ON THE DETERMINATION OF THE HYDROGEN FUGACITY IN AN ENVIRONMENTAL CELL TEM FACILITY

Observations were made on high purity (99. 999%) Al and on an Al/5. 5Zn/2. 5Mg alloy with similar behavior obtained for both materials. A range for the hydrogen fugacity in the environmental cell under the electron beam can be defined. The lower limit is set by an equation which gives a value of P equals 34. 0 plus or minus 13. 9 MPa and the upper limit is provided by an equation which gives Py equals 750 MPa. The origin of this increase (compared to the 10-16 kPa pressure in the environmental cell) appears to be dissociation of the H//2 molecules by the electron beam.