To resist spalling tendency, a refractory should have

Spalling resistance of a refractory can not be increased by

A

Increasing its porosity

B

Using a coarser grog during its manufacture

C

Decreasing its thermal co-efficient of expansion

D

Making it denser

Spalling of a refractory means its

A

Softening

B

Fracture due to uneven expansion at high temperature

C

Resistancce to compressive loads

D

Resistance to chemical action of gases and molten fluxes

Spalling tendency of refractories is reduced by increasing its

A

Porosity

B

Specific gravity

C

Thermal conductivity

D

Strength

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

Dry mix hydraulic compositions of refractory aggregates with suitable bonding materials are called refractory

A

Mortars

B

Cements

C

Castables

D

None of these

If a refractory contains high content of silicon, it means refractory is

A

Acidic

B

Basic

C

Neutral

D

Brittle

Ceramics make excellent refractory materials. A material is said to be refractory if it:

A

resists the flow of electric current

B

has high refractive index

C

retains its strength at high temperatures

D

all of the mentioned

Refractory timber catches fire readily while non-refractory timber does not catch fire readily.

A

True

B

False

A furnace is made of a refractory brick wall of thickness 0.5 metre and thermal conductivity 0.7 W/m.°K For the same temperature drop and heat loss, this refractory wall can be replaced by a layer of diatomaceous earth of thermal conductivity 0.14 W/m.K and thickness __________ metre.

A

0.01

B

0.1

C

0.25

D

0.5

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

A

Pottery furnace

B

Glass melting furnace

C

Crucibles

D

Gas retorts

To resist spalling tendency, a refractory should have

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