利用酚醛树脂制备复杂形状碳化硅复合材料零件

为了解决复杂形状陶瓷构件成型难的问题, 利用光固化快速成型技术, 以酚醛树脂为原料, 制作了陶瓷复合材料构件。用XRD 分析了炭支架和陶瓷构件的物相组成; 应用TGA 和SEM 研究了生成炭支架的热解特性、孔道系统和陶瓷构件的微观组织结构; 建立了渗硅的反应机理模型。结果表明: 炭支架主要为酚醛树脂热解后生成的无定形碳, 其残碳率为65 %; 渗硅温度为1500 ℃时生成的陶瓷构件是由Si 、SiC 和C 组成的致密复相陶瓷; 渗硅后如果温度升高至1650 ℃进行排Si , 则生成多孔复相陶瓷; 光固化树脂网格结构和淀粉结合生成的孔道系统, 能够有效避免制件的破裂并有利于渗硅反应; 在1500 ℃温度渗硅30 min 得到的SiC 层厚为20μm。      

熔融渗透工艺制备SiC-TiSi2复相陶瓷的反应机理

熔融Si渗透过程伴随着复杂的化学反应及多组分扩散,对该过程进行研究有助于更好地理解熔渗反应机理。本工作采用熔融渗透工艺制备SiC-TiSi2复相陶瓷,在生成SiC基体的同时原位生成TiSi2。通过扫描电子显微镜(SEM)、X射线能谱分析(EDS)和微区X射线衍射(micro-beam XRD)分别对熔融硅区域、Si/SiC界面以及SiC基体的微观结构和相组成进行表征和分析,研究了熔渗工艺制备SiC-TiSi2的反应机理。结果表明:高温下液Si渗入C-TiC预制体,发生化学反应生成SiC、TiSi2以及少量副产物Ti5Si3,其中Ti5Si3主要集中于Si/SiC界面处。随着反应进行,液Si与TiSi2形成液态Ti-Si共晶。该液态共晶通过流动扩散在Si区域中析出TiSi2。而预制体中的少量固态C在液Si中溶解、扩散,并在Si区域生成均匀分布的孤立SiC颗粒。     

混合酸(HNO3+HF)刻蚀法致霾汽车尾气过滤载体材料的设计与研究

以纺织加工过程中废弃的棉短绒为模板,经过溶胶法浸渍形成棉纤维/氧化硅复合体,再经常温树脂固化、低温真空碳化、高温碳热还原反应及液相渗硅等方式制备出SiC/Si复合材料,最后通过混合酸(HNO3+HF)循环氧化腐蚀制备出过滤汽车尾气陶瓷载体材料。扫描电镜(SEM)结果显示,多孔SiC具有不规则且相互连通的孔道结构,其微观形貌特征遗传于棉短绒和酚醛树脂制备的多孔碳;三点弯曲试验表明SiC/Si陶瓷复合材料的强度高达200MPa,多孔SiC的气孔率可达62%,混合酸腐蚀的多孔SiC的弯曲强度和断裂韧性均小于致密SiC/Si复合体,并提出了混合酸循环氧化-腐蚀机制解释游离态Si的腐蚀过程。     

液相渗Si工艺制备2D CF/SiC复合材料中SiC晶粒的生长机制

由液相渗硅工艺(LSI)制得了2D CF/SiC复合材料,经过XRD分析得知材料中SiC均为β相。经过同质量比的K_3Fe(CN)_6与KOH混合水溶液对其进行腐蚀,由SEM观察腐蚀后2D CF/SiC复合材料的形貌,发现其中SiC呈现细等轴晶和粗大晶粒两种不同的形貌。分析认为LSI工艺制备2DCF/SiC复合材料中生成的SiC有两种生成机制:Si原子通过空位机制向碳中扩散形成无定型SiC,在保温过程中结晶形成细晶SiC层;C原子扩散进入熔融态硅中形成C—Si基团,由于温度梯度和浓度梯度的存在,在远离C/SiC界面处过饱和析出,通过溶解-沉淀机制形成粗大的SiC晶体,在晶粒的长大过程中伴随着层错的出现。     

