A method for heating a powder material to induce a crystalline phase change in the grains of the particle comprising the steps of: a. preheating the powder from the high temperature streams generated from cooling the phase changed product; b. injecting the powder into a metal tube; c. controlling the gas composition in the metal tube by injecting a gas into the reactor; d. externally heating the first section of the tube by a first furnace segment system; e. externally heating the second section of the tube by a second furnace segment system; f: quickly quenching the powder product temperature in a cold third segment of the tube; g. collecting the processed powder at the base of the tube in a bed ejecting the powder from the tube; h. cooling the powder in a heat exchanger and using the heat to preheat the powder in step a.