3-Mercaptopropyltrimethoxysilane as a Cu corrosion inhibitor in KCl solution

3-mercaptopropyltrimethoxysilane (MPS) has been used as a copper corrosion inhibitor in 0.100 mol L^–1 KCl solution. The inhibition was studied as a function of the MPS pretreatment concentration in ethanol. The MPS concentration used was between 1.0 × 10^–8 mol L^–1 and 1.0 × 10^–1 mol L^–1. A freshly-cleaned Cu electrode was inserted in an ethanolic solution of MPS for 30 min for pretreatment, and was then exposed to a 0.100 mol L^–1 KCl aqueous solution for 1 h. From the polarization resistance, the inhibition efficiency improved with increase in MPS concentration during the pretreatment. The MPS adsorption on Cu followed a Langmuir adsorption behaviour. However, at MPS concentrations larger than 1.0 × 10^–4 mol L^–1 the inhibition decreased. Moreover, the inhibition efficiency decreased with increase in the exposure time of the MPS modified Cu electrode in the KCl aqueous solution. Polarization studies suggest that MPS is an anodic as well as a cathodic inhibitor, in the presence of dissolved oxygen. X-ray photoelectron spectroscopy (XPS) analysis of the Cu samples showed that the organic compound modifies the Cu surface and scanning electron microscopy (SEM) studies indicated that MPS protects the Cu surface when exposed for 350 h to laboratory environment. Polarized grazing angle Fourier transform-infrared (FTIR) microscopy analysis determined the presence of a polymer on the Cu surface.     

Ammonium nitrate wastewater treatment by coupled membrane electrolysis and electrodialysis

A process coupling membrane electrolysis and electrodialysis is implemented to treat ammonium nitrate wastewater. Membrane electrolysis produces ammonia and nitric acid while electrodialysis reconcentrates the depleted salt solution. Ammonia is removed continuously by in situ stripping; thus allowing gas production with a constant current efficiency (about 70%). Nitric acid up to 8 mol L^–1 is obtained. The current efficiency of acid production depends on nitric acid concentration. When this concentration varies from 1 to 8 mol L^–1 the average current efficiency is about 58%. Electrodialysis produces a rejected stream containing less than 3 × 10^–3 mol L^–1 of ammonium nitrate.     

Self-Assembly of Metalloporphyrin-L-Cysteine Modified Gold Electrode

A novel composite film containing metalloporphyrins was fabricated by in situ electrochemical scanning on an L-cysteine self-assembled monolayer modified gold electrode. SEM and ATR-FTIR were used to characterize the structure of the film. The electrochemical properties were investigated through techniques such as a.c. impedance, cyclic voltammetry and chronocoulometry. The porphyrin-L-cysteine film showed no peak in the first cycle, while each of the composite films derived from three different metalloporphyrin-L-cysteines presented a pair of reversible redox peaks in 1.0 mol L^–1 H₂SO₄. These peaks correspond to the rapid redox process of the metal. The supporting electrolyte and its pH value influenced the stability and sensitivity of the composite film. Cupric-porphyrin-L-cysteine film showed good catalytic activity for the reduction of H₂O₂. The catalytic current was linear to H₂O₂ concentration in the range 1.0 × 10^–6 to 3.0 × 10^–5 mol L^–1, with a correlation coefficient of 0.9995. The detection limit was 1.0 × 10^–7 mol L^–1 at a signal to noise ratio of 3. The relative standard deviation was calculated as 2.4% for solutions containing 1.0 × 10^–5 mol L^–1 H₂O₂(n= 11).     

A spectroelectrochemical investigation of the influence of sodium diisobutyldithiophosphinate on silver dissolution in aqueous cyanide

Polarization studies have been carried out to determine the influence of diisobutyldithiophosphinate (DIBDTPI) on the dissolution of silver in cyanide solutions at pH 11. DIBDTPI was found to inhibit dissolution at concentrations similar to those used when this compound is applied as a flotation collector. The inhibition efficiency in 10^–2 mol dm^–3 CN^– was found to increase with increase in DIBDTPI concentration in the range 10^–6–10^–4 mol dm^–3, and with increase in time of exposure of the silver to the DIBDTPI solution. The inhibition efficiency found for 10^–4 mol dm^–3 DIBDTPI in quiescent 10^–2 mol dm^–3 CN^– solution at 23 °C was 64.6% and 95.0% for exposure times of 10 min and 2 h, respectively. These values are significantly less than those found previously for 2-mercaptobenzothiazole under the same conditions. Surface enhanced Raman spectroscopy showed that inhibition was associated with adsorption of DIBDTPI displacing cyanide from the silver surface. Voltammetry at 0.5 mV s^–1 indicated that adsorption of DIBDTPI involves charge transfer.     

