Diffusion coefficients and electrical conductivities for calcium chloride aqueous solutions at 298.15 K and 310.15 K

Experimental values for mutual diffusion coefficients (interdiffusion coefficients) for CaCl₂ aqueous solutions at 298.15 K and 310.15 K, not available in the literature, were experimentally determined between 0.005 mol dm^?3 and 0.1 mol dm^?3. The measurements were performed by using a conductimetric open-ended capillary cell. Values at infinitesimal concentration, D⁰, were also obtained. These data were analysed using the Onsager–Fuoss and Gordon models. In addition, molar conductance data were measured at 310.15 K for CaCl₂ aqueous solutions at the same concentration range and the value at infinitesimal concentration determined. Afterwards, it was split into the ionic limiting values. By replacing them into the Nernst equation, diffusion coefficients at infinitesimal concentration were derived (1.335 × 10^?9 m² s^?1 and 1.659 × 10^?9 m² s^?1) at both temperatures (298.15 K and 310.15 K, respectively). They agree well with the extrapolated experimental ones (1.312 × 10^?9 m² s^?1 and 1.613 × 10^?9 m² s^?1).     

Characteristics of droplets generated by bubble bursting from chromic acid solutions

The effects of electrolyte concentration and gas flow rate on the characteristics of droplets generated from bubbles bursting on the surface of CrO₃ solution were studied with an experimental bubbling system. The experimental conditions included two electrolyte concentrations, 125 and 250 g l^-1 of CrO₃, and three flow rates of sparging air in the range of 4–8 l min^-1. A cascade impactor collected droplet samples for chemical analysis. A laser aerosol spectrophotometer and an aerodynamic particle sizer were employed simultaneously to measure the number concentration and size distribution of the droplets. A layer of foam formed on the liquid surface under all experimental conditions studied except at the gas flow rate of 4 l min^-1 in 125 g l^-1 CrO₃ solution. Foams had a significant effect on the characteristics of droplets generated from bursting bubbles. At identical gas flow rate and electrolyte concentration, the formation of foams led to a reduction in number concentration of droplets larger than 10 μm in aerodynamic diameter and a lower concentration of airborne Cr(VI). In the ranges of gas flow rate and electrolyte concentration tested, the results showed that the airborne Cr(VI) mass concentration increased significantly with gas flow rate and slightly with electrolyte concentration in the presence of foams. The results obtained in the present study should have applications in the emission control of Cr(VI)-containing droplets in chromium electroplating processes.     

Kinetic studies of the oxidation of quercetin,rutin and taxifolin in the basic medium by (ethylenediaminetetraacetato) cobalt(III) complex

The quercetin in 0.01 M NaOH solution underwent steady oxidation when it was exposed to air with the formation of the quinone product. For the taxifolin and rutin, the oxidation occurred only when the solutions were saturated with O₂, but very slowly. The kinetics of the oxidation of flavonoids in 0.01 M NaOH solution by Co(edta)^? complex was carried out and the rate constants are 3.44 × 10², 1.04 × 10^? 1 and 1.46 × 10^? 2 M^? 1 s^? 1 for quercetin, rutin and taxifolin, respectively, at μ = 0.10 M LiClO₄. The deprotonation of the C₃ hydroxyl group and the conjugation between pyrone and catechol rings account for the reactivity of quercetin.     

Effects of salicylate derivate on the competing reaction of chromium(III) complex [Cr(III)(R-SA)(en)2]Cl with apoovotransferrin

