Study on the preparation of indium tin oxide(ITO) sol for electrically conductive transparant coating and dispersion stability of ITO powder

Abstract

In this study, tin doped indium oxide(ITO) sol was prepared for electrically conductive and transparent coating. Commercialized ITO powder was dispersed in organic medium such as ethanol, N,N-dimethylformamide(DMF), and 2-isopropoxyethanol(IPC). Isopropyl tri(N-ethylenediamino)ethyl titanate(KR44) and 2,4-pentanedion(acetylacetone) were used as dispersants for ITO sol. From the adsorption isotherm of dispersants, it was found that acetylacetone showed more stronger affinity to ITO surface than KR44. However, the size of ITO aggregates was more easily reduced during milling process when KR44 was used due to its more effective steric hindrance. ITO sol was deposited on the cathode ray tube to estimate electrical and optical properties of coating layer. As the particle size of ITO dispersion becomes smaller, the sheet resistance and the reflectance decrease. When the particle size is larger than 130 nm, CRT looks white because of light scattering by coarse particles. As the concentration of KR44 increases, the sheet resistance increases since the adsorbed KR44 acts as insulating layer. However, the sheet resistance of coating film was independent on the concentration of acetylacetone due to the complete evaporation of the dispersant during baking of the coated film. The stability of ITO sol was estimated by measuring the particle size as a function of the storage time. As the concentration of KR44 was larger than 4.2 wt.%, ITO dispersion became unstable due to depletion flocculation. On the contrary, the stability of ITO sol was independent upon the concentration of acetylacetone since the depletion layer cannot be formed on the ITO surface. Though commercialized ITO was used for most of our dispersion study, ITO powder was also prepared by coprecipitation and sol-gel method in this study. During the preparation step of ITO powder, the dropping rate of precipitating agent affected the degree of crystallinity and the electrical conductivity of coating layer. W...