Corrosion of ZrO2 by slags and melts

• Applicant: Professor Klaus G. Nickel, Ph.D.
• Subject Area: Glass, Ceramics and Derived Composites
• Term: from 2010 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 165768209

Zirconia containing materials are potential candidates for the replacement of carbon containing refractories. In particular fully stabilized cubic materials are of great interest in this respect. The project investigates the corrosion of Zirconia by slags and melts relevant for such applications in order to provide the basics for the evaluation of reliability and life time prediction of refractories and thermal/environmental barrier coatings with a potential of beeing degraded by silicate melts. We have chosen seven slags from CAS, CMAS with varying complexity and made or bought substrates from YSZ materials. A heating satge microscope was renovated. We have shown that it is possible to investaigate the wetting behavior this way. We have simulated the basicity of the melts and the change in character by dissolution of Zirconia. Furthermore methods to measure saturation values for this dissolution were developed and first numbers extracted. A special crucible type of experiment was developed, with a protective crucible around a reactive crucible loaded with the melt. The technique is successful, if closed porosity is given. Otherwise we observe secondary sintering by infiltrating melt. The kinetics of corrosion are controlled by several processes: a) stabilser Y2O3 is leached from the grains, b) zirconia matrix is dissolved in the melt, c) existing grain boundaries get enlarged by process (b) and d) new grains are produced via phase transformations. Additional paths from primary porosity makes things more complex and faster. Despite these interactions we observe a "quasi-layer producing" advance of the corrosion front. Hence it is possible to follow the dissolution and penetration process simultaneously as a function of time. The most promising approach is the investigation of single crystals and the comparison to the sintered material. Thus in the first period we have provided the basement (in terms of apparatus, methods and analytics). This work is regarded as successful, but has lasted longer then anticipated. Therefore we apply for a further funding period of two years, which would prolong the total to 4 years.

• DFG Programme: Research Grants