Explosion energy in the synthesis of superhard phases

This article reviews works of the Institute for Problems of Materials Science evoted to the application of explosion energy for the synthesis of superhard phases (SHPs) based on phase transformations of layered structures of carbon and boron nitride at high pressures. Major attention is given to the development and application of the high-temperature shock compression method, which made it possible to synthesize a new structural form of carbon and to attain, for the first time, a 70% yield of cubic BN under shock compression. The diagram of BN phase transformations by different mechanisms is discussed, which demonstrates the dependence of the phase composition of shock compression products on the ordering degree of the starting graphite-like structure. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 1–2(453), pp. 3–10, 2007.     

The structural aspect of high-pressure superhard phase synthesis

Structural aspects are considered for the direct phase transitions in carbon and boron nitride at high pressures from the viewpoint of martensite and diffusion transitions. The mechanism for the transitions of graphite and graphite-type BN into superhardphases is controlled primarily by the crystalline perfection of the initial structures that show martensite transformations to metastable phases (lonsdaleite and BN wurtzite allotrope), while highly defective ones show diffusion transformation to high-pressure stable phases (diamond and cubic boron nitride). The perfection in the initial structure has a very marked effect on the transformation mechanism during shock compression, which is the main technique in the commercial production of superhard phases.Institute of Materials Science, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7/8(380), pp. 83–92, July–August, 1995.     

Effect of shock-wave treatment on the structure and hardening of austenitic steels

The structure and hardening of austenitic steels subjected to shock-wave treatment have been studied. This treatment is shown to form a structure whose cell size decreases with increasing pressure. The treatment-induced hardening of the steels can be estimated using the Hall-Petch relation. At the same degrees of residual deformation, shock-wave treatment results in a significantly higher degree of hardening of the austenitic steels as compared to cold rolling. The degree of hardening increases with decreasing stacking-fault energy in austenite.     

Physical properties of the boride phases of chromium

Summary Certain physical properties (specific conductivity, thermal coefficient of electrical resistance, thermal conductivity, thermal, emf, Hall constant, melting point, microhardness) of the boride phases of chromium-Cr₄B, Cr₂B, CrB, Cr₃B₄ and CrB₂-were determined in this investigation.On the basis of the regular change in the physical properties of the phases with a change in the boron content, the conclusion is drawn that the nature of the chemical bond in the phases changes from the metallic for low boride phases to the covalent-metallic for higher phases.     

Chiral PAF agonists: synthesis, theoretical analysis of their stereoelectronic properties and structure activity relationships

A series of chiral PAF agonists were synthesized. Modifications at the PAF structure were undertaken as far as the C2 substituents and the onium head groups are concerned. In parallel, molecular modelling studies including a MOPAC geometry optimization and the analysis of the electrostatic potential were performed on the newly synthesized and on already known PAF agonists, in order to gain a better insight into the stereoelectronic features required for interaction with the PAF receptor.     

马克思理解科学的哲学原则及其当代性

马克思理解科学的哲学原则,是马克思科学哲学思想的核心内容,实践生存论是马克思理解科学的哲学本体论,是马克思科学哲学的基本哲学原则.它界定和衍生出了马克思理解科学的其他三个哲学原则,即"人的历史性""资本及其生产方式"和"现实的人的自由与解放".马克思理解科学的哲学原则凸显和表征了马克思科学哲学思想的当代性.     

TRIP钢中相似结构相的区分及定量表征

为了对钢铁样品中不同相进行准确区分, 建立了一种较为直观的定量分析方法。试验以TRIP钢为例, 采用光学显微镜、X射线衍射仪及电子背散射衍射技术对试验钢的微观组织、物相及相似结构相进行了表征。结果表明:电子背散射衍射技术不仅可以区分出TRIP钢中的体心立方和面心立方结构, 而且能通过菊池带衬度图像对结构相似的铁素体、贝氏体以及马氏体3种相进行进一步细分, 并最终得出定性分布和定量结果:铁素体为45.10%, 贝氏体为47.80%, 奥氏体为5.23%, 马氏体为1.87%, 说明其在区分相似结构相方面优势显著。     

Physical properties and the fine structure of proteocines

Proteocines derived from twelve previously described bacteriocinogenic strains of Proteus mirabilis and Proteus vulgaris were investigated. All proteocine preparations were particulate, unaffected by trypsin, and destroyed by freezing and thawing or by heating at 60 degrees C for 30 minutes. Proteocine activity was removed by adsorption with the appropriate sensitive organisms. The active principles of all preparations were partially purified by precipitation with 70% (w/v NH4(SO4)2 followed by ultra-centrifugation. Column chromatography showed that proteocine activity was associated with only one of the peaks of material which absorbed strongly at 257 mu. All twelve proteocine preparations were revealed by electron microscopy as a phage-tail-like structure and each particle had a sheath, a core, and a base-plate from which spine-like fibres extend. Adsorption of these particles to the cell wall of sensitive strains did not disrupt the bacterial cell wall, but the cytoplasmic membrane and the cell contents shrank, with consequent death of the "infected" cell.     

Current challenges to the principles of medical law and their new interpretation

The traditional function of the principles of medical law has been to protect the person of the patient against the use of power in health care. These principles have not generally been seen as factors which would also protect the patient economically. An analysis of the significance of the use of power in health care and a review of the field of damage sustained through erroneous procedures in the care relationship, make it possible to observe that the patient's need for legal protection is particularly great not only as regards factors related to the person, but also as regards the finances of the patient. On the other hand, evaluation of the relevant contents of the principles shows beyond doubt that they are to be conceived of generally as norms safeguarding the patient's rights. In Western countries in particular, where some years ago an economic recession set in, serious note should be taken of the wider interpretation of the principles of medical law as one potential means of furthering the well-being of the patient. In the application of legal rules affecting the legal position of the patient the principles of medical law may--like legal principles in general--be utilized both to guide the choice of a solution norm and to complement/ specify the solution norm. In both these roles the principles yield criteria for application of the law which lead to the taking into consideration of aspects relating to the patient's financial interests and assessments.     

方解石晶体结构及表面活性位点第一性原理

基于密度泛函理论的第一性原理,采用Materials Studio 6.1软件的CASTEP模块对方解石的晶体结构及与水分子及水分子簇的吸附作用进行了研究.结果表明,方解石在参与化学反应时O的活性最强,C和Ca次之;其次确定了最稳定解离面为{10相似文献   

Thermodynamic properties and defect structure of semiconducting compound phases: Tin telluride

Defect equilibria for binary semiconducting compound phases which exhibit ionized native donor and acceptor defects were considered, and equations describing the pressure-temperature-composition relationships for these compound phases were derived. These equations were used to analyze experimental data from the literature for tin telluride. Excellent agreement was obtained between calculated thermodynamic and phase boundary values and experimental data. The approach presented is readily extended to obtain equations for the thermodynamic properties of ternary and higher order semiconducting compound phases.