Abstract
The porosity type in spark plasma sintered alumina was studied by variable energy positron beam technique. The gamma ray energy spectra of interest in the region of the annihilation peak were analyzed by means of Compton-to-peak ratio and deconvolution into Gaussians of the Doppler broadened annihilation peak. The contributions of the two narrow Gaussians (centered and red-shifted) revealed difference in the porosity type according to the heating rate. The samples sintered at low heating rate showed open porosity. Closed porosity appeared at 1050 °C as a result of formation of isolated pores. For the samples sintered at high heating rate, closed porosity was found to be significant even at comparatively low sintering temperatures which was explained by a blocking effect at the sample free surface.
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