A quantitative explanation for the apparent anomalous temperature dependence of OH + HO2 = H2O + O2 through multi-scale modeling

Kinetic models for complex chemical mechanisms are comprised of tens to thousands of reactions with rate constants informed by data from a wide variety of sources – rate constant measurements, global combustion experiments, and theoretical kinetics calculations. In order to integrate information from distinct data types in a self-consistent manner, a framework for combustion model development is presented that encapsulates behavior across a wide range of chemically relevant scales from fundamental molecular interactions to global combustion phenomena. The resulting kinetic model consists of a set of theoretical kinetics parameters (with constrained uncertainties), which are related through kinetics calculations to temperature/pressure/bath-gas-dependent rate constants (with propagated uncertainties), which in turn are related through physical models to combustion behavior (with propagated uncertainties). Direct incorporation of theory in combustion model development is expected to yield more reliable extrapolation of limited data to conditions outside the validation set, which is particularly useful for extrapolating to engine-relevant conditions where relatively limited data are available. Several key features of the approach are demonstrated for the H₂O₂ decomposition mechanism, where a number of its constituent reactions continue to have large uncertainties in their temperature and pressure dependence despite their relevance to high-pressure, low-temperature combustion of a variety of fuels. Here, we use the approach to provide a quantitative explanation for the apparent anomalous temperature dependence of OH + HO₂ = H₂O + O₂ – in a manner consistent with experimental data from the entire temperature range and ab initio transition-state theory within their associated uncertainties. Interestingly, we do find a rate minimum near 1200 K, although the temperature dependence is substantially less pronounced than previously suggested.     

Shock tube/laser absorption studies of the decomposition of methyl formate

Reaction rate coefficients for the major high-temperature methyl formate (MF, CH₃OCHO) decomposition pathways, MF → CH₃OH + CO (1), MF → CH₂O + CH₂O (2), and MF → CH₄ + CO₂ (3), were directly measured in a shock tube using laser absorption of CO (4.6 μm), CH₂O (306 nm) and CH₄ (3.4 μm). Experimental conditions ranged from 1202 to 1607 K and 1.36 to 1.72 atm, with mixtures varying in initial fuel concentration from 0.1% to 3% MF diluted in argon. The decomposition rate coefficients were determined by monitoring the formation rate of each target species immediately behind the reflected shock waves and modeling the species time-histories with a detailed kinetic mechanism [12]. The three measured rate coefficients can be well-described using two-parameter Arrhenius expressions over the temperature range in the present study: k₁ = 1.1 × 10¹³ exp(?29556/T, K) s^?1, k₂ = 2.6 × 10¹² exp(?32052/T, K) s^?1, and k₃ = 4.4 × 10¹¹ exp(?29 078/T, K) s^?1, all thought to be near their high-pressure limits. Uncertainties in the k₁, k₂ and k₃ measurements were estimated to be ±25%, ±35%, and ±40%, respectively. We believe that these are the first direct high-temperature rate measurements for MF decomposition and all are in excellent agreement with the Dooley et al. [12] mechanism. In addition, by also monitoring methanol (CH₃OH) and MF concentration histories using a tunable CO₂ gas laser operating at 9.67 and 9.23 μm, respectively, all the major oxygen-carrying molecules were quantitatively detected in the reaction system. An oxygen balance analysis during MF decomposition shows that the multi-wavelength laser absorption strategy used in this study was able to track more than 97% of the initial oxygen atoms in the fuel.     

