Corrosion reaction classification

The classification given in Table 1.2 is based on the various forms that corrosion may take, but the terminology used in describing corrosion phenomena frequently places emphasis on the environment or cause of attack rather than the form of attack. Thus the broad classification of corrosion reactions into wet or dry is now generally accepted, and the nature of the process is frequently made more specific by the use of an adjective that indicates type or environment, e.g. concentration—cell corrosion, crevice corrosion, bimetallic corrosion and atmospheric corrosion. 

On a basis of the preceding discussion, the classification and nomenclature outlined in Table l.Al is suggested as a possible alternative to the accepted classification of corrosion reactions into wet and dry . 

All these types of polarisation will be present to a greater or lesser extent in most corrosion reactions, but if one is more significant than the others it will control the rate of the reaction. This leads to a classification of corrosion reactions according to whether the cathodic or anodic reaction is rate... 

The starting point for such classification is the point of interference with the above sketched corrosion mechanism either in a phenomenological or in a mechanistic way, A simple system for classification, which will be discussed in more detail later, is based on whether the inhibitor interferes with the anodic or cathodic reaction. Thus inhibitors are classified as anodic or cathodic inhibitors. However, this distinction was shown to be too simplistic and a more complex classification was worked out by H. Fischer (JJ on the basis of where, instead of how, in the complex interphase of a metal-electrolyte system the inhibitor interferes with the corrosion reactions. The metal-electrolyte interphase can be visualized as consisting of (a) the interface per se, and (b) an electrolyte layer interposed between the Interface and the bulk of the electrolyte. On this basis Fisher distinguished as shown in Table 1, between "Interface Inhibition" and "Electrolyte Layer Inhibition."... 

A logical and scientific classification of corrosion processes, although desirable, is by no means simple, owing to the enormous variety of corrosive environments and the diversity of corrosion reactions, but the broad classification of corrosion reactions into wet or dry is now generally accepted, and the terms are in common use. The term wet includes all reactions in which an aqueous solution is involved in the reaction mechanism implicit in the term dry is the absence of water or an aqueous solution. 

Classification by the type of attack At room temperature most corrosion reactions are triggered by electrochemical reactions ( electrolytic corrosion ), whereas at higher temperatures metal/gas type reactions will prevail. In addition to chemical/electrochemical attack, friction or a mechanical load will cause specific corrosion reactions. 

To the uninitiated engineer, the plethora of available corrosion monitoring techniques can be overwhelming in the absence of a categorization scheme. The first classification can be to separate direct from indirect techniques. Direct techniques measure parameters that are directly associated with corrosion processes. Indirect techniques measure parameters that are only indirectly related to corrosion damage. For example, measurements of potentials and current flow directly associated with corrosion reactions in the linear polarization resistance technique represent a direct corrosion rate measurement. The measurement of the corrosion potential only is an indirect method, as there is at best an indirect relationship between this potential and the severity of corrosion damage. 

Hazard and operability studies (HAZOP), 396, 399 Hazard classification, 443, 452, 453, 455, 469, 477, 478 Hazard warning labels, 394, 446, 447, 452, 461, 464 Hazardous reactions. See Chemical reaction Corrosion ... 

Factors Involved in Galvanic Corrosion. Emf series and practical nobility of metals and metalloids. The emf. series is a list of half-cell potentials proportional to the free energy changes of the corresponding reversible half-cell reactions for standard state of unit activity with respect to the standard hydrogen electrode (SHE). This is also known as Nernst scale of solution potentials since it allows to classification of the metals in order of nobility according to the value of the equilibrium potential of their reaction of dissolution in the standard state (1 g ion/1). This thermodynamic nobility can differ from practical nobility due to the formation of a passive layer and electrochemical kinetics. 

DOT CLASSIFICATION 8 Label Corrosive SAFETY PROFILE Poison by ingestion, inhalation, skin contact, and intraperitoneal routes. See also HYDROBROMIC ACID and ACETIC ACID. Violent reaction on contact with water, steam, methanol, or ethanol produces toxic and reactive HBr. When heated to decomposition it emits highly corrosive and toxic fumes of carbonyl bromide and bromine. To fight fire, use dry chemical, CO2. 

ACGIH TLV TWA 2 mg(Al)/m3 DOT CLASSIFICATION 8 Label Corrosive SAFETY PROFILE Moderately toxic by ingestion. Experimental teratogenic and reproductive effects. Mutation data reported. The dust is an irritant by ingestion, inhalation, and skin contact. Highly exothermic polymerization reactions with alkenes. Incompatible with nitrobenzenes or nitrobenzene + phenol. Highly exothermic reaction with water or steam produces toxic ftimes of HCl. See also ALUMINUM COMPOUNDS, CHLORIDES, and HYDROCHLORIC ACID. 

DOT CLASSIFICATION 8 Label Corrosive SAFETY PROFILE Moderately toxic by ingestion, skin contact, subcutaneous, intraperitoneal, and intravenous routes. Human mutation data reported. Severe skin and eye irritant. A corrosive material. Combustible liquid. Could react with oxidizing materials. Incandescent reaction with chromium trioxide above 100°. To fight fire, use alcohol foam, CO2, dry chemical. When heated to decomposition it emits acrid smoke and irritating fumes. 

