苹果酸杂质存在条件下的乳酸锌结晶提纯

研究了苹果酸杂质存在条件下溶液结晶过程参数对乳酸锌晶体产品收率、纯度、晶体结构和形态的影响。结果表明,溶液结晶过程参数对乳酸锌晶体结构和形态没有明显影响,但与纯乳酸锌晶体相比,苹果酸的引入增加了乳酸锌晶体的长径比。晶体纯度的下降与产品收率的上升为近似线性关系,但如结晶过程中发生大量二次成核,晶体产品的纯度将显著下降。     

杂质对溶液结晶过程影响的研究进展

综述了杂质对结晶过程及结晶产品性质的影响。在溶液结晶过程中,杂质对溶液状态以及晶体成核、生长及团聚等过程产生影响,进而影响到晶体习性、粒径和粒度分布。从微观水平分析了杂质对晶体表面台阶生长速率的影响。阐述了杂质对结晶过程影响研究的重要性、该领域存在的问题及今后的研究方向。     

仲钨酸铵结晶成核速率的研究

提出了仲钨酸铵（APT）蒸发结晶过程酸碱反应→仲钨酸根A－B转变→相交的成核机理.讨论了现有直接统计的方法测定APT成核速率的困难.将最终产品的粒度分布数据与一定结晶时刻晶体生长质量速率的测试结果相结合，建立了APT成核速率的研究方法.并在研究APT晶体生长机理的基础上分析了大小晶粒线生长速率的差异，以及破碎、晶粒附聚和二次成核给结果带来的可能偏差.     

成核剂对聚氨酯泡沫成核性能的影响

主要研究了聚氨酯发泡过程中成核剂的添加量、颗粒大小及颗粒的表面状态对气泡成核过程的影响。结果表明:成核剂的加入可有效地促进气泡成核,降低泡孔尺寸;大尺寸颗粒的成核效果要好于小尺寸颗粒;成核剂的颗粒状态对气泡成核的影响不明显。     

冷却速率对β成核剂改性PP结晶行为的影响

利用差示扫描量热仪研究了冷却速率对β成核剂改性聚丙烯(PP)结晶行为的影响。冷却速率越慢,高温停留时间越长,则PP中β晶型含量越高,PP的冲击强度越高。冷却速率为5℃/min时,PP中β晶型质量分数达86.12%;冷却速率为20℃/min时,β晶型质量分数为72.04%;而当试样以极快速冷却时,β晶型含量为0。β晶型PP的结晶速率慢于α晶型PP,只有在较高的温度范围内等温结晶时,β晶型PP的结晶速率才快于α晶型PP。因此,一般加工工艺条件下β晶型含量较少。     

纳米氧化物作为成核剂对PET结晶速率的影响

研究了成核剂纳米氧化镁和纳米氧化硅对聚对苯二甲酸乙二醇酯(PET)结晶速率的影响。通过等温结晶差热分析(DSC)研究了纳米氧化镁在不同含量、不同温度下对PET等温结晶行为的影响。用纳米氧化镁和纳米氧化硅填充PET体系的非等温结晶DSC,由所得冷结晶峰温度值和热结晶峰温度值的对比,探索纳米成核剂对PET结晶速率的影响及其规律。研究结果表明:纳米成核剂均能明显提高PET的结晶速率,而纳米氧化镁比纳米氧化硅对促进PET的结晶效果更好;添加不同含量的纳米氧化镁对PET在不同温度下的等温结晶影响不同,在所研究的范围内,1.0%的添加量较有利于PET的结晶。     

基于BP神经网络的结晶成核速率预测

利用神经网络所具有的输入输出之间的高度非线性映射关系,给出了一种利用BP神经网络模型预测磷酸二氢铵结晶成核速率的方法。在对网络进行训练的基础上,建立了磷酸二氢铵结晶生长速率与过饱和度、冷却温度、饱和温度及悬浮密度和之间的数学模型。仿真结果表明,利用文中所提出的神经网络模型能够较准确、快速地预测结晶成核速率的变化,预测值与测量值的最大相对误差不超过5.9%,表明该网络预测模型有很大的实用性。     

