Aqueous Sulphuric Acid Solutions Research Articles

The Atmospheric Corrosion of Trivalent Cr Metal / Cr Oxide Coatings for Packaging Steels

The superior mechanical properties associated with steel mean that it is heavily utilized in many industries including automotive, and construction (1). Although steel offers desirable mechanical properties such as toughness and tensile strength, it is known to corrode, this having cost implications and raising safety concerns, for instance within the food packaging industry. Thus, steel is often used in conjunction with a coating as a preventative measure for corrosion.Within the food packaging industry, steel is often coated with a thin (~20 nm thick) chromium metal-chromium oxide coating, the product being referred to as electro chromium coated steel (ECCS), which is produced during a continuous electrodeposition process whereby a low carbon steel strip passes through baths of chromic acid electrolyte containing hexavalent chromium, Cr(VI). The final coating consists of two distinct layers; a 20-110 mg.m-2 chromium underlayer and a 2-20 mg.m-2 native (hydr)oxide outer layer (2). REACH, a regulation associated with the restriction of chemicals that are harmful to human health and the environment, have made a legislation that has imposed a restriction on the use of Cr(VI) due to its carcinogenic nature (3). This impact has resulted in the drive of the steel packaging industry to find a suitable, non-toxic replacement for ECCS.Coatings made with Trivalent Chromium Coatings Technology (TCCT®) are currently being developed as a potential replacement for ECCS. TCCT® production has developed to consist of a two-electrolyte process involving an aqueous solution of Cr(III) sulphate, sodium sulphate, sodium formate and sulphuric acid leading to the formation/application of a bilayer coating. Various issues including coating inhomogeneity have previously been reported (4).Due to the low coating weights involved, packaging products such as ECCS and TCCT® are also used in conjunction with an organic coating. Thus, they could be susceptible to various modes of organic coating failure including corrosion-driven cathodic delamination, whereby a coating becomes physically separated from the underlying substrate, a key failure process that affects organically coated metal products in high humidity, such as those experienced during storage in the packaging industry. Cathodic delamination occurs when an electrolyte comes into contact with the metallic substrate at a flaw in the organic coating at which anodic metal dissolution occurs. This is coupled to the cathodic oxygen reduction reaction which takes place at the delamination front. The hydroxide ions produced during the cathodic reduction of oxygen, or a reaction intermediate, disturb the bonds between the substrate and coating leading to adhesion failure and delamination of the coating (5).To ensure that new products such as TCCT® are successfully incorporated into the market it is important that they are comparable in performance to existing products. For example, TCCT® must provide sufficient delamination resistance. The scanning kelvin probe (SKP) is a technique which measures corrosion potential under a thin electrolyte film and organic coatings, which can be used to create a surface potential map (6).This study makes use of the SKP to investigate the rate of cathodic delamination as a function of TCCT® Cr(III) oxide (varying from 1.8 mg.m-2 to 23.35 mg.m-2). The results will help to determine the minimum satisfactory chromium oxide coating weight needed for commercial TCCT®.It was found that higher Cr(III) oxide coating weights had a positive effect on inhibiting cathodic delamination, confirming the mechanism. The results were explained using complementary electrochemical data including OCP measurements as well as potentiodynamic polarisation which showed that higher TCCT® Cr(III) oxide coating weights were acting to supress the cathodic reaction.The results also highlighted that a TCCT® Cr(III) oxide coating weight of around 7 mg.m-2 is sufficient with regards to resisting cathodic delamination completely. This work has determined that the Cr(III) oxide coating weight value is very important with regards to improving coating coverage and resisting cathodic delamination.References Singh MK. Application of Steel in Automotive Industry Application of Steel in Automotive Industry. Int J Emerg Technol Adv Eng. 2016;6(7):2250–459.Wijenberg J, Steegh M, Penning JP, Portegies Zwart I. Wo 2014/079909 2014.Petry T, Knowles R, Meads R. An analysis of the proposed REACH regulation. 2007;44(2006):24–32.Allman A, Whiteside J, Jewell E, Griffiths C, McMurray N, de Vooys A. Surface modification of Cr(III) packaging substrates for enhanced adhesion via citric acid processing. Surfaces and Interfaces. 2020 1;20:100545.Øystein O, Knudsen AF. Corrosion Control Through Organic Coatings. Second. Schweitzer PA, editor. New York: Taylor & Francis; 2017.Stratmann M, Streckel H, Feser R. A new technique able to measure directly the delamination of organic polymer films. Corros Sci. 1991;32(4):467–70.

