Soda–lime glass, also called soda–lime–silica glass, is the transparent glass, used for windowpanes and glass containers (bottles and jars) for beverages, food, and some commodity items. It is the most prevelant type of glass made. 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]
The manufacturing process for soda–lime glass consists in melting the raw materials, which are the silica, soda (Na2O), hydrated lime (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. [4] The soda and the lime serve as a flux 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 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. [5] 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.
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. [6] [7] It is used in preference to chemically-pure silica (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. [8] Other substances are therefore added to simplify processing. One is the "soda", or sodium 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 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.
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. [5] 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% |
|
| ||||||||||||||||||||||||||||||||||||||||
| Viscosity log(η, dPa·s or poise) = A + B / (T in °C − T0) |
|
| ||||||||||||||||||||||||||||||||||||||||
| 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 |
Glass is an amorphous (non-crystalline) solid. Because it is often transparent and chemically inert, glass has found widespread practical, technological, and decorative use in window panes, tableware, and optics. Some common objects made of glass are named after the material, e.g. "glass", "glasses", "magnifying glass".
Aluminium oxide (or aluminium(III) oxide) is a chemical compound of aluminium and oxygen with the chemical formula Al2O3. It is the most commonly occurring of several aluminium oxides, and specifically identified as aluminium oxide. It is commonly called alumina and may also be called aloxide, aloxite, or alundum in various forms and applications. It occurs naturally in its crystalline polymorphic phase α-Al2O3 as the mineral corundum, varieties of which form the precious gemstones ruby and sapphire. Al2O3 is used to produce aluminium metal, as an abrasive owing to its hardness, and as a refractory material owing to its high melting point.
Sodium carbonate is the inorganic compound with the formula Na2CO3 and its various hydrates. All forms are white, odourless, water-soluble salts that yield alkaline solutions in water. Historically, it was extracted from the ashes of plants grown in sodium-rich soils, and because the ashes of these sodium-rich plants were noticeably different from ashes of wood, sodium carbonate became known as "soda ash". It is produced in large quantities from sodium chloride and limestone by the Solvay process, as well as by carbonating sodium hydroxide which is made using the chloralkali process.
Glass fiber is a material consisting of numerous extremely fine fibers of glass.
Sodium silicate is a generic name for chemical compounds with the formula Na
2xSi
yO
2y+x or (Na
2O)
x·(SiO
2)
y, such as sodium metasilicate, sodium orthosilicate, and sodium pyrosilicate. The anions are often polymeric. These compounds are generally colorless transparent solids or white powders, and soluble in water in various amounts.
The Bayer process is the principal industrial means of refining bauxite to produce alumina (aluminium oxide) and was developed by Carl Josef Bayer. Bauxite, the most important ore of aluminium, contains only 30–60% aluminium oxide (Al2O3), the rest being a mixture of silica, various iron oxides, and titanium dioxide. The aluminium oxide must be further purified before it can be refined into aluminium.
Fernico describes a family of metal alloys made primarily of iron, nickel and cobalt. The family includes Kovar, FerNiCo I, FerNiCo II, and Dumet. The name is made up of the chemical symbols of its constituent three elements. "Dumet" is a portmanteau of "dual" and "metal," because it is a heterogeneous alloy, usually fabricated in the form of a wire with an alloy core and a copper cladding. These alloys possess the properties of electrical conductivity, minimal oxidation and formation of porous surfaces at working temperatures of glass and thermal coefficients of expansion which match glass closely. These requirements allow the alloys to be used in glass seals, such that the seal does not crack, fracture or leak with changes in temperature.
In materials science, a refractory is a material that is resistant to decomposition by heat or chemical attack and that retains its strength and rigidity at high temperatures. They are inorganic, non-metallic compounds that may be porous or non-porous, and their crystallinity varies widely: they may be crystalline, polycrystalline, amorphous, or composite. They are typically composed of oxides, carbides or nitrides of the following elements: silicon, aluminium, magnesium, calcium, boron, chromium and zirconium. Many refractories are ceramics, but some such as graphite are not, and some ceramics such as clay pottery are not considered refractory. Refractories are distinguished from the refractory metals, which are elemental metals and their alloys that have high melting temperatures.
Borosilicate glass is a type of glass with silica and boron trioxide as the main glass-forming constituents. Borosilicate glasses are known for having very low coefficients of thermal expansion, making them more resistant to thermal shock than any other common glass. Such glass is subjected to less thermal stress and can withstand temperature differentials without fracturing of about 165 °C (300 °F). It is commonly used for the construction of reagent bottles and flasks, as well as lighting, electronics, and cookware. For many other applications, soda-lime glass is more common.
Sodium oxide is a chemical compound with the formula Na2O. It is used in ceramics and glasses. It is a white solid but the compound is rarely encountered. Instead "sodium oxide" is used to describe components of various materials such as glasses and fertilizers which contain oxides that include sodium and other elements. Sodium oxide is a component.
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