Sulfuric Acid Solution Research Articles

A clean and efficient route for extraction of vanadium from vanadium slag by electro-oxidation combined with ultrasound cavitation

Extracting vanadium (V) from vanadium slag (VS) by the traditional roasting-leaching process has disadvantages of high energy consumption and high poisonous gases emission. In this work, a green and efficient route was developed to extract V from VS without roasting by electro-oxidation combined with ultrasound cavitation (EOUC) intensification in sulfuric acid solution. The leaching parameters (e.g., leaching temperature, sulfuric acid concentration, anodic current density, ultrasound power, liquid to solid ratio, leaching time and particle size) were optimized. The leaching mechanism was explored by comparing the leaching behavior and mineralogical evolution of the direct sulfuric acidic leaching (DSL), electro-oxidation-assisted sulfuric acidic leaching (EOSL), ultrasound cavitation-assisted sulfuric acidic leaching (UCSL) and EOUC methods. The results show that introducing electric field strengthens the ultrasound cavitation effect on slag particles in sulfuric acid solution. Under the optimum parameter of EOUC method, the leaching rate of V from VS is as high as 94.64 %. Using EOUC method can open the silicate-wrapped structure of the spinel, increase pore volume of VS from 0.00127 cm3 g−1 to 0.01124 cm3 g−1, decrease slag particle size from 26.8 μm to 16.4 μm and improve specific surface area from 0.508 m2 g−1 to 10.855 m2 g−1, which significantly accelerate V leaching process. The exposed spinel was oxidized by both electrochemical route and chemical route, forming a mixture of V3+ ion and VO2+ ion after leaching.

Effects of preparation method on thermoelectric properties of poly(aniline‐co‐3,4‐ethylenedioxythiophene)/SWCNT composites

AbstractComposites of conducting polymer and single‐walled carbon nanotubes (SWCNTs) are attracting great attentions in harvesting low‐grade waste heat. Prefabricated SWCNTs film used as the working electrode was placed at the liquid interface between the inorganic phase (dilute sulfuric acid solution) and the organic phase consisting of dichloromethane (DCM), aniline (ANI), and 3,4‐ethylenedioxythiophene (EDOT), together with a platinum wire (the counter electrode) and a silver chloride (AgCl/Ag) electrode (the reference electrode), to perform electrochemical polymerization of ANI and EDOT at the liquid interface. Thermoelectric (TE) composites of poly(ANI‐co‐EDOT) and SWCNTs were produced. Compared with composites from ultrasonic mixing and coating methods, the 10 wt% SWCNTs‐composites in situ formed in electrochemical polymerization have the highest power factor (PF) of 41.56 ± 3.58 μW m−1 K−2, higher than the PF values of the composites formed by other two methods. The work indicates that the TE properties of ANI‐EDOT copolymer/SWCNT (poly[ANI‐co‐EDOT]/SWCNT) composites prepared by electrochemical polymerization were better than those of the composites obtained by physical mixing the electrochemically synthesized poly(ANI‐co‐EDOT) with SWCNTs. Moreover, SWCNTs treated with sodium dodecylbenzene sulfonate (SDBS) could further improve the TE properties of the composites.

TRIBO-CORROSION INVESTIGATION ON MATERIAL 316LX MANUFACTURING RESULT OF 3D PRINTING MATERIAL ADDITIVES IN 5% H2SO4 SOLUTION

Tribocorrosion is a type of material degradation caused by simultaneous wear and corrosion of metal surfaces caused by laminar or turbulent flow. Additive manufacturing technology plays an important role in its application to precision components and complex assemblies. This study developed a 316LX material with Fe, Ni, Cr, and other powder alloys that was processed into an ultra-protective wire as a 3D printing filler. This simulation of tribocorrosion conditions was performed on a triboester machine. This simulation is expected to provide important insights and understanding into the behavior and properties of the 316LX 3D printing material, especially when exposed to abrasion and corrosion conditions in a sulfuric acid solution environment. Corrosion Rate Testing of 316LX Material Additives Using Potentiodynamic Methods in a Modified Rotating 5% Sulfuric Acid Fluid. In addition to corrosion rate, the Vickers hardness, metallography, and shrinkage of the 316LX green part material were also tested at 1000oC after sintering.

