AYAAN SHAH (L6P)
Take a look around you, how many different materials can you see? Your device, which you are using to read this article, is composed of hundreds of tiny components, each made up of a myriad of materials, each designed and used for a specific purpose. Or consider the window - decades of innovation in material production have led to the windows we have today, transparent yet insulative. Recently, I stumbled upon an exciting field of science that spans physics, chemistry, and biology: materials science. I believe that this field will play a crucial role in the future of society and civilization, and in this article, we will examine the history, technology, and employment of a material we rely on every day: glass!
The original raw materials of glass production comes from sand. Sand is formed when rocks compress with each other over a long period of time, creating small crystals known as quartz. These quartz crystals have a chemical composition of silicon dioxide, which is a compound of the two most abundant elements in the earth's crust: oxygen and silicon, forming silicon dioxide. When these silicon dioxide (giant covalent) structures are heated, they vibrate, and at 1700°C (the melting point), the bonds holding together the compound in its lattice break, changing the state of the solid to liquid silicon dioxide. This process is similar to the melting of water. However, silicon dioxide and water differ slightly in the post-melting point stage. Water can be cooled to form ice again, with the ice crystals maintaining the same symmetrical pattern as seen on snowflakes. Silicon dioxide, on the other hand, struggles to form its solid crystal again when cooled. As the liquid cools, the structure loses more and more energy, which limits their movement to re-establish their initial lattice configuration. The result of this heating and cooling process is a confused liquid/solid with the same oxygen and silicon atoms but not in the quartz form as seen in sand: and thus, we have a glass lattice.
The transparency of glass is due to the allocation of electrons to specific energy shells. When light passes through an atom, it provides a burst of energy to the electrons, causing them to move to a higher energy shell. By absorbing this energy, the electrons do not allow the light to pass through. However, for an electron to move to a higher energy level, it must be provided with the exact amount of energy required for the jump. For visible light, the energy required for electrons to jump to a free energy shell is much greater than the energy provided by visible light. As a result, visible light passes straight through the glass, but UV light is absorbed, making glass opaque for UV light.
It may be asked why the Sahara cannot be melted to create glass structures in place of the traditional glass blowing process. However, the glassblowing process requires sand that contains a specific combination of minerals, which is not found in the Sahara. If the Sahara were to be melted, the impurities in the sand would hinder the glass created and sand particles would remain, resulting in flaky glass that would likely return to its original structure as sand. Moreover, the temperature required to melt sand into liquid glass exceeds 1200 degrees Celsius, far greater than the potential combustion temperature of 700 degrees Celsius created by melting the Sahara, making it highly unlikely for glass to form there. Nonetheless, social media may have showcased the phenomenon of a lightning bolt hitting sand, creating a unique glass sculpture known as a fulgurite (a glass tube with a sand sarcophagus). Interestingly, the term "fulgurite" is derived from the Latin word "fulgur," which means thunderbolt. These fulgurites possess a hollow interior and are relatively lightweight. In the Libyan deserts, pure white sand dunes exist that are ideal for glass formation, and there is a significantly higher percentage of fulgurites found here than anywhere else on the planet. The intriguing nature of these fulgurites is exemplified by one being used as a centrepiece decoration on the mummified body of Tutankhamun (since glass production was unknown at the time, it is plausible to assume that the glass on the mummy was a fulgurite).
The ancient Romans are credited with the invention of glass, owing to their discovery of the "flux" effect in a mineral fertiliser called natron. This naturally occurring form of Na2CO3 allowed the Romans to create transparent glass at a lower temperature than quartz crystal. Furnaces were created throughout the Roman empire to produce glass in bulk, which added to their merchants' trade portfolios. Craftsmen used glass to create functional tools, including windows that revolutionised the idea of wind and rain protection. Before glass, people used wood as a barrier to the elements. Additionally, the Romans discovered that coating highly polished metal surfaces with a layer of glass would protect mirrors against the elements and reduce production costs.
As the Romans advanced their production process, they engineered methods of creating more advanced 3D sculptures such as wine glasses, which was a luxury trend at the time. Although these glasses had a multitude of advantages, they were unfortunately plagued by a significant issue: the presence of numerous air bubbles. Regrettably, these bubbles weakened the structural integrity of the glass, making it more susceptible to mechanical stress from even the slightest touch against another object or from the gentle pressure of a user's grip. As a result, the force of such stress is absorbed by the glass structures, which causes the force to be dispersed across all of the structures, thereby weakening their overall ability to withstand the impact. Even if a single structure is unable to withstand the force, it will result in the structures being displaced from its position in the glass, causing a crack to form. Despite this flaw, the Romans persevered to create works of art for Western appreciation, from stained-glass windows that opened up the glazing industry to larger household windows attached together by lead.
Glass manufacturing has been perfected over the years from different parts of the world: in the post-classical era (500 CE to 1500), Benin, Africa, become the epicentre of glass and glass beads manufacturing; at the same time glass manufacturing in Europe become so advanced that entire walls were being constructed with stain glass as seen in the Charles Cathedral and the Basilica of Saint Denis. Murano, a small island next to Venice became the manufacturing centre of these ornate pieces of art; by the 17th century, the Venetian craft had migrated to England where the Pilkington Bros. created a technique known as the float glass process for producing high quality glass: The process begins with the collection of raw materials such as sand, limestone CaCO3 and soda ash. These materials are then mixed in a fine tuned ratio to create a glass batch. This is then fed into a furnace of temperatures which are around 1600°C; at this temperature, the mixture becomes molten and forms a sticky liquid. This molten glass is then fed onto a bath of molten tin, which is kept at a temperature of around 1000°C; this temperature difference along with a density difference allows for the glass to float on top of the tin and spreads out to form a flat surface. The glass is then gradually cooled as it moves along the tin bath; this process is known as annealing and helps to remove any stresses in the glass which reduces the likelihood of breakage. Once the glass has cooled and solidified, it is taken off the tin bath and cut into the desired size and shape; these 5 steps, although very simple, have revolutionised the way the world creates its glass. The float glass process has been the most common glassmaking process in the world for the last 80 years.
In conclusion, the invention of glass revolutionised humanity's way of living. From functional tools to works of art, glass has been used for centuries and has continued to be developed and improved upon by scientists and chemists. The benefits of glass are immeasurable, and it has played a significant role in scientific and technological advancements throughout history. Glass remains an ever evolving field in materials science research, hence it is worth looking out for any recent developments and employment of glass.
The rich history and groundbreaking innovations of glass are truly captivating. For those intrigued by this field, I wholeheartedly recommend diving into Mark Miodownik's "Stuff Matters," a book that provided me with a wealth of fascinating glass facts and history. And if you crave more knowledge or simply want to discuss the topic further, feel free to join us at Science Club, held every Friday at lunchtime in the Chemistry department.
Here are the sources of information I have used for this article:
1.https://www.corning.com/worldwide/en/innovation/materials-science/glass/how-glassmade.html#:~:text=The%20kind%20of%20heat%20necessary,it%20re%2Denters%20earth's%20atmosphere.
2 https://www.discovermagazine.com/the-sciences/what-really-happens-when-lightning-strikes-sand-the-science-behind-a-viral-photo
3 https://www.grandviewresearch.com/industry-analysis/glass-manufacturing-market
4 https://www.amazon.co.uk/Stuff-Matters-Marvellous-Materials-Man-made/dp/0241955181
5 https://www.cmog.org/article/prince-ruperts-drop-and-glass stress#:~:text=These%20interesting%20demonstrations%20of%20the,were%20used%20as%20a%20joke.