| Summary: | Powder mixtures of MgSO<sub>4</sub> with 5–20 mol.% Na<sub>2</sub>SO<sub>4</sub> or K<sub>2</sub>SO<sub>4</sub> were used as precursors for making water-soluble ceramic molds to create thermoplastic polymer/calcium phosphate composites by low pressure injection molding. To increase the strength of the ceramic molds, 5 wt.% of tetragonal ZrO<sub>2</sub> (Y<sub>2</sub>O<sub>3</sub>-stabilized) was added to the precursor powders. A uniform distribution of ZrO<sub>2</sub> particles was obtained. The average grain size for Na-containing ceramics ranged from 3.5 ± 0.8 µm for MgSO<sub>4</sub>/Na<sub>2</sub>SO<sub>4</sub> = 91/9% to 4.8 ± 1.1 µm for MgSO<sub>4</sub>/Na<sub>2</sub>SO<sub>4</sub> = 83/17%. For K-containing ceramics, the values were 3.5 ± 0.8 µm for all of the samples. The addition of ZrO<sub>2</sub> made a significant contribution to the strength of ceramics: for the MgSO<sub>4</sub>/Na<sub>2</sub>SO<sub>4</sub> = 83/17% sample, the compressive strength increased by 49% (up to 6.7 ± 1.3 MPa), and for the stronger MgSO<sub>4</sub>/K<sub>2</sub>SO<sub>4</sub> = 83/17% by 39% (up to 8.4 ± 0.6 MPa). The average dissolution time of the ceramic molds in water did not exceed 25 min.
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