Reactive fabrication of spherical ZnO–MgO solid-solution submicrometer particles by pulsed laser melting in liquid

Abstract

Pulsed laser irradiation with an appropriate laser fluence (50–200 mJ pulse⁻¹ cm⁻²) onto photo-absorptive ceramic or metallic nanoparticles dispersed in liquid can induce a rapid rise in the local temperature to 1000–3000 K of the particles, instantaneous generation of melt droplets, and formation of spherical particles of high-temperature materials via quenching. Such space-selective pulsed heating through optical absorption may enable reactive powder processing through mimicking of conventional high-temperature ceramic or metallurgical-reaction processes. Here, by combining photo-absorptive ZnO and non-photo-absorptive MgO as raw particles, the laser irradiation technique for high-temperature powder reaction was applied to check whether submicrometer spherical ZnO–MgO solid-solution particles can be generated. Various raw-particle mixtures obtained by mechanical milling, coprecipitation from inorganic salts, and thermolysis of organic salts were tested; the produced particles were characterized to reveal the effects of temperature on the composition of MgO included in ZnO host crystals. The raw-particle mixtures composed of small particles tended to transform into ZnO–MgO particles with high MgO content. Physicochemical calculations and experimental results revealed the importance of appropriate particle sizes of photo-absorptive ZnO and non-photo-absorptive MgO, their mutual close contact, and laser irradiation conditions in the reactive fabrication of ZnO–MgO submicrometer particles.