Nano-Sized Compositions of the LaPO₄–ZrSiO₄ System: Synthesis and Physicochemical Properties

In accordance with the developed original method of the sol-gel synthesis of compositions, based on the separate precipitation of components (using the reverse precipitation technique) followed by their mixing and sintering, ceramic composites based on the LaPO₄–ZrSiO₄ system are obtained. The developed sol-gel synthesis technique is based on the separate preparation of colloidal solutions of LaPO₄·nH₂O and zirconium hydroxide ZrO(OH)₂, formed after adding ammonia solution (sols) and an alcohol solution of TEOS (gel) by reverse precipitation and subsequent mixing of the sols and gel with the addition of the ammonia solution to obtain the corresponding compositions ((1 – x)LaPO₄·nH₂O–x(H₂SiO₃‒ZrO(OH)₂)) in the form of gels. The physicochemical properties of the powders are studied using the X-ray diffraction, DSC/TG, and sorption methods. The Vickers microhardness of the ceramic samples sintered in the temperature range of 1000–1300°C is measured. A Russian patent was obtained for the method of synthesizing composites based on LaPO₄. Mineral-like matrices based on the LaPO₄–ZrSiO₄ system are intended to be used for the immobilization and disposal of individual isotopes of the actinide–rare earth fraction of high-level waste (HLW).