Showing papers in "Inorganic Materials in 2009"
TL;DR: In this paper, the authors present the data on the present degree of purity of chalcogenide glasses for fiber optics, on their methods of production and on the properties, which are essential for their actual application, are generalized.
Abstract: The data on the present degree of purity of chalcogenide glasses for fiber optics, on their methods of production and on the properties, which are essential for their actual application, are generalized. The content of limiting impurities in the best samples of chalcogenide glasses is 10–100 ppb wt.; of heterophase inclusions with size of about 100 nm is less than 103 cm−3. On the basis of chalcogenide glasses the multimode and single mode optical fibers are produced with technical and operation characteristics sufficient for a number of actual applications. The minimum optical losses of 12–14 dB/km at 3–5 µm are attained in the optical fiber from arsenic-sulfide glass. The level of losses in standard chalcogenide optical fibers is 50–300 dB/km in 2–9 µm spectral range. The factors, affecting the optical absorption of glasses and optical fibers, are analyzed, and the main directions in further development of chalcogenide glasses as the materials for fiber optics are considered.
236 citations
TL;DR: In this article, the thermophysical and mechanical properties of compacted expanded graphite (EG) were studied with application of similarity theory, and it was shown that the critical density corresponding to the observed jump in the thermal conductivity coefficient and elasticity modulus was dependent on the expandable graphite preparation method, EG bulk density, and dispersion degree and amounted to 0.01 and 0.005 g/cm3.
Abstract: The thermophysical and mechanical properties of compacted expanded graphite (EG) were studied. The experimental results were interpreted with application of similarity theory. The compacted EG critical density corresponding to the observed jump in the thermal conductivity coefficient and elasticity modulus was shown to depend on the expandable graphite preparation method, EG bulk density, and dispersion degree and amounted to 0.01 and 0.005 g/cm3 for the studied EGs.
53 citations
TL;DR: In this article, the average size, morphology, and magnetic properties of the YFeO3 nanoparticles are shown to be highly dependent on the preparation procedure, and coprecipitation of yttrium and iron(III) chlorides with aqueous ammonia.
Abstract: YFeO3 nanocrystals have been prepared via coprecipitation of yttrium and iron(III) chlorides with aqueous ammonia. The average size, morphology, and magnetic properties of the YFeO3 nanoparticles are shown to be highly dependent on the preparation procedure.
49 citations
TL;DR: In this article, a process has been developed for the fabrication of preforms and fibers with Al2O3-P2O5-SiO2 glass cores, and their optical properties have been investigated.
Abstract: A process has been developed for the fabrication of preforms and fibers with Al2O3-P2O5-SiO2 glass cores, and their optical properties have been investigated. The results demonstrate that the refractive index and optical losses of the glasses studied are nonadditive functions of Al2O3 and P2O5 contents in the range 0–20 mol %.
42 citations
TL;DR: In this paper, the heat capacities of PbSe and PbTe were evaluated up to 298.15 K. The low and high-temperature heat capacity data were matched, and the thermodynamic functions of pbSe were calculated from temperatures close to their melting points.
Abstract: Given that the heat capacities of PbSe and PbTe had been previously measured only below 240 and 260 K, respectively, we evaluated unreported heat capacity values up to 298.15 K. The low- and high-temperature heat capacity data were matched, and the thermodynamic functions of PbSe and PbTe were calculated from 298.15 K to temperatures close to their melting points.
40 citations
TL;DR: In this paper, the authors describe the synthesis and charac- terization of a concrete based on metakaolin geopolymer, and compare its physical, mechanical and thermal properties with those of concrete made from portland cement.
Abstract: Inorganic alumino-silicates polymer or geopolymers are amorphous materials with a chemical composition similar to zeolites and an empirical overall chemical formula: M n (-( SiO 2 ) z - AlO 2 ) n · w H 2 O where M is an atom of metal (Li, for example), and n , z , w - integers. This paper describes the synthesis and charac- terization of a concrete based on metakaolin geopolymer. In addition, its physical, mechanical and thermal properties are compared to those of a concrete based on portland cement. It was observed that the compressive strength properties in the concrete based on metakaolin geopolymer were higher than those in the concrete based on portland cement; besides, thermal conductivity was lower for the former than for the later. Those dif- ferences are attributed to intrinsic nature of the binding phase.
