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铁在自然界中含量丰富,化学性质活泼,能够形成多种应用广泛的物质及材料,富有发展潜力。简述了铁元素的发现与性质,并重点介绍了铁的功能与应用。其中铁的应用主要围绕铁及其化合物在医学治疗、能源材料和环境保护领域所发挥的重要作用进行了阐述。 相似文献
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钒是地壳中含量第21丰富元素,是人体必需的微量元素。介绍钒元素的发现、自然分布以及在人体内的循环。重点从化学结构分析钒酸盐磷酸盐的拮抗作用机制,从生化机理阐述钒化合物对激酶与磷酸酶的调节、对RNA和DNA功能的影响、对活性氧作用的影响,从人体健康视角探讨钒对治疗糖尿病和癌症及保护心血管等的潜在药理学作用。 相似文献
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目前国内化学基础课教材关于碰撞理论中活化能的定义存在严重分歧,简单总结了目前中文教材中的3种定义。通过对碰撞理论形成过程中部分历史背景的梳理,总结出碰撞理论所具备的2个基本要素即气体分子运动论的应用以及碰撞活化假设,然后溯源3种不同定义来源的历史文献,从2个基本要素的角度分析3种定义。研究发现中文教材广泛采用的Lewis活化能解说不承认碰撞活化假设,采用了辐射活化假说,同时表述笼统不严谨,Tolman活化能解说是单纯的统计力学处理,没有应用气体分子运动论,不属于碰撞理论范畴。而简单碰撞理论提出的有效碰撞的最低能量作为活化能的定义更能承载碰撞理论的基本要素。 相似文献
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运用内容分析法对我国改革开放以来40年人民教育出版社出版的6套高中化学教科书中的化学史内容进行分析,研究化学史的总体数量、图像、呈现位置、呈现形式、篇幅、涉及的区域及年代等方面的变化,获得我国高中化学教科书中的化学史在各方面的变化趋势,为教科书中化学史的编写及教学提供参考。 相似文献
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近年来,作为第三代有机发光二极管(organic light-emitting diodes, OLED)发光材料的热活化延迟荧光(thermally activated delayed fluorescence, TADF)材料受到了学术界和产业界的广泛关注. TADF分子由于其单线态与三线态之间的能级差较小,三线态激子可以被环境热活化而通过反系间窜越上转换至单线态,理论上可实现100%的激子利用率,从而使得OLED器件外量子效率显著提高.TADF材料被认为是突破高效稳定有机电致蓝光发射瓶颈的潜在解决方案.一般, TADF分子为含有电子给体(donor, D)和电子受体(acceptor, A)的纯有机推拉电子体系.通过改变给体单元和受体单元的结构、数量和取代基及其位置可以有效调节TADF分子的单线态-三线态能级差、前线轨道分布、聚集态结构、电致发光颜色及其性能.同时取代基在调控给、受体单元的推拉电子能力及TADF材料的分子构型、聚集态结构和稳定性等物化特性方面扮演着非常重要的角色.本综述分别对D-A型和多重共振型TADF蓝光分子的取代基效应进行了综述,以期为高效稳定的蓝光TADF分... 相似文献
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An incremental isoconversional method for kinetic analysis based on the orthogonal distance regression 下载免费PDF全文
The parameters obtained from a kinetic analysis of thermoanalytical data often exhibit a conversion‐dependent behavior. A novel incremental isoconversional method able to deal with this phenomenon is proposed. The kinetic model is directly fitted to the experimental data using nonlinear orthogonal least squares procedure. The data are processed without transformations, so their error distribution is preserved. As the objective function is based on a maximum likelihood approach, reliable uncertainties of the parameters can be estimated. In contrast to other methods, the activation energy and the pre‐exponential factor are treated as equally important kinetic parameters and are estimated simultaneously. Validity of the method is verified on simulated data, including a dataset with local nonlinearity in the temperature variation. A practical application on the nonisothermal cold crystallization of polyethylene terephthalate is presented. © 2014 Wiley Periodicals, Inc. 相似文献
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K. Nahdi P. Llewellyn F. Rouqurol J. Rouqurol N. K. Ariguib M. T. Ayedi 《Thermochimica Acta》2002,390(1-2):123-132
The present kinetic study is focused on one aspect of kaolinite dehydroxylation, namely the influence of water vapour pressure in the 10−3 to 5 hPa range and in the presence of crystalline defects. The experimental problem of keeping, throughout the dehydroxylation, the pressure gradients negligible around and within the sample is solved by means of Controlled Rate Evolved Gas Detection (CR-EGD). The dehydroxylation rate selected is as low as 0.014 h−1 (which corresponds to a duration of 70 h for the whole experiment). Moreover, more than 20 independent measurements of the apparent Arrhenius energy of activation are carried out all along the dehydroxylation, with help of the rate–jump method, and therefore, without any assumption about the rate law of the determining step. In these conditions, the apparent Arrhenius energy of activation measured during the dehydroxylation of a poorly crystallised kaolinite is shown to be constant in the range 0.02<<0.84 (under 10−3 hPa) and in the range 0.18<<0.80 (under 5 hPa), indicating that the rate law obeys the Arrhenius law in this range of extent of reaction. The corresponding activation energies obtained are (233±15) kJ/mol under 10−3 hPa and only (188±10) kJ/mol under 5 hPa. Although this decrease is in contradiction with previously published results, it can be interpreted by considering that, under 10−3 hPa, diffusion is the limiting step whereas, under 5 hPa, the part of water desorption probably becomes predominant. 相似文献
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在介绍阿仑尼乌斯速率方程基础上,从碰撞理论、过渡态理论和托尔曼统计等视角诠释活化能概念,认为仅以活化能大小作依据判断反应速率大小不严密,并从教学层面和试题角度进行了反思。 相似文献
