Synthesis and properties of cobalt-dispersed carbons by pressure pyrolysis of organocobalt polymers

Abstract

Cobalt-dispersed carbons were synthesized by pressure pyrolysis of cobaltocene-divinylbenzene and phenylallylcobaltocene-divi nylbenzene at 125 MPa below 700° C. The carbons resulting from cobaltocene-divinylbenzene contained uniformly dispersed fine particles, < 20 nm diameter, of metallic cobalt of lower crystallinity, which were composed of ferromagnetic and superparamagnetic particles. Metallic cobalt particles of cubic and hexagonal structures with higher crystallinity were formed during pyrolysis of phenylallylcobaltocene-divinyibenzene. Cobaltucence-divinylbenzene and phanylallylcobaltocene-divinylbenzene changed their magnetic properties from diamagnetism to paramagnetism at 250 and 200° C, respectively. The infrared absorption band of the cyclopentadienyl ring at 995 cm⁻¹ disappeared at 350° C in cobaltocene divinylbenzene and at 300° C in phenylallylcobaltocene-divinylbenzene. Superparamagnetic particles from cobaltocene-divinylbenzene aggregated and crystallized to produce larger particles of diameter 30 to 100 nm, which increased the magnetization during thermomagnetic measurement. The saturation magnetization of cobalt-dispersed carbons from phenylallylcobaltocene-divinylbenzene was higher by about 10% than that from cobaltocene-divinylbenzene. The coercive forces of cobalt-dispersed carbon from phenylallylcobaltocene-divinylbenzen and cqbaltocene-divinylbenzene were 350 and 250 Oe (2.79 × 10⁴ and 1.99 × 10⁴ Am⁻¹), respectively.