39 citations
TL;DR: In this paper, the thermal conductivity of thallium-doped PbTe single crystals has been measured in the temperature range 80 −310 K, and the electronic and lattice components of their thermal conductivities have been evaluated.
Abstract: The thermal conductivity of thallium-doped PbTe single crystals has been measured in the temperature range 80–310 K, and the electronic and lattice (χph) components of their thermal conductivity have been evaluated. The results indicate that thallium doping markedly reduces the lattice thermal conductivity of PbTe single crystals, by up to ∼29%. Heat treatment at ∼473 K reduces the density of structural defects in the crystals and increases their χph. Thallium doping has a significant effect on χph starting at 0.05 at % before annealing and starting at 0.01 at % after annealing. We have calculated the density of structural defects in the unannealed samples and the doping-induced thermal resistance Δ W of the unannealed and annealed samples. ΔW has been shown to increase with thallium content.
39 citations
TL;DR: In this article, the capabilities of modern quantum-chemical methods are analyzed with application to various structural defects in BeO, phase equilibria in the Be-O system, pressure-induced polymorphic transformations of BeO and its mechanical, thermal, and spectroscopic properties.
Abstract: This review focuses on computer simulation studies of the nature of chemical bonding in BeO and its electronic structure and physicochemical properties. The capabilities of modern quantum-chemical methods are analyzed with application to various structural defects in BeO, phase equilibria in the Be-O system, pressure-induced polymorphic transformations of BeO, and its mechanical, thermal, and spectroscopic properties.
35 citations
TL;DR: In this article, the precursor solutions were introduced into a muffle furnace (Lenton LTF 1500) and maintained at 500° C for 10 min, followed by decomposition with the evolution of large amounts of gases (CO 2, N 2, NO x and H 2 O).
Abstract: ≥ 99.5% ) and Pb ( NO 3 ) 2 (Riedel-de-Haen ≥ 99.5% ) were dissolved in a minimum amount of distilled water and placed in a porcelain container. The mole ratios of Pb 2+ ( x ) in Sr 1 – x B 2 O 4 are 0.001, 0.005, 0.010, 0.011, 0.012, 0.013, 0.014 and 0.020, respectively. The precursor solutions were introduced into a muffle furnace (Lenton LTF 1500) and maintained at 500° C for 10 min. Initially, the solutions boiled and underwent dehydration, followed by decomposition with the evolution of large amounts of gases (CO 2 , N 2 , NO x and H 2 O). The precursor powders were removed from the furnace, and then the voluminous and foamy combustion ashes were easily milled to obtain a precursor powder of Sr 1 – x Pb x B 2 O 4 . The well-mixed precursor powders were pressed into a pellet, typically cylindrical in shape. The pellets were then placed in an alumina crucible and heated in a muffle furnace (Lenton LTF 1500) for 2 h at 900° C in air. Pure SrB 2 O 4 was synthesized by the same method without using Pb ( NO 3 ) 2 (Riedel-de-Haen ≥ 99.5% ). The XRD structural analysis of the products was performed on an x-ray Rigaku Diffractometer Miniflex equipped with Cu K α (30 kV, 15 mA, λ = 1.54051 A) radiation at room temperature. Scanning was generally performed between 5°–85° 2 θ . Measurements were made with 0.05° steps and a 1°/ min scan rate. The divergence slit was variable, and the scattering and receiving slits were 4.2° and 0.3 mm, respectively. The Fourier transform infrared spectra between 500 and 1500 cm –1 were measured at room temperature with a Shimadzu FTIR spectrometer. The spectra were recorded on a KBr pressed disk. The photoluminescence excitation and emission spectra were measured at room temperature with a Varian Cary Eclipse spectrofluorometer equipped with a 15 W Xenon pulse lamp.
