Inorganic Materials (v.54, #5)
Control over the Size Effect in the Spectroscopic Properties of Zn x Cd1 – x S Colloidal Quantum Dots by M. S. Smirnov; O. V. Ovchinnikov; Nassra Amir Razuki Hazal; A. I. Zvyagin (413-420).
Approaches are developed for controlling the size effect in the absorption and photoluminescence properties of colloidal CdS and Zn0.5Cd0.5S quantum dots (QDs) in a gelatin matrix and thioglycolic acid. We analyze spectroscopic manifestations of dark Ostwald ripening and size-selective photoetching and demonstrate that the illumination of molten colloidal CdS and Zn0.5Cd0.5S QD solutions at a wavelength lying at the optical absorption edge in the presence of hydrogen peroxide as a catalyst for photoetching leads to a blue shift of the optical absorption and photoluminescence spectra of the QDs. Analysis of TEM images of QD samples leads us to conclude that photoetching reduces the average QD size as a consequence of the photodissolution of the CdS and Zn0.5Cd0.5S compounds. We demonstrate that, by contrast, heat treatment of the synthesized CdS and Zn0.5Cd0.5S QD sols at a temperature between 75 and 90°C leads to an increase in nanocrystal size through recrystallization, which shows up as a redshift of the optical absorption and photoluminescence spectra of the corresponding samples.
Keywords: photoetching; recombination luminescence
Interaction of Hydrogen Atoms with Grain Boundaries in Palladium Bicrystals by V. M. Ievlev; A. S. Prizhimov; A. V. Boldyreva (421-425).
Hydrogen diffusion in palladium bicrystals containing a small-angle twist or tilt boundary or a large-angle boundary similar to a special boundary is investigated using molecular dynamics simulation. We assess the effect of grain boundaries on the hydrogen diffusion process. The types of grain boundaries considered here are shown to differ in their absorption activity for hydrogen. The temporal grain-boundary segregation of hydrogen atoms can be accounted for in terms of their coordination, which differs significantly from that in the grain bulk.
Keywords: molecular dynamics; hydrogen diffusion; grain boundaries
Effect of the Surface Modification of Synthetic Diamond with Nickel or Tungsten on the Properties of Copper–Diamond Composites by A. V. Ukhina; D. V. Dudina; D. A. Samoshkin; E. N. Galashov; I. N. Skovorodin; B. B. Bokhonov (426-433).
Tungsten- and nickel-containing coatings have been produced on the surface of synthetic diamond crystals by rotary chemical vapor deposition (RCVD) using tungsten hexacarbonyl, W(CO)6, and nickelocene, Ni(C5H5)2, as gaseous precursors. The thickness, composition, and morphology of the coatings have been shown to depend on the RCVD process duration and reactant concentrations in the vapor phase. The synthetic diamond microcrystals with tungsten- and nickel-containing coatings have been used to produce copper–diamond heat-conducting composites. Powder mixtures containing 50 vol % diamond with a particle size of 50, 100, or 200 μm have been consolidated by spark plasma sintering or hot pressing. It has been shown that the highest relative density (97%) and thermal conductivity (340 W/(m K)) are offered by the composites produced by spark plasma sintering using tungsten carbide-coated 50-μm diamond crystals.
Keywords: copper–diamond composites; chemical vapor deposition; thermal conductivity
Effect of Oxygen Impurities on the Phase Composition of Self-Propagating High-Temperature Synthesis Products in the α-Si3N4–MgO System by V. V. Zakorzhevskii; V. E. Loryan (434-436).
It has been shown that raising the oxygen impurity concentration in starting-mixture components from 0.5 to 2.7 wt % reduces the content of the α-phase form 98 to 83 wt % at synthesis temperatures between 1400 and 1550°C. The role of magnesium oxide as a catalyst of the α → β phase transition becomes more important as the oxygen impurity concentration rises to 2.5 wt % and above. The use of starting-mixture components containing less than 0.3–0.6 wt % oxygen impurities has enabled the synthesis of Si3N4–MgO composites containing up to 95 wt % α-Si3N4 at temperatures in the range 1600–1700°C.
