Grain Growth in Sintered Natural Hydroxyapatite

Hydroxyapatite $(HA: Ca_{10}(PO_4)_6(OH)_2)$ can be synthesized using several methods or manufactured from natural materials such as coral or bone after removal of the organic matter by heating (denoted as NHA). The "in vitro" and "in vivo" studies showed that the natural apatite was well tolerated and has better osteoconductive properties than synthetic HA. In addition, the exploitation of natural source represents an economical way of synthesizing NHA by means of sintering, rather than by sol-gel techniques. For these reasons, the NHA was manufactured from cortical bovine bones in all our studies. Moreover, there has been much effort to improve the mechanical properties of HA by introducing foreign oxides or finding out other alternative processes such as grain growth control. Indeed, encouraging lower AGS instead of exaggerated grain growth may be jugged useful for many applications. Since the works carried out on the correlation between AGS and physico-chemical properties of NHA were very limited, the present study was mainly focused on its grain growth. A carful combination between the main parameters controlling NHA production such as milling techniques, compacting pressure, sintering temperature and holding time may lead to an interesting NHA based bio-ceramics. In this way, a simple and energetically vibratory multidirectional milling system using bimodal distribution of highly resistant ceramics has been used for obtaining sub-micron sized NHA powders. For example, the AGS was ranged between 0.75 and 1.40 μm (using intercept method) when NHA samples were sintered at 1250°C for 15 and 480 min, respectively

Grain Growth in Sintered Natural Hydroxyapatite

Hydroxyapatite (HA: Ca10(PO4)6(OH)2) can be synthesized using several methods or manufactured from natural materials such as coral or bone after removal of the organic matter by heating (denoted as NHA). The in vitro and in vivo studies showed that the natural apatite was well tolerated and has better osteoconductive properties than synthetic HA. In addition, the exploitation of natural source represents an economical way of synthesizing NHA by means of sintering, rather than by sol-gel techniques. For these reasons, the NHA was manufactured from cortical bovine bones in all our studies. Moreover, there has been much effort to improve the mechanical properties of HA by introducing foreign oxides or finding out other alternative processes such as grain growth control. Indeed, encouraging lower AGS instead of exaggerated grain growth may be jugged useful for many applications. Since the works carried out on the correlation between AGS and physico-chemical properties of NHA were very limited, the present study was mainly focused on its grain growth. A carful combination between the main parameters controlling NHA production such as milling techniques, compacting pressure, sintering temperature and holding time may lead to an interesting NHA based bio-ceramics. In this way, a simple and energetically vibratory multidirectional milling system using bimodal distribution of highly resistant ceramics has been used for obtaining sub-micron sized NHA powders. For example, the AGS was ranged between 0.75 and 1.40 µm (using intercept method) when NHA samples were sintered at 1250 C for 15 and 480 min, respectively

Effect of stabilized ZrO2, Al2O3 and TiO2 on sintering of hydroxyapatite

International audienceIn this work, the hydroxyapatite was prepared from cortical bone after calcination at 700°C during 1 hour. In order to improve mechanical properties of HA, 5 wt% of the ZrO2 (stabilized with 12.0 wt% CeO2), Al2O3 and TiO2 were added to HA powder as a reinforcing phase. All the powders were sintered at 1300°C for 2 hours. The XRD was utilized to identify the phases composition. It was found that the initial calcined powder is hydroxyapatite with the following chemical composition Ca5(PO4)3OH. In addition, the phenolphthalein test has put into evidence the existence of free CaO. For powders containing ZrO2, the XRD spectra has showed a little percent of formed b-tricalcium phosphate (b-TCP); the HA was decomposed to (b-TCP) and CaO which forms with ZrO2 the calcium zirconate (CaZrO3). Nevertheless, in powders containing TiO2, the XRD spectra showed that a partial decomposition of HA to b-TCP was occurred with formation of calcium titanium oxide (CaTiO3). However, for powders containing Al2O3, a nearly full decomposition of HA to b-TCP was occurred, the free Al2O3 was present. Finally, it has been found that HA composites containing a large amount of b-tricalcium phosphate are resorbale than HA composites containing a small amount of b-TCP and they were not well densified. The microhardness values of HA- ZrO2 composites were greater than those of HA- Al2O3 and HATiO2 composites

Dissolution kinetic and structural behaviour of natural hydroxyapatite vs. thermal treatment. Comparison to synthetic hydroxyapatite.

International audienceThe dissoln. kinetic and structural behavior of natural hydroxyapatite (N-HA) and synthetic hydroxyapatite (S-HA) was studied vs. sintering temp. and using 'in vitro' expts. Obtained results highlight the chem. stability of N-HA. Any structural modification was obsd. until 1200°C. In the fact S-HA undergoes some modifications. XRD diagrams show the tricalcium phosphate (TCP) phase formation between 800 and 1100°C and tetracalcium phosphate (TetCP) phase formation at 1200°C. The 'in vitro' assay shows that the dissoln. was occurred more in N-HA than in S-HA. The formed TCP activated the dissoln. kinetic and then the pptn. phenomena when a continuous dissoln. of TetCP leaded to slow down the kinetic pptn

Mechanical properties of anorthite based ceramics prepared from kaolin DD2 and calcite

Abstract Good quality ceramics costs a lot that has limited their use in developing countries. This work was devoted to prepare low-cost and good quality anorthite based ceramics. The proposed composition was 80 wt% kaolin (DD2 type) and 20 wt% calcium oxide (CaO). The choice of these raw materials was dictated by their natural abundance coupled with a modified milling system, as another interesting advantage. Previous studies have shown that a simple vibratory multidirectional milling system using bimodal distribution of highly resistant ceramic milling elements has been successfully applied for obtaining fine powders. The influence of the relatively lower sintering temperature, ranging from 800 to 1100 °C, on the porosity and the average pore size (APS) have been investigated. The APS and the porosity values of samples sintered at 950 °C were about 1 μm and 4%, respectively. The best Vickers microhardness and 3-point bending strength values for these sintered samples, using this proposed milling system, were 7.1 GPa and 203 MPa, respectively. Finally, the crystalline phase evolution during heat treatment was investigated by X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy techniques