Crystal Glass Development Direction

The pollution of lead in crystal glass has always been noticed. In 1976, the World Health Organization (WHO) noticed the amount of lead dissolved in glass and ceramics, and the U.S. Food and Drug Administration (FDA) regulated the amount of lead and cadmium dissolved in ceramic glaze. The International Organization for Standardization (ISO) specifies in ISO 7086/1 and ISO 7086/2 that 4% (v/v) acetic acid solution should be used to etch for 1 hour at 22°C. For hollow glass products with a volume less than 600 mL, the amount of Pb dissolved The allowable limit is 5 mg/L, and when the volume is greater than 600 mL, the allowable limit for Pb dissolution is 2.5 mg/L. In 1991, the European and American International Crystal Federation (International Crystal Federation) made stricter regulations than ISO. Under the same conditions, the allowable limit for the dissolution of Pb is 1.5 mg/L [4].

The National Safety Council of Canada (NSC National Safety Council) made recommendations on the safety of lead crystals, stating that the intake of lead per person per day should not be greater than 5μg/d. When lead crystal glass is filled with wine, the amount of lead dissolved can reach 1~500μg /L. It is recommended not to store acidic liquids in lead crystal bottles. Babies and children should not use lead crystal bottles and cups. Pregnant women should not drink the liquid in lead crystal glasses.

EU Parliament and Council Directive 2002/95/ec stipulates that starting from July 1, 2007, circuits and electronic equipment containing Pb, Hg, Cd, and Cr6+ hazardous substances are prohibited to be level 10-9, but lead crystal glass is temporarily shelved .

From the development trend, lead-free crystal glass is imperative. In the 1950s, Eastern European countries such as the Soviet Union and the Czech Republic had been conducting research on lead-free crystals. From the 1980s to the 1990s, some Western countries also issued patents for lead-free crystals. The earliest lead-free crystals studied are barium crystal and zinc crystal. For example, the barium crystal developed by the former Soviet Union contains 15% to 30% BaO, and the refractive index nD is 1.53 to 1.535. When the content of BaO is high, the corrosion of refractory materials is serious, and it is easy to appear twice. Bubbles, and transparency, whiteness and refraction are inferior to lead crystals, and barium crystals have higher hardness than lead crystals, and their engraving, grinding, and polishing performances are not as good as lead crystals, so ZnO is added to the barium crystals to replace part of BaO, such as SiO2 Lithopone crystal of 60%, BaO 10%, ZnO 10%, K2O 10%, Na2O 10% has a refractive index of 1.531, which is lower than that of lead crystal. In silicate glass, the refractive index of TiO2 is very high (additivity index 2.2~2.4) and ZrO2 is also relatively high. Soviet scholars have developed titanium crystal and zirconium crystal. Titanium has a high refractive index, but TiO2 will enhance iron. Coloring ability is not good for the transparency and whiteness of crystal glass. High-purity nano-titanium oxide is expensive.

The zirconium crystal developed by the former Soviet Union contains 64% SiO2, 9.5% CaO, 4.7% ZnO, 6.2% ZrO2, 3.0% K2O, 12.6% Na2O, and uses pure ZrO2 or zircon (ZrSiO4) as raw materials, with a refractive index of 1.542~1.547 and a density It is 2.59~2.75g/cm3, which is also equivalent to medium lead crystal. The transparency and whiteness of glass are still not as good as lead crystal, because zirconium ore contains more impurities and is difficult to purify, and ZrO2 is difficult to melt, which limits the production of zirconium crystal.

In order to improve the density and refractive index, while taking into account the process performance of melting and forming, most foreign lead-free crystal patents use a variety of oxides with high refractive index, such as SrO, ZnO, BaO, TiO2, ZrO2, etc. There are similar research reports in China [5], and its composition range (mass fraction) is SiO2 66%~75%, B2O3 1%, Al2O3 0%~0.5%, CaO 1%, BaO 7%~15%, ZnO 0.5% `1%, SrO 0.5%~1%, TiO2 0.5%~1%, Na2O 8%~10%, K2O 3%~7%, density 2.55~2.57g/cm3, refractive index 1.501, although the refractive index is not high, The acid resistance is very good, and the dissolution amount when placed in 4% HAC for 24 hours is <2×10-9 (ie <2ppb). Hybrid crystal is the research direction of lead-free crystal. How to optimize the type and amount of high refractive index oxide and the ratio of each composition to achieve the highest density, refractive index and dispersion, and at the same time make full use of the blockage between the two valent ions The effect and the accumulation effect of high-valent ions improve the acid resistance and weathering resistance of the crystal. In addition, the properties of glass melting, forming, hot working and cold working (engraving, grinding, polishing, etc.) should be taken into consideration, and should be as close as possible to lead crystal.

Scholars at home and abroad have also carried out research on glass surface coating. On the one hand, high silicon film is coated on the surface of lead crystal. After sintering at 500℃ and 1h, SiO2 film is formed, which can improve the acid resistance of lead crystal and reduce the dissolution of Pb [6]; on the other hand, use sol-gel method to coat SiO2-PbO-K2O on the surface of ordinary soda lime glass. The film can play the effect of lead crystal. For example, using ethyl orthosilicate, lead acetate, potassium acetate as precursors, and dimethyl sulfoxide as solvent, the sol prepared therefrom can be coated on the surface of the glass by the spin-off method. After heat treatment at 400°C, a glassy film is obtained with a refractive index of 1.565.

In the future development direction of crystal glass, in addition to the development of lead-free crystals, on the one hand, it is necessary to maintain the tradition, and traditional craftsmanship may become a historical heritage; on the other hand, it is necessary to adopt new technologies and new processes. It develops along this path, such as the Baccarat Group, which not only manufactures traditional hand-carved and ground glass, but also mass-produces cut and ground crystal glass products with 3D laser automatic cutting and engraving machines. The same is true for Slovakia, which not only produces lead crystal decorations and handicrafts, but also produces high-tech products such as binoculars, high-refractive microspheres, and optical fibers.

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