Papers by Keyword: Chemical Bonding

Abstract: The changes in the mechanical and physical properties of concrete prepared by incorporating various metal oxide nanoparticles into cement products used in both the oil/gas industry and construction have been analyzed in this review. The study compares the properties exhibited by transition metal oxide and some metal nanoparticles in both isolated and complex forms with polymers in concrete. Analyses were conducted primarily in the direction of changes occurring in properties due to the addition of metal oxide nanoparticles such as magnetite Fe₃O₄, TiO₂, ZnO, Fe₂O₃, Ag, CuO, TiO₂/SiO₂, Al₂O₃, ZrO₂, core/shell Fe₃O₄/SiO₂, in dispersed form as cement powder or in water. It has been showed that appropriate changes occur in properties such as compressive and flexural strength, adhesion, initial and final setting, water absorption, porosity, electrical conductivity, degradation when metal oxide nanoparticles are added to cement. The density and size of nanoparticles affect their response to various influences, alongside the fundamental properties of the material.

Abstract: The paper shows the possibility of using such quantitative characteristics of the element-oxygen chemical bond as the covalent character, metallic character and ionic character in substances to select a set of technological methods and develop a technology for nanomodification of natural bentonite aluminosilicates. The research results showed that thermal activation of bentonite at 200, 300, 380 and 400 °C with different modes of isothermal exposure (15, 30, 60, 120 minutes) does not significantly affect the efficiency of its modification with silicon (SS) and aluminum (AS) oxide nanoparticles, estimated by the increment of the compressive strength and the adsorption index for methylene blue. Obtaining a 46 % aqueous suspension of bentonite and modifying it with silicon and aluminum oxide nanoparticles followed by ultrasonic treatment after standing decreases the particle size by more than 4 times, which is a promising technological solution for improving the performance properties of ceramics, molding mixtures, adsorbents and other materials based on bentonite from various deposits.

Abstract: The reaction of Re₂O₇ with a mixed non-aqueous medium S₂Br₂+Se₂Br₂ at 100 °C gives Re₃Se₃S₄Br₁₃: own structure type, Z = 4, space group Pnma – d ⁹c ⁵, a = 14.0301(4), b = 17.7909(4), c = 10.8596(3) Å, R_I = 0.0491. The crystal structure can be described as a 3D-packing of isolated trinuclear cluster molecular cation-anionic complexes [Re₃(µ₃-S)(µ-S)₃(SeBr₂)₃Br₆]⁺Br^–. This compound displays a high catalytic activity in the hydrogenation of m-nitrobenzoic acid into m-aminobenzoic acid with 93 % yield in 5 % HBr aqueous solution.

Abstract: We have performed ab-initio calculations to investigate the structural and electronic behavior of TiN in the stable B1 and high pressure B2 phases using pseudo-potential plane wave approach within the framework of density functional theory. The calculated results show agreement with the experimental data. The present electronic behavior, determined by total energy calculations with generalized gradient approximation for exchange and correlation interactions, is observed to be similar in both B1 and B2 phases showing metallic, covalent as well as ionic bonding of TiN. The investigations in B2 phase need validation experimentally as well as theoretically.

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.

Abstract: Electronic structure and chemical bonding in tetragonal KNbO3 have been studied by first-principles calculations. The band gap is indirect and a value of 1.64 eV was determined. Chemical bonding feature shows that a significant hybridization between Nb 4d and O 2p states. The bonding between K and NbO3 is mainly ionic nature while covalent nature was confirmed between Nb and O.

Abstract: Self-healing concrete is a kind of smart concrete, and becoming one of research focus both in material and civil engineering field, in the paper, main self-healing methods concluded and partial technical problems of the self-healing facing, aim to these problems designed a kind of novel self-healing system, and experimental analyzed mechanism of self-healing.

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.

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.

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.