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tom haggen
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Pressurized Gas production.
Hello, everyone.
I'm embarking on a quest that involves a high energy out put of pressurized gas. The first thing that came to mind was this reaction:
2NaN3(s)---->2Na(s) + 3N2(g)
The energy out put in this reaction is great which makes it appealing to me. However, you are left over with very reactive elemental sodium. I’m
trying to harness the energy for some type of propulsion system, for a small appx. 16oz vehicle. The desired properties for of reagents are that when
they react, they produce large amounts of gas with no other byproducts such as solids, liquids, or poison gases. I'm thinking I want something
that will produce large amounts of gas with minimal amounts of reagents. Conventional explosives are not candidates for this experiment unless they
are considered to have some sort of use as a reagent. Any suggestions?
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BromicAcid
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I once tried to make a hydrogen candle type thing, I drilled a hole in the top of a pop bottle and put in a handful of galvanized nails and added some
HCl. Gas started coming out and I ignited it, of course the flame was colorless but it roared, but gas production was too great, the bottom rounded
out and it fell over, then propelled itself about fifty feet, exploded and the hydrogen exploded separately form the mechanical explosion. But the
byproducts are of course ZnCl2 and such, but without ignition the hydrogen could be safe. And of course you could substitute zinc with iron or
aluminum or magnesium.
Excess MnO2 and concentrated H2O2 can make large quantities of O2 quickly that could be used to propel an object. And your only byproducts are going
to be water and O2.
There really are not too many gasses that you could use that would not be hazardous in some way, oxygen is probably the most benign. Maybe you could
use some sort of xenon fluoride, with aluminum, forming solid aluminum fluoride and xenon gas. But that's stretching it a bit. There are of
course ways to produce nitrogen involving reacting sulfamic acid with sodium nitrite but that's somewhat of a waste if you ask me. The best gas
would probably be carbon dioxide, but of course that is the most time tested method, like a bottle with water and dry ice, or a vinegar and baking
soda volcano.
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tom haggen
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I don't know if my mind is just going blank or what, but I’m just having a hard time coming up with something off the top of my head. You would
think after a year of blowing shit up and burning metallic objects in strong acids I would be able to come up with something. I guess I might as well
go ahead and say that this is a project for my engineering class. The rules are that you have to use a chemical reaction to propel a small plastic
vehicle 25 feet. No brakes can be used; therefore the only way for the vehicle to stop is when the reaction is complete. The project can't leak
water or drip water, and it can not expel smoke (so no rocket engines). The only feasible way of propelling the vehicle is going to be with some kind
of pressurized gas stream. If any gas is expelled it has to be calculated via stoichiometry. The problem I’m having with visualizing this project is
this:
for example, if you use vinegar and NaHCO3 it will produces some CO2 but as CO2 spews out in a high pressure stream through some type of valve you are
also going to probably be dripping some vinegar unless you make vinegar your limiting reagent, but if you do that then you are probably going to spew
out some access baking soda. Also, my professor said that he will order any chemical we need for our groups design. This was sweet sweet music to my
ears. For the first time in my life I have access to any chemical I want and my mind goes blank... I'm also going to need to find some kind of
propulsion formulas. That way I can calculate how much pressure I will need to send a certain weight exactly 25 feet. I have five weeks so it's
not a time crunch. But I really would like to try and use some sort of exotic reagents since I have access. The only catch to that is, my budget is
only 15 American dollars.
[Edited on 5-11-2004 by tom haggen]
[Edited on 5-11-2004 by tom haggen]
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vulture
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Try a concentrated solution of ammoniumnitrate and potassiumcarbonate...
The ammonia stench isn't very pleasant though...
WARNING: This reaction can be violent, be prepared.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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neutrino
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Sodium azide is used in air bags with other stuff to take care of the sodium formed. I think this mainly consists of beningn stuff you could find
anywhere.
edit:
I didn't think this deserved a new post, but would it be feasible to filter out any solid components produced using some kind of filter like
glass wool?
[Edited on 6-11-2004 by neutrino]
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kyanite
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Yeah it's iron oxide they use. Your right, you can find that almost everywhere
It oxidizes the sodium so the driver doesn't get sprayed with atomized Na 
Wow, I wish my school wasn't that cheap... Our lab experiments consist of questions like what happens when you dissolve salt in water...
On Sam Borrows site he does this thing with liquid nitrogen and warm water in a pop bottle rocket . High gas output, non-toxic materials, and left over liquid nitrogen to play with when your done with your quest
http://www.powerlabs.org/rockets.html
Edit: If your worried about the water, I guess you could use less
[Edited on 6-11-2004 by kyanite]
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tom haggen
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Actually the reaction in an air bag uses potassium nitrate to stablize the elemental sodium created by the sodium azide reaction. So an ammonium
nitrate solution will react violently with potassium carbonate then... I didn't realize that NH4NO3 was so acidic that it would react violently
with a weak base like K2CO3.