A low cost, bulk synthesis of the thermally reduced graphene oxide in an aqueous solution of sulphuric acid & hydrogen peroxide via electrochemical method

The electrochemical approach is considered the simplest, most environmentally friendly, low-cost, and bulk synthesis route from graphite. The proposed approach is based upon the low cost, bulk synthesis of the thermally reduced graphene oxide (TrGO) by using the high voltage (DC power ∼56 V) electrochemical method in an aqueous solution of 0.5 M sulphuric acid (H2SO4) and 3% of hydrogen peroxide (H2O2) (electrolyte heating assisted method at 60 °C) as an electrolyte. The cylindrical graphite and cylindrical aluminium have been used as an anode and cathode. The sterilized water (for irrigation U.S.P.) has been used for the H2SO4 dilution and sonication instead of deionization water (DI water). The thermal stability, crystal structure, and interplanar distance of the TrGO seem to be unaffected by the re-annealing during the TGA and XRD analysis. After re-annealing, the Raman spectra and AFM analysis indicated that the degrees of defect increased in the low defect domain, while surface roughness decreased. FESEM, EDS, and TEM analyses were used to evaluate the microstructure and elemental composition.

Solution Electrochemical Approach to Synthesis of Low Stage Graphite Bisulphate

Since their discovery in 1841, Graphite Intercalation Compounds (GICs) have found tremendous applications in various industrial and research fields such as supercapacitors, superconductors, heterogeneous catalysts, anode materials, hydrogen and lithium-ion storage and notably in graphene synthesis. GICs are a type of graphitic compounds formed by the insertion of a different atomic, ionic or molecular species, known as intercalants between the layers of graphite host. Intercalation occurs in stages, and the phenomenon of staging is characterised by stage index n, which is the number of carbon layers present between two successive intercalate layers. The concentration of intercalant in graphite increases as the stage index decreases.Oxyacids readily intercalate in graphite. Researchers have studied intercalation of graphite in a wide variety of such acids such as H2SO4, HNO3, H2SeO4, HClO4 and H3PO4, and concluded that sulphuric acid is the best intercalant for graphite owing to higher efficiency and lesser reaction times. Intercalation in sulphuric acid gives Graphite Bisulphate (GB). Conventional GB chemical synthesis methods, pose an environmental and safety hazard due to the usage of hazardous and explosive oxidants. Moreover, chemical methods such as Hummers’ are primarily oxidation routes for the synthesis of Graphene Oxide (GO) wherein GB is believed to be the process intermediate, which is difficult to isolate.Electrochemical synthesis of GB is inexpensive, scalable and provides an easy defect-free transfer to the application substrate due to its ability to deliver the product in a suspension. Furthermore, the electrochemical approach provides an environment- friendly solution to the synthesis of GB because it replaces harsh chemical oxidants with an external polarisation potential. The quantity of electricity passed can also be controlled by changing the applied potential to obtain desired stages of GB.However, the synthesis of low stage GB by the electrochemical process in aqueous sulphuric acid solutions is an arduous task as a result of the excess water present in the system. Water molecules react with surface C atoms to form bulky surface groups which hinder the process of intercalation. Furthermore, undissociated water molecules may also co-intercalate with the bisulphate ions from aqueous sulphuric acid. Electrochemical oxidation of this intercalated water causes reduction of bisulphate ions and ultimately results in the vigorous evolution of oxygen and sulphur dioxide, which exfoliates graphite. Thus, GB formed before exfoliation is disintegrated and lost.On the other hand, water also facilitates intercalation by opening up graphitic grain boundaries for intercalation by carrying out a nucleophilic attack on the edge sites. Thus an optimal concentration of water in aqueous sulphuric acid along with an optimal positive polarisation potential is required for the synthesis and stability of GB. The present study aims at the electrochemical synthesis and characterisation of low stage GB and determination of optimal reaction conditions for the process. A pure stage GB synthesised and isolated this way can be particularly useful for the synthesis of layer-specific graphene flakes. Intercalation reduces the force of attraction between layers of graphite and hence makes selective cleaving possible by sonication. The stage index is strongly correlated with the number of graphene layers produced upon electrochemical exfoliation and is thus a key parameter to tune the electrochemical exfoliation of graphite.

