Influence of the Metal Particle Size on the Crack Growth Resistance in Mullite–Molybdenum Composites

The R -curve for mullite–molybdenum (32 vol%) composites, which were obtained at 1650°C under reducing conditions with three different Mo average grain sizes (1.5, 3, and 9 μm), was estimated by the indentation-strength method and compared with that monolithic mullite obtained under similar conditions. The composites material exhibited rising R -curve behavior. The composite with larger grain size, however, displayed better damage tolerance and higher resistance to crack growth. Microscopic observation of the crack path revealed, in the composites, the systematic presence of dispersoids acting as bridging sites in the crack wake. Therefore, the increased fracture toughness of these ceramic-matrix composites with adherent ductile phase can be attributed to clamping forces applied by metal ligaments that bridge the crack faces behind the crack front. These clamping forces retard the crack from opening as an external stress is applied. It was inferred that this superior performance of the larger Mo particle size composite can be attributed mainly to more effective bridging of the metal grains. Because of this, a higher applied stress intensity will be required to propagate the crack tip. These results suggest that the rising R -curve should be proportional to the metal grain size, since the grain bridging area is proportional to the metal grain size.     

前驱体热解法制备Al2O3的物相转变及其合成

本文着重考查了Al2O3的前驱体一碳酸铝铵沉淀的形成过程及煅烧过程物相变化，发现可通过调节反应条件和加入合适的表面活性剂，来控制碳酸铝铵晶核的形成及晶体的生长速度，有效地阻止了Al2O3的团聚，并在温度1150摄氏度下制备出分散的Al2O3，其平均粒径为－2um，比表面为－3m^2/g。     

高性能PAN原丝计算机仿真与信息管理系统开发

以聚丙烯腈（PAN）原丝实际生产过程为研究对象。以溶液聚合和湿法纺丝为基础。模拟PAN原丝纺制条件，设计开发了一套PAN原丝计算机仿真与信息管理系统。基于Windows视窗编程技术，利用VB和Access数据库。该系统将信息管理，工艺制订，性能预测，在线帮助等功能融为一体，界面友好，操作方便。利用该系统对现场生产过程进行仿真研究，仿真结果和实际测试结果比较表明，系统仿真精度误差小于5%，应用效果良好。     

镍盐前体对Ni-Fe/γ-Al2O3催化剂甲烷化性能的影响

以3种不同镍盐(硝酸镍、乙酸镍和氯化镍)为前体,采用等体积浸渍法制备了双金属Ni-Fe/γ-Al2O3催化剂,分别记作Ni-Fe-N、Ni-Fe-Ac和Ni-Fe-Cl,在浆态床反应装置上对各催化剂CO甲烷化催化活性进行评价。结果表明,Ni-Fe-N甲烷化催化活性最高,CO转化率、CH4选择性分别为97.2%和87.3%;而Ni-Fe-Cl甲烷化催化活性最低,CO转化率、CH4选择性分别为47.3%和58.7%。通过XRD、H2-TPR和CO-TPD等表征技术探讨了催化剂的微观结构与甲烷化催化活性之间的关系,发现Ni-Fe-N甲烷化活性高的原因是NiO晶粒小、分散好,Ni与Fe之间具有较好的协同作用,并且CO吸附量大。     

PAN原丝废丝制备新型季戊四醇酯及其应用

以PAN原丝废丝为原料合成新型季戊四醇酯,并将其运用于聚氯乙烯（PVC）共混助剂中.通过流变仪和热老化试验机测试研究了该季戊四醇酯在PVC共混中的稳定性.结果表明,采用PAN原丝废丝为原料合成的季戊四醇酯的热稳定性能相对较好,可作为PVC的稳定助剂,为PAN原丝废丝赋予了新的可利用性.     

水热前驱体组成对CoTiO3微晶结构的影响

以三氯化钛溶液、乙酸钴为主要原料,水热法制备CoTiO3微晶,系统研究前驱物pH值及引入不同模板剂(聚乙烯醇PVA、羧甲基纤维素CMC、聚乙二醇PEG、乙二胺四乙酸ED-TA)对产物结构的影响.采用X射线衍射(XRD)表征微晶的物相组成,环境扫描电子显微镜(SEM)表征微晶的形貌.结果显示:弱碱性前躯体可制备出CoTiO3微晶,当pH值为8.0～9.0时,产物结晶性高且不含杂质,显现出六边形片状结构.模板剂的加入促使晶粒长大,以CMC为模板剂时效果最明显;此外模板剂还会影响产物的形貌,当PEG或者EDTA为模板剂时,可导致棒状、多面体形貌颗粒产生.当模板剂为PVA时,CoTiO3微晶形貌基本不变,尺寸有所增大.     

THE EFFECT OF PRECURSOR PROPERTIES ON THE STRENGTH OF CARBON FIBER

In this article, lyocell fiber is used as a precursor for carbon fiber. The mechanical properties of lyocell fiber and tenacity of carbon fiber from this precursor have been determined. Gray-relation analysis is used to investigate the relation between precursor's properties and the strength of the carbon fibers. The results suggested that the strength, force at breaking, and fineness of precursor have greater influence on the strength of carbon fibers than precursor's elongation, and modulus.     

合成温度对堇青石—莫来石复相材料中堇青石、莫来石生成量的影响

以MgO-Al2O3-SiO2三元相图为依据,在M2A2S5－A2S3连线上进行了堇青石－莫来石复相材料组成点的设计,并在高温下合成了堇青石与莫来石比例为1：1的复相材料,重点讨论了烧成温度对堇青石－莫来石复相材料中堇青石,莫来石生成量的影响,XRD定量分析结果表明,当合成温度范围约在1380－1420℃之间时,可在复相材料中得到接近理论的相组成。     

左旋麻黄素半生物合成研究Ⅲ.L-苯基乙酰基甲醇的提取技术

对固相生物合成的L PAC(左旋麻黄素前体 )提取技术进行了研究。结果表明 ,采用H型大孔吸附树脂从生物合成的反应产物中提取L PAC最佳。当样品液pH为 6左右、过柱流速为0 2～ 0 3BV/min、柱直径与树脂高度比为 1 5∶11,用质量分数为 70 %丙酮水溶液洗脱 ,该大孔吸附树脂对L PAC的动态吸附量为 6 1 6 9mg/g。洗脱的丙酮水溶液经减压浓缩 ,获油状L PAC粗品 ,其质量浓度不低于 0 2 4g/mL     

炭／炭复合材料用基体前驱体的研究动态

介绍了几种炭／炭复合材料的基体前驱体的性质及制备方法。指出研制低成本、高性能、工艺性好的基体前驱体材料是研制低成本、高性能的炭／炭复合材料的关键。