Electrical Switching in Cu–As–Se Glasses

Electrical switching in Cu_xAs₄₀Se_60−x glasses has been studied over a wide composition range for 0≤x≤32. The glasses with lower Cu concentrations (x<15) do not exhibit switching, whereas glasses in the range 15≤x≤25 show a threshold type switching. The glasses in the range 26≤x≤29 exhibited an unusual switching from low-resistance to high-resistance state. For x≥30, the glasses are found to show a memory switching. The thermally crystallized samples indicate that the structural network is characterized by Cu₃AsSe₄ and As₂Se₃ for x<15 and by Cu₃AsSe₄ and Cu₂As₃ for x≥25. The composition range 15≤x≤20 is characterized only by Cu₃AsSe₄ structural units. The samples cooled from their melt show only the ternary Cu₃AsSe₄ for x≤20. For x>20, precipitates of “As” have also been observed along with Cu₃AsSe₄ and Cu₂As₃ phases. The present studies provided a unique way to understand the electrical switching exhibited by chalcogenide glasses based on the thermal model and the filament formation.     

Semi-Empirical Modeling of Gas–Liquid Mass Transfer in Gas–Liquid–Liquid Systems in Stirred Tanks

Two semi-empirical models of gas–liquid mass transfer in gas–liquid–liquid systems are presented, one for the case where the dispersed liquid phase has a positive spreading coefficient S > 0, the other for S < 0. The models are based on mathematical expressions inspired by assumed mass transfer mechanisms, which are different depending on the oil spreading characteristics. Model simulations compare well with experimental data (up to oil phase holdup ? ～ 0.1), managing to simulate the shape of the experimental curves of oxygen mass transfer enhancement factor E vs. ? for the air–water–heptane (S > 0) and air–water–dodecane (S < 0) systems, better than other models available in the literature.     

Isonitriles in Fischer–Tropsch catalysis

The growth of saturated carbon–carbon chains has been detected in the reaction of isonitriles with Raney nickel and Raney cobalt in liquid ammonia and under hydrogen pressure. The plausible mechanism for this Fischer–Tropschlike reaction with isonitrile instead of carbon monoxide is discussed.     

Heterogeneous Equilibria in the Yb–Mn–O System

The heterogeneous equilibria attained during thermal dissociation and hydrogen reduction of YbMnO₃ and YbMn₂O₅ are investigated using the static method (vacuum circulation setup) and X-ray powder diffraction analysis of quenched solid phases. It is found that, at the boundary of the low-oxygen homogeneity region of YbMn₂O₅, this compound dissociates into YbMnO₃ and Mn₃O₄ with the liberation of oxygen. Upon the reduction, YbMnO₃ dissociates with the formation of Yb₂O₃ and MnO and the liberation of oxygen. Equations for the dissociation and reduction reactions of YbMn₂O₅ and YbMnO₃ are derived, and mass balance equations for these processes are written. A fragment of the isothermal section of the phase diagram of the Yb–Mn–O system at 900°C is constructed in the composition–oxygen pressure coordinates.     

Vapor–liquid equilibrium in the sodium carbonate–sodium bicarbonate–water–CO2-system

Vapor–liquid equilibria of the carbon dioxide loaded sodium carbonate–water system were measured in the temperature range 40–80 °C and for sodium carbonate concentrations 8–12 wt%. In addition the vapor pressure of water over 10–30 wt% sodium carbonate solutions for the temperature range 27–100 °C was measured in an ebulliometer. The system was modeled using the electrolyte-NRTL model. Experimental vapor–liquid data from this study as well as data available in the literature from 25 to 195 °C and for sodium carbonate concentrations from 0.5 to 12 wt% were used for parameter fitting. The average deviation of the model predictions compared to all experimental data found is 9.8% for the partial pressure of CO₂. For vapor pressure of water the standard deviation is 0.6% up to 100 °C and 30 wt% sodium carbonate solutions.     