Titanium dissolution from decomposed Ilmenite using NaOH into the aqueous sulphuric acid solutions

At present work, the experiment to dissolve titanium from the Indonesian Ilmenite into the aqueous sulphuric acid solutions has been done through the following process: Ilmenite decomposition using NaOH at temperature 800°C for 5 hours to produced decomposed Ilmenite, followed with titanium dissolution from the decomposed Ilmenite into the aqueous sulphuric acid solutions in the glass reactor. The variables used for dissolution process were covering: dissolution temperature from 30°C to 70°C, sulphuric acid concentrations from 5% to 15%, and dissolution time from 30 minutes up to 180 minutes. The influence of those all variables were observed on the titanium dissolution from the decomposed Ilmenite. Result of the dissolution experiment show that the dissolved titanium in the aqueous sulphuric acid solutions increased when the dissolution temperature was increased from 30°C to 60°C, sulphuric acid concentration were increased from 5% to 15% and dissolution time were extended from 30 minutes to 180 minutes.

Investigating the chemistry of alumina based defluoridation using safe H+ source

The existence of high levels of fluoride in drinking water is a worldwide problem and activated alumina is an established adsorbent for fluoride removal. This article investigates factors governing rate of fluoride uptake, mechanical stirring as well as interference from competing ions, of the defluoridation employing activated alumina. Pre-treatment with aqueous solution of sulphuric acid has shown faster uptake in a small setup was demonstrated recently. An attempt to understand the phenomena by profiling ionic species on the active surface of activated alumina, native and acid treated. Presence of carbonate species was found, in Raman spectra, on native surface which can explain effectiveness of pre-treatment. Broadening of hydroxyl species profiles, in infrared and solid-state NMR spectra, suggests incorporation of water into new sites. Fluoride treatment of the pre-treated activated alumina leads to narrowing of hydroxyl species profiles suggesting incorporation of fluoride into new sites. A mechanism is being proposed wherein H+ ions in the presence of SO42- (from KHSO4 or NaHSO4) enables the energetics for faster defluoridation and regeneration of activated alumina.

ВОДОРОДОПРОНИЦАЕМОСТЬ ПЛЕНОЧНЫХ СПЛАВОВ Pd53Cu РАЗЛИЧНОГО ФАЗОВОГО СОСТАВА

Методом двухступенчатой катодно-анодной хроноамперометрии изучено влияние фазового состава пленочных сплавов Pd53Cu на процессы инжекции и экстракции атомарного водорода. Исследования проведены в водном растворе 0.1М H2SO4. Установлено, что инжекция атомарного водорода в сплав в начальный период протекает в диффузионно-фазограничном режиме, а затем - диффузионном. Найдены кинетические и диффузионные параметры фазограничного проникновения водорода и его последующей твердофазной диффузии. Выявлена роль фазового состава и кристаллографической ориентации сплава на водородопроницаемость. Показано, что перенос атомарного водорода в сплаве главным образом происходит по телу зерна, а не по межфазным границам.

Quantifying charge transfer to nanostructures: Polyaniline nanotubes

The nano-impact method is used to quantify electrolytic doping levels of single polyaniline nanotubes in aqueous sulphuric acid solution. Even at extreme potentials only partial (≤18%) doping of the tubes is observed. Comparisons are made with the doping of ensembles of tubes where the levels of charge transfer appears even less. The implications for practical applications are assessed.

