Sintered hydroxyfluorapatites. Part I: sintering ability of precipitated solid solution powders

Area of Science:

• Biomaterials Science
• Materials Chemistry
• Crystallography

Background:

• Fluoride occurs naturally in biological apatites.
• Hydroxyapatite is a key biomaterial component.
• Understanding fluoride's role in apatite sintering is crucial for biomaterial development.

Purpose of the Study:

• To synthesize and characterize hydroxyfluorapatites with varying fluoride substitutions.
• To investigate the sintering behavior and densification of these materials.
• To correlate structural composition with sintering properties and grain growth.

Main Methods:

• Synthesis of hydroxyfluorapatites with 0-100% fluoride substitution for hydroxyl ions.
• Calcination and characterization of synthesized powders.
• Sintering experiments at 1150°C, 1200°C, and 1250°C.
• Analysis of density, grain size, and activation energy for grain growth.

Main Results:

• Fluoride ion occupancy reached approximately 90% of the targeted value.
• True density remained constant for low-to-medium fluoride content, then increased sharply for fluorapatite.
• All compositions showed comparable densification, except for those with similar hydroxyl and fluoride concentrations.
• The composition with comparable hydroxyl and fluoride ions exhibited the smallest grain size and highest activation energy for grain growth.

Conclusions:

• Sintering ability of hydroxyfluorapatites is comparable across varying fluoride substitutions.
• A specific composition with balanced hydroxyl and fluoride ions hinders grain growth and densification due to reduced diffusion.
• This finding offers insights into tailoring hydroxyfluorapatite biomaterials for specific applications by controlling ion substitution.