We use two types of silica as a thickener in our grease range, both fumed silica and hydrophobic silica. Silica is not to be confused with silicon or silicone.
Fumed silica is hydrophilic (water-loving) and has a thixotropic behaviour due to it’s time dependent recovery of apparent viscosity after shear stress, also know as shear rate sensitivity. Once shear force is removed the bonds rebuild over time.
Hydrophobic (water-hating) silica is made by reacting the silica with silanes and silazenes. The hydrophobic silica is ideal when used as a thickener for a grease that is required to prevent water ingress or to give a grease excellent water washout resistance.
Both hydrophilic and hydrophobic silica are very efficient thickeners, meaning that a relatively small percentage (compared to other thickener types) is required for a grease to be formed when added to a base oil. What the heck are we talking about?….see the article What is a grease.
DON’T CONFUSE silica with silicone or silicon – completely different!