TiB2颗粒增强反应结合B4C陶瓷的显微结构与性能

以微孔碳、颗粒级配碳化硼粉体、钛粉和硅粉为原料, 通过多孔预制体真空熔渗Si工艺制备了硼化钛颗粒增强的反应结合碳化硼复相陶瓷, 并通过X射线衍射、扫描电子显微镜、EDS能谱和透射电子显微镜对复合材料的显微结构进行表征。结果表明: 在预制体中钛为15wt%时, 所制备的复相陶瓷抗弯强度和断裂韧性分别为313 MPa和5.40 MPa•m^1/2。原位反应生成的硼化钛对材料的增韧补强起到了积极的作用。     

仿生制备多孔氮化硅陶瓷

以松木炭化后形成的多孔木炭为模板,经Y2O3/SiO2混合溶胶浸渍生物碳模板形成Y2O3/SiO2/C复合体,在高压氮气氛下(0.6MPa),1600°C碳热还原氮化制备出牛物形态多孔氮化硅陶瓷.借助XRD、SEM研究了烧结助剂、烧结温度、反应时间和烧结气氛对烧结产物显微结构和晶相的影响,探讨了多孔Si3N4陶瓷的反应过程和机理.结果表明,多孔si3N4陶瓷是由主晶相β-Si3N4和少量晶间玻璃相YsSi4n4O14组成;多孔Si3N4不仅保留了松木的管胞结构,还在孔道中生长出纤维状形貌的β-Si3N4颗粒;Si3N4的反应烧结过程包括α-Si3N4的形成、晶形转变(α-β相变)和晶粒生长三个阶段.在1450°C烧结的机理是气-固和气-气反应机理,在1600°C通过液相烧结的溶解-沉淀机理形成纤维状的多孔Si3N4陶瓷.     

TiB_2颗粒增强反应结合B_4C陶瓷的显微结构与性能（英文）

以微孔碳、颗粒级配碳化硼粉体、钛粉和硅粉为原料,通过多孔预制体真空熔渗Si工艺制备了硼化钛颗粒增强的反应结合碳化硼复相陶瓷,并通过X射线衍射、扫描电子显微镜、EDS能谱和透射电子显微镜对复合材料的显微结构进行表征。结果表明:在预制体中钛为15wt%时,所制备的复相陶瓷抗弯强度和断裂韧性分别为313 MPa和5.40 MPa·m1/2。原位反应生成的硼化钛对材料的增韧补强起到了积极的作用。     

Fabrication of Tia SiC2 modified C/C - SiC composites by liquid silicon infiltration

采用浆料浸渗结合液硅渗透法原位生成高韧性Ti3SiC2基体,制备Ti3SiC2改性C／C—SiC复合材料。研究了TiC颗粒的引入对熔融Si浸渗效果的影响,分析了Ti3SiC2改性C／C-SiC复合材料的微结构和力学性能。实验结果表明：TiC与熔融si反应生成Ti3SiC2是可行的,而且c的存在更有利于生成Ti3SiC2;在含TiC颗粒的C／C预制体孔隙（平均孔径22．3μm）内,熔融si的渗透深度1min内可达10．8cm;Ti3SiC2取代残余Si后提高了C／C-SiC复合材料的力学性能,C／C-SiC-Ti3SiC2复合材料的弯曲强度达203MPa,断裂韧性达到8．8MPa·m^[1/2];对于厚度为20rllm的试样,不同渗透深度处材料均具有相近的相成分、密度和力学性能,无明显微结构梯度存在,表明所采用的浆料浸渗结合液硅渗透工艺适用于制备厚壁Ti3SiC2改性C／C-SiC复合材料构件。     

木材陶瓷化反应机理的研究

研究了木材制备ＳｉＣ陶瓷的反应过程及熔融硅与多孔木炭反应的机理．结果表明,木材制得的ＳｉＣ陶瓷的最终组织取决于渗硅处理温度．较低温度下形成碳化硅多孔材料,较高温度下形成 Ｓｉ／ＳｉＣ复相致密材料．分析指出,木材制备 ＳｉＣ陶瓷中 Ｓｉ／Ｃ反应的大致过程为：熔融硅沿木炭毛细管壁上升,同时与接触的碳反应形成碳化硅,碳化硅层不断向碳层推进直至多孔碳骨架完全转化为碳化硅．生成的碳化硅在反应后期会发生再结晶,最终组织形态表现为多边形大颗粒碳化硅分布在自由硅基体上．     

