Olof Forsén

Polyaniline/epoxy coatings with good anti-corrosion properties

We have studied polyaniline/epoxy blend coatings on mild steel in 0.6 M NaCl and 0.1 M HCl aqueous solutions with electrochemical methods. The corrosion protective performance was characterized by a permanent shift of corrosion potential by about 500 mV to the noble direction and by a decrease of five orders of magnitude in the redox current. The surface of mild steel was covered by a light gray protective layer due to the electrochemical interaction between the coating and steel. The chemical composition of the surface layer has been studied with X-ray photoelectron spectroscopy (XPS).

Corrosion protective polyaniline epoxy blend coatings on mild steel

Abstract Polyaniline epoxy blend coatings on mild steel have been studied in neutral, acidic and alkaline solutions with various electrochemical methods. It has been found that coatings containing emeraldine base provide better corrosion protection in NaCl solution than coatings based on conducting polyaniline. Good corrosion protection by emeraldine base was observed even when a hole was made to the coating. In HCl solution protonated polyaniline gave better performance.

Ion transport investigations of polypyrroles doped with different anions by EQCM and CER techniques

The ion transfer in redox processes of conducting polypyrrole doped with various anions, such as 1-naphthalenesulfonate, 10-camphorsulfonate, p-toluenesulfonate, dodecylbenzenesulfonate was investigated by electrochemical quartz crystal microbalance (EQCM), contact electric resistance (CER), and cyclic voltamperometry in situ techniques. By using this setup, the doping levels of the synthesized PPy films and mobility of charge carries in these materials in KCl aqueous solution under linear potential scan were determined.

Reaction product layer on chalcopyrite in cupric chloride leaching

Abstract During the leaching of chalcopyrite in cupric chloride solutions, a reaction product layer forms on the mineral surface. In the present work, the formation and the composition of the reaction product layer on solid stationary chalcopyrite was studied in a chemical environment similar to that of the HydroCopper® process. The effect of the process parameters on the reaction product layer was investigated. Electrochemical measurements, including A.C. impedance spectroscopy, were carried out and an equivalent circuit was used to estimate the surface parameters of the reaction product layer, such as resistance, capacitance and porosity. Scanning electron microscopy was used to complement the electrochemical measurements. The results suggest that at pH = 1, a fragile more resistive elemental sulphur layer forms, whereas at pH = 3, a porous less resistive FeOOH layer is formed. Lors de la lixiviation de la chalcopyrite en solutions de chlorure cuivrique, une couche de produit de reaction se forme a la surface du mineral. Dans le present travail, on a etudie la formation et la composition de la couche du produit de reaction sur de la chalcopyrite solide stationnaire dans un environnement chimique similaire a celui du procede d’HydroCopper®. On a etudie l’effet des parametres du procede sur la couche de produit de reaction. On a effectue des mesures electrochimiques, incluant la spectroscopie a impedance A.C., et l’on a utilise un circuit equivalent pour estimer les parametres de surface de la couche de produit de reaction, comme la resistance, la capacitance et la porosite. On a utilise la microscopie electronique a balayage pour completer les mesures electrochimiques. Les resultats suggerent qu’a un pH = 1, une couche fragile de soufre elementaire plus resistive se forme, alors qu’a un pH = 3, une couche poreuse moins resistive de FeOOH est formee.

Corrosion resistance of different materials in dilute ammonium chloride-bearing environments

Abstract Ammonium chloride precipitation is a widely-known problem in various units of many oil refineries. Precipitation can cause severe problems by clogging and fouling process equipment, heat exchangers, column trays, etc. One of the widely-used solutions to this problem is to add some water into the process stream in order to dissolve the precipitates. However, the addition of water into the process stream may cause some new problems. Process design and materials selection are normally carried out assuming that the process stream contains no water. The addition of water into the stream can drastically change the corrosivity of the process solution, resulting in heavy corrosion. In some unit processes, it is impossible to remove the chlorides and nitrogen compounds which cause this problem. Thus, in most cases, the only effective and economical way to combat corrosion is by materials selection. In this study, the corrosion behaviour of various materials in ammonium chloride-containing environments has been investigated. Practice has shown that the addition of water can increase the corrosion rate of mild steel about 100 times. Laboratory tests were made in order to screen potential highly-alloyed materials.

Transient Surface Analysis of Dissolving Chalcopyrite in Cupric Chloride Solution

