共查询到20条相似文献,搜索用时 753 毫秒
1.
2.
3.
Myron Pankevich Ju. Linhart 《人工晶体学报》2006,35(5):963-975
本文通过分析光学材料中光谱与温度之间的关系证实了晶体生长过程中的相变团簇模型,认为晶体内部热辐射流是引起固-液界边界层温度场发生传导的可能原因.引入了前结晶的概念,并结合实际中的不同晶体生长方法讨论了包裹体及气泡的抑止机理,通过计算得到了生长理想晶体的最大生长速率并且解释了由于界面层的摆动使得晶体生长过程中产生的微气泡没有被移动的界面层所捕获. 相似文献
4.
建立了一个120 kg单晶炉的二维轴对称全局模型,分别对无旋转、加入晶体旋转、加入坩埚旋转、同时加入晶体旋转和坩埚旋转的四种工况展开了数值模拟研究.得到了晶体旋转及坩埚旋转对晶体生长过程的拉晶功率、炉内温度分布和熔体流动的影响;得到了不同晶体长度下拉晶炉内的温度分布以及熔体流动的变化规律.结果显示,加入晶体旋转对晶体生长过程的拉晶功率、温度分布和熔体流动的影响小于坩埚旋转的影响;随着晶体长度的增加,晶体旋转及坩埚旋转对温度分布和熔体流动的影响不断减小.因此在单晶炉设计和优化过程中应考虑整个晶体生长过程. 相似文献
5.
蓝宝石晶体热性能的各向异性对SAPMAC法晶体生长的影响 总被引:1,自引:1,他引:0
采用有限元法对冷心放肩微量提拉法蓝宝石晶体生长过程中晶体内的温度、应力分布进行了模拟计算,结合实验结果讨论了蓝宝石晶体热性能的各向异性对晶体生长的影响.研究结果表明,对于冷心放肩微量提拉蓝宝石晶体生长系统,较大的轴向热导率有利于提高晶体的生长速率和界面稳定性,而稍大的径向热导率则有利于保持微凸的生长界面.晶体内的热应力受径向热膨胀系数的影响显著,随着径向热膨胀系数的增大而增大,最大热应力总是出现在籽晶与新生晶体的界面区域.在实验中选α轴为结晶取向,成功生长出了直径达230mm、高质量蓝宝石晶体. 相似文献
6.
7.
8.
9.
10.
11.
T. Fukuda Y. Okano N. Kodama F. Yamada S. Hara D. H. Yoon 《Crystal Research and Technology》1995,30(2):185-188
The behaviour of bubble entrapment in Ti-doped Al2O3 single crystals grown by the Czochralski method was studied from the view point of crystal growth conditions such as the crystal rotation rate and kinds of growth atmosphere. The entrapment of bubbles was not correlated with the shape of solid-liquid interface dependent on crystal rotation rate. We found that the use fo He atmosphere, instead of the conventional atmosphere such as Ar, suppresses the formation of bubbles. 相似文献
12.
本文使用金刚石磨料作为晶种颗粒,通过热丝化学气相法生长出单晶金刚石颗粒,并且建立三维的有限元模型,利用有限元仿真分析了生长过程中影响金刚石磨料生长速率以及沉积质量的各种因素,如热丝的排列方式,衬底的温度场,以及晶种的分布方式.通过固定在热丝CVD反应腔里的热电偶测量了实际的衬底温度分布,从而验证了仿真结果的正确性.另外,通过改变仿真模型优化了沉积单晶金刚石颗粒的工艺参数,获得适应于合成单晶金刚石颗粒的新技术,为化学气相沉积合成单晶金刚石颗粒奠定了基础,也为高温高压金刚石磨料品级的改进与提高提供了新途径. 相似文献
13.
O. M. Bunoiu I. Nicoara J. L. Santailler F. Theodore T. Duffar 《Crystal Research and Technology》2005,40(9):852-859
Ribbon and rod sapphire pulling has been performed in three different crystal growth equipments in order to study the effect of the installation, of the atmosphere, of the die shape, of the feed material and of the pulling rate on the distribution, number and diameter of the characteristic voids (micro‐bubbles) in the crystals. The location of the bubbles in the crystals depends on the die geometry; however, in most cases they are essentially located close to the crystal periphery and then can be efficiently removed by lapping. After statistical analysis of the results, it is demonstrated that the number of gas moles incorporated in the crystals, inside the voids, is totally independent of any growth parameter. It is also shown that the bubble diameter depends only on the pulling rate. Consequently, for a given pulling rate, the number of bubbles auto‐adjusts in order to satisfy the constant molar gas incorporation. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
14.
