Combinatorial ink-jet printing for ceramic discovery
An aspirating and dispensing printer established inside a robot gantry equipped with furnace and measurement table is used to prepare thick-film combinatorial libraries. Implementation of series of screening tests for ceramic inks that address stability against sedimentation, evaporation and particle segregation during drying, has provided a series of calibration inks can be used for calibration of this printer. The instrument can assemble ceramic mixtures with compositional accuracy of 1-3 wt %. By changing the amount of dispersant used in the inks or by printing onto a porous substrate, the geometry of residues from dried ceramic ink droplets can be modified to facilitate property measurements and uniform composition, as planned, can be achieved. The same material prepared in three ways, in the form of dried ink, ink-jet printed as for a combinatorial sample and by conventional compaction gave similar dielectric measurements. A combinatorial system has been developed so that combinatorial libraries can be printed, fired and screened automatically. A ternary A1203-TiO2-ZrO2 system was first studied using the developed combinatorial method. The particle segregation during drying of multi-component ceramic ink drops is not due to preferential sedimentation unless dispersant addition is restricted. The segregation is due to the partitioning of particles between the growing peripheral 'foot' that develops during drying and the diminishing liquid pool which contains vigorous recirculation flows. Better dispersed particles remain in the pool and hence are found in excess on the upper surface of residues. Less well dispersed particles join the 'foot' earlier in the drying process. The contact angle and height of droplets containing large amounts of dispersant, steadily reduced during drying until a minimum value was reached; the contact diameter being almost unchanged during drying. These droplet residues retained a dome shape. Droplets of suspensions containing small additions of dispersant terminated in a 'doughnut' shaped residue.