Okay, chemistry review. Combustion is an exothermic reaction between oxygen[1] and anything.
The "anything" has to be something that will react with oxygen and give off energy. These things are called "fuels". Since oxygen is way up in the top right of the periodic table, almost anything will give up electrons to it as long as it has free electrons to give. This includes:
- Hydrogen
- Carbon and all carbon-group elements
- Most metals (by definition, metals have free electrons)
- Nitrogen-group elements, except for nitrogen
- Oxygen-group elements, except for oxygen
- Compounds of any of the above. They can even contain some nitrogen or oxygen, as long as they still have free electrons to give.
The fuel reacts with oxygen to form a compound in which the oxygen is holding onto the free electrons. This will
not combust. Most minerals are in this category--they're combinations of metals, nonmetallic elements like silicon or sulfur, and oxygen. They tend not to have any of the standard metal properties, like flexibility, a mirror-shiny surface, or electrical conductivity, because those all result from having free electrons.
There's a race between heat production by the reaction and heat loss into the environment. If the reaction is too slow, it will cool down and go out. Grinding the fuel into a fine powder will expose more of its surface (where the reaction occurs[1]) to oxygen, which allows it to burn faster and can make it self-sustaining. This is where you're getting the idea that a fine powder will burn when the bulk material wouldn't--it
would burn, but so slowly that you'd never notice.
Stone, however, doesn't burn no matter what you do to it, because it has no free electrons. The most abundant minerals on Earth are silicon and aluminum oxides, none of which will react any further with oxygen.
Now, some specific responses:
Why it burns is because its ground up into fine dust the individual bits burn because they can get lots of oxygen because of large surface area.
Again, this is absolutely true for any combustible solid (or liquid). Things that don't react with oxygen at all won't react faster with more oxygen.
Its not really burning as much as hot from friction. In order to burn, something needs calories. Most stones don't burn unless there's some impurity in them that contains calories.
The friction ignites it; the steel then burns in the air.
Combustion is a reaction between carbon, hydrogen, and oxygen.
It goes something like this if I still remember my chemistry classes from a month ago-
xCxHxOx + xO2 => xCO2 + xH2O.
True for organic compounds, but many other things will react with oxygen.
4Fe + 3O
2 => 2Fe
2O
32Zn + O
2 => 2ZnO
etc.
Carbon burns. Carbon is the only thing in organic chemistry that burns. Simple as that. Trees, coal, people, vodka... it's all carbon.
No carbon = no burning.
This is a piece of magnesium being ignited. Are you going to tell me that that's not a fire, because it's not carbon?
[1] Okay, "an oxidant", meaning an electron acceptor. On this planet that's usually going to be oxygen. It could also be fluorine, chlorine, nitric acid, etc., but the mechanism is roughly the same.
[2] Some fuels actually vaporize, mix with the air, and
then burn, so the reaction takes place
near the surface. Take a close look at a candle flame. Still, more surface = more fuel/air contact = faster reaction.
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Topic: Solving all excess stone problems. (Read 9630 times)