*Corresponding author. Tel.: 1-847-573-3223; fax: 1-847-247-0882.E-mail address: Sergey

}Korenev@steris.com (S. Korenev).

Vacuum 62 (2001) 233}236

Electron beam curing of composites

Sergey Korenev*

STERIS Corporation, STERIS Isomedix Services, 2500 Commerce Drive, Libertyville, IL 60048, USA

Received 27 June 2000; accepted 5 September 2000

Abstract

The absorbed doses required for curing composites depend on many parameters of materials and conditions ofirradiation and the total range of absorbed doses is 50}200 kGy. The high level of absorbed doses and large depth ofpenetration of radiation means that electron accelerators need to be used as sources of ionized radiation. The maindemands on parameters of electron accelerators for this use and the required irradiation are described in thispaper. � 2001 Elsevier Science Ltd. All rights reserved.

Keywords: E-beam curing; Composites; Electron accelerators; Radiation processes

1. Introduction

The electron beam curing of composites includesthe irradiation of composites fabricated from car-bon "ber and epoxy. The process of curing consistsof three-dimensional polymerization of the epoxy.One method of curing is based on electron orgamma irradiation. Typical conditions of curingrequire the accumulation of total absorbed doses ofthe level (50}200)�10�Gy [1].Electron accelerators have found application in

these processes [2]. The questions of irradiationand parameters of electron beams and acceleratorsare very important and demand more detailed con-sideration.The development of this technology leads to pro-

gress in the understanding of chemical reactions

and mechanical properties of composites. The openquestion is which source of particles is preferred:electrons or X-rays.The main demands on the electron accelerators

to provide curing are considered in this report.

2. The particulars of irradiation

The curing composite methods use electron ac-celerators with a scanning electron beam. The useof the scanning mode for electron beam irradiationprovides a pulsed character of interaction forelectron beam and product. For example, forscanning frequencies 100Hz and 400Hz andfor width of scan 1m, the velocity of spread of thebeam is 2�10� cm/s and 8�10� cm/s. In thiscase, for a sample with width 2 cm, the time ofirradiation by the beam is, respectively, about 100and 25�s. The irradiation has a pulsed characterand this parameter we can consider as a pulsedbeam.

0042-207X/01/$ - see front matter � 2001 Elsevier Science Ltd. All rights reserved.PII: S 0 0 4 2 - 2 0 7 X ( 0 0 ) 0 0 4 2 1 - 8

Fig. 1. Typical distribution of absorbed doses of electrons ina solid material.

Fig. 2. The dependence of optimal thickness of a sample forirradiation on kinetic energy of electrons.

The absorbed doses D in the irradiated com-posite can be determined by the formula [3]

D"E�/m, (1)

where E�is absorbed energy from the electron

beam and m is the mass of the irradiated sample(assuming penetration of electrons through thewhole sample).For absorbed doses for electron beam irradiation

from accelerators formula (1) becomes

D";ItK�K

�K

�/m, (2)

where ; is the accelerating voltage (kinetic energyof electrons), I is the beam current, t is the time ofirradiation, K

�is factor comparing beam usage to

optimal absorption, K�is the time factor of the

scanning beam and K�is a factor of beam usage,

determined by the geometry of the electron beamand the irradiated product.The main demand of radiation processing is

a homogeneous distribution of absorbed doses inthe irradiated product (see Fig. 1 for one-sidedirradiation). The distribution of absorbed doseswithin 20% of the average dose D

���is

D���

"[D���

#D���

]/2, (3)

where D���

is max absorbed dose and D���

is minabsorbed dose.The optimal thickness ¸

�of an irradiated

sample is determined by this distribution. In thiscase, we can consider this distribution as a homo-geneous absorbed energy from the electron beam.The electron beam does not deliver 100% of theenergy by a factor K

�which is found from the

thickness of the irradiated sample. The correlationbetween kinetic energy of electrons and optimalthickness of composites with average density1.5 g/cm� is presented in Fig. 2 for one-sided ir-radiation. The correlation can help to determinethe kinetic energy for an electron beam for actualmaterials.

