Three-Dimensional Finite-Element Analysis of Viscous Sintering

A finite-element model is developed and implemented on a massively parallel supercomputer to study the viscous sintering of a three-dimensional (3-D) configuration of three particles. Model development is described, implementation is discussed, and calculations are compared with benchmark results for a two-dimensional (2-D) axisymmetric case. For the first time, detailed simulation results are shown for the viscous sintering of a 3-D, three-particle system. The calculations predict center approach of particle pairs concurrent with asymmetric neck growth, effects which ultimately lead to an inward rotation of the outer particles. Anisotropic shrinkage arises due to this 3-D rearrangement of the particles during sintering.     

Analysis of a Chevron-Notch Four-Point-Bend Specimen by the Three-Dimensional Finite-Element Method

This paper deals with a computation of the stress intensity factor (K_I) for a four-point-bend chevron-notch specimen of preselected geometry by the three-dimensional finite-element method. In addition, there is a comparison with the straight-through crack assumption and Bluhm models. The dependence of K_I on Poisson's ratio (v) is discussed for one of the crack lengths.     

Three-Dimensional Model for Calculating Duration of Viscous-Flow Sintering

A method for estimating the duration of isothermal sintering of a powdered body and its final porosity and shrinkage is considered. The method, based on a three-dimensional model in the form of a cubic packing of spherical particles, uses sintering physics equations, the physicochemical properties of materials, and particle sizes. The model allows for describing not only the initial state (coalescence of particles) and the final state (compression of individual pores), but also the intermediate consolidation stage according to the general mass transfer mechanism. The sintering parameters for a sample of container glass powder are calculated using the viscous flow mechanism. The absolute discrepancy between the estimated results and experimental data is equal to 2.0% in porosity and 1.5% in shrinkage. __________ Translated from Steklo i Keramika, No. 5, pp. 19 – 24, May, 2005.     

An Arrhenius-Type Viscosity Function to Model Sintering Using the Skorohod–Olevsky Viscous Sintering Model Within a Finite-Element Code

The ease and ability to predict sintering shrinkage and densification with the Skorohod–Olevsky viscous sintering (SOVS) model within a finite-element (FE) code have been improved with the use of an Arrhenius-type viscosity function. The need for a better viscosity function was identified by evaluating SOVS model predictions made using a previously published polynomial viscosity function. Predictions made using the original, polynomial viscosity function do not accurately reflect experimentally observed sintering behavior. To more easily and better predict sintering behavior using FE simulations, a thermally activated viscosity function based on creep theory was used with the SOVS model. In comparison with the polynomial viscosity function, SOVS model predictions made using the Arrhenius-type viscosity function are more representative of experimentally observed viscosity and sintering behavior. Additionally, the effects of changes in heating rate on densification can easily be predicted with the Arrhenius-type viscosity function. Another attribute of the Arrhenius-type viscosity function is that it provides the potential to link different sintering models. For example, the apparent activation energy, Q , for densification used in the construction of the master sintering curve for a low-temperature cofire ceramic dielectric has been used as the apparent activation energy for material flow in the Arrhenius-type viscosity function to predict heating rate-dependent sintering behavior using the SOVS model.     

Cell Models for Viscous Sintering

The kinetics of viscous sintering are determined for models consisting of cylinders intersecting so as to form cells with cubic, tetrahedral, and octahedral shapes. These models are shown to be quite resistant to Rayleigh instabilities, and to densify at similar rates. The constitutive parameters (free strain rate, uniaxial viscosity, and Poisson's ratio) are presented for all of the models.     

Numerical Simulation of Viscous Sintering by a Periodic Lattice of a Representative Unit Cell

In this paper numerical simulations of the viscous sintering phenomenon are presented, i.e., of the process that occurs (for example) during the densification of a porous glass heated to such a high temperature that it becomes a viscous fluid. The numerical approach consists of simulating the shrinkage of a two-dimensional unit cell which is in some sense representative for the porous glass. Hence it is assumed that the microstructure of the glass can be described by a periodic continuation in two directions of this unit cell. In this way it is possible to obtain insights into the viscous sintering process with respect to both pore size and pore distribution of the material. In particular this model is able to examine the consequences of microstructures on the evolution of the pore size distribution. The major finding is that the pores vanish in order of size one after another-the smallest pores first, followed by the larger ones. Moreover, it is shown that pores with concave boundary parts may initially grow before they start shrinking at a later stage.     

Device Simulation of Nanopillar-based n-CdS/p-CdTe Solar Cell with Enhanced and Efficient Carrier Collection

Silicon - With an objective of enhancing the device performance of a Nanopillar-based n-CdS/p-CdTe solar cell, an n-ZnO window and p-CdZnTe (CZT) electron reflecting layer has been proposed...     

Spectroscopic and Simulation Analysis of Facile PEDOT:PSS Layer Deposition-Silicon for Perovskite Solar Cell

In this research work, we have characterized and simulated a well-known hole transport material (HTM) for perovskite solar cell (PSC) and conductive polyme     

Numerical Simulation of Solid-State Sintering: I, Sintering of Three Particles

A kinetic, Monte Carlo model, capable of simulating microstructural evolution sintering in a two-dimensional system of three particles, has been presented. The model can simulate several mechanisms simultaneously. It can simulate curvature-driven grain growth, pore migration and coarsening by surface diffusion, and densification by diffusion of vacancies to grain boundaries and annihilation of these vacancies. Morphologic changes and densification kinetics are used to verify the model.     

