Heterogeneous Nucleation and Solidification Prediction of Sn-5wt.%Pb Droplets

We develop a model for heterogeneous nucleation catalyzed by oxidation on the droplet surface and the internal nucleation similar to surface oxidation. The fraction covered by oxide on the surface of the droplet is calculated as a function of time and temperature based on the chemical reaction dynamic and transition state theory, which is a reasonable expression for the oxidation behaviour of Sn-5wt.%Pb droplets. The continuous-cooling-transformation curves were computed using the above experimental results under the heterogeneous surface nucleation and the internal nucleation of droplets. Also, we predict the solidification behaviour of the droplet in gas-atomized spraying process using this model. The same model can be applied to predict the nucleation behaviour for any type of cooling schedule.     

单斜辉石固溶体CaMgSi2O6—N4AlSi2O6的合成机理研究

研究了压力和温度对单斜辉石的结晶和晶粒纤维编织的影响。在较低的晶化温度下压力对单斜辉石结晶的影响很明显，这种影响随温度升高而减弱。然而，压力对单斜辉石晶粒纤维编织的影响正相反，在相同的高温下，较高压力下晶化的单斜辉石晶粒纤维比较低压力下得到的晶粒纤维粗壮，而且编织紧密。     

Heterogeneous Nucleation Induced by Capillary Wave During Acoustic Levitation

The rapid solidification of acoustically levitated drops of Pb-61.9 wt. %Sn eutectic alloy is accomplished. A surface morphology of spreading ripples is observed on a sample undercooled by 15 K. The ripples originate from the centre of sample surface, which is also the heterogeneous nucleation site for eutectic growth. The Faraday instability excited by forced surface vibration has brought about these ripples. They are retained in the solidified sample if the sound pressure level exceeds the threshold pressure required for the appearance of capillary waves. Theoretical calculations indicate that both the pressure and displacement maxima exist in the central part of a levitated drop. The pressure near the sample centre can promote heterogeneous nucleation, which is in agreement qualitatively with the experimental results.     

一维随机成核生长模型的边界效应

通过计算机模拟，研究周期边界与固定边界对一维随机成生长模型的聚集生长图形形状及相应的分形维数的影响。     

仲钨酸铵的制备及研究

通过对比蒸发法与在蒸发法中添加晶种和钨酸铵溶液制备的仲钨酸铵产品,结果表明后者制备的晶形更完整、颗粒较粗,且是纯度更高的5水仲钨酸铵.对产品进行了X射线衍射分析与热重分析,并探讨了仲钨酸铵成核机制、动力学过程.最后讨论了添加晶种和钨酸铵溶液对晶体形貌的影响.     

气体水合物垂直换热管外融冰快速成核与静态渗透生长

通过HCFC141b气体水合物在一根垂直换热管外的生成过程可视化实验研究, 发现了融冰快速成核以及水沿垂直换热管自发渗透入客体相中连续生长气体水合物的现象, 并分别利用周公度和Sloan的假说以及表面自由能理论对这两种现象进行了机理性解释, 进而研究出一种新型的气体水合物生成方法——气体水合物换热管外融冰渗透生长方法. 由于不需要机械扰动, 利用该方法生成的气体水合物非常密实, 含水率低, 克服了机械扰动系统中能耗高且生成的水合物含水率高的缺点, 将促进气体水合物储气或蓄冷等应用技术的发展.     

NUCLEATION MECHANISM OF PEO BLOCK IN DOUBLE-CRYSTALLINE POLY（ETHYLENE-co-BUTENE）-b-POLY（ETHYLENE OXIDE） BLOCK COPOLYMERS

In this paper, we proposed a method to determine the nucleation effect of pre-existing crystals on crystallization of the second block in double crystalline block copolymers, which is usually covered by the suppression effect. The nucleation mechanism of poly（ethylene oxide） （PEO） block from the pre-crystallized polyethylene （PE） block in poly（ethylene-cobutene）-b-poly（ethylene glycol） （EmEOn） diblock copolymers was investigated under variable crystallization environments. The crystallization environment for the PEO block was altered by cooling at different cooling rates or successive selfnucleation （SSN） to the PE block. It was found that the presence of nucleation effect is strongly dependent on composition of the block copolymers. The crystallization temperature （Tc） of PEO block in E174EO90 increases as cooling rate applied to the PE block decreases, indicating that PE block can nucleate the crystallization of PEO block and more perfect PE crystals have stronger nucleation effect. In E182EO41 crystallization of the PEO block is confined, shown by the disappearance of selfnucleation domain, and the PE block has no nucleation effect on the crystallization of PEO block. Double crystallization peaks are observed for the PEO block in E182EO41 and the intensity of the crystallization peak at higher temperature increases as the PE crystals become more perfect. After exclusion of homogeneous nucleation mechanism, the higher temperature crystallization peak of the PEO block in E182EO41 is tentatively ascribed to surface nucleation.     

铝酸钠溶液种分过程的粒度变化规律研究

以Master-2000型激光粒度仪测定的粒度分布为基础,考察了种分过程中2μm和20-30μm粒径粒子总质量(Wt)随时间(t)的变化关系.分析了铝酸钠溶液种分过程的二次成核与苛性比(n x)、初始晶种量以及温度的关系,发现成核过程主要在种分前期进行,后期细颗粒因长大和附聚会减少,随温度升高,75℃下溶液几乎没有明显成核;20-30μm的粒子变化在α K较低的情况下(1.3),远大于相同初始晶种量的高α x铝酸钠溶液,表明可能其主要由附聚得到.     

由成核率数据拟合饱和蒸汽压力

Saturated vapor pressure was calculated from the nucleation experimental data using the thermodynamically consistent nucleation theory in which the effect of real gas is considered. The cubic polynomial fit equations of saturation pressure for several substances were obtained based on the calculation. The results of the calculations were compared to those of thermodynamic equilibrium equation and the empirical equation and applied to the predictions of the classical nucleation theory. The results show that the saturation pressures estimated from the nucleation data agree fairly well with those of empirical equations for the substances investigated, and this indicates that the predictions from the classical nucleation theory are close to the experimental data.