| A silica cellular structure was synthesized as a novel means of enhancing the geometrical surface area of a silicon microreactor with cell diameter, cell interconnectivity, and skeleton density as critical and controllable structural features. Based on theoretical considerations of the pressure drop, mixing, and mechanical stability issues associated with microreactor applications, cell diameter of ∼10 mum, cell interconnectivity of ∼0.4, and fully dense skeleton were determined as synthesis targets. In this synthesis method, surface-selective infiltration, assembly, and partial sintering of polystyrene microspheres in the microchannel were used as mechanisms to create a sacrificial template which represented an inverse structure of the final cellular structure. The polymer template was infiltrated with a silica precursor, and the infiltrated structure was dried and calcined at 500°C to remove the polymer phase and subsequently sintered at 1100°C to form dense silica skeleton. With the use of ∼16 mum polystyrene microspheres, the average cell diameter of ∼12 mum was achieved in the final cellular structure. Cell interconnectivity was controlled to be ∼0.4 by sintering the polystyrene microspheres at 100°C for 180 seconds. Volume shrinkage and crack formation during drying of the infiltrated template structure were significant when the precursor contained small silica particles in the range of several manometers. The volume shrinkage and crack formation could be prevented during drying using the silica precursor containing larger silica particles in the range of ∼40 to 500 nm. However, instability in the cellular structure occurred during sintering due to the delayed volume shrinkage of the specimens prepared with the larger silica particles. Also, the larger particles were more difficult to infiltrate into the interstitial space of the polymer template. In comparison to free-standing cellular specimens prepared by a similar template method, the volume shrinkage and crack formation issues offered a unique challenge for synthesizing the cellular structure which could be net-shaped into the spatial confinement of the microchannel geometry. |
