Static Electricity - 6

Simple static electricity experiments
Note: a humid atmosphere provides a conducting path for the rapid neutralization of static charge; hence the following examples work best in dry, winter conditions.

Static electricity is notable as a physical phenomenon that can be demonstrated using simple experiments that can convey genuine understanding of the physics involved.

Charged adhesive tape

Repulsion between lengths of tape with like charges.

Attraction between lengths of tape with opposite charges.

A simple and illuminating example of the effects of static electricity can be observed using adhesive tape (such as Scotch tape, on the negative side of the triboelectric series, hence tends to gain electrons and acquire negative charge) charged by peeling.

If a length of tape adhered to a smooth surface is rapidly peeled off, the tape will acquire an excess negative charge (generally polypropylene with an acrylic adhesive). Do this with two lengths of tape and they will repel each other, demonstrating the fact that like charges repel. Each individual length of tape will experience a small attraction to almost any object as the presence of the excess negative charge induces a charge separation in nearby objects. Negative charges are pushed farther away, while positive charges are attracted, and the strength of the attractive and repulsive forces falls off quite rapidly with distance. This effect is most pronounced in materials such as metals, that conduct electricity, as the negative charges are free to move within the material.

Finally, try attaching two lengths of tape together, exhaling on them along the entire length to neutralize the charge, then rapidly pulling them apart. There will be some imbalance in the distribution of negative charge between the two pieces such that one is more positive and the other more negative; you should now find that the two lengths of tape attract each other, demonstrating the fact that opposite charges attract. Attaching the adhesive side of one length of tape to the non-adhesive side of the other reduces the chance of tearing and increases the charge imbalance, and hence the strength of the attractive force.

Static electricity in fiction
In the 1963 British science-fiction television serial "Doctor Who", an alien creature encased in metal called a Dalek was powered by static electricity. In Atlas Shrugged, a novel by Ayn Rand, the principal character John Galt develops a perpetually running motor powered by static electricity but it most likely would have to be recharged every 30 minutes.


References:

1. http://en.wikipedia.org
2. "Franklin's Kite". http://www.mos.org/sln/toe/kite.html. Retrieved on 2008-02-19.
3. Krider, E. Philip (January 2006). "Benjamin Franklin and Lightning Rods". Physics Today. http://www.physicstoday.org/vol-59/iss-1/p42.html. Retrieved on 2008-04-06.
4. J. J. Lowke (1992). "Theory of electrical breakdown in air". Journal of Physics D: Applied Physics 25: 202–210. doi:10.1088/0022-3727/25/2/012. http://www.iop.org/EJ/article/0022-3727/25/2/012/jd920212.pdf?request-id=XIfZw4zI3BGDoxCz2wi7Kg.
5. Kassebaum, J. H. and Kocken, R. A. (1995). "Controlling Static Electricity in Hazardous (Classified) Locations". Petroleum and Chemical Industry 42nd Annual Conference Papers: 105–113. http://ieeexplore.ieee.org/iel3/4013/11530/00523945.pdf?tp=&arnumber=523945&isnumber=11530.
6. Wagner, John P.; Clavijo, Fernando Rangel [doi:10.1016/S0304-3886(00)00019-X Electrostatic charge generation during impeller mixing of used transformer oil] Department of Nuclear Engineering, Safety Engineering and Industrial Hygiene Program, Texas A&M University, College Station, online 21 August 2000; accessed Jan 2009
7. Hearn, Graham (1998). "Static electricity: concern in the pharmaceutical industry?". Pharmaceutical Science & Technology Today 1 (7): 286–287. doi:10.1016/S1461-5347(98)00078-9.
8. Egorov, V.N. Electrification of petroleum fuels Khimiya i Tekhnologiya Topliv i Masel, No. 4, pp. 20–25, April, 1970 accessed Dec 2008
9. Chevron Corporation Aviation Fuels Technical Review 2006, accessed Dec 2008
10. Hearn, Graham Static electricity - guidance for Plant Engineers - Wolfson Electrostatics University of Southampton 2002; accessed Dec 2008
11. Kinzing, G.E., 'Electrostatic Effects in Pneumatic Transport: Assessment, Magnitudes and Future Direction', Journal Pipelines, 4, 95-102, 1984
12. "Snopes.com: Fuelish Pleasures". http://www.snopes.com/autos/hazards/gasvapor.asp. Retrieved on 2008-04-19.
13. "NASA - Crackling Planets". http://science.nasa.gov/headlines/y2005/10aug_crackling.htm. Retrieved on 2008-01-20.
14. "Kids science projects". http://www.creativekidsathome.com/science/staticelectricity.html. Retrieved on 2008-01-20.
15. H. Yasuro, H. Makoto and I. Isao (2007). "Charging of Adhesive Tapes on Peeling". Journal of the Adhesion Society of Japan 43 (3): 97–103. http://sciencelinks.jp/j-east/article/200706/000020070607A0223458.php.
16. "3M Material Safety Data Sheet". http://multimedia.mmm.com/mws/mediawebserver?BBBBBBXeXgc1ZGXFEqZswKKgRmpBWHcbKGcByi5--. Retrieved on 2008-01-20.

