Preparation of magnetic composites through SrO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glass crystallization

Glasses with nominal compositions 11SrO · 5.5Fe₂O₃ · 4.5Al₂O₃ · 4B₂O₃ (1) and 15SrO · 5.5Fe₂O₃ · 4.5Al₂O₃ · 4B₂O₃ (2) were prepared by rapidly quenching oxide melts between counterrotating steel rollers. The glasses were then heat-treated in the range 650–950°C to produce glass-ceramic samples. The samples were characterized by X-ray diffraction, electron microscopy, and magnetic measurements. The phase composition of the glass-ceramics was determined, and their microstructure and magnetic properties were studied. The annealing temperature was shown to have a strong effect on the coercivity of the materials, which reaches 650 and 570 kA/m for compositions 1 and 2, respectively.     

Formation and structural phase transitions of mesoporous Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and TiO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> xerogels under hydrothermal conditions

We have studied the effect of the hydrothermal synthesis temperature on Al₂O₃ structure formation and examined the role of the phase composition of the precursor gel and surfactant in the formation of the pore structure of Al₂O₃. A technique has been proposed for the synthesis of TiO₂/Al₂O₃ binary xerogels, and the effect of TiO₂ content on the pore structure parameters and adsorption properties of TiO₂/Al₂O₃ has been investigated.     

Synthesis of WO<Subscript>3</Subscript>/mesoporous ZrO<Subscript>2</Subscript> catalyst as a high-efficiency catalyst for catalytic oxidation of dibenzothiophene in diesel

The catalyst of WO₃ highly dispersed on mesoporous ZrO₂ was prepared by hydrothermal treatment and calcination. Ionic liquid templates with different cations and various calcination temperatures were taken into account to investigate factors that affect the structure of the catalysts. Wide-angle XRD, Raman, low-angle XRD, N₂ adsorption–desorption, SEM, EDS-mapping and TEM analyses were employed to characterize the composition, morphology and the dispersion of WO₃. It was found that [C₁₆H₃₃N(CH₃)₃]₄SiW₁₂O₄₀ and 700 °C were the optimal ionic liquid template and calcination temperature; the obtained catalyst, expressed as 700-C₁₆-WO₃/ZrO₂, exhibited the best catalytic activity in oxidation desulfurization. Dibenzothiophene (DBT) in the model oil could be oxidized to DBT sulfone (DBTO₂) completely, certified by GC-MS analysis, under optimum conditions. The oxidative desulfurization efficiencies of different substrates catalyze by 700-C₁₆-WO₃/ZrO₂, and the cycle performance on the oxidation of DBT were studied.     

Electrical conductivity of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-Tm<Subscript>2</Subscript>O<Subscript>3</Subscript>-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> solid solutions

New solid solutions, Bi_2?x?y Tm _x Nb _y O_3+δ, with tetragonal and cubic structures have been synthesized in the Bi₂O₃-Tm₂O₃-Nb₂O₅ system, and their electrical conductivity has been measured at temperatures from 670 to 1020 K. The 1020-K conductivity of the tetragonal solid solution Bi_1.8Tm_0.15Nb_0.05O_3+δ is comparable to that of Bi_1.75Tm_0.25O₃, the best conductor in the Bi₂O₃-Tm₂O₃ system.     

Combustion synthesis of Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles

Nanophase of Ga₂O₃ has potentially important applications in photocatalysis. We report the synthesis of nanophase of the metastable γ- and stable β-Ga₂O₃ and demonstrate that it is possible to prepare a continuously varying mixture starting from the pure metastable γ- to the pure β-phase. This is achieved by employing a facile and reliable combustion route, using urea as a fuel. Typical grain sizes, as estimated from XRD studies, are about 3 nm. Given the importance of surface chemistry for potential applications, thermogravimetric coupled with mass spectrometry is used in conjunction with FTIR to elucidate the chemistry of the adsorbed surface layer. Studies on the γ-Ga₂O₃ phase indicate the occurrence of weight loss of 8.1% in multiple steps. Evolved gas analysis and FTIR studies show presence of physisorbed H₂O molecules and chemisorbed –(OH) ions bonded to active surface states and accounts predominantly for the observed weight loss.     