Four novel Cr(III) complexes, Bis(ethylenediamine-κ²N,N′)(R-SA-κ²O,O′)chromium(III) chloride (H₂SA = salicylic acid, R = 5-F, 5-Cl, 5-Br, 4-CH₃ ethylenediamine = en) have been synthesized and three of them are determined by X-ray crystallography. The competition reaction with EDTA and apoovotransferrin (apoOTf) was monitored by UV–Visible (UV–vis) and fluorescence spectra at 37 °C. The reaction with EDTA is only a simple competitive process and no specific selectivity was observed (k_EDTA/F410 = 4.07 × 10^?3–4.37 × 10^?3 M^?1 s^? 1). While for the reaction with apoOTf, an instable intermediate species (R-SA)–Cr(III)–OTf forms (k_OTf/F336 = 1.70 × 10^? 1–2.08 × 10^?1 M^?1 s^? 1), where R-SA^2? act as the role of synergistic anion. The intermediate is instable and the R-SA^2? ligand will then be released with the rate constants of 1.17 × 10^? 1 (5-F-SA^2?) ≈ 1.01 × 10^? 1 (4-CH₃-SA^2?) > 3.19 × 10^? 2 (5-Cl-SA^2?) > 3.25 × 10^? 3 (5-Br-SA^2?) M^?1 s^? 1. The substitutive groups R on SA have positive influence on charge density of O donor atom, which directly affect the stability of the (R-SA)–Cr(III)–OTf intermediate.     

High power density in a piezoelectric energy harvesting ceramic by optimizing the sintering temperature of nanocrystalline powders

Piezoelectric energy harvesting is the research hotspot in the field of new energy, and its core is to prepare piezoelectric ceramics with high transduction coefficient (d₃₃ × g₃₃) and large mechanical quality factor (Q_m) as well. In addition, the miniaturization of the piezoelectric energy harvester also requires the material to have a submicron fine grain structure. In this work, submicron-structured ternary system, MnO₂-doped Pb(Zn_1/3Nb_2/3)O₃-Pb(Zr_0.5Ti_0.5)O₃ was constructed by pressureless sintering of nanocrystalline powders, which has been synthesized for the first time by high-energy ball milling route thereby evading the calcination stage. The microstructure and the energy harvesting characteristics were tailored through changing the sintering temperature. It was found that 1000 °C sintered fine-grained specimen (mean grain size ∼0.95 μm) showed the maximum d₃₃ × g₃₃ value of 9627 × 10⁻¹⁵ m²/N, meanwhile Q_m was as large as 774, which was almost seven times larger than pure counterpart. In the mode of the cantilever-type energy harvester, a high power density of 1.5 μW/mm³ were obtained for 1000 °C sintered specimen at a low resonance frequency of 90 Hz and acceleration of 10 m/s², which were further increased to 29.2 μW/mm³ when the acceleration increased to 50 m/s², showing the potential applications as a next generation high power multilayer energy harvester.     

Micromechanisms of solid electrolyte interphase formation on electrochemically cycled graphite electrodes in lithium-ion cells

The microstructural and compositional changes that occurred in the solid electrolyte interphase (SEI) formed on graphite electrodes subjected to voltammetry tests (vs. Li/Li⁺) at different voltage scan rates were investigated. The microstructure of the SEI layer, characterized using high-resolution transmission electron microscopy, consisted of an amorphous structure incorporating crystalline domains of ～5–20 nm in size. Evidence of lithium compounds, namely Li₂CO₃ and Li₂O₂, and nano-sized graphite fragments was found within these crystalline domains. The morphology and thickness of the SEI depended on the applied voltage scan rate (dV/dt). The variations in the Li⁺ diffusion coefficient (D_Li⁺) at the electrode/electrolyte interface during the SEI formation process were measured and two regimes were identified depending on the scan rate; for dV/dt ≥ 3.00 mV s^?1, D_Li⁺ was 3.13 × 10^?8 cm² s^?1. At lower scan rates where D_Li⁺ was low, 0.57 × 10^?8 cm² s^?1, a uniform and continuous SEI layer with a tubular morphology was formed whereas at high dV/dt, the SEI formed had a columnar morphology and did not provide a uniform coverage.     