Preparation of synthetic rutile from Rosetta ilmenite concentrate

The hydrometallurgical procedure is suggested in this work to upgrade the ilmenite mineral which is separated from black sand at Rosetta, Egypt, to obtain high TiO2. The ilmenite concentrate is subjected to a digestion process using sulfuric acid solution in the presence of date molasses. Date molasses is chosen as new, cheap, eco-friendly and effective reductant. The relevant factors for titanium and iron dissolution from ilmenite concentrate include: the acid concentration, sample/acid ratio, reaction time, temperature in addition reductant percentage. These factors are studied and optimized. The optimum conditions are realized at 10 M H2SO4 acid with a solid/liquid ratio of 1/10 at 120 °C for 2 h in the presence of a definite amount of date molasses. Under these conditions, titanium and iron leaching efficiencies are attained at 98.4% and 92.8%, respectively. The resultant leach liquor is then subjected to a hydrolysis step for titanium separation as Ti(OH)2, dried at 110 °C and ignited at 850 °C to obtain high-grade titanium oxide (93.5%) TiO2.

Production of boric acid from colemanite ore in the semi-batch reactor: Investigation of product yield and impurity control

Boric acid is produced by the reaction between colemanite ore and sulfuric acid in industrial processes. Since colemanite ore is not pure, various side reactions, including partial clay decomposition, can occur in the reactor medium. These reactions also lead to the presence of impurities, specifically sulfate salts. In this context, semi-batch reactors (SBR) provide selectivity, and the rate of side reactions is reduced. However, batch reactors (BR) and continuous stirred tank reactors (CSTR) have been used for boric acid production both on an industrial scale and on a laboratory scale, and the semi-batch reactor has never been used for this area. This study used SBR to minimize the side reactions rate and impurities for boric acid production. In the experimental process, a specific concentration of sulfuric acid solution was fed to the reactor at varying flow rates. The yield in the SBR increased up to 99.6%, depending on the sulfuric acid feed rate. When the same conditions were applied in the BR experiment, the yield was calculated to be 90.8%. Compared with the batch reactor results, it was observed that the impurity concentration in the boric acid solution produced within the SBR decreased by 41.7% to 45.3%, depending on the feed rate. Consequently, the utilization of SBR demonstrated clear advantages over the BR in terms of both yield and impurity control. Furthermore, this study serves as a compelling illustration of the practical applications of solid–liquid heterogeneous phase reactions within the context of SBR technology.

Влияние внутренних напряжений на интенсивность коррозионных процессов конструкционной стали

Introduction. The behavior of metal in a corrosive environment can be ambiguous, which is due to the peculiarities of the corrosion process. Both external and internal factors influence the corrosion process. External factors are determined by temperature, humidity, type of corrosive medium, etc., while internal factors depend on the parameters of the system (material): the presence of inclusions, phase composition, structure, and the magnitude of internal residual stresses. Internal factors ambiguously affect the behavior of the material in a certain aggressive medium, which ultimately affects the time of corrosion damage of the material and, as a consequence, the time of operation of objects made of this material. Therefore, differentiation of the influence of various internal factors on the rate of corrosion process in an aggressive environment is a priority area of research. The purpose of the present work is to consider the influence of the magnitude of internal residual stresses on the rate of corrosion process in an aggressive medium — 5% sulfuric acid solution. The object of research conducted in the work is sheet rolled steel St3 as received after different magnitude of plastic deformation, from which the specimens under study were made. The methods of investigation: microstructural study of deformed specimens was carried out on optical microscope Olympus GX53; software SIAMS 800 was used to compare the structure of the obtained material with the atlas of microstructures, determine the score of grain structure, determine the anisotropy of the structure after deformation of the material; X-ray diffractometer DRON-7 was used to register diffraction patterns and determine internal stresses; laboratory scales SHIMADZU UW620h was used to measure the mass of the specimens under study; tensile strength of the material’s specimens was measured. Results and Discussion. The obtained results show that the plastic deformation of the material in the rolling direction has an ambiguous effect on the structure anisotropy. When the degree of plastic deformation increases, there is an ambiguous change in the grain anisotropy value, which is associated with the internal effects of the processes occurring in the material structure during plastic deformation, such as: sliding of the crystal lattice in the {111} <110> directions; the occurrence of reverse residual internal stresses due to the presence of inclusions in the steel structure. However, the degree of plastic deformation correlates quite well with the magnitude of internal residual stresses. The increase in the magnitude of internal residual stresses leads to an increase in the corrosion rate of structural steel St3 in 5 % hydrochloric acid solution. The obtained dependence is described by a linear equation with a high coefficient of determination, which indicates that there is a strong relationship between the magnitude of internal residual stresses and the rate of corrosion of the material. At the same time, the coefficient of influence of internal stresses on the corrosion rate is equal to 0.72, which additionally proves the existence of interrelation between the considered parameters.

