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Berkshire, United Kingdom

Gilbert M.R.,Materials Science Research Division
Journal of Physics and Chemistry of Solids | Year: 2014

A series of static lattice calculations were performed to determine the site selectivity of cations of differing size and valence when substituted onto the Ca sites of the calcium chlorosilicate (Ca3(SiO 4)Cl2) lattice, a potential host phase for the immobilisation of halide-rich wastes arising from the pyrochemical reprocessing of plutonium. Atomic-scale simulations indicate that divalent cations are preferentially substituted onto the Ca1 site, whilst tri- and tetravalent cations are preferentially hosted on the Ca2 site, with the Ca1 site favoured for forming the vacancies necessary to charge-balance the lattice as a whole. Multi-defect calculations reveal that the site selectivity of the dopant cations is dependent on their ionic radii; as the ionic radii of the divalent cations increase, substitution onto the preferred site becomes more and more strongly favoured, whereas the inverse is true of the trivalent cations. © 2014 Elsevier Inc. All rights reserved.

Donald I.W.,Materials Science Research Division | Mallinson P.M.,Materials Science Research Division | Metcalfe B.L.,Materials Science Research Division | Gerrard L.A.,Materials Science Research Division | Fernie J.A.,Materials Science Research Division
Journal of Materials Science | Year: 2011

There has, in recent years, been a major revival of interest in glass- and glass-ceramic-to-metal seals and coatings for new applications. Experience dictates that many factors need to be taken into consideration in the successful design and manufacture of high-quality seals, particularly if an adequate component lifetime is to be achieved. For example, during their preparation, undesirable reactions may occur between diffusing metal species and glass constituents, and these can lead to the formation of highly localized internal stresses, which can initiate failure of a seal either during manufacture or, more seriously, whilst in service due to the influence of static fatigue. In the case of high-temperature systems, reactions under hostile operating conditions also need to be taken into consideration. In this review, the factors learnt from past experience that influence the formation and lifetime behaviour of glass and glass-ceramic/metal systems are briefly introduced, and their relevance to the newer applications including solid oxide fuel cell sealants and coatings on titanium for biomedical applications is discussed. © 2011 Springer Science+Business Media, LLC.

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