An electrochemical investigation of the suppression of silver dissolution in aqueous cyanide by 2-mercaptobenzothiazole

Triangular potential sweep voltammetry, potentiokinetic generation of polarization curves, and coupon corrosion tests have been carried out to determine the influence of 2-mercaptobenzothiazole (MBT) on the dissolution of silver in cyanide solutions at pH 11. MBT has been shown to be an effective inhibitor for silver dissolution at concentrations similar to those used when MBT is applied as a flotation collector. The inhibition efficiency (i.e., [1 – the ratio of the corrosion rates in the presence and absence of MBT], expressed as a percentage) in 10^–2 and 10^–3 mol dm^–3 CN was found to increase with increase in MBT concentration in the range 10^–6 to 10^–4 mol dm^–3, and with increase in time of exposure of the silver to the MBT solution. The inhibition efficiency found for 10^–4 mol dm^–3 MBT in quiescent 10^–2 mol dm^–3 CN^– solution at 23 °C was 98.9%, 99.4% and 99.99% for exposure times of 10 min, 2 h and 5 days, respectively. Surface enhanced Raman spectroscopy showed that inhibition was associated with adsorption of MBT displacing cyanide from the silver surface.     

Synergistic effect of 2-mercapto benzimidazole and KI on copper corrosion inhibition in aerated sulfuric acid solution

2-Mercapto benzimidazole (MBI) was used as a copper corrosion inhibitor in aerated 0.5 mol L^–1 H₂SO₄ solutions. The inhibition efficiency (IE) increased with increasing MBI concentration to 74.2% at the 1 mM level. A synergistic effect existed when MBI and iodide ions were used together to prevent copper corrosion in sulfuric acid. It was found that IE reached 95.3% in 0.5 mol L^–1 H₂SO₄ solutions containing 0.75 mmol L^–1 MBI and 0.25 mmol L^–1 KI. X-ray photoelectron spectroscopy (XPS) analysis of the copper samples showed that a (Cu⁺MBI) complex film formed on the surface to inhibit the copper corrosion and the iodide ions did not participate in the formation of the inhibitor film. The synergistic effect was attributed to the adsorption of iodide anions on the copper surface, which then facilitated the adsorption of protonated MBI and the formation of an inhibitive film.     

Sensitive DNA impedance biosensor for detection of cancer, chronic lymphocytic leukemia, based on gold nanoparticles/gold modified electrode

A simple and sensitive DNA impedance sensor was prepared for the detection of chronic lymphocytic leukemia. The DNA electrochemical biosensor is worked based on the electrochemical impedance spectroscopic (EIS) detection of the sequence-specific DNA related to chronic lymphocytic leukemia. The ssDNA probe was immobilized on the surface of the gold nanoparticles. Compared to the bare gold electrode, the gold nanoparticles-modified electrode could improve the density of the probe DNA attachment and hence the sensitivity of the DNA sensor greatly. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy were performed in a solution containing 1.0 mmol L⁻¹ K₃[Fe(CN)₆]/K₄[Fe(CN)₆] and 50 mmol L⁻¹ phosphate buffer saline pH 6.87 plus 50 mmol L⁻¹ KCl. In the CV studied, the potential was cycled from 0.0 to +0.65 V with a scan rate of 50 mV s⁻¹. Using EIS, the difference of the electron transfer resistance (ΔR_et) was linear with the logarithm of the complementary oligonucleotides sequence concentrations in the range of 7.0 × 10⁻¹²–2.0 × 10⁻⁷ mol L⁻¹, with a detection limit of 1.0 × 10⁻¹² mol L⁻¹. In addition, the DNA sensor showed a good reproducibility and stability during repeated regeneration and hybridization cycles.     

