活性填料在先驱体转化制备陶瓷材料中的应用

综述了用先驱体法制备陶瓷材料的特点,针对先驱体法气孔率高及收缩率大的不足,提出了三个解决办法,其中着重讨论了活性填料的选择原则及其在先驱体裂解制备陶瓷中的特点、应用及国内外研究现状．     

先驱体法制备氮化硼陶瓷材料的研究进展

氮化硼陶瓷是一种性能优异并有很大发展潜力的新型陶瓷材料,但是传统的高温合成法无法制备高质量的BN纤维、薄膜、泡沫、涂层或复杂形状的复合材料,只能通过先驱体法实现。简单介绍了先驱体陶瓷技术,重点综述了先驱体法制备氮化硼陶瓷纤维和氮化硼陶瓷复合材料的研究进展,并对先驱体法制备氮化硼陶瓷的发展趋势做了展望。     

聚硅烷陶瓷先驱体研究进展

具有σ-共轭结构特点的聚硅烷有着特殊的性能及用途。概述了聚硅烷作为陶瓷先驱体在制备陶瓷纤维、多孔陶瓷、陶瓷基复合材料3个方面的应用研究进展,并针对目前存在的不足指出了今后的研究方向。     

填料辅助先驱体转化法制备陶瓷基复合材料的研究进展

先驱体转化法是一种比较成熟的制备陶瓷基复合材料的方法。填料在先驱体转化法制备陶瓷基复合材料的过程中起着重要作用。填料主要包括惰性填料和活性填料两种,阐述了两种填料的作用机理及选取原则,并对国内外填料的研究及发展现状进行了综述。最后对填料的发展趋势提出了自己的看法。     

由聚碳硅烷生成纳米SiC颗粒增强B4C基复相陶瓷的结构与性能

制备了由聚碳硅烷（PCS）为先驱体裂解形成的纳米SiC增强的B4C基复合材料，并与直接球磨混合法制备的纳米SiC增强的B4C基复合材料进行了对比研究。实验结果表明，先驱体法制备的复合材料形成一种复杂的晶内/晶间结构；B4C内部的纳米SiC和Al2O3内部的少量纳米SiC、晶界处的层片状SiC、B4C晶粒内部的SiC亚晶界结构。材料的断裂方式以穿晶断裂为主，形成晶内裂纹扩展路径，增强了材料的韧性，采用PCS为先驱体工艺制备高性能的纳米复相陶瓷，其组织均匀性、致密度和力学性能均优于直接机械混合制备的纳米复合材料。     

先驱体转化法制备连续纤维增强陶瓷基复合材料的研究

综述了先驱体转化法制备连续纤维增强陶瓷基复合材料在先驱体、致密化工艺、微观结构、性能等方面的国内外研究情况 ,最后提出了今后进一步研究的方向     

先驱体转化法制备连续纤维增强陶瓷基复合材料的研究

综述了先驱体转化法制备连续纤维增强陶瓷基复合材料在先驱体、致密化工艺、微观结构、性能等方面的国内外研究情况,最后提出了今后进一步研究的方向。     

活性填料在先驱体转化法纤维增强陶瓷基复合材料中的应用 Ⅰ.复合材料的致密化模型

在先驱体转化陶瓷基复合材料的制备中,坯体在裂解前后的体积发生变化。引入体系体积收缩率参数,对单一先驱体转化纤维增强陶瓷基复合材料致密化模型进行了修正。同时,分别对含惰性填料和/或活性填料的先驱体浆料浸渍-裂解纤维增强陶瓷基复合材料致密化进行了模型分析。从理论上揭示了复合材料的浸渍-裂解周期与材料的理论密度和理论孔隙率之间的关系。当先驱体浆料中含有活性填料时,复合材料的理论密度和理论孔隙率与活性填料的反应陶瓷产率、反应密度比、体积收缩率有密切的数学关系。在先驱体中引入活性填料比引入惰性填料能更为有效地提高材料的密度,降低材料的孔隙率。     

由聚碳硅烷生成纳米SiC颗粒增强B4C基复相陶瓷的结构与性能

制备了由聚碳硅烷（PCS）为先驱体裂解形成的纳米SiC增强的B₄C基复合材料,并与直接球磨混合法制备的纳米SiC增强的B₄C基复合材料进行了对比研究.实验结果表明,先驱体法制备的复合材料形成一种复杂的晶内/晶间结构;B₄C内部的纳米SiC和Al₂O₃内部的少量纳米SiC、晶界处的层片状SiC、B₄C晶粒内部的SiC亚晶界结构.材料的断裂方式以穿晶断裂为主,形成晶内裂纹扩展路径,增强了材料的韧性.采用PCS为先驱体工艺制备高性能的纳米复相陶瓷,其组织均匀性、致密度和力学性能均优于直接机械混合制备的纳米复合材料.     

