RAMAN-SPECTRA OF GRAPHITE AND DIAMOND MECHANICALLY MILLED WITH AGATE OR STAINLESS-STEEL BALL-MILL

The reduction of crystalline size and amorphization of graphite and di amond during agate and stainless ball-milling are investigated by Rama n spectroscopy. The ultimate crystalline size of,graphite, estimated b y the Raman intensity ratio, of 2.5 nm for the agate ball-mill is smal ler than that of 3.5 nm for the stainless ball-mill, while the milling time to reach the ultimate size for the former is about 10 times larg er than for the latter, indicating more stability of the nanocrystalli ne graphite. After reaching the ultimate crystalline size, a significa nt broadening of the Raman spectra, which indicates the completion of amorphization, is detected only for the stainless ball-milled graphite at similar to 500 h of milling. Also the increase rate of the Raman p eakwidth for the stainless ball-milled graphite before amorphization i s higher than that for the agate ball-milled graphite, indicating a la rger introduction of disorder from the start of milling. Amorphization of diamond is also observed for the stainless ball-mill. The differen ce in the results between the agate and the stainless ball-mill is dis cussed in terms of the effect of impurity mixed from the milling appar atus on the stability of nanocrystalline carbon materials.