| As stated above, only 24 tons of carbon will be needed to make 2400 tons of 1% carbon steel. That's a fairly high carbon content for steel. At 0.33% carbon, we would need only 8 tons of carbon per year. To protect the Moon's natural carbon resources, could we justify upporting 8 tons of carbon per year to the Moon even at $10,000 to $30,000 per pound or $160 million to $480 million??? Perhaps. Mining volatiles would be cheaper. In ten years we would produce 24,000 tons of steel. How much is that? Well, the Eiffel Tower's iron structure amasses 7300 tons. So we are talking about three Eiffel Towers worth of steel in 10 years!!! That's plenty. See:: |
| BLISTER STEEL by David A. Dietzler, 2007 Lunar Iron Fines Iron in pure form is not very useful. It could be used for habitat if the plates are thick, but it is to soft for any kind of machine part like gears, chains, drive shafts, axles, etc. These must be made of hard steel. Before we can have large scale ore smelting by Direct Reduction and CO recycling for iron and steel on the Moon we can get lots of iron from molten silicate electrolysis and iron grains separated magnetically from mare regolith. Regolith is 0.5% iron grains by mass by some estimates and this iron contains some nickel and cobalt because it is of meteoric origin (1). A more recent report states that iron fines are present at about 0.15% (2). We will use the latter figure, although there may be regions in the mare where iron fines are more abundant. Some of this iron is in elemental form and some is combined with glass in particles called agglutinates. Magnetic extraction will remove the agglutinates as well as the free iron. Grinding, sieving and further magnetic refining will be required to break up the agglutinates and separate failry pure iron grains. A Simple Way to Convert Iron to Steel This iron can be converted to steel by heating it with carbon for several days. Steel obtained this way is called blister steel because blisters form in it when gases escape from the coke; however, on the Moon we will by using very pure carbon instead of coke so blisters might not form. Blister steel can then be melted, mixed with flux (CaO and possibly MgO) that removes impurities like sulfur and silica (left over from the agglutinate glass that might still contaminate some of the iron) to get a high quality steel. So we will be able to obtain steel before we are able to build blast furnaces and CO2 recycling systems for really large scale steel making on the order of several hundred thousand tons per year for SPS, helium 3 mining machines and lunar populations and tourist resorts. Iron from solar or electric furnaces that the beneficiated iron grains are melted in will be poured out in trenches about a foot wide and 15 feet long to get slabs a few inches thick. These slabs will then be hammered to drive out any silica contaminants and cold rolled to strips less than an inch thick. A box made of ceramic blocks from magma electrolysis that melt about about 1500 C. will be constructed and embanked with regolith. A solid ceramic lid with iron reinforcing bars and a carbon black surface will cover the box. Alternating layers of iron strips and carbon dust will be placed in the box. Solar energy will be applied to heat it up until the iron is red hot at about 1100 degrees C. Or, electric heat will be used. |
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| At a concentration of 0.15% there are about 4800 tons of iron grains in 3.2 million tons of regolith that can be removed magnetically. Let us say simply that we want 2400 tons of steel per year. That would represent a reasonable 50% recovery rate. To make 2400 tons of 1% carbon medium steel we will only need 24 tons of carbon, so we will not starve our biospheres for CO2. Then we need 200 tons per month or Sunth if you like that term. Two hundred tons of iron will have a volume of about 5m x 5m x 1m or about 16ft x 16ft x 3.2ft So we would need a chamber about 17ft wide x 17ft long x 3 or 4 ft deep to allow expansion of the iron and have room for the thin carbon dust layers between the strips of pure iron. It would be wiser to make about ten smaller carburizing boxes about 2.5 cubic meters volume each in case one cracks. Induction heating could be used to heat the iron sheets until they are red hot and the carbon will be slowly absorbed. It will take 7 to 10 days to convert iron to steel this way. Thus, more sophisticated and more productive methods of smelting iron and steel will someday be called for on the Moon. See: The Damascus Project A 40 MW thermal power tower can concentrate the equivalent of 3.4 million BTUs or about 106,000 kilocalories in one hour, enough to heat almost a ton of iron from zero C. to 1000 deg. C in one hour. It might be possible to heat carburizing boxes with motlen salt pipes from power towers after more development on the Moon. Some complex engineering regarding heat flows and stresses is called for to make this seemingly simple system work effectively. Don't want the ceramic boxes to crack! |
