We reported on the synthesis of nanosized hydroxyapatite particles by wet chemical precipitation method and the consolidation of the nanoparticles by spark plasma sintering. We studied the effect of the synthesis temperature on the particle size and phase composition of the obtained HAp. During synthesis beyond HAp, another phase supposedly nonstoichiometric HAp was also formed as a by-product that can be detected by thermal analysis combined with XRD. Its amount gradually decreased with the increase in synthesis temperature and practically disappeared at 80°C. Using this nanopowder for sintering, the spark plasma-sintered ceramics retained their nanostructure comprising only HAp phase in contrast to the powders synthesized at lower temperature when transformed products of the nonstoichiometric HAp could also be detected.

A simple synthetic method was developed to prepare 4[Agpy 2 ClO 4 ]Á[Agpy 4 ]ClO 4 in a low-temperature decomposition process of [Agpy 4 ]ClO 4 . A detailed IR, Raman and far-IR study including factor group analysis has been performed, and the assignation of bands is given. The compound decomposes quickly with a multistep ligand loss process with the formation of [Agpy 2 ]ClO 4 and AgClO 4 intermediates and AgCl as an end product around * 85, * 350 and 450°C, respectively. During the first decomposition step, a small fraction of the ligands is lost in a redox reaction: perchlorate oxidizes the pyridine, forming carbon, carbon dioxide, water and NO, while it itself is reduced into AgCl. In the next step, when AgClO 4 forms after complete ligand loss and reacts with the carbon formed in the degradation of pyridine at lower temperatures and produces NO, CO 2 and H 2 O. This reaction becomes possible because the AgCl formed in the redox reactions makes a eutectic melt with AgClO 4 in situ, which is a favorable medium for the carbon oxidation reaction. AgCl is known to reduce the temperature of decomposition of AgClO 4 , in which process forms AgCl as well as O 2 and so is an autocatalytic process. The loss and degradation of pyridine ligand are endothermic; the redox reactions including carbon oxidation and AgClO 4 decomposition into AgCl and O 2 are exothermic. The amount of absorbed/evolved heats corresponding to these processes was determined by DSC both under N 2 and O 2 atmospheres. Keywords Pyridine-silver complexes Á Perchlorates Á Quasi-intramolecular solid-phase redox reaction Á Evolved gas analysis Á DSC Electronic supplementary material The online version of this article (

Hydroxyapatite / graphene (HAP/GNPs) composites were prepared by spark plasma sintering (SPS).Sintering was carried out at various temperatures (700°C and 900°C) and holding times (5 and 10 min). Mechanical and structural properties were studied. The highest relative density ~ 96% was