Defect structure analysis of B-site doped perovskite-type proton conducting oxide BaCeO3 Part 1: The defect concentration of BaCe0.9M0.1O3−δ (M = Y and Yb)

By means of a high-temperature gravimetry, the defect chemical relationships between oxygen nonstoichiometry and water content in BaCe_0.9M_0.1O_3?δ (M = Y and Yb) were investigated as functions of partial pressure of oxygen, P(O₂), partial pressure of water vapor, P(H₂O), and temperature. Concentrations of protonic defect and that of oxygen vacancy strongly depend on P(H₂O) and temperature, while the dependences on P(O₂) were weak. The equilibrium constants of the water vapor incorporation reaction H₂O + V_O^??? + O_O^× = 2OH_O^? were determined. Concentrations of hole, [h^?], in the dry-atmospheres were determined by the weight gain by the incorporation of oxygen from the gas atmospheres. The [h^?] values increased with decreasing temperature. The [h^?] values were estimated to be about 2 to 3 orders of magnitude less than [OH_O^?] values measured in the wet-atmospheres.     

On the kinetics of the C5H5 + C5H5 reaction

The possibility that the reaction between two cyclopentadienyl radicals (cC₅H₅) may lead to the production of naphthalene has been the subject of considerable theoretical and experimental studies. Though it has been proposed that this reaction may be the main channel for the formation of naphthalene in many combustion environments, the elementary mechanism leading from the initial adduct (C₅H₅_C₅H₅) to naphthalene is still not clear. In this study the portion of the C₁₀H₁₀ PES accessible to C₅H₅_C₅H₅ has been theoretically re-examined using density functional theory to locate stationary points and the CBS-QB3 computational protocol to determine energies. A new reaction pathway leading to the formation of a set of azulyl radicals was identified. Since it is known that azulyl radicals can easily decompose to naphthalene and atomic H, the proposed pathway provides an effective route for the formation of naphthalene. Channel specific kinetic constants were determined between 1100 K and 2000 K integrating the master equation for a PES comprising both this reaction pathway and the literature reaction pathway, which main product is the fulvalenyl radical. It was found that the main reaction channel is decomposition to reactants in the whole temperature range investigated and that the azulyl reaction channel is dominant over the fulvalenyl pathway up to 1450 K. The rate constants calculated at 1 bar for the azulyl and fulvalenyl reaction channels are 10^14.72T(K)^?0.853 exp(?3650/T(K)) and 10^10.30T(K)^0.951 exp(?7948/T(K)) cm³/mol/s, respectively. The rate constant for the formation of naphthalene through the azulyl channel is consistent with recent estimates based on the kinetic simulation of the pyrolysis and oxidation of cyclopentadiene.     

Dissociation of dimethyl ether at high temperatures

The decomposition of dimethyl ether (CH₃OCH₃) has been investigated behind incident shock waves in a diaphragmless shock tube using laser schlieren densitometry, LS (T = 1500–2450 K, P = 57 ± 4, 125 ± 5 and 253 ± 12 Torr). The LS density gradient profiles were simulated and excellent agreement was found between the simulations and experimental profiles. Rate coefficients for CH₃OCH₃ → CH₃O + CH₃ were obtained. They showed strong fall-off, and at the lower end of the experimental temperature range are close to the low pressure limit. First order rate coefficient expressions were determined over 1500 < T < 2450 K. k_57Torr = (3.10 ± 1.0) × 10⁷⁹T^?19.03 exp(?54417/T) s^?1, k_125Torr = (1.12 ± 0.3) × 10⁸³T^?19.94 exp(?55554/T) s^?1and k_253Torr = (1.02 ± 0.3) × 10⁷³T^?17.09 exp(?51500/T) s^?1. The effect of a roaming channel for decomposition of dimethyl ether was assessed and the best agreement was obtained with 1% dissociation of DME via the roaming path.     

Volumetric properties and viscosities of the 2-pyrrolidone + 1,2-propanediol + water ternary system and its binary constituents at T = 313.15 K

Densities and viscosities of ternary mixtures of 2-pyrrolidone + 1,2-propanediol + water and corresponding binary mixtures of 1,2-propanediol + water, 2-pyrrolidone + water and 2-pyrrolidone + 1,2-propanediol have been measured over the whole composition range at 313.15 K. From the obtained data, the excess molar volumes (V^E), the deviations in viscosity (Δη) and the excess Gibbs free energy of activation (ΔG^?E) have been calculated. The V^E, Δη and ΔG^?E results were correlated and fitted by the Redlich–Kister equation for binary mixtures and by the Cibulka equation for ternary mixtures, as a function of mole fraction. Several predictive empirical relations were applied to predict the excess molar volumes of ternary mixtures from the binary mixing data.     

