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1) 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______________? a. Cost b. Electrical conductivity c. Thermal conductivity d. Fusion point
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2) Water content in ground refractory material to be shaped into bricks by hand moulding is about _____________ percent? a. 5 b. 20 c. 40 d. 55
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3) Maximum alumina content in high alumina refractory can be as high as ____________ percent? a. 30 b. 50 c. 70 d. 90
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4) Panel test determines the ______________ of refractories? a. Fusion point b. Spalling resistance c. Slag penetration resistance d. Refractoriness under load (RUL)
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5) Chemically, mullite refractories is________________? a. 3Al2O3.2SiO2 b. Al2O3 c. ZrSO4 d. ThO2
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6) Presence of MgO in alumino-silicate refractories ______________ its refractoriness ? a. Increases b. Lowers c. Does not affect d. Either A. or B.; depends on its quantity
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7) Hot metal runner in blast furnace are lined with ______________ bricks? a. Silica b. Carborundum c. Fireclay d. Magnesite
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8) Fireclay bricks are not used in the________________? a. Beehive coke oven b. By-product coke oven walls c. Combustion chamber of B.F. stoves d. Coke oven regenerators
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9) High porosity refractory bricks have________________? a. Poor resistance to the penetration of molten slag, metal & flue gases b. Poor heat conductivity & low strength c. Better thermal spalling resistance d. All A., B. and C.
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10) Fireclay bricks are used in the______________? a. Coke ovens regenerator b. Outer lining of L.D. converter c. Hearth bottom of blast furnace d. Coke oven walls
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11) Fusion point of a basic refractory material is________________? a. Reduced by the addition of acid oxides b. Increased by the addition of acid oxides c. Not affected by the addition of acid oxides d. Always less than 1000°C
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12) Thermal diffusivity of a refractory brick is high, when its ______________ is high? a. Density b. Specific heat c. Thermal conductivity d. None of these
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13) With increase in the alumina content, the refractoriness of high alumina refractories_________________? a. Increases b. Decreases c. Remain same d. May increase or decrease
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14) Test piece for determination of RUL of a refractory is heated in a/an__________________? a. Oxidising atmosphere b. Reducing atmosphere c. Electric furnace d. Neutral atmosphere
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15) 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 ? a. Cork b. Saw dust c. Sand d. Chemically prepared foam
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16) Magnesite refractories are used for the construction of those furnaces, which are_______________? a. Not required to resist the corrosive action of basic slag b. Not subjected to fluctuation in temperature c. Used for raising & maintaining high temperature d. Both B. and C.
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17) Outer combustion chamber of blast furnace stove is lined with _______________ bricks? a. Fireclay b. Silica c. Chrome magnesite d. Zirconia
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18) Roof of a basic electric furnace is made of ______________ bricks? a. Superduty fireclay b. Silica c. Chromite d. None of these
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19) Which property of refractories is the most important for top section of the blast furnace ? a. Resistance to abrasion b. Resistance to slag penetration c. Stability of volume at high temperature d. Resistance to corrosion by slag
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20) Spalling of silica bricks occurs due to abrupt volume changes, when it is cooled below a temperature of ______________ °C? a. 770 b. 570 c. 270 d. 70
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