Maximum hole concentration for Hydrogen-terminated diamond surfaces with various surface orientations obtained by exposure to highly concentrated NO2

NO₂ exposure drastically increases the hole concentration on the surface of hydrogen (H)-terminated diamond. When the NO₂ gas concentration is higher than 300 ppm, the saturated hole sheet concentration p_s stays the same. Therefore, the p_s value is regarded as the high limit of the concentration of holes on H-terminated diamond surface, p_s,max. In this work, we compared p_s,max, mobility μ, and sheet resistance R_s for (100), (110), and (111) H-terminated surfaces of chemical-vapor-deposited single-crystal diamond. On (110), (111), (100) surfaces, the p_s,max values are 1.717 × 10¹⁴ and 1.512 × 10¹⁴ cm^− 2, and 0.981 × 10¹⁴, respectively. This result supports the first-principle calculations: the hole concentration depends on the energy difference between the valence band maximum and the unoccupied orbitals of adsorbent NO₂ molecules. We have achieved R_s of 719.3 Ω/sq (p_s = 1.456 × 10¹⁴ cm^− 2 and μ = 59.6 cm² V^− 1 s^− 1), the lowest reported so far, on (111) surfaces under 20,000-ppm NO₂ atmosphere.     

A dense and fine-grained SiC/Ti3Si(Al)C2 composite and its high-temperature oxidation behavior

A dense SiC/Ti₃Si(Al)C₂ composite was synthesized by in situ hot pressing powders of Si, TiC and Al as a sintering additive at 1500 °C for 2 h under 30 MPa in Ar atmosphere. This composite has a fine-grained and homogeneous microstructure with grain sizes of 5 μm for Ti₃Si(Al)C₂ and of 1 μm for SiC. The SiC/Ti₃Si(Al)C₂ composite possesses an improved oxidation resistance, with parabolic rate constants of 4.57 × 10^?8 kg²/m⁴/s at 1200 °C and 1.31 × 10^?7 kg²/m⁴/s at 1300 °C. This study provides an experimental evidence to confirm the formation of amorphous phases in the oxide scale of the SiC/Ti₃Si(Al)C₂ composite. Microstructure and phase composition of the SiC/Ti₃Si(Al)C₂ composite and oxide scales were identified by X-ray diffractometry and scanning electron microscopy. The mechanism for the enhanced oxidation resistance has been discussed.     

Thin layer drying kinetics of Gundelia tournefortii L.

The literature surveyed revealed that the drying kinetics of Gundelia tournefortii has not been investigated. In this study, mathematical modeling of the thin layer drying kinetics of G. tournefortii is investigated for both the microwave and open sun drying conditions. Five different microwave power levels ranging from 90 to 800 W were used for the microwave drying. Solar radiation for the open sun drying varied from 350 to 1100 W/m². Drying took place in the falling rate period. Increasing the microwave power caused a significant decrease in drying time. The experimental moisture loss data were fitted to the 14 thin layer drying models. Among the models proposed, the Midilli model precisely represented the microwave drying behavior of G. tournefortii with the coefficient of determination higher than 0.996 and mean square of deviation (χ²), root mean square error (RMSE) and mean bias error (MBE) lower than 1.82 × 10^?4, 12 × 10^?3 and 1.4 × 10^?4, respectively for all the microwave drying conditions studied. Values of drying constant (k) were in the range of 0.0098–0.2943 min^?1 and the effective moisture diffusivities (D_eff) of G. tournefortii ranged from 5.5 × 10^?8 to 3.5 × 10^?7 m²/s. The values of k and D_eff increased with the increase of microwave power level. The logarithmic model was found to best describe the open sun drying kinetics of G. tournefortii. The effective diffusivity of G. tournefortii under the sun drying condition was determined as 2.48 × 10^?10 m²/s.     

Exposure to welding particles in automotive plants

This work presents a monitoring study designed to evaluate workers' exposure to particles in several body shops within automotive plants. Concentrations in the proximity of welding activities were measured by a Fast Mobility Particle Sizer, several Condensation Particle Counters, a Nanoparticle Surface Area Monitor and a laser photometer, as well as by several gravimetric samplers. Average concentrations were found to be 1×10⁵ part cm^?3, 3×10³ μm² cm^?3 and 0.4 mg m^?3 for number, surface area and PM₁ concentration, respectively (worst case). Very high concentrations, particularly for surface area, were observed in locations with a high density of manual resistance welding activities or close to oxyacetylene welding activities. Welding emission factors in the automotive plants were also evaluated and in the most critical body shop, the overall welding activities led to emission factors of 2.8×10¹⁵ part min^?1, 7.0×10⁶ μm² min^?1 and 7.9 g min^?1 for number, surface area and PM₁ concentrations, respectively. Finally, particle concentration characterization, along with air exchange ratio measurements in the body shop, showed that the indoor concentrations and, hence, worker particle exposure can be reduced through the use of local exhaust ventilation.     

