High precision pulp-based sacrificial molds: A solution towards mass production of hollow ceramic spheres for deep sea applications

Abstract

Hollow ceramic spheres are considered as an excellent buoyancy unit for deep-sea applications (> 5,000 m). However, there is no successful commercialization due to the low productivity of conventional slip casting because of the short life span of gypsum molds. In this work, we have developed single-use pulp-based molds for ceramic slip-casting applications. The developed robust pulp mold offers the advantage of being combustible in a controlled manner during the ceramic sintering process. The smooth, wrinkle-free inner surfaces, controlled water swelling, high wettability, and ability to retain shape during wet casting make the molds highly suitable for producing hollow ceramic spheres on an industrial scale. Alumina-based spheres with 52.8 mm diameter, 1.08 mm wall thickness, 0.46 g/cm3 density, and 54% buoyancy were successfully produced in pulp molds after sintering at 1630 °C. The spheres show exceptionally high hydrostatic failure pressures of above 200 MPa (> 20,000 m) and can be safely operated at depths greater than 5,000 m below sea level. We envision this approach to facilitate the mass production of ceramic spheres with the possibility of creating other complex-shaped ceramics via slip casting in pulp-based molds.