Tham khảo tài liệu 'carbon alloys part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | polyimide molecules PMDA PPD is the most flat as shown in Fig. 4. This molecule does not contain ether oxygen but its film is very brittle. A PMDA PPD film named PPT was prepared at the Research Laboratory of Toho Rayon Co. Ltd. with a small amount of additive to keep the film flexible Fig. 4 . Rectangular specimens approximately 26 mm long and 10 mm wide were cut from a 45 jum thick PPT film sandwiched between polished artificial graphite plates and heated by infrared radiation to 900 C at a rate of 2 c min 1 in a flow of nitrogen for 1 h. These carbonized films were then stepwise heat-treated 1800-3200 c in flowing argon. The residence times at final temperatures were 30 min between 1800 and 3000 C and 10 min at 3200 C. Figure 5 shows changes in the X-ray 006 diffraction profiles using Cu Ka radiation of the specimen films with increasing HTT. For each film specimen in the 32OO C 24OO C 3000 C Fig. 5. 006 Diffraction profiles of PPT-derived carbon films heat-treated at various temperatures reprinted with the permission of Elsevier Science from Ref. 10 . 404 Chapter 24 2OO0 c 2600 C 2300 C 2250 C 2200 C 2100 0 29OO C 34 85 86 87 29 .ISOO C 39 85 86 87 88 89 20 28OO C 275O C 27OO C 25OO C Magnetoresistance 405 HTT C Fig. 6. tor PPT-derived carbon films heat-treated at temperatures between 1800 and 3000 C reprinted with the permission of Elsevier Science from Ref. 10 . 20 range from 82 to 89 only the 006 line was observed with no trace of the 112 line implying a high degree of orientation of graphene planes parallel to the film surface. After heat treatment above 2600 C each 006 line had clearly separated into the two lines of the and Ka radiation. The dnn2 values obtained are plotted as a function of HTT in Fig. 6. The dm2 values for the specimens of HTT 3000 C and 3200 C are nm namely that of natural graphite. The parameter mosaic spread measures the orientations of graphene layers and by the width at half the maximum height of the 002 diffraction when
