Structural and Morphological Investigation of Calcium-Silicate-Based Bioceramics Prepared from Eggshell via Conventional Approach

Calcium-silicate-based ceramic composites with different CaO/SiO2 weight ratios (10/90, 20/80, 30/70, 40/60, 50/50, 60/40, 70/30, 80/20, and 90/10) have been prepared from chicken eggshells and silica gel using attrition milling for 3 h in wet conditions and conventional pressing–heat treatment in the air at 800 °C for 1 h. The effect of the CaO/SiO2 weight ratio and the calcination period of the eggshells on the microstructural features including apparent density, phase evolution, and morphological properties were investigated. The phase transformation of the powder mixtures after attrition milling for 3 h in ethanol with powder/ball milling mass ratio of 0.0996 (110/1104.7) revealed to have calcium hydroxide (Ca(OH)2) as a dominate phase, which was observed to increase with the increase in calcium oxide (CaO) amount in the powder mixtures. The phase transformation of ceramic samples after heat treatment at 800 °C for 1 h, on the other hand, showed different phases depending on the CaO/SiO2 weight ratio. The results also show a linear relationship between the CaO/SiO2 weight ratio and apparent density when the CaO/SiO2 ratio increase from 0.11 (10/90) to 0.67 (40/60) due to the densification of ceramics. An inversely proportional relationship was found between CaO/SiO2 and density when the CaO/SiO2 weight ratio increased from 0.67 (40/60) to 9 (90/10).