Synthetic spinels of the system MgO-Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

Synthetic spinels of the system MgO-Cr₂O₃-Al₂O₃-Fe₂O₃ are considered and the desirability of organizing their production for the refractory industry is demonstrated. Translated from Novye Ogneupory, No. 6, pp. 32–35, June 2008.     

Optical Properties of CeO<Subscript>2</Subscript> Doped SiO<Subscript>2</Subscript>-Na<Subscript>2</Subscript>O-CaO-P<Subscript>2</Subscript>O<Subscript>5</Subscript> Glasses

Cerium oxide is one of the most important rare earth elements that is introduced into glass compositions due to its great effects on the optical properties. CeO₂ was introduced in Hench’s patented SiO₂-Na₂O-CaO-P₂O₅ glasses with different concentrations in order to study its effect on the optical behavior of this glass including optical band gap, transmittance, reflectance and refractive index and to give a complete view for the optical properties on cerium oxide-doped silicate glasses.     

Crystallization Behavior of Amorphous Zr<Subscript>55</Subscript>Cu<Subscript>20</Subscript>Ni<Subscript>10</Subscript>Al<Subscript>10</Subscript>Ti<Subscript>5</Subscript> Alloy

In the present study, the crystallization behavior and thermal stability of amorphous Zr₅₅Cu₂₀Ni₁₀Al₁₀Ti₅ alloy, obtained by melt-spinning, have been investigated using X-ray diffraction (XRD), differential thermal analysis (DTA) and transmission electron microscopy (TEM). The activation energy for crystallization has been evaluated by the Kissinger method, and it has been found that E _x obtained from the crystallization onset temperature (T _x) is lower than E _p determined by the crystallization peak temperature (T _P). During the continuous annealing process, ZrO and h-Al₃Zr₅ phases firstly precipitate from the amorphous matrix, then Zr₂Ni_0.66O_0.33 phase forms continuously and its relative content increases with increasing annealing temperature. However, no crystalline phases have been observed during the isothermal annealing process at 733 K (below T _x) for 90 min. The atomic clusters can keep the stability state through adjusting the short-range ordering.     

Electrical conductivity and structure of glasses in the Na<Subscript>2</Subscript>O-Na<Subscript>2</Subscript>S-P<Subscript>2</Subscript>O<Subscript>5</Subscript> and Na<Subscript>2</Subscript>S-P<Subscript>2</Subscript>S<Subscript>5</Subscript> systems

The glasses, in which oxygen was partially replaced with sulfur, have been synthesized in the Na₂O-P₂O₅-Na₂S system. The chemical and chromatographic analyses of the glasses synthesized have been performed. The temperature-concentration dependences of electrical conductivity of the glasses have been studied over a wide temperature range; the glass transition temperatures and the nature of charge carriers have been determined. The IR spectra and Raman spectra have been recorded at room temperature; the density and microhardness of the glasses and ultrasound velocity have been measured. A comparison of the electrical conductivities of the investigated glasses with those of the earlier studied glasses in the Na₂O-P₂O₅ system has shown their fair coincidence. The introduction of sodium sulfide into the Na₂O-P₂O₅ system is accompanied by an approximately threefold increase in electrical conductivity, although the concentrations of charge carriers (sodium ions) in the glasses amount to ∼17 and ∼26 mmol/cm³, respectively. The rise in electrical conductivity has been assumed to be caused by the increase in the degree of dissociation of polar structural chemical units including sulfide ions and by the higher mobility of sodium ions in the oxygen-free matrix.     

Phase equilibria in the Ho<Subscript>2</Subscript>O<Subscript>3</Subscript>-SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript> system

The phase formation is investigated and the phase diagram of the Ho₂O₃-SrAl₂O₄ system is constructed. A ternary compound, namely, Ho₂SrAl₂O₇, is revealed. It is established that this compound undergoes incongruent melting.     