29 citations
TL;DR: Extruded n-type materials based on Bi2Te3-Bi2Se3 alloys containing 6 to 40 mol % Bi2Se 3 have been investigated using microstructural analysis and thermoelectric measurements at room temperature and in the range 100-400 K.
Abstract: Extruded n-type materials based on Bi2Te3-Bi2Se3 alloys containing 6 to 40 mol % Bi2Se3 have been investigated using microstructural analysis and thermoelectric measurements at room temperature and in the range 100–400 K. Their electrical properties have been compared to those of single-crystal analogs. Compositions have been found at which the extruded materials offer the highest thermoelectric performance in different temperature ranges.
28 citations
TL;DR: In this article, the average size of the nanocrystals is 2.8-2.9 nm, with a 10% variance, as evaluated from their absorption spectra.
Abstract: Sols of stabilized copper-doped CdSe nanocrystals in a nonpolar high-boiling solvent have been synthesized using cadmium oleate, copper stearate, and trioctylphosphine selenide as starting reagents. The average size of the nanocrystals is 2.8–2.9 nm, with a 10% variance, as evaluated from their absorption spectra. The samples show excitonic luminescence and bright near-IR (700–900 nm) luminescence with a lifetime on the order of 0.5–1 μs. The luminescence spectroscopy data are consistent with the assumption that the copper distribution over the nanocrystals follows Poisson’s law. The average copper content of the samples is 0.1–2 atoms per nanocrystal.
TL;DR: In this article, the phase equilibrium, structure, polymorphism, and growth characteristics of a new nonlinear optical material BiB3O6 (BIBO) have been investigated.
Abstract: This review is devoted to a new nonlinear optical material BiB3O6 (BIBO). It systemizes data on the phase equilibrium, structure, polymorphism, and growth characteristics of single crystals of this compound and considers its main properties and fields of application. The bibliography includes 122 references.
TL;DR: In this article, the effect of La doping on structural, morphological and magnetic characteristics of BiFeO3 synthesized under mild hydrothermal conditions at 200°C for 16 h using the KOH concentration of 4 M.
Abstract: This study reports the effect of La doping on structural, morphological and magnetic characteristics of BiFeO3 synthesized under mild hydrothermal conditions at 200°C for 16 h using the KOH concentration of 4 M. The as-synthesized powders of Bi1−xLaxFeO3 for x = 0.05, 0.10, and 0.15 were characterized by X-ray powder diffraction scanning electron microscope and the vibrating sample magnetometer. The formation mechanism of Bi1−xLaxFeO3 powders can be expressed by “dissolution-nucleation-crystallization” process. The magnetism of Bi1−xLaxFeO3 increased with increase of La content due mainly to increscent suppressing spiral magnetic structure and magnetic contribution of La.
TL;DR: A two-step process has been proposed for the preparation of refractory rare-earth diborides: high-temperature high-pressure elemental synthesis followed by argon annealing.
Abstract: A two-step process has been proposed for the preparation of refractory rare-earth diborides: high-temperature high-pressure elemental synthesis followed by argon annealing. Using this process, we have synthesized terbium, erbium, thulium, and lutetium diborides containing no more than 3 wt % impurity phases.
TL;DR: Carbonate-substituted hydroxyapatites containing up to 9 wt % of carbonate groups were synthesized and fabricated in the form of porous granules with a view to developing materials for use in bone tissue repairs as discussed by the authors.
Abstract: Carbonate-substituted hydroxyapatites containing up to 9 wt % of carbonate groups were synthesized and fabricated in the form of porous granules with a view to developing materials for use in bone tissue repairs. The use of sintering additives forming a liquid phase allowed the granule sintering temperature to be reduced by 400–450°C. It was found that the carbonate groups enter into the structure of the ceramic by a mixed AB-type substitution; the microstructure of the granules depends substantially on the concentration of the carbonate groups; introduction of 6 wt % of carbonate groups into apatite ensures high biological properties of the granules in experiments in vivo.