Evaporative liquid jets in gas–liquid–solid flow system

Some aspects of the fundamental characteristics of evaporative liquid jets in gas–liquid–solid flows are studied and some pertinent literature is reviewed. Specifically, two conditions for the solids concentration in the flow are considered, including the dilute phase condition as in pneumatic convey and the dense phase condition as in bubbling or turbulent fluidized beds. Comparisons of the fundamental behavior are made of the gas–solid flow with dispersed non-evaporative as well as with evaporative liquids.For dilute phase conditions, experiments and analyses are conducted to examine the individual phase motion and boundaries of the evaporative region and the jet. Effects of the solids loading and heat capacity, system temperature, gas flow velocity and liquid injection angle on the jet behavior in gas and gas–solid flows are discussed. For dense phase conditions, experiments are conducted to examine the minimum fluidization velocity and solids distribution across the bed under various gases and liquid flow velocities. The electric capacitance tomography is developed for the first time for three-phase real time imaging of the dense gas–solid flow with evaporative liquid jets. The images reflect significantly varied bubbling phenomenon compared to those in gas–solid fluidized beds without evaporative liquid jets.     

Morphotropic phase boundary in the BNT–BT–BKT system

Lead-free x Bi_0.5Na_0.5TiO₃–y BaTiO₃–z Bi_0.5K_0.5TiO₃ piezoelectric ceramics were synthesized by a conventional solid state reaction method. The microstructure, ferroelectric and piezoelectric properties of the ceramics were investigated. Structure measurements by X-ray diffraction with Rietveld refinement have allowed us to specify more precisely the morphotropic phase boundary (MPB) in this system. For (1 ? x) BNT–x BT solid solution ceramics, the 0.94 BNT–0.06 BT morphotropic composition shows the higher values with d₃₃ = 170 pC/N, k_p = 0.35 and k_t = 0.53. In the case of (1 ? x) BNT–x BKT compositions, the d₃₃, k_p and k_t are, respectively, 137 pC/N, 0.39 and 0.54 for the 0.80 BNT–0.20 BKT ceramic. On the other hand, the ternary 0.865 BNT–0.035 BT–0.100 BKT morphotropic composition shows high piezoelectric constant and electromechanical coupling factors (d₃₃ = 133 pC/N, k_p = 0.26 and k_t = 0.57).     

Gas-solid displacement reactions in the Ti–W–C system

Displacement reactions between binary and ternary ceramics in the Ti–W–C system and reactive gaseous atmospheres are investigated in this work. Specifically, WC and 50:50 wt% TiC:WC solid solution powders were exposed to flowing hydrogen gas, or equilibrated against an excess of titanium in the presence of iodine, to form metallic tungsten and TiC solid products. In the case of pure WC reacting with hydrogen, transformation to metallic tungsten occurred as a result of removal of chemically bound carbon as gaseous hydrocarbons. In the case of pure WC reacting with titanium iodide vapors, transformation was accompanied by the appearance of TiC as a solid product formed at the gas-solid interface. In the case of 50:50 wt% TiC:WC solid solution powders, hydrogen was generally found to be an ineffective displacing reagent, whereas reaction with titanium iodide vapors was observed to proceed virtually to completion, resulting in a two phase product mixture comprising metallic tungsten and TiC. For the latter case, a variety of microstructures could be observed within a given batch, including tungsten platelets and/or lamellae in a TiC matrix, or coarse tungsten grains interspersed with TiC grains. These morphological variations are speculated to arise from compositional variation in the starting material and the occurrence of local rapid coarsening along fast diffusion pathways within reacting agglomerates and polycrystalline primary particles. The observed reaction products and relative efficacy of gaseous reagents to promote displacement reactions in the Ti–W–C system are rationalized on the basis of thermodynamic predictions. The reaction between 50:50 wt% TiC:WC solid solution powders and titanium iodide vapors constitutes the first known report of an internal displacement reaction proceeding via gaseous intermediates in a nonoxide ceramic system.     