多孔氮化硅/碳化硅复合材料制备的反应机理分析

为了探索碳热还原法制备多孔氮化硅/碳化硅(Si₃N₄/SiC)复合陶瓷材料在高温阶段的反应机理,采用固化的酚醛树脂为碳源,通过热解产生具有反应性的碳,使之在1300-1780℃等不同温度下与表面包裹的氮化硅粉反应,氩气为保护气氛.通过对试样的XRD、TEM分析和显微结构观察,结合反应的热力学和动力学结果计算推测,树脂裂解碳与Si₃N₄反应生成SiC的机理主要为Si₃N₄分解生成Si(l)与C进一步发生的液-固反应,和Si(l)与反应过程中的中间产物CO(g)之间发生的液-气反应.其他还包括C与Si₃N₄间直接进行的固-固反应;C与Si₃N₄表面的SiO₂间的气-固反应以及由SiO(g)、Si(g)参与的气-固反应.树脂裂解碳与Si₃N₄从1400℃左右开始发生反应形成SiC,温度升高对SiC层的生长有促进,保温时间的延长对SiC层的生长厚度影响较大.     

Reaction–formation mechanisms and microstructure evolution of biomorphic SiC

Biomorphic SiC is fabricated by liquid Si infiltration of a carbon preform obtained from pyrolized wood that can be selected for tailored properties. The microstructure and reaction kinetics of biomorphic SiC have been investigated by means of TEM, SEM, EBSD, and partial infiltration experiments. The microstructure of the material consists of SiC and Si and a small fraction of unreacted C. The SiC follows a bimodal size distribution of grains in the micrometer and the nanometer range with no preferential orientation. The infiltration-reaction constant has been determined as 18 × 10⁻³ s⁻¹. These observations suggest that the main mechanism for SiC formation is solution–precipitation in the first stage of growth. If the pores in the wood are small enough they can be choked by SiC grains that act as a diffusion barrier between Si and C. If that is the case, Si will diffuse through SiC forming SiC grains in the nanometer range.     

Preparation and R-curve properties of laminated Si/SiC ceramics from paper

Laminated Si/SiC ceramics were synthesized from paper via impregnation with phenolic resin, followed by lamination and carbonization of the paper–resin laminates and subsequent infiltration and reaction with liquid silicon at a temperature of 1550 °C for 10–90 min. Due to the capillarity infiltration and in situ reaction with liquid silicon, intrinsic micro- and macrostructure in the carbon preform was retained within the final ceramics. The XRD, TGA, and microscopy analysis indicated that the final material exhibited a distinguished laminar structure with alternating arrangement of SiC and silicon layers. The thick SiC layer was composed of beta-SiC and a little of free silicon and un-reacted carbon. Studies on the evaluation of R-curves behavior by the indentation-strength method indicated a strong R-curve behavior for the Si/SiC composites.     

Laminated biomorphous SiC/Si porous ceramics made from wood veneer

Biomorphous SiC/Si porous ceramics with laminated structure are prepared from beech veneer and phenolic resin. The preparation involves carbonization under vacuum and reaction with melted silicon to obtain the biomorphous carbide template. X-ray diffraction confirms that the biomorphous SiC/Si porous ceramics are mainly composed of β-SiC, free silicon and residual carbon. Scanning election microscopy observations indicate a laminated structure and 1–10 μm microporous structures, which suggest retention of the native characteristics of the wood. This paper examines mechanical properties of the final composite in relation to the lamination, porous structure, and free silicon content. The bending strength of the ceramics decreases as the apparent porosity increases. The fracture toughness increases initially with apparent density and then decreases. The fracture toughness load–displacement curve presents a step-like pattern, which suggests that the laminated SiC/Si porous ceramics have high fracture toughness.     

Manufacture of fibrous β-Si3N4-reinforced biomorphic SiC matrix composites for bioceramic scaffold applications

The manufacturing of the Si₃N₄ reinforced biomorphic microcellular SiC composites for potential medical implants for bone substitutions with good biocompatibility and physicochemical properties was performed in a two step process. First, wood-derived porous Si/SiC ceramics with various porosities were produced by liquid silicon infiltration (LSI) at 1550 °C with static nitrogen atmosphere protection (0.1 MPa), followed by subsequent partial removing of the Si in vacuo at 1700 °C for different periods of time. Secondly, the final porous Si₃N₄ fiber/SiC composite was obtained by further chemical reaction of nitrogen with the infiltrated residual silicon at 1400 °C for 4 h under high concentration flowing nitrogen atmospheres (0.5 MPa). The bending strengths of the porous Si₃N₄ fiber/SiC composite at axial and radial direction were measured as 180.03 MPa and 90 MPa respectively. The improvement in bending strength was primarily attributed to grain pull-out and bridging enhanced by the elongated β-Si₃N₄ grains cross-linked in the depth of the pore channels. The TG analysis showed an obvious improvement in oxidation resistance of the nitride specimens.     

