Influence of bismuth oxide as a sintering aid on the densification of cold sintering of zirconia

Nikhil Bhootpur, Hans Brouwer, Yinglu Tang*

*Corresponding author for this work

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In the past decades, Zirconia (ZrO2) has emerged as a promising technical ceramic, both as high temperature structural material and electrolyte for fuel cells, etc. The traditional synthesis of ZrO2 with spark plasma sintering (SPS) usually requires a sintering temperature as high as 1200 °C. General interest in lowering the sintering temperature to reduce energy consumption and thermal stresses has led to research on two promising routes – cold sintering via temperature-dependent chemical reactivity and sintering aids, which facilitates mass transport and improves densification. Here we combine both by developing a single-step sintering process benefitting from both water vapor through the in-situ conversion of Zr(OH)4 to ZrO2 and liquid phase Bi2O3 as a sintering aid. The resultant ZrO2 has a relative density above 80% with a sintering temperature as low as 900 °C, significantly higher than that of ZrO2 without sintering aids, which had a relative density of 54%, both sintered at 50 MPa. The dependence of porosity of sintered samples as a function of sintering pressure (range: 50 MPa–300 MPa) and temperature (range 400 °C–1200 °C) is mapped out as guidance for further material property design. A linear relationship between hardness and relative density was found, with a maximal hardness of 6.6 GPa achieved in samples with 30% porosity. In addition to sintered density, phase stabilization of tetragonal ZrO2 is enhanced at sintering temperature of 900 °C with water vapor and Bi2O3, respectively.

Original languageEnglish
Pages (from-to)33495-33499
Number of pages5
JournalCeramics International
Issue number21
Publication statusPublished - 2023


  • Low temperature (cold) sintering
  • Sintering aid
  • Spark plasma sintering
  • Zirconium hydroxide


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