Contact corrosion of metals in aqueous and aqueous-glycolic solutions

Corrosion behavior of aluminum, steel, and cast iron both without contact and in short-circuited aluminum-steel, aluminum-cast iron, steel-cast iron, and aluminum-steel-cast iron systems in fresh water, ethylene glycol, and its aqueous solutions of various compositions containing 5 to 95 vol % fresh water was studied.     

Electrochemical corrosion kinetics of tin and tin amalgams in NaCl aqueous solutions

Electrochemical techniques were used to determine the corrosion rate of pure tin metal as compared to 80 Sn/20 Hg tin amalgam. X-ray diagrams showed that this amalgam was a crystalline γ₂ phase, whereas a 50 Sn/50 Hg amalgam contained liquid alloy embedded in the same γ₂ phase. Open circuit potential measurements, combined with narrow range potential scanning voltammetry, lead to the conclusion that amalgamation resulted in enhancement of the corrosion current, mainly by increasing the cathodic electron transfer reaction kinetics both in deaerated and in oxygen-saturated NaCl solution. When maintained at zero current potential in a solution containing dissolved O₂ gas, the samples were gradually covered with an insulating oxide layer which was identified by a series of electrochemical impedance diagrams recorded at different time intervals. The oxide layer was firmly adherent to the bulk tin metal but was poor at protecting the amalgam electrode. Finally, at potential values where the anodic current reached a few mA/cm², the pure tin metal surface was suddenly deteriorated by the formation of extremely deep pinhole corrosion pits, while this effect was smoothed down by amalgamation. Electronic Publication     

Electrochemical behavior of aqueous acid perrhenate-containing solutions on noble metals: critical review and new experimental evidence

The actual state of the art in the reduction of perrhenate ions on noble metals is reviewed and discussed. Also, with the aim of contributing to better knowledge of this process, results of several experiments are presented. For the first time, spectroscopic evidence on the nature of the deposited rhenium layer on Pt and Rh and the detection of an intermediate in the reduction pathway toward metallic rhenium is provided. The role of the substrate in the electroreduction of perrhenate ions in aqueous acid media is emphasized, because it is directly associated with the formation of different H-containing species as reducing agents. Thus, those metals capable of adsorbing H atoms are able to reduce ReO(4)(-) to ReO(2) by H(ad) at potentials more positive than that of the hydrogen evolution reaction. Moreover, H(ad) reacts with the ReO(2) layer previously deposited, resulting in the formation of Re(III)-soluble species, which subsequently undergo disproportionation to Re and ReO(2). For metals that are not capable of adsorbing H, i.e., Au, molecular hydrogen is the reducing agent, leading to the formation of metallic Re. In addition, ReO(4)(-) is chemically reduced to metallic Re by hydride.     

Inhibition of galvanic corrosion in aqueous solutions

Electrochemical and weight loss tests have been carried on Steel-Cu Zn 22 Al 2 and Steel- Cu Al 7 galvanic couples in a completely closed recirculating system.The aggressive media were aqueous aerated solutions at various salinities, in the presence and in the absence of Benzimidazole-2-thiol.The action of such compound in reducing the corrosion rate of the materials and the efficiency of the galvanic couples has been evaluated, in comparison too with inhibitive action of other inorganic and organic additives.     

Electrochemical properties of aqueous solutions of fullerenol-d

Dependence of the pH value on the concentration of fullerenol solutions was studied by means of pH-potentiometry, and the apparent degree of dissociation and the dissociation constant of fullerenol were calculated. The dependence of the electrical conductivity of fullerenol solutions on their concentration was examined. The molar electrical conductivity and also the apparent degree of dissociation and the dissociation constant of fullerenol were calculated.     

Extraction of ethylene glycol from aqueous salt solutions

A method is proposed for extracting ethylene glycol from aqueous salt solutions by dialysis through ion-exchange membranes, based on the Donnan exclusion of the electrolyte. Dialysis is performed in the continuous and batch modes. It is found that the batch mode of dialysis is more effective for extracting ethylene glycol from its aqueous salt solutions. The effect of the ionic form of the membrane on ethylene glycol fluxes is explained through computer simulation.     

