Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Patent
1995-04-04
1996-10-29
Group, Karl
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
501905, 65 325, C03C 3095
Patent
active
055696309
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to novel glass compositions which possess various improved properties, including complete absorbance of harmful ultraviolet rays.
Most of the glasses manufactured today are based on three main constituents: silica, alkali metal oxide and oxides of metals belonging to Group II of the Periodic Table (calcium, magnesium, zinc). Silica in its fused state, is an excellent glass but, as the melting point of crystalline silica (i.e. sand) is above 1700.degree. C. and forms glass above 2200.degree. C., its production is very expensive so that its uses are restricted to a specific limited purposes. In order to reduce the melting point of silica, it is necessary to add a flux, such as sodium carbonate which provides the sodium oxide constituent. Thus, by adding about 25% of sodium oxide to silica, the melting point is reduced from 1723.degree. C. to 850.degree. C. and the glass forming temperature to 1400.degree. C. However, such glasses are easily soluble in water. The addition of a third constituent such as calcium oxide, magnesium oxide or zinc oxide, renders the glass insoluble, but too much of this third constituent renders the glass prone to devitrification, i.e. the precipitation of crystalline phases in certain ranges of temperature.
The optimum composition for glass which was considered to be useful for many purposes included 75% silica, 15% alkali oxide and 10% oxides of a metal from Group II. Of course, in addition to these main constituents, other materials are also incorporated in order to impart a specific property; for example, by adding small amounts of cobalt oxide together with traces of arsenic trioxide and sodium nitrate, the green color imparted by the iron impurity, generally present in sand, is substantially eliminated. Glasses of very different compositions are suggested when special physical and chemical properties are required. Among the properties which are particularly important for glass, the following can be mentioned: electrical properties including conductivity and dielectric constant, optical properties and ultraviolet ray transmission.
The electrical conductivity of glass varies with the composition and the temperature used in its manufacture. In most glasses, the current is carried by alkali metal ions moving through the material, but semiconducting glasses have recently been discovered in which the current is carried by electrons.
New uses for glass arise continuously, as also do new developments in the glasses themselves. In 1965, a glass was developed for use in the laser, possessing the property of light amplification by stimulated emission of radiation. In the laser device, it is necessary to have certain ions in surroundings that will permit them to be excited by incident light; the ions will be excited by incident light and will emit radiation of longer wavelength through the process known as fluorescence. When certain critical conditions associated with the electronic processes of the ions are accomplished, it is possible to produce in this way very intense and highly homogeneous beams of light. A glass containing about 5% of neodymium has been found to be suitable for some of these applications.
Scintillating glasses and fibers have been developed in the last twenty years as new materials for electromagnetic calorimetry as well as for tracking applications in high energy physics. Thus, a new glass composition, which is based on a cerium-doped lithium-aluminum-magnesium-silicate, was described by Atkinson et al (Nuclear Instr. Methods in Phys. Res. A 254, 500-514, 1987). It is mentioned that such glasses have a maximum absorption at 320 nm, an energy conversion coefficient of 0.55% which is equivalent to 2.1 photons/Kev.sub.1, refractive index of 1.46 and a fast decay time of about 100 nanoseconds. The main drawbacks of these scintillating glass fibres are: long decay time, low light yield in the range of 0.2 to 0.5, which is much below of that obtained today with various plastic materials and short radiation length
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Landa Ksenia
Landa Leonid
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