The rapid ageing of the population is leading to a weakening of the body’s ability to regenerate tissues, especially in the bone system. This increases the demand for developing and improving new treatment methods and materials for effective bone substitutes. Hydroxyapatite is the main inorganic component of bone tissue. There are different forms of hydroxyapatite, among which carbonized hydroxyapatite is most similar to natural bone. This form is also characterized by better biocompatibility and activity [1, 2]. Despite these advantages, the scientific literature provides limited data on carbonized hydroxyapatite (CHA) synthesis under hydrothermal conditions, which allow the production of materials with controlled crystallinity and composition.
This study aims to investigate the formation of CHA in a mixture of calcium carbonate and phosphoric acid under hydrothermal conditions. The amount of raw materials used in the experiments corresponds to the stoichiometric Ca/P ratio of CHA (1.67), and the syntheses were carried out at different temperatures (100–200 °C) and durations (4–16 h). To evaluate the outcomes, instrumental techniques, including XRD, STA, FT–IR, and SEM, were employed.
The experimental results showed that, despite the synthesis duration, a lower temperature (100–140 °C) is not suitable for the formation of CHA because other calcium phosphates, such as monetite, were formed. Additionally, a significant amount of unreacted calcium carbonate remained. An increase in synthesis temperature positively affected the formation of CHA, which became the dominant compound after synthesis at 180 °C. Thus, hydrothermal synthesis is a promising method for CHA synthesis in a mixture of calcium carbonate and phosphoric acid. This research was supported by Faculty of Chemical Technology of Kaunas University of Technology (Project BIOCHA).