Evaluation of Phosphopolyoxometalates with Mixed Addenda (Mo, W, V) as Corrosion Inhibitors for Steels.

Nowadays, choosing a corrosion inhibitor is not only based on efficiency, but must also consider the toxicity of the compound, the impact on the environment, and, obviously, the regulations in the field. In the last two decades, a special class of substances has begun to be studied, namely polyoxometalates (POMs). Their electronic properties and redox characteristics make the polyoxometalates potential candidates to be used in many electrochemical processes, and as potential corrosion inhibitors. Electrochemical methods such as a Tafel extrapolation plot, chronopotentiometry, or gravimetry have been used to establish the capacity of corrosion inhibition of S235 and SS304 steels in the presence of phosphovanadomolibdate acid (@PMoV) and phosphovanadotungstate acid (@PWV) in 0.5 M sulphuric acid solution. The inhibition efficiency for S235 steel is about 90.6% for @PMoV, and 69.5% for @PWV after 24 h of immersion. In the case of SS304 steel, polyoxometalates have similar effects: the inhibition degree, as a function of Flade potential, is 4.66 for @PMoV; better than 3.26 for @PWV, with both proving the passivant effect.

Acid leaching technology for post-consumer gypsum purification.

Contaminants and water-soluble salts present in mechanically recycled gypsum from refurbishment and demolition (post-consumer) plasterboard waste limit its use as a secondary raw material in plasterboard manufacturing. This research addresses this limitation, developing a novel acid leaching purification technology combined with an improved mechanical pre-treatment for post-consumer gypsum valorization. Laboratory-scale acid leaching purification was performed with a borosilicate beaker, hot plate, and overhead stirrer. Stuccos were produced after calcination of gypsum at 150 °C for 3 hours. Samples were characterized through X-ray fluorescence, X-ray diffraction, thermal gravimetric analysis, scanning electron microscopy and particle size analysis. Acid leaching at 90 °C for 1 h using a 5 wt% sulfuric acid solution was revealed to be the optimum purification conditions. Stuccos produced from purified gypsum under optimum conditions had similar initial setting times to that of a commercial stucco but with higher water demand, which could be reduced by optimizing the calcination conditions. A magnesium-rich gypsum was precipitated from the wastewater. Purified post-consumer gypsum with > 96 wt% chemical purity and calcium sulfate dihydrate content was produced. The research recommends acid neutralization prior filtration, use of gypsum particles < 2 mm in size, and stirring speed of 50 rpm to reduce the economic and environmental impacts of the acid leaching purification process at industrial scale. The magnesium-rich gypsum could potentially be marketed as soil fertilizer.

A comparative study on the role of nanotubes and micropores of titanium oxide interlayer on the electrochemical properties of the mixed metal oxide coating

In order to extend the service life of a typical mixed metal oxide (MMO) anode, titanium oxide nanotubes (TiO2-NTs) and micropores (TiO2-MPs) were produced on titanium substrate in this study. This was accomplished by anodizing titanium substrate in hydrofluoric acid and sulfuric acid solutions, respectively, to grow these interlayers. Next, the composition's mixed metal oxide (MMO) coating—which contained tantalum, ruthenium, and iridium oxide—was created by thermal decomposition of appropriate precursors at 480 °C. The corrosion pathways, electrochemical characteristics, and deactivation mechanism of anodes were assessed at various ALT test time intervals using the Accelerated Lifetime Test (ALT) and Electrochemical Impedance Spectroscopy (EIS). Additionally, field emission scanning electron microscopy (FE-SEM) was used to characterize the coatings and interlayers. In contrast to the base sample and the Ti/TiO2-MPs/MMO electrodes, the analysis of surface morphology revealed that the surface of the Ti/TiO2-NTs/MMO electrode following anode deactivation did not have a coating with the same structure as the base sample. Additional findings corroborated that the primary mechanism responsible for the deactivation of the Ti/TiO2-NTs/MMO electrode was the uniform dissolution of the coating. Conversely, it was found that the TiO2-MPs interlayer caused the anode's life to drop by 61% in comparison to the base sample, but the TiO2-NTs interlayer lengthened it. Thus, it can be concluded that the TiO2-NTs interlayer thickness the surface coating, preventing oxygen from reaching the substrate and preventing cracking as a result, potentially delaying passivation.

