Step 10: Hydrogen Production

You can do the math yourself and figure out how many grams of each reactant you need, but it's hard (or at least time-consuming) to estimate the volume of an envelope. I've found I get the best results with about 120g Al and 170 g NaOH -- the exact figures are 116g and 172 g respectively, but you won't notice the difference. When producing gas. you have three main concerns: generating the necessary volume, controlling reaction rate/ temperature, and preventing atmospheric contamination (letting air seep into your hydrogen gas). The less pure your gas is, the less its buoyant force. I always fill the reaction vessel up to about an inch below the spout, so that when the reaction begins there are only a few cubic inches of air left at the top, which you can let bleed out before filling. In my case, this means a lot of water-- several liters -- so the reaction starts slowly at first as the water absorbs the heat. It will get out of control if you let it. It might take a bit of of trial and error depending on the size of your container, but always err on the side of using more water, and always bring more ice than you think you need, and one or two large plastic basins. Maybe you cool it too much, and you have a slow, boring fill, but it's much better than having your basement floor plastered in steaming hot caustic slime releasing clouds of hydrogen gas all at once ( yes, I'm speaking from experience here). Personally, I like a long, cool "slow burn" reaction with lots of ice -- it takes hours, but you minimize the amount of water vapor that might enter your envelope and maximize the purity of your gas.
     Anyway, with the amounts of reactants previously mentioned, you should get enough gas to fill up your envelope completely -- maybe you need a little less, or a little more. If it's your first time, halve the number of ingredients and use a lot of water to get a feel for it before you go for the full amount. If you want to store the excess gas, be aware that any sort of container you put it in (hospital pouches, in my case), if it's not made of mylar or material of a similar quality, will leak relatively quickly and will not maintain the purity of the gas. In general, it's best to make only as much as you need.

When setting up your reaction, you should consider putting in some sort of buffer between the reaction vessel and the envelope -- mine is the pouch with the two tubes in it. If you start the reaction with the water line close to the spout, even at low temperatures, the sheer volume of bubbles produced will cause water to bubble into the tube leading from the spout. This is normal, and will not do any serious harm as long as you sufficiently separate your balloon from the reaction.

Never leave a reaction unattended, and check the temperature regularly -- if you let it get too hot, your envelope could be ruined.

Set up your reaction like in the two pictures: add the aluminum first, then water. At this point, attach your rubber tubing to the spout, and when you're ready, add the lye. Wait for about ten seconds to see how many bubbles form -- if the water level rises too much, just pour a bit out into your basin. Once you've got the level right, wipe the inside of the neck of the vessel with a rag to remove moisture (otherwise your plug will slip out) and then plug it with a rubber stopper. Use duct tape if necessary.

Within a few moments, you should feel/see a flow of gas from your tube.

<p>Can something be sprayed onto a plastic wrap skin, to help hold in the hydrogen gas? I'm trying to keep it light, but don't want the gas to leak out too quickly. Really cool project.</p>
<p>Do you have any idea how much weight (gram) the blimp can lift ? </p><p>Thanks</p><p>Sam</p>
You blimp looks awesome, only the code is without any doubt the most incomprehensible code I have ever seen! I can't make heads or tails from it. Could you explain the how te code works? I really like the 433 MHz set I got, but I haven't found a clear code that I can adapt to my homemade rover. <br> <br>Thom
Darn, I have been trying to figure out your code for quite some time, IT-IS-SO-SIMPLE, I have tried to use virtualwire but then I can't use the servo library (they hate each other). Thanks for sharing it!
when I first read the title I accidently read &quot;Hydrogen bomb.&quot;
Nice work on this project! I had the same 433 Rx Tx units and could never get them to communicate properly! Definitely one of the best troubleshooting sections I've read!
this soo reminds me of the hindenburg. tho to be fair, hydrogen had nothing to do with the explosion. zinc paint(?!) was the problem. <br>very cool project. <br>tho 433mhz might not be legal in USA, but even a toy car with arduino could work
You are my hero. I have tried filling a smaller blimp with hydrogen in the same way, but using only very small amounts of lye (five attempts with no success). I would love to build a setup like this some day, especially one using a hydrogen fuel cell for power. One question: does the water buffer remove any steam or water vapor from the hydrogen entering the envelope? I always worried about getting water in it. Thanks for a very informative 'ible.
You're right to be worried about water vapor. It will only be a problem if you let the reaction get too hot, which will make it start steaming or even boil if it gets out of hand. If you make sure it doesn't get more than a little warm ( I dunno, 75 deg F), the water vapor will be negligible. If you're really worried about it, you could try running the gas through a percolator to cool it down before it enters the envelope (meaning some of the vapor would condense out). The buffer I have is mainly to prevent any water in liquid form that bubbles up from getting close to the envelope. Don't give up on lye!
Awesome. Love the chemistry lab details and the troubleshooting section.

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