Electrochemical study and complete factorial design of Toluidine Blue immobilized on SiO2/Sb2O3 binary oxide

SiO₂/Sb₂O₃ of specific surface area S _BET = 788 m² g^–1 and 4.7 wt % of Sb was prepared by the sol–gel method. Toluidine Blue (TB⁺) was immobilized on SiO₂/Sb₂O₃ by ion exchange reactions and the amount of dye bonded to the substrate surface was 13.72 mol g^–1 for SiO₂/Sb₂O₃. This material was used to modify carbon paste electrodes and the electrochemical properties of Toluidine Blue (TB⁺) immobilized on a silica surface modified with antimonium trioxide were investigated by cyclic voltammetry. The electron mediator property of toluidine blue was optimized using a factorial design, consisting of four factors each at two levels. Factorial analysis was carried out by searching for better reversibility of the redox process, that is, the lowest separation between anodic and cathodic peak potentials and a current ratio near unity. The aqueous phase pH does not appear to influence the peak separation, E, and the |I _pa//I _pc| current ratio response. The other factors studied, the scan rate, type of electrolyte and electrolyte concentration are important for this chemically modified electrode system demonstrating significant influences on the reversibility of electron transfer. The experimental observations and data analyses on this system indicate that the smallest peak separation occurs using 20 mV s^–1 and 1.0 mol L^–1 KCl while values of |I _pa//I _pc| close to unity are found for 20 mV s^–1 with 1.0 mol L^–1 concentrations of either KCl or CH₃COONa. The electrodes presented reproducible responses and were chemically stable for various oxidation-reduction cycles.     

Electrochemical investigation of the dimeric oxo-bridged ruthenium complex in aqueous solution and its incorporation within a cation-exchange polymeric film on the electrode surface for electrocatalytic activity of hydrogen peroxide oxidation

Electrochemical behavior of oxo-bridged dinuclear ruthenium(III) complex ([(bpy)2(H₂O)Ru^III-O-Ru^III(H₂O)(bpy)2]⁴⁺) has been studied in aqueous solution (KCl 0.5 mol L⁻¹) by both cyclic and rotating disk electrode (RDE) voltammetry in order to identify and elucidate the reaction mechanism. Modified electrode containing the oxo-bridged ruthenium complex incorporated into a cation-exchange polymeric film deposited onto platinum electrode surface was studied. Cyclic voltammetry at the modified electrode in KCl solution showed a single-electron reduction/oxidation of the couple Ru^III-O-Ru^III/Ru^III-O-Ru^IV. The modified electrode exhibited electrocatalytic property toward hydrogen peroxide oxidation in KCl solution with a decrease of the overpotential of 340 mV compared with the platinum electrode. The Tafel plot analyses have been used to elucidate the kinetics and mechanism of the hydrogen peroxide oxidation. The first at low overpotential region there is no significant change in the Tafel slope (∼0.130 V dec⁻¹) with varying peroxide concentration. The second region at higher overpotential the slope values (0.91–0.47 V dec⁻¹) were depended on the peroxide concentration. The apparent reaction order for H₂O₂ varies from 0.16 to 0.50 in function of the applied potential. The apparent reaction order (at constant potential) with respect to H⁺ concentration of 10⁻⁵ to 10⁻¹ mol L⁻¹ was 0.25. A plot of the anodic current vs. the H₂O₂ concentration for chronoamperometry (potential fixed = +0.61 V) at the modified electrode was linear in the 1.0 × 10⁻⁵ to 2.5 × 10⁻⁴ mol L⁻¹ concentration range.     

Effect of sodium and potassium sulphates on zinc electrowinning

In order to evaluate the intrinsic effect of high concentrations of sodium and potassium sulphates in zinc electrowinning solutions, measurements of coulombic efficiency were carried out under mass transfer-controlled conditions in synthetic solutions of very high purity. A solution composition of 1 mol dm^–3 ZnSO₄+1.5 mol dm^–3 H₂SO₄ was employed with and without additions of 0.5 mol dm^–3 Na₂SO₄ and/or 0.25 mol dm^–3 K₂SO₄. With temperature and current density similar to plant practice (37° C, 650 A m^–2) and electrode rotation rates of 10 and 45 s^–1, the coulombic efficiency for three successive batch tests (200 mg zinc) increased by an average of 1.2% (from an average of 96.0%) for additions of 0.5 mol dm^–3 Na₂SO₄+0.25 mol dm^–3 K₂SO₄. The results were evaluated in terms of available theories, solution purity and predicted changes in solution composition (zinc and hydrogen ion activities) and physical properties following additions of Na₂SO₄/K₂SO₄. It was concluded that in the plant situation the increase in coulombic efficiency would probably be offset by an increase in cell voltage of about 2%, the net effect on power efficiency being a decrease of about 1%. The zinc deposit morphology and preferred orientation were also studied. The addition of sodium and/or potassium sulphate to the solution resulted in rougher, darker zinc deposits, a slight grain refining effect, and a change from random to predominantly basal (002), (004) crystal orientation (at 45 s^–1).     

