Rw. Trice et al., The role of NZP additions in plasma-sprayed YSZ: microstructure, thermal conductivity and phase stability effects, MAT SCI E A, 272(2), 1999, pp. 284-291
A concept for lowering the thermal conductivity of plasma-sprayed yttria-st
abilized 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-part
icle plasma-spray process. The amount of NZP phase in the YSZ varied from 4
to 18 vol.%. Transmission electron microscopy revealed that the plasma-spr
ayed NZP existed as 30-50 nm size grains when sprayed with YSZ. Between 100
and 1200 degrees C, reductions in the thermal conductivity of NZP/VSZ comp
osite coatings compared to YSZ-only coatings were traced to porosity effect
s. The NZP phase destabilized the t'-ZrO2 phase of the YSZ, favoring the fo
rmation of t-ZrO2, then m-ZrO2, a phase with a high-thermal conductivity. D
ue to this phase change, a large hysteresis was observed in thermal conduct
ivity during the initial heat-up and cool down cycles of the NZP containing
samples. (C) 1999 Elsevier Science S.A. All rights reserved.