The interaction of carboxylic acids with copper is a phenomenon found both outdoors and, more commonly, indoors. The influence on copper of some carboxylic acids (formic, acetic, propionic, and butyric) have so far been studied at concentrations levels at least three or four orders of magnitude higher than actual indoor conditions (< 20 ppb, volume parts per billion), and with only limited emphasis on any mechanistic approach. In this licentiate study a unique analytical setup has been successfully applied for in situ characterization and quantification of corrosion products formed during initial atmospheric corrosion of copper in the presence of acetic, formic or propionic acid. The setup is based on monitoring mass changes by the quartz crystal microbalance (QCM) and simultaneously identifying the chemical species by infrared reflection-absorption spectroscopy (IRAS). Post-analysis of corrosion products was performed by coulometric reduction (mass of copper (I) oxide formed), grazing incidence xray diffraction (phase identification) and atomic force microscopy (surface topography). The absolute amounts of mass of individual constituents in the corrosion products, mainly copper (I) oxide or cuprite, copper (II) carboxylate and water or hydroxyl groups, have been deduced in situ during exposure in 120 ppb of carboxylic acid concentration, 95% relative humidity and 20ºC. An overall result is the consistency of analytical information obtained. For copper (I) oxide the quantified data estimated from IRAS, QCM or coulomeric reduction agrees with a relative accuracy of 12 % or better. The interaction of copper with the carboxylic acids seems to follow two spatially separated main pathways. A proton-induced dissolution of cuprous ions followed by the formation of copper (I) oxide, and a carboxylate-induced dissolution followed by the formation of copper (II) carboxylate. The first pathway is initially very fast but levels off with a more uniform growth over the surface. This pathway dominates in acetic acid. The second pathway exhibits iii a more constant growth rate and localized growth, and dominates in formic acid. Propionic acid exhibits low rates for both pathways. The difference between the carboxylic acids with respect to both total corrosion rate and carboxylate-induced dissolution can be attributed to differences in acid dissociation constant and deposition velocity.

The initial atmospheric corrosion of copper was investigated by means of a quantitative in situ analysis in an atmosphere containing 120 ppb of acetic acid and 95% relative humidity using a quartz crystal microbalance ͑QCM͒ integrated with infrared reflection absorption spectroscopy ͑IRAS͒. Crystalline cuprous oxide ͑various structural forms of Cu 2 O͒ and hydrated copper acetate were detected as corrosion products during up to 100 h of exposure. The quantification of data was made possible through an observed linear relationship between the absorbance of vibrations ͑IRAS͒ of both phases and the corresponding mass ͑QCM͒. The quantification of cuprous oxide was further supported by ex situ coulometric reduction of the corrosion products. The growth rate of cuprous oxide was initially very fast but almost zero after 20 h exposure where it reached an average thickness of 13 ± 1 nm. Copper acetate exhibited a more constant growth rate. Atomic force microscopy showed a uniform growth of cuprous oxide with surface roughness that increased with time and localized formation of copper acetate. The quantified data are consistent with a previously proposed model that involves proton-and acetate-induced dissolution of copper and subsequent precipitation of cuprous oxide and copper acetate.

A computer simulation with a GILDES-based model using the COMSOL multiphysics software was performed for copper exposed to low concentrations of carboxylic acids in humidified air at room temperature. GILDES is a six-regime computer model (Gas, the Interface between gas and liquid, the Liquid, the Deposition layer, the Electrodic region near the surface and the Solid). The simulations were compared to previously published in-situ results for copper at the same conditions analysed by a quartz crystal microbalance (QCM) and infrared reflection absorption spectroscopy (IRAS). Experimental and calculated results agree with each other with respect to the effect of corrosion, showing formic acid as the most aggressive followed by acetic and propionic acid. This is supported by a higher ligand-and proton-promoted dissolution found in formic acid exposures, followed by acetic and propionic exposures. Atmospheric corrosion models are an important tool for the society. By aiding in proper material selection they can improve the functionality and safety of the different structures as well as electronic devices exposed to the atmosphere at different climatic conditions. Models of corrosion have traditionally been developed based on statistical analyses of field data by applying simple physical/chemical arguments, for example by separating the effect of dry and wet deposition into individual additive terms.1 The corrosion rate is usually correlated to measured environmental factors. These classification schemes have a limited accuracy, one reason being the effect of micro-climate, which means that corrosion rates can vary dramatically between locations that are only meters apart.2 However, examples of models based on first principles are starting to emerge. Spence and Haynie 3 and Lyon et al. 4 studied the processes of oxide dissolution and formation, and the electrochemical processes within a droplet on a metal surface. Cole et al.5 evaluated the deposition of gases and aerosols both inside and outside museums and the resulting effects on corrosion of cultural objects using a holistic model. The study shows the relative importance of different deposition mechanisms within a building, such as gravity, vortex shedding and, in the case of significant air flows, momentumdominated impact. Díaz and López 6 developed a deterministic model for the damage function of carbon steel expressed in terms of corrosion penetration as a function of environmental variables using an Artificial Neural Network (ANN) to fit the data. Cole et al.7 describe a multiscale (from global to micron) model for the prediction of atmospheric corrosion of zinc. The model is able to predict corrosion rates of metal components to enable appropriate material selection and to determine how microstructure and oxide development influence corrosion rates. Farrow et al. 8 in 1996, applied the mentioned GILDES model to perform the first theoretical mechanistic study of the atmospheric corrosion of zinc in a controlled environment. The results show that, under such co...

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