Lead-Free High-Quality Glass for Assorted Glassware
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NCE FOR GLASS PRODUCTION UDC 666.21:666.172
LEAD-FREE HIGH-QUALITY GLASS FOR ASSORTED GLASSWARE N. M. Bobkova,1 E. E. Trusova,1, 2 and G. B. Zakharevich1 Translated from Steklo i Keramika, No. 2, pp. 3 – 5, February, 2013.
Data on the synthesis of lead-free glass for assorted glassware are presented. Glasses in the system SiO2–SnO2–BaO–CaO–Na2O–K2O with 2 – 10% SnO2 are studied. The effect of introducing BaO and SnO2 together on the crystallizability, density, CLTE, index of refraction and microhardness of the glasses is studied. Compositions with 6 – 8% BaO and SnO2 4 – 6% are recommended for high-quality assorted glasses. The refractive index of the glasses obtained is in the range 1.540 – 1.550, the microhardness is 3700 – 4900 MPa and the CLTE is (95 – 98) ´ 10 – 7 K – 1. Key words: assorted glass, tin oxide, barium oxide, index of refraction, microhardness.
Of great interest here is research on the development of zirconium-containing glass for high-quality assorted glassware. G. Yu. Goikhman, et al. have made a systematic study of the properties of glasses based on the system Na2O–K2O– CaO–ZnO–ZrO2–SiO2 with 1 – 15% ZrO2. Glass with refractive index 1.530 – 1.580 and viscosity close to that of crystal and Bohemian glass have been obtained with the following compositions (%): 62.0 – 67.0 SiO2, 3.0 – 7.0 Zr2O, 0.1 – 0.5 B2O3, 1.0 – 6.0 ZnO, 8.0 – 12 CaO, 6.5 – 8.5 Na2O and 10.0 – 12.5 K2O. However, Zr2O significantly “shortens” glass, even glass with a high content of alkali metals. In addition, ZrO2 does not increase light transmission. Higher glass transparency is largely due to cations with a large ionic radius. This is why such high-transparency glass almost always contains the oxides K2O and BaO (the ionic radii of K and Ba are, respectively, 0.133 and 0.138 nm). In addition, a high index of refraction is very important, preferably at the level of leaded glass, i.e., not lower than 1.535, for high-quality assorted glass. In this case oxides with high partial refractive indices must be introduced into lead-free glass. They include, aside from PbO (the partial index for PbO is ni = 2.15 – 2.35), quite readily available oxides, such as TiO2 (ni = 2.2), BiO (ni = 1.88) and SnO2 (ni = 1.94) [10]. With respect to partial refractive indices titanium dioxide is closest to PbO, but titanium dioxide not only strongly “shortens” glass but it also decreases light transmission because coloring iron-titanium complexes tend to form even with a very low content of iron oxide impurities. For this reason, we became interested in developing compositions for
The problem of increasing the quality of lead-free glass for assorted articles is always topical. Giving assorted glass high transparency and increasing its refractive index makes it possible to expand considerably the range of assorted articles with new forms, demonstrating the high quality of the glass. The most striking examples of such glass are the articles manufactured by the Bohemia Company, which have proven their worth completely in the global market. The compos
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