Corrosive Chemical Agents

When an acid encounters body tissues, the hydrogen ion dissociates from its accompanying anion (chloride, nitrate, bisulphate, etc.). The hydrogen ion denatures proteins in the cells. This produces a characteristic acid bum where the dermis has suffered coagulative necrosis. This necrosis limits the penetration of the acid deeper into the skin. Heat is generated as the acid is further hydrated (heat of hydration) or 

When a base encounters body tissue, the hydroxide anion (OH ) dissociates from its accompanying cation. The hydroxide ion produces a chemical bum termed Uque-factive necrosis. Unlike necrosis due to acids, this necrotic tissue is not a coagulum or scab therefore, this permits deeper penetration of a base into the dermis. Generally, bases are injurious at the site of contact and are not significantly absorbed and distributed throughout the body to produce systemic toxicity. In other words, bases are corrosive, contact toxicants that produce chemical bums at their site of contact because of their local toxic effects. 

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We understand easily that the corrosive chemical agents can give very quickly a fatal blow to the cells constituing organic tissues of organs, in different ways ... 

A. Skin. Corrosive agents rapidly injure the skin and must be removed immediately. In addition, many toxins are readily absorbed through the skin, and systemic absorption can be prevented only by rapid action. Table 11-20 (p 158) lists several corrosive chemical agents that can have systemic toxicity, and many of them are readily absorbed through the skin. 

In total, as studied above, chemical injury always results from an elementary chemical reaction during the contact of two entities, one being the aggressor, the other one the assaulted. In chemistry, we call them the reagent and the reactant. We understand easily that the corrosive chemical agents can very quickly give a fatal blow to the cells composing tissues, in different ways such as ... 

In conclusion, it is important to be able to estimate the real effect and behavior of irritant/cor-rosive products for cosmetic use such as chemical peeling or hair relaxers. Controlling the pH after exposure to these aggressive products can stop the burning process and improves the awaited effect irritant/corrosive chemical agent for cosmetic use seems to be important. See also Sect. 4.11.3 on peeling. 

Chemical suppHers include basic manufacturers of active ingredients, formulators, and distribution or service industries. The relative importance of each depends greatly upon the industry being suppHed. In many instances, the vendor may supply a number of performance chemicals (eg, corrosion control agents or stabilizers) in addition to the antimicrobial agent. 

Corrosion also occurs as a result of the conjoint action of physical processes and chemical or electrochemical reactions (1 3). The specific manifestation of corrosion is deterrnined by the physical processes involved. Environmentally induced cracking (EIC) is the failure of a metal in a corrosive environment and under a mechanical stress. The observed cracking and subsequent failure would not occur from either the mechanical stress or the corrosive environment alone. Specific chemical agents cause particular metals to undergo EIC, and mechanical failure occurs below the normal strength (5aeld stress) of the metal. Examples are the failure of brasses in ammonia environments and stainless steels in chloride or caustic environments. 

Aluminium is a very reactive metal with a high affinity for oxygen. The metal is nevertheless highly resistant to most atmospheres and to a great variety of chemical agents. This resistance is due to the inert and protective character of the aluminium oxide film which forms on the metal surface (Section 1.5). In most environments, therefore, the rate of corrosion of aluminium decreases rapidly with time. In only a few cases, e.g. in caustic soda, does the corrosion rate approximate to the linear. A corrosion rate increasing with time is rarely encountered with aluminium, except in aqueous solutions at high temperatures and pressures. 

Impervious graphites, that is electro-graphites with appropriate resin impregnation are used in cascade-, shell- apd tube-type coolers, condensers, pre-heaters etc. in a wide variety of chemical plants. Similar resistance to corrosion applies to glassy carbon vessels and pyrolytic carbons and graphites. The corrosion resistance to principal chemical agents is given in Table 18.2. 

One of the most common impurities in coastal areas which acts in a chemical manner rather than a physical one is salt water. However, with the ever-increasing spread of the chemical industries, and the stepped-up use of gasoline powered vehicles, the problem of chemical degradation are also of interest particularly in inland areas. While plastics in general are corrosion resistant, the multiplicity of chemical agents which can be in the air in industrial atmospheres, plus the chemical nature of the various plastics indicates that it cannot be assumed that all plastics are chemically resistant to all atmospheres. 

As is apparent from the above information, there is no ideal disinfectant, antiseptic or preservative. All chemical agents have their limitations either in terms of their antimicrobial activity, resistance to organic matter, stability, incompatibility, irritancy, toxicity or corrosivity. To overcome the limitations of an individual agent, formulations consisting of combinations of agents are available. For example, ethanol has been combined with chlorhexidine and iodine to produce more active preparations. The combination of chlorhexidine and cetrimide is also considered to improve activity. QACs and phenols have been combined with glutaraldehyde so that the same effect can be achieved with lower, less irritant concentrations of glutaraldehyde. Some... 

Improvements have been identified and demonstrated that may afford a lower corrosion rate for SCWO liners and improve effluent quality for all chemical agents, including GB (see the two rightmost liner configurations in Figure 5-2). 

Certain products, in contact with water, react and release corrosive products. This reaction develops more or less violently according to the involved chemical agent. This rise of temperature may aggravate the bum. Some examples ... 

In a restricted sense, corrosion is considered toconsistof the slow chemical and electrochemical reactions between melals and their environments. From a broader point of view corrosion is the slow destruction of any material by chemical agents and electrochemical reactions. This contrasts with erosion, which is the slow destruction of materials by mechanical agents. The character of the atmospheres to which materials arc exposed may he classified as rural, urban, industrial, urban-marine, industrial-marine, marine, tropical, and tropical-marine. In addition to these general kinds of environments, corrosion is of particular concern in the environments of chemical, petrochemical, and otherprocessing and manufacturing environments where extremely corrosive substances may be encountered. 

The pnndpal unsaturated acids used are maleic and fumaric. Saturated acids, usually phthahe and adipic, may also be included. The function of these acids is to reduce the amount of unsaturation in the final resin, making it tougher and more flexible. The acid anhydrides are often used if available and applicable. The dihydroxy alcohols most generally used are ethylene, propylene, diethylene, and dipropylene glycols. Styrene and diallyl philialate are the most common cross-linking agents, Polyesters are resistant to corrosion, chemicals, solvents, etc. 

Downey KW, Snow RH, Hazlebeck DA, Roberts AJ. Corrosion and chemical agent destruction, research on supercritical waste oxidation of hazardous military waste. Innovations in Supercritical Fluids, Chapter 21. Washington, D.C. American Chemical Society, 1995. 

Environmental stress cracking or corrosion (ESC) is the phenomenon that materials fail, in the presence of relatively inert chemical agents (liquids or gasses) and /or radiation, at much lower stresses, than in their absence, under the formation of many little cracks. We distinguish real chemical corrosion and stress corrosion, each with its own characteristics. 

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