1. LEAD
Lead was probably one of the first metals to be produced by man, being known since 3500 B.C., in agreement with archaeological discoveries done in Egypt. The oldest lead piece is in the British Museum and dates from 3800 A.D..
1.1 WHAT IS LEAD?
Lead is a metal. Its symbol is Pb and atomic number is 82. It is soft, malleable poor metal and also considered to be one of the heavy metals.
1.2History
Lead was probably one of the first metals to be produced by man, being known since 3500 B.C., in agreement with archaeological discoveries done in Egypt. The oldest lead piece is in the British Museum and dates from 3800 A.D..
The manner in which prehistoric people extracted lead from its minerals is not well-known. However, there are vestiges of very rudimentary furnaces, done of stone, where these people heated up the lead minerals with bonfires (that burned wood and coal) to extract the element. There is also evidence that the Chinese already produced metallic lead about 3000 B.C., and that Phoenicians had explorations close to deposits in Spain, in 2000 A.C.. In the 5th century B.C. the Romans made an extensive exploration of lead deposits in the whole Iberian Peninsula.
In the period 700 A.D. to 1000 A.D. the German mines of lead and silver, in the Rhine valley and in the Hartz mountains, were very important, just as those of Saxony, Silesia and Bohemia in the 13th century.
In the 17th century, the lead foundries flourished in Great-Britain, specially those located in Wales and Derbyshire.[1]
1.2 Characteristic
Lead has a bluish white colour when freshly cut but tarnishes to a dull greyish colour when exposed to air .It has a shiny chrome silver lustre when melted into a liquid.
1.3 OccurrenceLead is not very abundant, its relative rates being smaller than those of other metals as the aluminium, iron, magnesium, titanium, nickel, etc.. However, it is more abundant than cobalt, tin, cadmium or gold.
The more important lead minerals are galena (PbS), anglesite (PbSO4) and cerussite (PbCO3), respectively with 86%, 68% and 77% of lead. Other minerals that contain lead are linarite, pyromorphite, mimetite, vanadinite, crocoisoite and wulfenite.
The main deposits of lead minerals are located in the USA, Peru, Argentina, Bolivia, Australia, Zambia, South Africa, Germany, Spain, Sweden, Italy and Serbia.[1]
1.4 Uses
1.5 Biological Action
Generally, lead compounds are noxious for the animals. The effect of the absorption of the element in plants does not seem serious. However, this accumulate lead will be absorbed by the animals in case of ingestion. That is why lead compounds are not used in pesticides or insecticides.
Lead and its sulphide are incapable of absorption, and are considered practically innocuous. However, the soluble salts, such as the chloride, the nitrate, the acetate, etc. are very poisonous. The main intoxication cause with lead is the exposure to vapors and dusts of its compounds. The intoxication symptoms are intestinal mal-function, strong abdominal pains, diarrhea, appetite loss, nausea, vomiting and cramps
1.6 Properties of Lead:
¯Density of Lead =11.3437gm/cm3
¯ Melting Point=327.35OC
¯Boiling Point=1515oC
¯Bulk Modulus =0.44×106Mbar ¯ Heat conductivity=0.081cal/cm-s-OC
¯Specific Heat =0.03046 cal/g-k
¯ Heat of fusion =6.26cal/gm
¯Electrical resistivity =20.648µΩ-cm
¯Tensile strength =2000psi
¯Young's Modulus = 2.56×106psi
¯Crystalline Form is Face-centred cubic,
¯Electronic configuration = 6s26p2
With Lattice constant 0.4939nm
¯Lead exhibit the oxidation state of +2 corresponding to loss of the two p electrons, in most of its common compounds. In this oxidation Lead is generally Basic the oxidation state of +4 also occurs and in this oxidation state Lead is more acidic.
1.7 Forms of Lead
Forms of Lead exist in both organic and inorganic forms.
Inorganic lead
The lead found in old paint, soil, and various products described below is inorganic lead. Leaded gasoline exhaust contributed to ambient inorganic lead contamination. For this reason, the focus of this document is on inorganic lead.
