共查询到19条相似文献,搜索用时 140 毫秒
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成核剂在聚丙烯的结晶过程中作为晶核,参与调节晶体的晶型、大小及其分布,促使形成不同性能的聚丙烯材料.成核剂促进聚合物结晶的机制是聚合物结晶领域的研究热点,但其结构对聚合物结晶的影响尚不清晰;而成核剂通常具有同分异构体,使其结构解析更加困难,但成核剂的结构解析是进一步研究其成核机理的基础.本文综合运用核磁共振(NMR)波谱、傅里叶变换-红外(FT-IR)光谱和扫描电镜能谱分析(SEM-EDS)表征了一种二元羧酸复合物类β晶型聚丙烯成核剂的结构和构型,结果表明该成核剂cis-△4-四氢邻苯二甲酸钙为消旋体,羧酸与钙以桥式螯合方式形成有机羧酸金属盐. 相似文献
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采用高压技术实现了500 MPa下聚左旋乳酸(PLLA)在稀薄二甲苯溶液中的单晶生长,采用透射电子显微镜、拉曼光谱和红外光谱对样品的结晶形态和结构进行了表征,考察了高压对聚左旋乳酸单晶生长行为的影响。结果表明,在相同的结晶温度和时间下,高压结晶PLLA的单晶仍为α-型晶体,但单晶尺寸明显大于常压样品;高压环境下PLLA分子链在晶核两端的生长扩散速率不同,容易形成非对称的菱晶形态;高压影响PLLA晶体中分子链的构象分布;在单晶生长期,高压诱导有利于PLLA晶体成核,但不利于单晶生长。 相似文献
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低温生物医学与热物理 总被引:8,自引:0,他引:8
本文阐述了低温生物学、低温医学与热物理的关系;着重讨论生物体低温保存的问题,细胞和组织的低温损伤是溶液冻结相变过程所引起的冰晶损伤和高浓度溶液的损伤;这个过程和传热传质密切相关;而低温保存的机理则是溶液的非晶态化(玻璃化)。本文还讨论了低温生物医学当前的研究热点,以及其中的热物理问题。 相似文献
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Guisheng Zeng Xianyong Wang Shenglian Luo Hui Li Xinman Tu Xubiao Luo Jianping Zou 《Acoustical Physics》2014,60(3):356-360
The effect of ultrasound vibrations on the cooling crystallization of sodium arsenate in supersaturated solutions was investigated. In particular, the effects of ultrasound vibrations on induction time and crystal size distribution were studied using a laser-based apparatus with relative supersaturation ranging from 1.3 to 1.8. The results show that ultrasound vibrations have a significant effect on reducing induction time and crystal size distribution. The application of ultrasound vibrations to the system resulted in a small change in surface tension; however, the induction time and crystal size significantly decreased. The mean size of sodium arsenate crystals decreased from 398.87 ± 3.27 to 168.68 ± 2.07 μm, as the ultrasound power increases from 26 to 130 W. Ultrasound vibrations significantly reduced the induction time in a highly supersaturated solution compared to that in a low supersaturated solution. 相似文献
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Colemanite is one of the most important boron minerals used for production of boric acid. Boric acid (H(3)BO(3)) is produced by the reaction of colemanite (2CaO.3B(2)O(3).5H(2)O) with sulfuric acid in a heterogeneous solid-liquid reaction leading to crystallization of gypsum as a byproduct.The influence of ultrasound on the dissolution of colemanite in H(2)SO(4) solution and on the precipitation of the gypsum during the reaction was investigated. Experiments have been carried out in a batch stirred vessel at 85 degrees C in the absence and presence of ultrasound. The stirring rates were chosen as 600 rpm (for 500-600 microm) and 800 rpm (for 1000-1180 microm) to provide a homogeneous suspension during the reaction. The boric acid and calcium ion concentrations in the solution were determined as a function of time. The results showed that ultrasound enhances the dissolution of colemanite and precipitation rate of the gypsum in the solution after 1h. It has been shown that the use of ultrasound decreases the size of gypsum crystals. 相似文献
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Sonocrystallization is the use of power ultrasound to control the crystallization process, commonly used during the nucleation phase of crystallization. However, in the present study a different approach has been tried, in which the whole process of lactose crystallization from model reconstituted lactose solutions was completed rapidly with the aid of ultrasound, in the presence of 'ethanol' as an anti-solvent, at temperature of 30+/-2 degrees C (ambient temperature). The lactose recovery and crystal properties from sonicated samples were compared with non-sonicated samples. For optimization of sonocrystallization process for rapid lactose recovery, variations in the time of sonication, lactose concentration, protein concentration and pH were tried. A lactose recovery of 91.48% was obtained in 5 min of sonication time, from a reconstituted lactose solution (17.5% w/v, pH 4.2) as against 14.63% under only stirring. Lactose recovery decreased with lowering of pH from 4.2 to 2.8. The protein showed maximum influence on lactose recovery even at concentration of 0.2% w/v. A rapid process of crystallization gave a better uniformity in crystal size distribution of lactose samples. 相似文献
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Ultrasound-assisted crystallization (sonocrystallization) 总被引:1,自引:0,他引:1
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. 相似文献
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Crystallization of potash alum: effect of power ultrasound. 总被引:6,自引:0,他引:6
