Synthesis of nickel ferrite-dispersed carbon composites by pressure pyrolysis of organometallic polymer

Abstract

Nickel ferrite-dispersed carbon could be synthesized by pressure pyrolysis of divinylbenzene (DVB)-vinylferrocene (VF)-nickelocene (Cp₂Ni) polymer in the presence of water under 125 MPa and at temperatures below 700°C. By heat treatment at 550°C with water, nickel ferrite particles could be dispersed finely in the carbon matrix, although a small amount of nickel-iron carbide also began to form above 600°C. The morphologies of the carbon particles formed were observed to be polyhedral, coalescing spherulitic and spherulitic. When 30 wt% H₂O, spherulitic carbons a few micrometres in diameter were prepared, in which nickel ferrite particles from 10–30 nm were dispersed in the carbon matrix. The saturation magnetization of carbon composites formed from DVB-3.0 mol% Cp₂Ni-6.0 mol% VF and 20 wt% H₂O at 550°C was about 30 e.m.u.g⁻¹ and increased with pyrolysis temperature. The coercive force of the carbon composite was 120 Oe and was affected by the amount of added water using pressure pyrolysis. Thermomagnetic measurement shows that the Curie temperature of nickel ferrite-dispersed carbon was about 580 °C.