By the way, I really like that glass wool idea you had neutrino.
What exactly initiates the sodium azide reaction? I assume it would be heat?
[Edited on 6-11-2004 by tom haggen]
[Edited on 6-11-2004 by tom haggen]
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neutrino
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The reaction of potassium carbonate and ammonium nitrate is not due to an acid-base reaction. It is due to the formation of ammonium carbonate, which
easily decomposes:
NH<sub>4</sub>NO<sub>3(aq)</sub> + K<sub>2</sub>CO<sub>3(aq)</sub> <->
2KNO<sub>3(aq)</sub> + (NH<sub>4</sub><sub>2</sub>CO<sub>3(aq)</sub>
(NH<sub>4</sub><sub>2</sub>CO<sub>3(aq)</sub>
-> 2NH<sub>3(g)</sub> + CO<sub>2(g)</sub> + H<sub>2</sub>O<sub>(l)</sub>
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vulture
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Not really, the fact that ammoniumcarbonate decomposes is because you have a base and an acid in one molecule.
As a result this reaction IS an acid-base reaction:
NH<sub>4</sub><sup>+</sup> <----> NH<sub>3</sub> + H<sup>+</sup>
CO<sub>3</sub><sup>2-</sup> + 2H<sup>+</sup> ---> H<sub>2</sub>CO<sub>3</sub> --->
H<sub>2</sub>O + CO<sub>2</sub>
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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Magpie
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Consider a voltaic cell driving an electric motor. But I don't see how to stop it at 25 feet. This is probably not what your professor has in
mind.
The solid or liquid entrainment proplem should be solvable with a knock-out screen of some sort, as previously mentioned. Consider kitchen srubbing
pads. A zig-zag path filled with scrubber pad might work. You don't need much of a punch to go just 25 feet. A chemical reaction that is
somewhat controllable like baking powder with vinegar added slowly via orifice might do it.
The single most important condition for a successful synthesis is good mixing - Nicodem
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tom haggen
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Actually polverone and I have been exchanging U2 messages about using some type of electric cell. He mentioned using a timer circuit to turn off the
power. Its definitely an option I'm keeping in mind.
[Edited on 7-11-2004 by tom haggen]
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neutrino
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It appears that ammonium carbonate is actually stable up to 60*C, so all you’d have to do is heat a known quantity and it would completely
decompose. With this in mind, Vulture’s reaction shouldn’t happen, though…? Could this be one of those things where it slightly decomposes at
STP and reaches equilibrium in a sealed container, preventing further decomposition? Or maybe it would have something to do with the slightly elevated
pH caused by an alkali carbonate?
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kyanite
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That sounds like that reaction that liberates ammonia from any ammonium ion by reaction with NaOH.
Like NH4NO3 and NaOH -> NH3, NaNO3, H20. Is that what your going at?
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Organikum
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tom haggen, I believe the solution would be a piston connected to a wheel or axis of the cart. The movement of the piston and the diameter of the
wheels define an exact way the cart moves.
Providing a reaction which makes the piston move a defined amount of strokes is possible IMHO, the lesser strokes the easier this comes.
A big-volume cylinder and a reaction as heatsource, some calibration for the losses, thats it. The reaction could be even sealed, hot air as driving
force (for free whereever ppl talk.....)
Of course I dont know if such a setup is inside the rules of the task.
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vulture
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| Quote: |
It appears that ammonium carbonate is actually stable up to 60*C, so all you’d have to do is heat a known quantity and it would completely
decompose. With this in mind, Vulture’s reaction shouldn’t happen, though…?
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Ammoniumcarbonate is stable when it's dry, because it isn't ionised then. In solution or when being melted however...
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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Magpie
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It seems that unless you use a timer or a gearing mechanism with a limit it is going to be difficult to go exactly 25 feet.
The trouble with a gas propulsion reaction is that it is momentum driven. Momentum depends not only on the mass expulsion rate but also the velocity
of expulsion. A simply built gas expulsion mechanism would likely ramp up then down, so trial & error are involved to get the distance. Then
back- calculate to get the theory right to satisfy herr professor. So it looks like a lot of work (fun) and possibly a bit of money to make this
work well. Is there a prize for 1st place? Money, women, or "engineer of the week" maybe?
What is the course you are taking and the discipline of the professor? I know you have your rules but this information may help to understand what
the prof is really looking for.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Taaie-Neuskoek
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Just an idea, I don't know or this is allowed, or practical.
