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The rates of densification and phase transformation undergone by α‐Si3N4 during hot‐pressing in the presence of Y2O3, Y2O3−2SiO2, and Li20−2Si02 as additives were studied. Although these systems behave less simply than MgO‐doped Si3N4, the data can be interpreted during the early stages of hot‐pressing as resulting from a solution‐diffusion‐reprecipitation mechanism, where the diffusion step is rate controlling and where the reprecipitation step invariably results in the formation of the β‐Si3N4 phase.

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