Showing papers in "Inorganic Materials in 2011"

Calcium phosphate bone cements

Abstract: The principles of developing calcium phosphate cements (CPCs) for replacement and regeneration of bone tissue are considered. The basic classification of CPCs is given according to the phase composition of the reaction products in the setting systems. Processes of phase composition and development of microstructure and properties are discussed. Injectable CPC compositions are considered, and the factors affecting the injectability, as well as the ways to modify the cement pastes to improve their properties, are discussed. The results of research and development in the field of composite CPCs, including those reinforced by disperse phases, are described. In the final part of the review, some data on commercial CPCs and their biological behavior are presented.

Thermal decomposition of natural dolomite

Abstract: We have studied thermal modification of natural dolomite chips, which has allowed us to optimize conditions for the preparation of supports for manganese oxide catalysts with appropriate physicochemical properties (elevated carbon dioxide partial pressure and calcination temperature no higher than 800°C).

Graphene: A novel carbon nanomaterial

Abstract: This review analyzes what the term graphene means today, and examines graphene preparation and identification methods and its chemical properties. The applications of this novel carbon nanomaterial are briefly discussed.

K2(Rb2,Cs2,Tl2)TeBr6(I6) and Rb3(Cs3)Sb2(Bi2)Br9(I9) perovskite compounds

Abstract: We systematize available experimental data on the crystal structure of the ternary halides K2(Rb2,Cs2,Tl2)TeBr6(I6) and Rb3(Cs3)Sb2(Bi2)Br9(I9), analyze the general trends in the properties of their single crystals, and examine the key features of the physicochemical interaction in related systems

Phase transitions and thermal expansion of apatite-structured compounds

Abstract: The phase transitions and thermal expansion of apatite-structured compounds with the general formula M5II(AVO4)3L (MII = Ca, Sr, Cd, Ba, Pb; AV = P, V; L = F, Cl) have been studied by high-temperature X-ray diffraction and differential thermal analysis. The Pb-containing apatites are shown to undergo phase transitions involving a reduction in unit-cell symmetry from hexagonal to monoclinic. The thermal expansion anisotropy in the hexagonal phases increases in the order Ca < Sr < Ba < Pb < Cd, and the monoclinic phases are less anisotropic but have larger thermal expansion coefficients in comparison with the hexagonal phases.

Total reflection X-ray fluorescence analysis: Physical foundations and analytical application (A review)

Abstract: The current state of the art in one of the most promising techniques of X-ray spectral analysis, namely, total reflection X-ray fluorescence analysis (TXRF), is summarized. The underlying physical processes, including reflection, refraction, total external reflection (TER) of X-rays, and formation of standing waves by TER, are considered. The construction and crucial components of a modern energy-dispersive TXRF spectrometer, involving X-ray tubes, monochromators, detectors, and reflectors, are described. Examples of analytical application of TXRF are given. High efficiency of this technique for qualitative and quantitative chemical analysis of liquids and solids of various natures is demonstrated. The main research trends in surface analysis and investigation of surface layers of solids by TXRF are discussed.

Sintering mechanism for high-density NZP ceramics

Abstract: We have studied the shrinkage kinetics and mechanism of NaZr2(PO4)3 containing inorganic additives. The sintering of NaZr2(PO4)3 containing ZnO microadditives is shown to follow a liquid-phase mechanism. Effective sintering aids include oxides of metals in the oxidation states 2+ and 3+ that are capable of reacting with sodium zirconium phosphate to form solid solutions. Ceramics having a relative density of 96–99% and isostructural with NaZr2(PO4)3 can be prepared by adding 0.75–2.0 wt % ZnO as a sintering aid capable of influencing the structure of grain boundaries in ceramic materials, pressing green bodies at 200–300 MPa, and sintering them at 1000–1100°C for 7–15 h.

