Refractory Technology

161. The largest consumer of refractories is the _________ industry.

1. Cement
2. Metallurgical
3. Fertiliser
4. Power

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162. The linear thermal expansion of _________ bricks upto 1000 °C is very low of the order of ≤ 0.5 percent.

1. Fireclay
2. Silica
3. Magnesite
4. Corundum

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163. The main raw material for manufacture of silicon carbide refractories is

1. Corundum
2. Carborundum
3. Bauxite
4. Periclase

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164. The maximum linear expansion of silica bricks during firing is about _________ percent.

1. 0.5
2. 1
3. 2
4. 3.5

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165. Thermal conductivity of refractory bricks

1. Increases with decrease in porosity
2. Decreases with decreases in porosity
3. Is independent of its porosity and is maximum for insulating bricks
4. Increases with the amount of air entrapped in pores

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166. Thermal diffusivity of a refractory brick is high, when its _________ is high.

1. Density
2. Specific heat
3. Thermal conductivity
4. None of these

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167. Thermal spalling mainly occurs during _________ of furnaces.

1. Cooling down
2. Warming up
3. Both (A) & (B)
4. Neither (A) nor (B)

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168. Thoria

1. Has high fusion temperature (> 3000°C) but poor resistance to thermal shock
2. Has high resistance to basic slags
3. Which is expensive & radioactive, is used in crucibles for melting high purity metals
4. All (A), (B) and (C)

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169. Thoria is an expensive refractory material and is radioactive in nature. Thorium oxide is used in the manufacture of

1. Segar cones
2. Muffles for muffle furnaces
3. Insulating bricks
4. Crucibles used for melting of high purity metals

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170. To resist spalling tendency, a refractory should have

1. Greater diffusivity
2. Low specific heat
3. Low thermal co-efficient of expansion
4. All (A), (B) and (C)

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