D.M. Bastidas

Copper deterioration: causes, diagnosis and risk minimisation

Abstract Copper is widely used in many applications such as heat exchangers, condensers, heating and air conditioning systems, electricity, electronic circuitry and ornamental parts. This paper reviews the issue of copper corrosion in different environments and applications. Special attention is paid to the influence of relative humidity and low molecular weight carboxylic acids. These acids are present in rain, snow, clouds and particulate matter and contribute about 15-35% of rain acidity. Attention is also paid to copper corrosion originated by formic, acetic, propionic and butyric acid vapours. Corrosion product layers (patina) are analysed, showing the relationship between potential and current density cathodic peaks, and models are proposed that show a proportionality factor of the dimensions of a resistor. These results are of practical importance in copper roofing applications. Before 1985, copper was almost universally considered to be a corrosion resistant conduit of potable water, and few instances of copper tube failure were reported. Where unacceptable performance was identified, the problem was usually attributed to reticulation and plumbing systems. In air conditioning applications, premature failure of copper tubing frequently occurs due to pitting corrosion after a short time in service or even during post-installation leakage tests. This type of corrosion is described in the literature as formicary corrosion, and its morphology is characterised by microscopic caverns connected by tunnels. Specimens are analysed to assess the reasons for such premature corrosion failure. Finally, procedures to mitigate copper corrosion are addressed. Pickling in dilute mineral acids (H2SO4 and HCl) is discussed as the most common method for removing oxides formed on the surface of copper based materials during mill processing and manufacturing operations. The use of corrosion inhibitors, such as immersion corrosion inhibitors and volatile corrosion inhibitors (VCI), is a widespread practice to reduce copper corrosion, achieving significant delays in the corrosion process. Reference is made to the search for new environmentally friendly inhibitors for copper and bronze using organic compounds in acid, neutral and alkaline media, and a number of ecological alternatives are reviewed.

Organic acid vapours and their effect on corrosion of copper: a review

Abstract Carboxylic acids of low molecular weight, such as formic, acetic, propionic and butyric acids, as well as other acids (n-pentanoic, hexanoic, heptanoic, etc.), are present in rain, snow, clouds and particulate matter. They contribute about 16–36% of rain acidity. It is estimated that ∼64% of formic acid and ∼88% of acetic acid are in the vapour phase. Carboxylic acids are produced by the combustion of biomass, and analyses of the smoke from fire events reveal concentrations of about 300–500 ppb for formic acid and 3000–5000 ppb for acetic acid. Industrial emissions of carboxylic acid are produced by plants processing biological materials, such as food, paper, wood, etc. Acetic acid vapours are found in several industrial atmospheres. Vinegar is one important source of acetic acid vapours in food processing plants. The present review shows that for copper specimens exposed to organic vapours for 21 days at 100% relative humidity (RH) and a contaminant level in the range of 10–300 ppm, the relative aggressiveness of these acids is (from high to low): acetic>formic>butyric>propionic.

Dicyclohexylamine Nitrite as Volatile Corrosion Inhibitor for Steel in Polluted Environments

Abstract Carbon steel volatile corrosion inhibitor monitors (VCIM) were used to study the inhibition mechanisms of dicyclohexylamine ([C6H11]2NH) and dicyclohexylamine nitrite ([C6H11]2NH·HNO2) on carbon steel in environments polluted with 50 ppm and 250 ppm acetic acid (CH3COOH) or formic acid (HCOOH) vapors and at 100% relative humidity for 21 days of experimentation at 25°C. Experiments were performed using the potentiodynamic polarization and the electrochemical impedance methods. The impedance data satisfy the Kramers-Kronig relationships. The electrochemical measurements indicate that the corrosion rate decreased significantly in the acid vapors at high humidity when a volatile corrosion inhibitor was also present.

Kinetic Study of Formate Compounds Developed on Copper in the Presence of Formic Acid Vapor

Ant-nest corrosion is a specific type of premature failure of copper tubes used in air-conditioning units causing the loss of refrigerant liquid and consequent environmental pollution. It is known that attack requires the simultaneous presence of moisture, oxygen, and a corrodent, usually formic acid. This type of corrosion occurs in thin-walled copper pipes, especially when copper is deoxidized high residual phosphorus. A study has been made of the copper corrosion products formed by the action of 1000 ppm formic acid vapor for 8 weeks exposure at 100% relative humidity and under thermal cycling. The corrosion-product layer was characterized using X-ray diffraction (XRD). The identified compounds were cuprite (Cu 2 O), copper hydroxide hydrate [Cu(OH) 2 ·H 2 O], copper hydroxyformate [Cu(OH)(HCOO)], anhydrous copper formate [Cu(HCOO) 2 ], copper formate dihydrate [Cu(HCOO) 2 ·2H 2 O], and copper formate tetrahydrate [Cu(HCOO) 2 ·4H 2 O]. Tentatively, the latter phase is described in relation with ant-nest corrosion in this paper. A kinetic study of the solid crystalline phases formed on copper has been performed using XRD patterns and the compound ratio has been compared over exposure time.