Preparation of nickel nanoparticles for catalytic applications

Abstract: Spherical oxidized nickel particles 15 to 200 nm in average size have been produced by a crucibleless aerosol method involving metal vapor condensation in an inert gas flow and oxidation processes. The particles have been characterized by scanning electron microscopy, X-ray microanalysis, X-ray diffraction, BET surface area measurements, and vibrating-sample magnetometry. The process parameters have been optimized for the preparation of particles with tailored size, specific surface area, and saturation magnetization. A dc electric field applied to the condensation zone during the oxidation process reduces the size and increases the extent of oxidation of the particles. We have studied low-temperature oxidation of carbon monoxide and propane on nickel nanopowders differing in particle size and extent of oxidation. The nanoparticles with optimized characteristics have been shown to have a marked catalytic effect on these processes.

Surface modification of carbon fibers with nitric acid solutions

Abstract: We have studied the surface modification of carbonized carbon fibers with nitric acid solutions, compared the effects of 60 and 98% HNO3, and examined the influence of the anodic polarization of the fiber for surface functionalization. Unmodified and surface-modified carbon fibers have been characterized by a variety of physicochemical techniques.

Preparation of finely dispersed nanographite

Abstract: We have developed a convenient single-step method for producing stable nanographite dispersions from natural graphite in various solvents using high-power sonication. Nanographite dispersions in water are shown to be stable for several weeks, and aqueous nanographite dispersions containing a surfactant are stable for several months. Nanographite samples prepared from aqueous nanographite dispersions have been characterized by various physicochemical techniques (including X-ray diffraction and Raman spectroscopy). Interference microscopy, transmission and scanning electron microscopy, and atomic force microscopy have been used to examine the morphology and determine the size of nanographite particles. The nanographite platelets are 300–500 nm in lateral size and 20–40 nm in thickness, which corresponds to 30–50 graphene layers.

Analysis of wetting as an efficient method for studying the characteristics of coatings and surfaces and the processes that occur on them: A review

Abstract: The use of a method of studying wetting both for the research of fundamental problems of surface physicochemistry, such as obtaining information on the structure and properties of the interface and the processes that occur with its participation, and for technological applications related to the preparation of new materials and coatings is analyzed. The fundamental relationships between the contact angle and the thermodynamic and geometric characteristics of the surface are discussed; the factors that have an effect on the contact angle value on nanocomposite surfaces are analyzed. It is shown that recent advances in digital processing of video images provide a qualitatively new level of measurement of contact angles and make the analysis of surface wetting one of the most efficient experimental methods for studying the processes that occur at interfaces. In some cases, the accumulated basic knowledge about the relationship between the measured contact angle and the properties of the surface under study makes it possible to rapidly and reliably obtain detailed information about the roughness, chemical composition, and topology of the surface without using expensive equipment; in other cases, it provides additional information that makes it possible to reveal the mechanisms of the surface phenomena under study. As a case in point, we describe the use of techniques of analysis of wetting for determining the surface porosity and surface topology, for estimating the pattern of interaction between polymer materials and aqueous media, and for revealing the efficiency of anticorrosion coatings on metal surfaces.

Self-propagating high-temperature synthesis of Y2O3 powders from Y(NO3)3x(CH3COO)3(1 − x) · nH2O

Abstract: We have studied the self-propagating high-temperature synthesis (SHS) of yttrium oxide from Y(NO3)3x(CH3COO)3(1 − x) · nH2O (0.3 ≤ x ≤ 0.7) acetate nitrates, calculated their standard enthalpies of formation using the method of valence states of atoms in a chemical compound, and compared calculated and experimentally determined yttrium oxide SHS temperatures. Using thermogravimetry and differential scanning calorimetry data and thermodynamic analysis, we have determined the optimal range of yttrium acetate nitrate compositions for the SHS of Y2O3 powder.

