Sintering behavior of hydroxyapatite ceramics prepared by different routes

The sintering behaviour of three different HA, i.e. a commercial HA(C) and synthesized HA by wet precipitation, HA(W) and mechanochemical method, HA(M) were investigated over the temperature range of 1000°C to 1350°C. In the present research, a wet chemical precipitation reaction was successfully employed to synthesize highly crystalline, high purity and single phase stoichiometric HA powder that is highly sinteractive particularly at low temperatures below 1100°C. It has been revealed that the sinterability and mechanical properties of the synthesized HA by this method was significantly higher than that of the commercial material and HA which was synthesized by mechanomical method. The optimum sintering temperature for the synthesized HA(W) was 1100°C with the following properties being recorded: 99.8% relative density, Vickers hardness of 7.04 GPa and fracture toughness of 1.22 MPam½. In contrast, the optimum sintering temperature for the commercial HA(C) and synthesized HA(M) was 1300°C with relative density of 98% and 95.5%, Vickers hardness of 5.47 GPa and 4.73 GPa, fracture toughness of 0.75 MPam½ and 0.82 MPam½ being measured, respectively

Synthesis of high fracture toughness of hydroxyapatite bioceramics

The sinterability of magnesium oxide (MgO) doped hydroxyapatite (HA) ranging from 1 to 10 wt% when sintered at 1150°C was investigated in terms of phase stability, bulk density, Young's modulus, Vickers hardness and fracture toughness. The addition of up to 1 wt% MgO as sintering additive was found to be beneficial in promoting the densification of HA. Further addition of MgO in the HA matrix would deteriorate its densification properties. Similar results were observed for its stiffness and Vickers hardness. Nevertheless, the fracture toughness of HA was greatly enhanced by the incorporation of 5 wt% MgO. An increased toughness of up to 35% was obtained for the MgOdoped HA when compared to the undoped HA. This improvement is associated to the smaller grain size of the doped sample as compared to the undoped HA

Pressureless sintering of electro-conductive zirconia composites

In the present work, 3 mol% Yttria-stabilized tetragonal zirconia (Y-TZP) composite containing 25 wt.% of zirconium diboride (ZrB2) was prepared via pressureless sintering method in an inert atmosphere over the temperature range of 1350-1550°C for one hour. The effect of zirconium diboride content in the zirconia matrix, as well as the sintering temperature on densification, phase stability and electrical properties of sintered samples have been studied. The results revealed that there was a significant increased in electrical conductivity of sintered samples when 25 wt.% of ZrB2 is incorporated into Y-TZP matrix

Dependence of the fracture toughness on the sintering time of dense hydroxyapatite bioceramics

Fracture toughness dependence of sintered hydroxyapatite (HA) bioceramics on the sintering time was studied. The nanocrystalline and highly pure Hydroxyapatite powders produced by wet chemical precipitation method were used as starting material. After uniaxial and cold isostatic pressing, the green HA samples sintered at temperatures ranging from 1000 °C to 1300 °C with different sintering time. Dense compacts with grain sizes in the nanometer to micrometer range were processed. The average grain size of HA compact sintered at 1000 °C was around 500 nm. Grain size increased to 3 μm when the compacts were sintered at higher temperature. The average microhardness value of sintered HA decreased with an increased in grain size. Indentation fracture toughness for HA compacts of 700 nm grain size was 1.41±0.4 MPa.m1/2 which is similar to fracture toughness of human cortical bone

Characterization of forsterite bioceramics

The present work is on the synthesis of forsterite (Mg2SiO4) powder using talc and magnesium oxide powders as the starting materials followed by a heat treatment process. Sintering behavior and mechanical properties of the forsterite bodies were evaluated from 1200ºC to 1500°C. Forsterite phase were detected in samples without any secondary phases at all sintering temperatures. A very high fracture toughness of 4.9MPa.m1/2 and Vickers hardness of 7.1GPa were measured for samples sintered at 1400°C, thus indicating the viability of this ceramic for biomedical application

