Current ratings aluminium

Conductor (Aluminium) Thickness Lead sheath Armouring Approx. Approx. Normal Drum Approx. Maxi- Approx. Approx. Approx. Current rating Short-... 

The above situation may not always be true particularly when the current rating is low, say up to 600 A and the system fault level is still high. In this case much less cross-section of aluminium would be used, and the number of supports and fasteners would also be less. Then the fasteners will also be of smaller cross-sections. In such cases the suitability of fasteners will be more relevant. 

Properties and current ratings for aluminium and copper conductors 30/915... 

Table 30.4 Current ratings for rectangular aluminium sections, grade E91-E (6101 A)...

Certainly a thermodynamically stable oxide layer is more likely to generate passivity. However, the existence of the metastable passive state implies that an oxide him may (and in many cases does) still form in solutions in which the oxides are very soluble. This occurs for example, on nickel, aluminium and stainless steel, although the passive corrosion rate in some systems can be quite high. What is required for passivity is the rapid formation of the oxide him and its slow dissolution, or at least the slow dissolution of metal ions through the him. The potential must, of course be high enough for oxide formation to be thermodynamically possible. With these criteria, it is easily understood that a low passive current density requires a low conductivity of ions (but not necessarily of electrons) within the oxide. 

In view of its position in the e.m.f. series ( °aj3+/ai = 166V (SHE)), aluminium would be expected to be rapidly attacked even by dilute solutions of relatively weak acids. In fact, the rate of chemical attack is slow, owing to the presence on the aluminium of a thin compact film of air-formed oxide. When a voltage is applied to an aluminium anode there is a sudden initial surge of current, as this film is ruptured, followed by a rapid fall to a lower, fairly steady value. It appears that this is due to the formation of a barrier-layer. Before the limiting thickness is reached, however, the solvent action of the electrolyte initiates a system of pores at weak points or discontinuities in the oxide barrier-layer. 

Radiochemical studies indicate that the pore base is the actual site of formation of aluminium oxide, presumably by transport of aluminium ions across the barrier-layer, although transport of oxygen ions in the opposite direction has been postulated by some authorities. The downward extension of the pore takes place by chemical solution, which may be enhanced by the heating effect of the current and the greater solution rate of the freshly formed oxide, but will also be limited by diffusion. It has been shown that the freshly formed oxide, y -AljOj, is amorphous and becomes slowly converted into a more nearly crystalline modifipation of y-AljO . 

Current work in our laboratory [3] indicates that in methyl bromide solution the ionogenic reaction is of second order with respect to [AlBr3], and the same has been found [14] for the ionisation of A1I3, Gal3, and Inl3 in EtI. Since it is known that the aluminium halides are monomeric in these solutions, it follows that the rate-determining step for the selfionisation is the reaction (10) ... 

For aluminium, the factor is 1.79 and for brass 7.69. The reciprocal of these factors will convert mdd to mpy. Some electrochemical techniques may express corrosion rates in terms of an electrical current. In such cases, the anodic reaction must he known so that Faraday s laws may he used in converting to a mass rate loss. Thus, an exchange current density of 8/iAcm 2 on mild steel will result in a corrosion rate of about 20mdd, i.e. 

Fig. 7.22 Thermally stimulated current spectra of FEP electret foils (aluminium, coated on one side) immediately after polarisation. The heating rate was 4 C min"1. Reproduced with permission of the American Institute of Physics from Sessler and West (1971).

Families of tensile stress-strain curves have been generated for strain rates in the range of 10 - 10 s " at 23°C, for both the epoxy adhesives. These are illustrated in Fig. 4 (a) and (b). The tensile properties were found to increase progressively with the increasing the rate. Calculated mechanical properties are summarised in Table 3. The properties of the aluminium alloys are not significantly affected by the rates considered and may be regarded as rate independent [13], The mechanical properties of the aluminium alloys used in the current research are summarised in Table 4. 

Table 4 Tensile properties of the aluminium alloys employed in the current research obtained at a constant strain rate of 10 s , at 23°C. (Typical number of test replicates was...

For the measurements of the ferroelectric hysteresis of P(VDF-TrFE) via the flatband shift, we used capacitors with oxidised p-type (-lO cm ) silicon substrate (100-235 nm Si02) to prevent large amoimts of leakage current. The copolymer film was prepared as described above. We used films of thickness fiom 100 nm to 1 pm. The structiues were prepared in top electrode geometry , with thermal evaporated aluminium, patterned via a shadow mask. The measiuements of capacitance versus voltage (CV) were carried out with an Agilent 4284A LCR meter at a frequency of 1 MHz with sweep rates fiom... 

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