Corrosion organic compounds

Organic compounds normally cause Htde or no corrosion of magnesium. Tanks or other containers of magnesium alloys are used for phenol [108-95-2] methyl bromide [74-96 ] and phenylethyl alcohol [60-12-8]. Most alcohols cause no more than mild attack, but anhydrous methanol attacks magnesium vigorously with the formation of magnesium methoxide [109-88-6]. This attack is inhibited by the addition of 1% ammonium sulfide [12135-76-1] or the presence ofwater. 

Strong oxidizers and strong acids are incompatible with nikanolamines. Reactions, generating temperature and/or pressure increases, may occur with halogenated organic compounds. Alkan olamines are corrosive to copper and brass and may react. Contact with aluminum by alkan olamines, particularly when wet or at elevated temperatures (60°C), should be avoided. 

The corrosion behavior of tantalum is weU-documented (46). Technically, the excellent corrosion resistance of the metal reflects the chemical properties of the thermal oxide always present on the surface of the metal. This very adherent oxide layer makes tantalum one of the most corrosion-resistant metals to many chemicals at temperatures below 150°C. Tantalum is not attacked by most mineral acids, including aqua regia, perchloric acid, nitric acid, and concentrated sulfuric acid below 175°C. Tantalum is inert to most organic compounds organic acids, alcohols, ketones, esters, and phenols do not attack tantalum. 

The effect of impurities in either structural material or corrosive material is so marked (while at the same time it may be either accelerating or decelerating) that for rehable results the actual materials which it is proposed to use should be tested and not types of these materials. In other words, it is much more desirable to test the actual plant solution and the actual metal or nonmetal than to rely upon a duphcation of either. Since as little as 0.01 percent of certain organic compounds will reduce the rate of solution of steel in sulfuric acid 99.5 percent and 0.05 percent bismuth in lead will increase the rate of corrosion over 1000 percent under certain conditions, it can be seen how difficult it would be to attempt to duplicate here all the significant constituents. 

Alkalizing and film-forming inhibitors are used to prevent corrosion in water containing Oj or salt. These include NajCOj, NaOH, Na3P04, Na2Si03, NaNOj and Na2Cr04. The number of organic compounds that effectively inhibit metal... 

Organic Chlorides/Halides — Several organic compounds also are hydrolyzed (or react with water) to produce corrosive materials. Notable inclusions among these compounds are acetic anhydride ([CH3COJ2O), and acetyl chloride (CH3COCI), both of which produce acetic acid upon reaction with water. Both acetic anhydride and acetyl chloride are corrosive in addition, mixtures of the vapors of acetic anhydride and acetic acid are flammable in air, and acetyl chloride itself is flammable. 

With many organic compounds, aluminium shows high corrosion resistance either in the presence or absence of water. The lower alcohols and phenols are corrosive when they are completely anhydrous —rarely encountered in practice —since repair of breaks in the natural protective oxide film on aluminium cannot take place in the absence of water. Amines generally cause little attack unless very alkaline. 

Sulphates, silicates, carbonates, colloids and certain organic compounds act as inhibitors if evenly distributed, and sodium silicate has been used as such in certain media. Nitrates tend to promote corrosion, especially in acid soil waters, due to cathodic de-polarisation and to the formation of soluble nitrates. Alkaline soils can cause serious corrosion with the formation of alkali plumbites which decompose to give (red) lead monoxide. Organic acids and carbon dioxide from rotting vegetable matter or manure also have a strong corrosive action. This is probably the explanation of phenol corrosion , which is not caused by phenol, but thought to be caused by decomposition of jute or hessian in applied protective layers. ... 

In general, near-neutral aqueous products are without action except for possible sulphide staining or, when there are dissolved salts present, some local corrosion. The slight acidity which may develop in solutions of some organic compounds such as formaldehyde or alcohols can be tolerated. 

Direct measurements on metals such as iron, nickel and stainless steel have shown that adsorption occurs from acid solutions of inhibitors such as iodide ions, carbon monoxide and organic compounds such as amines , thioureas , sulphoxides , sulphidesand mer-captans. These studies have shown that the efficiency of inhibition (expressed as the relative reduction in corrosion rate) can be qualitatively related to the amount of adsorbed inhibitor on the metal surface. However, no detailed quantitative correlation has yet been achieved between these parameters. There is some evidence that adsorption of inhibitor species at low surface coverage d (for complete surface coverage 0=1) may be more effective in producing inhibition than adsorption at high surface coverage. In particular, the adsorption of polyvinyl pyridine on iron in hydrochloric acid at 0 < 0 -1 monolayer has been found to produce an 80% reduction in corrosion rate . 

Adsorption is, of course, of major importance in the inhibition of corrosion by organic compounds (adsorption inhibitors) that have the ability to adsorb strongly on the metal surface, thus impeding the dissolution reaction and reducing the corrosion rate. It follows that the coverage of a metal surface by adsorbed inhibitor can be evaluated from the relationship... 

Sulfur in cmde oil is mainly present in organic compounds such as mercaptans (R-SH), sulfides (R-S-R ) and disulfides (R-S-S-R ), which are all relatively easy to desulfurize, and thiophene and its derivatives (Fig. 9.2). The latter require more severe conditions for desulfurization, particularly the substituted dibenzothiophenes, such as that shown in Fig. 9.2. Sulfur cannot be tolerated because it produces sulfuric add upon combustion, and it also poisons reforming catalysts in the refinery and automotive exhaust converters (particularly those for diesel-fueled cars). Moreover, sulfur compounds in fuels cause corrosion and have an unpleasant smell. 

The polarization characteristic of a corroding metal can be controlled by various additives to the solution, called corrosion inhibitors, which adsorb on the metal and lower the rates of the cathodic and/or anodic reaction. Inhibitors are used primarily for acidic electrolyte solutions, sometimes also for neutral solutions. Various organic compounds with -OH, -SH, -NHj, -COOH, and so on, as the functional groups are used as inhibitors. The effects of an organic inhibitor, tetradecylpiperidinium... 

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