先驱体转化含铝碳化硅陶瓷纤维的制备研究进展

先驱体转化含铝碳化硅陶瓷纤维具有高强度、高模量、耐高温、抗氧化等特性,是高温陶瓷基复合材料理想的增强体之一。基于含铝Si C陶瓷纤维的制备工艺路线,从聚铝碳硅烷(PACS)的合成方法及其机理、PACS纤维不熔化处理方法和控制Si(Al)C陶瓷纤维缺陷的研究现状方面综述了先驱体转化含铝Si C陶瓷纤维制备的最新研究进展。讨论了现有PACS合成路线和不熔化处理工艺的优缺点。此外,围绕含铝Si C陶瓷纤维的制备路线,认为后续可持续关注的主要有探索新的PACS合成路线、高效不熔化处理方法和提高Si(Al)C陶瓷纤维力学性能的方法等方面。     

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。     

聚合物先驱体法制备SiC/AlN

将乙基铝胺和聚碳硅烷的溶液混合反应,减压蒸去溶剂后制得混合先驱体,后者经裂解烧结而转化为ＳｉＣ／ＡｌＮ,通过ＩＲ和ＴＧ／ＤＴＡ等表征研究了混合过程的交联反应,结合对裂解产物的分析,表明,采用该工艺可提高裂解烧成率,控制裂解产物的成分并有利于提高其中Ｓｉ和Ａｌ分布的均匀程度。     

先驱体转化法制备含硼SiC纤维

通过二甲基胺硼烷（dimethylamine borane,DMAB）与低分子量聚碳硅烷（low-molecular mass polycarbosilane,LPCS）反应合成硼溶胶,将硼溶胶与高分子量聚碳硅烷（high-molecular mass polycarbosilane,HPCS）共混制备含硼聚碳硅烷先驱...     

先驱体法制备含异质元素SiC陶瓷纤维的现状与进展

先驱体聚碳硅烷进行物理与化学改性，可以制备出各种含Ti,Zr,Al,B等异质元素的耐温型和吸波型SiC陶瓷纤维。含异质元素的SiC陶瓷纤维，已成为当今SiC陶瓷纤维的发展主流，着承介绍了Si-C、O，Si-Ti、C-O，Si-B-Ti-C，Si-Zr-C-O,Si-Al-C纤维的先驱体的制备及其纤维的性能。介绍了我国含异质元素SiC纤维的现状与进展，指出国内SiC纤维的发展要立足于创新的基础上开发各种高性能SiC纤维，力争做到高起点、高瞻远瞩地发展新型SiC纤维，建立拥有自主知识产权的制备工艺。     

热压辅助先驱体裂解制备Cf/SiC复合材料的研究

以聚碳硅烷为先驱体 ,采用先驱体转化法制备三维编织Cf SiC复合材料。研究发现 ,第一次裂解时采用热压辅助可以明显提高材料的致密度和力学性能。第一次在 160 0℃、10MP的条件下热压裂解 60min ,后续真空浸渍—常压裂解处理五个周期所制得的材料具有较高的力学性能 ,其弯曲强度和断裂韧性分别为 5 64MPa、16MPa·m1 2 。讨论了制备工艺对材料结构和性能的影响     

先驱体转化法制备碳化硅纤维

简述了碳化硅纤维的发展简史 ;指出了优良的先驱体的特点和合成方法 ;为获得优异的高温性能的碳化硅纤维 ,应使先驱体聚合物中的n(C) /n(Si)比尽量接近 1 ,或引入金属元素或烧结助剂 ;介绍了影响碳化硅纤维力学性能的若干因素和目前已商品化的几种碳化硅陶瓷纤维的典型性质。     

SiC(Nb)陶瓷纤维先驱体聚铌碳硅烷的合成与表征

为了提高SiC陶瓷纤维的综合性能,利用聚二甲基硅烷热解制得的产物液态聚硅烷(liquid polysilane,LPS)与五氯化铌(NbCl5)反应,制各了含铌SiC陶瓷纤维的先驱体聚铌碳硅烷(polyniobiumcarbosilane,PNCS).研究表明:反应过程中存在LPS裂解重排反应,Si-H键在反应中显示出很高的活性,FNCS分子量的增加是LPS形成的Si-H键与NbCl5发生交联反应的结果,用LPS与NbCl5为原料不但能使铌元素成功地引入到先驱体中并且分布均匀,而且由于其成本比其他原料相对低廉便于大批量合成.利用PNCS制备的Si-Nb-C-O陶瓷纤维平均强度为1.8GPa,平均直径为12 μm,耐高温性能优异.     

