Short carbon fiber felts with an initial porosity of 89.5% were deposited by isobaric, isothermal chemical vapor infiltration using natural gas as carbon source. The bulk density of the deposited carbon/carbon （C/C）...Short carbon fiber felts with an initial porosity of 89.5% were deposited by isobaric, isothermal chemical vapor infiltration using natural gas as carbon source. The bulk density of the deposited carbon/carbon （C/C） composites was 1.89 g/cm3 after depositing for 150 h. The microstructure and mechanical properties of the C/C composites were studied by polarized light microscopy, X-ray diffraction, scanning electron microscopy and three-point bending test. The results reveal that high textured pyrolytic carbon is deposited as the matrix of the composites, whose crystalline thickness and graphitization degree highly increase after heat treatment. A distinct decrease of the flexural strength and modulus accompanied by the increase of the toughness of the C/C composites is found to be correlated with the structural changes in the composites during the heat treatment process.展开更多
This paper presents the thermodynamic performance analysis and comparison of four kinds of advanced pressurized fluidized bed combustion combined cycle (APFBC-CC) system schemes, two based on pressurized fluidized bed...This paper presents the thermodynamic performance analysis and comparison of four kinds of advanced pressurized fluidized bed combustion combined cycle (APFBC-CC) system schemes, two based on pressurized fluidized bed (PFB) combustion and the other two based on atmospheric circulating fluidized bed (CFB) combustion. The results show that the first scheme avoids high temperature gas filter, but has the lower cycle efficiency and syngas heating value. The second scheme can gain the highest cycle efficiency, however it is better to now lower the filter operating temperature. The third and fourth schemes, based on CFB, have lower efficiencies than the second one. But the fourth one, with preheating air/steam for gasification, can obtain the highest heating value of syngas and gain higher efficiency than the third one.展开更多
BN interphase was successfully synthesized on SiC fiber fabrics by dip-coating process using boric acid and urea as precursors under N2 atmosphere. The morphology of BN interphase was observed by SEM, and the structur...BN interphase was successfully synthesized on SiC fiber fabrics by dip-coating process using boric acid and urea as precursors under N2 atmosphere. The morphology of BN interphase was observed by SEM, and the structure was characterized by XRD and FT-IR spectra. The SiCf/SiC composites with dip-coated BN interphase were fabricated by chemical vapor infiltration （CVI） process, and the effects ofBN interphase on the mechanical properties of composites were investigated. The results show that the SiC fibers are fully covered by BN interphase with smooth surface and turbostratic structure （t-BN）, and the thickness is about 0.4 μm. The flexural strengths of SiCf/SiC composites with and without BN interphase are about 180 and 95 MPa, respectively. Compared with the as-received SiCf/SiC composites, the composites with BN interphase exhibit an obvious toughened fracture behavior. From the microstructural analysis, it can be confirmed that the BN interphase plays a key part in protecting the fibers from chemical attack during matrix infiltration and weakening interfacial bonding, which can improve the mechanical properties of SiCf/SiC composites remarkably.展开更多
Soil respiration is a main dynamic process of carbon cycle in wetland. It is important to contribute to global climate changes. Water table and nutritious availability are significant impact factors to influence respo...Soil respiration is a main dynamic process of carbon cycle in wetland. It is important to contribute to global climate changes. Water table and nutritious availability are significant impact factors to influence responses of CO2 emission from wetland soil to climate changes. Twenty-four wetland soil monoliths at 4 water-table positions and in 3 nitrogen status have been incubated to measure rates of CO2 emission from wetland soils in this study. Three static water-table controls and a fluctuant water-table control, with 3 nitrogen additions in every water-table control, were carried out. In no nitrogen addition treatment, high CO2 emissions were found at a static low water table (Ⅰ) and a fluctuant water table (Ⅳ), averaging 306.7mg/(m2·h) and 307.89mg/(m2·h), respectively, which were 51%-57% higher than that at static high water table (Ⅱ and Ⅲ). After nitrogen addition, however, highest CO2 emission was found at Ⅱ and lowest emission at Ⅲ. The results suggested that nutritious availability of wetland soil might be important to influence the effect of water table on the CO2 emission from the wetland soil. Nitrogen addition led to enhancing CO2 emissions from wetland soil, while the highest emission was found in 1N treatments other than in 2N treatments. In 3 nutritious treatments, low CO2 emissions at high water tables and high CO2 emissions at low water tables were also observed when water table fluctuated. Our results suggested that both water table changes and nutritious imports would effect the CO2 emission from wetland.展开更多
基金Projects(51221001,50972121)supported by the National Natural Science Foundation of ChinaProject(B08040)supported by the Introducing Talents of Discipline to Universities,ChinaProject(11-BZ-2012)supported by the Research Fund of the State Key Laboratory of Solidification Processing(NWPU),China
文摘Short carbon fiber felts with an initial porosity of 89.5% were deposited by isobaric, isothermal chemical vapor infiltration using natural gas as carbon source. The bulk density of the deposited carbon/carbon （C/C） composites was 1.89 g/cm3 after depositing for 150 h. The microstructure and mechanical properties of the C/C composites were studied by polarized light microscopy, X-ray diffraction, scanning electron microscopy and three-point bending test. The results reveal that high textured pyrolytic carbon is deposited as the matrix of the composites, whose crystalline thickness and graphitization degree highly increase after heat treatment. A distinct decrease of the flexural strength and modulus accompanied by the increase of the toughness of the C/C composites is found to be correlated with the structural changes in the composites during the heat treatment process.
