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  • Thanks to Brilliant for supporting  this episode of SciShow.

  • Go to to learn how you  can take your STEM skills to the next level!

  • [♪ INTRO]

  • If you bake a lot, you may have realized  that while glass cookware exists,

  • not all glass is okay to use in the oven.

  • Normal glass can actually  shatter and explode in there.

  • This happens because as the  glass warms up in the oven,

  • the molecules inside it try to expand.

  • But when you take that glass out and place  it on something cool, like a countertop,

  • then the part of the glass touching  that starts to contract instead.

  • And this fight between the  parts that are still expanding

  • and those that are contracting places  stress on the glass's internal structure.

  • That's a thing called thermal shock.

  • This stress is then released  by the whole thing shattering.

  • But something like your glass  brownie pan is different,

  • and the reason why comes down to the chemistry.  

  • Now, the main component in  glass is silicon dioxide.

  • And the glass takes the form of a network of  bridges between the silicon and oxygen atoms.

  • Except, pure silicon dioxide  glass is hard to manufacture

  • because the bonds between atoms are so strong,

  • and it takes a lot of heat to melt that stuff  to make glass, around 1700 degrees Celsius.

  • So, manufacturers add other  ingredients called fluxes

  • to make the glass melt at a lower temperature.

  • The most common extra ingredients  are sodium oxide, also known as soda,

  • and calcium oxide, also known as  lime, which acts as a stabilizer.

  • This type of glass is calledunsurprisingly, soda-lime glass,

  • and it makes up about 90% of the world's glass.

  • But adding these extra ingredients  can also make the glass weaker

  • and more vulnerable to thermal shock once  everything's cooled down and solidified.

  • And that's especially true  of the ingredient sodium.

  • Some of the oxygens in the  glass' silicon-oxygen chain

  • end up binding to the sodium  instead of continuing the network.

  • Those are called non-bridging oxygens.

  • And having them makes the whole  structure less well-connected

  • and more likely to expand when heated.

  • Hence why you shouldn't put  a Mason jar in the oven.

  • But there are types of glass you can put in  the oven and take out without shattering,

  • particularly one kind called borosilicate  glass, which contains the element boron.

  • The chemical boric oxide also reduces  the temperature needed to melt glass,

  • compared to pure silicon dioxide.

  • But unlike sodium, it can form  bridging oxygens in a glass,

  • typically three of them making a flat triangle.

  • You can make glasses that use just boron  and oxygen, or boron, silicon, and oxygen.

  • But having both boron and sodium in the mix,

  • if everything's in the right proportionsdoes something cool on the molecular level.

  • All the elements will interact in such a way

  • that boron will form bonds with  four oxygens as well as the sodium.

  • This is because the four oxygens  give the boron a negative charge,

  • which attracts the positively-charged sodium.

  • When the sodium and boron are in the  right proportions, this does two things.

  • First, it creates more bridges  than boron would make by itself,

  • increasing the network's rigidity.

  • Second, this leaves the sodium unable  to produce those non-binding oxygens,

  • since it's already tied up with the boron.

  • And that creates a strong and stable  network, which reduces the thermal shock

  • by reducing how much the glass wants  to expand when heated or cooled.

  • And you still get the benefit of it being easier  to manufacture than pure silicon dioxide glass.

  • Today, we have a huge number  of different types of glass,

  • thanks to chemical tricks like this.

  • Including ones that, yes, can go in the oven.

  • If you want to learn more about other clever  chemical tricks head out to Brilliant!

  • They have courses in scienceengineering, computer science, and math.

  • Their course content is curated  by math and science educators

  • and lifelong learners from  MIT, Caltech, Duke, and more

  • Go to to try  their course The Chemical Reaction,

  • where you'll learn all the  bits and bolts of chemistry,

  • from what a chemical reaction is, to how  you can predict when one will happen.

  • [♪ OUTRO]

Thanks to Brilliant for supporting  this episode of SciShow.


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B2 中高級 美國腔

为什么你不能烤梅森罐(Why You Can't Bake a Mason Jar)

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    joey joey 發佈於 2021 年 06 月 29 日