Studies on the Reaction of Thorium with Graphite at High Temperatures

The reaction of thorium metal with graphite was studied in the temperature range of 900℃ to 1600℃. It was found that the reaction rate was parabolic and the activation energy for the reaction was 53 kcal/mole below 1200℃. Marker experiments showed that the growth of the carbide film was due mainly to the migration of carbon. From these results the rate determining process of the reaction seems to be the diffusion of carbon through the carbide film formed on the metal surface. Hydrocarbons, yielded by hydrolysis of the carbide film, were analysed by the gas-chromatographic method, from which the ratio of ThC/ThC_2 in the carbide film was determined. The film formed below 1200℃ was composed of ThC only. However, in the film formed above 1300℃ the ratio of ThC/ThC_2 decreased with increasing temperature. These results were confirmed by the X-ray diffraction technique. Parabolic rate constants for ThC and ThC_2 formations and apparent rate constants for the carbide film growth were obtained from the rate constant of the total carbide formation and the ThC/ThC_2 ratio in the carbide. The activation energy for the ThC_2 formation was found to be 120 kcal/mole from the results above 1300℃. The diffusion coefficient of carbon in ThC was calculated from the rate constants for the carbide formation. The amount of thorium carbide which forms in a thorium blanket of a graphite matrix fuel reactor was estimated

Studies on the β-ε Transformation in Cobalt-Nickel Alloys. I : Propagation Process of the Transformation

The propagation of the diffusionless transformation of the f.c.c. structure (β) into the h.c.p. structure (ε) in cobalt-nickel alloys was microscopically investigated. As the transformation proceeds, many narrow relief markings such as slip lines appeared in parallel to the {111}_β in flat free surface of the alloy. The cross section of each marking was a ridge or a valley with almost definite slopes on both sides but not symmetrical, and their inclinations were always less than 20°; its width was about 1～2μ. In pure cobalt, however, no marking was observable. The rate of growth of an ε crystal was less than ten-thousandth of that of a "Umklapp" martensite in steel, and these transformation processes are very resemble, when viewed from the growth rate, habit plane and structure of relief marking, to the "Schiebung" type of martensite in steel

Studies on the β-ε Transformation in Cobalt-Nickel Alloys. II : Microstructure of Transformation Relief

The dislocation model for the mechanism of diffusion-less transformation of the f. c. c. structure β into the c. p. h. ε in cobalt-nickel alloys was studied from electron-microscopic observation of relief markings on the crystal surface formed by the transformation. It can be considered that the transformation of β into ε proceeds through the motion of half-dislocations (α/6) [121]_β, (α/6)[211]_β, and (α/6) [112]_β in the (111) plane of a f. c. c. crystal. When these half-dislocations move in all directions over the crystal surface, tilts having three different inclinations to the surface are formed, which can be estimated to be 19°28\u27, -10°2\u27 and -10°2\u27, respectively, if the surface is parallel to the (112)_β plane, while under an external stress only one type of half-dislocations similar in direction to the stress can be considered to move, and then only one sort of the tilts is preferred. These surface tilts result in the relief markings on the crystal surface. The above results predicted theoretically were confirmed by electron-microscopic observation of markings, and it was found that the width of the zone of homogeneous displacement in marking (about 0.1～1μ for 25 per cent nickel alloy) decreased slightly with decreasing nickel content, but in alloys containing less than a few per cent of nickel it decreased abruptly and in pure cobalt it was of the order of 100A

The Reaction of Uranium with Graphite at High Temperatures

The reaction of uranium metal with graphite was studied in the temperature range of 800°to 1100℃. It was found that the reaction rate is parabolic and that the activation energy for the reaction is 59 kcal/mole. Marker experiments showed that the growth of the carbide film was due mainly to the migration of carbon. From these results the rate determining process of the reaction seems to be the diffusion of carbon through the carbide film formed on the metal surface. Hydrocarbon, yielded by hydrolysis of the carbide film, was analysed by the gas-chromatographic method. From these results it was confirmed that the film formed in this temperature range was composed of UC only. These results were confirmed by the X-ray diffraction technique. From these parabolic rate constants, the self-diffusion coefficients of carbon in UC were calculated. These values were extrapolated and found to agree well with Chubb\u27s results by tracer technique

Th-ThC Phase Diagram

The partial phase diagram in the Th-C system between pure Th and ThC was studied by metallographic and X-ray techniques and by measurements of electrical resistivity in quenched and slow cooled Th-C alloys. The peritectic point of the reaction, liq.+ThC⇄α-Th, was found at 16 at%C and about 1875℃ and the peritectic composition of ThC was 33 at%C. The eutectic reaction occurred at 1650℃ and its composition of α-Th and β-Th was 6.5 and <0.5 at%C, respectively. The α⇄β transformation temperature rose gradually with the carbon content up to 2.3 at%C and rose rapidly between the compositions of 2.3 and 3.7 at%C. The phase boundaries of α/ThC+α, ThC+a/ThC. ThC/ThC+ThC_2 and liq.+ThC/ThC were also established

Solubility of Hydrogen in Titanium at 900°to 1500℃

The temperature-pressure-concentration relationships of the hydrogen-titanium system have been studied at 900°to 1500℃ by a modified volumetric method, and the solubilities of hydrogen at pressures of 1 to 760 mm of mercury have been determined. The free energy-mole fraction curves for β-hydrogen-titanium solutions have been plotted for a number of temperatures, and the results have been compared with Mc-Quillan\u27s results obtained at temperatures below 950℃

Charts for Determination of Crystal Orientation by Surface Traces in Cubic Crystals

A useful method for the determination of the orientations of crystal grains in polycrystalline specimens having cubic lattice structure was found from the observation of angles between the surface traces such as slip lines, annealing twins or etch-pits which are developed in {111} or {100} planes. From the computation of relations between the angular co-ordinates (ξ, η) of the crystal orientation and the intertrace angles (α, β, etc.) in various directions of {111} or {100} traces, isogonic lines of the intertrace angles were plotted at the interval of two degrees. The case of {111} traces only in three directions was also discussed, and the relations between the angles of the three traces and the number of possible orientations corresponding to the same traces were explained. When the angle between the {100} traces was large, considerable errors were unavoidable in determining the orientations, but an accurate determination was possible if {100} and {111} traces were used in combination. The relations for such a combination were also calculated and plotted in the form of chart. By using these charts, the crystallographic orientations of crystal grains could be determined very rapidly and accurately