PHOTOCATALYTIC OPTIMIZATION OF MR DYE BY K-ZnO AND ZnO CATALYSTS UNDER VISIBLE IRRADIATION

The lucubration on the visible light methyl red (MR) degradation using K-ZnO and undoped ZnO photo catalyst was investigated. The successive formation of K-ZnO was ascertained by several techniques such as scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), and UV-Visible spectrophotometer and solid state UV-Vis band gap energy determination by comparing the Kubelka-Monk equation with Tauc equation and the energy band gap was calculated to be 3.28ev. The influence of reaction variables such as MR concentration, reaction pH, catalyst loadings and temperature have been investigated for both process. The kinetics model was developed for both doped and undoped ZnO photocatalyst using pseudo first and second order kinetics, the result indicated that both doped and undoped ZnO followed pseudo first order kinetics due to higher correlation coefficient (R2) value of 0.985 and 0.922 with rate constant (k) of 0.026 min-1 and 0.062 min-1, respectively. Based on the rate constant value (k) obtained at different reaction temperatures, the Arrhenius expression was derived. The derived activation energy (Ea) for the degradation of MR by K-ZnO photocatalysis was 32.109x103JK-1. The optimum condition for K-ZnO showed nearly complete degradation (95%) of the dye molecules with slightly higher degradation efficiency compares to ZnO (91%).

High-Temperature Ignition Kinetics of Gas Turbine Lubricating Oils

Lubricant ignition is a highly undesirable event in any mechanical system, and surprisingly minimal work has been conducted to investigate the auto-ignition properties of gas turbine lubricants. To this end, using a recently established spray injection scheme in a shock tube, two gas turbine lubricants (Mobil DTE 732 and Lubricant A from Cooper et al. 2020) were subjected to high-temperature, post-reflected-shock conditions, and OH* chemiluminescence was monitored at the sidewall location of the shock tube to measure ignition delay time (τign). A combination of an extended shock-tube driver and driver-gas tailoring were utilized to observe ignition between 1183 K and 1385 K at near-atmospheric pressures. A clear, two-stage-ignition process was observed for all tests with Mobil DTE 732, and both first and second stage τign are compared. Second stage ignition was found to be more indicative of lubricant ignition and was used to compare τign values with lubricant A. Both lubricants exhibit three ignition regimes: a high-temperature, Arrhenius-like regime (> 1275 K); an intermediate, negative-temperature-coefficient-like regime (1230–1275 K); and a low-temperature ignition regime (< 1230 K). Similar τign behavior in the high-temperature regime was seen for both lubricants, and a regression analysis using τign data from both lubricants in this region produced the Arrhenius expression τign(μs) = 4.4 × 10−14exp(96.7(kcal/mol)/RT). While lubricant A was found to be less reactive in the intermediate-temperature regime, Mobil DTE 732 was less reactive in the low-temperature regime. As the low-temperature regime is more relevant to gas turbine conditions, Mobil DTE 732 is considered more desirable for system implementation. Chemical kinetic modeling was also performed using n-hexadecane models (a lubricant surrogate suggested in the literature). The current models are unable to reproduce the three regimes observed and predict activation energies much lower than those observed in the high-temperature regime, suggesting n-hexadecane is a poor surrogate for lubricant ignition. Additionally, experiments were conducted with Jet-A for temperatures between 1145 and 1419 K around 1 atm. Good agreement is seen with both literature data and model predictions, anchoring the experiment with previously established τign measurement methods and calculations. A linear regression analysis of the Jet-A data produced the Arrhenius expression: τign(μs) = 6.39 × 10−5exp(41.4(kcal/mol)/RT).