Electrochemical, spectroscopic, kinetic and surface analysis of the inhibitory performance of Alcian blue dye for copper corrosion in sulfuric acid solution

The use of corrosion inhibitors is considered as the supreme dominant approach to control the damage of metallic corrosion. Organic dyes are extensively employed as inhibitors for the corrosion of various metals and alloys in diverse media. Herewith, Alcian blue dye (ABD) was selected to investigate its inhibitive characteristics against the corrosion of copper in 1.0 M H2SO4 solution at 298 K. This investigation was monitored by various chemical, electrochemical, and spectroscopic techniques. The results indicated that the examined dye is a proficient inhibitor for the corrosion of copper in 1.0 M H2SO4 solution and its inhibition efficiency (% IE) was increased with augmenting its concentration and diminished with rising medium temperature. The high anti-corrosive ability of the selected dye was attributed to its adherent adsorption of such dye on the Cu surface and follows Langmuir isotherm. Thermodynamics and kinetics of corrosion of copper and its inhibition by the examined dye were inspected. The mechanisms of copper corrosion in H2SO4 solution and its inhibition by ABD were proposed. The obtained results illuminated that the examined dye acts as a mixed-type inhibitor with cathodic precedence. Finally, all gained results with respect to % IE values of the dye were compared and designated a good harmony between all applied techniques.

Photoinduced superlubricity on TiO2 surfaces

Superlubricity control is of great interest in both industry and scientific research, and several methods have been proposed to achieve this goal. In this work, ultraviolet (UV) light was introduced into titanium dioxide (TiO2) and silicon nitride (Si3N4) tribosystems to accomplish photoinduced superlubricity. The friction coefficients (COFs) between Si3N4 balls and TiO2 plates in the mixtures of sulfuric acid (H2SO4) solution and glycerol solution were obviously reduced, and the system entered the superlubricity region (COF < 0.01) after UV illumination at a speed of 56 mm/s. However, the COF was much larger without UV treatment than that with UV treatment. The formation of silica (SiO2) layers on the surfaces of Si3N4 balls and the elastohydrodynamic effects were determined to be fundamental to the low friction in this experiment, and the enhancement of the combination between the TiO2 surface and the hydroxy group of glycerol by UV illumination was the key to the photoinduced superlubricity in this system. These findings showed one method for achieving superlubricity by introducing a light field that could be further applied to special working conditions.

Electrode laminated with ion-selective blocking layer for use in vanadium redox flow batteries

2 μm thick meta-polybenzimidazole (PBI) films effectively block permeation of vanadium ions in vanadium redox flow batteries, but are usually reinforced with supports to guarantee mechanical stability. Here, we eliminate the use of an additional support by laminating a 2 μm thick 10-wt% dibromoxylene crosslinked PBI layer directly on carbon paper. The total area specific resistance (ASR) of the two PBI films is 156.8 mΩ cm2 in 1.5 M V4+/3 M sulfuric acid solution, 26 % lower than that of Nafion 211. VRFB cells are made by assembling a membrane between two PBI-laminated carbon paper electrodes. These electrodes simplify membrane selection, because high selectivity is not anymore required, and chemical stability of the membranes against VO2+ is less crucial. An example cell is made with a 70 μm thick Gel PBI membrane. Membrane and PBI layers exhibit an ASR of 177.8 mΩ cm2 in 1.5 M V4+/3 M sulfuric acid solution, 18 % lower than that of Nafion 211. The selectivity of proton over vanadium ion is 4.2 × 1014 S s m−3, 9 times better than that of Nafion 211. In a VRFB, a stable energy efficiency of 87.6 % at 75 mA cm−2 compared to 82.3 % for Nafion 211 is obtained.

An exploratory assessment supported by experimental and modeling approaches for dinitrophenylhydrazine compound as a potent corrosion inhibitor for carbon steel in sulfuric acid solution

Comprehensive electrochemical and theoretical investigations were conducted to assess the effectiveness of 2, 4-Dinitrophenylhydrazine (DNPH) as a corrosion inhibitor for carbon steel (CS) immersed in a 0.5 M H2SO4 solution. The results demonstrated significant corrosion inhibition efficiency of DNPH, reaching an impressive rate of 88 % at a concentration of 10−3 M. Polarization analysis revealed DNPH's role as a mixed-type inhibitor. Furthermore, the study elucidated that DNPH adsorption on the CS surface followed the Langmuir adsorption model, with a mechanism attributed to specific physical interactions. Scanning electron microscope (SEM) observations of both treated and untreated samples confirmed DNPH's efficacy in protecting carbon steel in a 0.5 M H2SO4 environment. Quantum chemical calculations using Density Functional Theory (DFT) parameters, in conjunction with molecular dynamics simulations, provided theoretical data strongly correlated with experimental results.

