三元巯基／乙烯基硅氮烷UV固化制备聚合物陶瓷前驱体

采用差光量热扫描研究了三元巯基化合物与乙烯基硅氮烷紫外光固化特性,结果表明,随着光引发剂浓度和辐照强度的增加,体系聚合速率增大,体系终止方式以自由基双基偶合终止为主。聚合反应为一级,且聚合速率与乙烯基浓度有关,而与巯基浓度无关。对制备的聚合物陶瓷前驱体的基本性能进行了分析,结果表明,玻璃化转变温度随巯基化合物用量的减少而降低,在巯基-乙烯基硅氮烷等摩尔比时,体系的固化度最大。     

三元巯基/乙烯基硅氮烷UV固化制备聚合物陶瓷前驱体

采用差光量热扫描研究了三元巯基化合物与乙烯基硅氮烷紫外光固化特性,结果表明,随着光引发剂浓度和辐照强度的增加,体系聚合速率增大,体系终止方式以自由基双基偶合终止为主。聚合反应为一级,且聚合速率与乙烯基浓度有关,而与巯基浓度无关。对制备的聚合物陶瓷前驱体的基本性能进行分析表明,玻璃化转变温度随巯基化合物用量的减少而降低,在巯基-乙烯基硅氮烷等摩尔比时,体系的固化度最大。     

光聚合陶瓷先驱体裂解制备陶瓷涂层及其抗氧化性能

炭材应用广泛,但在高于500℃的有氧气氛中氧化迅速,其结构和性能受到严重影响.为此,采用光聚合巯基/乙烯基聚硅氮烷(PSN-1)陶瓷先驱体在炭材料表面裂解制备抗氧化陶瓷涂层,采用偏光显微镜和X射线衍射技术探讨了涂层对炭材抗氧化性能的影响.结果表明:先驱体溶液浓度为30%时浸渍效果最好;加入质量比(Ti/PSN-1)为1/10～1/5的钛粉时,制备的涂层抗氧化性能最佳,恒温氧化120 min后,失重率仅为18%;最佳的浸渍/裂解循环次数为3次,恒温氧化120 min,失重率为15%;聚硅氮烷经高温裂解后最终生成氮化硅陶瓷.     

含乙烯基的聚硅氮烷先驱体纤维的制备

通过甲基乙烯基硅氮烷与聚硅氮烷共热聚反应,将乙烯基引入先驱体聚硅氦烷,分析了甲基乙烯基硅氦烷与降硅氮烷的结构。讨论了两者共热聚的反应过程,找到了适宜的制备方法。制得了几种不同乙烯基含量的聚硅氦烷,并经熔融纺丝制得的含乙烯基的聚硅氦烷纤维。     

SiBNC多元陶瓷先驱体的最新发展与展望

综述了近年来聚硅硼氮碳烷陶瓷先驱体的分子设计、合成和陶瓷性能的研究新进展,详细介绍了聚合物路径和单源先驱体路径两种合成方法,对两种方法合成的先驱体进行分类详述,比较了先驱体合成产率、陶瓷转化率及热稳定性。亦提出将紫外光固化陶瓷先驱体方法引入到SiBNC陶瓷的改性中来,将为先驱体转化法制备SiB-CN多元陶瓷材料提供一条新的技术途径。     

聚硅氮烷合成方法与应用研究进展

聚硅氮烷是分子主链中含有重复硅氮键的一类有机化合物,广泛应用于陶瓷先驱体制备、材料涂层合成、医学手术等领域。综述国内外聚硅氮烷合成及应用研究最新进展,重点论述了聚硅氮烷的不同合成方法和反应原理,提出合成耐热型高分子量聚硅氮烷的研究思路,展望聚硅氮烷的发展前景与研究方向,为合成具有特定性能的聚硅氮烷聚合物提供一定的设计思路与理论基础。     

两种先驱体低温裂解制备石英纤维增强氮化硅复合材料

以全氢聚硅氮烷( PHPS) 和聚甲基硅氮烷( PHMS) 为陶瓷先驱体, 通过循环浸渍和600 ℃低温裂解分别制备了三维石英纤维增强氮化硅复合材料, 对比研究了复合材料的力学性能和微观结构。结果表明: 由PHPS 制备的复合材料密度为1. 83 g/ cm3 , 气孔率10 % , 弯曲强度45. 4 MPa , 材料断口平整, 纤维基体界面结合强; 而由PHMS 制备的复合材料密度仅为1. 66 g/ cm3 , 气孔率16 % , 却具有更高的弯曲强度56. 3 MPa , 材料断面较粗糙,界面结合较弱。先驱体活性不同是导致复合材料界面结合强弱及力学性能不同的主要原因。      

