Preparation of mesoporous silica fiber matrix for VOC removal

A novel method for the preparation of the mesoporous silica fiber matrix was introduced for a removal of volatile organic compounds (VOCs). Paper making technology was applied to make a sheet of mesoporous silica fiber matrix. Reinforcing the mesoporous silica fiber with the ceramic fibers (50 wt.%) increased the mechanical strength of the matrix. Mesoporous silica fibers using TMOS (tetramethoxysilane) as a silica source and CTAC (cetyltrimethyl-ammoniumchloride) as a surfactant were drawn by the spinning method. The spinning process increased both the crystallinity and the fraction of mesopores (1.9 nm) of the fiber. As the spinning rate was increased both the crystallinity and the specific area of the mesoporous silica fiber increased, but the diameter of fiber decreased. We could control the size and morphology of mesoporous silica fiber matrix by changing the shape of substrates. This leads to easy fabrication of honeycomb-structured adsorbent which can be used for the VOC removal.     

Computer modeling of the jump-like deformation of AMg6 alloy

We describe a procedure for modeling the structural inhomogeneity of a material by the finite element method. We consider the material as a composite consisting of an elastoplastic matrix and brittle inclusions (dispersoids). The finite element model is based on experimental data on the concentration of inclusions and their geometrical sizes. The proposed finite element model describes well the jump-like deformation of AMg6 alloy. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 1, pp. 41–44, January–February, 2008.     

Dry etching of GaN and related materials: comparison of techniques

The etch rates and feature anisotropy for GaN, AlN, and InN etched in Cl₂-Ar plasmas with four different techniques were examined. Conventional reactive ion etching produces the slowest etch rates, even when high dc self-biases (>-900 V) are employed, and this leads to mask erosion and sloped feature sidewalls during ridge waveguide fabrication. Two high-ion-density techniques, inductively coupled plasma and electron cyclotron resonance, provide the highest etch rates and most anisotropic features through their combination of high-ion flux and moderate-ion energy. Etch selectivities of GaN to AlN and InN are typically ⩽4 in these tools. Reactive ion beam etching utilizing a high density (ICP) source is also an attractive option for pattern transfer in the nitrides, although its etch rates are slower than for ICP or ECR due to its lower operating pressure     

Modeling of combustion of a magnesium particle (Stefan Problem)

An adjoint distributed mathematical model is proposed to describe the ignition and combustion of a magnesium particle with allowance for the gas area surrounding the particle. The combustion process is modeled within the framework of the single-phase Stefan problem. Verification of the model on the basis of available experimental values of ignition and combustion times under various conditions is performed.     

Structure and luminescent properties of Cs<Subscript>2</Subscript>Sr(VO<Subscript>3</Subscript>)<Subscript>4</Subscript>:Mn<Superscript>2+</Superscript>

We have developed a procedure for thermally stimulated synthesis of a cesium strontium metavanadate, Cs₂Sr(VO₃)₄:Mn²⁺ (0.01, 0.50, 1.00, 5.00 at % Mn²⁺), using MnO-containing starting mixtures. The EPR spectrum of the material containing 0.01 at % Mn²⁺ shows a hyperfine structure due to the incorporation of a small amount of manganese into the diamagnetic double metavanadate host. The luminescent and optical properties of Cs₂Sr(VO₃)₄:Mn²⁺ depend on manganese content. In contrast to higher doping levels, doping with 0.01 at % Mn²⁺ increases the integrated emission intensity of the vanadate by 10% and improves its chromaticity characteristics (approaching them to those of white light). We assume that this is due to the reduction in the density of vacancy-type growth defects, such as oxygen vacancies.     

Thermal stability and cathodoluminescence of potassium strontium vanadates

We have studied the thermal stability of five potassium strontium vanadates: KSr(VO₃)₃, K₂Sr(VO₃)₄, K₄Sr(VO₃)₆, K₆Sr(VO₃)₈, and KSrVO₄. The double orthovanadate undergoes a reversible polymorphic transformation at 1117°C and is stable up to 1500°C. The double metavanadates melt peritectically in the range 490–517°C to give Sr₂V₂O₇ crystals and peritectic melt. Pulsed cathodoluminescence studies have shown that the potassium: strontium ratio in the vanadates and their crystal structure have little effect on their optical emission properties. The performance parameters of new vanadate-based phosphors have been determined.     

Effect of Reaction Solvent on the Hydrogenation of Isophthalonitrile for Meta‐Xylylendiamine Preparation

This study focused on the effects of reaction solvent on the hydrogenation of isophthalonitrile (IPN) to produce m‐Xylylenediamine (MXDA) over Ni‐based commercial catalyst. The hydrogenation was carried out using various reaction solvents such as 1‐methylimidazole, mesitylene, benzyl ether and isopropanol under various reaction conditions. It was observed that 1‐methylimiazole outperformed the other reaction solvent, exhibiting a high MXDA yield and producing a low concentration of undesirable products.     

UV-photoassisted etching of GaN in KOH

The etch rate of GaN under ultraviolet-assisted photoelectrochemical conditions in KOH solutions is found to be a strong function of illumination intensity, solution molarity, sample bias, and material doping level. At low e-h pair generation rates, grain boundaries are selectively etched, while at higher illumination intensities etch rates for unintentionally doped (n～ 3×10¹⁶cm^?3) GaN are ≥1000Å·min^?1. The etching is diffusion-limited under our conditions with an activation energy of ～ 0.8kCal·mol^?1. The etched surfaces are rough, but retain their stoichiometry.     

Binding energy of exciton-impurity complexes in semiconductors with diamond and zinc blende structure

The binding energies of four complexes — exciton + charged impurity, exciton + neutral impurity — were calculated by a variational method in semiconductors with diamond and zinc blende structure taking into account the degeneracy of the valence-band edge. The numerical calculations were performed for exciton-impurity complexes in a series of II–VI, III–V, and IV–IV crystals. Fiz. Tekh. Poluprovodn. 32, 583–587 (May 1998)     

Application of GDC-YDB bilayer and LSM-YDB cathode for intermediate temperature solid oxide fuel cells

Yttria-doped bismuth (YDB) and gadolinia-doped ceria (GDC) are investigated as a bilayer electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs). LSM-YDB is used as a cathode material in order to improve the poor ionic conduction of LSM and the compatibility with the YDB electrolyte. The performance of the bilayer cell was measured under humidified H₂ (3 % H₂O) atmosphere and an operating temperature between 500 °C and 650 °C. The polarization resistance and ohmic resistance of the GDC-YDB bilayer cell were 0.189 Ωcm² and 0.227 Ωcm² at 650 °C, respectively. The bilayer cell showed 0.527 Wcm^?2 in the maximum power density at 650 °C, which is about two times higher than the single-layer cell of 0.21 Wcm^?2. The OCV of the bilayer cell was 0.89 V at 650 °C, suggesting that the electronic conduction caused by the reduction of ceria was successfully suppressed by the YDB layer. The introduction of an YDB-GDC bilayer cell with LSM-YDB cathode thus appears to be a promising method for improving the performance of GDC-based SOFCs and reducing operating temperature.