Showing papers by "Masahiko Shimada published in 1987"

Synthesis and Thermal Stability of Aluminum Titanate Solid Solutions

Abstract: Aluminum titanate solid solutions with empirical formulas of Al2Ti1-xZrxO5, Al6(2-x)(6+x)Si6x/(6+x)□6x/(6+x)TiO5, and Al2(1-x)MgxTi1+xO5 were synthesized by reaction sintering and annealed at 900° to 1300°C in air to evaluate the thermal stability. Substitution of Al in Al2TiO5 by Si and 2Al by Mg and Ti ions to form solid solutions such as AI6(2-x)/(6+x)l-Si6x/(6+x)□6x/(6+x)TiO5, and Al2(1-x)MgxTi1+xO5 was effective in controlling the thermal decomposition, but substitution of Ti by Zr had little effect.

High-pressure synthesis of B2O with diamond-like structure

Abstract: Synthese d'un nouveau compose B 2 O ayant une structure diamant par reaction de BP avec l'oxygene, et determination de sa maille cristalline (groupe d'espace P3). Ce compose est un semiconducteur ayant une grande resistance a l'oxydation a haute temperature et a la corrosion

High temperature oxidation of hot-pressed aluminium nitride by water vapour

Abstract: Hot pressed AIN without additives was oxidized et 1100 to 1400°C in dry air, wet air and wet nitrogen gas atmospheres with 1.5 to 20 kPa of water vapour pressure. AIN was oxidized by both air and water vapour, and formed α-Al2O3 film on the surface above 1150°C. The oxidation kinetics in air were parabolic end were promoted by water vapour. On the other hand, the oxidation kinetics in wet nitrogen were linear below 1250°C and parabolic above 1350°C. The oxidation rate in wet nitrogen was much greater than that in wet air. The rate of oxidation increased with increasing temperature until 1350°C, and then decreased. The parabolic rate constant decreased with increasing temperature and increased linearly with increasing water vapour pressure. The linear rate constant at 1150 to 1250° C increased with increasing the temperature with the apparent activation energy of 250 kJ mol−1. The relation between the linear rate constant and water vapour pressure was of the Langmuir type.

Joining of silicon nitride to silicon nitride and to invar alloy using an aluminium interlayer

Abstract: Si3N4 has been bonded to Si3N4 and to the Invar alloy using an aluminium interlayer at temperatures above the melting point of aluminium. Reaction was hardly observed at the interface between Si3N4 and aluminium up to 1223 K. The highest strength of the Si3N4-Al-Si3N4 joints was beyond 500 M Pa. In the Si3N4-Al-Invar joint, two main intermetallic compound layers were formed at the AI-Invar interface. The strength of the joints was between 150 and 200 MPa. It is expected that the aluminium layer and the reaction layer with the fine cracks growing perpendicular to the interface play an important role to compensate for the thermal expansion mismatch.

High-temperature oxidation of silicon nitride-based ceramics by water vapour

Abstract: Hot-pressed Si3N4, sintered Si3N4 and three kinds of sialon with different compositions were oxidized in dry air and wet nitrogen gas atmospheres at 1100 to 1350° C and 1.5 to 20 kPa water vapour pressure. All samples were oxidized by both dry air and water vapour at high temperature, and formed oxide films consisting of SiO2, Y2Si2O7 and Y4A1209. The oxidation rate was in the order sialon > sintered Si3N4 > hot-pressed Si3N4. The oxidation rate of sialon increased with increasing Y2O3 content, and oxidation kinetics obeyed the usual parabolic law. The oxidation rates in dry air and wet nitrogen were almost the same: the rate in wet nitrogen was unaffected by water vapour pressure above 1.5 kPa. The activation energy was about 800 kJ mol−1.

Thermal stability and mechanical properties of yttria-doped tetragonal zirconia polycrystals with dispersed alumina and silicon carbide particles

Abstract: Yttria-doped tetragonal zirconia polycrystals in which were dispersed various amounts of Al2O3 and SiC particles were sintered at 1500° C for 3 h, and the mechanical properties and the thermal stability of the sintered bodies were evaluated. Dispersion of Al2O3 caused no significant effect on sinterability, and increased the hardness and elasticity of the composites. Dispersion of SiC particles decreased the relative density and the grain size of composites. Elasticity and hardness increased by dispersing less than 10 vol% SiC, but decreased above 10 vol% SiC due to the decrease of relative density. Dispersion of both Al2O3 and SiC particles slightly increased the fracture toughness of ZrO2-3 mol% Y2O3 ceramics but significantly decreased that of ZrO2-2 mol% Y2O3 ceramics. The rate of the tetragonal-to-monoclinic phase transformation decreased by dispersing both Al2O3 and SiC particles. The transformation depth increased rapidly and then slowly with increasing the annealing time. The rate of increase in the transformation depth greatly decreased by dispersing Al2O3 particles.

