Rapid Prototyping of Ceramic Based Photonic Bandgap Structures

摘要

A three-dimensional photonic bandgap (PBG) structure was fabricated from CAD models using a method based on lost wax rapid prototyping and ceramic gelcasting. The inverse PBG mold was constructed from a low melting point thermoplastic using a high precision Sanders Rapid Toolmaker. An aqueous stable slurry (200-300 cp) containing 50-75wt% of the ceramic powders (BaSrTiO_3, MgO), a 15wt% solution of monomer (Methacylamide) and crosslinker (Poly(ethylene glycol) dimethacrylate), and a free radical initiator (2,2'Azobis(2-amidino-propane) dihydrochloride) was cast into the mold. A polymerization reaction was thermally activated at 50℃ to immobilize the ceramic powders. The wax mold was then removed by drying the green body in a high humidity oven at 120℃. Scanning Electron Microscopy (SEM) of the unfired part showed that atmosphere hampered the polymerization reaction at the surface of the part. The green density, sintered density, and permittivity all increased as the solids loading increased. In order to optimize the dielectric properties and minimize cracking and warping in the sintered part, the solids loading had to be greater than 80 wt%. This study investigated several steps in the lost mold / gelcasting procedure including stabilizing the ceramic suspension, the correlation between the solids loading and the green and sintered densities, binder removal, and the effect of shrinkage during sintering on the net shape.