Glasses crystallization

A common processing defect associated with glass formation is the presence of crystallized regions such regions may result from bulk or surface devitrification or may be due to unmelted raw materials or undissolved refractory phases. Analytical optical and electron microscopic techniques are most useful in identifying these phases. 

In some cases, glass crystallization is desirable. Glass-ceramics are a class of materials that are processed and formed as glasses and then are carefully crystallized to 

Rgure 6.10 Scanning electron micrograph of a crystallized lithium aluminosilicate glass after etching in HF.  

Rgure 6.12 Transmission electron micrograph showing the epitaxial growth of lithium metasilicate (LS) on a lithium orthophosphate (IP) crystal in a glass-ceramic heated through a typical thermal cyde.  

The author wishes to thank a number of his Sandia colleagues, including G. W. 

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A listing of compounds evaluated in the laboratory as cockroach repeUents summarizes 872 synthetic compounds out of 901 bioassayed from 1953 to 1974 (43). EenchoHc acid [512-77-6] (3-isopropyl-1-methylcyclopentanecarboxyHc acid) has been used as a standard repeUent in tests conducted by placing 20 cockroaches in a glass crystallizing dish without food and water and offering them a choice of two cardboard shelters, one of which was treated with 1 or 2 mL of a 1% solution of the candidate in acetone. Counts were made daily for seven days. 

As already remarked in Sect. 4.5.1 (Introduction), LA was primarily designed as a technique for direct sampling in the bulk analysis of solid samples. The main advantages of LA are the possibility of ablating all types of solid material (metals, isolators, glasses, crystals, minerals ceramics, etc.), no special requirements on the... 

Dale Chihuly, Chlhuly Bridge of Glass, Crystal Towers detail, 2002, Tacoma, Washlngton/Scott M. Leen... 

Keywords Induction period Melt and glass crystallization Nucleation and growth Optical microscopy Scattering techniques Spinodal decomposition... 

Discovery of Spinodal Decomposition (SD) Prior to Crystallization—Glass Crystallization Near Tg... 

The results for the glass crystallization of PET annealed at 80 °C as before are shown in Fig. 8. In the early stage of spinodal decomposition up to 20 min, the characteristic wavelength A remains constant at a value of 15 nm, which agrees with the theoretical expectation that only the amplitude of density fluctuations increases whilst keeping a constant characteristic wavelength. In the late stage from 20 to 100 min it increases up to 21 nm just before crystallization. Such a time dependence of A in nm can be represented by... 

Fig. 9 Spinodal decomposition model for glass crystallization at a low temperature just above Tg. The indicated structure parameters mean (A), the average characteristic wavelength (D)y the average size of the dense domain (L), the average long period after crystallization. The numerical values are for PET crystallized at 80 °C...

In the case of the higher temperature crystallization, as will be shown in Sect. 4, the theory of Doi et al. is applicable without doubt since the primary phase separation involves the transition from the isotropic to nematic phase, but in the case of the glass crystallization near Tg described above its applicability is unclear since the observed data may correspond to the secondary phase separation. However, if the secondary phase separation occurs, the primary phase separation must have proceeded prior to that. In a rapidly quenched glass even if the primary phase separation had already taken place, it would be still incomplete, so that it will re-start by heating. 

Table 2 Apparent activation energies for each stage of the induction period of glass crystallization just above Tg for PET, PEN, sPS, and iPS [15]... 

Therefore, in the case of glass crystallization just above Tg we may possibly see a secondary phase separation of the spinodal decomposition (SD) type occurring inside the dense region caused by the first SD. 

Furthermore, it should be noted for glass crystallization that there might exist a boundary crystallization temperature Tbx between 115 and 120 °C because below 115 °C A is of the order of tens of nm while above 120 °C it becomes a few xm they are two orders of magnitude different. The cause of this is not clear at the moment, but one possibility is due to the range Zrmi of molecular interaction involved in Eq. 14. In order to understand this the detailed mechanism of the glass transition would be necessary. Although the problem of the glass transition is not completely solved, the concept has... 

Schubert DM, Alam F, Visi M, Knobler CB (2003) Chemistry of Materials, in press Bray PJ (1997) In Wright AC, Feller SA, Hannon AC (eds). Borate Glasses, Crystals Melts. Society of Glass Technology, Sheffield... 

Teter M (1997) In Wright AC, Feller SA, Hannon AC (eds). Borate Glasses, Crystals ... 

Glasses, Crystals 8 Melts. Society of Glass Technology, Sheffield... 

Wronkiewicz, D. L., Wolf, S. F. DiSanto, T. S. 1996. Apatite- and monazite-bearing glass-crystal composites for the immobilization of low-level nuclear and hazardous wastes. Materials Research Society Symposium Proceedings, 412, 345-352. 

Silicate of potassa and oxide of lead. Examples —Flint-glass, crystal, and slrass. 

Production. There are three important methods for manufacturing barium ferrite on an industrial scale the ceramic, hydrothermal, and glass crystallization methods. The main producers are Toshiba and Toda. 

Based on this simplified description of the melting and glass transitions, it is possible to propose six major types of mesophases. Figure 2 shows these mesophases in relation to the glass, crystal, and melt. First, it is possible to keep orientational order, but lose positional order. These positionally disordered crystals or orientationally ordered liquids 7) are widely known as liquid crystals 15). The name liquid crystal was given because of the obvious, liquid-like flow of these materials. By now it is too late to try to change the nomenclature, especially when the possible new names would be cumbersome 7). 

Fig. 15. DSC-trace of a mesophase macromolecule with flexible spacers in the main chain. Heating rate 50 K/min. Cooling rate 50 K/min. The mesophase glass crystallizes on heating at about 345 K. and melts then at about 385 K. The reversible mesophase-isotropic transition is at about 320 K. Drawn after data from Ref. 27)...

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