Synthesis of ultrafine pure and yttria-stabilized hafnia by solid-state reaction at relatively low temperature
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Highly reactive, ultrafine powders of pure hafnia as well as stabilized hafnia (8 mol% yttria) have been synthesized at relatively low temperature (500 °C) by solid-state reaction between standard coarse-grained powders of sodium metaphosphate (NaPO3) and sodium hafnate (Na2HfO3). The reaction product was found to be a two-phase mixture of sodium orthophosphate (Na3PO4) and hafnia. Subsequently, the orthophosphate phase was removed by washing with dilute nitric acid. The as-prepared powders were extremely fine (particle size < 20 nm) and crystalline (cubic fluorite structure). After cold pressing and heating to 1650 °C, the materials retained a fine-grained microstructure. Stable cubic HfO2 with Y2O3 addition (8 mol%) was obtained at a temperature which was not too high (1650 °C).
KeywordsNitric Acid Fluorite Yttria Sodium Orthophosphate Y2O3
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