Electrical Conductors
| Element | Resistivity @ 20°C | Density (~ r.t.) | Availability | Highland | Lowland |
| Silver | 15.87 nΩ·m | 10.490 g·cm−3 | Unknown | Unknown | Unknown |
| Copper | 16.78 nΩ·m | 8.960 g·cm−3 | Unknown | Unknown | Unknown |
| Gold | 22.14 nΩ·m | 19.300 g·cm−3 | Unknown | Unknown | Unknown |
| Aluminum | 26.50 nΩ·m | 2.700 g·cm−3 | Yes | 133,000 | 69,700 |
| Calcium | 39.1 nΩ·m | 1.6 g·cm−3 | Yes | 107,000 | 78,000 |
| Magnesium | 43.90 nΩ·m | 1.738 g·cm−3 | Yes | 45,500 | 57,600 |
| Sodium | 47.70 nΩ·m | 0.968 g·cm−3 | Yes | 3,100 | 2,900 |
| Potassium | needs ref ~70.00 nΩ·m | 0.890 g·cm−3 | Yes | 800 | 1,100 |
| Iron | 96.10 nΩ·m | 7.150 g·cm−3 | Yes | 48,700 | 132,000 |
| Chromium | 125.00 nΩ·m | 7.860 g·cm−3 | Yes | 850 | 2,600 |
| Titanium | 420.00 nΩ·m | 4.506 g·cm−3 | Yes | 3,100 | 31,000 |
| Manganese | 1440.00 nΩ·m | 7.210 g·cm−3 | Yes | 675 | 1,700 |
| Lower # => better | r.t. = room temperature | ppm by weight | ppm by weight |
Contents
Silver
Silver is the best known conductor, but in an oxygen rich environment it tarnishes. Silver is used in specialized equipment, such as satellites, and as a thin plating to mitigate skin effect losses at high frequencies.
In the Lunar outdoors, in a vacuum where it can't tarnish, silver would be a marginally better, if heavier, conductor than copper, and a much better, but much heavier, conductor than aluminum.
Silver is not known to be available on the Moon. If silver is absolutely required for some application, it might need to be imported, but for electrical conduction, aluminum and sodium can substitute. On the other hand, silver is not known to be absent from the moon. There could be considerable minable reserves that have not been found because little more has been done than imaging the surface at various wavelengths and particle energies. Mines could one day extend to a depth of 20 kilometers beneath the moon's surface before the moon's weak gravity would cause hydrostatic pressures that would cause a mine to collapse. It will be a long time before anyone can say there is no minable silver on the moon if that is the case.
Copper
As a general conductor copper is the most commonly used on Earth because it's cheap, reasonably flexible, reasonably light and the 2nd best conductor and the better per unit weight than silver. Copper allows for ease of soldered and crimped/clamped connections. It corrodes worse than silver, this is usually seen in older wires that have turned green.
Copper is not known to be available on the Moon.
Gold
Gold is not an especially good conductor at all, though it is better than aluminum but not per unit weight due to its much higher density. It is very expensive, but compared to the cost of transport to the Moon from Earth, the cost is not significant. Gold is usually only used as a conductor in very specialized applications such as very fine wires like those used to wire bond integrated circuits to their lead frames.
A more important everyday use of Gold is in connectors
For connectors gold reigns supreme because it lowers contact resistence. This results because:
- 1. It doesn't tarnish (important on Earth, important indoors on Luna)
- 2. It is soft, so you can make the connectors tight and they dig into each other forming a good connection.
Gold is not known to be available on the Moon.
Aluminum
Main article Aluminium
Aluminum is commonly used as a conductor here on earth, in fact you use it every day without realizing it. High Tension cables have a steel core and an aluminum outer layer. It's used because losses are fairly low at 110kV and the weight of the cable and cost of the towers is important. Steel cored aluminum cable allows a longer span and is the most common form of aluminum wire used for HT lines on Earth.
Given that the Moon lacks of copper, aluminium will become the base of all the electronics on the Moon. In some places on Earth it is illegal to use aluminum for general wiring mostly as a result of fire risk caused by contractors using too light a gauge in the past. The thin aluminum oxide coating makes connections unreliable and occasionally hot.
Other uses will include the construction of structures, solar power systems and relay satellites.
- "The main disadvantage of aluminium on the Moon is that it expands and contracts with temperature much more than most common metals, which could be an issue with large exposed structures on the Moon which are exposed to the extreme day/night temperature variations, or equipment which operates over a wide temperature range." -permanent.com [1]
Aluminium on Earth corrodes reacting with oxygen. The corrosion does not go rapidly, it only forms a thin layer on the surfaces exposed. The Alumina (aluminium oxide) layer then protects the Aluminium below from corrosion. On the moon wont be any corrosion outdoors.
Aluminum is abundant on the highlands (there is aluminium in the Maria as well) in form of Anorthite contained in the Anorthosite.
