Key Engineering Materials Vols. 512-515

Abstract: In this paper, Hf element was introduced into the Si-O-C network by the sol-gel method using the dimethyldiethoxysiloxane (DMDES, (CH3)2Si(OC2H5)2) and hafnium tetra(n-butoxide) (HfOR, Hf(OC4H9)4) as raw materials. The SiOC/HfO2 ceramic composite was obtained by pyrolyzing Si-Hf-O-C gel at 1000 °C in argon. FT-IR spectra revealed the presence of Si-O-Hf peaks at 932 cm-1. The weight loss of the as-prepared SiOC/HfO2 was about 0.2 wt.% under argon atmorsphere up to 1550 °C, which was much lower than the hafnia-free SiOC composites and exhibited a remarkable improved thermal stability.

Abstract: Fiber porous ceramics are the excellent candidates for a variety of applications, and thus, their research is a hotspot in recent years. In this study, carbon fiber reinforced phosphate porous ceramics composites were prepared by acupuncture and in-situ solidification vacuum-assisted liquid-phase infiltration method. The tensile strength of composite was tested by universal testing machine, the microstructures of the specimen were observed by scanning electron microscopy while the thermal analysis was detected by Thermo Gravimetric Analyzer. The results show that the carbon fiber reinforced phosphate porous ceramics composites which is prepared by the technology showed above have a pore rate of 63.7%.The tensile strength reached 50.2MPa with an average pore size of at most 50μm.It also has good thermal shock resistance.

Abstract: Thermal insulating behavior of silica glass fiber / aluminum phosphate composite was studied. The composite samples were prepared through hot-pressing of stacked pieces of plain woven fabric made from silica glass fiber with aluminum phosphate paste placed between the pieces of the fabric. When the mixture ratio of Al2O3:AlPO4:H2O was 10:2.88:2.88 in aluminum phosphate paste, the paste was suitable for preparing the composite. The thermal insulation of the composite was excellent, when volume content of fiber in the composite was from 27.6% to 33.57% and the densities of the composite were from 1.82 g/cm3 to 1.90 g/cm3. Heating test with oxyacetylene flame showed that when one face of the composite was heated up and hold at temperature of 1800°C for 10 mins, the temperature of the opposite face remained at 765°C to 775°C. The composite was not damaged during the above testing. As it was observed with microscope, there were little changes in microstructure of the composite after heat test.

Abstract: Ultrafine WC-Ni cemented carbides with addition of SiC whisker (SiCw) were fabricated by spark plasma sintering. The microstructure and mechanical properties of the fabricated cemented carbides were investigated. It was found that the addition of SiC whisker had no obvious influence on the phase compositions of the cemented carbides, but the mean grain size of the cemented carbides decreased as the addition fraction of SiC whisker increased. The fabricated WC-Ni cemented carbides presented the highest hardness when 0.75 wt% SiC whisker was added. However, the addition of SiC whisker was detrimental to the flexural strength of the cemented carbides because of the formation of inhomogeneous microstructure in the WC-Ni cemented carbides.

Abstract: WC-Ni-SiCw alloys were prepared through hot-pressed sintering by using WC, Ni, VC, TaC and SiC nano-whisker as raw materials. The influence of SiC whisker addition on the microstructure and mechanical properties of the as-prepared WC-Ni alloys was investigated. Except WC hard phase and Ni binder phase, no other phase was detected by X-ray diffraction. The observations by scanning electron microscope demonstrated that there were some micropores in the as-prepared materials, and their size and quantity increased with increasing amount of SiCw. Vickers hardness and flexural strength tests indicated that the bulk hardness of WC-Ni-SiCw alloys slightly decreased with increasing amount of SiCw; and the flexural strength increased at first and then decreased with increasing amount of SiCw. The alloys with 0.53 wt% SiCw presented the highest flexural strength of 1700 MPa.

Abstract: TiCN-based cermets with different amounts of SiC nano-whiskers were prepared by spark plasma sintering. The microstructure and mechanical properties of the as-prepared cermets were investigated. X-ray diffraction revealed that there were no SiC peaks detected, turning out some peaks of new carbide and silicate hard phases. Scanning electron microscopy indicated that there were more and more pores in the cermets with increasing amount of SiC whisker added, and the fracture mechanism of the cermets was mainly inter-granular fracture. With increasing addition amount of nano-SiC whisker, the hardness and flexural strength of the cermets increased first and decreased then, presenting the highest hardness (2170 HV) and flexural strength (750 MPa), respectively, when the addition content of nano-whiskers is 2.5 wt%.

Abstract: In this paper, the composite phase change materials for insulation were prepared by melt-soaking method. Trimethylolethane (PG) was chosen to be the phase change material (PCM) and two kinds of porous materials as the supporting matrices separately. The effects of both matrices to PG were analyzed by X-ray diffraction (XRD), and the heat insulation properties of composites were evaluated by Plat heat insulation test device. At last, microstructures of composites were observed by scanning electron microscope (SEM) and their effects to composites were discussed.

Abstract: Calcium hexaluminate (CA6) because of its high stability, high melting point and low thermal conductivity properties make it as a new high-temperature insulation materials are valued. In this paper, chemical analysis and XRD were used to investigate the composition of the white beach sand mineral from Perth coast of Western Australia. The main composition of it was carbonate. White beach sand as calcium source respectively, and industrial alumina as aluminum source synthesized CA₆ at 1550°C-1650°C for 3h. The results showed that: synthetic CA₆ shapes in platelet crystalline. Influence of different amounts of alumina and sintering temperature on synthesis of calcium hexaluminate are studied.The main phase of the samples with different amounts of alumina which decrease or increase 5%, 10% and 15% alumina around theory are CA₆. The porosity of the samples obtained is about 53%. The bending strength of Sample S-0 of theoretical ratio values up to 7.73Mpa. Sintering temperature from 1500°C to 1650°C is not conductive to the improvement of apparent porosity of CA₆ materials.

Abstract: Hybrid sol–gel process was used to fabricate the precursor particles of amorphous SiO₂ coating at the composites of SiC_p⁄Cu, and then formed by Vacuum hot-pressed method. Various methods were used to measure the sintered compacts of different SiC volume fraction. The results showed that the densities, bending strength and conductivity were decreased slightly with the increases in the amounts of SiC, and the vickers hardness were increased first and then decreased. The techniques of DTA–TG, SEM–EDS and XRD were used to characterize the phases and the morphologies of the composite particles and composites. It was inferred that the formation of SiO₂–Cu₂O eutectic mixture in this system and the viscous interaction of amorphous SiO₂ improved the interfacial modification of the composites of SiC_p⁄Cu.

Abstract: The SiC/Cu composite is one of the "structural-functional" materials. It shows good mechanical properties and very high thermal, high electrical conductivity etc. But the co-dispersion, wetting and bonding between SiC and Cu interface are of practical importance in the preparation of SiC/Cu composites. In this work, surface treatment techniques such as high-temperature oxidation, acid dipping and alkaline wash were adopted separately on silicon carbide particles, in order to improve the wettability and physical and chemical compatibility between silicon carbide and copper, then we used the replacement reaction method and decomposition-reduction reaction method to generate Cu coating on the surface of silicon carbide. The results shown that, the surface of silicon carbide particle which treated by alkaline wash was cleaner and more rough than that only treated by high-temperture oxidation, moreover, the specific surface of the particle was increased, which resulted in a compact layer of Cu coating. for the same silicon carbide particles, the effect of the Cu coating prepared by decomposition reaction method was better than that by reduction reaction method.