Crystallization kinetics of glassy Se90In10-xAgx alloys: Observation of Mayer-Neldel rule

Glassy alloys of Se90In10-xAgx were prepared using melt quenching technique. Non-isothermal differential scanning calorimetric (DSC) studies were done on Se90In10-xAgx (x = 0, 2, 4, 6, 8 at.%) glassy alloys at four different heating rates (? = 5, 10, 15, 20?C/min). Well defined endothermic and exothermic peaks were obtained at glass transition (Tg) and crystallization temperature (Tc), respectively. Augis and Bennett?s method was used to obtain the composition dependent crystallization activation energy (Ec) and the pre-exponential factor (?0) of the Arrhenius expression. A linear dependence between ln ?0 and Ec was observed showing the existence of compensation effects of the Meyer-Neldel type. These compensation effects confirm the applicability of Meyer-Neldel (MN) rule for the non-isothermal crystallization in the present case.

Kinetics of Leaching Silicon from the Acid Leaching Residue of Pyrolusite

The content of SiO2 was more than 60% in the residue of pyrolusite detached manganese by reduction roasted and acid leached, and it was a better siliceous raw material because of less other impurities. Through leaching silicon process in the residue of pyrolusite with alkali at atmospheric pressure, leaching kinetics of silica in the sodium hydroxide solution was researched. The effects of the leaching temperature and the concentration of sodium hydroxide solution on the leaching behavior of silica from acid-leached pyrolusite slag were examinted. It was found that the extracting rate of silica is significantly influenced by the temperature, and the concentration of NaOH solution. The experimental datas were well interpreted with a shrinking core model under chemical control. On the basis of the Arrhenius expression the apparent activation energy of 77.69 kJ/mol and a reaction order of 0.34 for the extraction of silica was evaluated.

Rate coefficients for the reaction of methylglyoxal (CH₃COCHO) with OH and NO₃ and glyoxal (HCO)₂ with NO₃

Rate coefficients, k, for the gas-phase reaction of CH3COCHO (methylglyoxal) with the OH and NO3 radicals and (CHO)2 (glyoxal) with the NO3 radical are reported. Rate coefficients for the OH + CH3COCHO (k1) reaction were measured under pseudo-first-order conditions in OH as a function of temperature (211–373 K) and pressure (100–220 Torr, He and N2 bath gases) using pulsed laser photolysis to produce OH radicals and laser induced fluorescence to measure its temporal profile. k1 was found to be independent of the bath gas pressure with k1(295 K) = (1.29 ± 0.13) × 10−11 cm3 molecule−1 s−1 and a temperature dependence that is well represented by the Arrhenius expression k1(T) = (1.74 ± 0.20) × 10−12 exp[(590 ± 40)/T] cm3 molecule−1 s−1 where the uncertainties are 2σ and include estimated systematic errors. Rate coefficients for the NO3 + (CHO)2 (k3) and NO3 + CH3COCHO (k4) reactions were measured using a relative rate technique to be k3(296 K) = (4.0 ± 1.0) × 10−16 cm3 molecule−1 s−1 and k4(296 K) = (5.1 ± 2.1) × 10−16 cm3 molecule−1 s−1. k3(T) was also measured using an absolute rate coefficient method under pseudo-first-order conditions at 296 and 353 K to be (4.2 ± 0.8) × 10−16 and (7.9 ± 3.6) × 10−16 cm3 molecule−1 s−1, respectively, in agreement with the relative rate result obtained at room temperature. The atmospheric implications of the OH and NO3 reaction rate coefficients measured in this work are discussed.

Kinetics of Leaching Vanadium with Sulfuric Acid from Carbonaceous Shale Containing Vanadium

ηA kinetic study of the leaching of stone coal ore with sulfuric acid has been investigated. The effects of the stirring speed, particle sizes of stone coal, acid concentration, leaching temperature and acid-ore ratio on the leaching rate of vanadium were examined. It was found that the leaching rate of vanadium was significantly influenced by leaching temperature. The shrinking core model was applied to the leaching process and the results showed that the process was based on chemical reaction control. And the rate of reaction was expressed as 1-(1-η)1⁄3=4.98×106·e-55488⁄RT·t. The apparent activation energy for the leaching of vanadium⁄ was calculated to be ¾5⁄5.49 kJ/mol using Arrhenius expression.