SYN NITROGEN CHLORIDE DOT CLASSIFICATION Forbidden SAFETY PROFILE Strong irritant by inhalation. An extremely unstable explosive. Reacts with liquid ammonia to form an explosive liquid. Explosive reaction with 1,3-butadiene, C2H6, C2H4, CH4, CsHs, phopshorus, silver azide, sodium. Reacts with water or steam to produce toxic and corrosive fumes of HCl. Has been used as an initiator in chemical gas lasers. When heated to decomposition it emits toxic fumes of Cr and NOx- See also CHLORINE and AZIDES. 

DOT CLASSIFICATION 6.1 Label KEEP AWAY FROM FOOD SAFETY PROFILE Poison by ingestion and subcutaneous routes. Moderately toxic by skin contact. Mildly toxic by inhalation. Corrosive. A severe skin and eye irritant. Flammable when exposed to heat or flame can react vigorously with oxidizers. Potentially explosive reaction with nitric acid at 145°C/14.5 bar. To fight fire, use alcohol... 

OSHA PEL TWA 1 mg(Fe)/m3 ACGIH TLV TWA 1 mg(Fe)/m3 DOT CLASSIFICATION 8 Label Corrosive SAFETY PROFILE Poison by ingestion and intravenous routes. Experimental reproductive effects. Corrosive. Probably an eye, skin, and mucous membrane irritant. Mutation data reported. Reacts with water to produce toxic and corrosive fumes. Catalyzes potentially explosive polymerization of ethylene oxide, chlorine + monomers (e.g., styrene). Forms shock-sensitive explosive mixtures with some metals (e.g., potassium, sodium). Violent reaction with allyl chloride. When heated to decomposition it emits highly toxic fumes of HCl. 

DOT CLASSIFICATION 8 Label Corrosive SAFETY PROFILE A poison by ingestion. Moderately toxic by skin contact. A corrosive irritant to skin, eyes, and mucous membranes. Moderately explosive when exposed to heat. Reacts with water or steam to produce toxic and corrosive fumes. Dangerous reactions with metals e.g., sodium (mixture explodes on impact), potassium (explodes on contact), aluminum (ignition after a delay period). Reacts violently with A1 foil. CdS. PbS. organic matter. P. PCI3. rubber. Ag2S. ZnS. When heated to decomposition it emits highly toxic fumes of CL and I and may explode. See also IODINE and CHLORIDES. 

DOT CLASSIFICATION 8 Label Corrosive SAFETY PROFILE Poison by inhalation. Moderately toxic by ingestion. A severe eye, skin, and mucous membrane irritant. Corrosive to body tissues. Flammable by chemical reaction. Explosive reaction with chlorine dioxide + chlorine, sodium, urea + heat. Reacts to form explosive products with carbamates, 3 -methyl-2-nitroben2anilide (product explodes on contact with air). Ignites on contact with fluorine. Reacts violently with moisture, CIO3, hydroxyl-amine, magnesium oxide, nitrobenzene, phosphorus(III) oxide, K. To fight fire, use CO2, dry chemical. Incompatible with aluminum, chlorine dioxide, chlorine. 

DOT CLASSIFICATION 8 Label Corrosive SAFETY PROFILE Poison by inhalation. A corrosive irritant to the eyes, skin, and mucous membranes. With the appropriate conditions it undergoes hazardous reactions with formic acid, hydrogen fluoride, inorganic bases, iodides, metals, methyl hydroperoxide, oxidants (e.g., bromine, pentafluoride, chlorine trifluoride, perchloric acid, oxygen difluoride, hydrogen peroxide), 3-propynol, water. When heated to decomposition it emits toxic fumes of POx. 

DOT CLASSIFICATION 2.2 Label Nonflammable Gas SAFETY PROFILE This material is chemically inert in the pure state and is considered to be physiologically inert as well. However, as it is ordinarily obtainable, it can contain variable quantities of the low-sulfur fluorides. Some of these are toxic, very reacdve chemically, and corrosive in nature. These materials can hydrolyze on contact with water to yield hydrogen fluoride, which is highly toxic and very corrosive. In high concentrations and when pure it may act as a simple asphjudant. Incompatible with disilane. Vigorous reaction with disilane. May explode. When heated to decomposition emits highly toxic fumes of F" and SOx. 

DOT CLASSIFICATION 8 Label Corrosive DOT Class 8 Label Corrosive, Poison SAFETY PROFILE Confirmed human carcinogen. A poison. Moderately toxic by inhalation. A corrosive irritant to skin, eyes, and mucous membranes. A very dangerous fire hazard by chemical reaction with reducing agents and carbohydrates. A severe explosion hazard by chemical reaction with acetic acid, acetic anhydride, acetonitrile, acrolein, acrylic acid, acrylonitrile, aUyl... 

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