Fluorination synthesis of MgF2 nanoparticles synthesized for manufacturing IR windows by hot-pressing

Abstract In this study, magnesium fluoride (MgF2) nanoparticles were synthesized through the fluoridation method, by dissolving magnesium chloride and hydrofluoric acid (HF) in deionized water. The influences of some parameters, including pH, concentration ratio of reactants, F:Mg mole ratio, washing method and calcination temperature were investigated on the particle size, morphology, chemical purity and phase purity of MgF2 nanoparticles. In order to study the impact of pH on the properties of MgF2 nanoparticles, different samples at pH values of 1, 5 and 9 were synthesized. The obtained results revealed that as pH value increased from 1 to 9, the morphology of MgF2 nanoparticles changed from rod to spherical shape. The effect of mole ratio of fluorine ions to magnesium ions on the MgF2 nanoparticles at three ratios of 2, 6 and 12 also demonstrated that by increment of F:Mg mole ratio, the particle size was decreased from 150 nm to 30 nm. In addition, it was figured out that by the increment of F:Mg mole ratio, the MgO phase was eliminated. Afterwards, by decreasing the HF:MgCl2 molar ratios from 0.1 to 0.03 the particle size reduced from 300 nm to 30 nm. After determining the optimal synthesis conditions, magnesium fluoride nanoparticles were calcined at 470, 530 and 600 °C. Regarding the results, the powder that was calcined at 600 °C with a particle size of about 30–40 nm was selected as the optimal sample. Ultimately, the resulting powder was sintered using hot-press (HP) at a temperature of 700 °C for 45min in the vacuum pressure of 10−3 bar. After polishing the sintered piece, its inferred (IR) transparency was over 90% in the wavelength ranges of 3–5 μm.