Contact corrosion, definition

Corrosion is generally taken to be the waste of a metal by the action of corrosive agents. However, a wider definition is the degradation of a material through contact with its environment. Thus, corrosion can include non-metallic materials such as concrete and plastics and mechanisms such as cracking in addition to wastage (i.e. loss of material). This chapter is primarily concerned with metallic corrosion, through a variety of mechanisms. 

A general definition of a corrosive substance is A substance, which may destroy living tissues with which it comes into contact. 

All in all, in an optimal way, an effective capture and a definitive neutralization of the corrosive within the 10 s following the contact with the eye can guarantee the absence of lesions and so avoid the bum. By intervening within the first minute, the eye chemical bum shall be avoided or minimized. Beyond this first minute, the lesions gradually and inexorably settle down. This does not mean that there is no more profit to intervene It is what demonstrates the study of a clinical case of bum with late care [3,4]. 

Under the above definitions the strong mineral acids act as corrosives rather than as poisons. They produce their injuiious results by destroying the tissues with which they come in contact, and will cause death as surely by destroying a lai e surfiice of skin aa when they are taken into the stomach. 

Definition of Corrosive Section 2(i) of the FHSA defines the term corrosive as any substance which in contact with living tissue will cause destruction of tissue by chemical action. CPSC regulations elaborate on this definition by providing as follows ... 

Corrosives are not usually thought of as poisonous materials. However, if the combined chemical definition is applied to corrosives, then, in fact, they are poisonous to the tissues they contact. Allyl alcohol (DOT/UN identification number 1098) is toxic by absorption, inhalation, and ingestion. However, like many other hazardous materials, it also has multiple hazards. AUyl alcohol is placarded as a 6.1 poison primary hazard,... 

Corrosives are the largest class of chemicals used by industry, so it stands to reason that they would frequently be encountered in transportation and at fixed facilities. DOT Class 8 materials are corrosive liquids and solids. There are no DOT subclasses of corrosives. There are, however, two types of corrosive materials found in Class 8 acids and bases. Acids and bases are actually two different types of chemicals that are sometimes used to neutralize each other in a spill. They are grouped together in Class 8 because the corrosive effects are much the same on tissue and metals, if contacted. It should be noted, however, that the correct terminology for an acid is corrosive and for a base is caustic. DOT, however, does not differentiate between the two when placarding and labeling. The DOT definition for a corrosive material is a liquid or solid that causes visible destruction or irreversible alterations in human skin tissue at the site of contact, or a liquid that has a severe corrosion rate on steel or aluminum. This corrosive rate on steel and aluminum is 0.246 inches per year at a test temperature of 131 F. ... 

Epoxy coated rebars present particular problems to determining the corrosion condition of the Steel. In the first place the bars are electrically isolated from the concrete except at areas of damage. The size and locations of the areas of damage are obviously unknown. Attempts to carry out reference electrode potential surveys and linear polarization measurements have therefore been unable to come up with definitive criteria for corroding and non-corroding areas. The other problem is that the bars are isolated from each other, therefore a connection must be made to each bar measured to be sure that there is electrical contact. 

The definition of corrosive has been extended beyond that in 40 CFR Part 261 to include materials that cause visible destruction or irreversible alterations of the skin tissue at the site of contact when tested on the intact skin of an animal for 3 minutes besides its effect on steel. 

Definition Mixture of laurate esters of sorbitol and sorbitol anhydrides, with 4 moles ethylene oxide Properties HLB 13.3 nonionic Toxicology Moderately toxic by intraperitoneal, intravenous routes mildly toxic by ingestion skin irritant TSCA listed Uses Emulsifier for PVC polymerization solubilizer for colorants dye leveling agent emulsifier, solubilizer, wetting agent for cosmetics, foods, and pharmaceuticals corrosion inhibitor antistat, fiber lubricant for textiles in resinous/polymeric food-contact coatings... 

An inhibiting mechanism similar to that for nontransition metals in contact with passivators probably also applies to steel in concentrated refrigerating brines (NaCl or CaCy to which chromates are added as inhibitors (approximately 1.5-3. Og Na2Cr207/liter adjusted with NaOH to form CrOi ). In the presence of so large a Cr concentration, passivity of the kind discussed under Definition 1 (Section 6.1) does not take place. The reduction in corrosion rate is not as pronounced as when chlorides are absent [14] (see Table 17.1), and any reduction that occurs apparently results from formation of a surface diffusion barrier of chromate reduction products and iron oxides. Chromates are not adequate inhibitors for the hot concentrated brine solutions that, in the past, were sometimes mistakenly proposed as antifreeze solutions for engine cooling systems. 

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