Chemisorption of Organofunctional Silanes on Silicon Nitride for Improved Aqueous Processing

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Abstract
Different chem‐adsorbed silane molecules have been used to produce weakly attractive silicon nitride particle networks for aqueous colloidal processing. Silanes with diamino and poly(ethylene glycol) hydrophilic heads yielded slurries with the lowest viscosity, longest sedimentation stability, and highest packing density. Chem‐adsorbed silane molecules protected silicon nitride and yttrium oxide, a common processing aid, from hydrolysis at pHs between 5.5 and 11. A novel approach was used to produce short‐range repulsive potentials necessary to yield the weakly attractive networks. Addition of salt to dispersed silicon nitride slurries with particles coated with poly(ethylene glycol)‐silane caused the collapse of the 22‐atom‐long chains and residual electrical double layer. This produced a weakly attractive network which persisted during consolidation to yield a plastic body with a flow stress that was dependent on the counterion size. When 0.5M tetramethylammonium chloride was used at pH 10, plastic bodies had a flow stress similar to clay, whereas lithium counterions produced bodies with a much higher flow stress.