Temperature effect on the chemical composition of a polytetrafluoroethylene surface under the irradiation of synchrotron radiation by means of the X-ray photoelectron spectroscopy

The chemical composition and components of a polytetrafluoroethylene (PTFE) surface was investigated as a function of the temperature under the irradiation of synchrotron radiation (SR) by the X-ray photoelectron spectroscopy (XPS). When the temperature of PTFE under the SR irradiation was less than 100 °C, the C-rich surface appeared. With increasing the temperature more than 150 °C, the relative intensity of the F 1s peak to the C 1s peak increased markedly. At the temperatures of 150–180 °C, the C–C component became small and the CF₂ component was dominant. With further increasing the temperature more than 200 °C, CF₃, CF and C–CF components grew in addition to CF₂ component. Based on these XPS results, the temperature effect on the chemical composition and components is discussed.     

Free volume evolution in polyoxymethylene studied by positron annihilation spectroscopy

The free volume hole and its distribution in polyoxymethylene have been studied over the temperature range (5–90 °C) by positron annihilation lifetime spectroscopy. At a certain temperature (20 °C) the variation of ortho-positronium lifetime shows a distinct increase in its slope. The hole volume shows a small linear increase with temperature below glass transition temperatue and a steeper increase above it. A linear relation between ln(σT^0.5) and 1/V_h was observed and the critical hole volume was estimated.     

Influence of thermal treatment on the glass transition temperature of thermosetting epoxy laminate

The influence of accelerated thermal treatment of thermosetting epoxy laminate on its glass transition temperature was studied. Lamplex^® FR-4 glass fibre-reinforced epoxy laminate (used for printed circuit board manufacturing) was used in these experiments. The composite was exposed to thermal treatments at temperatures ranging from 170 °C to 200 °C for times ranging from 10 to 480 h. The glass transition temperature (T_g) was analysed via dynamic mechanical analysis (DMA). It has been proven that the glass transition temperature rapidly decreases in reaction to thermal stress. The obtained T_g data were used for Arrhenius plots for different critical temperatures (T_g-crit. = 105–120 °C). From their slopes (?E_a/R), the activation energy of the thermal degradation process was calculated as 75.5 kJ/mol. In addition to this main relaxation mechanism, DMA also recorded one smaller relaxation process in the most aged samples. Microscopic analysis of the sample structure showed the presence of pronounced small regions of degradation both on the surface and in the inner structure, which are probably the causes of microscopic delamination and the smaller relaxation process.     

Temperature and sodium chloride effects on the solubility of anthracene in water

The solubility of anthracene was measured in pure water and in sodium chloride aqueous solution (salt concentration, m/mol · kg^?1 = 0.1006, 0.5056, and 0.6082) at temperatures between (278 and 333) K. Solubility of anthracene in pure water agrees fairly well with values reported in earlier similar studies. Solubility of anthracene in sodium chloride aqueous solutions ranged from (6 · 10^?8 to 143 · 10^?8) mol · kg^?1. Sodium chloride had a salting-out effect on the solubility of anthracene. The salting-out coefficients did not vary significantly with temperature over the range studied. The average salting-out coefficient for anthracene was 0.256 kg · mol^?1.The standard molar Gibbs free energies, Δ_trG°, enthalpies, Δ_trH°, and entropies, Δ_trS°, for the transfer of anthracene from pure water to sodium chloride aqueous solutions were also estimated. Most of the estimated Δ_trG° values were positive [(20 to 1230) J · mol^?1]. The analysis of the thermodynamic parameters shows that the transfer of anthracene from pure water to sodium chloride aqueous solution is thermodynamically unfavorable, and that this unfavorable condition is caused by a decrease in entropy.     