High temperature reactions between SiC and platinum

Solid state reactions between SiC and platinum have been studied at temperatures between 900 and 1100 °C. In the reaction zones, alternating layers of Pt₃Si and carbon, and Pt₂Si and carbon were formed at 900 and 1000 °C, respectively. Both the Pt₃Si and Pt₂Si phases were stable at respective temperatures. Annealings at 1100 °C, however, produced alternating layers of mixed Pt-silicides and carbon. The formation of platinum silicides gave rise to interfacial melting between SiC and platinum at all the temperature regimes. Laser Raman microprobe indicates that SiC decomposes into carbon and silicon at all the temperatures. The silicon reacts with platinum and forms platinum silicides, while the carbon forms clusters and stays unreacted. Based on the Raman results, the carbon exists in two different crystalline states depending upon its location from the SiC reaction interface. The reaction kinetics between SiC and platinum and the formation of periodic structure, respectively, are discussed based on the decomposition of the SiC and the phase separation of carbon from platinum silicides.     

反应烧结微米级SiC陶瓷材料的结构与力学性能

选用粒径为7μm的SiC粉体,采用反应烧结工艺制备致密的SiC陶瓷材料,研究了反应烧结SiC陶瓷材料的物相组成、显微组织结构与力学性能及其断口形貌。结果表明:通过优化制备工艺,SiC陶瓷素坯中的SiC颗粒和纳米炭黑粉体分布均匀,且具有三维联通的孔隙结构,有良好的硅熔渗性能。反应烧结SiC陶瓷材料中的SiC含量高,游离硅含量少,密度可达3.01g.cm-3,抗弯强度达到410MPa,洛氏硬度达到95HRA,综合性能达到陶瓷机械密封件的技术要求。     

泡沫碳化硅陶瓷表面原位生长碳化硅晶须

采用固相和液相反应法在泡沫碳化硅陶瓷骨架表面原位生长碳化硅晶须,研究了催化剂和反应温度的影响．结果表明,催化剂氯化镍的作用使硅与碳直接反应生长出细长的碳化硅晶须．在适当的反应温度下生长的碳化硅晶须的表面光滑,线径比较大,有少量的呈弯曲状或竹节状;反应温度过高使得硅晶须的缺陷较多．在泡沫碳化硅陶瓷骨架的表面原位生长出碳化硅晶须属于LS生长机理．具有表面晶须的碳化硅陶瓷以深床体积过滤的方式用于过滤柴油机汽车尾气中的碳颗粒,表面晶须既能提高泡沫陶瓷过滤器的过滤能力,又有利于过滤器的再生．     

液硅渗透法制备Ti3SiC2改性C/CSiC复合材料

采用浆料浸渗结合液硅渗透法原位生成高韧性Ti₃SiC₂基体, 制备Ti₃SiC₂改性C/C-SiC复合材料。研究了TiC颗粒的引入对熔融Si浸渗效果的影响, 分析了Ti₃SiC₂改性C/C-SiC复合材料的微结构和力学性能。实验结果表明: TiC与熔融Si反应生成Ti₃SiC₂是可行的, 而且C的存在更有利于生成Ti₃SiC₂; 在含TiC颗粒的C/C预制体孔隙(平均孔径22.3 μm)内, 熔融Si的渗透深度1 min内可达10.8 cm; Ti₃SiC₂取代残余Si后提高了 C/C-SiC复合材料的力学性能, C/C-SiC-Ti₃SiC₂复合材料的弯曲强度达203 MPa, 断裂韧性达到8.8 MPa·m1/2; 对于厚度为20 mm的试样, 不同渗透深度处材料均具有相近的相成分、 密度和力学性能, 无明显微结构梯度存在, 表明所采用的浆料浸渗结合液硅渗透工艺适用于制备厚壁Ti₃SiC₂改性C/C-SiC复合材料构件。