Mercury battery

Source: Wikipedia, the free encyclopedia.

Mercury battery "РЦ-53М"(RTs-53M), Russian manufactured in 1989

A mercury battery (also called mercuric oxide battery, mercury cell, button cell, or Ruben-Mallory

button cells
for watches, hearing aids, cameras and calculators, and in larger forms for other applications.

For a time during and after World War II, batteries made with

ANSI and IEC
have withdrawn their standards for mercury batteries.

Cross section through a button-type mercury battery

History

The mercury oxide-zinc battery system was known since the 19th century,

RCA Corporation, and Burgess Battery Company
.

Chemistry

Mercury batteries use either pure mercury(II) oxide (HgO)—also called mercuric oxide—or a mixture of HgO with manganese dioxide (MnO2) as the cathode. Mercuric oxide is a non-conductor, so some graphite is mixed with it; the graphite also helps prevent collection of mercury into large droplets. The half-reaction at the cathode is:[4]

with a

standard potential
of +0.0977 V.

The

electrochemical reaction step:[4]

followed by the chemical reaction step:[4]

yielding an overall anode half-reaction of:[4]

The overall reaction for the battery is:

In other words, during discharge, zinc is oxidized (loses electrons) to become zinc oxide (ZnO) while the mercuric oxide gets reduced (gains electrons) to form elemental mercury. A little extra mercuric oxide is put into the cell to prevent evolution of hydrogen gas at the end of life.[4]

Electrolyte

hearing aids, calculators, and electronic watches. Potassium hydroxide cells, in turn, provided constant voltage at higher currents, making them suitable for applications requiring current surges, e.g. photographic cameras with flash, and watches with a backlight. Potassium hydroxide cells also have better performance at lower temperatures. Mercury cells have very long shelf life, up to 10 years.[4]

Mercuric oxide and cadmium

A different form of mercury battery uses mercuric oxide and cadmium. This has a much lower terminal voltage around 0.9 volts and so has lower energy density, but it has an extended temperature range, in special designs up to 180 C. Because cadmium has low solubility in the alkaline electrolyte, these batteries have long storage life.[4] A 12 volt battery of this type was formerly used for residential smoke detectors. It was designed as a series stack of cells, where one cell had a reduced capacity resulting in a very distinct two-step voltage discharge characteristic. When reaching the end of its life, this smaller cell would discharge first causing the battery terminal voltage to drop sharply by 0.9 volts. This provided a very predictable and repeatable way to warn users the battery needed replacement while the larger capacity cells kept the unit functioning normally.[6]

Electrical characteristics

Mercury batteries using a mercury(II) oxide cathode have a very flat discharge curve, holding constant 1.35 V (open circuit) voltage until about the last 5% of their lifetime, when their voltage drops rapidly. The voltage remains within 1% for several years at light load, and over a wide temperature range, making mercury batteries useful as a voltage reference in electronic instruments and in photographic light meters.[7]

Mercury batteries with cathodes made of a mix of mercuric oxide and manganese dioxide have output voltage of 1.4 V and a more sloped discharge curve.[4]

Product ban

The 1991

European commission directive 91/157, when adopted by member states, prohibited the marketing of certain types of batteries containing more than 25 milligrams of mercury, or, in the case of alkaline batteries, more than 0.025% by weight of mercury. In 1998 the ban was extended to cells containing more than 0.005% by weight of mercury.[2]

In 1992, the state of New Jersey prohibited sales of mercury batteries. In 1996, the United States Congress passed the Mercury-Containing and Rechargeable Battery Management Act that prohibited further sale of mercury-containing batteries (with an exception for up to 25 mg of mercury per button cell). In some specific cases large mercury-containing batteries can continue to be produced if manufacturers provide a system to collect waste batteries and a reclamation facility.[8][9]

Substitutes

The ban on sale of mercury oxide batteries caused numerous problems for

silver-oxide batteries
with higher voltage (1.55 V) and very flat discharge curve, which makes them possibly the best, though expensive, replacement after recalibrating the meter to the new voltage.

Special adapters with voltage dropping

negative voltage regulator design further reduces the choice of suitable electronic parts.[11]

Use in zinc batteries

Formerly, the zinc anodes of dry cells were amalgamated with mercury, to prevent side-reactions of the zinc with the electrolyte that would reduce the service life of the battery. The mercury took no part in the chemical reaction for the battery. Manufacturers have changed to a purer grade of zinc, so amalgamation is no longer required and mercury is eliminated from the dry cell.

See also

References

  1. ^
    ISBN 978-1-4684-9047-3
    .
  2. ^
    ISBN 0-911937-82-X
    .
  3. ^ Clarke, Charles Leigh (1884-06-06). Galvanic battery. US Patent 298175. [1]
  4. ^
    ISBN 0-07-135978-8
    .
  5. ^ "Engineering data - Energizer No. E146X" (PDF). Energizer. Archived (PDF) from the original on 2018-11-18. Retrieved 2019-05-11.
  6. ^ Crompton, Thomas Roy. Battery reference book. pp. 5–23.
  7. ISBN 0-93557826-9
    .
  8. ISBN 0-07-135623-1
    .
  9. ^ "IMERC Fact Sheet: Mercury Use in Batteries". Northeast Waste Management Officials' Association. January 2010. Retrieved 2013-06-20.
  10. ^ Paul, Matthias R. (2009-03-14). "Minolta SR-T Batterieadapter" [Using a 7×7 mm SMD transistor-based low-side voltage regulator circuit as Mercury battery replacement]. Minolta-Forum (in German). Archived from the original on 2016-03-27. Retrieved 2011-02-26.
  11. ^ a b c Paul, Matthias R. (2005-12-12). "Minolta SR-T Batterieadapter" [Using a Bandgap voltage reference as Mercury battery replacement]. Minolta-Forum (in German). Archived from the original on 2016-10-11. Retrieved 2011-02-26.

External links

Wikimedia Commons has media related to Mercury batteries.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Mercury_battery&oldid=1167403523"