Lead-free glasses

Details Lead-free glasses Lead-free glasses

1999-07-16

2001-02-06

Group, Karl (Department: 1755)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

C501S026000, C501S065000, C501S067000, C428S426000, C428S427000, C428S428000

Reexamination Certificate

active

06184166

ABSTRACT:

FIELD OF THE INVENTION
Lead-free glasses having properties that render them useful for production of crystal glassware and laminated ware.
BACKGROUND OF THE INVENTION
Silicate glasses, having a relatively high content of lead oxide in their compositions, have unique properties that particularly adapt them to use in production of crystal glassware. The properties of interest include a low liquidus temperature and a long viscosity range. These properties avoid the occurrence of devitrification during forming processes.
Environmental and health concerns have led to a desire to eliminate, insofar as possible, use of toxic oxides, in particular lead oxide, in glass compositions. U.S. Pat. No. 5,270,269 (Hares et al.) describes one approach to meeting this desirable end in the production of crystal glassware. The present invention provides a different approach.
The production of crystal glassware is usually a hand crafting operation. This involves several cycles of working and reheating a glass shape. It is, of course, desirable to complete as much of the shaping operation as possible during each cycle. This requires a low, liquidus temperature and a long, viscosity curve. The latter property translates into a long working range of temperatures without devitrification, that is, without any crystal formation in or on the glass.
Other properties of interest in crystal glassware include high refractive index, dispersion, and density values; also, good scratch resistance, and high chemical durability, that is, resistance to chemical attack and weathering. Another property of particular interest in thin-walled artware is the resonating sound that occurs when the rim of an article is lightly struck with another body such as a table utensil. This resonating sound is commonly known as the sonority, or ring, of a thin-walled article, such as a vase or goblet.
It is a purpose of the present invention to provide a family of glass compositions possessing properties useful both for crystal glassware and for laminated ware.
It is another purpose to provide a family of glass compositions free of toxic materials, in particular, free from lead compounds.
It is a further purpose to provide glasses having a CTE of 70-110×10
−7
/° C., a density of at least 2.70 g/cm
3
, a long viscosity curve, and a low liquidus value, such glasses being especially suited to production of crystal glassware.
It is a still further purpose to provide a family of glasses, as an alternative to the family disclosed in U.S. Pat. No. 5,270,269, for the production of crystal glassware.
SUMMARY OF THE INVENTION
The invention resides in part in a glass that is essentially lead-free, that exhibits a density of at least 2.70 g/cm
3
, a liquidus below 1000° C., a long viscosity curve, a CTE of 70-110×10
−7
/° C., good scratch resistance, and chemical durability, and that has a composition, expressed in terms of weight percent on an oxide basis, consisting essentially of:
SiO
2
52-66
ZnO
15-30
Al
2
O
3
0-3
BaO
0-7
Li
2
O
0-4
MgO + CaO + SrO
0-5
Na
2
O
 3-16
ZrO
2
0-4
K
2
O
 0-12
The invention further resides in an article of crystal glassware molded from the above glass; also, in an article in which surfaces of two bodies are joined by laminating.
DESCRIPTION OF THE INVENTION
The glass family of the present invention was developed for use in production of crystal glassware. It represents an alternative to the glass family disclosed in the '269 patent for that purpose. While the present glass family is well-suited to that purpose, it has also been found to have properties adapted to certain glass laminating processes.
The glass composition of the earlier Hares et al. patent, is characterized by substantial contents of BaO and SrO with lesser amounts of ZnO. The present glass family requires neither BaO or SrO. At most, the presence of these oxides is permitted in limited amounts. Rather, the present glasses contain a relatively large amount of ZnO in contrast to the earlier glasses.
The present glasses are characterized by a low, liquidus temperature and a long, viscosity curve. The optimum viscosity for working an art glass is accepted as about 10
4
Pa.s (10
5
poises). This may also be stated as Log Viscosity in Pa.s equals 4. The present glasses will have this viscosity at temperatures in the range of 850° C. to 900° C. A long viscosity curve is measured in terms of the temperature range over which the glass viscosity varies by no more than a factor of 10 from the optimum value of 10
4
Pa.s, e.g., a temperature range of 750° to 975° C.


REFERENCES:
patent: 2913345 (1959-11-01), Duncun
patent: 3148073 (1964-09-01), Englert et al.
patent: 3754816 (1973-08-01), Ritze
patent: 4106946 (1978-08-01), Ritze
patent: 4297141 (1981-10-01), Tokunaga et al.
patent: 4970178 (1990-11-01), Klimas et al.
patent: 5270269 (1993-12-01), Hares et al.

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