51. Which is the stable form of silica upto 1470°C ?
Quartz
Cristobalite
Tridymite
None of these
✅ The correct answer is option C.
Refractory Technology MCQs
52. The highest melting pure oxide (m.p. > 3000°C)is
thoria
alumina
beryllia
zirconia
✅ The correct answer is option A.
53. Refractories are dried in the
rotary kilns
tunnel kilns
sun
none of these
✅ The correct answer is option B.
54. Carbon refractories
do not burn/oxidise, when exposed to air on heating.
are not attacked by slags, as they are not wetted by melts.
do not resist temperature fluctuations.
have extremely low thermal & electrical conductivities.
✅ The correct answer is option B.
55. Spalling of a refractory means its
softening.
fracture due to uneven expansion at high temperature.
resistancce to compressive loads.
resistance to chemical action of gases and molten fluxes.
✅ The correct answer is option B.
56. PCE value (Segar cone) of superduty refractories is more than 33, which is equivalent to a temperature of __________ °C.
1520
1630
1670
1730
✅ The correct answer is option D.
57. Colour of fireclay bricks is
light buff to reddish buff
yellow
black
none of these
✅ The correct answer is option A.
58. Porosity is induced in insulating refractories by adding
powdered naphthalene.
ammonium chloride/sulphate.
calcium phosphate.
all (a), (b) and (c).
✅ The correct answer is option D.
59. Refractory bricks with lower permeability is produced by using
higher firing temperature.
higher moulding pressure.
finer grog size.
all (a), (b) and (c).
✅ The correct answer is option D.
60. Panel test determines the __________ of refractories.
fusion point
spalling resistance
slag penetration resistance
refractoriness under load (RUL)
✅ The correct answer is option B.