Refractory Technology

151. Skull is not formed on the carbon blocks in the hearth of a blast furnace, when it becomes cold, because of its

1. Non-wetting characteristic
2. High thermal conductivity
3. High crushing strength
4. None of these

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152. Slide gates in teeming laddie used for steel pouring in ingot moulds is lined with _________ bricks.

1. Bakelite impregnated or fused periclase
2. Silica
3. Semi-silica
4. Fireclay

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153. Spalling of a refractory means its

1. Softening
2. Fracture due to uneven expansion at high temperature
3. Resistance to compressive loads
4. Resistance to chemical action of gases and molten fluxes

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154. Spalling resistance of a refractory cannot be increased by

1. Increasing its porosity
2. Using a coarser grog during its manufacture
3. Decreasing its thermal co-efficient of expansion
4. Making it denser

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155. Spalling tendency of refractories is reduced by increasing its

1. Porosity
2. Specific gravity
3. Thermal conductivity
4. Strength

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156. Spray test determines the _________ of refractories.

1. Resistance to slag penetration
2. Resistance to CO attack
3. RUL
4. Permanent linear change

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157. Tar bonded dolomite bricks

1. Are stored under controlled temperature & humidity to avoid hydration
2. Are used in outer lining of L.D. converters
3. Have poorer hydration resistance than pitch bonded bricks
4. All (A), (B) and (C)

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158. Tar dolomite bricks are used in the

1. Basic Bessemer converter
2. Basic open hearth furnace
3. Electric furnaces
4. All (A), (B) and (C)

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159. Test piece for determination of RUL of a refractory is heated in a/an

1. Oxidising atmosphere
2. Reducing atmosphere
3. Electric furnace
4. Neutral atmosphere

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160. The highest melting pure oxide (m.p. > 3000°C)is

1. Thoria
2. Alumina
3. Beryllia
4. Zirconia

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