Glass fabrics self-cracking catalytic growth of boron nitride nanotubes

Glass fabrics were used to fabricate boron nitride nanotubes (BNNTs) with a broad diameter range through a combined chemical vapor deposition and self-propagation high-temperature synthesis (CVD-SHS) method at different holding times (0min, 30min, 90min, 180min and 360min). SEM characterization has been employed to investigate the macro and micro structure/morphology changes of the glass fabrics and BNNTs in detail. SEM image analysis has provided direct experimental evidences for the rationality of the optimized self-cracking catalyst VLS growth mechanism, including the transformation situations of the glass fabrics and the BNNTs growth processes respectively. This paper was the further research and compensation for the theory and experiment deficiencies in the new preparation method of BNNTs reported in our previous work. In addition, it is likely that the distinctive self-cracking catalyst VLS growth mechanism could provide a new idea to preparation of other inorganic functional nano-materials using similar one-dimensional raw materials as growth templates and catalysts.     

预烧温度对0.363BiScO3-0.637PbTiO3高温压电陶瓷性能的影响

研究了不同预烧温度对反应烧结0.363BiScO3-0.637PbTi O3陶瓷的微观结构及压电介电性能的影响。根据0.363BiScO3-0.637PbTi O3的配方,通过热失重-差热分析判断Sc2O3、Bi2O3、Pb3O4、Ti O2粉末混合物分解、化合反应点和预烧温度范围;运用XRD、SEM研究了不同预烧温度下制备陶瓷样品的微观结构;通过压电介电性能测试,确定出最佳预烧工艺条件。结果表明,最佳的预烧条件为740℃保温2 h。经1 080℃、2 h烧成陶瓷的压电常数d33=308 pC/N,机电耦合系数kp=0.437,介电常数ε3T3/ε0=1 560,介电损耗tanδ=0.021,退极化温度TD=460℃。在此工艺条件下,该陶瓷性能优良、制备重复性好,在高温压电陶瓷传感器、换能器等方面显示出实用化前景。     

激光熔化沉积Ti60合金和TiC_P/Ti60复合材料的显微组织及高温拉伸性能

通过激光熔化沉积工艺制备出Ti60合金和TiCP(质量分数为5%)/Ti60复合材料薄壁材料,分析了两种材料的显微组织及600℃下的高温拉伸性能。结果表明,激光熔化沉积Ti60合金具有典型的魏氏组织特征,在亚晶界处和α/β界面处存在球形富钕稀土相;TiCP/Ti60复合材料中存在少量未完全熔化的TiC颗粒,熔化析出的TiC相呈断续链状,均匀分布于基体中,TiC与钛合金基体的界面结合良好。在600℃下,TiCP/Ti60复合材料的拉伸强度比Ti60合金提高了65 MPa,而延伸率明显降低。Ti60合金在高温下发生韧性断裂,而TiCP/Ti60复合材料的断口特征比较复杂,既有沿晶断裂和准解理断裂也有局部的韧性断裂。     

An internally heated composite gasket for diamond-anvil cells using the pressure-chamber wall as the heating element

The implementation of a heating element to a composite gasket for high-temperature applications in the diamond-anvil cell was developed based on a double-gasket assemblage. The heating element is a thin platinum wall that covers the central borehole of the metal–ceramic–metal composite gasket and interconnects the two metal component parts of the gasket. Applying electric powers up to 35 W to the two gasket metal components result in ring-like heating around the sample inside the pressure chamber with temperatures exceeding ～2000 K in individual cases. The ring-like distribution of the maximum temperature located at the pressure-chamber wall facilitates a homogeneous temperature distribution at the sample position. As a consequence of the concentration of the heating power to the pressure chamber region, gradients of surface temperatures, both at the gasket and the diamond anvil, appear to be more pronounced compared with those known for classical external electrical heating. Apart from the tests of the mechanical stability on high-pressure operation in the diamond anvil cell at room temperature, the influence of the anvils in contact with the gasket on the characteristic power–temperature curves, temperature gradients and thermal equilibration resulting from changes in electrical power settings have been evaluated within the scope of a series of experimental investigations.     

1V电源非线性补偿的高温度稳定性电压带隙基准源

阐述了电源电压为1V的非线性补偿CMOS电压带隙基准源,该基准源具有很高的温度稳定性.基准源电路中运用了rail-to-rail运算放大器(OPA).根据测试结果,室温下的输出电压为351.9mV,当温度在15～100℃变化时,输出电压在351.5～352.0mV之间变化,温度系数约为16.7ppm/℃.电路的功耗为0.16mW,芯片面积是0.18mm2.     

