Aluminum will be essential on the Moon. We need it for wires, cables, electric motor windings and possibly for vehicles. How to produce it though??? This warrants some discussion. Direct electrolysis in FFC cells to produce oxygen, silicon and calcium (also a good electrical conductor) as well as aluminum looks good. This works at lower temperatures than many other processes but it requires imported FFC cells with non-consumable tin oxide or calcium ruthenate electrodes and calcium chloride electrolyte. Maybe the cost of these imports is worth it? I don't think the Hall-Heroult process is viable on the Moon. Not only would we have to recycle carbon electrodes which to the best of my knowledge burn up in just a few week's time we'd need pitch to bind the carbon and a way to bake the electrodes....also cyrolite has a way of breaking down over time, releasing F vapors, etc. If we use the AlCl3 process the carbon electrodes won't burn up for years but we need LiCl and NaCl for flux....and we have to carbochlorinate the Al2O3 and recover the carbon by shifting it to CH4 and pyrolyzing at 900 C. to get carbon dust which we can use as is and recover hydrogen. This seems to require a lot of heat energy. And we need chlorine which is not plentiful on the Moon. Solar carbothermal reduction of alumina is appealing in its simplicity and it won't require any imported reagents. Carbon could be harvested with Mark 3 volatiles miners and recycled. We could make retorts out of lunar alumina bricks, possibly with some added imported zirconia, and silica for windows and use aluminum sheets or foils for reflectors. Very high temps. (2100-2300C) are involved. There's lots of work being done on solar carbothemic Al production and plenty on the web about this. Somehwere i read that if CH4 is used as the reductant the job can be done at only 1500 C. and the result is Al, CO and H2....It seems this method would be "cheap" given we can make everything on the Moon...but we might make parts of FFC cells too in order to reduce import costs!!! There's really no way to know what costs are gonna be without actual experiments on the Moon. Unless some real smart characters can model everything in computers!!! As for roasting anorthite at up to 2000 C. in solar furnaces to get CaAlO4 and directly electrolyzing that, I have doubts. I wrote about that because i thought that might be the most barbaric thing to do!!!! Perhaps CaAlO4 could be electrolyzed in FFC cells?? Whenever i start talking to engineers about refining regolith they always ask, "Why can't we just roast all that stuff at superhigh temps.?" Getting temps. of 6000 K with solar furnaces might be possible but what could contain such heat??? Pyrolysis of regolith has been experimented with and seems like the simplest most aggressive way to do the job...but the temps. involved make me wary. Until we have an International Lunar Research Park and some experimental data we just won't be able to predict financial costs...and companies want to know what the bottom line is.
How could the heat be contained?
For the highest temperature melts the container can be the same substance as the melt, just cooled on the outside. Such a container would typically be supported by the cooling coils and have a rather thick layer of material being melted to act as the structure of the crucible. The thickness of the material reduces the thermal flux and so reduces the cooling expense. The thickness is also necessary for strength, since materials near their melting points are weak. A disadvantage with such a thick container is that it usually must remain stationary rather than being tilted to pour. A dipper can be used to transfer material if needed. The dipper is insulated by the layer of material that solidifies on its surface as soon as it is dipped in, and is in contact with the melt only a short time. Farred 19:20, 1 May 2012 (UTC)
We have articles related to this discussion. There are Lunar Aluminium Production and FFC Cambridge Process. There is some trade off between using more imports to get things working quicker and making more things locally and taking life times to do it. Whatever we do there will need to be some soft landed exploration missions to get more ground truth and some process demonstration missions. Most of what needs demonstrating can be done on Earth in simulated lunar conditions, but getting good estimates of cost will require some on Luna demonstrations. There is some carbon on Luna, but a successful colony will seek imports. It will always be expensive.
By the way, thanks for your contributions and welcome aboard!
- Farred 21:23, 1 May 2012 (UTC)
We find that a mining machine that can go through six million tons of regolith per year and heat it up to 700 C. will obtain 109 tons of H2O, 201 tons of H2, 16.5 tons of N2, 56 tons of CO2, 63 tons of CO, 53 tons of CH4, 102 tons of He4 and 33 kg. of He3. That's 82 tons of carbon contained in CO2, CO and CH4. If 201 tons of H2 is combined with 1600 tons of O2 that's another 1800 tons of H2O. There is also evidence of carbon compounds in polar ices....as for the feasibility of getting that ice i can only wonder. It seems we can obtain some significant amounts of carbon but we will still need to recycle it. If lunar industry ever grows to the point at which millions of tons of metals are produced every year for a space based solar power satellite building project we will need more carbon and other elements like nitrogen. Not only will carbon be valuable for atmospheres, steel and industrial processes but it would help to have some industrial plastics and silicones.
Carbide Versus Corundum on the Moon
According to your figures above, carbon would be present in typical regolith at a concentration of about 14 parts per million. That does not qualify as an ore of carbon but we would be recovering it as a byproduct. Thank God it is there for the many uses for which it would be difficult to replace. Whether or not it would be worth while to import carbon from Ceres or Mars would depend upon many factors that I only guess at. The average composition of samples from different Apollo missions ranged between 17.4% and 10.3% aluminum oxide according to PERMANENT or 9.2 to 5.5 percent aluminum. So, for abrasives corundum ought to have a significant economic advantage over carbides.
Artificial corundum is made by melting and recrystallizing aluminum oxide. The broken bits are what is abrasive. Variations in the purity of the alumina result in variations in the micro hardness of the grit. Silica should be particularly excluded from artificial corundum but requirements are not so difficult as in producing artificial ruby for lasers. According to The Great Soviet Encyclopedia, 3rd Edition (1970-1979) artificial corundum makes up roughly 80 percent of all abrasive production. See THE FREE DICTIONARY. Corundum can have a hardness of 9 Mohs. So it should be sufficient for abrading cast basalt, iron and steel. Farred 04:13, 2 May 2012 (UTC)
Based on Apollo data there are 80ppm to 200ppm carbon in the regolith. The Mark 3 volatiles miner doesn't recover 100% of the carbon because it only heats the regolith to 700 C. to avoid sulfuric acid formation but this is hot enough to get most of the hydrogen and helium.
Corundum would certainly be a better choice for abrasives than carbides.
No individual ownership of articles on Lunarpedia
I see that you have added an article [[Sand casting]] to Lunarpedia. You identify yourself by name as the author at the start of the article. That is not the way wikis are set up to operate. Wikis are intended to be collaborative works in which the individual contributors are identified by their name and a record of their contribution in the history section but the article is attributed to the wiki itself not any particular author. The main page declares that all articles in the main namespace are released to the public domain. Articles are generally available for anyone to add to and improve as they see fit. If you want to be the sole author of an article, excluding others from editing it, then you should not post it on Lunarpedia. Posting links to a website where you do exclude others from editing is proper, if the website deals with moon settlement topics or technical topics related to moon settlement articles. I hope to avoid any misunderstanding. Talk pages, like this one, are reserved for identifying the individual contributors by name and discussing Lunarpedia. - Farred 09:49, 2 May 2012 (UTC)
I stand corrected
I removed my name from that article. I still have much to learn about posting on this Wiki.