Submillimeter-wave measurements of N2 and O2 pressure broadening for HO2 radical generated by Hg-photosensitized reaction

The N₂ and O₂ pressure broadening coefficients of the pure rotational transitions at 625.66 GHz (N_KaKc=10_1?9–10_0?10, J=10.5–10.5) and 649.70 GHz (N_KaKc=10_2?9–9_2?8, J=9.5–8.5) in the vibronic ground state X²A′ of the perhydroxyl (HO₂) radical have been determined by precise laboratory measurements. For the production of HO₂, the mercury-photosensitized reaction of the H₂ and O₂ precursors was used to provide an optimum condition for measurement of the pressure broadening coefficient. The Superconducting Submillimeter-wave Limb Emission Sounder (SMILES) was designed to monitor the volume mixing ratio of trace gases including HO₂ in the Earth's upper atmosphere using these transitions. The precise measurement of pressure broadening coefficient γ in terms of the half width at half maximum is required in order to retrieve the atmospheric volume mixing ratio. In this work, γ coefficients of the 625.66 GHz transition were determined for N₂ and O₂ at room temperature as γ(N₂)=4.085±0.049 MHz/Torr and γ(O₂)=2.578±0.047 MHz/Torr with 3σ uncertainty. Similarly, the coefficients of the 649.70 GHz transition were determined as γ(N₂)=3.489±0.094 MHz/Torr and γ(O₂)=2.615±0.099 MHz/Torr. The air broadening coefficients for the 625.66 GHz and 649.70 GHz lines were estimated at γ(air)=3.769±0.067 MHz and 3.298±0.099 MHz respectively, where the uncertainty includes possible systematic errors. The newly determined coefficients are compared with previous results and we discuss the advantage of the mercury-photosensitized reaction for HO₂ generation. In comparison with those of other singlet molecules, the pressure broadening coefficients of the HO₂ radical are not much affected by the existence of an unpaired electron.     

The reaction of 2,5-dimethylfuran with hydrogen atoms – An experimental and theoretical study

The kinetics of the reaction of hydrogen atoms with 2,5-dimethylfuran (25DMF), a promising liquid transport biofuel, was experimentally studied in a shock tube at temperatures between 970 and 1240 K and pressures of 1.6 and 4.8 bar. The hydrogen atoms were produced by pyrolysis of ethyl iodide and monitored by atom resonance absorption spectrometry. From the hydrogen atom concentration–time profiles, overall rate coefficients for the reaction H + 25DMF → products (R1) were inferred. The results can be expressed by the Arrhenius equation k₁ = 4.4 × 10^?11 exp(?1180 K/T) cm^?3 s^?1 with an estimated uncertainty of ±30%. A significant pressure dependence was not observed. The results were analyzed in terms of statistical rate theory with molecular and transition state data from quantum chemical calculations. Three different compound methods were used to characterize the potential energy surface: CBS-QB3, CBS-APNO, and G3. It is found that reaction (R1) mainly (>75%) proceeds via an addition–elimination mechanism to yield 2-methylfuran + CH₃. Kinetic parameters for the most important competing channels of the net reaction (R1) were calculated.     

