A. Mainly contains quartz
B. Is not stable at high temperature
C. Transforms to other allotropic forms i.e. Tridymite and Cristobalite involving very high
volume changes
D. All A., B. and C.
Related Mcqs:
- Which is not a natural insulating material ?
A. Diatomaceous earth/kieselgur
B. Asbestos
C. Vermiculite
D. None of these - Lower part of hot metal mixer are lined with _____________ bricks?
A. Superduty fireclay
B. High alumina
C. Silica
D. Carborundum - Which of the following bricks has the most close values of RUL and PCE ?
A. Silica bricks
B. Fireclay bricks
C. High alumina bricks
D. Tar dolomite bricks - RUL of refractories depends on the _____________________?
A. Chemical composition
B. Physical structure
C. Presence of impurities like iron & alkali
D. All A., B. and C. - High alumina refractories are used in the ___________________?
A. Dome of blast furnace stoves
B. Electric arc furnace roof
C. Glass melting furnaces
D. All A., B. and C. - With increase in the alumina content in firebricks, its fusion point (refractoriness) ?
A. Decreases linearly
B. Remains unchanged
C. Increases
D. Decreases - 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 - Pick out the wrong statement ?
A. Electrical conductivity of refractory is not important, when these are to be used in electrical
furnaces
B. Graphite and metals are the good electrical conductor among the refractories and others are all
electrical insulators
C. Refractories used for lining electrical furnaces should ordinarily have very low electrical
conductivity
D. Electrical conductivity of porous refractory material is low - Cold crushing strength of ordinary fireclay brick is about 950 kg/cm2. On exposure to a temperature of about 1500°C, its crushing strength may come down to as low as ______________ kg/cm2?
A. 450
B. 250
C. 150
D. 65 - Refractory bricks with lower permeability is produced by using __________________?
A. Higher firing temperature
B. Higher moulding pressure
C. Finer grog size
D. All A., B. and C.
