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. Some glass bakeware is made of soda-lime glass, as opposed to the more common borosilicate glass.[1] Soda–lime glass accounts for about 90% of manufactured glass.[2][3]

Reusable soda–lime glass milk bottles
Old window made from soda-lime flat glass, Jena, Germany: The distorted reflections of a tree indicate that the flat glass was possibly not made by the float glass process.

Soda–lime glass is relatively inexpensive, chemically stable, reasonably hard, and extremely workable. Because it can be resoftened and remelted numerous times, it is ideal for glass recycling.[4] It is used in preference to chemically-pure silica, which is silicon dioxide (SiO2), otherwise known as fused quartz. Whereas pure silica has excellent resistance to thermal shock, being able to survive immersion in water while red hot, its high melting temperature (1723 °C) and viscosity make it difficult to work with.[5] Other substances are therefore added to simplify processing. One is the "soda", or sodium carbonate (Na2CO3), which lowers the glass-transition temperature. However, the soda makes the glass water-soluble, which is usually undesirable. To provide for better chemical durability, the "lime" is also added. This is calcium oxide (CaO), generally obtained from limestone. In addition, magnesium oxide (MgO) and alumina, which is aluminium oxide (Al2O3), contribute to the durability. The resulting glass contains about 70 to 74% silica by weight.

The manufacturing process for soda–lime glass consists in melting the raw materials, which are the silica, soda, lime (in the form of (Ca(OH)2), dolomite (CaMg(CO3)2, which provides the magnesium oxide), and aluminium oxide; along with small quantities of fining agents (e.g., sodium sulfate (Na2SO4), sodium chloride (NaCl), etc.) in a glass furnace at temperatures locally up to 1675 °C.[6] The temperature is only limited by the quality of the furnace structure material and by the glass composition. Relatively inexpensive minerals such as trona, sand, and feldspar are usually used instead of pure chemicals. Green and brown bottles are obtained from raw materials containing iron oxide. The mix of raw materials is termed batch.

Soda–lime glass is divided technically into glass used for windows, called flat glass, and glass for containers, called container glass. The two types differ in the application, production method (float process for windows, blowing and pressing for containers), and chemical composition. Flat glass has a higher magnesium oxide and sodium oxide content than container glass, and a lower silica, calcium oxide, and aluminium oxide content.[7] From the lower content of highly water-soluble ions (sodium and magnesium) in container glass comes its slightly higher chemical durability against water, which is required especially for storage of beverages and food.

Typical compositions and properties
Typical transmission spectrum of a 2 mm glass[curve is not representing the data of the source, the lambda scale is wrong][8]

Soda–lime glass undergoes a steady increase in viscosity with decreasing temperature, permitting operations of steadily increasing precision. The glass is readily formable into objects when it has a viscosity of 104 poises, typically reached at a temperature around 900 °C. The glass is softened and undergoes steady deformation when viscosity is less than 108 poises, near 700 °C. Though apparently hardened, soda–lime glass can nonetheless be annealed to remove internal stresses with about 15 minutes at 1014 poises, near 500 °C. The relationship between viscosity and temperature is largely logarithmic, with an Arrhenius equation strongly dependent on the composition of the glass, but the activation energy increases at higher temperatures.[9]

The following table lists some physical properties of soda–lime glasses. Unless otherwise stated, the glass compositions and many experimentally determined properties are taken from one large study.[7] 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 Container glass Flat glass
Chemical
composition,
wt%
74SiO20.3K2O
13Na2O0.2MgO
10.5CaO0.04Fe2O3
1.3Al2O30.01TiO2
0.2SO3
73SiO20.03K2O
14Na2O4MgO
9CaO0.1Fe2O3
0.15Al2O30.02TiO2
 
Viscosity
log(η, dPa·s or poise)
= A + B / (T in °C − T0)
550 °C (1,022 °F)1,450 °C (2,640 °F)
A
B3922
T0291
550 °C (1,022 °F)1,450 °C (2,640 °F)
A−2.585
B4215
T0263
Glass transition
temperature, Tg		 573 °C (1,063 °F) 564 °C (1,047 °F)
Coefficient of
thermal expansion,
ppm/K, ~100–300 °C (212–572 °F)		 9 9.5
Density
at 20 °C (68 °F), g/cm3		 2.52 2.53
Refractive index
nD at 20 °C (68 °F)		 1.518 1.520
Dispersion at 20 °C (68 °F),
104 × (nF − nC)		 86.7 87.7
Young's modulus
at 20 °C (68 °F), GPa		 72 74
Shear modulus
at 20 °C (68 °F), GPa		 29.8 29.8
Liquidus
temperature		 1,040 °C (1,900 °F) 1,000 °C (1,830 °F)
Heat
capacity at 20 °C (68 °F),
J/(mol·K)		 49 48
Surface tension,
at ~1,300 °C (2,370 °F), mJ/m2		 315
Chemical durability,
Hydrolytic class,
after ISO 719[10]		 3 3...4
Critical stress
intensity factor,[11]
(KIC), MPa.m0.5		 ? 0.75

See also
  • Glass batch calculation

References
  1. Estes, Adam Clark (March 16, 2019). "The Pyrex Glass Controversy That Just Won't Die". Gizmodo. Retrieved 2019-03-22.
  2. "Borosilicate Glass vs. Soda Lime Glass? - Rayotek News". rayotek.com. Archived from the original on 23 April 2017. Retrieved 23 April 2017.
  3. Robertson, Gordon L. (22 September 2005). Food Packaging: Principles and Practice (Second ed.). CRC Press. ISBN 978-0-8493-3775-8. Archived from the original on 2 December 2017.
  4. "Calcium Carbonate - Glass Manufacturing". congcal.com. congcal. 28 June 2012. Retrieved 5 August 2013.
  5. "Glass – Chemistry Encyclopedia". Archived from the original on 2 April 2015. Retrieved 1 April 2015.
  6. B. H. W. S. de Jong, "Glass"; in "Ullmann's Encyclopedia of Industrial Chemistry"; 5th edition, vol. A12, VCH Publishers, Weinheim, Germany, 1989, ISBN 978-3-527-20112-9, pp. 365–432.
  7. "High temperature glass melt property database for process modeling"; Eds.: Thomas P. Seward III and Terese Vascott; The American Ceramic Society, Westerville, Ohio, 2005, ISBN 1-57498-225-7
  8. "Sodalime Optical Glass – Internal transmittance (2 mm)". vpglass.com. Archived from the original on 2011-09-09. Retrieved 2013-08-24.
  9. Thomas H. Sanders Jr. "Viscosity Behavior of Oxide Glasses". Coursera.
  10. "ISO 719:1985 - Glass -- Hydrolytic resistance of glass grains at 98 degrees C -- Method of test and classification". iso.org.
  11. Wiederhorn, S.M. (1969). "Fracture stress energy of glass". Journal of the American Ceramic Society. 52 (2): 99–105. doi:10.1111/j.1151-2916.1969.tb13350.x.
  12. Gondret, P.; M. Lance; L. Petit (2002). "Bouncing Motion of Spherical Particles in Fluids". Physics of Fluids. 14 (2): 643–652. doi:10.1063/1.1427920.
  13. Janssen, L. P. B. M., Warmoeskerken, M. M. C. G., 2006. Transport phenomena data companion. Delft: VVSD.
  14. "Soda-Lime (Float) Glass Material Properties :: MakeItFrom.com". makeitfrom.com.
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