Chelate-setting calcium-phosphate cements (CPCs) have been developed using inositol phosphate (IP6) as a chelating agent. However, the compressive strength of the CPC fabricated from a commercially available Hydroxyapatite (HAp) powder was approximately 10 MPa. In this study, we miniaturized HAp particles as a starting powder to improve the compressive strength of chelate-setting CPCs and examined the adsorption properties of IP6 onto HAp powders. An HAp powder with a specific surface area (SSA) higher than 200 m2/g (HApHS) was obtained by ultrasonic irradiation for 1 min in a wet synthesis process, greatly improving the SSA (214 m2/g) of the commercial powder without ultrasonic irradiation. The HApHS powder was found to be a B-type carbonate-containing HAp in which the phosphate groups in apatite were replaced by carbonate groups. Owing to the high SSA, the HApHS powder also showed high IP6 adsorption capacity. The adsorption phenomena of IP6 to our HApHS and commercially available Hap powders were found to follow the Freundlich and Langmuir models, respectively. We found that IP6 adsorbs on the HApHS powder by both physisorption and chemisorption. The fine HapHS powder with a high SSA is a novel raw powder material, expected to improve the compressive strength of chelate-setting CPCs.
This study investigated the properties of fine Sr2+-substituted hydroxyapatite (SrHAp) synthesized using ultrasonication. SrHAp was synthesized by the addition of phosphoric acid solution to an ultrasonicated calcium hydroxide suspension containing strontium hydroxide. The X-ray diffraction peaks for SrHAp were shifted to low angle with increasing Sr/(Ca + Sr) atomic ratio. X-ray diffraction, energy dispersive X-ray spectroscopy and inductively coupled plasma spectroscopy measurements confirmed that HAp and strontium apatite (Sr10(PO4)6(OH)2;SrAp) formed a complete solid solution. When the Sr/(Ca + Sr) atomic ratio was 0.3 or less, the (Ca + Sr)/P atomic ratio was 1.67 or less, and the specific surface area was also large. The bending strength of a SrHAp sintered body was increased and the bending strength of the SrAp sintered body became 40 MPa when the Sr/(Ca + Sr) atomic ratio was above 0.3. The ethanol conversion rate using SrAp as catalyst was 7% for 1 hour and was 40% of HAp reagent. However, selectivity of SrAp from ethanol to butanol was 70%.
This paper reports the application of ultrasound irradiation in the synthesis of ultrafine hydroxyapatite (HAp) with a high specific surface area of 300 m 2 /g. We examined the effects of initial temperature, horn diameter and suspension concentration on the powder properties, especially specific surface area, of ultrafine HAp. Amorphous calcium phosphate (ACP), which is a precursor of HAp, was formed in the early stage of the reaction, and then rapidly crystallized to form HAp. In the case of an initial temperature at 30ºC, the largest specific surface areas of 250 m 2 /g and 300 m 2 /g were obtained using horn diameters of 19 mm and 6 mm, respectively. Based on particle size distribution measurements, the mode and average diameters of the HAp powders were found to be 5.0 and 6.3 nm, respectively. These values were well-agreed with the average diameter calculated from the specific surface area.
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