Definitions

lime glass

Soda-lime glass

Soda-lime glass, also called soda-lime-silica glass, is the most prevalent type of glass, used for windowpanes, and glass containers (bottles and jars) for beverages, food, and some commodity items. Also Pyrex brand kitchen glassware manufactured since 1998 (when the brand was spun off under World Kitchen) is made of soda-lime glass (previously, it was made of better quality, thermal shock resistant borosilicate glass).

Soda-lime glass is prepared by melting the raw materials, such as soda, lime, silica, alumina, and small quantities of fining agents (e.g., sodium sulfate, sodium chloride) in a glass furnace at temperatures locally up to 1675°C. The temperature is only limited by the quality of the furnace superstructure material and by the glass composition. Green and brown bottles are obtained from raw materials containing iron oxide. For lowering the price of the raw materials, pure chemicals are not used, but relatively inexpensive minerals such as trona, sand, and feldspar. The mix of raw materials is termed batch.

Soda-lime glass is divided technically into glass used for windows, called float glass or flat glass, and glass for containers, called container glass. Both types differ in the application, production method (float process for windows, blowing and pressing for containers), and chemical composition (see table below). Float glass has a higher magnesium oxide and sodium oxide content as compared to container glass, and a lower silica, calcium oxide, and aluminium oxide content. From this follows a slightly higher quality of container glass concerning the chemical durability against water (see table), which is required especially for storage of beverages and food.

Typical compositions and properties

The following table lists some physical properties soda-lime glasses. Unless otherwise stated, the glass compositions and many experimentally determined properties are taken from one large study. Those values marked in italic font have been interpolated from similar glass compositions (see calculation of glass properties) due to the lack of experimental data.

Properties Soda-lime glass
for containers
Soda-lime glass
for windows
Chemical
composition,
wt%
74 SiO2, 13 Na2O,
10.5 CaO, 1.3 Al2O3,
0.3 K2O, 0.2 SO3,
0.2 MgO, 0.01 TiO2,
0.04 Fe2O3
73 SiO2, 14 Na2O,
9 CaO, 0.15 Al2O3,
0.03 K2O, 4 MgO,
0.02 TiO2, 0.1 Fe2O3
Viscosity
log(η, Pa·s) = A +
B / (T in °C - To)
550-1450°C:
A = -2.309
B = 3922
To = 291
550-1450°C:
A = -2.585
B = 4215
To = 263
Glass transition
temperature, Tg, °C
573 564
Coefficient of
thermal expansion,
ppm/K, ~100-300°C
9 9.5
Density
at 20°C, g/cm3
2.52 2.53
Refractive index
nD at 20°C
1.518 1.520
Dispersion at 20°C,
104×(nF-nC)
86.7 87.7
Young's modulus
at 20°C, GPa
72 74
Shear modulus
at 20°C, GPa
29.8 29.8
Liquidus
temperature, °C
1040 1000
Heat
capacity at 20°C,
J/(mol·K)
49 48
Surface tension,
at ~1300°C, mJ/m2
315
Chemical durability,
Hydrolytic class,
after ISO 719
3 3...4

Coefficient of Restitution (glass sphere vs. glass wall): 0.97 ± 0.01

Thermal Conductivity: 0.9-1.3 W/m.K

Hardness (Mohs Scale): 6–7

Knoop Hardness: 585 kg/mm2 + 20

See also

References

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