The enigine can be anything, as long as it comes further then 25ft. If you are allowed to draw a white fat line at 25ft, it is easy to build/purchase
a print which recognizes the white line, and then brakes the car via a relay and a motor, just disable the wheels one or another way...electromagnets
are good as well for braking...
To recognize the white line you'll need something like a licht sensitive diode, with a transistor and a relay coupled to it. The transistor
triggers the relay.
[Edited on 8-11-2004 by Taaie-Neuskoek]
Never argue with idiots, they drag you down their level and beat you with experience.
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tom haggen
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The class is a freshman chemcial engineering course. There is no prize. The professor is a Dr. and specializes in polymers. He said that a lot of
times someone in one of the groups will come up with a really good idea and then all the other group's projects will start taking the same form.
Since this happens, he allows a fake pattent on your project which he issues. I have lab on thursday so after then I will probably have a much better
idea on what exactly i'm going to be able to do for this lab. I.E. electric cell, a huge piston attached to the cart, etc...
oh ya new guy with the scandinavian name. No Breaks Allowed!
[Edited on 8-11-2004 by tom haggen]
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Organikum
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The decomposition of sodium bicarbonate at temperatures of 50°C+ to sodium carbonate yields CO2 and might be a easy, low-temp and non-toxic
gas-source. Simplicity and availability.
I define here everything below the boiling point of water as low-temp.
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mick
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Not sure how complicated it can be, but maybe you could use a fast reaction to power up a fly wheel or clock-work mechanism or some thing with
overload protection (a polymer that shears at the right torque or a bursting disc to vent xs pressure) and a basic clutch to engage at the right time.
The fly wheel or whatever should hold a known amount of power.
mick
[Edited on 9-11-2004 by mick]
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Magpie
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Gasoline engines use chemical reactions. A model airplane engine could be used as a power source.
In line with mick's suggestion you could use the power source to wind a spring. This would store an exact and reproduceable amount of energy for
release to the drive train.
The single most important condition for a successful synthesis is good mixing - Nicodem
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garage chemist
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I would use high conc. H2O2 and a solid catalyst on an inert carrier (so that the catalyst doesn't get dispersed in the liquid).
Try to coat pieces of broken pottery with finely divided silver (from the well- known reaction AgNO3 + NH3 + glucose, lots of recipes for this on the
net), that is the standard catalyst for monopropellant rockets using H2O2.
Then secure the pieces to the opening of a narrow- mouthed aluminium bottle, fill it halfway full with atleast 70% conc. H2O2 without touching the
catalyst.
When you lay the bottle flat, the H2O2 touches the catalyst and the rocket starts.
Make some kind of delayed tilting mechanism for the bottle on the vehicle.
When calculating the volume of produced gas, keep in mind that the water is also gaseous.
The heat of the reaction is enough to turn the entire liquid into steam.
I would be interested if your teacher is able to order high- conc H2O2.
I have produced about 3ml of 90%+ H2O2 about a year ago (by evaporating the water from 30% H2O2 in vacuum- works great, the water boils at 25- 30°C
and the H2O2 at ca. 56°C when using an aspirator) and it is great fun to play with. When you soak a piece of wood with it and light it, it burns away
rapidly with a yellow flame and hissing noise without making any smoke.
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uber luminal
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dry ice and an adjustable overflow valve.
once the pressure gets to whatever the valve is set for, it releases the pressure at a steady rate.
You could make one out of an old regulator something with the valve, just by adjusting the diaphram screws.
what are the reqs. for launching the car? can it be launched by another system (im guessing not, since that would be more of a mechanics feat than a
chemical one)
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vulture
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| Quote: |
Then secure the pieces to the opening of a narrow- mouthed aluminium bottle, fill it halfway full with atleast 70% conc. H2O2 without touching the
catalyst.
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70% H2O2 is complete overkill and very dangerous. Remember, we're not trying to build a rocket that has to fight with gravity.
30% H2O2 will do just fine for propelling a small cart.
It doesn't have to be silver either. MnO2 on a carrier works too.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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tom haggen
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Could you just mill your own silver powder instead of trying to liberate it out of silver nitrate? Also what exactly happens when silver or
manganese(II) oxide reacts with Conc. H2O2? I assume this is the type of reaction they use in a jet pack? I talked with polverone about this same
topic and he said the exact same thing as you vulture. "Over kill."
I might try messing around with this type of reaction anyway since I have these types of reagents lying around. I have lab tomorrow, and I think I
will have a much better idea of how I'm going to work this out. I starting to rule out using a high pressure stream of gas for propulsion, just
because it seems impossible to accurately get a small vehicle to land on 25' with that method.
[Edited on 10-11-2004 by tom haggen]
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