Aluminium coatings vacuum deposited

To increase the barrier to oxygen, polymer packaging is coated with impermeable layers of metal or silicate glass. Aluminium, if vacuum deposited, is less than a micron thick. Table 11.4 shows that it reduces the permeability of a PET/ PE composite film by a factor of 10. Such collapsible bags are used inside wine boxes, as a method of increasing the shelf life of the partly consumed wine. 

Sprayed, vacuum-deposited and plated coatings can be applied to most metals and to many non-metals, e.g. vacuum deposition is applied to many substrates including plastics spray application can be used for coating fabric, plastic and paper. Hot dipping and other diffusion processes are dependent on the nature of the substrate for the properties of the coating. Most commercial applications of aluminium coatings are on iron and steel with smaller quantities applied to aluminium alloys and plastics. 

Vacuum-deposited and electroplated coatings are pure metal with no chemical bond to the underlying surface. The properties will be those of pure aluminium. The presence of lacquer, in the case of vacuum-deposited coatings will, however, afford resistance to the passage of electricity and limit the maximum temperature of use. 

Vacuum Deposited Coatings Aluminium coatings have been strongly considered as a replacement for cadmium in the protection of high-tensile steel... 

To test the corrosion protection conferred by LMP - produced films, glass microscope slides bearing 5000 A - thick layers of aluminium (by vacuum evaporation) were overcoated with P-PHMDSO films. In this experimental series plasma deposits were maintained at thicknesses near 1000 A, and were produced at T ranging from 100 C to about 300 C. Plasma-coated and control samples were placed in a bath of alkaline cleaning fluid (pH 8.5) and Inspected periodically for loss of Al, as described in an earlier publication (5). 

The technique may be said to combine the advantages of vacuum evaporation and sputtering, so that excellent qualities of adhesion are obtained without a limitation of maximum thickness of the coating—while at the same time the rate of deposition can be comparatively high. Many metals, alloys, and compounds may be deposited, on both metallic and non-metallic articles. However, its use at present is mainly for functional and protective applications, particularly where high resistance to corrosion is required. Thus, as examples, aluminium may be deposited on various types of steel and on titanium for uses in the aerospace and defence industries—and can be regarded as a less hazardous replacement for cadmium electroplating. 

In television tube fabrication, vacuum evaporated high reflecting aluminium coatings are used to increase the brightness of the pictures by more than 80%. For that purpose, the A1 film is deposited on the rear inner surface of the phospor layer in a similar coating plant as shown in Fig.67a, b of Chapter 6. Because of the relatively high electron permeability of aluminium in the form of very thin layers, practically no absorption of the electron beam is observed. 

Traditionally, where good shielding was required, equipment cases were made from metal, but more recently polymers have become widely used. These polymers are rendered conductive by processes such as electroplating, electroless plating, vacuum deposition, sputtering and flame spraying. Alternatively, they can be compounded with conductive fillers such as carbon blacks, carbon fibres, aluminium flakes, stainless steel fibres and various metal-coated fillers. 

These are produced by several conversion processes (evaporation, sputtering, chemical plasma deposition). Evaporation is the same method as that used to create metallisation using aluminium. A material is heated in a crucible by either a resistive heat or an electron beam gun (hence the name electron beam deposition), whereby the material evaporates and subsequently condenses on a chilled film in a vacuum chamber. In the case of Sit), coatings, the aluminium used in metallisation is replaced by SiO/Si02. 

A surface mirror for the UV is an aluminium mirror which is deposited very fast in a very good vacuum to prevent detrimental oxidation, and is then coated immediately with a protective magnesium fluoride film [75-83] sometimes LiF is also used. This film combination gives excellent reflectance in the ultraviolet region of200 nm up to 400 nm, as can be seen in Fig.12. 

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