Investigations on glass-to-mold sticking in the hot forming process

The sticking behavior of various mold materials and coatings for hot glass melt forming processes, like, e.g. glass container manufacturing, was investigated using a new testing procedure. The mold material specimens under test were subjected to frequent contact with hot viscous glass gobs in a pressing process with presetting well defined non-isothermal pressing parameters to simulate industrial working conditions. Three different glass compositions were used in this investigation, soda-lime silicate glass, lead crystal glass, and borosilicate glass. The sticking characteristics of the tested mold materials and coatings were described by two quantities, a ‘lower’ and an ‘upper’ sticking temperature, which are specific for each mold material and type of glass in the non-isothermal pressing process. The ‘lower’ sticking temperatures of uncoated mold materials were found to depend monotonically on the thermal effusivity (heat penetration coefficient) of the bulk mold materials. All of the coating materials applied to various substrate mold materials were found to reduce the ‘lower’ sticking temperature as compared to the uncoated materials. Most of the coating materials were found to reduce also the ‘upper’ sticking temperature.     

半绝缘磷化铟中与非化学配比有关的深能级缺陷

在不同的化学配比条件下制备了半绝缘磷化铟材料,其中包括配比和富铟熔体中的铁掺杂以及磷气氛和磷化铁气氛下高温退火非掺杂晶片.在这些半绝缘磷化铟材料中检测到了与非化学配比有关的深能级缺陷.通过对大量的原生掺铁和非掺退火半绝缘磷化铟材料中的缺陷的研究,发现原生深能级缺陷与材料的电学参数质量密切相关.迁移率低、热稳定性差的掺铁半绝缘磷化铟材料中有大量的能级位于0.1～0.4eV之间的缺陷.高温退火非掺磷化铟抑制了这些缺陷的产生,获得了迁移率高、均匀性好的高质量半绝缘材料.根据这些结果,我们提出了一种通过控制化学配比制备高质量半绝缘磷化铟材料的方法.     

负热膨胀铁电晶体研究进展

近些年来,负热膨胀材料已成为材料科学的研究热点之一.本文总结了负热膨胀材料发展历程及负热膨胀机理,重点介绍钙钛矿结构和钨青铜结构铁电晶体的生长和热膨胀特性,探讨了晶体结构、铁电相变及负热膨胀机理的关系,对负热膨胀铁电晶体研究和应用提出了建议.     

传统合金型热电材料研究进展

随着热电材料制备方法的多样化和性能表征手段的具体化,合金型热电材料以其优异性能在众多热电材料中脱颖而出,成为拥有高热电性能和高转换率的热电材料.主要介绍了根据适用温度划分的三类传统合金型热电材料:低温热电材料Bi2 Te3、中温热电材料PbTe和高温热电材料SiGe,重点归纳总结了金属合金热电性能优化方法,最后概述了其实际应用领域并展望其未来的发展前景.     

ZrO2对Ho∶(Y0.7Sc0.3)2O3激光陶瓷致密化和光学性能的影响

2 μm 波段处于人眼安全波长,在医疗、加工、红外探测与对抗,以及大气环境监测等军、民两用领域有着重要潜在和实际应用。Ho³⁺掺杂倍半氧化物陶瓷具有宽的吸收和发射光谱、高热导率以及低声子能量等优点,是一类重要的 2 μm 波段激光材料。通过材料固溶原理,可以实现光谱更加宽化,这使其有可能成为一类性能优异的中红外固体激光材料。本文以商业Y₂O₃、Sc₂O₃以及Ho₂O₃粉体为原料,添加少量ZrO₂(原子比为0~1.0%)作为烧结助剂,采用真空预烧,结合热等静压烧结的工艺,成功制备出高透明的0.5%Ho∶(Y_0.7Sc_0.3)₂O₃陶瓷。研究了ZrO₂掺杂浓度(0~1.0％)对Ho∶(Y_0.7Sc_0.3)₂O₃激光陶瓷致密化过程和光学性能的影响。通过添加ZrO₂有效抑制了高温下Ho∶(Y_0.7Sc_0.3)₂O₃陶瓷晶粒的生长,掺杂1.0％ZrO₂的Ho∶(Y_0.7Sc_0.3)₂O₃陶瓷经1 690 ℃下真空预烧结4 h和1 600 ℃/190 MPa热等静压烧结3 h后,其透过率在1 100 nm处达到79.1％(厚度为4.4 mm),接近理论透过率。     