TL;DR: In this paper, a new red emitting phosphors, Ca3(VO4)2:Eu3+, Bi3+,Bi3+, Ca3((P,V)O4))2: Eu3+ were synthesized by low temperature solid-state reaction and characterized by X-ray diffraction, scanning electron microscopy, photoluminescence spectra and Fourier transform infrared spectroscopy.
Abstract: New red emitting phosphors, Ca3(VO4)2:Eu3+,Bi3+, Ca3((P,V)O4)2:Eu3+ were synthesized by low temperature solid-state reaction and characterized by X-ray diffraction, scanning electron microscopy, photoluminescence spectra and Fourier transform infrared spectroscopy. The results show that the red emission located at about 613 nm was ascribed to 5D0-7F2 transition of Eu3+. The effect of by Bi doping and by P doping was also investigated systematically.
TL;DR: In this paper, the positions of edge excitons and the band gaps were determined by the optical and photoelectric measurements, and it was found that the maxima in the temperature dependences of dielectric constants of pure polytypes are situated at different temperatures.
Abstract: The polytypes of monoclinic TlInS2 (c ∼ 15, 60, 120 A) and triclinic TlInS2 (c ∼ 30 A) were prepared. The positions of edge excitons and the band gaps were determined by the optical and photoelectric measurements. It was found that the maxima in the temperature dependences of dielectric constants of pure polytypes are situated at different temperatures. The photoconductivity spectra and the capacitive measurements showed that pure polytypes are unstable and transform with time into a mixture of the monoclinic polytypes of TlInS2. It is also established that all polytypes of monoclinic crystals tend to transform to the triclinic system.
TL;DR: In this paper, gas-tight electrolyte films are obtained by chemical vapor deposition for solid oxide fuel cells from yttria-stabilized zirconia (YSZ) with a thickness of 4-15 μm on supporting porous ceramic anodes.
Abstract: Gas-tight electrolyte films are obtained by chemical vapor deposition for solid oxide fuel cells from yttria-stabilized zirconia (YSZ) with a thickness of 4–15 μm on supporting porous ceramic anodes (YSZ/NiO). Volatile metal complexes with dipivaloylmethane Zr(dpm)4 and Y(dpm)3 are used as precursors. On the basis of an analysis of thermal properties of the starting compounds, parameter ranges in deposition processes are determined. Dependences of the structure, composition, and electrical characteristics on deposition conditions are found for YSZ electrolyte films. Electrochemical solid oxide fuel cells that operate at low temperatures with an open circuit voltage of 0.98–1.08 V and specific power up to 440 mW/cm2 at 1073 K and 1200 mW/cm2 at 1173 K are constructed.
TL;DR: In this article, a model of mechanical milling of powders is proposed and the average particle size and the value of the microstrains in the as-milled powder are determined from the broadening of x-ray diffraction reflections.
Abstract: A model of mechanical milling of powders is proposed. It is demonstrated that, during milling, the energy is partially spent in generating microstresses, which hinders the milling process. The model is compared with experiment for tungsten carbide (WC) powder. The average particle size and the value of the microstrains in the as-milled powder are determined from the broadening of x-ray diffraction reflections. Particle size is also evaluated by scanning electron microscopy and sedimentation analysis. It is shown that, with all other things being equal, upon grinding in a planetary-type mill, the resulting particle size is less, the greater the angular velocity of the mill rotation, the longer the milling time, the lighter the weight of the powder milled, and the smaller the initial powder particle size.
TL;DR: In this article, the dependence of fluorine incorporation into silica glass on conditions of the optical waveguide blank manufacture using the method of modified chemical vapor deposition (MCVD) was studied.
Abstract: The dependence of fluorine incorporation into silica glass on conditions of the optical waveguide blank manufacture using the method of modified chemical vapor deposition (MCVD) is studied. The degree of fluorine incorporation at constant consumption of a fluoridizer (SiF4) is shown to increase with an increase in the volume of deposited material. Samples of multimode optical waveguides with a core from pure silica glass and a reflective coating made of fluorine-doped silica glass with a numerical aperture of ∼0.18 are obtained. Optical losses in such optical waveguides reach 0.5 dB/km in the long-wavelength region of the spectrum.
