Hydrothermal Synthesis of CoAl2O4 Blue Nano Structure Pigment

In this research, in order to synthesize nano structure cobalt aluminate pigments hydrothermal method was used. First, appropriate amounts of CoCl2.6H2o and AlCl3.6H2 were disolved in distilled water and titrated by 3M NaOH and NaOH/Na2CO3 mineralizers with the molar ratio of 1:3 in order to achieve desired pH. Then samples were put into a teflon lined stainless steel autoclave and hydrothermally treated at different temperatures and times. Finally, the prepared precipitates were washed with distilled water, filtered and dried at 80oC. The powders were analyzed for the formed phases, colorimetry, and morphology and particle size distribution by XRD, CIELab, SEM and TEM. The XRD results showed that by increasing time and temperature of hydrothermal treatment, CoAl2O4 formed in expense of Co-Al LDH and AlO(OH) phases. Also, by increasing hydrothermal time in a fixed temperature (245oC), because of decreasing Co Al-LDH and formation of CoAl2O4, a* parameter decreased and b* parameter (representing blue color) became more negative. L* parameter also increased by increasing purity of the samples. Thus, the sample synthesized at 245oC for 24 hr with NaOH/Na2CO3 mineralizer was selected as the optimum sample. TEM analysis showed that the size of grains were about 100-15 nm. Also particle size distribution results and SEM images showed agglomeration of particles in different hydrothermal times.