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[♪ INTRO]
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If you bake a lot, you may have realized that while glass cookware exists,
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not all glass is okay to use in the oven.
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Normal glass can actually shatter and explode in there.
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This happens because as the glass warms up in the oven,
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the molecules inside it try to expand.
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But when you take that glass out and place it on something cool, like a countertop,
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then the part of the glass touching that starts to contract instead.
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And this fight between the parts that are still expanding
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and those that are contracting places stress on the glass's internal structure.
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That's a thing called thermal shock.
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This stress is then released by the whole thing shattering.
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But something like your glass brownie pan is different,
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and the reason why comes down to the chemistry.
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Now, the main component in glass is silicon dioxide.
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And the glass takes the form of a network of bridges between the silicon and oxygen atoms.
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Except, pure silicon dioxide glass is hard to manufacture
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because the bonds between atoms are so strong,
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and it takes a lot of heat to melt that stuff to make glass, around 1700 degrees Celsius.
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So, manufacturers add other ingredients called fluxes
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to make the glass melt at a lower temperature.
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The most common extra ingredients are sodium oxide, also known as soda,
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and calcium oxide, also known as lime, which acts as a stabilizer.
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This type of glass is called, unsurprisingly, soda-lime glass,
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and it makes up about 90% of the world's glass.
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But adding these extra ingredients can also make the glass weaker
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and more vulnerable to thermal shock once everything's cooled down and solidified.
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And that's especially true of the ingredient sodium.
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Some of the oxygens in the glass' silicon-oxygen chain
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end up binding to the sodium instead of continuing the network.
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Those are called non-bridging oxygens.
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And having them makes the whole structure less well-connected
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and more likely to expand when heated.
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Hence why you shouldn't put a Mason jar in the oven.
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But there are types of glass you can put in the oven and take out without shattering,
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particularly one kind called borosilicate glass, which contains the element boron.
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The chemical boric oxide also reduces the temperature needed to melt glass,
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compared to pure silicon dioxide.
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But unlike sodium, it can form bridging oxygens in a glass,
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typically three of them making a flat triangle.
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You can make glasses that use just boron and oxygen, or boron, silicon, and oxygen.
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But having both boron and sodium in the mix,
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if everything's in the right proportions, does something cool on the molecular level.
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All the elements will interact in such a way
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that boron will form bonds with four oxygens as well as the sodium.
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This is because the four oxygens give the boron a negative charge,
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which attracts the positively-charged sodium.
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When the sodium and boron are in the right proportions, this does two things.
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First, it creates more bridges than boron would make by itself,
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increasing the network's rigidity.
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Second, this leaves the sodium unable to produce those non-binding oxygens,
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since it's already tied up with the boron.
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And that creates a strong and stable network, which reduces the thermal shock
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by reducing how much the glass wants to expand when heated or cooled.
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And you still get the benefit of it being easier to manufacture than pure silicon dioxide glass.
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Today, we have a huge number of different types of glass,
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thanks to chemical tricks like this.
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Including ones that, yes, can go in the oven.
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If you want to learn more about other clever chemical tricks head out to Brilliant!
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They have courses in science, engineering, computer science, and math.
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Their course content is curated by math and science educators
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and lifelong learners from MIT, Caltech, Duke, and more
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Go to Brilliant.org/SciShow to try their course The Chemical Reaction,
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where you'll learn all the bits and bolts of chemistry,
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from what a chemical reaction is, to how you can predict when one will happen.
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[♪ OUTRO]