The influence of power ultrasound on the crystallization of potash alum was investigated. Experiments have been carried out in a batch stirred vessel. It was found that ultrasonic waves decrease the supersaturation limits and modify the morphology of the crystals produced. The average crystal size decreases with an increase of ultrasonic power. To investigate also the action of ultrasound on already existing crystals, crystals produced in silent conditions were suspended in saturated potash alum solution at various ultrasonic powers. The results show that ultrasound has also an abrasive effect on potash alum crystals for high power inputs. 相似文献
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In this paper, the crystallization of L-glutamic acid with application of ultrasound was explored in detail, including the process of nucleation, polymorphic control and polymorphic transformation. The induction time and metastable zone widths (MSZWs) were measured with and without ultrasound during the nucleation process. The induction time and MSZWs were decreased by ultrasound and the induction time was further decreased by higher ultrasonic power. The calculated nucleation parameters (such as interfacial energy, critical nucleus size and critical Gibbs energy) showed an obvious decrease in the presence of ultrasound, indicating that the nucleation was enhanced with application of ultrasound. By adjusting the ultrasonic power in the quench cooling process, the difference in nucleation temperatures would determine the distribution of polymorphs. In further, the polymorphic transformation was investigated quantitatively, and to the best of our knowledge, it was the first time to study the transformation kinetics with ultrasound using Avrami-Erofeev model. In the transformation process, the crystallization mechanism of the stable form was modified by ultrasound. The ultrasound eliminated the nucleation element in the rate-limiting step and facilitated the crystal growth of stable form. Thus, the ultrasound has a profound influence on L-glutamic acid crystallization. 相似文献
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Sonocrystallization implies the application of ultrasound radiation to control the nucleation and crystal growth depending on the actuation time and intensity. Its application allows to induce nucleation at lower supersaturations than required under standard conditions. Although extended in inorganic and organic crystallization, it has been scarcely explored in protein crystallization. Now, that industrial protein crystallization is gaining momentum, the interest on new ways to control protein nucleation and crystal growth is advancing. In this work we present the development of a novel ultrasound bioreactor to study its influence on protein crystallization in agarose gel. Gel media minimize convention currents and sedimentation, favoring a more homogeneous and stable conditions to study the effect of an externally generated low energy ultrasonic irradiation on protein crystallization avoiding other undesired effects such as temperature increase, introduction of surfaces which induce nucleation, destructive cavitation phenomena, etc. In-depth statistical analysis of the results has shown that the impact of ultrasound in gel media on crystal size populations are statistically significant and reproducible. 相似文献
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In this work, NaX zeolite was synthesized and the effect of ultrasound irradiation on reaction kinetics, morphological and structural properties was investigated. Ultrasound was applied, by using a plate transducer (91.8 kHz), for the first time during the crystallization of zeolite NaX, at high temperature, varying the irradiation moment and its duration. Furthermore, ultrasound was applied after the crystallization by a horn-type transducer (20–24 kHz) at low temperature. The effects of irradiated volume (100–300 mL), sonication time (2–10 min) and ultrasound power (10–200 W) were studied with a power intensity up to 100 W/cm2. It was found that the application of ultrasound during the first hour of crystallization resulted in 20% reduction of reaction time compared to a standard crystallization. Ultrasound can also reduce the agglomeration degree of the final powder by combining high power and long sonication time. After 5 min sonication time at 0.3 W/mL, the tapped density of the powder was increased by 10%, from 0.37 to 0.41 g/mL. Finally, by scanning electron microscopy (SEM) it was demonstrated that ultrasound can disrupt the agglomerates without affecting the morphology of individual crystals. 相似文献
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The application of power ultrasound to reaction crystallization 总被引:5,自引:0,他引:5
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. 相似文献