- List of coating techniques
This list contains an overview of coating techniques for
thin-film deposition, found in the field of materials science. The techniques can be classified as follows: Chemical vapor deposition(CVD)
Metalorganic vapour phase epitaxy
Electrostatic Spray Assisted Vapour Deposition(ESAVD) Physical vapor deposition(PVD)
Cathodic Arc Deposition
Electron beam physical vapor deposition(EBPVD)
Ion beam assisted deposition(IBAD)
Pulsed laser deposition
Vacuum evaporation, Evaporation (deposition)
Chemical and electrochemical techniques
Plasma electrolytic oxidation
High velocity oxygen fuel(HVOF)
Molecular beam epitaxy
Safety in Metal Spraying
Metal spraying need not be a dangerous process, if the equipment is treated with care, and correct spraying practices are followed. As with any industrial process, there are a number of hazards, of which the operator should be aware, and against which specific precautions should be taken.
Ideally, equipment should be operated automatically, in enclosures specially designed to extract fumes, reduce noise levels, and present direct viewing of the spraying head. Such techniques will also produce coatings that are more consistent. There are occasions when the type of components being treated, or their low production levels, require manual equipment operation. Under these conditions, a number of hazards, peculiar to thermal spraying, are experienced, in addition to those commonly encountered in production or processing industries.
Metal spraying equipment uses compressed gases, which create noise. Sound levels vary with the type of spraying equipment, the material being sprayed, and the operating parameters. Typical sound pressure levels taken 1 meter behind the arc.
Combustion spraying equipment produces an intense flame, which may have a peak temperature more than 3,100°C, and is very bright. Electric arc spraying produces ultra-violet light, which may damage delicate body tissues. Spray booths, and enclosures, should be fitted with ultra-violet absorbent dark glass. Where this is not possible, operators, and others in the vicinity, should wear protective goggles containing BS grade 6 green glass. Opaque screens should be placed around spraying areas. The nozzle of an arc pistol should never be viewed directly, unless it is certain that no power is available to the equipment.
DUST AND FUMES
The atomization of molten materials, produces a certain amount of dust and fumes. Proper extraction facilities are vital, not only for personal safety, but to minimize entrapment of re-frozen particles in the sprayed coatings. The use of breathing masks, fitted with suitable filters, is strongly recommended, where equipment cannot be isolated. Certain materials offer specific known hazards.
1. Finely divided metal particles are potentially pyrophorric and none should be allowed to accumulate.
2. Certain materials e.g. aluminum, zinc and other base metals may react with water to evolve hydrogen. This is potentially explosive and special precautions are necessary in fume extraction equipment.
3. Fumes of certain materials, notably zinc and copper alloys are unpleasant to smell, and, in certain individuals, may cause a fever-type reaction. This may occur some time after spraying and usually subsides rapidly. If it does not, medical advice must be sought.
Combustion spraying guns use oxygen and fuel gases. The fuel gases are potentially explosive. In particular, acetylene may only be used under approved conditions. Oxygen, while not explosive, will sustain combustion, and many materials will spontaneously ignite, if excessive oxygen levels are present. Care must be taken to avoid leakage, and to isolate oxygen and fuel gas supplies, when not in use.
Electric arc guns operate at low voltages (below 45 dc), but at relatively high currents. They may be safely hand-held. The power supply units are connected to 440 volt AC sources, and must be treated with caution.
The air supply, to spray guns, is at high pressure. It should not be directed towards people. The motor air supply is lubricated, and should never be fitted to a breathing apparatus. Any breathing equipment, used with the thermal spraying process, must be supplied with air of breathing quality.
* "Titanium and titanium alloys", edited by C. Leyens and M. Peters, Wiley-VCH, ISBN 3-527-30534-3, table 6.2: "overview of several coating systems and fabriction processes for titanium alloys and titanium aluminides" (amended)
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