Key Engineering Materials Vols. 368-372

Abstract: A novel, online-joining of C/SiC-C/SiC method, precursor infiltration and pyrolysis, was used to obtain high temperature stable joining SiC composition, while joining process was highly consistent with C/SiC preparation process. The compositions of joining ingredients and process parameters were investigated to determine the maximum joining strength of C/SiC-C/SiC at room and high temperatures. The optimum weight ratio of (polycarbosilane/divinyl benzene)/SiC powder is 3/1, and ramping rate of pyrolysis is 2°C/min, and cycles of infiltration and pyrolysis is 6. The flexural strengths of joining components remained stable up to 1200°C (50.8MPa), but decreased to 30.5MPa at 1500°C, while the tensile strengths remained rather stable (20.5MPa) up to 1500°C, and decreased to 8.4MPa at 1800°C.

Abstract: In this paper a pseudo-HP process, which uses solid powder to transfer pressure to prepare complex shape articles, was adopted to prepare 2D C/SiC composites. Nano-SiC powder was used to lower the sintering temperature, thus decreasing the damage to carbon fibers. The optimum processing parameters are as follows: sintering temperature 1850°C, holding time 60min, sintering pressure 10MPa. The maximum strength is over 300MPa, and toughness is around 8MPa·m1/2. BN powder is more lubricous than carbon powder, and thus is more convenient for demoulding and pressure transferring. Precursor Infiltration and Pyrolysis (PIP) was used to further densify the composites after HP process, and strength and toughness of the samples were slightly enhanced.

Abstract: In this paper the preparation of carbon fiber reinforced ultra-high temperature ceramic matrix composites was reported. Polymer infiltration and pyrolysis process was used to prepare 2D C/TaC-SiC, C/NbC-SiC, and C/ZrC-SiC composites. The fracture strengths of all the samples were around 300MPa and toughness around 10MPa-m1/2. Standard oxyacetylene torch tests (>3000°C, 30s) showed that the minimum ablative rate of 2D C/SiC-ZrC was as low as 0.026 mm/s, much smaller than that of 2D C/SiC composites (0.088mm/s).

Abstract: A new technology, prefabricating pore media (PPM) technology that adopt glass fiber as pore media, for porous transpiration cooling C/SiC composites was studied. The result shows that the technology can control the pore structure successfully by the volume content and distribution of glass fiber in the braid, and the porous C/SiC composites have good bending strength above 300MPa.

Abstract: Two-dimensional waved carbon fiber preforms were chemical vapor infiltrated under forced flow, thermal gradient mode for preparation of 2D C/SiC composites. In order to improve the oxidation resistance of the C/SiC composites, B4C powders were added into the preforms and aqueous silica sol-B4C compound coating was claded on the surfaces of composites. It was found that the oxidation resistance of 2D C/SiC composites at temperatures lower than 1273K was improved because of the formation of B2O3 and borosilicate glass by preventing the diffusion of oxygen.

Abstract: Spark plasma sintering was used to fabricate the LaPO4 ceramics and the effect of SPS holding time and sintering temperature on the densification and texture of LaPO4 ceramics were studied. The results revealed that holding time had no obvious influence on the densification of LaPO4 ceramics under the present process. The density increases with the increase of sintering temperature, when it reached 1350°C, the relative density kept nearly constant of 98.6 %. The preferred orientation of LaPO4 ceramics approximately increases with the increase of sintering temperature, but contrary impact in holding time.

Abstract: Industrial wood cutting is a highly demanding application for cutting tool materials as a wedge angle of ~50°, a tip radius in the 1 m range, and high wear, temperature and corrosion resistance are needed. For this application Si3N4 based ceramic matrix composites (CMC) were developed. Cutting tests showed that reinforcing Si3N4 with 30 wt.% SiC gives a good balance between fracture toughness and wear resistance. The use of an yttria / lanthana sintering aid system resulted in a fine-grained microstructure without degrading the fracture toughness. Post heat treatment was essential for the integrity of the cutting edge. Finally, cutting tests proved that the CMC cutting tips had a 3-fold lifetime compared to tungsten carbide.

Abstract: Kaolinite-glucose intercalation compound was synthesized by the intercalation of polar organic big molecule dodecylamine and then displaced by glucose in the layer of kaolinite. XRD, FT-IR, TG and DSC were used to study the reaction process and the characters of the products. The results indicated that the basal spacing of kaolinite increased to 2.280 nm from 0.717 nm, and the hydrogen bonds were formed between dodecylamine NH and kaolinite Si-O after dodecylamine intercalation. Kaolinite-dodecylamine intercalation compound was stable below 295 °C. After displacement reaction by glucose, the basal spacing of kaolinite increased to 3.364 nm, and the intercalation rate reached 87%, the hydrogen bonds were formed between glucose C=O and kaolinite inner surface hydroxyl. Kaolinite-glucose intercalation compound was stable below 302 °C.

Abstract: New electric molding composites were fabricated with hybridizing epoxy and several fillers. The examined fillers were β-Si3N4, BN and fused silica or their combinations. The thermal conductivity of β-Si3N4 filler was compared with BN as filler for advanced epoxy molding compounds. The influence of pure resin matrix and mixture matrix on the thermal conductivity of EMC was discussed. The results were explained with Maxwell equation.

Abstract: Calcium chloride hexahydrate (CaCl2·6H2O) is an important inorganic phase change material used for heat storage at lower storage temperature. Heat storage in a PCM heat exchanger is an effective means of energy conservation or recovery in many engineering applications. A study was made on heat storage performance of a PCM heat exchanger with staggered tube bank in which there are full of calcium chloride hexahydrate solution. The experimental measurements of its heat storage and discharging performances during the heating/cooling cycle were carried out at a given rate of air flow. The analyses and discussion of its experimental results were also made. Its prospect in the industrial applications as heat energy storage was forecasted.