Fine metallic particles in graphite matrix

Abstract

The reduction of metal chloride in the interlayer spacing of graphite has been a subject of interest during recent years [1-5]. However, few studies of the reaction mechanism have been described in the literature. In a previous letter [6], we discussed factors determining the size of fine metallic particles formed in the graphite matrix. Atoms of zero-valent metal generated by the reduction of metal chloride at respective sites in the graphite intercalation compound (GIC) start moving in the interlayer spacing of graphite to aggregate. The aggregate of metallic atoms also moves in the interlayer spacing of graphite and coalesces with other aggregates or metallic atoms. The activity to move decreases with increasing size. After this aggregate grows to a certain size and its spontaneous movement is restricted, its growth is carried out by coalescence with other aggregates or atoms, which can move actively due to smaller size and coalesce into this immobile aggregate. As the activity of particle precursors (i.e. metal atoms or their aggregates) to move in the graphite gallery is determined by the bulk melting point of the metal, the lower the bulk melting point, the better the chance the precursor has of growing to a great size, which explains the order of the particle size Fe < Ni < Cu. The dependence of the stage number of starting GICs on the particle size is explicable, assuming the mechanism described above. In this letter, we discuss temperature dependence on the size of fine metallic particles and the form of particles. The preparation method of stage 2 FeC13, NiC12 and CuC12 GICs was shown in the previous letter [6]. Each metal chloride GIC ( -10 rag) was immersed in 2 ml tetrahydrofuran (THF) in the presence of 50 mg naphthalene and 200 mg lithium. The mixture was sealed in a Pyrex glass tube and allowed to stand for 21 days at various temperatures: -70 °C, 0 °C, 25 °C and 50 °C. The size of metallic particles, obtained in the graphite matrix, was estimated from the line width of the X-ray diffraction (XRD) profiles, based on Scherrer's formula. The estimated size is listed in Table I. When atoms of zero-valent metal or their aggregates move in the interlayer spacing of graphite, the activity to move is expected to be