Powder requirements for aerosol deposition of alumina films

• Aerosol deposition (AD) of thick film alumina is correlated to powder characteristics.
• Hard Al2O3 substrates require a powder with high surface area.
• Glass substrates favor powder with larger particle size and compressibility index.
• Correlations are explained in the context of two stages of deposition.
• Observations help to better understand the consolidation mechanisms in AD.

Dry powder aerosol deposition (AD) potentially offers several advantages over conventional ceramic coating processes. AD takes place at room temperature, and a variety of materials can be utilized as the substrate. Deposition occurs at a relatively rapid rate, and the product is a dense, nano-crystalline thick film. One limitation for AD is related to the suitability of powders. In addition to the many other process variables, the success of the deposition depends on the starting powder and its preparation, determined by trial and error. In this work, a broad experimental study about the suitability of 14 alumina powders for AD was carried out on two different substrates, alumina and glass. Three powder properties, particle size, d50, specific surface area, SBET, and compressibility index, CI, were measured and associated with the success of the subsequent deposition. For alumina substrates (high hardness), it was found that a relatively high powder specific surface area (5.5–8 m2/g) correlated with good film deposition and adhesion. For glass substrates, initial deposition was obtained with almost all powders; however, problem with long term stability, apparently related to residual strain, was witnessed using many powders. Hi quality, well-adhered, stable AD films in this case were associated with comparatively lower SBET and a compressibility index within a tight range of about 44–47%.

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