Glass make from sand the windows

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Glass is made from liquid sand. More specifically, glass is made by heating ordinary sand (mostly composed of silicon dioxide SiO2) until it melts and turns into a liquid. The molten sand is allowed to cool, and it turns into a frozen liquid or an amorphous solid.

Over the course of human history, there was a Stone age, and then a Bronze age, and there’s even been an Iron age. The question is, what moniker would you give to the age in which we’re presently living? Personally, I vote for calling it the Glass Age!

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Science of Glass Making: How is Glass Made?

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Glass Is Ubiquitous

Today, there is hardly any area of life in which glass is not used in one form or another. The windows of houses, cars, ships, trains, and even the airplanes are made from glass sheets. The list of glass products is practically endless, from water vessels, tumblers, decoration articles, different kinds of bottles and sunglasses to spectacles, flasks, lab items, incandescent bulbs, fluorescent tubes and hundreds of other items we use directly or indirectly in our daily life. Have you ever wondered how this incredibly useful material is made?

Mysticism Of Glass: Is Glass A Liquid?

Although glass has a plethora of applications, it also has a tinge of mysticism around it—likely due to its strange chemical and physical behavior. It is strong enough to protect us, but it can also shatter frantically into thousands of pieces. It’s made from opaque sand, yet it’s completely transparent. And, perhaps most startling of all—it appears and behaves like a solid, but it’s actually a form of weird liquid in disguise!

The Science Of Making Glass

This might be hard to believe, but glass is made from liquid sand. More specifically, glass is made by heating ordinary sand (mostly composed of silicon dioxide SiO₂) until it melts and turns into a liquid. You may wonder why the same thing doesn’t happen on hot days at the beach, but the answer to that is quite simple—the melting temperature that the sand needs is very high, around 1700° Celsius.

When the molten sand is allowed to cool, it doesn’t return back to its gritty yellow state that you began with—the heating causes it to undergo a complete chemical transformation, thus attaining a new inner structure. Regardless of the technique employed for cooling the molten sand, it never quite sets into a quintessential solid. Instead, it turns into a frozen liquid or—what a material science graduate would like to call—an amorphous solid. Basically, glass is more like a cross between a solid and a liquid, featuring some crystalline structures generally found in solids, as well as some molecular randomness often seen in liquids.

Also Read: Is Glass A Solid Or Liquid?

The History Of Making Glass

The art of making glass is very old. It is not known with certainty when man first learned to make glass, but some glass beads made as far back as 2500 BC were recently recovered in Egypt. A blue glass rod made around 2600 BC was found in Babylonia. It is clear from these findings that even ancient man understood how to make glass.

How Is Glass Manufactured In Industry?

I have already provided you with a rough idea of how glass is made, but now let’s look at how glass is made in a proper industrial situation. In an industrial glass plant, sand is mixed with waste glass pieces (often collected from recycling), limestone (calcium carbonate CaCO₃) and soda ash (sodium carbonate Na₂CO₃) before being heated in a furnace. The soda ash added to the mixture is solely for the purpose of reducing the sand’s melting point, in a bid to save energy in the manufacturing process. However, this also has an unwanted drawback—it produces a type of glass that would dissolve in water. To control against this, limestone is added to the mixture. The end product obtained from this process is technically called soda-lime-silica glass. This soda-lime-silica glass is the general-purpose glass we commonly see around us.

Tinted Glass

In a bid to make different types of glass, commercial glass manufacturers often use slightly different glass manufacturing processes. This change often comes in the form of adding other chemicals. Chemicals are added with the purpose of changing the appearance or properties of the finished glass. For example, chromium- or iron-based chemicals are added to the molten sand mixture to make green-tinted glass, whereas mixing in cobalt salt produces blue glass. To make oven-proof glass, boron oxide is added to the molten mixture. Lead oxide is added to make a fine crystal glass that can be more easily cut when required.

Toughened Glass

Some highly specialized and super strong variants of glass, such as bullet-proof or tempered glass, is made through a different manufacturing process. Sandwiching multiple layers of glass and plastic is done to make bulletproof glass. Toughened or tempered glass used in car windshields and automobiles is usually made by cooling molten glass very rapidly to make it much harder.

Also Read: Can Glass Be Formed When Lightning Hits Sand?

There are innumerable places where you’ll find glass—from bulbs tucked in thermometers and the fiberglass hulls of boats, to the sandpaper (also called glasspaper) we use for decorating and the strain gauges that warn us when buildings are cracking. Glass is clear, clean, cheap, unreactive, strong and endlessly useful. What more do you want? Glass is one of those magic materials that we absolutely take for granted, but it unrelentingly serves the purpose it is intended for, provided you use it with care!

