Phase relations and homogeneity region of the hightemperature superconducting phase (Bi,Pb)2Sr2Ca2Cu3O10+d

For the nominal composition of Bi_2.27−xPb_xSr₂Ca₂Cu₃O_10+d, the lead content was varied from x < 0.05 to 0.45. The compositions were examined between 800 and 890‡C which is supposed to be the temperatue range over which the so-called 2223 phase (Bi₂Sr₂Ca₂Cu₃O_10+d) is stable. Only compositions between x < 0.18 to 0.36 could be synthezised in a single phase state. For x <0.36, a lead-containing phase with a stoichiometry of Pb₄(Sr,Ca)₅CuO_d with a small solubiliy of Bi is formed, for x > 0.18 mainly Bi₂Sr₂CaCu₂O_8+d and cuprates are the equilibrium phases. The temperature range for the 2223 phase was found to be 800 to 890‡C but the 2223 phase has extremely varying cation ratios over this temperaure range. Former single phase 2223 samples turn to multiphase samples when annealed at slightly higher or lower temperaures. A decrease in the Pb solubility with increasing as well as decreasing temperature with a maximum at about 850‡C was found for the 2223 phase.     

工具钢CO2激光熔凝和相变硬化的研究现状

综述了CO2激光熔凝和相变硬化的国内外研究现状，就目前该领域中存在的问题及其发展方向提出了自己的看法。     

激光相变硬化工艺参数的选择

激光在工业应用中,相变硬化是一个重要方面。其工艺选择直接影响着相变硬化层的深度和宽度。从热传导基本方程出发,得出了相变硬化过程中工艺参数(激光功率、光斑直径、离焦量、扫描速度)与硬化层深度、宽度之间的关系。用编制的工艺参数选择的计算机软件计算的结果与实验结果进行了比较,其相对误差为:硬化层宽度平均相对误差为3.7%,硬化层深度为18.7%。     

脉冲激光熔凝和相变硬化的研究现状

综述了脉冲激光熔凝和相变硬化的国内外研究现状,就目前该领域中存在的问题及其发展方向提出了自己的看法。     

CO2激光器混沌运转的实验方法

从MB方程出发,简单分析了CO2激光器的动力学过程。从实验角度对实现CO2激光器混沌运转的各种方法作了概述,并结合多电极对CO2激光器提出了可行的实现混沌的方法。     

CO2激光诱导金属沉积机理研究

利用低功率CO2激光,从水性溶液中诱导沉积金属Ag,存在物理化学过程。电子探针分析表明,激光束作用下的金属颗粒在基材表面进行纵向沉积和横向沉积。结果表明,溶液中的Ag+在激光作用下,发生氧化还原反应生成Ag;基材表面在激光作用下产生“熔融”现象,金属颗粒在其表面的沉积存在一个熔融和渗透的过程,金属颗粒向基材内部渗透并在表面堆积的同时,也在表面横向渗透沉积。     

同轴射频激励CO2激光器的热效应研究

通过求解放电等离子体中的带电粒子密度和能量的平衡方程、电流连续性方程以及热传导方程,研究了同轴射频(RF)激励CO2激光器中放电混合气体的温度效应,分析了有关放电参数对温度分布的影响。     

Effect of site-selective substitution in bulk superconducting Tl2Ba2CaCu2O8

Magnetization measurements were carried out on bulk Tl₂Ba₂CaCu₂O₈ (referred to as Tl-2212) and on various site-selective substituted Tl-2212 samples. At 5K between 0 and 4.5 T, the 5 at. % Mg-doped Tl-2212 (Tl,Mg-2212) samples displayed enhanced pinning as demonstrated by a field dependent increase of the magnetic critical-current density J_c by 18 to 25 percent over that of pristine Tl-2212. Excess Mg (10–15 at. %), however, is deleterious. Rietveld refinement of the x-ray diffraction pattern showed Mg on the Tl sites. Auger electron spectroscopy analysis showed part of the Mg on grain boundaries. The flux-creep activation energies are higher for flux expulsion than for flux penetration in both Tl-2212 and Tl,Mg-2212 samples; the latter displays higher individual values. Our results demonstrate an increase in the number density of flux lines as a result of increased density of atomic-size-structural, defects by Mg (5 at. %) doping. In the Tl_2−yBa₂(Ca_1−zY_z)Cu₂O_8−x(z=0–0.3; single phase; x and y represent oxygen and thallium vacancies) system also studied, the T_c decreases as z increases. At z=0.3, the sample becomes an antiferromagnetic semiconductor.     

CO2激光抑制熔石英损伤增长的研究进展

综述了熔石英光学材料激光诱导损伤增长机制,定性地描述了CO₂激光抑制损伤增长的物理过程。总结了近几年CO₂激光修复所取得的进展,最后阐述了目前CO₂激光抑制损伤增长所存在的问题和今后需努力突破的方向。     

激光焊接技术的发展与展望

介绍激光焊接技术的发展历史,阐明激光焊接的发展与应用现状及未来的发展前景,论述激光焊接工艺的特点及需进一步研究与探讨的问题,将激光焊接(LBW)与电子束焊接(EBW)、惰性和活性气体保护电弧焊(GTAW和GMAW)及电阻焊(RW)工艺进行了全面的对比,指出激光焊接工艺的优势所在及其存在的问题。     

激光熔覆硬质合金WC-TiN-Co特性的研究

本文介绍大功率CO2激光束在45钢表面涂敷WC-TiN-Co,进行了激光熔覆处理,对处理后样品的显微组织、物相、硬度分布和耐磨性能进行了测试和分析,结果表明:45钢表面的化学成分和显微组织发生了根本性的变化,硬度和耐磨性得到了很大提高。     

