Mercury battery 3298170 223403003 2008-07-03T22:46:04Z Speight 465800 /* Chemistry */ fix typos A '''mercury battery''' (also called '''mercuric oxide battery''', or '''mercury cell''') is a non-rechargeable [[battery (electricity)|electrochemical battery]], a [[primary cell]]. Due to the content of [[Mercury (element)|mercury]], and the resulting environmental concerns, the sale of mercury batteries is banned in many countries. Both [[ANSI]] and [[IEC]] have withdrawn standards for mercury batteries. Mercury batteries were made in button types for watches and calculators, and in larger forms for other applications. ==History== The mercury oxide-zinc battery system was known about 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> David Linden, Thomas B. Reddy (ed). Handbook Of Batteries 3rd Edition. McGraw-Hill, New York, 2002 ISBN 0-07-135978-8, chapter 11 page 11.1 </ref> The battery system had the advantages of long shelf life (to 10 years) and steady voltage output. After the war the battery system was widely applied for small electronic devices such as cardiac [[pacemaker]]s. ==Chemistry== Mercury batteries use either pure [[mercury(II) oxide|mercuric oxide]] or a mix 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 elementary 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]]. [[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. 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> Linden, ''Batteries'' ch. 11, page 11-2</ref> <ref> Linden, ''Batteries'', page 11.15 </ref> ==Electrical characteristics== Mercury batteries using [[mercury(II) oxide]] [[cathode]] have a very flat discharge curve, holding constant 1.35 V (open circuit) voltage until about 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. Mercury batteries with cathodes made of a mix of mercuric oxide and [[manganese dioxide]] have output voltage of 1.4 V and more sloped discharge curve. ==Substitutes== 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 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. ==References== <references/> ==See also== *[[Button cell]] *[[Battery recycling]] [[Category:disposable batteries]] [[Category:Mercury (element)]] [[Category:Recyclable materials]] [[de:Quecksilberoxid-Zink-Batterie]] [[fr:Pile au mercure]] [[ja:水銀電池]] [[ru:Ртутно-цинковый элемент]] [[zh:水銀電池]]