Borosilicate Glass is a specialized form of glass that uses boric acid as a component in its fabrication. The result of the addition of the element boron is a type of glass that is very resistant to thermal shock and exhibits a much lower coefficient of thermal expansion than that of common silicate glass. In this article, a review of borosilicate glass will be presented, including its development, properties, and uses.
Development of Borosilicate Glass
Back in 1882, a German chemist named Otto Schott was interested in experimenting with ways to create glass that had the ability to withstand sudden changes in temperature or exposure to uneven temperatures without shattering. In that year, he made the discovery that ushered in the creation of the Schott discovered that the addition of the element Boron to the glass fabrication process resulted in a heat-resistant form of glass.
Later work by chemists W.C. Taylor and Eugene Sullivan at Corning Glass refined the efforts of Otto Schott and expanded the temperature resistant properties of borosilicate glass. As a result of these innovations, customized glass fabrication grew, where there is now over a million different formulations of glass that can be customized for specific product needs by enhancing the desired physical and mechanical properties of glass.
Perhaps the most well-known application for borosilicate glass grew from further research at Corning Glass. After joining the company in 1914, physicist Jesse Littleton was given the task of testing and evaluating the physical properties of the newly created glass formulation. After his wife’s ceramic casserole dish accidentally broke, she suggested that perhaps this newly developed heat resistant glass might prove to be a useful product for baking. After she tested the notion by baking a cake in a sample glass container that Littleton had brought home, a new use for was born – glass cookware. Corning Glass introduced a line of products known as Pyrex®[1], which was for many years of its manufacturing run produced using borosilicate glass.
Properties of Borosilicate Glass
Borosilicate glass is generally chemically resistant, but perhaps its most remarkable physical property is its low coefficient of thermal expansion, which explains why the glass can resist shattering under sudden rapid changes in temperature. Glass generally is a poor conductor of heat, so when you take hot glass and immerse it in cold water, the exterior of the glass cools rapidly while the interior does not. The stresses caused by the temperature differential cause the glass to shatter.
With the addition of boric acid (H3BO3) to the formulation results in a glass that has a low coefficient of thermal expansion, which means that when the glass is heated or cooled, it does not expand or contract very much. This dimensional stability is what enables borosilicate glass to be capable of withstanding rapid and extreme temperature changes without cracking.
The chemical composition of borosilicate glass typically consists of around 81% silicon dioxide (SiO2) and 13% boron trioxide (B2O3) with lesser concentrations of sodium oxide and aluminum oxide. (Note that the concentrations of boric oxide can vary, 5-13% is typical). The element Boron is what provides the glass with its dimensional stability so that the material doesn’t shrink or grow as the temperature to which it is exposed changes.
Applications of Borosilicate Glass
The initial problem that was attempting to be solved at the time that Otto Schott began experimenting with glass formulations was to create a glass that could stand up against extreme temperature exposure. For example, the glass that was used in lanterns at that time would end up shattering or cracking in rainy conditions because the cold rain on the exterior surface of the glass caused a large temperature gradient when compared with the temperature of the hot interior face.
Once borosilicate became available, its applications became immediately apparent. Some of the common uses for borosilicate glass include:
Laboratory glassware
The high dimensional stability and ability to tolerate exposure to different temperatures at the same time make borosilicate glass a natural material choice from which to create laboratory also called labware. Petri dishes, microscope slides, beakers, flasks, test tubes, funnels, and measuring instruments such as graduated cylinders are all common examples. Besides the favorable thermal properties, borosilicate glass is very resistant and non-reactive to most chemicals.