Rate coefficients for the reaction of methylglyoxal (CH₃COCHO) with OH and NO₂ and glyoxal (HCO)₂ with NO₃

Rate coefficients, k, for the gas-phase reaction of CH3COCHO (methylglyoxal) with the OH and NO3 radicals and (CHO)2 (glyoxal) with the NO3 radical are reported. Rate coefficients for the OH + CH3COCHO (k1) reaction were measured under pseudo-first-order conditions in OH as a function of temperature (211–373 K) and pressure (100–220 Torr, He and N2 bath gases) using pulsed laser photolysis to produce OH radicals and laser induced fluorescence to measure its temporal profile. k1 was found to be independent of the bath gas pressure with k1(295 K) = (1.29 ± 0.13) × 10−11 cm3 molecule−1 s−1 and a temperature dependence that is well represented by the Arrhenius expression k1(T) = (1.74 ± 0.20) × 10−12 exp[(590 ± 40)/T] cm3 molecule−1 s−1 where the uncertainties are 2σ and include estimated systematic errors. Rate coefficients for the NO3+ (CHO)2 (k3) and NO3+ CH3COCHO (k4) reactions were measured using a relative rate technique to be k3(296 K) = (3.7 ± 1.0) × 10−16 cm3 molecule−1 s−1 and k4(296 K) = (4.1 ± 1.2) × 10−16 cm3 molecule−1 s−1. k3(T) was also measured using an absolute rate coefficient method under pseudo-first-order conditions at 296 and 353 K to be (4.2 ± 0.8) × 10−16 and (7.9 ± 3.6) × 10−16 cm3 molecule−1 s−1, respectively, in agreement with the relative rate result obtained at room temperature. The atmospheric implications of the OH and NO3 reaction rate coefficients measured in this work are discussed.

Isotope Exchange of Gaseous Oxygen with Oxide LaMno3+δ Nanograins Boundary

Isotope exchange of oxygen 18О2 with the boundary of nanograins of oxide LaMnO3+ obtained by the method of shock-wave loading was investigated in the temperature range of 400 – 500 °C. It was established that the temperature dependence of the isotope exchange rate is described by the Arrhenius expression, the activation energy and the pre-exponential factor being 1.67 eV and 1.8∙102 cm/s, respectively. Comparison with literature data has shown that for oxide LaMnO3+, a significant difference in activation energies and pre-exponential factors is observed for the isotope exchange rate with a ‘defect-free’ surface and the nanograin boundary. In case of the boundary, these parameters were higher: the activation energy about two times, and the pre-exponential factor, by almost 7 orders of magnitude.

High Temperature Diffusion of Oxygen in Chromite

Molecular dynamics was used to calculate the diffusion coefficient of oxygen over a temperature range of 900–1700K. The chromite (FeCr2O4) system used consisted of 448 ions in a spinel structure. The spinel consisted of Fe2+ in tetrahedral sites and Cr3+ ions in octahedral sites surrounded by O2− ions. Schottky defects were made in the system by removing 10 oxygen ions, 4 iron ions and 4 chromium ions. The trajectory files from the simulations were examined for oxygen movement via a vacancy hopping mechanism and the mean-squared displacement of oxygen was plotted against time. A linear fit was performed to the plots and Einstein’s relationship was used to derive the diffusion coefficient from the gradient. The diffusion coefficients were then plotted against temperature and an Arrhenius expression was fitted to the trend and compared with the experimental trend calculated by Takada & Adachi.

Detection of 1CH2 Radicals in Hydrocarbon Pyrolysis Behind Shock Waves Using FM Spectroscopy

Singlet methylene radical ((1an extented Arrhenius expression ofand futhermore rate coefficients for(7)(11)and for the intersystem crossing via(6)were determined.The experimental conditions ranged from 1900 to 4000 K with corresponding pressures between 0.23 to 0.54 bar.Theα(reflects well the experimental results obtained for the b˜