Determination of nitrofurans in feeds based on silver nanoparticle-catalyzed chemiluminescence

A highly sensitive chemiluminescence (CL) method for the determination of nitrofurans (NFs) was developed based on the enhancement of CL intensity of luminol–H₂O₂–NFs system by silver nanoparticles (AgNPs). It was supposed that the oxygen-related radicals of OH and superoxide radical (O₂^?) could be produced when NFs reacted with H₂O₂. Furthermore, the enhancement mechanism was originated from the reinforcer of AgNPs, which could catalyze the generation of the OH radical. Then OH radicals reacted with luminol anion and HO₂^? to form luminol radical (L^?) and O₂^?. The excited state 3-aminophthalate anion was obtained in the reaction of L^? and O₂^?, which was the emitter (luminophor) in the luminol–H₂O₂ CL reaction system and the maximal emission of the CL spectrum was at 425 nm. The experiments of scavenging oxygen-related radicals were done to confirm these reactive oxygen species participated in the CL reaction. The limits of detection (LOD) (S/N=3) were 8×10^?7 g mL^?1 for furacilin, 8×10^?8 g mL^?1 for furantoin, 4×10^?8 g mL^?1 for furazolidone and 2×10^?7 g mL^?1 for furaltadone. The proposed method was successfully applied to the determination of NFs in feeds and pharmaceutical samples.     

La0.75Sr0.25Cr0.5Mn0.5O3−δ + Cu composite anode running on H2 and CH4 fuels

La_1−xSr_xCr_1−xM_xO_3−δ (M = Cr, Fe, V) system has been studied as anode materials for solid oxide fuel cells (SOFCs). The perovskite La_0.75Sr_0.25Cr_0.5Mn_0.5O_3−δ (LSCM) is stable in both H₂ and CH₄ atmospheres at temperatures up to 1000°C. However, in the reducing atmospheres of H₂ and CH₄, its electronic conductivity is greatly reduced from its value in air. We have characterized LSCM as the anode of a SOFC having 250 μm-thick La_0.8Sr_0.2Ga_0.83Mg_0.17O_2.815 (LSGM) as the electrolyte and SrCo_0.8Fe_0.2O_3−δ (SCF) as the cathode. We report a comparison of the overpotentials at the following anodes: (1) La_0.4Ce_0.6O_1.8 (LDC) + NiO composite in H₂, (2) porous LSCM in H₂ and CH₄, (3) porous LSCM impregnated with CuO in H₂ and CH₄ and (4) porous LSCM impregnated with CuO and sputtered with Pt in H₂ and CH₄. An LSCM + CuO + Pt anode gave a maximum power output at 850 °C of 850 mW/cm² and 520 mW/cm², respectively, with H₂ and CH₄ as fuel whereas anode (1) gave 1.4 W/cm² at 800 °C in H₂. There was no noticeable coke formation in CH₄ with anodes (2), (3) and (4), which demonstrates that the perovskite oxide is a plausible option for the anode of a SOFC operating with hydrocarbon fuels. We also report the moisture effect in the H₂ and CH₄ fuel-oxidation process.     

Kinetics for the reactions of phenyl with methanol and ethanol: Comparison of theory and experiment

The kinetics of the C₆H₅ reactions with CH₃OH and C₂H₅OH has been measured by pulsed-laser photolysis/mass-spectrometry (PLP/MS) employing acetophenone as the radical source. Kinetic modeling of the benzene formed in the reactions over the temperature range 306–771 K allows us to reliably determine the total rate constants for H-abstraction reactions. In order to improve our low temperature measurements down to 304 K we have also applied the cavity ring-down spectrometric technique using nitrosobenzene as the radical source. Both sets of data agree closely. A weighted least-squares analysis of the two complementary sets of data for the two reactions gave the total rate constants k(CH₃OH) = (7.82 ± 0.44) × 10¹¹ exp [?(853 ± 30)/T] and k(C₂H₅OH) = (5.73 ± 0.58) × 10¹¹ exp [?(1103 ± 44)/T] cm³ mol^?1 s^?1 for the temperature range studied. Theoretically, four possible product channels of the C₆H₅ + CH₃OH reaction producing C₆H₆ + CH₃O, C₆H₆ + CH₂OH, C₆H₅OH + CH₃ and C₆H₅OCH₃ + H and five possible product channels of the C₆H₅ + C₂H₅OH reaction producing C₆H₆ + C₂H₅O, C₆H₆ + CH₂CH₂OH, C₆H₆ + CH₃CHOH, C₆H₅OH + CH₃CH₂ and C₆H₅OCH₂CH₃ + H have been computed at the G2M//B3LYP/6?311+G(d, p) level of theory. The hydrogen abstraction channels were predicted to have lower energy barriers than those for the substitution reactions and their rate constants were calculated by the microcanonical variational transition state theory at 200–3000 K. The predicted rate constants are in good agreement with the experimental values. Significantly, the rate constant for the CH₃OH reaction with C₆H₅ was found to be greater than that for the C₂H₅OH reaction and both reactions were found computationally to be dominated by H-abstraction from the hydroxyl group attributable to the affinity of the phenyl toward the OH group and the predicted lower energy barriers for the OH attack.     