Electrochemical rehabilitation methods for reinforced concrete structures: advantages and pitfalls

Abstract There are still many unresolved issues concerning the efficiency of electrochemical realkalisation and electrochemical chloride removal as electrochemical rehabilitation methods for corroding reinforced concrete structures. The present paper seeks to answer a number of questions which, though seemingly elementary, continue to arouse controversy in scientific, technical and economic communities, despite the vast amount of work that has been devoted to research on corrosion in concrete embedded steel, such as whether corrosion can be stopped once it has started, whether corroded reinforced concrete structures can be repassivated, and whether it is sufficient to remove the sources of corrosion in order to stop rusting. A discussion is conducted on the relationship between the prerusting grade of rebars and the possibility of their repassivation; on whether electrochemical rehabilitation methods treatments are efficient, and if so, when and on whether a simple potential measurement can determine the passive or active state of a rebar. For this purpose an analysis is made, using electrochemical, gravimetric and metallographic techniques, of the response of clean and previously corroded steel electrodes in a Ca(OH)2 saturated solution with and without a sodium nitrite corrosion inhibitor and in cement mortar. The effectiveness of electrochemical realkalisation and electrochemical chloride removal for repassivating prerusted steel in concrete is found to depend heavily on the prerusting grade.

A Quantitative Study of Concrete-Embedded Steel Corrosion Using Potentiostatic Pulses

Abstract The corrosion rate of steel in reinforced concrete structures may be estimated from the potential decay curve after a pulse interruption, provided that the steel surface area intervening in the measurements is known. Considering that the time constant (τ) of the corrosion process is independent of the surface area, it is also possible to determine the corrosion rate from direct measurements of τ without the need to know the rebar surface area, provided that the double-layer capacitance value is previously known or a reasonable value of this variable is assumed. The method may also be applied in real-sized structures, using small, easy-to-use counter electrodes. Experiments have been performed using small mortar specimens (8.0 cm by 5.5 cm by 2.0 cm) and larger-sized slabs (90 cm by 65 cm by 10 cm) simulating real structures. Rebars were embedded in concrete with and without additives (chlorides and nitrites) and with a cement/sand/water ratio of 1/3/0.5. The reliability of the data obtained is co...

Precipitation mechanism of soluble phosphates in mortar

Abstract The penetration of three phosphate compounds in mortar bulk matrix, sodium monofluorophosphate (Na2FPO3) (MFP), disodium hydrogen phosphate (Na2HPO4) (DHP) and trisodium phosphate (Na3PO4) (TSP) has been evaluated using two water:cement ratios (0.5 and 0.6). The mortar samples were immersed in a 5% MFP, DHP or TSP solution for a period of 40 days. Microprobe line profile analysis for phosphorus (P) and fluorine (F) showed similar behaviour for the three soluble phosphates, which penetrated the mortar to a depth of more than 2 mm, below which the P and F contents dropped to almost zero. The stability of the phosphate ions vs. pH was calculated using thermodynamic data to obtain the following stability ranges: pH 2–4 for ion, pH 5−9 for ion, pH 3–6 for ion, pH 8–12 for ion, and pH above 11 for ion. The use of the MFP, DHP and TSP as corrosion inhibitors presents some limitations in the case of total or partial immersion.

Methods for analysing nanocoatings and ultra-thin films

Abstract: Linear potential sweep and impedance measurements are methods frequently used for studying corrosion behaviour, mass transport processes and the protective properties of coatings applied on metal substrates. Surface-sensitive analytical techniques are useful for understanding the composition and structure of ultra-thin film coatings. Among these techniques, atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), specular reflectance infrared, Raman and Mossbauer spectroscopies supply excellent results. Ion spectroscopy and glow discharge optical emission spectroscopy provide information about the concentration and the depth of the elements on the surface of a coating. Finally, electron microscopy provides morphologic and topographic information about the surface of solids.