Mult-920成核剂对iPB晶型转变速率的影响

采用红外光谱法研究了室温条件下Mult-920成核剂对全同聚1-丁烯(iPB)的晶型转变速率的影响。结果表明,成核剂对iPB具有很好的成核作用;成核剂对晶型转变速率的影响较大,加有成核剂的iPB的晶型转变完成一半的时间只需要1.6 h,明显低于iPB的28.5 h;在力学性能方面,iPB需要72.0 h左右达到性能稳定,加有成核剂的iPB只需要24.0 h便可以达到性能稳定,从而说明成核剂能很好地加快iPB的晶型转变速率。     

成核剂A对聚甲醛结构与性能的影响

本文利用差热分析仪、偏光显微镜、广角Ｘ射线衍射仪及力学性能测试设备考察了成核剂Ａ对聚甲醛结构与性能的影响．研究发现，成核剂Ａ的加入，使得聚甲醛球晶细化，结晶速度加快，结晶过程为异相成核三维生长过程；且不改变ＰＯＭ的结晶晶型．但结晶度下降，微晶尺寸增大；含有成核剂Ａ的ＰＯＭ具有较高的缺口冲击强应，使得ＰＯＭ的缺口敏感性下降，因而可扩大ＰＯＭ的应用领域．     

Effect of solvent and impurity on synthesis of ethyl lactate from fermentation-derived ammonium lactate

Fermentation-derived ammonium lactate was converted into ethyl lactate by decomposition in various organic solvents followed by esterification with ethanol over Amberlyst catalyst. The ammonium lactate was decomposed more efficiently in an organic solvent with high boiling point, where the produced lactic acid was stabilized well as a monomer without oligomerization. However, only the nonreactive phosphate-type solvent such as triethyl phosphate and tributyl phosphate showed a notable ethyl lactate yield in the subsequent esterification reaction compared with dimethyl sulfoxide and N-methyl pyrolidine. The lactic acid yield in ammonium lactate decomposition and the subsequent ethyl lactate yield were also highly dependent on solvent ratio to ammonium lactate, temperature and pressure in ammonium lactate decomposition reaction. The amino acid impurity contained in the fermented ammonium lactate as well as the unreacted ammonium lactate reduced the acid strength of Amberlyst-36, which resulted in the final ethyl lactate yield.     

Effect of surface conditioning on zinc nucleation using aluminium cathodes

The effect of the aluminium cathode microstructure on zinc nucleation has been investigated through surface examination by SEM and cyclic voltammetry. Zinc nucleation is strongly affected by the surface preparation and impurities present in the aluminium. For chemically pure aluminium, the oxide film on the surface plays an important role during zinc nucleation and crystal growth. Thickening the barrier oxide film inhibits nucleation while a reverse effect can be obtained by thinning or removing the oxide film. In the case of a dilute aluminium with iron alloy, following anodization, the Al–Fe intermetallic phases provide conductive paths through the oxide film resulting in zinc nucleation.     

Effect of nucleation mode on the morphology and texture of electrodeposited zinc

The effect of temperature, pH and current density on the morphology and texture of electrodeposited zinc on mechanically polished steel was studied. The electrodeposited zinc had mostly basal (0 0 0 2) and low angle planes (1014, 1013, 1012) parallel to the surface. At pH 2, increasing overvoltage (i.e., increasing current density or decreasing temperature) reduced the percentage of basal plane and increased the percentage of low angle planes parallel to the substrate surface. Increasing overvoltage decreased the zinc crystal size. At pH 4, increasing current density increased the percentage of both basal and low angle planes parallel to the surface, but increased the zinc crystal size. This variation of behaviour at pH 4 was explained by a change in nucleation mode due to hydroxide adsorption. The nucleation mode was determined by comparing dimensionless (i/i _m)² vs (t/t _m) potentiostatic current–time transient graphs with models for instantaneous and progressive nucleation. It was shown that at pH 2, instantaneous nucleation was predominant, whereas at pH 4, it was close to progressive.     

