Multicomponent glass-ceramics

Findings from the theories of nucleation have also contributed to the optimization of these comprehensive experimental investigations. As a result, glass-ceramics with improved properties have been produced, specifically glass-ceramics with specific solid-solution limits like j3-spodumene and stuffed P-quartz or with stoichiometric compositions like cordierite and lithium disilicate. Initial results for the successfU application of the theory of nucleation to multicomponent glass-ceramics with a nonstoichiometric composition were achieved with mica and anosovite glass-ceramics. 

Rgure 3-23 High-temperature X-ray diffraction, HT-XRD, of a multicomponent glass-ceramic of lithium disilicate type. A = Li SiOg, B = U2Si205, C = Si02 (cristobalite), and D = U3PO4. 

Selected examples in Section 4.4.2.6.B are used to describe the processes that are suitable to achieve optimal joining of the different materials. In addition, measuring methods for evaluating the results were carried out. These glass-ceramic-metal composites for dental applications demonstrate that a multicomponent glass-ceramic and metals can be used for a variety of applications in medical and technical fields. 

M. Kinoshita, M. Satou and K. Uematsu, Dispersant Affects Glass-Based Multicomponent Slurries, Ceram. Bull. 76 [10], 55-58 (1997). 

Predominantly simplified model glasses with stoichiometric compositions were used to test the different nucleation theories. Multicomponent glasses were examined in few cases. Thus simple glass systems that are significant for the development of glass-ceramics will be discussed at this stage. 

The development of glass-ceramics with a barium disilicate primary crystal phase was conducted in two diflFerent ways. The first type of glass-ceramic was produced from base glasses with a composition almost corresponding to the stoichiometric composition of barium disilicate. The second type of glass-ceramic with sanbornite crystals was developed from multicomponent glasses using controlled crystallization. 

Stangar U., Orel B., Krajnc M., Korosec R., Bukovec P. Sol-gel derived thin ceramic C0AI2O4 coatings for optical applications. MTAEC 9 2002 36 387-393 Stuart B., George B., McIntyre P. Modem Infrared Spectroscopy. Chichester, 1996 Thomas I.M. Multicomponent glasses from the sol-gel process. In Sol-Gel Technology for Thin Films, Fibres, Preforms, Electronics and Specialty Shapes. L.C. Klein, ed. New Jersey Noyes Publications, 1988... 

Ceramics and glasses are generally multicomponent sohds that are chemically bonded by ionic or covalent bonding such that there are no free electrons. Therefore, the electrical conductivity and the thermal conductivity are low and the material is brittle. If there is crystallinity the material is called a ceramic and if there is no crystallinity (i.e. the material is amorphous) the material is called a glass. Ceramics and glasses are characterized by low ductility and low fracture toughness. Some elemental materials, such as boron, carbon, and silicon, can be formed as amorphous materials, so the definitions must be taken with some exceptions. 

The sol-gel process was first focused on silica glasses and then on multicomponent ceramics. The aim was to... 

A. Douy, Polyacrylamide gel an efficient tool for easy synthesis of multicomponent oxide precursors of ceramics and glasses. Int. J. Inorg. Mater. 3(7), 699-707 (2001). 

A.I. Kingdon, R. F. Davis, and M. M. Thackeray, Engineering properties of multicomponent and multiphase oxides, in Engineered Materials Handbook, Vol. 4, Ceramics and Glasses, ASM international. Metals City, OH (1991). p. 758-774. 

The classic procedure for the sol-gel synthesis of high purity glasses and ceramics starts from a mixture of alkoxides and water in a common solvent, usually an alcohol. Tarasevich [17] proposed an alternative route to obtain silica gels, in the absence of a solvent, by means of ultrasonic activation. This procedure has been extended to the preparation of multicomponent systems [18]. Materials obtained in this unconventional way are called sonogels. 

A wide range of ceramic and glass compositions have been prepared by sol-gel processing and details of the experimental procedure can be found in the literature (see, for example. Ref. 44 for a partial list). We will not repeat the procedure for the preparation of specific gel compositions. Instead, the common techniques will be outlined with the aid of a few specific examples. To keep the discussion at a suitable level, we shall limit the consideration of multicomponent gels mainly to the case of gels containing two metal cations only. 

TABLE 10-2. MULTICOMPONENT OXIDE GLASS AND CERAMIC FIBERS PREPARED BY THE SOL-GEL METHOD... 

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