含—NH2基团的有机改良硅酸盐材料合成及IR,DTA和TG分析

以正硅酸乙酯，γ－缩水甘油醚基丙基三甲基硅烷「ＣＨ２ＯＣＨＣＨ２Ｏ（ＣＨ２）３Ｓｉ（ＯＣＨ３０３，简称ＫＴＨ５６０」，胺基三甲基三乙氧基硅烷「ＮＨ２（ＣＨ２）３Ｓｉ（ＯＣ２Ｈ５）３简称ＫＨ５５０」，二乙烯三胺基甲基三乙氧基硅烷「ＮＨ２ＣＨ２ＣＨ２ＮＨＣＨ２ＣＨ２ＮＨＣＨ２Ｓｉ（ＯＣ２Ｈ５）３，简称ＮＤ－２３０」为原料，用溶胶－凝胶（ｓｏｌ－ｇｅｌ）工艺，把胺基引入材料基质中，制备了一些有机必良材料     

涂敷型铬酸盐钝化膜的结构与耐蚀性

采用ＳＲＤ，ＥＤＸＡ，ＧＤＳ等方法研究了镀锌钢板表面涂敷型ＣｒＯ３－Ｈ３ＰＯ４－ＳｉＯ２系钝化膜的成分与结构。该钝化膜是一种由ＣｒＯ３，Ｃｒ（ＯＨ）３，ＣｒＯＯＨ，ＺｎＣｒＯ４，ＺｎＳｉＯ３，Ｚｎ３（ＰＯ４）２，ＣｒＰＯ４和ＳｉＯ２组成的凝胶网络状结构的涂敷型复合转化膜。探讨了其耐蚀机理，中性盐雾试验表明：该钝化膜的耐蚀性大大优于ＣｒＯ３－ＳｉＯ２系钝化膜。     

溶胶—凝胶法合成了BaAl2Si2O8超细粉末的研究

以Ｂａ（ＯＨ）２．８Ｈ２Ｏ，Ａｌ（ＮＯ３）３．９Ｈ２Ｏ，ＴＥＯＳ为原料，采用溶胶－凝胶法制备ＢａＯ－Ａｌ２Ｏ３－ＳｉＯ２三元系粉末，研究了不同因素对生成稳定溶胶和胶化时间的影响，用ＴＧ－ＤＴＡ，ＸＲＤ研究了溶胶－凝胶的热处理过程，用ＴＥＭ观察了粉体的粒径。     

CaO—SiO2—P2O5—H2O系统中CBC材料的溶胶—凝胶过程研究：I.溶胶的形…

以溶胶－凝胶方法制备ＣａＯ－ＳｉＯ２－Ｐ２Ｏ５－Ｈ２Ｏ系统中ＣＢＣ材料工艺流程为基础，利用ＸＲＤ，ＩＲ及固体核磁共振（＾２９Ｓｉ，＾３１Ｐ－ＮＭＲ）等测试方法研究了溶胶的形成及溶胶－凝胶转变过程中的物相变化及物相间发生的化学反应，结果表明，在多组分溶胶的形成过程，由Ｃａ（ＮＯ３）２．４Ｈ２Ｏ和Ｈ３ＰＯ４反应生成Ｃａ２Ｏ２Ｏ７和Ｃａ１０（ＰＯ４）６（ＯＨ）２（羟基磷灰石，简写为ＯＨＡｐ，下同），两者     

SiC—Al2O3基复相陶瓷的N2—HIP研究

通过对热压ＳｉＣ－Ａｌ２Ｏ３复合材料进行了Ｎ２－ＨＩＰ后处理，制备得到Ｓｉ３Ｎ４－ＡｌＮ＝ＳｉＣ－Ａｌ２Ｏ３梯度材料，经Ｎ２－ＨＩＰ处理后，材料抗弯强度提高３５％－９５％，并得到经强度达１０３０ＭＰａ的ＳｉｅＮ４－ＡｌＮ／ＳｉＣｐ－ＳｉＣＷ－Ａｌ２Ｏ３复合材料。     