Ultrapurification of archaeological lead

Abstract: Based on purification efficiency calculations for lead distillation, we developed a combined process for the ultrapurification of archaeological lead. We obtained pilot amounts of high-purity archaeological lead and PbO with the following contents of detrimental impurities: U, <2 ppb; Th, <1 ppb; Ni, Cu, Fe, Si, Ti, Mg, Al, Mn, Cr, V, Co, < 0.1 ppm; K, Ca, Zn, Cd, Ag, Sb, < 1 ppm. Lead of such purity can be used in low-background experiments as a protective shield material and in the growth of low-background PbWO4 and PbMoO4 scintillator crystals. From an isotope ratio, we were able to identify the origin of the archaeological lead.

Mechanochemical synthesis and hydrogen sorption properties of nanocrystalline TiFe

Abstract: The equiatomic intermetallic compound TiFe has been prepared by elemental mechanochemical synthesis in a planetary ball mill from Fe and Ti powders. The structural and phase transformations during synthesis were followed using X-ray diffraction. The reaction of the synthesized compound with hydrogen was studied volumetrically. The results demonstrate that the hydrogen capacity of the mechanochemical TiFe is 1.2 wt % at 2.5 MPa. Its absorption isotherm has an extended plateau in the range 1.6–1.7 MPa at room temperature.

Influence of lanthanum content and annealing temperature on the size and magnetic properties of sol–gel derived Y1 − xLaxFeO3 nanocrystals

Abstract: Y1 − xLaxFeO3 (x = 0, 0.1, 0.2, 0.3, 0.4) nanocrystals have been prepared by a sol-gel process. With increasing lanthanum content (x from 0 to 0.4), their size decreases significantly (from 34 to 16 nm), whereas their magnetization increases. Raising the annealing temperature increases their size.

Effect of particle size on the oxidation of WC powders during heating

Abstract: The oxidation of tungsten carbide powders ranging in average particle size -D from 20 to 6000 nm has been studied by thermal analysis. Independent of particle size, the WC powders oxidize to the higher oxide WO3. With decreasing particle size, the oxidation rate increases, and the exothermic peak temperature decreases. Empirical relations are presented for the peak temperature and activation energy of oxidation as functions of the particle size of the powders.

Electrical properties of perovskite-like compounds in the Bi2O3-Fe2O3-TiO2 system

Abstract: The electrical properties of layered perovskite-like compounds with the general formula Bim + 1Fem − 3Ti3O3m + 3 have been studied in relation to their physicochemical properties and structure.

Emission from rare-earth ions in GaN wurtzite crystals

Abstract: Intense studies of a wide-gap direct-zone semiconductor represented by GaN wurtzite crystals doped with rare-earth ions, namely, Eu, Er, Sm, and Tm, suggest the development of an alternative (compared to that with the use of InGaN layers) technology of fabrication of light-emitting diodes of white color. The opportunities of increasing the intensity of emission of intracenter 4f transitions are demonstrated for rare-earth ions in GaN wurtzite crystals by the optimization of doping technology, concentration of rareearth ions, and use of an additionally introduced impurity. The form of electroluminescence spectra of the GaN

Transport properties of silicon doped with manganese via low-temperature diffusion

Abstract: We have studied the transport properties of silicon doped with manganese via low-temperature diffusion. The material exhibits colossal photoconductivity in the extrinsic region (1.5–3 μm), an abnormally high negative magnetoresistance, and a temperature variation of hole mobility atypical of silicon. The state of the manganese atoms has been probed by electron paramagnetic resonance spectroscopy and atomic force microscopy. The results are used to infer the structure of nanoclusters consisting of manganese atoms and to develop an approach to controlling the charge state and magnetic moment of the nanoclusters.

Effect of mechanical activation on the properties of natural zeolites

Abstract: We have examined the effect of mechanical activation on the Sr2+ and Cu2+ ion exchange selectivity of Russian natural zeolites: clinoptilolite-containing tuffs and chabazite concentrates. We have studied their structural changes and thermal properties and determined the specific surface area and porosity of the mechanically activated zeolites. At specific milling energies below 0.5–0.7 kJ/g, the dominant process is disintegration of zeolite particles and changes in their bulk porosity. At higher milling energies, amorphization prevails. Our results demonstrate that, in the initial stage of activation, one can markedly raise the Sr2+ selectivity of some zeolites (e.g., by 16 times for Shivyrtuiskoe clinoptilolites and by 300 times for chabazite) and increase the Cu2+ selectivity (by 40 to 100 times), which will persist at high specific milling energies.

