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Means have to be found to discharge carts which may carry such liquids in [[hospital]]s. Even where only a small charge is produced, this can result in dust particles being attracted to the rubbed surface. In the case of [[textile]] manufacture this can lead to a permanent grimy mark where the cloth has been charged. Some [[electronic device]]s, most notably [[CMOS]] [[integrated circuit]]s and [[MOSFET]] transistors, can be accidentally destroyed by high-voltage static discharge. Such components are usually stored in a conductive [[foam]] for protection. Grounding oneself by touching the workbench, others, or using a special [[Anti-static wrist strap|bracelet]] or anklet is standard practice while handling unconnected [[integrated circuit]]s. Another way of dissipating charge is by using conducting materials such as [[carbon black]] loaded [[rubber]] mats in operating theatres, for example. |
Means have to be found to discharge carts which may carry such liquids in [[hospital]]s. Even where only a small charge is produced, this can result in dust particles being attracted to the rubbed surface. In the case of [[textile]] manufacture this can lead to a permanent grimy mark where the cloth has been charged. Some [[electronic device]]s, most notably [[CMOS]] [[integrated circuit]]s and [[MOSFET]] transistors, can be accidentally destroyed by high-voltage static discharge. Such components are usually stored in a conductive [[foam]] for protection. Grounding oneself by touching the workbench, others, or using a special [[Anti-static wrist strap|bracelet]] or anklet is standard practice while handling unconnected [[integrated circuit]]s. Another way of dissipating charge is by using conducting materials such as [[carbon black]] loaded [[rubber]] mats in operating theatres, for example. |
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==Observation on Helicopter Rotors== |
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The triboelectric effect has been observed on rotor blades in dusty environments. |
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The abrasion strips on helicopter rotor blades are made of titanium, which is very hard, but less hard than sand; so when a helicopter is flown near to the ground in desert environments abrasion occurs, and at night there is a visible corona or halo around the rotor blades, caused by the sand hitting the titanium and causing it to spark and oxidize.<ref name="AHS-paper">{{cite web | url = http://www.vtol.org/f65_bestPapers/productSupport.pdf | title = Enhanced Erosion Protection for Rotor Blades: Paper presented at the American Helicopter Society 65th Annual Forum, Grapevine, Texas, May 27 – 29, 2009. | accessdate = 2009-09-02 | author = Warren (Andy) Thomas | coauthors = Shek C. Hong;, Chin-Jye (Mike) Yu, Edwin L. Rosenzweig | date = 2009-05-27 | format = pdf | publisher = [[American Helicopter Society]] | quote =A secondary concern with the erosion of metal abrasion strips pertains to the visible signature that occurs when microscopic metallic pieces are eroded away. In the erosion process, they often oxidize, giving off a visible spark and causing a corona effect in sandy environments. }} </ref> |
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<ref name="BAA 08-11">{{citation| url = http://www.onr.navy.mil/02/baa/docs/BAA%2008-011_ONRBAA%2008-011.pdf| title = Office of Naval Research Broad Agency Announcement(BAA): Advanced Helicopter Rotor Blade Erosion Protection|id=BAA 08-011| accessdate = 2009-09-02 |
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| format = pdf| publisher = United States Department of the Navy, Office of Naval Research| page = 3| quote = Although both Ni and Ti are hard metals, their hardness values are significantly lower than that of sand, which is primarily made up of quartz. This hardness differential results in the excessive erosion/degradation of rotor blades in desert environments. An equally important problem with Ti protection is that a visible corona or halo is generated around the rotor blades at night from the sand impacting the Ti leading edge and causing Ti to spark andoxidize.}}</ref> |
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The result of [[static electricity]] created by friction as materials of dissimilar material rapidly strike against each other.{{cn}} In the case of [[helicopter]] rotors at night, it is the [[titanium]]/[[nickel]] blades moving through the air and dust. It also occurs on the ground, but is not usually seen unless aircraft are landing or taking off, as the aircraft are generally earthed by contact with the ground. |
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==See also== |
==See also== |
Revision as of 20:29, 2 September 2009
Triboelectric series: |
Most positively charged |
+ |
Air |
Human skin |
Leather |
Rabbit's fur |
Glass |
Quartz |
Mica |
Human hair |
Nylon |
Wool |
Lead |
Cat's fur |
Silk |
Aluminum |
Paper (Small positive charge) |
Cotton (No charge) |
0 |
Steel (No charge) |
Wood (Small negative charge) |
Lucite |
Amber |
Sealing wax |
Acrylic |
Polystyrene |
Rubber balloon |
Resins |
Hard rubber |
Nickel, Copper |
Sulfur |
Brass, Silver |
Gold, Platinum |
Acetate, Rayon |
Synthetic rubber |
Polyester |
Styrene (Styrofoam) |
Orlon |
Plastic wrap |
Polyurethane |
Polyethylene (like Scotch tape) |
Polypropylene |
Vinyl (PVC) |
Silicon |
Teflon |
Silicone rubber |
Ebonite |
− |
Most negatively charged |
The triboelectric effect (also known as 'triboelectric charging') is a type of contact electrification in which certain materials become electrically charged after they come into contact with another different material and are then separated (such as through rubbing). The polarity and strength of the charges produced differ according to the materials, surface roughness, temperature, strain, and other properties.