Long wavelength Eu2+ emission in Eu-doped Y–Si–Al–O–N glasses

A number of (Eu,Y)–Si–Al–O–N glasses have been prepared and their optical properties examined. Eu was found to be present in the divalent instead of in the trivalent state due to a reaction between the Eu³⁺ and the chemically incorporated N^3- during the preparation of the glasses. The luminescence characteristics were found to be negligibly influenced by the O/N and Si/Al ratio, but appear to be strongly dependent on the concentration and type of modifying cations (Eu,Y). As a function of the cationic composition the emission shifts from wavelengths below 500 nm to wavelengths as long as 640 nm, which is very unusual for Eu²⁺ containing compounds. This shift to longer wavelengths is ascribed to a combination of energy transfer between the different sites and change of the Eu²⁺ site distribution.     

Dye–surfactant interaction in aqueous solutions

The interaction of four ionic dyes, C.I. Mordant Black 11, C.I. Mordant Black 17, C.I. Direct Yellow 50 and C.I. Basic Blue 9, with cationic and anionic surfactants was studied by absorption spectroscopy. The dyes interact strongly with oppositely charged surfactant in the premicellar concentration range and the appropriate values of constant of dye–surfactant complex formation were estimated. In addition, the most important factor affecting the number of dye particles solubilized in the surfactant micelle was its molecular mass.     

Residual stresses in alumina–zirconia laminates

Significant residual stresses can arise in hybrid ceramic laminates during the densification and cooling processing cycles. The densification stresses in alumina–zirconia laminates were calculated assuming the layers to be linear viscous with data obtained by cyclic loading dilatometry. These stresses placed the zirconia layers in biaxial tension and even at 1 MPa or less, they were sufficient to cause a type of linear cavitation damage. The methodology was also applied to asymmetric laminates, successfully predicting their observed curling behaviour. Thermal expansion mismatch stresses arise during cooling, again placing the zirconia layers in residual biaxial tension and leading to the formation of transverse (channelling) cracks. The stresses were calculated using both elastic and viscoelastic formulations and were confirmed with indentation measurements. Additions of alumina to the zirconia layers were effective in reducing both sources of residual stress and allowed crack formation during processing to be avoided. Residual stresses were also shown to improve mechanical performance.     

Gravity–capillary evaporation regimes in microgrooves

The gravity–capillary evaporation phase change in microgrooves inside a heat pipe is experimentally investigated by a visualization system. The evaporation regime, startup temperature response, and evaporation thermal resistance for gravity–capillary evaporation are evaluated and compared with those for capillary evaporation. The results identify oscillatory motion of vapor–liquid interface for gravity–capillary evaporation in rectangular microgrooves arising from the competition between gravity, the capillary force, and the shear force. In addition, the presence of gravity introduces the transition from fin–film evaporation regime to corner–film evaporation regime in rectangular microgrooves, and hence results in an overshoot startup and temperature oscillation during the process of gravity–capillary evaporation. Interestingly, the corner–film evaporation improves the evaporation phase change performance in the microgrooves. © 2018 American Institute of Chemical Engineers AIChE J, 65: 1119–1125, 2019     

Electron–hole drops in synthetic diamond

In this paper we give the first report of a high-density phase of condensed electron–hole drops in diamond. Synthetic crystals grown by the high pressure–high temperature technique were optically highly excited by laser pulses with photon energies above the band-gap of diamond. At temperatures below ≈170 K we observe novel broad luminescence bands, in addition to the well-known free exciton spectra, with characteristic features identifying them as originating from electron–hole drops. Fits to the photoluminescence spectra yield an electron–hole density within the drops of n₀=9.6×10¹⁹ cm⁻³, a reduced band-gap of E_g′=5.224 eV (instead of E_g=5.49 eV) due to the attractive interaction of the particles in the condensed phase, and a work function of φ=52 meV with respect to the free exciton threshold E_gx.     

Structure and phase formation in the Ti–Al–Nb system in the thermal explosion mode

This paper presents the results of the structure and phase formation in the Ti/Nb/2Al, Ti/Nb/2.5Al and Ti/Nb/3Al systems in the thermal explosion mode of self-propagating hightemperature synthesis. The morphology, phase composition, microstructure, and physical properties have been studied. It has been found that compounds with the highest content of aluminum have the most homogeneous composition and the lowest porosity. The main phase of the synthesis product is a phase based a solid solution of Nb in γ-TiAl.     