High-pressure dielectric studies of a novel hydrogen-bonded ferroelectric (NH4)2H2P2O6

The hydrostatic pressure effect on the dielectric properties of (NH₄)₂H₂P₂O₆ ferroelectric crystal was studied for pressures from 0.1 MPa to 360 MPa and for temperatures from 100 to 190 K. The pressure–temperature phase diagram obtained is linear with increasing pressure. The paraelectric–ferroelectric phase transition temperature decreases with increasing pressure with the pressure coefficient dT_c/dp=?5.16×10^?2 K MPa^?1. Additionally, the pressure dependences of Curie–Weiss constants for the crystal in paraelectric (C₊) and ferroelectric (C_?) phases are evaluated and discussed. The possible mechanism of paraelectric–ferroelectric phase transition is also discussed.     

Multi-species time-history measurements during high-temperature acetone and 2-butanone pyrolysis

High-temperature acetone and 2-butanone pyrolysis studies were conducted behind reflected shock waves using five species time-history measurements (ketone, CO, CH₃, CH₄ and C₂H₄). Experimental conditions covered temperatures of 1100–1600 K at 1.6 atm, for mixtures of 0.25–1.5% ketone in argon. During acetone pyrolysis, the CO concentration time-history was found to be strongly sensitive to the acetone dissociation rate constant k₁ (CH₃COCH₃ → CH₃ + CH₃CO), and this could be directly determined from the CO time-histories, yielding k₁(1.6 atm) = 2.46 × 10¹⁴ exp(?69.3 [kcal/mol]/RT) s^?1 with an uncertainty of ±25%. This rate constant is in good agreement with previous shock tube studies from Sato and Hidaka (2000) [3] and Saxena et al. (2009) [4] (within 30%) at temperatures above 1450 K, but is at least three times faster than the evaluation from Sato and Hidaka at temperatures below 1250 K. Using this revised k₁ value with the recent mechanism of Pichon et al. (2009) [5], the simulated profiles during acetone pyrolysis show excellent agreement with all five species time-history measurements. Similarly, the overall 2-butanone decomposition rate constant k_tot was inferred from measured 2-butanone time-histories, yielding k_tot(1.5 atm) = 6.08 × 10¹³ exp(?63.1 [kcal/mol]/RT) s^?1 with an uncertainty of ±35%. This rate constant is approximately 30% faster than that proposed by Serinyel et al. (2010) [11] at 1119 K, and approximately 100% faster at 1412 K. Using the measured 2-butanone and CO time-histories and an O-atom balance analysis, a missing removal pathway for methyl ketene was identified. The rate constant for the decomposition of methyl ketene was assumed to be the same as the value for the ketene decomposition reaction. Using the revised k_tot value and adding the methyl ketene decomposition reaction to the Serinyel et al. mechanism, the simulated profiles during 2-butanone pyrolysis show good agreement with the measurements for all five species.     

