Synthesis of boron

Boron is an interesting element used in high strength fibers. It burns with a nice green flame. I plan to use it to make boron tribromide. I tried making some boron from boric acid.

The first step is to convert the boric acid to boron trioxide.

To a metal can, I added 15g of boric acid. Then I heated the can on a medium heat. After 5 minutes the boric acid had began to melt and decompose. Ten minutes after this, the mixture had turned to a bubbling sticky mess. I kept the heat on for another 10 minutes. After this, a sticky glassy mass remained in the can. Upon cooling, it solidified into rock-hard crystals of boron trioxide. The boron trioxide was scraped off the can and collected.

The final step is to reduce the boron trioxide to elemental boron.

I ground up the boron trioxide crystals from step one into a fine powder. This was very difficult and took several hours. Then I added a roughly equal amount of magnesium powder and cuttings to the boron trioxide. I blasted the mix with a butane torch until all the mixture had turned black. I was expecting the mixture to act like a thermite and not need to be torched. I think the reason this didn't happen was because half my magnesium was not powdered. Anyway, after this I added the black residue to a beaker and added about 50ml of water. I then slowly added 12M hydrochloric acid until the acid stopped affecting the mixture. The mixture fizzed and lots of gas was produced during the addition.

I noticed a disgusting smell. This is most likely borane gas. Once the mixture had stopped bubbling, I added 400ml of water to dissolve any residual boron trioxide. Then I filtered the mixture to collect the boron product. I got 0.06g of boron as a black powder, which is a miserable 1.2% yield.

I blame the extremely low yield on the thermite not working. The butane torch probably didn't do a very good job.

2 B(OH)3 ==> B2O3 + 3 H2O  /  B2O3 + 3 Mg ==> 3 MgO + 2 B