Aluminium coatings cladding

Aluminium may be applied as coatings by metal spraying, cladding, hot-dipping and electrodeposition, though the last-named process is difficult to apply and by far the largest proportion of aluminium-coated metals are produced by the first two methods. 

This appears as a random non-branching white tunnel of corrosion product either on the surface of non-protected metal or beneath thin surface coatings. It is a structurally insensitive form of corrosion which is more often detrimental to appearance than strength, although thin foil may be perforated and attack of thin clad sheet (as used in aircraft construction) may expose the less corrosion resistant aluminium alloy core. Filiform corrosion is not commonly experienced with aluminium, as reflected by the insignificance afforded it in reviews on the phenomena (Section 1.6). 

Probably the most familiar coated steel sheets are the ubiquitous galvanised corrugated roofing and cladding sheets which have been used for many years, particularly for farm buildings, either painted or unpainted. In addition to zinc other metallic coatings are available, e.g. hot dip aluminium and hot dip aluminium-zinc alloys. 

Calorised and heat-treated mechanically-clad products have coating structures similar to hot-dip aluminised coatings, but the degree of alloying with iron is variable (Fig. 13.5). With Calorised products the surface layers usually contain 25-50% aluminium. 

In the second paper [118] tin, iron and nickel organometallic compounds were separated using aluminium-clad high temperature columns coated with 0.1 xm films of HT-5. Various column lengths and temperature gradients were used to separate the species. Helium was used as the carrier gas. The same GC-ICP-MS set up was used as in the previous paper with slight modification of the transfer line for the analysis of nickel diethyldithiocar-... 

Thick compact exterior grade laminates are self-supporting and suitable for applications such as infill panels or the decorative cladding of exterior walls. They are available with surfaces of anodized aluminium and coloured lacquer-coated foil as well as normal melamine. 

In addition to the methods just described, several other principles for applying metal coatings exist, such as cladding (e.g. application by rolling nickel or stainless steel on carbon steel, or pure aluminium on a strong but less corrosion-resistant... 

The corrosion of aluminium alloys in high purity water is complex and many of the factors responsible for this corrosion are interrelated. In high purity, deionized water, general thinning of the cladding caused by uniform corrosion is very low. The fuel enters the basin with, in some cases, several millimetres of protective oxide coating formed at high temperatures. When corrosion by water... 

Blister formation or raised areas in the cladding of spent nuclear fuel can lead to breach of the aluminium cladding and subsequent corrosion of the fuel core. This blistering is a manifestation of internal gas pressurization and/or internal oxide formation. Blistering is facilitated under coatings and oxides because hydrogen has low diffusion rates in aluminium, so trapped hydrogen disperses slowly. Blisters can be formed by several mechanisms. 

This is the case, for instance, for K2Sip6 which in an aluminothermic reaction provides in situ the Al-Si clad (molten fiUer metal) normally used for controlled atmosphere brazing (CAB) of aluminium. In the case of zinc, the primary objective is not only to form a clad but to obtain a homogeneous diffusion layer into the aluminium, which is needed for some applications and which would have to be otherwise applied by costly intensive methods like electrochemical galvanization, plasma coating or thermal spray coating. 

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