Glasses Tech – Prescription Glasses, Prescription Eyeglasses

In this study, short bar fracture toughness samples were used to determine the effects of radiation and hydrogen on the resistance to fracture of vitreous silica and four commercial borosilicate glasses. The results showed that neither exposure to 10^10 rads of γ-radiation nor saturation to a room-temperature-equivalent exposure of 408 atm of hydrogen had an effect on fracture resistance. Nevertheless, when samples were saturated with hydrogen and then exposed to radiation,resistance of fracture increased significantly in some of the glasses. The increase in the resistance to fracture correlated directly with the increase in concentration of hydroxyl and hybride groups created by exposure to radiation and hydrogen. The concentration of these groups differs with glass composition and accounts for the difference in behavior between the types of glass studied.

Moody, Neville R.　Robinson, Steven L.　

Homogeneous Y-Si-O-N glasses containing 15 or 20 eq% nitrogen (N) were preparedfrom compositions with Y/Si ratios in the vicinity of that of the lowest eutectic point on the Y//2O//3-SiO//2 phase diagram. The liquidus on the phase diagramshifted toward lower temperatures by incorphoration of N. The density, the elastic moduli, and the glass transition temperature of the Y-Si-O-N glasses increased with incorporation of N. This is due to the closer packing of atoms in the glasses by the substitution of N, which is in three-fold coordination with Si, forO which is in two-fold coordination, and the stronger covalent nature of the Si-N bond compared with the Si-O bond. The coefficient of thermal expansion of theY-Si-O-N glasses increased with increasing Y content, because the discontinuityof the glass network developed with increasing nonbridging anions by the introduction of Y. In contrast, the glass transition temperature and the elastic moduli increased with Y content due to the high coordination of Y for O, and the relatively high cationic field strength of Y. Furthermore, the effect of cationic field strength on properties of Ln-Si-O-N glasses (Ln-lanthanides or Y) is discussed.

Ohashi, Masayoshi.　Kazuo Nakamura.　

Kinetics for nucleation and growth of α-Agl crystals in Agl-based silver ortheoborate glasses, in which only α-Agl crystals we fiend og cfystallize in e hation prcess f te glassesw studied hy isothermal na onisotermla measuets usig differetnial scaaning calorimetry dn by observatos of the microstructues f et glsses uisng scannng electon miocroscopy. Teh values of but n ad M, depoendent on et crystalizoatn mecanisms, e ofed t be 3, Indicaton the a constnt nuber o nuclei of α-Agl precipitatied i a glass matricx grew three-dimensionallly. The perannealing of te gasses ta temerates betwen glas trnsition an crystlizaotn did ont affect th DSC isoteral urves in te crystal growth roces witsuggestedtha teh numbe o α-Agl nucli wod have bene saturated ineh glasswne tat glsssar prepared by quenching teh Agl-based melts.

Silicon oxycarbide glasses have been synthesized by inert atmosphere pyrolysis at 1000 degree C of gel precursors obtained by cohydrolysis of triethoxysilane, HSi(OEt)//3, and methyl-diethoxysilane, HMeSi(OEt)//2. The oxycarbide structures have been carefully characterized by means of different techniques such as **2**9Si magic angle spinning nuclear magnetic resonance (MAS-NMR) and Raman spectroscopies, X-ray diffraction (XRD), and chemical analysis. Experimental results clearly indicate that, depending on the composition of the starting gels, the resulting oxycarbide glass either is formed by a pure oxycarbide phase or contains an extra carbon or silicon phase. By increasing the temperature up to 1500 degree C, the oxycarbide glasses display compositional and weight stability; however, the amorphous network undergoes structural rearrangements that lead to the precipitation of nano-sized beta -SiC crystallites into amorphous silica. Crystallization of metallic silicon is also clearly observed at 1500 degree C for the samples in which the presence of Si-Si bonds was postulated at 1000 degree C. ( Author abstract) 40 Refs.

