Tadao Sano

A study of hydrogen absorption and desorption by titanium

Abstract The hydrogen absorption and desorption behavior of titanium in a constant volume system has been investigated in the temperature range of 450 to 800°C. A method of the reaction rate analysis was proposed and examined for determining the rate constant. The activation energy values obtained by this analysis for the absorption and the desorption were 74 and 25 kJ/mol, respectively. When the absorption and the desorption was repeated, the absorption rate constant for the second run was found to be appreciably larger than that for the first run whereas the desorption rate constant did not show any marked change.

Statistical model for the non-stoichiometric Cr2N phase

Abstract In order to obtain some information on the bonding in the non-stoichiometric Cr 2 N 1 − x phase, a statistical thermodynamic approach has been made. The interaction energy between the nitrogen atom and the chromium atom, E N-Cr , was estimated to be −34.4 kcal/mole, and that between chromium atoms, E Cr-Cr , to be −13.4 kcal/mole. The interaction energy between nitrogen atoms, E N-N , was found to have positive values, varying with temperature. These results show that both the metal-metal and metal-nonmetal bonds play an important role in the Cr 2 N phase. The atomic partition functions, which have been conventionally put equal to unity in almost all the statistical thermodynamic considerations, were also evaluated for the nitrogen atom and the chromium atom in the Cr 2 N lattice. From the evaluated values for these atomic partition functions, the importance of the contribution of the electronic structures to the atomic partition functions may be appreciated.

Chemical vapor deposition of niobium on graphite

Abstract Chemical vapor deposition of niobium on a graphite rod has been carried out at temperatures exceeding 1200 °C using NbBr 5 as a feed material. The properties of the deposits have been studied by X-ray diffraction analysis, surface hardness measurements, metallographic and scanning electron microscopy observations. It was found that coatings deposited at a low temperature (below 1300 °C) have a smooth surface and a fine grained structure with layers consisting of Nb + Nb 2 C or Nb 2 C + NbC depending on their deposition temperature. In contrast, the coatings deposited at a higher temperature were found to have decreased smoothness of the surface and a coarse grained structure with a single layer consisting of NbC. Annealing experiments on the coatings with Nb and Nb 2 C layers showed that these layers readily transformed to a single layer of NbC at 900 °C within 10 h. It was found that the layer growth rates of carbides in the deposits are much faster than the layer growth rates estimated from ordinary diffusion data.

Self-Diffusion of Carbon in Uranium Monocarbide

The diffusion of C in UC has been measured using radioactive tracer and sectioning technique. Self-diffusion coefficients of C in UC are described well by the equation over the temperature range of 1,400°–2,000°C.

Self-diffusion of carbon in hyperstoichiometric uranium monocarbide

Abstract The self-diffusion of C in hyperstoichiometric UC has been measured in the single-phase region of UC, using a radioactive tracer and sectioning technique. The diffusion equations as a function of temperature are: 1. (i) for UC1.38, D = 0.10 exp (−(53.5 ± 10.6)/RTkcal/mole) cm2/sec for the temperature range 2100–2230°C; 2. (ii) for UC1.52, D = 0.11 exp (−(54.6 ± 4.6)/RTkcal/mole) cm2/sec for the temperature range 1950–2150°C. The dependence of the diffusion coefficients and the activation energy is described as follows, 1. (i) when x (C/U molar ratio) ≲ 1.11, the diffusion coefficients increase with x, while the activation energy decreases, 2. (ii) when ≳, the diffusion coefficients no longer increase with x but remain constant, as does the activation energy, r.e., E is about 54 kcal/mole. The mechanism for C diffusion in hyperstoichiometric UC is considered to be an interstitial or interstitialcy.