Effect of Eu<Subscript>2</Subscript>O<Subscript>3</Subscript> doping on the crystallization behavior of BaO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

We gave studied the crystallization behavior of 30BaO · 25Bi₂O₃ · 45B₂O₃ glasses doped with Eu₂O₃ to different levels. At a Eu₂O₃ content of 7 mol % or higher, the glasses undergo volume crystallization. The only precipitating phase is a solid solution between europium and bismuth oxides. With increasing europium concentration in the glass, the structure of the crystallites changes from cubic to rhombohedral. We have investigated the morphology, physicochemical properties, and luminescence spectra of the glasses and glass-ceramics.     

Thermal Expansion of Ni<Subscript>3</Subscript>S<Subscript>2</Subscript> in Ni<Subscript>3</Subscript>S<Subscript>2</Subscript>-Ni Alloys

The thermal expansion of nickel sulfide in Ni₃S₂-Ni alloys (a sample synthesized in this work and a commercial Ni₃S₂-Ni-Cu₉S₅ converter matte) is measured using high-temperature x-ray diffraction. The best fit equations are derived for the temperature-dependent (≤980 K) parameters of the rhombohedral (hexagonal) and cubic cells of nickel sulfide, and the thermal expansion coefficients of Ni₃S₂ are determined. The results demonstrate that the thermal expansion of Ni₃S₂ is influenced by impurity phases: Ni metal and Cu₉S₅. The chemical strain arising from the dissolution of the copper sulfide in Ni₃S₂ cancels out the shear strain near the polymorphic transformation.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 8, 2005, pp. 1005–1010.Original Russian Text Copyright ¢ 2005 by Vershinin, Selivanov, Gulyaeva, Sel’menskikh.     

Facile synthesis and electrochemical properties of layered Li[Ni<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>]O<Subscript>2</Subscript> as cathode materials for lithium-ion batteries

A layered oxide Li[Ni_1/3Mn_1/3Co_1/3]O₂ was synthesized by an oxalate co-precipitation method. The morphology, structural and composition of the as-papered samples synthesized at different calcination temperatures were investigated. The results indicate that calcination temperature of the sample at 850°C can improve the integrity of structural significantly. The effect of calcination temperature varying from 750°C to 950°C on the electrochemical performance of Li[Ni_1/3Mn_1/3Co_1/3]O₂, cathode material of lithiumion batteries, has been investigated. The results show that Li[Ni_1/3Mn_1/3Co_1/3]O₂ calcined at 850°C possesses a higher capacity retention and better rate capability than other samples. The reversible capacity is up to 178.6 mA?h?g^-1, and the discharge capacity still remains 176.3 mA?h?g^-1 after 30 cycles. Moreover, our strategy provides a simple and highly versatile route in fabricating cathode materials for lithium-ion batteries.     

Composites of mesoporous Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Fe- or Co-containing nanoparticles

Composites of mesoporous alumina and Fe- or Co-containing ferromagnetic nanoparticles have been prepared from appropriate aqueous metal chloride solutions by a sol-gel process. The synthesis products were heat-treated at different temperatures in air or vacuum and then characterized by a variety of techniques. The results indicate that the mesoporous structure of the nanostructured composites has a large specific surface area, a narrow, unior bimodal pore size distribution, and high thermal stability. The phase composition of the magnetic particles in the X-ray amorphous oxide matrix strongly depends on the heat-treatment conditions.     

Direct synthesis of mesoporous Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> through citric acid-assisted solid thermal decomposition

A simple and inexpensive approach to synthesizing mesoporous Fe₃O₄ is developed by using citric acid-assisted solid thermal decomposition of ferric nitrate. The structure and magnetic property of mesoporous Fe₃O₄ were characterized by XRD, FT–IR, N₂ adsorption–desorption isotherms, TEM, and vibrating sample magnetometer. It was shown that the decomposition of citric acid results in the formation of the mesoporous structure and narrow pore-size distribution. The reducing atmosphere which created by the decomposition of the ferric nitrate–citric acid complex caused the partial reduction of Fe(III) to Fe(II) and in turn the formation of Fe₃O₄. Moreover, the strength of the coordination between carboxyl group and Fe³⁺ also affected the phase composition of the iron oxides.     

Luminescence of europium-doped BaO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

We have prepared europium-doped BaO-Bi2O₃-B2O₃ glasses and investigated the doping effect on the main physicochemical properties and local structure of the glasses. Using Judd-Ofelt analysis, we calculated intensity parameters (Ω₂, Ω₄, and Ω₆), spontaneous emission probabilities, the radiative lifetime, luminescence branching factors, the quantum yield of luminescence, and the stimulated emission cross sections for ⁵ D ₀ → ⁷ F _J transitions.     

