两面顶模具结构的研究进展

本文简要介绍了两面顶装置在合成高档金刚石工艺中的优势,以及两面顶模具技术在欧、美、日和中国的发展历程及研究进展情况,给出了各类两面顶模具的结构示意图及模具相关技术的有限元研究,对今后两面顶模具的结构设计与力学分析提供了依据.通过对比不同两面顶模具的结构形式,对压缸的几何参数进行了系统的分类和汇总.简要分析了我国人造金刚石行业的发展现状.     

Belt型超高压模具若干问题研究和降低金刚石生产成本的途径

本文研讨了提高Ｂｅｌｔ型模具寿命的若干关键技术。介绍了国外模具寿命，容积大小与金刚石生产成本的关系现状。指出了我国两面顶技术大幅度降低金刚石生产成本，提高模具寿命的途径。     

我国两面顶合成金刚石发展浅析

中国与世界的第一颗人造金刚石都是在两面顶压机,Ｂｅｌｔ型模具合成成功的。但由于中国的研究与开发投入很少,加之中国的工业基础水平低,至使我国的两面顶装备和工艺水平与国外相距甚远。六面顶技术以其投资小,工艺简单而占领中国市场,但产品质量炽低档水平。     

Belt型两面顶模具温度场和应力场有限元分析及钢带缠绕数值模拟初探

在人造金刚石合成工艺中,两面顶模具合成腔体内的压力和温度起着至关重要的作用.根据对叶蜡石力学和热学行为的研究,基于MSC·Mare非线性有限元软件,建立了压缸温度场和应立场的有限元模型,模型中考虑了热导率等物理参数随温度的变化规律.采用FORTRAN语言开发了适用于温度和压力边界条件加载的相应程序,获得了合成状态下压缸的温度场和应力场分布情况.由温度梯度引起的热应力数值较小,对压缸所产生的影响程度较小.压缸内壁径向应力达到5GPa,接近硬质合金极限抗压强度.轴向应力最大值1GPa,出现在压缸外壁中心处.同时还建立了钢带缠绕模具其动态缠绕过程的简化模型,采用一种修正的库仑摩擦边界条件,模拟了钢带的缠绕过程,获得了钢带缠绕层间的应力、应变分布情况.     

静压触媒法人造金刚石晶体表面微形貌研究

通过对六面顶压机和两面顶压机生产的静压触媒法人造金刚石晶体表面微形貌图案的研究,发现了人造金刚石晶体表面的胞状图案和枝蔓状+胞状+层状的组合图案.对这些形貌研究表明,这类人造金刚石晶体是在远离平衡的条件下快速长成的.     

两面顶金刚石杂质的中子活化分析

金刚石里的杂质一直被人们所关注,相关的报道也较多,然而对于两面顶压机合成的高品级金刚石的杂质确很少有报道.本文采用一种新的检测手段-中子活化分析发现金刚石里除了含有触媒的杂质外,还含有十几种稀有金属元素,含量已达到10-9或10-6的数量级别.这些稀有元素的发现有利于我们更好的研究金刚石的性能,提高它的质量.此外,将国内和国外的两面顶金刚石杂质含量进行了对比,发现他们的含量已非常接近,这说明了我国的金刚石制造业已经发展到了一个新的阶段.     

应用Topas和Eva软件计算纳米材料晶粒尺寸的数值观察

随着纳米材料科学的发展,材料的晶粒尺寸是科研工作者在研发过程中十分重要的数据.Topas和Eva是两种常用的X-射线衍射数据分析软件,都可以进行晶粒尺寸的计算.选取6种具有代表性的高级晶族和中级晶族纳米材料,通过X-射线衍射仪测试获得衍射谱,分别应用两种软件对6种材料晶粒尺寸进行计算,发现其结果存在一定差异.为了说明计算结果存在差异的原因,本文详细介绍了两种软件计算晶粒尺寸的方法和步骤,并通过比较说明由于两种软件计算方法不同是产生计算结果差异的直接原因,这对于材料科学工作者在进行相关计算时提供了较好的借鉴以及理论依据.     

Al-Y合金中金属间化合物力热性能的第一性原理计算

针对Al-Y合金中的AlY、Al2Y、Al3Y金属间化合物有关力热性能,采用密度泛函理论、第一性原理以及CASTEP软件进行了理论计算.首先,对五种不同结构金属间化合物的结构进行了优化,并得出了平衡晶格常数.在此基础上,计算得到了它们的生成热、结合能以及弹性系数,并对计算结果进行了理论分析.计算结果表明:在上述五种不同结构的金属间化合物中,其主要的强化相Al2Y合金化形成能力最强,而且结构也较稳定,脆性最强.     

KDP晶体中铝取代钾点缺陷第一性原理计算

为了明确Al3+在KDP晶体生长过程中对光学性质和力学性质的具体影响,采用第一性原理计算程序包VASP软件计算并分析了Al取代K对KDP晶体的晶体结构、电子能态密度和光学性质,并同理想KDP晶体进行对比研究.结果表明,KDP晶体中Al取代K的缺陷形成能为0.974 eV,并且Al替位K点缺陷引起的晶格畸变非常微弱,缺陷比较容易形成. Al取代K后晶体能带中价带顶附近的态密度发生了变化,并且带隙中存在缺陷能级,取代后KDP晶体的带隙宽度减小为4.37 eV,缺陷增加了KDP晶体对可见到紫外波段的光子吸收,影响KDP晶体光学质量及其激光损伤性能.计算力学性质发现,Al替位掺杂KDP晶体比理想KDP晶体的杨氏模量增加了,这会减弱晶体抗激光损伤能力.     