Design,synthesis and characterization of a novel self‐doped polyaniline derivative

A type of self‐doped polyaniline derivative was successfully synthesized using an oxidative coupling polymerization approach. The structure of the electroactive polymer was investigated using Fourier transform infrared and ¹H NMR spectroscopy and gel permeation chromatography. Its thermal and spectral properties were characterized using thermogravimetric analysis and UV‐visible spectroscopy. The electrochemical activity of the polymer was studied using cyclic voltammetry (CV) in 1.0 mol L^?1 H₂SO₄ solution with various scan rates. The peak current increases linearly with scan rate from 10 to 120 mV s^?1, which indicates that the electrode reaction is controlled by a surface process. In addition, the self‐doped characteristic was investigated using CV in 1.0 mol L^?1 KCl solution with pH value changing from 1 to 12, and the results indicate that the polymer has excellent electrochemical activity even in neutral and alkaline environments. Copyright © 2010 Society of Chemical Industry     

Effects of boric acid on hydrogen evolution and internal stress in films deposited from a nickel sulfamate bath

The effects of boric acid additions on the pH close to the electrode surface, on the hydrogen evolution reaction and on the internal stress in the plated films were studied for the high speed electroplating of nickel from a nickel sulfamate bath at a current density close to the nickel ion limiting current density. The study was carried out at 50 °C and pH 4.0 using a 1.55 M nickel sulfamate plating bath containing boric acid at concentrations ranging from 0 to 0.81 mol L^–1. The variation of the internal strain in the plated nickel films was determined in situ using a resistance wire-type strain gauge fitted to the reverse side of the copper electrode substrate. The solution pH at a distance of 0.1 mm from the depositing nickel film was measured in situ using a miniature pH sensor assembly consisting of a thin wire-type antimony electrode and a Ag/AgCl/sat. KCl electrode housed in a thin Luggin capillary. The addition of boric acid was shown to effectively suppress the hydrogen evolution reaction at nickel electrodeposition rates (18.0 A dm^–2) close to the limiting current density (~20 A dm^–2). Consequently, the solution pH adjacent to the plating metal surface was maintained at a value close to that in the bulk solution and the development of high internal stresses in the deposited nickel films was avoided.     

Inhibitory mechanism of low-carbon steel corrosion by mimosa tannin in sulphuric acid solutions

Mimosa tannin was investigated as inhibitor of low-carbon steel sulphuric acid corrosion in concentrations from 10^–5 to 10^–1 mol L^–1, at the temperature of 298 K in the solutions of pH 1, 2 and 3. The inhibitor effectiveness increases with increase in concentration. The adsorptive behaviour of mimosa tannin in solutions of pH 1 and 2 may be approximated, both by Temkin and Frumkin type isotherms, probably due to the chemisorption of tannin molecules on the metal surface. The free energies of adsorption are in the range from –35.1 to –39.5 kJ mol^–1. At pH 3, a Freundlich type isotherm is obeyed, probably due to the physisorption of ferric-tannate that forms at this pH, both on the metal surface and in the bulk electrolyte. The free energy of adsorption at pH 3 is –11.8 kJ mol^–1. The activation energy of the iron dissolution process at pH 1 was found to be 51.4 kJ mol^–1 and decreased to 48.0 kJ mol^–1 on the addition of 1.25 × 10^–2 mol L^–1 mimosa tannin. The addition of the same amount of mimosa tannin into solutions of pH 2 and 3, increased the activation energy of iron dissolution from 15.6 to 34.3 kJ mol^–1 and from 12.0 to 19.2 kJ mol^–1, respectively.     

Selective and sensitive detection of dopamine in the presence of ascorbic acid by molecular sieve/ionic liquids composite electrode

A simple, sensitive, and reliable method based on a molecular sieve/ionic liquids composite electrode has been successfully developed for selective determination of dopamine (DA). The electrochemical behavior of dopamine (DA) at the modified electrode was investigated by cyclic voltammetry (CV) and square wave voltammetry (SWV). The influence of experimental parameters including pH of solution, amount of modifier, accumulation potential and time on the response of DA was investigated. At the optimum conditions, the peak current of DA was linear with the concentration of DA in the wide range of 5.0 × 10⁻⁸ mol L⁻¹ to 8 × 10⁻⁴ mol L⁻¹, with the correlation coefficient of 0.9982. The detection limit was 1.0 × 10⁻⁸ mol L⁻¹ (S/N = 3) in the presence of 0.2 mM ascorbic acid (AA). The interference studies showed that the modified electrode had excellent selectivity. What's more, the modified electrode also exhibited good reproducibility and stability for determination of DA, and could be applied to determine human serum samples.     