Electrochemical behavior of mesidine in aqueous solutions

The electrochemical oxidation of mesidine has been investigated in the pH range 0.7–11 at a platinum electrode with periodical renewal of the diffusion layer and at a stationary carbon paste electrode. A E_1/2/pH relation for the platinum electrode has been derived in the pH range 0–7. It has been indicated that the only oxidation products of mesidine are 2,6-dimethylbenzoquinone-4-(2′,4′,6′-trimethyl)-anil at pH <8 and 2,4,6,2′,4′,6′-hexamethylazoxybenzene at pH>8. Oxidation mechanisms consistent with the kinetic parameters and the oxidation products are discussed.     

Contact corrosion of metals in concentrated aqueous-glycolic solutions

Corrosion behavior of aluminum, steel, and cast iron was studied both in their individual state and in systems constituted of aluminum and steel, aluminum and cast iron, steel and cast iron, and aluminum, steel, and cast iron in ethylene glycol solutions containing 5 and 30 vol % of fresh water.     

Inhibitor effect of sodium benzoate on the corrosion behavior of nanocrystalline pure iron metal in near-neutral aqueous solutions

Nanocrystalline iron coating was produced on carbon steel surface by pulse electrodeposition using citric acid bath. The grain size of a nanocrystalline surface was analyzed by X-ray diffractometry and scanning electron microscopy. The electrochemical behavior of nanocrystalline iron coating in the presence of sodium benzoate was evaluated in 30 mg l^-1 NaCl + 70 mg l^-1 Na₂SO₄ aqueous solution using potentiodynamic polarization curves and electrochemical impedance spectroscopy. The results were compared with that of the coarse-grained iron surface. The thermodynamic properties of the inhibitor adsorption were also determined. The results indicated that corrosion inhibition of sodium benzoate in near-neutral aqueous solution was increased as the grain size of iron was decreased from micro- to nanocrystalline surface. This was reported in terms of excess free energy of nanocrystalline surface.     

Solvent extraction of some metals from aqueous solutions

The results for the extractions of divalent (manganese, cobalt, zinc and cadmium) and trivalent (gallium and indium) metals and hexavalent uranium from aqueous solutions by various extractants such as organophosphorus compounds (tributyl phosphate, trioctylphosphine oxide, di-(2-ethylhexyl)phosphoric acid and 2-ethylhexyl 2-ethylhexylphosphonic acid), sulfur-containing compound (dihexyl sulfoxide), high-molecular weight amines (trioctylamine and trioctylmethylammonium chloride) and 7-alkylated hydroxyquinoline (7-(5,5,7,7-tetramethyl-1-octen-3-yl)-8-hydroxyquinoline are discussed in the viewpoint of separation chemistry.     

Electrochemical investigation of corrosion and corrosion inhibition of iron in hydrochloric acid solutions

The inhibition effect of 1-methyl pyrazole (MPA) on the acidic corrosion of iron in 1.0 M HCl was studied at different concentrations (10^?3–10^?2 M) by potentiodynamic polarization and electrochemical impedance spectroscopy, and EIS measurements. It is found from the polarization studies that methyl pyrazole (MPA) behaves mainly as anodic inhibitor in HCl. Values of polarization resistance (R_p) and double layer capacitance (C_dl) in the absence and presence of MPA in 1.0 M HCl are determined. The adsorption of MPA on iron surface from HCl is found to obey Temkin adsorption isotherm.     

Fast procedure for no-reference inversion-voltammetric determination of lead in aqueous solutions

Possibility of no-reference inversion-voltammetric determination of lead in aqueous solutions with the use of a preliminarily determined coulometric constant of the electrochemical cell, which enables substantially faster analysis as compared with the known analogs, was studied. The coulometric constants of electrochemical cells with a mercury film electrode were found for different solution volumes.     

Molar volumes of aqueous and ethylene glycol solutions of tetrahydrofuran

The densities of ethylene glycol solutions of tetrahydrofuran (THF) with 0–20 mol % THF were measured at 20–60°C and atmospheric pressure to an accuracy of 5 × 10⁻⁵ g/cm³. The apparent molar volumes of THF in the solutions were calculated and their concentration and temperature dependences determined. The results were compared with the apparent molar volumes of THF in aqueous systems calculated from the literature data. Minima were found on the concentration dependence of the apparent volume of THF for both aqueous and ethylene glycol solutions and changed differently as the temperature increased. The data obtained were discussed from the standpoint of solvophobic effects in aqueous and ethylene glycol solutions of THF.     

