Keiji Naito

Studies on cubic magnesium uranate, MgyU1−yO2+x—I: Phase relations and crystal chemistry

Abstract Cubic magnesium uranate, Mg y U 1− y O 2+ x , was prepared by the reaction of the mixtures of MgUO 4 , MgU 3 O 10 and/or UO 2 in a stream of helium. The cubic region and the values of x and y in Mg y U 1− y O 2+ x were studied under various reaction conditions. Density measurements of this compound gave a strong support to a substitutional structure. The variation of lattice constant with composition was observed to follow a linear equation, a 0 = 5·4704−0·1170x−0·5677 y . Equilibrium oxygen pressure was found to increase with magnesium concentration. The results were discussed by modifying the equation to express partial molar entropy of oxygen given by Aronson and Clayton to valence control type Mg y U 1− y O 2+ x .

X-ray study on a phase transition of U4O9

Abstract Some features of the transition of U 4 O 9 were investigated by means of X-ray diffractometry. Transition temperature of the U 4 O 9 phase varies from 65 to 96°C with O/U ratios and, at the transition, a notable increase in the intensity of superlattice reflection of U 4 O 9−y with temperature was observed.

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.

Study on U4O9—part I. An anomaly of the heat capacity near the room temperature

Abstract The specific heat of U 4 O 9 was measured over the range 300–520°K. A λ-type anomaly with a maximum at 330°K was observed. The entropy and enthalpy increments associated with the λ-type transition are about 2.00 e.u. and 680 cal per mole of U 4 O 9 , respectively. This transition may be related to a small contraction of the lattice constant of U 4 O 9 from room temperature to 80°C.

On the dielectric properties of U4O9 and UO2

Abstract Dielectric properties of U4O9 and UO2 were measured at various temperatures and at various frequencies. From the experimental result the phase transition in U4O9 at about 80°C is not considered to be ascribed to dielectric origin. The dielectric constants of both U4O9 and UO2 increase as the temperature increases.

A study of ammonium plutonium(IV) fluorides—II: The thermal decomposition of ammonium plutonium(IV) fluorides, ammonium cerium(IV) fluoride and ammonium uranium(IV) fluoride

Abstract Thermal decomposition of PuF 4 · 7 6 NH 4 F (or PuF4·NH4F), PuF4·2NH4F, CeF 4 · 7 6 NH 4 F (or CeF4·NH4F) and UF 4 · 7 6 NH 4 F (or UF4·NH4F) have been studied under vacuum and in inert gas flow, using a microthermobalance. The anhydrous PuF3, CeF3 and UF4 were obtained as the decomposition products. The following reactions appeared to occur in thermal decomposition of these double salts. 1 M F 4 · 7 6 NH 4 F = M F 3 + 5 6 NH 4 F + 8 6 HF + 1 6 N 2 (M = Pu and Ce ) 2 UF 4 · 7 6 NH 4 F = UF 4 + 7 6 NH 4 F .

A study of ammonium plutonium(IV) fluorides—I: The preparation of ammonium plutonium(IV) fluorides

Abstract The preparation of ammonium plutonium(IV) fluorides from the mixed solution of 0–10M NH4F and 0–10M HF has been studied. The valency of Pu(IV) was adjusted by controlled potential electrolysis or by addition of NH4NO2 solution. The precipitates obtained from Pu(IV) adjusted by controlled potential electrolysis were pink 6PuF4·7NH4F (or PuF4 · NH4F) and green PuF4·2NH4F; the former was precipitated from 0·5-2M NH4F, while the latter from 4–10M NH4F, and mixed precipitates were obtained in the concentration region of 2–4M NH4F. The solubility of plutonium has a minimum at 0·5M NH4F and then increases rapidly with the concentration of NH4F. The precipitates obtained from Pu(IV) adjusted by NH4NO2 solution were a pink 6PuF4·7NH4F(or PuF4 ·NH4F) and a red new compound showing a different X-ray pattern and PuFNH3 mole ratio 1·0:5·6-5·8:0·7-0·8.

Studies on cubic magnesium uranate MgyU1−yO2+χ,—II

Abstract Cubic magnesium uranate, Mg y U 1− y O 2+ x , was prepared by the reaction of the mixtures of MgUO 4 , MgU 3 O 10 and/or UO 2 in a stream of helium. The cubic region and the values of x and y in Mg y U 1− y O 2+ x were studied under various reaction conditions. Density measurements of this compound gave a strong support to a substitutional structure. The variation of lattice constant with composition was observed to follow a linear equation, a 0 = 5·4704−0·1170x−0·5677 y . Equilibrium oxygen pressure was found to increase with magnesium concentration. The results were discussed by modifying the equation to express partial molar entropy of oxygen given by Aronson and Clayton to valence control type Mg y U 1− y O 2+ x .