About the effects of hydrogen gas on electronic circuits/CO2 sensors
ElectricAye
Posts: 4,561
I need to maintain a 100 ml volume gaseous atmosphere of mostly Hydrogen gas mixed with about 1 to 2 percent CO2, and I've been considering the Parallax CO2 sensor module. To keep things simple, I was hoping to insert the entire CO2 sensor module inside a flask, but, knowing how H2 can affect metals, I was wondering if anyone here knows anything about how such a gas mix might affect the CO2 sensor, its circuit board, the wires leading to it, heat shrink tubing, solder joints, etc.
I think the Parallax CO2 sensor can sense up to only 1% CO2 but 1% might provide a good enough threshold to keep things under control.
http://www.parallax.com/StoreSearchResults/tabid/768/List/0/SortField/4/ProductID/598/Default.aspx?txtSearch=carbon+dioxide
I think the Parallax CO2 sensor can sense up to only 1% CO2 but 1% might provide a good enough threshold to keep things under control.
http://www.parallax.com/StoreSearchResults/tabid/768/List/0/SortField/4/ProductID/598/Default.aspx?txtSearch=carbon+dioxide
Comments
That's what I'm unsure about. I know it's a big problem in making alloys and with higher temperature operations, but I'm not sure if the application of electric fields would somehow cause similar problems at room temperature. Some metals, such as palladium and maybe nickel(?) do some weird things when exposed to hydrogen, so I was concerned, too, about the sensor itself.
CO2 sensors are probably semiconductor surfaces, which may not have the same catalytic properties.
Cool. I've never heard of that demonstration. Thanks for telling me about that. I'll have to try that sometime.
And that reminds me: I suppose if the gas mix isn't totally dry, there's always the risk of the CO2 forming acids here and there.
Thanks.
I'm pretty sure I remember seeing a graph of hydrogen and oxygen mixtures. In most combinations the gases were explosive. But if the there isn't any oxygen, the hydrogen by itself isn't explosive. (Neither is oxygen by itself.) I'm pretty sure CO2 wouldn't cause the hydrogen to be any more explosive than pure hydrogen.
Could you use some sort of spectroscopy to detect the CO2? Are there wavelengths of light that are absorbed more by CO2 than hydrogen? I'm pretty sure there are, but having a detector sensitive enough to detect a difference after passing through a foot (or so) of gas is likely to be difficult to find/make.
Perhaps a laser of the appropriate wavelength could bounce back and forth between a set of mirror to increase the volume of gas it passes through? (The problem with this approach is any dirt on the mirrors will throw off the results.)
I wonder if you could measure the density of the gas? CO2 weighs a lot more than H2. Could you have some sort of balance within the container to measure the buoyancy of an object? I think it would take a pretty precise balance to detect this change and then you have the same problem of H2 gas in your metal. (Are there non-metal balances?)
Perhaps a fan wheel could be driven with the resistance a function of the density (CO2 content).
Just some ideas.
Duane
Good points. This source may shed some light on mixtures when in the presence of air. It's possible to use other mixtures to squelch flammability, including CO2.
http://www.gexcon.com/handbook/gexhbchap4.htm
By adding inert gases, such as nitrogen, N2, or carbon dioxide, CO2, the explosion hazard can be reduced... As we can see from this figure, the ratio inert gas / flammable gas has to be fairly large for the gas to be outside the flammable range.
Figure 4.10. Flammability limits as function of the ratio of inert gas to flammable gas. Inerting requirements to prevent flame propagation in fuel-air with N2 , CO2 , Halon 1211 and 1301 at 25°C and 1 atm. (Kuchta, 1985).
Source: http://www.gexcon.com/handbook/gexhbchap4.htm
As seen here, hydrogen would require a 57% mixture of CO2 to become nonflammable.
Interesting brain storming. And for the 1% to 2% region, I wonder if an IR emitter couldn't be used somehow. I'm trying to do this as cheaply as possible, with an accuracy needing to be maybe only 0.2% for the CO2, so maybe something like that could be good enough??? I'll have to look into that.
Humanoido,
hey, thanks for looking into the flammability issues on this. It's definitely a concern, but the hydrogen is generated very slowly and under very controlled circumstances via electrolysis, so the danger of a leak is inherently limited - I hope. Also, if all goes well, the O2 levels inside the flask should be very, very small. This experiment is in support of studying microbes that can live on hydrogen and carbon dioxide but oxygen will mess up their metabolism, so I'm hoping the O2 levels will be too small to be a threat.
Many thanks for the information and suggestions!
Edit: Consider an Oxigen trap from the generation to the storage vessel, that would keep it in the ppm level. Glass can also be used without problems as long as the pressure is low, I mean 1 atm or less.
Yes, good point. All of this is running at roughly atmospheric pressure, so I'm using a glass flask.
An oxygen trap would be nice, but I don't want to do anything cryogenic. A dry chemical trap would be best, but then I have to worry about what chemicals might get suspended in the gas and end up poisoning the culture tube. If you have any cheap, biologically friendly chemicals in mind, that would be great. Somebody suggested using damp steel wool, and I'm fairly sure tiny amounts of iron won't harm these critters.
The initial post mentioned that there had to be an atmosphere of a certain percentage. It does not specifically say a homogeneous mixture must be maintained. I will guess that without some form of stirring going on, the H and CO2 will rather quickly separate out due to the differences in molecular weights. Same reason as the hazards to humans with heavier than air gasses in confined spaces. But if the volume of the container is known and it has a fairly predictable/regular shape, then perhaps the idea of the IR sensor may be usable by placing it at a level such that the CO2 reaching that level would then by definition be at the volumetric percentage required. The sensors also could be mounted outside a glass container.
