Method for the synthesis of CrO2 at ambient pressure and temperature

Abstract

In this article, we report the synthesis of metastable chromium dioxide at ambient temperature and pressure. The formulation of this method is based on the fact that the CrO2 particles used in magnetic recording tapes are chemically unstable and react with the organic binder, leading to a disproportionate reaction that produces nonmagnetic Cr(III)OOH and H2Cr(VI)O4 compounds. This suggests that it is also possible to synthesize CrO2 by reacting Cr(III) with Cr(VI) under appropriate conditions. Thus, metastable chromium dioxide (CrO2) powder was synthesized by mechanically grinding a mixture of CrO3 and Cr(OH)3 to induce a solid–solid reaction at atmospheric temperature and pressure. The characteristics of the product obtained after mechanical grinding of the above mixture depended on parameters such as the preparation conditions for the starting material Cr(OH)3, the grinding time, the rotational speed of the mill and the mole ratio of CrO3 and Cr(OH)3. An x-ray diffraction pattern of the product obtained under optimum conditions was in excellent agreement with the profile of CrO2. Furthermore, the powder was strongly ferromagnetic, with saturation magnetization of 63 emu/g in an applied field of 1 T.