Processing thin (<10 µm), dense, flexible α-Al₂O₃ films from nanopowders

抄録

Normally, it is very difficult to process thin ceramic films (<10 µm) except by vapor deposition methods. This is because in traditional ceramics processing, initial powder particle sizes (typical average particle sizes, APSs >200 nm) make it difficult to realize mechanically robust thin films after sintering to full density due to excessive grain growth. One solution to this problem is to start with nanopowders (APSs <100 nm). Here we present efforts to use simple, easily available nano δ-Al₂O₃ (transition or t-Al₂O₃) nanopowders (NPs) to process the subject films. Thus t-Al₂O₃ NPs when properly dispersed, doped with 0.5–5 wt.% MgO and ball milled with a polymeric binder provide castable systems. Wire wound roller drawing/tape casting provides access to thin green films (10–30 µm) with ≈75 wt.% ceramic loadings. Following binder burnout and careful sintering to temperatures of up to 1500°C/7 h/air but preferably slightly lesser conditions leads to dense ≤10 µm films with average α-Al₂O₃ grain sizes of 500–800 nm. At higher MgO concentrations, spinel phase separates during sintering likely inhibiting grain growth. These relatively dense films are flexible and translucent. Such films, because of their flexibility, may offer utility as catalyst supports, electronic substrates or as hard facings for other materials.