Phase Equilibria in the Gd<Subscript>2</Subscript>O<Subscript>3</Subscript>-SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript> System

The phase equilibria are investigated and the phase diagram is constructed for the Gd₂O₃-SrAl₂O₄ pseudobinary join of the Gd₂O₃-SrO-Al₂O₃ ternary oxide system. One ternary compound, namely, Gd₂SrAl₂O₇, is revealed in the Gd₂O₃-SrAl₂O₄ join. It is found that this compound undergoes congruent melting.     

Structure and properties of glasses in the MgSO<Subscript>4</Subscript>-Na<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript>-KPO<Subscript>3</Subscript> system

A glass formation region has been established in the MgSO₄-Na₂B₄O₇-KPO₃ system. This region is located in the borate-phosphate part of the concentration triangle and occupies ∼40% of the triangle area. Based on the spectral data obtained (nuclear magnetic resonance, IR and Raman spectroscopy), a model is proposed in terms of which the physicochemical properties (such as the linear thermal expansion coefficient, the softening temperature, and the glass transition temperature) of the samples are discussed.     

Formation of La<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript> crystals from amorphous La<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> powders synthesized by the polymerized complex method

Amorphous La₂O-TiO₂ powders were synthesized by the polymerized complex (PC) method. The activation energies for crystallization and grain growth of La₂Ti₂O₇ from these precursors were determined from results of XRD and DTA and compared with those for La₂Ti₂O₇ precursors by the conventional solid-state reaction (SSR). Activation energy of grain growth of La₂Ti₂O₇ in PC-sample was determined to be 7.1 kJ/mol while that of SSR sample was 14.8 kJ/mol. The energy required for the phase transformation from amorphous PC sample to layered perovskite was 432 kJ/mol, while the SSR sample did not show this transition below 900‡C. It was clearly demonstrated that the La₂Ti₂O₇ crystals were formed at a lower temperature and they grew in size faster in the sample prepared by the PC method relative to the sample prepared by the SSR method. Mixing of elements in molecular level in PC preparation appeared responsible for these differences.     

Photoreduction of CO<Subscript>2</Subscript> into CH<Subscript>4</Subscript> using Bi<Subscript>2</Subscript>S<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> double-layered dense films

Nano-sized bismuth sulfide (Bi₂S₃) and titanium dioxide (TiO₂) with the orthorhombic and anatase tetragonal structures, respectively, were synthesized for application as catalysts for the reduction of carbon dioxide (CO₂) to methane (CH₄). Four double-layered dense films were fabricated with different coating sequences—TiO₂ (bottom layer)/Bi₂S₃ (top layer), Bi₂S₃/TiO₂, TiO₂/Bi₂S₃: TiO₂ (1 : 1) mix, and Bi₂S₃: TiO₂ (1 : 1) mix/Bi₂S₃: TiO₂ (1 : 1) mix—and applied to the photoreduction of CO₂ to CH₄; the catalytic activity of the fabricated films was compared to that of the pure TiO₂/TiO₂ and Bi₂S₃/Bi₂S₃ doubled-layered films. The TiO₂/Bi₂S₃ double-layered film exhibited superior photocatalytic behavior, and higher CH₄ production was obtained with the TiO₂/Bi₂S₃ double-layered film than with the other films. A model of the mechanism underlying the enhanced photoactivity of the TiO₂/Bi₂S₃ double-layered film was proposed, and it was attributed in effective charge separation.     

