氧化物溶液表面张力对流速度场研究

利用示踪粒子获得直径为２ｍｍ的环状铂金坩埚内Ｌｉ_２Ｂ_４Ｏ_７＋ＫＮｂＯ_３熔体近坩埚区域的表面张力对流速度场;并从理论上推导出表面张力对流速度场解析表达式,推导结果与实测结果一致．     

磁场对KNbO3熔体中温度分布影响的实验研究

研究了磁场对ＫＮｂＯ３熔体中的温度分布的影响,利用加磁场的休仑微分干涉显微实时观察装置及一种近似的间接测量方法。对在不同磁场强度０、７０、１１７、１３５ｍＴ下,ＫＮｂＯ３Ｏ熔体中的径向温分布进行测量。     

高温氧化物晶体界面非稳定性研究

设计了一套模拟实验,以获得关于晶体形态和界面非稳定性的差异的可靠数据,如高温溶液生长的骸晶和枝蔓晶．这些实验是在高温实时观察装置（ＨＩＴＩＳＯＴ）内进行的．高温溶液晶体生长实验是在环形铂金丝炉圈内进行的．炉圈直径为２ｍｍ．铂金丝既起加热又起支撑熔体的作用．选用ＫＮｂＯ_３和Ｌｉ_２Ｂ_４Ｏ_７的混合物进行晶体生长实验．在只存在扩散机制的快速生长过程中,会形成不同的晶体不完整性,如晶面凹坑、骸晶和枝蔓晶．采用淬火实验以分辨不同的ＫＮｂＯ_３晶体形态,并用扫描电镜研究Ｌｉ_２Ｂ_４Ｏ_７溶体中ＫＮｂＯ_３晶体生长的形貌．在一般情况下,当晶体在气液界面附近液相区成核时,会产生晶体界面非稳定性．导致晶体形状不稳定的溶液层的厚度为６０μｍ．通过扫描电镜观察,发现晶体在这一溶液层中由多面体晶变为枝蔓晶．骸晶和枝蔓晶的各向异性反映了ＫＮｂＯ_３的立方特性,也反映了界面非稳定性是沿［１１０］晶棱扩大的,［１１０］晶棱方向的分支证实了晶体生长形状的各向异性·形成界面非稳定性的临界尺寸为１０μｍ．与此相反,中持稳定的晶面形状是通过６０μｍ厚度以下的溶液内的晶体生长来实现的．晶体生长过程是由高温实时观察装置进行实时观察和记录的,并能观察到晶体固液     

Nb2O5对ZTM-Al2O3性能及ZrO2增韧机制的影响

探讨了Ｎｂ_２Ｏ_５对ＺＴＭ－Ａｌ_２Ｏ_３的性能和ＺｒＯ_２在瓷体中增韧机制的影响．发现Ｎｂ_２Ｏ_５的引入可明显提高瓷体中ｍ－ＺｒＯ_２含量而降低ｔ－ＺｒＯ_２含量,材料的机械性能也随Ｎｂ_２Ｏ_５添加量的增大出现了显著的改善,并且有韧性的平方正比于ｍ－ＺｒＯ_２含量的关系．ｍ－ＺｒＯ_２含量的增加强化了微裂纹增韧是材料性能改善的原因．     

NaOH-KOH熔盐中合成BaTiO3反应过程电导率的变化

用交流阻抗谱法测量了３５０℃时共晶成分的ＮａＯＨ－ＫＯＨ熔盐中加入ＴｉＯ_２和ＢａＣＯ₃时体系电导率的变化,准确给出了３５０℃共晶成分ＮａＯＨ－ＫＯＨ熔盐的电导率为１．０５３Ω－１·ｃｍ^－１,确认了在ＮａＯＨ－ＫＯＨ熔盐中ＴｉＯ_２与ＢａＣＯ_３反应,生成ＢａＴｉＯ_３时熔盐不参与反应．实验数据表明３５０℃ＴｉＯ_２与ＢａＣＯ_３在共晶成分的ＮａＯＨ－ＫＯＨ熔盐中的溶解过程可在短时间内达到平衡．     

