A theoretical analysis of solution-precipitation controlled densification during liquid phase sintering

Models for solution-precipitation controlled, intermediate stage liquid phase sintering (LPS) have been derived by assuming a tetrakaidecahedron grain geometry with cylindrical pore channels along the grain edges and incorporating the liquid content and dihedral angle by adapting Wray's two phase grain model. The stress distribution of a thin liquid film between the grains is modelled as a hydrostatic squeeze film. The model predicts that a thin viscous liquid film is stable and suppors the normal stress arising from the Laplacian force at the liquid-vapor interface. The derived equations for both diffusion and interface reaction controlled liquid phase sintering show significant differences with respects to Kingery's LPS models, but are in good agreement with those based on liquid phase controlled creep models. Comparative analyses of the derived models indicate that the rate controlling mechanism during solution-precipitation shifts from diffusion to interface reaction control or vice versa as a function of particle size and/ or grain growth.     

宝钢烧结系统锌平衡测试研究

对宝钢2DL、3DL两台450m^2烧结机现场取样，测定试样中的锌含量，进行锌平衡计算，研究烧结系统锌的平衡状态及其影响因素。为解决含锌尘泥的回收利用提供基础数据。     

典型褐铁矿烧结试验研究

采用电炉烧制压制小饼的微型烧结方法对褐铁矿进行烧结,利用扫描电镜、X射线衍射对单一褐铁矿在不同烧结温度下的矿物组成以及矿相结构进行分析研究,利用万能压力机测定相应烧结试样的抗压强度,揭示矿物组成和结构与其抗压强度间的相互关系。研究表明:单一褐铁矿烧结矿相主要是赤铁矿和复合铁酸钙形成的交织熔蚀结构,随着烧结温度的升高,复合铁酸钙的微观尺寸明显增大,试样的抗压强度在1 260℃时最大。     

A theoretical study of grain growth in porous solids during sintering

The processes of grain boundary migration, pore drag and pore/boundary separation are described on the basis of the phenomenological equations for boundary migration and surface diffusion. Cylindrical pores on triple grain junctions are assumed to represent the open porosity during intermediate-stage sintering. It is found that cylindrical pores can hardly detach from migrating boundaries. Three-dimensional closed pores, however, which predominate during final stage sintering, can separate from migrating grain junctions. The separation process is modelled numerically and the conditions for separation are formulated. Analytical approximations for the pore mobility are shown to describe the numerical results well. They serve to establish effective mobilities of grain boundaries bearing pores in various configurations. Classical theories of grain coarsening are modified by using these effective mobilities. Mechanical constitutive models of sintering contain the grain size as an internal variable. The present analysis leads to an evolution equation for the average grain size, which depends on the volume fraction of the pores and on their configuration.     

Oven operation in sintering powder components plasticized with zinc stearate

A mechanism is described for the pyrolysis of zinc stearate in relation to the processes that occur in each sintering zone. The mechanism of formation is considered for the deposits in the working space. This is based on the flow of heavy vapor from the decomposition products under gravity. Designs are considered for the preheating chamber, which provide almost ideal conditions for the removal of the destruction products not only from the oven but also from the components.Translated from Poroshkovaya Metallurgiya, No. 5, pp. 96–100, May, 1993.     

Experimental and theoretical analysis of roll flattening in the deformation zone for ultra-thin strip rolling

For ultra-thin strip rolling, the conventional rolling force models are no longer applicable. To obtain accurate rolling force in the shape and gauge control process, Fleck proposed a new roll flattening model. In this study, experimental analysis, finite element simulation, and theoretical analysis were conducted to evaluate the Fleck model. The experiments and simulations show a clear neutral zone in the deformation zone with decreasing strip thickness. The finite element simulation results show that the proportion of the elastic unloading zone is small, when an elastic unloading phenomenon appears in the neutral zone. Thus, to simplify the rolling force model, the effect of an elastic zone could be ignored. Based on this finding, we develop a rolling force model with quick calculation speed, high precision, and convenient online application. Finally, the accuracy of the simplified model is verified by the measured rolling force.     