TL;DR: In this paper, the authors demonstrate that heat treatment of the composites leads to crystallization of the titanium-containing component and, accordingly, reduces their specific surface area, and demonstrate that this leads to the fabrication of materials in which TiO2 nanocrystals are evenly distributed over an amorphous SiO2 matrix.
Abstract: Composites in the form of precipitated powders, hybrid xerogels, and SiO2 core/TiO2 shell particles have been produced via hydrolysis of precursors (alkoxides and inorganic derivatives of titanium and silicon) and have been characterized by differential thermal analysis, X-ray diffraction, adsorption measurements, and macroelectrophoresis. The results demonstrate that heat treatment of the composites leads to crystallization of the titanium-containing component and, accordingly, reduces their specific surface area. Hydrothermal treatment enables the fabrication of materials in which TiO2 nanocrystals are evenly distributed over an amorphous SiO2 matrix.
TL;DR: In this article, the minimum average size of nanoparticles in synthesized metal-carbon materials promising as electrocatalysts in low-temperature fuel cells was 2 nm for Pt/C (for about 20 wt % Pt) and 1.8 nm for 2.8 nd % Pt2Ni.
Abstract: Nanostructured Pt/C and Pt
x
Ni/C materials containing from 4 to 30 wt % Pt were prepared using the method of chemical reduction of platinum and nickel compounds in the liquid phase by sodium borohydride solution. The change in the nature of the organic component (ethylene glycol, dimethyl sulfoxide, dimethyl formamide, tetrahydrofuran, acetone, ethyl alcohol, and glycerin) of binary water-organic solvent influences considerably the reaction product yield, structural characteristics (average nanoparticle size) of the material, mass fraction of metals in the nanocomposite, and the PtNi alloy composition. The fundamental possibility of controlling the PtNi alloy composition and structural characteristics of Pt/C and Pt
x
-Ni/C nanocomposites by variation of the water-organic solvent composition was demonstrated. The minimum average size of nanoparticles in synthesized metal-carbon materials promising as electrocatalysts in low-temperature fuel cells was 2 nm for Pt/C (for about 20 wt % Pt) and 1.8 nm for Pt2Ni (for about 30 wt % Pt).
TL;DR: In this article, a model is proposed in which aligned zinc oxide nanorod arrays may grow by the vapor-liquid-solid (VLS) mechanism, and liquid zinc nanodroplets forming on the substrate surface at the beginning of the process catalyze one-dimensional growth.
Abstract: We systematize experimental data on the elemental vapor-phase synthesis of zinc oxide nanocrystal arrays on substrates. This process may yield nanostructures differing in shape and dimensions, in particular, well-aligned ZnO nanorod arrays. A model is proposed in which aligned zinc oxide nanorod arrays may grow by the vapor-liquid-solid (VLS) mechanism, and liquid zinc nanodroplets forming on the substrate surface at the beginning of the process catalyze one-dimensional growth. The VLS process is accompanied by zinc oxide deposition onto the lateral surface of the nanorods from the vapor phase. The relative rates of these processes influence the shape of the nanorods and the thickness of the polycrystalline underlayer. Optimizing the deposition conditions, one can grow uniform arrays of aligned high-quality ZnO nanorods with no catalysts and with no special substrate preparation steps.
TL;DR: In this paper, a composite with hardness over 55 GPa was obtained by cobalt infiltration into a nanodiamond at a pressure of 8 GPa, where graphitization of a diamond in pores was found to precede cobalt penetration into them.
Abstract: A composite with hardness over 55 GPa is obtained by cobalt infiltration into a nanodiamond at a pressure of 8 GPa. Graphitization of a nanodiamond in pores is found to precede cobalt infiltration into them. In the presence of cobalt, graphite-like carbon is inversely transformed into diamond with a slight time delay and the nanodiamond recrystallizes, a polycrystal diamond frame being formed. The minimum cobalt concentration in compacts required for nanodiamond sintering using the infiltration technique is 6 vol %.
