The repeating unit in silicon (IV) oxide is tetrahedral ‘SiO4’ unit. The ration of silicon to oxygen in the giant structure is 1:2. Hence, the empirical formula is ‘SiO2. The giant structure is responsible for the high melting point and hardness of silicon (IV) oxide. When heated to about 870 0C, quartz passes into another crystalline form called tridynamite. At about 1740 0C a further change occurs, into cristobalite. The relationships between the three forms are as shown below:
Quartz → tridynamite → cristobalite
Silicon (IV) oxide is completely molten at about 1710 0C. However, the melting point is not sharp; liquefaction begins at around 16000C. when molten silica is cooled, the liquid forms a glassy solid that has extremely low coefficient of expansion. Vessels made from fused quartz can be put into cold water while still red-hot, without breaking. 2
Chemical properties of Silicon (IV) Oxide
Silicon (IV) oxide is chemically inert. It is attacked only by hydrofluoric acid and concentrated alkali. Silicon (IV) oxide dissolves in concentrated hydrofluoric acid to form the water soluble hexaflurosilicate (IV) complex.
SiO2 (s) + 6HF (aq) → 2H+ (aq) + [SiF6]2- (aq) + 2H2O (l)
APPLICATION
(silica) used in the manufacture of all silicones. This is what remains when one burns silicone; burning silicone caulking or foam produces silica (as well as char) as a white powder–silica fume.
Silicon is a very useful element that is vital to many human industries. Silicon is used frequently in manufacturing computer chips and related hardware.
Silicon and
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The largest application of pure silicon (metallurgical grade silicon) is in - silicon alloys, often called "light alloys", to produce parts, mainly for automotive industry (this represents about 55% of the world consumption of pure silicon).
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The second largest application of pure silicon is as a raw material in the production of (about 40% of the world consumption of silicon)
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Pure silicon is also used to produce ultra-pure silicon for electronic and applications :
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- Ultrapure silicon can be with other elements to adjust its electrical response by controlling the number and charge ( or ) of current carriers. Such control is necessary for , , and other which are used in electronics and other high-tech applications.
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- Silicon can be used as a continuous wave to produce coherent light (though it is ineffective as a light source).
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and - is widely used in the production of low-cost, in applications such as LCDs. It has also shown promise for large-area, low-cost thin-film solar cells.
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and - Silicon is an important constituent of some steels, and it is used in the production process of cast iron. It is introduced as ferro-silicon or silico-calcium .
Silicon compounds
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: or in the form of and is an important ingredient of and and is also used to produce .
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Pottery/ - It is a refractory material used in high-temperature material production and its silicates are used in making enamels and pottery.
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Glass - Silica from sand is a principal component of glass. Glass can be made into a great variety of shapes and with a many different physical properties. Silica is used as a base material to make window glass, containers, insulators, and many other useful objects.
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- is one of the most important abrasives.
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Medical materials - are flexible compounds containing silicon- and silicon- bonds; they are widely used in applications such as artificial and contact lenses. Silicones are also used in many other applications.
was originally made by adding to . Now name-brand Silly Putty also contains significant amounts of elemental silicon (silicon binds to the silicone and allows the material to bounce 20% higher). 8
GLASS
When silica is heated it melts at around 1710 0c to viscous liquid. When the liquid is allowed to cool, silicate glass(or quartz glass formed). Quartz glass are transparent to infra-red and ultra-violet radiation. They are inert except hydrofluoric acid and concentrated alkalis. Other substances are often added to quartz to produce glass with specific properties.
The glass used for window panes, bottles and dishes is known as soda-lime glass. The main components are silica, sodium oxide and calcium oxide.
Potash glass or hard glass is made as above but using potassium carbonate instead of sodium carbonate. It is harder and is used in making combustion tubes and similar uses.
If calcium oxide is replaced by lead (II) oxide, a glass of high density and refractive index is formed. This is flint glass or lead glass where is used in making lenses and other optical devices. However it is soft, and easily scratched.
Borosilicate glass is obtained when a little boron oxide is added to the soda glass. It is used to make test tubes, flasks and other laboratory glassware’s because it is resistant to sudden change in temperature and chemical action.
Aluminosilicate glass contains boron (III) oxide, B2O3 in place of sodium oxide, mixed with magnesium oxide and aluminium oxide. It can withstand extreme temperature. It is used to make cooking utensils.