Electrochemical performance of La<Subscript>0.75</Subscript>Sr<Subscript>0.25</Subscript>Cr<Subscript>0.9</Subscript>M<Subscript>0.1</Subscript>O<Subscript>3</Subscript> perovskites as SOFC anodes in CO/CO<Subscript>2</Subscript> mixtures

The performance of La_0.75Sr_0.25Cr_0.9M_0.1O₃ (M = Mn, Fe, Co, and Ni) perovskitic materials as anodes was studied for a CO-fueled solid oxide fuel cell. The electrocatalytic performance and the tolerance to carbon deposition were investigated, while electrochemical characterization was carried out via AC impedance spectroscopy and cyclic voltammetry. The La_0.75Sr_0.25Cr_0.9Fe_0.1O₃ perovskite showed the best anode performance at temperatures above 900 °C; while at temperatures below 900 °C, the best performance was achieved with the La_0.75Sr_0.25Cr_0.9Co_0.1O₃ material. AC impedance spectroscopy was used for a semi-quantitative analysis of the LSC-M_0.1 anodes performance in view of total cell and charge transfer resistance. All anode materials exhibit high electronic conductivity and presumably do not substantially contribute to the overall cell resistance and concomitant ohmic losses.     

Investigation of a new lead-free Bi<Subscript>0.5</Subscript>(Na<Subscript>0.40</Subscript>K<Subscript>0.10</Subscript>)TiO<Subscript>3</Subscript>-(Ba<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>)TiO<Subscript>3</Subscript> piezoelectric ceramic

Lead-free piezoelectric compositions of the (1-x)Bi_0.5(Na_0.40K_0.10)TiO₃-x(Ba_0.7Sr_0.3)TiO₃ system (when x = 0, 0.05, 0.10, 0.15, and 0.20) were fabricated using a solid-state mixed oxide method and sintered between 1,050°C and 1,175°C for 2 h. The effect of (Ba_0.7Sr_0.3)TiO₃ [BST] content on phase, microstructure, and electrical properties was investigated. The optimum sintering temperature was 1,125°C at which all compositions had densities of at least 98% of their theoretical values. X-ray diffraction patterns that showed tetragonality were increased with the increasing BST. Scanning electron micrographs showed a slight reduction of grain size when BST was added. The addition of BST was also found to improve the dielectric and piezoelectric properties of the BNKT ceramic. A large room-temperature dielectric constant, ε _r (1,609), and piezoelectric coefficient, d ₃₃ (214 pC/N), were obtained at an optimal composition of x = 0.10.     

Electrical conductivity of CuI-AsI<Subscript>3</Subscript>-As<Subscript>2</Subscript>Se<Subscript>3</Subscript> and CuI-SbI<Subscript>3</Subscript>-As<Subscript>2</Subscript>Se<Subscript>3</Subscript> chalcogenide films prepared by chemical deposition

The electrical conductivity of chalcogenide semiconductor films in the CuI-AsI₃-As₂Se₃ and CuI-SbI₃-As₂Se₃ systems, which have been prepared by chemical deposition from mono-n-butylamine, has been studied as a function of the temperature and film composition. It has been established that the electrical conductivity of the CuI-AsI₃-As₂Se₃ and CuI-SbI₃-As₂Se₃ films is predominantly determined by the copper iodide content. It has been demonstrated that the electrical properties of the chalcogenide glasses and the related films are characterized by the same values to within the experimental error, which is explained by the same model of dissolution of vitreous semiconductors in amines with the retention of the electrical properties of chalcogenide glasses after the deposition of films from their solutions.     

Enhanced cyclic stability of CO<Subscript>2</Subscript> adsorption capacity of CaO-based sorbents using La<Subscript>2</Subscript>O<Subscript>3</Subscript> or Ca<Subscript>12</Subscript>Al<Subscript>14</Subscript>O<Subscript>33</Subscript> as additives

