P.L. Higby

GLASS FORMATION AND THERMAL PROPERTIES OF LOW-SILICA CALCIUM ALUMINOSILICATE GLASSES

Calcium aluminosilicate glasses with small percentages of silica have been prepared. The limits of glass formation at 1600°C were found to expand as silica is added to calcium aluminate base compositions. The behavior of such physical properties as glass transition temperature and transition range viscosity has indicated that the structural role of silica changes as its concentrations is increased, keeping the CaO/Al2O3 ratio constant.

Properties of barium gallium germanate glasses

Abstract The glass-forming region density, index of refraction, glass transition temperature, Tg, chemical durability and viscosity of BaO-Ga2O3-GeO2 (BGG) glasses have been determined. In general, the physical properties of these ternary germanate glasses behave in a similar manner to comparable silicate glasses. Three series of BGG glasses containing a constant Ga2O3 content were formulated to approximate the physical property behavior of alkaline earth germanate glasses. The molar volume of the glasses in these series passes through a minimum with increasing BaO content, indicating a maximum in packing density and therefore the possibility of the existence of six-coordinated germanium ions.

29Si NMR and infrared reflectance spectroscopy of low-silica calcium aluminosilicate glasses

Abstract Selected calcium aluminosilicate glass compositions have been investigated using nuclear magnetic resonance (NMR) and infrared reflectance spectroscopy, with emphasis on compositions in the silica-poor portion of the system. In particular, a structural explanation for a maximum observed in the glass transition temperature at roughly 15 mol% SiO 2 was sought. 29 Si chemical shifts from magic-angle spinning NMR data are nearly constant in the low-silica glasses and are consistent with depolymerized Q 2 species, or fully polymerized Q 4 tetrahedra with 4 Al next-nearest neighbors. Static 29 Si NMR spectra bear no evidence of asymmetric Q 2 or Q 3 sites; however, the asymmetric component could be hidden by extreme broadening due to structural disorder. The functions ϵ″ and −Imag(1/ϵ) have been calculated from infrared reflectance spectra by a Kramers-Kronig transformation. A change in lineshape which parallel the maximum in T g is attributed to variation in the distribution of tetrahedral aluminate species.

An electron spin resonance study of X-irradiated calcium aluminosilicate glasses

Abstract An electron spin resonance investigation of a series of low-silica-content (≤ 20 mol%) calcium aluminosilicate glasses has been performed. The compositional dependence of the X-ray-induced defects is found to be consistent with the proposed dependence of the number of non-bridging oxygens on the CaO/Al 2 O 3 ratio and the silica content. Computer lineshape simulations of the experimental data have led to the identification of two variations of aluminum-oxygen hole centers.

Compositional dependence of trapped hole centers in gamma-irradiated calcium aluminosilicate glasses

Abstract The electron spin resonance (ESR) spectra of a series of γ-irradiated calcium aluminosilicate glasses with compositions CaO/Al2O3 = 1.50 and 0–80 mol% SiO2 have been measured at 9.3 GHz. The ESR spectra have been analyzed using spin-Hamiltonian parameters previously attributed to aluminum- and silicon-associated hole centers. Defect concentrations calculated from computer lineshape simulations based on the spin-Hamiltonian parameters are analyzed in terms of proposed defect precursor 3tructures and a simple tetrahedral coordination model.

Gallogermanate Glasses As Near IR Optical Waveguides

Alkaline earth gallogermanate glasses are a possible low-loss oxide optical material which would be able to operate in the 1.6–2 μm wavelength range. Processing techniques investigated to date and pertinent optical property data are presented.

Structural relaxation following crystallization in high purity GeO2 glass

Abstract Crystallization of high purity GeO 2 glass heat treated for various lengths of time at temperatures between 373 and 1273 K was monitored by X-ray diffraction. Structural relaxation at and slightly above room temperature in these partially crystalline samples was studied by electron spin resonance (ESR) spectroscopy as a function of time. Broken bonds are created during the structural relaxation of the glassy phase as evidenced by the increase in the concentration of Ge E ′ centers.

Effect of small silica additions on the properties and structure of calcium aluminate glasses

Calcium aluminate glasses are transparent to a longer wavelength than silicate gI asses. However it is well known that they are difficult to form into conventional optics due to their high tendency to crystallize. To increase the understanding of aluminate glasses a study of the effect of small silica additions on such properties as viscosity and crystallization tendency has been combined with a study of such optical properties as infrared cut-off and UVVis-NIR spectroscopy. 1.

Radiation Effects On The Low Temperature Coefficient Of Thermal Expansion Of Low-CTE Materials

Materials for large space optics require low coefficients of thermal expansion (CTE) in order for the components fabricated from them to maintain their strict figure specifications under thermal gradients and cycling. The environment in space contains high energy photons and charged particles such as electrons and protons, which can cause electronic defects, leading to such physical effects as compaction and discoloration. The change in CTE upon exposure to ionizing radiation has been studied here, and it has been found that the low-CTE characteristics of some materials are severely effected by electron irradiation.