Thus, it is not very predictable, and only broad generalizations can be made. Amber, for example, can acquire an electric charge by contact and separation (or friction) with a material like wool. This property, first recorded by Thales of Miletus, suggested the word "electricity", from the Greek word for amber, ēlektron. Other examples of materials that can acquire a significant charge when rubbed together include glass rubbed with silk, and hard rubber rubbed with fur.
Triboelectric Series
Materials are often listed in order of the polarity of charge separation when they are touched with another object. A material towards the bottom of the series, when touched to a material near the top of the series, will attain a more negative charge, and vice versa. The further away two materials are from each other on the series, the greater the charge transferred. Materials near to each other on the series may not exchange any charge, or may exchange the opposite of what is implied by the list. This depends more on the presence of rubbing, the presence of contaminants or oxides, or upon properties other than on the type of material. Lists vary somewhat as to the exact order of some materials, since the charge also varies for nearby materials.
Cause
Although the word comes from the Greek for "rubbing", tribos, the two materials only need to come into contact and then separate for electrons to be exchanged. After coming into contact, a chemical bond is formed between some parts of the two surfaces, called adhesion, and charges move from one material to the other to equalize their electrochemical potential. This is what creates the net charge imbalance between the objects. When separated, some of the bonded atoms have a tendency to keep extra electrons, and some a tendency to give them away, though the imbalance will be partially destroyed by tunneling or electrical breakdown (usually corona discharge). In addition, some materials may exchange ions of differing mobility, or exchange charged fragments of larger molecules.
The triboelectric effect is related to friction only because they both involve adhesion. However, the effect is greatly enhanced by rubbing the materials together, as they touch and separate many times. For surfaces with differing geometry, rubbing may also lead to heating of protrusions, causing pyroelectric charge separation which may add to the existing contact electrification, or which may oppose the existing polarity. Surface nano-effects are not well understood, and the atomic force microscope has made sudden progress possible in this field of physics.
Because the surface of the material is now electrically charged, either negatively or positively, any contact with an uncharged conductive object or with an object having substantially different charge may cause an electrical discharge of the built-up static electricity; a spark. A person simply walking across a carpet may build up a charge of many thousands of volts, enough to cause a spark one centimeter long or more. Low relative humidity in the ambient air increases the voltage at which electrical discharge occurs by increasing the ability of the insulating material to hold charge and by decreasing the conductivity of the air, making it difficult for the charge build-up to dissipate gradually. Simply removing a nylon shirt or corset can also create sparks, and car travel can lead to a build-up of charge on the metal car body (which acts as a Faraday cage). When the driver alights, sparks jump from frame to driver as he makes contact with the ground.
This type of discharge is often harmless because the energy ((V2 * C)/2) of the spark is very small, being typically several tens of micro joules in cold dry weather, and much less than that in humid conditions. However, such sparks can ignite methane-air mixtures, and is a danger when leaks of natural gas occur in domestic buildings, for example. Gas leaks are a serious hazard and can cause physical damage and death.
