Nanosize cobalt boride particles: Control of the size and properties

Cobalt boride is obtained by the reduction of cobalt (2-ethyl hexyl) sulfosuccinate, Co(AOT)(2), by sodium borohydride either in reverse micelles or in a diphasic system. In Co(AOT)(2)/Na(AOT)/H2O reverse micellar solution, the size and polydispersity of the Co2B particles is controlled by the size of the water droplets, which increases from 4 to 7.5 nm by increasing the water content. In a diphasic system of Co(AOT)(2)/isooctane and sodium borohydride in aqueous solution, large and polydisperse particles of cobalt boride are formed (similar to 10 nm), and their magnetization properties are presented. The smallest particles are in a superparamagnetic regime at room temperature, whereas the largest particles show ferromagnetic behavior.