Development of a novel redox flow battery for electricity storage system

A novel cylindrical battery which uses carbon fibres with high specific surface area as electrodes and a porous silica glass with high chemical stability as membrane has been fabricated. The results obtained from electrolysis of 0.5 M K₃Fe(CN)₆–0.5 M KCl and of 85 mM V(IV)–1 M H₂SO₄ indicate that the cell possesses excellent electrolytic efficiency. As a redox flow battery (RFB) its performance was investigated by employing all-vanadium sulfate electrolytes. The results of the cyclic voltammetry measurements indicate that at a glassy carbon electrode the electrochemical window for 2 M H₂SO₄ solution could reach 2.0 2.4 V. Constant current charging–discharging tests indicate that the batteries could deliver a specific energy of 24 Wh L^–1 at a current density of 55 mA cm^–2. The open-circuit cell voltage, after full charging, remained constant at about 1.51 V for over 72 h, while the coulombic efficiency was over 91%, showing that there was negligible self-discharge due to active ions diffusion through the membrane during this period.     

Limiting current on porous graphite electrodes under flow conditions

The flow electrolysis of a solution of 2.0×10^–3 M K₃Fe(CN)₆ in 2 M KCl in water on porous graphite electrodes is described. The electrodes have been composed of crushed graphite of three grain size ranges: 0.7÷1.0, 0.4÷0.7, and 0.25÷0.4 mm. Electrodes of three different heights have been investigated, and the solution flow rate ranged between 0.009 and 0.25 ml s^–1. The dependence of the logarithm of the limiting current and of the limiting degree of conversion on the logarithm of the flow rates is shown for the electrodes. The obtained experimental results are interpreted by means of the described earlier semiempirical model of the limiting current on flow-through porous electrodes.     

Simultaneous electrosynthesis of alkaline hydrogen peroxide and sodium chlorate

Simultaneous electrosynthesis of alkaline hydrogen peroxide and sodium chlorate in the same cell was investigated. The alkaline hydrogen peroxide was obtained by the electroreduction of oxygen in NaOH on a fixed carbon bed while the chlorate was obtained by the reaction of anodic electrogenerated hypochlorite and hypochlorous acid in an external reactor. An anion membrane, protected on the anode side with an asbestos diaphragm, was used as the separator between the two chambers of the cell. The trickle bed electrode of dimensions 0.23 m high ×0.0362 m wide × 0.003 m thick was used on the cathode side. The anolyte chamber of the cell, 0.23 m high × 0.0362 m, wide × 0.003 m thick was operated at a fixed anolyte flow of 2.0 × 10^–6 m³ s^–1 while the oxygen loadings in the trickle bed was kept constant at 0.102 kg m^–2 s^–1. Other operating conditions include inlet and outlet temperatures of 27–33°C (anode side), 20–29°C (cathode side), cell voltages of 3.0–4.2 V (at current density of 1.2–2.4 kAm^–2) and a fixed temperature of 70°C in the anolyte tank.The effects of superficial current density, NaOH concentration (0.5–2.0 M) and catholyte liquid loadings (0.92–4.6 kg m^–2 s^–1) on the chlorate and peroxide current efficiencies were measured. The effect of peroxy to hydroxyl mole ratio on the chlorate current efficiency was also determined.Depending on the conditions, alkaline peroxide solution and sodium chlorate were cogenerated at peroxide current efficiency between 20.0 and 86.0%; chlorate current efficiency between 51.0 and 80.6% and peroxide concentration ranging from 0.069 to 0.80 M. The cogeneration of the two chemicals was carried out at both concentrated (2.4–2.8 M) and dilute (0–0.5 M) chlorate solutions. A relative improvement on the current efficiencies at concentrated chlorate was observed. A chloride balance indicated a less than 0.4% chloride loss to the catholyte. The results are interpreted in terms of the electrochemistry, chemical kinetics and the hydrodynamics of the cell.Nomenclature C _i concentration of speciesi (mol m^–3) - F Faraday constant (96 500 C mol^–1) - I current (A) - Q catholyte flow rate (m³s^–1) - total time of cell operation (s) - _i current efficiency of speciesi (%)     