大功率脉冲TEA CO2激光器控制系统设计

大功率脉冲TEA CO₂激光器不仅设备复杂,而且具有高电压、高激光功率、强电磁干扰的特点。本文采用工控机、可编程控制器和触摸屏,设计并实现了两级分布式大功率脉冲TEA CO₂激光器控制系统。详细阐述了系统硬件和软件的设计方案及实施过程。实际应用表明,该控制系统工作稳定可靠,具有较好的实际应用价值。     

Effects of platinum and oxygenation on microstructure in YBa2Cu3O7−δ/Y2BaCuO5 bulk materials

Transmission electron microscopy examinations have been conducted on undoped and PtO₂ doped YBa₂Cu₃O_7−δ, with excess Y₂BaCuO₅ (211) in the molar ratio of 5∶1 (123/211), processing using the solid liquid melt growth technique. Magnetization hysteresis suggests that addition of Pt strongly influences the pinning behavior. Considerable differences in dislocation and stacking fault densities were observed. Dislocation nets and tangles were commonly observed in the Pt doped samples. In both samples, stacking faults were observed near 211 precipitates, interplatelet boundaries, and dislocations. Dislocations appear to be formed during high temperature processing, while stacking faults appear to be generated during the final oxygenation step. The density and distribution of fine precipitates (∼25–100 nm) were comparable in both specimens suggesting that Pt additon affects the size and acicular morphology of only the coarser 211 (∼1–10 μm). It is proposed that the observed increase in J_c due to Pt addtion may be attributed to the increase in defect density rather than fine precipitates.     

约束放电激励千瓦级基模CO2激光器增益分布的测量

利用放大法进行约束放电激励千瓦级基模CO2激光器增益的测量,分析增益区的横向分布,得知此种激光器的增益值较高,增益区宽(与同类横流激光器进行比较),适合使用多折腔,并获得了优良的激光模式输出。     

CO2激光打孔的折衍混合f-θ 透镜设计

激光打孔广泛应用于印刷电路板处理等领域,在该技术中f-θ透镜起到扫描成像的重要作用。利用折衍混合系统设计了f-θ透镜，在满足性能要求的前提下，减少了透镜的个数，降低了系统成本。该系统采用像方远心光路，工作波长为9.25 μm，打孔直径50 μm，深度182 μm，扫描面积达70 mm×70 mm。     

基于CO2激光的AgGaS2差频产生太赫兹波的数值分析

采用中红外CO₂激光差频产生太赫兹波是提高转换效率和输出功率的一种有效方法。根据差频过程中的三波互作用对AgGaS₂晶体进行了理论分析,数值模拟了oeo类和oee类两种匹配条件下差频产生太赫兹波的角度调谐曲线,并计算了光波在晶体中的走离角和允许参量。另外,还考虑了晶体的有效非线性系数和理论功率转换效率。研究结果表明,AgGaS₂晶体适用于中红外CO₂激光差频产生可广泛调谐的太赫兹波。     

粘接剂对CO2激光器Pt/SnO2催化剂性能的影响

就不同的粘接剂对小型封离式CO2激光器内CO转化催化剂的物理性能和反应性能的影响进行了研究。得出用铝基型粘结剂比用硅基型粘结剂制备出的催化剂其机械强度几乎高1倍,但用硅基型粘结剂制出的催化剂其反应活性好。如以硅溶胶或硅溶胶加碳纤维作粘结剂制备出的催化剂,在室温和-20℃时,于1×104h-1空速条件下,其CO的转化率都是100%,在-35℃时也有很好的反应活性,其CO的转化率为79.3%和95%。     

磁约束放电激励对N2激光输出特性的影响

对磁约束放电激励技术在N2激光器上的应用进行了实验研究。结果显示,横向磁场的引入可以大大提高N2激光的输出,扩展工作气压范围,提高最佳工作气压值。     

The preparation of CdSnP2/InP heterojunctions by liquid phase epitaxy from Sn-solution

Heterojunctions of n-type CdSnP₂ on p-type InP substrates are prepared by LPE from Sn-solutions. The significance of the tipping arrangement, of the initial solution composition and of the temperature program for preparing LPE layers of high quality is discussed. Heterodiodes cleaved from such LPE wafers electroluminesce under forward bias between 1 μm and 1.8 %m with internal quantum efficiencies approaching 1.8% at room temperature. When used as photovoltaic detectors, the quantum efficiency of these diodes surpasses that of Si for λ > 1.09 μ, and exceeds 1% for all wave-lengths between 0.96 and 1.3 μ.     

Microstructural study of the effect of an excess of Y2BaCuO5 and BaSnO3 doping on the texturing process of YBa2Cu3O7−x bulk superconductors

Melt texture process of YBCO leads to a YBa₂Cu₃O_7−x matrix where Y₂BaCuO₅ particles are observed. The Y₂BaCuO₅ inclusions size and distribution depend upon several parameters: YBa₂Cu₃O_7-x grain size in the presintered, heating rate, dopants. The influence of an excess of Y₂BaCuO₅ and/or BaSnO₃ on these Y₂BaCuO₅ particles are observed in the liquid phase and in the texture domain. According to the dopant used, two kinds of coarsening of Y₂BaCuO₅ can be observed: an isotropic and an anisotropic. The control of the distribution of Y₂BaCuO₅ particle size is of primary interest to improve the efficiency of the MTG process. In particular large cooling rate (5°C/h) during the texture formation could be used by adding Y₂BaCuO₅ + BaSnO₃ to YBa₂Cu₃O_7−x composition.