21. Which of the following does not occur during firing/burning of refractories ?
Removal of water of hydration.
Vitrification.
Decrease in crushing strength.
Development of stable mineral form.
✅ The correct answer is option C.
Refractory Technology MCQs
22. Thoria
has high fusion temperature (> 3000°C) but poor resistance to thermal shock.
has high resistance to basic slags.
which is expensive & radioactive, is used in crucibles for melting high purity metals.
all (a), (b) and (c).
✅ The correct answer is option D.
23. Which is not a natural insulating material?
Diatomaceous earth/kieselgur
Asbestos
Vermiculite
None of these
✅ The correct answer is option D.
24. High refractorinness of refractory bricks means, that it has a
high spalling resistance.
low spalling resistance.
high resistance to fusion.
low porosity.
✅ The correct answer is option C.
25. Thermal spalling mainly occurs during __________ of furnaces.
cooling down
warming up
both (a) & (b)
neither (a) nor (b)
✅ The correct answer is option C.
26. In panel test for spalling resistance, the average face temperature of panel assembly is maintained at __________ °C for 24 hours.
700
1000
1600
2000
✅ The correct answer is option C.
28. __________ is the measure of the strength of refractory under the combined effect of temperature & load.
Porosity
RUL
Specific gravity
Thermal conductivity
✅ The correct answer is option B.
29. Capacity of a refractory brick to withstand-sudden changes in temperature is denoted by the property called
spalling resistance.
refractoriness.
refractoriness under load (RUL).
none of these.
✅ The correct answer is option A.
30. Magnesite refractories are generally not used in the
electric furnace walls.
steel melting furnace.
open hearth furnace.
burning zone of cement kilns.
✅ The correct answer is option B.