功率超声强化溶液冻结机理的研究进展

功率超声波强化溶液结晶是一种新型的结晶技术,由于其具有促进溶液冻结、控制晶体粒径分布和提高冻结产品质量的作用,近年来受到越来越多的关注。从过冷溶液的一次冰晶成核、二次冰晶成核以及树枝状冰晶体的生长速度等方面对超声波强化溶液结晶的机理进行了综述,并对超声结晶机理研究的发展方向提出了建议。     

CXF—O型超声成核装置及其在制糖工业中的应用

针对目前制糖工业成核方法所存在的问题,急待寻求更理想的成核方法。 本文设计制作了一台CXF-O型超声成核装置,用以研究蔗糖溶液成核过程。经过较长时间的反复试验,认为超声成核方法优于目前制糖工业所采用的成核方法;既可间歇成核又可连续成核。可望提高间歇结晶过程的经济效益和促进蔗糖连续、自动结晶的实现。     

在熔融金属溶液中石墨在金刚石稳定区结晶的可能性

本文给出了在超高压高温条件下,碳的亚稳相石墨从熔融金属溶液中结晶的实验现象,并以此为例分析了亚稳相从溶液结晶的热力学可能性。提出了促使亚稳相结晶的过饱和的概念,指出:溶液体系中的温度差是亚稳相结晶的推动力。重点给出在一个结晶条件下亚稳相石墨可能结晶的临界温度差的计算。 关键词：     

纳米微粒对低温保护剂溶液结晶性质的影响

为了研究纳米微粒对低温保护剂溶液结晶性质的影响,实验利用差示扫描量热仪(DSC)测量了加入不同粒径、不同质量分数的HA纳米微粒的乙二醇(EG)低温保护剂溶液的成核温度和结晶焓。实验结果表明:纳米微粒加入EG溶液后,成核温度明显升高,并且随着纳米微粒粒径的和质量浓度的增大而升高显著;加入一定质量浓度(>0.2%)的纳米微粒后,同浓度的低温保护剂溶液的结晶焓稳定地升高。成核温度与结晶焓的升高说明,纳米微粒能够促进低温保护剂溶液的结晶。     

冻干溶液的低温显微研究与热分析

利用低温显微系统研究了叔丁醇水溶液降温时的晶体形态,并利用差示扫描量热法(DSC)研究了溶液的反玻璃化结晶。低温显微实验表明:叔丁醇／水溶液结晶形状、大小与叔丁醇的浓度有关,浓度为10％时形成粗大的针状结晶, 有利于升华速率的提高。DSC实验表明:10％叔丁醇／10％蔗糖／水三元溶液的临界复温速率为250℃／min左右。     

等组分(浓度)溶液晶体生长方法及其应用

等组分（浓度）溶液晶体生长方法是研究晶体生长动力学、生物体结晶和工业结晶的有效手段，它是七十年代末期发展起来的晶体生长新技术．其理论基础是电解质溶液的热力学平衡和动力学反应原理．其方法要点是：根据生长体系的内参量和外参量，建立溶液体系各类离子的反应方程；用德拜－许克尔理论计算各类离子的活度系数；根据质量和电荷平衡原理决定在某一过饱和浓度б条件下的生长驱动力；技术上保证结晶过程中驱动力不变，从而保持反应过程中组分和浓度的恒定．     

基于溶液温度差谱分析的ATR-FTIR原位测量方法

作为一种原位、快速、无损坏的中红外光谱分析技术,ATR-FTIR已在很多工程领域得到越来越多的应用,尤其是针对结晶过程溶液浓度的原位实时测量。水是一种常用的结晶溶剂,在中红外波段具有强吸收峰,并且在不同温度下具有光谱吸收差异性,因而不能忽略溶剂水和温度对溶液浓度的中红外光谱测量带来的影响。以朗伯-比尔定律为基础,提出采用溶液光谱减去相应温度下的溶剂光谱的方法,从而能准确地测量溶液浓度。以L-谷氨酸溶液结晶过程为例,对L-谷氨酸水溶液的原始光谱数据、溶液光谱扣除常温(25℃)溶剂水的光谱数据以及溶液光谱对应温度扣除溶剂水的光谱数据分别进行建模。结果表明,提出的对应温度差谱法能有效消除溶剂水峰对溶质光谱测量的干扰,明显地降低了溶液浓度光谱标定模型的预测误差。该方法对提高原位ATR-FTIR光谱检测精度的实际应用具有一定的参考价值。     

掺杂NaCl水溶液结晶形貌的分形研究

水溶液结晶是研究分形形貌的重要实验之一。本文通过改变溶液浓度,溶质组分和结晶温度等宏观实验参数,用分形维数的方法研究了这些参数对结晶形貌的影响。指出在低浓度下的非平衡态中溶液结晶形貌具有分形结构;不同晶体的生长作用力相互竞争,混乱度最大的情况下形成的分形结构最凸出,生长作用力是影响晶体形貌的主要因素;同时,分子热运动也是影响结晶形貌的因素之一。     

铜管表面水合物晶体生长特性研究

实验研究了浓度分别为5 wt%、15 wt%、20 wt%、30 wt%的四丁基溴化铵(TBAB)溶液在外径为21mm的铜管外表面的结晶特性.实验首先以15 wt%TBAB溶液为例,观察其降温结晶过程,得到了TBAB水合物晶体在不同阶段生长的特征.然后对不同浓度、不同过冷度条件下的TBAB溶液进行降温结晶实验,观察并测...     