Keywords: silicon nitride; composite powder; oxygen impurities; α-phase; phase transition
Structure, Composition, and Properties of Arc PVD Mo–Si–Al–Ti–Ni–N Coatings by I. V. Blinkov; A. O. Volkhonskii; A. V. Chernogor; V. S. Sergevnin; D. S. Belov; A. M. Polyanskii (437-445).
Using an arc physical vapor deposition process, we have produced nanostructured Mo–Si–Al–Ti–Ni–N coatings with a multilayer architecture formed by Mo2N, AlN–Si3N4, and TiN–Ni and a crystallite size on the order of 6–10 nm. We have studied the physicomechanical properties of the coatings and their functional characteristics: wear resistance, adhesion to their substrates, and heat resistance. According to high-temperature (550°C) wear testing and air oxidation (600°C) results, the coatings studied here are wearand heat-resistant under appropriate temperature conditions. Their properties are compared to those of Mo–Si–Al–N coatings.
Keywords: arc PVD Mo–Si–Al–Ti–Ni–N coatings; phase formation; structure of coatings; hardness; wear resistance; heat resistance; adhesion to substrates
Radiation-Induced Effects in Ce3+- and Eu2+-Doped Al5O6N by V. V. Yagodin; A. V. Ishchenko; M. N. Sarychev; G. F. Babailova; N. S. Akhmadullina; A. S. Lysenkov; Yu. F. Kargin; B. V. Shul’gin (446-453).
Polycrystalline Al5O6N samples have been prepared by sol–gel synthesis followed by carbothermal reduction and nitridation. X-ray luminescence (XRL) spectra and thermoluminescence (TL) curves of Ce3+- and Eu2+-doped aluminum oxynitride have been measured in the temperature range 5–380 K and analyzed. Working TL peaks have been detected in the range 150–250 K for the Al5O6N:Ce3+ sample and in the range 140–200 K for the Al5O6N:Eu2+ samples. There are also lower temperature peaks: in the ranges 10–60 and 20–100 K. The XRL spectra of the samples have been measured at temperatures of 8 (for the first time) and 300 K.
Keywords: X-ray luminescence; thermoluminescence
Phase Formation in Al2O3–ZrO2–CeO2 Nanopowders Modified with Calcium Cations by L. I. Podzorova; A. A. Il’icheva; O. I. Pen’kova; V. P. Sirotinkin; O. S. Antonova; A. A. Konovalov (454-459).
We have studied phase formation in calcium-modified Al2O3–ZrO2–CeO2 nanopowders during sol–gel synthesis. The results demonstrate that heat treatment of the nanopowders first leads to the formation of a zirconium dioxide-based solid solution stabilized with cerium cations. Raising the heat treatment temperature helps the crystallization of corundum, a stable phase of aluminum oxide, to reach completion. In the temperature range 1400–1550°C, we observe the formation of a second aluminum-containing phase: calcium cerium hexaaluminate consisting of long prismatic grains.
Keywords: ceramic composites; aluminum oxide; zirconium dioxide; nanopowders; phase composition
Luminescence Properties of Eu3+-Doped K1 – x Mg1 – x Sc(Lu)1 + x (MoO4)3 (0 ≤ x ≤ 0.5) Solid Solutions by N. M. Kozhevnikova; S. Yu. Batueva; R. M. Gadirov (460-465).
K1 – x Mg1 – x Sc(Lu)1 + x (MoO4)3 (0 ≤ x ≤ 0.5) solid solutions have been prepared by solid-state reactions. The synthesized phases of variable composition have been characterized by X-ray diffraction and differential thermal analysis, and their luminescence excitation and luminescence spectra have been obtained. We have measured their spectroscopic and luminescent characteristics (luminescence excitation spectra, short- and long-lived photoluminescence spectra, and long-lived emission lifetime).
Keywords: NASICON structure; solid-state synthesis; cation substitution; red phosphor
Structure–Composition Relationship of Platelike Ferrospheres in Calcium-Rich Power Plant Ash by N. N. Anshits; M. A. Fedorchak; O. M. Sharonova; N. P. Kirik; N. N. Shishkina; A. M. Zhizhaev; A. G. Anshits (466-472).
