An improved process for preparation of chromium dioxide.

The process comprises charging a container containing chromium trioxide, water, alkali metal salts or ammonium salts, and a modifier into an autoclave at 500xB0;C, passing oxygen gas into the autoclave to generate an initial pressure of 8-12 MPa, heating the autoclave to 300-450xB0; C and 500-800 bars, maintaining the autoclave at maximum temperature for 1-4 hours, cooling to room temperature, removing CrO2 formed, washing, drying, and grinding into a free flowing powder. The modifier used is antimany trioxide and 1.3 wt% of CrO3