HA纳米微粒对PEG-600低温保护剂反玻璃化结晶的影响

为了研究羟基磷灰石HA纳米微粒对低温保护剂反玻璃化结晶的影响,本文利用DSC和低温显微镜研究了含有不同粒径(20nm、40nm、60nm)和不同质量浓度(0.1%、0.2%、0.4%、0.8%)HA纳米微粒的PEG-600(50%,w/w)溶液反玻璃化过程中的结晶现象.试验结果表明:与未添加纳米微粒的PEG-600溶液相比,加入40nm、0.4%纳米微粒的HA-PEG600溶液的反玻璃化温度升高了7℃;加入20nm、0.4%和40nm、0.8%纳米微粒的HA-PEG600溶液的冰晶生长速率分别降低了35%和提高了50%;纳米低温保护剂溶液的冰晶形貌从大圆形变成了小圆形、枝晶或小圆形中夹带枝晶.     

新型硬盘基板微晶玻璃的晶核剂研究

采用差热分析(DTA)、X-射线衍射分析(XRD)和扫描电镜(SEM)等分析手段研究了P2O5、TiO2、ZnF2作为晶核剂对Li2O-Al2O3-SiO2(LAS)系统微晶玻璃形核和晶化的影响。结果表明:P2O5晶核剂能获得小尺寸的晶粒,晶型为球形或多面体形,析晶的可控制性良好;TiO2晶核剂析晶温度较高,析晶强烈,形成条状细晶;ZnF2晶核剂能获得小尺寸球状晶粒,析晶温度较低,但对温度过于敏感。P2O5作为晶核剂可以获得理想小晶粒的透明微晶玻璃,从而适合于用作新型硬盘基板。     

Ultrasound-assisted solution crystallization of fotagliptin benzoate: Process intensification and crystal product optimization

The ultrasound-assisted crystallization process has promising potentials for improving process efficiency and modifying crystalline product properties. In this work, the crystallization process of fotagliptin benzoate methanol solvate (FBMS) was investigated to improve powder properties and downstream desolvation/drying performance. The direct cooling/antisolvent crystallization process was conducted and then optimized with the assistance of ultrasonic irradiation and seeding strategy. Direct cooling/antisolvent crystallization and seeding crystallization processes resulted in needle-like crystals which are undesirable for downstream processing. In contrast, the ultrasound-assisted crystallization process produced rod-like crystals and reduced the crystal size to facilitate the desolvation of FBMS. The metastable zone width (MSZW), induction time, crystal size, morphology, and process yield were studied comprehensively. The results showed that both the seeding and ultrasound-assisted crystallization process (without seeds) can improve the process yield and the ultrasound could effectively reduce the crystal size, narrow the MSZW, and shorten the induction time. Through comparing the drying dynamics of the FBMS, the small rod-shaped crystals with a mean size of 9.6 μm produced by ultrasonic irradiation can be completely desolvated within 20 h, while the desolvation time of long needle crystals with an average size of about 157 μm obtained by direct cooling/antisolvent crystallization and seeding crystallization processes is more than 80 h. Thus the crystal size and morphology were found to be the key factors affecting the desolvation kinetics and the smaller size produced by using ultrasound can benefit the intensification of the drying process. Overall, the ultrasound-assisted crystallization showed a full improvement including crystal properties and process efficiency during the preparation of fotagliptin benzoate desolvated crystals.     

Ultrasound-assisted crystallization (sonocrystallization)

The positive influence of ultrasound (US) on crystallization processes is shown by the dramatic reduction of the induction period, supersaturation conditions and metastable zone width. Manipulation of this influence can be achieved by changing US-related variables such as frequency, intensity, power and even geometrical characteristics of the ultrasonic device (e.g. horn type size). The volume of the sonicated solution and irradiation time are also variables to be optimized in a case-by-case basis as the mechanisms of US action on crystallization remain to be established. Nevertheless, the results obtained so far make foreseeable that crystal size distribution, and even crystal shape, can be ‘tailored’ by appropriate selection of the sonication conditions.     

AlN晶体物理气相传输法生长坩埚的热场分析

采用物理气相传输法在钨制坩埚上制备AlN单晶.通过采用COMSOL软件中的固体传热和磁场模块,对AlN晶体生长的坩埚的热场进行仿真,同时针对不同的线圈直径以及不同的线圈位置对坩埚热场的影响进行模拟,提出了相应的处理方式.结果表明:当线圈直径增大,坩埚结晶区和升华区的温度在相同的加热时间下会增加,并且增加的温度存在峰值.当线圈的垂直位置发生变化的时候,结晶区和升华区的温度场也会发生变化,从上向下移动的过程中仍然存在温度的峰值,并且结晶区和升华区的温度关系会发生翻转,导致温度梯度阻碍晶体生长.在晶体生长过程中升华区和结晶区的温度关系依旧会发生翻转.但是通过线圈跟随籽晶表面生长层的变厚而同步移动,可以保持相对稳定的温度关系,维持晶体正常持续生长.     