Effects of bismuth oxide on the sinterability of hydroxyapatite

The sinterability of Bi2O3-doped hydroxyapatite (HA) has been studied and compared with the undoped HA. Varying amounts of Bi2O3 ranging from 0.05 wt% to 1.0 wt% were mixed with the HA. The study revealed that most sintered samples composed of the HA phase except for compacts containing 0.3, 0.5 and 1.0 wt% Bi2O3 and when sintered above 1100 8C, 1000 8C and 950 8C, respectively. In general, the addition of 0.5 wt% Bi2O3 was identified as the optimum amount to promote densification as well as to improve the mechanical properties of sintered HA at low temperature of 1000 8C. Throughout the sintering regime, the highest value of relative bulk density of 98.7% was obtained for 0.5 wt% Bi2O3-doped HA when sintered at 1000 8C. A maximum Young’s modulus of 119.2 GPa was measured for 0.1 wt% Bi2O3-doped HA when sintered at 1150 8C. Additionally, the ceramic was able to achieve highest hardness of 6.08 GPa and fracture toughness of 1.21 MPa m1/2 at sintering temperature of 1000 8C

Sintering of hydroxyapatite ceramic produced by wet chemical method

In the present work, densification of synthesised hydroxyapatite (HA) bioceramic prepared via chemical precipitation method was investigated. HA samples was prepared by compaction at 200 MPa and sintered at temperatures ranging from 800°C to 1400°C. The results revealed that the HA phase was stable for up to sintering temperature of 1250°C. However, decomposition of HA was observed in samples sintered at 1300°C with the formation of tetra-calcium phosphate (TTCP) and CaO. Samples sintered above 1400°C were found to melt into glassy phases. The bulk density increases with increasing temperature and attained a maximum value of 3.14 gcm-3 at 1150°C whereas maximum hardness value of 6.64 GPa was measured in HA sintered at 1050°C. These results are discussed in terms of the role of grain size. © (2011) Trans Tech Publications, Switzerland

Effects of powder synthesis method on the sinterability of hydroxyapatite

The sinterability of hydroxyapatite (HA) powder synthesized through a novel wet chemical method (HAp) and a wet mechanochemical method (HAwm) was investigated over a temperature range of 1000oC to 1400oC in terms of phase stability, bulk density, hardness and fracture toughness. The results indicated that the sinterability of HAp powder were significantly better than HAwm powder. Moreover, the XRD traces of HAwm sintered samples showed signs of decomposition into TTCP when sintered at 1300oC and above. Densification of ~98% of theoretical density was attained by HAp compacts at 1100oC while the HAwm compacts exhibited only ~96% of theoretical density even at 1350oC with no significant increase of density at 1400oC. The Vickers hardness of HAp showed increasing trend for temperature range of 1000oC to 1100oC with the compacts attaining HV of ~7 GPa at 1100oC. Subsequently, the hardness decreased with increasing sintering temperature though the value does not dropped below ~5 GPa. Similarly, HAwm compacts showed an increasing trend from 1000oC to 1300oC with the largest HV attained was ~4.57 GPa. Further increased in sintering temperature resulted in the decreased of Vicker’s hardness. Moreover, the HAp samples reached a maximum fracture toughness of ~0.9 MPam1/2 at 1050oC while the HAwm attained maximum KIc of only ~0.7 MPam1/2 at 1300oC

Effects of bismuth oxide on the properties of calcium phosphate bioceramics

The aim of this work is to study the phase stability and sinterability of bismuth oxide (Bi2O3) doped HA ranging from 0.05 wt% to 1 wt%. The green samples were sintered in air at temperature ranging from 1000oC to 1400oC. In this experiment, the results from XRD analysis revealed that the stability of HA phase was disrupted when addition of 0.3, 0.5 and 1.0 wt% Bi2O3 were used and when samples sintered above 1100oC, 1000oC and 950oC, respectively. In general, HA containing 0.5 wt% of Bi2O3 and when sintered at 1000oC was found to be beneficial in enhancing densification, Young’s modulus, Vickers hardness and fracture toughness. Throughout the sintering regime, the highest value of relative bulk density of 98.7% was obtained for 0.5 wt% Bi2O3-doped HA when sintered at 1000oC. A maximum Young’s modulus of 119.2 GPa was observed for 0.1 wt% Bi2O3-doped HA when sintered at 1150oC. Additionally, 0.5 wt% Bi2O3-doped HA was able to achieve highest hardness of 6.04 GPa and fracture toughness of 1.21 MPam1/2 at sintering temperature of 1000oC. Furthermore, the Young’s modulus of HA was found to vary linearly with bulk density