High-purity SiC Research Articles

Processing of high-purity SiC composites by chemical vapor infiltration (CVI)

Carbon fiber/SiC(C/SiC) and SiC fiber/SiC(SiC/SiC) composites were fabricated by a chemical vapor infiltration method to obtain composites with high purity and high strength. The impurity concentrations in the materials were measured by neutron radioactivation analysis and their mechanical properties were examined with bending tests at room temperature. Neutron radioactivation analyses showed that the purities of C/SiC and SiC/SiC were better than 99.99 and 99.999 wt%, respectively. As a result of the evaluation of the induced activity under the simulation of fusion neutron irradiation, the composites were estimated to behave excellently in terms of low activation. The fracture strength of both C/SiC and SiC/SiC composites prepared from 2D preforms with five-layered cloths was about 200 MPa. Higher strength can be expected if the interlaminar strength of the composites was improved.

特集 ニューコンポジット材料 炭素繊維強化ＳｉＣ複合セラミックスの機械特性に及ぼす炭素繊維へのＳｉＣ被覆の影響 １

SiC thin film were continuously coated by CVD method on carbon bundle, which were consisted of thousands filaments. The film was made from high purity SiC and it was high dense. Each filaments of the bundle was coated homogeneously by sub-micron SiC. SiC⋅Cf/SiC composites were fabricated by using these surface modified carbon fibers. Characteristics and mechanical properties of SiC⋅Cf/SiC composite were compared with those of Cf/SiC composite. Mechanical properties of SiC⋅Cf/SiCcomposite differed from those of Cf/SiC composite. It was considered that the difference of them was caused by the decrease of the interfacial strength between fiber and matrix in SiC⋅Cf/SiC composites.

Wear of Media Balls during the Ball Milling of Si<sub>3</sub>N<sub>4</sub> Powder

Wear of six kinds of media balls during the ball milling of Si3N4 raw powder with additives was tested. The materials of the ball were α′/β′-SiAlON, β-Si3N4, high purity Al2O3, Al2O3 (HD-11), SiC and tetragonal ZrO2. The material of the least wear was α′/β′-SiAlON. The Si3N4 powder milled with SiC ball resulted in the mixture of Si3N4 with 13vol% of SiC. The powder consolidated to almost full density by the conventional gas pressure sintering.

特集 微粉末・微粒子・超微粒子技術 高純度ＳｉＣセラミックス

特集 微粉末・微粒子・超微粒子技術 高純度ＳｉＣセラミックス

The hierarchy of grain boundary structures

Grain boundaries in high-purity SiC bicrystals produced by sublimation-deposition were examined by high resolution electron microscopy, in order to elucidate the basic nature of the boundary atomic structures. The boundaries were found to be periodically ordered, and the classic coincidence-site lattice theory [Kronberg and Wilson, Trans. AIME 185 (1949) 501] was found to be useful not only as a geometrical basis for predicting low-energy interfaces, but also for finding the atomic structure. A description in terms of a hierarchy of atomic structures enabled the authors to characterize twin-related polytype crystal boundaries.

Solid Particle Erosion of Brittle Materials (Part 7)

Ten kinds of commercial ceramic tools were eroded by SiC and Al2O3 abrasives with an average diameter of 500μm at 250-300m/s. These ten kinds of commercial ceramic tools were classified into four groups from matrices (Al2O3 or Si3N4) and additives present. The hardness of ceramic tool consisting of Al2O3 as the matrix and TiC as the main additive is 20-22GPa (at a 20kg load), and the fracture toughness is 5.3-6.4MPa·m1/2. The erosive wear resistance of this type of Al2O3/TiC composites was better than that of other three groups of ceramic tools, hot-pressed Si3N4, high purity Al2O3 and SiC whisker reinforced Al2O3, for both SiC and Al2O3 abrasives. The erosion rate of the ceramic tools was in the order of 10-3cm3/cm3 for SiC abrasive and 10-4cm3/cm3 for Al2O3 abrasive. The difference in erosion rate was caused by different erosion mechanisms depending on whether the Vickers hardness ratio of the ceramic tool to the abrasive is larger or smaller than unity.

SiC sintered bodies with three-dimensional polycarbosilane as binder

As is well known, silicon carbide is a practical heat-resisting material, because it has high strength and excellent oxidation, corrosion and thermal shock resistance. It is, however, difficult to obtain it as a sintered body because of its poor sintering characteristics. The usual method1 for obtaining SiC with high flexural strength are to add a sintering promoter to fine SiC powder followed by hot pressing. The process is complicated and not suitable for obtaining large products. We here report the synthesis of high purity SiC mouldings with high mechanical strength by low temperature (1,000−1,400 °C) sintering of SiC powders bond with three-dimensional polycarbosilanes. The method is based on the conversion of an organosilicon polymer to the inorganic compound by heat treatment2–5.

Thermal Conductivity of Pure and Impure Silicon, Silicon Carbide, and Diamond

Thermal conductivity measurements on high-purity SiC and impure Si and SiC have been made over the temperature range from 3° to 300°K. These results show that the thermal conductivity K, of the highest purity SiC is intermediate between those of pure Si and pure diamond, and at 300°K is greater than that of copper. The heat transport in SiC is produced by phonons and these are scattered by other phonons, isotopes, and the crystal boundaries in the pure material. In impure SiC the phonons are also scattered by the electrically active impurities Al and N. These impurities reduce the K of SiC in much the same way that B and P impurities do in Si. The N impurities in natural diamonds also reduce their K below that of ideally pure diamond, but the effect is rather different since N is not electrically active.

On the Photocurrent of High Purity SiC Single Crystal

On the Photocurrent of High Purity SiC Single Crystal