TL;DR: In this paper, the authors discuss the reasons for the limited visible and near-IR transmittance of polycrystalline zinc sulfide produced by chemical vapor deposition (CVD).
Abstract: We discuss the reasons for the limited visible and near-IR transmittance of polycrystalline zinc sulfide produced by chemical vapor deposition (CVD). Comparison of measured scattering indicatrices, depolarization ratios, and transmission spectra in the range 0.4–4 m with theoretical predictions leads us to conclude that a significant contribution to optical losses in CVD ZnS comes from light scattering by faceted submicron inclusions with a refractive index of 1 (pores). Assuming that these defects play a key role in determining the optical loss in the material, we have estimated the pore concentration and pore size distribution in CVD ZnS before and after hot isostatic pressing.
TL;DR: In this paper, the effect of WC particle size (20 to 150 nm) on the optimal sintering temperature of the WC-8 wt % Co alloy and its phase composition, density, and microhardness was studied.
Abstract: Using X-ray diffraction, scanning electron microscopy, and density measurements, we have studied the effect of WC particle size (20 to 150 nm) on the optimal sintering temperature of the WC-8 wt % Co alloy and the effect of sintering temperature (800–1600°C) on its phase composition, density, and microhardness. The results indicate that, during sintering of the starting powder mixture, the first to form is the ternary carbide phase Co6W6C. At sintering temperatures of 1100°C and above, this phase reacts with carbon to form Co3W3C. Sintering above 1000°C leads to the formation of a cubic solid solution of tungsten carbide in cobalt, β-Co〈WC〉, along with the ternary carbide phases. The density and microhardness of the alloy have been measured as functions of sintering temperature. The use of WC nanopowder has been shown to reduce the optimal sintering temperature of the WC-Co alloy by about 100°C.
TL;DR: In this paper, a low-temperature process for the synthesis of the multiferroic compound BiFeO3 was proposed, which enables the preparation of nanoparticulate material at temperatures as low as 200-250°C.
Abstract: A novel, low-temperature process is proposed for the synthesis of the multiferroic compound BiFeO3. It enables the preparation of nanoparticulate material at temperatures as low as 200–250°C. An important role in the low-temperature synthesis of bismuth orthoferrite is played by ammonium nitrate additions and excess bismuth oxide.
TL;DR: A process for the synthesis of nanocrystalline VMg(OH)x and VOx · MgO with specific surface areas of up to 1200 and 470 m2/g, respectively, was proposed in this paper.
Abstract: A process is proposed for the synthesis of nanocrystalline VMg(OH)x and VOx · MgO with specific surface areas of up to 1200 and 470 m2/g, respectively. The synthesized VOx · MgO oxides consist of nanocrystals (2′–5 nm), which form platelike agglomerates. As distinct from conventional impregnation of magnesium oxide, the aerogel process for VOx · MgO synthesis ensures a uniform vanadium distribution in MgO.
TL;DR: In this article, the compaction and sintering behaviors of various powder mixtures and the properties of the resultant fine-grained, dense, high-strength ceramics have been obtained with a microhardness of up to 16-18 GPa.
Abstract: Fine-grained (on the order of several microns in grain size) ceramics have been produced from various nano- and submicron-sized powders (silica, alumina, titania, aluminum nitride, and tungsten carbide). The compaction and sintering behaviors of various powder mixtures and the properties of the resultant ceramics have been studied. For a number of compositions, fine-grained, dense, high-strength ceramics have been obtained with a microhardness of up to 16–18 GPa.
TL;DR: The boundaries of the V14O6 + VxOz two-phase region in the V-O system at temperatures from ≃ 1050 to ≃ 1650 K have been determined experimentally as discussed by the authors.
Abstract: The boundaries of the V14O6 + VxOz two-phase region in the V-O system at temperatures from ≃ 1050 to ≃ 1650 K have been determined experimentally. The V-O phase diagram has been refined in the range 25–50 at % oxygen using structural and microstructural data for vanadium oxides containing less than 50 at % oxygen in conjunction with earlier results. The possibility of ordering of cubic vanadium monoxide has been examined.