Pore closure in spark plasma sintered alumina studied by variable energy positrons

¹ Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee Blvd, 1784 Sofia, Bulgaria
² Université de Lyon, Laboratoire MATEIS UMR CNRS 5510, INSA Lyon, Bât. B. Plascal, 5e, av. Jean Capelle, 69621 Villeurbanne Cedex, France
³ Université de Savoie, Laboratoire LMOPS, UMR 5041 CNRS, av. du Lac d’Annecy, 73370 Le Bourget du Lac, France
⁴ Université de Lyon, Laboratoire IPNL, UCB Lyon 1, Bâtiment Paul Dirac, 4 rue Enrico Fermi, 69622 Villeurbanne Cedex, France

^a e-mail: nikdjour@inrne.bas.bg

Received: 24 February 2011
Revised: 15 November 2011
Accepted: 4 January 2012
Published online: 30 January 2012

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.