Crystalline cerium(III) phosphate (CePO₄), cerium(IV) phosphates, and nanocrystalline ceria are considered to be promising components of sunscreen cosmetics. This paper reports on a study in which, for the first time, a quantitative comparative analysis was performed of the UV-shielding properties of CePO₄, Ce(PO₄)(HPO₄)_0.5(H₂O)_0.5, and CePO₄/CeO₂ composites. Both the sun protection factor and protection factor against UV-A radiation of the materials were determined. Ce(PO₄)(HPO₄)_0.5(H₂O)_0.5 was shown to have a sun protection factor of 2.9, which is comparable with that of nanocrystalline ceria and three times higher than the sun protection factor of CePO₄. Composites containing both cerium dioxide and CePO₄ demonstrated higher sun protection factors (up to 1.8) than individual CePO₄. When compared with the TiO₂ Aeroxide P25 reference sample, cerium(III) and cerium(IV) phosphates demonstrated negligible photocatalytic activity. A cytotoxicity analysis performed using two mammalian cell lines, hMSc and NCTC L929, showed that CePO₄, Ce(PO₄)(HPO₄)_0.5(H₂O)_0.5, and nanocrystalline ceria were all non-toxic. The results of this comparative study indicate that cerium(IV) phosphate Ce(PO₄)(HPO₄)_0.5(H₂O)_0.5 is more advantageous for use in sunscreens than either cerium(III) phosphate or CePO₄/CeO₂ composites, due to its improved UV-shielding properties and low photocatalytic activity.

This study presents the fabrication possibilities of ultra-high-temperature ceramics of ZrB₂-30 vol.%SiC and (ZrB₂-HfB₂)-30 vol.% SiC composition using the reaction spark plasma sintering of composite powders ZrB₂(HfB₂)-(SiO₂-C) under two-stage heating conditions. The phase composition and microstructure of the obtained ceramic materials have been subjected to detailed analysis, their electrical conductivity has been evaluated using the four-contact method, and the electron work function has been determined using Kelvin probe force microscopy. The thermal analysis in the air, as well as the calcination of the samples at temperatures of 800, 1000, and 1200 °C in the air, demonstrated a comparable behavior of the materials in general. However, based on the XRD data and mapping of the distribution of elements on the oxidized surface (EDX), a slightly higher oxidation resistance of the ceramics (ZrB₂-HfB₂)-30 vol.% SiC was observed. The I-V curves of the sample surfaces recorded with atomic force microscopy demonstrated that following oxidation in the air at 1200 °C, the surfaces of the materials exhibited a marked reduction in current conductivity due to the formation of a dielectric layer. However, data obtained from Kelvin probe force microscopy indicated that (ZrB₂-HfB₂)-30 vol.% SiC ceramics also demonstrated enhanced resistance to oxidation.