Calcium
A calcium wire about 2.5 times the cross sectional area of a copper wire would have the same resistance per meter. Copper is 5.8 times as dense as calcium so a copper wire carrying the same current as a calcium wire at the same voltage would weigh twice as much per meter. At elevated temperatures calcium burns in air producing the nitride and oxide. It reacts with water yielding hydrogen. So it is unsuitable as an electrical conductor on Earth. On Luna in a vacuum, inert atmosphere or reducing atmosphere it could serve as an electrical conductor.
Magnesium
Magnesium is not an especially good conductor, being less conductive than aluminum but it is lighter. It has some other major drawbacks which make it completely unsuitable for use in electrical installations. This metal burns in oxygen, or nitrogen (forming magnesium nitride) or even carbon-dioxide (forming magnesium oxide and carbon). Once burning, it's very difficult to extinguish. Magnesium also reacts with water.
This is a highly flammable metal, but while it is easy to ignite when powdered or shaved into thin strips, it is difficult to ignite in mass or bulk.
There are many other uses for magnesium but it is completely unsuitable for normal electrical wiring on Earth or in oxygen atmospheres. On Luna in a vacuum, inert atmosphere or reducing atmosphere it could serve as an electrical conductor.
A possible fuse-wire material?
Magnesium is readily available on the Moon.
Sodium
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Sodium is about one half as good an electrical conductor as Aluminum by cross sectional area. However, it is more conductive per unit weight. It is so abundant on the Moon that it is expected to be a significant by-product of the production of Volatiles. At room temperature it is a soft shiny metal and is easily worked.
It melts at a very low temperature (98 C) which can be both an advantage and a limitation. In use, care must be taken not to overheat it, but even this can be an advantage. Aluminum, in contrast, requires a very large amount of high quality energy to smelt.
On Earth, Sodium has been used as an electrical conductor only in unusual circumstances. The primary problems are that it reacts violently with oxygen and water, even the water in human skin. At elevated temperature, sodium burns in air near its boiling point at about 883 degrees celsius. Even at room temperature, sodium reacts with oxygen to form a nonconductive oxide. This is not a problem in external applications on the Moon as there is no oxygen or water at all. Indoors, the oxygen required by people would render wire made of pure sodium useless.
However, a patent is pending for a safe sodium wire that protects the sodium from the environment and furthermore has a number of safety features that prevent and extinguish fire. Additionally, the new wire is designed to operate even when the sodium is in the liquid state, a useful feature in a lunar environment where the lack of heat rejection can cause temperatures to climb above sodium's melting point. These useful features are provided with very little additional weight. The protective wall of the wire can be made with metals that are abundant on the moon. A wire that is simply a steel tube with a sodium core should be simpler than what pending patent describes. If the tube can be drawn fine enough, molten sodium would not leak out of the tube until the steel melts.
Sodium is available on the Moon. It is also available on the earth in massive quantities in the form of inexpensive ordinary salt. Sodium would appear to be a metal to consider for lunar electrical wire. The above pending patent makes claims for terrestrial use of composite conducting wire containing sodium. However this sort of conductor has failed to be adopted in any notable quantity to date.
Potassium
The second least dense metal, after lithium. A soft solid that can be easily cut with a knife, it has a low-melting point. Freshly cut potassium is silvery in appearance, but in air a gray tarnish appears almost immediately.
Potassium must be protected from air for storage to prevent disintegration of the metal from oxide and hydroxide corrosion. Often samples are maintained under a reducing medium such as kerosene.
Like the other alkali metals, potassium reacts violently with water producing hydrogen. The reaction is notably more violent than that of lithium or sodium with water, and is sufficiently exothermic that the evolved hydrogen gas ignites. (This may only apply in an atmosphere)
Potassium compounds are Widely used in fertilizers and table salt substitutes. It is not suitable for indoor wiring use.
Potassium is available on the Moon.
Iron
Iron is widely used in many applications, not an especially good conductor, very prone to corrosion in a oxygen atmosphere.
Iron is rarely used in its pure form for anything. Railroads use steel, an iron alloy, for their tracks. Not suitable for flexible wiring, too brittle. The lower gravity on Luna may make it usable for some outdoor electric railroad applications.
Iron is abundant on the Moon. It is found in minerals such as ilmenite and as free iron bits scattered in the regolith. The free iron comes from meteorites and can be magnetically separated from the regolith.
Chromium
Not a very good electrical conductor by any means, but it does have its uses in this field. Chromium Boride (CrB) is used as a high temperature electrical conductor.
There are many other uses for this metal.
Chromium is available on the Moon. (Boron is not known to be available)
Titanium
Titanium's properties as an electrical conductor can best be described as hopeless.
There are many far more suitable uses for this metal.
Titanium is readily available on the Moon.
Manganese
Manganese is an even more hopeless electrical conductor than titanium.
There are many far more suitable uses for this metal.
Manganese is available on the Moon.
