机械合金化合成(ZrC+TiC)/Cu复合材料的研究

以Zr、Ti、Cu和C元素粉末为原料,用XRD、EPMA、SEM、力学性能检测等方法,研究机械合金化合成的ZrC/C和(ZrC FiC)/Cu复合材料的力学和电学性能.实验结果表明:可以用机械合金化合成TiC、ZrC粉末.力学性能方面,经ZrC弥散的Cu基复合材料抗拉强度为359.45MPa,布氏硬度为146.2,经(ZrC TiC)弥散的复合材料抗拉强度为377.3MPa,布氏硬度为166.5,说明ZrC作为第二相可以明显改善Cu基材料的力学性能,而且(ZrC TiC)两相强化效果更好.由断口形貌分析,复合材料主要发生沿界面脆性断裂.电学性能方面,由于致密度不够高以及其他杂质相的引入,材料的相对电导率(IACS标准)有待提高.     

钎焊工艺参数对C/C复合材料/Cu/Mo/TC4钎焊接头微观组织的影响

在钎焊温度为820～940℃,钎焊时间为1～30min的条件下,采用TiZrNiCu钎料、Cu/Mo复合中间层对C/C复合材料和TC4进行了钎焊实验。利用扫描电镜及能谱仪对接头的界面组织进行了研究。结果表明:在较低工艺参数下,Cu/C/C复合材料界面结构为Cu/Cu51Zr14/Ti2(Cu,Ni)+Ti(Cu,Ni)+TiCu+Cu2TiZr/TiC/C/C复合材料。随着工艺参数的提高,TiCu和Cu2TiZr反应相逐渐消失,Ti(Cu,Ni)2新相生成,此时的界面结构为Cu/Cu51Zr14/Ti2(Cu,Ni)+Ti(Cu,Ni)+Ti(Cu,Ni)2/TiC/C/C复合材料。钎焊工艺参数较高时界面结构为Cu/Cu51Zr14/Cu(s.s)+Ti(Cu,Ni)2/TiC/C/C复合材料。随着钎焊温度的增加以及保温时间的延长,界面反应层Cu51Zr14和TiC反应层厚度增加。     

反应法制备硼化锆耐超高温涂层

为了提高C/SiC复合材料的超高温抗烧蚀性能,以锆粉、硼粉和酚醛树脂为原料,通过泥浆涂刷后高温烧结的方法在C/SiC表面制备了ZrB2涂层,研究了涂层的烧结反应过程,并对其组成、结构和抗烧蚀性能进行了表征.结果表明:1200℃前Zr先与碳反应生成ZrC,然后在1400～1600℃时ZrC与B反应生成ZrB2.浆料配比为n(Zr):n(B):n(C)=1.0:1.5:1.0时,1600℃制备的涂层由ZrB2、少量的ZrC及ZrO2组成.氧乙炔焰烧蚀60s后,由于ZrB2氧化形成了ZrO2熔融层,涂层后的C/SiC复合材料的线烧蚀率几乎为零,而未涂层的C/SiC复合材料的线烧蚀率为0.064mm/s.     

TiB2-Cu基复合材料的燃烧合成研究

通过燃烧合成工艺制备了TiB2-40%Cu(质量分数）基复合材料，对复合材料的反应热力学、相组成以及微观组织进行了研究。热力学计算结果表明TiB是最稳定的相，中间相Ti-Cu化合物最终转变为TiB2相；XRD结果显示复合材料的相组成为TiB2相和Cu相，没有生成其他中间相；微观组织观察表明，合成产物组织致密，增强体TiB2陶瓷颗粒尺寸细小，形貌主要呈近等轴状和块状，Cu作为金属粘结剂将TiB2陶瓷颗粒相互连接在一起，Cu的存在促进了燃烧合成过程中材料的致密化行为。Cu的加入使TiB2-Cu基复合材料的致密度、弯曲强度和断裂韧性较TiB2纯陶瓷均有大幅度提高，材料的韧化机制为裂纹尖端塑性钝化机制。     

Ti-B4C-xCu体系自蔓延高温合成过程及机理

对自蔓延高温合成法制备Ti-B4C-xCu体系复合材料的燃烧反应过程及结构、形成机理进行了探讨,结果表明,随着Cu含量的增加,体系反应温度和速度降低,材料颗粒尺寸变小;燃烧波淬熄法实验表明,整个合成过程经历了金属的熔融、Ti向B4C中的扩散、大团聚的形成、小的TiC和TiB2颗粒的长大等阶段;同时由于各阶段反应温度不同,体系经历了Ti-Cu及Ti-B等中间产物阶段,但最终产物只有TiC,TiB2和Cu三相.     

