Biological apatites contain several elements as traces. In this work, magnesium and fluorine co-substituted hydroxyapatites with the general formula Ca 9 Mg(PO 4 ) 6 (OH) 2-y F y , where y = 0, 0.5, 1, 1.5 and 2 were synthesized by the hydrothermal method. After calcination at 500˚C, the samples were pressureless sintered between 950˚C and 1250˚C. The substitution of F − for OH − had a strong influence on the densification behavior and mechanical properties of the materials. Below 1200˚C, the density steeply decreased for y = 0.5 sample. XRD analysis revealed that compared to hydroxylfluorapatite containing no magnesium, the substituted hydroxyfluorapatites decomposed, and the nature of the decomposition products is tightly dependent on the fluorine content. The hardness, elastic modulus and fracture toughness of these materials were investigated by Vickers's hardness testing. The highest values were 622 ± 4 GPa, 181 ± 1 GPa and 1.85 ± 0.06 MPa·m 1/2 , respectively.
Phosphate(III)-tetrahedra, NaO 6-and ScO 6-octahedra together form a (3, 6)-connected net. Thermochemical property studies show that during heating hydrogen and water are released while part of the phosphate(III) groups are oxidized to phosphate(V). Sc[PO 3 ] 3 is formed as the main crystalline decomposition product. NaSc 3 [HPO 3 ] 2 [HPO 2 (OH)] 6 represents the first example containing scandium within the family of M Ι M III metal phosphates(III). The replacement of phosphate(V) tetrahedra by phosphate(III) groups leads to a reduction of M-O-P connections, resulting in more open frameworks.[2]
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