Metallizing
Encyclopedia
Metallizing is the general name for the technique of coating metal
on the surface of non-metallic objects.
Techniques for metallization started as early as mirror
making. In 1835, Justus von Liebig
discovered the process of coating a glass surface with metallic silver
, making the glass mirror one of the earliest items being metallized. Plating other non-metallic objects grew rapidly with introduction of ABS
plastic. Because a non-metallic object tends to be a poor electrical conductor, the object's surface must be made conductive before plating can be performed. The plastic part is first etched chemically by a suitable process, such as dipping in a hot chromic acid
-sulfuric acid
mixture. The etched surface is sensitised and activated by first dipping in tin(II) chloride
solution, then palladium chloride solution. The processed surface is then coated with electroless copper or nickel before further plating. This process gives useful (about 1 to 6 kgf
/cm or 10 to 60 N/cm or 5 to 35 lbf
/in) adhesion force, but is much weaker than actual metal-to-metal adhesion strength.
Vacuum metallizing
involves heating the coating metal to its boiling point in a vacuum chamber, then letting condensation deposit the metal on the substrate's surface. Resistance heating
, electron beam, or plasma
heating is used to vaporize the coating metal. Vacuum metallizing was used to deposit aluminum on the large glass mirrors of reflecting telescopes, such as with the Hale telescope
.
Thermal spray processes are often referred to as metallizing.
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
on the surface of non-metallic objects.
Techniques for metallization started as early as mirror
Mirror
A mirror is an object that reflects light or sound in a way that preserves much of its original quality prior to its contact with the mirror. Some mirrors also filter out some wavelengths, while preserving other wavelengths in the reflection...
making. In 1835, Justus von Liebig
Justus von Liebig
Justus von Liebig was a German chemist who made major contributions to agricultural and biological chemistry, and worked on the organization of organic chemistry. As a professor, he devised the modern laboratory-oriented teaching method, and for such innovations, he is regarded as one of the...
discovered the process of coating a glass surface with metallic silver
Silvering
Silvering is the chemical process of coating glass with a reflective substance. When glass mirrors first gained widespread usage in Europe during the 16th century, most were made of an amalgam of tin and mercury, but by the 19th century mirrors were commonly made through a process by which silver...
, making the glass mirror one of the earliest items being metallized. Plating other non-metallic objects grew rapidly with introduction of ABS
Acrylonitrile butadiene styrene
Acrylonitrile butadiene styrene is a common thermoplastic. Its melting point is approximately 105 °C ....
plastic. Because a non-metallic object tends to be a poor electrical conductor, the object's surface must be made conductive before plating can be performed. The plastic part is first etched chemically by a suitable process, such as dipping in a hot chromic acid
Chromic acid
The term chromic acid is usually used for a mixture made by adding concentrated sulfuric acid to a dichromate, which may contain a variety of compounds, including solid chromium trioxide. This kind of chromic acid may be used as a cleaning mixture for glass. Chromic acid may also refer to the...
-sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
mixture. The etched surface is sensitised and activated by first dipping in tin(II) chloride
Tin(II) chloride
Tin chloride is a white crystalline solid with the formula 2. It forms a stable dihydrate, but aqueous solutions tend to undergo hydrolysis, particularly if hot. SnCl2 is widely used as a reducing agent , and in electrolytic baths for tin-plating...
solution, then palladium chloride solution. The processed surface is then coated with electroless copper or nickel before further plating. This process gives useful (about 1 to 6 kgf
Kilogram-force
A kilogram-force , or kilopond , is a gravitational metric unit of force. It is equal to the magnitude of the force exerted by one kilogram of mass in a gravitational field...
/cm or 10 to 60 N/cm or 5 to 35 lbf
Pound-force
The pound force is a unit of force in some systems of measurement including English engineering units and British gravitational units.- Definitions :...
/in) adhesion force, but is much weaker than actual metal-to-metal adhesion strength.
Vacuum metallizing
Vacuum metallizing
In vacuum metallizing a metallic coating material placed in a vacuum chamber with the workpiece to be coated. The material that is being applied is then heated until it starts to evaporate, this vaporized metal condenses on the product or workpiece as a thin metallic film...
involves heating the coating metal to its boiling point in a vacuum chamber, then letting condensation deposit the metal on the substrate's surface. Resistance heating
Heating element
A heating element converts electricity into heat through the process of Joule heating. Electric current through the element encounters resistance, resulting in heating of the element....
, electron beam, or plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
heating is used to vaporize the coating metal. Vacuum metallizing was used to deposit aluminum on the large glass mirrors of reflecting telescopes, such as with the Hale telescope
Hale telescope
The Hale Telescope is a , 3.3 reflecting telescope at the Palomar Observatory in California, named after astronomer George Ellery Hale. With funding from the Rockefeller Foundation, he orchestrated the planning, design, and construction of the observatory, but did not live to see its commissioning...
.
Thermal spray processes are often referred to as metallizing.