For continuous casting of strong reducing steels, the low-reactive aluminate-based mold flux consisting of CaO-SiO2-Al2O3-CaF2-Li2O-B2O3-Na2O with low SiO2 content was designed. The correlation between the melt structure under high temperature and the crystallization phases during the cooling process and the change of viscosity was analyzed. The following conclusions were obtained. The polymerization degree of the mold flux consistently decreased as the w(CaO)/w(Al2O3) ratio increased from 0.93 to 1.65. Due to melt structure depolymerization, the viscosity at 1300 degrees C dropped from 0.132 Pa & centerdot;s to 0.054 Pa & centerdot;s. As the w(CaO)/w(Al2O3) ratio increases near the breaking temperature, the crystalline phases in the mold flux transition from LiAlO2 to Ca2Al2SiO7, and finally to a combination of Ca12Al14O32F2 and LiAlO2. The rapid viscosity increase at the breaking temperature was primarily due to the precipitation of these phases. Furthermore, influenced by the changes in crystallization tendency and crystalline phase precipitation, the breaking temperature first decreased and then increased. Increasing the Li2O mass fraction from 5% to 9% led to a decrease in the polymerization degree of the mold flux. Due to the depolymerizing impact of Li2O on the slag network, the mold flux viscosity at 1300 degrees C decreased from 0.102 Pa & centerdot;s to 0.047 Pa & centerdot;s. The breaking temperature of the mold flux rose notably with a higher Li2O mass fraction. At the breaking temperature, the crystalline phases in the mold flux transition from Ca2Al2SiO7 to a combination of LiAlO2 and Ca12Al14O32F2. The precipitation of these phases at the breaking temperature directly caused a rapid increase in viscosity. The results systematically reveal the coupling mechanism between melt structure, crystalline phase evolution, and viscosity variation of low-SiO2 aluminate-based mold flux, which provides an important theoretical basis for composition design and performance regulation of mold fluxes for high-aluminum steel continuous casting.
In this study, zinc-modified biochar (ZBC) was prepared from rose willow, and NiCoMn-LDHs@ZBC composites were synthesized using a hydrothermal method. The composites were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area analysis, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The adsorption mechanism of As(V) from aqueous solution onto NiCoMn-LDHs@ZBC was investigated through a series of arsenic adsorption experiments. The effects of various experimental parameters (including adsorbent composition and ratio, adsorbent dosage, solution pH, contact time, temperature, and coexisting ions) on the adsorption capacity were evaluated. Additionally, adsorption model fitting and kinetic analysis were conducted. The results indicate that the adsorption process follows the pseudo-second-order kinetic model (linear correlation coefficient R2 = 0.99), while the isothermal adsorption process adheres to the Langmuir model, with a maximum adsorption capacity of 159.780 mg/g. The adsorption process is primarily dominated by chemisorption and involves three pathways: first, electrostatic attraction between the material surface and arsenic-containing ions; second, ion exchange between arsenic-containing ions and interlayer carbonate ions; and third, coordination reactions between the surface hydroxyl groups (-OH) of NiCoMn-LDHs@ZBC and As, forming As-O-M inner-sphere complexes as adsorption proceeds. Furthermore, the NiCoMn-LDHs@ZBC composite exhibits relatively stable reusability, demonstrating significant potential for the treatment of arsenic pollution in water bodies.
The Oxygen Evolution Reaction (OER) is the bottleneck in the water splitting reaction since it involves four intermediate steps, constituting the adsorption-desorption of oxygen-based radical groups, and not all of them are energetically favorable. Rapidly growing research interest is focusing on carbon-based materials as novel, highly active and durable non-precious electrocatalysts for the OER, representing a valuable alternative to precious and rare materials with electrochemical properties tuned by defect creation. In this work, we propose a facile and green methodology based on the modification of graphene oxide by laser irradiation to obtain an alternative OER catalyst. GO flakes were chemically and physically modified using pulsed laser irradiation at 532nm with fluences of 1.5J/cm2 and 2.5J/cm2. Different analyses were carried out to correlate the electrochemical performance with the structural, optical, and morphological properties; after that, we correlated the improvements in the OER with respect to the pristine GO with the increase in OH functional groups obtained by laser treatment. The best-performing sample exhibited an overpotential of 380mV, comparable to that of catalysts reported in the literature but with the advantage of not being a precious or rare material.
Monohalogen-substituted (F-, Cl-, Br-) phenylethylamine derivates are a valuable class of chiral compounds, e.g., for C-C-coupling reactions, which are the basis for multiple pharmaceuticals and resolving agents. Here, the solid phase behavior of the underlying phenylethylamine derivates, especially of the corresponding hydrochloride salts, is highly relevant as those compounds are often applied in enantiopure form during the production processes. In this study, the solid phase behavior of 20 synthesized chiral phenylethylamine hydrochloride derivates (both enantiomers and racemates) was investigated including detailed information regarding melting behavior, powder X-ray diffraction data and the type of the chiral system present. Further, the binary melt phase diagram of a found conglomerate system and two novel enantiomer crystal structures were determined. This study is aimed at revealing structure-phase behavior relationships for the 20 monohalogen-substituted compounds investigated as well as providing basic solid-phase-related data required for later crystallization-based enantioseparation processes.
Agmatinase (SpeB) catalyzes the hydrolysis of agmatine to produce putrescine, a key step in bacterial polyamine biosynthesis. Here, we report the crystal structure of SpeB from Klebsiella pneumoniae (kpSpeB) and characterize its oligomeric and active-site architecture. SEC-MALS analysis demonstrates that kpSpeB forms a canonical hexamer in solution. Structural comparison reveals high similarity to Escherichia coli SpeB and other members of the arginase superfamily, including proclavaminic acid amidino hydrolase (PAH) and guanidine hydrolase (GdmH). Despite strong conservation of residues coordinating the binuclear Mn2+ center, subtle differences in metal positioning and cavity geometry were observed. Surface analysis indicates variations in active-site cavity volume among homologues, with partial occlusion in GdmH due to a bulky tryptophan residue. These findings suggest that minor adjustments in metal coordination and cavity architecture may fine-tune substrate selectivity while preserving the conserved catalytic framework of the arginase superfamily.
