Philip N. Sturzenegger

Ceramic Spheres—A Novel Solution to Deep Sea Buoyancy Modules

Ceramic-based hollow spheres are considered a great driving force for many applications such as offshore buoyancy modules due to their large diameter to wall thickness ratio and uniform wall thickness geometric features. We have developed such thin-walled hollow spheres made of alumina using slip casting and sintering processes. A diameter as large as 50 mm with a wall thickness of 0.5–1.0 mm has been successfully achieved in these spheres. Their material and structural properties were examined by a series of characterization tools. Particularly, the feasibility of these spheres was investigated with respect to its application for deep sea (>3000 m) buoyancy modules. These spheres, sintered at 1600 °C and with 1.0 mm of wall thickness, have achieved buoyancy of more than 54%. As the sphere’s wall thickness was reduced (e.g., 0.5 mm), their buoyancy reached 72%. The mechanical performance of such spheres has shown a hydrostatic failure pressure above 150 MPa, corresponding to a rating depth below sea level of 5000 m considering a safety factor of 3. The developed alumina-based ceramic spheres are feasible for low cost and scaled-up production and show great potential at depths greater than those achievable by the current deep-sea buoyancy module technologies.

Hollow calcium aluminate microcapsules with porous shell microstructure and unique mechanical properties

Since the mid-1970s, microencapsulation has become increasingly popular in food, detergent, cosmetic and pharmaceutical industries to protect active agents from degradation or facilitate their controlled release or targeted delivery. Here we report on a synthesis route of a novel class of hollow inorganic microcapsules with unique microstructural and mechanical properties. The method is based on the adsorption of calcium aluminate particles at the interface of water droplets of an oil-continuous emulsion. Upon contact with water, these particles hydrate and form a mechanically stable, porous capsule shell. After solvent evaporation, hollow microcapsules can be harvested with diameters between 30 and 200 μm and yields of up to 75%. The mechanical characterization of entire capsules is accomplished using a uniaxial, micromechanical compression setup installed in a scanning electron microscope. We show that these inorganic calcium aluminate microcapsules are highly crack tolerant owing to their porous shell microstructure. Such a behavior is in strong contrast to the one of hollow aluminosilicate cenospheres, which feature dense shells and show therefore brittle failure in our compression tests.