An improvised method for the synthesis of ZnAl<Subscript>2</Subscript>O<Subscript>4</Subscript>/ZnO nanocomposite and its use as a photocatalyst

Nanocomposite material ZnAl₂O₄/ZnO was prepared via layered double hydroxides co-precipitation method in the presence of triblock copolymer, Pluronic F127 as the template with different concentrations at pH 7. The material was characterized by XRD, N₂ adsorption/desorption, UV–Vis diffused reflectance, TGA–DTA and SEM. XRD and SEM results reveal that ZnAl₂O₄/ZnO was highly ordered nanocrystalline material. N₂ adsorption/desorption studies indicate that the pore size and pore volume increased significantly with the increase in concentration of F127 copolymer template, while the surface area is slightly decreased with increase of F127 template. TGA–DTA results reveal that the thermal stability of material increased after adding F127 template. The material was tested for its photocatalytic activity for a solution containing methyl orange dye and the 95.6% decolorization was achieved within 1 h. The intensive absorption light observed by UV–Vis reflectance of the catalyst confirmed high activity of the catalyst and suggest the probable photocatalytic degradation mechanism.     

In<Subscript>2</Subscript>O<Subscript>3</Subscript>-decorated ordered mesoporous NiO for enhanced NO<Subscript>2</Subscript> sensing at room temperature

In this work, ordered mesoporous structures of In₂O₃-decorated NiO were prepared by a two-step process, comprising of the synthesis of ordered mesoporous NiO followed by injection of In³⁺ into their pores. The pore size distribution of the as prepared samples was between 4.1 and 21.1 nm. Furthermore, their sensing performances toward NO₂ were tested systematically. The results showed the highest response about 3 towards 15 ppm NO₂ sensing at room temperature for 5.0 at.% In₂O₃-decorated NiO compared to other decorated and pure samples. Moreover, the sensor displayed excellent selectivity towards NO₂ in the presence of other interfering gases, such as carbon monoxide, ammonia, ethanol, methanol, formaldehyde, toluene, acetone. The exceptional NO₂ sensing performance of the In₂O₃-decorated mesoporous NiO may be attributed to their high specific surface area and the formation of p–n junction with modified carrier concentration caused by In³⁺ doping. This method can act as an effective strategy for enhancement of gas-sensing properties of pure metal oxides.     

Fabrication of Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite nanofibers by electrospinning

PVA(Polyvinyl alcohol)/chromium nitrate/aluminum nitrate composite nanofibers were prepared by using sol–gel processing and electrospinning technique. By high temperature calcinating the above precursor fibers, Cr₂O₃/Al₂O₃ composite nanofibers were successfully obtained. The fibers were characterized by XRD, IR, and SEM, respectively. The results showed that the crystalline phase and the morphology of the fibers depended on the calcination temperatures.     

Y<Subscript>2</Subscript>O<Subscript>3</Subscript> and Nd<Subscript>2</Subscript>O<Subscript>3</Subscript> co-stabilized ZrO<Subscript>2</Subscript>-WC composites

Y₂O₃ + Nd₂O₃ co-stabilized ZrO₂-based composites with 40 vol% WC were fully densified by pulsed electric current sintering (PECS) at 1350 °C and 1450 °C. The influence of the PECS temperature and Nd₂O₃ co-stabilizer content on the densification, hardness, fracture toughness and bending strength of the composites was investigated. The best combination of properties was obtained for a 1 mol% Y₂O₃ and 0.75 mol% Nd₂O₃ co-stabilized composite densified for 2 min at 1450 °C under a pressure of 62 MPa, resulting in a hardness of 15.5 ± 0.2 GPa, an excellent toughness of 9.6 ± 0.4 MPa.m^0.5 and an impressive 3-point bending strength of 2.04 ± 0.08 GPa. The hydrothermal stability of the 1 mol% Y₂O₃ + 1 mol% Nd₂O₃ co-stabilized ZrO₂-WC (60/40) composites was compared with that of the equivalent 2 mol% Y₂O₃ stabilized ceramic. The double stabilized composite did not degrade in 1.5 MPa steam at 200 °C after 4000 min, whereas the yttria stabilized composite degraded after less than 2000 min. Moreover, the (1Y,1Nd) ZrO₂-WC composites have a substantially higher toughness (~9 MPa.m^0.5) than their 2Y stabilized equivalents (~7 MPa.m^0.5).     