Fiber glass is produced by dropping molten glass onto refractory rotating disc where the glass flies off the disc forming the fibres. Fiber glass is used to make car panels, aircraft components and body of boats.
Coloured glass is produced by introducing various metallic oxides into the oxides.
e.g: copper (I) oxide for ruby glass, cobalt (II) oxide for blue glass, iron (II) oxide for green glass10
.Application in Medical Field
Menstrual cups
A is a type of cup or barrier worn inside the vagina during menstruation to collect menstrual fluid. Menstrual cups are often made of silicone for its durability and reusability 9
Silicone breast implants
Controversy developed in the 1980s and 1990s around claims that the silicone gel in was responsible for a number of systemic health problems, including and cancer. Multiple lawsuits claiming injury from implants resulted in the 1998 of and a moratorium on the use of silicone implants for breast augmentation in the US and Canada pending study. However, multiple studies and expert review panels performed worldwide since then have consistantly concluded that women with silicone breast implants are no more likely to develop systemic illness than women without breast implants. In 2006 both and the US adopted positions similar to other countries in permitting the use of silicone implants for cosmetic breast augmentation in their respective countries 9
Optical devices
lead (II) oxide, a glass of high density and refractive index is formed. This is flint glass or lead glass where is used in making lenses and other optical devices. However it is soft, and easily scratched. 10
Lab Apparatus
Borosilicate glass is obtained when a little boron oxide is added to the soda glass. It is used to make test tubes, flasks and other laboratory glassware’s because it is resistant to sudden change in temperature and chemical action10
Silicon Rubber
Classes of Silicone Rubbers
According to ASTM D1418 there are various classes of silicone rubbers outlined in table below:
11
Examples of medical applications include 11 :
- Tubing for dialysis and transfusion equipment
- Bellows for artificial respirators
- Catheters
- Dummies for babies .
Using silicon chemistry in a way that had not been previously explored produced a high-molecular-weight, thermoplastic silicone poly(amide) copolymer that has value in a variety of products, such as:
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Antiperspirant and deodorant sticks, gels, and roll-on products
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Skin care lotions and creams
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Lip products
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Hair care products
This copolymer has a unique feel, which is “harder” than most product solutions and yields products with enhanced “glide.” It also has the capability to form solid products with significant strength when compared with other siloxanes – and even with many organic structurants. It has also been found that this material’s structuring properties add sensory benefits to existing formulations when used at the additive level12
Silicon bandgap temperature sensor
The silicon bandgap temperature sensor is an extremely common form of temperature sensor () used in electronic equipment. Its main advantage is that it can be included in a silicon at very low cost. The principle of the sensor is that the forward voltage of a is temperature-dependent.
An electronic circuit, such as the , that measures ΔVBE can therefore be used to calculate the temperature of the diode. The result remains valid up to about 200 °C to 250 °C, when leakage currents become large enough to corrupt the measurement. Above these temperatures, materials such as can be used instead of silicon. 13
1) Slim-line silicon speeds up protein separation
Tough, ultra-slim silicon membranes could drastically improve the performance of lab-on-a-chip micro-analytical systems, kidney dialysis machines and, in the future, even produce an artificial kidney, claim researchers.
Christopher Striemer, Philippe Fauchet and colleagues at Rochester University New York, US, fashioned the new 15 nm-thick porous nanocrystalline silicon (pnc-Si) membranes using standard semiconductor micro-fabrication techniques.
Compared with commercial ultrafiltration and dialysis membranes, the new silicon films speed up protein separation by at least an order of magnitude.
The secret is fine tuning the size of miniscule pores produced as silicon crystallises during the manufacturing process. 'We discovered it by chance while looking at how thin films of amorphous silicon crystallise when sandwiched between silicon dioxide layers.' Striemer told Chemistry World. 'You need to control the silicon crystallisation temperature.'
The pores, averaging from 9 to 30 nm in diameter, are formed during rapid thermal annealing from spontaneously-produced voids as silicon nanocrystals nucleate and grow in the 15 nm thick amorphous films. The voids span the whole thickness of the membrane, producing the pores. The pnc-Si thin films are surprisingly tough, able to withstand around an atmosphere of pressure without plastic deformation or cracking.
