Noriyasu Hotta

Particulate characteristics and deposition features of fine AIN powder synthesized by vapour-phase reaction

Fine AIN powder was synthesized by the vapour-phase reaction of AICl3 and NH3 at 600 to 1100° C, and the particulate characteristics and the deposition features were investigated. The powder deposited near the AlCl3-feeding nozzle included radially-grown particles with columnar crystals. The powder deposited apart from the AlCl3-feeding nozzle consisted of only fine, spherical particles. Vapour-phase reaction at 1100° C produced fine powder, which was characterized by uniform and fine particle size; its distribution width was from 0.1 to 0.3μm, and median diameter was 0.18μm. Deposition area of the powder was affected by the reaction temperature and the temperature profile in the reactor.

Sintering and characterization of Al2O3-TiB2 composites

Abstract Al 2 O 3 -TiB 2 composites containing 0–50 wt% TiB 2 were prepared by sintering at 1600–1750°C for 15–120 min in a vacuum. Relative density increased with TiB 2 addition from 97% (no TiB 2 ) to about 99% (10–40 wt% TiB 2 ) on sintering at 1750°C for 60 min. TiB 2 behaved as a sintering aid to promote densification by inhibiting rapid grain growth of Al 2 O 3 . Bending strength and microhardness increased with increasing relative density. In particular, microhardness was so improved as to exceed that of Al 2 O 3 and reach 30·1 GPa. Resistivity decreased with increasing TiB 2 content and dropped down to 3 × 10 −2 ω m with 30 wt% TiB 2 .

Synthesis of AlN/SiC composite powders by floating-type fluidized-bed CVD

Abstract Floating-type fluidized-bed CVD was studied with the aim of synthesizing fine particulate composites having a high uniformity of dispersion. SiC powder was floated into the reactor with an N 2 NH 3 gas mixture. The behavior of the floating SiC particles was observed, and it was found possible to steadily float finer particles in the floating-type fluidized-bed as compared with conventional fluidized-beds. AlCl 3 was fed into the reactor to deposit AlN particles onto the floating SiC particles at 800 to 1 100 °C. The composite ratio of AlN to SiC can be controlled by controlling the synthesis temperature, the AlCl 3 -feeding rate, and the flow rate of the gas mixture for flotation.

Synthesis of AlN by the nitridation of the floating Al particles in N2 gas

The nitriding reaction of floating Al particles in N2 gas was studied at 1350°-1550°C. The hollow spherical and fibrous AlNs formed were examined by X-ray diffraction and scanning electron microscopy. The nitriding reaction of floating Al particles in N2 gas proceeded in the following four steps: (i) floating Al particles melted and became spherical by surface tension, (ii) up to 1350°C the nitriding reaction was controlled by the diffusion of nitrogen through the AlN surface layer, (iii) cracks propagated in the AlN layer at 1400°-1550°C. The nitriding reaction rapidly proceeded with the eruption of internally melted Al, (iv) the eruption of Al also caused the nitriding reaction between vaporized Al and N2 gas to form AlN, resulting in hollow spherical AlN and fibrous AlN. The synthesized AlN was white, indicative of high purity. Since the particle size of floating Al was determined by controlling the N2 gas velocity, the classification of Al particles was possible. The mean size and size distribution of hollow spherical AlN particles formed were controlled within the range 4 to 12μm. The hollow spherical AlN particles were so brittle that they were easily crushed to fine particles even by fingers. Thus obtained AlN particles were very fine and had narrow size distribution of 0.1-0.2μm.

Effect of alumina and titania additions on properties of porcelain bodies from murakami sericite

Abstract The effect of alumina and titania additions on the properties of porcelain bodies fabricated from Murakami sericite by firing at 1100–1300°C was investigated. Additional alumina might have the dispersion strengthening effect so that the strength increased to 180 MPa, which was observed for the body fabricated by adding 30 wt% alumina and firing at 1200°C, approximately 50% higher than one with no addition. Furthermore, titania additions of 5 wt% caused the strength to improve markedly to 240 MPa by promoting formation of acicular mullite which may have a fiber-reinforcing effect. The Vickers micro hardness was also improved from 4·9 GPa to 7·3 GPa. The resistivity was 1012Ω.m, sufficient for an electric insulator.

Preparation of AlN-Al2O3 fibre composites using chemical vapour infiltration

Vapour-phase reaction of AlCl3 and NH3 at 800 to 1000 °C was performed, and AIN produced was made infiltrate an Al2O3 fabric to form AlN matrix-Al2O3 fibre composites. The composites were characterized by observation of the appearances and by analyses with X-ray diffraction and scanning electron microscopy. The matrices of the composites prepared at above 900 °C had lustrous, smooth surfaces and revealed the preferred orientation toc-axis. The composite was constituted by the substrate layer and the surface layer. The fibres in the substrate layer were covered with radially-grown, columnar AlN grains with a maximum height of 15 μm. The surface layer was a dense AlN film 50 μm thick. Both the layers interlocked each other with mediation of the radially-grown AlN grains covering the fibres. The formation mechanism of the composites was deduced from the morphology. The wettability with a molten dental alloy was very low.

Synthesis of Nitride Compounds Using Fluidized Bed

Compositionally uniform nitride powders were synthesized from metal oxide powders using a fluidized bed in NH3 or NH3-N2 flows. GaN was synthesized by a two-step heating ; the first step was done at 700°C for 1 h; the second step was done at 900°C for 4 h. GaN-ZnO solid solution was synthesized at 900°C for 4 h. The grain sizes of the products were smaller than those of the starting materials.

Solid State Reaction between Nb2O5 and CaO

Nb2O5焼結体とCaO焼結体とを重ね合わせて拡散対とし, Arガスふん囲気中1150°-1300℃で加熱してNb2O5-CaO系固相反応を調べた.生成する反応層を電子顕微鏡観察, X線マイクロアナライザー分析, X線回折及び熱膨張測定し, 次のような結果を得た.Nb2O5層とCaO層の境界面において, 1150℃と1200℃の温度でCaO・Nb2O5, 2CaO・Nb2O5, 立方晶3CaO・Nb2O5と斜方晶系化合物2相共存する層, 計3種類の反応層が生成し, 1250℃と1300℃の温度でCaO・Nb2O5, 2CaO・Nb2O5, 立方晶3CaO・Nb2O5, 立方晶3CaO・Nb2O5と斜方晶系化合物2相共存する層, 計4種類の反応層が生成した. これらはNb2O5中へのCaOの一方拡散により生じた. 生成した反応層の幅の大きさは, 2相共存層>3CaO・Nb2O5>2CaO・Nb2O5>CaO・Nb2O5, の順であった. この斜方晶系化合物は4CaO・Nb2O5よりもCaO成分が多い組成を有していると考えられた. また1150°-1300℃の温度ではこの斜方晶系化合物よりもCaO成分の多い化合物は存在しなかった.