模具法制备CVD金刚石热沉片的温度场与流场研究

本文通过有限元仿真研究了模具法制备CVD金刚石热沉片的温度场和流场,并对制备参数进行了优化.实验与仿真的结果均表明,进气量的大小对衬底附近流场的均匀性影响显著,热丝温度、热丝间距以及热丝到衬底的距离对衬底的平均温度影响显著,热丝间距和热丝温度对衬底温度的均匀性影响显著;模具法制备的CVD金刚石复制了模具型腔,保证了热沉片的结构完整性和尺寸精度,最终制备了精度较高的小型CVD金刚石热沉片.     

Computer simulation of dispersive transport in amorphous materials: Time-of-flight-signals

A method of computer simulation of charge transport in amorphous materials, based on the Scher-Montroll hopping transport model is presented. The method can be applied to a broader range of problems than the original analytical solution because it allows the introduction of an arbitrary distribution of hopping times, space distribution of charge carriers etc.Results of the simulation of time-of-flight experiments with the same initial conditions as in Scher-Montroll's work are found to agree with the analytical solution in asymptotic behaviour (the slope in bilogarithmic coordinates changes from ?1 ?α to ?1 +α) and in the thickness dependence of the transit time. This is considered to be an argument that the simulation method reflects the properties of the model itself.It is further shown, that the electric field dependence introduced in the model by an asymmetry factor ν does not lead to the field dependence of transit time consistent with experiments, because it imposes both upper and lower limits on its values.     

A plausible interpretation of the density scaling of the diffusivity in viscous liquids

Fundamental thermodynamic concepts and an earlier elastic solid-state point defect model are employed to formulate an analytical second-order polynomial function describing the density scaling of the diffusion coefficient in viscous liquids. The scaling exponent is correlated, within the approximations made in the present approach, with the pressure derivative of the isothermal bulk modulus. Our findings are compared with computer simulation results.     

金刚石膜/硅基体热残余应力场有限元分析

运用ANSYS软件建立了有限元模型,对化学气相沉积在硅基体上的金刚石膜内部和膜/基交界面处的各热残余应力分量的分布作了计算与分析.所建模型与已有的一维解析模型都能得出厚度截面上的法向应力分量的分布,且吻合较好,而前者的优点在于它还能模拟切向应力和剪应力等其它应力分量,这对分析膜/基界面的粘附与失效是至关重要的.     

Verification of an analytical method for measuring crystal nucleation rates in glasses from DTA data

A recently proposed analytical (DTA) method for estimating the nucleation rates in glasses has been evaluated by comparing experimental data with numerically computed nucleation rates for a model lithium disilicate glass. The time and temperature dependent nucleation rates were predicted using the model and compared with those values extracted from an analysis of numerically calculated DTA curves. The validity of the numerical approach was demonstrated earlier by a comparison with experimental data. The excellent agreement between the nucleation rates from the model calculations and the computer generated DTA data demonstrates the validity of the proposed analytical DTA method.     

Axial Solute Transport during Bridgman Growth of BiSbTe3‐Mixed Crystals ‐ a comparison of analytical and numerical results

2D/3D‐transient finite‐element computer simulations of heat and mass transport including convection have been performed for a Bridgman configuration close to real growth conditions. The results for the axial distribution of the excessive tellurium in BiSbTe₃ semiconductor crystals grown from the melt are compared with the predictions of analytical segregation models.It is shown that Favier's model can be successfully applied for quantitatively estimating model parameters of segregation. Finally, the transition from normal gravity to microgravity conditions is discussed.     

A phase field model with electric current

A diffuse interface model is presented for the solidification or melting of a pure single crystal that includes the effect of an applied electric current. A coupled set of differential equations modelling the evolution of the phase, the temperature and the current density are derived by applying principles of non-equilibrium thermodynamics. An asymptotic analysis shows that as the diffuse interfacial region tends to zero thickness, classical results are recovered. For this model classical results mean that Joule heating and the Thomson effect in the bulk phases and the Peltier effect at the interface are included. A one-dimensional numerical solution is presented and compared to an analytical solution verifying the model and asymptotic analysis. This phase field model is relevant for solid–liquid phase changes occurring in pure metallic and semi-conductor materials.     

Experimental and theoretical study of the transport of silver nanoparticles at their prolonged administration into a mammal organism

The transport of silver nanoparticles in the organism of laboratory animals has been investigated. A mathematical model of the biokinetics of prolonged administration of nonmetabolizable and nonaglomerating pharmaceutical preparations is proposed, and its analytical solution is found. Based on the experimental data on the prolonged introduction and excretion of colloidal silver nanoparticles and the numerical approximation of the solutions to the equations for the proposed model, time dependences of the silver mass content in brain and blood are obtained and some other important biokinetic parameters are determined. It is concluded that both chronic¹ and subchronic² peroral application of these nanoparticles as an biologically active additive or antiseptic is potentially dangerous.     

Temperature distribution in growing semi-transparent crystals (I). Theory

Simplified analytical and computational solutions of the temperature distribution in crystals grown by Czochralski method including the temperature difference on the liquid/solid interface are given. The model used is based on experiments with oxide crystals with melting points above 2000 K. Computational solution was more extended because it enables to calculate actual temperature distribution with a relatively small error.