Permitted and forbidden structural units in vitreous systems

A central cation in oxide glasses may be surrounded as next neighbors by bridging or passive O ions, the no. of which det. the nos. of network-modifiers and O ions that must be accommodated in the second sphere. By comparing these nos. with those calcd. from the space available, the conclusion was drawn that certain structural units may be permitted and that others must be forbidden. [on SciFinder (R)

Glass ceramics

The literature on ceramic-like glassy cryst. products from glass is reviewed. The crystal phase of Pyroceram 9609 is cordierite (2MgO.2Al2O3.-5SiO2), with TiO2 as a seed-forming addn.: tan d = 3 * 10-4 at 100 Deg for a frequency of 24 * 1010 cycles. With Pyroceram 9608, TiO2 is also used for the seed formation, and the main crystal phases are: b-spodumene (Li2O.Al2O3.4SiO2) or b-eucryptite (Li2O.Al2O3.2SiO2), or a mixt. of the 2; the thermal expansion was 0 in the range -75 Deg to +60 Deg and 11 * 10-7/ DegK. in the range 0-500 Deg. A new method is described for increasing the mech. strength of glass. [on SciFinder (R)

Local motions in vitreous systems

The dielectric relaxation phenomena (dielectric losses) which are found in crystals and glasses in the region of 50 K (if measured with medium frequencies (103-106 s-1) must be assigned to local motions of ions. They show activation energies of the order of 0.1 eV. Two types of dielectric losses due to local motions can be distinguished: (1) The inherent dielectric losses due to local motions, since they are inherent to situations existing in the original crystal lattice or glass network; and (2) the induced dielectric losses due to local motions, since they are due to situations induced in the crystal lattice or the glass network, for instance by stress or radiation. There are also induced dielectric losses due to local motions of electrons, for instance in radiation induced colour centers. These losses show activation energies of the order of 0.01 eV. In this paper a number of cases described in the early as well as the recent literature is summed up and their physical background is discussed

Rheological properties of alkali borate glasses

A survey is given of the recent work in the Department of Inorganic Chemistry of the Eindhoven University of Technology on the rheological properties of alkali borate glasses. With the help of a specially adapted viscosimeter the rheological properties of systematically varied series of alkali borate glasses are measured. These include the coefficients of viscosity in the 109–1012 poise region and the corresponding yield values; they are discussed as a function of composition and of the water content of the samples. Conclusions can be drawn about the structure of borate glasses in question and the manner in which the water is built into the network. Whereas relative small amounts of alkali oxides built into the network of B2O3 give rise to boron atoms with a tetrahedral coordination, small amounts of water are taken up by the mechanism of breaking B—O—B bonds

Influence of electromagnetic radiations on vitreous systems

A review and theoretical discussion of the mechanism of color center production by uv, soft x-ray, and g-radiations in silicate glasses including quartz, fused SiO2, simple glasses of SiO2 and alkali or alk. earth oxides, and simple glasses contg. Al2O3. [on SciFinder (R)

Glass. Old material with new possibilities

A review, with no refs., of the phys. structure of glass in relation to its properties and new uses of glass in fiber-optics, display-panels, and light intensifiers. [on SciFinder (R)