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(Note: The May 15 Science Cafe NH in Concord is going to discuss the technology and markets of recycling, prodded by stories like this.)

As municipalities wrestle with marketplace changes that are making it almost impossible to recycle glass, the second “R” in the environmental slogan Reduce-Reuse-Recycle is becoming more attractive.

In the town of Warner, the attraction of reusing rather than recycling glass has been obvious for decades.

“Since we started the transfer station, in 1989 … we have been diverting glass out of the waste stream,” said Varick Proper, foreman of the Warner transfer station.

The town grinds up the bottles and jars that residents drop off and uses the resulting material as a substitute for gravel or sand. After the glass is crushed, it looks surprisingly drab and is sometimes given the punning name “glassphalt,” in various construction projects.

“We have just an old grinder that has been converted to beat up the glass,” said Tim Allen, the town’s director of public works. He said the town generates around 80 to 90 tons of material a year, which is used along with gravel and sand, or even in place of it, for such things as roadbeds or doing remediation work at the town gravel pit.

This has a two-fold financial benefit: It makes use of material that the town would otherwise pay to get rid of, probably by shoving into a landfill, and replaces some sand and gravel that the town would have to buy or dig up itself.

Warner may have been ahead of the curve but it’s not alone in seeking to turn residents’ glass into usable material. In nearby New London, Director of Public Works Richard Lee is such an advocate of crushed glass that he’s featured in a video from the Northeast Resource Recovery Association, a recycling industry group, in which he talks about how properly processed, it can be used to make the surface of roads without endangering rubber tires.

The NRRA is trying to increase reuse of old glass in construction. It owns a portable crusher that it takes to various collection points around the region to help communities that don’t have their own systems.

The video also discusses research by the U.S. Army Corps of Engineers that said processed glass aggregate is as good or better than gravel in terms of “frost susceptibility,” or the ability to cope with the expansion and contraction of freezing water during winter.

Elsewhere, efforts are underway to develop other uses for recycled glass, including a new factory in Philadelphia that seeks to use glass to replace aggregate in making concrete, or to use foaming agents with it to create a lighter-weight filler material.

The reason for all this activity is that the obvious thing to do with glass – turning old bottles into new bottles – is increasingly difficult. The major reason is that fewer things are packaged in glass, as compared to plastic, these days, so the market for recycled glass is shrinking.

The problem has been growing for several years but really hit home for New England in January when a bottle-making factory in Medford, Mass., closed because of a decline in business from national beer companies. It annually bought some 2,000 tons of “cullet,” the industry term for recyclable glass.

Combine this market decline with the difficulties of handling glass, keeping different colors of glass separate, and keeping out similar but unusable material that often gets mixed with bottles at transfer stations, like window glass and ceramics, and recycling glass has become almost impossible.

“It’s a problem nationwide. There are a number of places that have gone back to trashing it – done so reluctantly,” said Proper. “The problem with reclaiming glass, recycling it back into a glass bottle, is that you have to hit such a degree of purity that it’s very hard in a post-consumer state. One bottle cap or the wrong color glass can really foul the whole mix.”

Turning used bottles and jars into what is officially called processed glass aggregate has long been encouraged by the state, which instituted rules back in 1999.

“It can be used in public works and other construction systems, including materials for roads, bedding for pipes, and filler around retaining walls and foundations,” said Jaime Colby from the solid waste division of the Department of Environmental Services.

The only limits are that it can’t include pieces larger than an inch in diameter and can’t be left exposed or uncovered.

That latter issue is why Warner doesn’t use crushed glass around culverts that carry streams under roads, said Allen. If the culvert gets washed out during flooding, the glass might be exposed.

Glass is not the only trashed material that can be turned into usable products, of course. The state’s Solid Waste Division has a long list of what it calls certified waste-derived products, which include “clean, shucked clam or mollusk shells” that can be used as cover around driveways, “spent brewery diatomaceous earth” that can be used in place of silt, old asphalt shingles that can be turned into asphalt for roads, and a variety of materials including shredded automobiles that can be used as temporary cover on landfills.

Such reuse is becoming more important as China, which has long been the world’s largest market for used material to be recycled, cracks down on the amount and quality that it will purchase. This crackdown has sent the price of most recycled materials such as paper, rubber and tin plunging, turning many profitable municipal recycling programs into budget sinkholes.

The environmental benefits of recycling remain, of course. That includes not only keeping material out of landfills but the fact that recycled items almost always require less energy to make than items from raw materials.