Soraru, Gian Domenico　D’Andrea, Gennaro　Campostrini, Renzo　Babonneau, Florence　Mariotto, Gino

Potassium borosilicate glasses were prepared in families having the general formula of RK//2O·B//2O//3·NSiO//2, where R is the ratio of potassium oxide to boron oxide and N is the ratio of silicon dioxide to boron oxide. The glasses wereprepared for values of R ranging from 0 to 7.0 in the families N=0.5, 1.0, 2.0,and 4.0. ^29Si MAS-NMR measurements were performed on these glasses to determine the shortrange order around the silicon atom. a model of proportional sharing of the added potassium oxide between the silicate and the borate groups was suggested. This model was tested against other suggested models where proportional sharing begins after a minimum amount of potassium oxide, R//0, and was observed to provide a better fit to the ^29Si chemical shifts obtained. As was observed in the ^29Si MAS-NMR studies of the RLi//2O·B//2O//3·NSiO//2 glasses, the proportional sharing model with R//0=0 is in stark disagrement with that proposed by the ^11B NMR studies of the alkali borosilicate glasses. This problem is as yet no understood. Since K//2CO//3 was used as the starting material for K//2O, its was observed that at large R values, R＞R//CO//2, where R//CO//2=2.3 for N=1, R//CO//2=4.0 for N=2, and R//C2=5.0 for N=4, CO//2 was retained in the melt in thefashion similar to that observed for other high-alkali borate and silicate glasses. The N=0.5 family did not exhibit retention at the compositions studied. ^29SI MAS-NMR could be used to determine where CO//2 retention began in composition

Martin, Steve W.　Ajay Bhatnagar.　

The dynamic fatigue characteristics of silica glasses with fictive temperaturesof 1000°, 1100°, and 1300℃ and sodalime glasses with fictive temperatures of470° and 530℃ were measured in air. For both glasses, samples with higher fictive temperatures had a greater fatigue resistance. Inert strength of silica glasses with fictive temperature of 1000° and 1300℃ was also measured at liquid nitrogen temperature. Glass with higher fictive temperature had a greater inert strength.

Li, Hong.　Agarwal, Anand.

Accurate refractive indexes of oxide glasses—silica, silicate, borate, aluminate, tellurite, antimonate, and heavy metal gallate glasses—are presented in thewavelength range 0.265 to 1.710 μm. Factors affecting the refractive index dispersion are discussed by using the single-oscillator Drube-Voigt equation. The values of n//d at 0.5876 μm are affected mainly by the average resonance wavelength at the ultraviolet region through all of the glass systems. The distinguishing features of borate glasses—relatively high refractive index and low dispersion—are related to the large number of molecules, N, in a unit volume, compared with those of the other glasses. The number N determined by density measurementsis related to the fraction of the four-coordinated borons estimated by Greenblatt and Bray.

Fujino, Shigeru.　Takebe, Hiromichi.　　

Judd-Ofelt parameters Ω//t with t=2,4,5 for the rare-earth ions Pr^3+, Nd^3+, Sm^3+, Tb^3+, Dy^3+, Ho^3+, Er^3+, and Tm^3+ in alkali and/or alkaline-earth silicate, borate, and phosphate glasses have been determined. The variations of Ω//t with the number of 4f electrons of the rare-earth ions are demonstrated, and factors affecting the Judd-Ofelt parameter Ω//6 are discussed. The intensity parameter Ω//6 depends on the ionic packing ratio of the glass host by changing modifier type in silicate and borate glasses, and it is independent of that in a series of borate glasses, and it is independent of that in a series of borate glasses as a function of modifier content and phosphate glasses. The peak wavenumbers of the transitions whose intensities are determined mainly by the Ω//6＜‖U(6)‖＞^2 term—where ＜‖U(6)‖＞ is one of the reduced matrix elements—shift systematically with the values of Ω//6 for all the rare-earth ions.

Takebe, Hiromichi.　Nageno, Yoshikazu.　　

CdS-doped SiO//2 glasses were prepared via silica gels containing diethyldithiocarbamatocadmium Cd(S//2CN(C//2H//5)//2)//2. Heat treatment of the gels gave transparent yellow SiO//2 glasses doped with hexagonal CdS crystals. In optical absorption and fluorescence spectra, the optical absorption edge and the emission peak clearly exhibited a blue shift, which was attributed to the quantum size effect of the carrier confinement, as the CdS content was decreased. In the fluorescence spectra of the CdS-doped silica glasses, the emission peak was observed only near 500 nm and not observed at longer wavelengths which were known to be present if there were sulfur vacancies. (Author abstract) 27 Refs.

Iwami, Tomoaki　Tadanaga, Kiyoharu　Tatsumisago, Masahiro　Minami, Tsutomu　Tohge, Noboru