PMN-PT弛豫铁电粉体的溶胶-凝胶法制备及其性质

以无机盐或氧化物Ｎｂ_２Ｏ_５、ＭｇＯ、ＴｉＣｌ_４和Ｐｂ（ＡＣ）_２、３Ｈ_２Ｏ为原材料,柠檬酸和ＥＤＴＡ为复合螫合剂,乙二醇为溶剂,分别制备Ｎｂ、Ｍｇ－Ｎｂ、Ｔｉ和Ｐｂ的有机化合物前驱液,采用溶胶－凝胶工艺制备ＰＭＮ－ＰＴ弛豫铁电陶瓷粉体及其烧结体．讨论了制备工艺和螯合剂等对金属有机化合物溶液的性质、材料物相形成和介电性能的影响．     

PTCR陶瓷材料的超低温烧结

主要研究了ＢＮ对ＰＴＣＲ陶瓷材料低温烧结的作用．对Ｌａ掺杂ＢａＴｉＯ_３ＰＴＣＲ陶瓷,在１１００℃的低温下烧结可以得到室温电阻率为１５０Ω·ｃｍ、升阻比为４．９个数量级的样品．对居里温度为３６０℃的高居里点（Ｂａ_０．４Ｐｂ_０．６）ＴｉＯ_３ ＰＴＣＲ陶瓷材料,选用 Ｎｂ_２Ｏ_５为半导化剂,ＢＮ和ＡＳＴ为助烧剂时,可以在１０００℃左右的超低温下烧成．同时,对ＢＮ助烧剂的液相烧结机制进行了初步的探讨．     

CaO-Y2O3添加剂对AlN陶瓷显微结构及性能的影响

研究了掺杂ＣａＯ－Ｙ_２Ｏ_３热压烧结和常压烧结ＡｌＮ陶瓷的性能和显微结构．结果表明：热压烧结ＡｌＮ陶瓷的第二相为Ｙ_３Ａｌ_５Ｏ_１２,常压烧结ＡｌＮ陶瓷的第二相为Ｙ_３Ａｌ_５Ｏ_１2和Ｃａ_３Ｙ_２Ｏ_６;热压烧结ＡｌＮ的第二相体积百分数和晶格氧含量均低于常压烧结;热压烧结ＡｌＮ陶瓷的微观结构良好,其热导率达到２００Ｗ／ｍ·Ｋ．     

BT-PMN共烧陶瓷的新的介温特性

具有不同居里点的两种铁电体粉末在共烧时会产生过渡相．这种过渡相的特性与原始物相的性质密切相关·ＢａＴｉＯ_３（简称ＢＴ）和Ｐｂ（Ｍｇ_１／３Ｎｂ_２／３）Ｏ_３（简称ＰＭＮ）共烧时,介温特性发生异常变化．结果显示,在低温端介温曲线明显抬起,表明具有更低居里温度（Ｔ_ｃ）的新相形成．而在高温端ＢＴ的^Ｔ_ｃ值升高,表明Ｐｂ进驻ＢＴ的晶格．共烧体的性能可以达到室温介电常数＞３０００,损耗＜６０,容温变化率符合Ｘ７Ｒ标准．     

