Refractory Technology

141. Silica bricks are attacked by basic slags at high temperature. Which of the following is not used solely as a binding material?

1. Aluminium phosphate
2. Water
3. Lime
4. Plaster of Paris

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142. Silica bricks are never used for lining the

1. Beehive coke ovens
2. By-product coke ovens
3. Dome of blast furnace stoves
4. Roof of open hearth furnace

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143. Silica bricks have low spalling resistance below 600°C, due to its

1. Very high thermal conductivity
2. High co-efficient of expansion upto this temperature
3. High thermal diffusivity
4. Low refractoriness

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144. Silica refractories

1. crack when subjected to sudden change of temperature
2. Cannot be used in the dome of hot blast stoves
3. Have lower thermal conductivity than fireclay bricks
4. All (A), (B) and (C)

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145. Silica refractories are not used in

1. Coke oven walls
2. Beehive coke ovens
3. Dome and upper portion of B.F. stoves
4. Open hearth furnace roof

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146. Silicon carbide refractories are used in the

1. Muffle furnace
2. Zinc smelting furnace
3. Ceramic recuperators
4. All (A), (B) and (C)

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147. Silicon carbide refractories have very low

1. Refractoriness (< 1700°C)
2. Thermal conductivity
3. Resistance to thermal shock
4. None of these

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148. Sillimanite (Al2O₃.SiO₂) refractory, which is a neutral refractory, is not used in

1. Pottery furnace
2. Glass melting furnace
3. Crucibles
4. Gas retorts

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149. Sillimanite is a _________ refractory.

1. Basic
2. Neutral
3. High alumina
4. Insulating

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150. SiO₂ percentage in firebrick is about

1. 35-40
2. 55-60
3. 80-85
4. > 94

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