A Comparative Performance Analysis of Nanoporous Alumina Moisture Sensors Fabricated by Anodizing Aluminum in Aqueous Oxalic and Sulphuric Acid Solutions

A Comparative Performance Analysis of Nanoporous Alumina Moisture Sensors Fabricated by Anodizing Aluminum in Aqueous Oxalic and Sulphuric Acid Solutions

Analysis of the Quintilii’s Villa Bronzes by Spectroscopy Techniques

The aim of this work is the characterization, with different diagnostic tests, of three fragments of bronze artefacts recovered from the Villa of the Quintilii (located in the south of Rome). In particular, the sample alloys were investigated by different chemical and morphological analysis. Firstly, an analysis of the alloy, implemented through the electronic spectroscopy, was taken to discriminate the bronze morphology and its elemental composition. Subsequently, a surface analysis was realized by molecular spectroscopy to identify the alteration patinas on surfaces (such as bronze disease). Two diagnostic techniques are used for the alloy analysis: scanning electron microscopy (SEM) connected to the EDX spectroscopy (to study the morphology and alloy composition) and Auger electron spectroscopy (AES) (to identify the oxidation state of each element). Moreover, for the study of surface patinas, IR and Raman spectroscopies were implemented. All studies were performed on the “as received” samples, covered by a thin layer of excavated soil and on samples processed in an aqueous solution of sulphuric acid (10%), to remove patinas and alterations.

Electrochemical synthesis and corrosion behaviour of polypyrrole and polypyrrole/carbon nanotube nanocomposite films

This study examines the use of polypyrrole and polypyrrole/multi-walled carbon nanotubes composite coatings for corrosion protection of 304 stainless steel in 3% NaCl solution. Polypyrrole and polypyrrole/multi-walled carbon nanotubes composite coatings were electropolymerised on 304 stainless steel surfaces by the potentiodynamic method in aqueous sulphuric acid solutions. The coatings were characterised via cyclic voltammetry, Fourier transform infrared spectroscopy and scanning electron microscopy. The corrosion behaviour of the polymer-coated stainless steel electrodes was investigated in a 3% NaCl solution by open-circuit potential measurements, Tafel polarisation and electrochemical impedance spectroscopy. Potentiodynamic polarisation, impedance measurements and open-circuit potential data revealed that the polypyrrole and polypyrrole/multi-walled carbon nanotubes composite coatings effectively protected the stainless steel substrates from corrosion in chloride solution. However, the corrosion resistance of the substrates was reduced after longer immersion times.

Analysis of Water-Soluble Vitamins in Honey by Isocratic RP-HPLC

An isocratic RP-HPLC method has been developed for the identification and quantification of water-soluble vitamins in honey. The mobile phase tested was an aqueous solution of sulphuric acid and the detection was carried out simultaneously by UV and fluorescence. The separation of vitamins C (l-ascorbic acid), B1 (thiamine), B3N (nicotinamide), B3H (nicotinic acid), B5 (d-pantothenic acid) and B6 (pyridoxine) is achieved in these conditions in 15 min. The addition to the mobile phase of methanol 2 % v/v reduced significantly the analysis time in the separation of these vitamins up to 10 min. Moreover, in presence of a cationic surfactant hexadecyltrimethylammonium bromide (CTAB) in the mobile phase, the separation of vitamin C, B1, B3N, B3H, B2 (riboflavin) and B6 is possible in 6 min. The combination of both mobile phases, H2SO4/methanol and H2SO4/methanol/CTAB, has been applied to the analysis, in isocratic mode, of several monofloral honeys (rosemary, thyme, lavender, chestnut, echium) and a honeydew honey in a short time analysis.