Properties of nanocrystalline ZrO<Subscript>2</Subscript>-Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-CeO<Subscript>2</Subscript>-CoO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> powders

We have studied the properties of nanocrystalline ZrO₂-Y₂O₃-CeO₂-CoO-Al₂O₃ powders prepared via hydrothermal treatment of a mixture of coprecipitated hydroxides at 210°C. A number of general trends are identified in the variation of the properties of the synthesized powders during heat treatment at temperatures from 500 to 1200°C. Our results demonstrate that the addition of 0.3 mol % CoO to nanocrystalline ZrO₂-based powders containing 1 to 5 mol % Al₂O₃ allows one to obtain composites with good sinterability at a reduced temperature (1200°C).     

Temperature-stable and low loss Fe-containing dielectrics in BaO-Ln<Subscript>2</Subscript>O<Subscript>3</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> system

Polycrystalline samples of Ba₄Ln₂Fe₂Ta₈O₃₀ (Ln = La and Nd) were prepared by a high temperature solid-state reaction technique. The formation, structure, dielectric and ferroelectric properties of the compounds were studied. Both compounds are found to be paraelectrics with filled tetragonal tungsten bronze (TB) structure at room temperature. Dielectric measurements revealed that the present ceramics have exceptional temperature stability, a relatively small temperature coefficient of dielectric constant (τ _ε ) of −25 and −58 ppm/°C, with a high dielectric constant of 118 and 96 together with a low dielectric loss of 1.2 × 10⁻³ and 2.8 × 10⁻³ (at 1 MHz) for Ba₄La₂Fe₂Ta₈O₃₀ and Ba₄Nd₂Fe₂Ta₈O₃₀, respectively. The measured dielectric properties indicate that both materials are possible candidates for the fabrication of discrete multilayer capacitors in microelectronic technology.     

Facile synthesis of SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript> nanoparticles and its photocatalyst application

The strontium hexaferrite (SrFe₁₂O₁₉) nanoparticles have been successfully synthesized by co-precipitation route. The effect of various parameters such as calcination temperature and chelating agents were screened to achieve optimum condition. Different chelating agents such as amino acids (proline, alanine, aspartic acid) and surfactants (SDBS, PVP, and EDTA) were used. Compared with the amino acids, the surfactants increase the particle size and the best result was observed for alanine. The SrFe₁₂O₁₉ nanoparticles showed enhanced photocatalytic activity in the degradation of methyl orange under visible light irradiation (λ?>?400 nm). The degradation rates of the methyl orange were measured to be as high as 95% in 220 min. The nanoparticles were also characterized by several techniques including FT-IR, XRD, SEM, and VSM. The VSM measurement showed a saturation magnetization value (Ms) of 32 emu/g. The SEM images proposed that the particles are almost spherical with an average particle size of 90 nm.     

Effect of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> on the crystallization behavior of SiO<Subscript>2</Subscript>–MgO–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

A series of glass comprising of SiO₂–MgO–B₂O₃–Y₂O₃–Al₂O₃ in different mole ratio has been synthesized. The crystallization kinetics of these glasses was investigated using various characterization techniques such as differential thermal analysis (DTA), thermo gravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Crystallization behavior of these glasses was markedly influenced by the addition of Y₂O₃ instead of Al₂O₃. Addition of Y₂O₃ increases the transition temperature, T _g, crystallization temperature, T _c and stability of the glasses. Also, it suppresses the formation of cordierite phase, which is very prominent and detrimental in MgO-based glasses. The results are discussed on the basis of the structural and chemical role of Y³⁺ and Al³⁺ ions in the present glasses.     

Phase composition and microstructure of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> solid solutions prepared by self-propagating high-temperature synthesis

The combustion synthesis, microstructure, chemical composition, and phase composition of cast Al₂O₃-Cr₂O₃ materials are described. The synthesized solid solutions are based on corundum or chromia, depending on the Al₂O₃ and Cr₂O₃ contents. Using self-propagating high-temperature synthesis, a cast aluminum oxynitride is obtained for the first time.