The Institute for Plasma Research (IPR) has developed a technique to deposit silicon dioxide films on brassware using the process of plasma polymerisation of organosilicon monomers and a radio frequency discharge of plasma. The workpiece is kept inside a vacuum chamber and a suitable mixture of gases are introduced into it.

A radio frequency power source generates a plasma in the vicinity of the workpiece.

The plasma dissociates the monomer as well as other oxygen bearing gases releasing the metal donor and oxygen, which reacts near the surface, gets deposited by condensation.

Appropriate pre-treatment of the surface before deposition and post-deposition treatment renders the silicon dioxide coating hard, pin-hole free and transparent with necessary adhesion.

The present process is done in batches and takes approximately three hours which includes pumpdown and pre-treatment phases.

Applications: The application of silicon dioxidecoating is not confined to brassware, but covers a wide range of industrial and household articles. Protective overcoats of this coating on evaporated aluminium in automotive headlight reflectors is extensively used in Germany.

This coating protects metals and alloys from corrosive environment. Acrylic and polycarbonate, which are transparent polymers but have poor scratch resistance and quartz like coating, make their surfaces scratch proof without affecting their transparency.

There is protective barrier against diffusion and loss of aroma of packaged food in the food packaging industry.

Parameters: No. of pieces/batch-100;
area of one piece-100 sq.cm.;
working days/year-300;
land area-500 sq.ft.;
covered area-225 sq ft.
Manpower: manager-1,skilled-3.
Raw materials: Monomer, chemicals, gases.

Plant and machinery: Reaction chamber, radio frequency power supply, mass flow controllers, monomer container, diffusion pump, rotary pump, pirani gauge, thermostat.

Economy: Plant andmachinery - Rs 28 lakh.

For enquiries: National Research Development Corporation (NRDC),`Anusandhan Vikas', 20-22, Zamroodpur Community Centre, Kailash Colony Extension, New Delhi-110048. Phone: 6417942, 6434265, Fax: 011-6460506; E-mail: nrdc@x400.nicgw.nic.in.

-- Compiled by G K Pillai