# Temperature when we strike a spark in vacuum

In "Artemis" Andrew Weir says that the hot flakes produced by striking flint and steel together do not ignite acetylene in vacuum. He says that the reason steel flakes get white-hot on Earth is that they have very high surface to volume ratio and oxidize in air so fast that they basically burn. No air -> no oxidation -> no white-hot flakes. In air, the process is as follows:

1) Flint striking steel scrapes off a flake, exposing fresh iron at a certain temperature $X$ before oxidation.

2) The iron oxidizes. This is an exothermic chemical reaction, which raises the temperature of the flake from $X$ to well above 1000 °C. This high temperature is what causes the flake to glow white-hot.

3) Acetylene's autoignition temperature is 300 °C, so the white-hot flake is more than enough to ignite/oxidize the acetylene.

What is the initial temperature $X$ of flakes just after the strike, assuming no oxidation (e.g. we are striking in vacuum)?

• "at least some sparks should be able to ignite acetylene" doesn't matter how hot the little bits of metal are, if there is no oxygen then acetylene will not burn Jan 5, 2018 at 4:16
• @pentane, bad wording of mine, in Artemis they use acetylene/oxygen mixture. It does not burn till oxygen proportion is increased. Jan 5, 2018 at 9:12
• By definition before they start to burn the particles are just below the autoignition temperature... once they reach that temperature they start to burn Jan 5, 2018 at 23:32
• hey Vashu what do you think of my statement directly ^above? Maybe we can make your question a bit clearer if we work together Jan 16, 2018 at 4:55
• Can you provide the full direct quote? You can't have an oxyacetylene mixture "in vacuum"-- if you release gas into vacuum it's not a vacuum anymore (at least not locally where the gas is being released). Jan 20, 2018 at 10:20

I doubt that you can see sparks only when the spark material burns in air. I even remember that as a child hitting two stones together produced sparks that were visible in the dark. If the sparks are hot enough the spark material should glow and emit light. Stone age humans used flint (which is quartz) for producing sparks to initiate fire. Flint cannot oxidize in air.

Extension following comments by @pentane. He has kindly pointed out in his comments (see below), that there exist scientific investigations regarding the pre-historic fire-making with the help of flint stones. The scientific consensus seems to be that in spite of visible sparks produced by hitting flint on flint, these do not produce sufficient heat to ignite a fire. Therefore in the stone ages, for producing fire, flint was used together with stones of other chemical composition like pyrite, which oxidize in air and therefore produce hot sparks.

The references provided by pentane are: