Formation of Phosphorus Monoxide (PO) in the Interstellar Medium: Insights from Quantum-chemical and Kinetic Calculations

In recent years, phosphorus monoxide (PO), an important molecule for prebiotic chemistry, has been detected in star-forming regions and in the comet 67P/Churyumov-Gerasimenko. These studies have revealed that, in the interstellar medium (ISM), PO is systematically the most abundant P-bearing species, with abundances that are about one to three times greater than those derived for phosphorus nitride (PN), the second-most abundant P-containing molecule. The reason why PO is more abundant than PN remains still unclear. Experimental studies with phosphorus in the gas phase are not available, probably because of the difficulties in dealing with its compounds. Therefore, the reactivity of atomic phosphorus needs to be investigated using reliable computational tools. To this end, state-of-the-art quantum-chemical computations have been employed to evaluate accurate reaction rates and branching ratios for the P + OH → PO + H and P + H2O → PO + H2 reactions in the framework of a master equation approach based on ab initio transition state theory. The hypothesis that OH and H2O can be potential oxidizing agents of atomic phosphorus is based on the ubiquitous presence of H2O in the ISM. Its destruction then produces OH, which is another very abundant species. While the reaction of atomic phosphorus in its ground state with water is not a relevant source of PO because of emerged energy barriers, the P + OH reaction represents an important formation route of PO in the ISM. Our kinetic results show that this reaction follows an Arrhenius–Kooij behavior, and thus its rate coefficients (α = 2.28 × 10−10 cm3 molecule−1 s−1, β = 0.16 and γ = 0.37 K) increase by increasing the temperature.

Effect of the Process Atmosphere Composition on Alloy 718 Produced by Laser Powder Bed Fusion

The detrimental effect of nitrogen and oxygen when it comes to the precipitation of the strengthening γ’’ and γ’ phases in Alloy 718 is well-known from traditional manufacturing. Hence, the influence of the two processing atmospheres, namely argon and nitrogen, during the laser powder bed fusion (L-PBF) of Alloy 718 parts was studied. Regardless of the gas type, considerable losses of both oxygen of about 150 ppm O2 (≈30%) and nitrogen on the level of around 400 ppm N2 (≈25%) were measured in comparison to the feedstock powder. The utilization of nitrogen as processing atmosphere led to a slightly higher nitrogen content in the as-built material—about 50 ppm—compared to the argon atmosphere. The presence of the stable nitrides and Al-rich oxides observed in the as-built material was related to the transfer of these inclusions from the nitrogen atomized powder feedstock to the components. This was confirmed by dedicated analysis of the powder feedstock and supported by thermodynamic and kinetic calculations. Rapid cooling rates were held responsible for the limited nitrogen pick-up. Oxide dissociation during laser–powder interaction, metal vaporization followed by oxidation and spatter generation, and their removal by processing atmosphere are the factors describing an important oxygen loss during L-PBF. In addition, the reduction of the oxygen level in the process atmosphere from 500 to 50 ppm resulted in the reduction in the oxygen level in as-built component by about 5%.

Biosorption of Cu2+ by Pseudomonas putida Immobilized on Loofa Sponge (Luffa cylindrica L.)

Cu2+ contaminated areas pose serious health risk for the living organisms. In this study, the biosorption of Cu2+ by Pseudomonas putida immobilized on loofa sponge (Luffa cylindrica L.) was investigated. Effects of the particle size of loofa sponge, initial pH, temperature, initial Cu2+ concentration and the stirring speed on the adsorption of Cu2+ were examined. Optimum conditions were determined as follows: loofa sponge particle size is 0.42 - 0.85 mm, initial pH is 5.0, temperature is 30 °C, initial Cu2+ concentration is 25 mg/l, and stirring speed is 130 rpm. According to the results of kinetic calculations, Qmax and ro values were determined as 0.394 mg/g and 0.077 mg/g.min for P. putida immobilized on loofa sponge, respectively, while they were found to be 0.096 mg/g and 0.052 mg/g.min for the loofa sponge only. It is thought that Cu2+ can be removed effectively from the wastewaters by using P. putida immobilized on loofa sponge.

Direct Yellow 8 Azo Removal by Bentonite Clay Solution: Experimental and Theoretical Studies

In the theoretical part, removal of direct yellow 8 (DY8) from water solution was accomplished using Bentonite Clay as an adsorbent. Under batch adsorption, the adsorption was observed as a function of contact time, adsorbent dosage, pH, and temperature. The equilibrium data were fitted with the Langmuir and Freundlich adsorption models, and the linear regression coefficient R2 was used to determine the best fitting isotherm model. thermodynamic parameters of the ongoing adsorption mechanism, such as Gibb's free energy, enthalpy, and entropy, have also been measured. The batch method was also used for the kinetic calculations, and the day's adsorption assumes first-order rate kinetics. The kinetic studies also show that the intraparticle diffusion process was active. Density Functional Theory (DFT) was used to study the dye structure with Gaussian 09 and predict the active site in a molecule using total electron density (TED) and electrostatic surface potential (ESP).

