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| Home > Publications database > Green film characterisation by optical profilometry |
| Conference Presentation (After Call) | FZJ-2013-03496 |
; ; ;
2013
Abstract: Packing density, roughness, and drying stresses of green ceramic layers determine the mechanical and micro structural properties after final sintering. Utilising laser profilometry, the green density of screen printed layers (20-50 µm) were determined with an accuracy of 0.1-0.2% theoretical density. Several effects that affect the accuracy of the results were taken into account and are discussed (e.g. waviness of substrate, penetration depth of the laser beam, deformation of the substrate due to drying stresses). The method can be applied on all layer materials and thick-film deposition methods with a dried thickness of 10 µm or larger that either allow a removal of the applied layer or do not deform the substrate during the coating process. In a case study, the influence of ink parameters (grain size 0.1..0.5 µm, solid content, binder, and dispersing agent) on the green density was studied systematically for electrolyte screen printing inks (8 mol.-% yttria stabilised zirconia = 8YSZ) typically used in solid oxide fuel cell applications. Additional characterisation of the drying stresses by substrate bending measurements and the roughness, together with rheological data, allowed further interpretation of the data and an understanding of how varying ink components influence the state of the dried layer. It could be shown that a minimal binder content is required to achieve acceptable green densities whereas the solid content in well de-agglomerated inks has only little influence. Ethyl cellulose binder was found both to act as a dispersant (especially for larger grain sizes) and to exert high tensile stresses on the particles, thereby contributing to a higher green density. Drying stresses up to 10 MPa were measured for a binder with a short chain length and 2 MPa for a binder with longer chain length. Pre-calcination of the powder and the presence of dispersants, in particular for small grain sizes, significantly increased the film densities. Combing the favourable parameters, the highest green density achieved was 63% theoretical density.
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