Structural and Thermal Studies of Graphite from East Antarctica

We report here powder X-ray diffraction, differential thermal analysis and Laser-Raman spectroscopic data on the graphite from Schirmacher Oasis (70°45' S, 11°40' E), East Antarctica. The sample was collected from Precambrian garnet-biotite gneiss. The present X-ray studies show that the structural parameters like inter-planar spacing, d₀₀₂ (3.3500 A), and crystallite size, L_c (552 A) of this sample. These values are found to be very close to that of well-crystallized graphite. All the five observed X-ray diffraction peaks have been indexed to the hexagonal phase of graphite, indicating the metamorphic origin of graphite. The observed full width at half maxima (FWHM) of the (002) peak is 0.148 A and the estimated graphitizing degree (GD=13lA) showed the high-grade metamorphism of the host rock. The estimated peak metamorphic temperature is found to be ∼973 K (700°C). DTA studies on the same graphite sample show a strong exothermic peak at 1023 K, which corresponds, to the combustion of carbonaceous matter under atmospheric condition. The absence of extra weak peak in the range 1090-1110 K, indicates the absence of any noticeable detntal graphite in the sample. The first order Laser - Raman spectra of the sample shows a strong well-ordered Raman peak (O) at 1581cm"¹ and a weak broad peak due to disorder (D) at 1354cm"¹. The intensity ratio disordered-to-ordered Raman peak (D/O) area has been used to estimate the in-plan crystallite size (La) of the graphite. The experimental values of D/O = 0.143 and D/D+O = 0.125 indicate that the sample is well crystallized graphite, thereby indicating the high metamorphic grade of the host rocks. The structural parameters obtained by Raman spectroscopic method and the estimated in-plane crystallite size (La = 298 A) indicate that the metamorphic grade of the host rock of the studied sample falls in the sillimanite zone. The present study suggests that the peak metamorphic temperature of the host rock could be in the temperature range of about 973 K (700°C).