18.4.08

LOx

Today I'll be talking about an important part of all combustion, oxygen. I decided to condense some oxygen and see what I could burn. To condense the oxygen I put a glass tube in some liquid nitrogen and started blowing oxygen into the tube. The boiling point of nitrogen is 77.36 K while the boiling point of oxygen is 90.2 K so the oxygen readily condenses in the glass. I then poured the lovely blue liquid oxygen onto some cotton and set it on fire. What you see below is what followed. Notice that there is no black charred cotton at the end.

video

Cotton is primarily cellulose so the chemical reaction for what is happening is:

(C6H10O5)n + n (6O2) --> n(6CO2 + 5H2O)

There is no leftover charred cotton because I had an excess of O2 the reaction went to completion turning all of the cotton into CO2.

4.4.08

Cogito Ergo Boom

I was walking home from school one day thinking about explosives and I overheard someone say cogito ergo sum. My brain interpreted this as Cogito Ergo Boom. I knew that I couldn't have been the first to come up with the phrase and I was right. But that won't stop me from using it.

For my next few posts I though that I'd talk a little about explosives. There are three main types of explosives: mechanical, chemical, and atomic. We'll start with mechanical explosives.

Mechanical explosions occur due to a physical change in the system. Examples of mechanical explosions are pipes freezing in the winter, dry ice bombs, popping balloons, and the heating of a whole egg in a microwave. In each of these pressure is built up in side of a closed system. Ice expands by about 10% in volume compared to the unfrozen water causing the pipes to burst.

The CO2 in the dry ice bomb goes from 1.5g/cm^3 to 0.044g/cm^3 at STP. So while the 40 grams of
dry ice that go into the 1 L bottle only take up 26 cm^3 once it all sublimes it will take up 224,000 cm^3 at STP.

While these are impressive displays of mechanical explosions the largest mechanical explosion to ever occur was the explosion of Krakatoa. The explosion of Krakatoa was equivalent to 200 megatons of TNT. For scale purposes the largest bomb that the US stockpiles is the Mk-B53 at 9 megatons. The bomb Little Boy, dropped on Hirosima, was about 13 kilotons or 13,000 times weaker than the explosion at Krakatoa. The largest bomb ever detonated was only 25% of Krakatoa. There are reports of people hearing the explosion over 3,000 miles away. It is the loudest sound in recorded history.

So while mechanical explosions are as easy to make as popping a balloon they are also the most powerful explosions know to man.