Enzyme Sensors Based on Coated-Wire Electrode. Use of Carboxyl-Substituted Poly(vinyl chloride) as a Support for Immobilizing Penicillinase

Abstract: A poly(vinyl chloride) derivative which contained 1.8% carboxyl residue was used to prepare a potentiometric sensor sensitive to penicillin G. A pH-sensitive base electrode was fabricated by covering an Ag wire electrode with the membrane composed of the carboxyl-substituted poly(vinyl chloride), o-nitrophenyl octyl ether, and tridodecylamine. The sensitive layer of the pH-sensitive electrode was modified with penicillinase to make a penicillin-sensitive electrode. Penicillinase was adsorbed to the surface of the polymer membrane by immersing the sensitive layer of the electrode in the penicillinase solution. Treatment of the pH-sensitive electrode with ca. 0.3% penicillinase solution at pH 6.7 (1 mM phosphate buffer) resulted in favorable performance of the penicillin sensor. The long-term stability of the penicillin sensor thus prepared was satisfactorily good.

Sintering and Mechanical Properties of Yttria‐Doped Tetragonal ZrO2 Polycrystal/Mullite Composites

Abstract: Yttria-doped tetragonal ZrO/sub 2/ polycrystal (Y-TZP)/mullite composite were sintered at 1450/sup 0/ to 1500/sup 0/C in air to disperse rodlike mullite grains at the grain boundary of Y-TZP and the mechanical and thermal properties were investigated. The aspect ratios of mullite grain were >2. High fracture strength of 1000 MPa and fracture toughness of 12 MPa.m/sup 1/2/ were obtained by dispersing <20 vol% of mullite into Y-TZP. The thermal expansion coefficient of Y-TZP/mullite composites decreased with increasing mullite content. The thermal shock resistance of Y-TZP was greatly improved by dispersion of rodlike mullite grains.

Corrosion of Si sub 3 N sub 4 in molten alkali sulfate and carbonate

Abstract: Corrosion behavior of Si{sub 3}N{sub 4} ceramics in various molten alkali sulfates and carbonates exposed to air and nitrogen gas were investigated at 900{degree} to 1,200{degree}C and 700{degree} to 1,013{degree}C, respectively. The minimum reactant molar ratios of K{sub 2}SO{sub 4}/Si{sub 3}N{sub 4} and K{sub 2}CO{sub 3}/Si{sub 3}N{sub 4} necessary for complete reactions in a nitrogen gas were 1.6 and 3.5, respectively. The surface chemical reaction control shrinking core model adequately described the relation between reaction time and fractional extraction of Si{sub 3}N{sub 4} in alkali sulfate and alkali carbonate exposed to nitrogen gas atmosphere. The apparent activation energies for the reactions of Si{sub 3}N{sub 4} in alkali sulfate and alkali carbonate melts exposed to nitrogen gas were 430 kJ/mol and 106 kJ/mol, respectively, and were independent of the alkali cation species in the melt.

Fabrication of Potentiometric Enzyme Sensors Based on a pH-Sensitive Polymer-Coated Ag Electrode

Abstract: A silver wire electrode coated with a poly (vinyl chloride) /tri-n-dodecylamine composite membrane was used to fabricate potentiometric enzyme sensors. The coated Ag electrode was further covered with a penicillinase or urease membrane to make a penicillin or urea sensor, respectively. The penicillin sensor was useful for determining penicillin at concentrations of millimolar level. Some operating variables such as pH and ionic concentration of the working buffer of the sensor were examined. The urea sensor could be used to determine urea in human blood.

