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The whisker growing and matrix filling process was applied to reduce the canning effect during the CVI process. Grown whiskers may serve to divide the large natural pores between fibers or bundles and then matrix filling may be efficiently carried out through the modified pore structure. In this study, the multi-step of the in situ whisker growing and matrix filling process were performed to investigate the densification behaviors of SiCf/SiC composite. MTS (CH3SiCl3) and H2 were used as source and diluent gases, respectively. The process cycles were repeated three times. The whisker growth and densification behaviors with the number of the process cycles were evaluated. SiC whiskers were grown in the SiC fiber preforms at the input gas ratio of 60 and the total reaction pressure of 5 Torr. As the number of process cycles increased, the maximum size of the large voids decreased and homogeneity of the voids distributions increased. [Copyright &y& Elsevier]

A hybrid process of SiC slurry impregnation (SI) and hot pressing (HP) has an advantage for the fabrication of dense SiCf/SiC (silicon carbide fiber reinforced/silicon carbide matrix) composite. An effective impregnation of the SiC slurry into the voids of a fiber preform is important to fill the dense matrix phase in the SI and HP processes. An electrophoretic deposition (EPD) technique was applied to effectively increase the densification of the matrix phases by a fast, simple, and efficient impregnation of the SiC slurry. An EPD was performed using a dual electrode system under an applied voltage of 10V for 30min with/without ultrasonification. The maximum density of SiCf/SiC composite fabricated by an EPD with ultrasonification was 3.14±0.04g/cm3. The flexural strength was 531±26MPa for a composite with a single interlayer of (200nm PyC (pyrolytic carbon)+600nm SiC). [ABSTRACT FROM AUTHOR]

Abstract: The incorporation of SiC nanowires in the SiC fiber preform was clearly shown to be effective in increasing the efficiency of the matrix infiltration for the fabrication of SiCf/SiC composites, and thus resulted in a higher density in a shorter CVI (chemical vapor infiltration) time. Generally, tailoring the interface between fibers and the matrix is known to be a way to control the mechanical behaviors of SiCf/SiC composites. In this study, the PyC interface was coated on SiC nanowires as well as SiC fibers to supply the additional interfaces and enhance the mechanical properties of SiCf/SiC composite prepared by the nanowire-growth assisted CVI process (NW-CVI). NW-CVI composites with or without PyC coating on the SiC nanowires had the average flexural strength of 450 and 510MPa and the average tensile strength of 226 and 253MPa. [Copyright &y& Elsevier]

Abstract: Nano-sized Li2TiO3 powder was fabricated by an organic–inorganic solution route. A steric entrapment route employing ethylene glycol was used for the preparation of the nano-sized Li2TiO3 particles. Titanium isopropoxide and lithium nitrate were dissolved in liquid-type ethylene glycol without any precipitation. With the optimum amount of the polymer, the metal cations (Li and Ti) were dispersed in the solution and a homogeneous polymeric network was formed. The organic–inorganic precursor gels were turned to crystalline powders through an oxidation reaction during a calcination process. The dried precursor gel showed the carbon-free Li2TiO3 crystalline form which was observed above 400°C. The primary particle size of the carbon-free Li2TiO3 was about 70nm, and the structure of the crystallized powder was porous and agglomerated. The powder compact was densified to 92% of TD at a relatively low sintering temperature of 1100°C for 2h. [Copyright &y& Elsevier]