Three-Dimensional Computer Simulation of Ferroelectric Domain Formation

Three-dimensional (3-D) computer simulations of ferroelectric domain formation and evolution were performed, using a computer simulation model based on the time-dependent Ginsburg-Landau equations. A cubic-to-tetragonal ferroelectric phase transition is considered. It is shown that the initial stage of the transition during the annealing of a quenched cubic paraelectric phase involves the nucleation and growth of the ferroelectric domains, followed by the domain coarsening leading to the formation of 90° and 180° domain structures. Part of the 3-D results reported here confirm our conclusions made earlier for the two-dimensional (2-D) case, namely, the nonlocal elastic interactions are critical to the formation of twin structure and the dipole-dipole interactions are responsible for the head-to-tail arrangements of dipoles at twin boundaries. In contrast to our previous work, and others; the effect of the depolarization energy was explicitly incorporated into the simulation model. It is found that when there are no surface charges to compensate the Lorentz field due to the polarization charges, and if the system is mechanically clamped, both 90° and 180° domains are thermodynamically stable.     

太阳电池EVA胶膜的研究

本文研究了EVA胶膜在太阳电池封装工艺中的作用。当EVA胶膜受热熔融时，胶膜中的复合交联剂引发EVA分子发生热交联；同时引发不饱和偶联剂与EVA发生接枝反应。本文还披露EVA胶膜对玻璃透过可见光的增透功能与EVA腹膜吸收紫外光的功能作用。     

Three-Dimensional Cell Culture: A Breakthrough in Vivo

Cell culture is an important tool for biological research. Two-dimensional cell culture has been used for some time now, but growing cells in flat layers on plastic surfaces does not accurately model the in vivo state. As compared to the two-dimensional case, the three-dimensional (3D) cell culture allows biological cells to grow or interact with their surroundings in all three dimensions thanks to an artificial environment. Cells grown in a 3D model have proven to be more physiologically relevant and showed improvements in several studies of biological mechanisms like: cell number monitoring, viability, morphology, proliferation, differentiation, response to stimuli, migration and invasion of tumor cells into surrounding tissues, angiogenesis stimulation and immune system evasion, drug metabolism, gene expression and protein synthesis, general cell function and in vivo relevance. 3D culture models succeed thanks to technological advances, including materials science, cell biology and bioreactor design.     

铁矿石低碳烧结的数值模拟

建立了烧结过程传热模型,利用Fluent软件对常规烧结及以10%, 20%, 30%(等能量输出)竹炭和板栗壳炭替代常规燃料进行烧结的温度场进行数值求解,计算值与测定值对比验证模型的可靠性,以料层最高温度和料层冷却速率对各方案进行评价. 结果表明,竹炭和板栗壳炭20%替代方案最高温度高于1573 K时的料层厚度分别为0.49和0.47 m,大于常规烧结及10%和30%替代方案,能有效提高烧结矿成块固结量;竹炭和板栗壳炭30%替代方案料层冷却速率小于120 K/min时的料层厚度分别为0.458和0.480 m,大于常规烧结及10%和20%替代方案,有助于提高烧结矿机械强度;用燃点较高的生物质炭替代常规燃料有利于提高料层最高温度,用燃点较低的生物质炭替代常规燃料有利于加快烧结速率.     

太阳能电池研究现状

随着工业的发展以及能源需求量的不断攀升,传统化石能源资源已不能满足人类社会的要求。太阳能具有极大的应用潜力,而探索太阳能材料非常重要。本文调研了太阳能电池材料的发展、太阳能电池现阶段状况、太阳能电池的商业化发展趋势。     

Simulation of the Viscous Sintering of Coated Particles

Problems associated with the sintering of mixtures of hard and soft particles can be obviated by coating the hard particles (e.g., alumina) with a soft phase (e.g., glass). An analysis of the sintering kinetics of such materials based on finite-element simulations of the sintering of a pair of rigid spheres coated with a viscous material is presented. Until the contact radius is greater than the thickness of the coating, the sintering kinetics are very similar to those obtained if the rigid core is not present. The sintering rate decreases as the rigid cores approach each other and is limited by flow in the gap between the core particles. If the coating thickness is in excess of 20%, the simulations predict that a packing of such particles sinters to full density at a rate comparable to that of particles without a rigid core.     

Mathematical Simulation of Sintering of an Ultrafine Powder

A pointwise mathematical model of sintering of a compact of an ultrafine metal powder in the thermal explosion mode is developed. A condition for occurrence of this reaction mode is found. The model is verified by results on the delay and temperature of the beginning of Ptblack powder sintering.     

有机太阳能电池材料研究进展

对有机太阳能电池(Organic Solar Cells,OSCs)的研究背景、基本结构与原理进行了简单介绍。主要针对具有代表性的OSCs材料做了系统综述,并对该领域的发展进行了展望。     

薄膜太阳能电池研究进展

薄膜太阳能电池是缓解能源危机的新型光伏器件。综述了硅基薄膜太阳能电池、CdTe薄膜太阳能电池、CIS（CIGS）薄膜太阳能电池、TiO2薄膜太阳能电池、ZnO薄膜太阳能电池和有机薄膜太阳能电池的研究现状,展望了太阳能电池的发展趋势。     

Simulation of the Viscous Sintering of Two Particles

The viscous sintering of two initially spherical particles is modeled as creeping flow in response to surface tension. The governing equations are solved using the finite-element method. The condensed results of this simulation, the center-to-center approach velocity, and the rate of change of contact area were presented earlier. Some details of the flow field during sintering and the evolution of the neck geometry in the early stages of sintering are presented here. Important numerical issues are detailed.