CaO-SiO_2-P_2O_5-H_2O体系中CBC材料的水化产物(二)水化产物的相分析

利用ＳＥＭ－ＥＤＳ和相分析技术对ＣａＯ－ＳｉＯ２－Ｐ２Ｏ５－Ｈ２Ｏ系统中ＣＢＣ材料的水化２８ｄ和３６５ｄ试样的抛光表面进行了观察分析，发现水化初期的物相分布以Ｃａ、Ｓｉ、Ｐ矿相为基体，占总相的６８．０５％；水化后期该相的量减少，Ｃａ、Ｐ相和Ｃａ、Ｓｉ相增多，并出现了纯Ｓｉ相，表明随水化进行，ＳｉＯ２和Ｐ２Ｏ５之间的相互固溶现象减少，最后详细分析了水化反应过程、强度机理以及水化后期体系出现较多ＳｉＯ２的原因     

SiC-CVD过程的人工神经网络建模

ＳｉＣ－ＣＶＤ过 本质复杂性制约 了碳／碳复合材料表面有效地制备高性能抗氧化涂层。本研究在对ＣＶＤ工艺过程及机理试验研究的基础上,采用人工神经网络技术对ＳｉＣ－ＣＶＤ过程进行了辨识与模拟研究,建立了ＳｉＣ－ＣＶＤ过程的神经网络的模型。     

Na2O—Al2O3—B2O3—SiO2系统溶胶,凝胶涂层的振动光谱研究

本文用振动光谱分析了Ｎａ２Ｏ－Ａｌ２Ｏ３－Ｂ２Ｏ３－ＳｉＯ２系统溶胶中的化学反应和用浸渍法制备的凝胶涂层结构。结果表明：部分硼、铝在溶胶陈化初期就与Ｓｉ（ＯＣ２Ｈ５）４的水解或缩聚产物反应形成线性聚合物，宜于浸涂。热处理时涂层中继续形成Ｓｉ－Ｏ－Ｓｉ、Ｓｉ－Ｏ－Ａｌ和Ｓｉ－Ｏ－Ｂ键；基本结构单元为［ＳｉＯ４］、［ＢＯ４］、［ＢＯ３］和［ＡｌＯ４］。     

CaO—SiO2—P2O5—H2O系统中CBC材料的溶胶—凝胶过程研究：II.凝胶的…

利用ＸＲＤ，ＩＲ，ＳＥＭ及＾２９Ｓｉ，＾３１Ｐ－ＮＭＲ等测试技术研究了ＣａＯ－ＳｉＯ２－Ｐ２Ｏ５－Ｈ２Ｏ系统中干凝胶在烧成过程中的物相变化及物相间发生的化学反应，认为凝胶在烧成过程的不同阶段发生的主要化学反应如下：（１）６７３～７７３Ｋ，由Ｃａ２Ｐ２Ｏ７和Ｃａ（ＮＯ３）２．４Ｈ２Ｏ反应生成了ＯＨＡｐ；（２）７３３～８７３Ｋ，由Ｃａ２Ｐ２Ｏ７和ＣａＯ反应生成了β－Ｃ３Ｐ；（３）８７３～９７３Ｋ；由Ｃ     

CaO—Al2O3—SiO2系统玻璃晶化时首析晶相及TiO2的作用机理预测和…

通过ＣａＯ－Ａｌ２Ｏ３－ＳｉＯ２系统玻璃的结构分析预测玻璃晶化时首析晶相是钙长石。选取ＣａＯ－Ａｌ２Ｏ３－ＳｉＯ２三元相图成玻璃区内的某点作为基础玻璃的组成，在基础玻璃吕加入ＴｉＯ２。用ＤＴＡ，ＸＲＤ和ＳＥＭ方法的研究结果表明，不玻璃中加ＴｉＯ２与否，晶化时首先析出的晶相都是钙长石，且均为从表面向内部生长，驰预测相符。     

