Borosilicate Glass: Properties and Diverse Applications
Borosilicate Glass
Properties and Applications
Virtually all modern laboratory glassware is borosilicate glass. It is so widely used in this application due to its chemical and thermal resistance and good optical clarity. However, the glass can be reacted with sodium hydride to produce sodium borohydride, a common laboratory reducing agent. Fused quartz is also found in some laboratory equipment when its higher melting point and transmission of UV are required (e.g., for tube furnace liners and UV cuvettes), but the cost and difficulty of working with quartz make it excessive for most laboratory equipment.
Uses of Borosilicate Glass
Electronics
During the mid-twentieth century, borosilicate glass tubing was used to pipe coolants (often distilled water) through high-power vacuum tube-based electronic equipment, such as commercial broadcast transmitters.
Cookware
Glass cookware is another common usage. Borosilicate glass is used for measuring cups, featuring screen-printed markings providing graduated measurements, which are widely used in American kitchens.
Aquarium Heaters
Aquarium heaters are sometimes made of borosilicate glass. Due to its high heat resistance, it can tolerate the significant temperature difference between the water and the nichrome heating element.
Sex Toys
Many current glass sex toys use high-grade borosilicate glass. The toys are generally hand-blown; their beauty combined with ease of cleaning and a long service life make them a popular material.
Flashlights
Many high-quality flashlights use borosilicate glass for the lens. This allows for a higher percentage of light transmittance through the lens compared to plastics and lower-quality glass.
Lighting
Several types of high-intensity discharge (HID) lamps, such as mercury vapor and metal halide lamps, use borosilicate glass as the outer envelope material.
Smoking Accessories
Specialty marijuana and tobacco pipes are made from borosilicate glass. The high heat resistance makes the pipes more durable.
Musical Instruments
Most premanufactured glass guitar slides are also made of borosilicate glass.
Art and Design
New lampworking techniques led to artistic applications such as contemporary glass marbles. The modern studio glass movement has responded to color. “The availability of colors began to increase when companies such as Glass Alchemy introduced the Crayon Colors, which brought a whole new vivacity to the glass industry.” Borosilicate is commonly used in the glassblowing form of lampworking, and the artists create various products ranging from jewelry and kitchenware to sculpture, as well as artistic glass tobacco pipes.
Beverageware
Borosilicate glass is sometimes used for high-quality beverage glassware. Borosilicate glass lends kitchen- and glassware increased durability along with microwave and dishwasher compatibility.
Telescopes
Most astronomical reflecting telescope glass mirror components are made of borosilicate glass because of its low coefficient of expansion with heat. This makes very precise optical surfaces possible that change very little with temperature, and matched glass mirror components that “track” across temperature changes and retain the optical system’s characteristics.
Lenses
The optical glass most often used for making instrument lenses is Schott BK-7 (or the equivalent from other makers), a very finely made borosilicate crown glass. It is also designated as 517642 glass after its 1.517 refractive index and 64.2 Abbe number. Other less costly borosilicate glasses, such as Schott B270 or the equivalent, are used to make “crown glass” eyeglass lenses. Ordinary lower-cost borosilicate glass, like that used to make kitchenware and even reflecting telescope mirrors, cannot be used for high-quality lenses because of the striations and inclusions common to lower grades of this type of glass. The maximum working temperature is 515 Fahrenheit (268.3 °C). While it transitions to a liquid starting at 550 degrees Fahrenheit (just before it turns red-hot), it is not workable until it reaches over 1000 Fahrenheit. That means that, in order to industrially produce this glass, oxygen/fuel torches must be used. Glassblowers borrowed technology and techniques from welders.
Solar Thermal Technology
Borosilicate is also a material of choice for evacuated tube solar thermal technology because of its high strength and heat resistance.
Microelectromechanical Systems (MEMS)
Borosilicate glasses also find application in the semiconductor industry in developing microelectromechanical systems (MEMS), as part of stacks of etched silica wafers bonded to the etched borosilicate glass.
Aerospace
The thermal insulation tiles on the Space Shuttle were coated with borosilicate glass.
Lighting
Lighting manufacturers use borosilicate glass in their refractors.
Organic Light Emitting Diodes (OLEDs)
Organic light-emitting diodes (for display and lighting purposes) also use borosilicate glass (BK7). The thicknesses of the BK7 glass substrates are usually less than 1 millimeter for OLED fabrication. Due to its optical and mechanical characteristics in relation to cost, BK7 is a common substrate in OLEDs. However, depending on the application, soda-lime glass substrates of similar thicknesses are also used in OLED fabrication.
Pharmaceutical Packaging
Additionally, borosilicate tubing is used as the feedstock for producing parenteral drug packaging, such as vials and pre-filled syringes, and is also used for producing ampoules and dental cartridges. The chemical resistance of borosilicate glass minimizes the migration of sodium ions from the glass matrix, thus making it well suited for injectable drug applications. This type of glass is typically referred to as USP/EP JP Type I.
Radioactive Waste Disposal
Borosilicate glasses are used for immobilization and disposal of radioactive wastes. In most countries, high-level radioactive waste has been incorporated into alkali borosilicate or phosphate vitreous waste forms for many years, and vitrification is an established technology. Vitrification is a particularly attractive immobilization route because of the high chemical durability of the vitrified glass product. This characteristic has been used by industry for centuries. The chemical resistance of glass can allow it to remain in a corrosive environment for many thousands and even millions of years.