先驱体转化法制备含锆SiC纤维及其组成

以聚硅碳硅烷(polysilacarbosilane,PSCS)与乙酰丙酮锆为原料,用常压高温裂解法制备了Si-Zr-C-O纤维先驱体聚锆碳硅烷(polyzirconocar-bosilane,PZCS),经过熔融纺丝、空气预氧化、惰性气氛烧成等工艺,制得Si-Zr-C-O纤维.通过元素分析、Auger电子能谱、X射线衍射、核磁共振和扫描电子显微镜等一系列分析测试手段研究了Si-Zr-C-O纤维的组成结构与性能.结果表明:Si-Zr-C-O纤维的元素组成为SiC1.24HxO0.56Zr0.0129(摩尔比),平均强度为2.5GPa,平均直径为11 μm,纤维表面光滑平坦,没出现孔洞、裂纹、沟槽等缺陷,直径均匀.Si-Zr-C-O纤维表层和内部元素组成不同.Si-Zr-C-O纤维为非晶SiC纤维,纤维中包含较多的不定形游离C和O,以不定形SiCxOy复合相的形式存在,Zr则与复合相中的O相结合.     

流化床化学气相沉积法制备近化学计量比的Ti N粉体

传统气-固反应工艺制备Ti N粉体存在难以逾越的内扩散控制过程,导致制备高纯、正化学计量比的Ti N粉体至今存在巨大困难。提出了流态化化学气相沉积工艺(FBCVD)制备高质量TiN粉体,即基于TiCl₄-N₂-H₂体系,在往复运动的TiN种子粉体上沉积新生高质量TiN粉体的新方法。实验发现,当TiN种子粉体粒径大于52.95μm时,即使在1000℃沉积2 h也不会失流,同时在TiN种子粉体上获得了亚微米级的结节状新生TiN颗粒。通过氧氮分析仪和XRD分析发现,新方法显著提升了粉体的氮含量,获得了近化学计量比的TiN0.96,且氧含量下降了约40%。此外,流化床中气相沉积TiN的生长模式为岛状生长模式,为工业中制备高质量TiN粉体提供了一种新的方法。     

Revealing the formation mechanism of the skin-core structure in nearly stoichiometric polycrystalline SiC fibers

The polymer-derived SiC fibers have broad application prospects in the fields of aerospace, nuclear industry and high-tech weapon. Oxygen plays an essential role in adjusting the composition, structure and tensile strength of SiC fibers. Our studies have found that introducing too much oxygen during air curing process will form the skin-core structure in nearly stoichiometric polycrystalline SiC fibers. In order to reveal the formation mechanism of the skin-core structure, gradient oxygen was introduced into the fibers. The morphologies, phase distributions and defects of the fibers were well characterized. By strictly controlling the introduction of oxygen, the polycrystalline product fiber exhibits intragranular fracture behavior and excellent high-temperature resistance. The retention rate of its tensile strength can reach up to 91% and 61% after exposure at 1800 °C for 1 h and 10 h, respectively. The present results give valuable insights into the structural optimization of the nearly stoichiometric polycrystalline SiC fibers.     