Evaluation of adsorption and corrosion inhibition properties of Solanum Macrocarpon leaves extract on mild steel in sulphuric acid solutions

Corrosion of mild steel (MS) in industries has become a menace that has led to the use of organic green inhibitors from plant origin, which is seen as a cheap, eco-friendly substitute for inorganic inhibitors. This work employed Solanum macrocarpon (SM) methanol leaf extract as a green inhibitor using a gravimetric method at 303–323 K, respectively. The phytochemical screening was done using standard methods to identify the phytochemical compounds in the leave extract. The Fourier transform infrared (FTIR) analysis was also done to elucidate the functional groups that contain heteroatoms responsible for the inhibition efficiency. The effectiveness of the inhibition efficiency increased with concentration and decreased with rising temperature. The results demonstrated that Solanum macrocarpon leaf methanol extract is an effective mild steel corrosion inhibitor in 0.5 M H2SO4. 95% optimum inhibition efficiency (I.E) was observed at 0.5% w/v concentration for 303 K. The inhibition potential was attributed to the phytochemical compounds in the leaf extract, which contain polar functional groups and hetero-atoms in their structures. The Ea\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${E}_{a}$$\\end{document} and ΔGads\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta {G}_{ads}$$\\end{document} showed that the adsorption mechanism followed physisorption. The results showed the potential use of SM methanol extract as a corrosion inhibitor in mild steel, which can decrease corrosion in industries.

Biological resistance of cellular and porous glass composites

Various types of concrete are widely used for the manufacture of bridge structures. Alkali-activated binders are now often offered in place of cement and other binders. They are formed as a result of the reaction of an aluminosilicate material with an alkaline agent such as sodium hydroxide. Currently, more attention is being paid to research on the stability of materials under the influence of biologically active media. The article describes in detail the method of testing materials for fungal resistance and fungicidal properties. This paper presents the results of studies of the biological resistance of the compositions of binders and cellular composites based on glass in comparison with traditional materials of inorganic and organic nature. In addition to the control additive-free compositions of cellular stellated composite, compositions modified with biocidal additives such as «Teflex» and «Biocic-T» were considered, and studies were conducted to study the effect of the aging process of a glass-alkali binder and traditional materials on their biological resistance. It was found that the introduction of biocidal additives did not affect the biological stability of the material and only in some cases led to an increase in the radius of the inhibition zone. The results obtained during the experiment indicate that the maximum decrease in the biological resistance of materials occurs after exposure to an aqueous solution of sulfuric acid. A comparison of the results of an experiment to study the biostability of binders based on glass waste with similar indicators of composites based on Portland cement, epoxy resins shows the consistency of using the developed binder in the manufacture of products operated under the influence of biologically active media.

Effect of relative humidity on the thin-layer chromatographic separation of E 472 emulsifiers

E 472 emulsifiers are organic acid esters of mono- and diacylglycerides. These emulsifiers are categorized into six subgroups (E 472a-f) based on the specific acid component, e.g., acetic acid, lactic acid, citric acid, tartaric acid, or mixtures of tartaric and acetic acid. The present study investigated the effect of relative humidity (RH) on the thin-layer chromatographic separation of four E 472 emulsifier subgroups, addressing practical concerns due to RH variations between seasons and within laboratories. Three RH-setting techniques affecting plate activity and chamber climate were assessed using saturated salt and aqueous sulfuric acid solutions. Aqueous sulfuric acid solutions for RH adjustment resulted in decreased hRF values, while no trends in hRF value changes were observed for saturated salt solutions. Unlike RH itself, the RH setting technique led to substantial changes in the chromatographic fingerprint. Thus, the choice of the RH setting method should be tailored to the specific analyte and analysis goal. Despite variations in chromatographic fingerprints between the three RH setting techniques, the fingerprint remained consistent within the same technique across the tested RH range.

