Alejandro Echavarría

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.

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.

Fusion por plasma.

The use of plasma in the foundry process it is today an important application, hence it posses several advantages, e.g. the very high temperatures that it can offer, the use of argon as ionization gas give to the media of melting the inert behavior, reducing at maximum level the lost by oxidation of the alloying elements. It can allow the melting of new alloys with high grade of difficult manufacture.