https://link.springer.com/article/10.1007/s11051-022-05518-z
“Twenty milliliters of 1 M CaCl2 × H2O (≥ 95%, Sigma-Aldrich) and 20 ml of 2 M NaOH (≥ 98%, VWR Ltd.) were used as initial reagents for the synthesis of Ca(OH)2 powder. During synthesis, the reagents are used in stoichiometric Ca+2:OH− = 1:2 mol ratio. First, both aqueous solutions (CaCl2 and NaOH) were heated up to 80 °C. At this fixed temperature, a given NaOH solution was added dropwise to a given CaCl2 solution under stirring (1300 rpm) by magnetic stirrer for 30 min. The process takes place according to the following reaction:
The suspension obtained was washed five times with 120 ml of distilled water per occasion to remove NaCl from the suspension. The duration of each filtering process was 2.5 h. As a result, a white precipitate Ca(OH)2 occurred according to the process (left from/the solution passes the filter, while right from/the precipitate is captured by the filter):
The wet precipitate Ca(OH)2 was dried in air at room temperature over one night to collect a semi-dry precipitate Ca(OH)2. Of collected semi-dry precipitate of Ca(OH)2, 1.24 g was calcined in air at 650 °C for 1 h in the furnace with a heating rate of 15 °C/min. As a result, 0.92 g of calcium oxide (CaO) powder was produced by calcination while the dissociation product H2O was evaporated as shown in the following equation:
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“Figure 5 shows SEM and EDS examination of samples 3–4. The SEM images prove that the CaO particles have flake shape morphology. The particle sizes found from the SEM images are too large (115–255 nm), proving that the particles are agglomerated. The EDS investigation confirmed the presence of Ca and O (a small amount of C comes from the sample holder). Figure 5b shows the SEM image of CaO (sample 4) after the sample was kept in normal air at room temperature for 3 weeks. As follows from the comparison of Fig. 5a, b, the C and O contents of CaO increased significantly proving that it adsorbed CO2 with the formation of CaCO3 (for details see below).”
“Figure 5 SEM image (left) and EDS spectrum (right) of fresh CaO (sample 3; a) and for the sample kept in air at room temperature for 3 weeks (sample 4; b). The peaks for gold in EDS spectra correspond to the gold coating added during sample preparation”