resumo
A recent application for nanometric CaO powder is its use as a spallation target material for the production of isotope beams at CERN. The stability of the nanostructure at high operation temperatures is a crucial feature to provide stable and improved isotope release rates. Prior to operation, sintering studies under thermal conditions similar to those of the target operation are required to establish the microstructural evolution due to coarsening and densification processes. This knowledge enables the identification of the limiting temperatures for the target operation, ensuring a stable nanostructure for higher and constant isotope release rates. In this study, nanometric CaO powder with 58 m(2) g(-1) of specific surface area was obtained from vacuum decomposition of calcium carbonate at 800 degrees C. The microstructure evolution of porous powder compacts was investigated under vacuum atmosphere, from 1000 to 1250 degrees C, for holding times from 3 to 600 min. For temperatures higher than 1000 degrees C, a significant surface area reduction was observed, accompanied by porosity decrease. The morphological analysis of the pore evolution revealed a differential sintering of the porous compacts, mainly occuning inside the aggregates. The kinetic analysis of the surface area reduction pointed to aggregate shrinkage controlled by volume diffusion with surface diffusion as an underlying mechanism for lower temperatures. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
palavras-chave
SELF-DIFFUSION; SURFACE-AREA; CAO; DECOMPOSITION; ISOLDE; TARGET; CACO3; BEAMS
categoria
Materials Science
autores
Ramos, JP; Fernandes, CM; Stora, T; Senos, AMR
nossos autores
Ana Maria de Oliveira e Rocha Senos
Colaborador
Cristina Maria da Silva Fernandes
ColaboradorGrupos
G2 - Materiais Fotónicos, Eletrónicos e Magnéticos
G3 - Materiais Eletroquímicos, Interfaces e Revestimentos
agradecimentos
The author J.P. Ramos gratefully acknowledges the financial support from Agencia de Inovacao, S.A. (AdI) and CERN, through the Grant SFRH/BEST/51352/2011 for the traineeship at CERN. The authors acknowledge Fundacao para a Ciencia e a Tecnologia (FCT), Fundo Europeu de Desenvolvimento Regional (FEDER), QREN-COMPETE, the European Union, and the Associate Laboratory CICECO (PEst-C/CTM/LA0011/2013) for continued support and funding. The authors would also like to thank M. J. Bastos, C. Miranda and A. Ribeiro for the XRD and N