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In this paper we study a method for the determination of the micropore volume distribution function of activated carbons. This method is based on the Integral Adsorption Equation concept (IAE). The micropore volume distribution function is assumed to be a Gaussian of which the parameters are unknown. These parameters are determined using adsorption isotherms of carbon dioxide on a given activated carbon (F30/470 CHEMVIRON CARBON) at 278, 288, 298, 303, 308, 318 and 328 K and for pressures up to 100 kPa. Several local adsorption models are used (Langmuir, Volmer, Fowler-Guggenheim, Hill-de Boer). The influence of the choice of the local model on the pore volume distribution function is discussed. The physical validity of this function and the performances of the different models are presented. It appears that the effect of the temperature on the adsorption isotherms is difficult to model over a wide range of relative pressure. The Hill-de Boer and the Langmuir local models are the most efficient (average errors respectively equal to 3.53% and 2.80% in the studied range of temperature and pressure). They provide the most meaningful parameters for the pore volume distribution function. 相似文献
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通过对4个版本九年级化学教材中化学史内容选取与编排情况的统计和分析,发现随着新课程改革的不断深入,教材中化学史案例数量明显增多,其教育价值已经被广泛认可。虽然教材中关于化学史的内容编排图文并茂,但改进空间依然存在,例如化学家介绍过于简略,介绍角度不够全面;化学发展的描述局限于个别科学家的贡献和孤立的科学事件;化学史学习形式单一、地位不高。为更好地发挥化学史蕴含的教育功能,建议教材中化学家的形象更加丰满,化学研究过程更加完整真实,设计丰富的化学史学习活动,以使学生更加重视化学史的学习,从中受益。 相似文献
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Dr. Justus Masa Dr. Stefan Barwe Dr. Corina Andronescu Prof. Dr. Wolfgang Schuhmann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(1):158-166
Svante Augustus Arrhenius (1859, Vik - 1927, Stockholm) received the Nobel Prize for Chemistry in 1903 “in recognition of the extraordinary services he rendered to the advancement of chemistry by his electrolytic theory of dissociation”. Arrhenius was a physicist, and he received his PhD from the University of Uppsala, where he later became a professor for phyiscal chemistry, the first in the country for this subject. He was offered several positions as professor abroad, but decided to remain in Sweden and to build a Nobel Institute for physical chemistry using the Nobel funds. He remained director of the Institute until his death. There are powerful lessons to take from Svante August Arrhenius’ journey leading to a Nobel laureate as there are from his tremendous contributions to chemistry and science in general, including climate science, immunochemistry and cosmology. The theory of electrolytic dissociation for which Arrhenius received the 1903 Nobel Prize in Chemistry has had a profound impact on our understanding of the chemistry of solutions, chemical reactivity, mechanisms underlying chemical transformations as well as physiological processes. As a tribute to Arrhenius, we present a brief historical perspective and present status of the theory of electrolytic dissociation, its relevance and role to the development of electrochemistry, as well as some perspectives on the possible role of the theory to future advancements in electroanalysis, electrocatalysis and electrochemical energy storage. The review briefly highlights Arrhenius’ contribution to climate science owing to his studies on the potential effects of increased anthropogenic CO2 emissions on the global climate. These studies were far ahead of their time and revealed a daunting global dilemma, global warming, that we are faced with today. Efforts to abate or reverse CO2 accumulation constitute one of the most pressing scientific problems of our time, “man's urgent strive to save self from the adverse effects of his self-orchestrated change on the climate”. Finally, we review the application of the Arrhenius equation that correlates reaction rate constants (k) and temperature (T); , in determining reaction barriers in catalysis with a particular focus on recent modifications of the equation to account for reactions exhibiting non-linear Arrhenius behavior with concave curvature due to prevalence of quantum mechanical tunneling, as well as infrequent convexity of Arrhenius plots due to decrease of the microcanonical rate coefficient with energy as observed for some enzyme catalyzed reactions. 相似文献