体材料结晶能力的理论预测

引入评价晶体材料缺陷的残缺度及描述晶面表面势场的结晶势两个概念,针对Ni,Cu,Al,Ar单质在不同温度条件下的再结晶过程进行了大量的分子动力学模拟,发现残缺度随结晶势的增大而单调地减小,即结晶势越大则形成单晶体能力越强.由于结晶势能够唯一地确定结晶能力并且其计算简单,因此可从理论上快速方便地预测材料形成单晶体的能力. 关键词： 单晶 结晶 分子动力学 材料设计     

冷却速率对温敏聚N-异丙基丙烯酰胺胶体结晶过程的影响

冷却速率对结晶过程具有重要的影响. 本文采用温敏poly-N-isopropylacrylamide (PNIPAM) 胶体晶体体系实时观察了冷却速率对结晶晶粒尺寸的影响. 通过高倍透射明场观察和Bragg衍射观察研究连续冷却下的晶粒形核和生长实时演化过程, 发现随着冷却速率的增加, PNIPAM胶体晶体晶粒尺寸不断减少. 晶粒尺寸与冷却速率符合幂指数关系, 与金属体系具有相似的演化规律.     

Colloids as model systems for metals and alloys: a case study of crystallization

Metallic systems are widely used as materials in daily human life. Their properties depend very much on the production route. In order to improve the production process and even develop novel materials a detailed knowledge of all physical processes involved in crystallization is mandatory. Atomic systems like metals are characterized by very high relaxation rates, which make direct investigations of crystallization very difficult and in some cases impossible. In contrast, phase transitions in colloidal systems are very sluggish and colloidal suspensions are optically transparent. Therefore, colloidal systems are often discussed as model systems for metals. In the present work, we study the crystallization process of charged colloidal systems from the very beginning. Charged colloids offer the advantage that the interaction potential can be systematically tuned by a variation of the particle number density and the salt concentration. We apply light scattering and ultra-small angle x-ray scattering to investigate the formation of short-range order in the liquid state even far from equilibrium, crystal nucleation and crystal growth. The results are compared with equivalent studies on metallic systems.     

功率超声在结晶过程中应用的进展

功率超声在结晶过程中的应用研究促进了结晶技术的发展,丰富了功率超声学和相关学科相互交叉的学术内容。以实例陈述了超声强化溶液结晶过程在化工、食品和制药行业中的应用,从熔融结晶和电结晶两方面阐述了超声改善金属结晶,综述了高分子材料和生物大分子等聚合物结晶过程中超声波的应用,总结了超声波对纳米晶型材料制备和性能的影响,着重说明了功率超声在食品冷冻中冰结晶过程的研究现状和发展方向。最后,总结了超声对结晶的强化机理。     

The application of power ultrasound to reaction crystallization

The action of power ultrasound in controlling the supersaturation, nucleation and crystal growth during the acid-base reaction crystallization of 7-amino-3-desacetoxy cephalosporanic acid (7-ACDA) has been investigated. The experimental results show that ultrasound can mix the reaction more efficiently and uniformly than conventional agitation methods. Insonation leads to the reduction of both the induction period and metastable zone width of the crystallization, so that the process of crystallization can be more efficiently controlled than without insonation. Agglomeration is also greatly reduced. Adjusting the ultrasonic parameters can modulate the crystal size and size distribution. The mechanism of the sonoprocess has been analyzed and comments are made on the potential applicability of sonication in large-scale crystallization practice.     

20GeS2·80Sb2S3硫系玻璃的析晶行为及动力学机理研究

实现玻璃微晶化过程控制的基础是要充分认识其析晶行为及动力学机理. 利用示差扫描量热法和析晶热处理等手段, 研究发现 20GeS₂·80Sb₂S₃硫系玻璃属于表面析晶, 在268℃(T_g+30℃)下热处理60 h, 可以获得表面约40 μm的Sb₂S₃晶层复合玻璃陶瓷样品. 在此基础上, 利用非等温法从理论上分析该玻璃的析晶动力学机理. 计算得到其析晶活化能E_c为(223.6±24.1)kJ·mol^-1, 在热处理温度(268℃)下的析晶速率常数K为1.23×10^-4 s^-1, 属于较难析晶的玻璃组成; 玻璃的晶体生长指数m和晶体生长维数n均为2, 表明其Sb₂S₃相的析晶行为是二维生长过程, 与析晶实验结果完全相符. 由此可知, 对于Sb₂S₃晶体复合的硫系玻璃陶瓷样品可通过玻璃粉末压片烧结、带铸法或丝网印刷法制备获得, 为今后功能硫系玻璃的开发提供实验依据和理论指导. 关键词： 硫系玻璃 微晶化 析晶动力学 析晶行为