Corrosion film forming compounds

Corrosion inhibition by organic compounds was also investigated and either 2-D adsorption [78] or more often 3-D adsorption, particularly with film forming compounds [79-81], or both effects [82] were observed. 

The film forming compounds are generally surfactants so that during initial application they clean the surface, and corrosion products are removed. Unless the addition of the agent is applied slowly to a system that has been in use for some time, the cleaning effect may produce quantities of particles of corrosion products that may give rise to a particulate fouling problem downstream. 

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... 

The corrosion resistance of lithium electrodes in contact with aprotic organic solvents is due to a particular protective film forming on the electrode surface when it first comes in contact witfi tfie solvent, preventing further interaction of the metal with the solvent. This film thus leads to a certain passivation of lithium, which, however, has the special feature of being efiective only while no current passes through the external circuit. The passive film does not prevent any of the current flow associated with the basic current-generating electrode reaction. The film contains insoluble lithium compounds (oxide, chloride) and products of solvent degradation. Its detailed chemical composition and physicochemical properties depend on the composition of the electrolyte solution and on the various impurity levels in this solution. 

Corrosion-inhibiting properties of fuel stabilizers can be a secondary effect of the dispersing action of a fuel stabilizer. By functioning as a dispersant, sludge and water are held in suspension and prevented from initiating metal surface corrosion. Also, some stabilizer dispersants can form a thin film on the metal surfaces of fuel system components. This film-forming property enables the stabilizer-dispersant to function in corrosion control. A typical oil-soluble dispersant compound is shown in FIGURE 6-3. 

The filament occurs on metals covered by an organic film and because of a certain discontinuity in the film, air and water penetrate through the coating and reach the underlying metal. This adjacent humid layer becomes saturated or rich in corrosive ions from soluble salts, and forms the zone called the active head of the filament. The dissolution of metal decreases as the solubility of the oxygen increases. The metallic ions oxidize and form compounds or corrosion products. These zones are called tails. Figure 6.22 illustrates a section and explains the mechanism of initiation and propagation of the filament. 

Copper does form compounds with BTA in solutions. The pH of the solution influences the stability of these compounds and thereby the effectiveness of their corrosion inhibition. For the same reason, for this chemical, pH also influences the removal of BTA from a copper film after copper CMP. The reaction between BTA and copper favors the release of BTA at low pH. In order to minimize organic contamination, the interaction between the organic chemical and the film to be polished has to be... 

Stress-corrosion cracking of copper-zinc alloys can occur in environments other than ammoniacal solutions (Ref 114, 147, 151, 152). Included are nitrogen-bearing compounds such as amines and aniline, as well as sulfates, nitrates, nitrites, acetates, formates, and tartrates. These environments can produce tarnish films of Cu20 similar to the films formed in ammoniacal solutions. Both the rate of formation and... 

Dissolution of the chlorides from the corrosion products is an essential part of the conservation process. It is essential that the artefact is immersed in an electrolyte that will not corrode the metal any further, while this dissolution is taking place. Corrosion scientists have developed redox potential - pH diagrams from thermodynamics in order to predict the most stable form of the metal. These diagrams are divided into three zones. Where metal ions are the most stable phase, this is classed as a zone of corrosion. If the metal itself is the most stable species, this is said to be the zone of immunity. The third zone is where solid metal compounds such as oxides, hydroxides, etc, are the most stable and may form a protective layer over the metal surface. This zone is termed passivity and the metal will not corrode as long as this film forms a protective barrier. The thickness of this passive layer may only be approximately 10 nm thick but as long as it covers the entire metal surface, it will prevent further corrosion. 

Film-forming anions (phosphates, polyphosphates, and carbonates) can also form sparingly soluble salts on the metal surface that hamper corrosion propagation. These anions can become an active part of rust converters that transform corrosion products into insoluble compounds. For instance, orthophosphoric acid transforms rust into insoluble iron phosphates. 

A reduction in the corrosive action of water is an extremely important property of surfactants. The mechanism of this phenomenon has been presented in a work by Somasundaran and Huang [89], The authors assume that the adsorbed film formed at the interface efficiently separates the water from the metal surface. Experiments confirming the anticorrosive action of surfactants have been presented in several works [90-94]. The following compounds were used in the experiments as additives cationic surfactants (cetyl pyridinium chloride and trimethyl ammonium bromide) [89], ethoxylated fatty acids [90], ethoxylated fatty alcohols [91], and ethoxylated sorbitan esters [92-94]. 

Corrosion inhibitor. Easily formulated for desired dispersibility with good film-forming persistency. The acetic acid and hydroxyacetic salts are highly water soluble. Useful in non-metallic mineral flotation. Wetting, emulsifying and antistripping agent with asphalt compounds and coal-tar pitches. 

Lead is one of the most stable of fabricated materials because of excellent corrosion resistance to air, water, and soil. An initial reaction with these elements results in the formation of protective coatings of insoluble lead compounds. For example, in the presence of oxygen, water attacks lead, but if the water contains carbonates and siUcates, protective films or tarnishes form and the corrosion becomes exceedingly slow. 

Batteries. Many batteries intended for household use contain mercury or mercury compounds. In the form of red mercuric oxide [21908-53-2] mercury is the cathode material in the mercury—cadmium, mercury—indium—bismuth, and mercury—zinc batteries. In all other mercury batteries, the mercury is amalgamated with the zinc [7440-66-6] anode to deter corrosion and inhibit hydrogen build-up that can cause cell mpture and fire. Discarded batteries represent a primary source of mercury for release into the environment. This industry has been under intense pressure to reduce the amounts of mercury in batteries. Although battery sales have increased greatly, the battery industry has aimounced that reduction in mercury content of batteries has been made and further reductions are expected (3). In fact, by 1992, the battery industry had lowered the mercury content of batteries to 0.025 wt % (3). Use of mercury in film pack batteries for instant cameras was reportedly discontinued in 1988 (3). 

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