Application of radioisotope XRF for the determination of noble metals in aqueous solutions

Radiometric methods of determination of platium and palladium (0.1 to 5% of Pt and 0.1 to 2% of Pd), gold and indium (0.01 to 1% of Au and 1 to 4 g In/l) and of platinum and rhodium (0.1 to 9% of Pt and 0.05 to 1% of Rh) in aqueous solution has been worked out. A suitable measuring device has been designed and constructed. The methods are based on the measurement of characteristic radiation of the L_α line for gold and platinum and of the K-series for indium, palladium and rhodium, as well as on the measurement of scattered radiation from a²³⁸Pu source. The r.m.s. error of the determination varies from 0.01 to 0.10% of Pt, 0.002 to 0.01% of Au and 0.01 to 0.15% of Pd depending on the concentration. In the case of Rh and In the errors are 0.008% and 0.04 g In/l, respectively.     

Fire and explosion hazard evaluation for the acetone aqueous solutions

The prevention of fire and explosion is recognized as an imperative necessity that is a first priority in all operating management details of the chemical process industries. Based on significant research and original emphasis on loss control and disaster prevention, this study investigated the flammability characteristics, comprising the lower/upper explosion limit (LEL and UEL), maximum explosion overpressure (P _max), maximum rate of explosion pressure rise [(dP dt ⁻¹)_max], gas or vapor deflagration index (K _g), and explosion class (St class) of four acetone aqueous solutions [water vapor (steam)/acetone: 75/25, 50/50, 25/75, and 0/100 vol.%], and discussed the effect of inert steam (H₂O_(g)) on them. Interactive influences of various loading fuel concentrations and initial testing conditions of 150, 200 °C, and 101, 202 kPa on flammability characteristics were revealed via a 20-L-apparatus. Weighting analysis of the above influence factors was explored by employing the GM(h,N) grey system theory for rating their fire and explosion hazard degrees both specifically and quantitatively. The results indicated that the most important influence factor was the initial pressure that the manager or engineer in such a steam/acetone mixing system should consider to be well-controlled first. The second influence factor in GM(1,N) and GM(0,N) model was the initial temperature and steam/acetone mixing concentration, but the third influence factor was individual contrariwise. This study established a complete flammability hazard evaluation approach that is combined with an experimentally and theoretically feasible way for fire/explosion prevention and protection. The outcomes would be useful for positive decisions for safety assessment for the relevant practical plants or processes.     

Electrochemical formation of zinc selenide from acidic aqueous solutions

An investigation on electrochemical ZnSe thin film growth from acidic aqueous baths of Se(IV) and Zn(II) species is described. The range of co-deposition potentials is predicted on a thermodynamic basis according to a known electrochemical model. A study on the voltammetric behavior of Ti and Ni electrode substrates in the working solutions at various temperatures provides the main features of the applied electrochemical process. Cathodic electrodeposition at high temperatures (>65 °C) results in the formation of polycrystalline cubic, randomly oriented, ZnSe crystallites suffering, in general, from the presence of a crystalline Se phase in excess. Annealing of as-grown films adjusts the stoichiometry and leads to the production of semiconductive ZnSe with a band gap width of 2.7 eV. Electronic Publication     

A rapid enrichment method for the analysis of traces of metals in aqueous solutions

Summary For the determination of traces of heavy metals e. g. from distilled water, drinking water or waste water generally a suitable pretreatment of the samples is necessary. For this reason an enrichment method was developed which makes it possible to precipitate several metals together with carrier elements from aqueous solutions. To carry out the method, 10 to 500 ml of the sample are mixed with 1 ml of a diluted nitric acid to produce a weak acid starting state for the diverse samples. After addition of a reduction solution and the collector solution the metals are precipitated at a constant pH between 5.0 to 5.5 with diethylammonium-N,N-diethyldithio-carbamate. The precipitate can be collected by filtration on a membrane filter. It forms a thin layer on the membrane filter and adheres without any auxiliary products for a long time. The time required for the complete process is less than 15 minutes if the starting volume was about 100 ml. A special equipment is not necessary. In the determination of traces of metals from organic substances a special rapid decomposition method with the decomposition device BIOKLAV^® was developed. By this method it is possible to convert the organic matter into an aqueous solution without addition of any chemicals. The BIOKLAV is a cylindrical pressure vessel with a safety rapid lock. A 20 g sample of organic material, e. g. meat or similar foodstuff, with a water content of 70–80% is pre-dried in the closed vessel and thereafter burnt in oxygen with elevated pressure. After this procedure all traces of metals present in the starting sample are contained in an aqueous solution consisting on the condensed water from drying and the burning products of the organic matter. The time required for the complete process is less than 30 min. From the obtained solution traces of metals are to enrich by precipitation with carbamate. The determination of the traces of metals is possible by a suitable method of analysis like atomic absorption, ICP or X-ray fluorescence. In various water samples, like drinking water and waste water, traces of Cr, Ni, Fe, Cu, Zn, Cd, Pb, As, Hg and Se in amounts of 5–100g were determined. The recovery rate was 80–90%. In organic substances Hg, Cd, Pb and As in amounts ranging from 50–250 ng/g resp. in amounts of 1–5g were detected with recoveries of more than 80%.

