| Abstract [eng] |
Recently, extensive interest has been shown to developing of bioactive materials containing CaOSiO2 components for biomedical applications. One of the most recognized bioactive ceramics is hydroxyapatite because of its bioactivity and osteoconductivity. However, the low hardness of mentioned material limits its application [1]. Thus, importance of calcium silicates (CaO-SiO2 component) is becoming very important not only for traditional ceramics (cement industry), but also for bioactivity technologies. Because of the favorable properties such as low shrinkage, good strength, lack of volatile constituents, body permeability, fluxing characteristics etc. [2]. Usually, calcium silicates are synthesized during solid-state sintering at high temperature (1100- 1450 °C) [3]. However, it can be received by two-stages approach. Firstly, hydrothermal treatment is carrying out in CaO-SiO2-H2O system at 100-200 °C temperature; then synthesis products are treating by 800-1000 °C temperature for a final product [4]. Following method is better not only because of lower temperature, but also for opportunity by changing temperature, pressure, C/S ratio, etc., control synthesis products structure and other properties. Moreover, Al3+ ions can improve mentioned compound properties [5]. Thus, the aim of this work is to investigate Al3+ influence on the formation of calcium silicates by using two steps synthesis. The molar ratio of primary mixture was equal to CaO/SiO2 = 1.5 and Al2O3/(Al2O3+SiO2) = 0.05. Dry primary mixture (with Al3+ additive or without) was mixded with H2O to reach solution/solid ratio of the suspension equal to 10.0. The synthesis carried out in unstired suspensions, isothermal treatment at 200 °C temperature duration changing from 8 to 72 h. The structure synthesis products mainly were characterized by XRD and thermal properties investigated by STA. XRD showed that after 8 h of isothermal treatment in both systems (with and without Al3+ additive) unreacted raw material – portlandite was identified and semi-crystalline type C-S-H (I) and/or C-S-H (II) formed. However, other results differed from each other. In CaO-SiO2-H2O system hydraulically active α-C2SH formed, while in CaO-SiO2-Al2O3-H2O system γ-C2S was observed, which are stable even at room temperature. Moreover, together with mentioned compounds calcium alumosilicate hydrate – katoite was identified. By prolonging synthesis duration to 72 h, in both systems observed that higher crystallinity compounds formed: xonotlite, kilchoanite, pavloskyite and scawtite. Although the XRD results were similar, simultaneous thermal analysis confirmed, that Al3+ had positive influence on wollastonite recrystallization from primary synthesis products. Exothermic effects on temperature higher than 850 °C showed that small amount of aluminium ions let to compose higher quantity of wollastonite. |
