Control of nucleation in glass ceramics

Abstract

Glass ceramics are advanced materials composed of one or more glass and crystal phases. By developing base glasses with appropriate compositions and by controlling crystal nucleation and growth in these glasses, glass ceramics with tailor-made properties can be fabricated. The key to developing this type of material is control of the nucleation processes. Both volume and surface nucleation can be exploited. Heterogeneous volume nucleation has been used to develop glass ceramics showing minimal thermal expansion and high strength. Two nucleation mechanisms can be combined and the precipitation of two crystal phases can be controlled. That the nucleation processes can be controlled by nano-and microscale immiscibility is a special feature, allowing selective nanophase formation or the development of needle-like apatite phases demonstrating a natural morphology. This represents a biomimetic process. The control of nucleation has enabled the development of biomaterials for dental applications.

Microstructural evolution and physical behavior of a lithium disilicate glass–ceramic

“…Again, this gradual enlargement of the lithium metasilicates' peak intensities indicated that the development of lithium metasilicates was postulated to be temperature dependent and to involve the epitaxial growth of lithium metasilicate on a lithium orthophosphate crystal [32,55].…”

Degradability of fluorapatite-leucite ceramics in naturally acidic agents

“…These very small crystals in dental microstructures result in very special optical properties such as translucence and opalescence. Hence, the presence of these crystals in IPS d.SIGN also imparts these special optical properties to fluorapatite-leucite ceramic restorations 11) . As for the leucite crystals (less than 3 µm in diameter of flower-like morphology) also present in IPS d.SIGN ceramic, they contribute to the overall strength 12) .…”

P<SUB>2</SUB>O<SUB>5</SUB> AS AN EFFECTIVE NUCLEATING AGENT OF LITHIUM DISILICATE GLASS-CERAMICS

“…It was possible to precipitate both lithium metasilicate, Li2SiO3, to develop Fotoform (R) or lithium disilicate , Li2Si2O5,to develop F otoceram(R) as devices for micromechanics (Beall[1]) .High strength glass-ceramics with flexural strength of 400 to 500 MPa were developed in multi -component glassceramics with the main crystal phase of lithium disilicate as a material with a self glazing effect (Echeverria [4]), or oriented crystals prepared by extrusion (Russel [5]) , or prepared by p ressing an SiO2-Al2O3-ZnO-Li2O-K2O-P2O5 glass-ceramic(Schweiger et al [6], HOland et al [7]) . Recently, the authors of this paper reported on nucleation ,phase formationand solid state reaction in a colored ZnO-free lithium disilicate glass -ceramic characterized by translucent properties and unexpected high flexural strength of more than 700 MP a (HOl and et al [8]).…”