聚乙烯醇(PVA)对无支撑氧化铝膜微观结构的影响

聚乙烯醇（ＰＶＡ）能够避免溶胶－凝胶法制备的Ａｌ_２Ｏ_３膜在干燥阶段产生微裂纹,同时也对Ａｌ_２Ｏ_３膜的微观结构产生影响．利用ＸＲＤ、ＤＴＡ、ＴＧＡ、ＦＴ－ＩＲ及Ｎ_２吸附等手段研究掺杂ＰＶＡ对Ａｌ_２Ｏ_３膜的物相组成、热稳定性以及比表面积、孔径分布、孔表面分形性等微观结构的影响．研究表明,经过４００℃煅烧ＰＶＡ完全排除．与纯Ａｌ_２Ｏ_３膜相比,添加ＰＶＡ的Ａｌ_２Ｏ_３膜吸附量较大,比表面积有所增大,但并不随着ＰＶＡ含量的增多而增加．ＰＶＡ有利于 Ａｌ_２Ｏ_３膜孔径的调整,使孔径分布更狭窄,孔体积也有较大程度的增加．随着 ＰＶＡ的加入,Ａｌ_２Ｏ_３膜的孔表面分形维数降低．     

轴向磁场对硅单晶Czochralski生长过程的影响

利用有限元方法对炉内的传递过程进行了全局数值模拟,假定熔体和气相中的流动都为准稳态轴对称层流,熔体为不可压缩流体,Cz炉外壁温度维持恒定,模拟磁场强度范围为(0～0.3)T,研究了用Czochralski(Cz)法生长单晶硅轴向磁场对熔体流动和氧传输过程的影响.结果表明:轴向磁场可有效地抑制熔体内的流动,但增大加热器功率和结晶界面处晶体内的轴向温度梯度;对于常规Cz炉,轴向磁场可增大结晶界面平均氧浓度,而对于具有气体导板的Cz炉,则会减小结晶界面平均氧浓度.     

A numerical simulation study for the Czochralski growth process of Si under magnetic field

The article presents results of the numerical simulations carried out for the transport phenomena occurring during the Czochralski crystal growth process. Due to computational constraints, the simulations were kept limited to axisymmetric geometries. The simulation model gives special attention to the crystal–melt interface and oxygen transport, and treats the crystal–melt interface according to Stefan’s balance, by explicitly moving the grids. Oxygen evaporation at the free surface is expressed by balancing the corresponding fluxes. Marangoni convection due to temperature gradients is also incorporated into the model. The role of an applied axial magnetic field in controlling fluid flow, interface shape, and oxygen levels is studied in detail. The effect of crystal and crucible rotations is also examined under the influence of the magnetic field. Simulation results show that the application of an axial magnetic field leads to flatter interfaces and lower oxygen concentration levels, but makes the oxygen distribution non-uniform at the crystal–melt interface.     

Axial Magnetic Field Influence on Thermocapillary Convection in Detached Solidification under Microgravity

Control of melt flow in crystal growth process by application of the magnetic field is a practical technique. In order to investigate the effects of the magnetic field on the thermocapillary convection in the detached solidification, the finite-difference method is adopted to carry on numerical simulation. It is assumed that the melt is incompressible, the value of the aspect ratio (height/radius) of the crucible equals to 1, and the non-dimensional width of the gas gap equals to 0.1. The growth of crystal is studied when the Hartmann number is equal to 0, 25, 50 and 75, respectively. The results indicate that the axial magnetic field can effectively inhibit the strength of the flow, and with the strength of magnetic field increasing, the inhibition effects of magnetic field further enhances.     

垂直布里奇曼法CdZnTe晶体生长过程的数值分析

模拟计算了半导体材料CdZnTe布里奇曼法单晶体生长过程，分析了熔体的过热温度、坩埚侧面强化换热以及坩埚加速旋转(ACRT)等因素对结晶界面的形态和晶体组分偏析的影响。结果表明：当熔体的过热温度减小时，熔体中自然对流的强度显著降低，固液界面的凹陷深度有所增加，晶体的轴向等浓度区显著加长，而晶体组分的径向偏析明显增大，坩埚的侧面强化换热增加了自然对流强度，也增大了固液界面的凹陷，但是对溶质成分的偏析影响较小，坩埚加速旋转引起的强迫对流强度远大于自然对流，显著增大了固液界面的凹陷，使熔体中的溶质分布成为均一的浓度场，显著减小了晶体组分的径向偏析，增加了晶体组分的轴向偏析。     