Treatment and characterization of gas diffusion layers by sucrose carbonization for PEMFC applications

In this article, a new treatment of gas diffusion layers (GDLs) was proposed by sucrose carbonization in order to obtain high hydrophobicity with low PTFE loading. Carbon was coated both on the cross position and stem of carbon fiber, resulting in the enhancement of carbon paper roughness, which improved the hydrophobicity of carbon paper with low PTFE loading. The water contact angle of carbonized carbon paper with 10 wt.% PTFE loading was measured as 137 ± 1° at 25 °C, which was higher than 125 ± 1° for non-carbonized carbon paper with the same PTFE loading. The performances of MEAs prepared by carbonized carbon paper were higher than those of MEAs prepared by non-carbonized carbon paper. The MEA prepared by carbonized carbon paper with 10 wt.% PTFE loading showed excellent performance compared to the other MEAs.     

Effect of Dissolving Temperature on the Amount of Palladium Dissolved in Borosilicate Glass

To clarify the dissolving behavior of palladium, the effect of temperature on the amount of palladium dissolved in borosilicate glass was investigated. Glass and palladium oxide, selected as a starter material, were mixed and heated at prescribed temperature. The amount of dissolved palladium became higher with temperature increasing up to 850 °C, and lower above 850 °C. Above 850 °C, the reduction of palladium oxide was accelerated. For palladium dissolution in borosilicate glass, not only the viscosity and basicity of the glass but also the decomposition temperature of the initial palladium species seemed to affect the amount of palladium dissolved in glass.     

Preferential crystallization in an unusual case of conglomerate with partial solid solutions

Ethanolamine mandelate (E.M.) crystallizes as a stable conglomerate and has been found to form partial solid solutions. The crystal structure of the pure enantiomer has been solved from single-crystal X-ray diffraction. In order to determine the extreme compositions of the partial solid solutions in equilibrium (87% ee), the isothermal ternary section in the system [(+)-E.M.–(−)-E.M.–(ethanol–water azeotropic mixture)] was established at 25 °C. Several consecutive preferential crystallization attempts (AS3PC method) were undertaken between T_B = 41 °C (starting temperature) and T_F = 25 °C (final temperature) on a 2-L scale.We initially expected to obtain crude crops whose enantiomeric purities would be close to that defined by the isothermal ternary phase diagram (T_F). In fact, the filtered solid phases are of lower enantiomeric excesses: ca. 62% ee. The monitoring of the mother liquor composition over the course of the entrainment shows that the enantiomeric composition of the filtered solid is related to the metastable equilibria involved in the preferential crystallization.     

Facile synthesis of flat crystal ZnO thin films by solution growth method: A micro-structural investigation

Flat crystal ZnO thin films were prepared by chemical bath deposition technique onto glass substrates. XRD patterns of the films deposited at about 80 °C and annealed at 200 °C for 1 h in oxygen environment revealed the existence of polycrystalline hexagonal wurtzite phase with c-axis orientation of crystallites in the films. The crystallite size and lattice strain from X-ray line broadening profile were evaluated using the Scherrer method and Williamson–Hall method. Structural parameters such as dislocation density, stacking faults probability, lattice constants, lattice stress, unit cell volume, internal parameter, texture and number of crystallites per unit area have also been calculated. Surface morphology of the films was analyzed by scanning electron microscopy and atomic force microscopy. Photoluminescence spectrum at room temperature exhibited two luminescence centers, one is for UV emission (near band edge emission) located at 3.18 eV and another is for deep level emission located at 2.56 eV.     

Phase transitions of CaTiO3 ceramics sintered with the aid of NaF and MgF2

New phases with initial composition (1 ? x)CaTiO₃ ? xNaF ? xMgF₂ (0 ≤ x ≤ 0.20) have been prepared at low temperature (950 °C) from mixtures of CaTiO₃ and fluorides NaF and MgF₂. The oxyfluorides obtained have been characterized by X-ray diffraction at room temperature and indexed by isotypy with orthorhombic CaTiO₃. The microstructures of these phases are observed by scanning electron microscopy. Dielectric measurements have been carried out during cooling cycle from 500 °C to room temperature at two frequencies (100 Hz, 1 kHz). Differential scanning calorimetry (DSC), thermogravimetry (TG) and differential thermogravimetry (DTG) analyses have been performed, respectively, from room temperature up to 550 °C (DSC) and 920 °C (TG–DTG). The dielectric measurements revealed two anomalies which have been confirmed by DSC analyses. These phenomena are ascribed to second order phase transitions. The variation of the real permittivity with temperature is in agreement with the class I capacitor specifications. However, the dielectric losses have to be improved.     

