An Investigation of Some Banded Structures in Metal Crystals

C. F. Elam, G. I. Taylor
1928 Proceedings of the Royal Society A  
Crystals of the native metals gold, silver and copper have been found which exhibit twinning on an octahedral plane of the spinel type. Metallurgists have described as twins the banded structures which are of very frequent occurrence in these metals when prepared commercially, as they resemble lamellar twinning in calcite and felspar very closely. A few quantitative measurements have been made to determine the relationship between such bands in a metallic crystal; but the value of the results
more » ... pends on the correct determination of the orientation of the respective parts, and this can only be done by means of X-rays or by indirect methods such as the measurement of slip-bands, etching-pits, etc., which are not always trustworthy. McKeehan* measured some structures resembling twins in nearly pure iron by obtaining reflections from the deeply etched surface of a wire mounted in a goniometer. He concluded that the crystals were twins in a crystallo graphic sense, the twin plane being of the form {211} and the twin axis of the form [111]. A. J. Phillipst made some measurements of the angles between more than one set of bands in the same crystal in specimens of copper and brass, and found that they were inclined at approximately 70° to each other. (The angle between octahedral planes of a cubic crystal is 70° 31'.) Similarly, he measured the inclinations of traces of secondary bands in the principal bands, and found that these also could be considered as being traces of octahedral planes in the bands, provided that the two were related to each other as the two parts of the spinel twin. From this he concluded that the bands were true twins. No direct measurements of the orientation of either the original crystal or of the bands were made, and in many cases the bands could not be traced over the edge between the two faces of the specimen, so that there was a certain amount of conjecture as to whether two traces really belonged to the same plane. In a letter to ' Nature 'J the present writer pointed out that banded
doi:10.1098/rspa.1928.0193 fatcat:nx4z2pu2l5bbjkzmc4njniuokm