Metallizing

 As can most probably be deduced from the name, the term ‘metalising’ (also spelt as ‘metallizing’) is used to describe the process of coating a thin layer of metal onto the surface of a non-metallic substance. One of the oldest known examples of such a process is the technique of ‘silvering’, a practice first used in the nineteenth century by the German chemist Julius von Liebig, and which has been used ever since in the process for the manufacturing of mirrors. In this particular form of the metalizing process, the non metallic surface of the glass is coated with a thin layer of silver, but nowadays it is more common for the metallic layer to be formed by sputtering powdered aluminium or other such similar compounds onto the glass surface. The plating of non-metallic objects could be seen as having really increased in popularity rapidly with the introduction of Acrylonitrile Butadiene System (ABS) plastic, typically used for the manufacture of pipe systems, musical instruments (like plastic clarinets and recorders), golf club heads (because of its good shock absorbance) as well as car parts and protective headgear.

 Due to the fact that a non-metallic substance tends to be a poor electrical conductor, the surface of the object has to be made conductive before the plating process can commence. In order for this to occur, the plastic component is firstly etched chemically by a suitable process (such as submerging the component in a hot chromic-acid sulphuric acid solution). The etched plastic surface is then sensitised and activated by first being dipped in a solution of tin (II) chloride and then again in a solution of palladium chloride. Finally, the processed surface is coated with a layer of electroless copper or nickel before being plated even further. Although this process provides the surface with a useful adhesion force of some strength, it is considerably weaker than actual metal to metal adhesion strength.

 One of the most famous variations of the typical metallizing process is ‘vacuum metallizing’.

 In the process of ‘Vacuum Metallizing’, the coating metal is heated until it reaches its boiling point in a vacuum chamber. The process then involves letting condensation deposit the metal onto the surface of the substrate. The coated metal is then vaporised by extremely high temperatures generated from either resistance heating, electron beam or plasma heating and the metal condenses on the work piece or product as a thin metallic film.