Aircraft flying in weather will develop a static charge from air friction on the airframe. The static can be discharged with static dischargers or static wicks.
Risks and counter-measures
The effect is of considerable industrial importance in terms of both safety and potential damage to manufactured goods. The spark produced is fully able to ignite flammable vapours, for example, petrol, ether fumes as well as methane gas.
Means have to be found to discharge carts which may carry such liquids in hospitals. Even where only a small charge is produced, this can result in dust particles being attracted to the rubbed surface. In the case of textile manufacture this can lead to a permanent grimy mark where the cloth has been charged. Some electronic devices, most notably CMOS integrated circuits and MOSFET transistors, can be accidentally destroyed by high-voltage static discharge. Such components are usually stored in a conductive foam for protection. Grounding oneself by touching the workbench, others, or using a special bracelet or anklet is standard practice while handling unconnected integrated circuits. Another way of dissipating charge is by using conducting materials such as carbon black loaded rubber mats in operating theatres, for example.
Observation on Helicopter Rotors
The triboelectric effect has been observed on rotor blades in dusty environments.
The abrasion strips on helicopter rotor blades are made of titanium, which is very hard, but less hard than sand; so when a helicopter is flown near to the ground in desert environments abrasion occurs, and at night there is a visible corona or halo around the rotor blades, caused by the sand hitting the titanium and causing it to spark and oxidize.[1] [2]
The result of static electricity created by friction as materials of dissimilar material rapidly strike against each other.[citation needed] In the case of helicopter rotors at night, it is the titanium/nickel blades moving through the air and dust. It also occurs on the ground, but is not usually seen unless aircraft are landing or taking off, as the aircraft are generally earthed by contact with the ground.
See also
- Antistatic agent
- Capacitor
- Contact electrification
- Dipole moment
- Dust explosion
- Electric charge
- Electric dipole
- Electrical conductivity
- Electrical generator
- Electrical phenomena
- Electronegativity
- Electrophorus
- Faraday cage
- Friction
- Kopp-Etchells effect
- Lightning
- Static electricity
- Triboluminescence
- Wimshurst machine
- Xerography
References
- Allen, Ryne, C, Triboelectric Generation: Getting Charged
- EvaluationEngineering.com
- ESDSystems.com
- School-For-Champions.com, Background of the triboelectric effect.
- Besançon, Robert M. (1985). The Encyclopedia of Physics, Third Edition. Van Nostrand Reinhold Company. ISBN 0-442-25778-3.
External articles
- Patents
- U.S. patent 3,086,131 — Earle W. Ballentine — "Triboelectric Generator"
- U.S. patent 4,990,813 — Gabriel L. Paramo — "Rolling triboelectric generator"
External links
- General
- Charged Rod Demonstration, University of Minnesota
- NASA, Science Crackling Planets
- ^ Warren (Andy) Thomas (2009-05-27). "Enhanced Erosion Protection for Rotor Blades: Paper presented at the American Helicopter Society 65th Annual Forum, Grapevine, Texas, May 27 – 29, 2009" (pdf). American Helicopter Society. Retrieved 2009-09-02.
A secondary concern with the erosion of metal abrasion strips pertains to the visible signature that occurs when microscopic metallic pieces are eroded away. In the erosion process, they often oxidize, giving off a visible spark and causing a corona effect in sandy environments.
{{cite web}}
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suggested) (help) - ^ Office of Naval Research Broad Agency Announcement(BAA): Advanced Helicopter Rotor Blade Erosion Protection (pdf), United States Department of the Navy, Office of Naval Research, p. 3, BAA 08-011, retrieved 2009-09-02,
Although both Ni and Ti are hard metals, their hardness values are significantly lower than that of sand, which is primarily made up of quartz. This hardness differential results in the excessive erosion/degradation of rotor blades in desert environments. An equally important problem with Ti protection is that a visible corona or halo is generated around the rotor blades at night from the sand impacting the Ti leading edge and causing Ti to spark andoxidize.