under load (RUL).
ঘ) none of these.
১৬। Carbon bricks are not used in the lining of the
ক) combustion chamber of blast furnace stoves.
খ) electric furnaces.
গ) highly chemical resistant equipments.
ঘ) blast furnace hearth.
১৭। Carbon refractories
ক) do not burn/oxidise, when exposed to air on heating.
খ) are not attacked by slags, as they are not wetted by melts.
গ) do not resist temperature fluctuations.
ঘ) have extremely low thermal & electrical conductivities.
১৮। Carbon refractories are exclusively used in the