SWANSEA. Institute of Metals, September 21.—J. E. Clennell: Experiments on the oxide method of determining aluminium (Report to the Aluminium Corrosion Research Sub-Committee of the Corrosion Research Committee of the Institute). It was desired to find a direct method of determining aluminium in presence of iron and other impurities. Precipitating aluminium as hydroxide by alkali thiosulphates was fairly satisfactory, but the weight of precipitate generally exceeded the theoretical amount calculated from the aluminium known to be present. This excess was traced to small quantities of absorbed substances, notably salts of iron and sulphates, probably of aluminium. A better method is as follows: Pass sulphur dioxide through the slightly ammoniacal solution, precipitating in dilute, faintly acid, boiling solution with sodium thiosulphate with addition of dilute acetic acid, washing by decantation with hot 1 per cent, ammonium chloride, filtering and washing with hot water. Iron, zinc, manganese, and magnesium in ordinary amounts do not interfere, but when the first two are present in large quantity a double precipitation is necessary.—Marie L. V. Gayler: The constitution and age-hardening of alloys of aluminium with copper, magnesium, and silicon in the solid state. Constitution.—These alloys have been regarded as a ternary system since magnesium and silicon are added in the proportions of the compound magnesium silicide, which is very stable at all temperatures. Microscopic examination shows that the solubility of copper is reduced from 4.5 per cent, to 2 per cent, at 500° C. by the presence of 0.7 per cent, magnesium silicide; while 2 per cent, of copper reduces the Solubility of magnesium silicide from 1.2 per cent, to 0.7 per cent, at 500° C. At 2500 C. both constituents are turned out of solution when only 0.5 per cent, of each are present. Age-Hardening.— Brinell hardness measurements were made on alloys in which the percentage content of one constituent only was varied; they were quenched from 500° C. and allowed to age-harden at room temperature. Age-hardening is due to the difference in solubility at high and low temperatures of both copper and magnesium silicide, and the solubility in aluminium of both in the presence of each other. Heat treatment of age-hardened alloys caused a preliminary softening before an increase in hardness; this is probably due to the process by which both compounds tend to come out of solution. Derived differential curves of alloys which had been quenched, but not aged, show three critical points; the lowest is at a constant temperature; the temperature of the two upper critical points is lowered with increasing copper content; the intensity of the uppermost varies with the copper content. Probably this point is due to the precipitation of the copper compound and the second to the precipitation of magnesium silicide.—D. Stockdale: The copper-rich aluminium-copper alloys. Alloys of copper with aluminium up to 20 per cent, of aluminium have been investigated. Thermal data from the cooling-curves and from quenching experiments in conjunction with microscopic examination were used to obtain equilibrium diagrams. The minimum in the liquidus curve at 1031° C. with 8.3 per cent, of aluminium is a true eutectic point; a small arrest point at 1017° with alloys containing between 16.5 and 18 per cent of aluminium has been discovered. Copper at 1000° C. can hold only 7.4 per cent, of aluminium in solid solution; at 500° C. and at lower temperatures, 9.8 per cent., although to obtain such an alloy a long annealing is required.— R. Seligman and P. Williams: Cleaning aluminium utensils. Aluminium is not attacked by water-glass solutions or by hot soda solution containing a little sodium silicate1. Attack by a 5 per cent, soda solution is immediately-arrested by the addition of an amount of sodium silicate equal to 1/100 of the soda. Satisfactory detergents consisting of a mixture of soda and sodium silicate are articles of commerce; among them are “Carbosil,” “Pearl Dust,” and “Aquamol.”—W. Rosenhain and J. D. Grogan: The effects of overheating and melting on aluminium. Exposure to an unduly high temperature during melting, and repeated re-melting even at ordinary melting temperatures, are thought to cause deterioration approximating to the condition generally described as “burnt” aluminium. High-grade aluminium was poured at temperatures up to 1000° C. and also at the usual pouring temperature after heating for some hours at 1000° C. The castings rolled and tested in the annealed state showed no deterioration. High-grade aluminium and also aluminium containing 3/4 per cent, each of iron and silicon were cast to 3/4-in, slabs and rolled to 0.01 in. sheet; the sheet was re-melted and the process repeated ten times. Test pieces from each melt showed no systematic change.
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Aug 1, 2008
Luciano José De Oliveira + 1
Open Access