Immersion In Acid Solution Research Articles

Studies of latex paint films exposed to aqueous SO2: pH effects

AbstractLatex paint films containing the acid‐soluble extender calcium carbonate have been exposed to aqueous SO2 and other acidic solutions to evaluate the effects of acidic deposition at different pH values on the coatings. CaCO3 is completely removed from these films upon immersion in acidic solutions. The leaching process was monitored with weight loss and infrared measurements. The removal rate was found to be strongly dependent on pH, decreasing with increasing pH. Removal of CaCO3 occurs even for distilled water which has been allowed to equilibrate with atmospheric CO2 (pH 5.6). The removal rate seems to depend only on [H+]; the identity of the acidic anion is apparently insignificant. An empirical relation between the rate of removal and pH was formulated from the weight loss data. The analyses of the results from both weight loss and infrared methods suggested that the mechanism of removal at pH 2.0 is diffusion controlled, whereas a chemical reaction involving H+ becomes more important at higher pH values.

Surface pretreatments of aluminium for electroplating

The effects of concentration and temperature of sodium hydroxide and nitric acid + hydrofluoric acid pretreatment solutions on the morphology of aluminium surfaces have been studied. SEM/EDS observations indicated that NaOH solutions produced etch concavities on the surface, but failed to etch second-phase particles, namely FeAl 3. The acid solutions, however, succeeded in preferentially removing these particles, while they did not change the surface roughness of the aluminium. In an attempt to improve the coverage rate of zinc alloy films, chemically deposited prior to nickel electroplating, a new pretreatment sequence has been designed. It consists of a double-step nitric + hydrofluoric acid solution immersion, with NaOH immersion treatment between the two acid immersion steps. The results obtained with this new sequence indicate that the first acid step removes most of the biggest FeAl 3 particles, as well as the previous oxide layer, while the alkaline step generates a micro-roughness on the surface whereby a net of shallow cellular cavities, as in a honeycomb structure, forms. The last acid treatment preferentially etches the small FeAl 3 particles and the most protuberant inhomogeneities of the surface. This new pretreatment sequence proved to be more effective than those previously reported in the literature, in terms of producing a good surface on which zinc alloy films could develop. The adhesion of nickel electrodeposits to such a surface reached values one order of magnitude higher than those for conventional two-step sequences. Interpretation of these results is based on the improved chemical homogeneity of the surface resulting from the removal of second-phase particles and on the small (ca. 1 μm in diameter) and uniform dimensions of the cells produced by the etch treatment. This effectively leads to a good surface coverage during the zincate treatment, as intially intended.

The influence of surface roughness on the impedance data for iron electrodes in acid solutions

It is verified by impedance measurements on iron electrodes pretreated in various manner that the frequency dispersion occurring during the initial phase of immersion in acid solutions, represented by the depression angle Φ , is a quantity which depends upon the roughness of the electrode surface only. It is shown that Φ is more appropriate for assessing the initial state of a metal for the purpose of subsequent corrosion studies than the polarization resistance R p or the apparent double layer capacity C′ dl or that corrected for its dispersion elements C dl .

Etude electrochimique de la corrosion d'acier massif et d'acier fritte, en milieu acide sulfurique, avant et apres chromisation

Chemical vapor deposition (C.V.D.) of chromium on bulk steel and on sintered steel, increases the corrosion resistance at first sight, if results of potentiokinetic polarisation in a normal sulfuric acid solution are only considered. Nevertheless a decrease of the polarisation resistance and a localized corrosion occur on chromised samples after a few hours of immersion in acid solution.

Influence of Arsenic on Pickling of And Hydrogen Absorption by Mild Steel In Sulfuric Acid Solutions

Abstract A description is given of the effect of arsenic on hydrogen behavior and pickling rate of low-carbon steel immersed in sulfuric acid solutions without applied current. Addition of 1 mg/liter of arsenic (in the form of arsenic trioxide) to 2N sulfuric acid significantly increased pickling rate at 38 C above that of arsenic-free acid, but additions of arsenic greater than 4 mg/liter inhibited the solution of steel in the acid. Addition of up to 4 mg/liter of arsenic to 2N sulfuric acid did not significantly alter the quantity of hydrogen absorbed over that of arsenic-free acid, but additions of 8 mg/liter or more inhibited hydrogen absorption. These results help to explain some apparent discrepancies in the literature on the influence of arsenic on pickling rate and on hydrogen behavior in steel during immersion in acid solutions without applied current. 5.9.2

THE PICKLING OF NON-FERROUS METALS

AbstractThe term “pickling” is applied to the removal from metals of scale and oxide coatings, usually resulting from heat-treatment, forging, or casting operations. The thickness, composition, and structure of the scale depend on the conditions under which it is formed. The temperature and duration of heating and the nature of the atmosphere (whether oxidizing or reducing) have a profound influence on the scale and hence on the ease or otherwise with which it can be removed. Pickling is generally carried out by immersion in acid solutions or, in certain instances, in alkaline solutions.