Hydroxyapatite (HA) refers to biomaterials that have components with similar compositions and structures as natural bone in the human body and used widely in the medical field. Recently, HA has become a huge demand worldwide for bone tissue engineering applications. Therefore, specific research on both physical and chemical properties of HA is very important for bone tissue engineering applications which are practically excellent in biocompatibility, bioactivity, osteoconductivity and biodegradability.

In this study, HA derived from ark clam shell (ARC) was used as calcium precursor due to the high composition of calcium. HA synthesis via wet chemical method by controlling Ca:P ratio at ~1.69 to study the effect of pH values an HA phases, composition and structure. The range of pH values was set to be in the range of 8 to 10. In addition, in every HA sample with pH values varies were extended to synthesize at various sintering temperatures from 200 to 1400°C for 4 hours. The entire sintered HA samples were analyzed by XRD, FTIR, FESEM, density measurement and Vickers microhardness to investigate physical and chemical behavior.

From the XRD results, the single phase of HA is obtained and remains stable at sintering temperature between 200 to 1000  °C with both pH value of 8 and 10. At pH 9, the single phase of HA stable until at 800°C and starts to decompose into different phases of HA and b-TCP at 1000°C. However, both pH of 8 and 10 sintered HA samples start decompose into b-TCP when sintered higher than 1100°C. Single phase HA decompose into another single phase b-TCP at 1100 °C and 1400°C. Difference condition is observed for pH of 9 and 10 where the biphase of HA/b-TCP is present in the XRD result sintered at 1100°C to 1400°C. However, the peak intensity of both HA and /b-TCP in the XRD shows the HA is the dominant phase compared to b-TCP phase on both pH 9 and 10 at that range of sintering temperature.

Besides that, the FTIR results proved that the chemical groups composition of HA and b-TCP shows the presence of CO₃^2-, PO₄^3- and OH^- vibration groups. All the three pH values show the increasing density as sintering temperature increases but the density drops when the single phase of HA starts to decompose to the different phase of HA and b-TCP. It can be related to their hardness which is increasing as sintering temperature increases but it is started to decrease since the HA start to decompose to different phase of HA and b-TCP.

Based on the result, it shows the optimal condition for single phase of HA at pH of 10 from 200 to 1200°C, and the maximum hardness is 6.05 GPa at 1100°C with pH 9. The FESEM morphology of HA at all pH value shows the identically which is irregular in shape of grains. The pores can be seen at the low sintering temperature increases due to densification process and crystal growth.

Fig.1: XRD pattern of HA with initial pH value of 8 at different sintering temperature a) 200°C, b) 600°C, c) 800°C, d) 1000°C

Fig. 2: XRD pattern of HA with initial pH value of 9 at different sintering temperature a) 200°C, b) 600°C, c) 800°C, d) 1000°C.

Fig. 3: XRD pattern of HA with initial pH value of 10 at different sintering temperature a) 200°C, b) 600°C, c) 800°C, d) 1000°C.

Table 1: The crystalline phase of HA and P-TCP with different initial pH values at the various sintering temperature in a range of 200 to 1400°C

*Abstract of the thesis (MSc) by Mohammad Zulhasif bin Ahmad Khiri

For further information, please contact:

Khamirul Amin Matori, PhD
khamirul@upm.edu.my

Date of Input: 12/11/2025 | Updated: 12/11/2025 | roslina_ar