Stoichiometry of the C + SiO2 Reaction

The reaction of one-to-one molar carbon/silica powder mixtures was studied using simultaneous thermogravimetric analysis and mass spectroscopy with crystalline and amorphous silica. Reaction proceeded via a two-stage path in which there are at least three identifiable competing global reactions. During the first stage, silicon carbide is formed along with small amounts of silicon monoxide. The most likely reaction path during this stage is the following: SiO₂( s ) + C( s ) → SiO( g ) + CO( g ); SiO( g ) + 2C( s ) → SiC( s ) + CO( g ). The second stage consists of reactions between silica with silicon carbide which form silicon monoxide and, where conditions permit, may also form silicon metal. The major reaction during this stage is 2SiO₂( g ) + SiC( s ) → 3SiO( g ) + CO( g ).     

多孔碳化硅陶瓷的抗热震性研究

本文考察了多了孔碳化硅陶瓷的抗热震性,并探讨了不同制造工艺对多孔碳化硅陶瓷抗热震性的影响。同时研究了ＳｉＣ陶瓷在热处理过程中ＳｉＣ颗粒表面氧化形成的ＳｉＯ２在不同热处理温度的状态变化及其对试样抗热震性的影响。     

Y2O3—Al2O3—SiO2添加剂在低温烧结SiC中的作用

本文探讨了Ｙ２Ｏ３－Ａｌ２Ｏ３添加剂在低温无压烧结ＳｉＣ中的作用以及在Ｙ２Ｏ３－Ａｌ２Ｏ３添加剂中引入ＳｉＯ２的作用及机理,从而阐明了通过多项合理、有效复合添加降低ＳｉＣ烧结温度的可能性。     

Fabrication of wood-like porous silicon carbide ceramics without templates

The porous silicon carbide ceramics with wood-like structure have been fabricated via high temperature recrystallization process by mimicking the formation mechanism of the cellular structure of woods. Silicon carbide decomposes to produce the gas mixture of Si, Si₂C and SiC₂ at high temperature, and silicon gas plays a role of a transport medium for carbon and silicon carbide. The directional flow of gas mixture in the porous green body induces the surface ablation, rearrangement and recrystallization of silicon carbide grains, which leads to the formation of the aligned columnar fibrous silicon carbide crystals and tubular pores in the axial direction. The orientation degree of silicon carbide crystals and pores in the axial direction strongly depends on the temperature and furnace pressure such as it increases with increasing temperature while it decreases with increasing furnace pressure.     

纳米SiO2对先驱体浸渍裂解法制备SiCf/SiC复合材料力学性能的影响

以纳米SiO2为填料,采用先驱体浸渍裂解法制备2.5D-SiCf/SiC（D为维数,SiCf为SiC纤维）复合材料,研究了前驱液中纳米SiO2含量对复合材料力学性能的影响。结果表明,纳米SiO2的添加能有效抑制先驱体裂解过程中的体积收缩,提高致密度,但过量引入易导致浸渍液黏度过高,浸渍效率降低。纳米SiO2含量对材料力学性能有较大影响,添加纳米SiO2后材料的抗弯强度和断裂韧性均高于没有添加的样品,材料抗弯强度随纳米SiO2含量的增加先增大后降低。当浸渍液中纳米SiO2含量为6%时,复合材料具有优异的力学性能,抗弯强度达到211.1MPa。     

从含碱硅酸钠溶液中水热合成硅灰石

以含碱硅酸钠溶液为原料,在常压下加入石灰乳,先水热合成CaO·SiO2·H2O,再将CaO·SiO2·H2O在850℃下焙烧2 h可制备硅灰石.研究了溶液中SiO2浓度、钙硅摩尔比(C/S)及反应时间对硅灰石合成的影响.热力学计算结果表明,常压下Na2O-CaO-SiO2-H2O体系中,最有可能形成CaO·SiO2·H2O及2CaO·SiO2·1.17H2O.实验结果表明:当C/S为1.0时,随着溶液中硅浓度的增加,硅酸根离子的聚合程度增加,有利于硅灰石的制备;随着时间的延长,硅灰石结晶程度越高;当C/S为0.6、0.8、1.0时,最终产物为CaSiO3;当C/S为1.5、2.0时,最终产物中含有大量的Ca2SiO4.适宜的水热合成条件为:SiO2浓度>30 g/L、C/S 0.6～1.0、温度98℃、反应时间>3 h.     

