Search results

The purpose of this paper is to investigate how to improve the corrosion inhibition behavior of molybdate‐based inhibitors for mild steel, using organic compounds containing a phenyl ring together with nitrite agent. As picrate contains a phenyl ring together with three substituent nitrite anions, it is used as an organic compound. In this study a new molybdate‐based inhibitor was introduced with the composition of 60 ppm molybdate/40 ppm nitrite/20 ppm picrate. Inhibition efficiency of molybdate alone and with nitrite and picrate on the uniform corrosion of mild steel in stimulated cooling water was assessed.

The inhibition efficiency of molybdate alone and with nitrite and picrate on the uniform corrosion of mild carbon steel in stimulated cooling water (SCW) was assessed by electrochemical techniques such as potentiodynamic polarization, electrochemical impedance (AC impedance) measurements and weight loss determinations at the room temperature. Studies of electron microscopy included scanning electron microscopy (SEM) photography and X‐Ray energy dispersive (EDS) microanalysis were used.

The results obtained from the polarization and AC impedance curves were in agreement with those from the corrosion weight loss results. The results indicated that the new inhibitor was as effective as molybdate alone, though at one quarter of the concentration range of molybdate, which is economically favorable.

The paper demonstrates improvement in corrosion inhibition of mild steel in SCW via a blend of molybdate, nitrite and picrate as a new anodic inhibitor.

This paper aims to study the corrosion behavior of molybdate conversion coatings on AZ31 magnesium alloy in NaCl solution.

The open circuit potential curves, anodic polarization curves, electrochemical impedance spectroscopy and immersion tests were used to study the corrosion behavior of molybdate conversion coatings on AZ31 magnesium alloy in NaCl solution.

The molybdate conversion coatings were homogeneous and uniform. The corrosion resistance of AZ31 magnesium alloy had been improved evidently through the molybdate conversion treatment.

The molybdate conversion coatings possess favorable feasibility in practice for the corrosion protection of AZ31 magnesium alloys in NaCl solution.

This paper aims to synthesise anticorrosion pigments containing molybdenum for paints intended for corrosion protection of metals.

The anticorrosion pigments were prepared by high-temperature solid-state synthesis from the appropriate oxides, carbonates and calcium metasilicate. Stoichiometric molybdates and core-shell molybdates with a non-isometric particle shape containing Ca, Sr, Zn, Mg and Fe were synthesised. The pigments were examined by X-ray diffraction analysis and scanning electron microscopy. Paints based on an epoxy resin and containing the substances at a pigment volume concentration of 10 volume per cent were prepared. The paints were subjected to physico-mechanical tests and to tests in corrosion atmospheres. The corrosion test results were compared to those of the paint with a commercial pigment, which is used in many industrial applications.

The molybdate structure of each pigment prepared was elucidated. The core-shell molybdates exhibit a non-isometric particle shape. The pigments prepared were found to impart a very good anticorrosion efficiency to the paints. A high anticorrosion efficiency was found with the pigments Fe₂(MoO₄)₃ and Fe₂(MoO₄)₃/CaSiO₃ and with Mg and Zn molybdates.

The pigments can be used for the formulation of paints intended for the corrosion protection of metals. The pigments also improve the paints’ physical properties.

The use of the pigments in anticorrosion paints for the protection of metals is new. The benefits include the use and the procedure of synthesis of the anticorrosion pigments which are free from heavy metals and are acceptable from the aspect of environmental protection. Moreover, the core-shell molybdates, whose high efficiency is comparable to that of the stoichiometric molybdates, have lower molybdenum contents.

Two corrosion inhibitors for closed cooling water systems, nitrite-based and mixture of nitrite and molybdate corrosion inhibitor, are often compared to each other. This study aims to optimize these two inhibitors in terms of concentration and pH for carbon steel protection, with insights into the double layer structure on surface and its impact on corrosion inhibition.

Electrochemical analysis including electrochemical impedance spectroscopy and potentiodynamic test are carried out for quick assessment of corrosion inhibition efficiency and optimization, which is confirmed by immersion test and microscopic analysis. The electronic properties of the surface film are analyzed through Mott–Schottky method which provides new insights into the inhibition mechanism and the role of each component in mixture inhibitor.

Mixture of nitrite and molybdate is shown to present higher inhibition efficiency, owning to the double layer structure. Nitrite alone can form a protective surface film, whereas molybdate leads to an n-type semiconductive film with lower donor density, hence giving rise to a better inhibition effect.

Surface after inhibitor treatment has been carefully characterized to the microscopic scale, implying the effect of micro-structure, chemical composition and electronic properties on the corrosion resistance. Inorganic corrosion inhibitors can be tuned to provide higher efficiency by careful design of surface film structure and composition.

Almost every study on corrosion inhibitor applies such method for quick assessment of corrosion inhibition effect. Mott–Schottky test is one of electrochemical methods that reveals the electronic properties of the surface film. Previous works have studied the surface layer mainly through X-ray photoelectron spectroscopy. This study provides another insight into the surface film treated by nitrite and molybdate through Mott–Schottky analysis, and relates this structure to the corrosion inhibition effect based on multiple analysis including electrochemistry, microscopic characterization, thermodynamics and interface chemistry.

