Shigeyuki Somiya

Microstructure and mechanical properties of hydroxyapatite ceramics with zirconia dispersion prepared by post-sintering.

Hydroxyapatite ceramics with zirconia dispersion from fine powders synthesized hydrothermally were post-sintered at 1000-1300 degrees C under 200 MPa of argon for 1 h without capsules, after normal sintering in air at 1200 degrees C for 3 h. Densification was most significant with post-sintering at 1200 degrees C. Fracture toughness, Vickers hardness and elastic properties of these materials were investigated. Post-sintering gave twice the K1c value of transparent pure hydroxyapatite ceramics. Vickers hardness and Youngs modulus of the ceramics were increased by post-sintering.

Oxygen isotope fractionation factors between anhydrite and water from 100 to 550°C

Oxygen isotope exchange between anhydrite and water was studied from 100 to 550°C, using the partial equilibrium method. The exchange rate was extremely low in NaCl solution. In the lower-temperature range, acid solutions were used to produce sufficient reaction to determine the oxygen isotope fractionation factors. The fractionation factors obtained in the present study are definitely different from those given by Lloyd [8]. They are similar to those for the HSO4−-water system studied by Mizutani and Rafter [19], and are consistently 2‰ higher than those of the barite-water system by Kusakabe and Robinson [5]. The temperature dependence of the oxygen isotope fractionation factors was calculated by the least squares method in which the weight was taken to be inversely proportional to the experimental error. The fractionation is given by:103lnαanhydrite-water=3.21×(103/T)2−4.72 Available δ18O values of natural anhydrite were used to test the validity of this expression. It is shown that this newly revised geothermometer can be successfully applied to natural hydrothermal anhydrite.

Hydrothermal crystal growth of magnetite in the presence of hydrogen

Magnetite single crystals have been grown by spontaneous nucleation on the inner wall of a gold capsule under hydro-thermal conditions which included hydrogen. The hydrogen for the control of the reduced atmosphere was supplied by the reaction of charged metallic iron with water. The leakage of the hydrogen through a gold capsule was found to be 2% of the net quantity of the hydrogen calculated from the charged iron at 550°C for 21 days under 1000 kg/cm2. The leakage was increased due to the grain growth of the wall of the gold capsule with the increases of the growth period and the concentration of solution used. The {l 10} faces of magnetite were found to predominate over the normal {111} faces as the concentration of the hydrogen was increased. Optimum conditions to grow bulky single crystals of magnetite were as follows: 10m NaOH as a solution; crystallization temperature 500°C; percent fill of free volume, about 55%; ΔT, 50°C. No formation of hematite was observed in the present work. Dendritic magnetite crystals were grown in 5m NH4CI solution at 500°C under 1000 kg/cm2.

Synthesis of vanadium sulfides under high pressure

Vanadium sulfides were synthesized in a temperature range of 350–750°C and in a pressure range of 10–250 MPa (1 MPa = 9.87 atm), with an apparatus used for hydrothermal synthesis. The nonstoichiometric compositional range of the V1+x S2 phase, which cannot be prepared under atmospheric pressure, is VS1.661−VS1.732 (0.155 <x < 0.204). It was impossible to synthesize vanadium disulfide VS2 under the present experimental conditions. Equilibrium phase diagrams for the V5S8−S system under 100 and 200 MPa have been proposed on the basis of the present results. Also, the phase relationship between V5S8 and V1+x S2 has been established and a pressure-temperature phase diagram for the V−S system has been drawn.

Crystal Growth of Sodium Iron Titanium Bronze Compounds under Hydrothermal Conditions

Single crystals of four types of oxides consisting of sodium iron and titanium were grown hydrothermally under reduced conditions starting with a mixture of TiO2 (rutile) and metallic Fe powder in the ratio 5:1 (weight basis) at 650°C and 1000kg/cm2 in 10m NaOH solution for different durations. Formation of single crystals having an orthorhombic cell was observed after one week. In longer runs under the same conditions the initial phase undergoes transformation to form crystals having hexagonal and orthorhombic cells and finally to monoclinic freaudenbergite (Na2O·Fe2O3·7TiO2). From Mossbauer and EPMA data, the common chemical formula for these new phases can be written as (NaxFe y 2+ ) · [TipFe q 2+ Fe r 3+ O2-δ)]n.

Preparation of Zirconia-Alumina Fine Powders by Hydrothermal Oxidation of Zr-A1 Alloys

Fine powders of pure metal oxides can be prepared by hydrothermal oxidation method. This technique can provide the fine powders of homogeneous ZrO2-Al2O 3 mixtures from Zr-Al alloys at temperatures 600-700 °C under 100 MPa pressure for 3 h, according to the reactions,

Stability regions of cubic and tetragonal phases in the system ZrO2YF3YO1.5

Abstract The phase relations in the system ZrO 2 YF 3 YO 1.5 have been investigated. Solid state reactions were carried out using encapsulated samples to prevent compositional changes. At 1300°C the ternary system contains 2 single-phase regions of tetragonal (T) and cubic (C) phases, 3 two-phase regions of T+YF 3 , C+YF 3 and C+T, and 1 three-phase region of C+T+YF 3 . The solubility limits determined from lattice parameters were found to be 8.5 mol% YOF along the ZrO 2 YOF join for the tetragonal phase, and 4.5 mol% YF 3 for the cubic phase, respectively.

Catalytic properties of Hf−Eu oxide fine crystalline powders. Isomerization of n-butenes

Catalytic properties of a series of HfO2−Eu2O3 fine crystalline powders were examined by the isomerization of n-butenes. HfO2 pretreated at 873 K showed a high activity. It decreased with the addition of the Eu component. The product distributions are discussed on the basis of the acid-base properties.AbstractКаталитические свойства ряда тонкокристаллических порошков HfO2−Eu2O3 исследовали в изомеризации н-бутенов. HfO2, подверженный предварительной обработке при 873 K, обладает высокой активностью. Последняя уменьшается с добавкой Eu. Распределение продуктов обсуждается на основе кисло-основных свойств.

The Processing of a Permalloy-Magnetite Composite by Hydrothermal Reaction Sintering

The water-atomized permalloy powder and redistilled water were hermetically sealed in a platinum capsule and treated in a high pressure, high temperature apparatus using Ar gas as the pressuring medium. The sintered composites thus produced were examined by X-ray diffraction, optical and scanning electron microscopy, and energy dispersive spectroscopy. The sintered composite of Fe-Ni alloy and iron oxide can be made by hydrothermal reaction sintering, where the composition of iron oxide is controlled by the water/alloy ratios and temperatures.