Cytostatic Drug 6-Mercaptopurine Degradation on Pilot Scale Reactors by Advanced Oxidation Processes: UV-C/H2O2 and UV-C/TiO2/H2O2 Kinetics

6-Mercaptopurine (6-MP) is a commonly used cytostatic agent, which represents a particular hazard for the environment because of its low biodegradability. In order to degrade 6-MP, four processes were applied: Photolysis (UV-C), photocatalysis (UV-C/TiO2), and their combination with H2O2, by adding 3 mM H2O2/L (UV-C/H2O2 and UV-C/TiO2/H2O2 processes). Each process was performed with variable initial pH (3.5, 7.0, and 9.5). Pilot scale reactors were used, using UV-C lamps as radiation source. Kinetic calculations for the first 20 min of reaction show that H2O2 addition is of great importance: in UV-C experiments, highest k was reached under pH 3.5, k = 0.0094 min−1, while under UV-C/H2O2, k = 0.1071 min−1 was reached under the same initial pH; similar behavior was observed for photocatalysis, as k values of 0.0335 and 0.1387 min−1 were calculated for UV-C/TiO2 and UV-C/TiO2/H2O2 processes, respectively, also under acidic conditions. Degradation percentages here reported for UV-C/H2O2 and UV-C/TiO2/H2O2 processes are above 90% for all tested pH values. Ecotoxicity analysis of samples taken at 60 min in the photolysis and photocatalysis processes, suggests that contaminant degradation by-products present higher toxicity than the original compound.

Phase Equilibrium of Petroleum Dispersion Systems in Terms of Thermodynamics and Kinetics

The process of paraffin formation has been considered, including the peculiarities of the paraffin structure as a result of phase transitions with a decreasing temperature. Mathematical models for thermodynamic and kinetic calculations of the "solid-liquid" system phase equilibrium have been developed. To shift the "fuel oil-paraffin" balance towards the liquid, it is necessary to reduce the activity ratio of solid and liquid phases by introducing into the system a substance with a lower solubility parameter. To increase the stability, as well as structural and mechanical characteristics of fuel oil, the additive of plant origin was synthesized. The phase transitions in fuel oil depending on the temperature when adding different amounts of additives have been studied.

Analysis of Lyα Dielectronic Satellites to Characterize Temporal Profile of Intense Femtosecond Laser Pulses

In the paper, an X-ray spectroscopy-based approach on laser pulse temporal profile characterization is described. The structure of dielectronic satellites to H-like Lyα lines strongly depends on a plasma electron density, so it can be applied for diagnostics. These spectral lines are mainly emitted during initial stage of laser plasma expansion. It means that plasma parameters obtained via them characterizes matter conditions in a region surrounding a spot of laser-matter interaction. In the case when a laser contrast is high enough, the radiation interacts with cold matter, which had not been preliminary perturbed by a laser prepulse, and the satellites structure shape corresponding to high densities should be observed. It allows us to consider the satellites as a diagnostic tool for the laser temporal profile quality. In the paper dependencies of the dielectronic satellites structure on electron densities obtained from detailed kinetic calculations in the wide range of plasma parameter for different elements are under discussion. Fundamental theoretical aspects of plasma diagnostic based on the feature of satellite structures shape in hot dense plasma, which led to development of the proposed method, are also explained.

Simulation and analysis of the solidification characteristics of a Si-Mo ductile iron

High silicon and molybdenum ductile cast irons (Si-Mo alloys) are commonly used as exhaust manifold materials suffering from high temperature-oxidation and thermal-mechanical fatigue. The structural integrity of cast Si-Mo alloys under these service conditions is attributed to their microstructure consisting of spheroidal graphite and Mo-rich carbide embedded in a ferritic matrix. However, the cast structure includes also pearlite structure having a detrimental effect on the mechanical properties, therefore the cast matrix needs to be heat treated. In this study, the solidification of a Si-Mo ductile iron was investigated using (i) thermodynamic and kinetic calculations by Thermo-Calc and DICTRA software and (ii) thermal analysis in order to reveal out the sequence of phase formation and the phase transformations during solidification and (iii) microanalysis by energy dispersive spectrometer in order to determine elemental segregation and compare with the calculated values. The solidified structure was also characterized and all microstructural features were specified.

Comparative analysis of the effect of Ca and Mg-Al modification on the composite inclusions in S50C Die steel

At present, the effective ways to improve the cleanliness of S50C die steel are Ca or Mg-Al treatment processes. In order to explore the effect difference of two kinds of modification process of S50C killed steel, evaluate the industrial application prospect of the two processes, and clarify the modification mechanism. In this paper, the advantages of Mg-Al modification are demonstrated from the aspects of theoretical basis and actual sample modification effect. The thermodynamics and kinetics of inclusion precipitation, composition, morphology, and distribution are analyzed. The results show that: the precipitation temperature of MnS in S50C die steel is 1686 K, the corresponding solid-phase rate is 0.98. In Mg-Al modification, when the Al content is 332 ppm, the Mg content should be controlled below 14.1 ppm. When the Al content is higher than 0.02%, the Ca content should be controlled below 28.7 ppm. Kinetic calculations show that the equilibrium shape size of MnS is in the range of 0.3‑1.4 µm. Both modifications increase the nucleation rate of inclusions and control the shape and size of inclusions by pre-precipitation. Ca treatment is preventing the formation of large inclusions by forming calcium aluminate. Mg can provide more uniform nucleation sites and form smaller inclusions.