In this study, DCPD used as a starting powder was prepared by mixing 1.0M calcium nitrate solution and 1.0M ammonium hydrogen phosphate solution. The mixing was carried out at a room temperature. In order to control the pH value of the mixing solution, acetic acid and ammonia solution were added. The value of pH was kept around 8.5 initially, and then changed to 6.0 using the acetic acid and ammonia solution after the mixing in order to prevent the formation of impurities and to produce pure DCPD powders. It has been shown from preliminary tests that when no control of the pH was conducted the synthesized DCPD contained the impurities such as CaHPO4 (DCPA), and amorphous calcium phosphate (ACP). The precipitate from the mixture was filtered and washed with deionized water and acetone.

 The washed filter cake was oven-dried at 50ËšC for 24 hours, and then the dried cake was ground to a powder. No impurity in the synthesized DCPD used was detected by powder X-ray diffraction. The synthetic DCPD and calcium hydroxide were mixed in a mortar for 60min with a ratio of 1.67 which was stoichiometric ratio of HA. A commercially available pure Ti rod, 20mm in diameter, was used in this experiment. The Ti rod was cut into disks with a thickness of 10mm. The disks were cleaned in deionized water and acetone by using an ultrasonic cleaner. The Ti surfaces were finished using 1500# emery paper. After the surface finish with emery paper, the titanium disks were washed again by deionized water, and then dried in air. The powder mixture and Ti disks were placed into the middle of the autoclave simultaneously. The autoclave made of steel has a pistons-cylinder structure with an inside diameter of 20 mm. The pistons possess escape space for hydrothermal solution squeezed from the sample, and this space regulates the appropriate hydrothermal conditions in the sample. A grand packing of polytetrafluoroethylene (PTFE) is placed between a cast rod and push rod. The PTFE was used to prevent leakage of the hydrothermal solutions.

The stainless steel (SUS304) autoclave has pistons within a cylindrical structure with an inside diameter of 20 mm. The pistons enable the hydrothermal solution squeezed from the sample to escape, and this regulates the appropriate hydrothermal conditions in the sample. Polytetrafluoroethylene (PTFE) is packed between a cast rod and a push rod. The PTFE was used to prevent leakage of the hydrothermal solutions. Pressure of 40 MPa was initially applied to the sample through the push rods from the top and bottom at room temperature. After initial loading the autoclave was heated to 150°C at 10°C/min with a sheath-type heater, and then the temperature was kept constant for two hours. The axial pressure was kept at 40 MPa during the hydrothermal hot-pressing treatment. After the HHP treatment, the autoclave was naturally cooled to room temperature, and the sample was removed from the autoclave. 3-point bending tests were conducted to obtain an estimate of the fracture toughness for the HA/Ti interface as well as for the HA ceramics made by the HHP method. Core-based specimens were used for the fracture toughness tests following the configuration of the core-based specimen are schematically.

Thanks & Regards,
Nicola B
Editorial Team
Journal of Biochemistry & Biotechnology