He Pyrex glass is a special borosilicate glass whose brand (Pyrex) made its appearance in the city of New York in 1915, manufactured by Corning Glass. It emerged as a material for modern food packaging, also used to store and bake food in the same type of container.
The origin of the word Pyrex has generated certain discrepancies, but it is accepted that it is derived from the most sold article in the initial moments of its commercialization: a plate in which a cake was baked. With this glass many laboratory materials and equipment are manufactured in many forms, such as sheets or plates, tubes, cells and rods.
These instruments have different sizes, thicknesses and have different applications and uses, which require different degrees of precision, chemical, mechanical and thermal resistance. Likewise, with glass Pirex volumetric glass materials (pipettes, burettes, graduated cylinders, etc.) are made.
Its molecules do not react chemically with the liquids it contains, either acids or bases; therefore, it does not alter the pH of the packaged substances either. In the beginning they were considered heavy and expensive as kitchen utensils.
Index
- 1 Chemical composition
- 2 Characteristics and properties of pyrex glass
- 2.1 Structure of borosilicates
- 3 Advantage
- 4 Disadvantages
- 5 Pyrex glass in the kitchen
- 6 References
Chemical composition
According to the National Institute of Standards and Technology of the United States, all manufacturers of equipment and instruments Pyrex -such as Corning, the Arc Pyrex International and Pyrex laboratories- have in common that they manufacture it starting from a borosilicate glass that has the following elements Chemicals:
Several manufacturers or suppliers of Pyrex glass have standardized the composition as specified below, also in units of percentage concentration p / p:
Characteristics and properties of pyrex glass
The following table summarizes the properties or general, mechanical, thermal and electrical characteristics attributed to Pyrex glass or borosilicate glass:
The chemical composition of Pyrex, its properties and the quality of the processes in its manufacture allow to summarize then the following properties:
- Chemically, borosilicate glass is resistant to contact with water, the vast majority of acids, halogens, organic solvents and saline solutions. For this reason, glass flasks and balloons are manufactured with this material.
- It has high hydrolytic resistance, which is why it supports high temperatures and the repeated thermal stresses to which it is subjected. For example, it is resistant to consecutive sterilization processes that can be subjected to the use of moist heat (autoclave).
- Because Pyrex has a low coefficient of thermal expansion, it can be used at 500 ° C, but it is recommended that it be for a short time.
- Its material is homogeneous, pure, and its content of bubbles and inclusions is very low.
- It is very resistant to shock.
- It has a good refractive index.
- With regard to optical properties, the pyrex's ability to transmit light in the visible range of the spectrum, near ultraviolet light, is maximized in the area of chemical photometry.
Structure of borosilicates
The upper image illustrates an ordered structure of silicates, which contrasts with the true amorphous arrangements of pyrex glass. Viewed from above, it gives the impression that it consists of yellow triangles, but they are actually tetrahedrons, with a metallic silicon atom in the center and oxygen atoms at their vertices.
Despite the crystalline appearance, molecularly the borosilicate mesh presents disordered patterns; that is, it is an amorphous solid. Thus, silicate tetrahedra bind to boric oxides (B 2 OR 3 ). Boron here is found as a trigonal plane. In other words, they are tetrahedra linked to flat triangles of boron.
However, this disorder - or amorphous structure - allows it to accommodate cations, which reinforce molecular interactions.
Advantage
- It is very useful for the manufacture of equipment and glass materials used in chemistry and scientific research laboratories, such as centrifuge tubes, volumetric glassware, pipettes and disks for borosilicate filters, all of them standardized according to quality standards International ISO.
- Conical pyrex, spherical, flat and screw glass joints are also produced.
- Glass substrates are made for dielectric coating, and to manufacture lenses and very thin precision optical material.
- It is used in the aerospace industry, specifically for the manufacture of optical reflection equipment due to its low thermal expansion. Likewise, mirrors for telescopes have been manufactured with the Pyrex.
- Allows the manufacture of very thick glass containers
- Used in the preparation of surfaces used as a substrate with sensor function.
- It is used in the manufacture of instruments and protective covers of high temperatures.
- It serves as material for glass artefacts that absorb neutrons.
Disadvantages
So far there are very few relevant aspects that can be identified as disadvantages of Pyrex glass:
- From the chemical point of view, it is recognized that Pyrex glass is attacked by hydrofluoric acid, by concentrated and hot phosphoric acid, and by strong alkaline solutions that cause a corrosive effect.
- Pyrex glass manufacturers do not guarantee the stability of the materials when they are used under different conditions of vacuum and pressure. For this reason it is essential to take into account the information provided by the manufacturer and follow their instructions to ensure the protection of both the material and the user.
- There are few reviews of consumer protection agencies with situations regarding safety in use with containers used to bake food after suffering fractures due to bumps or falls.
Pyrex glass in the kitchen
In relation to this type of utensils used in the kitchen, several comparative studies have been presented between the containers made with the borosilicate Pyrex and utensils made with glass tempered with sodium lime.
It has been confirmed that Pyrex is more resistant to high temperatures, but that it has less mechanical resistance than the containers of tempered glass used for this same purpose.
References
- Präzisions Glas & Optik GmbH. Stephan Köthe, Marc Mennigmann. PYREX ® 7740 Retrieved on April 22, 2018, from: pgo-online.com
- Wikipedia. (2018). Pyrex. Retrieved on April 22, 2018, from: en.wikipedia.org
- Azo Materials. (2009) Borosilicate Glass - Properties of Borosilicate Glass (Pyrex / Duran) by Goodfellow Ceramics & Glass Division. Retrieved on April 22, 2018, from: azom.com
- Bibby Sterilin. Technical Information. Pyrex ® Borosilicate Glass. Retrieved on April 22, 2018, from: sciencemadness.org
- Othree. (February 28, 2017). Pyrex. [Figure]. Retrieved on April 22, 2018, from: flickr.com
- Actualist. (April 24, 2013). Silicate structures. [Figure]. Retrieved on April 22, 2018, from: commons.wikimedia.org