可加工微晶玻璃的微结构及其强韧化机理研究进展

对国内外可切削微晶玻璃的微观结构、可切削机理及强韧化机理的研究现状进行了综述。介绍了相互交联的卡片状和“卷心菜”状微观结构特征 ,讨论了其各自的优点及局限性。并就该新材料今后的发展趋势提出了作者的观点。     

工程塑料难以切削加工对策的研究

阐述了对工程塑料进行切削加工的必要性，对高聚物的结构及与切削有关的性能进行了评述，研究了工程塑料切削加工的特点，并针对影响工程塑料切削加工质量的因素提出了具体的对策，以及经实践验证可改善和提高工程塑料切削加工质量的方法。     

可切削微晶玻璃的研究现状及进展

可切削生物活性微晶玻璃是近年来新兴的一种生物材料，本文综述了可切削微晶玻璃的组成、结构、制备工艺、组成特性、生物活性评价及研究状况，并对可切削生物微晶玻璃的应用前景进行分析展望。     

工程陶瓷切削加工技术研究

工程陶瓷因其具有的优良特性广泛应用于诸多行业中。本文概述了工程陶瓷切削机理,分析了几何形状、刀具前角、切削刃钝圆半径等刀具参数和切削速度、进给量、切削深度、冷却润滑等加工工艺对切削过程的影响,指出高效加工是工程陶瓷切削加工技术的发展方向。     

牙科可切削陶瓷材料国内临床应用及研究进展

伴随着CAD/CAM技术引入到口腔医学领域中来,打破了人们传统手工制作义齿的方式,同时也给材料学领域带来了新的生机,对以往所用材料也带来了新的挑战.用于口腔中的可切削材料不仅要求其要有良好的生物相容性,而且还要求具有良好的机械加工性能,其中陶瓷以其生物相容性好、材料性能接近牙齿、美学效果好等优点最为突出.而现应用于临床中的可切削陶瓷材料,从抗弯强度低的长石类可切削材料发展到抗弯强度高的氧化锆类可切削材料,逐步实现了从嵌体、前牙单冠到后牙固定桥修复体的制作.本文综述了近年来国内学者对这些材料的应用和研究现状及各自特点.     

特殊分相结构对生物微晶玻璃微结构和性能的影响

以K2O-MgO-Al2O3-B2O3-SiO2-F为基础玻璃体系,按氟磷灰石元素组成向其中添加不同含量的Ca、P和F,配合料经过1500℃高温熔化后在580℃退火处理1.5h,具有特殊分相结构的前躯体玻璃经过两步晶化后得到了不同微观结构与性能的微晶玻璃。X射线衍射和扫描电镜测试结果表明:微晶玻璃的主晶相为片状氟金云母和针状氟磷灰石;随着分相结果的不同,针状磷灰石表现出随机分布和取向聚集分布两种分布形式;在具有磷灰石取向性的样品中,平行于磷灰石c轴方向的可切削性明显低于垂直方向的,而在磷灰石随机分布的微晶玻璃中,可切削性则介于两者之间。     

医用可切削微晶玻璃的研究进展

主要阐述了医用可切削微晶玻离的形成、结构和性能及其在修复学领域的应用.     

可切削生物活性微晶玻璃

本文综述了几类具有生物活性的可切削微晶玻璃的特性,探讨了组成、结构与性能之间的相互关系,并介绍了这类材料的研究现状和应用前景。     

CePO4/Ce-ZrO2可加工陶瓷加工机理的研究

以CePO4／Ce-ZrO2为基体，通过复合不同加入量的第二相CePO4颗粒，并借助扫描电子显微镜对材料压痕、磨削及切削表面进行分析，研究了CePO4／Ce-ZrO2陶瓷材料的可加工机理。单相CePO4材料的弯曲断口显示出层片状断裂机制；而复相CePO4／Ce-ZrO2陶瓷由于两相之间弱结合界面的存在，压痕裂纹扩展形式发生明显变化，由连续扩展机制过渡为不连续扩展。基于上述两种重要机制形成的大量微裂纹是赋予材料可加工性的主要原因，材料加工去除是以微裂纹的连接来实现的。同时，大量微裂纹起到耗散主裂纹扩展能量的作用，有效阻止了较大裂纹的形成，使材料加工损伤大大降低。最后，给出了CePO4／Ce-ZrO2陶瓷加工机理的简单模型。     

磁化高速钢刀具的磨损性能研究

本文对非磁化和磁化高速钢刀具分别切削大理石和45号钢时的磨损性能进行了试验研究,研究了磁化对刀具抗磨损能力的影响规律,并初步探讨了刀具的磁化机理。     

Cyclic voltammetric behaviour of polyfuran perchlorate doped films

Electroactivity with continuous cycling and the electrochemical behaviour of polyfuran perchlorate films (PFu/ClO₄) were investigated to determine the reversibility of doping/dedoping processes and the electrochemical mechanism of these processes as a function of the electropolymerization potential. A surface capacitive oxidation mechanism and a diffusion controlled mechanism in the dedoping process were detected when the potential scan rate was varied in D films (_p = 2.3 V). Moreover, D films (_p = 2.1 V ) showed a mixture of mechanism in the reduction processes. The polymeric material was found to deteriorate with continuous charge–discharge over successive days.     

