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我们都知道你能将金属充分加热使它融化或折叠
So we all know that you can get metal hot enough to melt and fold
或者将它锤成一米长的双刃宽剑
or be hammered into meter-long double-edged claymores
但是你真的能燃烧它们吗
but can you actually burn it?
你可能从金属最常见的形态了解它们
You probably know metals from their most familiar forms
金戒指 壁炉拨火棍 汽水罐
a gold ring, a fireplace poker, a soda pop can
但是金属其实有很多种
but metals are actually a pretty diverse group.
事实上 它们构成了元素周期表中的大部分元素
In fact, they make up most of the elements in the periodic table.
我们一般根据相关联的物理性质定义金属
Metals are generally defined by the physical traits we associate with them
它们都很硬 但具有可塑性 这意味着它们能被锤成薄片
they’re hard but malleable, meaning they can be hammered into thin sheets, but
但它们也有延展性 可以被拉成电线
they’re also ductile or can be pulled into wires.
但也许它们最重要且最著名的特性是 它们是电和热的良导体
But probably their most important and well-known property is that they’re awesome conductors of heat and electricity.
它们大都是银白色 有光泽的
They’re also generally gray and shiny.
它们能作为电的良导体 主要上是因为它们中的一些能够燃烧
And the reason they’re so good at conducting electricity is basically the same reason that some of them can burn.
大多数金属的原子很容易失去电子 所以当热或电穿过一片金属时
Atoms in most metals tend to give up electrons really easily, so when heat or electricity run through a piece of metal
那基本上是一股活跃的电子 然后当它们燃烧时
that’s basically a stream of excited electrons. And when they burn
金属放弃了一些电子 但是这个过程并不总是像你想象的那样
metals are giving up some of their electrons. But the process doesn’t always look like you might imagine.
例如 一大块纯铁不能长时间保持它的纯度
A hunk of pure iron, for example, doesn’t tend to stay pure for very long.
这是因为 那些铁原子真的很想和氧私奔
That’s because those iron atoms really wanna hang out with oxygen.
氧气喜欢电子 对带走铁急切想交出的珍贵的电子 感到非常开心
Oxygen loves electrons, and is more than happy to take up all the precious electrons that iron is eager to surrender.
所以 当暴露在氧气里时 无论是在空气中还是水中
So, when exposed to oxygen either in air or water
铁会生锈并且变成氧化铁
the iron rusts and becomes iron oxide.
这和燃烧有什么关系呢
What does that have to do with burning?
这是一种叫做氧化的化学反应
Well that is a chemical reaction called oxidation.
燃烧也是氧化 只是快得多
Burning is also oxidation, just much faster
所以 生锈也是一种燃烧
so rusting is a kind of burning
实际上 它的确产生了少许热量 只是非常缓慢 也没有点燃任何东西
it actually does give off a little bit of heat, it’s just very slow and doesn’t actually ignite anything
但是在特定情况下 铁是可以点燃的 铁越热 或者任何一种金属变得
but iron can ignite under the right circumstances. The hotter the iron, or really any metal gets
和氧气的关系更密切
the greater its affinity for oxygen becomes.
所以 如果你有足够小足够热的金属块 它会达到一个让它发生剧烈氧化的燃点
So if you get small enough pieces of it hot enough, it’ll reach a point where it undergoes what’s basically very rapid oxidation.
这个点就是能点燃它的温度
This point is its ignition temperature.
你可以在家里尝试!你只需要一些精钢丝 钳子
You can try it at home! All you need is some extra fine steel wool, some pliers,
一个打火机之类的 能点火的东西
and like a lighter or something that makes fire,
一个你能放置热金属薄片的容器
and something that you can catch the hot flakes of metal in
好让它们不掉在你的柜台上 把你的房子烧着 当心
so that they don’t fall on your counter and catch your house on fire. Be careful.
钢丝大概就是削得很细的金属 大部分是铁 并且
This steel wool is basically just thinly shaved metal that’s mostly iron, and
更精纯 金属的接触面越大 越容易燃烧
the more fine, the more surface area the metal has, the easier it is to burn.
来看看我们怎么实现这个
Let’s see if we can make this happen.
哇 这很漂亮
Oh wow, that’s pretty!
做到了!
IT WORKS!
它有没有伤到我的脸 弄得有点痛呢 有
And did it hit me in the face with a little bit of pain? Yes!
所以为什么钢丝会烧着 但布鲁克林大桥不会
So why will steel wool burn but not the Brooklyn bridge?
一个铁铸煎锅也不会 好吧,因为一些原因
Or a cast iron skillet? Well, for a few good reasons
首先因为金属是这么优秀的热导体
first because metal is such an excellent heat conductor
它传递作用于它的热量 这更难让它的某个特定部分达到燃点温度
it disperses heat that’s applied to it, which makes it harder for any particular part of it to reach its ignition temperature.
把一个煎锅放在火上 热量会很快分散到整个金属上
Put a skillet on a flame, and the heat quickly disperses through all of the metal
于是表面的温度并没有高到 可以支撑一个 让整个锅烧着的反应
so the surface doesn’t get hot enough to sustain a reaction that would actually set the whole skillet on fire.
但是那些小钢丝线那么细 以至于没有可以传递热量的余地
But those tiny little threads of steel wool are so thin that there isn’t any room for the heat to spread out
所以铁丝很快就达到燃点
so the iron quickly reaches its ignition temperature.
第二个主要因素和接触面有关
A second major factor has to do with surface area.
这个锅的大部分铁都在锅内部
Most of the iron in this skillet is inside the skillet.
不能和空气接触
It doesn’t come into contact with the air.
钢丝烧得很快 因为这些长线有更大接触面暴露(在空气中)
Steel wool burns because these long strands have huge surface areas that are exposed
准备与空气中的氧发生反应
and ready to react with the oxygen in the air.
这就像一张纸很容易烧着 但是一个大的旧木头却很难做到
It’s like a piece of paper is super easy to light on fire, but a big ol’ log is hard to get going..
铁屑会燃烧 铁棒却不会
Iron filings will burn, iron rods will not.
最后 这也是一个很好的提醒 (提醒我们)所有东西 无论发不发生反应 是怎样烧成微粒的
In the end it’s a good reminder of how everything boils down to particles either reacting or not reacting.
如果你把金属形象化为铁铸煎锅 你只能看见它转移火焰 却永远不会真正烧着
When you visualize metal as a cast iron skillet, you only see it deflecting flames and never actually burning
但如果你在它的元素状况上思考 并回想铁和许多其他金属
but if you think of it in its elemental state and remember how iron and many other metals
对氧有着怎样大且久的迷恋 这会拓宽你对 几乎所有事情的理解
have big ol’ crushes on oxygen, it’ll broaden your understanding of — pretty much everything.
感谢您收看本集SciShow 也感谢我们Subbable的订阅者让这期节目成为可能
Thank you for watching this episode of SciShow, and thank you to our Subbable subscribers for making this possible.
如果您有任何问题 评论 或建议给我们 我们会在Facebook和Twitter上处理评论
If you have any questions or comments or suggestions for us, we’re on Facebook and Twitter and down in the comments below
如果你想和我们Scishow一起变得更聪明 你可以去youtube.com/scishow订阅(我们的节目)
and if you wanna keep getting smarter with us here at SciShow, you can go to youtube.com/scishow and subscribe.
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