Abstract
MR. MALLOCK has shown that the colour of the oxide film is an intrinsic property of the material of which it is composed and the material retains this property as it is gradually ground down from its original thickness to the vanishing point. Sir George Beilby's observations have confirmed this, and have further shown that the film is an aggregate in open formation through which oxygen molecules can penetrate to the metallic surface. For each temperature above the tempering range the thickness of the film is determined by the porosity of the aggregate to the oxygen molecules at that temperature. Direct experimental observations have shown the part played by time of heating at any given temperature. For example, at 275° C. a deep purple was reached in ten minutes, and this changed to blue from the margin inwards during a further period of twenty minutes. It was thus shown that the watchspring-blue, which could immediately be produced by a temperature of 300° C., could also be produced by heating at 275° for thirty minutes. Sir George Beilby's view is that the intrinsic colours of the films which are produced at different temperatures result from changes in molecular aggregation in relatively open formation of a similar nature to those which have been shown to occur in thin metal films, e.g. gold. This is referred to in his recently published volume entitled “Aggregation and Flow of Solids,” sections 3 and 10.—ED. NATURE.
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The Colours of Tempered Steel. Nature 109, 106 (1922). https://doi.org/10.1038/109106a0
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DOI: https://doi.org/10.1038/109106a0
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