TWO-STAGE SYNTHESIS OF Caa Sib TiOc COMPOUNDS

Ričardas Kleinauskas; Anatolijus Eisinas; Jolanta Donėlienė

ᐊ P1-40

Open Readings 2025 • P1-41

P1-42 ᐅ

TWO-STAGE SYNTHESIS OF Ca_a Si_b TiO_c COMPOUNDS

Ričardas Kleinauskas¹, Anatolijus Eisinas¹, Jolanta Donėlienė^{2, 3}

¹ Department of Silicate Technology, Kaunas University of Technology, Lithuania

² Applied Research Institute for Prospective Technologies, Vilnius, Lithuania

³ Public Institute "Perspektyvinių technologijų taikomųjų tyrimų institutas", Vilnius, Lithuania

[email protected]

$ Si$_{b}$ TiO$_{c}$ COMPOUNDS} Due to their high thermal resistence, biological compatibility and modifiable optical properties, Ca$_{a}$Si$_{b}$TiO$_{c}$ compounds are widely used in bioceramics, glazes [1], semiconductors and photocatalytic materials [2]. Ca$_{a}$Si$_{b}$TiO$_{c}$ compounds are produced by high temperature (1200-1400°C) solid phase sintering of crystalline raw materials (CaO, SiO$_{2}$, TiO$_{2}$) [3]. In contrast, the use of initial dissolved organic (Ca/Si/Ti) salts and sol-gel synthesis can reduce the synthesis temperature to ~1000 °C. However, the application of this method is limited by expensive raw materials and high solvent consumption. Therefore, this work proposes to synthesize (sol-gel) an amorphous TiO$_{2}$ additive, study its influence on the formation of calcium silicate hydrates under hydrothermal synthesis conditions and their crystalisation into Ca$_{a}$Si$_{b}$TiO$_{c}$ compounds during sintering. It is assumed that, unlike its crystalline forms, amorphous TiO$_{2}$ can intercalate into calcium silicate hydrates’ lattice and that hydrothermal curing will lead to formation of purer Ca$_{a}$Si$_{b}$TiO$_{c}$ phases at lower sintering temperatures.

In this work, amorphous titanium dioxide was prepared in accordance to our earlier experiments [4]. Two base samples were prepared by mixing amorphous TiO$_{2}$, amorphous SiO$_{2}$ and CaO equal to molar ratio of 1. One of the samples was then mixed with H$_{2}$O to reach the water/solid ratio of 10. The hydrothermal synthesis was performed under saturated steam pressure of 15 bar at a temperature of 200 °C for 4 hours. After treatment, synthesis products were filtered, dried and sieved (<80 μm). Both raw crystaline and hydrothermally cured mixtures were then calcinated at temperatures of 900-1200 °C for 1 hour. Synthesis products were characterized by XRD and STA instrumental methods.

**Fig. 1.** a) XRD and b) DSC patterns of 1) hydrothermally cured and uncalcinated; 2) hydrothermally cured and 3) dry CaO-SiO₂-TiO₂ mixtures after calcination in 2) 900 and 3) 1200 °C. Indexes – T – titanite; W – wollastonite; P – CaTiO₃; L – larnite; R – rutille; C - lime

The most important aspect of two-stage preparation method is the formation of homogenous amorphous CaO-SiO$_{2}$-TiO$_{2}$-H$_{2}$O compounds (I stage) {(Fig 1. a. 1)}, which promote the formation of dominant Ca$_{a}$Si$_{b}$TiO$_{c}$ compounds during calcination (II stage) {(Fig 1. a. 2)} at low temperatures {(Fig 1. b; 800-880 °C)}. Meanwhile after calcination of dry sample, it was determined that crystaline CaO-SiO$_{2}$-TiO$_{2}$ mixture did not form Ca$_{a}$Si$_{b}$TiO$_{c}$ compounds, as secondary phases rutille, lime and calcium silicates (larnite and wollastonite) are dominant in the synthesis products {(Fig 1. a. 3)}.

[1] L. Zhihong, et al. High-solar-reflectance building ceramic tiles based on titanite (CaTiSiO5) glaze. Solar Energy, 153, 623-627, (2017).

[2] H. Shouqiang, et al. CaF2-based near-infrared photocatalyst using the multifunctional CaTiO3 precursors as the calcium source. ACS Applied Materials & Interfaces, 7.36: 20170-20178, (2015).

[3] L. Yangzi, et al. Synthesis of sphene by TiO2 combined with CaCO3 and SiO2 in solid phase and its application as ceramic opacifier. Chemical Physics, 575: 112076, (2023).

[4] J. Doneliene, et al. Effect of Precursor Nature and Sol-Gel Synthesis Conditions on TiO2 Aerogel’s Structure. Molecules, 26, 5090, (2021).