Structural changes of thermally sprayed hydroxyapatite investigated by Rietveld analysis

Area of Science:

• Materials Science
• Biomaterials Engineering
• Crystallography

Background:

• Hydroxyapatite (HA) is crucial for biomedical implants due to its biocompatibility.
• Thermal spraying is a common method for applying HA coatings.
• Understanding structural changes in HA during spraying is vital for coating performance.

Purpose of the Study:

• To investigate the structural modifications of hydroxyapatite (HA) coatings after thermal spraying.
• To compare the effects of flame spraying, high velocity oxygen fuel (HVOF) spraying, and plasma spraying on HA.
• To analyze the formation of oxyapatite and unit cell distortions.

Main Methods:

• Preparation of HA coatings using flame spraying, HVOF spraying, and plasma spraying.
• Rietveld analysis using General Structure Analysis Software package (GSAS) for structural characterization.
• Spectral analysis to detect changes in hydroxyl groups and assess oxyapatite formation.

Main Results:

• All spraying methods induced unit cell distortion (a-axis decrease, c-axis increase).
• Flame and HVOF spraying increased unit cell volume; plasma spraying decreased it.
• Formation of oxyapatite was observed, indicated by reduced hydroxyl peaks and occupancy.
• Plasma spraying resulted in a significantly higher distortion index compared to other methods.

Conclusions:

• Thermal spraying techniques significantly alter HA crystal structure, forming oxyapatite.
• Plasma spraying induces more substantial structural distortions than flame or HVOF spraying.
• These findings are critical for optimizing HA coating properties for biomedical applications.