Papers by Author: Jing Kun Guo

Abstract: Aluminum borate whiskers with TiB2 as borate source were prepared in this paper. The phase transformation process was analyzed by XRD and TG-DSC. The results indicate that TiB2 was decomposed into TiO2 and B2O3 in the calcining process in the active [O] atmosphere. 2Al2O3.B2O3 was formed in the lower temperature with reaction of Al2O3 and B2O3, while 9Al2O3.2B2O3 whiskers were grown by compensation of 2Al2O3.B2O3 at higher temperature (above 1050oC)

Abstract: SiC matrix composites can be reinforced and toughened by the second phase of AlN particles. SiC-AlN composites are mixed by ball milling of the SiC and AlN powders, and then hot pressed under 40 MPa at 1950oC in Ar atmosphere. The object of this paper is to understand the effect of AlN contents on the properties of SiC-AlN particulate composites. AlN content is between 5 and 40wt%. For improving to mechanical properties of siC-AlN composites, the composition range of SiC-AlN composites are between 90SiC-10AlN and 80SiC-AlN20(wt%). Less or more than this ratio would result in a microstructure with much pores or AlN grain-growth, respectively, two phenomena would decrease in the mechanical properties of SiC-AlN composites.

Abstract: Coating process is attracting more and more attention in the preparation of composite materials mainly due to its predominance in the improvement of the uniformity for different phases. The formation of nanosize alumina shells on the aluminum core particles by a wet-chemical based route was investigated and the composite particles were characterized using TG/DSC, XRD, SEM, TEM, XPS. An enhancement of cermet properties can be expected by using these coated particles as initial powders.

Abstract: In the present study, the processing-properties relationships of the ZrO2/(Ni+Al2O3) composites are examined. Dense composites were prepared either by pulse electrical current sintering (PECS) at 1350C for 5 minutes or by pressureless sintering (PLS) at 1600C for 1 h. The size of Ni particles is as small as 30 nm to 50 nm. Though the size of ZrO2 grains in the matrix increases as alumina and nickel particles are added, the strength of the ZrO2/(Ni+Al2O3) composites is significantly higher than that of monolithic ZrO2.

Abstract: Silicon carbide is widely used as an important structural material. It is known for its extreme hardness, high temperature antioxygenic properties and good tribological properties. Moreover, SiC is also an intrinsic semiconductor. SiC can react with AlN and form an extensive solid solution at temperatures between 1800 to 21000C, and has excellent mechanical properties. However, in this article, we study the influence of the microstructure and the dielectric properties of SiC ceramics. SiC-AlN solid-solution ceramics were prepared by hot-pressed sintering using Y2O3 as the sintering additive. The size of SiC and AlN powders were 0.6μm and 1.06µm respectively. The content of AlN starting powders was 14vol%. The hot-processing sintered SiC-AlN multiphase ceramics have reached high density at 1950oC in Ar atmosphere under 30MPa.The hot-processed ceramics were subjected to thermal treatments in a range of temperatures between 11000C and 16000C for 3hr. The grain size increased with the annealing temperature. X-ray diffraction profiles show that phase relationships. Scanning electron microscopy (SEM)) was used to determine fracture surface and the local compositions. Dielectric permittivities and dissipation factor of SiC-AlN composites were investigated with the varieties of annealing temperature and the content of AlN particles. Dielectric constants (ε) and Dielectric loss tangents (tanδ) were measured within the microwave frequency range from 40Hz to10MHz.

Abstract: Commercial Y2O3 powders were subjected to high energy ball milling in a planetary ball mill using high purity alumina balls and vial. The refined Y2O3 power ,with commercial high-purity Al2O3, Cr2O3 and Yb2O3 powders, were used as raw materials. Transparent ytterbium and chromium codoped yttrium aluminum garnet (Yb,Cr:YAG) ceramics were fabricated by a solid-state reaction method. The Yb,Cr:YAG ceramics exhibit a pore free structure and the average grain size is about 10 micron. The strong absorptions at 940 and 968 nm of Yb3+ are suitable for InGaAs diode laser pumping, and there is an absorption band at 1030 nm, which is suitable for passive Q-switch laser output at 1030 nm. Transparent Yb,Cr:YAG ceramics may be a potential material for compact, efficient, high-stability diode-laser-pumped passive Q-switched solid-state lasers.

Abstract: Al/Al2O3 cermet composites were fabricated by hot-pressing at the temperature range of 1350~1450oC from commercial γ - Al2O3 reinforced by Al/Al2O3 core-shell particles, which were synthesized via calcining the Al/AlOOH·nH2O core-shell particles prepared by wet-chemical based method. This newly designed aluminum coated with alumina composite structure can not only reduce or resist the oxidization of Al at elevated temperature but also make it possible to control inter-particle and particle-matrix interactions, and this predesigned structure is expected to improve the following sintering ability and therefore the properties of final products.