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In this work, the phase purity and size of zirconia nanocrystals samples were studied in terms of zirconium concentration, added water content and subsequent use of a post solvothermal treatment. The progressive tetragonal-to-monoclinic transformation of zirconia sample was observed to be strongly related to the water content of the alcoholic medium. But more surprisingly, it has been shown that even under initially anhydrous conditions and for particle size below 5 nm, the phase purity of the samples was deteriorated by a side-reaction of alcohol dehydration catalyzed by the surface of the nanoparticles (NPs). Since the phase transformation is essentially driven by the water content of the reaction mixture, we have shown that it was possible to recover an excellent phase purity without the help of any usual dopants

In this study, nanocrystalline hydroxyapatite and biphasic calcium phosphate prepared via wet chemical precipitation technique in an isolated N2 environment that utilizes calcium hydroxide and ammonium dihydrogenphosphate as main precursors, is presented. Formation of predominantly hydroxyapatite with increasing crystallinity from 39.6 to 88.3% with corresponding crystallite sizes of ∼20.6 and ∼46.6 nm were found for the as‐grown and the annealed powders, respectively. Partly phase transition of hydroxyapatite to β‐TCP phase forming biphasic calcium phosphate was observed in the 900 oC annealed powders. Aggregated structures with nanopores were depicted on the surface of the as‐grown sample while interconnected worm‐like structures with voids forming nanopores were found for the sample annealed at 900 oC. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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