Papers by Keyword: Chemical Bonding

Paper TitlePage

Authors: E.F. Sheka
Abstract: A brief review of fascinating properties of fullerene is presented on the basis of the concept of effectively non-paired electrons. A versatile chemistry of fullerenes follows from the regioselectivity of their atoms and the uniqueness of donor-acceptor abilities. Computational synthesis of the fullerene derivatives is discussed. Applications of the basic concepts to medicinal applications of fullerenes as well as their magnetic properties and ability to form technomimetic species are considered.
1
Authors: Sachi Taniguchi, Masaru Aniya
Abstract: In complex perovskite-type oxides which have been studied as cathode materials, the thermal expansion coefficient increases with the increase in the oxygen ionic conductivity. In the present study, with the aim to explain such a behavior, a research has been carried out from a chemical bond point of view. For oxides A1-xA′xB1-yB′yO with perovskite structure, the ionicity of the individual bond, A-O and B-O, and the thermal expansion coefficient of mixed compounds were estimated by using semiempirical methods. It has been shown that the thermal expansion coefficient and the oxygen ionic conductivity decrease with the increase in the difference of the ionicity between A-O and B-O bonds. It is also found that the tolerance factor and the specific free volume are linearly correlated with the difference of ionicity.
343
Authors: E.F. Sheka
Abstract: A unified theoretical and/or computational odd-electrons approach is suggested for molecules, surfaces and magnetic solids making possible their consideration on the same conceptual basis as well as on the same computational footing. The current paper presents the approach application to the chemistry of fullerenes, carboneous nanotubes, surface science of silicon crystal, as well as to the molecular magnetism of both solid polymerized fullerenes and molecular crystals composed of transitional metal complexes.
19
Authors: B. Mednikarov
Abstract: Traditionally, the term hard coatings refer to the property of high hardness in mechanical sense with good tribological properties [1]. With the development of modern technology in the areas of optical, optoelectronic, microelectronic and related defense applications, the definition of the term hard coatings can be extended. Thus, a system which operates satisfactorily, in a given environment can be said to be hard with respect to that environment [2]. Most of the hard coatings are ceramic compounds such as oxides, carbides, nitrides (AlN), ceramic alloys, cermets, metastable materials such as Diamond-Like Carbon (DLC). Their properties and environmental resistance depend on the composition, stoichiometry, impurities, microstructure, imperfections, and in the case of coatings, the preferred orientation (texture). In this paper we shall take a look at some characteristics - physicochemical and optical of AlN and DLC layers synthesized by physical vapor deposition – RF magnetron sputtering in an industrial high vacuum deposition system. The influence of the process parameters on the growth rate, morphology, topography and chemical bonding structure will be presented.
63
Authors: Bing Qiang Liu, Chuan Zhen Huang, Han Lian Liu, Xue Wen Chong
Abstract: While whisker toughening ceramic cutting tool composites have excellent mechanical properties at either room or high temperature, the development of them is often limited by some difficulties in the fabrication and application. Here a TiC whisker toughening Al2O3 ceramic cutting tool composite is developed by in situ synthesis technology. Experimental results show the flexure strength, fracture toughness and Vickers hardness of the composite can achieve to 855.7MPa, 7.63 MPa•m1/2 and 19.5GPa, respectively. Being different to that of conventional whisker toughening ceramic composites, the toughness of the composite is dominated by the chemical interface bonding between TiC and Al2O3, which increases with increasing sintering temperature, and the sliding resistance is suggested to be due to the physical absorption and mechanical meshing between the two debonded surfaces.
201
Authors: Xing Sen Che, Zheng Tang Liu
Abstract: Amorphous hydrogenated Ge1-xCx films are prepared by radio frequency (RF) magnetron cosputtering using Ge/graphite composite target and their composition, optical and chemical bonding properties as a function of bias have been investigated. The results show a decrease in the deposition rate with increasing bias, and the optical gap nearly keep constant due to effects of both composition and chemical bonding. Through the analysis of X-ray photoelectron spectroscopy, we find that the content of Ge-C bonds first increases and then decreases as increasing bias while the Ge-O bond decreases monotonically.
1074
Authors: Bao Jun Wang, Lu Jia Zhu
Abstract: We performed first-principles calculations to the electronic structure and bonding characteristic of LaMgNi4H4. The calculation results show that the H—Ni units are formed by the covalent H—Ni bonds, the surrounding Mg and La atoms provide electrons to the H—Ni units, and the Ni-Ni bonds between the different H—Ni units are covalent, making the H—Ni units not isolated. These bonding characteristics show that LaMgNi4H4 is similar with interstitial metal hydride in some aspects, and similar with complex metal hydrides in other aspects, indicating LaMgNi4H4 is the intermediate between interstitial metal hydrides and complex metal hydrides.
876
Authors: Bao Jun Wang, Rui Ying Li, Xiao Ping Dong, Li Guan, Jian Gang Niu
Abstract: We performed first-principles calculations to the electronic structure and bonding characteristic of NdMgNi4H4. The calculation results show that the H—Ni units are formed by the covalent H—Ni bonds, the surrounding Mg and Nd atoms provide electrons to the H—Ni units, and the Ni-Ni bonds between the different H—Ni units are covalent, making the H—Ni units not isolated. These bonding characteristics show that NdMgNi4H4 is similar with interstitial metal hydride in some aspects, and similar with complex metal hydrides in other aspects, indicating NdMgNi4H4 is the intermediate between interstitial metal hydrides and complex metal hydrides.
1422
Authors: Qian Wang
Abstract: In order to produce new generation monolayer brazing CBN(cubic boron nitride) grinding wheels, an active filler alloys(Ag-Cu-Ti) were tested in vacuum furnace. The results show that Ag-Cu-Ti alloy exhibits good wetting and bonding toward as CBN grits. SEMEDS microanalyses have shown that during brazing Ti in Ag-Cu-Ti alloy segregated preferentially to the surface of the CBN to form a Ti-rich reaction produce. X-ray diffraction reveals that the wetting and bonding behaviour on CBN surface by Ag-Cu-Ti alloy melt is realized through TiN and TiB2 which is produced by interaction between Ti atoms of Ag-Cu-Ti alloy and N or B atoms of CBN surface.
209
Showing 1 to 10 of 20 Paper Titles