Effect of pH on the Catalytic Properties of Mo–V–Te–P–O Catalysts for Selective Oxidation of Isobutane

Mo–V–Te–P mixed oxide catalysts, prepared by a dry-up method at various pHs (in the range of about 1.0–9.0), have been tested in the partial oxidation of isobutane. The best catalytic performance was achieved over a catalyst prepared at a pH about 7.0. In this case, high selectivity to methacrolein (37.0%) at an isobutane conversion of 12.7% has been obtained at 380 °C. The surface V⁴⁺/V⁵⁺ ratios of the calcined samples were strongly influenced by the pH in the synthesized solution, which is one of the key factors in the catalytic performance for selective oxidation of isobutane.     

Electrical transport properties of Co–Zn–Y–Fe–O system

Co–Zn substituted nanoferrites having stoichiometric composition Co_1?xZn_xY_0.15Fe_1.85O₄ (x = 0.0–1.0, step: 0.2) were synthesized by chemical co-precipitation method. Analysis of the XRD patterns confirms the formation of cubic spinel phase as main phase along with few traces of secondary phase. The lattice constant was found to increase from 8.378 Å to 8.438 Å with zinc contents which can be explained on the basis of difference in ionic radii. SEM micrographs indicate nearly uniform distribution of grains. The average crystal size was found to decrease from 38.41 nm to 14.25 nm with the increase of Zn contents. The physical density increases with the increase of Zn contents from 3.95 g/cm³ to 4.42 g/cm³. It was found that the resistivity decreases with the increase of Zn contents from 9.20 × 10⁷ Ω cm to 5.26 × 10⁶ Ω cm which may be attributed to the increase in the number of Fe²⁺/Fe³⁺ ions pairs at B-sites. The transition temperature of the samples with substitution level x = 0.6, 0.8, 1.0 changes at 373, 333 and 313 K, respectively. The transition temperature of the sample with x = 1.0 is close to the room temperature. This may be the Curie temperature. Low Curie temperature material can be used for the preparation of temperature sensitive ferrofluid. Dielectric loss tangent (tan δ) has been observed to increase with the increase of zinc contents. This can be attributed to the decrease in resistivity which in turn increases the dielectric loss tangent.     

Effect of sintering temperature electrical properties of ZNR doped with Pr–Co–Cr–La

The microstructure, electrical properties, and dielectric characteristics of the ZNR (zinc oxide-based nonlinear resistors), which are composed of zinc oxide-based ceramics doped with Pr–Co–Cr–La, were investigated at different sintering temperatures (1240, 1245, 1250, 1255, 1260, and 1300 °C). The increase of sintering temperature led to more densified ceramics, whereas it decreased the nonlinear properties and breakdown voltage. The highest nonlinearity was obtained from 1240 °C, with 79.3 in nonlinear coefficient and 0.3 μA in leakage current. As the sintering temperature increased, the donor density increased from 0.90 × 10¹⁸ to 2.59 × 10¹⁸/cm³, and the barrier height decreased from 1.90 to 0.67 eV, and the dielectric dissipation factor increased from 0.0874 to 0.2839.     

Investigation of the curing kinetics of alkyd–melamine–epoxy resin system

Properties of coatings based on alkyd resin can be improved via blending with other suitable resins. Recent studies assessed that many properties could be improved by blending with epoxy resins as well as with melamine resins. The aim of this work was to investigate the effect of epoxy resin content on the curing process in alkyd–melamine–epoxy three component blends. The coatings with two mixing ratios of alkyd/melamine (70:30 and 80:20) were formulated. They were made into baking enamels by blending with 3 and 5 wt% of epoxy resin on total resin solid. Curring kinetics was investigated by differential scanning calorimetry (DSC) and application of Ozawa isoconversional method. Fourier transform infrared spectroscopy (FTIR) was used to follow major curing reactions. The absorbance of –OH and –N–CH₂R, showed significant reduction and confirmed that the epoxy resin reacts and inserts in enamel structure. It was found that resin system with alkyd/melamine ratio of 70:30 and 3 wt% of epoxy resin has the lowest apparent activation energy of 141.5 kJ mol⁻¹ and needs the shortest time of 34.2 min to reach final apparent degree of cure. Isothermal DSC experiments have confirmed these findings. The samples with 30 wt% of melamine resin had higher hardness of baked enamels then samples with 20 wt%. They also showed an increase of hardness with the increase of epoxy resin content.     