转炉含铁废料用于烧结的试验研究

在一定的烧结原料条件下进行了钢渣与转炉尘泥不同配比的烧结试验研究.研究表明:加入钢渣对制粒效果有不利影响,但适宜配比的钢渣使烧结速度、成品率及利用系数都有所提高,烧结矿强度下降不明显,总的影响较小;烧结混合料中加入OG泥悬浮液有利于混合料制粒,随OG泥配量增加,混合料中-1 mm粒级比率迅速降低,对改善混合料透气性、提高产量、降低成本及保护环境十分有利.     

强化烧结添加剂的烧结试验研究

添加烧结强化剂1、2号进行烧结试验，结果表明，无论是四烧原料条件（全粉矿）还是一烧原料条件（配用精矿40％）烧结，均可降低固体燃料消耗，改善烧结矿冷强度，提高烧结矿产量。     

达钢烧结配矿试验研究

根据达钢烧结生产实际情况,研究了钒钛铁精矿配比对烧结过程和烧结矿冶金性能的影响。结果表明：在烧结杯实验条件下,随着钒钛铁精矿配比增加（达到12%）,垂直烧结速度会下降（低于25mm/min）,低温还原粉化指标也会变差。综合考虑,钒钛铁精粉比例目前控制在5%左右为宜。     

Experimental and theoretical analysis on the charge transfer band of Y_2O_3:Eu nanocrystals

Nanocrystalline cubic Y2O3:Eu were prepared by combustion reaction.The crystal structure and morphology were analyzed by means of X-ray diffraction(XRD) and transmission electron microscopy(TEM).The luminescent properties of the powder were investigated.The charge transfer band position showed redshift from 241 to 251 nm,which was related to the change of the local surroundings of Eu3+ ions in nanocrystalline Y2O3:Eu.The ground-state electronic structure and charge transfer transition of both the bulk and nanocrystalline cubic Y2O3:Eu crystals were calculated by the ab initio self-consistent relativistic DV-Xα(discrete variational Xα) method.A complete 35-ion cluster was selected to simulate the local coordination surroundings of Eu doped in Y2O3 bulk crystals while five additional incomplete clusters were also selected to simulate the local surroundings of Eu ions in nanocrystals.It could be found that the charge transfer energies of the nanocrystalline Y2O3:Eu were less than that of the bulk counterpart,which was consistent with the redshift phenomenon of the CT band in the excitation spectrum of the nanocrystalline Y2O3:Eu.     

McCollough effects: Experimental findings and theoretical accounts.

Presents a review of the literature on McCullough effects, a group of visual contingent aftereffects involving color and contour. While a number of investigations have simply reported variations of the original phenomenon, others have closely examined characteristics of these effects and the conditions under which they can be optimally produced. Indications that their spatial specificity is similar to that of single cortical cells investigated electrophysiologically in animals have inspired several models; however, the extraordinary persistence of the effects is difficult to explain at a single-unit level. Findings which suggest that McCullough effects have characteristics like those of learned responses may help to resolve this paradox. (52 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Experimental and theoretical evidence for carbon-vacancy binding in austenite

Our research and results from the literature all consistently suggest a binding energy of nearest-neighbor carbon-vacancy (C-V) pairs of the order 35 to 40 kJ/mole in austenitic alloys. Results examined include point-defect anelasticity, self-diffusion, high-temperature creep, strain aging, strain-age hardening, radiation damage, and point-defect structure modeling. Increases in the height of carbon-based anelastic peaks by quenching, cold work, and electron irradiation are consistent with a substantial nonexclusive contribution of C-V complexes. Increased carbon content in austenite increases the iron self-diffusivity and the high-temperature creep rate of fcc Fe, implying a C-V binding energy of ∼40 kJ/mol. Dynamic strain aging of carbon-containing austenites occurs in temperature ranges too low to involve interstitial solute mobility and requires an interpretation of large C-V binding wherein the vacancy is the more mobile component. Strengthening in heavily deformed austenitic stainless steels associated with strain aging or long-term aging near room temperature implies solution hardening by tetragonal-like C-V complexes formed at these temperatures. Results on radiation damage of austenitic steels show effects of carbon on irradiation susceptibility. Finally, we have performed first-principles gradient-corrected density functional calculations to determine the binding energy of nearest-neighbor C-V pairs in fcc iron; a value of ∼35 kJ/mol is obtained. This article is based on a presentation in the symposium “Terence E. Mitchell Symposium on the Magic of Materials: Structures and Properties” from the TMS Annual Meeting in San Diego, CA in March 2003.