陶瓷先驱体催化裂解研究进展

有机聚合物衍生陶瓷技术具有聚合物分子可设计性强、成型容易和制备温度低等优点,已经成为陶瓷及其复合材料的主要制备技术之一。裂解是陶瓷先驱体实现从有机到无机转化的关键步骤,对目标陶瓷的组成、结构和性能有着决定性的影响。在陶瓷先驱体中添加过渡金属进行催化裂解,可以改变其裂解行为,进而调控和拓展裂解产物的结构和性能。本文从不同过渡金属对陶瓷先驱体的催化裂解作用入手,总结了陶瓷先驱体催化裂解的研究现状,探讨了催化机理,并就后续深化研究与应用提出了发展建议。     

硅树脂高温转化陶瓷结合层连接陶瓷材料

由硅树脂作为先驱体,在高温(800～1400℃)转化陶瓷结合层对石墨、SiC陶瓷及3D(dimension)-Cf(carbon fiber)／SiC复合材料进行了连接实验,着重探讨了硅树脂固化裂解过程、裂解温度、保温时问及升温速率对连接性能的影响。研究表明;硅树脂的交联固化主要是通过消耗Si-OH来完成。对于石墨、SiC的连接,1200℃是较佳的处理温度,而对于Cf／SiC则最佳的处理温度为1400℃。随着保温时间由1h延长到5h,SiC陶瓷连接强度得到提高,但对复合材料的连接不利。低升温速率(2℃／min)时的连接强度比10℃/min时的高很多。     

碳化硅陶瓷先驱体聚甲基硅烷的研究进展

介绍了聚甲基硅烷的主要合成方法和性能,特别是其反应活性和高温热裂解性能.综述了聚甲基硅烷及其改性先驱体应用于制备碳化硅纤维、碳化硅基复合材料、多孔陶瓷材料等领域的研究进展.聚甲基硅烷作为碳化辞陶瓷先驱体,其制备简单、热解产物接近碳化硅的化学计量比,具有广阔的应用前景.未来该领域的研究重点是聚甲基硅烷的规模化合成,低成本改性聚甲基硅烷先驱体研究,聚甲基硅烷系列复合先驱体的制备等.     

SiC陶瓷及其复合材料连接的研究进展

SiC陶瓷及其复合材料（SiCf／SiC、Cf／SiC）由于具有优良的高温强度、耐磨和抗腐蚀的性能而被广泛关注，而SiC陶瓷及其复合材料的连接是获得这一性能的关键技术之一。综述了SiC陶瓷及其复合材料连接的一般方法和连接技术，同时指出了连接技术的发展趋势。     

SiC陶瓷基体及抗氧化涂层

介绍了5种主要SiC基体的成型方法,分别是化学气相渗透(CVI)、聚合物先驱体浸渍-裂解法(PIP)、液相硅渗透法(LSI)、反应烧结法、化学气相反应法(CVR)。阐述了各种基体的组织结构、致密效率及陶瓷基复合材料的性能,其中CVI+PIP/LSI的复合成型技术可达到优化的制备过程,提高基体的组织结构和致密化效率;C/C及C/SiC复合材料表面化学气相转换法SiC涂层及多层涂层技术是提高CMC抗氧化性能的有效途径,并已得到工程实际验证。     

Si-B-O-N陶瓷粉末的制备与性能表征

本文使用溶胶凝胶法制备了有机聚合物先驱体，通过高温裂解得到了不含氧化硼的Si—B-O-N陶瓷粉末。采用XRD、FT-IR和TEM等技术分析了Si—B-O-N陶瓷粉末结构特性。研究表明Si—B-O-N陶瓷粉体呈非晶态，其中含有B—N，Si-O，Si—N-O等结构单元。粉末由球形粒子组成，其粒径在50nm左右。     

纤维用含硼SiC陶瓷先驱体的研究进展

综述了硅硼碳(SiBC)先驱体、硅硼碳氧(SiBCO)先驱体和硅硼碳氮(SiBCN)先驱体等纤维用含硼碳化硅(SiC)陶瓷先驱体的合成方法,分析了不同陶瓷先驱体的组成、结构和性能,比较了几种合成含硼SiC先驱体方法的优缺点,提出了纤维用含硼SiC陶瓷先驱体的合成新思路。     

以SiC为连接层主相的SiC陶瓷及其复合材料连接研究进展

由于高脆性、高硬度、高耐磨等特点,SiC陶瓷较难直接加工成大型结构复杂的零部件,发展连接技术是推动其工程化应用的主要方法之一。在众多连接方法中,以SiC为连接层主相的连接方法制备的接头具有连接强度高、接头应力小、抗辐照、抗化学腐蚀和耐高温等优势,成为SiC陶瓷连接重点关注的技术,包括纳米浸渍瞬态共晶相连接(NITE相连接)、硅—碳反应连接(Si—C反应连接)和前驱体连接。本工作从连接机理、连接工艺、接头成分、微观结构和连接强度等方面综述了上述3种以SiC为连接层主相的SiC陶瓷及其复合材料的连接技术,并对3种连接技术的优缺点进行了对比分析,最后对发展趋势进行了展望。     

