We studied the characteristics of two-scale pore structure of preform in the deposition process and the mass transfer of reactant gas in dual-scale pores, and observed the physiochemical phenomenon associated with the...We studied the characteristics of two-scale pore structure of preform in the deposition process and the mass transfer of reactant gas in dual-scale pores, and observed the physiochemical phenomenon associated with the reaction. Thereby, we established mathematical models on two scales, respectively, preform and reactor. These models were used for the numerical simulation of the process of ceramic matrix composites densified by isothermal chemical vapor infiltration(ICVI). The models were used to carry out a systematic study on the influence of process conditions and the preform structure on the densification behaviors. The most important findings of our study are that the processing time could be reduced by about 50% without compromising the quality of the material, if the processing temperature is 950-1 000 ℃ for the first 70 hours and then raised to 1 100 ℃.展开更多
Leucite particles were synthesized from feldspar mixed with 0% to 52% potassium nitrate fired from 800 ℃ to 1 200 ℃ by solid state method. The X-ray Diffraction （XRD） patterns show that in the temperature range fr...Leucite particles were synthesized from feldspar mixed with 0% to 52% potassium nitrate fired from 800 ℃ to 1 200 ℃ by solid state method. The X-ray Diffraction （XRD） patterns show that in the temperature range from 800 ℃ to 1 200 ℃, the leucite can be removed as the single crystalline phase. Kalsilite may be crystallized with leucite at 800 ℃, but can be eliminated after prolonged heating. The scanning electron Microscopy （SEM） images clearly display the that crystals of micrometer scale leucite, and the leucite crystals distribute evenly in the matrix. The Thermal expansion coefficient （TEC） of the samples fabricated is as high as 20.52×10^-6 ℃^-1 measured from 20 ℃ to 500 ℃. The mechanism of transformation from feldspar to leucite was proposed.展开更多
基金Funded by the National Natural Science Foundation of China(No.51472092)
文摘We studied the characteristics of two-scale pore structure of preform in the deposition process and the mass transfer of reactant gas in dual-scale pores, and observed the physiochemical phenomenon associated with the reaction. Thereby, we established mathematical models on two scales, respectively, preform and reactor. These models were used for the numerical simulation of the process of ceramic matrix composites densified by isothermal chemical vapor infiltration(ICVI). The models were used to carry out a systematic study on the influence of process conditions and the preform structure on the densification behaviors. The most important findings of our study are that the processing time could be reduced by about 50% without compromising the quality of the material, if the processing temperature is 950-1 000 ℃ for the first 70 hours and then raised to 1 100 ℃.
基金the National High Technology Research and Development Program of China(No.2002AA302204)Science and Technology Program of Guangdong Province of China(No.2001A1070102)Science and Technology Program of Guangzhou City of China
文摘Leucite particles were synthesized from feldspar mixed with 0% to 52% potassium nitrate fired from 800 ℃ to 1 200 ℃ by solid state method. The X-ray Diffraction （XRD） patterns show that in the temperature range from 800 ℃ to 1 200 ℃, the leucite can be removed as the single crystalline phase. Kalsilite may be crystallized with leucite at 800 ℃, but can be eliminated after prolonged heating. The scanning electron Microscopy （SEM） images clearly display the that crystals of micrometer scale leucite, and the leucite crystals distribute evenly in the matrix. The Thermal expansion coefficient （TEC） of the samples fabricated is as high as 20.52×10^-6 ℃^-1 measured from 20 ℃ to 500 ℃. The mechanism of transformation from feldspar to leucite was proposed.
