Materials Science Forum Vols. 745-746

Abstract: A simple two-step procedure towards the Pt nanoparticles and mesoporou silicate SBA-15 composite was developed in this work. The ultrasonic irradiation and the calcinations involved in the preparation did not destroy the size and morphology of prepared Pt nanoparticles, and no agglomeration of Pt nanoparticles was observed, thus stable Pt nanoparticles supported by SBA-15 host were formed. The hexagonal ordered structure of SBA-15 also remained. This stable composite are mainly used as the starting material in fabricating stable Pt nanoparticles doped glass.

Abstract: nclusion pigments of ZrSiO₄/C were prepared by nonhydrolytic sol-gel (NHSG) method combined with the process of carbon black modification. The crystalline phases, microstructure, functional groups on the surface of carbon black and chromatic value of the pigments were characterized by XRD, TEM, FTIR and Colorimeter, respectively. The surface structural changes of the carbon black modified by nitric acid and the influences of process parameters on the chromatic value of the pigments were also investigated. The results show that the process of carbon black modification enhances the affinity and binding force between carbon black and ZrCl₄ sol, which contributes to improve the effect of carbon black wrapped by ZrSiO₄. The ZrSiO₄/C inclusion pigment were obtained after calcining at 1000 °C for 8 h, and the L*, a* and b* value is 53.88, 0.74, and 1.88, respectively.

Abstract: TiB₂/TiN nanocomposites were in-situ fabricated by spark plasma sintering (SPS) technique using Ti and BN powders as starting materials. The phase constituents and microstructures of the samples were analyzed by X-ray diffraction (XRD) techniques, scanning electron microscopy (SEM) and transmission electron microscope (TEM), respectively. The results showed that the average grain size of TiB₂ and TiN was 1m and 300nm respectively. Furthermore, high resolution TEM analysis indicated that the as-prepared TiB₂/TiN nanocomposites had very clean grain boundaries, and no amorphous phase or oxide layer was observed.

Abstract: La-modified 0.75Pb (Mg_1/3Nb_2/3)O₃-0.25PbTiO₃(PLMNT) electro-optic (EO) transparent ceramics were synthesized through a columbite precursor method. Excess PbO (10, 15 and 20 mol %) was added to study the effect on the transparency, electro-optic effect, and microstructures of PLMNT transparent ceramics. The phase structure of different samples can be identified as single perovskite structure with no second phase detected. The average grain size increased as the concentration of excess PbO increased from 10 mol% to 20 mol%. On the contrary, the transparency decreased with the increase of the concentration of excess PbO. When the concentration of excess PbO was 10 mol%, the transmittance was about 62% at 632.8nm. The EO coefficient was calculated through measuring the birefringence as a function of electric field. The EO coefficient increased with the increase of the concentration of excess PbO and the maximum EO coefficient reached 40.6×10^-16(m/V)² when the excess PbO was 20 mol%.

Abstract: ZrB₂-based ceramic composites were prepared through hot-pressing at a temperature of 1880°C. An intragranular microstructure was achieved because of the existence of nanoSiC. In this paper, the mechanical properties of ceramic materials of ZrB₂-SiC-G were studied, and the influence of intragranular microstructure on the mechanical properties was analyzed. The values of flexural strength and fracture toughness of ZrB₂-20vol%SiCnp-15vol%G reached 551.9MPa and 5.25MPa·m^1/2, respectively. Compared to ZrB₂-20vol%SiC-15vol%G with micro-SiC, the fracture toughness was improved.

Abstract: Porous ceramics with a framework structure of the polycrystalline mullite fibers, in which the silica sol were impregnated into the intertwined points, were synthesized by the infiltration method. The sample has a porosity of 90 %, and the compression strength was significantly improved compared with the matrix without any addictives. The elastic behavior was investigated by changing the loading speeds. It is found that the elastic behavior of the porous ceramics was different from the traditional ceramics. The compression set is about 15% and the rebound resilience is 85 % at room temperature. The composite can keep good performance of compression-rebound.

Abstract: The aluminum phosphate adhesive was prepared by aluminum dihydrogen phosphate and ceramic fillers. The mullite, silica and silicon powders were added as the fillers to improve the mechanical property and high temperature property. The specimens were prepared by joining the mullite ceramic/ceramic by phosphate adhesive. The strengths of the specimens treated at different temperatures were studied. The results indicated that the tensile strength at room temperature was 2.02 MPa, and it reached 5.06 MPa when the specimen was treated at 800°C. The bonding effect and bonding property at high temperature were discussed through the SEM analysis. Besides, the bonding mechanism was also explored.

Abstract: SiC/Al co-continuous phase composites were fabricated by pressureless infiltration technology with reticulated silicon carbide porous ceramics as matrix and aluminum or magnesium as reinforcement phase. The effect of magnesium addition and holding time on the relative density, mechanical properties and macro morphology of the composites was investigated. The results showed that the porosity of SiC/Al co-continuous phase composites decreased with the increase of the holding time. The wettability of SiC and Al was improved with the addition of Mg. The hardness of SiC/Al co-continuous phase composites increased with the increase of the holding time. SiC and Al combined closely at longer holding time.

Abstract: C_f/SiC composites were fabricated through in situ growth of carbon nanotubes (CNTs) on three-dimensional needle-punched carbon fabric via chemical vapor deposition and polymer impregnation and pyrolysis process. The mechanical and thermal properties of the composites were investigated. The flexural strength and fracture toughness were decreased due to the fiber volume fraction loss and much shorter pull-out length of fibers which was caused by the higher interfacial bonding strength between fiber and matrix after the growth of CNTs. Brittle fracture character of CNTs was observed due to the strong interfacial bonding strength between CNTs and matrix. The parallel thermal conductivity and perpendicular thermal conductivity were improved to 14.5% and 8.0% respectively.

Abstract: The reaction mechanism of self-propagating high-temperature synthesis of MoSi₂ was investigated by means various methods. The result of activation energy calculation indicates that the synthesis reaction is controlled by a single mechanism. Analysis on the microstructure of Mo/MoSi₂ and Si/MoSi₂ interfaces reveals that Mo reacts with Si to directly form MoSi₂ without any transient product (s). Morphology comparison between the reactants and the product demonstrates that the reaction mechanism is not reactive diffusion. Microstructural observation on the materials from quenched zone shows MoSi₂ particles precipitate from liquid phase. A mechanism may be proposed based on the above results: Mo particles are covered by molten Si and dissolve into the melt, and then MoSi₂ particles precipitate from the melt due to super saturation.