石墨烯及其纳米复合材料的制备与应用研究

石墨烯作为一种新兴二维碳纳米材料,具有完美的晶体结构和诸多优异的物理化学性能.石墨烯独特的电学、热学、光学和力学性能,使其在电子器件、导热材料、气体传感器、感光元件以及环境科学等领域具有广阔的应用前景.其潜在的实际应用价值,使石墨烯材料的开发成为当前最受关注的研究热点之一.本文从石墨烯的来源、结构、分类和基本性质出发,概述了石墨烯及其衍生物的制备方法及属性特征,进而介绍了石墨烯及其衍生物纳米复合材料在电子、材料、储能和环境等领域中的最新研究进展,并对石墨烯及其纳米复合材料的发展前景进行了展望.     

Sr掺杂对Ca3Co4O9基材料热电性能的影响

采用溶胶-凝胶法,结合常压烧结工艺制备了Ca3-xSrxCo4O9(x=0～0.5)热电陶瓷材料,并对材料的热电性能进行了测试。结果表明,Sr掺杂对Ca3Co4O9基材料的热电性能有较大影响。随着掺杂量的增加,电导率逐渐增大,Seebeck系数略有减小。Sr掺杂能显著降低热导率,而且随着掺杂量的增加,热导率的下降幅度逐渐增大。Sr掺杂显著改善Ca3Co4O9材料的热电性能,当掺杂量为0.5时获得最佳热电性能,573 K时Z值达1.07×10-4 K-1。     

二维层状金属碘化物的制备及光电磁器件的应用进展

二维金属碘化物,呈现范德瓦耳斯层状堆垛结构,平均原子序数大,具有合适的能带间隙、强的磁电耦合效应,是一种新型的光电探测材料,能被用于制备高能射线探测器,且一些磁性二维金属碘化物能被用于磁电器件。由于其在光电磁器件方面的潜在应用,近期成为了低维材料研究的热点。并且在材料制备方面,层状金属碘化物一般熔点较低,制备条件温和简单,可用于二维层状材料生长机理的研究。本文首先介绍了层状金属碘化物的结构、性质,然后着重阐述了二维层状金属碘化物的制备方法,最后讨论了层状金属碘化物在光电磁器件方面的应用。期望读者对二维层状金属碘化物有更深入的了解,更好地推动二维层状金属碘化物的应用。     

Undoped semi-insulating GaAs crystals grown by a modified low pressure LEC method

A modified low pressure in-situ synthesis LEC method of growing undoped SI (semi-insulating) GaAs crystals has been established. The key points for controlling melt composition and As evaporation during synthesis and growth have been described. Using this novel approach, crystals are able to be grown from the nominal melt composition in the range of 0.491–0.499 As fraction with high reproducibility. Some characteristics of the undoped SI crystals grown by the present work including electrical properties, dislocation density, carbon and EL2 concentrations and thermal annealing effects have been studied.     

坩埚下降法中各向热异性坩埚热场的数值模拟

本文对不同坩埚热物性组合时计算得到的结果进行了比较.对各向异性坩埚而言,纵向导热系数应该优先选择较小的材料;也可选择具有与晶体和熔体的导热系数相当导热系数的材料.横向导热系数则越大越有利于晶体生长.复合坩埚两种坩埚材料的导热系数最好不要相差太大.     

Bridgman法晶体生长的热物性各向同性坩埚的选择

本文对不同坩埚热物性组合时计算得到的结果进行了比较.对各向同性坩埚而言,应该优先选择具有与晶体和熔体的导热系数相当导热系数的材料,也可选择导热系数较大的材料.在强度允许的情况下,减小坩埚壁厚对晶体生长有利.     