文摘This paper presents the thermodynamic performance analysis and comparison of four kinds of advanced pressurized fluidized bed combustion combined cycle (APFBC-CC) system schemes, two based on pressurized fluidized bed (PFB) combustion and the other two based on atmospheric circulating fluidized bed (CFB) combustion. The results show that the first scheme avoids high temperature gas filter, but has the lower cycle efficiency and syngas heating value. The second scheme can gain the highest cycle efficiency, however it is better to now lower the filter operating temperature. The third and fourth schemes, based on CFB, have lower efficiencies than the second one. But the fourth one, with preheating air/steam for gasification, can obtain the highest heating value of syngas and gain higher efficiency than the third one.
基金Project(51072165)supported by the National Natural Science Foundation of ChinaProject(KP201307)supported by the Fund of the State Key Laboratory of Solidification Processing in NWPU
文摘BN interphase was successfully synthesized on SiC fiber fabrics by dip-coating process using boric acid and urea as precursors under N2 atmosphere. The morphology of BN interphase was observed by SEM, and the structure was characterized by XRD and FT-IR spectra. The SiCf/SiC composites with dip-coated BN interphase were fabricated by chemical vapor infiltration （CVI） process, and the effects ofBN interphase on the mechanical properties of composites were investigated. The results show that the SiC fibers are fully covered by BN interphase with smooth surface and turbostratic structure （t-BN）, and the thickness is about 0.4 μm. The flexural strengths of SiCf/SiC composites with and without BN interphase are about 180 and 95 MPa, respectively. Compared with the as-received SiCf/SiC composites, the composites with BN interphase exhibit an obvious toughened fracture behavior. From the microstructural analysis, it can be confirmed that the BN interphase plays a key part in protecting the fibers from chemical attack during matrix infiltration and weakening interfacial bonding, which can improve the mechanical properties of SiCf/SiC composites remarkably.
文摘Soil respiration is a main dynamic process of carbon cycle in wetland. It is important to contribute to global climate changes. Water table and nutritious availability are significant impact factors to influence responses of CO2 emission from wetland soil to climate changes. Twenty-four wetland soil monoliths at 4 water-table positions and in 3 nitrogen status have been incubated to measure rates of CO2 emission from wetland soils in this study. Three static water-table controls and a fluctuant water-table control, with 3 nitrogen additions in every water-table control, were carried out. In no nitrogen addition treatment, high CO2 emissions were found at a static low water table (Ⅰ) and a fluctuant water table (Ⅳ), averaging 306.7mg/(m2·h) and 307.89mg/(m2·h), respectively, which were 51%-57% higher than that at static high water table (Ⅱ and Ⅲ). After nitrogen addition, however, highest CO2 emission was found at Ⅱ and lowest emission at Ⅲ. The results suggested that nutritious availability of wetland soil might be important to influence the effect of water table on the CO2 emission from the wetland soil. Nitrogen addition led to enhancing CO2 emissions from wetland soil, while the highest emission was found in 1N treatments other than in 2N treatments. In 3 nutritious treatments, low CO2 emissions at high water tables and high CO2 emissions at low water tables were also observed when water table fluctuated. Our results suggested that both water table changes and nutritious imports would effect the CO2 emission from wetland.
