Date

2014-04-25

Author

Erözbek Güngör, Ümmügül

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In this study, high frequency (40.68 MHz) RF capacitively coupled discharge was used to modify tensile strain and chemical structure of unsized PAN-based carbon fiber under different RF powers, pure nitrogen gas pressures and exposure times. The plasma parameters were diagnosed by using single and double Impedans Langmuir probe techniques to understand physics of high frequency RF-CCP treatment processes. The power range was P = 50-200 Watt and the pressure range was p ≈ 0.1-0.8 Torr. The measured plasma parameters by using single Langmuir probe were Ne ≈ 10exp13-10exp15 m-3, Ni ≈ 10exp11-10exp17 m-3 and kTe ≈ 3.3-37.5 eV while the parameters measured by using double Langmuir probe were Ni ≈ 10exp15-10exp16 m-3 and kTe ≈ 4.77-12.2 eV. In addition, the plasma diagnostic results revealed that there are two transition points in the plasma. The first one (α-γ) was seen at 0.3 Torr whereas the other one (γ-α) was observed at 0.3 Torr-150 Watt. Moreover, tensile strain of the fibers was tested with single filament-cardboard testing method by using Instron micromechanical analyzer. Gauge length of the tested filaments was 25 mm and crosshead speed was 2.5 mm/min. All the experiments were repeated four times for each fiber samples. It was found that the fibers were generally more strengthened (the highest one is ∼24 %) after γ-mode plasma treatments while they were more weakened (the highest one is ∼12 %) with α-mode plasma treatments. Also, according to the strain results, the Grüneisen parameter of D-band was calculated as γD ≈ 1.6 whereas the Grüneisen parameter of G-band was found as γG ≈ – 2.5. Furthermore, the FT-IR spectrum has been recorded in the region between 400 and 4000 cm-1 using Bruker Equinox 55 FT-IR spectrometer. It was found that the untreated (as-received) fiber has the C=C, C=N and C≡N chemical bonds. When the gas pressure (p > 0.3 Torr) increased, the C=C bound was disappeared and only carbon to nitrogen bonds were generated. The carbon fiber treated at 0.3 Torr-200 Watt-30 min had C≡N bond whereas the carbon treated at 0.3 Torr-200 Watt-60 min had C=N bond. And, the C=C bond was disappeared in the fiber structure that treated at 0.5 Torr-50 Watt when the treatment time increased from 30 to 60 min.

URI

https://hdl.handle.net/11511/73716

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Department of Physics, Conference / Seminar