BN-SiC复相泡沫陶瓷的制备与应用研究
文献类型：学位论文
| 作者 | 沈志洵 |
| 学位类别 | 博士 |
| 答辩日期 | 2012-06-02 |
| 授予单位 | 中国科学院研究生院 |
| 导师 | 张伟刚 |
| 关键词 | 陶瓷前驱体 六方氮化硼 碳化硅 泡沫陶瓷 高温隔热性能 |
| 其他题名 | Preparation and Application of a Polymeric Precursor Derived BN/SiC Composite Ceramic Foam |
| 学位专业 | 化学工程 |
| 中文摘要 | 现代航空航天高技术产业的快速发展对具有耐高温、抗氧化、高强度等特性的先进陶瓷材料提出了迫切需求。近年来采用有机前驱体转化法制备BN、SiC等非氧化物耐高温陶瓷或陶瓷基复合材料成为研究的热点。本文通过控制工艺条件合成h-BN前驱体单体三氯环硼氮烷 (Tricholoroborazine，TCB)，将之应用于SiC前驱体聚合物聚碳硅烷(PCS)的改性，并在一定条件下将其转化为泡沫陶瓷材料。研究了反应条件等对前驱体组成、结构及热转化陶瓷的组成和性能的影响。主要的研究内容和结果如下： (1) 以三氯化硼和氯化铵为原料，分别以微米级的Fe、Co及Ni粉为催化剂，在溶剂回流条件下合成并提纯得到TCB晶体。利用红外光谱、核磁共振11B谱及1H谱进行表征。结果表明，以氯苯为溶剂时，所得晶体为纯TCB，收率为约40wt%；加入催化剂后，TCB的收率均有提高，其中Fe粉的催化效果最好，可将TCB的收率提高至83wt%。 (2) 采用密度泛函理论(DFT)的B3LYP方法，在Gaussian2003程序中采用6-31G(d)基组对TCB及其取代产物的可能构型进行几何构型优化计算，得到稳定的几何构型。在同等条件下进一步进行自然键轨道计算分析，得到其电子结构、前线轨道。在B3LYP/6-31G(d)基组对TCB-二甲胺反应体系进行优化计算，用线性内坐标QST3法搜索得到取代反应的过渡态，对过渡态进行内禀反应坐标的计算验证。并对反应物、中间体、产物和过渡态分别进行几何结构优化和频率计算，从而确定反应物、中间体、和产物的稳定构型。在此基础上以TCB为原料，与甲胺/二甲胺进行取代反应，分别制备了TCB的三取代产物：2,4,6-三(甲胺基)硼吖嗪(MAB)和2-二甲胺-4,6-二(甲胺基)硼吖嗪，利用红外光谱、核磁共振11B谱和13C谱进行表征，证实为目标产物。并以2,4,6-三（甲胺基）硼吖嗪为原料，在N2保护下，通过控制反应温度及时间可得到一系列硼氮聚合物前驱体。 (3) 以TCB和聚合硼氮烷(PBN)为改性剂与PCS反应，制备了改性PCS聚合物。着重研究了TCB与PCS的反应性以及TCB用量对改性PCS结构、陶瓷收率、可加工性及SiC产物微结构的影响。利用红外光谱、热重、XRD等测试分析技术对相应产物进行表征。结果表明，PCS分子中的Si-H键可部分地与TCB中的Cl-反应生成HCl；随着TCB添加量的增加，PCS中Si-H键含量呈下降趋势。TCB的加入可显著提高PCS的陶瓷收率，当TCB添加量大于8wt%时，陶瓷收率约增加10wt%。当TCB添加量为5～8wt%时，可在提高PCS收率的同时使其保持较好的可加工性能，而当TCB添加量大于8wt%时，可加工性能变差。B、N元素的引入对SiC的微结构产生影响：在氩气保护下，经1000℃热处理时，TCB的加入促进了SiC晶粒的生长；而经1500℃热处理时，能够抑制SiC晶粒的生长。此外，MAB也可显著提高PCS的陶瓷收率。 (4) 分别以TCB改性PCS、PBN改性PCS聚合物为原料，采用前驱体自发泡技术在400℃、5MPa下制备泡沫体，发现后者可制得泡孔较为均匀的SiC泡沫体。后者制备的轻质SiC-BN复相泡沫陶瓷孔隙率高、孔径较大，其压缩强度约为纯SiC陶瓷泡沫的5～10倍；在800℃至1100℃的温度区间内具有显著的抗氧化性能。 (5) 采用本研究组研制的高温隔热效果测试装置对BN/SiC多孔陶瓷材料进行隔热性能测试。发现其在1400℃左右的高温隔热效果与ZrO2纤维板的隔热效果相当，可适用于对结构强度要求较高的服役环境。所得BN/SiC多孔陶瓷的热导率在500℃时仅为1.5W/m•K；在1500℃时仍小于4.0W/m•K，是理想的高温隔热候选材料。采用有限差分法数值模拟了背部升温历程，将其有效导热系数代入计算模型，得到材料背部中心温度升温历程的数值模拟结果，与实际升温历程基本吻合，表明模拟计算所选取的模型能够用于模拟实测热导率随温度的变化，从而预测隔热材料的有效导热系数，为工程应用提供数据。 |
| 英文摘要 | With the development of hi-tech industries such as aerospace, advanced materials with excellent properties such as high temperature, anti-oxidation, high strength, etc. were urgently needed. Recently, some non-oxide high-temperature ceramics such as BN, SiC and their composites prepared at relatively low temperature from polymeric precursors have been drawn attention. In this study, the ceramic precursors, BN precursors were synthesized by polymerization procedure and were used to fabricate BN/SiC open cell ceramic foams under certain conditions. The main research work and results are summarized as follows: (1) Trichloroborazine (TCB) was synthesized by the reaction of boron trichloride and ammonium chloride in refluxing solvents with Fe, Co, Ni powder as the catalyst. The products were characterized using FTIR, 11B NMR and 1H NMR. It was found that pure crystalline TCB was obtained with a yield of 40 wt% with the chlorobenzene as solvent. Addition of these catalysts enhanced the formation of TCB, in which Fe powder was an efficient catalyst which improved the TCB yield up to 83.4wt%. (2) The substitution process was simulated employing B3LYP/6-31G* basis set in GAUSSIAN2003 series program. Structure optimization and energy analysis of the TCB molecule and its substituents were carried out. IRC calculation of the TCB substitution reactions was also performed. The results also show that the intermediate state of the substitution contains a Cl-B-N-H-Cl tetratomic ring. It can be further postulated from the simulation that a mixture of several different products could result from the substitution. 