Thermogravimetric and FTIR studies of chitosan blends

Results of spectrophotometric and thermogravimetric studies of chitosan (CH) blends with polyvinyl alcohol (PVAL), starch (S) and hydroxypropylcellulose (HPC) obtained by casting from solutions in the form of transparent films containing 0–1.0 weight fraction of CH were discussed. Blends containing S are homogeneous only in the case of low-weight fraction of S (to 0.3).On the basis of results of thermodegradation in dynamic and isothermal conditions, thermal stability of the tested systems was estimated. Thermogravimetric measurements in dynamic conditions were carried out in the temperature range of 100–450 °C at constant heating rate 15 °C/min. From thermogravimetry (TG) and DTG curves the activation energy and characteristic parameters of degradation of the tested blends were determined. The observed growth of activation energy and T_p—temperature of initial weight loss, T_max—temperature of maximal rate and C_e—degree of conversion at the end of the measurement (at temperature 450 °C) along with the increase of polymer fraction (HPC and S) in the CH blend provides an evidence of improved thermal stability of the systems tested.Investigations in isothermal conditions in air at temperature from 100 to 200 °C confirmed appreciable improvement of CH thermal stability in the blends being tested.Infrared spectroscopic analysis of the blends showed a distinct stabilization of the process of chain scission. In the band at 1080 cm⁻¹ associated with absorption in –C–O–C– group during degradation of the blends at temperature 200 °C much smaller decrease due to molecular scission were observed than in the case of pure CH.     

Effect of the Different Sr Dopant Contents on NiO Ceramic

Sr - doped NiO ceramic was studied. The effect of composition variation of Ni_(1-x)Sr_xO where x = 0, 0.01, 0.02, 0.03, 0.05 and 0.10 mole % was prepared by using solid state method. The calcination temperature used at 950 °C for 4 hours and the sintering temperature used at 1200 °C for 3 hours. The results depict the microstructures increase in grains size (0.43 - 3.30 μm) by increase of Sr dopant contents. The density and porosity testing support the result of microstructures analysis. The larger grains size led to increase in density and lower in porosity. The dielectric properties is observed in a wide frequency range of (1 - 1 000 MHz). The increase of dielectric constant is associated with the decrease of dielectric loss. The optimum composition was obtained for the x = 0.03 mole % sample with highest dielectric constant (3.24 x 10³) and lowest dielectric loss (1.42) at 1 MHz.     

High oxygen-reduction activity of silk-derived activated carbon

Activated carbon prepared from silk fibroin, which is free of metal elements, showed a high catalytic activity for the oxygen-reduction reaction (ORR). The activated carbon had a very high onset potential of E_onset = 0.83 V (vs. RHE) in oxygen-saturated 0.5 M H₂SO₄ at 60 °C. The ORR on the activated carbon proceeded by a four-electron process in the high-electrode-potential region; this gradually decreased to a 3.5-electron reaction below about 0.6 V (vs. RHE). Only about 1% of nitrogen atoms (mostly quaternary) remained in the activated carbon by heat-treatment at up to 1200 °C are responsible for the high catalytic activity. The open circuit voltage of a polymer electrolyte fuel cell using the activated carbon as the cathode and a platinum/carbon black anode under pure oxygen and hydrogen gases, respectively, both at one atmosphere, was 0.96 V at 27 °C.     

Lipase catalyzed enantioselective desymmetrization of a prochiral pentane-1,3,5-triol derivative

The enantioselective desymmetrization of the prochiral 3-O-silyl protected pentanetriol derivative 3 was carefully investigated. At −10 °C, the bacterial lipase from Burkholderia cepacia immobilized on ceramic particles led to monoacetate (S)-4 in 52% yield and >99.9% ee. At a reaction temperature of −40 °C the yield and enantioselectivity were even higher, but the reaction time was very long. Theoretical simulations of the reaction progress indicated an enantioselectivity of 25:1 at −10 °C and 35:1 at −40 °C. (S)-4 was converted into the enantiomerically pure building block 5-azidopentane-1,3-diol (S)-7 in two steps. The absolute configuration of (S)-7 was determined by exciton-coupled circular dichroism (ECCD) of diester (S)-8.     