Direct electron transfer in a mediator-free glucose oxidase-based carbon nanotube-coated biosensor

A novel biosensor was prepared by immobilizing glucose oxidase on multi-walled carbon nanotube (MWCNT)-coated electrospun gold fibers. Homogeneous coating of the electrospun gold fibers by MWCNTs was achieved by electrophoretic deposition at 20 V (40 V cm^?1), a deposition time of 30 s and a solution concentration of 0.25 mg mL^?1. Scanning electron microscopy confirmed the complete coverage of MWCNTs on the fiber surface. The carboxylated MWCNTs on the gold fibers provided an anchor for covalent immobilization of glucose oxidase (GOX). GOX covalently coupled to conductive carbon nanotubes demonstrated direct electron transfer between the enzyme and the electrode surface without the need for a redox active mediator. Electrochemical characterization of the fabricated sensor by cyclic voltammetry revealed that the immobilized GOX exhibited a surface-confined reversible two-electron and two-proton reaction, with an electron transfer rate constant, k_s, of 1.12 s^?1 and a surface coverage of 1.1 × 10^?12 mol cm^?2. The sensor produced a linear response to glucose concentration up to 30.0 mM with a sensitivity of 0.47 μA mM^?1 cm^?2 and a detection limit of 4 μM.     

Thin layer solar drying characteristics of silkworm pupae

Thin layer solar drying experiments of silkworm pupae using a solar tunnel dryer were conducted under the tropical weather conditions of Mahasarakham, Thailand. The dryer consisted of a transparent glass covered flat-plate collector and a drying tunnel connected in series to supply hot air directly into the drying tunnel using a blower. During the experiments, silkworm pupae were dried to the final moisture content of 0.15 kg water kg^?1 dry matter from 4.37 kg water kg^?1 dry matter in 373 min at the corresponding air flow rate of 0.32 kg s^?1. Ten different thin layer drying models were compared according to their coefficient of determination to estimate drying curves. The Midilli–Kucuk model precisely represents the solar tunnel drying behavior with the coefficient of determination (R²) of 0.9982. The maximum drying rate and effective moisture diffusivity were 0.6723 kg water kg^?1 dry matter h^?1 and 2.7696 × 10^?10 m² s^?1, respectively, on the drying air flow rate of 0.32 kg s^?1. A quality assessment shows that the lipid content of the dried silkworm pupae was not affected by the solar tunnel dryer. A slight decrease of polyunsaturated fatty acid (PUFA) was observed.     

Electrochemical and peroxidase-catalyzed oxidation of epinephrine

Electrochemical and peroxidase-catalyzed oxidation of epinephrine (EPI) has been studied. In the electrochemical studies a single well-defined, 4e, 4H⁺, pH-dependent oxidation peak was observed in square wave and cyclic sweep voltammetry at edge plane pyrolytic graphite electrode. In the reverse sweep a redox couple was observed. The decay of the UV-absorbing intermediate generated and the first-order rate constants were calculated at different pH and were found to be ～6.3 × 10^?3 s^?1. The detection limit and sensitivity are found to be 17 × 10^?8 M and 2.325 μA μM^?1 respectively. At pH 7.2, the electro-oxidation product was characterized using NMR and DEPT studies as leucoadrenochrome. The peroxidase-catalyzed oxidation was carried out using horseradish peroxidase and initiated by adding H₂O₂. The identical spectral changes, rate constants and product formed during electrochemical and enzymatic oxidation suggest that the same intermediate species is generated during both the oxidations. A tentative pathway for the oxidation of EPI has been suggested. It is concluded that the electrochemical and peroxidase-catalyzed oxidation of EPI proceed by an identical pathway.     

