Why the name sol-gel and technique
The sol-gel technique for synthesis of nanomaterials is a wet- chemical technique. It is also known as chemical solution deposition. Such techniques are used for the fabrication of materials starting from a chemical solution (sol, short for solution) which acts as the precursor for an integrated network (or gel) of either discrete particles or network polymers. Precursors in the form of acetates or carbonates or nitrates are taken and then dissolved in deionized water. This starting material is used to produce a colloidal suspension known as gel. After that a gelling agent for example, polyvinyl alcohol is added and this will produce a gel.
A this fil coating is made on a substrate for example, Ni or Ti sheets, glass. It depends upon the requirement. The pH, temperature and viscosity should be under control. At last the film is annealed at suitable temperature and then characterized.
Common precursors are metal alkoxides and metal chlorides, which undergo hydrolysis and olycondensation reactions to from either a network “elastic solid” or a colloidal suspension or dispersion– a system composed of discrete often amorphous submicrometer particles dispersed to various degrees in a host fluid. In the case of the colliod, the volume fraction of particles (or particle density) may be so low that a significant amount of fluid may need to be removed initially for the gel like properties to be recognized.
sol-gel synthesis Merits:
- Produce materials at ultra-low temperatures (around 150-600 oF vis –a- vis 2500-6500 OF for conventional techniques),
- Synthesise Large quantities relatively cheaply,
- Co-synthesize two or more materials simultaneously,
- Coat one or more materials onto materials (metals or ceramic particulates, and three-dimensional objects),
- Produce extermely homogenous alloys and composites,
- Synthesize ultra- high purity (99.9999%) materials,
- control the microstructure of the final products, and precisely control the physical, mechanical, and chemical properties of the final products.