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Preparation and Dielectric Properties of Nonstoichiometric β-SiC Powder by Combustion Synthesis

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Journal of Materials Science & Technology 2009年第3期25卷 401-404页

作者： Xiaolei Su Wancheng Zhou Zhimin Li fa luo Dongmei Zhu State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi＇an 710072 China College of Mechanical ＆ Electronic Engineering Xi＇an Polytechnic University Xi＇an 710048 China School of Technical Physics Xidian University Xi＇an 710071 China

The nonstoichiometric β-SIC powders were synthesized via combustion reaction of Si and C system in a 0.1 MPa nitrogen atmosphere, using Teflon as the chemical activator. The prepared powders were invistigated by XRD and Raman spectra. The results indicates that the cell parameters of all the prepared β-SIC powder are smaller than the standard value of β-SIC because of generation of CSi defects. The complex permittivity of prepared products was carried out in the frequency range of 8.2-12.4 GHz. It shows that the dielectric property of prepared β-SiC powder decrease with increasing PTFE content. The effect of CSi defects on dielectric property of β-SiC powder has been discussed.

关键词： Silicon carbide Carbon antisite Dielectric property

Nine new species of the spider genus Stedocys (Araneae, Scytodidae) from China and Thailand

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Zoological Research 2017年第5期38卷 215-242页

作者： Jiang-Lang Wu Yu-fa luo Shu-Qiang Li Southeast Asia Biodiversity Research Institute Chinese Academy of Sciences Yezin Nay Pyi Taw 05282 Myanmar Institute of Zoology Chinese Academy of Sciences Beijing 100101 China School of Life and Environment Sciences Gannan Normal University Ganzhou Jiangxi 341000 China University of Chinese Academy of Sciences Beijing 100049 China

Nine new species of the genus Stedocys Ono, 1995 are described： Stedocys gaolingensis Wu ＆ Lisp. n. （♂♀, Guangxi）, S. huangniuensis Wu ＆ Lisp. n. （♀, Guangxi）, S. ludiyanensis Wu ＆ Lisp. n. （♂♀, Guangxi）, S. matuoensis Wu ＆ Lisp. n. （♀, Guangxi）, S. pulianensis Wu ＆ Lisp. n. （♂, Guangxi）, S. shilinensis Wu ＆ Lisp. n. （♂♀, Hainan）, S. xianrenensis Wu ＆ Li sp. n. （♂♀, Guangxi）, S. xiangzhouensis Wu ＆ Li sp. n. （♂♀, Guangxi） from China, and S. zhaoi Wu ＆ Li sp. nov. （♂♀, Kanchanaburi） from Thailand. Diagnoses of nine new species are provided. DNA barcodes for six new species are documented for future use and as proof of molecular differences between these species.

关键词： Taxonomy Morphology Diagnosis Biodiversity Caves

Dielectric Properties of Porous Reaction-boned Si_3N_4 Ceramics with Controlled Porosity and Pore Size

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Journal of Materials Science & Technology 2008年第2期24卷 207-210页

作者： Jie XU Dongmei ZHU fa luo Wancheng ZHOU Peng LI State KeyLaboratory of Solidification Processing Northwestern Polytechnical University Xi＇an 710072 China

This paper presents the microwave dielectric properties of reaction bonded porous silicon nitride ceramics with variant porosity and pore size, which were prepared by adding pore-forming agent grains into the silicon powders. The experimental results show that the dielectric constant and the dielectric loss of the samples reduce evidently with increasing porosity in the sample. When the porosity is constant, the dielectric constant and the dielectric loss of the ceramics decrease visibly as the pore size increases. Among all the obtained samples, the minimum dielectric constant is about 2.4.

关键词： Porous silicon nitride ceramics Reaction bonded Dielectric properties Radome

Preparation and characteristic of NASICON ceramics

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Rare Metals 2006年第z1期25卷 39-42页

作者： ZHU Dongmei luo fa XIE Zhanglong ZHOU Wancheng State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi''an 710072 China State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi''an 710072 China State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi''an 710072 China State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi''an 710072 China

Hot-pressed sintering was employed to prepare the sodium super ionic conductor (Na1+xZr2SixP3-xO12, 1.8≤x≤2.2) ceramics and compare with the sample obtained from normal-press sintering. The phase formation, density, and conductivity of the hot-press sintered and the normal-press sintered samples were investigated in detail. Results show that the density of NASICON ceramics and the degree of crystallization can be improved by hot-press process efficiently. The density of the sample sintered by normal sintering is obviously lower than that sintered by hot press. XRD analysis indicates all the hot press sintered samples contain mainly monoclinic NASICON and no ZrO2 phase was found. The ionic conductivity of normal-press sintered sample is much lower than that of hot-press sintered sample. When the composition is close to Na3Zr2Si2PO12, the dc conductivities of the hot press sintered samples were in the order of 10-3 S·cm-1. The variation of the ac conductivity with frequency in the high frequency region agrees with the power law feature of σ(ω)∝ωn(0