Transformation of Tetragonal Zirconia Polycrystals by Annealing under Humidity Controlled Conditions

Abstract: Changes in the crystalline phase and microstructure on the surface resulting from low-temperature annealing of tetragonal zirconia polycrystals doped 2, 3 and 4 mol% Y2O3 were investigated under humidity controlled conditions at 0-7.35kPa of water vapor pressure and 100-600°C for 1-50hr. The tetragonal phase ZrO2 transformed to the monoclinic structure by annealing at low temperature conditions such as 100-500°C. The phase transformation caused microcracks on the surface and resulted in significant loss of fracture strength. The critical temperatures of the phase transformation of ZrO2-2 mol% Y2O3, ZrO2-3 mol% Y2O3 and ZrO2-4 mol% Y2O3 were 500, 400 and 350°C, respectively. The phase transformation proceeded rapidly on the surface but quite slowly inside the body. The rate of the phase transformation on the surface was first order with respect to the concentration of the tetragonal ZrO2 and increased with increasing water vapor pressure by Langmuir type relation. The appearent activation energy of the phase transformation was about 85kJ/mol.

Production of long fibrous alkali metal salt of titanic acid

Abstract: PURPOSE:To obtain a long fibrous alkali metal salt of a titanic acid which has a large aspect ratio and high mechanical strength such as bending strength and tensile strength by calcining a mixture composed of a titanium source compd, oxygen-contg alkali metal compd and a slight amt of oxygen-contg iron compd in a specific temp range CONSTITUTION:The mixture composed of the titanium source compd, oxygen- contg alkali metal compd and a slight amt of the oxygen-contg iron compd is calcined in a temp range of about 900-1,350 degC The mixing ratio of the titanium source compd and the oxygen-contg alkali metal compd is preferably 40-22 molar ratio of TiO2/M2O (M is an alkali metal) and the ratio of the oxygen-contg iron compd to be added is preferably not in excess of 04 molar ratio of Fe2O3/TiO2 The nitrate of an alkali metal is particularly preferable as the oxygen-contg alkali metal compd The oxygen-contg iron compd is exemplified by the nitrate, sulfate, chloride, oxide, hydroxide, etc, of iron The titanium source compd is exemplified by titanium oxide, rutile ore, titanium hydroxide wet cake, hydrous titania, etc

Synthesis and Thermal Stability of Aluminum Titanate Solid Solutions.

Abstract: Aluminum titanate solid solutions with empirical formulas of Al2Ti1-xZrxO5, Al6(2-x)(6+x)Si6x/(6+x)□6x/(6+x)TiO5, and Al2(1-x)MgxTi1+xO5 were synthesized by reaction sintering and annealed at 900° to 1300°C in air to evaluate the thermal stability. Substitution of Al in Al2TiO5 by Si and 2Al by Mg and Ti ions to form solid solutions such as AI6(2-x)/(6+x)l-Si6x/(6+x)□6x/(6+x)TiO5, and Al2(1-x)MgxTi1+xO5 was effective in controlling the thermal decomposition, but substitution of Ti by Zr had little effect.

Germanide manganease and its production

Abstract: PURPOSE: To produce monogermanide manganese having a B20 type structure, by mixing nearly the stoichiometric amount of Mn and Ge and bringing them into reaction with under specific high pressure and high temp. conditions. CONSTITUTION: Nearly the stoichiometric amount of Mn and Ge are mixed to bring them into reaction with under the pressure of ≥1 GPa and at the temp. of 600W1,300°C in the base of producing monogermanide manganese which has the B20 type structure and can be expressed by the empirical formula MnGe. High purity Mn and Ge are preferably used as the above-mentioned materials and are preferably subjected to a reduction treatment with hydrogen, etc., at need, to remove an oxide. Said high temp. high pressure synthesis is executed under the pressure of ≥1 GPa, more preferably about ≥3 GPa by using a belt type high pressure apparatus, etc. The reaction temp. is furthermore required to regulate to 600W1,300°C since Ge is not melted at 1,300°C. COPYRIGHT: (C)1988,JPO&Japio

Enzyme-reaction-dependent Photoresponse of Poly (vinyl chloride)/spirobenzopyran Membrane

Abstract: The magnitude of photoinduced membrane potential across a poly (vinyl chloride) /spirobenzopyran membrane highly depended upon the urease-catalysed decomposition reaction of urea on the surface of the membrane.

Solid State Bonding of Alumina and Steel by Hiping

Abstract: The internal stress due to thermal expansion mismatch between alumina and steel with and without an interlayer is evaluated. On the basis of the results of calculation, solid-state bonding experiments between alumina and steel using the interlayer method are carried out at 1000–1400°C under a pressure of 100 MPa for 30 min using hot isostatic pressing technique. When the laminated interlayer (niobium/molybdenum) is used, the joint with high bonding strength of 500 MPa is obtained and no significant microstructural change in interface is observed. The results of thermal cycle tests between 25°C and 500°C reveal that the laminated interlayer is superior as the interlayer material.