粉末冶金原位合成VC/Fe复合材料的动力学过程研究

应用不同烧结温度制备VC颗粒增强铁基复合材料,用扫描电镜(SEM)观察各烧结温度下的微观结构,应用该组分做差热分析(DTA)、高温X射线衍射分析(XRD)对Fe-V-C体系原位合成VC的动力学过程进行研究,该动力学研究将为VC/Fe复合材料制备提供了理论依据。结果表明,在700℃时左右σ相(Fe V)在石墨的作用下发生分解,变成固溶了大量钒的α-Fe,随着温度的升高,V与C发生反应生成VC;温度越高,VC发生反应越激烈,并释放出大量的热量;1 100℃真空烧结后的组织为珠光体基体上分布着大小均匀呈球形的VC颗粒。     

液相先驱体制备ZrC粉末研究

采用氯氧化锆、丙醇、丙三醇和乙酰丙酮为基本原料合成了锆的先驱体溶液,通过液相先驱体转化法合成了ZrC粉末.研究了先驱体溶液组成和热处理温度对合成ZrC粉末的成分和显微结构的影响,结果表明,随丙三醇用量的增加,干燥时间延长,提高碳和锆的物质的量比和温度都能够提高ZrC粉末的生成率.在高温热处理后合成了面心立方的ZrC粉末,1500℃处理后,粉末颗粒呈不规则的形状.1800℃热处理后,颗粒为球型,颗粒长大的趋势明显.     

TiCp/W及ZrCp/W复合材料的组织结构与性能

设计并采用热压烧结的方法成功制备了TiCp/W和ZrCp/W两个系列碳化物颗粒增强钨基新型复合材料,并对其组织结构、室温力学性能及高温力学性能进行了系统研究.结果表明,复合材料体系的组元间有很好的热力学相容性和化学相容性;在异相界面处发生了W原子向TiC和ZrC晶格的扩散,分别形成了(Ti,W)C和(Zr,W)C固溶体,促进了两相界面结合和复合材料的致密化.碳化物颗粒的加入强烈阻碍了W晶粒的长大,并显著提高了复合材料的室温和高温力学性能.复合材料的抗弯强度和抗拉强度均随着试验温度的升高先增大后减小,在800～1400℃C时出现峰值,而抗压强度则随着温度的升高而单调下降.室温强化机制是细晶强化和第二相弥散强化,高温强化机理有:位错强化、细晶强化、界面强化及碳化物颗粒的弥散强化.     

TiCP/W及ZrCP/W复合材料的组织结构与性能

设计并采用热压烧结的方法成功制备了TiCp/W和ZrCp/W两个系列碳化物颗粒增强钨基新型复合材料,并对其组织结构、室温力学性能及高温力学性能进行了系统研究.结果表明,复合材料体系的组元间有很好的热力学相容性和化学相容性;在异相界面处发生了W原子向TiC和ZrC晶格的扩散,分别形成了(Ti,W)C和(Zr,W)C固溶体,促进了两相界面结合和复合材料的致密化.碳化物颗粒的加入强烈阻碍了W晶粒的长大,并显著提高了复合材料的室温和高温力学性能.复合材料的抗弯强度和抗拉强度均随着试验温度的升高先增大后减小,在800～1400℃时出现峰值,而抗压强度则随着温度的升高而单调下降.室温强化机制是细晶强化和第二相弥散强化,高温强化机理有:位错强化、细晶强化、界面强化及碳化物颗粒的弥散强化.     

