1794 ZR. Yue et al./ Carbo37(1999)1785-17%6 o 1s N1s 0009008007 600500400 30020010b0 BE (ev) Fig. 11. XPS survey spectra of (1)as-received carbon fiber, (2) electrochemically oxidized carbon fiber(5300 C/g), and oxidized fiber which was post-heat-treated at, (3)550C and(4)850C under flowing nitrogen. creased after electrochemical oxidation, especially in peak progressive electrochemical oxidation (Fig. 1)and was IV(carboxyl and ester groups). However, the relative approximately proportional to the extent of oxidation. concentration of carbon-oxygen complexes decreased NaoH uptake demonstrated that acidic functions were significantly(especially, the magnitude of peak IV) after generated in direct proportion to the extent of oxidation up post heating at 550C. Peak IV becomes smaller than that to 4000 C/g [19]. Eventually, a huge number of acidic of the as-received fibers after heating the oxidized fibers functions were generated (1060 mol/g and 2476 umol 850C. In contrast, the relat e size of peak Ill /g and 10 600 C/g of electrooxidation, (assigned to carbonyl groups)increases 2-fold after heating respectively)[60]. To accommodate this number of acidic at 550C. Heating at 850C caused the relative amount of functions a very large internal microporeous surface area carbon-oxygen complexes to fall below that found on was generated. XPS studies indicated that the concen- as-received fibers as both oxygen and nitrogen are lost. tration of oxygen within the outer 50 A of the fibers This also can be seen in Table 2 ncreased on oxidation. The o/C atomic ratio determined from O Is and C Is spectra(Fig. 2)rose rapidly with oxidation to 0. 24(133 C/g) and then remained approxi- 4. Conclusions mately constant upon continued oxidation to 10 600 C/g Electrochemical oxidation formed a progressively larg rength pAN-based carbon fibers were continuous proportion of oxygen functional groups as indicated in chemically oxidized in 1% wt KNO,. The fibers reaction (1). XPS C Is spectra( Fig. 3)showed the anode. Fiber weight loss increased with primarily in carboxyl(COOH) or lactone(COOR)groups Table 2 Changes in the XPS atomic ratios upon heat treating electrochemically oxidized fibers under nitrogen Atomic ratIo (1)As-received fiber 0.158 (2)Electrochemically oxidized (5300 C/g)carbon fiber (3)Sample(2)after heating at 550C for 30 min (4)Sample(2)after heating at 850C for 30 min 0.0171794 Z.R. Yue et al. / Carbon 37 (1999) 1785 –1796 Fig. 11. XPS survey spectra of (1) as-received carbon fiber; (2) electrochemically oxidized carbon fiber (5300 C/g); and oxidized fiber which was post-heat-treated at, (3) 5508C and (4) 8508C under flowing nitrogen. creased after electrochemical oxidation, especially in peak progressive electrochemical oxidation (Fig. 1) and was IV (carboxyl and ester groups). However, the relative approximately proportional to the extent of oxidation. concentration of carbon–oxygen complexes decreased NaOH uptake demonstrated that acidic functions were significantly (especially, the magnitude of peak IV) after generated in direct proportion to the extent of oxidation up post heating at 5508C. Peak IV becomes smaller than that to 4000 C/g [19]. Eventually, a huge number of acidic of the as-received fibers after heating the oxidized fibers to functions were generated (1060 mmol/g and 2476 mmol/g 550 and 8508C. In contrast, the relative size of peak III after 6360 C/g and 10 600 C/g of electrooxidation, (assigned to carbonyl groups) increases 2-fold after heating respectively) [60]. To accommodate this number of acidic at 5508C. Heating at 8508C caused the relative amount of functions a very large internal microporeous surface area carbon–oxygen complexes to fall below that found on was generated. XPS studies indicated that the concen- ˚ as-received fibers as both oxygen and nitrogen are lost. tration of oxygen within the outer 50 A of the fibers This also can be seen in Table 2. increased on oxidation. The O/C atomic ratio determined from O 1s and C 1s spectra (Fig. 2) rose rapidly with oxidation to 0.24 (133 C/g) and then remained approxi- 4. Conclusions mately constant upon continued oxidation to 10 600 C/g. Electrochemical oxidation formed a progressively larger High strength PAN-based carbon fibers were continuous- proportion of oxygen functional groups as indicated in ly electrochemically oxidized in 1% wt KNO . The fibers reaction (1). XPS C 1s spectra (Fig. 3) showed a rise 3 served as the anode. Fiber weight loss increased with primarily in carboxyl (COOH) or lactone (COOR) groups Table 2 Changes in the XPS atomic ratios upon heat treating electrochemically oxidized fibers under nitrogen Samples Atomic ratio O 1s/C 1s N1s/C 1s (1) As-received fiber 0.158 0.022 (2) Electrochemically oxidized (5300 C/g) carbon fiber 0.263 0.025 (3) Sample (2) after heating at 5508C for 30 min 0.194 0.054 (4) Sample (2) after heating at 8508C for 30 min 0.048 0.017