Cyanides, corrosive effect

Although hydrogen cyanide is a weak acid and is normally not corrosive, it has a corrosive effect under two special conditions (/) water solutions of hydrogen cyanide cause transcrystalline stress cracking of carbon steels under stress even at room temperature and in dilute solution and (2) water solutions of hydrogen cyanide containing sulfuric acid as a stabilizer severely corrode steel (qv) above 40°C and stainless steels above 80°C. 

Hydrogen cyanide is moderately lipid-soluble, which, along with its small size, allows it to rapidly cross mucous membranes, to be taken up instantly after inhalation, and to penetrate the epidermis. In addition, some cyanide compounds, such as potassium cyanide, have a corrosive effect on the skin that can increase the rate of percutaneous absorption (NIOSH 1976). Information regarding dermal absorption in animals and evidence that cyanide can be absorbed through the skin of humans is provided in Sections 2.3.1.3 and 2.2.3, respectively. 

Other metals, such as copper, nickel, or silver, have been used as electrode materials in connection with specific applications, such as the detection of amino acids or carbohydrates in alkaline media (copper and nickel) and cyanide or sulfur compounds (silver). Unlike platinum or gold electrodes, these electrodes offer a stable response for carbohydrates at constant potentials, through the formation of high-valence oxyhydroxide species formed in situ on the surface and believed to act as redox mediators (40,41). Bismuth film electrodes (preplated or in situ plated ones) have been shown to be an attractive alternative to mercury films used for stripping voltammetry of trace metals (42,43). Alloy electrodes (e.g., platinum-ruthenium, nickel-titanium) are also being used for addressing adsorption or corrosion effects of one of their components. The bifunctional catalytic mechanism of alloy electrodes (such as Pt-Ru or Pt-Sn ones) has been particularly useful for fuel cell applications (44). 

For carbon steels, however, a full stress-relief heat treatment (580-620°C) has proved effective against stress-corrosion cracking by nitrates, caustic solutions, anhydrous ammonia, cyanides and carbonate solutions containing arsenite. For nitrates, even a low-temperature anneal at 350°C is effective, while for carbonate solution containing arsenite the stress-relief conditions have to be closely controlled for it to be effective . 

Charcoal does not bind iron, lithium, or potassium, and it binds alcohols and cyanide only poorly. It does not appear to be useful in poisoning due to corrosive mineral acids and alkali. Recent studies suggest that oral activated charcoal given alone may be just as effective as gut emptying followed by charcoal. Also, other studies have shown that repeated doses of oral activated charcoal may enhance systemic elimination of some drugs (including carbamazepine, dapsone, and theophylline) by a mechanism referred to as "gut dialysis."... 

The presence of specific chemical species in the corrosive environment poisons or retards the rate of the Hads atom combination reaction, thereby permitting a higher fraction of the H atoms generated by corrosion to become absorbed by (enter into) the steel. Bisulfide ions (HS ), formed when H2S molecules are dissolved in water, are very effective H atom combination poisons. Other effective H atom combination poisons are cyanide ions (CN ) and arsenic ions (As3+). 

OSHA PEL CL 0.3 ppm ACGIH TLV CL 0.3 ppm DOT CLASSIFICATION 2.3 Label Poison Gas, Flammable Gas SAFETY PROFILE Poison by ingestion, subcutaneous, and possibly other routes. Toxic by inhalation. Human systemic effects by inhalation lachrymation, conjunctiva irritation, and chronic pulmonary edema or congestion. A primary irritant. A severe human eye irritant. An insecticide. Flammable when exposed to heat or flame. When heated to decomposition or on contact with water or steam, it will react to produce highly toxic and corrosive fumes of Cr, CN, and NOx. See also other cyanogen entries, CYANIDE, and CHLORIDES. 

SAFETY PROFILE Poison by ingestion, intravenous, and intracerebral routes. Moderately toxic by skin contact. Experimental reproductive effects. Mutation data reported. Highly toxic to fish and bees. Corrosive, causes eye damage. A skin irritant. When heated to decomposition it emits toxic fumes of Cl , NOx, and CN . See also CYANIDE. 

Vinyl cyanide, Acritet, Fumigrain, Ventox. Colourless, explosive, flammable liquid. Yellow on standing. Reacts violently with oxidizing agents. Absorbed all routes. Eye and respiratory tract irritant, corrosive to skin, sensitizer. Partly metabolized to cyanide. Effects CNS, liver, kidney, cardiovascular system, gut. Headache, nausea, vomiting, weakness, jaundice, coma, convulsions and cardiac arrest can occur without warning. 

Used by Austrians, September 1917 as a mixture with benzene, bromacetone and benzene Campiellite. Crystalline, mp 52°C, vapour pressure at 25°C 119.5 mmHg, volatility at 16°C 155 000 mg/m3. Soluble in organic solvents, sparingly soluble in water. Corrosive to metals. Irritant to eyes and airways at 6 mg/m3. Effects as per cyanide. 

The most common agglomeration technology for the conversion of sodium cyanide into a safe product is briquetting with roller presses. Almond- or pillow-shaped compacts are made. The systems are completely enclosed, equipped with highly effective dust collection systems to safeguard the operators, and executed in stainless steel to keep corrosion in check. The discharge from the roller press is screened within the enclosed system, fines are recirculated internally to the briquetter feed bin, and dean product is immediately packed into sealed containers. 

Fleischmann et al [22] compared benzotriazole and 2-mercaptobenzoxazole as inhibitors of copper corrosion in KCl solutions containing low concentrations of cyanide. Benzotriazole proved to be an ineffective inhibitor in cyanide media, while 2-mercaptobenzoxazole remained effective. SERS showed that cyanide, revealed by a broad band centred at 2090 cm displaced benzotriazole from the Cu surface, whereas 2-mercaptobenzoxazole displaced adsorbed cyanide. A synergetic inhibition of Cu corrosion by benzotriazole and benzylamine, both in chloride and chloride/cyanide media, was also shown [22]. As SERS showed that benzylamine had not been adsorbed, its beneficial effect was ascribed to an improved film formation. Subsequent 4or measurements showed that benzotriazole, MBO, 2-mercaptobenzothiazole and 2-mercaptobenzimidazole were all effective inhibitors of copper corrosion in neutral chloride solutions, but the inhibition efficiency of benzotriazole was decreased at pH 1-2 [23]. SERS spectra showed that, at pH 7, benzotriazole and its anionic form were coadsorbed and Cl was excluded from the interface. However, at pH < 2 undissociated benzotriazole and CH were coadsorbed, such that Cu underwent corrosion. In contrast, the anion from 2-mercaptobenzothiazole was the only adsorbed species at pH between 7 and 2 only at pH 1 was the neutral 2-mercaptobenzothiazole molecule detected. Competitive adsorption experiments showed that the inhibitive action of benzotriazole and 2-mercaptobenzothiazole in neutral/acid media could be explained in terms of adsorption strength. 

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