Haven't been up to a whole lot lately. I ordered all the parts I need to build the peroxide test stand last monday and am waiting on them to arrive. Hopefully they will be here before the end if the week so I can start work on the test stand that weekend. I decided to reuse the thrust chamber from the nitrous-ethanol engine which should speed up construction. The control system still needs a little work, particularly in the reliability of the communication protocol. The strings over serial work quite well, but I would like to add in some reduncencey. The electronics system also needs some work but more on that later.
Last weekend I also experimented with other methods of evaporating peroxide. I tried plain evaporation at 75 degrees and forced evaporation (blowing a fan on the liquid) and was quite surprised with how well even plain evaporation worked. In about 10 hours about 2L of peroxide went from 45 to about 75% with just plain evaporation, with a stainless bowl about 45cm in diameter. I stopped forced evaporation after dust and bugs found their way into the peroxide, and started to fizzle. The hydrometer I have only goes from 1.2-1.3 Kg/L so I am not sure of the exact concentration but it was just above 1.3. I had previously thought that the losses from decomposition would be too great (even at low concentrations) to make the method viable, and it still might be at higher concentrations but it seems like it will be an efficient way to get to %80 which is quite usable. I also bought another 25L container of %50 last weekend as I was running low. I really need to do some experiments varying temperature and surface area to try to work out a relationship between time, concentration and yield. I also came across an interesting paper which uses a desiccant suspended just above the surface of a peroxide solution to concentrate it. The paper suggested that it worked quite well, although was slow at room temperature. Even if it did take a few weeks to concentrate, I could just leave a large amount concentrating, changing the desiccant when necessary.
I seem to have found a source of %90 commercially which I understand is propellant grade. There are still a few unknowns but If all goes to plan I will be buying 40L early next month. Including shipping it works out to only slightly more expensive than buying %50 and concentrating assuming a %35 yield. I think the yield from DIY would be a bit better than %35, so cheaper not counting the investment I have already made in equipment and the cost of my time, but I would much prefer to buy if I can. Also from what I understand the %90 is propellant grade so I will be able to use a silver catalyst later if I like. Still I would like to not have to rely on a supplier so I will continue to experiment with concentration.