- Leclanché cell
Georges Leclanché invented and patented in 1866 his battery, the Leclanché cell. It contained a conducting solution (electrolyte ) ofammonium chloride , acathode (positive terminal) ofcarbon , adepolarizer ofmanganese dioxide , and ananode (negative terminal) ofzinc . The Leclanche battery was essentially a self-contained version of anearth battery , and fairly copied its design. [The Electrical Review, 1892. Page 68.]Construction
The original form of the cell used a porous pot. This gave it a relatively high internal resistance and various modifications were made to reduce it. These included the "Agglomerate block cell" and the "Sack cell".
Porous pot cell
In Leclanché's original cell the depolarizer, which consisted of crushed manganese dioxide, was packed into a porous pot, and a carbon rod was inserted to act as the cathode. The anode, which was a zinc rod, was then immersed along with the pot in a solution of ammonium chloride. The liquid solution acted as the electrolyte, permeating through the porous pot to make contact with the cathode.
Agglomerate block cell
In 1871 Leclanché dispensed with the porous pot and replaced it with a pair of "agglomerate blocks", attached to the carbon plate by rubber bands. These blocks were made by mixing the manganese dioxide with binding agents and pressing the mixture into moulds.
ack cell
In this cell the porous pot was replaced by a wrapping of canvas or sacking. In addition, the zinc rod was replaced by a zinc cylinder to give a larger surface area. It had a lower internal resistance than either of the above(porous and agglomerate).
Chemistry
The chemical process which produces electricity in a Leclanché cell begins when zinc atoms on the surface of the anode
oxidize , ie they give up both their electrons to become positively-chargedions . As the zinc ions move away from the anode, leaving their electrons on its surface, the anode becomes more negatively charged than the cathode. When the cell is connected in an externalelectrical circuit , the excess electrons on the zinc anode flow through the circuit to the carbon rod, the movement of electrons forming anelectrical current .When the electrons enter the rod, they combine with molecules of manganese dioxide and molecules of water, which react with each other to produce manganese oxide and negatively charged hydroxide ions. This is accompanied by a secondary reaction in which the negative hydroxide ions react with positive ammonium ions in the ammonium chloride electrolyte to produce molecules of ammonia and water.
Zn(s) + 2 MnO2(s) + 2 NH4Cl(aq) → ZnCl2 + Mn2O3(s) + 2 NH3(aq) + H2O
Usage
The
electromotive force (emf) produced by a Leclanche cell is typically around 1.5volt s with a resistance of severalohm s where a porous pot is used. It saw extensive usage intelegraphy ,signalling ,electric bell s and similar applications where intermittent current was required and it was desirable that a battery should require little maintenance.The Leclanché battery (or
wet cell as it was referred to) was the forerunner of the moderndry cell zinc-carbon battery .ee also
*
History of the battery
*Primary cell terminology References
ources
* "Practical Electricity" by W. E. Ayrton and T. Mather, published by Cassell and Company, London, 1911, pp 188-193
Wikimedia Foundation. 2010.