Synthesis Of Blue CoAl₂O₄Pigments For Ceramic Ink Jet Printing

Cobalt aluminate （CoAl₂O₄）, known as Thenard’s blue, has been widely used in theceramics, glass, paint and coating industry, due to its excellent heat stability, chemicalresistance and bright blue color. Compared with the traditional ceramic decoration technology,ceramic ink-jet printing technology puts forward higher requirements of average particle size,particle size distribution, morphology, and dispersion for ceramic pigments. In this work blueCoAl₂O₄pigments for ceramic ink jet printing were prepared by molten salt synthesis,co-precipitation method and hydrothermal method. The powders are mainly characterized byXRD, DSC-TG, SEM, and FT-IR techniques.CoAl₂O₄powders with good performances were prepared via optimized molten saltsynthesis. Experiment results indicated the raw materials, ball-milling and mineralizer playedan important role in the performances of CoAl₂O₄powders. The optimized processingconditions for molten salt synthesis were: the ratios of Co/Al in raw materials, Co/Na, andNaCl/Na2SO4in mineralizers were0.5,1and0.85, respectively. The mixed salts werecalcined at400℃for1h, then were ground for6h in a planetary ball mill using absolutealcohol as dispersing media. The mixed salt powders were calcined at1000℃for2h.CoAl₂O₄powders with fine crystallinity, bright color, uniform particle distribution and regularmorphology were obtained from such process, but the shortage is there existed severeaggregation.The effect of precipitant, washing process, calcination temperature and dispersantsapplied in co-precipitation method on CoAl₂O₄particle morphology, size and distributionwere investigated. The results indicated that when cobalt sulfate and aluminum sulfate wereused as raw materials, trisodium phosphate was used as precipitant and urea used asprecipitator, the CoAl₂O₄pigments with uniform morphology, uniform particle size weresynthesized with co-precipitation method after water and alcohol leaching and two hours’calcination at1200℃. Finally, non-agglomerated nano-sized cobalt aluminate powders wereprepared hydrothermally at250℃for24h by adjusting the concentration of Co2+and Al3+,pH, temperature, type of precipitants, raw materials, etc. The particle size ranged from80to500nm, the particle size distribution was narrow, and the particles had round and plump edges. The formation process of CoAl2O4was discussed.