Chromic acid, safety

Copper and Copper-Containing Alloys. Either sulfuric or hydrochloric acid may be used effectively to remove the oxide film on copper (qv) or copper-containing alloys. Mixtures of chromic and sulfuric acids not only remove oxides, but also brighten the metal surface. However, health and safety issues related to chromium(VT) make chromic acid less than desirable. 

Workplace. The Occupational Safety and Health Administration (OHSA) has estabUshed workplace permissible exposure limits (PEL) for chromium metal and three forms of chromium compounds. OSHA s PEL for chromic acid and chromates is 0.1 mg/m 3 both a ceiling, ie, no exposure above this concentration is allowed, and an 8-h time-weighted average (TWA). Chromium metal and insoluble chromium salts have an 8-h TWA PEL of 1.0 mg/m Cr, and the same standard is 0.5 mg/m Cr for soluble Cr(III) and Cr(II) compounds (144). 

Safety. The addition of concentrated sulphuric acid on sodium (or potassium) dichromate is to produce chromium trioxide, which is a powerful oxidizing agent capable of oxidizing carbon to carbon dioxide. The solution is loosely called chromic acid, but although true chromic acid H CrO has not been isolated, the aqueous solution contains dichromic acid, The... 

American Chrome and Chemicals. 1989. Chromic acid. Material safety data sheets. Corpus Christi, TX American Chrome and Chemicals, Inc. 

Criteria for a Recommended Standard Occupational Exposure to Chromic Acid," DHEW Publication No (HSM-11021), National Institue for Occupational Safety and Health, Cincinnati, Ohio, 45226, 1973 ... 

Chromic acid or nitric + sulfuric acid cleaning solutions are corrosive and need to be handled with care see p. 642. Wear safety goggles and gloves while cleaning the viscosimeter. 

SAFETY PROFILE Chromate salts are suspected human carcinogens producing tumors of the lungs, nasal cavity, and paranasal sinus. Chromic acid and its salts have a corrosive action on the skin and mucous membranes. The lesions are confined to the exposed parts, affecting chiefly the skin of the hands and forearms and the mucous membranes of the nasal septum. The characteristic lesion is a deep, penetrating ulcer, which, for the most part, does not tend to suppurate, and which is slow in healing. Small ulcers, about the size of a matchhead, may be found, chiefly around the base of the nails, on the... 

Strong. However, some of the aerospace aluminum alloys (e.g., 2024-T3) are very prone to corrosion. In order to combat corrosion of aluminum alloys, chromic acid anodization and chromate conversion have thus far proved most effective. Both processes, however, use and release hexavalent chromium, a proven human carcinogen, causing serious environmental and worker health and safety concerns. Thus, a chromium-free alternative with equivalent or superior corrosion performance has long been desired. 

The first method, although effective, was soon abandoned for safety reasons, while the use of chromic acid has been largely discontinued. The other two have remained the most widely used pre-treatments, not only for LDPE but also for high-density polyethylene (HDPE) and polypropylene (PP). Other methods have been found to be effective, but for reasons of cost, safety or convenience, they have not been widely used. The pre-treatments include fuming nitric acid, potassium permanganate, ammonium peroxydisulphate, ozone, fluorine, peroxides, UV radiation, grafting of polar monomers, plasmas (see Plasma pretreatment), electrochemical oxidation (see Electrochemical pre-treatment of polymers) and the use of solvent vapours. The corona, flame and plasma methods and the use of trichloroethylene are now discussed briefly the latter is included because it involves a different mechanism. 

Cadmium - health and safety precautions Chromium - health and safety precautions Aniline - health and safety precautions Trichloroethylene health and safety precautions Chromic acid concentrations in air Petroleum based adhesives in building operations Arsenic - toxic hazards and precautions Spraying of highly flammable liquids... 

Chromic acid is corrosive and extremely dangerous by inhalation, ingestion, or skin absorption. Wear appropriate gloves and safety goggles. Keep away from heat, sparks, and open flame. 

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