The new membranes rapidly and efficiently separate proteins from small molecules, different sized proteins under physiological conditions, and can separate similar sized molecules carrying different electrical charges. To demonstrate, the Rochester team chose two common blood proteins with slightly different molecular weights and sizes - bovine serum albumin (BSA) and immunoglobulin-gamma (IgG) - each fluorescently labelled with different dyes. Using real-time fluorescence microscopy, the researchers monitored their passage through two separate membranes with different average pore diameters.
Compared to the hours-long separation times required by commercial dialysis membranes, the smaller pore-diameter silicon membrane completely separated BSA protein from much smaller free dye molecules in little over 6.5 minutes. In the same time, the larger-pore membrane achieved a greater than fourfold separation of the BSA and IgG proteins. Once they thoroughly optimise membrane pore diameters, however, the Rochester team expect to produce even better membranes that selectively exclude IgG, but allow the passage of BSA. Also, by modifying the electrical charge on the membranes' surfaces, the team selectively blocked dye molecules carrying similar charges.
The new membranes have many potential applications. 'Standard separation techniques are not easy to miniaturise, making protein purification, for example, difficult for today's lab-on-a-chip systems,' said Striemer. 'Our pnc-Si membranes could be directly inserted into such micro-fluidic systems, making separation steps potentially simple and highly efficient.'
But the new membranes could have far-reaching bio-medical applications. Given their efficiency, Striemer predicts pnc-Si membranes could greatly simplify dialysis systems, and even lead to better patient outcomes.
And an artificial kidney? 'Practically impossible, using commercial polymer dialysis membranes' said Striemer. 'But our material might prove useful here. Our primary concern with artificial organs is the issue of long-term bio-stability for our 15 nm thick material. We just don't know, and regulatory hurdles in the US would make this very difficult. But in principle, why not?”14
2) Reshapes Ultrasonic Sensing
New silicon-based ultrasonic sensors stand ready to join silicon pressure sensors and accelerometers as popular and cost-effective microelectromechanical system (MEMS) sensors.
These new devices bring revolutionary improvements in cost and performance and represent a major advance in ultrasonic sensor technology.
The new sensors benefit from the economies of scale found in semiconductor manufacturing and are well suited for high-volume applications that demand high-performance sensors at low costs. The sensors also offer a high degree of reliability and consistent performance found in other MEMS sensors.
Operating Principles
Like MEMS pressure sensors and accelero-meters, silicon ultrasonic sensors use a
suspended membrane. From a conceptual standpoint, the sensors resemble thousands of tiny drums on the surface of a silicon chip, where each is only as large as the width of a human hair (see Photo 1). The drum structure consists of a thin nitride membrane and aluminum electrode suspended over a cavity. Nitride sidewalls support the membrane above the silicon substrate that forms the bottom electrode (see Figure 1).
The drums are capacitive structures that operate under an applied electrostatic field. A DC bias voltage applied across the top and bottom electrodes establishes an electric field that creates tension in the nitride membrane. An AC signal voltage applied across the membrane varies the tension and causes it to vibrate and emit ultrasonic waves. Conversely, during reception of ultrasound, an acoustic wave impinges on the top electrode membrane and causes the membrane to move. The movement alters the capacitance of the sensor and creates an output current. For air or gas applications, the sensor operates in a resonant mode to maximize its sensitivity. However, in immersion or water applications, the sensors are designed to be nonresonant for optimal pulse-echo signal quality and broadband frequency response.
Immersion Sensor Advantages
For immersion applications--those applications in which the sensor launches sound into a liquid or gel--silicon sensors offer excellent performance. This type of sensor has substantially improved broadband response and better insertion loss than piezoelectric ultrasonic sensors. These advantages offer the potential for significantly improved signal and image quality for medical and industrial applications.
Trends for the Future
Future generations of silicon sensors will add system features on the chip to reduce the cost and complexity of ultrasonic systems. New devices with multiple-element sensor arrays have the potential of bringing major advances to NDT and medical imaging applications (e.g., 3D ultrasonic imaging of the human body).
More specifically, integrated electronics may add onchip transmit-and-receive circuitry to simplify board-level system design and to reduce system costs. The basic silicon ultrasonic sensor chip could then evolve into a low-cost, generic ultrasonic transceiver with supporting electronics.
