3181. Quartz is
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.
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.
3191. The maximum linear expansion of silica bricks during firing is about __________ percent.
0.5
1
2
3.5
✅ The correct answer is option D.
3202. Rate of slag attack on refractories increases with rise in temperature due to the
decreased viscosity of slag.
increased thermal conductivity of brick.
oxidising condition in the furnace.
none of these.
✅ The correct answer is option A.
3207. Use of higher percentage of lime for bonding silica bricks, reduces their
strength
abrasion resistance
both (a) & (b)
neither (a) nor (b)
✅ The correct answer is option C.
3214. Addition of grog in fireclay brick during its manufacture is advantageous, because it results in
less shrinkage in heating, decreased apparent porosity & increased specific gravity.
high strength & thermal spalling resistance.
less addition of water to get a workable plasticity & lesser time required for drying the raw refractories and hence increased rate of production.
all (a), (b) and (c).
✅ The correct answer is option D.
3217. Chromite refractories are
acidic refractory.
neutral refractory.
basic refractory.
fired at a temperature of 600°C only.
✅ The correct answer is option B.
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.
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.