Phase purity of sol-gel-derived hydroxyapatite ceramic

Area of Science:

• Biomaterials Science
• Materials Chemistry
• Solid State Chemistry

Background:

• Sol-gel synthesis of hydroxyapatite (HA) often results in calcium oxide (CaO) impurities.
• Controlling impurity formation is crucial for HA's application in biomedical fields.

Purpose of the Study:

• To explore the phase purity of sol-gel-derived HA.
• To investigate the effect of drying methods on CaO impurity formation.
• To identify strategies for minimizing and removing CaO impurities.

Main Methods:

• Synthesis of HA using calcium nitrate tetrahydrate and triethyl phosphate via sol-gel route.
• Employing fast drying of as-prepared precursors and slow drying of aged precursors.
• Calcination of dried gels up to 600°C.
• Characterization using X-ray diffraction (XRD), thermogravimetric analysis (TGA), and P-31 Nuclear Magnetic Resonance (NMR).

Main Results:

• Fast drying led to significant CaO impurity formation, evident in XRD patterns.
• Slow drying of aged precursors resulted in a 2-step weight loss during heating.
• XRD analysis of slow-dried, calcined powder showed predominantly HA with minimal CaO.
• P-31 NMR indicated the formation of a calcium phosphate complex during aging, which incorporates calcium nitrate and reduces CaO formation.
• Minor CaO impurities from slow drying were removable with distilled water.

Conclusions:

• Aging precursors and employing slow drying are effective methods to minimize calcium oxide impurities in sol-gel derived hydroxyapatite.
• The formation of a calcium phosphate complex during aging plays a key role in preventing CaO formation.
• The residual CaO impurities can be easily removed through simple water washing, enhancing the purity of the synthesized HA.