On the Accuracy of Measuring Small Contact Angles by the Sessile Drop Method

The errors arising in measuring the contact angles of a sessile drop by the mirror method are analyzed. The formulas are derived enabling one to take into account the distortions of a visible image and enhance the accuracy of measuring contact angles. The derived formulas are experimentally verified.     

Gas Holdups of Small and Large Bubbles in a Large-scale Bubble Column with Elevated Pressure

Gas holdups of large bubbles and small bubbles were measured by means of dynamic gas disengagement approach in the pressured bubble column with a diameter of 0. 3 m and a height of 6.6 m. The effects of su-perficial gas velocity, liquid surface tension, liquid viscosity and system pressure on gas holdups of small bub-bles and large bubbles were investigated. The holdup of large bubbles increases and the holdup of small bub-bles decreases with an increase of liquid viscosity. Meanwhile, the holdup of large bubbles decreases with in-creasing the system pressure. A correlation for the holdup of small bubbles was obtained from the experimen-tal data.     

金属的冶炼中值得注意的几个问题

从自由能变的角度,分析金属冶炼的一般原理,重点讨论了反应的条件和常用还原剂的选择。讨论了钾、镁、钛等金属的冶炼方法。     

Work of Adhesion of a Sessile Drop to a Clean Surface

According to the Young-Dupré equation, as interpreted by Bangham and Razouk, the work of adhesion of a sessile drop to a smooth solid surface is given by WS(V)L = gammaL (1 + cos θ), where θ is the equilibrium contact angle measured at equilibrium of the system with the saturated vapor of the liquid, and WS(V)L is the work of adhesion of that drop to the solid surface which is in equilibrium with that vapor and may contain an adlayer of the vapor. For calculation of WSL, the work of adhesion of a sessile drop to a clean solid surface, the equation WSL = gammaL (1 + cos θ) + Pie is generally used (although Bangham and Razouk never proposed it). Pie is the negative of the free energy of formation of the adlayer, sometimes called the spreading pressure. In the present work it is shown that the latter equation cannot be accurate. Copyright 1999 Academic Press.     

当前化学教学改革若干问题的意见

理科化学学科教学指导委员会会议 1 999年 1 2月中旬在合肥中国科技大学召开 ,会议就当前化学教学改革的若干问题进行了认真的讨论。现总结如下 ,供各校参考。1　关于教学改革立项　　教学指导委员会会议分析了当前教学改革的形势和存在的主要问题 ,认为原来化学专业、应化专业及非化学类专业化学教学的“面向 2 1世纪课程体系及教学内容改革”已取得了一定成果 ,处于结题验收阶段 ,但教学改革是一项长期任务 ,任重而道远 ,而实验教学改革、化学信息学课程建设及教学方式现代化等方面更是当前迫切需要解决的问题。　　 ( 1 )纵观当前化学实…     

化学课堂设问的几个误区

课堂教学设问已成为化学教师组织教学活动的自觉行为,然而有些老师在设计问题时常常会偏离学生的认知水平,导致学生在课堂上的认知过程受阻,这类设问并不利于学生掌握基础知识和发展能力.笔者认为有几个误区值得我们注意纠正.     

有机化合物命名的若干问题讨论

现行教材对于有些有机化合物的命名论述过于简单,有的甚至与中国化学会命名原则矛盾。这样的问题也时常出现在历年的有机化学考研试卷中。本文讨论了比较典型的几个命名问题。这些问题的存在会影响到学生的学习和考试结果,因此,在教学尤其是考研试卷中要避免类似问题的出现。     

Some Observations Concerning the Quality of Murexide End Points

Abstract

Observations are made on the end point of the photometric EDTA titration of nickel in the presence of large amounts of cobalt using murexide as indicator. Difficulties with the end point are believed due to an ionic strength effect and may be remedied by dilution of the sample to be titrated.     

Some New Data Concerning The Chromatographic Purity Test for Nifedipine

Abstract

The analysis of different Nifedipine commercial samples indicated the presence of impurities other than the nitroso- and nitrophenylpyridine analogues of Nifedipine generally are included in the pharmacopoeia-monographs. Besides the two latter photodegradation products isonifedipine and a tetrahydropyrimidine derivative as by products of nifedipine-synthesis were identified. HPLC procedure is suitable for the separation Nifedipine and all of the four contaminants is published.     