Effect of chemical degradation on the mechanical properties of ethylene–propylene–diene (5-ethylidene-2-norbornene) terpolymer-BaSO4 nano composites

Time dependent degradation of the gum vulcanizates of ethylene propylene diene (EPDM) and EPDM-barium sulphate nano composites in sulphuric acid were studied. Impact of degradation on the mechanical properties of these composites was also evaluated. Gum compounds and nanocomposites cured with efficient vulcanisation system were subjected to an aggressive acidic medium containing 60% aqueous solution of sulphuric acid (H2SO4). The changes in functional groups were monitored using Fourier transform infrared spectroscopy (FTIR). The results reveal the formation of several oxygenated species on the EPDM rubber molecule due to acid attack; which is enhanced in the absence of barium sulphate nanofillers. Crosslink densities of acid aged samples were measured by the swelling method. An initial decrease in crosslink density as observed in EPDM gum vulcanizates is an indicative of hydrolytic attack at the crosslink sites, whereas the effect is less pronounced in nano composites. The effects of acid attack on mechanical properties were traced out by evaluating the percentage retention in tensile, elongation at break, compression set and abrasion resistance. For aged EPDM gum vulcanizates the retention in tensile showed a positive sign for a given increase in crosslink density, but on further increase of crosslink density due to combination of species formed during decrosslinking, tensile strength decreases. In the case of nano composites the retention in tensile properties was well around 100%. Scanning electron microscopy was used to monitor the changes in surface topography due to attack of acid and it well supports the degradation phenomenon and stabilisation of mechanical properties in the presence of barium sulphate nanoparticles.

Corrosion protection of stainless steel plates in fuel cells environment by conducting polymers

The electrodeposition of polypyrrole and polyaniline has been performed in aqueous solutions of sodium saccharinate and sulphuric acid, respectively. The coatings were obtained by voltamperometric and galvanostatic methods. The corrosion behaviour of polypyrrole and polyaniline coated stainless steel (SS) in sulphuric acid medium was investigated by linear polarisation, open circuit potential and electrochemical impedance spectroscopy. The polyaniline coatings doped with sulphate anions (SO42−) showed more resistance to protect SS to corrosion than the polypyrrole coatings doped with saccharinate anions (C7H4NO3S−).

Corrosion resistance of explosion cladding plate of carbon steel and 316L stainless steel

The ASME AS-240TP-316L stainless steel in the form of a sheet 3 mm in thickness and the ASTM SA-516 grade 60N steel substrate are joined by explosion cladding. The objective of this paper is to evaluate the electrochemical behaviour of a cladding plate of carbon–manganese steel and stainless steel 316L when compared to non-cladding plate 316L steel. The effect of the cladding process on the corrosion resistance was evaluated in a medium of aqueous solution of sulphuric acid. Anodic potentiodynamic polarisation curves were obtained to study the passivation behaviour of the cladding plate. Electrochemical impedance spectroscopy was performed to elucidate the corrosion mechanism of the cladding plate. The non-cladding ASME AS-240 TP-316L steel showed a higher corrosion potential, a lower passivation current density and a higher polarisation resistance, exhibiting a higher corrosion resistance than cladding 316L steel.

Modeling of continuous diffusion dialysis of aqueous solutions of sulphuric acid and nickel sulphate

At steady state, the simultaneous transport of sulphuric acid and nickel sulphate through an anion-exchange membrane Neosepta-AFN (Astom Corporation, Tokyo, Japan) was investigated in a two-compartment counter-current dialyzer with single passes. The transport was quantified by the recovery yield of acid, rejection of salt and four phenomenological coefficients, which were correlated with the acid and salt concentrations in the feed. The phenomenological coefficients were determined by the numerical integration of the basic differential equations describing the concentration profiles of the components in the dialyzer. This integration was combined with an optimizing procedure. The experiments proved that the acid recovery yield is in the limits from 63 to 91 %, while salt rejection is in the limits from 79 to 97 % in the dependence on the volumetric liquid flow rate and composition of the feed.

