Electron-beam processing

Source: Wikipedia, the free encyclopedia.
For Electron beam, see Cathode ray.

Electron-beam processing or electron irradiation (EBI) is a process that involves using electrons, usually of high energy, to treat an object for a variety of purposes. This may take place under elevated temperatures and nitrogen atmosphere. Possible uses for electron irradiation include sterilization, alteration of gemstone colors, and cross-linking of polymers.

Electron energies typically vary from the

Mrads
(1 Gy is equivalent to 100 rad).

The basic components of a typical electron-beam processing device include:[1] an electron gun (consisting of a cathode, grid, and anode), used to generate and accelerate the primary beam; and, a magnetic optical (focusing and deflection) system, used for controlling the way in which the electron beam impinges on the material being processed (the "workpiece"). In operation, the gun cathode is the source of thermally emitted electrons that are both accelerated and shaped into a collimated beam by the electrostatic field geometry established by the gun electrode (grid and anode) configuration used. The electron beam then emerges from the gun assembly through an exit hole in the ground-plane anode with an energy equal to the value of the negative high voltage (gun operating voltage) being applied to the cathode. This use of a direct high voltage to produce a high-energy electron beam allows the conversion of input electrical power to beam power at greater than 95% efficiency, making electron-beam material processing a highly energy-efficient technique. After exiting the gun, the beam passes through an electromagnetic lens and deflection coil system. The lens is used for producing either a focused or defocused beam spot on the workpiece, while the deflection coil is used to either position the beam spot on a stationary location or provide some form of oscillatory motion.

In polymers, an

SEM.[2]

In poly(vinylidene fluoride-trifluoroethylene) copolymers, high-energy electron irradiation lowers the energy barrier for the ferroelectric-paraelectric phase transition and reduces polarization hysteresis losses in the material.[3]

Electron-beam processing involves irradiation (treatment) of products using a high-energy

electron-beam accelerator. Electron-beam accelerators utilize an on-off technology, with a common design being similar to that of a cathode ray
television.

Electron-beam processing is used in industry primarily for three product modifications:

Nanotechnology is one of the fastest-growing new areas in science and engineering. Radiation is early applied tool in this area; arrangement of atoms and ions has been performed using ion or electron beams for many years. New applications concern nanocluster and nanocomposites synthesis.[5]

Crosslinking

The

thermoset.[2][6] When polymers are crosslinked, the molecular movement is severely impeded, making the polymer stable against heat. This locking together of molecules is the origin of all of the benefits of crosslinking, including the improvement of the following properties:[7]

  • Thermal: resistance to temperature, aging, low-temperature impact, etc.
  • Mechanical:
    tensile strength
    , modulus, abrasion resistance, pressure rating, creep resistance, etc.
  • Chemical: stress crack resistance, etc.
  • Other:
    positive temperature coefficient
    , etc.

Cross-linking is the interconnection of adjacent long molecules with networks of bonds induced by chemical treatment or electron-beam treatment. Electron-beam processing of thermoplastic material results in an array of enhancements, such as an increase in tensile strength and resistance to abrasions, stress cracking and solvents. Joint replacements such as knees and hips are being manufactured from cross-linked ultra-high-molecular-weight polyethylene because of the excellent wear characteristics due to extensive research.[8]

Polymers commonly crosslinked using the electron-beam irradiation process include polyvinyl chloride (

ethylene tetrafluoroethylene (ETFE). Some of the polymers utilize additives to make the polymer more readily irradiation-crosslinkable.[9]

An example of an electron-beam crosslinked part is connector made from polyamide, designed to withstand the higher temperatures needed for soldering with the lead-free solder required by the RoHS initiative.[10]

Cross-linked polyethylene piping called PEX is commonly used as an alternative to copper piping for water lines in newer home construction. PEX piping will outlast copper and has performance characteristics that are superior to copper in many ways.[11]

Foam is also produced using electron-beam processing to produce high-quality, fine-celled, aesthetically pleasing product.[12][13]

Long-chain branching

The resin pellets used to produce the foam and thermoformed parts can be electron-beam-processed to a lower dose level than when crosslinking and gels occur. These resin pellets, such as polypropylene and polyethylene can be used to create lower-density foams and other parts, as the "melt strength" of the polymer is increased.[14]

Chain scissioning

Chain scissioning or

molecular weight. The chain scissioning effects observed in polytetrafluoroethylene (PTFE) have been used to create fine micropowders from scrap or off-grade materials.[4]

Chain scission is the breaking apart of molecular chains to produce required molecular sub-units from the chain. Electron-beam processing provides Chain scission without the use of harsh chemicals usually utilized to initiate chain scission.