Kinetics of lithium deintercalation from LiFePO 4

Abstract: We have studied the kinetics of lithium deintercalation from lithium iron phosphate in a cathode material for batteries. The main contribution to the resistance of the cell is made by interfaces and the resistance of LiFePO4 grains. The FePO4 solubility in LiFePO4 is 4.0%. The lithium deintercalation process can be described in terms of a heterogeneous grain model and its rate is controlled by the lithium diffusion across the layer of the forming product (FePO4).

Synthesis and morphology of anatase and η-TiO2 nanoparticles

Abstract: Samples containing anatase and η-TiO2 nanoparticles have been prepared from titanyl sulfate solutions and characterized by X-ray diffraction, transmission electron microscopy, and electron diffraction. Unit-cell parameters of η-TiO2 have been proposed that do not rule out a relationship between the anatase and η-TiO2 structures. The samples containing anatase and η-TiO2 differ in crystallite size and specific surface area and consist of agglomerates of particles of various sizes covered with an amorphous layer. We have studied the effect of synthesis conditions on the ability to prepare a particular titania polymorph with various functional characteristics.

Stability and recrystallization of PbS nanoparticles

Abstract: The recrystallization and thermal stability of nanocrystalline lead sulfide have been studied by X-ray diffraction and scanning electron microscopy. PbS nanoparticles ranging in size from 10 to 20 nm were prepared by chemical precipitation from aqueous solutions. To assess the thermal stability of the size of PbS nanoparticles, the nanocrystalline powders were annealed in air or under dynamic vacuum (10−3 Pa) at a temperature varied from 433 to 930 K in 50-K steps. Annealing at temperatures of up to 700 K increases the particle size only slightly but relieves the lattice strain, suggesting that the nanocrystalline state of lead sulfide is thermally stable in this temperature range. The temperature range 700–900 K, where the particle size increases by a factor of 5–10, corresponds to the secondary recrystallization of nanocrystalline PbS. The temperature 700 K is half the melting temperature of macrocrystalline PbS, indicating that PbS nanoparticles have higher thermal stability in comparison with other nanomaterials.

Crystal structure and magnetic properties of high-coercivity Sr1 − xPrxFe12 − xZnxO19 solid solutions

Abstract: Sr1−xPrxFe12 − xZnxO19 ferrites with x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5 have been prepared by solid-state reactions between praseodymium, iron, and zinc oxides and strontium carbonate in air at 1470 K. According to X-ray diffraction results, the samples with x ≤ 0.2 were single-phase and those with 0.3 ≤ x ≤ 0.5 contained, in addition to the magnetoplumbite phase, small amounts of α-Fe2O3, ZnFe2O4, and PrFeO3. The mixed-phase samples further fired twice at 1470 K for 4 and 2 h contained no impurity phases at x = 0.3 and contained only α-Fe2O3 at x = 0.4 and 0.5. In the composition range 0 ≤ x ≤ 0.3, the a and c cell parameters, unit-cell volume V, and X-ray density ρx of the magnetoplumbite phase vary linearly according to the relations a(A) = 5.8869 − 0.0162x, c(A) = 23.027 + 0.449 x, V(A3)= 691.10 + 9.65x, and ρx(g/cm3) = 5.102 + 0.230 x. The highest degree of combined heterovalent substitution of Pr3+ for Sr2+ and Zn2+ for Fe3+ in the SrFe12O19 ferrite (formation of Sr1−xPrxFe12 − xZnxO19 solid solutions) at 1470 K is x = 0.32−0.36. The saturation magnetization per formula unit (ns) of the x = 0.1 ferrite exceeds that of SrFe12O19 by 1.7% at 6 K and by 15.2% at 308 K. The 308-K ns and coercive force (σHc) of the x = 0.2 ferrite exceed those of SrFe12O19 by 7.6 and 8.5%, respectively.

