Microwave synthesis for Preparation of Crystal
Microwave synthesis: In some cases microwave ovens rather than conventional heating is used to speed up the reactions. Solid state materials such as mixed oxides have been synthesized by this method. Microwave heating offers better control over the reaction conditions. A number of superconductors have been prepared by this method.
Extreme exothermiticity of a reaction can be used to provide high temperatures needed for diffusion
– Thermite Fe2O3 + Al → Al2O3 +Fe
Has been used to make a number of useful materials including refractory ceramic parts that can be pressed and machined to final size
- Si3N4 + SiC + TiN
Can produce functionally graded materials. Have a composition and hence property gradient.
In a liquid or solid, the molecules of ions are not free to rotate. The alternating electric field of the radiation:
- If charged particles are present, these move under the influence of the field and produce an oscillating electric current. Resistance to the movement causes energy to be transferred to the surroundings as heat, known as conduction heating.
- If no particles are present that can move freely, but molecules or units with dipole moments are present, then the electric field acts to align the dipole moments. This is dielectric heating. This is the type of heating that acts on water molecules in food.