Photoinducedly electrochemical preparation of Prussian blue film and electrochemical modification of the film with cetyltrimethylammonium cation

This work presents a photoinducedly electrochemical preparation of Prussian blue from a single sodium nitroprusside and insertion of cetyltrimethylammonium cations into Prussian blue as counter ions. The product of photoinducedly electrochemical reactions has a couple of voltammetric peaks at E° = 0.266 V in 0.2 mol l⁻¹ KCl solution, the measurements of X-ray powder diffraction and FT-IR spectroscopy show that it is Prussian blue (PB). The formation mechanism of a pre-photochemical reaction and subsequent electrochemical reaction is suggested. The cyclic voltammetric treatment of the freshly as-prepared PB film in 1.0 mmol l⁻¹ cetyltrimethylammonium (CTA) bromide solution leads to the insertion of cetyltrimethylammonium cations into the channels of Prussian blue, which substitutes for potassium ions as counter ions in Prussian blue. The Prussian blue containing CTA counter ions shows two couples of voltammetric peaks at E° = −0.106 V and E° = 0.249 V in 0.2 mol l⁻¹ KCl solution containing 1.0 mmol l⁻¹ cetyltrimethylammonium bromide. Compared with the electrochemical behaviors of KFeFe(CN)₆ in 0.1 mol l⁻¹ KOH alkali solution, CTAFeFe(CN)₆ shows relatively durable voltammetric currents due to the hydrophobic effects of cetyltrimethylammonium. The diffusion coefficients for CTA and potassium cations were estimated to be D_CTA 1.25 × 10⁻¹² cm² s⁻¹, D_K 2.59 × 10⁻¹² cm² s⁻¹, respectively. The peak current of electro-catalytic oxidization on hydrogen peroxide showed a linear dependence from 6.59 × 10⁻⁶ to 2.20 × 10⁻⁴ mol l⁻¹ with R = 0.99947 (n = 8). The linear regression equation was I_p (mA) = 0.82949 + 0.00594C (μmol l⁻¹) with errors of ±7.92833 × 10⁻⁵ for the slope and ±0.01085 for the intercept with the detection limit of 1.46 × 10⁻⁶ mol l⁻¹. Thus, it is expected to find its application in neutral or weak alkali medium for biosensors.     

Effects of AOT reverse micelle extraction on structure and emulsifying properties of soybean protein

The present study aimed to investigate the forward and backward extraction efficiency, structure, and emulsifying properties of soybean proteins obtained through bis (2-ethylhexyl) sulfosuccinate sodium salt (AOT) reverse micelle, as well as their relationship. The results showed that the extraction efficiency was the highest with the forward extraction time of 25 min, pH of 3.0, temperature of 45°C, KCl concentration of 0.0 mol L⁻¹, and the backward extraction time of 10 min, pH of 4.0, temperature of 30°C, KCl concentration of 0.5 mol L⁻¹. Significant changes in the secondary structure and fluorescence intensity of soybean protein after AOT reverse micelle extraction were observed. More β-sheet structure and higher fluorescence intensity corresponded to the higher emulsion stability of soybean protein. The results indicated that reverse micelle extraction shows great application in food industry.     

3-Hydroxybenzoic acid as AISI 316L stainless steel corrosion inhibitor in a H<Subscript>2</Subscript>SO<Subscript>4</Subscript>–HF–H<Subscript>2</Subscript>O<Subscript>2</Subscript> pickling solution

3-Hydroxybenzoic acid (3-HBA) was studied for possible use as a AISI 316L stainless steel (SS) corrosion inhibitor in an environmental-friendly aqueous pickling solution of 75 g l^–1 sulphuric acid (H₂SO₄), 25 g l^–1 hydrofluoric acid (HF) and 30 g l^–1 hydrogen peroxide (H₂O₂). 3-HBA was tested in concentrations from 5 × 10^–5 to 5 × 10^–1 M at 298 and 313 K temperature. Inhibition efficiency increased with the 3-HBA concentration. The inhibitor mechanism is discussed in terms of the properties of the isotherm equations of Frumkin, Hill-de Boer and Kastening–Holleck mainly. The shape, the trend of the slopes along the curve and the existence of inflection points, were analysed as the characteristics that differentiate one adsorption equation from another. The best fit was obtained using the Frumkin isotherm model. The projected molecular area of 3-HBA was calculated as a structural parameter to elucidate its optimal inhibition mechanism.