Abstract This study presents an investigation of chalcopyrite surfaces dissolving in concentrated cupric chloride solutions similar to those used in the HydroCopper® process, [NaCl] = 280 g/L, [Cu2+] = 30 g/L and T = 90 °C. The leaching of chalcopyrite and the parameters of the reaction product layer formed on the mineral surface were studied at the open circuit potential as a function of time (0.5 – 22 hours) and at pHs in the range 1 - 3. The electrochemical impedance spectroscopy (EIS) data indicated that there were two or three time constants present. These were suggested to be due to the double layer and to elemental sulphur and FeOOH. With pH 1 at OCP the reaction product layer was a single-phase layer of elemental sulphur (t = 0.5 – 9 h) or two-phase layer with elemental sulphur and FeOOH (t = 22 h). The apparent charge transfer resistance was higher (>25 Ωcm2) at the beginning of leaching (t ≤ 4 h), but decreased to about 4 Ωcm2 with increasing time to 22 hours. The reaction product layer resistance did not change markedly. It is likely that the apparent charge transfer resistance reflects the resistance of the reaction product layer at pH 1, showing apparent changes in the calculated charge transfer resistance values. At pH 2, the reaction product layer was an elemental sulphur layer at t ≤ 2 h, becoming a two-phase layer of elemental sulphur and FeOOH at t = 3 – 22 h. The apparent charge transfer resistance was <8 Ωcm2 at all times, whereas the reaction product layer resistance decreased with time from 30 Ωcm2 to about 4 Ωcm2. The two-phase layer at pH 2 was electrically less resistive than the one-phase layer at pH 1. At pH 3 the reaction product layer was a two-phase layer at all times, consisting of goethite and S8. This layer allowed more rapid dissolution at the beginning, but with time a reaction product layer grew, increasing the electrical resistance as well as decreasing the dissolution rate of chalcopyrite. The apparent charge transfer resistance at pH 3 was constant at all times.

The Use of Polarization Curves to Evaluate Stainless Steels in Highly Oxidizing Solutions

The corrosion behaviour of stainless steels in very oxidizing solution with redox-potential + 1200 mV vs. SCE was studied by corrosion potential and anodic polarization measurements. Some weight loss immersion tests were also carried out in order to verify the results of the electrochemical tests. Because the polarization curves and corrosion potentials for stainless steels give only a rough estimate of the corrosion behaviour, polarization curves and corrosion potentials were also measured for pure chromium, molybdenum, nickel and platinum as well as carbon steel in order to estimate the effect of alloying elements and the possibility of other chemical reactions in the transpassive region. It was found that this combination of measurements is a reliable method to evaluate the corrosion behaviour of stainless steels in dissolved ozone-containing solutions. .

Formation of Reaction Product Layers on Copper Alloys in Chloride Solutions

Copper and copper alloys are widely used in marine applications. This is mainly due to their inherent corrosion resistance and antifouling capability. The corrosion resistance of copper and its alloys depends on the formation of a protective reaction product layer. Various opinions on reaction product layer formation mechanisms have been presented. In this paper the formation of reaction product layers on copper and copper alloys was studied in the laboratory and under field conditions in brackish sea water. The laboratory studies included polarization curves, cyclic voltammetry and Contact Electric Resistance measurements. During immersion tests passivation was monitored by polarization resistance and corrosion potential measurements. The polarization curves showed, that addition of chlorides in the solution will decrease corrosion potential and cause a rapid dissolution reaction at the same potential that is the corrosion potential in chloride-free solution. Cyclic voltammetry results showed, that without chlorides the layer may contain several oxide and hydroxide phases. The pH and copper chloride complex concentration at the surface must be high enough for nucleation of cuprous oxide. The Contact Electric Resistance results showed, that the first anodic current peak in cyclic voltammograms is not necessarily caused by reaction layer product formation. The CER results show that the reaction product layer resistance begins to increase at 100-200 mV higher potentials in chloride solutions than in chloride-free solutions. The immersion tests showed again, that the formation of the reaction product layer may take a long time. Especially corrosion resistant copper-nickel alloys in lean brackish sea water had a stable corrosion potential only after several weeks.

Factors Affecting Corrosion in Gulf of Finland Brackish Water

The Baltic Sea is a relatively shallow inland sea surrounded by the countries of North-Eastern Europe and Scandinavia. The brackish water in the Baltic Sea has low salt concentration and it is typically one-sixth of the ocean seawater. The “nominal” amount of dissolved solids, upon which formulae for artificial seawater are based, is about 34,500 ppm, of which most is sodium chloride. The major constituents are those whose concentrations are greater than 1 mg/L and are not greatly affected by biological processes. The ratio of concentrations of these ions and molecules to each other is relatively constant. Corrosion rates were determined in long-term tests in Gulf of Finland brackish water off Helsinki. The water temperature varies through the year from about 0°C in January to 15-16°C in June to August. Salinity is 4–6, highest at the end of summer and lowest when ice melts. pH is between 7.0 and 8.1. Weight loss tests from one- to four-year tests for steel, stainless steel, copper, aluminium, zinc, and galvanized steel are reported and compared to short term laboratory tests in artificial seawater. Tests for passivation rates and crevice corrosion for stainless steel are discussed in terms of environment variation. The effect of corrosion on strength of steel is also discussed.

In-situ characterization of the polypyrrole films by EQCM and CER techniques

A novel setup for the investigation of ion moving processes occurring in polymer films is proposed. The special crystal holder capsule was created to include EQCM (Electrochemical Quartz Crystal Microbalance) into CER (Contact Electric Resistance) equipment and provide its reliable operation. The dependence of the resistance and the mass change of the polypyrrole films on the polarisation potential in potassium iodide aqueous solutions were investigated combining the EQCM and CER techniques. The CER method reinforced with the EQCM technique gives us a helpful tool for the better understanding of the polymeric films preparation processes with well-defined physical and chemical properties.