The structure–composition relationship for polished sections of individual platelike ferrospheres in the–0.04 + 0.032 mm size fraction isolated from fly ash from the combustion of brown coal has been studied systematically by scanning electron microscopy and energy dispersive X-ray spectroscopy. We have identified groups of globules whose overall composition, as well as the composition of local areas on their polished sections, can be represented by general equations for component concentrations: CaO = f(FeO) and SiO2 = f(FeO). Analysis of the structure–composition relationship for the globules leads us to conclude that their structure is determined by transformations that occur in the CaO–Fe x O y system in response to an increase in its oxidation potential. It has been shown that the platelike globules containing 68–73 wt % FeO are made up of Ca2Fe2O5 and CaFe2O4 crystallites resulting from the oxidative transformation of Fe, Ca, and Mg complex humates in the parent brown coal. The ferrospheres containing 79–90 wt % FeO have a fragmentary core–shell structure, where the platelike shell consists of Ca2Fe2O5 and CaFe2O4 crystallites, and the core consists of Fe2O3 and a Ca-, Mg-, and Al-promoted magnetite. Precursors for the formation of this type of globule are pyrite associates with complex humates. It has also been demonstrated that the low concentration of aluminum and silicon oxides in the composition of the globules and the viscosity of their melt have no effect on the structure of the platelike ferrospheres.
Keywords: ferrospheres with a platelike structure; formation paths
Low-Temperature Combustion Synthesis and Properties of CoFe2O4 and CoGa x Fe2 – x O4 (x = 0.05, 0.10) Nanoparticles by Sh. M. Qasanli; A. Q. Quseinova; M. R. Allazov (473-477).
CoFe2O4 and CoGa x Fe2 – x O4 (x = 0.05, 0.10) nanopowders have been synthesized via low-temperature combustion using cobalt, gallium, and iron complexes of malonic acid dihydrazide as precursors. Presynthesized precursors have been shown to decompose at temperatures as low as 250–300°C to form mineral residues with an amorphous structure after the combustion of the organic component. Heat treatment above 700°C leads to an onset of crystallization. The formation of the spinel structure reaches completion at 1200°C. The average particle size of the CoFe2O4, CoGa0.05Fe1.95O4, and CoGa0.1Fe1.9O4 powders has been determined to be 476, 435, and 317 nm, respectively. The electrical resistance and dielectric permittivity of the samples have been measured as functions of annealing temperature.
Keywords: low-temperature combustion; spinel ferrites; electrical resistance
Development of a Model for the Formation of Materials with a Hierarchical Pore Structure Produced under Sol–Gel Processing Conditions by I. E. Kononova; P. V. Kononov; V. A. Moshnikov (478-489).
We have developed a model for the formation of silica-containing synthetic functional materials with a hierarchical pore structure and a large specific surface area under self-assembly conditions of sol–gel processes. The model includes the formation of a three-dimensional core (of a cristobalite type) of sol particles consisting of joined polymorphoids in the form of n-membered rings and a continuous transition between fractal aggregate growth mechanisms, from diffusion-limited to cluster–cluster aggregation, followed by evolution culminating in spinodal decomposition. Hierarchical structures have been studied using three-dimensional simulation with Autodesk 3ds Max software.
Keywords: hierarchical porous materials; sol–gel processing
An Effective Approach to the Synthesis of Nanocrystalline PbMoO4 in Na2Mo4O13–PbCO3 Melts by G. K. Shurdumov; Z. A. Cherkesov; E. F. Kandurova (490-496).
This paper presents thermodynamic analysis of reactions of sodium tetramolybdate with Pb3O4, PbO2, PbO, and lead carbonate and describes an effective approach to PbMoO4 synthesis in melts of the Na2Mo4O13–PbCO3 system, which offers a low synthesis temperature, waste-free character of the process, high rate, and high yield of a reagent-grade synthesis product in a nanocrystalline state. The synthesis product has been identified by chemical analysis, X-ray diffraction, and particle size measurements.