Microstructure and mechanical properties of TiC–TiN–Zr–WC–Ni–Co cermets

Cermet cutting tools are widely used for semi-finishing and finishing work on steel and cast iron. However, their brittleness is still an unavoidable limitation for their utilizations. Zirconium was added to improve the fracture toughness of Ti(C, N) based cermets. The microstructure and the fracture surfaces of cermets were studied by using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The experimental results reveal that Zr dissolved and formed solid solutions during the sintering process. The amount of grains with typical core/rim structure decreases and that of coreless grains increases with increasing Zr addition. Moreover, the fracture toughness is improved clearly due to the increased amount of the coreless grains, the spinodal decomposition in cermets, as well as the crack deflection and crack branching mechanisms. Additionally, hardness and relative density were also measured, respectively.     

Properties of MgO–Fe–C refractories as linings of vanadium-extraction converter

For the purpose to extend the service life of MgO–C bricks used as linings of vanadium-extraction converters, MgO–Fe–C bricks with different carbon content were designed and the properties of this novel refractory were investigated by comparing to the traditional MgO–C bricks. The results showed that the poor service life of MgO–C bricks was due to the poor sinterability of the oxidized layer at 1400 °C, whereas the oxidized layer of MgO–Fe–C brick was well sintered due to the oxidation of Fe particles in the oxidized layer and formation of MgO–FeO_ss in air atmosphere. Excellent oxidation resistance and corrosion resistance against vanadium containing slag were also obtained due to the increase of compactness of oxidized layer and concentration of FeO in the oxidized layer compared to MgO–C bricks, and it is considered that MgO–Fe–C brick is a favorable substitute of MgO–C refractory to be used as linings of vanadium-extraction converters.     

Processing–microstructure–properties relationships of MoSi2–SiC composites

Silicon carbide green bodies with and without carbon-fibre reinforcement have been infiltrated with MoSi₂–Si–X in order to produce high-temperature resistant materials. X is Cr, Ti, Al or B respectively. By adding silicon and one of these components to MoSi₂ the melting point is lowered dramatically. The composites therefore could be gained by melt infiltration at max. 1600 °C. During infiltration the additives react within the infiltrated body with carbon or silicon to form high-temperature resistant carbides or silicides. Thermodynamic calculations have been performed to analyse the reactions during infiltration. The infiltration parameters have been studied with respect to the resulting microstructure and properties. By fitting the amount of additives to the quantity of carbon in the SiC-body (or vice versa) no decrease in strength could be observed up to 1500 °C. The fracture toughness can be increased by the use of high-modulus carbon fibres. The most promising X-element for a high-temperature resistant material is titanium.     

Pulse plating of cobalt–iron–copper alloys

Pulse plating of cobalt–iron–copper (CoFeCu) alloys was studied. A simple theoretical model with an analytical solution developed for binary alloys is applied to predict the copper content of the pulse plated ternary alloys. Studied compositions are in the range of Co_90-x Fe₁₀Cu _x with x varying between 5 to 20 wt%. These compositions are of interest as soft magnetic materials with high saturation magnetization. The deposits were produced from a boric acid and sodium acetate electrolyte with low concentrations of copper and iron. All experiments were carried out under well-controlled mass transport conditions and current distribution using a recessed rotating cylinder electrode (rRCE) or an inverted rotating disc electrode (IrRDE). With the latter design alloys can be plated on flat substrates with or without application of a magnetic field to induce uniaxial magnetic anisotropy. Results show that by changing pulse parameters one can increase and decrease in opposite ways the copper and the iron content in the deposits. To test the influence of pulse parameters on the coercive field strength, a microstructure dependent property, theoretical predictions were used to produce films of identical composition with different pulse parameters. Within the range of pulse parameters studied the coercive field strength of this alloy does not vary. Transmission electron microscopy confirms that the deposits have the same nano-size grain structure.     