The emergence of 1D and 2D sensor arrays will have a significant impact on ultrasonic imaging applications. With multiple-element arrays, electronic beam steering or focusing is possible, as is off-axis beam radiation. This is particularly relevant for new ultrasound imaging systems for 3D medical imaging, where an ultrasonic beam is scanned across the body to generate a 3D image. Other ultrasonic systems could dynamically monitor the changing position of a target or adapt ultrasonic flowmeters to changing gas flow rates15.
3) Silicon Sensing Systems
Health effects of silicon
Silicon concentrates in no particular organ of the body but is found mainly in in connective tissues and skin. Silicon is non-toxic as the element and in all its natural forms, nameli silica and silicates, which are the most abundant.
Elemental silicon is an inert material, which appears to lack the property of causing fibrosis in lung tissue. However, slight pulmonary lesions have been reported in laboratory animals from intratracheal injections of silicon dust. Silicon dust has little adverse affect on lungs and does not appear to produce significant organic disease or toxic effects when exposures are kept beneath exposure limits. Silicon may cause chronic respiratory effects. Crystalline silica (silicon dioxide) is a potent respiratory hazard. However, the likelihood of crystalline silica generation during normal processing is very remote. LD50 (oral)- 3160 mg/kg. (LD50: Lethal dose 50. Single dose of a substance that causes the death of 50% of an animal population from exposure to the substance by any route other than inhalation. Usually expressed as milligrams or grams of material per kilogram of animal weight.)
Silicon crystalline irritates the skin and eyes on contact. Inhalation will cause irritation to the lungs and mucus membrane. Irritation to the eyes will cause watering and redness. Reddening, scaling, and itching are characteristics of skin inflammation.
Lung cancer is associated with occupational exposures to crystalline silica specifically quartz and cristobalite. An exposure-response relationship has been reported in studies of miners, diatomaceous earth workers, granite workers, pottery workers, refractory brick workers, and other workers
Several epidemiological studies have reported statistically significant numbers of excess deaths or cases of immunologic disorders and autoimmune diseases in silica-exposed workers. These diseases and disorders include , rheumatoid arthritis, systemic lupus erythematosus, and .
Recent epidemiological studies have reported statistically significant associations of occupational exposure to with renal diseases and subclinical renal changes
Crystalline silica may affect the immune system, leading to mycobacterial infections (tuberculous and nontuberculous) or fungal, especially in workers with silicosis
Occupational exposure to breathable crystalline silica is associated with bronchitis, chronic obstructive pulmonary disease (COPD) and emphysema. Some epidemiologic studies suggest that these health effects may be less frequent or absent in nonsmokers.17
Silicon
Silicon is the most abundant electropositive element in The Earth’s crust. It’s a metalloid with a marked metallic luster and very brittle. It is usually tetravalent in its compounds, although sometimes its bivalent, and it’s purely electropositive in its chemical behaviour. Moreover, pentacoordinated and hexacoordinated silicon compounds are also known.
Silicon is the principal component of glass, cement, ceramics, most semiconductor devices, and silicones, the latter a plastic substance often confused with silicon. Silicon is also an important constituent of some steels and a major ingredient in bricks. It is a refractory material used in making enamels and pottery.
Elemental raw silicon and its intermetallic compounds are used as alloy integrals to provide more resistance to the , , and other metals. Metallurgic silicon with 98-99% purity is used as raw material in the manufacture of organosilicic and silicon resins, seals and oils. Silicon chips are used in integrated circuits. Photovoltaic cells for direct conversion of solar energy use thin cut slices of simple silicon crystals of electronic grade. Silicon dioxide is used as raw material to produce elemental silicon and silicon carbide. Big silicon crystals are used for piezoelectric glasses. Melted quartz sands are transformed in silicon glasses which are used in laboratories and chemical plants, as well as in electric insulators. A colloidal dispersion of silicon in water is used as a coating agent and as ingredient for certain enamels.18
Major advances in biotechnology are converging with information technologies to create new opportunities in the emerging fields of bioinformatics, biomaterials, and biochips. The commercialization of nanotechnology holds the potential to revolutionize chip and computer manufacturing while creating a new foundation for further developments in information and biotechnology.
