Mercury battery: Difference between revisions
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Mercury batteries were used in the shape of [[button cells]] for watches, hearing aids, and calculators, and in larger forms for other applications. |
Mercury batteries were used in the shape of [[button cells]] for watches, hearing aids, and calculators, and in larger forms for other applications. |
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Due to the content of [[Mercury (element)|mercury]], and the resulting |
Due to the content of [[Mercury (element)|mercury]], and the resulting |
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==History== |
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The ercury oxide-zinc battery system was known more than 100 years ago<ref>C. L. Clarke, US Patent 298175, 1884.</ref> but did not become widely used until 1942, when [[Samuel Ruben]] developed a balanced mercury cell which was useful for military applications such as metal detectors, munitions, and [[walkie-talkie]]s.<ref name=Linden02>David Linden, Thomas B. Reddy (ed). Handbook Of Batteries 3rd Edition. McGraw-Hill, New York, 2002 ISBN 0-07-135978-8, chapter 11.</ref> The battery system had the advantages of long shelf life (to 10 years) and steady voltage output. After the Second World War the battery system was widely applied for small electronic devices such as cardiac [[pacemaker]]s and [[hearing aid]]s. Mercury oxide batteries were made in a range of sizes from miniature [[button cell]]s used for [[hearing aid]]s and electric [[wrist watch]]es, cylindrical types used for portable electronic apparatus, rectangular batteries used for transistor radios,<ref>http://data.energizer.com/PDFs/E146X.pdf Energizer obsolete type E146, in NEDA 1604 size.</ref> and large multicell packs used for industrial applications such as radio [[remote control]] for overhead crane systems. In the United States, mercury oxide batteries were manufactured by companies including [[P. R. Mallory and Co Inc]], (now [[Duracell]]), [[Union Carbide Corporation]] (whose former battery division is now called [[Energizer Holdings]]), [[RCA Corporation]], and [[Burgess Battery Company]]. |
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==Chemistry== |
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Mercury batteries use either pure [[mercury(II) oxide|mercuric oxide]] or a mixture of mercuric oxide with [[manganese dioxide]] 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 [[anode]] is made of [[zinc]] and separated from the cathode with a layer of paper or other porous material soaked with electrolyte. During discharge, zinc oxidizes to [[zinc oxide]] and mercuric oxide gets reduced to elemental mercury. A little extra mercuric oxide is put into the cell to prevent evolution of hydrogen gas at the end of life. Mercury batteries are very similar to [[silver-oxide battery|silver-oxide batteries]].<ref name="Linden02"/> |
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The overall reaction is: |
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<math>Zn + HgO \rightarrow ZnO + Hg </math><ref name="Linden02"/> |
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[[Sodium hydroxide]] or [[potassium hydroxide]] are used as an [[electrolyte]]. Sodium hydroxide cells have nearly constant voltage at low discharge currents, making them ideal for [[hearing aids]], [[calculator]]s, and electronic [[watch]]es. 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.<ref name="Linden02"/> |
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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.<ref name="Linden02"/> A 12 volt battery of this type was formerly used for residential [[smoke detector]]s, where the two-step voltage characteristic gave a useful warning for replacement.<ref>Thomas Roy Crompton ''Battery reference book'' page 5-23.</ref> |
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==Electrical characteristics== |
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Mercury batteries using [[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 reference voltage in electronic instruments and in photographic [[light meter]]s. 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.<ref name="Linden02"/> |
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==Product ban== |
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The 1991 [[European commission]] [[Battery Directive|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 battery|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.<ref>Rod Hunter, Koen J. Muylle (ed.) ''European Community deskbook'' Environmental Law Institute , 1999 ISBN 0-911937-82-X, p. 75.</ref> |
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In the United States, 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 unless manufacturers provided a reclamation facility, effectively banning the sale.<ref>Frank Kreith, George Tchobanoglous ''Handbook of solid waste management'', McGraw-Hill Professional, 2002 ISBN 0-07-135623-1, pp. 6-34.</ref> |
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==Substitutes== |
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The ban on sale of mercury oxide batteries caused numerous problems for photographers, whose equipment frequently relied on their advantageous discharge curves and long lifetime. Alternatives used are [[zinc-air battery|zinc-air batteries]], with similar discharge curve, high capacity, but much shorter lifetime (a few months) and poor performance in dry climates, [[alkaline battery|alkaline batteries]] with voltage widely varying through their lifetime, and [[silver-oxide battery|silver-oxide batteries]] with higher voltage (1.55 V) and very flat discharge curve, making them possibly the best, though expensive, replacement after recalibrating the meter to the new voltage. Special adapters with voltage dropping [[Schottky diode|Schottky]] or [[Germanium diode]]s allow silver oxide batteries to be used in equipment designed for mercury batteries. Since the voltage drop is a non-linear function of the current flow, diodes don't represent a very accurate solution for applications where the current flow alters significantly. Currents drawn by old CdS light meters are typically in the 10 µA to 200 µA range (Minolta SR-T range). Various kinds of active voltage regulation circuits using SMD transistor <ref>{{cite web|url=http://www.mi-fo.de/forum/index.php?showtopic=11119&view=findpost&p=241848 |title=Matthias Paul: Using a 7x7 mm SMD transistor-based low-side voltage regulator circuit as Mercury battery replacement |date=2009-03-14 |accessdate=2011-02-26}}</ref> or integrated circuits<ref>{{cite web|url=http://www.mi-fo.de/forum/index.php?showtopic=11119&view=findpost&p=130223 |title=Matthias Paul: Using a Bandgap voltage reference as Mercury battery replacement |date=2005-12-12 |accessdate=2011-02-26}}</ref> have been devised, however, they are often difficult to integrate into the battery compartment space. Replacements must operate on the low voltage of a single cell. Lack of a power switch on many old light meters makes an ultra-low-power design mandatory. |
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==See also== |
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*[[Battery recycling]] |
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*[[Battery nomenclature]] |
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== References == |
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{{Reflist}} |
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== External links == |
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{{Commons category|Mercury batteries}} |
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{{Galvanic cells}} |
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[[Category:Disposable batteries]] |
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[[Category:Metal oxide-zinc batteries]] |
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[[Category:Mercury (element)]] |
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Revision as of 15:04, 30 April 2013
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A mercury battery (also called mercuric oxide battery, or mercury cell) is a non-rechargeable electrochemical battery, a primary cell.
Mercury batteries were used in the shape of button cells for watches, hearing aids, and calculators, and in larger forms for other applications.
Due to the content of mercury, and the resulting