关键词： NASICON normal sintering hot pressed sintering electronic conductivity

Preparation and Mechanical Properties of Glass Coats with High Temperature Radar Absorber

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Chinese Journal of Aeronautics 2006年第B12期19卷 102-105页

作者： ZHU Dong-mei luo fa XIONG Liang-ming ZHOU Wan-cheng State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi＇an 710072 China

BaO-La2O3-B2O3 （BLB） glass, suitable to be used as a sealing between metals, was chosen to be the binder in preparing glass coats on the Ti-alloy substrate. The SiCN nano-powder was introduced as the filler for the absorbing coat because it is considered to be a good high temperature absorber. The effect of the coating temperature and coating time on the tensile strength of the glass coat was investigated and the proper coating parameters to get good mechanical properties were determined. In addition, the effects of the SiCN content on the tensile strength of the absorbing coat were also discussed. Results show that it is possible to prepare the glass coat using the BLB glass as a binder. That the coat formed at 730℃ for 30 min has the best tensile strength witnesses 730 ℃, 30 min to be the proper parameter to prepare the glass coat. The BLB glass coat without SiCN powder possesses good tensile strength and the introduction of the SiCN absorber into the glass coat will lower the tensile strength. As the SiCN content increases, the tensile strength of the absorbing coat decreases, which could be attributed to the aggregation of SiCN in the coats.

关键词： BaO-La2O3-B2O3 glass SiCN nano powder tensile strength absorbing coat

Ammonia volatilization losses and ^(15)N balance from urea applied to rice on a paddy soil

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Journal of Environmental Sciences 2006年第2期18卷 299-303页

作者： faN Xiao-hui SONG Yong-sheng LIN De-xi YANG Lin-zhang luo Jia-fa Institute of Soil Science Chinese Academy of Sciences Nanjing 210008 China Land and Environmental Management Group AgRsearch Ruakura Research Centre East Street Private Bag 3123 Hamilton New Zealand

Ammonia volatilization loss and ^15N balance were studied in a rice field at three different stages after urea application in Taihu Lake area with a micrometeorological technique. factors such as climate and the NH4^＋-N concentration in the field floodwater affecting ammonia loss were also investigated. Results show that the ammonia loss by volatilization accounted for 18.6%-38.7% of urea applied at different stages, the greatest loss took place when urea was applied at the tillering stage, the smallest at the ear bearing stage, and the intermediate loss at the basal stage. The greatest loss took place within 7 d following the fertilizer application. Ammonia volatilization losses at three fertilization stages were significantly correlated with the ammonium concentration in the field floodwater after the fertilizer was applied. ^15N balance experiment indicated that the use efficiency of urea by rice plants ranged between 24.4% and 28.1%. At the early stage of rice growth, the fertilizer nitrogen use efficiency was rather low, only about 12%. The total amount of nitrogen lost from different fertilization stages in the rice field was 44.1%-54.4%, and the ammonia volatilization loss was 25.4%-33.3%. Reducing ammonia loss is an important treatment for improving N use efficiency.

关键词： ammonia volatilization urea ^15N balance rice influence factors, Taihu region

Study on Microwave Dielectric Property of Carbon Black and Short Carbon Fibers

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Chinese Journal of Aeronautics 2006年第B12期19卷 130-133页

作者： WUHong-huan ZHU Dong-mei luo fa ZHOU Wan-cheng WANG Xiao-yan State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi＇an 710072 China

Carbon black and carbon fibers of different lengths were introduced in different matrices at different ratios to explore their microwave dielectric properties under 8.2 GHz-12.4 GHz. It is found that the actual dielectric constants of the samples containing carbon black are in a two-order function of the contents of carbon black （ε＇, ε＂=Av2＋Bv＋C） and the complex dielectric constants show an obvious frequency response. Of the added fibers of different lengths, the 4 mm-long one could well disperse in the matrices having not only good frequency response, but also larger real parts, imaginary parts and loss values. The imaginary parts and the loss values （tanδ）of the samples with 4 mm-long carbon fibers added increase linearly with the contents of fiber increasing. So it is practicable to adjust the dielectric parameters of the material in a wide range by changing the added amount of carbon black, and the carbon fiber or altering the lengths of the carbon fiber added.

