Shinzo Nomura

Study on U4O9—part II. Magnetic susceptibility of U4O9

Abstract The magnetic susceptibility of U 4 O 9 has been measured over the temperature range 77–500°K, showing paramagnetic behavior. At 330°K where U 4 O 9 shows a λ-type anomaly in the specific heat, no magnetic transition has been observed. The susceptibility of 1 4 U 4 O 9 after correction for diamagnetism is expressed by the equation X = 420 × 10 −6 + 0.530/( T +55) cm 3 from which the effective moment and the Weiss constant of 1 4 U 4 O 9 can be derived as 2.06 B.M. and 55°K respectively. The susceptibility data have been discussed in terms of ground state configurations f 2 and f 1 perturbed by the crystalline field, and it is likely that the composition of U 4 O 9 involved a U(IV)-U(V) mixture.

The effect of organic substituents and structure of organophosphorus compounds on their extraction abilities for uranium

Abstract With 12 phosphates, 1 phosphonate, 1 phosphinate and l phosphine oxide, the pattern of uranium extraction from nitric acid media was investigated. The extraction was affected by the nature of the organic substituents attached to the phosphoryl group as well as by the solvent structure. Phosphates with aryl groups were not satisfactory extractants. The extraction ability increased as the alkyl group was made larger; phosphates with branching alkyl groups were better than phosphates with normal alkyl groups. Removal of the alkoxyl oxygen enhanced the extracting abilities. The relative order of the extracting abilities were: tri-nbutyl phosphine oxide and tri-n-butyl phosphinate > tricyclohexyl phosphate > diethylbutly phosphonate > phosphates with; branching alkyl groups > phosphates with normal alkyl groups > phosphates with arly groups.

The reaction of nuclear graphites with hydrogen

Abstract The corrosion reactions of various nuclear graphites with hydrogen were studied in the temperature range 970–1090°C at hydrogen partial pressures between 7 and 48 torr in helium stream of total pressure of 1 atm. Methane was the only gaseous product found in this reaction. The rates of corrosion reaction were found to be 10−1 ~ 10−2 μg/cm2 hr on the basis of methane yield at 28 torr hydrogen pressure at 1025°C. The influence of the hydrogen partial pressure on the methane production rate is expressed as: R=K(P H 2 ) 3 2 . The apparent activation energy for the reaction was found to be 22 kcal/mol, independent of the impurity content of the graphite. No clear correlations were found between the production rate of methane and the total ash content in the graphite, its degree of crystallinity (determined by X-ray diffraction) and its degree of graphitization (infered from butanol immersion density).

Functionally gradient material of silicon carbide and carbon as advanced oxidation-resistant graphite

For advanced graphite materials, functionally gradient material (FGM) of silicon carbide and carbon (SiC/C) has been prepared in order to improve the oxidation resistance. The FGM of SiC/C prepared by the reaction between graphite and gaseous silicon monoxide, 2C(solid) + SiO(gas) → SiC(solid)+ CO(gas), at high temperatures of around 1350°C has a gradient in the concentration of SiC in the graphite matrix, i.e. the ratio of SiC to C in the matrix gradually decreases toward inside, and exhibites better oxidation resistance compared with virgin graphite material.

Changes in young's modulus and electrical conductivity of nuclear grade graphites oxidized with air

Abstract Five kinds of nuclear grade graphites were oxidized to study thermal oxidation effects on Youngs modulus and electrical conductivity. The property changes were measured on specimens which were oxidized uniformly throughout their whole volume in the temperature range 500–600°C in air. The following relations were derived as a function of the bulk density of the graphites: E/E0 = (ρ/ρ0)nE and R0/R = (ρ/ρ0)nR, where E, R and ρ are Youngs modulus, specific electrical resistivity and bulk density, respectively, and subscript zero refers to the initial unoxidized condition. The exponents nE and nR were found to be dependent on both the kind of graphite and the oxidation temperature, and the dependences were discussed in connection with selective oxidation in the graphite texture. It was also tried to relate the property changes with oxidation rate.

Oxidation behavior of boronated graphite in helium, containing water vapor

Abstract Oxidation tests of boronated graphite, which has been adopted as a neutron absorber material in the HTTR (High Temperature Engineering Test Reactor), were carried out in helium, containing water vapor, at up to 1000°C from a viewpoint of oxidation of B4C. It could be shown that the oxidation reaction of the boronated graphite consists of three reactions, i.e. B4C + 6H2O → 2B2O3 + 6H2 + C(freecarbon), C(freecarbon) + H2O → CO + H2 and C(graphite) + H2O → CO + H2, and that the oxidation rates of the boronated graphite do not monotonously increase with temperature and are lower than that of graphite material due to the production of B2O3