stable form of silica upto 870°C.
converted to tridymite on firing between 870 to 1470°C.
transformed to crystoballite on heating above 1470°C.
all (a), (b) and (c).
✅ The correct answer is option D.
Engineering
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3182. RUL of refractories depends on the
chemical composition.
physical structure.
presence of impurities like iron & alkali.
all (a), (b) and (c).
✅ The correct answer is option D.
3183. Sillimanite is a __________ refractory.
basic
neutral
high alumina
insulating
✅ The correct answer is option C.
3184. Which form of silica has the highest specific gravity ?
Quartz
Cristobalite
Tridymite
All have the same specific gravity
✅ The correct answer is option A.
3185. Porosity of silica bricks varies from __________ percent.
5 to 10
20 to 30
45 to 60
60 to 75
✅ The correct answer is option B.
3186. Addition of zircon to silica refractory brick improves its
crushing strength
resistance to slag attack
both (a) and (b)
neither (a) nor (b)
✅ The correct answer is option B.
3187. 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 ?
Cork
Saw dust
Sand
Chemically prepared foam
✅ The correct answer is option C.
3188. Magnesite refractories have low resistance to
attack by basic slag.
abrasion.
disintegration on sudden change of temperature.
both (b) and (c).
✅ The correct answer is option D.
3189. Vacuum steel degassing units are lined with
silica bricks
low duty firebricks
high alumina bricks
graphite blocks
✅ The correct answer is option C.
3190. Grog addition in fireclay during brick manufacture is done to
reduce its shrinkage on heating.
impart greater spalling resistance.
enhance the strength of fired refractories.
all (a), (b) and (c).
✅ The correct answer is option D.