Simulation of nucleation kinetics—an application to secondary nucleation

In order to study the effect of a disturbance on a supersaturated system (as occurs during secondary nucleation), the kinetics of the nucleation process has been simulated. During the process of secondary nucleation the currently accepted survival theory predicts that only clusters whose sizes are greater than the critical size will survive. This study has shown, however, that the critical size does not establish a sharp cutoff point. Rather, certain conditions can cause subcritical clusters (embryos) to survive and supercritical clusters (nuclei) to dissolve.     

Method of determining the kinetics of spherulite primary nucleation from the truncation of spherulites

Synopsis An attempt is made to describe mutual truncation between two coinciding spherulites. It is shown that if in a sample the borderlines between spherulites are not straight lines, the spherulites did not arise simultaneously. Using. a mathematical approach it is possible to determine the time distribution of primary nucleation from the shapes of truncated spherulites. This was done for polyoxymethylene samples at two different crystallization temperatures. The superiority of thermal over athermal type of nucleation depends on the crystallization temperature which lead to different spherulite size distributions.     

对苯二甲酸锌初级成核过程研究

为研究对苯二甲酸锌的成核过程,实验采用平衡法测量对苯二甲酸锌在苯二甲酸钠溶液中的溶解度计算成核过程的过饱和度;298.15 K下用聚焦光束发射测量仪在线监测对苯二甲酸锌反应结晶过程中诱导期,并计算临界成核半径和临界成核自由能与过饱和度的关系。结果表明:过饱和度越大,诱导期时间越短;根据经典成核理论,在过饱和度S大于8.16时,发生的是均相成核过程,过饱和度S小于6.66时,发生的是非均相成核过程;其中在均相成核中,临界成核半径和临界成核自由能都是随着过饱和度的增加不断减小。因此,提高过饱和度使成核过程更加容易进行。     

Effect of surface nucleation on isothermal crystallization kinetics: Theory, simulation and experiment

Surface nucleation of poly(l/d-lactide) at the interface with aluminum was studied by performing isothermal DSC analysis of amorphous samples of varying thickness between 100 °C and 130 °C. To ensure complete wetting of the aluminum surface, a hot melt laminating process was used to prepare the samples. Theoretical aspects of surface crystallization kinetics were explored and the resulting model was compared with the results of Monte-Carlo simulations. Three stages of surface crystallization were identified depending on the growth geometry: (1) impingement-free growth, (2) increasingly laterally-constrained transverse growth, and (3) interstitial growth. By fitting the Monte-Carlo simulation to the experimental half-times of crystallization the surface nucleation concentration and the bulk nucleation rate was estimated at 4 different temperatures. It was found that both surface nucleation concentration and the bulk nucleation concentration decrease with increasing crystallization temperature.     

Critical seed loading from nucleation kinetics

A method is presented for preparing critical seed loading diagrams for nonaggregating systems knowing only the nucleation kinetics. This is advantageous because it is much less time‐consuming than developing and solving a complete batch process model including solubility expressions and growth rate kinetics. Furthermore, there are many more reports available in the literature of nucleation kinetics alone than there are of complete batch crystallization process models, because expressions for the nucleation rate as a function of crystal growth rate can be rapidly determined from mixed‐suspension, mixed‐product‐removal (MSMPR) data without measuring the supersaturation. The results for 43 systems show that there is a great deal of variability in the critical seed loading, and a single correlation is inadequate to describe the relationship between critical seed loading and seed size. For a seed size of 10 µ, seed loading can effectively suppress nucleation in 92% of cases, while for seeds of size 50, 100, and 200 µ, seed loading can suppress nucleation in 74, 61, and 39% of cases, respectively. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1645–1653, 2014     

Method of determining the kinetics of spherulite primary nucleation from the spherulite shapes in bulk samples

Summary Using the mathematical approach it was shown that it is possible to find the time lag between nucleation acts of two adjacent spherulites from the curved border lines seen in the thin section of a bulk sample. The method of the determining time distribution of the primary nucleation is proposed to be done in the similar way as it was done in the two dimensional case (PAKUA et al. 1979).Based on the above the measurements of the nuclei succesion were reconstructed in two different injection moulded poly methylene oxide samples. This shows a marked number of thermal nuclei.