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Endimion17
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Quote: Originally posted by KonkreteRocketry  | hehe yes, but here it is only nitrogen gas, magnesium oxides out there, no CO2 or SO2 or any O2 or anything else, so the K2O is alone, what will
happen then ? become a gas ?
Also, what will happen to K2CO3 at 1900 degree ? I see that it decomposes to K2O and CO2 ... ummm ? so if at 1900 degree, K2O will be alone ?
[Edited on 5-5-2013 by KonkreteRocketry] |
As usual, Wikipedia is wrong on potassium oxide. It won't decompose above 350 °C. Simple ionic compounds like sodium chloride have a melting and
boiling point and above that their constituents lose electrons and become a mix of ions and electrons, therefore plasma.
Potassium metabisulphite bought at the store won't decompose neatly. It won't give pure potassium oxide. That would be too easy, now wouldn't it? 
The stuff is ~95% pure, so you get a mixture. I don't know what you get, but it isn't a simple compound.
Potassium carbonate decomposes to potassium oxide and carbon(IV) oxide at very high temperatures. Every carbonate does that.
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woelen
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As I wrote before, the K2O only exists fleetingly. It may be at 1900 C when it leaves the rocket, but it very soon cools down and then it combines
with other chemicals in the smoke and with constituents of air.
What kind of propellant mix are you takling about which only gives N2 and MgO besides K2O? That seems like a very special propellant to me. If there
is only N2, MgO and K2O, then no further reactions occur, but I can hardly believe that you have such a system and then you still have the daunting
task of collecting the K2O and MgO and separating these.
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KonkreteRocketry
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| Quote: Originally posted by woelen | As I wrote before, the K2O only exists fleetingly. It may be at 1900 C when it leaves the rocket, but it very soon cools down and then it combines
with other chemicals in the smoke and with constituents of air.
What kind of propellant mix are you takling about which only gives N2 and MgO besides K2O? That seems like a very special propellant to me. If there
is only N2, MgO and K2O, then no further reactions occur, but I can hardly believe that you have such a system and then you still have the daunting
task of collecting the K2O and MgO and separating these. |
alright nvm about that thing, i was just confused a bit...
can you tell me what happenes to K2CO3 at 1900 degree ? does it become a gas ? i saw that it decomposes at 1500 to form K2O which already will
decompose at 350 degree, umm what ? so potassium end up being alone ?
and if k2o does not further decompose is it a gas or a solid or what ? cus i need to know the % of gas mass being expelled to get further
calculations.
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woelen
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K2O does not decompose at 350 C, whoever writes that makes a mistake. K2O may absorb oxygen at 350 C to form K2O2, but that is something different
than decomposition. I expect true decomposition of K2O not to occur at all, unless you get VERY high temperatures (thousands of C) at which it will
fall apart in ions and electrons (i.e. a plasma). I expect that at 1900 C K2O simply escapes as solid and that CO2 escapes as gas. I'm not sure though
whether you can simply assume that the exit-temperature is 1900 C as well. In the mix (the front of burning) you might have 1900 C, but near the exit
the temperature may have fallen considerably already, due to expansion of gasses and due to loss of heat through the mantle of the rocket.
If you really want to do computations on your rockets, then try to find literature about that. I am no expert on this at all. Maybe someone else can
help you with this. I am inclined to think that good rocket design is not easy at all and should be considered a science and an art on its own.
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AJKOER
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More science (or junk) from Wikipedia (https://en.wikipedia.org/wiki/Alkoxide ) with possible implications for the stability/formation of K2O:
"Thermal stability
Many metal alkoxides thermally decompose in the range ~100–300 °C. Depending on process conditions, this thermolysis can afford nanosized powders
of oxide or metallic phases. This approach is a basis of processes of fabrication of functional materials intended for aircraft, space, electronic
fields, and chemical industry: individual oxides, their solid solutions, complex oxides, powders of metals and alloys active towards sintering.
Decomposition of mixtures of mono- and heterometallic alkoxide derivatives has also been examined. This method represents a prospective approach
possessing an advantage of capability of obtaining functional materials with increased phase and chemical homogeneity and controllable grain size
(including the preparation of nanosized materials) at relatively low temperature (less than 500−900 °C) as compared with the conventional
techniques."
The apparent existing commercial significance of the above statement, however, appears to lend to its credibility, although I make no such assertion.
If however accurate, the implications for the possible thermal decomposition of a compound like Potassium tert-butoxide would be interesting (K2O or
even K (?!) under the right 'process conditons'), but, of course, this is only as reliable/accurate as the references supplied by Wikipedia (cited
below, and note the recent years 2001, 2002, 2004, 2005 and 2012):
" References
1. Bradley, D. C.; Mehrotra, R.; Rothwell, I.; Singh, A. "Alkoxo and Aryloxo Derivatives of Metals" Academic Press, San Diego, 2001. ISBN
0-12-124140-8.
2. Turova, N.Y.; Turevskaya, E.P.; Kessler, V.G.; Yanovskaya, M.I. "The Chemistry of Metal Alkoxides" Kluwer AP, Dordrecht, 2002. ISBN 0-7923-7521-1.
3."Single and mixed phase TiO2 powders by excess hydrolysis of titanium isopropoxide". Advances in Applied Ceramics 111 (3). 2012.
4. P.A. Shcheglov, D.V. Drobot. Rhenium Alkoxides (Review). Russian Chemical Bulletin. 2005. V. 54, No. 10. P. 2247-2258. doi:
10.1007/s11172-006-0106-5
Further reading
N.Ya. Turova. Metal oxoalkoxides. Synthesis, properties and structures (Review). Russian Chemical Reviews. 2004. V. 73, No. 11. P. 1041-1064.
doi:10.1070/RC2004v073n11ABEH000855 "
[Edited on 6-5-2013 by AJKOER]
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AJKOER
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More on K2O from one of my favorite sources:
"The Potassium monoxide, K2O, is formed by incomplete oxidation of potassium by dry oxygen at reduced pressure, and removal of the excess of metal by
distillation in vacuum. The product forms microscopic octahedra, which become pale-yellow at 200° C., and have a density of 2.32 at 0° C. Above
400° C. in vacuum it is decomposed into the metal and the peroxide. The heat of formation of the monoxide from its elements is 86.80 Cal. It is
reduced by hydrogen to the hydride and hydroxide. With water it reacts energetically to form the hydroxide, the heat of solution being 75.0 Cal. It
also combines with fluorine, chlorine, and iodine. The heat of formation from the elements is 86.8 Cal."
Source: http://potassium.atomistry.com/potassium_monoxide.html
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