Georges LeclanchéGeorges Leclanché was a French electrical engineer chiefly remembered for his invention of the Leclanché cell, one of the first modern electrical batteries and the forerunner of the modern dry cell battery.-Biography:...
invented and patented in
1866 his battery, the
Leclanché cell. It contained a conducting solution (
electrolyteIn chemistry, an electrolyte is any substance containing free ions that behaves as an electrically conductive medium, usually when in a solution...
) of
ammonium chlorideAmmonium chloride is, in its pure form, a clear white water-soluble crystalline salt of ammonia. The aqueous ammonium chloride solution is mildly acidic. Sal ammoniac is a name of natural, mineralogical form of ammonium chloride...
, a
cathodeA cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .A widespread misconception is that cathode polarity is always negative...
(positive terminal) of
carbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
, a
depolarizerA depolarizer or depolariser is a substance used in an electrochemical cell, which takes up electrons during discharging the cell; therefore, it is always an oxidizing agent...
of manganese dioxide, and an
anodeAn anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID . Electrons flow in the opposite direction to the electric current...
(negative terminal) of
zincZinc , also known as spelter, is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
. The Leclanche battery was essentially a self-contained version of an
earth batteryAn Earth battery is a pair of electrodes made of two dissimilar metals, such as iron and copper, which are buried in the soil or immersed in the sea. It can act as a receiver of Telluric radiant energy and as a water activated battery...
, and fairly copied its design. The chemistry of this cell was later successfully adapted to manufacture of
dry cell-Dry Cell's formation:Part of the band formed in 1998 when guitarist Danny Hartwell and drummer Brandon Brown met at the Ratt Show on the Sunset Strip. They later met up with then-vocalist Judd Gruenbaum. The original name of the band was "Beyond Control"....
s.
The original form of the cell used a porous pot.
Georges LeclanchéGeorges Leclanché was a French electrical engineer chiefly remembered for his invention of the Leclanché cell, one of the first modern electrical batteries and the forerunner of the modern dry cell battery.-Biography:...
invented and patented in
1866 his battery, the
Leclanché cell. It contained a conducting solution (
electrolyteIn chemistry, an electrolyte is any substance containing free ions that behaves as an electrically conductive medium, usually when in a solution...
) of
ammonium chlorideAmmonium chloride is, in its pure form, a clear white water-soluble crystalline salt of ammonia. The aqueous ammonium chloride solution is mildly acidic. Sal ammoniac is a name of natural, mineralogical form of ammonium chloride...
, a
cathodeA cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .A widespread misconception is that cathode polarity is always negative...
(positive terminal) of
carbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
, a
depolarizerA depolarizer or depolariser is a substance used in an electrochemical cell, which takes up electrons during discharging the cell; therefore, it is always an oxidizing agent...
of manganese dioxide, and an
anodeAn anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID . Electrons flow in the opposite direction to the electric current...
(negative terminal) of
zincZinc , also known as spelter, is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
. The Leclanche battery was essentially a self-contained version of an
earth batteryAn Earth battery is a pair of electrodes made of two dissimilar metals, such as iron and copper, which are buried in the soil or immersed in the sea. It can act as a receiver of Telluric radiant energy and as a water activated battery...
, and fairly copied its design. The chemistry of this cell was later successfully adapted to manufacture of
dry cell-Dry Cell's formation:Part of the band formed in 1998 when guitarist Danny Hartwell and drummer Brandon Brown met at the Ratt Show on the Sunset Strip. They later met up with then-vocalist Judd Gruenbaum. The original name of the band was "Beyond Control"....
s.
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.
Sack 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-charged ions. 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 external electrical circuit, the excess electrons on the zinc anode flow through the circuit to the carbon rod, the movement of electrons forming an electrical current.
When the electrons enter the rod, they combine with manganese dioxide and 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 MnO
2(s) + 2 NH
4Cl(aq) → ZnCl
2 + Mn
2O
3(s) + 2 NH
3(aq) + H
2O
Usage
The
electromotive forceIn physics, electromotive force, or most commonly emf , or electromotance is "that which tends to cause current to flow."...
(emf) produced by a Leclanche cell is typically around 1.5
voltThe volt is the SI derived unit of electromotive force, commonly called "voltage". It is also the unit for the related but slightly different quantity electric potential difference...
s with a
resistanceThe electrical resistance of an object is a measure of its opposition to the passage of a steady electric current. An object of uniform cross section will have a resistance proportional to its length and inversely proportional to its cross-sectional area, and proportional to the resistivity of the...
of several
ohmThe ohm is the SI unit of electrical impedance or, in the direct current case, electrical resistance, named after Georg Simon Ohm.- Definition :...
s where a porous pot is used. It saw extensive usage in
telegraphyTelegraphy is the long-distance transmission of written messages without physical transport of letters. It is a compound term formed from the Greek words tele = far and graphein = write. Radiotelegraphy or wireless telegraphy transmits messages using radio...
, signaling,
electric bellAn electric bell is a mechanical bell that functions by means of an electromagnet....
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 modern
dry cell-Dry Cell's formation:Part of the band formed in 1998 when guitarist Danny Hartwell and drummer Brandon Brown met at the Ratt Show on the Sunset Strip. They later met up with then-vocalist Judd Gruenbaum. The original name of the band was "Beyond Control"....
zinc-carbon batteryA zinc-carbon dry cell or battery is packaged in a zinc can that serves as both a container and negative terminal. It was developed from the wet Leclanché cell . The positive terminal is usually a carbon rod or graphite rod surrounded by a mixture of manganese dioxide and carbon powder . The...
.
Sources
- Practical Electricity by W. E. Ayrton and T. Mather, published by Cassell and Company, London, 1911, pp 188-193