碳纤维增强SiC陶瓷复合材料的研究进展

碳纤维增强SiC陶瓷基复合材料具有良好的高温力学性能，是航空航天和能源等领域新的高温结构材料研究的热点之一．本文回顾了增强体碳纤维的发展，对材料的成型制备工艺，材料的抗氧化涂层研究进展和现有的一些应用做了综述，并展望了碳纤维增强SiC陶瓷基复合材料以后的研究重点及发展前景．     

ZrB2陶瓷制备研究进展

航天航空、新兵器、新能源等高科技领域的快速发展对超高温陶瓷材料提出了迫切的需求,ZrB2陶瓷材料是最重要的超高温陶瓷材料之一。本文阐明了ZrB2陶瓷拥有优异性能的原因,综述了ZrB2陶瓷材料的制备研究进展,介绍了固相法、气相法、前体法制备ZrB2陶瓷材料的机理,对比了各种ZrB2陶瓷材料制备方法的优缺点,并指出了有机前体转化法具有可设计性好、不含杂质元素、成型可控、陶瓷转化温度低等优点。本文总结得出有机前体转化法是制备ZrB2超高温陶瓷复合材料较理想的方法,以及基于有机聚合物的ZrB2陶瓷前体是未来重要的发展方向之一。     

Joining of Silicon Carbide/Silicon Carbide Composites and Dense Silicon Carbide Using Combustion Reactions in the Titanium–Carbon–Nickel System

A new ceramic joining technique has been developed that utilizes an exothermic combustion reaction to simultaneously synthesize the joint interlayer material and to bond together the ceramic workpieces. The method has been used to join SiC/SiC composites and dense SiC ceramics using TiC-Ni powder mixtures that ignite below 1200°C to form a TiC-Ni joining material. Thin layers of the powder reactants were prepared by tape casting, and joining was accomplished by heating in a hot-press to ignite the combustion reaction. During this process, localized exothermic heating of the joint region resulted in chemical interaction at the interface between the TiC-Ni and the SiC ceramic that contributed to bonding. Room-temperature four-point bending strengths of joints produced by this method have exceeded 100 MPa.     

Joining oxide ceramic matrix composites by ionotropic gelation

The production of complex-shaped all-oxide ceramic matrix composites (Ox-CMC) is somewhat restricted by their current processing methods, as well as by the lack of applicable joining techniques. Thus, we present a new method for joining Ox-CMCs based on the gelation of slurries with the polysaccharide polymer alginate. For this investigation, Nextel 610/alumina-zirconia composites were produced using alginate as binder and aluminum acetate as gelling agent. The joining capabilities of this technique were investigated with microstructural analyses and single-lap compression shear tests. For that, a slurry-containing alginate was used to join two composite plates at different stages of the processing: gel state, dried green body and after sintering. Joining composites plates in their gel or green state was successful as the joints showed shear strength values similar to the interlaminar shear strength of the composites plates. The quality of the joints was attributed to the interactions between the alginate chains of the composite plates and the joint. We also show that even the joining of already sintered Ox-CMCs is feasible. However, densification cracks and lower shear strength are observed for such cases.     

聚合物制备工程陶瓷的研究概况

随着聚碳硅烷、聚硅氮烷、聚硅氧烷以及聚硅硼烷等先进前驱体材料的开发,由含硅陶瓷预制体聚合物制备的工程陶瓷在Si-O-C-N-B体系中占有重要的地位。耐高温的SiC和SiN陶瓷纤维增强陶瓷基复合材料(CMC)已在航空、航天结构中获得应用,而耐中、低温的新型涂层、单向带,泡沫和复杂形状的构件在未来将在能源、环境、运输和通讯领域占有重要的地位。综述了陶瓷预制体聚合物的合成、聚合物制备陶瓷的性能、聚合物制备陶瓷的方法以及影响聚合物热解的主要因素。     

Processing and properties of Nextel™ 720 fiber reinforced alumina-zirconia ceramic matrix composites

The continuous Nextel? 720 fiber-reinforced zirconia/alumina ceramic matrix composites (CMCs) were prepared by slurry infiltration process and precursor infiltration pyrolysis (PIP) process. The introduction of submicron zirconia powders into the aqueous slurry was optimized to offer comprehensively good sintering activity, high thermal resistance and good mechanical properties for the CMCs. Meanwhile, the zirconia and alumina preceramic polymers were used to strengthen the porous ceramic matrix through the PIP process. The final CMC sample achieved a high flexural strength of 200 MPa after one infiltration cycle of alumina preceramic polymer and thermal treatment at 1150 °C for 2 h. The flexural strength retention of the improved CMC sample was 104% and 89% respectively after thermal exposure at 1100 °C and 1200 °C for 24 h.     