Graphitization of free carbon precipitating through the reaction of UC2 with N2

Abstract The degree of graphitization of the carbon formed through the reaction of UC2 with nitrogen gas was studied as a function of temperature and nitrogen pressure. The degree of graphitization increases with increasing temperature and with decreasing nitrogen pressure. From these results, it might be concluded that the scattering results obtained by the reaction of UC with nitrogen gas is due to the different degree of graphitization of the precipitating carbons. In order to study the equilibrium of the two-phase region of UC-UN solid solution and free carbon, that is, the relation between temperature, nitrogen pressure and the composition of the UC-UN solid solution, it should be necessary to employ the mixture of UN and graphite as the starting material.

Reaction of several iron and nickel based alloys with sintered Li2O Pellets

Abstract The reaction of type 316 stainless steel, Incoloy 800, Hastelloy X-R, Inconel 600 and pure Ni with sintered Li 2 O pellets has been studied between 800 and 1100°C under dynamic vacuum. The reaction products were analyzed by means of metallographic, microprobe and X-ray diffraction methods. The reactions proceeded measurably between 800 and 950°C and appreciably at 1000°C, being greatest with Incoloy 800 and least with Hastelloy X-R. Among the primary alloy constituents, chromium was exclusively attacked by lithium and oxygen diffusing from the Li 2 O into the alloys to form LiCrO 2 . This phase grew into a reaction zone (subscale) of uniform thickness beneath the surface of each alloy. Preferential growth of LiCrO 2 along the grain boundaries was observed only in the case of Inconel 600 below 950°C. On the other hand, iron diffused toward the Li 2 O pellets to form volatile Li 5 FeO 4 . However, any reaction product associated with Ni was not detected and Ni metal was little attacked by the Li 2 O pellet over the whole range of reaction temperature.

On the formation of UC-UN solid solutions

Abstract In order to elucidate the mechanisms of the formation of the solid solution between UC and UN, some experiments were carried out using several kinds of combination as the starting materials; (i) UC, (ii) UC 2 , (iii) UC + UN and (iv) UN+graphite. The conclusions drawn from these experiments are: 1. (1) Free carbon precipitating through the reaction of UC with nitrogen gas is not graphite but amorphous carbon with more or less incomplete graphitization. The degree of graphitization is a function of temperature. These amorphous carbons may have been a frequent cause of the scattering results obtained by many workers up to the present time. 2. (2) The mixture of UN and graphite is the best combination as the starting materials to investigate the equilibrium of the region consisting of UC-UN solid solution and free carbon, from both equilibrium and kinetic points of view. 3. (3) During the course of the reactions, UC + N 2 and UN + graphite, an intermediate state may appear, which includes two phases of UC-UN solid solutions, one having the composition corresponding nearly to the equilibrium one and the other being a solid solution with the composition different from the equilibrium one. The diffusion of non-metal atoms through the UC-UN solid solution-layer may control the overall reaction.

Graphitization of free carbon precipitating due to the reaction of UC with N2

Abstract The degree of graphitization of the carbon precipitating due to the reaction of UC with nitrogen gas was studied as a function of temperature and nitrogen pressure. The degrees of graphitization were investigated in terms of the reflection angle 2θ B , half-width B M and crystallite size t , which were determined from the (002) peaks of X-ray diffractometer patterns for these carbons. The result of the present work shows that the degree of graphitization increases with increasing temperature and with decreasing nitrogen pressure. The dependence of graphitization on nitrogen pressure can be explained well by a thermodynamical analysis of the reaction of UC with nitrogen gas.

The solubility of hydrogen in NbMo alloy

Abstract The solubility of hydrogen in Nb and in alloys of Nb and Mo containing an atomic fraction of Nb between 0.90 and 0.50 was measured in the temperature range 300 – 600 °C, at hydrogen pressures of 3 – 600 mmHg. From the results thermodynamic quantities of dissolved hydrogen were evaluated. It was found that the nature of the interaction between the hydrogen atoms changes from attractive to repulsive as the molybdenum content increases. The variation of the relative partial molar enthalpy of the dissolved hydrogen with the Mo content is discussed in terms of the electronic structure of the alloy.