Constant Values Research Articles

Investigations on the complexation and binding mechanism of bovine serum albumin with Ag-doped TiO2 nanoparticles.

It is essential to study the interactions between nanoparticles and proteins to better understand the biological interactions of nanoparticles. In this study, we studied the protein adsorption mode on the surface of Ag-doped TiO2 nanoparticles (NPs) using a model protein, bovine serum albumin (BSA). The mechanism of binding BSA to the Ag-doped TiO2 NPs was studied by applying fluorescence quenching, absorbance measurements, circular dichroism (CD) and Fourier transform infrared (FT-IR) spectroscopy techniques. The strong binding between BSA and Ag-doped TiO2 NPs was confirmed by a high value of binding constant (K = 2.65 × 105 L mol-1). We also studied the thermal stability of BSA in the presence of the Ag-doped TiO2 NPs. Thermodynamic parameters indicated that the adsorption of BSA on the Ag-doped TiO2 NPs was a spontaneous, natural and exothermic process. The effect of Ag-doped TiO2 NPs on the transportation function of BSA was also studied using a fluorescence spectroscopic technique. Fluorescence spectroscopic data suggested the existence of a strong interaction between BSA and the surface of the Ag-doped TiO2 NPs, which indicated that the binding affinities of some selected amino acids in BSA changed. This, in turn, clearly confirms that the Ag-doped TiO2 NPs affect the transportation capability of BSA in blood.

A simple model of magnetic universe without singularity associated with a quadratic equation of state

A model of magnetic universe based on nonlinear electrodynamics has been introduced by Kruglov (Phys Rev D 92:123523, 2015). This model describes an early inflation era followed by a radiation era. We show that this model is related to the model of universe based on a quadratic equation of state introduced in our previous paper (Chavanis in Universe 1:357, 2015). This correspondence may provide a more fundamental justification of our equation of state. It may arise from quantum corrections to linear electrodynamics when the electromagnetic field becomes very high. We discuss two quantitatively different models of early universe. In Model I, the primordial density of the universe is identified with the Planck density. At t=0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$t=0$$\\end{document}, the universe had the characteristics of a Planck black hole (“planckion” particle). During the inflation, which takes place on a Planck timescale, the size of the universe evolves from the Planck length to a size comparable to the Compton wavelength of the neutrino. If we interpret the radius of the universe at the end of the inflation (neutrino’s Compton wavelength) as a minimum length related to quantum gravity and use Zeldovich’s first formula of the vacuum energy, we obtain the correct value of the cosmological constant. In Model II, the primordial density of the universe is identified with the electron density as a consequence of nonlinear electrodynamics. At t=0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$t=0$$\\end{document}, the universe had the characteristics of an electron. This can be viewed as a refinement of the “primeval atom” of Lemaître. During the inflation, which takes place on a gravitoelectronic timescale, the size of the universe evolves from the electron’s classical radius to a size comparable to the size of a dark energy star of the stellar mass. If we interpret the radius of the universe at the beginning of the inflation (electron’s classical radius) as a minimum length related to quantum gravity and use Zeldovich’s second formula of the vacuum energy, we obtain the correct value of the cosmological constant. This provides an accurate form of Eddington’s relation between the cosmological constant and the mass of the electron. We use these arguments to show that the present universe contains about 1080\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10^{80}$$\\end{document} protons (Eddington’s number). We also introduce a nonlinear electromagnetic Lagrangian that describes simultaneously the early inflation, the radiation era, and the dark energy era. It may account for a form of “generalized radiation” that is present from the beginning to the end of the cosmic evolution. Baryonic and dark matter are treated as independent noninteracting species. The dark energy era is due to the electromagnetic vacuum energy (zero-point radiation). In this approach, both the early inflation and the late acceleration of the universe (dark energy) arise as a consequence of nonlinear electrodynamics. This leads to a simple model of magnetic universe without singularity (aioniotic universe).

