Method for manufacturing calcium phosphate materials using eggshells and phosphoric acid-ammonia solution

Method for selectively synthesizing HA and β-TCP from eggshells by adjusting phosphoric acid-ammonia solution composition

This technology synthesizes highly biocompatible hydroxyapatite or tricalcium phosphate by reacting nano-sized calcium oxide eggshell powder—obtained by calcining and pulverizing discarded eggshells—with a phosphoric acid-ammonia solution, followed by heat treatment. Depending on the ratio of phosphoric acid to ammonia in the solution, either of the two calcium phosphates can be selectively produced.

While hydroxyapatite and tricalcium phosphate are key biocompatible minerals found in bones and teeth, calcium phosphate ceramics have historically been limited in biomedical applications due to insufficient mechanical strength and difficulty in controlling crystal phases and particle morphology. Research into using natural calcium sources like tuna bone, oyster shells, and eggshells has been conducted, but changing crystal phases as desired has been limited by the need for complex temperature and pH control, such as in hydrothermal synthesis.

This technology uses the amount of phosphate ions to determine the product type and particle shape, while ammonia ions promote the formation of calcium hydroxide as an intermediate, allowing for the separate synthesis of HA and β-TCP under the same reaction conditions. Higher phosphoric acid concentrations produce whisker-shaped particles, increasing specific surface area and reactivity. Applicable to bone grafts, dental bone fillers, implant surface coatings, and artificial bone scaffolds, this method enables the recycling of waste eggshells into high-value bioceramic materials with excellent cell compatibility.

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Key Features:

• Wet-milling eggshells calcined at 900°C with isopropyl alcohol and zirconia balls, followed by drying to obtain calcium oxide eggshell powder with an average particle size of 20nm
• Preparing a phosphoric acid-ammonia solution by mixing phosphoric acid, ammonia, and water, adjusted to pH 0.5 for hydroxyapatite and pH 0.69 for tricalcium phosphate
• Mixing the eggshell powder and the phosphoric acid-ammonia solution in a 1:1.5 mass ratio and reacting at room temperature while increasing the formation of the intermediate calcium hydroxide using ammonia
• Drying the reacted eggshell solution, then heating the calcium phosphate powder to 800°C at a rate of 3°C per minute and maintaining it for 4 hours for heat treatment

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