Synergistic influences of titanium,boron, and oxygen on large-size single-crystal diamond growth at high pressure and high temperature

The synergistic influences of boron, oxygen, and titanium on growing large single-crystal diamonds are studied using different concentrations of B₂O₃ in a solvent-carbon system under 5.5 GPa-5.7 GPa and 1300 ℃-1500 ℃. It is found that the boron atoms are difficult to enter into the crystal when boron and oxygen impurities are doped using B₂O₃ without the addition of Ti atoms. However, high boron content is achieved in the doped diamonds that were synthesized with the addition of Ti. Additionally, boron-oxygen complexes are found on the surface of the crystal, and oxygen-related impurities appear in the crystal interior when Ti atoms are added into the FeNi-C system. The results show that the introduction of Ti atoms into the synthesis cavity can effectively control the number of boron atoms and the number of oxygen atoms in the crystal. This has important scientific significance not only for understanding the synergistic influence of boron, oxygen, and titanium atoms on the growth of diamond in the earth, but also for preparing the high-concentration boron or oxygen containing semiconductor diamond technologies.     

超中立型泛函微分方程的稳定性及其应用

关于超中立型泛函微分方程零解的一致稳定、一致渐近稳定及强渐近稳定等有关理论,文献[4—6]在时滞r(t)满足:0<τ≤ r(t)≤r的条件下,利用V函数法进行了研究.本文中,在放弃时滞r(t)上述限制的情况下,通过建立一类重要的向量微分差分不等式,得到了超中立型泛函微分方程(包括无界时滞系统)零解在度量空间C中的全局指数稳定性及渐近稳定性的若干具体、简洁的充分判定准则,避免了求P函数的困难.作为应     

基于HART协议的二线制涡轮流量变送器的开发

以HART协议为通信标准,提出了系统的总体方案设计,通过对HART协议的理解与掌握,详细的给出了基于涡轮流量变送器的软硬件设计;硬件设计部分包括涡轮脉冲采集模块,微处理器模块,HART通信模块和4~20 mA环路电流模块4个模块,其中HART通信模块采用HART调制解调器芯片AD5700实现,4~20 mA环路电流模块采用环路供电专用芯片AD5421实现,二者共同构成了HART协议的物理层接口,文章硬件电路所采用的都是低功耗芯片,用纯硬件的方法解决了HART总线设备的低功耗难点;软件设计部分包括主监控程序、变送计算程序和HART协议通信程序3个程序模块,重点讲述了HART协议的数据链路层和应用层的实现过程;最后文章对涡轮流量变送器的二线制传输功能和HART通信功能进行了测试;测试结果表明,变送器的设计要求基本实现了。     

Properties of B_4C-TiB_2 ceramics prepared by spark plasma sintering

By doping titanium hydride(TiH2) into boron carbide(B4C), a series of B4C + x wt% TiH2(x = 0, 5, 10, 15, and 20)composite ceramics were obtained through spark plasma sintering(SPS). The effects of the sintering temperature and the amount of TiH2 additive on the microstructure, mechanical and electrical properties of the sintered B4C-TiB2 composite ceramics were investigated. Powder mixtures of B4C with 0–20 wt% TiH2 were heated from 1400℃ to 1800℃ for 20 min under 50 MPa. The results indicated that higher sintering temperatures contributed to greater ceramic density. With increasing TiH2 content, titanium diboride(TiB2) formed between the TiH2 and B4C matrix. This effectively improved Young’s modulus and fracture toughness of the composite ceramics, significantly improving their electrical properties: the electrical conductivity reached 114.9 S·cm-1 at 1800℃ when x = 20. Optimum mechanical properties were obtained for the B4C ceramics sintered with 20 wt% TiH2, which had a relative density of 99.9±0.1%, Vickers hardness of 31.8 GPa,and fracture toughness of 8.5 MPa·m1/2. The results indicated that the doping of fine Ti particles into the B4C matrix increased the conductivity and the fracture toughness of B4C.