Synthesis of high-surface-area complex zirconium phosphates via mechanochemical activation route

High-power ball mill activation of the mixture of hydrated zirconium and la nthanum salts (oxonitrates, oxochlorides) with ammonium phosphate followed by hydrothermal treatment at temperatures not exceeding 200 degrees C and a nearly neutral pH was found to yield crystalline dispersed phase of a cubi c NH4Zr2(PO4)(3) type along with admixtures of disordered orthorhombic comp ounds of a zirconium orthophosphate type. In the same conditions and at the same Zr/P ratio, hydrothermal treatment of gels obtained by reacting mixed zirconium and lanthanum nitrates solutions with ammonium phosphates yields no crystalline products, and only treatment in acid media generates a phas e of the alpha-ZrPO4(OH) type coexisting with the NH4Zr2(PO4)(3) phase if p olyethylene oxide is present. X-ray powder diffraction, transmission electr on microscopy, (31)MAS-NMR, FTIRS and thermal analysis were applied to eluc idate factors affecting crystallization of complex zirconium phosphates in the hydrothermal conditions. The most essential factor appears to be genera tion of some nuclei of zirconium phosphates under high pressures developed in the course of mixed solids mechanical activation. These nuclei are embed ded into matrix of such well-crystallized solid products as ammonium nitrat e or chloride. Hence, metastable cubic or orthorhombic structure of the pha ses obtained via mechanical activation route can be assigned to the nuclei- matrix orientation relationship. Due to easily scaled-up synthesis procedur e, these results appear to be very promising for manufacturing of dispersed framework zirconium phosphates as acid catalysts or fast proton conductors .