Picric acid is known to react with metals to form highly unstable metallic picrates, which are known to have been involved in serious explosive accidents. In this study, alkaline-earth metal picrates of magnesium, calcium, strontium and barium salts are synthesized. Then, their thermodynamic and explosive properties such as initiation sensitivity are examined.
The decomposition of alkaline-earth metal picrates begins at a higher temperature than that of picric acid. The heat of decomposition of alkaline-earth metal picrates was found to be lower than that of picric acid. Alkaline earth-metal picrates contain crystalline H2O, which dehydrates stepwise with increasing temperature. Experimental results show that the amount of crystalline H2O in picrate in metastable phase is 9.2 - 9.9 H2O for Mg-picrate, 10.4 - 10.7 H2O for Ca-picrate, 5.0 - 5.1 H2O for Sr-picrate, and 5.9 - 6.4 H2O for Ba-picrate. However, the respective picrates changed to the stable form which contained the following amounts of crystalline water such as 6.5 H2O for Mg-picrate, 4.8 H2O for Ca-picrate, 4.0 H2O for Ba-picrate (Sr-picrate was not changed). The dehydration of crystalline water occurred between room temperature (about 298 K) and 480 K. Alkaline-earth metal picrates were dehydrated by heating in a vacuum at 473 K under 133 Pa. The activation energies at the initiation stage of exothermic decomposition are 125.6 kJ for Mg-picrate, 140.3 kJ for Ca-picrate, 171.3 kJ for Sr-picrate, and 257.7 kJ for Ba-picrate. Drop hammer test results show that Sr-picrate and Ba-picrate are more sensitive than picric acid.