各向异性表面张力对深胞晶界面形态稳定性的影响

应用匹配渐近展开法和多变量展开法研究各向异性表面张力对定向凝固中深胞晶界面形态稳定性的影响, 通过寻找定向凝固系统的模式解获得了深胞晶界面形态满足的量子化条件. 结果表明, 与各向同性的定向凝固系统中深胞晶界面形态稳定性比较, 考虑各向异性表面张力的定向凝固中深胞晶生长界面形态也有两种整体不稳定性机制: 整体波动不稳定性和低频不稳定性. 随着各向异性表面张力的增加, 中性模式产生强振荡的枝晶结构的整体波动不稳定性的不稳定区域减小, 中性模式产生弱振荡的胞晶结构的低频不稳定性的不稳定区域增加.     

溶液中球形晶体溶解的分析

从物质溶液浓度变化角度考虑了球形晶体在溶液中溶解随表面张力的变化,利用渐近方法求出了在溶液中球形晶体溶解的浓度和界面的近似解析解,能够计算出溶解过程中球形晶体溶解的浓度、界面演化形态.研究了表面张力对于溶液中溶质浓度分布、球晶界面形态和溶解速度的影响.结果表明,表面张力促进了球形晶体在溶液中的溶解.随着表面张力参数增大,溶液中在界面前沿的溶质浓度升高,球形晶体的溶解速度增大;随着时间的增加,溶解速度逐渐变大,球形晶体半径逐渐变小,直至溶解结束.     

对流条件下球状晶核生长摄动分析

本文建立了含有小雷诺数对流项的晶核生长的数学物理模型,利用摄动方法对数学模型进行了详细地分析,研究了熔体的小雷诺数对流对球状晶核生长的影响.结果分析表明,在强加来流作用下球状晶界面不再稳定,而是沿远场来流方向进行演化.     

体积排阻色谱和激光光散射对大豆蛋白热诱导聚集体的研究

采用体积排阻色谱(SEC-HPLC)和激光光散射(LLS)研究了不同浓度和离子强度下大豆蛋白热诱导聚集体的分子量分布和粒径分布。在离子强度为0时,SEC-HPLC的结果表明,热处理后的蛋白溶液主要由3部分组成,即聚集体、中间体和未聚集部分。聚集体部分随着浓度增加而逐渐增加;LLS的结果表明:体系有不均一的粒径分布,且浓度增加时体系的平均粒径增加。上述样品在较高离子强度下加热时,SEC-HPLC和LLS的结果都证明溶液中的中间体部分逐渐消失。因此,控制浓度和离子强度可以制备不同性质的大豆蛋白聚集体。     

Effect of buoyancy-driven convection on steady state dendritic growth in a binary alloy

The effect of buoyancy-driven convection on the steady state dendritic growth in an undercooled binary alloy is studied. For the case of the moderate modified Grashof number, the uniformly valid asymptotic solution in the entire region of space is obtained by means of the matched asymptotic expansion method. The analytical results show that the buoyancy- driven convection has a significant effect on the needle-like interface of dendritic growth. Due to the buoyancy-driven convection, the needle-like interface shape of the crystal is changed. When the Peclet number that is not affected by the buoyant flow is less than a certain critical value, the interface shape of the dendrite becomes thinner as the Grashof number increases; when it is larger than the critical value, the interface shape becomes fatter as the Grashof number increases. In the undercooled binary alloy the morphology number plays an active role in the interface shape and leads to the buoyancy effect that is different from the situation for the pure melt. The smaller the morphology number is, the more significant change the interface shape has. As the Peclet number further increases, the effect of buoyancy on the interface diminishes eventually.     

弱熔体对流对定向凝固中棒状共晶生长的影响

利用渐近方法求出在弱对流熔体中定向凝固棒状共晶生长的浓度场的渐近解,研究了弱熔体对流对定向凝固中棒状共晶生长的影响.结果表明,弱熔体对流对定向凝固中棒状共晶生长有显著的作用;平均界面过冷度不仅与棒状共晶的棒间距、生长速度有关,还与流动强度有关;当生长速度一定时,随着流动强度增大,棒状共晶的平均界面过冷度减小.利用最小过冷原则,获得棒间距与生长速度和流动强度的关系.结果表明,当生长速度比较小时,随着流动强度增大,棒状共晶的棒间距增大;当生长速度比较大时,随着流动强度增大,棒状共晶的棒间距变化减弱;棒状共晶的生长速度越小,流动对棒状共晶生长的影响越大.利用本文的解析结果计算在对流条件下Al-Cu共晶的棒间距,结果显示随着转速增大或径向距离增大,共晶的间距增大,这与Junze等的实验结果相符合.     

Dendritic sidebranches of a binary system with enforced flow

In the present paper, the problem of sidebranches in the binary dendritic growth with enforced flow is studied. The positions of the first sidebranch and spacing of dendritic sidebranches are presented. For the neutral stable mode of dendritic growth, effects of various parameters on sidebranches are analysed. Our result shows that sidebranches are produced behind a critical point ξ'_C.     

电渣感应连续定向凝固过程温度场计算与实验研究

自行研制了电渣感应连续定向凝固系统,该系统保证金属液能连续供给,结晶器能连续加热及结晶器轴向存在一定的温度梯度.本系统可用红外线测温仪控制结晶器出口的温度,用热电偶控制结晶器内的温度,用位移传感器控制拉伸速度,实现了对系统主要工艺参数进行监控.本文对此系统的传热过程进行了数值模拟并进行了实验验证,结果表明:所得试样的轴向温度分布与固液界面位置的理论计算值与实验值基本吻合.这样可以利用计算结果来预定工艺参数的范围,为指导电渣感应连续定向凝固的生产奠定了基础.     

Interfacial evolution of a spherical particle in a uniaximal straining flow

The growth behavior of a spherical particle in undercooled melt,affected by uniaxial straining flows,is studied.The analytical solution obtained by the matched asymptotic expansion method shows that the uniaxial straining flow effect results in higher local growth rate near the surface where the flow comes in and lower local growth rate near the surface where the flow goes out,and that the uniaxial straining flow causes an initially spherical particle to evolve into an oblate spheroid.