Study on Safety Improvement of Carbon Fibres as Chaff
HU Xiaochun1,2, QIAO Xiaojing1, ZHANG Tonglai1, ZHENG Qiuyu1 & WU Ruifeng1
(1 State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing 100081, China;
2 The 3rd department, Institute of Chemical Defen, Beijing 102205, China)
Abstract: To reduce the long-term danger to the f lights and improve the safety to environment, the electrical conductivity evanescence of the Ni-coated carbon f ibers (CF) was studied. According to the theory analysis, Ni-coated carbon f ibers were treated using FeCl3. The metal of the CF surface is oxidized when it is expod to air moisture, so its conductivity reduces greatly. The diff erent temperature, relative humidity and coat thickness are studied, what are the f actors inf luencing the degrade rate of metal coat. The results show that under some temperature and humidity, the conductivity of t he Ni-coated carbon f ibers changes 10% in 0.5－5.6min, and it expends at least 44 minutes if the conductivity changes 95%. Humidity inf luences the degrade rat e of metal coat more than temperature.
Keywords: degradable; chaff; coat; carbon f ibre; interfere; electromagnetic wave
考博1Introduction
The chaff is generally made of metal-coated strip to disturb enemy electromagnetic wave in warfare[1-3]. When the chaff is relead for operational or training purpo, some problems may be brought about. One of the most rious problems is the electromagnetic pollution that may endanger the planes passing by. It is suspicious that the relead chaff with electromagnetic activity has the potential to disturb the navigation system of the flights and then caus the air crash or that sort of accident [4-5]. It is also recognized that long-term physical health risks may result from the persistence of the undecomposable chaff [4-7]. So it is necessary to develop the degradable chaff. The danger of the metal-coated chaff to airplanes mainly lies in electrical conductivity of the metal coat. Considering the metal coat to be oxidized can lo conductibility, thereby losing its interferential ability, iron or aluminum coated chaff is developed which can easily be degraded [8-9]. However, the iron or aluminum coat is also easy to be oxidized before ud. To solve the problem, the special technology to prevent the coat from contacting with oxygen was adopted but that is difficult to do. It also increas the difficulty of conrvation for long term.
For the stockpile reason the coat can be made of Ni which is more stable metal, and Ni coating can be obtained by chemical plating that needs no the complicated equipment and technology[10]. Ni-co
ated carbon fibres (CF) are also good smoke materials for obscuring millimeter wave and so on. The degradability of them was rearched in the paper becau Ni is difficult to be degraded by oxidation under natural condition. Some oxidative salts are considered to deal with the Ni-coated CF. The salts easily absorb water in air, so the rate of Ni degrading is accelerated consumedly for the oxidation-reduction reaction of the gas-solid pha taking place on the surface of Ni-coated CF changes into that of the liquid-solid pha.
Salts of Fe3+and Cu2+have the characteristics mentioned above. When they are ud as oxidants their standard electrode potentials are higher than tho of Ni salts (as shown in Table 1)[11]. Fe3+ salts are more satisfactory for their water absorbing trend are more than that of Cu2+ salts. Another reason that the Cu2+ salts are not lected is that the product of their electrochemistry reaction is electric metal Cu, which still adheres to chaff.
bogdanTable 1 Standard Electrode Potential
Ion Half-reaction Standard electrode potential /V
Fe3+，Fe2+/Pt Fe3+ + e－→ Fe2+ +0.771
Cu2+/Cu Cu2+ + 2e－→ Cu+0.337
card是什么意思
Ni 2+/Ni Ni2+ + 2e－→ Ni－0.250
Fe2+/Fe Fe2+ + 2e－→ Fe－0.4402
2Experiment
Firstly the oxidative salt is put into the anhydrous organic solvent like methanol, ethanol or acetone. Secondly the electrical resistance of a thread of Ni-coated CF 100mm long is mesured fixed between two poles of the test board. After the oxidative salt is adhered to the surface of Ni-coated CF, and it is dried for about 15 minutes under 100 degree celsius, the electrical resistance of the sample is mesured as the origingal value, that is approximately equal to that of Ni-coated CF without salt. Then the sample is put in a ca which is maintained a certain of temperatur and the humidity. For the electrical resistance of the sample changing with time is mesured in the temperatur and the humidity.
3Results and Discussion
Suppo the initial resistance of a sample is zero, the final resistance of the sample is 100% when the electric al resistance is invariable owing to oxidizing enough. The results are showed as Fig.1 an
d Table 2. In Table 2, T1 or T2 is the time for the electrical resistance changing 10% or 95%, respectively, and its number corresponds to that in Fig.1.
功耗英文The results showed that for the electrical resistances of the samples changing 10% takes the time from 0.5 minutes to 5.6 minutes. If the electrical resistance of chaffs changes 95%, it takes 111 minutes if the thickness of the metal coat is 0.129 µm, and it needs 794 minutes when the thickness of the metal coat is 0.212 µm. Obviously, the thinner the coat is, the shorter the decomposition time is taken. So the coat should be made as thin as it can be done if it is ensured that the hostility radars are effectively jammed.
