Papers by Author: Shou Hong Tan

Abstract: With use of electron-assisted chemical vapor deposition technology, nanocrystalline diamond films were deposited on SiC ceramics substrates at various gas pressure ( 0.5 ~ 2 kPa ). Effect of the gas pressure on optical properties of the nanocrystalline diamond films was studied. Raman scattering spectra were measured. Photoluminescence spectra were investigated in the range of 420 ~ 680 nm. Spectroscopic ellipsometry were analyzed from the near IR to the UV region ( 1.5 ~ 5.0 eV ). Results show that, when the gas pressure increased from 0.5 to 2 kPa, Raman scattering intensity of diamond increase and D/G ratio decrease; when the gas pressure was 0.5kPa and 2kPa, there is not any PL peak, however, there is a stronger PL peak at 485 nm when the gas pressure was 1kPa; extinctive coefficient k for the nanocrystalline diamond films deposited at 1kPa increase obviously with increase of photo energy.

Abstract: Amorphous SiC coatings were deposited by RF magnetron sputtering from a sintered SiC target onto Si(100) substrate at room temperature. The influence of RF power on the surface morphology and the RMS surface roughness of the resulting SiC coatings was studied by using atomic force microscopy. Two types of surface morphologies were obtained. The corresponding forming mechanisms were also discussed.

Abstract: The effects of microstructure on strength, toughness and corrosion resistance of reactionformed silicon carbide and heat treatment on the properties of reaction-formed silicon carbide have been investigated in this paper. The results show strength and corrosion resistance of reaction-formed silicon carbide decrease with increasing Si content. Fracture toughness shows no rule with free Si content. The average SiC grain size and bonding area of SiC grain increase during heat treatment at 1850°C. The strengths of the samples after heat treatment decrease compared with that of the samples before heat treatment due to the pores in the heat treatment bodies.

Abstract: The microstructure and microwave dielectric properties of inhomogeneous SiC-AlN solid solutions, hot pressed under a pressure of 40 MPa, have been investigated. Microstructure analysis detected the existence of BN in the resulted samples, which may be a reason that homogeneous solid solution was not formed for the samples with AlN content higher than 20%. The dc resistivity of the solid solutions at room temperature varies from 8 × 103 Ω m to 1 × 109 Ω m. Ion jump and dipole relaxation losses are the main mechanism of dielectric losses.

Abstract: This work will report the deformation behavior of silicon carbide reticulated porous ceramics (SiC RPCs) under three-point bend test. SiC RPCs were fabricated by replication processing using an open-cell polyurethane sponge with cell size of ~ 13 pores per inch (ppi). It is shown that the deformation behavior strongly depends on the loading uniformity and the macrostructure. Using a compliant layer (0.5 mm paper pad), the uniform loading leads to a significant transition in the load-displacement curve of RPCs from the complex saw-tooth shape to the one similar to dense ceramics, despite the presence of some macrostructural flaws and partial clogged cells. However, this dependence of loading uniformity is alleviated by developing highly uniform macrostructure with fewer flaws and clogged pores. Even, this dependence becomes less important as the struts become thicker and stronger, leading to an increase in relative density, accordingly. The bend result of RPCs with highly uniform macrostructure is in excellent agreement with the GA (Gibson and Ashby) model, but the one with un-uniform macrostructure deviates from the GA model. This work shows that the macrostructure plays an important role in deformation behavior of RPCs under bend.