Glass is a material with many faces: it is both ancient and modern, strong yet delicate and capable of adopting almost any shape or colour. These properties of glass are why people use it to make everything from smartphone screens and fiber-optic cables to vials that hold vaccines.

Mankind has used glass in some way for millennia and researchers are still finding new uses for it today. It’s not uncommon to hear the oft-repeated factoid that glass is actually a liquid, not a solid. But the reality is much more interesting: glass falls neatly into none of these categories and is in many ways a state of matter all its own. As two materials scientists studying glass, we are constantly looking to improve our understanding of this unique material and discover new ways to use glass in the future.

What is Glass?

The best way to understand glass is to understand how it’s made.

The first step in making glass requires heating a mixture of minerals, often soda ash, limestone and quartz sand, until they melt into a liquid at about 2,700 degrees Fahrenheit (1,480 degrees Celsius). In this state the minerals flow freely in the liquid and move in a disorderly manner. If this liquid cools fast enough, instead of solidifying into an organized crystalline structure like most solids, the mixture solidifies while retaining the disordered structure. It is the atomically disordered structure that defines glass.

Three graphs showing atomic structure going from ordered to chaotic.

As the molten glass cools, it freezes the messy, amorphous structure it had as a liquid. Cdang/Wikimedia Commons, CC BY-SA

It’s not uncommon to hear the oft-repeated factoid that glass is actually a liquid, not a solid. But the reality is much more interesting

In the short term, glass behaves much like a solid. But the liquid structure of glass means that over a long enough period of time, the glass undergoes a process called relaxation. Relaxation is an ongoing but extremely slow process in which the atoms in a piece of glass will slowly rearrange themselves into a more stable structure. In 1 billion years, a typical piece of glass will change shape by less than 1 nanometer about 1/70,000th the diameter of a human hair. Due to the slow rate of change, the myth that old windows are thicker at the bottom due to centuries of gravity pulling on the slowly flowing glass isn’t true.

Colloquially, the word glass often refers to a hard, brittle, transparent substance made of molten sand, soda, and lime. Yet there are many types of glass that are not transparent, and glass can be made from any combination of elements as long as the liquid mixture can be cooled fast enough to avoid crystallization.

From the Stone Age to today

A decorative cup made of yellowish glass.

Humans have been making tools out of glass for thousands of years, like this 4th-century Roman goblet. Matthias Kabel/Wikimedia Commons, CC BY-SA

Humans have used glass for more than 4,000 years, with some of the earliest uses for decorative glass beads and arrowheads. Archaeologists have also uncovered evidence of 2,000-year-old glass workshops. One such ancient laboratory was discovered near Haifa in present-day Israel and dates back to around 350 AD. There, archaeologists have uncovered chunks of raw glass, glass melting furnaces, utilitarian glass vessels, and glassblowing debris.

Modern glassmaking began in the early 20th century with the development of mass production techniques for glass bottles and flat glass sheets. Glass became an essential part of the electronics and telecommunications industry in the latter part of the 20th century and now forms the backbone of the internet.

A cable with light coming out of both ends.

Fiber optic cables use glass to efficiently transmit information. Hustvedt/Wikimedia Commons, CC BY-SA

Enabling technologies for tomorrow’s glass

Scientists today go far beyond simply using glass as a material for a cup or mirror. At the forefront of glass research is the ability to manipulate its complex atomic structure and relaxation process to achieve certain properties.

Because glass is atomically messy and constantly changing, it’s likely that any two points on a piece of glass will have slightly different properties, whether it’s strength, color, conductivity, or something else entirely. Because of these differences, two similar pieces of glass made in the same way using the same materials can behave very differently.

To better predict how a piece of glass behaves, our team investigated how to quantify and manipulate glass’s chaotic and ever-changing atomic structure. Recent advances in this field have had direct benefits for existing technologies.

For example, phone screens don’t crack as easily as they did in 2014, in part because new processing techniques reduce differences in atomic bond strengths to make it more difficult for cracks to propagate. Similarly, Internet speeds have improved dramatically over the past 20 years as researchers have devised ways to make the density of the glass used for optical fibers more uniform, and thus more efficient at transmitting data.

A deeper understanding of how to manipulate the changing and chaotic structure of glass could lead to major technological advances in the coming years. Researchers are currently working on a number of designs, including glass batteries that could enable faster charging rates and greater reliability, fiberglass wind turbines that require less maintenance than existing turbines, and improved memory devices.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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