Hydrocracking of cumene over Ni/Al2O3 as influenced by CeO2 doping and γ-irradiation

Cumene hydrocracking was carried out over pure and doped Ni/Al₂O₃ solids and also, on these solids after exposure to different doses of γ-rays between 0.4 and 1.6 MGy. The dopant concentration was varied between 1 and 4 mol% CeO₂. Pure and doped samples were subjected to heat treatment at 400°C and cumene hydrocracking reaction was carried out using various solids at temperatures between 250°C and 400°C by means of micropulse technique. The results showed that both CeO₂ doping and γ-irradiation of the investigated system brought about an increase in its specific surface area. γ-irradiation of pure samples increased their catalytic activities effectively. However, the doping caused a decrease in the catalytic activity. γ-irradiation of the doped samples brought about a net decrease in the catalytic activity.The catalytic reaction products over different investigated solids were ethylbenzene as a major product together with different amounts of toluene, benzene and C₁–C₃ gaseous hydrocarbons. The selectivity towards the formation of various reaction products varies with the reaction temperature, doping and γ-irradiation.     

Serum albumin ligand binding volumes using high pressure denaturation

The pressure shift assay (PSA, also termed either PressureFluor or differential pressure fluorimetry) was used to study the thermodynamics of decanoate and dodecanoate lipid binding to human serum albumin (HSA) in the temperature range from 25 °C to 80 °C and the pressure range from 0.1 MPa to 400 MPa. The ligands stabilized HSA against both pressure and temperature denaturation. The P–T phase diagram for HSA bound to saturated fatty acids is shown. Pressure induced HSA denaturation reversibility is demonstrated via either intrinsic tryptophan or extrinsic probe 1,8-anilinonaphthalene sulfonate (ANS) fluorescence. The effect of guanidinium in a PSA was studied. PSA provides information on ligand binding volumes. The volume changes from protein–ligand binding are thermodynamically important and could be used in designing compounds with specific volumetric binding properties.     

Preparation via microemulsion method and proton conduction at intermediate-temperature of BaCe1−xYxO3−α

The ceramic powders of BaCe_1?xY_xO_3?α (x = 0.05, 0.10, 0.15, 0.20) have been prepared via a microemulsion method. Green compacts of the powders were sintered to densities higher than 95% of theoretical at the lower temperature (1500 °C). The obtained ceramics showed a single-phase of orthorhombic perovskite. The proton conduction was investigated by employing the techniques of AC impedance and electrochemical hydrogen permeation (hydrogen pumping) at 300–600 °C. It was found that the ceramics were almost pure proton conductors in wet hydrogen, and the highest proton conductivity was observed for x = 0.15 at 600 °C. Ammonia was synthesized successfully from nitrogen and hydrogen at atmospheric pressure in the electrolytic cell using BaCe_0.85Y_0.15O_3?α. The maximum rate of NH₃ formation was found to be 2.1 × 10^?9 mol s^?1 cm^?2 at 500 °C with an applied current of 0.75 mA.     

Cationic concentration effects on electron beam cured of carbon-epoxy composites

Electron beam (e-beam) curing is a technology that offers advantages over the thermal curing process, that usually requires high temperature and are time-consuming. E-beam curing is faster and occurs at low temperatures that help reduce residual mechanical stresses in a thermoset composite. The aim of the present study is to analyze the effects of cationic initiator (diaryliodonium hexafluoroantimonate) ranged from 1 to 3 wt% in DGEBA (diglycidyl ether of bisphenol A) epoxy resin when cured by a 1.5 MeV electron beam. The specimens were cured to a total dose of 200.4 kGy for 40 min. Analyses by dynamic mechanical thermal analysis (DMTA) and differential scanning calorimetry (DSC) show that the e-beam irradiated samples with 2 wt% cationic initiator were 96% cured obtained a glass transition temperature (tan δ) of 167 °C. The same epoxy resin, thermally cured for 16 h with an anhydride hardener, reached a T_g (tan δ) of 136 °C. So, the irradiated sample had its T_g increased approximately 20% and the curing process was much less time consuming.     

