Alumina extraction from northeastern red soils of Argentina

A laboratory-scale acid process to produce alumina with a purity higher than 98.4% from the northeastern red soils of Argentina is proposed. Leaching was carried out with 6 M hydrochloric acid at several molar ratios both with and without previous thermal treatment of the mineral. The relationship between the extent of dissolution of iron (II), iron (III), aluminium (III) and titanium (IV) and the structure of the principal minerals of the soils were analyzed. The solutions obtained after leaching, containing about 30 g/l of aluminium and iron oxides and 1 g/l of titanium oxide, were purified by solvent extraction and hydrolytic precipitation. The related behavior of the system aluminium (III) - iron (III) in hydrochloric acid with the organic solvent tributyl phosphate and the conditions suitable for titanium hydrolysis were studied. Then, hydrated aluminium chloride was obtained by crystallization and thermal decomposition of the salt was carried out to produce alumina.     

Influence of some anions on the stress corrosion of low alloy steels in aqueous solutions

Polarization and stress corrosion behaviour of two types of low alloy steels, AISI 4130X and AISI 4145, were studied in agitated 0.05 M sodium acetate and 0.05 M trisodium phosphate solutions saturated with natural gas at room temperature. The magnitude of currents, shown in potentiokinetic polarization curves in the range of —0.8 V(SCE) to +0.8 V(SCE) in these media, is very small compared with earlier results obtained in sulphate and chloride solutions.Stress corrosion experiments conducted using a slow strain rate technique under cathodic conditions indicate the onset of hydrogen embrittlement on both types of steel in sulphate, chloride, acetate and phosphate solutions. Under anodic conditions, the results in 0.05 M sodium acetate solutions indicate strong susceptibility to stress corrosion compared with no susceptibility in 0.05 M trisodium phosphate solutions if there is no onset of pitting. These results are in contrast with results showing strong anodic dissolution and consequent absence of stress corrosion under anodic conditions in sulphate and chloride media.Results of Auger and IR analyses of anodic surface films formed in acetate and phosphate solutions are presented and discussed in relation to their observed mechanical behaviour.     

Evaluation of biosynthesized nickel oxide nanoparticles from Clerodendrum phlomidis: A promising photocatalyst for methylene blue and acid blue dyes degradation

In the present investigation, nickel oxide nanoparticles (NiO) were biosynthesized utilizing an extract of Clerodendrum phlomidis leaves. Their size, phase study, and shape were investigated using a variety of research methods. In addition, we assessed the photocatalytic effects of NiO nanoparticles on the degradation of methylene blue (MB) and acid blue (AB) dyes. Throughout the research process, we found that these nanoparticles had extraordinary potential for photocatalysis when exposed to UV light. This is a 100% environmentally friendly method that makes no use of any harmful or poisonous solvents. High-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and ultraviolet–visible spectroscopy (UV–Vis) were used to analyze the biosynthesized NiO nanoparticles. The catalytic activity of the newly synthesized nanoparticles was evaluated by seeing how well they degraded dyes called methylene (MB) and acid blue (AB). Following the first-order reaction, kinetics was the photocatalytic effectiveness against the methylene blue (MB) and acid blue (AB) dyes, both of which exhibited a maximum degradation efficiency of 92% and 63%. Because of this, the biosynthesized NiO nanoparticles synthesized utilizing the extract of Clerodendrum phlomidis leaves have the potential to be used in photocatalytic applications.     

Curing performance and print accuracy of oxidized SiC ceramic via vat photopolymerization

To improve the print quality of SiC ceramic, an amorphous SiO₂ layer is prepared on the surface of SiC by oxidation (SiC@SiO₂). The changes in curing depth and width direction of SiC@SiO₂ curing sheets with different degrees of oxidation were investigated. The results showed that curing depth increased while curing width decreased with an increasing degree of oxidation. The edge morphologies of SiC@SiO₂ curing sheets changed from serration to flat shape with increasing degree of oxidation, and uneven overcuring regions appear in the width direction. Additionally, 12% SiC@SiO₂ ceramic was fabricated via vat photopolymerization combined with reaction sintering. The dimensional deviation ratio of printed green bodies increased with decreasing printed line width and pore diameter. The minimum printed line width of 329 μm and pore diameter of 483 μm with good print quality were obtained. Furthermore, the flexural strength of 225.4 MPa and bulk density of 2.77 g cm⁻³ for sintered 12% SiC@SiO₂ parts were obtained.     