The electrochemical discharges for the synthesis of nickel oxide nanoparticles: Characterization and mechanism

Electrochemical discharges in aqueous solution of sulphuric acid and ethanol as scavenger of hydroxyl radicals, in addition to polyvinylpyrrolidone as stabilizing agent are used for the synthesis of nano-sized nickel oxide colloids. Morphological characterization by electron microscopy and powder X-ray diffraction has been performed to examine the obtained particles at different terminal voltages and experiment durations. From the qualitative resemblance of the electrochemical discharges to the radiolysis technique, a microscopic mechanistic model is proposed giving an overall picture of the physicochemical phenomenon for the synthesis of fine particles.

Study of Platinum Deposition on Untreated and Thermally Modified Glassy Carbon

Platinum was deposited from aqueous sulphuric acid solution of hexachloroplatinic acid under potentiostatic conditions upon untreated as well as thermally treated glassy carbon (GC). The influence of thermal treatment of GC on electrochemical platinum deposition was thoroughly investigated in terms of the size, the size distribution and coverage of Pt deposits, using scanning electron microscopy and X-ray photoelectron spectroscopy. A decrease in Pt particle diameter and an increased Pt coverage was observed for various deposition pulse lengths on thermally pre-treated GC. This thermal pre-treatment led to a formation of a microporous layer on the substrate surface, thus influencing particle size distribution and coverage. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) measurements have shown that the chemical composition and surface roughness of GC are not affected by the treatment.

Rhenium cementation on zinc in aqueous acidic solutions

Rhenium has been cemented on Zn sheet in aqueous sulphuric acid solutions. The cementation took place concurrently with hydrogen evolution from the Zn substrate. The Re source was NH4ReO4. At the highest tested temperature (40°C), hydrogen evolution was intense, and the Re deposit was powdery and detached easily from the Zn surface. The higher the sulphuric acid concentration, the higher the rate of hydrogen evolution, which ranged between 15 and 200 cm3 h−1; this phenomenon enhanced the powdery character of the deposit. Continuous deposits, with high Re content (up to ∼96·5%) and a metallic shine, were obtained at low acid concentration (0·025–0·050M) and low temperatures (25°C). Perrhenate concentration variations did not affect the deposit quality in the studied conditions.

DESULPHURIZATION STUDY OF PETROLEUM PRODUCTS THROUGH EXTRACTION WITH AQUEOUS IONIC LIQUIDS

Desulphurization of jet fuel, diesel oil, heavy residue and commercial furnace oil is carried out through extraction with aqueous solutions of sodium chloride, barium chloride, sodium hydroxide, mercury chloride, arsenic trioxide, potassium iodide, lead acetate, calcium hydroxide, zinc chloride, aluminum chloride, hydrochloric acid and sulphuric acid. Among the solutions used, HgCl2 and Ca(OH)2 were found to be the most efficient for the removal of sulphur compounds from the fractions understudy at 40 °C temperature and 30 min of shaking time. The total sulphur depletion of 60 % and 58 % has been achieved in case of jet fuel oil, 71 % and 62 % in case of diesel oil, 68 % and 67 % in case of heavy residue and 67 % and 69 %in case of commercial furnace oil with 10% HgCl2 and 5% Ca(OH)2 aqueous solutions, respectively.

Coprecipitation of gadolinium with calcium sulphate dihydrate

Abstract The present study reports the coprecipitation of gadolinium with calcium sulphate dihydrate, in aqueous solutions of sulphuric acid, at constant ionic strength using a radiotracer technique. The experimental results obtained at ambient temperature, show that the quantity of gadolinium ions coprecipitated in gypsum identified by X-ray diffraction (XRD) and elemental analysis is very small, lower than 4ߙat.ߙ%. The mechanism of coprecipitation of Gd(III) has been discussed, although the elementary processes of the mechanism are not clear. The distribution of gadolinium between precipitate of gypsum and saturated aqueous solutions of H2SO4 has been measured between 30 and 70 °C. Experiments of coprecipitation indicate that the coefficient of distribution of Gd(III) depends on the solubility and nature of solid calcium sulphate phase.