What Is Glass?

What Is Glass?

by Jasmine Chan 

Source: shutterstock.com

INTRODUCTION

Glass, a common transparent object, is a substance that is usually laying around the house, whether it be our windows, our screen monitors and even our dishwares. Glass is often a substance that is neglected due to its transparent nature - but what makes it so special?

Fig.1 Example of Windows - A Common Object Made of Glass.

Source: “What Size Is a Standard House Window?” Everest, www.everest.co.uk/double-glazing-windows/standard-house-window-size/.

INTRODUCTION TO TRANSPARENCY

Before I address what glass is, the definition of transparency must be mentioned. Transparent objects are things which allow all wavelengths of visible light to travel through them. When light passes through a transparent object, almost all light present is able to pass directly through the object. [1] An object that is transparent does not absorb or diffract light. If the refractive index of the material is the same outside and in of the material when light passes through it, the material is known as transparent. [2] 

Fig.3 Example of A Wine Glass Showing Transparency.

Source: Wiltse, Ron. “Wine Glass on Ice Sunset.” Pixels, pixels.com/featured/wine-glass-on-ice-sunset-ron-wiltse.html.

When light hits glass, photons move towards the glass and interacts with it. In electrons, there is a large band gap. This means that an extremely large amount of energy is required for the electron in the valence band (the band of electron orbitals that electrons can jump out of) of glass to promote to the conduction band (the band of electron orbital that electrons can jump up into from the valence when excited) of glass when it becomes excited with the presence of light. [3, 4] Light waves, from 400-700nm, all do not carry enough energy required to promote the electron to the conduction band and hence, photons travel through glass instead of being absorbed or diffracted and therefore making glass transparent. [5]

Fig.3 Visual Diagram of The Meaning of Valence Band, Conduction Band and Band Gap.

Source: “Band Gap.” Wikipedia, 27 Dec. 2020, en.wikipedia.org/wiki/Band_gap.

INTRODUCTION TO GLASS

Glass is an inorganic material that is transparent. It is commonly used for practicality such as cups and windows. [6] Glass is made of silicon and oxygen atoms, which means that it is made of sand. [7] How is it possible for glass to be transparent, but sand is opaque?

Fig.4 Picture With Glass and Sand (Bottle is Made of Glass; Ground Contains Sand).

Source: “Glass Bottle Buried in Sand.” Shutterstock, www.shutterstock.com/sv/video/clip-3602507-glass-bottle-buried-sand-on-beach.

Glass was discovered by American scientists when they were used the testing the atomic bomb in 1945. When the bomb exploded, sand on the beach immediately turned into glass. 

Glass is a substance made of molten sand - sand which is heated at high temperatures (1700°C) until it has melted into a liquid. Hence, glass formation can never occur in nature, only by human interference. [7] Glass is made through a process known as quenching - when a substance is heated to high temperatures and is then rapidly cooled down at low temperatures. [5] When the molten sand cools down, that is when the formation of glass begins, meaning that the transparency is formed at this stage instead of the beige, yellowish sand on the beach. [7] 

STATE OF GLASS

As mentioned previously, glass is made from the abrupt change from high to low temperature. However, no matter how large the change in temperature is, it would still not set into a solid. [7] Interestingly, glass is actually neither a solid nor a liquid. It is classified as a special solid known as an amorphous solid. This is a state of matter where atoms and molecules are locked into a fixed place (like a solid), but the molecules are arranged randomly, meaning that crystals cannot be formed. They have the property of slides where they are rigid but have the disordered arrangement like liquids. [5] 

Fig.5 Visual Diagram of the Structure of Glass (Left: What Glass Would Look Like If It Were Theoretically A Solid; Right: How Glass Actually Looks Like Molecularly).

Source: “All About Glass.” Corning Museum of Glass, www.cmog.org/article/glass-nature.

HOW ARE COMMERCIAL GLASS MADE?

Windows are a type of commercial glasses. Recycled glass, sand, sodium carbonate and limestone are all placed into a furnace with high temperatures. Sodium carbonate is used to reduce the melting temperature of the sand, which cuts the cost during manufacturing as the energy requirement has decreased. Limestone is required to inhibit the creation of glass which can dissolve in water. [7] When sand melts it is poured into moulds to create glass bottles and other containers. To make flat sheets of glass, it is poured on top of a large volume of molten tin. The molten sand is then left to cool which then forms glass. [8]  

Fig.6 Example of Commercial Glass.

Source: “Glass.” Wikipedia, 23 Jan. 2021, en.wikipedia.org/wiki/Glass.

PROPERTIES OF GLASS

Aside from glass being transparent, glass has a few properties which make desirable to use. Glass can be easily recycled. By crushing unused glass during manufacturing and melting the glass again, it can then be used for moulding again. [7] Glass does not degrade over time, meaning that the quality of glass would remain unchanged no matter how many times it is recycled. [9] Additionally, it is also chemically inert, meaning that it is resistant to hear, unreactive to most substances (eg. components in the air). [7] Glass is also an excellent insulator, making it good to use as a building material. Not only does it allow people living in the building to see outside due to its transparency, it can also insulate against heat, electricity and even other electromagnetic radiations (eg. wavelengths shorter than ultraviolet). [10] 

BIBLIOGRAPHY

[1] “Transparent, Translucent, or Opaque? .” Virginia Department of Education, 2012, www.doe.virginia.gov/testing/sol/standards_docs/science/2010/lesson_plans/grade5/force_motion_energy/sess_5.3c.pdf. 

[2] “What Determines Whether a Substance Is Transparent? For Instance, Why Is Silicon Transparent When It Is Glass but Not When It Is Sand or a Computer Chip?” Scientific American, 21 Oct. 1999, www.scientificamerican.com/article/what-determines-whether-a/. 

[3] Hanania, Jordan, et al. “Valence Band.” Energy Education, 4 June 2018, energyeducation.ca/encyclopedia/Valence_band. 

[4]  Dharan, Gokul, et al. “Conduction Band.” Energy Education, 4 June 2018, energyeducation.ca/encyclopedia/Conduction_band. 

[5] Harris, William. “What Makes Glass Transparent?” HowStuffWorks, 30 June 2020, science.howstuffworks.com/question404.htm. 

[6] “Glass.” Encyclopædia Britannica, 1 Feb. 2021, www.britannica.com/technology/glass. 

[7] “What Is Glass?: How Is Glass Made?” Explain That Stuff, 19 Jan. 2021, www.explainthatstuff.com/glass.html. 

[8] “How Is Commercial Glass Made?” Northern Utah Glass, www.northernutahglass.com/how-is-commercial-glass-made/. 

[9] “The Glass Recycling Process: How Is Glass Recycled?” Gaskells, gaskellswaste.co.uk/recycling/glass-reprocessor/. 

[10] Baraiya, Krunal. “Characteristics & Properties of Glass as Building Material.” GharPedia, 15 June 2020, gharpedia.com/blog/characteristics-properties-glass-building-material/.