The three of us – me, my wife, and my son – are on our way home from dinner yesterday, and my son’s been talking excitedly about a video game he got to play in a store. “And then I knocked him into the water,” he announces, “and then I knocked him into the air, and then I won! Daddy didn’t win a lot, though.”
“I made the mistake of trying to figure out what the buttons do,” I add. “Our son just pushed things at random. It’s nice to see that button-mashing is still a strategy.”
“Can metal turn into fire?” my son asks.
Eh? Where did that come from? My wife and I look at each other quizzically. “It can melt,” she says, slowly.
“But can it turn into fire?”
“Do you mean ‘can it burn?'” I ask.
“I… think so?”
Can metal burn?
Like I told my son, I think so. Long ago, I was told that burning is just a special form of oxidation (aka “rusting”). I don’t remember who told me that, or when, or why, so I don’t know that I can trust it. Also, I vaguely recall that thermite is a metal that burns, and that titanium can burn. So, yeah. I’m utterly ignorant on the subject.
Let’s start with “burning”.
Conveniently, a while back I wrote an article titled “When Ice Is On Fire, Does The Ice Melt” where I discussed the concept of burning. Here’s what I wrote:
Burning, more properly called a combustion reaction, is a little more complicated. There’s an entire subfield of chemistry called thermochemistry that deals with burning (or, more properly, the energy release from a combustion reaction). In general, though, you need a compound to combust and an oxidant to react with the combusting compound, and some energy to get it started. The oxidant and the combusting compound then combine in a chemical reaction to produce one or more new compounds, and since the reaction is exothermic the process of making the new compound(s) generates more energy than it gives off.
Yes, that does mean that once you get a combustion reaction started it will continue as long as it has combustible compounds and oxidants. That’s why fire spreads.
It turns out that I’d missed two important concepts when I wrote that article, though: flash point and ignition temperature. The flash point is the lowest temperature at which a combustable substance vaporizes into an ignitable gas, while the ignition temperature is the lowest point at which a combustable substance vaporizes into a gas that will self-ignite. Note that word “combustable”, though. Not every substance has a flash point or ignition temperature, because some substances (such as water and other combustion reaction products) are simply not combustable.
Look, we’ve been patient. Can metal burn?
Well, some can. If they’re combustible, which gets to the best definition I’ve seen in a long time: “A combustible metal is defined as any metal composed of distinct particles or pieces, regardless of shape, size or chemical composition that will burn.” Literally, a metal is defined as a metal that can burn if it is a metal that burns. Although, in fairness, “burns” means “sustains ignition”.
The combustible metals that are :
- Alkali metals: Cesium, Francium, Lithium, Potassium, Rubidium, Sodium and alloys of these metals
And because I know you’re curious, here’s some sample solid metal ignition temperatures. Bear in mind that, for comparison purposes, a Bic lighter can reach temperatures of 3,590.6 F (1,997 C):
- Aluminum: 1,832 F (555 C)
- Barium: 347 F (175 C)
- Calcium: 1,300 F (704 C)
- Iron: 1,706 F (930 C)
- Lithium: 356 F (180 C)
- Magnesium: 1,153 F (623 C)
- Plutonium: 1,112 F (600 C)
- Potassium: 156 F (69 C)
- Sodium: 239 F (115 C)
- Strontium: 1,328 F (720 C)
- Thorium: 932 F (500 C)
- Titanium: 2,900 F (1,593 C)
- Uranium: 6,900 F (3,815 C)
- Zinc: 1,652 F (900 C)
- Zirconium: 2,552 F (1,400 C)
Hang on. I have so many questions now.
Yeah, probably. Let me anticipate them.
A metal doesn’t have to be a “combustible metal” to burn. Any number of other metals will burn as well, but only as long as you apply heat. Combustible metals, however, sustain burning even after the outside heat source is removed. Aluminum will burn like a log, but copper will only burn as long as you apply sufficient heat.
Your pocket lighter will probably not set your cast iron skillet on fire, for the same reason that it will not set a log on fire. A significant percentage of the object that you are trying to burn has to be heated to the flash point before it will catch fire. You could probably set a super-thin iron wire on fire with a lighter, but you’d need a larger and sustained flame to ignite something big.
Oh, and here’s two more useful facts to know:
- “Burning combustible metals can extract water from concrete, intensifying burning to cause spalling and explosion of the concrete.”
- “Water applied to alkali metals will result in hazardous decomposition, ignition or explosion. Alkali metals include lithium, sodium, potassium, cesium and francium.”
So, if you do manage to set your cheap fake diamond on fire? Call a professional.