A Novel Route for the Easy Production of Thermochromic VO2 Nanoparticles

Abstract

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.