| LINKS TO MORE INFORMATION ABOUT BLISTER STEEL http://en.wikipedia.org/wiki/Cementation_process http://www.tilthammer.com/timeworks/steel.html http://www.channel4.com/history/microsites/T/timeteam/2004_sheff_steel.html |
| It seems reasonable that we could obtain 2400 tons of iron in the form of fines containing a few percent nickel from 250 acres (1 square km.) mined to a depth of one and a half meters per year. This would be about three million tons of regolith. At 0.15% iron fines 4800 tons of iron would be present, but mining recovery rates never equal 100%.. So 2400 tons is a safe bet. Even so, some mare regions may contain more iron fines. Major objections have been raised by those who feel that steel making will deprive Moon base biospheres of precious carbon that is so rare on the Moon. |
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| Note: Calcium aluminate can be used as flux in the steel cleaning furnace. It could be likened to a ladle furnace. Only 10-15 kg of CaAl2O4 per ton of steel might be needed. See: http://www.fuzing.com/vli/002021123289/HOT_-Calcium-Aluminate-For-Refined-Steel_making-Fused-Type Calcium aluminate might be obtained by solar thermal decomposition of anorthostie. See: Flux |
| 1) Phinney et al., 1977. http://www.islandone.org/MMSG/aasm/AASM5E.html#5e 2)William N. Agosto "Lunar Beneficiation" http://www.belmont.k12.ca.us/ralston/programs/itech/ SpaceSettlement/spaceresvol3/lunarben1b.htm |
| What would all this steel be used for? Heavy frames for rolling mills, tube steel supports for solar furnace reflectors, frames and coverings for garages and unpressurized work areas covered with regolith for radiation and thermal protection, pressurized (3psi) work modules, polished sheet metal reflectors for solar furnaces, machine tools and mountings, vehicle chassis by hot extrusion of frame parts, railway tracks, mass driver coil mountings, pipes, compressors, etc. |
| Mining and Beneficiation of Regolith for Iron Fines Mining Dr. Gerald Kulcinski of the U of Wisconsin and his associates have designed a lunar volatiles miner that can excavate one square kilometer (250 acres to us farmer types) of regolith to a depth of three meters in one year's time. This is about six million tons. This Mark 3 miner will amass 10 tons empty, use 350 kWe, and extract 1650 kg. of volatiles every 24 hours. One of these machines could mine 82 tons of carbon in one year. It will mine over 1000 tons of regolith in an hour. Rather amazing. I suggest that a similar and even simpler mining tractor could harvest vast amounts of free iron fines with a magnetic separator and when fully loaded return to base and offload the iron fines for further beneficiation. An iron fines miner would not even need to capture large amounts of beamed solar energy as will the Mark 3 volatiles miner to heat regolith and release volatiles. see: http://fti.neep.wisc.edu/pdf/wcsar9311-2.pdf and http://www.nasa-academy.org/soffen/travelgrant/gadja.pdf Beneficiation How do we extract enough iron particles to produce 200 tons of iron and steel per lunar dayspan (328 hours) and what will this equipment mass be? Dr. W.N. Agosto proposed a system that used screening, low intensity magnetic separators (1000 gauss), an impact grinder to break up agglutinates, and a second magnetic separation in the same device used for the first magnetic separation. The input would be 6.8 tons per hour and output 10.8 kg/hr of iron particals. Equipment mass for two magnetic separators would be 3.5 tons and for one grinder, screens and a radiator another 0.5 tons for a total of 4 tons. An 8kW power source would energize these devices (1). That's about as much electricity as could be obtained from merely 80 square meters of 10% efficient solar panels. This set up would produce about 20 kg. of iron per hour. Agosto suggested 10 hr. shifts for the machines(2). What if we could run the machines for 300 hours out of 328 hours per lunar dayspan? We could produce 6000 kg. or 6 tons of iron fines per dayspan. To produce 200 tons we would need, by simple extrapolation, 33 times as much equipment mass or 132 tons (33x4t grinder, screens, separators). This might be too much to upport at first given the costs of rocket transport. Perhaps we could produce 12 tons of iron fines and steel every dayspan or 144 tons in one year with 8 tons of these devices or 12 tons with backups. With the right machine tools (mass?) we could fabricate the 132 tons of magnetic separators, screens and grinders on the Moon at a small manned and robotic base. Some of the FeNi particals could be put thru powder metal sintering or electroforming or perhaps even 3D laser additive manufacturing devices to make parts. I would imagine that machine tools would include plastic forms for making sand molds in mare regolith to cast steel, arc welders, electron beam welders, drill presses, a small lathe to make screws and bolts, grinders, parts for a small rolling mill with heavy