Tips from the Glass Room: Are All Glass Bottles the Same? – DWK Life Sciences
There are many different types of glass. They differ in terms of their chemical composition, the method used to produce them or their processing behavior. Generally, they are categorized according to their chemical composition. The three types of glass (soda-lime glass, lead glass and borosilicate glass) make up around 95 percent of the cullet glass used in the production process. The remaining 5 percent of glass is special-purpose glass. Wheaton uses both soda-lime glass and borosilicate glass for our products.
Soda-lime glass is the most common commercial glass, and also the least expensive. Soda-lime glass is not very resistant to high temperatures, sudden thermal changes or corrosive chemicals. Soda-lime glass is the glass produced in by far the largest quantities of all mass produced glass types. As the name indicates, the main constituents,in addition to sand, are soda and lime. A typical soda-lime glass contains 71 to 75 percent silicon dioxide (SiO2), 12 to 16 percent sodium oxide (Na2O), 10 to 15 percent calcium oxide (CaO) and small quantities of other substances such as dyes.
Borosilicate glass is a premium glass when compared to soda-lime glass. Borosilicate is glass made from sand and boron compounds. 70 to 80 percent by weight of borosilicate glass is sand. Seven to 13 percent is boron trioxide, four to eight percent is sodium and potassium oxide and two to seven percent aluminum oxide.
Borosilicate glass has a low thermal expansion coefficient and high chemical resistance, making it ideal for use in laboratories and the medical and pharmaceutical industries. The advantage is that it has a much lower coefficient of expansion (COE) which means it doesn’t change size much when heated, which means it doesn’t crack when heated. The disadvantage is that while it softens when heated in a torch, it doesn’t flow much and needs to be heated hotter than soda-lime glass.
The smaller the linear expansion coefficient, the more resistant the glass is to temperature variations. The larger expansion coefficients, the temperature difference during heating causes stresses in the glass and, thus, possible breakage. Soda-lime glass has a higher coefficient of expansion than borosilicate glass.
Borosilicate glass is used for scientific glass apparatus, bottles and ampules. It is also used for cookware in the home. When you see someone working with glass in a mall or arts showcase with a torch with a strong blue flame, they are working with borosilicate glass. It can be heated and cooled without cracking easier than for soda-lime glass. We invite you to post your questions regarding glass types.