The Life of a Surface Bubble

Surface bubbles are present in many industrial processes and in nature, as well as in carbonated beverages. They have motivated many theoretical, numerical and experimental works. This paper presents the current knowledge on the physics of surface bubbles lifetime and shows the diversity of mechanisms at play that depend on the properties of the bath, the interfaces and the ambient air. In particular, we explore the role of drainage and evaporation on film thinning. We highlight the existence of two different scenarios depending on whether the cap film ruptures at large or small thickness compared to the thickness at which van der Waals interaction come in to play.     

Some Observations Concerning the Thermally Induced Oxy‐Ene Reaction

Several examples of thermally induced intramolecular oxy‐ene reactions leading to six‐ or five‐membered rings are reported. The yields vary from poor to good, depending on the thermal lability of the substrate. Considering the high temperatures required to effect these transformations (several hours at ca. 250°), the observed diastereoselectivities favoring the trans‐1,2‐substituted cycloalkane derivatives are excellent. In the case of product 26 , these substituents were shown to prefer a trans‐diaxial orientation both in the solid state (X‐ray evidence) and in solution, presumably to avoid the allylic strain prevailing in the diequatorial conformer.     

Sessile droplet spread into porous substrates--determination of capillary pressure using a continuum approach

The problem of primary and secondary spread of sessile droplets into a porous substrate was formulated and solved numerically. A continuum approach for liquid- and gas-phases was utilized. The governing equations were discretized by finite difference method and solutions for both phases are obtained by marching in time using the fourth-order Runge-Kutta integration algorithm. This type of spread is a purely momentum-driven process that is caused by gradients both in capillary pressure and in saturation. A methodology was developed for finding the capillary pressure function for sessile droplets, which has not been described before. This approach was based on experimental data for a liquid/porous medium pair, and using universal, non-dimensional curves. Similar solutions were generated by the continuum approach and validated using experimental results. The model shows qualitative and quantitative agreement with experimental data. Although the focus of this work was to understand the interaction of chemical warfare agents with porous media, the approaches are universal and can be applied to determining the spread of any liquid into a porous material.     

美国中学科学教育改革的一些情况和问题

1990年6月,美国《化学和工程》新闻中发表了一篇正题为“革命之风席卷科学教育”,副题为“作为造成人才渠道上的危机和大众素养问题的回答,包括化学在内的科学教育在作较大的调整”一文。这篇文章介绍了美国培养科学人才上的危机,科学教育,特别是化学教育上存在的问题发生这些问题的原因,解决这些问题的办法和建议以及政府、国家科学基金会、各个学会(特别是美国化学会)以及商业界在解决这些问题上应起的作用,等等。本编译稿是根据这篇文章的内容整理而成的,着重介绍有关中学科学教育、包括中学化学教育的一些情况和问题。     

课堂教学中运用PPT课件应注意的几个问题

多媒体技术具有多种优势,如何从学生的视角来运用多媒体技术,既减轻教学负担又能促进学生学习,达到促进学生有效、高效学习的效果,是应予关注的一个重要问题。     

我国化学教学论课程革新的几个问题

紧密结合当前基础教育课程改革的实际,对化学教学论从课程内容、编制理念、教学方式、学习方式和评价体系等层面进行深入改革是我国高等师范院校的一项迫切任务.     

Hydrodynamic Behavior in a Tapered Bubble Column

IntroductionBubble column( BC) and slurry bubble column( SBC) reactors have emerged as one of the mostpromising devices in chemical,biochemical and en-vironmental engineering operations because of theirsimple construction,isothermal conditions,highheat and mass transfer rates,and on- line catalystaddition and withdrawal[1_ 4] .The utilization of ta-pered slurry bubble column( TSBC) reactorshas re-cently received much attention ofsome scholars andscientists who are engaged in biochemical rea…     

A Mesoscopic Self-assembled Ring of a Femtomole Fluorescein Sessile Droplet on Glass Slide Support

Since the solvent evaporation of a droplet on a hydrophobically pretreated glass slide, femtomole amount of fluorescent materials is carried by the evaporation and results in outward capillary flow to the perimeter of the droplet spot where the solute deposits, and forms afluorescent ring like deposit (RLD) with submicrometer-scale structures.