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研究了硅粉直接氮化反应合成氮化硅粉末的工艺因素(包括硅粉粒度、氮化温度、成型压力、稀释剂含量等),借助XRD、SEM等测试手段测定和观察了氮化产物的物相组成和断口形貌。研究结果表明:硅粉在流动氮气氛下,高于1200℃氮化产物中氮含量明显增加;在氮化反应同时还伴随着硅粉的熔结过程,它阻碍硅粉的进一步氮化,其影响程度与氮化温度、氮化速度,素坯成型压力及硅粉粒度等工艺因素有关。在硅粉素坯中引入氮化,其影响程度与氮化温度、氮化速度,素坯成型压力及硅粉粒度等工艺因素有关。在硅粉素坯中引入氮化硅作为稀释剂,提高了硅粉的氮化率,使产物中残留硅量降低;同样在实际生产中可以通过控制适当热处理制度(如分段保温、慢速升温),达到硅粉的完全氮化。在生产中批量合成了含氮量为32.5%,残留硅量为0.05%,主要为α相,含少量β相的针状、柱状的氮化硅。 相似文献
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硅粉直接氮化反应合成氮化硅研究 总被引:15,自引:2,他引:15
研究了硅粉直接氮化反应合成氮化硅粉末的工艺因素(包括硅粉粒度、氮化温度、成型压力、稀释剂含量等),借助XRD,SEM等测试手段测定和观察了氮化产物的物相组成和断口形貌.研究结果表明:硅粉在流动氮气氛下,高于1200℃氮化产物中氮含量明显增加;在氮化反应同时还伴随着硅粉的熔结过程,它阻碍硅粉的进一步氮化,其影响程度与氮化温度、氮化速度,素坯成型压力及硅粉粒度等工艺因素有关.在硅粉素坯中引入氮化硅作为稀释剂,提高了硅粉的氮化率,使产物中残留硅量降低;同样在实际生产中可以通过控制适当热处理制度(如分段保温、慢速升温),达到硅粉的完全氮化.在生产中批量合成了含氮量为32.5%,残留硅量为0.05%,主要为α相,含少量β相的针状、柱状的氮化硅. 相似文献
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以平均粒径为2.8μm的硅粉为原料,添加氮化硅粉作为稀释剂,对常压氮气下直接氮化制备Si3N4粉的工艺进行了研究,借助于氮氧测定仪、XRD、SEM等检测方法,分析了硅粉常压直接氮化制备Si3N4粉过程中稀释剂种类、稀释剂添加比例、氮化温度、氮化时间等因素对硅的氮化过程的影响.研究结果表明:硅粉在流动常压氮气下,当氮化温度高于1410℃时,硅的转化率迅速增加,氮化产物中β相含量也增加;通过控制稀释剂的添加种类和添加比例、氮化时间和氮化温度,可合成高α相含量的Si3N4.采用平均粒径为2.8μm的硅粉,在常压氮气下,当添加30%的α-Si3N4粉作为稀释剂、氮化温度为1550℃、氮化时间为10min时,合成了氮含量为39.4%,游离硅为0.7%,主要为α相、含部分β相的Si3N4粉. 相似文献
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钙镁磷肥中硅测定采用氟硅酸钾容量法时 ,由于溶样存在问题 ,使硅含量偏离真实值 ,通过试验 ,认为 w(Si O2 ) >30 %或 Mg O含量偏低 (<10 % )的样品 ,不能用盐酸溶样 ,需用王水 ,并提出分析硅含量应注意的事项 相似文献
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用4mol/LHNO3做溶剂来溶解稳定性较强的SAPO系列分子筛母液以便测定其化学组成,溶样仅需5min。此种溶样方法明显优于传统方法。溶样完全、操作简便重现性好且对溶样后分子筛母液中铝、硅、磷含量的测定无影响。此外,本文对SAPO系列分子筛母液中中铝、硅、磷含量的多种测量方法进行了比较,发现用固体二甲酚橙作指示剂的Zn(Ⅱ)盐返滴定法测铝含量比PAN作指示剂的Cu(Ⅱ)盐返滴法更好、氟硅酸钾容量法测定硅含量比重量法更合适、用二甲酚橙作指示剂的Bi(Ⅲ)盐返滴定法测磷含量比哇钼柠酮重量法更准确。所得结果均能达到与XRF分析法相同的准确度。 相似文献
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本文提出了一次溶样测硅、镁的方法,试样用碱溶解后,用硝酸酸化。取所制溶液采用吸光光发法分析硅、镁含量,该法准确、简便、快捷。 相似文献
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Hironori Kodama Hiroshi Sakamoto Tadahiko Miyoshi 《Journal of the American Ceramic Society》1989,72(4):551-558
SiC-monofilament-reinforced SiC or Si3 N4 matrix composites were fabricated by hot-pressing, and their mechanical properties and effects of filaments and filament coating layers were studied. Relationships between frictional stress of filament/matrix interface and fracture toughness of SiC monofilament/Si3 N4 matrix composites were also investigated. As a result, it was confirmed experimentally that in the case of composites fractured with filament pullout, the fracture toughness increased as the frictional stress increased. On the other hand, when frictional stress was too large (>about 80 MPa) for the filament to be pulled out, fracture toughnesses of the composites were almost the same and not so much improved over that of Si3 N4 monolithic ceramics. The filament coating layers were found to have a significant effect on the frictional stress of the SiC monofilament/Si3 N4 matrix interface and consequently the fracture toughness of the composites. Also the crack propagation behavior in the SiC monofilament/Si3 N4 matrix composites was observed during flexural loading and cyclic loading tests by an in situ observation apparatus consisting of an SEM and a bending machine. The filament effect which obstructed crack propagation was clearly observed. Fatigue crack growth was not detected after 300 cyclic load applications. 相似文献
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Michael Kmetz Steven Suib Francis Galasso 《Journal of the American Ceramic Society》1990,73(10):3091-3093
Composites of SiC/Si and SiC/SiC were prepared from single yarns of SiC. The use of carbon coatings on SiC yarn prevented the degradation normally observed when chemically vapor deposited Si is applied to SiC yarn. The strength, however, was not retained when the composite was heated at elevated temperatures in air. In contrast, the strength of a SiC/C/SiC composite was not reduced after this composite was heated at elevated temperatures, even when the fiber ends were exposed. 相似文献
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Tyrone Mitchell Jr. † ‡ Lutgard C. De Jonghe † ‡ Warren J. MoberlyChan Robert O. Ritchie† ‡ 《Journal of the American Ceramic Society》1995,78(1):97-103
α-silicon carbide platelet/β-silicon carbide composites have been produced in which the individual platelets were coated with an aluminum oxide layer. Hot-pressed composites showed a fracture toughness as high as 7.2 MPa·m1/2 . The experiments indicated that the significant increase in fracture toughness is mainly the result of crack deflection and accompanying platelet pullout. The coating on the platelets also served to prevent the platelets from acting as nucleation sites for the α- to β-phase transformation, so that the advantageous microstructure remains preserved during high-temperature processing. 相似文献