Residual thermal stress analysis of SiC joint by polysiloxane silicon resin YR3187

Reaction-bonded silicon carbide was joined using a polysiloxane silicon resin YR3187. Residual thermal stress distribution in joint structure was calculated by finite element analysis method. Factors influencing the distribution of residual thermal stress, including joining temperature, thickness of join layer, and presence of crack in join layer, were studied. The simulated results were compared with actual joint strength. It is showed that in determining the joining temperature, the pyrolysis procedure of silicon resin should be taken into consideration; in addition, the reasonable thickness of the join layer and the reduction of cracks in join layer are important to obtain higher joint strength.     

Optimized preceramic polymer for 3D structured ceramics via fused deposition modeling

3D structured ceramics stemmed from preceramic polymers via additive manufacturing have attracted much attention recently. However, these polymers with high ceramic yield are so brittle that extrusion-based additive manufacturing techniques are hardly able to be utilized for assembling 3D structures. Herein, we developed a strategy to prepare feedstocks for these manufacturing techniques, i.e., utilizing a small amount of thermal-plastic polymer to optimize the preceramic polymer while good compatibility is required between the two polymers to ensure a homogeneous mixture. Polycarbosilane and polypropylene were selected as the representative materials. Polypropylene occupied a small proportion (≤5wt.%) and significantly improved the formability of the precursor. Three-dimensional SiC were obtained via fused deposition modeling combined with crosslinking and pyrolysis. The SiC ceramic filaments showed a mean tensile strength of 471 MPa. The strategy is also applicable to a large field of ceramic systems with corresponding precursor, such as sialon ceramic and multicomponent Si-based ceramics.     

Novel application of ceramic precursors for the fabrication of composites

Preceramic polymers are enabling the development of a variety of advanced shaping methods which, in turn, make possible new and cost-effective approaches for the fabrication of composite materials. This opens new perspectives for the mass production of composites which might, for example, be used in cost-sensitive areas of application in the machine and automobile industries. In two examples it will be shown how preceramic polymers can be used to obtain both metal matrix composites (MMC) and ceramic matrix composites (CMC). Their properties will be discussed in particular with respect to the usage of a preceramic polymer.The first example shows an approach to manufacturing short-fibre-reinforced CMCs by means of a plastic forming technique which involves mixing of either carbon or SiC fibres, ceramic fillers and a viscous ceramic precursor. The precursor permits a fibre-reinforced ceramic with a low porosity to be obtained. The role of the precursor in the whole process and the resulting material properties will be discussed.The second example shows a method for fabricating porous SiC ceramic preforms which are subsequently infiltrated with aluminium to form a MMC. By using the precursor route, a machinable preform with tailored porosity can be produced. Correlations between precursor, preform and MMC properties will be drawn.     

Ceramic Microtubes from Preceramic Polymers

A novel process for the production of ceramic microtubes involving the microextrusion of preceramic polymers was studied. Microtubes with a wide range of inner and outer diameters and several centimeters long were produced from two silicone resins. A coextrusion approach was also used to extend the forming capability of the technique. The addition of carbon black resulted in electrically conductive silicon oxycarbide (SiOC) ceramic microtubes. SiOC microtubes possessed a high bending strength, ranging from ∼30–1100 MPa.     

Study on crosslinking of polymers and joining mechanism of SiC ceramic

ABSTRACT

Based on crosslinking of polymers with different vinyl contents at low temperature and pyrolysis of the polymer at high temperature, joining temperature and impregnation cycles of an SiC joint were discussed. Polyvinylphenylsiloxane as the polymer with active groups of Si–OH and CH=CH₂ by crosslinking enhances ceramic yield and thermal stability. The microstructure of the polymer changes from amorphous ceramic into grains of SiO₂ and SiC, grains can dispersion strengthening enhances strength of joint layer. Shear strength of SiC joints reaches the maximum at 1200°C. A relatively good interface between the SiC substrate and pyrolysis product of the polymer is formed, but there exist loose cracks or voids in the joint layer which affect the shear strength of the joint. The shear strength of the SiC joint reaches 69.2?MPa through seven times of vacuum impregnation/pyrolysis enhancement. According to the microstructure and properties of the SiC joint, the pyrolysis mechanism of the joining layer as part of the joint by using polyvinylphenylsiloxane is explained.     

Joining of SiC ceramic by using the liquid polyvinylphenylsiloxane

ABSTRACT

The joining of SiC ceramic using the liquid polyvinylphenylsiloxane at the high temperature was investigated. The characteristic evolution of polyvinylphenylsiloxane during heating process, shear strength and microstructure of joint were especially discussed. The results show that active groups Si-OH and CH=CH₂ of polyvinylphenylsiloxane through cross-linking at low temperature (200°C) form the macromolecular structure, crosslinked polyvinylphenylsiloxane possess the higher ceramic yield and structure stability at high temperature. Shear strength of SiC joints increase with the joining temperature from 1000 to 1200°C, and then decrease when the joining temperature reaches to 1350°C. Combination with microstructure of fine grains of SiO₂ and SiC dispersion in the Si–O–C ceramic of the join layer and new phase SiC formation on the joint interface through the gas–solid reactions, the shear strength of joint achieves the maximum at 1200°C. The defects of joint increase with temperature higher than 1200°C, and the shear strength of joint begin to decrease.