Question

A) What are cryogenic materials? Show how ductile to brittle transition zone takes place.
Determine its applicability.
B) Distinguish between thermosetting and thermoplastics polymers.
C) Discuss the nitriding process.

Answer 1

A)Cryogenic Materials : first let us consider the term cryogenic, in this we study the behaviour of the material at very low temperature (cryogenic temperature). Beacause the property of the material changes when cooled to the low temperature.  

For example ; rubber when quenched into liqquid nitrogen it turns hard and breaks like brittle material.  

we can see that the wire made up of niobium and titanium it exhibit zero resistance when subjected to liquid hilium temperature (superconductivity).

examples of the cryogenic materials are aluminium, stainless steel , pyrex, invar, silica glass, titaneum alloys etc.,  

Ductile to brittle transition : The yield and the ultimate strength of the matrial goes high when the temperature gets decreases. That means increasing the brittleness behaviour. This is because at low temperature the vibration and the thermal agitation of the material decreases and this will decrease the interatomic space reducing the strain at low temperature increasing the brittlness of the material. So due to the low thermal energy at low temperature the even all plastic shows the brittle behaviour at 0- 4 degree temperature.

Inmetal the stainless steel is the best material for cryogenic application.

B) Difference between the thermosetting and thermoplastics polymers

- thermoplastic can be remelted where as the thermosetting polymers cannot be remelted.

- example of thermosetting plastics are hypalon, nitrile, neoprene, SBR , silicon etc., while the example of thermostting plastics are ABS, acetol, nylon polycorbonate etc.,

- thermoplastics are having low temperature while thermosetting polymers are having more tempearature.

- while curing after heating thermosetting polymers forms permanent chemical bond while the thermoplastic polymers does not form any bond while getting cured.

-thermosetting polymers are high resistant to temperature while thermoplastics are having low temperature resistance.

- thermoplastics are costlier than that of thermosetting.

C)Nitriding Process:

Nitriding is a heat treat ment process in which the nitrogen is get heated and diffused and then it is deposited on the surface of metal to create hard surface.

this methos is suitable for low corban alloys.

this process is done to increase the mechanical properties.

applications : gears, crankshafts , camshaft ,cam follower etc.,