Magnesium hydroxide

Monetite (CaHPO₄)-based CPC was developed following a detailed procedure described by Koju et al. and Zhou et al. [12 (link),13 (link)]. Briefly, the aqueous setting solution was added to a powder mixture containing calcium hydroxide (Ca(OH)₂ Fischer Scientific, Waltham, MA, USA) and magnesium hydroxide (Mg(OH)_2, Fischer Scientific, Waltham, MA, USA) and mixed. Subsequently, the resultant mass was microwave-irradiated until it resulted in a rock-like material that was crushed to make fine CPC powder. As mentioned in Table 1, varying cement compositions were developed by combining powder mixtures with an aqueous solution. The powder mixture comprised CPC powder, magnesium oxide (MgO Millipore Sigma, St. Louis, MO, USA), sodium phosphate dibasic (Na₂H₂PO₄, Fischer Scientific, Waltham, MA, USA), and different concentrations of magnetite powder. The aqueous solution comprised a clear blend of Na₂H₂PO₄ in 2.5 wt.% colloidal silica. The liquid-to-powder ratio was always maintained at 0.35 mL/g. After mixing the powder mixture and the liquid, they were put in molds to form pellets. The compositions were referred to as MCPCs-xFe, which means magnetic calcium phosphate cements, with x indicating the varying weight content of magnetite incorporation, as shown in Table 1.

Barium titanate (IV) (BaTiO₃, 99.5%, particle size ≤2 µm) and colloidal silica were procured from Sigma–Aldrich (Saint Louis, MO, USA) and used without further modification. The detailed information of colloidal silica is presented in Table 1. Calcium hydroxide (Ca(OH)₂, >95%), magnesium hydroxide (Mg(OH)₂, 95%), sodium bicarbonate (NaHCO₃, >99.7%) and magnesium oxide (MgO, 98%) from Fischer Scientific (Fair Lawn, NJ, USA) and sodium tetraborate decahydrate as known as borax decahydrate (Na₂B₄O₇·10H₂O, >99.5%) from Alfa Aesar (Ward Hill, MA, USA) were used for the preparation of the cement samples.