3. Accelerators in the curing composite technologies

The composite curing methods have at presentR&D status. The status determines the type andkind of accelerator. The progress and developmentof this technology will solve the problems of produ-cing of an optimal accelerator. Research Centers orResearch groups use standard electron acceleratorswith large cross-section electron beams having lowenergy (to 300 keV) and electron accelerators(1}10MeV) with scanning electron beams on thebasis of DC, continuous wave (CW) (Rhodotron),and RF Linac electron accelerators.

4. Main conditions of curing technologies

The structure of carbon "ber/epoxy compositematerial [4] is given in Fig. 3 (the nano"brils arenot typical).

234 S. Korenev / Vacuum 62 (2001) 233}236

Fig. 3. The structure of a composite.

Fig. 4. The time diagram of a typical electron beam curingprocess.

Fig. 5. The dependence of duration of irradiation on beamcurrent for dose increments 1 and 5kGy/Cycle.

The time diagram of a typical curing processwith total accumulated dose 200kGy from [5] ispresented in Fig. 4. The diagram shows that, foreach cycle of irradiation, the composite must ab-sorb doses 1}5kGy. The time delay between thenext cycle can be 5.0}20.0min.The calculation of the main parameters

of the electron beam for a composite with thick-ness 2mm and with cross section a dimensions2.0�1.0 cm� and average density 1.5 g/cm� showsthat

� absorbed energy is 24}120 J;� kinetic energy is 1MeV.

The main parameters of the electron beams inthis case are as follows:

E�"EIt"24!120J. (4)

We have the same range E�for thickness 1mm and

kinetic energy 0.5MeV.A more detailed consideration shows the univer-

sal dependence parameter of the accelerator I

K�"It"D/E. (5)

The parameter I�is constant for the same scale of

dose/cycle. It also can apply to di!erent types ofelectron accelerators: DC [6], RF, CW and pulsed[7], and high current pulsed accelerators [8]. Thevariation of current and time of irradiation is pre-sented in Fig. 5 for samples with thickness 0.1 and0.2 cm and dimensions 2.0�1.0 cm� for dose in-crements 1 and 5 kGy/cycle.

5. Conclusion

As a result of this study we can make the follow-ing conclusions:

� an analysis of the present status of irradiation ofcomposites by electron accelerators shows

S. Korenev / Vacuum 62 (2001) 233}236 235

a complex task for the development of acceler-ator technology.

� the question of an optimal electron accelerator isonly at its starting point in the "eld of compositecuring.

Acknowledgements

I would like to ask say many thanks for usefuldiscussion of considered questions to C. Eberle,J. Kriebel and L. Vorob'ev.

References

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[3] McLaughlin WL, Boyd AW, Chaadwick KH, McDonaldJC, Miller A. Dosimetry for radiation processing. London:Taylor & Francis, 1989.

[4] Janke C, Yarborough K, Dzal L. Fiber-matrix studies onelectron beam cured composites. Proceedings of the 30thInternational SAMPE Symposium, 1999. p. 647}659.

[5] Wilenski M, Eberle C, Korenev S, Lopata V, Stein M.A method for specifying consistent radiation for the pro-cessing of electron beam cured composites. Proceedings ofthe 31st International SAMPE Symposium, 2000.p. 1888}97.

[6] Abramian EA, Alterkop BA, Kuleshov GD. Intense elec-tron beams: physics, equipment, applications. Moscow:Atomizdat, 1984.

[7] Wangler T. Principles of RF linear accelerators. New York:Wiley, 1998.

[8] Korenev SA. Pulsed electron sources for modi"cation ofmaterials. Proceedings of the First USSR Conference onModi"cation of Materials by Charged Particle Beams,Tomsk, USSR, vol. 1, p. 28, 1988.

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