共查询到16条相似文献,搜索用时 46 毫秒
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几年前,声化学(Sonochemistry)这一术语很多人还是陌生的。由于超声在化学合成,金属有机化学,化学结构的解释,聚合物科学等领域中有了大量成果,引起了人们对声化学这门新学科的重视。 事实上,声化学已有相当长的历史,50年代就有研究论文发表。那时大多是研究声波对水的分解作用。在沉寂了20年之后,声化学复兴了,出于探索新技术与新材料的动机,得到了更加广泛深入的研究。 从根本上讲,化学乃是能量与物质的一种互作用。传统的能量形式是热学的、光学的或是离子辐射的。声能则是另一种独特的形式。声波与化学分子并不直接发生互作用。超声在… 相似文献
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工业规模液体内的声处理应用越来越多地得到国内外声学工作者的关注。一般认为,液体内声处理的机理是声空化,因此要扩大声处理的规模,应把研究的重点放在声空化的优化,而不是一味提高声能输入。而对声空化优化的前提则需要找到简单易行、生产上可用的空化测量方法。回顾了声空化检测、测量方法,分析比较后认为:实时谱分析方法更适用于大规模液体声处理的空化测量,需加大力度深入研究。 相似文献
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In terms of the mixture theory and phase field theory, a phase field model is developed for the saturated porous medium undergoing phase transition. In the proposed model, it is postulated that during the phase transition of the porous medium, both the solid skeleton and pore fluid will undergo phase transition. The phase states of the solid skeleton and pore fluid are characterized by respective order parameters. To simplify the proposed phase field model, the temperatures and order parameters of the solid skeleton and pore fluid are assumed to be equal. The balance laws of the porous medium are given by the conventional mixture theory. The order parameter and the porosity of the porous medium are considered as internal variables and their evolution equations are determined by the entropy inequality of the porous medium. The constitutive representations for the stresses, entropies, heat fluxes, drag force and the evolution equations for the order parameter and porosity are derived by exploitation of the entropy inequality. To illustrate the proposed model, a concrete phase field model for the freezing porous medium is established in the paper. In the model, the memory effect associated with phase transition of the porous medium is taken into account by assuming Stieltjes integral for the strain energy of the porous medium. The constitutive representations for the above variables are then derived according to the proposed free energy expression for the porous medium. Finally, the boundary condition associated with the proposed model and the determination of some parameters involved in our model are discussed in the paper briefly. 相似文献
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《Drug development and industrial pharmacy》2013,39(5):570-580
Background: It was of interest to investigate the factors affecting kinetics of transformation of fluconazole polymorph II (the metastable form) to fluconazole polymorph I (the stable form) using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Method: Fluconazole polymorphs I and II both were prepared by crystallization in dichloromethane. The two forms were characterized using differential scanning calorimetry, thermogravimetric analysis, powder X-ray diffraction, solubility, and DRIFTS. Transformation of polymorph II to polymorph I was also studied under different isothermal temperatures using DRIFTS. Kinetic analyses of the data were done using model-dependent and model-independent methods. Eighteen solid-state reaction models were used to interpret the experimental results. Results: Based on statistics, the Prout–Tompkins model provided the best fit for the transformation. The activation energy (Ea) value derived from the rate constants of the Prout–Tompkins model was 329 kJ/mol. Model-independent analysis was also applied to the experimental results. The average values calculated using both methods were not significantly different. Factors affecting kinetics of transformation such as mechanical factors, relative humidity, and the effect of seeding were also studied. Mechanical factors, which included trituration and compression, proved to enhance transformation rate significantly. Relative humidity proved to transform both polymorphs to monohydrate form. The presence of seed crystals of polymorph I was proved not to affect the transformation process of polymorph II to polymorph I. Effect of solvent of crystallization (dichloromethane) was studied. A significant change of the rate of transformation was proved in the presence of solvent vapors, and a change on the mechanism was proposed. 相似文献