高压热处理石墨-六角氮化硼微晶混合物的结果分析

 为了进一步研究用球磨法制备B-C-N物质的规律性,在4.5~5.8 GPa压力、800~1 300 ℃温度条件下,对用球磨法获得的石墨-六角氮化硼微晶混合物进行高压热处理。热处理后产物的XRD、XPS及FT-IR测试表明：在4.5 GPa、800 ℃时,样品中出现部分hBN晶化现象,但石墨仍然保持微晶状态;当温度升到1 300 ℃时,样品中不仅存在晶化的hBN,而且出现一种类石墨结构的B-C-N三元化合物。与相关研究资料对比后认为：这一新化合物近似于BC₃N。压力增加到5.8 GPa而温度保持1 300 ℃时,结果变化不大。     

Quantitative Depth Profiling Using Online-Laser Ablation of Solid Samples in Liquid (LASIL) to Investigate the Oxidation Behavior of Transition Metal Borides

The increased demand for sustainability requires, among others, the development of new materials with enhanced corrosion resistance. Transition metal diborides are exceptional candidates, as they exhibit fascinating mechanical and thermal properties. However, at elevated temperatures and oxidizing atmospheres, their use is limited due to the fact of their inadequate oxidation resistance. Recently, it was found that chromium diboride doped with silicon can overcome this limitation. Further improvement of this protective coating requires detailed knowledge regarding the composition of the forming oxide layer and the change in the composition of the remaining thin film. In this work, an analytical method for the quantitative measurement of depth profiles without using matrix-matched reference materials was developed. Using this approach, based on the recently introduced online-LASIL technique, it was possible to achieve a depth resolution of 240 nm. A further decrease in the ablation rate is possible but demands a more sensitive detection of silicon. Two chromium diboride samples with different Si contents suffering an oxidation treatment were used to demonstrate the capabilities of this technique. The concentration profiles resembled the pathway of the formed oxidation layers as monitored with transmission electron microscopy. The stoichiometry of the oxidation layers differed strongly between the samples, suggesting different processes were taking place. The validity of the LASIL results was cross-checked with several other analytical techniques.     

基于LabVIEW的高温超导材料特性测试实验

高温超导体临界特性的测量是近代物理实验中最为经典的实验之一,本文通过使用GM制冷机,利用Lab-VIEW虚拟仪器软件和高性能采集卡,改进了传统的测量高温超导材料临界特性的实验装置.本测试系统不仅可以测量高温超导体在不同温度下的临界电流,还可以测量其失超传播特性.该实验对于学生了解超导体特性和培养严谨的科学作风十分有益.     

石墨-六角氮化硼微晶混合物与水高压反应产物分析

 利用球磨法制备石墨-六角氮化硼微晶混合物，并在6.1 GPa、800~1 500 ℃条件下与水进行高压反应，以便研究用水作触媒合成B-C-N三元化合物的可能性。通过对反应产物的XRD、XPS谱分析发现：高压下随着温度的升高，反应产物中出现再结晶石墨，其晶化程度逐渐提高；但没有出现再结晶六角氮化硼，也未出现立方氮化硼。在球磨不充分条件下，石墨-六角氮化硼混合物的XRD谱没有完全弥散，它们与水高压反应时，能观察到石墨与立方氮化硼分别结晶的现象，但都没有形成B-C-N晶化结构。     

CO2高温光谱参数测量系统设计与实验

CO_2和CO被称为燃烧效率指示性气体,燃烧流场中CO_2的精确测量对工业燃烧过程的节能减排和发动机燃烧状态诊断等都具有重要意义.研究CO_2气体的高温光谱参数,包括:线强、自加宽系数、温度系数,可提高燃烧过程中CO_2浓度的测量精度和可靠性.为了获得可用于燃烧诊断的CO_2吸收线的高温光谱参数,基于可调谐半导体激光吸收光谱技术设计了一套最高温度可达2 073 K的精确控温控压气体光谱参数测量系统.采用该系统开展了CO_2R(50e)吸收线(中心频率为5 007. 787 cm-1)的高温光谱测量实验,获得了温度范围1212～1873 K内多个压强下的纯CO_2气体的大量高温吸收光谱,经热辐射背景扣除、基线拟合、时频转换、多线组合非线性最小二乘法拟合等数据处理过程,得到温度范围1 212～1 873 K内CO_2R(50e)吸收线的线强、自加宽系数及温度系数,其中线强不确定度1. 5%,自加宽系数不确定度小于4. 5%.这些参数是对现有数据库的补充和完善,对燃烧诊断中的CO_2浓度检测有很大帮助,能够满足燃烧过程中CO_2浓度精确反演的需求.