Preparation and properties of Ge–Ga–La–S–AgI chalcogenide glass

Chalcogenide glasses of 65GeS₂–(25–x)Ga₂S₃–10AgI–xLa₂S₃ (x=0, 1, 3, and 5 mol%) were fabricated through the traditional melt-quenching method. The effects of addition of La₂S₃ on physical, thermal and optical properties of the glass system were investigated. The results showed that the fabricated glasses possess considerably high glass transition temperature, exhibit improved mechanical property and excellent infrared transmission. A redshift at the visible absorbing cut-off edge is observed with increasing of La₂S₃ content. The direct and indirect optical band gap values are also calculated. Raman spectra analysis indicated that the band at 265 cm⁻¹ decreased in amplitude and a new peak at 230 cm⁻¹ was detected manifesting the formation of La-S bond in the network. In addition, the mid-infrared emission at 3.74 µm of the glasses doped with Tm³⁺ ions was achieved. The results indicated that the glasses are promising materials for mid-infrared applications such as imaging, remote sensing and lasers.     

Preparation of Mesoporous V–Ce–Ti–O for the Selective Oxidation of Methanol to Dimethoxymethane

Mesoporous V–Ce–Ti–O oxides were synthesized through the combination of sol–gel and hydrothermal methods and were characterized by different techniques. N₂ adsorption showed that the mesoporous oxides with 0–20 wt.% V₂O₅ possessed the surface areas of about 160 m² g^?1 with narrow pore size distribution centered around 4–5 nm. Vanadium species were highly dispersed in the samples, as confirmed by the wide angle XRD and Raman spectroscopy. The surface acidity of the materials was determined by the microcalorimetric adsorption of NH₃. Temperature programmed reduction and O₂ chemisorption were used to probe the redox property of the materials. It was found that the mesoporous V–Ce–Ti–O possessed bifunctional characters of acidic and redox properties that catalyzed the oxidation of methanol to dimethoxymethane (DMM). These bifunctional characters were further enhanced by the addition of V₂O₅ and SO₄ ^2? onto V–Ce–Ti–O simultaneously. Such supported catalysts exhibited excellent performance for the selective oxidation of methanol to DMM. Specifically, 72% conversion of methanol with 85% selectivity to DMM was achieved at 423 K over a SO₄ ^2?–V₂O₅/V–Ce–Ti–O catalyst.     

An experimental study of immiscible liquid–liquid dispersions in a pump–mixer of mixer–settler

Drop size distribution(DSD) or mean droplet size(d32) and liquid holdup are two key parameters in a liquid–liquid extraction process. Understanding and accurately predicting those parameters are of great importance in the optimal design of extraction columns as well as mixer–settlers. In this paper, the method of built-in endoscopic probe combined with pulse laser was adopted to measure the droplet size in liquid–liquid dispersions with a pump-impeller in a rectangular mixer. The dispersion law of droplets with holdup range 1% to 24% in batch process and larger flow ratio range 1/5 to 5/1 in continuous process was studied. Under the batch operation condition, the DSD abided by log-normal distribution. With the increase of impeller speed or decrease of dispersed phase holdup, the d32 decreased. In addition, a prediction model of d32 of kerosene/deionized system was established as d_(32)/D = 0.13(1 + 5.9φ)We~(-0.6). Under the continuous operation condition, the general model for droplet size prediction of kerosene/water system was presented as d_(32)/D = C_3(1 + C_4φ)We~(-0.6). For the surfactant system and extraction system, the prediction models met a general model as d_(32)/D = bφ~nWe~(-0.6).     