Phase equilibria in the calcium nitrate–water–isopropyl alcohol system

Results of an investigation of the solubility of the components of the water–isopropyl alcohol system in the temperature range of 253–268 K are given. Using fractional fusion, the concentrations of twocomponent water–isopropyl alcohol system have been determined, where fusion occurs more homogeneously. Phase diagrams of the calcium nitrate–water–isopropyl alcohol systems have been plotted at temperatures of 253, 263, and 268 K. The working area where compositions can be chosen for preparing the process liquid with a low freezing point has been determined.     

Bubble lengths in the gas–liquid Taylor flow in microchannels

Experimental results of measurements of the bubble and slug lengths in Taylor (slug) flow are presented. The experiments were carried out using 3 different straight microchannels (microreactor with square cross-section made of polydimethyloxosilane (PDMS); microreactor with circular cross-section made of glass; microreactor with rectangular cross-section made of polyethylene terephthalate modified by glycol (PETg)) and 4 different liquids (water, ethanol propanol and heptane). The results have been compared with the available literature correlations. It is concluded, that the values obtained from the correlation proposed by Laborie et al. [Laborie, S., Cabassud, C., Durant-Bourlier, L., Laine, J.M., 1999. Characterization of gas–liquid two-phase flow inside capillaries. Chem Eng Sci 54, 5723–5735] do not agree with the results of measurements, while the agreement of these results with the predictions obtained using the correlation proposed by Qian and Lawal [Qian, D., Lawal, A., 2006. Numerical study on gas and liquid slugs for Taylor flow in a T-junction microchannel. Chem Eng Sci 61, 7609–7625] is good. New, corrected values of the pre-exponential constant and the exponents in the Qian and Lawal [Qian, D., Lawal, A., 2006. Numerical study on gas and liquid slugs for Taylor flow in a T-junction microchannel. Chem Eng Sci 61, 7609–7625] correlation are proposed.     

Corrosion of Au–Pd–In alloy in simulated physiological solutions

The corrosion of Au–Pd–In alloy, which is of great importance in dentistry, has been studied using an electrochemical quartz crystal microbalance (EQCM) in simulated physiological solutions. The alloy was deposited on quartz substrates by means of magnetron sputtering (MS). Analysis performed using X-ray photoelectron spectroscopy showed that the chemical composition of the sputtered deposit was similar to that of the MS target made of conventional casting alloy. Investigations by X-ray diffraction indicated a crystalline structure of the MS alloy. The electrochemical and corrosion behaviour of the Au–Pd–In alloy was studied in three simulated physiological solutions: 0.9 M NaCl, 0.1 M NaCl + 0.1 M lactic acid and artificial saliva. Determination of break down potential was complicated by the anodic gold dissolution due to formation of a chloride complex. The onset of anodic currents, therefore, indicated not the potential at which the passive layer starts to be destroyed, but the exceeding of the Au/AuCl₄ ^– equilibrium potential, which does not directly reflect corrosion resistance. The EQCM measurements under open circuit conditions indicated corrosion as an increase in mass, caused by the accumulation of corrosion products on the alloy surface. The increase in mass in acidic solution (pH 2.2) was similar to that in neutral solution (pH 6.5), which implies dissolution of corrosion products to be insignificant.     

Structure–Function Relations in Supported Ni–W Sulfide Hydrogenation Catalysts

Ni–W catalysts were prepared by impregnation of commercial -alumina and silica supports. The sulfidation, performed directly after drying at 100°C, yielded fully sulfided Ni–W species on both supports (SEM-EDAX, XPS, XRD). At optimal metals loading (50 wt% NiO + WO₃, Ni/W = 2), the sulfided catalysts had similar texture (N₂ adsorption) and displayed similar activity in dibenzothiophene hydrodesulfurization (DBT HDS), while the activity of the Ni–W/SiO₂ catalyst in toluene hydrogenation (HYD) was six times higher than that of Ni–W/Al₂O₃. This is due to the more than two times higher WS₂ slabs stacking number in Ni–W/SiO₂ compared with Ni–W/Al₂O₃ (XRD, HR-TEM), yielding stronger adsorption of toluene (TPD).