Static Electricity - 5

Fueling Operations
The flowing movement of flammable liquids like gasoline inside a pipe can build up static electricity. Non-polar liquids such as paraffin, gasoline, toluene, xylene, diesel, kerosene and light crude oils exhibit significant ability for charge accumulation and charge retention during high velocity flow. Static electricity can discharge into a fuel vapor. When the electrostatic discharge energy is high enough, it can ignite a fuel vapor and air mixture. Different fuels have different flammable limits and require different levels of electrostatic discharge energy to ignite.

Electrostatic discharge while fueling with gasoline is a present danger at gas stations. Fires have also been started at airports while refueling aircraft with kerosene. New grounding technologies, the use of conducting materials, and the addition of anti-static additives help to prevent or safely dissipate the build up of static electricity. The flowing movement of gases in pipes alone creates little, if any, static electricity. It is envisaged that a charge generation mechanism will only occur when solid particles or liquid droplets are carried in the gas stream.

Mobile Phones and Gasoline Pumps
Although there have been numerous media reports and posted warnings at gasoline pumps about the risk of fire caused by mobile phones, there has not been a confirmed case of an electrical discharge from a mobile phone ever causing a fire or explosion among gasoline fumes. To date, it is simply an urban legend. This legend was further investigated on an episode of Mythbusters (and also on Brainiac), where the protagonists tried to ignite gasoline using a cell phone. The show showed educational and very shocking footage of how most gas pump fires start. In almost all cases, the fire is caused by the person pumping the gas re-entering the car after the fuel has begun to fill the tank, and then step out to take the pump nozzle out. When they grab the pump nozzle, the static discharge occurs from the built up of static electricity on the person, usually from friction that occurred inside the car between the carpet or seat and said person. This discharge can cause the ignition of the highly explosive gasoline vapor by the gas tank opening. This possible fire scenario has led many gas stations to remove the automatic locking mechanism on the gas pump nozzles that were designed to make it easier to fill up an empty tank, as this mechanism also allows a person to step away from the automobile during filling.

Static Discharge in Space Exploration
Due to the extremely low humidity in extraterrestrial environments, very large static charges can accumulate; causing a major hazard for the complex electronics used in space exploration vehicles. Static electricity is thought to be a particular hazard for astronauts on planned missions to the Moon and Mars. Walking over the extremely dry terrain could cause them to accumulate a significant amount of charge; reaching out to open the airlock on their return could cause a large static discharge, potentially damaging sensitive electronics.

Ozone cracking
A static discharge in the presence of air or oxygen can create ozone. Ozone can attack rubber parts. Many elastomers are sensitive to ozone cracking. Exposure to ozone creates deep penetrative cracks in critical components like gaskets and O-rings. Fuel lines are also susceptible to the problem unless preventative action is taken. Preventative measures include adding anti-ozonants to the rubber mix, or using an ozone-resistant elastomer. Fires from cracked fuel lines have been a problem on vehicles, especially in the engine compartments where ozone can be produced by electrical equipment.

Applications of Static Electricity
Static electricity is commonly used in xerography, air filters (particularly electrostatic precipitators), automotive paints, photocopiers, paint sprayers, theaters, flooring in operating theaters, powder testing, printers, and aircraft refueling.