Modeling and analyzing stability of hybrid stars within [formula omitted] gravity

This study uses the Krori–Barua type metric to represent hybrid stars within the f(Q) theory of gravity. We postulate that the hybrid star also contains strange quark matter in addition to regular baryonic matter. To investigate the physical viability of the hybrid star model, we present the graphical behavior of the energy density, radial pressure, and tangential pressure, equation of state parameters, anisotropy, and stability analysis, respectively, by choosing the compact star EXO 1785-248 with a mass of 1.3−0.2+0.2M⊙ and radius 8.849−0.4+0.4 km with five different values of the coupling constants as a=2, a=4, a=6, a=8, and a=10. The maximum allowed masses and corresponding radii have been calculated using the M−R curve for three different coupling parameter ’a’ values which match the observational data of three distinct compact stars, namely LMC X-4, SMC X-1, and 4U 1538-52. So, the f(Q) theory of gravity can provide results that are plausible for describing the macroscopical characteristics of hybrid star candidates.

Azobenzene-Based Main-Chain Liquid Crystalline Polymers Bearing Periodically Installed Alkyl, PEG, or Fluoroalkyl Segments and Photoisomerization Studies

ABSTRACT In the present study, liquid crystalline polymers (LCPs) were prepared by melt-transesterification of azobenzene-bearing diols and diethyl malonate (DEM) derivatized monomers. The effect of the nature and length of the installed pendant segments on the mesomorphic properties of the prepared LCPs was investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD), and polarized optical microscopy (POM) studies. The formation of layered morphology was inferred from X-ray scattering analysis arising from the colocation of rigid azobenzene moieties in one layer and the flexible pendant segments in alternate layers due to the zigzag folding of the polymer backbone. The linear variation of the interlamellar spacing with the number of carbon atoms in the pendant alkyl segments corroborates the proposed zigzag backbone folding in the polymers. The rate constant values obtained from the photoisomerization studies of the isomeric polymers and model compound, which are in the same ballpark, reveal that the photoisomerization process of such polymers is not affected by the position or size of the azobenzene unit.

Nonminimal coupling holographic superconductors

We explore a holographic superconductor model in which a real scalar field is nonminimally coupled to a gauge field. We consider several types of the nonminimal coupling function h(ψ) including exponential, hyperbolic (cosh), power-law, and fractional forms. We investigate the influences of the nonminimal coupling parameter α on condensation, critical temperature, and conductivity. We can categorize our results in two groups. In the first group, conductor/superconductor phase transition is easier to occur for larger values of α, while in the second group stronger effects of the nonminimal coupling makes the formation of scalar hair harder. Although the real and imaginary parts of conductivity are impressed by different forms of h(ψ), they follow some universal behaviors such as connecting with each other through Kramers–Kronig relation in ω → 0 limit or the appearance of gap frequency at low temperatures around ωg ∼ 8 Tc, which shifts to larger values by increasing the strength of α. Among all forms of h(ψ) we observe that h(ψ) = 1 + αψ2 gives us better information in wide range of nonminimal coupling constant and temperature. Choosing the best form of h(ψ), we construct a family of solutions for holographic conductor/superconductor phase transitions to discover the effect of the hyperscaling violation when the gauge and scalar fields are nonminimally coupled. we find that the critical temperature increases for higher effects of hyperscaling violation θ and nonminimal coupling constant α. By increasing these two parameters, we obtain lower values of condensation which means that conductor/superconductor phase transition will acquire easier. Furthermore, we understand that the hyperscaling violation affects the conductivity σ of the holographic superconductors and changes the expected relation in the gap frequency. Some universal behaviors like infinite DC conductivity are observed. In addition, we consider a five-dimensional Gauss–Bonnet (GB) black hole with a flat horizon. We find out that the critical temperature decreases for larger values of GB coupling constant, λ, or smaller values of nonminimal coupling constant, α, which means that the condensation is harder to form. Moreover, we study the electrical conductivity in the holographic setup. We observe that the gap frequency shifts to larger values for stronger λ, and becomes flat by increasing α.

