Electrical Resistivities and Temperature Coefficients of Lead, Tin, Zinc and Bismuth in the Solid and Liquid States

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Abstract
A method of measuring the resistance-temperature coefficients of low melting point metals in the solid and liquid states is described. Previous difficulties in the way of making such measurements have been largely eliminated by employing oxide films as containers for the molten metals. The resistivity-temperature curves are shown for the metals (Pb, Sn, Zn, Bi), and the resistance-temperature coefficients are given for 20° intervals throughout the range 20° to 460°C. The temperature coefficients of resistance of zinc above the melting point are found to be positive instead of negative as reported by Northrup and Suydam. Variations in the resistivity values indicate that there are allotropic transformations in zinc slightly above 180°C and at about 340°C. The coefficients of the metals investigated are all positive except those for nonannealed bismuth in the regions 160° to 180°C and 225° to 275°C and those for annealed bismuth in the latter region. The high resistivity values of nonannealed bismuth below 160°C are attributed to three possible factors, (a) lack of random orientation of the crystals, (b) cracks and imperfections in the crystal lattice, and (c) amorphous solid bismuth which may be formed between cleavage faces and in reentrant angles. The origin of these factors is accounted for by a crystalline transformation, in the region 160° to 180°C, which gives rise to them only when the metal is cooled rapidly. When nonannealed bismuth passes through this region from the lower to the higher temperature the negative coefficients are then to be expected. In the range 225° to 275°C the negative coefficients of bismuth are due to a molecular derangement of the metal as it approaches the melting point and passes from the solid to the liquid state.

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