φ300mm的大直径直拉单晶硅勾形磁场下生长的数值模拟

直径300mm硅片的生产技术是当今硅材料生产研究的重要方向之一,而晶体生长 界面的形状、温度分布、晶体中氧的浓度和均匀性等对熔体流动状态十分敏感,采用实验的方 法来测量熔体的流动、温度场分布是很困难的,因此很难通过实验的方法获得熔体的流动是如 何影响晶体生长的质量的,而数值模拟能提供熔体流动、温度分布等详细内容,为单晶硅的生 长提供有利的指导.本文采用低雷诺数的K-ε紊流模型,对直径300mm的大直径单晶硅生 长进行了数值模拟,通过熔体在有、无勾形磁场作用时的流场、温度场的分析,阐明了勾形磁 场影响熔体流动的机理.     

狭缝宽度及坩埚半径对分离结晶法制备CdZnTe晶体的影响

借助有限元法,在常重力条件下对分离结晶过程进行全局数值模拟,研究了狭缝宽度及坩埚半径对CdZnTe晶体生长过程中整体传热与流动特性的影响。模拟结果表明系统内传热特性、熔体流型与狭缝宽度及坩埚半径密切相关:(1)狭缝宽度对分离结晶有决定性的作用,当狭缝宽度较小时,气-液弯界面两端的温差很小,导致增大晶体重新粘附于坩埚壁面的风险;随着狭缝宽度的增大,流动不稳定性增加,很难保持稳定的气-液弯界面形状,增加了实现晶体稳定生长的难度;(2)随着坩埚半径增大,Marangoni对流对熔体流动影响逐渐增大,结晶界面附近的熔体流动不稳定性增加,这不利于晶体的稳定生长。     

Improved multi-orientation dispersion of short carbon fibers in aluminum matrix composites prepared with square crucible by mechanical stirring

In order to improve the strength of short carbon fibers reinforced aluminum matrix(Csf/Al) composite, the dispersion of short carbon fibers with multi-orientation was controlled with a square crucible by mechanical stirring. The three-dimensional flow field models of liquid aluminum melt in the square/round crucibles were established and calculated, and the results were compared. The calculated results show that turbulent flow could be induced both in the square and round crucible, while the non-axisymmetric structure of the square crucible results in higher turbulent kinetic energy in the melt. Therefore, the uniformity and multi-orientation dispersion of the short fibers can be improved by the intensive turbulent flow in the square crucible, which will be increased by increasing the rotational velocity. The distribution of the short carbon fibers in the aluminum matrix prepared under different rotation velocities in square crucible was experimentally investigated. With the increase of stirring velocity, the multi-orientation dispersion of the short fibers in the composites increased gradually. The experimental results are consistent with the calculation results. The tensile testing results show that the strength of the Csf/Al composite can reach 172 MPa when the rotational velocity is 1000 rpm, and it is 48.3% higher than that prepared by the round crucible under the same conditions, which results from the improved multi-orientation dispersion of short carbon fibers in aluminum matrix.     

Physical Simulation of Mold-Filling Processing of Thin-Walled Castings under Traveling Magnetic Field

Mold-filling process of thin-walled castings under the condition of traveling magnetic field has been studied by physical simulation method using gallium melt and fast speed photography. Flow morphology and its formation mechanism were obtained and discussed for thin-walled casting. The influences of magnetic field density on the filling ability, filling velocity and mold filling time have been studied. The differences in filling capability between gravity casting and casting under the traveling magnetic field have been compared. The results indicate that the mold filling ability of the gallium melt increases greatly under the condition of traveling magnetic field; the filling time is shortened from 18 s under gravity field to 3 s under the traveling magnetic field and average flow rate of the melt increases from 1.6 to 8.68 cm3/s; the change law of the cross-section morphology of the gallium melt during the mold filling is that at first, the cross-section area does not change, then it decreases gradual