Electron paramagnetic resonance study of the paramagnetic centers in gamma-irradiated 2-nitrobenzoic acid single crystal

2-nitrobenzoic acid (C7H5NO4) (2NBA) single crystals were made paramagnetic using 60Co-gamma rays. An attempt was made to detect the resonance form formed in 2-nitrobenzoic acid single crystal with Electron Paramagnetic Resonance (EPR) Spectroscopy. EPR spectra were taken at 125 K in three different axes of the crystal. As a result of EPR analysis of gamma irradiated 2NBA single crystal, it was understood that 2NBA anion radical was formed. The principal values of the hyperfine structure constants, the principal values of the g-tensor and their direction cosines were calculated.

Flavones Suppress Aggregation and Amyloid Fibril Formation of Human Lysozyme under Macromolecular Crowding Conditions.

The crowded milieu of a biological cell significantly impacts protein aggregation and interactions. Understanding the effects of macromolecular crowding on the aggregation and fibrillation of amyloidogenic proteins is crucial for the treatment of many amyloid-related disorders. Most in vitro studies of protein amyloid formation and its inhibition by small molecules are conducted in dilute buffers, which do not mimic the complexity of the cellular environment. In this study, we used PEGs to simulate macromolecular crowding and examined the inhibitory effects of flavones DHF, baicalein, and luteolin on human lysozyme (HuL) aggregation at pH 2. Naturally occurring flavones have been effective inhibitors of amyloid formation in some proteins. Our findings indicate that while flavones inhibit HuL aggregation and fibrillation in dilute buffer solutions, complete inhibition is observed with a combination of flavones and PEGs, as shown by ThT fluorescence, light scattering, TEM, and AFM studies. The species formed in the presence of PEG 8000 and flavones were less hydrophobic, less toxic, and α-helix-rich compared to control samples, which were hydrophobic and β-sheet-rich, as demonstrated by ANS hydrophobicity, MTT assay, and CD spectroscopy. Fluorescence titration studies of flavones with HuL showed a significant increase in binding constant values under crowding conditions. These findings highlight the importance of macromolecular crowding in modulating protein aggregation and amyloid inhibition. Further studies using disease-causing mutants of HuL and other amyloidogenic proteins are needed to explore the role of macromolecular crowding in small-molecule-mediated modulation and inhibition of protein aggregation and amyloid formation.

Investigation of the reaction of hydrogen iodide with a chlorine atom in the atmosphere above the sea

By the method of resonant fluorescence (RF) of chlorine atoms and iodine atoms, the rate constant of the reaction of a chlorine atom with hydrogen iodide at a temperature of 298 K. The values of the reaction constants measured by both methods turned out to be quite close. The role of this reaction in the chemistry of the troposphere above the surface of the oceans is discussed.

Does the cosmological constant really indicate the existence of a dark dimension?

According to the “dark dimension” (DD) scenario, we might live in a universe with a single compact extra dimension, whose mesoscopic size is dictated by the measured value of the cosmological constant. This scenario is based on swampland conjectures that lead to the relation [Formula: see text] between the vacuum energy [Formula: see text] and the size of the extra dimension [Formula: see text] ([Formula: see text] is the mass scale of a Kaluza–Klein tower), and on the corresponding result [Formula: see text] from the effective field theory (EFT) limit. We show that [Formula: see text] contains previously missed UV-sensitive terms, whose presence invalidates the widely spread belief (based on existing literature) that the calculation gives automatically the finite result [Formula: see text] (with no need for fine-tuning). This renders the matching between [Formula: see text] and [Formula: see text] a nontrivial issue. We then comment on the necessity to find a mechanism that implements the suppression of the aforementioned UV-sensitive terms. This should finally allow to frame the DD scenario in a self-consistent framework, also in view of its several phenomenological applications based on EFT calculations.