To improve the stability of CaO adsorption capacity for CO₂ capture during multiple carbonation/calcination cycles, modified CaO-based sorbents were synthesized by sol-gel-combustion-synthesis (SGCS) method and wet physical mixing method, respectively, to overcome the problem of loss-in-capacity of CaO-based sorbents. The cyclic CaO adsorption capacity of the sorbents as well as the effect of the addition of La₂O₃ or Ca₁₂Al₁₄O₃₃ was investigated in a fixed-bed reactor. The transient phase change and microstructure were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FSEM), respectively. The experimental results indicate that La₂O₃ played an active role in the carbonation/calcination reactions. When the sorbents were made by wet physical mixing method, CaO/Ca₁₂Al₁₄O₃₃ was much better than CaO/La₂O₃ in cyclic CO₂ capture performance. When the sorbents were made by SGCS method, the synthetic CaO/La₂O₃ sorbent provided the best performance of a carbonation conversion of up to 93% and an adsorption capacity of up to 0.58 g-CO₂/g-sorbent after 11 cycles.     

Structure and crystallization of ZnO-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Structure and crystalline behavior of the ternary system ZnO-B₂O₃-P₂O₅ glasses were investigated by means of X-ray diffraction (XRD) and infrared Raman spectra. The research showed that number of the planar [BO₃] units increases with the increase of B₂O₃ content. When the B₂O₃ content is above ≥10 mol %, the relative content of planar [BO₃] units increases rapidly and causes weakening of the glass structure and decrease in the chemical stability. In the crystallized glasses the predominant crystal phase Zn₂P₂O₇ decreases with the increase of B₂O₃ content, while the crystal phase BPO₄ increases with it, which cause the declining of chemical stability and the decrease of thermal coefficients of expansion.     

Mechanism of formation of the complex oxide Na<Subscript>2</Subscript>Nd<Subscript>2</Subscript>Ti<Subscript>3</Subscript>O<Subscript>10</Subscript>

The processes of phase formation in the Nd₂O₃-TiO₂-Na₂CO₃ system have been investigated in the temperature range 500–1100°C. The mechanism of the high-temperature solid-phase reaction of formation of the complex oxide Na₂Nd₂Ti₃O₁₀ has been studied. It has been established that the Na₂Nd₂Ti₃O₁₀ compound is formed from the intermediate product Na_0.5Nd_0.5TiO₃ with a perovskite structure in the temperature range 830–890°C and from the NaNdTiO₄ oxide with a perovskite-like layered structure in the temperature range 960–1100°C.     

Atomic Structure of the Amorphous Metallic Alloy Al<Subscript>83.5</Subscript>Ni<Subscript>9.5</Subscript>Si<Subscript>1.4</Subscript>La<Subscript>5.6</Subscript>

The atomic structure of the amorphous metallic alloy Al_83.5Ni_9.5Si_1.4La_5.6 is investigated based on the analysis of the experimental atomic radial distribution function (ARDF) in the fragmentary model. A comparative analysis of the most probable interatomic distances in the alloy and possible compounds based on it has demonstrated the presence of crystalline nuclei of the following phases: Al₃La, Al₃Ni, Al_2.12La_0.88, Al₃Ni₅, and Al. The largest ones (1–2 nm) are nuclei of the Al₃Ni and Al compound, while the majority nuclei of all the other phases had sizes of about 7 Å. Al and Al₃Ni, as well as Al₁₁La₃ and Al_5.56LaNi_1.44 are observed in the crystallized alloy.     

Highly ordered mesoporous CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> and CuFe<Subscript>2</Subscript>O<Subscript>4</Subscript> with crystalline walls

The highly ordered mesoporous CoFe₂O₄ and CuFe₂O₄ with crystalline walls can be synthesized by hard template with using mesoporous silica SBA-15 as hard template and using ferric nitrate, cobalt nitrate, and copper nitrate as metal precursors. These new mesoporous materials above have high surface areas, narrow pore size distribution, and large pore volumes, which are believed to be valuable for the potential application in the field of sensors, catalysis, message recording, magnetics, and biology. This work provides a method to fabricate the highly ordered mesoporous materials composed of multi-metal oxides with crystalline walls. The development of such versatile approach is of great significance in practical application. It can be envisaged that this established method is significantly expandable to the controlled synthesis of the mesoporous functional materials with diverse compositions.