_______________ is the hardest oxide and is hence used where high wear resistance at high temperature is required?

Related Mcqs:

1. Principal alloying elements of cast tool alloys which have very high wear resistance & high temperature strength are ?

   A. Cobalt, chromium & tungsten
   B. Cobalt, chromium & nickel
   C. Molybdenum, tungsten & chromium
   D. Cobalt, zirconium & molybdenum

2. _____________ is the process of coating the surface of steel with aluminium oxide, thereby imparting it increased resistance to corrosion & oxidation upto a temperature of 700°C ?

   A. Veneering
   B. Galvanising
   C. Electroplating
   D. Calorising

3. High relative humidity decreases the evaporative process and as the temperature is increased, the relative humidity decreases. The comfort range for human body is the ambient temperature of 22 to 27°C with relative humidity ranging from _______________ percent ?

   A. 5 to 10
   B. 15 to 25
   C. 45 to 50
   D. 75 to 80

4. The thickness of oxide film is y at time t. If K1, K2 and K3 are the temperature dependent constants, the parabolic law of oxidation is given by __________________?

   A. y2 = 2k1t + k2
   B. y = k1 ln (k2t + k3)
   C. y = k1 t + k2
   D. y = k1t3 + k2

5. ________________ is the hardest material out of the following ?

   A. Boron carbide
   B. Tungsten carbide
   C. Hardened steel
   D. Silicon carbide

6. The refractory brick which has good thermal shock resistance at high temperature but cracks on cooling below 400°C is__________________?

   A. Magnesite
   B. Chrome
   C. Silica
   D. Fireclay

7. Which of the following is the most wear resistant grade of carbide used for the cutting tools ?

   A. Aluminium carbide
   B. Tungsten carbide
   C. Nickel carbide
   D. Iron carbide

8. The boiling & freezing points on a newly defined temperature scale in degree ‘D’ are 400°D & 100°D respectively. The temperature reading corresponding to 60°C on this new temperature scale will be equal to _____________ °D ?

   A. 140
   B. 180
   C. 240
   D. 280

9. Heating the Hypo-eutectoid steels to 30°C above the upper critical temperature line, soaking at that temperature and then cooling slowly to the room temperature to form a pearlite & ferrite structure is called_______________________?

   A. Tempering
   B. Hardening
   C. Annealing
   D. Normalising

10. The ratio of thermal & electrical conductivity is same for all the metals at the same temperature; and at around room temperature, this ratio is proportional to(where, T = absolute temperature, °K) ?

    A. T
    B. 1/T
    C. T2
    D. 1/T2