Tachyonic effects on Kähler moduli stabilized inflaton potential in type-IIB/F theory

We investigate the effects of inclusion of charged tachyonic open-string scalars in the perturbative and the non-perturbative Kähler moduli stabilizations in a geometry of three intersecting magnetized D7-brane stacks in type-IIB/F theory and also study the overall influence of this process on the inflaton potential, in a hybrid inflation scenario. We find that a tachyon lowers the minimum of the inflaton potential and assists to end the inflation. For simplicity, we have included one tachyon at a time in the present work and observe that this procedure preserves the features of slow-roll plateau of the potential. An interesting observation here is that the tachyonic part of the potential can be fine-tuned to get an almost zero minimum of the potential, thereby conforming to the small experimental value of the cosmological constant.

Revealing the Structure of Sheer N-Acetylglucosamine, an Essential Chemical Scaffold in Glycobiology.

We explored the conformational landscape of N-acetyl-α-d-glucosamine (α-GlcNAc), a fundamental chemical scaffold in glycobiology. Solid samples were vaporized by laser ablation, expanded in a supersonic jet, and characterized by broadband chirped pulse Fourier transform microwave spectroscopy. In the isolation conditions of the jet, three different structures of GlcNAc have been discovered. These are conclusively identified by comparing the experimental values of the rotational constants with those predicted by theoretical calculations. The conformational preferences are controlled by intramolecular hydrogen bond networks formed between the polar groups in the acetamido group and the hydroxyl groups and dominated in all cases by a strong OH···O═C interaction. We reported an exception to the gauche effect due to the enhanced stability observed for the Tg+ conformer. All the structures present the same disposition of the acetamido group, which explains the highly selective binding of N-acetylglucosamine with different amino acid residues. Thus, the comprehensive structural data provided here shall help to shed some light on the biological role of this relevant amino sugar.

Magnetically separable Bi2O2CO3/MIL-101(Fe)/CoFe2O4 nanostructured catalysts for heterogeneous reductive remediation of nitrophenols and organic dyes

A new magnetically separable nanocomposite, Bi2O2CO3/MIL-101(Fe)/CoFe2O4, was successfully synthesized through a hydrothermal method. The composite was characterized through various analytical techniques. The nanocomposite demonstrated good catalytic efficiency in reducing nitroaromatic compounds and organic dyes by using NaBH4 reducing agent in aqueous solutions at room temperature. The apparent rate constant (kapp) values for 4-nitrophenol, 2-nitrophenol, 2-nitroaniline, and 4-nitroaniline were recorded at 0.457, 0.253, 1.52, and 0.564 min⁻¹, respectively, achieving complete conversion in just 2 to 9 min. Under similar conditions, methylene blue, methyl orange, rhodamine B, congo red, and crystal violet organic dyes were reduced to 98–100 % within 4 to 20 min, with kapp values ranging from 0.157 to 0.885 min⁻¹. Furthermore, the influence of catalyst dosage, NaBH4 concentration, and substrate concentration on the reduction process was examined. Importantly, the nanocomposite can be recovered using an external magnet and reused over four consecutive cycles without a significant reduction in catalytic efficiency.

Physiology-based pharmacokinetic model with relative transcriptomics to evaluate tissue distribution and receptor occupancy of anifrolumab.