Chromium based conversion coatings have been used widely to delay the formation of white rust on galvanized steel sheets. As chromium is carcinogenic, an alternative chromium‐free conversion coating was developed for use on galvanized steel surfaces to delay the onset of white rusting. This paper seeks to address this issue.

The molybdate coating was produced on galvanized steel surface by dipping in a phosphate solution bath using Na₂MoO₄ as a corrosion inhibitor.

The cyclic polarization tests conducted on molybdates‐treated samples showed a wider potential band in 3.5 per cent NaCl solution, indicating that the coating is passivating in nature. The polarization (R_p) of both treated and untreated samples was evaluated in 3.5 per cent NaCl solution by electrochemical impedance spectroscopy (EIS) technique. It was observed that the polarization resistance (R_p) of molybdate treated galvanized sample is 2.3 times higher compared with the untreated one. The improved corrosion resistance also was evident from the simulated salt spray test results where the treated sample showed a five times improvement over the untreated sample.

The corrosion resistance of inorganic‐based chromium‐free conversion coatings has not been equivalent to that of chromium based conversion coatings. A chromium‐free conversion coating with enhanced corrosion performance by using water reducible polymer will be described in a future paper.

The developed chromium‐free passivation solution has been implemented for galvanized tube passivation. It is one of the best alternative chromium‐free chemicals for the prevention of white rust formation on galvanized materials during transit and storage.

This paper describes a new coating system for the galvanized material which will provide a significant improvement to white rusting resistance for the galvanizing industry.

Several corrosion inhibitors, such as, HEDP, sodium molybdate and zinc ions, were added to an aqueous corrosive media containing different concentrations chloride ions, and the corrosion rates (CRs) of carbon steel were measured at various temperatures. It was shown that, in the presence of more than 1,200 ppm of chloride ions, and temperatures greater than or equal to 42.5°C, the combination of HEDP, molybdate and zinc could not control the corrosion in a cooling water system. Then four different models were designed to represent the CR of carbon steel in presence of various corrosive parameters.

This paper aims to clarify the corrosion inhibition effect of different corrosion inhibitor systems on the corrosion of metal pipe string by potassium persulfate plugging agent, so as to improve the injection capacity of polymer plugging well and reduce the corrosion of steel by oxidant plugging agent.

The effect of different corrosion inhibitors on the corrosion inhibition of N80 carbon steel in 1% potassium persulfate solution was studied by electrochemical experiment and weight loss experiment. The corrosion inhibition mechanism of potassium persulfate inhibitor and the synergistic mechanism among different inhibitors were analyzed.

The results indicated that when the temperature was 50°C, the inhibition effect of 0.2% sodium molybdate with a single inhibitor was the best at pH 8.5, and the inhibition rate was 70.17%. The inhibition efficiency of 0.2% sodium molybdate + 0.3% sodium silicate in the composite inhibition system can reach 94.38%. In the temperature range of 20°C–60°C, with the increase of system temperature, the inhibition effect of corrosion inhibitor will gradually weaken.

The corrosion inhibition system of N80 steel in potassium persulfate oxidant was mainly studied, and it clarified the influence of temperature and pH value on the corrosion inhibition effect, which provided guidance and suggestions for the corrosion inhibition of tubular string in the oilfield.

There is an increasing demand for eco‐friendly inhibitors for use in cooling water systems. Both calcium gluconates and molybdate are eco‐friendly, non‐toxic chemicals. The corrosion inhibition of calcium gluconate and sodium molybdate on carbon steel in neutral aqueous media was evaluated by means of weight loss, electrochemical polarisation and impedance techniques. A synergistic effect was observed when these two eco‐friendly non‐toxic inhibitors were used in protecting carbon steel. A non‐linear relationship existed between the concentrations of the two inhibitors showing a synergistic effect.

The inhibition efficiency of the formulation consisting of 1‐hydroxyethane‐1, 1‐diphosphonic acid (HEDP), molybdate and Zn²⁺ in controlling the corrosion of mild steel in neutral aqueous environment containing 60ppm Cl‐ has been evaluated by the weight‐loss method. The formulation consisting of 50ppm HEDP, 300ppm molybdate and 10ppm Zn²⁺ has 97 per cent inhibition efficiency. The nature of the protective film has been analysed by using x‐ray diffraction (XRD), FTIR and fluorescence spectra. The protective film is found to be fluorescent and to consist of Fe²⁺‐HEDP complex, Fe₂(MoO₄)₃ complex and Zn(OH)₂. A suitable mechanism of corrosion inhibition is proposed based on the results obtained from the weight‐loss method, polarisation study, XRD, FTIR, fluorescence and atomic absorption spectra.

The conjoint effect of the binary inhibitors molybdate and phosphate on Type A20 carbon steel has been studied, using electrochemical measurement tests. The compatibility between molybdate and phosphate can achieve synergistic benefits, and the inhibitive mechanism was investigated.