Aluminium contacts

The electrode potential of aluminium would lead us to expect attack by water. The inertness to water is due to the formation of an unreactive layer of oxide on the metal surface. In the presence of mercury, aluminium readily forms an amalgam (destroying the original surface) which is. therefore, rapidly attacked by water. Since mercury can be readily displaced from its soluble salts by aluminium, contact with such salts must be avoided if rapid corrosion and weakening of aluminium structures is to be prevented. 

Jimdnez AE, Bermudez MD, Iglesias P et al (2006) l-N-aUcyl-3-methylimidazolium ionic liquids as neat lubricants and lubricant additives in steel-aluminium contacts. Wear 260 766-782... 

Jimenez AE, Bermudez MD, Carri6n FJ et al (2006) Room temperature ionic liquids as lubricant additives in steel-aluminium contacts influence of sliding velocity, normal load and temperature. Wear 261 347—359... 

Chen YX, Ye CF, Wang HZ (2003) Tribological performance of an ionic liquid as a lubricant for steel/aluminium contacts. J Synth Lubr 20 217-225... 

We have elaborated a simple model to explain this situation [83] [84]. Suppose we have a ferroelectric thin film of thickness I and d is the distance between the tip and the sample, S is the surface area of the tip front end, and U is the applied voltage between the tip and the sample. To model our system, we assume that the tip is covered with a thin layer of silver and that all the electric connections in our system are done through aluminium contacts. P5 is the spontaneous polarization of the material, <7 is the surface... 

Fig. 5. Metal-insulated semiconductor field effect transistor with n-channel (n-MISFET). (A) the state with uncharged G-I-Su capacitor, (B) open transistor with charged G-I-Su capacitor. Abbreviations S, source electrode D, drain electrode G, gate electrode Su, substrate Al, aluminium contact I, insulator (dielectric) n-Si, p-Si, n- or p-type of silicone...

In another design (8) contact to the stabilised zirconia is via lanthanum chromite itself connected at 300 C with classical aluminium contact. Other lanthanxmi chromite elements are used to bring the zirconia to a temperature at which it can operate. 

Figure 13. Modulus of current versus implied bias voltage for a Schottky barrier diode formed with an aluminium contact to provide the hottky barrier and a gold contact to provide the ohmic junctioa The device area is 0.64 cm and the thickness of the polyacetyloie film is 500 nm.

If Ihe main incoming male contacts are made ol aluminium alloy, which is normally a eompnsilioii of aluminium-magnesium and silicon, they must be provided wiili a coat of bron/e. copper and tin to give it an adequate mechanical hardness and resistance to corrosion. For more details refer to Section 27.2..5. 

The physical structures of microchip assemblies usually contain a number of thin films in contact, each of which plays a separate role in the performance of the device. As an example, in one structure a silicon thin film would be contacted on one face by a copper rod which conducts away die heat generated during computer operations, and on the other face by an aluminium thin film which acts as a connector to other silicon films. This aluminium film is in turn in contact with a ceramic layer containing other thin film devices, and widr copper pins which plug into the circuit board. 

Another problem in the construction of tlrese devices, is that materials which do not play a direct part in the operation of the microchip must be introduced to ensure electrical contact between the elecuonic components, and to reduce the possibility of chemical interactions between the device components. The introduction of such materials usually requires an annealing phase in the construction of die device at a temperature as high as 600 K. As a result it is also most probable, especially in the case of the aluminium-silicon interface, that thin films of oxide exist between the various deposited films. Such a layer will act as a banier to inter-diffusion between the layers, and the transport of atoms from one layer to the next will be less than would be indicated by the chemical potential driving force. At pinholes in the AI2O3 layer, aluminium metal can reduce SiOa at isolated spots, and form the pits into the silicon which were observed in early devices. The introduction of a tlrin layer of platinum silicide between the silicon and aluminium layers reduces the pit formation. However, aluminium has a strong affinity for platinum, and so a layer of clrromium is placed between the silicide and aluminium to reduce the invasive interaction of aluminium. 

The contact between the aluminium layers and the ceramic substrate requires a joining material which will wet both metal and ceramic, and solders such as the conventional Pb-Sn alloy have been used which are molten during the annealing process. The contact between the solder and the aluminium layer is frequently unsatisfactoty because of the intervention of the AI2O3 layer, and a practical solution appears to be to place drree layers of metal clrromium in contact widr the aluminium, copper in contact with the clrromium, and gold between the copper layer and the solder. 

So aluminium alloy is good it resists all the fluids likely to come in contact with it. What about GFRP The strength of GFRP is reduced by up to 20% by continuous immersion in most of the fluids - even salf water - with which it is likely to come into contact but (as we know from fibreglass boats) this drop in strength is not critical, and it occurs without visible corrosion, or loss of section. In fact, GFRP is much more corrosion-resistant, in the normal sense of loss-of-section, than steel. 

In addition to the fluoroplastics and fluororubbers already described other fluoropolymers have been marketed. Polymers of hexafluoropropylene oxide are marketed by Du Pont (Krytox). These materials have a low molecular weight (2000-7000) and are either oils or greases. The oils are uses as lubricants, heat transfer fluids and non-flammable oils for diffusion pumps. The greases are also used as lubricants. They have good heat and oil resistance but it is said that explosions may result from contact with the surfaces aluminium or magnesium cuttings. 

The effect of thermal aging on polyethylene and isotactic polypropylene have been studied by Konar et al. [49]. They used contact angle, contact angle hysteresis, and XPS to characterize the modified surfaces of the polymers. Hysteresis increased with aging temperature. In the case of polyethylene, thermal aging led to a significant increase in adhesion strength of polyethylene with aluminium, but the increase in the case of polypropylene was much less marked. 

Videm, K., Pitting Corrosion of Aluminium in Contact with Stainless Steel , Proc. Conf. on Corrosion Reactor Mater., Salzburg, Austria, 1, 391 (1962) C.A., 60, 1412g Lyon, D. H., Salva, S. J. and Shaw, B. C., Etch Pits in Germanium Detection and Effects , J. Electrochem. Soc., 110, 184c (1963)... 

Black, J. R., Etch Pit Formation in Silicon at Al-Si Contacts Due to the Transport of Silicon in Aluminium by Momentum Exchange with Conducting Electrons , J. Electrochem. Soc., 115, 242c (1968)... 

Videm, K., Pitting of Aluminium in Contact with Stainless Steel , Tek. Ukeblad, 108, 775 (1961) C.A., 57, 109I2h... 

Two dissimilar metals, such as iron and aluminium, may cause aggravated corrosion effects even if they are not in electrical contact. This subject is, however, outside the scope of this section, and has been treated in detail elsewhere. Heavy metal ions, such as copper ions, are particularly liable to produce galvanic effects by redeposition on a less noble metal the phenomenon is discussed in Sections 4.1, 4.2 and 9.3. 

Meat and fish are very liable to bacterial putrefaction in this connection an interesting innovation is the increasing use of easily cleaned aluminium fish boxes. It is also possible that copper should be avoided in contact with herrings, which have a high fat content. 

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