Papers by Keyword: Rod-Like Crystals

Abstract: Silicon carbide (SiC) ceramics have excellent properties such as high thermal conductivity, heat resistance and high hardness. However, their low strengths due to the low fracture toughness make it difficult to produce SiC ceramics with large size and complicated shapes. The purpose of this study is to fabricate SiC/Si₃N₄ composite materials (SiC > Si₃N₄) reinforced by β-Si₃N₄ rod-like crystals (whiskers) in order to improve the mechanical properties of SiC ceramics. In this work, following two methods for fabricating SiC/Si₃N₄ composites have been developed. Method Ⅰ: porous β-Si₃N₄ with porosity more than 50 % was infiltrated by phenolic resin, heat-treated in N₂ atmosphere to convert phenolic resin to carbon, and finally infiltrated by molten Si into the porous β-Si₃N₄-carbon composites (reaction bonding). Method Ⅱ: hot-pressing the powder mixture of SiC and the β-Si₃N₄ whiskers with sintering additive. The microstructures and mechanical properties of SiC/Si₃N₄ composites fabricated by two methods were investigated.

Abstract: In this paper, a simple precursor thermolysis method is applied to prepare calcium phosphate crystals and macroporous ceramic. The phase composition of sample was determined by XRD and the morphology of sample was observed by TEM and SEM. The macroporous ceramic was observed by 3D digital microscope. Results show that 25-100 nm HAP nanocrystals were obtained at 500°C and HAP rod-like crystals with an equivalent diameter of about 0.50-1.6μm and a length of about 5-10μm were obtained at 700°C. In addition, about 100 nm β-TCP nanoparticles were also obtained at 900°C. The colloidal precursors can also be used to fabricate macroporous calcium phosphate ceramic. The size of pores is about 100-200μm. Pores are well opened and interconnected in three dimensions.

Abstract: A hyrdrothermal reaction process has been developed to prepare rod-like crystals of copper oxide using copper nitrate trihydrate as a function of synthesis temperature, stirring speed and solution pH value. The properties of the fabricated crystals were studied using scanning electron microscopy, X-ray diffraction and particle size analysis. The morphology of the synthesized CuO was dependent on both the pH value of the solution and the morphology of the seed materials. Synthesized particles have regular morphologies and a uniform size distribution.

Abstract: The purpose of this paper is to investigate the possibility of rod-like Al2TiO5 formation via a mechanical activation process. A QM-ISP-4 Planetary Mill was employed to activate mechanically the mixtures of anatase and corundum in air at room temperature for different times. The milled powder mixtures were then sintered in air at 1300°C for 1 h. The XRD results showed that the milled powder mixtures were completely transformed into Al2TiO5 after sintering, except the mixtures milled for 5 and 10 hours. The SEM observations showed the typical morphology of rod-like Al2TiO5 vary in the range: widths from 0.6 to 1.2 μm, and lengths from 3.0 to 6.0 μm. The rod-like Al2TiO5 formation was attributed to the positive effects caused by the mechanical activation.