Figure 5. XRD spectra of GST, -400MSIP (reference standards, panel A), ICM, and GCI, using our previous method and GCIP using our optimized method13 (panel B), and 10:1 to 1:10 mixes of GST/GCIP (panel C). In panel A, GST had a G-002 reﬂection at ∼26.5° while -400MSIP had R-Fe-110 and R-Fe-200 reﬂections at ∼45° and ∼65°, respectively. Also, the G-002 reﬂection was more sensitive than either the R-Fe or Fe3C crystal reﬂections. In panel B, ICM, GCI, and GCIP spectra had no (<2 mg of graphite crystal) detectable G-002 reﬂection, but they did have detectable Fe3C crystal and R-Fe crystal reﬂections at 35°-70°. Absence of a G-002 reﬂection indicated that ICM, GCI, and GCIP each consisted of a mix of Fe3C crystal, i-C, and g-C rather than being a single graphite crystal. In panel C, the sum of GST+GCIP in the mix was 22 mg. In all ratios of GST/GCIP, the G-002 reﬂection was more sensitive than that of Fe3C or R-Fe crystals. Also, the graphite crystal mass of ICM, GCI, and GCIP was e2 mg. The ICM was mostly Fe3C crystal and the ICM contained less than half as much g-C compared to GCI and GCIP. ∼1350 cm-1 and the other at ∼1580 cm-1. The band at ∼1350 cm-1 often combined with the band at 830 cm-1 to appear as a weak band at ∼2200 cm-1. Therefore, FT-IR spectra of graphite (devoid of a-C and of aromatic impurity) would be devoid of the 830-, ∼1350-, and ∼2200-cm-1 bands.26,27 The Raman spectroscopy is more useful than FT-IR to determine the presence and features of graphite and disordered carbon, yet we found no information on iron carbide using the Raman in literature.30 The main features of graphitic materials in the Raman spectra were called G (∼1560 cm-1, E2g mode, sp2) and D (∼1360 cm-1, A1g mode, sp3) bands for visible excitation, (30) Park, E. Y.; Zhang, J. Q.; Thomson, S.; Ostrovski, O.; Howe, R. Metall. Mater. Trans. B 2001, 32B, 839–845. while the a-C band (T band) appears at ∼1060 cm-1 seen in UV excitation.26,29,31,32 The iron carbide band was expected to appear between 200 and 600 cm-1 by Raman, but it was not detected because the low-energy vibration frequencies are too close to the laser line to be detected.33 The D band was ﬁrst reported as a disorder-induced mode.28 The sp3 carbon bond content (D band) increased as amorphization and micro- and nanocrystalline gra- phitic materials were observed.34 The origin of the D band at 1350 (31) Merhari, L.; Belorgeot, C.; Quintard, P. J. Mater. Sci. Lett. 1994, 13, 286– 288. (32) Ferrari, A. C.; Robertson, J. Phys. Rev. B 2001, 64, 075414. 13 pages. (33) Bi, X. X.; Ganguly, B.; Huffman, G. P.; Huggins, F. E.; Endo, M.; Eklund, P. C. J. Mater. Res. 1993, 8, 1666–1674. Analytical Chemistry, Vol. 80, No. 20, October 15, 2008 7667