Structure and properties of ceramic fibers prepared from organosilicon polymers

This paper is a review of structure and properties of ceramic fibers derived from organosilicon polymers, with emphasis on the author's research. Ceramic fibers are prepared from organosilicon polymers by melt-spinning, cross-linking, and pyrolysis. Desirable polymeric precursors display the following properties: high char yield of desired composition, thermal stability at melt-spinning temperature, stable rheology, high purity and freedom from particulate impurities, and ability to undergo rapid cure (cross-linking). Ceramic fibers in the Si-C-O or Si-C-N-O systems display a rich nanostructure consisting of some or all of the following metastable phases: (1) an amorphous, continuous siliconoxycarbide or siliconoxycarbonitride phase; (2) dispersed carbon nanocrystallites; (3) dispersed -SiC or Si₃N₄ nanocrystallites; and (4) closed, globular nanopores. The crystalline phases increase in volume fraction and crystallite size as stoichiometry approaches the crystalline composition and as pyrolysis temperature increases. The Si-C-N-O fibers are amorphous. Pore size increases and total pore volume decreases with increasing pyrolysis temperature. Considerable variation in ceramic fiber composition can be achieved by varying cure conditions and pyrolysis atmosphere. Polycrystalline SiC fibers can be produced by pyrolysis above 1600°C. Fiber diameters range from 7 to 20 µm. Elastic moduli vary from 140 to >420 GPa (20 to >60 Msi) and are controlled by composition, nanostructure, and fiber density. Fiber densities range from 2.2 to >3.1 g/cm³. Tensile strengths range up to 5 GPa (700 ksi) and are Griffith flaw-controlled.This review is from the Second International Topical Workshop, Advances in Silicon-Based Polymer Science.     

聚丙烯腈原丝的预氧化

主要阐述了预氧化反应的机理、改善预氧化的方法和与预氧化研究相关的表征技术,制备高性能碳纤维所需预氧丝的预氧化程度,以及预氧化工艺和预氧丝的表征参数与最终碳纤维性能的关系。     

Low-temperature preparation of novel stabilized aluminum titanate ceramic fibers via nonhydrolytic sol-gel method through linear self-assembly of precursors

Stabilized aluminum titanate fibers were prepared via nonhydrolytic sol-gel (NHSG) method through linear self-assembly of precursors. The results show that NHSG method generates the heterogeneous condensation with the formation of Al–O–Ti, Mg–O–Ti, Fe–O–Ti, Mg–O–Al, Fe–O–Ti bonds, which ensures that magnesium ions and iron ions can enter aluminium titanate lattice and stabilize it at 750 °C. Bimolecular associated structure of chlorotitanium ethoxide titanium precursor promotes the self-linear-assemble of all precursors, which enables the excellent spinnability of sol. Stabilized aluminum titanate fibers have excellent corrosion resistance. The thermal expansion coefficient of stabilized aluminum titanate ceramic is −0.142 × 10⁻⁶°C⁻¹.     

Fabrication of nearly stoichiometric polycrystalline SiC fibers with excellent high‐temperature stability up to 1900°C

Due to the extensive applications of SiC fiber‐reinforced composite materials in the fields of aviation, aerospace, and nuclear power, there are increasing demands for SiC fibers with both excellent mechanical performance and high‐temperature stability. In this work, nearly stoichiometric polycrystalline SiC fibers were fabricated using amorphous Si–C–Al–O fibers with excess carbon and oxygen (C/Si = 1.34, O content: 7.74 wt%). The nearly stoichiometric composition (C/Si = 1.05) of the product fibers was achieved by thermal decomposition of the starting fibers. The fibers were well‐crystallized with grain sizes of ~200 nm due to sintering at a high temperature of 1900°C. The fibers exhibited a high tensile strength and a high elastic modulus and were composed of SiC grains with twins and stacking‐faults, exhibiting intragranular fracture behavior. Furthermore, the fibers maintained their original tensile strength after being maintained at 1800°C for 5 hour or at 1900°C for 1 hour under an inert atmosphere, and they exhibited a high strength retention (97%) after exposure at 1300°C for 1 hour under air. The high‐temperature stability and creep resistance of the fibers were comparable to that of commercial Hi‐Nicalon S and Tyranno SA fibers.     

Synthesis and pyrolysis of non-oxide precursors for ZrC/SiC and HfC/SiC composite ceramics

Multiphase ceramics like ZrC/SiC are promising candidates as ultra-high temperature ceramics for applications in extreme environments. In this work, non-oxide precursors for ZrC/SiC and HfC/SiC composite ceramics were synthesized by a one-pot reaction of three components – metal source, silicon source, and activating reagent. Molecular structures of the precursors were identified by ¹H NMR and FTIR. Transformation process of the precursors to the ZrC/SiC ceramics was investigated via XRD and SEM. After heat-treatment at 1600 °C under argon, the obtained ZrC/SiC and HfC/SiC ceramics features a particle size of 100–200 nm and high metal content without excess carbon. The elemental composition of pyrolyzed ceramics can be tuned by varying the ratio of the reagents in the synthesis of precursors. This strategy also inspires a facile fabrication of composite ceramics with other elemental compositions.     