References:

1. http://en.wikipedia.org
2. "Franklin's Kite". http://www.mos.org/sln/toe/kite.html. Retrieved on 2008-02-19.
3. Krider, E. Philip (January 2006). "Benjamin Franklin and Lightning Rods". Physics Today. http://www.physicstoday.org/vol-59/iss-1/p42.html. Retrieved on 2008-04-06.
4. J. J. Lowke (1992). "Theory of electrical breakdown in air". Journal of Physics D: Applied Physics 25: 202–210. doi:10.1088/0022-3727/25/2/012. http://www.iop.org/EJ/article/0022-3727/25/2/012/jd920212.pdf?request-id=XIfZw4zI3BGDoxCz2wi7Kg.
5. Kassebaum, J. H. and Kocken, R. A. (1995). "Controlling Static Electricity in Hazardous (Classified) Locations". Petroleum and Chemical Industry 42nd Annual Conference Papers: 105–113. http://ieeexplore.ieee.org/iel3/4013/11530/00523945.pdf?tp=&arnumber=523945&isnumber=11530.
6. Wagner, John P.; Clavijo, Fernando Rangel [doi:10.1016/S0304-3886(00)00019-X Electrostatic charge generation during impeller mixing of used transformer oil] Department of Nuclear Engineering, Safety Engineering and Industrial Hygiene Program, Texas A&M University, College Station, online 21 August 2000; accessed Jan 2009
7. Hearn, Graham (1998). "Static electricity: concern in the pharmaceutical industry?". Pharmaceutical Science & Technology Today 1 (7): 286–287. doi:10.1016/S1461-5347(98)00078-9.
8. Egorov, V.N. Electrification of petroleum fuels Khimiya i Tekhnologiya Topliv i Masel, No. 4, pp. 20–25, April, 1970 accessed Dec 2008
9. Chevron Corporation Aviation Fuels Technical Review 2006, accessed Dec 2008
10. Hearn, Graham Static electricity - guidance for Plant Engineers - Wolfson Electrostatics University of Southampton 2002; accessed Dec 2008
11. Kinzing, G.E., 'Electrostatic Effects in Pneumatic Transport: Assessment, Magnitudes and Future Direction', Journal Pipelines, 4, 95-102, 1984
12. "Snopes.com: Fuelish Pleasures". http://www.snopes.com/autos/hazards/gasvapor.asp. Retrieved on 2008-04-19.
13. "NASA - Crackling Planets". http://science.nasa.gov/headlines/y2005/10aug_crackling.htm. Retrieved on 2008-01-20.
14. "Kids science projects". http://www.creativekidsathome.com/science/staticelectricity.html. Retrieved on 2008-01-20.
15. H. Yasuro, H. Makoto and I. Isao (2007). "Charging of Adhesive Tapes on Peeling". Journal of the Adhesion Society of Japan 43 (3): 97–103. http://sciencelinks.jp/j-east/article/200706/000020070607A0223458.php.
16. "3M Material Safety Data Sheet". http://multimedia.mmm.com/mws/mediawebserver?BBBBBBXeXgc1ZGXFEqZswKKgRmpBWHcbKGcByi5--. Retrieved on 2008-01-20.

Static Electricity - 4

Electronic Components
Many semiconductor devices used in electronics are extremely sensitive to the presence of static electricity and can be damaged by a static discharge.

Static Build-up in Flowing Flammable and Ignitable Materials
Discharge of static electricity can create severe hazards in those industries dealing with flammable substances, where a small electrical spark may ignite explosive mixtures. The flowing movement of finely powdered substances or low conductivity fluids in pipes or through mechanical agitation can build up static electricity. Dust clouds of finely powdered substances can become combustible or explosive. When there is a static discharge in a dust or vapor cloud, explosions have occurred. Major industrial incidents occurred at a grain silo in southwest France, a paint plant in Thailand, and a factory making fiberglass mouldings in Canada.

The ability of a fluid to retain an electrostatic charge depends on its electrical conductivity. When low conductivity fluids flow through pipelines or are mechanically agitated, contact-induced charge separation called flow electrification occurs. Fluids that have low electrical conductivity (below 50 pico siemens/m), are called accumulators. Fluids having conductivities above 50 pico siemens/m are called non-accumulators. In non-accumulators, charges recombine as fast as they are separated and hence electrostatic charge accumulation is not significant. In the petrochemical industry, 50 pico siemens/m is the recommended minimum value of electrical conductivity for adequate removal of charge from a fluid.