Magnetoresistance hysteresis of bulk textured Bi1.8Pb0.3Sr1.9Ca2Cu3Ox + Ag ceramics and its anisotropy

Magnetoresistance of bulk textured Bi_1.8Pb_0.3Sr_1.9Ca₂Cu₃O_x + Ag ceramics has been studied in the magnetic fields applied parallel and perpendicular to a–b planes of Bi2223 crystallites. Besides well known anisotropy of magnetoresistance of textured superconductors (R_H || c > R_H || a–b), anisotropic hysteresis of R(H) dependences was investigated. Parameters characterizing hysteretic R(H) curves differ for the cases H || c and H || a–b. This behavior is explained within the model of a granular superconductor where the total magnetic induction in the intercrystallite boundaries is superposition of the external field and the magnetic field induced by dipole magnetic moments of neighbor crystallites.     

Polymorphic phase transition and thermal stability in squaric acid (H2C4O4)

Phase transformations in squaric acid (H₂C₄O₄) have been investigated by thermogravimetry and differential scanning calorimetry with different heating rates β. The mass loss in TG apparently begins at onset temperatures T_di=245±5 °C (β=5 °C min^?1), 262±5 °C (β=10 °C min^?1), and 275±5 °C (β=20 °C min^?1). A polymorphic phase transition was recognized as a weak endothermic peak in DSC around 101 °C (T_c⁺). Further heating with β=10 °C min^?1 in DSC revealed deviation of the baseline around 310 °C (T_i), and a large unusual exothermic peak around 355 °C (T_p), which are interpreted as an onset and a peak temperature of thermal decomposition, respectively. The activation energy of the thermal decomposition was obtained by employing relevant models. Thermal decomposition was recognized as a carbonization process, resulting in amorphous carbon.     

Modeled quenching limits of spherical hydrogen diffusion flames

Hydrogen–air diffusion flames were modeled with an emphasis on kinetic extinction. The flames were one-dimensional spherical laminar diffusion flames supported by adiabatic porous burners of various diameters. Behavior of normal (H₂ flowing into quiescent air) and inverse (air flowing into quiescent H₂) configurations were considered using detailed H₂/O₂ chemistry and transport properties with updated light component diffusivities. For the same heat release rate, inverse flames were found to be smaller and 290 K hotter than normal flames. The weakest normal flame that could be achieved before quenching has an overall heat release rate of 0.25 W, compared to 1.4 W for the weakest inverse flame. There is extensive leakage of the ambient reactant for both normal and inverse flames near extinction, which results in a premixed flame regime for diffusion flames except for the smallest burners with radii on the order of 1 μm. At high flow rates H + OH(+M) → H₂O(+M) contributes nearly 50% of the net heat release. However at flow rates approaching quenching limits, H + O₂(+M) → HO₂(+M) is the elementary reaction with the largest heat release rate.     

Fragmentation of 370 MeV/n 20Ne and 470 MeV/n 24Mg in light targets

Total charge-changing cross sections and cross sections for the production of projectile-like fragments were determined for fragmentation reactions induced by 370 MeV/n ²⁰Ne ions in water and lucite, and 490 MeV/n ²⁴Mg ions in polyethylene, carbon and aluminum targets sandwiched with CR-39 plastic nuclear track detectors. An automated microscope system and a track-to-track matching algorithm were used to count and recognize the primary and secondary particles. The measured cross sections were then compared with published cross sections and predictions of different models. Two models and the three-dimensional Monte Carlo Particle Heavy Ion Transport Code System (PHITS) were used to calculate total charge-changing cross sections. Both models agreed within a few percent for the system ²⁴Mg + CH₂, however a deviation up to 20% was observed for the systems ²⁰Ne + H₂O and C₅H₈O₂, when using one of the models. For all the studied systems, PHITS systematically underestimated the total charge-changing cross section. It was also found that the partial fragmentation cross sections for ²⁴Mg + CH₂ measured in present and earlier works deviated up to 20% for Z = 6–11. Measured cross sections for the production of fragments (Z = 4–9) for ²⁰Ne + H₂O and C₅H₈O₂ were compared with predictions of three different semi-empirical models and JQMD which is used in the PHITS code. The calculated cross sections differed from the measured data by 10–90% depending on which fragment and charge was studied, and which model was used.     