Microscopic mechanical properties of silicon nitride ceramics corroded in sulfuric acid solution

The microscopic mechanical properties including the bending strength and Young’s modulus for Si3N4 ceramics doped with Y2O3 and Al2O3 which was immersed in 5 wt% sulfuric acid solution using microcantilever beam specimens was investigated in comparison with the macroscopic results obtained in conventional three-point bending tests. Both the properties sharply dropped in very short periods of the corrosion in the microcantilever tests, resulting from the dissolutions of yttrium and aluminum ions of grain boundary glass networks, followed by the hydration. After the drops at the beginning of the corrosion, they showed little degradation afterwards. The degradation behaviors of the mechanical properties are basically the same as those in conventional macroscopic approaches; however, they changes appear in very short periods of the corrosion in the microcantilever bending tests. This study also verified that a small difference of a ratio of sintering additives results in different grain boundary strengths of Si3N4 ceramics.

Efek Pre-Roasting Terhadap Parameter Kinetika Leaching Cr dari Limonit

Hydrometallurgical processes such as leaching of limonite ore to extract valuable metals including Ni and Co are often non-selective, including other metals in the leachate product. The leaching behavior of Cr from the chromite mineral contained in limonite ore is of concern due to the high Cr content of the leachate effluent. The pre-roasted process is frequently used to pre-treat limonite to increase the precious metal content. This study aims to determine the leaching behavior of Cr and the effect of pre-roasting on its kinetic parameters. The pre-roasting process was carried out at 280 and 610 oC for 4 hours. Observation of Cr leaching behavior was carried out in the leaching temperature range of 30-90 oC for 0-120 minutes using sulfuric acid solvent. The highest Cr recovery was achieved in pre-roasted ore leaching at 610 oC with leaching operating conditions of 2 M sulfuric acid, solid-liquid ratio of 5 g/50 mL, 200 rpm, for 120 minutes, at a leaching temperature of 90 oC, under these conditions Cr recovery reached 53.16%. The higher the roasting temperature, the lower the activation energy required for the leaching process. Cr leaching from raw and pre-roasted ore is controlled by the diffusion process through the ash layer with activation energies (EA) of 21.41, 18.64, and 14.71 kJ/mol for raw ore, pre-roasted ore 280 oC, and pre-roasted ore 610 oC, respectively. The comparison of kinetics data from several roasting products for atmospheric leaching feeds will provide industry with information to integrated pyro-hydrometallurgical process to increase Cr production from laterite.

TRAITEMENT DU PHOSPHATE NATUREL DE LA TAPOA (NIGER) PAR DES ACIDESMINERAUX ET ORGANIQUES

This study propose away for the development of hardly soluble natural phosphate. Thusitwascarried out, the dissolution of natural phosphate from Tapoa (Niger) in solutions of mineralacids (nitricacid and sulfuricacid) and in solutions of organicacids (citricacid and ethylene diamine tetraacetic EDTA) in function of pH and attack time. The resultsobtainedshowedthat the maximum rate of dissolvedphosphorus as a percentage of phosphoric anhydride (P2O5) is 14.08% and 15.99% respectively in solutions of nitricacid and sulfuricacid at the concentration of after 7 hours of attack. In organicacid solutions, the dissolution rate is 4.67% and 5.17% respectively in citricacid and EDTA solutions at the same concentration. In addition, the dissolution rate decreaseswhen the acid concentration decreaseswhileit tends to increasewith the attack duration regardless of the acid solution used (mineral or organic). Also, this dissolution rate isalmostzero in solutions of organicacidswhen the concentrationis.

Convenient preparation of expanded graphite and graphite nanosheets as well as improvement of electrical conductivity of polyurethane by filling graphite nanosheets

Expandable graphite precursors were firstly prepared by the oxidative intercalation of natural flake graphite powders with mean lateral particle sizes of 25–100 μm in concentrated sulfuric acid solutions using Ca(ClO)2 as an oxidant. Higher oxidative intercalation extent increased the thermal expansion of expandable graphite to obtain expanded graphite with a larger volume ratio of 162 mL⋅g−1. Graphite nanosheet samples were facilely and eco-friendly prepared by sand milling of expanded graphite in an aqueous solution. The thicknesses of as-prepared graphite nanosheets could be decreased from 15–20 to 4.8–5.5 nm with the prolonging of sand milling time from 4 to 12 h. As compared with polyurethane/natural flake graphite composite films, the electric conductivity of polyurethane/graphite nanosheet composite films was increased by 6 orders of magnitude at a lower filler content of 5 wt%. The filling of graphite nanosheets endows polyurethane with good electrical conductivity.