Equilibrium and kinetic studies for removal of malachite green from aqueous solution by a low cost activated carbon

A low cost activated carbon was synthesized from coconut coir and was applied for the removal of malachite green (MG) from its aqueous solutions. Characterization of the adsorbent was carried out and BET surface area of the adsorbent was found to be 205.27 m²/g. The process of removal of MG was better governed by second order kinetics with a rate constant of 0.21 g mg^?1 min^?1 at 323 K. The coefficient of mass transfer was found to be 3.70 × 10^?5 cm s^?1. The value of ΔG° was found to be negative indicating feasibility and spontaneity of the adsorption process.     

Thermal,mechanical and electrical properties of hard B4C,BCN, ZrBC and ZrBCN ceramics

We study the thermal, mechanical and electrical properties of B₄C, BCN, ZrBC and ZrBCN ceramics prepared in the form of thin films by magnetron sputtering. We focus on the effect of Zr_x(B₄C)_1−x sputter target composition, the N₂+Ar discharge gas mixture composition, the deposition temperature and the annealing temperature after the deposition. The thermal properties of interest include thermal conductivity (observed in the range 1.3–7.3 W m⁻¹ K⁻¹), heat capacity (0.37–1.6×10³ J kg⁻¹ K⁻¹ or 1.9–4.1×10⁶ Jm⁻³ K⁻¹), thermal effusivity (1.6–4.5×10³ J m⁻² s^−1/2 K⁻¹) and thermal diffusivity (0.38–2.6×10⁻⁶ m² s⁻¹). We discuss the relationships between materials composition, preparation conditions, structure, thermal properties, temperature dependence of the thermal properties and other (mechanical and electrical) properties. We find that the materials structure (amorphous×crystalline hexagonal ZrB₂-like×nanocrystalline cubic ZrN-like), more than the composition, is the crucial factor determining the thermal conductivity and other properties. The results are particularly important for the design of future ceramic materials combining tailored thermal properties, mechanical properties, electrical conductivity and oxidation resistance.     

Effects of mechanical milling on preparation and properties of CuAl1−xFexO2 thermoelectric ceramics

CuAl_1?xFe_xO₂ (x = 0, 0.1, and 0.2) thermoelectric ceramics produced by a reaction-sintering process were investigated. Pure CuAlO₂ and CuAl_0.9Fe_0.1O₂ were obtained. Minor CuAl₂O₄ phase formed in CuAl_0.8Fe_0.2O₂. Addition of 10 mol% Fe lowered the sintering temperature obviously and enhanced the grain growth. At x = 0.1, electrical conductivity = 3.143 Ω^?1 cm^?1, Seebeck coefficient = 418 μV K^?1, and power factor = 5.49 × 10^?5 W m^?1 K^?2 at 600 °C were obtained. The reaction-sintering process is simple and effective in preparing CuAlO₂ and CuAl_0.9Fe_0.1O₂ thermoelectric ceramics for applications at high temperatures.     

Casting and characterization of LiMgPO4 glass free LTCC tape for microwave applications

The LiMgPO₄ ceramic has been prepared through the solid state ceramic route. The powder has an average particle size of 1.1 μm and BET surface area of 2.7 m² g^?1. Good dispersion of LiMgPO₄ has been achieved in ethanol/xylene mixture with the addition of 2 wt.% fish oil. The tape casting slurry of LiMgPO₄ with typical pseudoplastic behavior has been prepared and cast into thin tapes of thickness 70 μm. LiMgPO₄ green tape shows a tensile strength of 0.22 MPa and average surface roughness of 0.25 μm. The green tape has an ?_r of 3.2 and tan δ of 0.0688 at 5 GHz. The thermo-laminated tape (4 layers) sintered at 950 °C/2 h shows good microwave dielectric properties: ?_r = 6.4 and tan δ = 0.0002. LiMgPO₄ has a coefficient of thermal expansion of 10.5 ppm/°C and thermal conductivity of 7.1 W m^?1 K^?1.     