Thermo,Iono and photoluminescence properties of 100 MeV Si7+ ions bombarded CaSiO3:Eu3+ nanophosphor

This paper reports on the thermo (TL), iono (IL) and photoluminescence (PL) properties of nanocrystalline CaSiO₃:Eu³⁺ (1–5 mol %) bombarded with 100 MeV Si⁷⁺ ions for the first time. The effect of different dopant concentrations and influence of ion fluence has been discussed. The characteristic emission peaks ⁵D₀→⁷F_J (J=0, 1, 2, 3, 4) of Eu³⁺ ions was recorded in both PL (1×10¹¹–1×10¹³ ions cm^?2) and IL (4.16×10¹²–6.77×10¹² ions cm^?2) spectra. It is observed that PL intensity increases with ion fluence, whereas in IL the peaks intensity increases up to fluence 5.20×10¹² ions cm^?2, then it decreases. A well resolved TL glow peak at ～304 °C was recorded in all the ion bombarded samples at a warming rate of 5 °C s^?1. The TL intensity is found to be maximum at 5 mol% Eu³⁺ concentration. Further, TL intensity increases sub linearly with shifting of glow peak towards lower temperature with ion fluence.     

Ultrasound (US), Ultraviolet light (UV) and combination (US + UV) assisted semiconductor catalysed degradation of organic pollutants in water: Oscillation in the concentration of hydrogen peroxide formed in situ

Application of Advanced Oxidation Processes (AOP) such as sono, photo and sonophoto catalysis in the purification of polluted water under ambient conditions involve the formation and participation of Reactive Oxygen Species (ROS) like OH, HO₂, O₂⁻, H₂O₂ etc. Among these, H₂O₂ is the most stable and is also a precursor for the reactive free radicals. Current investigations on the ZnO mediated sono, photo and sonophoto catalytic degradation of phenol pollutant in water reveal that H₂O₂ formed in situ cannot be quantitatively correlated with the degradation of the pollutant. The concentration of H₂O₂ formed does not increase corresponding to phenol degradation and reaches a plateau or varies in a wave-like fashion (oscillation) with well defined crests and troughs, indicating concurrent formation and decomposition. The concentration at which decomposition overtakes formation or formation overtakes decomposition is sensitive to the reaction conditions. Direct photolysis of H₂O₂ in the absence of catalyst or the presence of pre-equilibrated (with the adsorption of H₂O₂) catalyst in the absence of light does not lead to the oscillation. The phenomenon is more pronounced in sonocatalysis, the intensity of oscillation being in the order sonocatalysis > photocatalysis ⩾ sonophotocatalysis while the degradation of phenol follows the order sonophotocatalysis > photocatalysis > sonocatalysis > sonolysis > photolysis. In the case of sonocatalysis, the oscillation continues for some more time after discontinuing the US irradiation indicating that the reactive free radicals as well as the trapped electrons and holes which interact with H₂O₂ have longer life time (memory effect).     

In situ characterization of transport properties of superconducting (Cu, C)-system thin films

Transport properties of (Cu, C)Ba₂CuO_x [(Cu, C)-1201] thin films have been characterized by in situ temperature dependence of resistivity, without breaking vacuum from the deposition to the measurement. In in situ transport properties measurements, the obtained results reveal that (Cu, C)Ba₂CuO_x films exhibit T_c > 20 K on the cased of conductivity at 290 K (σ_[290 K]) > 4 × 10² S/cm and temperature coefficient of resistivity (TCR) > 1.5 × 10^?3 K^?1, and doping level of them should be in between under-doped and optimally-doped states. Their results suggest that there would be possible to further increases of T_c, and XPS data suggest that (Cu, C)-system should have the excellent dopability in their charge reservoir and the possibility of low anisotropy.