Organic Lead
Leaded gasoline contained organic lead before it was burned; however, since the elimination of lead from gasoline in the U.S. starting in 1976, exposure to organic lead is generally limited to an occupational context. However, organic lead can be more toxic than inorganic lead because the body more readily absorbs it. Potential exposures to organic lead should be taken very seriously. [2a]
2. BATTERY
2.1 Introduction
Much energy is stored by nature in chemical compounds (combinations of elements). Coal, wood, and oil have tremendous stores of energy which are released as heat when these compounds are burned. Oxygen and hydrogen have so much energy that they explode when they combine. The electrician is interested in these - substances only because he can get some of this energy as emf. [3]
Releasing electrical energy from chemical energy is surprisingly simple. If two dissimilar metals i.e. copper and zinc, for example - are placed in certain chemical solutions, an emf results. This is the principle employed in all cells and batteries - a battery is simply two or more cells connected together.
2.2 History
The name "battery" was coined by Benjamin Franklin for an arrangement of multiple Leyden jars (an early type of capacitor) after a battery of cannon. Strictly, a battery is a collection of two or more cells, but in popular usage battery often refers to a single electrical cell.
An early form of electrochemical battery called the Baghdad battery may have been used in antiquity. However, the modern development of batteries started with the Voltaic pile, invented by the Italian physicist Alessandro Volta in 1800. [4]
2.3 Definition
A battery is a device for converting chemical energy into electrical energy. Batteries can consist of a single voltaic cell or a series of voltaic cells joined to each other. (In a voltaic cell, electrical energy is produced as the result of a chemical reaction between two different metals immersed in a solution, usually a liquid.) Batteries can be found everywhere in the world around us, from the giant batteries that provide electrical energy in spacecraft to the miniature batteries that power radios and penlights.
The correct use of the term battery is reserved for groups of two or more voltaic cells. The lead storage battery found in automobiles, for example, contains six voltaic cells. However, in common usage, a single cell is often referred to as a battery. For example, the common dry cell battery found in flashlights is really a single voltaic cell.
A rechargeable battery (Storage battery) is a group of one or more secondary cells. Rechargeable batteries use electrochemical reactions that are electrically reversible.
A group of reversible of rechargeable secondary cells acting as a unit is called secondary battery. Storage battery:-A voltaic battery that stores electric charge.
2.4 Types of batteries:
Batteries are divided into two general groups:
Primary batteries:
A primary battery is one designed to be used just once. When the battery has run down (produced all the energy it can), it is discarded.
Secondary batteries (or cells):
Secondary batteries, on the other hand, can be recharged and reused. Primary batteries are designed to be used until the voltage is too low to operate a given device and then discarded. Secondary batteries have many special design features, as well as particular materials for the electrodes that permit them to be reconstituted (recycled). After partial or complete discharge, they can be recharged by DC voltage and current to their original state. While this original state is usually not restored completely, the loss per cycle in commercial batteries is only a small fraction of 1 percent even under varied conditions.
2.5 Uses of Rechargeable Batteries:
They are used for applications such as:
¯Automobile starters
¯Portable consumer devices
¯Light vehicles
¯Uninterruptible power Supplies
¯Emerging Application in hybrid electric vehicles and electric vehicles are driving the technology to improve cost, reduce weight, and increase lifetime
3. LEAD STORAGE BATTERY
3.1 Discovery of Lead Storage Batteries:
Gaston Plante (1834-1889) discovered the lead -acid battery
Observation of Gaston Plante:
When he had allowed the current to pass for some time and then disconnected the battery, the Lead plates acted like a battery on their own.