Electrochemical characterization of tenoxicam using a bare carbon paste electrode under stagnant and forced convection conditions

From potentiostatic current transients and voltammetry studies, carried out under both stagnant and forced convection conditions, the tenoxicam electrochemical behavior on a bare carbon paste rotating disk electrode was assessed in an aqueous solution (pH = 0.403). It was found that tenoxicam's electrochemical oxidation is a mass transfer-controlled process where a current peak is clearly formed at around 0.74 V when the potential scan was varied in the positive direction. However, when the potential was switched to the negative direction, up to the initial potential value, no reduction peak was formed. Tenoxicam's electrochemical oxidation follows an EC mechanism where the electrodic and chemical kinetics are fast. From sample-current voltammetry both the number of electrons, n, that tenoxicam losses during its electro-oxidation and its half-wave potential, E_1/2, were determined to be 2 and 0.770 V vs. Ag/AgCl, respectively. Moreover, from differential pulse voltammetry plots it was confirmed that effectively in this case n = 2. Considering 2 electrons and both the Randles-Sevcik and Cotrell equations, the tenoxicam's diffusion coefficient, D, was determined to be (3.745 ± 0.077) × 10^?6 and (4.116 ± 0.086) × 10^?6 cm² s^?1, respectively. From linear sweep voltammetry plots recorded under forced convection conditions, it was found that Levich's equation describes adequately the limiting current recorded as a function of the electrode rotation rate, from where the D value was also found to be (4.396 ± 0.058) × 10^?6 cm² s^?1. Therefore, the average D value was (4.09 ± 0.33) × 10^?6 cm² s^?1. Furthermore, from the radius of the tenoxicam molecule, previously optimized at M052X/6-31 + G(d,p) level of theory, and using the Stokes–Einstein approach, D was also estimated to be 4.54 × 10^?6 cm² s^?1 which is similar to the experimentally estimated values, under both stagnant and forced convection hydrodynamic conditions.     

Deformation behavior and joining of a MgF2 optical ceramic

Compressive deformation behavior of a polycrystalline magnesium fluoride (MgF₂) ceramic was investigated at temperatures ranging from 760 to 830 °C in an argon atmosphere at strain rates between 2 × 10⁻⁶ and 4 × 10⁻⁵ s⁻¹. Steady-state flow stresses increased with increasing strain rates and ranged between 2 and 38 MPa. Stress exponents of ≈1.4 ± 0.2 were determined at temperatures >760 °C, indicative of a viscous diffusion-controlled deformation mechanism. Activation energy, determined from flow stress as a function of temperature, at a constant strain rate, was ≈476 ± 60 kJ/mol. Self-joining by plastic deformation of MgF₂ was demonstrated at 830 °C at a strain rate of 5 × 10⁻⁶ s⁻¹. The joined samples were characterized by optical transmission measurements and their transmittivity was ≈80% of the unjoined sample in the 2.5–8 μm wavelength range.     

Ultrasound assisted synthesis of Gd and Nd doped ceria electrolyte for solid oxide fuel cells

In this study, the ceramic powders of Ce_1?xGd_xO_2?x/2 and Ce_1?xNd_xO_2?x/2 (x=0.05, 0.10, 0.15, 0.20 and 0.25) were synthesized by ultrasound assisted co-precipitation method. The ionic conductivity was studied as a function of dopant concentration over the temperature range of 300–800 °C in air, using the impedance spectroscopy. The maximum ionic conductivity, σ_800 °C=4.01×10^?2 Scm^?1 with the activation energy, E_a=0.828 kJmol^?1 and σ_800 °C=3.80×10^?2 Scm^?1 with the activation energy, E_a=0.838 kJmol^?1 were obtained for Ce_0.90Gd_0.10O_1.95 and Ce_0.85Nd_0.15O_1.925 electrolytes, respectively. The average grain size was found to be in the range of 0.3–0.6 μm for gadolinium doped ceria and 0.2–0.4 μm for neodymium doped ceria. The uniformly fine crystallite sizes (average 12–13 nm) of the ultrasound assisted prepared powders enabled sintering of the samples into highly dense (over 95%) ceramic pellets at 1200 °C (5 °C min^?1) for 6 h.