氮化硅陶瓷的液相连接研究

本文研究了用氧氮玻璃作为中间层材料连接氮化硅陶瓷．结果表明,在1600℃×30min、5MPa的外加压力条件下,氮化硅陶瓷的结合强度达到基体氮化硅陶瓷的57％．结合层内的结构与基体氨化硅十分相似,但是晶粒尺寸较细,两者结构上的一致性对于提高结合强度起着重要的作用．     

先驱体转化法制备连续纤维增韧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韧陶瓷基复合材料在先驱体、填料、浸渍裂解工艺、热处理工艺以及微观结构(界面层、气孔)等方面的研究状况.先驱体主要有聚碳硅烷、聚硅氮烷、聚硅氧烷等,填料包括活性填料和惰性填料两种,温度、压力、时间等因素对浸渍裂解过程的影响很大,界面结合的强度关系到复合材料的性能,所以制备复合材料时,各方面的因素都得不断摸索,确定最佳的制备方案.最后,提出了目前该方法存在的问题以及未来的研究方向.     

不同分子量的陶瓷前驱体聚硅氮烷的结构与性能的研究

以甲基氢二氯硅烷、甲基乙烯基二氯硅烷为原料,采用氨解反应以及热聚合反应合成了一系列乙烯基氢基甲基聚硅氮烷(PSZ135-170),其数均分子量(Mn)在2.9×103~1.9×105之间,单位浓度聚合物的粘度(ηred)在0.06~0.49mL/g之间。通过FTIR和1H NMR对聚硅氮烷结构进行了表征,该系列聚硅氮烷具有无定型结构,可溶解于正己烷、甲苯、乙酸乙酯、二氯甲烷和N,N-二甲基甲酰胺等常用有机溶剂中,通过TGA分析了该系列聚硅氮烷的热性能,发现随着聚硅氮烷分子量的增加,在N2中25~700℃热解后剩余物的百分含量逐渐升高,最高可达72.58%。     

巯基化合物的合成及巯基-乙烯基光固化工艺

合成出三种不同官能度的巯基化合物,在对其表征的基础上,利用傅立叶变换红外光谱原位跟踪和紫外光差示扫描量热实时跟踪方法,研究了巯基化合物官能度、巯基与乙烯基配比和辐照强度对巯基-VL20体系光固化反应的影响规律。结果表明:高官能度的巯基化合物,反应速率较快;光聚合反应速率约与光强的0.5次方成正比。     

Dispersion of ceramic powders into particulate superplastic Al-Li alloy

A new method for dispersing homogeneously fine ceramic powders into a particulate alloy matrix has been developed. The Al-Li matrix alloy, with controlled crystal grain size and shape, shows superplastic behaviour under certain conditions. The homogeneous dispersion of SiC in the matrix alloy was achieved by introducing the fine particles of filler along the grain boundaries within the alloy particles. This new compounding method yields a composite powder (i.e. each particle itself is a composite) rather than a mixture of different components.     

Polymer/filler derived NbC composite ceramics

NbC containing ceramic composites were manufactured from poly(siloxane)/Nb/NbC filler mixtures by a high temperature reaction bonding process. During heating in an inert atmosphere the Si—O—C ceramic residue of the polymer reacted with the metallic Nb filler to form Nb _x Si _y , NbO and NbC. Samples with a high Nb/NbC ratio showed reduced porosity and increased hardness after pyrolysis at 1200°C.     

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。     

先驱体陶瓷

综述了用先驱体法制备陶瓷纤维、陶瓷基复合材料等的特点及其研究进展,针对制备陶瓷基复合材料基体的有机聚合物先驱体,提出了先驱体必须满足的理化特性和结构特征,同时还针对先驱体法高气孔率及高收缩率的不足,提出了３个解决办法,并着重讨论了活性填料在先驱体裂解制备陶瓷基复合材料中的特点与应用。     

Characterization of the metal particles fraction in ceramic matrix composites fabricated under high pressure

This paper presents preliminary results concerning Al₂O₃–Ni composites fabricated by sintering under a high pressure of 7.7 GPa, at a temperature below the melting temperature of nickel. The microstructure of composites was characterized by scanning and transmission electron microscopy. Quantitative measurements of size, shape and distribution of metal particles were based on image analysis.