先驱体法合成氮化硼研究进展

综述了无氧有机先驱体法合成氮化硼的研究进展 ,系统介绍了由硼烷、硼吖嗪、卤化硼合成氮化硼的工艺条件 ,及由这些化合物制备聚合物先驱体的合成途径及其陶瓷转化 ,概述了先驱体法待研究的问题 .     

液相聚合物前驱体法制备高熵碳化物纳米粉体

高熵碳化物陶瓷是近年来发展的新型材料,由于具有高硬度、高模量和低热导率等优异性能而备受关注。液相聚合物前驱体法在陶瓷化过程中可以实现多元素的均匀分散,制备高熵陶瓷具有独特的优势,但是相关报道较少。本研究以金属醇盐为原料,通过可控水解缩合反应制备了金属醇盐共聚物溶液,加入碳源烯丙基酚醛(AN)后得到了澄清的粘稠液相高熵碳化物前驱体(PHEC),在真空下1800℃裂解2 h获得了(Ti, Zr, Hf, Ta)C高熵碳化物陶瓷纳米粉末。通过不同手段对前驱体和陶瓷粉体进行表征,结果表明:裂解温度低于800℃所获得的样品主要为t-ZrO₂及氧化物固溶体, 1000℃开始发生碳热还原反应形成碳化物固溶体,温度升高至1800℃后转化为高熵碳化物陶瓷;所得陶瓷粉末纯度高,元素分布均匀,颗粒尺寸一致,粒径～100 nm。制备的液相陶瓷前驱体具有高陶瓷产率(28.6 wt%)和低黏度(150 mPa·s)的特点,在极性溶剂中溶解性良好。所开发的液相前驱体法在制备高熵陶瓷纳米粉体、陶瓷纤维和陶瓷基复合材料领域具有重要应用价值。     

Al作为活性填料对前驱体法复相陶瓷性能的影响

采用微米级Al粉作为活性填料, SiC微粉作为惰性填料, 聚碳硅烷作为陶瓷前驱体制备SiC基复相陶瓷. 研究了热解温度和保温时间对陶瓷产率、线收缩率、力学性能以及微观结构的影响. 研究表明, 由于活性Al粉颗粒在热解过程中与含碳的有机小分子以及反应性气氛发生氮化和碳化反应, 产生体积膨胀效应, 热解陶瓷表现为小收缩、高产率, 可以满足近净尺寸成型的要求. 在1000℃热解保温1h, 线收缩率为0.08%, 陶瓷产率为99.68%, 材料的三点弯曲强度达到293MPa.     

活性填料在制备陶瓷基复合材料中的应用

研究了Ｔｉ,ＴｉＨ２等活性填料在聚碳硅烷先驱体裂解制备ＳｉＣ陶瓷材料中的应用,Ｔｉ、ＴｉＨ２等可增加聚碳硅烷的裂解陶瓷产率,可与Ｎ２气氛反应生成氮化物,导致体积膨胀而降低陶瓷的气孔率,提高材料性能。     

Polymer-filler derived Mo2C ceramics

Manufacturing, microstructure and properties of novel reaction bonded Mo₂C materials derived from polymer/reactive filler mixtures were investigated. Mo powder was used as a filler to react with carbon bearing decomposition products of poly(methyl- and phenysiloxanes) during pyrolysis in nitrogen atmosphere. Microcrystalline composites with the filler reaction products Mo₃C, Mo₃Si, Mo₅Si₃ embedded in a silicon oxycarbide glass matrix could be formed with complex geometry owing to near net shape polymer/ceramic conversion. Depending on the precursor composition and pyrolysis conditions, ceramic hard materials with a density up to 97% theoretical density, a hardness of 10 GPa, a Young’s Modulus of 250 GPa, a fracture toughness of 5 MPam^1/2 and a flexural strength of 330 MPa were obtained.     

Ceramic fibres from polymer precursor containing Si-O-Ti bonds

By the reaction between organosilicon compounds and titanium alkoxides, polymers (atom ratio Ti/Si = 0.045 to 0.12) as the precursors for ceramic fibre were synthesized. Titanium in the precursors was bonded to organosilicon compounds in the Si-O-Ti bond. The synthesis process of the fibre is melt-spinning of the precursor, curing of the precursor fibre, and its heat-treatment. Curing was achieved by cross-linking of the polymer by the oxidation of Si-H bonds or hydrolysis of Ti-OR bonds in the precursor. The formation mechanism of the precursors and their pyrolysis process were examined in an inert gas atmosphere and in a vacuum. It was shown that the Si-O-Ti bond in the precursors is cleaved by pyrolysis of the Ti-O bond, so that TiC is formed. The tensile strength of the ceramic fibre obtained, is relatively high even by the heat-treatment at temperatures higher than 1200° C. Further, the Young's modulus is little changed.     

