Hydration control in the fabrication of high-density magnesia products via slip casting

Abstract

To tackle the hydration problem in magnesia (MgO) aqueous suspension during slip casting fabrication, we explored the casting performance of four distinct MgO slips. Through the comparison of properties and performance between aqueous and organic MgO slips, we introduced criteria for selecting the appropriate suspension medium to prepare a good MgO slip. Moisture absorption in raw MgO powders leading to Mg(OH)₂ formation was observed, undetectable by X-ray diffraction (XRD) but identified through thermogravimetric analysis (TGA). Moisture release occurred at temperature < 100 °C, followed by loosely bound water release between 160 °C and 310 °C, and then Mg(OH)₂ decomposition occurred at 310 °C to 430 °C, constituting 1.05, 1.66, and 1.34 wt%, respectively. Subjecting raw powders to pre-firing at 1000 °C led to the formation of larger MgO particles, characterised by a D50 value twice that of the previous size. This transformation shifted their morphology from random rods to more durable spherical shapes, thereby improving their resistance to hydration when subjected to wet ball milling with water. Pre-firing MgO at 1000 °C resulted in a favourable aqueous slip, enabling problem-free casting of small-sized products with high density and purity.