A correlation between the size of the Ni particles and their location has been found. Small Ni particles, with a grain size in the range of 50–500 nm, are mostly located inside the ceramic grains. Some Ni particles are also situated at the grain boundaries, and large particles are surrounded by ceramic grains. The shape of the ceramic grains suggests that the ceramic powder particles underwent deformation during the process of consolidation under high pressure.     

Abnormal Hall–Petch behavior in nanocrystalline MgO ceramic

Pure and dense nanocrystalline MgO with grain size ranging between 25 and 500 nm were prepared by hot-pressing. Vickers microhardness was found to increase with decrease in the grain size down to 130 nm, following the Hall–Petch relation. Further decrease in the grain size was followed by continuous decrease in microhardness. A composite model was used to describe the microhardness behavior in terms of plastic yield of the nanocrystalline grains accompanied by strain accommodation and nanocracking at the grain boundaries (gb’s). Good agreement between the experimental and the calculated values indicates that gb’s may have significant effect on strengthening and ductility of nanocrystalline-MgO ceramics in the nanometer size range. Critical grain size exists below which limited plastic deformation within the grains and nanocracking at gb’s enhance the brittleness of the ceramic.     

Reaction bonded niobium carbide ceramics from polymer-filler mixtures

Manufacturing of novel reaction bonded Niobium Carbide (NbC) containing ceramic composites derived from polymer/filler mixtures was investigated. Poly(methylsiloxane) filled with 40 vol.% of a mixture of metallic Niobium (Nb) (reactive filler) and alumina powder (inert filler) was pyrolysed in inert atmosphere up to 1450°C. During pyrolysis metallic niobium reacted with carbon from the decomposition products of the preceramic polymer binder to form microcrystalline composites of NbC, Al₂O₃ and a silicon oxycarbide glass. Microstructure formation of specimens prepared with different niobium to alumina ratio in the starting mixture was experimentally examined and compared to thermodynamic phase equilibria calculations. Materials of high NbC content exhibit high hardness and wear resistance.     

AFM and SEM characterization of iron oxide coated ceramic membranes

Alumina–zirconia–titania (AZT) ceramic membranes coated with iron oxide nanoparticles have been shown to improve water quality by significantly reducing the concentration of disinfection by-product precursors, and in the case of membrane filtration combined with ozonation, to reduce ozonation by-products such as aldehydes, ketones and ketoacids. Commercially available ceramic membranes with a nominal molecular weight cut-off of 5 kilodaltons (kD) were coated 20, 30, 40 or 45 times with sol suspension processed Fe₂O₃ nanoparticles having an average diameter of 4–6 nm. These coated membranes were sintered in air at 900 °C for 30 min. The effects of sintering and coating layer thickness on the microstructure of the ceramic membranes were characterized using atomic force microscopy (AFM), scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). AFM images show a decreasing roughness after iron oxide coating with an average surface roughness of ∼161 nm for the uncoated and ∼130 nm for the coated membranes. SEM showed that as the coating thickness increased, the microstructure of the coating changed from a fine grained (average grain size of ∼27 nm) morphology at 20 coating layers to a coarse grained (average grain size of ∼66 nm) morphology at 40 coating layers with a corresponding increase in the average pore size from ∼57 nm to ∼120 nm. Optimum water quality was achieved at 40 layers, which corresponds to a surface coating morphology consisting of a uniform, coarse-grained structure with open, nano-sized interconnected pores.     

Effect of sintered temperature on structural and piezoelectric properties of barium titanate ceramic prepared by nano-scale precursors

Lead-free piezoelectric ceramics barium titanate has been successfully fabricated by a facile modified (nano-scale precursors) solid phase method. The sintered temperature was employed as the main regulatory factor to control the growth of the grain size and crystallinity of the sample. When the sintered temperature was set as 1350?°C, the pure phase barium titanate ceramics could be prepared with the grain size of about 1 μm. In addition, piezoelectric tests showed that, the samples sintered at this temperature possessed the maximum ?_r, P_r and d₃₃ values, 3533, 16.24 μC/cm² and 420 pC/N, respectively. These characteristics make them promising candidates as lead-free piezoelectric ceramic materials.