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Silicon/Silicon Carbide Composites Fabricated by Infiltration of a Silicon Melt into Charcoal 总被引:4,自引:0,他引:4
Dong-Woo Shin Sam Shik Park Yong-Ho Choa Koichi Niihara 《Journal of the American Ceramic Society》1999,82(11):3251-3253
Dense Si/SiC composites were fabricated via a conventional reaction-bonding process, using oak charcoal that exhibited a honeycomb structure. The silicon melt was infiltrated into the porous oak charcoal (density of ~0.6 g/cm3 ) while the sample was heated to 1700°C under vacuum (10-3 torr (~0.133 Pa)), which resulted in in situ silicon-fiber/SiC composites. The reaction product had an average density of 2.8 g/cm3 and showed three-point flexural strengths of 330 MPa at room temperature and 280 MPa at 1300°C. Good oxidation resistance also was observed at temperatures up to 1300°C in flowing air. This process provided excellent shape-making capability, because the charcoal that was used as a preform was readily machinable. 相似文献
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Ethanolic silicon suspensions, with and without a polyethoxylated amine of low molecular weight, were studied by rheological, adsorption, electrophoretic, and sedimentation methods. Pellets were pressure-cast and nitrided to form reaction-bonded silicon nitride. Density and binding strength in the green state relate well to rheological behavior and other collodial aspects of the suspensions used, particularly the additive's role and distribution. Density and degree of nitridation in the final state are not importantly affected by the additive's use. Its greatest benefit is to modify the binding strength in the green state. The mode by which this small molecule affects the processing of silicon consists of adsorption, combined with an increased electrostatic interparticle repulsion which increases the suspension viscosity and that of undried pellets. Although the improved binding strength is accompanied by decreased green and nitrided densities, high degrees of conversion to silicon nitride are still achieved. 相似文献
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Doo J. Choi David B. Fischbach William D. Scott 《Journal of the American Ceramic Society》1989,72(7):1118-1123
Oxidation of {111} single-crystal silicon and dense, chemically-vapor-deposited silicon nitride was done in clean silica tubes at temperatures of 1000° to woo°C. The oxidation rates of silicon nitride under various atmospheres (dry O2 , wet O2 , wet inert gas, and steam) were several orders of magnitude slower than those of silicon under the identical conditions. The activation energy for the oxidation of silicon nitride decreased from 330 to 259 kJ/mol in going from dry O2 to steam while that for Si decreased from 120 to 94 kJ/mol. The parabolic rate constant for Si increased linearly as the water vapor pressure increased. However, the parabolic rate constant for silicon nitride showed nonlinear dependency on the water vapor pressure in the presence of oxygen. The oxidation kinetics of silicon nitride is explained by the formation of nitrogen compounds (NO and NH3 ) at the reaction interface and the counterpermeation of these reaction products. 相似文献
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SiC was synthesized via the gas-phase reaction between SiO and CH4 at 1500° and 1560°C in a tubular flow reactor. SiO vapor was generated from equimolar powder mixtures of Si and SiO2 in the reactor while CH4 was externally supplied. Products of different morphologies were collected at different longitudinal locations: whiskers, crystal aggregates, scale, and powder. The total yield of SiC, based on the amount of SiO generated, reached as high as 99%, of which 25–46% by mass was fine powder with sizes ranging from 60 to 300 nm. 相似文献
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R. R. WILLS I. SEKERCIOGLU D. E. NIESZ 《Journal of the American Ceramic Society》1980,63(7-8):401-403
Silicon aluminum oxynitride solid solutions (sialons) based on β-Si3 N4 and Si2 N2 O behave differently in contact with molten sih'con. The Si2 N2 O-based sialons convert to almost pure Si3 N4 , apparently through a two-step decomposition and solution-precipitation reaction, whereas the β-Si3 N4 sialons are preferentially attacked at the grain boundaries. The composition of the grain-boundary phase appears to control the rate of reaction. 相似文献