Comparison of the Pyrolysis Products of Dichlorodimethylsilane in the Chemical Vapor Deposition of Silicon Carbide on Silica in Hydrogen or Argon

A chemical analysis of the pyrolysis gases and solids formed during the deposition of silicon carbide from the decomposition of dichlorodimethylsilane in argon and hydrogen is reported. Depositions were performed at 1 atm pressure, temperatures from 700° to 1100°C, and a mean residence time of approximately 1 min. The chemical analysis shows that, under reactor conditions, the gases formed were mainly methane, hydrogen, silicon tetrachloride, trichloro-silane, and trichloromethylsilane. The presence of hydrogen chloride was not examined. The use of hydrogen, as a carrier gas, decreased the trichloromethylsilane and solid aerosol (smoke) in the reaction products, compared to that present in the argon system, and increased methane, trichlorosilane, and silicon production. Primarily, silicon and silicon carbide were deposited when hydrogen was used as the carrier gas. When argon was used, a complex mixture of silicon carbide and organosilicon compounds was formed. It is hypothesized that, when hydrogen was used as the carrier gas, silicon carbide formed from chlorosilanes and methane, which were products from the decomposition of dichlorodimethylsilane. These products subsequently reacted to form silicon, which then reacted with methane to form silicon carbide. In argon, however, it is hypothesized that silicon carbide can be formed in two ways: (1) from the pyrolysis of solid organosilicon compounds which are products from the pyrolysis of dichlorodimethylsilane in argon and (2) as the reduction of dichlorodimethylsilane to chlorosilanes and methane, caused by the hydrogen produced from the pyrolysis of dichlorodimethylsilane in argon.     

The degradation behavior of C/SiC composites fabricated by polymer impregnation and pyrolysis process under simulated space atomic oxygen environment

Carbon fiber reinforced silicon carbide (C/SiC) composites fabricated by polymer impregnation and pyrolysis (PIP) have been exposed in simulated space atomic oxygen (AO) environment for up to 15 h. The mechanical properties and chemical composition of PIP C/SiC composites have been studied. The results show that the mass loss of the composites increases at the beginning and then decreases as the exposure time lasts. The flexural properties of C/SiC composites have no obvious changes after up to 15 h exposure in AO. C/SiC composites have been oxidized slightly by AO. The amorphous carbon in the matrix has been oxidized to CO or CO₂ gas and SiC has been oxidized to SiO gas and SiO₂.     

Si-C-O复杂体系中的化学反应

由热力学分析了Si-C -O系中一些化学反应之间的关系以及SiC制品的钝化氧化。在有固体碳过剩存在的条件下 ,绘制了该体系凝聚相的稳定区域图。计算表明 ,气相中SiO气体含量不小 ,这就为生产SiO2 微粉创造了条件。文中针对SiC制品的钝化氧化与活化氧化进行了分析     

Kinetic studies on production of silicon carbide from rice husks

Abstract

A kinetic study on a non-conventional route for the production of silicon carbide was carried out on a laboratory scale. Silicon carbide was produced by vacuum pyrolysis of rice husks in the temperature range 1200–1600°C. The resulting products were characterised by XRD and chemical analysis. Attempts were made to develop the parametric relationships correlating the yield of silicon carbide to the process variables and starting material characteristics. Empirical relationships defining the rate of silicon carbide formation as a function of temperature, compaction pressure, CO gas diffusion, and compact porosity are proposed.