frame made by sand cast steel and bolted to a heavy cast basalt slab base, parts for a milling machine, etc. Even the machine tools would be partly made on the Moon. A small carburizing box for producing 12 tons of blister steel (crucible steel) every 328 hour dayspan period could be made of cast basalt blocks from mare regolith melted in a small solar furnace. Thin film solar panels would be transported from Earth. The iron in the carburizing box could be heated by induction. A small steel fluxing box might be made of cast basalt blocks with an upported refractory lining, small steel ladle and small slag ladle. Calcium oxide and calcium aluminate flux would also be needed. Perhaps flux could be produced in solar furnaces that decompose anorthite. These furnaces would be made of casat basalt and ceramic blocks from a small molten silicate electrolysis unit in addition to foil reflectors. So it seems we could reach a stage of development on the Moon within a year that would enable us to produce 24,000 tons of steel in ten more years by clever selection of parts for machines, tools and other items transported to the Moon and use of lunar materials without incurring enormous costs for rocket transport. 1) H. H. Koelle "Pilot Production at the Moonbase 2015" pg. 11 <http://www.highfrontier.org/Archive/Jt/Koelle%20PILOT%20PRODUCTION%20at%20the%20 MOONBASE%202015.pdf> 2) ditto pg. 12 |
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| 1) Solar wind implanted carbon must be harvested by flushing with an inert gas or by heating regolith. Heating will cause carbon to react with O2 in minerals to form CO and CO2. This must be converted to methane in Sabatier reactors and the CH4 pyrolized to get pure carbon black. 2) Iron fines extracted magnetically from mare regolith will be melted in solar or electric furnaces and poured into sand molds to form slabs. These slabs will then be rolled into sheets of iron. |
| 3) Sheets of iron with carbon dust laid between them will be induction heated until cherry red, about 1000 C., for 7 to 10 days. Iron will absorb carbon and become steel. |
| 4) Steel in carburizing box(es) will be allowed to cool then removed with electromagnet crane. Using multiple small carburizing boxes will allow use of smaller robot crane, in addition to more reliable production in case a box cracks. The steel will be placed in a fluxing box, or the carburizing boxes if equipped with tap tubes could be used if we remove the steel, pour some flux in the bottom of the box, then reinsert the steel. Flux will float up thru the motlen steel and remove impurities of silica and sulfur. The induction heating coil will set up eddy currents in the steel and mix the flux thoroughly. Flux will consist of MgO, CaO and CaAl2O4 obtained by solar thermal decomposition of anorthositic highland regolith. |
| Afterthoughts: A) Plain iron might make a better base for heavy machines than cast basalt, as it will stand up to vibration better. Cast basalt might crack. Iron could come from molten silicate electrolysis units. Iron might make a better heavy machine frame than steel because it is more flexible. Cast iron contains flakes and nodules of carbon that act as cushioning to give cast iron good compressive strength and vibration resistance; however, cast iron contains about ten times as much carbon as steel (2% to 4%), so we will have to try pure iron, a soft ductile metal. It can't take as much compression as cast iron, but in low lunar G this might not be a problem. B) Sand casting steel on the Moon has never been tried. Lunar regolith is not green sand, so we are in the dark when it comes to using it for sand castings. We will have to screen out the finest particles and get the coarser ones. Then we need to wet the sand to make it hold a shape so we will need to work in some kind of partially pressurized chamber. Perhaps an inflateable polymer work chamber will suffice as long as no molten metal is spilled in there. We might want to cover the floor with a foot of regolith just in case. Perhaps we can make sand cores by mixing the screened and sized regolith with sodium silicate. Even so, we don't know how regolith consisting of sharp particles that have never endured wind and water erosion like the rounded sand particles of Earth will take up water, mix with sodium silicate, hold shape, etc. This calls for experimentation. Many of our lunar industrial proposals involve assumptions. In this case the assumption that we can bootstrap up equipment on the Moon by sand casting in regolith. If we really want to get down to "square one" on this we must experiment with regolith. Green volcanic glass ground if necessary, screened and sized might make an excellent sand for casting. It would be nice to have tons of the stuff to experiment with! A lunar research base must proceed all other industrial actions on the Moon or we could find ourselves "in over our heads." Fools rush in. And don't forget another engineer's saying, "The devil is in the details." |