Inhibitors continued inorganic

Corrosion inhibition Is a very important but still poorly understood process. The aim is to inhibit the continuous oxidation or reduction of metals. This requires insight into the electrochemistry of the process. A host of interwoven phenomena are involved, including redox reactions on the surface, in the solution and Intervention by inorganic or organic molecules. The complexity is illustrated by the fact that there is often no simple correlation between the coverage of a certain inhibitor on the surface and the extent of Inhibition. 

The corrosion inhibitors appear to possess properties that impart to metals resistance to attack by a variety of corrosive agents, such as brines, weak inorganic acids, organic acids, COj, HjS, etc. The method of carrying out this process is relatively simple in principle the corrosion preventive reagent is dissolved in the liquid corrosive medium in small amounts and is thus kept in contact with the metal surface to be protected. Alternatively, the corrosion inhibitor may be applied first to the metal surface, either as it is or as a solution in some carrier liquid or paste. Continuous application, as in the corrosive solution, is the preferred method, however. The concentration of the corrosion inhibitors varies widely, but the preferable concentrations are 15-250 ppm. 

Sulfonation of aromatic hydrocarbons can be accomplished by using SO3 directly in the reaction, usually in a continuous sulfonater. This reaction is instantaneous and does not require the removal of water from the reaction. However, it gives a higher yield of sulfones and other nnwanted by-products. Chemical inhibitors can reduce sulfone production in this reaction. Interestingly, the sodium salt of the sulfonic acid, the actual hydrotrope, inhibits sulfone formation [3]. Inorganic sulfites [4] as well as acetic acid [5] can also be used. 

Corrosion inhibitors in paints protect metallic surfaces from oxidation. Coating primers are used when there is continuous exposure to corrosive elements, e.g., in marine applications. Examples are coal-tar derivatives, epoxy resins and coal-tar modified epoxies. Primers that inhibit corrosion by anodic or cathodic polarization contain inorganic metallic pigments such as chromates or leads or both. Composite pigments containing calcium oxide, zinc, silica, and oxides of phosphorus and boron can also be used (Mathias 1984). Nowadays, powder paints such as polyester and epoxy powder paints can also be used for corrosion inhibition (Rose and Vance 1997). 

The inhibition of metal corrosion in industrial water systems was first achieved by the use of inorganic salts or their blends, including chromates (Evans, 1936 Mayne and Pryor, 1949), nitrites (Hatch, 1952), phosphates (Patterson and Jones, 1952), borates (Mercer, 1990), silicates (Lehrman and Shuldenen, 1952), zinc salts (Hatch, 1965 a) and other cations (Hinton, 1989). Additionally, chromates and nitrites were mainly applied, and from the end of the 1950s the use of polyphosphates increased (May et al., 1981 Hwa, 1971). Treatments with anodic inhibitors such as nitrites or chromates require a high initial dose and a relatively high continuous dose in order to achieve an effective passive layer on the metal surface. The concentration of chromate and nitrite can be decreased in the presence of polyphosphates and zinc ions. 

Corrosion inhibitors for steels are being continuously developed because of the ubiquitous use of steel in construction and its somewhat limited corrosion resistance, especially in the presence of water. A great number of papers are on the effect of corrosion inhibitors, and the overwhelming majority deals with the effect of inhibitors on uniform corrosion. Due to environmental restrictions on common inorganic inhibitors (Freedman, 1986), several studies suggest derivatives of some amino acids as corrosion inhibitors. A survey of a number of different organic compounds commonly used as uniform corrosion inhibitors showed that most compounds hardly affect the pitting corrosion of stainless steel however, one of... 

During the past 30 years many new solvents for inorganic deposits were developed. Low hazard corrosion inhibitors have replaced some of the more toxic materials used to protect the structural surfaces during cleaning. Development of nuclear cleaning methods has extended the life of some very valuable nuclear generating plants. New waste disposal methods have enabled the industry to continue to operate, but have required new chemicals to be developed. Modest improvements for cleaning CP/R equipment include ways to remove FeS and we have seen the development of more environmentally friendly solvents. 

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