Crystallographic characterization of non-stoichiometric glass-ceramics in LiO2-SiO2 system containing CeO2

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Abstract
02-049 Manuel Fellipe Rodrigues Pais Alves Alves, M.F.(Universidade do Estado do Rio de Janeiro); Suzuki, P.A.(Escola de Engenharia de Lorena - Universidade de São Paulo); Freitas, B.X.(Universidade de São Paulo); Ghussn, L.(UERJ-FAT); SANTOS, C.(UERJ); Moreira, L.P.(Universidade Federal Fluminense); The non-stoichiometric glasses of LiO2-SiO2 systems have been extensively studied due to the possibility of formation of the crystalline phase Li2Si2O5 composed of high aspect-ratio grains that allow unique mechanical strength among glass-ceramics. For particular interest in dentistry, this material presents high levels of lithium disilicate, besides considerable amount of residual amorphous phase after devitrification heat treatment. In this work, glasses containing 65.0 SiO2-27.5 Li2O-2.2 Al2O3-2.3 K2O-2.0 ZrO2-1.0 P2O5 (mol%) were prepared with additions of 0.61, 1.22 or 2.44 mol% of CeO2. The blends were calcined, melted at 1450°C, and annealed at 450°C, with controlled cooling to room temperature. The compositions were characterized by TG-DSC, and then heat treated in two stages: 660°C-12h, and then at 830°C-3h, with controlled cooling. Glass-ceramics were fragmented, sieved (20?m) and characterized by High Resolution X-ray Diffraction using Synchrotron light source. The results of the thermal analyses indicated that the crystallization of the Li2SiO3 and Li2Si2O5 phases occurs on-set at about 580°C, and 800°C, respectively. Compositions containing 1.22% and 2.44% of CeO2 show crystallization peaks of a new phase. Phase quantification indicated that after heat treatment at 660°C-12h, 57-59% amorphous phase, 39% of Li2SiO3 and Li2Si2O5 contents of 1% to 8%, associated with increased CeO2 in the overall composition. After heat treatment at 830°C-3h, the following behaviours were observed as a function of the addition of CeO2: The amorphous phase content reduced from 42% to 35.3% (0 to 2.44% CeO2) and 55-57% of Li2Si2O5 were observed. Due to the addition of CeO2, Ce2Si2O7 was crystallized. In addition, residual contents (<4%) of Li2PO4 and SiO2 are observed.
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