Electrochemical performance study of proton exchange membrane electrolyzer considering the effect of bubble coverage

Bubble dynamics are closely related to the electrochemical performance of a proton exchange membrane electrolyzer (PEMEC). However, tiny bubbles need to be clustered together to affect the electrochemical performance of PEMEC significantly. In this paper, the effect of microscopic bubbles on macroscopic electrochemical properties were assessed by bubble coverage. The bubble dynamics, two-phase flow, and electrochemical performance were captured under different conditions using a high-speed, microscopic visualization experimental system. The results show that various factors influence the two-phase flow pattern. At 60 °C, 1.5 A/cm² and 5 mL/min, the annular flow occupied 76.8% of the gas phase area, and when the water flow increased to 80 mL/min, the annular flow ratio decreased substantially to 2.7%. The two-phase flow of bubbles in the flow channel showed different flow patterns over time. Under the experimental conditions (60 °C, 20 mL/min, 0.8 A/cm²), the bubble flow pattern experienced the emergence of bubbles, bubble flow, segmental plug flow, annular flow, and final steady state with the occurrence times of 0.15 s, 1.5 s, 5.0 s, 10.5 s, and 21.2 s, respectively. The bubble coverage increased with current density and temperature, while it decreased with the increase of water velocity. In addition, the effects of temperature and water velocity on bubble coverage and PEMEC performance vary in principle. Specifically, higher temperature mainly improves the bubble coverage by increasing the electrochemical performance of PEMEC. In contrast, higher water velocity mainly improves the electrochemical performance of PEMEC by decreasing the bubble coverage. This study elucidates the relationship between microscopic bubbles and macroscopic electrochemical performance, contributing to a better understanding of the processes and principles of bubble effects on the electrochemical performance of PEMEC. The results may provide a theoretical basis and experimental data for operating condition optimization, operating efficiency improvement, multiphase flow study, gas diffusion layer structure, and flow field design of PEMEC.     

Crystal engineering of platinum to enhance the efficiency of hydrogen isotopes enrichment via water vapor adsorption

Catalytic exchange technology is state-of-the-art to enrich hydrogen isotopes in nuclear wastewater through platinum (Pt)-based catalyst. Most researchers focus on developing hydrophobic supports to inhibit direct coverage of Pt by liquid water, while the structure-activity relationship between active sites and water vapor is ignored. Herein, we prepare a series of Pt-based model catalysts (Pt/MON-t) by crystal engineering of Pt to determine the effect of water vapor. Combining the results of X-ray diffraction characterization, density functional theory calculation, and catalyst evaluation, the quantitative results of water vapor adsorption behavior are found to show a linear correlation with catalytic efficiency (R² = 0.94), proving the water vapor adsorption behavior is mainly responsible for the difference in efficiency, and the weaker water vapor adsorption is more favorable to achieve higher catalytic efficiency. As the weakest adsorption energy of water molecule, Pt/MON-120 exhibits the highest catalytic efficiency with 91.4% at 353.15 K, and maintains excellent stability.     

Luminescent ionic lattice occupation and wide tunable emission spectra of La2MgZrO6:Bi3+,Eu3+ double perovskite phosphors for white light LED

La₂Mg_1-x/2Zr_1-x/2O₆:xBi³⁺(x=0.01-0.035,abbreviated as LMZ:Bi³⁺) and La_2-yMg_0.99Zr_0.99O₆:0.02Bi³⁺,yEu³⁺(y=0.1-0.11,abbreviated as LMZ:Bi³⁺,Eu³⁺) double-perovskite phosphors were prepared through high-temperature solid-phase method.The emission spectrum of LMZ:xBi³⁺(x=0.01-0.035)phosphors excited at 353 nm is asymmetric in the range be...     

Hydrogenation properties of nanocrystalline TiVMn body-centered-cubic alloys

An effect of Mn content in nanocrystalline TiVMn alloy on hydrogenation properties has been investigated systematically in this work. Ti_0.5V_1.5-xMn_x (x = 0, 0.1, 0.2, 0.3) alloys are synthesized by mechanical alloying method. It has been shown that all alloys need to be activated in order to present the best hydrogenation properties. With increasing Mn content in TiVMn alloys, the maximum hydrogen storage capacity at room temperature firstly increases to reach 3.07 wt% for Ti_0.5V_1.4Mn_0.1 alloy and then gradually decreases. Reversibility of hydriding-dehydriding process improves after chemical modification of TiV alloy. Hydrogen storage properties result from phase composition and structure of alloys. All samples are composed of a major body-centered-cubic (BCC) phase. In Mn-containing materials also a second BCC phase has been detected. Its abundance increases with higher content of Mn in the alloy. Moreover, with increasing Mn content, the lattice parameters of both phases decrease.     

Extraction and separation of yttrium from other rare earths in chloride medium by phosphorylcarboxylic acids

Two phosphorylcarboxylic acids, 3-((bis(2-ethylhexyloxy))phosphoryl)propanoic acid (PPA) and 3-((bis(2-ethylhexyloxy))phosphoryl)-3-phenylpropanoic acid (PPPA), were synthesized for separating yttrium from other rare earths in the chloride feed of ion-adsorption type rare earth concentrate. The effect of the factors such as pH_1/2, temperature, saponification degree and phase modifiers was investigated. The separation efficiencies of PPA and PPPA are obviously better than the typical extractants such as sec-octylphenoxy acetic acid (CA-12) and naphthenic acid (NA). The extraction process of rare earths by PPA and PPPA is a cation exchanging reaction, which is similar to those of CA-12 and NA. The loaded rare earths in both PPA and PPPA systems can be effectively back-extracted by 0.5 mol/L HCl or higher concentration. A cascade extraction process for separating yttrium from other rare earths was developed using PPPA as the extractant. The yttrium product with the purity of 97.20 wt% was obtained by 35 stages of extraction and 12 stages of scrubbing.