Structural and Transport Properties of the Layered Cuprate Pr2CuO4

Abstract: The structural and transport properties of the layered cuprate Pr2CuO4 have been studied in the temperature range 300–2100 K using molecular dynamics simulation. The first evidence is presented for a premelting effect in Pr2CuO4: disordering on one of its oxygen sites and abnormally fast oxygen diffusion at temperatures above 1700 K. We have clarified the microscopic mechanism of oxygen ion transport in this material. The large oxygen diffusion coefficient (D > 10−7 cm2/s) obtained in our simulations of the layered cuprate Pr2CuO4 suggests that it has considerable potential as a host for electrode materials with mixed ionic-electronic conductivity.

Preparation of boron microcrystals via high-pressure, high-temperature pyrolysis of decaborane, B10H14

Abstract: Crystalline boron has been prepared via high-pressure, high-temperature pyrolysis of decaborane, B10H14. We obtained α-tetragonal boron crystals at a pressure of 8–9 GPa and temperatures in the range 1100–1600°C and β-rhombohedral boron intergrowths at 3 GPa and 1200°C.

Cation mobility in Li1 + xHf2 − xScx(PO4)3 NASICON-type phosphates

Abstract: Li1 + xTi2 − xCrx(PO4)3 NASICON-type materials have been prepared and characterized by X-ray diffraction, scanning electron microscopy, and impedance spectroscopy. The results demonstrate that Cr3+ doping increases the ionic conductivity of LiTi2(PO4)3 within the single-phase region of the doped material, which extends to x = 0.7. From temperature-dependent ionic conductivity data, the activation energy for lithium transport through interstitial sites and the enthalpy of defect formation in LiTi2(PO4)3 are estimated at 30.0 ± 0.5 and 56 ± 1 kJ/mol, respectively.

Synthesis and magnetic properties of nanocrystalline Y 1 − x Cd x FeO 3 − δ (0 ≤ x ≤ 0.2)

Abstract: We report the synthesis of Y1 − x Cd x FeO3 − δ nanocrystals in the range x = 0–0.2. The Y1 − x Cd x FeO3 − δ materials were shown to be single-phase by X-ray diffraction, with an average crystallite size from 23 to 34 nm, depending on composition. With increasing cadmium oxide content, the size of the Y1 − x Cd x FeO3 − δ nanocrystals decreases and their magnetization rises.

Low-loss, high-purity (TeO2)0.75(WO3)0.25 glass

Abstract: By melting a mixture of high-purity oxides in a platinum crucible under flowing purified oxygen, we have prepared (TeO2)0.75(WO3)0.25 glass with a total content of 3d transition metals (Fe, Ni, Co, Cu, Mn, Cr, and V) within 0.4 ppm by weight, a concentration of scattering centers larger than 300 nm in size below 102 cm−3, and an absorption coefficient for OH groups (λ ∼ 3 μm) of 0.008 cm−1. The absorption loss in the glass has been determined to be 115 dB/km at λ = 1.06 μm, 86 dB/km at λ = 1.56 μm, and 100 dB/km at λ = 1.97 μm. From reported specific absorptions of impurities in fluorozirconate glasses and the impurity composition of the glass studied here, the absorption loss at λ ∼ 2 μm has been estimated at ≤100 dB/km. The glass has been drawn into a glass-polymer fiber, and the optical loss spectrum of the fiber has been measured.

Fluorescent CdS nanoparticles for cell imaging

Abstract: Fluorescent cadmium sulfide nanoparticles stabilized by an organic shell based on ethylenediaminetetraacetic acid have been prepared by chemical condensation in an aqueous solution. The nanoparticle concentration in aqueous solutions has been optimized and it has been shown that such hybrid nanoparticles can be used to image cell cultures and explore the cell structure. Not only the nanoparticle concentration but also the incubation time of the nanoparticle solution with the cell culture are essential for observing structural details.