Feb
28
2008
Arthur Ashe, the legendary Wimbledon player was dying of AIDS which he got due to infected blood he received during a heart surgery in 1983.
From world over, he received letters from his fans, one of which conveyed: “Why does GOD have to select you for such a bad disease”?
To this Arthur Ashe replied:
“The world over 50 million children start playing tennis, 5 million learn to play tennis,
500,000 learn professional tennis, 50,000 come to the circuit, 5000 reach the grand slam,
50 reach Wimbledon, 4 to semi final, 2 to the finals,
when I was holding a cup I never asked GOD ‘Why me?’.
And today in pain I should not be asking GOD ‘Why me?’ “
Feb
20
2008
Fact about Fat
Based on a paper published in British Medical Journal, results of a longitudinal study conducted in Finland indicate that obesity has worse heath consequences for men than for women. Nearly 8000 male and female Finns were observed for seven years and concluded that the obesity was “a significant predictor” of heart attacks among men, but “did not contribute significantly” to heart attacks among women. The season is that men carry their weight in the abdominal area, which may allow it to exert more bad effect on the liver, digestive system and heart.
So man, it’s time to run again?
Feb
20
2008
Electrolytes
An aqueous solution of pure sodium or potassium hydroxide is used as electrolyte in the system. For room temperature application, 20-25% sodium hydroxide solution is used, but 30-40% potassium hydroxide solution is preferred.
Separator
The separator material used in the secondary metal-air battery must be inert to oxidation by the evolving oxygen during charging process. It must have a fine porous capillary structure to hold the electrolyte in the pores and limit the oxygen gas cross diffusion, retard metal dendrite growth and shape change.
Feb
20
2008
Metal-Air Batteries
Generally metal-air cell system consists of a :
i. metal anode
ii. air-electrode
iii. electrolyte/separator
Metal-air cell are unique compared with other batteries in that one of the electroactive material (oxygen) does not require storage, oxygen comes from the air (through the air-electrode) making it an inexhaustible source and light cell.
Feb
20
2008
Metal Anodes
Zinc anode is the most attractive material for electrically rechargeable metal-air systems because of its relative stability in alkaline electrolytes and also because it is the most active metal that can be electrodeposited from an aqueous electrolyte solution. Other metals have also been investigated as electrode materials for metal-air batteries such as iron, aluminium, lithium, magnesium, cadmium, calcium, gallium and cobalt which have attractive energy density. Several materials under MH-air system have been used for anodes such as LaNi5-xMnx, MmNi3.6Co0.7Al0.6Mn0.1, La0.8Ce0.2Ni4.25Co0.5Sn0.25, SrTiO3-LaNi3.76Al1.24Hn, MmNi3.6Co0.7Al0.3Mn0.4 and MmNi3.5Co0.7Al0.7Mn0.1.
Feb
20
2008
Air-electrode
The function of the air-electrode (also called air-cathode or oxygen-electrode) is to permit atmospheric oxygen and react electrochemically at an electrocatalytic site. The commercial air-electrode is designed to maximize the catalyst area for the electrochemical reactions and to maintain the electrolyte within the cell. It consists of two active layers bonded to each side of a nickel mesh (as current collector). The active layers consist of a mixture of catalyst on carbon fibers with a hydrophobic Teflon binder. The white Teflon layer is porous to air, but not water to maintain the electrolyte within the cell.
Fig. 1: Laminated air-cathode layers
Fig. 2: Carbon Fiber Substrate
Successful operations of metal-air batteries depend on an effective air-electrode. Early studies of air-electrodes found interest in fuel cells. The air-electrode must have important properties such as:
a. High resistance to chemical corrosion and electrochemical oxidation and/or reduction (stable in alkaline solution).
b. Good electrical conductivity to minimize the internal resistance of the battery.
c. Porosity for air permeation and non-wettability to prevent water permeation.
d. Electrocatalysts, in addition, must exhibit high bifunctional electrocatalytic activity (O2 evolution and reduction).
A major breakthrough in air-electrodes was the development of various alternatives as a replacement for expensive platinum. Air-electrode catalysts material can be divided into two types:
a. Monofunctional – air-electrode only reduces O2 during cell discharge.
b. Bifunctional – air-electrode can reduce O2 during cell discharge and evolves O2 during cell charge.
The main problem of air-cathode is its stability and efficiency during charging. Monofunctional air-cathode easily oxidizes or degrades during charging. Therefore it cannot be used for the next discharge process. The battery is of the primary type. Batteries utilizing bifunctional air-cathode are rechargeable.
Monofunctional catalyst materials based on carbon black and MnO2 show some promising success due to its high catalytic activity for oxygen reduction and its low cost. Other materials that have been used are platinum or carbon support platinum, carbon support silver, spinel-type oxides, non-metallic materials such as metal oxides and metal phthalocyanines. Catalytic materials currently used in bifunctional air-electrodes are Ag, mixed oxides, noble metals and perovskite-type oxides. Researchers have developed a low cost perovskite-type oxide catalyst, which shows potential application in bifunctional air-electrode. The perovskite-type oxides La0.6Ca0.4CoO3 composition has gained much attention.
Jan
25
2008
Li-ion battery has been widely applied to portable electronic devices, such as handphone, cameras, camcorders, laptops etc, due to its relative high energy density and power compared with other batteries. The most popular electrolyte used in the Li-ion battery by manufacturers and researchers is LiPF6 salt dissolved in a binary or ternary solvent mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).