Type I interferons contribute to the pathogenesis of several autoimmune disorders, including systemic lupus erythematosus (SLE), systemic sclerosis, cutaneous lupus erythematosus, and myositis. Anifrolumab is a monoclonal antibody that binds to subunit 1 of the type I interferon receptor (IFNAR1). Results of phase IIb and phase III trials led to the approval of intravenous anifrolumab 300 mg every 4 weeks (Q4W) alongside standard therapy in patients with moderate-to-severe SLE. Here, we built a population physiology-based pharmacokinetic (PBPK) model of anifrolumab by utilizing the physiochemical properties of anifrolumab, binding kinetics to the Fc gamma neonatal receptor, and target-mediated drug disposition properties. A novel relative transcriptomics approach was employed to determine IFNAR1 expression in tissues (blood, skin, gastrointestinal tract, lungs, and muscle) using mRNA abundances from bioinformatic databases. The IFNAR1 expression and PBPK model were validated by testing their ability to predict clinical pharmacokinetics over a large dose range from different clinical scenarios after subcutaneous and intravenous anifrolumab dosing. The validated PBPK model predicted high unbound local concentrations of anifrolumab in blood, skin, gastrointestinal tract, lungs, and muscle, which exceeded its IFNAR1 dissociation equilibrium constant values. The model also predicted high IFNAR1 occupancy with subcutaneous and intravenous anifrolumab dosing. The model predicted more sustained IFNAR1 occupancy ≥90% with subcutaneous anifrolumab 120 mg once-weekly dosing vs. intravenous 300 mg Q4W dosing. The results informed the dosing of phase III studies of anifrolumab in new indications and present a novel approach to PBPK modeling coupled with relative transcriptomics in simulating pharmacokinetics of therapeutic monoclonal antibodies.

Probe substrates assay estimates the effect of polyphyllin H on the activity of cytochrome P450 enzymes in human liver microsomes.

Cytochrome P450 enzymes (CYPs) play a crucial role in phase I metabolic reactions. The activity of CYPs would affect therapeutic efficacy and may even induce toxicity. Given the complex components of traditional Chinese medicine, it is important to understand the effect of active ingredients on CYPs activity to guide their prescription. This study aimed to evaluate the effect of polyphyllin H on the activity of CYPs major isoforms providing a reference for the clinical prescription of polyphyllin H and its source herbs. The effects of polyphyllin H were evaluated in pooled human liver microsomes using probe substrates of CYP1A2, 2A6, 2C8, 2C9, 2C19, 2D6, 2E1, and 3A4 to determine their activities. The Lineweaver-Burk was used to model the inhibition, and a time-dependent inhibition experiment was performed to understand the characteristics of the inhibition. Polyphyllin H significantly suppressed the activity of CYP1A2, 2D6, and 3A4 with IC50 values of 6.44, 13.88, and 4.52 μM, respectively. The inhibition of CYP1A2 and 2D6 was best fitted with a competitive model, yielding the inhibition constant (Ki) values of 3.18 and 6.77 μM, respectively. The inhibition of CYP3A4 was fitted with the non-competitive model with the Ki value of 2.38 μM. Moreover, the inhibition of CYP3A4 was revealed to be time-dependent with the inhibition parameters inhibition constant (KI) and inactivation rate constant (Kinact) values of 2.26 μM-1 and 0.045 min-1. Polyphyllin H acted as a competitive inhibitor of CYP1A2 and 2D6 and a non-competitive and time-dependent inhibitor of CYP3A4.

Novel structures and collapse of solitons in nonminimally gravitating dark matter halos

Ultralight dark matter simulations predict condensates with short-range correlation, known as solitons or boson stars, at the centers of dark matter halos. This paper investigates the formation and collapse of dark matter solitons influenced by nonminimal gravitational effects, characterized by gradient-dependent self-interactions of dark matter and an additional source in Poisson's equation for gravity. Our simulations suggest that the initial evolution of dark matter resembles that without nonminimal gravitational effects. However, regions with negative potential curvature may develop, and solitons will collapse when their densities reach certain critical values for both positive and negative coupling constants. With strong nonminimal gravitational effects, we verify that linear density perturbations could grow on both large and small scales, potentially enhancing structure formation.