Effect of “Ph–NH–CH2–” group on the luminescence properties of sol–gel silica xerogel

The effect of Ph–NH–CH₂– group (Ph: phenyl) on the luminescence properties of silica xerogel by sol–gel method has been investigated. The absorption spectra, excitation spectra and emission spectra of Ph–NH–CH₂– group embedded in the network of silica xerogel have a red shift with increasing the ratios of Ph–NH–CH₂– group in the samples. The relative photoluminescence (PL) intensity of the hybrid silica xerogel sample decreases with increasing the ratios of Ph–NH–CH₂– group. From the complex luminescent centers, the novel luminescence properties have been observed from the hybrid silica xerogel sample containing Ph–NH–CH₂– group.     

Prediction of solid–gas equilibria with the Peng–Robinson equation of state

In many applications related to Supercritical-Fluid (SCF) technology, solids are dissolved in SC fluids. Experimental data are now available for many systems but cannot cover all cases of potential practical interest. The prediction of solid solubilities in SC fluids, often in the presence of co-solvents, is useful for rational design of SCF extraction and related processes. Recently, thermodynamics has made considerable steps towards describing complex systems (gases with polar compounds) at high pressures using the so-called Equation of State/Excess Gibbs Free Energy (EoS/G^E) models. The success of these models is so far restricted to Vapor–Liquid Equilibria (VLE) for which they have been primarily developed and tested. In this work we evaluate such a predictive model, the LCVM EoS, for solid–gas equilibria (SGE) including systems with co-solvents. LCVM is chosen due to its success for VLE of asymmetric systems such as CO₂ with heavy alkanes and alcohols. Successful predictions are obtained for several solids as well as for some systems with co-solvents, but the results are less satisfactory for complex, multifunctional solids. A discussion of several factors, which affect modeling of SGE with cubic EoS, is included.     

Enhanced properties of poly(styrene–b–ethylene–co–butylene–b–styrene) nanocomposites with in situ construction of interconnected graphene network

In this work, such elastomeric nanocomposites were fabricated with graphene (GE) sheets selectively distributing between polymer matrices and forming three-dimensional networks. The solvent evaporation process was first introduced to produce poly(styrene–ethylene–co–butadiene–b–styrene) (SEBS) microspheres and then reduced GE oxide attached to the surface of SEBS microspheres via electrostatic interaction and sonication-assisted reduction. The microstructure of nanocomposites, prepared by compression molding using SEBS/GE microspheres, was investigated using scanning electron microscopy and transmission electron microscopy. The results showed that interconnected GE networks formed in heat-pressing composite and was destroyed after twin-roll mixing. The SEBS/GE nanocomposites showed enhanced electrical, thermal, and mechanical properties. The electrical resistivity of nanocomposites obtained via heat-pressing reached to 1.1 × 10³ Ω m at a 2.5 wt % (1.07 vol %) content of GE. The thermal and mechanical properties were also characterized. It was found that the initial degradation temperature increased by nearly 40 °C and the mechanical properties continued to rise with GE content below 0.5 wt %. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47118.     

Quantitative EFTEM study of precursor-derived Si–B–C–N ceramics

Ceramic materials derived from a boron modified polysilazane were investigated by means of energy-filtering transmission electron microscopy (EFTEM). After cross-linking of the polymer and subsequent thermolysis, a coarse powder with average composition Si_24.0B_8.0C_44.0N_24.0 is obtained. For further investigation, monolithic particles with sizes of several millimeters were heat treated in crucibles under a flowing nitrogen atmosphere at 1800 °C for 10 h. During thermolysis, the particles developed internal cracks on the macroscopic scale. At the crack surfaces, a layer of pure carbon was found. In the crack-free region, the material is composed of Si₃N₄ and SiC nano crystallites which are embedded in a turbostratic BNC-matrix. Quantitative electron spectroscopic imaging (ESI) shows an atomic ratio of the elements B:C:N of 1.0:4.0:1.1 in this matrix. In the vicinity of the cracks, silicon nitride locally decomposes with formation of silicon carbide because of its reaction with excess carbon. A detailed EFTEM study of the phase distribution near the crack surfaces showed that the first Si₃N₄ crystallites occur at a distance of approx. 5 μm from the carbon covered crack surface. In additional experiments the composition of the BNC-layers as a function of the distance from the crack surface was investigated.     