Polypyrrole/carbon supercapacitor electrode with remarkably enhanced high-temperature cycling stability by TiC nanoparticle inclusion

In the potential applications for electric vehicle and stand-alone renewable energy storage, supercapacitors are likely to constantly operate at elevate temperatures, and yet the study on high-temperature cycling behavior of conducting polymer-containing supercapactors is scarce. Polypyrrole (PPy) film, doped with p-toluenesulfonate, has been coated onto activated carbon (AC) electrode preform. Although the specific capacitance of the electrode is doubled, from 176 F/g to 352 F/g, with coating of 17.7 wt.% PPy, the capacitance lost nearly 60% after 10,000 cycles at 40 °C, in contrast to 20% loss at 25 °C. It is demonstrated that the problem of accelerated fading at high temperature is effectively alleviated, in conjunction with significant (up to 50%) improvement in power performance, by embedding conductive TiC nanoparticles within the PPy layer via co-electroplating. With addition of 1.7 wt.% of TiC in the composite electrode, the capacitance retains 92% of its initial capacitance under the same cycling condition (40 °C, 10,000 cycles). The enhanced high-temperature cycling stability has in part been attributed to the reduction in the mismatch of thermal expansion coefficient between the conducting polymer layer and the AC substrate.     

Unveiling the crucial role of temperature on the stability of oxygen reduction reaction electrocatalysts

The stability of Pt-based/C electrocatalysts used in proton exchange membrane fuel cell (PEMFC) systems is commonly evaluated via accelerated stress testing in half-cell configuration at temperature close to ambient (20 ≤ T ≤ 25 °C), and 100% relative humidity (liquid electrolyte). Those conditions are by far different from those encountered in PEMFC systems (solid electrolyte, 60 ≤ T ≤ 80 °C, 0 ≤ relative humidity ≤ 100%), and fail in reproducing the morphological changes and the performance losses encountered during real life. Here, using a high surface area Pt/C electrocatalyst, we show that the gap between half-cell and real PEMFC configurations can be bridged by considering the pronounced effect of the temperature. The accelerated stress tests (ASTs) conducted in liquid electrolyte at T = 80 °C more accurately reflect the changes in morphology and surface reactivity occurring in real PEMFC environment, and provide gain in time. Due to massive release of Pt^z + ions in the electrolyte during ASTs performed at T = 80 °C, using fresh electrolyte is strongly recommended for correct determination of the oxygen reduction reaction (ORR) kinetics.     

Structure characteristics contributing to flame retardancy in diazo modified novolac resins

The physical characteristics of two modified novolac resins (carbonyl phenyl azo novolac resin; CPAN and 4-(4-hydroxyphenyl azo) benzyl ester novolac resin; HPDEN) bearing nitrogen and aromatic functional groups by diazo-coupling or esterification in the branch structure of phenol novolac resin were examined. Presence of the modifiers raised the phenolic decomposition temperature (5% weight loss) from 300 °C (pure Phenolic) to 330 °C and 380 °C, while the char residue increased from 45% to 56% and 68%, respectively. The kinetics for thermal degradation energies (E_a) also rose from 151 kJ/mol K to 254 kJ/mol K (CPAN) and 273 kJ/mol K (HPDEN). The retarded decomposition kinetics is attributed both to the increase of crosslink densities and high aromatic content in the derivative resins. On the other hand, the diazo-coupling or phenyl diazenyl ester produces non-combustible gases (N₂, CO₂ and CO) during formation of aromatic char which dilute the ambient oxygen gas. Both the production of gases and the retarded kinetics due to cross-linking are definitive for the improved flame resistance.