原位热压TiC/Ti/Al合成Ti2AlC的研究

以TiC/Ti/Al为原料,采用热压工艺在1400℃原位合成和烧结了含少量第二相Ti3AlC2的Ti2AlC材料.通过不同温度和不同热压时间下合成试样的XRD分析探讨了Ti2AlC的合成过程.结果表明,高温下Ti与Al反应生成中间相TiAl金属间化合物,然后TiC与TiAl金属间化合物反应生成Ti2AlC.初期反应非常迅速,大部分Ti2AlC在此阶段生成.反应后期反应物减少,速度变慢,同时生成少量第二相Ti3AlC2.不同温度下合成的Ti2AlC颗粒具有不同的形貌特征.     

Gender differences in publication productivity in psychology in India

An analysis of gender differences in psychology in India provides quantitative and qualitative assessment of R&D output contributed by psychologists with the indication of the trend of growth, skewness, relatedness, co-authorship pattern of productivity.     

Metrology in Chemistry in Germany

The system for Metrology in Chemistry in Germany is described. At the national standards level, a network of high-level chemistry institutes coordinated by the national metrology institute, PTB, provides the primary references for chemical measurements. A dissemination mechanism employs chemical calibration laboratories accredited within the framework of the German Calibration Service (DKD). They act as “multipliers” between the national standards level and the user level by providing the user with calibration means which are traceable to the SI via national standards. Traceability structures in clinical chemistry, electrochemistry, elemental analysis and gas analysis are described     

Natural radioactivity in drinking water in private wells in Finland

Natural radioactivity in drinking water was determined in population-based random study of 472 private wells. The mean concentrations of (222)Rn, (226)Ra, (234)U, (238)U, (210)Pb and (210)Po in drilled wells were 460, 0.05, 0.35, 0.26, 0.04 and 0.05 Bq l(-1), and in wells dug in the soil were 50, 0.016, 0.02, 0.015, 0.013 and 0.007 Bq l(-1), respectively. Approximately 10% of the drilled wells exceeded a radon concentration of 1000 Bq l(-1) and 18% a uranium concentration of 15 microg l(-1). The mean annual effective dose from natural radionuclides for a drilled well user was 0.4 mSv and 0.05 mSv for a user of a well dug in the soil. The effective dose arising from (222)Rn was 75% of the total of all natural radionuclides for drilled well users. As regards long-lived radionuclides, (210)Po and (210)Pb caused the largest portion of the effective dose. The dose arising from (238)U, (234)U and (226)Ra was only 8% of the total of all natural radionuclides.     

Natural radioactivity in drinking water in private wells in Finland

Radiation Protection Dosimetry     

Radioactivity in building materials in Iraq

Activity concentrations of (226)Ra, (232)Th and (40)K in 45 samples of different building materials used in Iraq were measured using gamma-spectroscopy system based on high-purity germanium detector with an efficiency of 40 %. Radium equivalent activity, air-absorbed dose rate, annual effective dose, external and internal hazard indices and alpha index due to radon inhalation originating from building materials were measured to assess the potential radiological hazard associated with these building materials. The activity concentrations of the natural radionuclides (226)Ra, (232)Th and 40K were found to range from below detection limit (BDL) to 223.7 ± 9, BDL to 93.0 ± 3 and BDL to 343.1 ± 12, respectively. Values of average radium equivalent activity, air-absorbed dose rate, indoor and outdoor annual effective doses, external and internal hazard indices and alpha index ranged from 6.5 to 124.9, 16.2 to 89.5 (nGy h(-1)), 0.08 to 0.44 mSv, 0.02-0.11 mSv, 0.09 to 0.53, 0.13 to 0.69 and 0.03 to 0.62, respectively. These values indicate a low dose. Therefore, the building materials used in the current study are quite safe to be used as building materials.     

Optische in situ Schichtdickenmessung in Bedampfungsanlagen. Optical in situ film thickness monitoring in coating systems

Optical film thickness monitoring is more precise than crystal monitoring. The optical measurement makes use of the fact that the intensity of a monochromatic light beam which is reflected on a film will change periodically with increasing film thickness. The measurement is performed at an exchangeable test glass that is positioned beside the substrates and is therefore coated in the same way as the substrates. The accuracy of cut‐off is achieved by a “fit” of a theoretical curve shape to the measured values. Order filters are used to ensure that, at a certain wavelength, higher deflection orders do not influence the measurement when a monochromator grating is used.