Influence of ball milling on the sintering behaviour of ZnO powder

A high purity ZnO powder was milled with either YSZ or Al₂O₃ balls. The weight losses of YSZ and Al₂O₃ balls after milling for 4 h are 10 and 40 ppm, respectively. The debris of the milling media acts as sintering aid to the ZnO powder. As a result, the grain size of the sintered ZnO specimens is reduced. The ratio of the grain boundary energy over surface energy is also decreased.     

Microstructure and mechanical behaviour of transient liquid phase spark plasma sintered B4C–SiC–TiB2 composites from a B4C–TiSi2 system

Almost fully-dense B₄C–SiC–TiB₂ composites with a high combination of strength and toughness were prepared through in situ reactive spark plasma sintering using B₄C and TiSi₂ as raw materials. The densification, microstructure, mechanical properties, reaction, and toughening mechanisms were explored. TiSi₂ was confirmed as a reactive sintering additive to promote densification via transient liquid-phase sintering. Specifically, Si formed via the reaction between B₄C and TiSi₂ that served as a transient component contributed to densification when it melted and then reacted with C to yield more SiC. Toughening mechanisms, including crack deflection, branching and bridging, could be observed due to the residual stresses induced by the thermoelastic mismatches. Particularly, the introduced SiC–TiB₂ agglomerates composed of interlocked SiC and TiB₂ played a critical role in improving toughness. Accordingly, the B₄C–SiC–TiB₂ composite created with B₄C-16 wt% TiSi₂ achieved excellent mechanical performance, containing a Vickers hardness of 33.5 GPa, a flexural strength of 608.7 MPa and a fracture toughness of 6.43 MPa m^1/2.     

Microstructures and Mechanical Properties of Multi-component Al_xCrFe_2Ni_2Mo_(0.2) High-Entropy Alloys

A series of Al_xCrFe_2 Ni_2 Mo_(0.2) alloy consisting of FCC+BCC phases have been designed,and their as-cast microstructures and mechanical properties were also investigated with x ranging from 0.6 to 0.9.It was found that with the addition of Al element,the solidified structures changed from dendrite to columnar crystal then back to dendrite again.Moreover,the increased amount of BCC phase resulted in finer and more uniform microstructures of FCC [FeCrNi(Mo)] and BCC(Al-Ni)phases.Tensile yield strength and hardness of alloys showed a similar increasing trend as the volume fraction of BCC phase increased.Both strain hardening rate and strain hardening exponent were calculated to assess the tensile properties of the alloys.It was shown that A1_(0.6)CrFe_2 Ni_2 Mo_(0.2) exhibited the most excellent and comprehensive mechanical properties due to its high work hardening ability and stable strain hardening rate.The product of strength and elongation of Al_(0.6)CrFe_2 Ni_2 Mo_(0.2)reached up to 38.6 GPa%,which was higher than most of the reported as-cast high-entropy alloys.     

Physics basis for the advanced tokamak fusion power plant, ARIES-AT

The advanced tokamak is considered as the basis for a fusion power plant. The ARIES-AT design has an aspect ratio of A≡R/a=4.0, an elongation and triangularity of κ=2.20,δ=0.90 (evaluated at the separatrix surface), a toroidal beta of β=9.1% (normalized to the vacuum toroidal field at the plasma center), which corresponds to a normalized beta of β_N≡100×β/(I_P(MA)/a(m)B(T))=5.4. These beta values are chosen to be 10% below the ideal MHD stability limit. The bootstrap-current fraction is f_BS≡I_BS/I_P=0.91. This leads to a design with total plasma current I_P=12.8  MA, and toroidal field of 11.1 T (at the coil edge) and 5.8 T (at the plasma center). The major and minor radii are 5.2 and 1.3 m. The effects of H-mode edge gradients and the stability of this configuration to non-ideal modes is analyzed. The current drive system consists of ICRF/FW for on-axis current drive and a Lower Hybrid system for off-axis. Transport projections are presented using the drift-wave based GLF23 model. The approach to power and particle exhaust using both plasma core and scrape-off-layer radiation is presented.     

圆钢管T型相贯节点面内弯曲刚度及等效支管长度分析

简述了国内外圆钢管T型相贯节点面内弯曲试验研究和理论研究现状.试验研究表明,节点位置支管达到承载力前,相贯节点局部变形与节点弯矩成线性关系,节点受力可以按线弹性考虑.本文以线弹性为基础,以某工程为背景,对圆钢管T型相贯节点面内弯曲进行了有限元分析.用壳单元模型考虑节点局部变形影响,用管单元模型考虑节点为刚接,根据2种模...     

燃烧辐射的研究与实践

炉内的辐射传热作用通常是由温度决定的，但因条件变化时辐射率与辐射特性便随其变化，故炉内辐射可人为地得到强化．在不提高供入热的情况下，介绍了强化辐射的三个途径。     

预时效工艺对Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe钛合金组织与性能的影响

对Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe钛合金分别进行单级和双级时效热处理,对比研究双级时效工艺对高强β钛合金组织与性能影响。单级时效温度为550℃,双级时效工艺采用在400℃预时效之后再进行550℃下的再时效处理。研究结果表明,合金在400℃预时效时析出了ω相,随着预时效时间的延长,ω相最终转变为α相。相比单级时效而言,合金经双级时效后其次生α相显微组织得到明显细化,其原因主要是因为预时效阶段为后续较高温度下次生α相的形核与长大提供了更多的形核质点。双级时效工艺可以大幅提高合金的强度及硬度,但是塑性略有下降。     

壳聚糖交联特性对壳聚糖／β-TCP微球成球性的影响

采用反相乳液悬浮法制备壳聚糖／β-TCP复合微球，在乳化前通过向壳聚糖／β-TCP溶液中加入戊二醛溶液的方法引入初交联工艺，目的在于提高复合微球的交联强度。通过动态流变学方法研究发现，加入交联剂后，壳聚糖溶液的粘度随搅拌时间的延长而增加，最后形成凝胶。根据所需微球的形貌及球径要求选择适当粘度的壳聚糖／β-TCP溶液作为水相进行乳化，结合所制备微球的形貌特点发现，在加入3m10．5％（质量分数，下同）的戊二醛溶液，初交联时间为10min时，制得的微球形貌最佳，其球径在100-450μm范围内且分布均匀。     

厌氧滤池的动力学特性

本文对杨和麦卡蒂（１９６８年）提出的厌氧滤池动力学关系式进行了验证和修正。结果表明，该关系式用来预测厌氧滤池对有机物的去除率在一定条件下具有相当准确性。关系式中参数ｅ主要由温度、污泥浓度、有机负荷等运行条件确定。以溶解性ＣＯＤ代替ＢＯＤ计算有机物去除率Ｅ、以填料区有效容积代替空池容积计算水力停留时间ＨＲＴ更为合理。