Dissociative chemisorption and surface restructuring: A simplistic model

The cooperative mechanism for dissociative chemisorption is discussed using a very simple, all or none model. This suffices to recover the essential aspects of the equilibrium behavior. In particular it is pointed out that the mechanism is equally applicable either to molecules which dissociate already at very low temperatures or those at which low temperatures are physisorbed. A similar mechanism can operate for interconversion of two adsorbed species. The physical assumptions of the model are discussed.     

复合肥的结块与“肥特利”复合肥防结块剂

针对复合肥结块的普遍现象,就其结块机理、影响因素以及防结块的方法进行了阐述,并详细介绍了"肥特利"复合肥防结块剂的作用机理、使用方法和应用效果.     

Understanding nature's strategies for enzyme-catalyzed racemization and epimerization

Epimerases and racemases are enzymes that catalyze the inversion of stereochemistry in biological molecules. In this article, three distinct examples are used to illustrate the wide range of chemical strategies employed during catalysis, and the diverse set of ancestors from which these enzymes have evolved. Glutamate racemase is an example of an enzyme that operates at an "activated" stereocenter (bearing a relatively acidic proton) and employs a nonstereospecific deprotonation/reprotonation mechanism. UDP-N-Acetylglucosamine 2-epimerase acts at an "unactivated" stereocenter and uses a mechanism involving a nonstereospecific elimination/addition of UDP. L-Ribulose phosphate 4-epimerase also acts at an unactivated stereocenter and uses a nonstereospecific retroaldol/aldol mechanism.     

Lewis Acid – Complexed Tetramethylene Biradicals Can Initiate the Thermal Copolymerization of Indene with Acrylonitrile

Summary To clarify the mechanism of the spontaneous copolymerization of styrene with acrylonitrile, the corresponding reaction of its analog, indene, was investigated. The spontaneous free radical copolymerization of indene with acrylonitrile was promoted by Lewis acids. Spontaneous copolymerization rates comparable to those of styrene with acrylonitrile were found. For indene, the Mayo [⁴+²] initiation mechanism, initially postulated for the spontaneous polymerization of styrene, cannot occur. Therefore the Flory mechanism, postulating a tetramethylene biradical initiating species, is proposed.     

Mechanistic study on Sn(Oct)<Subscript>2</Subscript>-catalyzed,ring-opening polymerization of <Emphasis Type="Italic">p</Emphasis>-dioxanone by surface-initiated polymerization and x-ray photoelectron spectroscopy

Two mechanisms on Sn(Oct)₂-catalyzed, ring-opening polymerization of p-dioxanone (PDX) were mainly proposed: activated monomer mechanism and coordination-insertion mechanism. The activated monomer mechanism assumes that alcohol complexed with Sn(Oct)₂ reacts with monomer and forms a ternary complex. The initiation and chain growth then proceeds within the complex with liberation of the intact Sn(Oct) ₂. In contrast, the coordination-insertion mechanism hypothesizes that an actual initiator is the -Sn(OR) species and the polymerization proceeds on the -Sn-O-polymer. In this paper, to investigate the presence/absence of the Sn species in the PPDX chain, we used X-ray photoelectron spectroscopy (XPS) of poly(p-dioxanone) (PPDX) grown from a gold surface using the grafting-from approach, and the XPS data supports the coordination-insertion mechanism. After the polymerization of PPDX from the surface, the peaks from Sn were observed at 153, 486, and 495 eV in XPS spectrum, and the peaks disappeared after quenching with 1N HCl.     

基体韧性对PS改性PVC体系性能的影响

研究了PS对未增韧PVC体系及用CPE预增韧PVC体系韧性的影响,发现在用CPE预增韧PVC基体后,PS的增韧效果更为显著,但增韧机理井无改变,仍可用"空穴增韧"的机理来解释。     

丙烯酸酯类无皂复合乳液聚合机理的研究

从热力学、接枝工艺方面阐述了丙烯酸酯类复合乳液聚合机理,同时用实验验证了机理的合理性,提出了“涂层－接枝”核／壳结构机理。     

钾钒系和钾钠钒系催化剂上SO_2氧化反应机理和反应动力学——(Ⅰ)催化剂物化性质与SO_2氧化反应机理研究

本文在不同条件下,用热重(TGA)、差热(DTA)、电导(ECA)、X-射线衍射(XRD)和电子显微镜(SEM)等方法,测定和研究了钾钒系和钾钠钒系催化剂的热、电性能及活性组分的组成分布和相态变化.在此基础上讨论了SO_2在两种钒催化剂上的氧化过程,提出了双温双钒两段反应机理:     

Investigation of the Properties of a Kinetic Mechanism Describing the Chemical Structure of RDX Flames. II. Construction of a Reduced Kinetic Scheme

A reduced kinetic mechanism is constructed taking into account various boundary conditions and the considerable spread of data on rate constant of elementary steps. Kinetic schemes describing the chemical structure of flame with various degrees of accuracy are considered. The shortest mechanism consists of 83 steps and 29 species. The heat fluxes, temperature profiles, and concentration profiles of the main (by mass) species calculated from the complete and reduced mechanisms are in good agreement.