Patterns of interaction between peptides of various structures and pyrimidine nucleic bases in a buffered saline medium according to the analysis of thermodynamic parameters

Complexation of cytosine, uracil and thymine with the dipeptides glycyl-glycine, glycyl-l-phenylalanine, alanyl-l-glutamine and with the tripeptide γ-l-glutamyl-l-cysteinyl-glycine in a buffered saline has been studied using dissolution calorimetry. The values of the reaction constant, the change in Gibbs energy, enthalpy, and entropy have been found (log Kr, ΔrG, ΔrH, TΔrS). By analyzing the obtained data together with previous results for other peptides, it was found that peptides bind to pyrimidine nucleic bases in a solution in several important patterns. No pattern depending on the charge of the peptide is observed in the obtained thermodynamic values, which indicates a minor role of electrostatic interaction in their binding by the nucleic base. The effect of the structure of the peptide and the nucleobase on the thermodynamic parameters of complexation is manifested in the fine balance of the enthalpy and entropy factors of the process. The Gibbs energy of complexation depends on the number of potential H-bonding sites of the peptide, which shows the major contribution of H-bonding between the reagents. The reduction in the favorable entropy factor is responsible for the tendency of negative ΔrG values to decrease with increasing number of sites. It was found that positive values of entropy change during complex formation increase with increasing hydrophobicity index of the peptide, which is interpreted within the framework of the overlapping hydration sphere model. Strengthening the hydrophobic properties of the nucleic base from uracil to thymine due to the additional CH3 group slightly changes the enthalpy and entropy of the process of binding the +AlaGln− zwitterion but significantly affects the thermodynamic parameters of binding the anion of peptide +/−GluCysGly−.

Two new cyclobutane derivatives of thiazolidin-4-ones: Synthesis, spectroscopic characterization, DFT quantum chemical calculations and determination of protonation constants

In the first stage of this study, 2-((4-(4-(3-methyl-3-phenylcyclobutyl)thiazol-2-yl)imino)thiazolidin-4-one (compound 1) and 2-((4-(3-(2,5-dimethylphenyl)-3-methylcyclobutyl)thiazol-2-yl)imino)thiazolidin-4-one (compound 2) were synthesized, characterized using FT-IR and NMR methods, and a combination of experimental and theoretical studies of the title compounds was performed. With the aid of the 6-311+G(d,p) basis set, all theoretical computations were performed using the density functional theory (DFT) B3LYP approach. The GIAO approximation was used to compute the chemical shifts of 1H and 13C-NMR. Theoretical calculations provide detailed information on chemical activity and molecular properties by determining electrophilic and nucleophilic properties. Accordingly, global chemical activity descriptors (FMOs, hardness, and softness parameters) were investigated, natural bond orbital (NBO) analyses were performed, thermodynamic properties at different temperatures were calculated, and the related relationships with temperature were obtained. The experimental and calculated NMR data presented consistent results for both compounds. R2 values for the 1H-NMR and 13C-NMR of compound 1 are 0.9914 and 0.9988, respectively. For the second compound, 2, these values are 0.9957 and 0.9962, respectively.In the second stage, the acid-base equilibria of title compounds containing cyclobutane, thiazole, and thiazolidinone functional groups were investigated potentiometrically in 60% dioxane-water media at room temperature and constant ionic strength. The values of the protonation constants determined in this study, logKNH(1) and logKNH(2), are related to the protonation of the azomethine nitrogen atom and the nitrogen atom on the thiazole ring, respectively. The sum of these values is the total protonation value of title compounds. The total protonation constants for compounds 1 and 2 are 10.59 and 10.58, respectively.

Synthesis, comprehensive characterization and investigation of biological properties of newly synthesized Pt(II)-aminothiazole complexes: Combining experimental and computational approach

