Environmental Health and Safety

Perchloric Acid

Perchloric acid is a strong mineral acid. Under some circumstances it may act as an oxidizer and/or present an explosion hazard. Perchloric acid fumes can also deposit into ducts over time and form explosive metallic perchlorates. In addition to explosion hazards, perchloric acid has similar corrosive properties to other strong acids and causes severe burns on contact with skin, eyes, and mucus membranes. For this reason work with perchloric acid must be carried out according to these guidelines.

General precautions

These precautions apply when using unconcentrated perchloric acid (<72%) at room temperature. When used under these conditions, perchloric acid reacts as a strong non-oxidizing acid. The following precautions should be taken when using perchloric acid under these conditions:

  1. Substitute with less hazardous chemicals when appropriate. Use dilute solutions (< 60%) whenever possible.
  2. Conduct operations in a properly functioning chemical fume hood with current EH&S certification. If operations are conducted frequently or in large quantities contact EH&S to determine if a specially designed fume hood dedicated to perchloric acid use is required.
  3. Always use impact-resistant chemical goggles, a face shield, neoprene gloves, and a rubber apron when handling perchloric acid.
  4. When using or storing even dilute perchloric acid solutions avoid contact with strong dehydrating agents (concentrated sulfuric acid, anhydrous phosphorous pentoxide, etc.). These chemicals may concentrate the perchloric acid and make it unstable.
  5. Avoid contact with cellulose materials such as wood, paper and cotton. Perchloric acid may become concentrated and cause a fire or explosion.

Using perchloric acid (<72%) at elevated temperatures

When heated to temperatures above 150° C perchloric acid becomes a strong oxidizer and eventually becomes unstable. Concentrated solutions are very dangerous and can react violently with many oxidizable substances, such as paper and wood, and can detonate. Vapors may also contaminate work surfaces or ventilation equipment with perchlorate residues, which may form highly unstable compounds. These compounds may ignite or detonate under certain conditions. The following additional precautions should be followed when heating perchloric acid:

  1. Perchloric acid digestions and other procedures performed at elevated temperatures must be done in a specially designed perchloric acid fume hoods. If you have been performing perchloric acid digestions in a fume hood not designed for perchloric acid, Contact EHS immediately for an evaluation of perchlorate contamination of the hood.
  2. Never heat perchloric acid in an oil bath or with an open flame. Electric hot plates, electrically or steam-heated sand baths, heating mantles, or steam baths are preferred. Use explosion proof electrical equipment.
  3. Avoid allowing hot perchloric acid to come into contact with any organic materials. Avoid using greases or hoses that are incompatible with perchloric acid.
  4. Be sure you understand the reaction(s) that can occur when using perchloric acid. Perchloric acid may react violently with many chemicals, including acetic anhydride, alcohol, reducing agents, and many metals.
  5. In wet digestions with perchloric acid, treat the sample first with nitric acid to destroy easily oxidizable matter.
  6. Do not distill perchloric acid in a vacuum, because the unstable anhydride may be formed and cause a spontaneous explosion.
  7. Prior to use with perchloric acid, vacuum pumps should be thoroughly flushed and refilled with Kel-F or Fluorolube.
  8. Wash down perchloric acid hoods after each use, following operating instructions provided by the manufacturer of the perchloric acid hood.
  9. Strongly consider using quartz apparatus which can handle temperature shock to handle perchloric acid, since it is necessary in many experiments to chill perchloric acid rapidly from the boiling point.
  10. Glass-to-glass unions, lubricated with 72% perchloric acid, seal well and prevent joint freezing arising from the use of silicon lubricants. Rubber stoppers, tubes, or stopcocks are incompatible with perchloric acid.
  11. When handling beakers of hot acid use properly designed tongs or other remote-handling devices.

Using anhydrous perchloric acid

Anhydrous perchloric acid (> 85% concentration) is very unstable and will usually explode when it comes in contact with organic materials. Use of anhydrous perchloric acid is prohibited.

Perchloric acid spills

CLEAN UP SPILLS OF PERCHLORIC ACID ONLY IF YOU HAVE BEEN TRAINED TO DO SO AND THE APPROPRIATE EQUIPMENT IS AVAILABLE

If you need assistance, call EHS. To clean a spill, neutralize it with soda ash (sodium carbonate) or other appropriate neutralizing agent. Soak up the neutralized spill with an inorganic based absorbent, if possible. If rags, paper towels are used, wet them and place them in a plastic bag and seal it. Do NOT use rags, paper towels, or sawdust and then put them aside to dry out, as such materials may spontaneously ignite. A second neutralization and rinsing of the wetted area is recommended. Label waste as flammable hazardous waste and submit an On-line Request for Hazardous Waste Pickup.

Storage

Perchloric acid should be stored in its original container within compatible secondary containment, preferably glass or porcelain. Secondary containment should be wiped periodically. It should be separate from organic chemicals, flammable or combustible materials, and strong dehydrating agents, but may be stored with other inorganic acids in an acid cabinet. It may also be stored in a perchloric acid fume hood. If a bottle containing perchloric acid exhibits signs of concentration, such as crystal formation or has turned dark there is a potential explosion hazard. Do NOT move the bottle, but Contact EHS for immediate assistance.

Inappropriate and Appropriate Materials

The following materials are not recommended for use with 72% perchloric acid: Nylon/polyamides, Dynel/modacrylic ester, Dacron/polyester, Bakelite, Lucite, vegetable-based Micarta, cellulose-based lacquers, copper/brass/bronze (which form shock sensitive salts), aluminum (dissolves), high nickel alloys (dissolve), cotton, wool, wood, and litharge (glycerin and lead oxide).

The following are suitable for use with 72% perchloric acid: Viton, tantalum, chemically pure titanium, zirconium, niobium, Hastelloy C (slight corrosion rate), PVC, Teflon, polyethylene, polypropylene, Kel-F, vinylidene fluoride, Saran, epoxy resins, glass, glass-lined steel, alumina, and Fluorolube.