High-Temperature Physical Properties of Carbide-Iodide Thorium

Abstract

Methods have been developed for measuring several of the physical properties of pure, freshly deposited carbide-iodide thorium over a range of temperatures without exposing the metal to atmospheric or other contamination. The allotropic transition of such material has been located at 1325 ~ _ 10~ the transition from fcc thorium to bcc thorium being complete at 1335~ in less than 1 min. New values are given for the electrical resistivity and total emissivity of thorium, these properties being markedly influenced by impurities in materials used by previous investigators. The morphology of the deposits has been studied and related to the composition and physical properties of the metal.

Filament Temperatures from Geometry-Independent Electron Emission Functions

“…Experimentally, also, EI1/8/L has a considerably different value for a growing thorium filament than for the same filament annealed in vacuum (5), and the same effect was observed for zirconium, Table VI. In Table IV it can be seen that the temperature prediction differences between the filaments grown in bulb 2, in which impurity effects were evident, and those grown in bulb 3 for example, were much greater when based on EIII3/L than on log f(i).…”

“…This spread was in part attributable to observed impurity effects in bulb 2 introduced by a departure from normal preparative procedure, and resulting in changes in physical and emission properties, but also caused in part by apparently random variations in the surface morphology of thorium filaments (5). The function values obtained for bulb 3, filament No.…”

“…Equations [5] and [6] are diameter independent and require the measurement of only one electrical characteristic other than electron emission. Since the function of Eq.…”

“…[3], [5], and [8] of values of p, ~, 4, and A at two temperatures. Experimentally, plots of log f(i) vs. 1/T (see Fig.…”

“…In cases where a filament of length L is of unknown diameter, it is in principle possible to regard the function EP/3/L as being constant at a fixed temperature (1-3) for a cylindrical filament; the function can be determined experimentally for filaments of irregular surface (2). Although this function can be used to regulate the growth temperature in a vapor deposition process (2,4) it is found to give variable temperature definition (5,6) and to be impurity sensitive (5). In the converse case of filament vaporization (3) the function was found to decrease in value as vaporization proceeded.…”