Thermomagnetic studies of thermoexfoliated graphite-transition metal composites

Abstract

Thermal stability and magnetic susceptibility of thermoexfoliated graphite-metal (TEG-Me) composites have been investigated in the temperature range 300-850 K. The TEG-Me (Co, Ni) composites have been produced by the metal cation reduction in aqueous medium with sodium tetrahydroborate. The structure and phase composition of the products was characterized using X-ray diffraction, scanning electron microscopy, Auger electron spectroscopy and secondary ion mass spectrometry. The results of these investigations show that the metal in the green composites must exist in the bound state as Me—B and Me—H. The gradual heating (up to 850 K) or annealing (at 825 K) of the TEG-Me composites results in the appearance of ferromagnetic properties. Thermal cycling of TEG-Me composites results in a decreased magnetic susceptibility due to oxidation of metallic particles.