title: Crystal structure and microstructure of synthetic hexagonal magnesium-cobalt cordierite solid solutions (Mg(2-2x)Co(2x)Al4Si5O18).
abstract: Co(2+)-containing cordierite glasses, of nominal compositions (Mg(1-x)Co(x))2Al4Si5O18 (with x = 0, 0.2, 0.4, 0.6, 0.8 and 1), were prepared by melting colloidal gel precursors. After isothermal heating at 1273 K for around 28 h, a single-phase α-cordierite (high-temperature hexagonal polymorph) was synthesized. All materials were investigated using X-ray powder diffraction and field-emission scanning electron microscopy. The crystal structure and microstructure were determined from X-ray diffraction patterns. Rietveld refinement confirmed the formation of magnesium-cobalt cordierite solid solutions. The unit-cell volume increased with the increase of cobalt content in the starting glass. The crystalline microstructure of the cordierites was interpreted using a mathematical model of a polycrystalline material and characterized by prevalent crystallite shape, volume-weighted crystallite size distribution and second-order crystalline lattice-strain distribution. Hexagonal prismatic was the prevalent shape of α-cordierite crystallites. Bimodality in the size distribution was observed and interpreted as a consequence of two paths of the crystallization: the nucleation from glass of μ-cordierite, which transformed into α-cordierite with annealing, or the nucleation of α-cordierite directly from glass at high temperatures. Scanning electron microscopy images agreed well with crystalline microstructure characteristics determined from the X-ray diffraction line-profile analysis.
authors.affiliation: Department of Geology, University of Valencia, 46100 Burjasot, Spain.
authors.forename: Francisco Javier
authors.initials: FJ
authors.lastname: Serrano
authors.forename: Noemí
authors.initials: N
authors.lastname: Montoya
authors.forename: José Luis
authors.initials: JL
authors.lastname: Pizarro
authors.forename: María Mercedes
authors.initials: MM
authors.lastname: Reventós
authors.forename: Marek Andrzej
authors.initials: MA
authors.lastname: Kojdecki
authors.forename: José María
authors.initials: JM
authors.lastname: Amigó
authors.forename: Javier
authors.initials: J
authors.lastname: Alarcón
keywords: Rietveld analysis; X-ray diffraction line-profile analysis; cordierite; crystalline microstructure; crystallite shape; glass; powder X-ray diffraction pattern modelling; second-order crystalline lattice-strain distribution; volume-weighted crystallite size distribution