Abnormal grain growth in iron-containing SiC fibers

Understanding the role of sintering aids during microstructure evolution is critical to the manufacture of densified SiC fibers. A variety of TEM characterization techniques are combined to investigate grain growth behavior in iron-doped SiC fibers. Ultra-large SiC grains in micron size, as the self-assembly of nano sub-grains into a similar orientation, were consistently discovered at the surface and indicative of abnormal grain growth. The growth front consisted of polycrystalline nanograins wetted by iron-rich particles, where several sub-grains were found to unify their (111) planes with a misorientation angle less than 10°, indicating grain rotation at the growth front. It is proposed that iron-rich particles form a quasi-liquid interfacial phase during sintering, which facilitates coherent attachment of grains and results in fast grain growth using neighboring irregular-shaped nanograins as building blocks. The imperfect ordered coalescence of nanograins introduces structural heterogeneities, including low angle grain boundaries and porosities.     

高性能碳纤维原丝与干喷湿纺

干喷湿纺兼备干法和湿法的优点,是新一代纺丝方法．此法在国外已用在工业生产线上,并纺出高性能PAN原丝和制得高质量碳纤维．此法还在完善和提高,普及已为期不远．     

Modeling environmentally induced property degradation of SiC/BN/SiC ceramic matrix composites

The degradation of SiC‐based ceramic matrix composites (CMCs) in conditions typical of gas turbine engine operation proceeds via the stress rupture of fiber bundles. The degradation is accelerated when oxygen and water invade the composite through matrix microcracks and react with fiber coatings and the fibers themselves. We review micromechanical models of the main rate‐determining phenomena involved, including the diffusion of gases and reaction products through matrix microcracks, oxidation of SiC (in both matrix and fibers) leading to the loss of stiffness and strength in exposed fibers, the formation of oxide scale on SiC fiber and along matrix crack surfaces that cause the partial closure of microcracks, and the concomitant and synergistic loss of BN fiber coatings. The micromechanical models could be formulated as time‐dependent coupled differential equations in time, which must be solved dynamically, e.g., as an iterated user‐defined material element, within a finite element simulation. A paradigm is thus established for incorporating the time‐dependent evolution of local material properties according to the local environmental and stress conditions that exist within a material, in a simulation of the damage evolution of a composite component. We exemplify the calibration of typical micromechanical degradation models using thermodynamic data for the oxidation and/or volatilization of BN and SiC by oxygen and water, mechanical test data for the rate of stress rupture of SiC fibers, and kinetic data for the processes involved in gas permeation through microcracks. We discuss approaches for validating computational simulations that include the micromechanical models of environmental degradation. A special challenge is achieving validated predictions of trends with temperature, which are expected to vary in a complex manner during use.     

Na2SO4 deposit-induced hot corrosion of SiC fibers relevant for SiC CMCs

Hi Nicalon, Hi Nicalon S, Sylramic, and Sylramic iBN SiC fibers were exposed to ~60 μg/cm² of Na₂SO₄ in a 0.1% SO₂/O₂ gaseous environment for times between 0.75 and 24 h at 1000°C. After exposure, the corrosion products were characterized using SEM, EDS, ICP-OES, TEM, and EFTEM to determine their high-temperature resistance to Na₂SO₄ and key reaction mechanisms. All SiC fiber types tested in this work exhibited little resistance to Na₂SO₄ deposit-induced attack relative to their behavior in dry O₂ environments. It was found that Hi-Nicalon displayed the least resistance to Na₂SO₄ deposit-induced attack due to excess carbon content resulting in the formation of a highly porous crystalline oxide and promotion of basic corrosion conditions. All fiber types formed a crystalline SiO₂ reaction product, either cristobalite or tridymite. Sylramic and Sylramic iBN formed a crystalline SiO₂ reaction layer containing TiO₂ needles due oxidation of TiB₂ particles. Additionally, Na₂SO₄ deposits resulted in pitting of all fiber surfaces.