Enhancement of thermoelectric efficiency in vapor deposited Sb2Te3 and Sb1.8In0.2Te3 crystals

Pure and indium doped antimony telluride (Sb₂Te₃) crystals find applications in high performance room temperature thermoelectric devices. Owing to the meagre physical properties exhibited on the cleavage faces of melt grown samples, an attempt was made to explore the thermoelectric parameters of p‐type crystals grown by the physical vapor deposition (PVD) method. The crystal structure of the grown platelets (9 mm× 8 mm× 2 mm) was identified as rhombohedral by x‐ray powder diffraction method. The energy dispersive analysis confirmed the elemental composition of the crystals. The electron microscopic and scanning probe image studies revealed that the crystals were grown by layer growth mechanism with low surface roughness. At room temperature (300 K), the values of Seebeck coefficient S (⊥ c) and power factor were observed to be higher for Sb_1.8In_0.2Te₃ crystals (155 μVK⁻¹, 2.669 × 10⁻³ W/mK²) than those of pure ones. Upon doping, the thermal conductivity κ (⊥ c) was decreased by 37.14% and thus thermoelectric efficiency was improved. The increased figure of merit, Z = 1.23 × 10⁻³ K⁻¹ for vapour grown Sb_1.8In_0.2Te₃ platelets indicates that it could be used as a potential thermoelectric candidate.     

Vapour phase epitaxy of II–VI compounds: A review

This paper is mainly concerned with a critical review of the present situation in the field of vapour phase epitaxy of II–VI compounds. LPE-methods have been less successful. Single-crystal films have been grown by vacuum deposition, sublimation, chemical transport and chemical vapour deposition (including metalorganic-hydride processes). Remarkable results h have been obtained with the close-spaced technique and the chemical vapour deposition methods. The following topics from the point of view of the most suitable operating conditions for epitaxy will be discussed: preparation of substrates and source materials, chemical equilibria and material transport, supersaturation in the growth zone and growth temperature. The compounds ZnS, ZnSe, ZnTe exhibit systematic connections for the material transport, orientation dependence of growth rates and the crystal structures. Considerable interest is shown in the epitaxy of II–VI compounds, because of interesting properties with regard to opto-electronic applications, as in electro-optic information storage devices, light emitting diodes and electroluminescent displays.     

Al2O3-TiO2 and Al2TiO5 ceramic materials by the sol-gel process

Ceramic materials with a very low thermal expansion coefficient are synthesized by the sol-gel process. The binary gel is obtained by hydrolysis and polycondensation reactions of organometallic compounds of aluminium and titanium. The thermal evolution of the amorphous powder is followed by DTA and TGA measurements. Structural evolution is followed using X-ray diffraction. The crystallization of the TiO₂ rutile and Al₂O₃ corindon starts at 700 and 900°C respectively. The transformation of Al₂O₃ and TiO₂ into Al₂TiO₅ appears between 1200 and 1300°C. The densification of the powder is performed by the hot pressing process. The shrinkage of the powder was previously followed by dilatometric measurements. The physical properties of the final material are studied as a function of pressing parameters.     

熔体法生长大尺寸有机晶体

大尺寸有机晶体在太赫兹波产生、中子探测、微波激射等多个关系国计民生、涉及国家安全的领域具有重要应用前景。但大尺寸有机单晶生长一直是国际公认的难题,无论是在生长理论、生长方法还是生长设备方面都远远落后,在整个人工晶体领域相对小众;而且有机晶体硬度低、脆性高、易解理等本征特性为加工和后期应用带来了很多困难,制约了相关领域的发展。有机分子晶体的物化性质决定了其生长方法多采用溶液或气相方法,熔体生长方法在结晶质量控制方面难度更大;但针对上述应用所需的大尺寸单晶和掺杂要求,熔体生长方法相比溶液和气相方法更具优势。本文对熔体法生长大尺寸有机晶体进行分类总结,对影响生长过程和晶体质量的原料提纯、籽晶生长、安瓿设计、固液界面控制、生长及降温速度调控、加热温区等因素进行分析,结合本课题组近年来利用熔体法生长大尺寸有机晶体的实际经验,旨在为大尺寸有机晶体的生长研究提供理论基础和实践经验,突破高质量、大尺寸有机单晶生长的国际难题。     

