Structure refinement and thermal stability of gibbsite

The crystal structure of gibbsite (aluminum hydroxide) has been refined by Rietveld powder diffraction analysis, and the thermal stability of the crystal structure of the mineral has been studied in detail by high-temperature X-ray diffraction. The X-ray diffraction data obtained in the temperature range from 25 to 300°C indicate that the crystal structure of gibbsite is stable up to 200–250°C. The unit-cell parameters of gibbsite increase with temperature. Above 200°C, the gibbsite to boehmite (AlO(OH)) phase transformation begins.     

基于微博重复发送的垃圾用户甄别

针对微博平台上的垃圾用户甄别问题,本文提出了基于微博重复发送行为的垃圾用户行为建模和甄别算法。在真实微博垃圾用户数据分析的基础上,本建模方法综合考虑了微博垃圾用户的行为信息、社交网络信息和文本信息,从不同的角度对垃圾用户进行了分析和建模。在真实数据集上的实验证明了方法的有效性,并且对模型中若干参数进行了优化,同时也分析了垃圾用户行为信息、社交网络信息和文本信息对模型的影响程度。     

Metallographic examination of the structure of the metal of cold arms of the nineteenth-early twentieth centuries made at the Zlatoust arms factory

Data are given concerning the structure and the chemical composition of carbon steel used for making cold arms, which was produced at the Zlatoust arms factory in the nineteenth and early twentieth centuries. The results of the analysis of the structure of metal demonstrates the general trend of the development of metallurgy both at the Ural plants and in the world: from the creation of the crucible methods of production of cast steel to the mass production of cast steel by the Bessemer and Martin methods.     

Structural peculiarities of Bi,Pb-2223/Ag composites annealed in an N<Subscript>2</Subscript>-O<Subscript>2</Subscript> atmosphere

X-ray diffraction analysis, transmission and scanning electron microscopy, and electron microprobe analysis were used to study Bi,Pb-2223/Ag composites annealed in a low-oxygen atmosphere (7.5% O₂ + 92.5% N₂). The ceramics was found to be characterized by some nonuniformity in the distribution of all the components. Two structural peculiarities of the 2223 phase were found. These are the existence of atomic displacement waves, which are related to the oxygen deficiency or nitrogen substitution for oxygen, and a more intense Ag penetration into the ceramics, which results from the annealing in the O₂-N₂ atmosphere at a pressure of 10 atm. The unstable state of the lattice characterized by oxygen atomic displacement waves is due to the prolonged annealing in oxygen-depleted atmosphere. Usually, in the case of other favorable factors of the ceramics structure, the lattice instability positively affects the superconducting properties of the ceramics.     

Control of the magnetic state of arrays of ferromagnetic nanoparticles with the aid of the inhomogeneous field of a magnetic-force-microscope probe

The work presents a survey of the results of studies of the processes of magnetization reversal of ferromagnetic nanoparticles under the action of the field of a magnetic force microscope probe.     

Effect of mechanical milling on the mobility of hydrogen in the ZrTi<Subscript>2</Subscript>-H system stabilized by hydrogen: NMR data

Methods of X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) were used to investigate the effect of milling on the properties of the hydrogen-stabilized compound ZrTi₂H_3.9 with the structure of the metallic sublattice of the C15 type. It has been found that the milling leads to a phase separation in the initial sample: there appears an additional phase with a structure of the TiH₂ type and an average grain size of approximately 10 nm. The mobility of hydrogen in the phase of the TiH₂ type is considerably lower than in the phase of the C15 type. An analysis of the results of measurements of rate the spin-lattice relaxation of 1H nuclei in wide ranges of temperatures (20–420 K) and resonance frequencies (14.6–90 MHz) allowed us to estimate the parameters of the hopping motion of hydrogen atoms in the phase of the C15 type. It has been established that an increase in the time of milling leads to a decrease in the mobility of hydrogen in this phase.     

Effect of external force fields on the domain structure of equiatomic CuAu alloy

Peculiarities of the ordered-structure formation in the equiatomic CuAu alloy, which are caused by changes in the sample dimensions and by an applied external force field, have been studied. The rate of the microstructure transformation in the ordered alloy has been found to increase with increasing thickness of the sample. It has been shown that tensile stresses applied during heat treatment can affect the growth direction of c domains and, thus, makes it possible to avoid the low-temperature cracking of the material.     

Process of faceting in nanoparticles of FCC metals: Results of simulation by the molecular-dynamics method

The process of formation of facets (faceting) in Ni, Al, and Au nanoparticles has been investigated by the molecular-dynamics method. It has been established that the surface of nanoparticles of fcc metals with attainment of a low-energy habit can be transformed via correlated displacements of atomic groups of the facet in the octahedral plane. It has been shown that such a process is similar to the surface diffusion of atomic n-mers with the activation energy depending on the facet size, and for particles with a diameter d < 3.0 nm the correlated displacement of atomic layers proves to be the dominant mechanism of faceting.     

The synthesis of novel fluorine-containing random polymer and application in modification of solid surfaces

The novel fluorine-containing random polymers, poly (2, 3, 4, 5, 6-pentafluorostyrene)-r-poly (4-vinyl benzocyclobutene) random copolymer was synthesized, which can effectively decrease the surface energy and provide a good corrosion protection for some metals. Additionally, textured silicon was fabricated by an optically assisted electrochemical etching process to study the effect of the random copolymer modification on the binary geometric structures of the solid surface. After modification the superhydrophobic property can easily be obtained, which show long-term stability and good superhydrophobicity in corrosive solutions over a wide pH range, including acidic and basic solutions.