Kerosines may have conductivity ranging from <1 pico siemens/m to 20 pico siemens/m. For comparison, deionized water has a conductivity of about 10,000,000 pico siemens/m.
An important concept for insulating fluids is the static relaxation time. This is similar to the time constant (tau) within an RC circuit. For insulating materials, it is the ratio of the static dielectric constant divided by the electrical conductivity of the material. For hydrocarbon fluids, dividing the number 18 by the electrical conductivity of the fluid sometimes approximates this. Thus a fluid that has an electrical conductivity of 1 pico siemens /m will have an estimated relaxation time of about 18 seconds. The excess charge within a fluid will be almost completely dissipated after 4 to 5 times the relaxation time, or 90 seconds for the fluid in the above example.

Charge generation increases at higher fluid velocities and larger pipe diameters, becoming quite significant in pipes 8 inches (200 mm) or larger. Limiting fluid velocity best controls static charge generation in these systems. The British standard BS PD CLC/TR 50404:2003 (formerly BS-5958-Part 2) Code of Practice for Control of Undesirable Static Electricity prescribes pipe flow velocity limits. Because water content has a large impact on the fluids dielectric constant, the recommended velocity for hydrocarbon fluids containing water should be limited to 1 meter/second.

Bonding and earthing are the usual ways by which charge buildup can be prevented. For fluids with electrical conductivity below 10 pico siemens/m, bonding and earthing are not adequate for charge dissipation, and anti-static additives may be required.

References:

1. http://en.wikipedia.org
2. "Franklin's Kite". http://www.mos.org/sln/toe/kite.html. Retrieved on 2008-02-19.
3. Krider, E. Philip (January 2006). "Benjamin Franklin and Lightning Rods". Physics Today. http://www.physicstoday.org/vol-59/iss-1/p42.html. Retrieved on 2008-04-06.
4. J. J. Lowke (1992). "Theory of electrical breakdown in air". Journal of Physics D: Applied Physics 25: 202–210. doi:10.1088/0022-3727/25/2/012. http://www.iop.org/EJ/article/0022-3727/25/2/012/jd920212.pdf?request-id=XIfZw4zI3BGDoxCz2wi7Kg.
5. Kassebaum, J. H. and Kocken, R. A. (1995). "Controlling Static Electricity in Hazardous (Classified) Locations". Petroleum and Chemical Industry 42nd Annual Conference Papers: 105–113. http://ieeexplore.ieee.org/iel3/4013/11530/00523945.pdf?tp=&arnumber=523945&isnumber=11530.
6. Wagner, John P.; Clavijo, Fernando Rangel [doi:10.1016/S0304-3886(00)00019-X Electrostatic charge generation during impeller mixing of used transformer oil] Department of Nuclear Engineering, Safety Engineering and Industrial Hygiene Program, Texas A&M University, College Station, online 21 August 2000; accessed Jan 2009
7. Hearn, Graham (1998). "Static electricity: concern in the pharmaceutical industry?". Pharmaceutical Science & Technology Today 1 (7): 286–287. doi:10.1016/S1461-5347(98)00078-9.
8. Egorov, V.N. Electrification of petroleum fuels Khimiya i Tekhnologiya Topliv i Masel, No. 4, pp. 20–25, April, 1970 accessed Dec 2008
9. Chevron Corporation Aviation Fuels Technical Review 2006, accessed Dec 2008
10. Hearn, Graham Static electricity - guidance for Plant Engineers - Wolfson Electrostatics University of Southampton 2002; accessed Dec 2008
11. Kinzing, G.E., 'Electrostatic Effects in Pneumatic Transport: Assessment, Magnitudes and Future Direction', Journal Pipelines, 4, 95-102, 1984
12. "Snopes.com: Fuelish Pleasures". http://www.snopes.com/autos/hazards/gasvapor.asp. Retrieved on 2008-04-19.
13. "NASA - Crackling Planets". http://science.nasa.gov/headlines/y2005/10aug_crackling.htm. Retrieved on 2008-01-20.
14. "Kids science projects". http://www.creativekidsathome.com/science/staticelectricity.html. Retrieved on 2008-01-20.
15. H. Yasuro, H. Makoto and I. Isao (2007). "Charging of Adhesive Tapes on Peeling". Journal of the Adhesion Society of Japan 43 (3): 97–103. http://sciencelinks.jp/j-east/article/200706/000020070607A0223458.php.
16. "3M Material Safety Data Sheet". http://multimedia.mmm.com/mws/mediawebserver?BBBBBBXeXgc1ZGXFEqZswKKgRmpBWHcbKGcByi5--. Retrieved on 2008-01-20.