Effect of a novel sintering process on mechanical properties of hydroxyapatite ceramics

Nanocrystalline hydroxyapatite with simultaneous enhancements in hardness and toughness

“…Nevertheless, one study [14] has shown that dense HA bodies (w99%) exhibit an increase in the hardness with decreasing the grain size from 8.8 to w0.5 mm. In contrast, a separate study [11] reveals that the hardness of HA shows little dependence on grain sizes with almost no change in the hardness when the grain size decreases from 1.7 to 0.19 mm. The same study [11], however, demonstrates that in the same grain size range the indentation toughness of HA is increased substantially from 0.98 to 1.92 MPa m 1/2 .…”

“…In contrast, a separate study [11] reveals that the hardness of HA shows little dependence on grain sizes with almost no change in the hardness when the grain size decreases from 1.7 to 0.19 mm. The same study [11], however, demonstrates that in the same grain size range the indentation toughness of HA is increased substantially from 0.98 to 1.92 MPa m 1/2 . Using a HA nanopowder and two different densification techniques (i.e., sintering and hot pressing), Veljovic et al [12] have shown that both the hardness and toughness of HA can be improved with a decrease in the grain size.…”

“…Thus, different approaches have been extensively investigated in order to improve the mechanical properties of HA. These approaches include adding dopants [4,5], making composites [3,[6][7][8], and controlling microstructures via novel sintering techniques or utilization of nanopowders [9][10][11][12][13][14][15][16][17][18][19][20].…”

Effect of grain size and microporosity on the in vivo behaviour of β-tricalcium phosphate scaffolds

“…Therefore, full densification can be achieved by two-step sintering: in a first stage, the ceramic is heated up at high temperature to rapidly reach a density superior to ≈ 75 %, and then the temperature is reduced by a few hundred degrees to fully densify the ceramic without concomitant grain growth (Chen and Wang, 2000). For example, Mazaheri et al sintered 98 % dense hydroxyapatite 60 s at 900 °C and 2 h at 800 °C and were able to reduce the grain size from 1.7 μm to 190 nm (Mazaheri et al, 2009).…”

Textured and hierarchically structured calcium phosphate ceramic blocks through hydrothermal treatment

“…With such methods, the final grain size strongly depends on the particle size of the initial powder, hence requiring nano-powders followed by quick sintering or two-step sintering processes in order to obtain a small final grain size [31]. Hydrothermal synthesis has already shown the potential of forming fine CaP (particularly HA) particles [32e34].…”