(169d) Measurement of Diffusion Coefficient of Cr(acac)3 in High Temperature Supercritical Carbon Dioxide

Supercritical fluid deposition (SFD) has focus of attention because metal can be deposited onto nano- or micro structural surfaces of substrates having high aspect ratios without deforming/destructing the structures. In the process organo-metal complexes dissolved in scCO2 are conveyed in the vicinity of substrates and metal is deposited on the inside surface via thermal decomposition of the complex. The process is operated by widely changing temperature from low for carrying metal complex to the substrate to high for depositing metal by thermal decomposition of the complex, i.e. above 100 deg C. Although binary diffusion coefficients D12 as well as other physical properties of the system are required for designing reactors, the diffusion data at high temperatures are scarcely available in the literature since the data were obtained mainly for separation/fractionation of heat-labile natural compounds at ambient temperatures. In this study diffusion coefficients of metal complexes, mainly Cr(acac)3were measured by the chromatographic impulse response(CIR) method at high temperatures, up to 150 deg C and 20 MPa. While the D12 data for all compounds we measured so far by the Taylor dispersion and CIR method were well correlated by the equation, D12/T=A(viscosity)^B over a wide region from liquid to supercritical state, where T is the temperature, and A and B are the constants, the D12 data measured at higher temperatures in the present study more deviated significantly. The accuracies of predictive equations are discussed.