Kinetic Mechanisms of Ignition of Isooctane–Air Mixtures

A kinetic scheme was developed to describe the autoignition of isooctane in air. The scheme includes 976 reactions and 126 species and adequately describes the process at both low and high initial temperatures of the mixture. The results of numerical modeling agree with experimental data on isooctane pyrolysis and autoignition delay of isooctane–air mixtures at initial pressures of 0.1–4.5 MPa, initial temperatures of 700–1300 K, and a fueltoair ratio of 0.5–2.0 with an accuracy not worse than 30%.     

The high temperature–high pressure sintering of diamond–Cu–Si–B composite

Such elements like Si, B and Cu have been utilized as components of binder aiming at acquiring high adhesion of the binder with the diamond grains, thermal stability of the composite and, relatively low fusion temperature of the binder. The present work has as its main objective the study of the interaction between components during sintering of polycrystalline diamonds with addition of binders under high pressures, in the range from 5.0 to 6.0 GPa and high temperatures, in the range from 1473 to 1773 K with process time between 15 and 30 s. After sintering the compacts were subjected to investigations concerning the influence of the mixture composition and of the process parameters on the density and wear resistance of the compacts. The method of factorial planning was utilized in order to obtain model which describes influence of sintering parameters on the properties of compacts.     

Chemical modification of styrene–butadiene–styrene co-polymer by grafting of N-carbamyl maleamic acid

A styrene–butadiene–styrene (SBS) block co-polymer was functionalized using different amounts of N-carbamyl maleamic acid (NCMA) and benzoyl peroxide as initiator. NCMA, which is a bifunctional monomer, was synthesized in our laboratories. The concentration of NCMA used in the functionalization of SBS ranged from 0.5 to 3% (w/w) based on the co-polymer mass. Benzoyloxy radicals generated from the thermal decomposition of benzoyl peroxide initiated the grafting reaction. The concentration of the initiator was kept constant at 0.076% (w/w). FT-IR spectroscopy was used to determine the amount of NCMA effectively grafted onto the SBS. The maximum amount of monomer grafted was about 0.3% (w/w) when the SBS was modified with 1% (w/w) NCMA. The effect of grafting on the surface properties and the adhesion to polyurethane adhesive of the modified SBS were evaluated. Contact angle values were obtained using liquid droplets. When the concentration of the NCMA used in the grafting reaction was 1% (w/w), the contact angles with water on original and modified SBS were 95° and 77°, respectively. Adhesion properties were evaluated by standard peel tests employing a commercial polyurethane adhesive. The modified SBS having the largest amount of NCMA displayed a T-peel strength value 5-times higher than the corresponding value measured with the original SBS.     

Evaluation of Physicochemical and Antifungal Properties of Polylactic Acid–Thermoplastic Starch–Chitosan Biocomposites

Biocomposites of polylactic acid, thermoplastic starch, chitosan powder, and chitosan lyophilized powder were prepared using an extrusion process. The color, thermal, structural, mechanical, morphology, and antimicrobial properties were evaluated. The addition of thermoplastic starch and chitosan (chitosan powder and chitosan lyophilized powder) produced significant changes in color and heterogeneous surface morphology of the polylactic acid biocomposites. The thermal, mechanical, and morphometric properties of the material showed changes with the addition of thermoplastic starch and chitosan (chitosan powder and chitosan lyophilized powder). The biocomposites formulated with chitosan powder and chitosan lyophilized powder showed antifungal activity when evaluating this property. The biocomposites produced could be used in packaging applications.