An example of this process is the breaking down of cellulose fibers extracted from wood in order to shorten the molecules, thereby producing a raw material that can then be used to produce biodegradable detergents and diet-food substitutes.

"Teflon" (PTFE) is also electron-beam-processed, allowing it to be ground to a fine powder for use in inks and as coatings for the automotive industry.[15]

Microbiological sterilization

Electron-beam processing has the ability to break the chains of DNA in living organisms, such as bacteria, resulting in microbial death and rendering the space they inhabit sterile. E-beam processing has been used for the sterilization of medical products and aseptic packaging materials for foods, as well as disinfestation, the elimination of live insects from grain, tobacco, and other unprocessed bulk crops.[16]

Sterilization with electrons has significant advantages over other methods of sterilization currently in use. The process is quick, reliable, and compatible with most materials, and does not require any quarantine following the processing.[17] For some materials and products that are sensitive to oxidative effects, radiation tolerance levels for electron-beam irradiation may be slightly higher than for gamma exposure. This is due to the higher dose rates and shorter exposure times of e-beam irradiation, which have been shown to reduce the degradative effects of oxygen.[18]

Notes

  1. ISBN 978-981-4307-04-8
    .
  2. ^
    doi:10.1142/S0219581X15500313
    .
  3. S2CID 22081881
    .
  4. ^ a b Bly, J. H.; Electron Beam Processing. Yardley, PA: International Information Associates, 1988.
  5. ^ Chmielewski, Andrzej G. (2006). "Worldwide developments in the field of radiation processing of materials in the down of 21st century" (PDF). Nukleonika. 51 (Supplement 1). Institute of Nuclear Chemistry and Technology: S3–S9.
  6. ^ Berejka, Anthony J.; Daniel Montoney; Marshall R. Cleland; Loïc Loiseau (2010). "Radiation curing: coatings and composites" (PDF). Nukleonika. 55 (1). Institute of Nuclear Chemistry and Technology: 97–106.
  7. better source needed
    ]
  8. ^ "Harris Orthopaedics Lab (HOL) - Massachusetts General Hospital, Boston, MA". Archived from the original on 2014-08-26. Retrieved 2014-08-21.
  9. ^ "Fluorinated Polymers". BGS.
  10. ^ "Archived copy" (PDF). Archived from the original (PDF) on 2014-08-26. Retrieved 2014-08-21.{{cite web}}: CS1 maint: archived copy as title (link)
  11. ^ "Cross-Linking". Iotron Industries: Electron Beam Sterilization Processing Services. Archived from the original on 2012-12-25. Retrieved 2013-02-11.
  12. ^ "Technology | Toray Plastics (America), Inc". Archived from the original on 2014-08-26. Retrieved 2014-08-21.
  13. ^ "Electron beam processing, e-beam processing, plastics crosslinking, medical device sterilization - E-BEAM News". Archived from the original on 2014-08-26. Retrieved 2014-08-21.
  14. ^ http://www.ebeamservices.com/pdf/E-BEAM-Foam-Applications.pdf [bare URL PDF]
  15. ^ "Chain Scission". Iotron Industries: Electron Beam Sterilization Processing Services. Archived from the original on 2012-12-25. Retrieved 2013-02-11.
  16. ^ Singh, A., Silverman, J., eds. Radiation Processing of Polymers. New York, NY: Oxford University Press, 1992.
  17. better source needed
    ]
  18. ^ "Material Considerations: Irradiation Processing" (PDF). Sterigenics. Archived from the original (PDF) on 2016-06-21. Retrieved 2010-11-29.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Electron-beam_processing&oldid=1211392984"