The effects of heat treatment on the magnetic properties of coals doped with metallic Ni

Abstract

The magnetic susceptibility and magnetic resonance spectroscopy of coals doped with Ni have been measured as a function of heat treatment temperature (HTT). Both the susceptibilities and magnetic resonance signals began increasing at HTT of 300 to 500°C by a factor of 10 2 to 10 3. The HTT corresponding to this steep increase shifted to higher temperatures with coal rank; 300°C for brown coal, 400°C for bituminous coal and 500°C for anthracite. With the changes in the magnetic properties, the state of aggregation of Ni particles in coals changed. From the parameters of magnetic resonance spectroscopy combined with x-ray diffraction data, it is presumed that ultrafine Ni particles (<100 Å) showing superparamagnetic behavior were formed in the brown coal, whereas relatively larger Ni particles (>100 Å) were produced in the bituminous coal and anthracite.