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Ein schnelles Anreicherungsverfahren zur Bestimmung von Schwermetallspuren in wärigen Lösungen

Zusammenfassung Zur Bestimmung von Schwermetallspuren z. B. in destilliertem Wasser, Trinkwasser oder Abwasser ist im allgemeinen eine geeignete Probenvorbereitung erforderlich. Für diesen Zweck wurde ein Anreicherungsverfahren ausgearbeitet, um gleichzeitig mehrere Metalle zusammen mit Spurenfänger-elementen aus wäßrigen Lösungen ausfällen zu können. Danach werden 10–500 ml Probenlösung mit 1 ml verd. Salpetersäure versetzt, um bei den verschiedenen Proben jeweils einen schwach sauren pH-Wert einzustellen. Anschließend werden eine Reduktionslösung sowie die Spurenfängerlösung zugegeben und mit einer Pufferlösung ein pH von 5,0–5,5 eingestellt. Die gelösten Metallspuren werden mit Diäthylammonium-N,N-diäthyldithio-carbamat ausgefällt. Der Niedersclhlag wird auf einem Membranfilter gesammelt. Man erhält ohne Hilfsmittel einen dünnen elastischen Film, der lange Zeit auf dem Filter haftet. Bei einem Ausgangsvolumen von 100 ml dauert der gesamte Vorgang weniger als 15 min. Für die Bestimmung von Metallspuren in organischen Substanzen wurde ein Schnellaufschlußverfahren mit dem Aufschlußgerät BIOKLAV^® entwickelt. Damit ist es möglich, die organische Matrix ohne Zusatz von Chemikalien in eine wäßrige Lösung zu überführen. Der BIOKLAV ist ein zylindrisches Druckgefäß mit einem Sicherheitsschnellverschluß. 20 g Probenmaterial mit einem Wassergehalt von 70–80%, z. B. Fleisch oder ähnliche Lebensmittel, werden im geschlossenen Gefäß zuerst vorgetrocknet und anschließend in Sauerstoff bei erhöhtem Druck verbrannt. Nach dem Aufschluß befinden sich die zu erfassenden Metallspuren in einer wäßrigen Lösung, die aus dem kondensierten Wasser des Probenmaterials und den Verbrennungsprodukten der organischen Matrix herrührt. Der gesamte Aufschluß dauert weniger als 30 min. Aus der Lösung können die Metallspuren durch Fällung mit Carbamat angereichert werden. Die Bestimmung der Elementspuren erfolgt z. B. mit Atom-Absorptions-Spektrometrie (AAS), Optischer Emissions-spektrometrie mit Plasma-Anregung (ICP) oder Röntgen-Fluoreszenz-Analyse(RFA). In verschiedenen Wasserproben, wie z. B. Trinkwasser und Abwasser wurden Spuren von Cr, Ni, Fe, Cu, Zn, Cd, Pb, Hg und Se in Mengen von 5–100g bestimmt. Die Wiederfindungsrate war 80–90%. In organischen Substanzen wurden Hg, Cd, Pb und As in Massenanteilen von 50–250 ng/g bzw. in Mengen von 1–5g mit einer Wiederfindungsrate von mehr als 80% bestimmt.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

Swelling of polyacrylamide gels in aqueous solutions of ethylene glycol oligomers

Addition of a small amount of ethylene glycol oligomers (OEG), with the number of repeat units y = 2–4, in an aqueous solution leads to the contraction of both linear and cross-linked poly(acrylamide-co-acrylic acid) chains. The results present clear evidence for the screening effect of OEG on the ionic groups of the polymer chains. Measurements indicate that the pre-swollen poly (acrylamide-co-acrylic acid) gels immersed in aqueous OEG solutions are at equilibrium. However, as the molecular weight of OEG increases, these gels cannot attain their equilibrium swelling ratio due to the appearance of non-equilibrium structures. The stability of these structures increases as the initial swelling degree of the gels increases.