Subject:- Applied Chemistry 2.

Topic:- Composite Materials

Difficulty:- Medium

1. Particle reinforced composite: Particles are made from metal powder, mineral powder, ceramic powder & carbon black. Particles increases elasticity modulus & decreases ductility & permeability. It also produces inexpensive composite material. i) Large particle composite: Its features are as follows
2. Particulate phase is harder & stiffer than matrix phase.
3. There is restriction of movement of matrix phase surrounding the dispersed phase.
4. Matrix phase transfer some of the applied stress to the particles.

5. The strength of bonding between matrix phase & dispersed phase at the interface decides the mechanical properties. Examples:

   Material	Matrix	Dispersed	Properties	Uses
   1.Concrete	cement	Sand & gravel	Harder & stronger than plain cement	Construction purpose
   2.Oxide based cermets	Cr	Al2O3	Good strength & good shock resistance properties	Shock resistant equipment
   3.Carbide based cermets	Co & Ni	1.WC &TiC	1.increases surface hardness	Wire drawing, dyes& machine parts
   	Co & Ni	2.CrC	2. High abrasion & resistance resistance	Valves, Spray nozzles & pump parts
   4.Modern rubber	Vulcanized rubber	Carbon black,(Stiffer)	Enhancement in mechanical properties	Used in automobile industry for making tires
   5.Spherodized steel	α Iron( ductile)	Fe3C cementite(brittle)	Ductility of composite decreases	Spherical steel structure for fixing tires

ii) Dispersion strengthened composite: Its features are as follows:

1. Very small particle of the range 10 to 100nm are used
2. The particle-matrix interactions leading to strength are on atomic or molecular level. The mechanism on strengthening in this case is similar to that of precipitation hardening
3. Matrix phases bear the major load, & particle improves yield, tensile strength & hardness. In case of Al, the strength & hardness is improved by the formation of extremely small uniformly dispersed particle of dispersed particle of a second phase within the original matrix phase with the help of heat treatments. This process is called precipitation hardening because small particle of new phase is called as precipitate. The procedure is also called as age hardening because strength develops with time & as the alloy ages. E.g. the high temperature strength of Ni alloy can be considerably enhanced by adding about 3% by volume ThO2 in the form of dispersed particles.