关键词： microwave dielectric property short carbon fibers carbon black

Ammonia Volatilization and Nitrogen Utilization Efficiency in Response to Urea Application in Rice Fields of the Taihu Lake Region,China

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Pedosphere 2007年第5期17卷 639-645页

作者： LIN De-Xi faN Xiao-Hui HU Feng ZHAO Hong-Tao luo Jia-fa Institute of Soil Science Chinese Academy of Sciences Nanjing 210008 （China） Department of Soil and Water Science Tropical Research and Education Center Institute of Food and Agricultural Sciences University of Florida Homestead FL33031 （USA） College of Resource and Environmental Sciences Nanjing Agricultural University Nanjing 210095 （China） College of Resource and Environmental Sciences Fujian Agriculture ＆ Forestry University Fuzhou 350007 （China） Land and Environmental Management Group AgResearch Ruakura Research Centre Private Bag 3123 Hamilton （New Zealand）

Ammonia volatilization losses, nitrogen utilization efficiency, and rice yields in response to urea application to a rice field were investigated in Wangzhuang Town, Changshu City, Jiangsu Province, China. The N fertilizer treatments, applied in triplicate, were 0 （control）, 100, 200, 300, or 350 kg N ha^-1. After urea was applied to the surface water, a continuous airflow enclosure method was used to measure ammonia volatilization in the paddy field. Total N losses through ammonia volatilization generally increased with the N application rate, and the two higher N application rates （300 and 350 kg N ha^-1） showed a higher ratio of N lost through ammonia volatilization to applied N. Total ammonia loss by ammonia volatilization during the entire rice growth stage ranged from 9.0% to 16.7% of the applied N. Increasing the application rate generally decreased the ratio of N in the seed to N in the plant. For all N treatments, the nitrogen fertilizer utilization efficiency ranged from 30.9% to 45.9%. Surplus N with the highest N rate resulted in lodging of rice plants, a decreased rate of nitrogen fertilizer utilization, and reduced rice yields. Calculated from this experiment, the most economical N fertilizer application rate was 227 kg ha^-1 for the type of paddy soil in the Taihu Lake region. However, recommending an appropriate N fertilizer application rate such that the plant growth is enhanced and ammonia loss is reduced could improve the N utilization efficiency of rice.

关键词： ammonia volatilization N application rate N utilization efficiency paddy soil rice yield

Influence of ash composition on the sintering behavior during pressurized combustion and gasification process

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2012年第3期13卷 230-238页

作者： Ni-jie JING Qin-hui WANG Yu-kun YANG Le-ming CHENG Zhong-yang luo Ke-fa CEN State Key Laboratory of Clean Energy Utilization Zhejiang University Hangzhou 310027 China

To determine the ash characteristics during fluidized bed combustion and gasification purposes, the investigation of the impacts of chemical composition of Jincheng coal ash on the sintering temperature was conducted. A series of experiments on the sintering behavior at 0.5 MPa was performed using the pressurized pressure-drop technique in the combustion and gasification atmospheres. Meanwhile, the mineral transformations of sintered ash pellets were observed using X-ray diffractometer （XRD） analyzer to better understand the experimental results. In addition, quantitative XRD and field emission scanning electron microscope/energy dispersive X-ray spectrometer （FE-SEM/EDS） analyses of ash samples were used for clarifying the detailed ash melting mechanism. These results show that the addition of Fe203 can obviously reduce the sintering temperatures under gasification atmospheres, and only affect a little the sintering temperature under combustion atmosphere. This may be due to the presence of iron-bearing minerals, which will react with other ash compositions to produce low-melting-point eutectics. The FE-SEM/EDS analyses of ash samples with Fe203 additive show consistent results with the XRD measurements. The CaO and Na20 can reduce the sintering temperatures under both the combustion and gasification atmospheres. This can be also contributed to the formation of low-melting-point eutectics, decreasing the sintering temperature. Moreover, the fluxing minerals, such as magnetite, anhydrite, muscovite, albite and nepheline, contribute mostly to the reduction of the sintering temperature while the feldspar minerals, such as anorthite, gehlenite and sanidine, can react with other minerals to produce low-melting-point eutectics, and thereby reduce the sintering temperatures.

关键词： Ash composition Sintering temperature X-ray diffractometer (XRD) Field emission scanning electron microscope/energy dispersive X-ray spectrometer (FE-SEM/EDS)