At the same time, nanotechnologies are being recognized as a foundation for both advances in bio and info technologies. Nanotechnology refers to the manipulation of matter at the atomic and molecular scale (where the objects are 0.1 to 100 nanometers in size, hence the term). Nanotechnology is a multi-disciplinary field that borrows from physics, engineering, molecular biology, and chemistry. It has been pursued very actively in university, government and commercial laboratories worldwide for more than 15 years and yielded a set of building block materials, tools, and techniques that are being applied in a variety of industries including bioscience (as tools for drug discovery and delivery), information technologies (as a next generation to microprocessors and self-assembly) and materials (as new carbon fibers and high performance composites).
However every advancement or discovery has its own pro and contra. It’s the responsibility of us, human to ensure the best practice to apply the knowledge of silicon based in human daily life by measuring the advantages and disadvantages.
Silicon Medicines May Be Effective In Humans
— As carbon-based life forms, humans and other animals, invariably, are treated for disease with the help of carbon-based medicines.
But now, in a promising new study, scientists have shown that silicon - the stuff of computer chips, glass and pottery - may have extraordinary therapeutic value for treating human disease.
"All medicines are carbon-based - like we are," says Robert West, a University of Wisconsin-Madison chemist and one of the world's leading authorities on silicon chemistry. "There are about 50,000 biologically active molecules, and they're all mainly carbon-based."
But now, West and his colleagues report in the January edition of the journal Silicon Chemistry that the effectiveness and safety of an important anti-inflammatory and anti-cancer drug were enhanced remarkably by replacing one of the molecule's carbon atoms with a silicon atom.
The drug, indomethacin, is used to treat arthritis and some cancers, but the drug is little used because it is quite toxic.
"Our thought was, maybe we could tame it," says West, a UW-Madison professor of chemistry.
The idea, according to West and colleague Galina Bikzhanova, was to make a simple chemical change to see if the biological properties of the drug could be modified to be safer and more effective. By trading one of the drug's carbon atoms for a silicon atom and exposing the modified agent to cancer cells in culture, West's group found that the molecule's effectiveness was enhanced and its toxicity greatly reduced.
Indomethacin is an anti-inflammatory drug belonging to a family of compounds known as COX inhibitors. COX inhibitors selectively block an enzyme that causes pain and swelling.
"Our molecule is a COX-2 inhibitor like Tylenol and Vioxx and other such drugs," notes West.
How the drug and other COX inhibitors work against cancer is not well understood, but they clearly demonstrate anti-cancer properties, according to West. The modified molecule with the silicon atom was exposed to several types of cancer cells in culture in the new study. The agent had significant effects on skin and prostate cancer cells, but showed the greatest efficacy against pancreatic cancer cells.
"The results are very promising, especially in using our compound in combination with standard anticancer drugs," says West, who conducted the study in collaboration with Bikzhanova, Irina Toulokhonova of UW-Madison and Stephen Gately of RND Pharmaceuticals in Scottsdale, Ariz.
Tested on cancer cells in cultures, the modified drug both slowed the growth of cancer cells and killed cancer cells directly. The high activity was against pancreatic cancer cells. This is important because pancreatic cancer responds poorly to any therapy and is almost always fatal because it is hard to detect and spreads rapidly.
Perhaps just as important, the silicon-modified molecule exhibited far less toxicity than the all-carbon-based form of the drug.
"We tested for toxicity and it is well tolerated," West explains. "That's really different than indomethacin and the other indomethacin derivatives that have been made."
West and his colleagues made four variants of the drug, each with a slightly different chemical structure but all containing the silicon atom.
Why does silicon have this effect?
"It changes the property of the molecule, but not drastically," the Wisconsin chemist explains.
"It's fine tuning," says Bikzhanova. "We don't know why, but it led to this unexpectedly strong effect against cancer cells."
Note: This story has been adapted from a news release issued by University of Wisconsin-Madison.
New Battery Technology Helps Stimulate Nerves
— MADISON -- With the help of new silicon-based compounds, scientists --and patients -- are getting a significant new charge out of the tinylithium batteries used in implantable devices to help treat nervous system and other disorders.
