THERMAL-STABILITY OF THE BETA'' PHASE IN THE ZRO2-ZR3N4 SYSTEM

Annealing of ZrO2 in a nitrogen atmosphere leads to a nitrogen contain ing phase called beta '' phase having a trigonally distorted fluorite structure with ordered anion vacancies. DTA/TG investigations indicate d that the beta '' phase decomposes into m-ZrO2 above 500 degrees C re leasing nitrogen during the reaction with oxygen. Prevention of oxygen uptake by use of closed tantalum tubes instead of open platinum cruci bles enabled the detection of a new reversible phase transition at sim ilar to 965 degrees C. The thermoanalytical results have been confirme d by high temperature-X-ray investigation.