Comparing (e) with (f) in Table 2, it shown that the higher relative humidity it is, the faster the decomposition rate is. The same
results are obtained by comparing (a) with (c). Owing to absorbing the moisture more easily in higher relative humidity, the oxidative salt on the surface takes place the liquid-solid pha reaction that increas the decomposition rate of the Ni coat more quickly than the solid-solid pha reaction in dryness.
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When the surface of Ni-coated CF is covered with Fe 3+, oxidation-reduction reaction occurs betwee
n Ni coat and Fe 3+. The Ni coat is eroded from many tiny points. Then this process expands, and it gradually spreads the ent ire coat. Some rotten crackles appear and the whole tight coat is parated to veral parts ，and Ni coat finally comes off the chaff. The electromagnetic wave is disturbed by the absorption and reflection of the conducting coat Chaffs. The conductivity of chaffs losing Ni coat has fallen so that interfere ability of chaffs decread even lost. Then the long interference to the navigation system of the flight is removed, and the safety of the aviation and lives are ensured.
Cu 2+ ud as oxidative ion is compared with Fe 3+ to degrade the Ni coat of CF. For a moment, the color of the Ni-coated CF surface has been changed from silver-like to golden-like. It shows that copper is produced and replaces nickel on the CF surface. The conductance of chaffs isn’t destroyed yet; so Cu salts aren’t suitable as oxidants.
020406080
1000.1
101000
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ΔR %/%
0204060801000.1
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t /m i n
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onaccountof
(a) (b)
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20406080
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1
10
100
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20406080
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Fig. 2 Electrical Resistance Change in Decomposition Process
Table 2 Results of Decomposition of Ni-coated CF
juggling12a 0.129 16－17 60－80 0.5 44 b 0.129 10－11 36－40 1.6 71 c 0.129 15－16 18－22 1.4 111 d 0.212 10－15 25－40 2.7 794 e 0.212 15－16 66－74 0.5 545 f
0.212
12－18
27－37
5.6
964
4 Conclusions
Under the atmospheric moisture condition, the electrical conductivity of the Ni-coated CF having been treated by oxidative salts is evanescent for the coat metal to be oxidized. Under different condition, it takes more than 44 minutes that the electrical resistance of the CF changes 95%, and 0.5 to 5.6 minutes are needed if the electrical resistance of the CF changes 10%. The rate for the metal-coated fibers to lo their conductivity is quickened under high temperature and humidity condition. FeCl 3 is suitable to be ud to decompo the Ni coat on the CF. In the future developing ba materials of chaffs can solve the problem of electromagnetic pollution of chaffs thorough.
References
[1]Qiao Xiaojing, Wang Changf u, Ren Hui. New Concept f or passive interfering technologies. Initialtors and Pyrotechnics, 2001,23(1): 47-50(in Chine)
[2]Qiao Xiaojing, Y u Renguang, Ren Hui, Wang Changf u. Comparison of Intercalated Carbon Fibers with Copper-plated Carbon Fibers. Journal of Materials
Engineering, 2004,49 (7): 47-50(in Chine)
[3]Koch, Ernst-Christian, Schneider, et al. Pyrotechnic smoke screen units f or producing an aerosol impenetrabl e in the visible, inf rared and millimetric wave
range. US Patent 6 578 492. 2003
[4]Environmental Protection, DOD Management Issures Related to Chaff. AD-A354323. Washington. DC: United States General Accounting Off i ce, 1998
[5]Barry J. Spargo. Environmental Eff ects of RF Chaff. AD-A379848. Washington. DC: Naval Rearch Laboratory, 1999onmonday
[6]Robert L.Carpenter. The Inhalation Toxicity of Glass Fibers －A Review of the Scientif ic Literature. AD-A386508. 1999
[7]Darryl P. Arf sten, Cody A. Wilson, Kenneth R. Still, Barry J. Spargo, and John Callahan. Characterization of the Ecotoxity of Five Biodegredable
Polymers under Consideration by Navair f or U in Chaff-Dispensing Systems. AD-A399776. 2002
[8]Stevens, Ward C, Sturm, et al. Metal-coated substrat e articles responsive to electromagnetic radiation, and method of making and using the sam e. United
States, US Patent 6 017 628. 2000
[9]Stevens, Ward C., Sturm, Edward A., Metal-coated substrate articles responsive to electrom agnetic radi ation, and method of making the same. US Patent 5
686 178. 1997
[10]Zhang Yuncheng, Hu Runan, Xiang Rong. Plating Handbook. Beijing: National Def ence Industry Press, 1997(in Chine)
[11]Fu Xiancai, Shen Wenxia, and Y ao Tianyang. Physical Chemistry.4t h edition. Beijing: High Education Press, 1990.10(in Chine)