Then again, thermal currents or Brownian movement diffusion may cause the gasses to not be entirely separated.
An odd thought or two,
Frank
I guess this is obvious to all of you, another problem in using the CO2 sensor in a H2 environment may be linked to the actual surface chemistry on the sensor. The sensor itself is a solid electrolyte electrocemical cell : Air，Au|NASICON|| carbonate|Au, air，CO2
When the sensor exposed to CO2，the following electrodes reaction occurs：
Cathodic reaction：2Li + + CO2 + 1/2O2 + 2e - = Li2CO3
Anodic reaction：2Na+ + 1/2O2 + 2e- = Na2O
Overall chemical reaction：Li2CO3 + 2Na + = Na2O + 2Li + + CO2, with its thermodynamic potential related by Nernst's equation to CO2 partial pressure.
Oxygen is the involved in the sensor chemistry; infact, one side of the cell is kept in pure air without CO2. Maybe this reaction is occurring even in the absence of gaseous O2, just using surface oxygen atoms as in ceria-based catalysts;however, this surface oxygen might be depleted by the presence of H2 gas, preventing the electrocemical cell to be working.
I will therefore recommend you to use a more sophisticate, infrared sensor for CO2 measurement; NDIR sensor are widely adopted in the chemical community.
Carlo
Dear Carlo,
yours is exactly the kind of insight I was hoping somebody could provide for me. I was worried mostly about the chemistry of the sensor itself, and your analysis of the sensor is excellent.
I will look into your suggestion for the NDIR sensor and see if I can find an economical way to approach this.
many thanks!
Mark
Hi Frank,
I hadn't really thought about gases separating. There is some stirring going on but it's not very thorough. I'll keep an eye on that and see if diffusion is not enough.
thanks for the suggestion! :-)
The laser idea isn't so bad, but its prohibitive costwise. This is really what you need - http://www.infratec-infrared.com/products_variable-color.htm With that product you wouldn't need the second internal sensor for calibration(like for dirty mirror for example). You can do a sweep and read all gasses that absorb in that range. Problem is, I think they want around $500 each for these, at least in small quantities.
Here is a site - http://webbook.nist.gov/chemistry/ where you can find absorption charts.
That's really cool. Probably out of my price range, though, but I'll look into it. Thanks for all the other links, too! :-)
I know that Na2O is not so stable, but it can be bought, although being impure of sodium peroxide. I was obviously discussing about surface Na2O entities, which are involved in many electrochemical solid-state cell (based on Na+ ionic conductors) for CO2 measurements in air.
Anyway, many colleagues are often talking of "sodium oxides (NaOx)" surface species, so we can discuss on this.
Sincerely
Carlo
KA-Boom!
Hey Carlo! Thanks for the info, it isn't pbvious to me at all, in fact it way outside my field, that might go for some of the others too. Great tip!
Funny you should ask that. The short answer is no, this is for learning more about how some types of photosynthesis work to use and/or produce hydrogen (Their hydrogen enzymes can work both ways). But insofar as terraforming goes, these little critters were probably around before earth had an oxygen atmosphere, about 2.3 billion years ago. I've been told these microbes, or some fairly close relative of them, have been around since maybe 3.2 billion years, and it was from these critters that other forms of life evolved to give rise to microbes that used photosynthesis to generate our oxygen atmosphere, thus clearing the way for life on land and animal life in general. So, in some respects, they and their descendants are what terraformed earth. Nowadays, they reside in the bottom of stagnant ponds, lakes, mud puddles, polluted swamps, etc. where they can still get some light but avoid earth's oxygen, which is poison to them.
http://en.wikipedia.org/wiki/Great_Oxygenation_Event
There are a number of researchers studying how microbes can turn waste materials into hydrogen or other clean sources of energy. Nature has done an excellent job of developing enzymes for this purpose but there's a long way to go to make it practical. I'm working toward understanding how these microbes adapt to their environments. Because they are so old and are found practically everywhere around the world, they have developed an amazing variety of metabolic strategies. If you give them nothing but lemons, they make lemonade. And if you give them automobile exhaust on a sunny day...
But as for powering robots... to have microbes make hydrogen and then macroscopically convert that into electricity with a fuel cell does work, in fact people have been playing around with that since at least the early 1960's, but the ultimate goal would be to figure out how microbes can convert one form of energy into another and then just tap into that system or develop that system for direct application. That would require an integration of biologicals, chemistry, electronics, etc. from the molecular level on up. In other words, the goal would be to cut out all the middle men in the energy transfer chains and just directly tap into the system. To eat fast food or some other waste materials, burp up hydrogen, then convert that to electricity would not be as efficient as doing things directly. I'm guessing that by that time, computers will be based more on what's learned from biology, too, so the computers of tomorrow won't look or work anything like what they do today. Recent research has shown that biological systems, even as simple as enzyme interactions, appear to rely on some sort of quantum computational processing, so this idea of biomolecules doing computation will perhaps lead to the next generation of circuit design and so forth. Recently, bacteria have been seen creating biowires toward minerals in rocks so they can create localized electrochemical reactions for their metabolism, so if researchers can figure out how to control how such bio/nanowires grow, then... well... I'm just guessing what your next Big Brain project would then look like. :-)
http://news.discovery.com/tech/bacterial-nanowires-electronics-110811.html
http://en.wikipedia.org/wiki/Microbial_fuel_cell