Lattice parameters, densities and imperfections in indium and indium-cadmium alloys rich in indium

Publication Year:
1962
Usage 4
Abstract Views 4
Repository URL:
http://scholarsmine.mst.edu/doctoral_dissertations/967
Author(s):
Rao, Paluri Bhimeswara
Publisher(s):
Missouri School of Mines and Metallurgy
Tags:
Chemical Engineering
thesis / dissertation description
"An investigation of perfection of the structure of the indium-cadmium system was suggested by the interesting properties of indium and its cadmium alloys. The lattice of indium, though tetragonal, may be considered as distorted cubic, its axial ratio being 1.0767 at 20°C. Furthermore earlier studies have revealed a transformation of the tetragonal structure to cubic in the presence of cadmium.To determine the perfection or soundness of the indium and indium-cadmium alloys rich in indium, pure indium (99.999 per cent purity) and eight samples of the indium-cadmium alloys ranging in composition from 2.977 to 10.015 per cent by weight of cadmium were studied by the X-ray and density method. This method in brief requires the precise determination of lattice parameters and densities permitting the calculation of n' (the actual number of atoms or molecules per unit cell) which may then be compared to n (the number of atoms or molecules in the ideal cell).Rotation patterns were prepared from a single crystal of indium using copper Kα radiation to assist in indexing the powder patterns of indium and also to obtain the coefficients of linear thermal expansion of the single crystal. A plot of the lattice constants of indium, determined with a precision of ± 0.0002 kX, over the temperature range 20-60⁰C resulted in a straight line.The perfection of the structure of indium was then determined from the volume of the unit cell, atomic weight, and density. A value of n' = 3.9999 was obtained, which within the limits of error, indicated the structure, although distorted cubic, to be sound.Powder patterns of the alloys containing 5.827 per cent or less of cadmium showed two structures, one tetragonal and the other most probably cubic. Alloys containing 6.105 per cent or more of cadmium were cubic. However, in the case of alloy containing 10.015 per cent of cadmium, the tetragonal structure began to appear at temperatures below 10°C. The lattice constants and densities were determined as before to a fairly high degree of precision. For the tetragonal structures a increased and c decreased with increasing cadmium content whereas a decreased for the cubic structures.The expansion coefficients for the alloys were calculated within the range 10 to 65°C and found to change gradually with temperature.The volume of the unit cell decreased with increasing cadmium content as would be expected on the basis of smaller cadmium radius. Breaks in the slope were observed in the volume composition plots for the temperatures 10°, 35° and 65°C at 5, 6.1 and 8.1 per cent by weight of cadmium, respectively. It is possible that these points may correspond to the solubility limits of cadmium in indium at these temperatures.A plot of axial ratios (c/a) for the alloys containing 2.977, 3.816 and 4.322 per cent of cadmium versus cadmium content appeared to converge at a value of 1.00 between 5.827 and 6.105 per cent by weight of cadmium, independently of the temperatures used.The perfection of the structures of the alloys were determined in the same manner as for indium. The values of n for the alloys containing 2.977, 3.816 and 4.322 per cent of cadmium on the basis of tetragonal structure and for the alloys containing 6.105 and 7.996 per cent of cadmium on the basis of cubic structure, were within the limits of error in n' and thus indicate substitutional solid solutions. The values of n' calculated for the alloys containing 2.977, 3.816, 4.322 and 10.015 per cent by weight of cadmium on the basis of a cubic structure indicated the presence of interstitial atoms. However there is some uncertainty in the indexing of the cubic patterns for the alloys containing 2.977, 3.816 and 4.322 per cent by weight of cadmium"--Abstract, page ii.