Crystallization in glass

Devitrification. This process is the uncontrolled formation of crystals in glass during melting, forming, or secondary processing. 

A novel technique of producing waveguiding structures by growth of crystals in glass capillaries is presented. This method of crystal growth is simple and is particularly suited to organic materials. 

The maximum of the kisc-values at undecahelicene may correspond to a maximum departure from coplanarity or to an optimization of the spin-orbit coupling of L, and 3Lb due to degeneracy 125). Later on it was shown with the aid of ESR-spectra in single crystals, in glass and in streched films that there is a transient magnetization in triplet hexahelicene 131), which demonstrates that the predominant path of intersystem-crossing leads to the population of the Ty> state but that a small rate of population of the TZ> state cannot be excluded. 

Fig. 5.24. Variation of hardness Hy with volume fraction Vf of gahnite crystals in glass-ceramic.

Devitrification is the uncontrolled formation of crystals in glass during melting, forming, or secondary processing. The optical properties, mechanical strength, and sometimes the chemical durability of the glass can be adversely affected by devitrification. 

Sufficiently long heating at suitable temperatures brings about crystallization in glass, either in the form of isolated crystalline formations or as a layer growing from the surface. The final stable state is a totally transformed polycrystalline system. Exceptions to this rule are represented by B2O3 among oxides and by feldspar K2O. ... 

A. Marotta, A. Buri, F. Branda and S. Saiello, Nucleation and crystallisation of Li20.2Si02 Glass—A DTA Study, in Advances in Ceramics, Vol. 4, Nucleation and Crystallization in Glasses, American Ceramic Society, Columbus, OH (1982), pp. 146-152. 

M, Mortier, A, Bensalah, G, Dantelle, G, Patriarche, D, Vivien, Rare-earth doped oxyfluoride glass-ceramics and fluoride ceramics Sintesis and optical properties. Opt. Mat., 29, 1263-1270 (2005), Patterning of non-linear optical crystals in glass by laser-induced crystallization, J. Am. Ceram. Soc. 90, 699-705 (2007),... 

W. Pannhorst, Nucleation and Crystallization in Glass and Liquids, ed. M. Weinberg, American Ceramics Society, WesterviUe.OH261 (1993). 

D.R.Stewart, Advances in Nucleation and Crystallization in Glasses, The American Ceramic. Society, 83-90 (1971). 

Many other methods of strengthening are based on formation of composites by inclusion of fibers or whiskers or by crystallization to form glass-ceramics. Phase separation may also affect strength by altering crack propagation mechanisms. Transformation toughening has also been attained by formation of a small concentration of zirconia crystals in glasses. 

On cooling formation of Celsian crystals in glass matrix... 

Varga J, Karger-Kocsis (1993) Direct evidence of row-nucleated cylindritic crystallization in glass liber-reinfOTced polypropylene composites. J Polym Bull 30 105-110... 

The ability of polymers to inhibit crystallization in glass solutions is primarily related to the overall increase in the glass transition temperature (Tg) of the dispersion. 

Microstructure is of equal importance to composition. This feature is the key to most mechanical and optical properties, and it can promote or diminish the characteristics of key crystals in glass-ceramics. It is clear that microstructure, is not an independent variable. It obviously depends on the bulk composition and crystalline phase assemblage, and it also can be modified, often dramatically, by varying the thermal treatment. 

In this case, y represents the interfacial energy, is a function of the activity ( ) for foreign substrates, which is different for different substrates. Z is the attachment probability (sticking coefficient) of molecules of the parent phase to the nucleus. Therefore, Z is related to epitaxy. For crystallization in glass, Z is approx. lO". The viscosity of the parent phase is represented by J. The difference between the chemical potentials of the melt and the crystal is represented by p. It is determined by Eq. 1-13. 

BCinetic examinations of crystallization in glass, according to Gutzow (1980) for example, demonstrate the relationship between crystal growth rates and viscosity in more detail. In these studies, the growth rate (V) in the crystalline phase of a viscous glass melt is determined as a function of temperature. 

The neutral silver is formed by this reaction. During the subsequent heat treatment of the glass at approximately 600 C, colloids of metallic silver are formed (Beall 1992). This colloidal silver forms heterogeneous nuclei of approximately 80 A for the subsequent crystallization of a lithium metasilicate primary crystal phase, Li2Si03. Lithium metasilicate possesses a chain silicate structure. The crystallization of this compound proceeds dendritically. The dentritic growth of crystals in glass-ceramics is discussed in Section 3.2.4. 

The formation of P-quartz solid solution and gahnite crystals in glass-ceramics from the Si02-Al203—ZnO allowed specific properties, such as translucency and even transparency, to be combined with variable coefficients of thermal expansion of... 

Machinable glass-ceramics are based on internally nucleated fluoromica crystals in glass (Beall 1971a). One commercial material has been marketed for 20 years under the trademark MACOR and has found wide application in such diverse and speciality areas as precision electrical insulators, vacuum feedthroughs, windows for microwave-type parts, samples holders for field-ion microscopes, seismograph bobbins, gamma-ray telescope frames, and... 

Beall G.H., "Glass-Ceramics Recent Development and Application" pp. 241-66 in Nucleation and Crystallization in Glasses and Liquids. Ceramic Transactions, Vol 30, Editol by... 

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