The plate that had been connected to the positive pole of the battery is called Anode and was at a higher potential than the plate that had been connected to the negative pole of the battery, called Cathode. Now current flowed in the opposite direction. The Lead plate observed to collect a layer of a white substance, Lead sulphate, as this happened. When the current finally stopped the cycle could be repeated by reconnecting the power source. [7]
3.2 Working of lead storage battery
Inside a lead storage battery is a series of plates. Half of the plates are made of lead dioxide and the other half are made of a spongy form of lead. The plates are bathed in a solution of sulphuric acid which serves as an electrolyte (a chemical solution that conducts electricity). Two posts extend to the outside of the battery through sealed openings in the battery wall. One of the posts---the negative post---is connected to the lead plates, and the other---the positive post---to the lead dioxide plates.
Sulphuric acid, chemically, is composed of two hydrogen atoms, a sulphur atom and four oxygen atoms. Inside the battery, the sulphuric acid molecules are in solution with water and so are dissociated. This means that the sulphur atom with the four oxygen atoms attached to it are in the water, separated from the hydrogen atoms. The sulphur with the four oxygen atoms is called a sulphate ion and has a double negative charge. The free hydrogen atom is called a hydrogen ion and has a positive charge. (An ion is simply an atom or a molecule with a positive or negative charge.)
The battery performs its function through a series of chemical reactions involving these ions. In the condition described in the introductory paragraph, the battery is charged and has the capacity to supply an electric current through cables connected to the two posts. As the battery supplies electric current, the sulphuric acid reacts by giving up its sulphate ions to the lead and lead dioxide plates. This forms lead sulphate that deposits on the plates. While this process occurs, the sulphuric acid concentration is decreasing, and the battery is discharging.
Supplying an electric current to the battery rather than drawing it out---such as what happens in an automobile when the engine is running---reverses the chemical reaction and the battery recharges. When recharging, the lead and lead dioxide plates give up sulphate ions to the electrolyte solution. This restores the amount of sulphuric acid in the electrolyte solution and restores the lead and lead dioxide plates to their charged condition.
[A] Fig1.1 Working of Lead storage battery
3.3 Chemical Reaction:
During discharging:
At Anode:
Pb(s) + SO42-(aq) à PbSO4(s) + 2e-
At Cathode:
PbO2(s) + SO42-(aq) + 4H+(aq) +2e- à PbSO4(s) + 2H2O
Overall Reaction: Pb(s) +PbO2(s) + 4H+(aq) + 2SO42-(aq) à2PbSO4(s) + 2H2O
[9]During Recharging:
At Anode:
PbSO4(s) + 2e- à Pb(s) + SO42-(aq)
At Cathode:
PbSO4(s) + 2H2O à PbO2(s) + SO42-(aq) + 4H+(aq) +2e-
Overall Reaction: 2PbSO4(s) + 2H2O à Pb(s) +PbO2(s) + 4H+(aq) + 2SO42-(aq)
3.4 Shortcomings of Lead Storage batteries:
The following is a short summary of the main performance shortcomings, or “bottlenecks” of existing lead acid batteries.
3.5 Modification: For better output
3.6 New formula: Time for discharging a battery
Mr Peukert first devised a formula that showed numerically how discharging at higher rates actually removes more power from the battery than a simple calculation would show it to do. For instance discharging at 10 amps does not remove twice as much power as discharging at 5 amps. It removes slightly more. Therefore a 100 amp hour battery (at the 20hr rating) could provide 5 amps for 20 hours, but it could not provide 10 amps for 10 hours. The available time would actually be slightly less.
"Mr Peukert first devised a formula for....". This is because he is generally regarded as being the man who first discovered the phenomenon. This is incorrect. The effect had been known for many years beforehand and was first noted by a certain Mr Schroder several years before Peukert devised his formula. Mr Peukert simply quantified it in a way that had never been done before. However the effect is now known as Peukert's effect, the formula for calculating it is known as Peukert's equation, and the important number, unique to each battery type that is put into the equation in order to perform the calculation, is known as Peukert's exponent. Note that Peukert's exponent changes as the battery ages.
So Peukert's equation is: T = C/ (I/(C/R))n * (R/C)
Where: I = the discharge current
T = the time
C = capacity of the battery
n = Peukert's exponent for that particular battery type
R = the battery hour rating, i.e. 100 hour rating, 20 hour rating, 10 hour rating etc.
