§ 4.3.4 Glasses

A great variety of glass products can be produced from lunar and asteroidal materials, including fiberglass, clear glass, and materials for items such as walls, pipes and some kinds of structural members.

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 and from asteroid impacts, 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. This glass can be separated using simple electrostatic beneficiation.

On Earth, glass isn't used for structural applications because glass produced on Earth is heavily contaminated by water vapor present in the atmosphere which makes the material brittle, weak and prone to cracks. "Anhydrous" glass, i.e., glass produced in the absence of hydrogen or water, has significantly better mechanical properties. This has led some researchers to analyze the potential use of glasses for structural components, e.g., the General Dynamics report endorses use of foamed glass in solar power satellites, Blacic covers wider uses, and Carsley, