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Enthalpy

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  1. For copper, electrorefining needs a minimum of 0.5V to start (so the theories are oversimplified), and industries operate around 2V for decent speed. Monovalent ions consume then 0.2MJ/mol of electricity, an expensive energy that makes a significant fraction of copper cost, less so for silver. The evaporation of silver costs 0.3MJ/mol of much cheaper energy: heat. I found quickly the compared costs of energy for households, not industries. In €/MWh, including VAT. 150 Electricity (in France! Germany rather 300!) 100 Heating fuel 86 Natural gas 43 Logs 35 Wood chips xx Sunheat And a price for natural gas "at city gate", it's 4usd/1000cuft or variable 6usd/1000cuft for "industrial price" eia.gov and eia.gov 1000cuft contain 1156mol whose lower heating power is 242+394-75=561kJ/mol so 6usd buy 649MJ=0.18MWh. Electricity in industrial amount costs rather 0.08€/kWh: statista.com 80 Electricity, industry amount 30 Natural gas, industry amount The metal condensation heat is available at a lesser temperature than is needed to evaporate it. A kind of heat pump would save much heat but isn't trivial to build at such temperatures. After JC's comment, I also suggested the separation of Zn from CuZn, where distillation advantageously leaves all element in metallic form. Different aspect.
  2. The effect of atom size matching between metal solute and solvent is long known. One example there (I access only the abstract) sciencedirect.com They measured the solubility of Ta and W in lanthanides at varied temperatures, and: "The solubility of [small] Ta and W vary inversely with the atom size of the lanthanide solvent." "W is a much better crucible material for the lanthanides than Ta" There too I access only the abstract: aip.scitation.org "Mol/mol solubility of W in Ce is 2ppm at 800°C, increasing to 240ppm at 1540°C." There on page 25: ameslab.gov "Sm, Eu, Yb and Tm can be melted in Ta crucible without contamination" (1815K for Tm) Also, they use metallic Ca to reduce R from RCl3, and later Ca is evaporated away from R. This gives me hope that, as I suggested previously Some refractory materials let a distillation apparatus separate the most volatile lanthanides. Liquid Ca or other can selectively dissolve the biggest (smallest too?) lanthanides and be later evaporated away.
  3. The Moon has no significant atmospheric pressure, so the equilibrium would tell that ice sublimes. But this equilibrium can take very long to achieve if the ice is cold. Comets can keep ice for billions of years and release vapour only when passing nearer to the Sun. This leaves open the question of the origin of this ice on the Moon, since we don't find significant free water elsewhere. I could imagine - with no figures to support nor invalidate it - that the solar wind brings hydrogen that somehow reacts with local oxygen, say from silicates. The situation is quite different on Mars, which has an atmosphere with significant pressure. Water vapour in the atmosphere, even if in tiny proportion, can freeze on a soil cold enough, and sublime when the ground warms up. Very similar to Earth, just colder and with less vapour pressure.
  4. The electron affinity does count, but not in a simple way. For instance the dipole moment of CO is small with 0.122D. So while it's a matter of charge and distance, predictions are difficult. Experiment tells. Heavy software that computes molecular orbitals from first principles has a chance. I wouldn't trust too much estimation software that supposes additive rules on molecule subsets.
  5. I suggested to replace Picea abies (spruce) with lighter Paulownia tomentosa (kiri) at the table of bowed instruments too, here on March 05, 2019 Koto luthiers reportedly don't get their Paulownia tomentosa from a company that selects the trees and quarter-saws them. They season the pieces in 2 years and carve plates along the L and T directions. Though, the length-to-width ratio of the violin family fits the L and R directions from quarter cuts. To balance the instrument, the back should be lightened too. Presently of Acer pseudoplatanus (sycamore), it sounds less strongly than the table if I read properly violin frequency responses, so it would need a bigger change than the table. Replacing Acer pseudoplatanus with Picea abies at the back would change more than Paulownia tomentosa does at the table. For instance some Pinus have intermediate properties, but they are not available in music instrument quality. Thinner Acer pseudoplatanus can be stiffened by a bass bar or bracings that pass under the sound post. The replacements must keep the resonant frequencies, not the thicknesses nor the mass. The frequencies depend on EL and on ER, not so simple. Maybe two different thickness ratios can be computed, from the ratios in EL, ER and rho between the materials, and some mean value used for a first prototype. The bass bar should change like the table; bending it would matter more with Paulownia tomentosa. The width could be kept and the height scaled like the table thickness. The anisotropic stiffnesses act differently on the bass bar, so the height needs further tuning. Replacing only the table and bass bar in a first prototype would already tell the effect and whether the back needs improvement too. Marc Schaefer, aka Enthalpy
  6. An ascending gas jet can levitate an alloy drop to evaporate the more volatile metals without any polluting contact. If for instance the drops are 10mm3 small on a 10mm×10mm pattern, then 1m2 can process 0.5-1kg at once. A robot would place and possibly pick the samples. Hot argon is one natural choice to levitate and heat the droplets. It would carry away the vapour of the more volatile metal. The nozzles must resist the temperature but don't risk to dissolve in the melt. The heat source can be cheaper than electricity. Maybe the condensation heat coud be recycled, but being available at a lower temperature than evaporation needs, it would take some heat pump equivalent, which isn't trivial at these temperatures. Smooth evaporation seems preferable to boiling. The carrier gas pressure shall realize that. Marc Schaefer, aka Enthalpy
  7. Levitation melting lifts the melt from the crucible to avoid pollution at high temperature. Patented a century ago, it's often a demonstrator or a research tool, but one team melts 0.5kg for instance to cast titanium impellers for turbochargers 01336015 at hal.archives-ouvertes.fr pdfs.semanticscholar.org and one company melts 500kg 01333975 at hal.archives-ouvertes.fr Most designs are very crude: no magnetic material, hence coils of small section, cooling fluid parallel to the current, wires too wide for the frequency. An expert magnetic designer should improve that. The 0.5kg team claims with citation that an axisymmetric field can't levitate metal at its centre, which has to hold by capillarity. To my understanding, the outlet at the centre prohibits coils there, and this is what reduces the force. A temperature not limited by the crucible would let evaporate less volatile metals. Density would prevent boiling at depth: 10mm of 10000kg/m3 melt add already 1kPa. Possibly metal would evaporate from the lower faces too because the electromagnetic pressure needs a Kelvin effect depth to build up, but any layer of the volatile metal condensed in the magnetic field would evaporate quickly. So I suppose distillation accepts coils up to the centre in a simpler apparatus, shallow and wide. Once the evaporation is finished, the melt can levitate and cool in a lower frequency induction before landing. Many small melts, down to individual drops, could be better than one big to accelerate the evaporation and save electricity. Very small melts could evaporate more quietly, without boiling. Marc Schaefer, aka Enthalpy
  8. From Wiki and interpolating: K for K for K for K for K for K for 1Pa 10Pa 100Pa 1kPa 10kPa 100kPa ==================================================== 610 670 750 852 990 1185 Zn 882 997 1097 1412 1660 2027 Pb 1283 1413 1575 1782 2055 Ag 1509 1661 1850 2089 2404 Cu 1497 1657 1855 2107 2438 Sn 1783 1950 2154 2410 2741 Ni ==================================================== Zn is easily evaporated from brass CuZn. At 1356K to melt Cu, Zn has roughly 750kPa and Cu 0.1Pa, clear case with one crucible. Even a few per-cent Pb in brass (664Pa) separate easily from both, optionally in two steps for Pb-Cu. Pb is easily evaporated from Sn63 Pb37. At 1660K for 10kPa Pb, Sn has 10Pa. Leaving a bit over 0.1% impurity in each takes two steps, so crucibles suffice. Ag could be recovered from Sn95.9 Ag3.8 Cu0.7 solder where it makes half the value. At 1782K that give 1kPa Ag vapour pressure, Sn has 43Pa and Cu 44Pa. The pressure ratio 4/100 is also the initial composition ratio, making few steps inefficient. A distillation column is better. Ag could be recovered from Sn61 Pb37 Ag2 solder. At 1660K for 10kPa Pb, Ag has 257Pa so Pb would separate first with very few stages, but then the separation of Ag from Sn needs a distillation column anyway. Cu and Ni can be separated by a distillation column or several crucible steps. This needs high temperatures. Cu and Sn shouldn't be separated that way. With Pb, Ag, Cu, Sn, Ni more noble than Mg and Al, the ceramics MgO and Al2O3 have chances to resist the molten alloys and possibly molten Zn. Suggested operating temperatures in air are 2500K for MgO, 1800-2100K for Al2O3, with big variations. Marc Schaefer, aka Enthalpy Hi JC, thanks for your interest, I'll come back!
  9. Hello everybody! Pure silver is too soft and often alloyed to make objects. For instance sterling silver often contains 92.5% Ag, plus Cu, possibly Ni and others. Recycling may need to separate Ag from cheaper alloy elements. I propose to distill Ag away from Cu, Ni and others. The 1atm boiling points spread nicely: Ag 2162°C – Cu 2927°C – Ni 2913°C Reduced pressure would make at least the temperature compatible with ceramics like MgO, ZrO2 and maybe Al2O3. Distillation would take far less energy than electrorefining. One step, without a distillation tower, seems to suffice. Marc Schaefer, aka Enthalpy
  10. Even if I completely botched the explanation based on molar volumes, but some melt achieves to dissolve selectively some of the lanthanides from mischmetal powder, I'll be happy of course. The molar volumes could be computed, but this is already done at webelements.com The ratios of molar volumes are 1.4 = 18.3/13.0 for Pb/Li, they mix 1.6 = 16.3/10.2 for Sn/Au and Sn/Ag, dissolve 2.3 = 16.3/7.1 for Sn/Cu, no or little dissolution The situations aren't quite the same because Pb and Li have melting points (601K and 454K) closer to an other, while I wonder about "dissolution" for Au, Ag, Cu which are far below their melting point (around 1300K) in just molten Sn-Pb (456K).