以硅酸盐为基质的白光LED用荧光粉,具有原料丰富、成本低廉、合成工艺简单、组成多样、发光可调等优点,是当前研究的热点。助熔剂在硅酸盐荧光粉制备过程中起到了至关重要的作用。本文介绍了硅酸盐荧光粉体系中助熔剂的使用情况,助熔剂类别和用量对荧光粉的晶相、发光强度和形貌都有一定的影响。添加不同的助熔剂以及同类不同量的助熔剂会使硅酸盐荧光粉形成不同的晶相种类;助熔剂阳离子围绕在激活剂离子周围,引起发光中心的数量变化,从而改变发射光谱形状并能很大程度提高发光强度,但是过量的助熔剂则会降低荧光粉的发光强度;助熔剂用量对荧光粉表面形貌影响明显,适量的助熔剂能细化晶粒,使晶粒尺寸均匀,晶粒球化,但是助熔剂过量则会使样品结块。加强荧光粉制备过程中助熔剂的机理研究,选择合适的助熔剂及其用量,是合成高性能荧光粉的关键。 相似文献
15.
16.
《Journal of Crystal Growth》2003,247(3-4):516-522
A new way for heterogeneous nucleation of crystals from the solution is described: 3D crystalline structure can nucleate and grow encompassing gaseous cavities, formed on solid substrates in the aqueous solution, so giving rise to crystal bubbles. The double surface of a crystal bubble is made, in this case, by the faces of the cleavage calcite rhombohedron separating the solution from the enclosed gas cavity. The faces thickness and the edges length amount to a few nanometers and to about 5 μm, respectively. Then, the surface-to-volume ratio is the highest obtained for 3D crystals, amidst the consulted literature. Bubbles’ shape is explained through the equilibrium properties of crystal–cavity and crystal–solution interfaces and in terms of growth mechanisms operating on the separate interfaces. The nucleation of the crystals around gas cavities can provide new insight on those mineralization phenomena where the gas phase participate in crystal growth. Potential applications are also envisaged concerning the nucleation of the gas cavities on peculiar templates which impose 1D (or 2D) periodicity to crystal bubbles, in order to obtain 1D and/or 2D photonic crystals. 相似文献
17.
Large eddy simulation model is used to simulate the fluid flow and heat transfer in an industrial Czochralski crystal growth system. The influence of Marangoni convection on the growth process is discussed. The simulation results agree well with experiment, which indicates that large eddy simulation is capable of capturing the temperature fluctuations in the melt. As the Marangoni number increases, the radial velocity along the free surface is strengthened, which makes the flow pattern shift from circumferential to spiral. At the same time, the surface tension reinforces the natural convection and forces the isotherms to curve downwards. It can also be seen from the simulation that a secondary vortex and the Ekman layer are generated. All these physical phenomena induced by Marangoni convection have great impacts on the shape of the growth interface and thus the quality of the crystal. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
18.
Lunyong Zhang Hongbo Zuo Ji Zhou Jianfei Sun Dawei Xing Jiecai Han 《Crystal Research and Technology》2011,46(7):669-675
Haze defect in SAPMAC method grown sapphire crystal was studied in detail. It is shown that haze is composed by a large number of CO2 bubbles, and haze always appears in the axis region of the crystal since the bubbles formed in front of the crystallization surface are most always draged to the convection rolls in front of the central part of the crystallizaiton surface by melt and then engulfed by the rolls. Moreover, the effects of pulling rate on the formation of haze were analyzed and means for restraining haze was suggested. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
19.
O.M. Bunoiu Th. Duffar I. Nicoara 《Progress in Crystal Growth and Characterization of Materials》2010,56(3-4):123-145
Shaped sapphire single crystals almost always contain a typical defect: small bubbles also known as “micro-voids”. The goal of this paper is to review the existing literature and give a survey of our recent work on this specific defect. As a conclusion to our review we propose a mechanism for bubble formation and its occurrence and distribution in shaped sapphire.The bubbles contain CO which originates as a result of complex reactions between the molten alumina, Mo crucible and graphite pieces. The CO dissolves in the molten alumina and is probably present as a saturated solution whatever the growth conditions. Then the dissolved gas is rejected at the solid–liquid interface and bubble nucleation occurs where the concentration of CO is highest. Therefore, the location of the bubbles in the crystal is governed by the hydrodynamics in the meniscus, which include Marangoni convection. The bubble is finally incorporated in the crystal when it reaches a critical size which depends only on the growth rate.When a central capillary channel is used, the bubbles are located in a layer close to the surface of the crystal from where they can be easily removed by polishing. Also, all the literature agrees on the fact that interface destabilization at high velocity results in the presence of bubbles throughout the entire crystal and should be avoided. 相似文献
20.
太空、军事和科研等高科技领域的持续发展极大促进了对蓝宝石晶体的需求,泡生法是蓝宝石晶体的主要制造方法之一;热场结构对所得蓝宝石晶体的质量具有重要影响.本文对采用泡生法工艺制造蓝宝石单晶过程中,具有内置7层氧化锆外置8层钼金属的新型热屏结构间距进行研究.通过数值模拟考察热屏间距对单晶炉功率、固-液界面形状和晶体热应力的影响确定了合理的热场结构;并与试验生产结果进行对比验证.结果表明:热屏间距增大使得单晶炉功率明显提升,并引起固-液界面凸度增大;而蓝宝石晶体热应力出现减小.综合考察三个影响因素的影响,最后确定热屏间距为5 mm时单晶炉能耗较低,可用于制造高质量的蓝宝石晶体. 相似文献