Carlos Arroyave

The effect of nitrogen oxides in atmospheric corrosion of metals

Abstract This paper is a state of the art survey on the current understanding of the effect of the atmospheric nitrogen oxides on structural materials. Atmospheric nitrogen dioxide, its chemistry, and its effect on metals are considered, particularly on steel, copper and zinc. It is shown that the detrimental effects of nitrogen dioxide are not well known. A number of conclusions are made which may improve further work in order to obtain a better understanding of the role of nitrogen dioxide and the controlling factors in the corrosion behaviour of materials in the atmosphere.

The early atmospheric corrosion stages of carbon steel in acidic fogs

Abstract The aim of this work is to report the results of a study on plain steel exposed for four weeks to acidic fogs. These included two levels of NO3−, both alone and in combination with SO42−, at 35 °C and 90% RH. Gravimetric analysis, XRD, FTIR and polarized light microscopical examinations were used to follow the corrosion effects and the rust trasformations. As a major conclusion, it was found that atmospheric NOx deposited by fogs had no important effect.

Copper Corrosion Originated by Propionic Acid Vapors

Copper corrosion originated by propionic acid vapors (CH 3 CH 2 COOH ), ranging from 10 to 300 ppm, at 100% relative humidity. was studied. At 300 ppm pollutant level, the copper corrosion rate was 3.3 mg/dm 2 day. The cathodic reduction technique showed that the amount of corrosion products grew with both exposure time and pollutant level. Corrosion products were also characterized using X-ray diffraction and Fourier transform infrared techniques, and their morphology was observed by scanning electron microscope methodology. The main compounds identified were cuprite (Cu 2 O), copper hydroxide [Cu(OH) 2 ], and a copper propionate compound. Important amounts of an organic copper compound were observed at propionic acid vapor concentrations higher than 50 ppm.

CHARACTERIZATION OF DEPOSITS FORMED IN A WATER DISTRIBUTION SYSTEM

The development of unwanted deposits in any water distribution system is unavoidable under standard conditions. Knowing the composition of such deposits will help to establish the causes of deposit formation and consequently to be able to keep water quality as high as possible. This paper presents the results of an extensive study of deposits found in a water distribution system of a tropical city. Characterization of materials collected across the system was made by infrared spectroscopy (IR), X ray diffraction (XRD), energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). Analysis of the samples taken at several sites of the system reveals the presence of three predominant deposits: a brown coloured deposit, tubercles and white deposits. Aluminosilicates and humic acids were found to be main constituents in brown deposits. Tubercles were mostly mixtures of magnetite, goethite and in some cases lepidocrocite. White deposits were formed by calcite, aluminosilicates and quartz. Organic matter as volatile solids were 14.0 ± 5.0% for brown deposits and 11.2 ± 2.0% for tubercles.

Properties of goethite grown under the presence of Cr3+, Cu2+ and Mn2+ ions

This study is focused on properties of goethite related to the inhibition of the corrosion process in low alloy, weathering steels. These steels are characterized by the presence of small amounts of Cr3+, Cu2+ and Mn2+ ions, which drive their protecting behavior in mild atmospheres. Several goethite samples with 5 mole % content of the alloying elements in nominal composition are synthesized by a hydrolysis route. Additionally, Cl−, SO42− are used as precursor ions in order to simulate the presence of atmospheric pollutants. All samples are analyzed by X-ray diffraction and 57Fe transmission Mössbauer spectroscopy (MS). The presence of the alloying elements and pollutant ions reduces the overall magnetic interactions in goethite, which is reflected in the lowering of the hyperfine field of maximum probability at 77 K, in comparison to that of pure goethites. However, the mechanisms of the magnetic interaction reductions are different for each combination of alloying element and pollutant ions. Finally the combined effect of anions and cations produces a wider distribution of particle sizes.

Carboxilic acids in the atmosphere and their effect on the degradation of metals

Metallic atmospheric corrosion is due to deposition of the pollutants found in the different phases of the atmosphere (especially in clouds, spray, rain and fog) onto the metallic surface, reacting with the substrate and leading to corrosion. Those pollutants are either organic or inorganic. Within the inorganic pollutants found in the atmosphere are NO 2 , SO 2 , NH 3 , HCI, CO 2 and O 3 . The organic compounds in the atmosphere, also known as volatile organic compounds (VOC), are several hydrocarbons and vapours of organic acids such as formic, acetic and propionic. In general, most of the pollutants contribute to the total acidity of rain in urban areas and it is estimated that the contribution of organic acids is about 35% of the total. VOC emissions can be either anthropogenic or biogenic; the average contents measured in the atmosphere for formic, acetic and propionic acids are about 8, 9 and 0.3 ppb respectively. On the other hand, organic acids appear related to corrosion products of lead, zinc, nickel and copper. A review of the published results on the effect of organic acids on corrosion of metals is presented.

Study of the copper corrosion mechanism in the presence of propionic acid vapors

The interaction mechanism between copper and propionic acid vapors is shown. Exposures were carried out to various pollutant concentrations and times. Cathodic scan, x-ray diffraction (XRD) and scanning electrode microscope (SEM) were used to quantify the degree of deterioration. The results obtained were explained by the following mechanism: A cuprite (Cu2O) layer covers the copper surface immediately; this compound in presence of adsorbed water is oxidized to tenorite (CuO). The hydration of the tenorite layer benefits the formation of a hydroxide compound such as CuO•xH2O. As the pollutant level is increased, insoluble basic propionate is formed (Cu(OH)x(CH3CH2 COO)2-x). Higher concentrations of propionic acid acidify the monolayers and a new compound Cu(CH3CH2COO)2•H 2O begins to precipitate at low pH, this is the main constituent of the green olive patina formed under these conditions. This mechanism agrees, in general terms, with those proposed in previous works to study the interaction between copper and the acetic and formic acids.

INFLUENCE OF ENVIRONMENTAL FACTORS IN THE ATMOSPHERIC CORROSION OF COPPER IN THE PRESENCE OF PROPIONIC ACID

Exposure time, pollutant concentration, and relative humidity (RH) are important environmental variables for the atmospheric corrosion of copper in the presence of propionic acid vapors. This paper shows the most outstanding results into the effect of these variables. This study was carried out by mean of exposures at dynamic conditions in 260, 380, and 680 ppbv propionic acid, with relative humidities of 70% and 90%. The effect of the propionic acid was also evaluated in static conditions with 4, 40, and 120 ppmv propionic acid with relative humidities of 40%, 80%, and 100% RH. All the samples were evaluated by triplicate within 21 days of exposure. The corrosion rate was used to quantify the degradation of copper by mean of weight loss and coulometric reduction technique. Coulometric reduction indicates that the charge needed to reduce the oxides increases as exposure time, relative humidity and pollutant concentration increases. On the other hand, the corrosion rate determined gravimetrically, confirms that at a higher relative humidity and higher propionic acid concentration the copper deterioration is also higher.