  11. Most electrical engineers have seen soldering tips eroded over time. Up to now I believed it resulted from the acidity of the flux. If copper in SnPb improves that, fine! But why don't do they it all the time since Cu is cheaper than Sn, instead of selling "neutral flux"? My point is, if you weld with Sn-Pb once on 5µm Au or Ag, the 5µm are gone immediately. If you weld 7 times on 35µm Cu, the Cu is still there. So Cu is observably less soluble in Sn-Pb, or less quickly, than Ag and Au. Yes, an attempt as tritium regenerator blankets for tokamaks. I rang the bell about the pollution by these blankets. I guess solubility rules address only small solute concentrations. Around 1:1 mole, it's no more a matter of solvent and solute and more of intermetallics. Yes! The sole reason for my ramblings is that I don't have the means to experiment.
  12. Eu, Yb, La have a molar volume distinctly bigger than the other lanthanides. Could this serve to scoop them from the mischmetal? cm3 ========= Sr 33.94 Ba 38.16 K 45.94 ========= Er 18.46 ... Ce 20.69 La 22.39 Yb 24.84 Eu 28.97 ========= Ligands make complexes selectively with preferred ion sizes. I bet this is already done for lanthanides. Alternately, I suggest the selective dissolution of Eu, then Yb, later La, in a molten metal, if there is such a selectivity. Still stretching the previous logic, the solvent would be a metal with huge molar volume: Sr, Ba, K and few others, at a temperature where lanthanides are little soluble. Then, Eu would dissolve preferentially from mischmetal powder. With more heat, Yb would be scooped, and even more heat would extract La. Extraction could evaporate the solvent. Moving the mischmetal and the solvent in opposite directions would extract much of the target element but evaporate only well loaded solvent. Maybe. And playing with matches, the big way. Marc Schaefer, aka Enthalpy
  13. Ramblings about the solubility of metals in melts. Ag and Au dissolve in molten Sn63Pb37 but Cu doesn't. The difficulty to separate atoms from the solid metal, represented by the vapour pressure, is one factor. The temperature for 1kPa is 1782K for Ag, 2281K for Au, 2089K for Cu, so there are other factors. The strength with which the melt incorporates foreign metal atoms is the other factor. Cu, Ag and Au have similar valences, so this isn't the reason. But the molar volumes can explain these metal solubilities. Nothing revolutionary to metallurgy. cm3 ========= Cu 7.11 Ag 10.27 Au 10.21 ========= Sn 16.29 Pb 18.26 ========= Sn and Pb being much bulkier, they dissolve Ag and Au a bit, and the smaller Cu less. So to build a distillation tower, what metal would not dissolve in molten mischmetal? Refractory metals are small and lanthanides rather big: cm3 ========= Re 8.86 W 9.47 Ta 10.85 ========= Er 18.46 ... La 22.39 Yb 24.84 Eu 28.97 ========= This gives some hope that they dissolve little (or slowly). If following that stretched logic, W would dissolve less than Ta, and expensive Re even less. Marc Schaefer, aka Enthalpy
  14. Nb and Ta too are reportedly difficult to separate, so a centrifuge might help too. A mole of Nb weighs 93g, Ta 181g, so TaCl5 is 88g heavier than NbCl5, 30* easier than uranium enrichment. Isotopes let that fluctuate by +-5g. After the centrifuge is built, it can optionally spend some time separating 35Cl from 37Cl to save time separating Nb from Ta. NbCl5 melts at +205°C and boils at +248°C under 1atm, TaCl5 at +216°C and +239°C (decomp). A tube of 2000MPa Maraging steel rotating at 416m/s makes 7.7kJ/mol difference in the kinetic energy. At arbitrary +127°C=400K, that's 2.3RT, so the metals are pure in half a dozen steps, or 1 or 2 steps with tubes of graphite fibres. The oxides mix is reduced, Cl2 or HCl give the mix of pentachlorides, centrifuges separate the pentachlorides before reduction. No fluorine needed. I can't tell whether the process is globally advantageous. Marc Schaefer, aka Enthalpy
  15. The more refactive lanthanides would distill under lower pressure to spare the column's materials. Beginning here with terbium, all data from Wiki: 10Pa 100Pa 1kPa mp Element K K K K =================================================== 1979 2201 2505 1629 65 Tb terbium 1973 2227 2571 1208 59 Pr praseodymium 2028 2267 2573 1585 64 Gd gadolinium 2103 2346 2653 1925 71 Lu lutetium 2194 2442 2754 1068 58 Ce cerium 2208 2458 2772 1193 57 La lanthanum =================================================== Tb and Pr spread more at 1kPa, Pr and Gd spread less badly at 10Pa and 100Pa, Ce and La remain close. The process speed must be a limit. Marc Schaefer, aka Enthalpy Hi JC, thanks for your interest! I have data about Nb, Ta, W, Re creep at heat and could have a look. In the low-pressure distillation tower, the trays don't feel the atmospheric pressure. Several thin cylinders of refractory material can enclose the trays as a heat insulation that limits the condensation, enclosed in a strong cylinder that operates at a lower temperature. This may need an additional gas like argon. Marc Schaefer, aka Enthalpy
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