Glass matrices

Examples include luminescence from anthracene crystals subjected to alternating electric current (159), luminescence from electron recombination with the carbazole free radical produced by photolysis of potassium carba2ole in a fro2en glass matrix (160), reactions of free radicals with solvated electrons (155), and reduction of mtheiiium(III)tris(bipyridyl) with the hydrated electron (161). Other examples include the oxidation of aromatic radical anions with such oxidants as chlorine or ben2oyl peroxide (162,163), and the reduction of 9,10-dichloro-9,10-diphenyl-9,10-dihydroanthracene with the 9,10-diphenylanthracene radical anion (162,164). Many other examples of electron-transfer chemiluminescence have been reported (156,165). 

Fig. 10. Crack pinning by a SiC fiber in a glass matrix, photographed using an optical microscope and Nomarski contrast. Fiber ties perpendicular to plane of micrograph lines represent crack position at fixed intervals of time, crack mnning left to right.

Aesthetic dental ceramics are essentially glass-matrix materials with varying volume fractions of crystalline fillers. Crystalline fillers are used in the glass matrix both for dispersion strengthening, usually at volume fractions of 40—70%, and for altering optical properties, usually at low volume fractions. Dental ceramics are generally manufactured from two distinct classes of materials, ie, beneficiated feldspathic minerals and glass—ceramics. 

Scaiano and Kim-Thuan (1983) searched without success for the electronic spectrum of the phenyl cation using laser techniques. Ambroz et al. (1980) photolysed solutions of three arenediazonium salts in a glass matrix of 3 M LiCl in 1 1 (v/v) water/acetone at 77 K. With 2,4,5-trimethoxybenzenediazonium hexafluorophos-phate Ambroz et al. observed two relatively weak absorption bands at 415 and 442 nm (no e-values given) and a reduction in the intensity of the 370 nm band of the diazonium ion. The absence of any ESR signals indicates that these new bands are not due to aryl radicals, but to the aryl cation in its triplet ground state. 

Part cures were characterized by exothermic reaction wave propagation. Figures 6a-9b show the development of the reaction waves. The waves propagate from the walls of the part towards the center. A comparison of the temperature and epoxide conversion profiles revealed that the highest temperature corresponded to the highest conversion. As the part initially heats the resin/glass matrix nearest the walls heats fastest however, as the part exotherms the temperatures in the interior of the part exceeded the wall temperatures. The center temperature does not become the hottest temperature until the waves intersect. It must be noted that the hottest temperature does not always occur at the center of the part. The wave velocities are proportional to the wall temperatures. In Figures 6a to 9b the mold temperature was 90 C and the press temperature was elevated to 115 C. Since the press does not heat the part until after it is wound, the press temperature was elevated to accelerate the reaction wave from the press so that the waves would intersect in the center of the part. 

FC as sensor molecule has been used to investigate the low-energy mobility, i.e., the nature of the Boson peak and of the trawi-Boson dynamics, of toluene, ethylbenzene, DBF and glycerol glasses [102]. The spectator nucleus Fe is at the center of mass of the sensor molecule FC. In this way, rotations are disregarded and one selects pure translational motions. Thus, the low-energy part of the measured NIS spectra represents the DOS, g(E), of translational motions of the glass matrix (below about 15 meV in Fig. 9.39a). 

L. Zheng and J.D. Brennan, Measurement of intrinsic fluorescence to probe the conformational flexibility and thermodynamic stability of a single tryptophan protein entrapped in a sol-gel derived glass matrix. Analyst 123, 1735-1744 (1998). 

S. Shtelzer, S. Rappoport, D. Avnir, M. Ottolenghi, and S. Braun, Properties of trypsin and of acid phosphatase immobilized in sol-gel glass matrixes. Biotechnol. Appl. Biochem. 15, 227-235 (1992). 

A number of other up-conversion processes are known. The blue emission from a Yb3+/Tm3+ couple in which the active emitters are defect Tm3+ centers is mainly due to the efficient excitation ET process from Yb3+ centers. Two-frequency up-conversion has been investigated using Pr3+ defects in a fluoride glass matrix. Illumination with one pump wavelength results in GSA, while simultaneous irradiation with a second pump wavelength further excites the GSA centers via ESA. The doubly excited defects emit red light. Up-conversion and visible output only takes place at the intersection of the two beams. 

Aluminide alloys, 13 530 Aluminium powder, 10 738. See also Aluminum entries Aluminohydride derivatives, 13 624 Aluminohydrides, 13 621-624 Aluminophosphate zeolites, 14 98 Aluminosilicate gels, 16 830 Aluminosilicate glass, matrix for... 

Cordierite glass, matrix for ceramic-matrix composites, 5 553t... 

Larvik furnaces, 21 395—396 LASIII glass, matrix for ceramic—matrix composites, 5 553t LAS acid, 23 554. See also Linear alkylbenzene sulfonate (LAS)... 

An additional assumption is that diffusion is independent of other species in the glass matrix. This cannot be strictly true because interdiffusion of at least one additional species is necessary to maintain charge balance within the glass. Sodium is most likely to be the dominant interdiffusion ion, as has been demonstrated for Sr and Cs diffusion in rhyolite glass at higher temperatures (10) and as supported by rapid release rates of Na to solution found in the present study. Codiffusion of hydronium and alkali ions are ignored in the model. 

The activation energies calculated for Rb, Cs and Sr in the present study (Table III and Figure 8) are considerably lower than those calculated for high temperature diffusion in both crystalline and glass silicates. This discrepancy in the latter case implies that the glass matrix may be significantly different in high and low temperature diffusion studies. 

Bright, J.D., Shetty, D.K., Griffin, C.W. and Limaye, S.Y. (1989). Interfacial bonding and friction in SiC filament-reinforced ceramic and glass matrix composites. J. Am. Ceram. Soc. 72, 1891-1898. 

---