A Novel Route for the Easy Production of Thermochromic VO₂ Nanoparticles

In this work, a simple, fast and dry method for the fabrication of a thermochromic product with a high load of VO₂ (M1) consisting of the controlled heat treatment of pure vanadium nanoparticles in air is presented. After a complete design of experiments, it is concluded that the most direct way to attain the maximum transformation of V into VO₂ (M1) consists of one cycle with a fast heating ramp of 42 °C s^-1 , followed by keeping 700 °C for 530-600 seconds, and a subsequent cooling at 0.05 °C s^-1 . Careful examination of these results lead to a second optimum, even more suitable for industrial production (quicker and less energy-intensive because of its lower temperatures and shorter times), consisting of subjecting V to two consecutive cycles of temperatures and times (625 °C for 5 minutes) with similar preheating (42 °C s^-1 ) but a much faster postcooling (∼ 8 °C s^-1 ). These green reactions only use the power for heating a tube open to atmosphere and a vanadium precursor; without assistance of reactive gases or catalysts, and no special vacuum or pressure requirements. The best products present similar thermochromic properties but higher thermal stability than commercial VO₂ particles. These methods can be combined with VO₂ doping.