The synthesis of new platinum(II) complexes with 2-amino-6-methyl-benzothiazole and 2-amino-6-chlorobenzothiazole as ligands were reported and the proposed structure of the complexes were determined using elemental microanalysis, infrared, 1H and 13C NMR spectroscopy. To verify the suggested structures a computational approach utilizing Density Functional Theory was implemented. The results showed a strong correlation with experimental data, confirming the hypothesized structures of investigated compounds.The interactions of novel platinum(II) complexes with human serum albumin and calf thymus DNA were studied by fluorescence spectroscopy and UV-Vis absorption. The predominantly elevated values of the binding constant, Kb, and the Stern-Volmer quenching constant, KSV, stem from the effective attachment of complexes to both HSA and CT-DNA. To establish the mode of interaction, viscosity measurements were conducted. The results showed that complexes are not performing intercalation between the DNA bases, and which probably bind to minor/major grooves.In vitro cytotoxic effect of ligands and platinum(II) complexes was evaluated in the panel of cancer cell lines (mouse mammary carcinoma and colon cancer, and on human mammary carcinoma and colon cancer), and on non-tumor cells, mouse mesenchymal stem cell line using MTT assay. Platinum(II) complex with 2-amino-6-methyl-benzothiazole showed a very good cytotoxic activity mainly by inducing apoptosis.In vitro antimicrobial assay of ligands and complexes was tested against 11 microorganisms using microdilution method and the minimum inhibitory concentration and minimum microbicidal concentration were identified. All tested compounds exhibited moderate antifungal activity and significantly better action on S. aureus ATCC 25923.

Steam oxidation of thermally deposited coatings from 304 L and recycled 316 L/Z100 steels: Influence of temperature, coatings microstructure and steel recycling

The application of thermally sprayed stainless steels coatings is a well-established approach to protecting low-alloy steels against high-temperature degradation. In this study, we investigated both: (1) the influence of microstructural features of the coatings and (2) the recycling of stainless steels on the course of high temperature steam oxidation. It was achieved by thermally spraying coatings on C45 steel from 304 L and a new type of 316 L/Z100 steel, obtained as a result of mixed scraps recycling. Steam oxidation tests carried out in the temperature range 600–800 °C for 500 h in pure steam show temperature depended mechanism of oxidation, which was defined and described. The formation of the scales with a multi-layered structure was observed, consisting of Fe2O3, Fe3O4, Cr2O3, Fe- or Cr-rich CrxFex-2O3 and (Mn,Cr,Ni)xFe3-xO4 spinels. The relative ratio of the phases and their presence in particular scale layers varied depending on the material studied and the exposure temperature. The key findings are that recycling of steel deposited as protective coating has led to an unintended change in Si and C concentrations, which may affects course of oxidation. Also, the microstructure of the initial coatings, consisting of porosity and a significant volume of oxides formed during steel deposition, inhibits the formation of a homogeneous layer of protective Cr2O3. As a result, the established values of oxidation kinetics constants (in range of 8.55E-12 to 1.50E-10 g3·cm−6·s−1 for 316 L/Z100 and 2,71E-12 to 4.60E-10 g3·cm−6·s−1 for 304 L coatings) and oxidation activation energies (156.4 kJ·mol−1 for 316 L/Z100 and 211.5 kJ·mol−1 for 304 L coatings) differ significantly from those of bulk steels under the same conditions reported in the literature.

Effect of pre-oxidation on the rate of formation of sulfur-containing aromatic compounds during vacuum gas oil thermal cracking

It was shown that oxidation followed by heat treatment is an effective method for desulfurization of vacuum gas oil. Patterns of changes in the quantitative content of the thiophene series compounds in liquid cracking products of vacuum gas oil and liquid cracking products of pre-oxidized vacuum gas oil are described. A mixture of hydrogen peroxide and formic acid (molar ratio 3:4) was used as the oxidation system. The hypothetical mechanism for the formation of thiophene, benzo- and dibenzothiophene and their homologues from high-molecular weight components of the initial vacuum gas oil and its oxidation products is proposed. Presumably, main path of formation considerate compounds is thermal decomposition of high-molecular weight sulfur-containing components. On the basis of IR spectroscopy and structure-group analysis data, the averaged structures of such components were constructed. The influence of pre-oxidation and its conditions on the value of the rate constants for the formation of thiophene, benzo- and dibenzothiophene and their homologues during thermal cracking of initial and oxidized vacuum gas oils is studied.