New lithium battery technology developed by UW-Madison emeritus professor of chemistry Robert West powers this tiny microstimulator, a device that effectively jump-starts broken nerve connections in conditions like Parkinson's, epilepsy and incontinence. The device was developed by a consortium including UW-Madison's Organosilicon Research Center, Argonne National Laboratory, Advanced Bionics Corp., the Alfred Mann Foundation and Quallion, LLC. It was recognized earlier in 2005 with an "R&D 100 Award" from R&D magazine. (Photo courtesy of Argonne National Laboratory)
The lithium battery is the workhorse in implantable devices --stimulators used to jump start the heart and help the central nervoussystem make critical connections in, for example, Parkinson's andepilepsy patients. Designed to be extraordinarily reliable and workcontinuously for years, the tiny batteries that power implantables areindispensable in everything from pacemakers to the electronicstimulators that help restore function in the brains of Parkinson'spatients.
But lithium batteries don't last forever and new surgery to maintainmany devices seeded into the body is required, as it is to replacebatteries and devices at the end of their lives. Moreover, a newgeneration of tiny electrical devices to stimulate the nervous system,treat incontinence and overcome muscular impairment is coming on lineas scientists and engineers continue to shrink the components that makeup the devices.
Central to that ability, according to University ofWisconsin-Madison Professor Emeritus of chemistry Robert West, is newlithium battery technology, technology capable of making batteriessmaller, last longer and, soon, accept a charge from outside the bodywithout the need for surgery.
Using organosilicon compounds, West and his UW-Madison colleagues havedeveloped a new generation of rechargeable lithium ion batteries whoselifetimes are more than twice as long as the batteries now used in thetiny medical devices.
"It turns out the organosilicon compounds are really good for improvinglithium battery technology," says West, whose new battery technologypowers a "microstimulater" not much larger than a pencil lead and thatcan be injected near target nerves to help overcome the faulty nervoussystem wiring at the heart of Parkinson's, epilepsy and incontinence.
"The idea is that whenever you have a broken nerve connection, you cansupply the electrical impulse to complete the circuit," West explains.
The microstimulator was developed by a consortium includingUW-Madison's Organosilicon Research Center, Argonne NationalLaboratory, Advanced Bionics Corp., the Alfred Mann Foundation andQuallion, LLC. The device was recognized earlier this year with an"R&D 100 Award" from R&D Magazine.
West's group developed the electrolyte, theelectricity-conducting liquid that is the heart of the battery. The neworganosilicon compounds developed by the Wisconsin chemists, says West,have numerous advantages over traditional lithium battery chemistry.
"They're very flexible. They don't solidify. They're stable,nonflammable, non-toxic and they pose no threat to the environment,"says West, an international authority on silicon chemistry. Silicon,the stuff computer chips are made of, is one of the Earth's mostabundant elements. Organosilicons are compounds composed of silicon andother natural materials.
In the context of the lithium battery, West's group has beenmaking and testing "designer silicons" that are specially formulated toconduct electricity in a very compact environment. In the lithiumbattery, charge is maintained as lithium ions flow between thebattery's positive and negative electrodes.
"The battery requires something the ions can go through easily. We hadto tweak the (organosilicon) molecules to get higher conductivity andstability," says West.
A critical advantage of the new battery technology is lifespan: "Ifyou're going to implant these things, you want a (battery) lifetime ofat least 10 years," says West, whose organosilicon batteries areprojected to power the tiny implantable devices for more than 12 years.
In addition to implantable devices for medicine, lithium batteries are used in scores of applications, from spacecraft to iPods.
Patented through the Wisconsin Alumni Research Foundation, the neworganosilicon compound technology is also being developed through a newstart-up company, Polyron, Inc. The work to develop the neworganosilicon compounds was funded by the National Institute ofStandards and Technology, a federal technology agency that works withindustry to develop and apply technology, measurements and standards.
Note: This story has been adapted from a news release issued by University of Wisconsin-Madison.
REFERENCES
1.http://web1.caryacademy.org/chemistry/rushin/StudentProjects/ElementWebSites/silicon/history.htm
2. INORGANIC CHEMISTRY , Text for Pre-U by LIM YOU SIE
3.
4.
5.
6.
7.
8.
9.
10. INORGANIC CHEMISTRY BOOK , Text for Pre-U, STPM by LIM YOU SIE Longman, Pearson Malaysia SDN BHD.
11.
12.
13."
14.
15.
16.http://www.sensorsmag.com/sensors/product/productDetail.jsp?id=355266&searchString=silicon
17.
18.