2,4,6-tris(methylamino)borazine (MAB) and 2-dimethylamino-4,6-bis(methylamino)- borazine were synthesized by substitution of TCB with methyl amine (CH3NH2) and dimethyl amine (CH3)2NH, which were characterized by FTIR, 11B NMR and 13C NMR. Furthermore, a series of BN polymeric precursors were prepared from 2,4,6-tris(methylamino)borazine by the control of reaction temperature and time for the fabrication of BN ceramics. (3) TCB modified polycarbosilanes (PCS) were synthesized by adding TCB to PCS polymer at ambient temperature. Reactivity of TCB and PCS, effect of TCB contents on the PCS structure，ceramic yield，processability and SiC microstructure were investigated by FTIR, TG, XRD, etc. The results revealed that Si-H bonds in the PCS may partly react with TCB at room temperature to the gas HCl and Si-H bond content almost decreased with the increase of TCB content. When the TCB content is more than 8 wt%, TCB markedly increased the ceramic yield by about 10wt%. And with the TCB Content about 5-8 wt%, modified PCS had higher ceramic yield and good processability in harmony. With the TCB content about 10-15 wt%, the processability became poor. Further, the addition of TCB may influence on the growth of β-SiC crystal grain, that is, the crystal grain of SiC obtained from TCB modified PCS at 1000 ℃ in Ar, is higher than that of pure PCS, while the former showed a lower crystallity at 1400℃. (4) SiC foams were produced from TCB modified PCS and PBN modified TCB at foaming pressure 3 MPa and the latter had a relatively uniform pore structure. A kind of BN/SiC open cell ceramic foams were fabricated from complex co-polymeric precursors of polycarbosilane and tris(methylamino)borane [B(NHCH3)3] using a high pressure pyrolysis foaming technique. The obtained foams exhibited cell sizes ranging from 1 to 5mm with bulk densities varying from 0.44 to 0.73g/cm3, depending on the proportion of the starting materials. Studies on microstructure and thermal properties of the porous material showed that addition of BN into SiC can improve dramatically its oxidation resistance from 800 to 1100℃ and compression strength. The compression strength of the composite foam increased with increasing of BN content in the ceramics, which possessed about 5-10 times higher compression strength than a pure SiC foam. (5) Heat insulation performance of the as-fabricated ceramic foam with a proportion of 1:1 was analyzed by a device designed for insulation performance of high-temperature when temperature at the center point of hot face was 1600±10℃, and heating history of the foam was simulated by finite-difference method. The results showed that thermal conductivity of the composite foams prepared with a proportion of 1:1 in weight was 4.0 W/m•K at 1500℃, which was almost identical to the simulation. |
| 语种 | 中文 |
| 公开日期 | 2013-09-25 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1794]  |
| 专题 | 过程工程研究所_研究所（批量导入） |
| 推荐引用方式 GB/T 7714 | 沈志洵. BN-SiC复相泡沫陶瓷的制备与应用研究[D]. 中国科学院研究生院. 2012. |
入库方式： OAI收割
来源：过程工程研究所
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