Soda–lime glass, also calledsoda–lime–silica glass, is the transparentglass used for windowpanes and glass containers (bottles and jars) for beverages, food, and some commodity items. It is the most prevalent type of glass made. Some glass bakeware is made of soda-lime glass, as opposed to the more common and heat-tolerantborosilicate glass.[1] Soda–lime glass accounts for about 90% of manufactured glass.[2][3]
The manufacturing process for soda–lime glass consists in melting the raw materials, which are thesilica,soda (Na2O),hydrated lime (Ca(OH)2),dolomite (CaMg(CO3)2), which provides the magnesium oxide), and aluminium oxide; along with small quantities offining agents (e.g.,sodium sulfate (Na2SO4),sodium chloride (NaCl), etc.) in aglass furnace at temperatures locally up to 1675 °C.[4] The soda and the lime serve as aflux lowering the melting temperature of silica (1580 °C) as well as causing the mixture to soften as it heats, starting at as low as 700 °C. The temperature is only limited by the quality of the furnace structure material and by the glass composition. Relatively inexpensive minerals such astrona,sand, andfeldspar are usually used instead of pure chemicals. Green and brown bottles are obtained from raw materials containingiron oxide. The mix of raw materials is termedbatch.
Soda–lime glass is divided technically into glass used for windows, calledflat glass, and glass for containers, calledcontainer 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 highermagnesium oxide andsodium oxide content than container glass, and a lower silica,calcium oxide, andaluminium oxide content.[5] From the lower content of highly water-soluble ions (sodium and magnesium) in container glass comes its slightly higherchemical durability against water, which is required especially for storage of beverages and food.
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 forglass recycling.[6][7] It is used in preference to chemically-puresilica (SiO2), otherwise known asfused quartz. Whereas pure silica has excellent resistance tothermal 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.[8] Other substances are therefore added to simplify processing. One is the "soda", orsodium oxide (Na2O), which is added in the form of sodium carbonate or related precursors. Soda lowers the glass-transition temperature. However, the soda makes the glasswater-soluble, which is usually undesirable. To provide for better chemical durability, the "lime" is also added. This iscalcium oxide (CaO), generally obtained fromlimestone. In addition,magnesium oxide (MgO) and alumina, which isaluminium oxide (Al2O3), contribute to the durability. The resulting glass contains about 70 to 74% silica by weight.
Soda–lime glass undergoes a steady increase inviscosity with increase temperature, permitting operations of steadily increasing precision. The glass is readily formable into objects when it has a viscosity of 104poises, 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 anArrhenius 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.[5] Those values marked initalic font have been interpolated from similar glass compositions (seecalculation of glass properties) due to the lack of experimental data.
| Properties | Container glass | Flat glass | ||||||||||||||||||||||||||||||||||||||||
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| Chemical composition, wt% |
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| Viscosity log(η, dPa·s or poise) =A +B / (T in °C −T0) |
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| 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 |