| Popis: |
The dehydroxylation of brucite was determined in the presence of NaCl-H2O fluids containing 0, 2, 6, 11, 14, 18, 30, and 38 mol% NaCl (0.0, 5.5, 17.0, 28.8, 34.5, 41.7, 58.2, and 66.6 wt% NaCl) to ;2500 bars and ;700 8C by high-pressure differential thermal analysis (HP-DTA). At pressures below 150 bars, brucite dehydrates in two separate reactions involving at least one intermediate phase. The dehydroxylation reaction of brucite at pressure to ;2 kbars follows lnP(bars) 5 22.23 2 13620/T(K). In the presence of NaClH2O fluids, the dehydroxylation temperature is lowered because of the reduction of the activity of H2O in these fluids. At 1 kbar pressure, mixing in the NaCl-H 2O fluids is virtually ideal, assuming a nearly complete association of NaCl, but at 2 kbars, the dissociation of NaCl is substantial. The phase relations in the system MgO-NaCl-H2O show five univariant reactions emanating from an invariant assemblage, periclase 1 brucite 1 halite 1 liquid 1 vapor, located at 565 6 5 8C and 440 6 30 bars. |
