Thermal behavior of aluminum fluoride trihydrate

The thermal decomposition of aluminum fluoride trihydrate was investigated by TG-DTG. The process was recognized to involve three stages: I AlF3 . 3H(2)O(108-227 degrees C) --> AlF3 . 0.5H(2)O + 2.5H(2)O II AlF3 . 0.5H(2)O(277-550 degrees C) --> AlF3 + 0.5H(2)O III AlF3. 3H(2)O(>380 degrees C) --> Al2O3 + 6HF It was found that the apparent activation energy, E, and the preexponential factor, A, for stage I reaction were 41.9 kJ mol(-1) and 10(2.49) s(-1), r espectively. For stage II reaction, the value of E was 47.5 kJ mol(-1) and the most probable differential mechanism function was in the form of (1-alp ha), and magnitude of 80.4 kJ mol(-1) of E and a function in the form of 3/ 2(1-alpha)[-ln(1-alpha)(1/3)] were derived fur stage III reaction, From the measurements conducted under increasing temperature conditions, contents o f fluorine, C-F(%), on moisture-free basis and water, C-W(%), on current ma ss basis contained in the AlF3. 3H(2)O sample were determined and correlati on between the temperature range dictated by the quality specification of A lF3, C(F)greater than or equal to 61.0%, C-W<0.5%, and the heating rate wer e presented. The content of fluorine and water were also determined under i sothermal conditions and correlation between the time duration of the treat ing temperature necessary for the quality specification to be met, and the magnitude of temperature were presented. (C) 2000 Elsevier Science B.V. All rights reserved.