Processing and thermal stability of a Cfiber/SiCfiller/Si–C–Nmatrix composite: effect of oligomer vaporization and the surface oxide layer of SiC filler

The processing of carbon fiber-reinforced ceramic matrix composites (CMC) made by the precursor impregnation and pyrolysis (PIP) method was improved, and factors which deteriorate the thermal stability of the CMC were investigated. The processing time for cross-linking of a precursor polymer was substantially reduced by the application of a sealed metal container due to the suppression of the vaporization of oligomers. The strength of the as-fabricated CMC was 286 MPa and 77% of the original strength was retained after a heating at 1350 °C for 24 h in Ar. The reduction of the strength after the heating was due to the decomposition of SiO₂ which remained at the surface of the SiC filler particles. The decomposition reaction induced deterioration of carbon fibers and the matrix of the CMC at high temperature.     

Modelling of dimensional changes during polymer-ceramic conversion for bulk component fabrication

Shrinkage and porosity generation during conversion of polymer-filler systems into ceramic bodies during pyrolysis is examined. In the presence of an inert filler phase such as Si₃N₄ or SiC powder dispersed in an organosilicon polymeric matrix only porous microstructures may be obtained without any shrinkage. By using an active filler phase such as carbide- or nitride-forming transition metals, however, shrinkage of the polymer matrix may be compensated by appropriate expansion of the filler phase. A model is derived to predict the critical volume fractions of various potential active filler systems in inert and reactive gas atmospheres, which can be effective in controlling shrinkage and porosity during the fabrication of ceramic components from polymer-derived precursor materials.Nomenclature P Polymer phase - C Condensed polymer pyrolysis product (ceramic) - G Gaseous polymer decomposition product - F Inert filler phase - T Active filler phase (e.g. transition metal) - M Reaction product of active filler phase (e.g. carbide, nitride) - m Mass - V Volume fraction - V _F,T ^max Maximum packing density of an inert (F) or active (T) filler powder - V _F,t ^* Critical volume fraction of an inert (F) or active (T) filler powder in the starting polymer-filler mixture - V _v Residual porosity in the polymer pyrolysis product - V _v ^pf Residual porosity in the polymer-inert filler system after pyrolysis - Ceramic yield of polymer after pyrolysis - Weight change of active filler phase during reaction pyrolysis - Density ratio of polymer to polymer pyrolysis (ceramic) product - Density ratio of active filler to filler reaction product - ^P Linear shrinkage of the polymer phase during pyrolysis - ^pf Linear shrinkage of a polymer-inert filler system during pyrolysis - ^paf Linear shrinkage of a polymer-active filler system during reaction pyrolysis - Linear shrinkage/expansion of the filler phase during reaction - Density     

Chemische Zusammensetzung und Mikrostruktur polymerabgeleiteter Gläser und Keramiken im System Si–C–O. Teil 1: Phasenidentifikation mittels Si‐L2,3‐Ionisationskanten‐Elektronenenergieverlustspektroskopie nach dem Fingerprint‐Verfahren und energiegefilterter Durchstrahlungselektronenmikroskopie

Chemical Composition and Microstructure of Polymer‐Derived Glasses and Ceramics in the Si–C–O System. Part 1: Phase identification by means of Si‐L_2,3‐ionisation edge electron energy‐loss spectroscopy according to the fingerprinting technique and energy‐filtered transmission electron microscopy Polymer or precursor ceramics represent a novel class of high‐performance materials that are produced by controlled pyrolysis of organometal compounds. Shrinkage and porosity resulting from thermal decomposition can be compensated by adding chemically reactive filler powders. This technique permits manufacturing of dense ceramic bulk components true to size by cost‐effective near‐net‐shape forming of cross‐linked green compacts. For process control, definition of the course of the reaction of the active fillers and thus the exact knowledge of the chemical composition and the microstructure development of the solid residues during pyrolysis of the polymer precursor is required. Due to both the great technical importance of the final ceramic products and their economical availability, in the present work, thermal decomposition of a silicone resin (polymethylsiloxane) at temperatures between 525 and 1550 °C was characterized nanochemically and microstructurally. In part 1, the results of the quantitative phase identification by means of analytical electron microscopy are reported. The bonding state of silicon was determined by fine structure analysis (Si‐L_2,3‐ionisation edge) of the electron energy‐loss spectrum and has proved to be always mainly oxidic. By means of energy‐filtered transmission electron microscopy, elemental distributions in the nanometre range were recorded. The phase separation of the polymer‐derived Si–C–O matrix into SiO₂, C and SiC could be proved definitely. The characterization of structure formation by high‐resolution imaging and diffraction methods follows in part 2.     

Polymer-derived microcellular SiOC foams with magnetic functionality

SiOC microcellular ceramic foams possessing soft-ferromagnetic properties were produced from a pre-ceramic polymer, poly-methyl-methacrylate microbeads (PMMA) (used as sacrificial pore formers) and iron silicide micro-powders (as functional filler). The interactions between the matrix and the filler were studied as a function of the amount of powders introduced and the pyrolysis temperature. Magnetic and mechanical properties were also investigated.