Guanghui Min

Reaction synthesis and formation mechanism of barium hexaboride

Abstract The synthesis and formation mechanism of BaB6 powder by the reaction of BaCO3 with B4C and carbon was investigated systematically in the present study. The influences of heating temperature and holding time on the reaction products were studied by X-ray diffractometry, and the morphologies of BaB6 were investigated by scanning electron microscopy. The interaction in the BaCO3–B4C–C system by which BaB6 is formed was found to be a solid-phase process that passes through Ba3B2O5 and BaB2O4 transition phases. The optimal conditions for BaB6 synthesis are a holding time of 2 h at 1673 K, under vacuums, at 10−2 Pa of pressure.

THE INFLUENCE OF SPUTTERING BIAS-VOLTAGE ON LaB6 FILM'S CHARACTERISTICS

The deposition of lanthanum boride (LaB6) thin films by the d.c. magnetron sputtering were studied. XRD, AFM and Stylus Profiler were used to characterize the properties of the deposited films. The XRD was used to study the crystallinity. The results of the XRD showed that the dominant crystal face is (100) face. The crystallinity decreased with the increased bias-voltage value, but the influence of bias-voltage on the films is different on different crystal face. The intensity (100) face was influenced by the bias-voltage more obviously than other faces except the influence of thickness. The diffraction peak maximal intensity of (100) face changed from 1256(on 0V) to 580(on -150V), but the intensity of (110) face changed from 614(on 0V) to 486(on -150V). The rel. int(100%) of (110) face changed from 38.70 to 74.52. The deposition rate decreased with the increased bias-voltage value, but the decreased was not obviously. The maximum and minimum of the deposition ratio were 17.53nm and 13.75nm respectively....

Fabrication, microstructure and properties of SiCp/Cu heat sink materials

Abstract Cu-coated powder was fabricated by electroless plating process, and the composition and morphology of coated powder were studied. Moreover, Cu-30, 40, 50 vol.% SiCp heat sink materials were fabricated by hot pressing using coated and uncoated powder. And the microstructure and thermophysical properties of the heat sink materials were also studied. The results show that SiCp particles distribute uniformly in heat sink materials and the interface between SiCp particles and Cu matrix is clear and well bonded. On the condition of same volume fraction of SiCp, the thermal conductivity of the material using coated powder is larger than that of the material using uncoated powder. Under experiment conditions, the thermal conductivity and coefficient of thermal expansion of Cu-30 vol.% SiCp heat sink material is 236.2 W.m−1.K−1 and 9.9 × 10−6/K (30–200 °C) respectively. It provides important reference data for future experiments.

LOW TEMPERATURE SYNTHESIS OF BaB6 NANOMETER POWDERS

The reaction synthesis of barium boride (BaB6) nanoparticles under low temperature was investigated in this study. X-ray diffraction (XRD) was used to investigate the phase and the structure of BaB6. The characterization for microstructure was performed by Field Emission Scanning Electron Microscope (FESEM) with EDS, TEM, Fourier transform infrared (FTIR) spectroscopy and Raman scattering spectroscopy. It is concluded that BaB6 nanoparticles can be successfully prepared under low temperature at 500°C. XRD pattern shows that the nanoparticles are consisted of predominantly (110)-oriented BaB6 phase. The powders are polygonal-like shape with the average size of 200 nanometers. TEM identified that each nanoparticle shows perfect single crystal and cubic structure. The boron-to-barium atomic ratio of 5.24:1 was determined, less than the stoichiometric ratio of 6:1. BaB6 nanoparticles can absorb infrared spectrum at 459, 690, 993, 1329, 1619, 2449 and 3423cm-1 in the test range of 400~4000cm-1, respectively. Three peaks at 677.1, 823.5 and 1116.4cm-1 can be observed clearly from the Raman spectra of BaB6 nanoparticles at room temperature. The results showed that the electron dispersion of B6 octahedron in BaB6 is two-dimensional pancake-type without lattice distortion, which may account for the unique physical properties of BaB6 nanoparticles.

Effect of trace Ag on the microstructure and precipitation of an Al–Cu–Mg alloy

Abstract This paper investigated the effect of different amounts of Ag addition on the microstructure, properties and precipitation processes of Al–4·6Cu–6·9Mg(wt-%) alloy using various analytical methods. It was found that Ag addition stimulated new X′ 9 and Ω phases precipitated finely and dispersively in the matrix, as a result of Mg–Ag co-clusters; the volume fraction of precipitates increased with the content of Ag addition. Such precipitation improved the mechanical performance of the Al–Cu–Mg alloy significantly. The mechanism for the formation of new precipitates is also described in this paper.

Microstructure and fracture characteristics of alumina-based prismatic ceramic composites

Abstract Al 2 O 3 /SiC prismatic ceramic composites have been prepared by a structure-controlled process, in which the high-aspect-ratio alumina-based cells with a distinct prismatic texture were separated in three dimensions by thin SiC cell boundaries. The work-of-fracture of the composites has been improved greatly due to the developed paths for crack propagation by the weak cell boundaries, corresponding to longer displacement under reasonable load-carrying condition. The route of crack propagation depended greatly on the interfacial shear strength and boundary thickness. Crack deflecting and delamination are considered as two main contributions at the earlier stage, whereas frictional sliding of fibrous cells becomes more dominant after cracking occurs, especially at lower loading condition. These mechanisms are different from those observed in multilayered monolithic ceramics due to the controlled structures of present materials.