Impact of electrical resistance and TEP in layered SnSe crystals under high pressure

SnSe crystals belong to IV–VI layered binary semiconducting compound category. These layered compounds have generated a great deal of interest due to their interesting electronic properties. These electronic materials are useful because of their applications in holographic‐recording systems, optoelectronics and memory switching. Earlier, several investigators have studied and reported the influence of temperature and pressure over the phase transitions in SnS and SnSe semiconductors. They also utilized Mossbauer Spectroscopy and Hydrostatic Pressure techniques to examine the bonding of the Sn atoms in SnS and SnSe. It is therefore thought worthwhile to study the effect of pressure on the thermoelectric power and the electrical resistance of SnSe crystals synthesized by a modified direct vapour transport technique. The electrical resistance has been found to be pressure dependent. The transition in electrical resistance behaviour, observed at 65 Kbar, has been explained on the basis of transition from a predominantly two‐dimensional material to a more three‐dimensional one. Similar to the resistance behaviour, the thermoelectric power is also found to be pressure dependent. The increase in thermoelectric power with pressure at the transition pressure of 65 Kbar has been explained. The implications are discussed. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermal balancing via distributed inert-gas streams for high-meniscus ribbon crystal growth

Superior melt growth of ribbon crystals by thermal profile control that is continuously variable, inert, and capable of heat extraction has been achieved. In the device developed, multiple inert-gas jets are directed at various parts of the hot zone, each with individually controlled flow adjustment. In a furnace at 1200°C, the temperature at one edge of a 38-mm-wide ribbon growth zone can be varied at a rate of 6.8°C per liter per minute of argon flow. Asymmetrical temperature profiles in the zone can be flattened to within ±1°C or symmetrically tailored. Silicon ribbons having uniform widths of 38 and 50 mm and grown with a high melt meniscus have been produced by the capillary action shaping technique with inert-gas thermal balancing. Such crystals show minority carrier lifetime values of up to about 300 μs.     

Heat and Momentum Transfer Numerical Analysis in a Vertical Bridgman Growth System

In this work the momentum and heat transfer on a Bridgman system for the growth of GaSb has been studied. The main objective was to obtain some information about the role of the different processes like conduction, radiation and convective effects both in the melted material and the surrounding environment. These simulations are based on a 2D axi‐symmetrical model using a finite element method based code. The simulations have been carried out both in steady and transient states. It has been demonstrated that the consideration of a moving environment is important in the distribution of temperatures. The effects of the variations of thermal conductivities and emisivities on the thermal and velocity fields have been investigated. The results show that the key parameters are the thermal conductivities of the different materials present in the system, which produce significant changes in the convective flows inside the melt.     

Features of bicrystal growth during the directional crystallization of metal melts

The factors responsible for the formation of different configurations of boundaries between adjacent crystallites during their growth from melt by Bridgman and Czochralski methods have been considered by an of example Fe–20 wt % Ga alloy and Ni bicrystals. It is found that the configuration of intercrystallite boundary is related to the features of crystallite growth, caused by the strained state of intercrystallite and interphase (crystal–melt) boundaries, the difference in the linear thermal expansion coefficients of the crystallite boundaries and bulk, and the shape (geometry) of the bicrystal cross section. It is suggested that the strained state of boundaries and the formation of substructure in crystallites during directional crystallization from metal melt are significantly affected by their deformation under the melt weight.

     

半导体碳化硅湿法腐蚀工艺研究

碳化硅(SiC)具有禁带宽度大、电子饱和漂移速度高、击穿场强高、热导率高、化学稳定性好等优异特性,是制备高性能功率器件等半导体器件的理想材料。得益于工艺简单、操作便捷、设备要求低等优点,湿法腐蚀已作为晶体缺陷分析、表面改性的常规工艺手段,应用到了SiC晶体生长和加工中的质量检测以及SiC器件制造。根据腐蚀机制不同,湿法腐蚀可以分为电化学腐蚀和化学腐蚀。本文综述了不同湿法腐蚀工艺的腐蚀机理、腐蚀装置和应用领域,并展望了SiC湿法腐蚀工艺的发展前景。