The role of NZP additions in plasma-sprayed YSZ: Microstructure, thermal conductivity and phase stability effects

Rodney W. Trice, Y. Jennifer Su, K. T. Faber, Hsin Wang, Wally Porter

Research output: Contribution to journalArticlepeer-review

15 Scopus citations

Abstract

A concept for lowering the thermal conductivity of plasma-sprayed yttria-stabilized zirconia (YSZ) was evaluated by adding a low thermal conductivity secondary phase. Ca0.5Sr0.5Zr4P6O24, a member of the zirconium phosphate or NZP family, was co-sprayed with YSZ using the recently patented small-particle plasma-spray process. The amount of NZP phase in the YSZ varied from 4 to 18 vol.%. Transmission electron microscopy revealed that the plasma-sprayed NZP existed as 30-50 nm size grains when sprayed with YSZ. Between 100 and 1200°C, reductions in the thermal conductivity of NZP/YSZ composite coatings compared to YSZ-only coatings were traced to porosity effects. The NZP phase destabilized the t′-ZrO2 phase of the YSZ, favoring the formation of t-ZrO2, then m-ZrO2, a phase with a high thermal conductivity. Due to this phase change, a large hysteresis was observed in thermal conductivity during the initial heat-up and cool down cycles of the NZP containing samples.

Original languageEnglish
Pages (from-to)284-291
Number of pages8
JournalMaterials Science and Engineering: A
Volume272
Issue number2
DOIs
StatePublished - Nov 30 1999

Funding

The authors wish to thank Rick Marzec for fabrication of the coatings used in this study, Dr Chiou for assistance with the TEM, and Tom Easley and Luke Brewer for help in editing the final document. Also, Rama Nageswaran provided valuable insight into NZP. This work was supported by the U.S. Department of Energy, Federal Energy Technology Center, Cooperative Agreement No. DE-FC21-92MC29061, under subcontract 96-01-SR047. The thermal conductivity testing was supported by the U.S. DOE, Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Transportation Technologies, as part of the HTML User Program under contract DE-AC05-96OR22464, managed by Lockheed Martin Energy Research Corporation.

Keywords

  • Thermal barrier coatings
  • Thermal conductivity
  • Yttria stabilized zirconia
  • Zirconium phosphate

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