DYNAMIC EVAPORATION BEHAVIOR OF DIKETONATE COMPOUNDS OF YTTRIUM, COPPER AND BARIUM

The dynamic evaporations of Y(thd)3, Cu(thd)2 and Ba(thd)2, where thd is 2,2,6,6-tetra-methyl-3,5-heptane dionate, were studied using a microbalance technique. Our primary objective here was to investigate the evaporation stability of these compounds with respect to time. Our results showed that the evaporation rates of these compounds decreased inevitably with time due to the decrease in sample weight. The reasons for the decrease in evaporation rate with sample weight are: (i) the decrease in effective surface area with sample weight and (ii) the increase in diffusion distance in the region above the sample within the cell. Our results indicated that by preparing Cu(thd)2 and Y(thd), as pellets and then placing them level with the cell rim produces uniform evaporation rates. For Y(thd)3, an additional decrease in evaporation rate occurred at high temperatures due to coalescence between particles and, hence, a decrease in surface area. The evaporation rate of Ba(thd)2 decreased quite significantly with time. An empirical equation of the form n = n0(T) + a exp(-bt) fitted our results quite well. There were some oligomers in the original sample, whose quantities seemed to decrease after thermal treatments. A species like Ba(thd)2 . Hthd, may also exist which would make the Ba content in the original sample lower than in pure Ba(thd)2.