§ 4.3: Construction Materials from Minimally Processed Bulk Lunar and Asteroidal Soils
§ 4.3.1 Overview of "lunarcrete", "astercrete", fiberglass, ceramics and glasses
Perhaps even more commonly than metals, we will use fiberglass, "lunarcrete" concretes, ceramics, glass, foamed glass and clear glasses.
These will be used to make structural beams, walls, floors, sinks, pipes, electrical insulators, waveguides on SPSs and communications antenna farms, and substrates to mount things on. Clear glass will be used for windows and solar cell covers.
Ovens, metal casting molds, and other industrial refractory needs can be satisfied by sintered calcia (CaO), silica (SiO2), magnesia (MgO), alumina (Al2O3) and titania (TiO2). Of course, these stable materials are commonly used on Earth for the same purposes, due to their great resistance to heat, oxidation (they are already fully oxidized), corrosion and abrasion. Some ceramics have low thermal expansion and are attractive for space environments where a wide range of temperatures are experienced.
Glasses and ceramics generally work well in compression but not well in tension.
Foamed glass structural beams could be reinforced with asteroidal nickel-iron steel so that they withstand a wide range of both tension and compression. However, many researchers think that steel reinforcement will usually not be necessary. For example, NASA-sponsored experiments using simulated Apollo 12 soil has produced glass-ceramics with "superior mechanical properties ... with tensile strengths in excess of 50,000 p.s.i." which can be "used as structural components of buildings in space or on the Moon."
Clear, pure silica glass (SiO2) is readily manufacturable from lunar materials, as are other clear glasses that are made of simply beneficiated lunar soil.
Free natural glass is more common on the lunar surface than on Earth. The lack of water on the Moon has preserved these glasses from their volcanic inception billions of years ago, in contrast to Earth where "devitrification" (i.e., decomposition by the chemical action of water in the environment) breaks down natural glass over the period of millions of years. Notably, lunar-derived clear glass can be made optically superior to that produced on Earth because lunar glass can be made completely "anhydrous" -- lacking in hydrogen.
"With the possibility of containerless melting plus the ready availability of ultra high vacuum, the processing of high purity glass fibers [for fiber optics, e.g., on large communications satellite platforms] can probably be achieved at much reduced costs in space..."
Using a simpler process, we can produce bulk fiberglass. "The manufacture of glass filaments is a standard, highly developed process and no problems are foreseen in transferring this process to the lunar surface or to [an orbital based facility]."
The conservative General Dynamics study designed a 4 ton fiberglass plant that would produce 750 tons per year of fiberglass assuming operation 91% of the time, though Darwin Ho and Leon E. Sobon have followed up on this work to improve the design of the plant.
Hard ceramics used for industrial processes, called "refractories", e.g., calcia, magnesia, titania, silica and alumina, are used for casting molds and other high temperature, high pressure and highly abrasive processes, as well as contact with highly reactive chemicals without being corroded. On Earth, ceramic ball bearings are even used in special aircraft engines. These refractory ceramics are produced by "sintering", whereby powdered material of the same composition (e.g., CaO) is put together and melted at a very high temperature then cooled slowly to a solid and held for long periods of time at that temperature. While this is a routine process on Earth, it's easy in orbital space with large solar ovens, and works better in vacuum where there is no oxygen, water, or other molecules to create impurities, poison the pristine surfaces and decrease molecular attraction within the desired pure material.
See also the following bulk processes:
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