Keywords: sodium tetramolybdate; lead carbonate; thermodynamics; synthesis; lead molybdate; identification
Calculation of Distillation Refining of a Substance Containing Low and Highly Volatile Impurities by A. I. Kravchenko (497-499).
This paper considers the distillation refining of a material containing highly volatile and low-volatile impurities and demonstrates the possibility of evaluating the fraction of residue, g r, during the removal of the highly volatile impurity and the degree of subsequent distillation, g c, necessary for achieving a predetermined decrease in impurity concentrations at a predetermined product yield and known separation factors. Examples are presented for the distillation in real host–impurity systems: Ga–(Pb,Al), Be–(Al,Fe), and Cr–(Si,Fe).
Keywords: distillation; degree of distillation
Resorption of Ca3 – x M2x (PO4)2 (M = Na, K) Calcium Phosphate Bioceramics in Model Solutions by N. K. Orlov; V. I. Putlayev; P. V. Evdokimov; T. V. Safronova; E. S. Klimashina; P. A. Milkin (500-508).
The resorbability of bioceramics in the Ca3(PO4)2–CaNaPO4–CaKPO4 system is evaluated in an approach involving thermodynamic assessment of solubility and investigation of the dissolution kinetics in model media, in particular in citric acid solutions. Thermodynamic calculation indicates high solubility of the Ca5Na2(PO4)4, α-CaМPO4, β-CaKPO4, and β-СаK0.6Na0.4PO4 phases. Investigation of the dissolution kinetics of ceramics has made it possible to identify two distinct types of behavior of resorbable materials in weakly acidic solutions: with fast resorption kinetics in the case of the phases based on nagelschmidtite solid solutions and α-CaМPO4 disordered high-temperature solid solutions, and with a nearly constant, relatively low dissolution rate and a high solubility limit in the case of β-СaK1 – x Na x -based phases.
Keywords: bioceramics; calcium sodium potassium mixed-cation phosphates; resorption; solubility; lattice energy; hydration; ionic equilibria; dissolution kinetics
Synthesis and Properties of Ceramics Based on a Layered Bismuth Calcium Cobaltite by A. I. Klyndyuk; N. S. Krasutskaya; A. A. Khort (509-514).
Bi2Ca2Co x O y (x = 0.5, 1.7, 2.8) ceramics have been prepared by solid-state reactions and their thermophysical, electrical-transport, and thermoelectric (functional) properties have been studied. The results demonstrate that increasing the cobalt oxide concentration in the ceramics leads to an increase in their thermal conductivity, electrical conductivity, and thermal diffusivity and a reduction in their apparent density. The largest Seebeck coefficient is offered by a single-phase ceramic with the composition Bi2Ca2Co1.7Oy, which in addition has the highest power factor (P 300 = 26.0 μW/(m K2)) and thermoelectric figure of merit (ZT 1000 = 0.019) and the smallest linear thermal expansion coefficient (α = 9.72 × 10–6 K–1).
Keywords: oxide thermoelectrics; layered bismuth calcium cobaltite; thermal expansion; thermal conductivity; electrical conductivity
Extraction Separation of Rare Earth Elements of the Medium Group with Isomolar Mixtures of Aliquat®336–TBP and Cyanex ®572–TBP from Nitric Solutions by S. S. Shulin; G. N. Galieva; S. V. Chighevskaya; J. V. Pletuhina; N. S. Saveliev (515-519).
The results of extraction separation of the medium group of rare earth elements in the composition of the concentrate of JSC SMF with isomolar mixtures of Aliquat®336–TBP and Cyanex®572–TBP from nitric solutions are discussed. The influence of acidity of an aqueous solution on separation factors of representative pairs of REE and on the value of the capacity of mixtures of extractants is studied. The possibility of extraction separation on the lines of Sm–Gd and Eu–Gd (Aliquat®336–TBP) and on the line of Eu–Sm (Cyanex®572–TBP) is shown.
Keywords: medium group of REE; separation; nitric solution; isomolar mixture of extractants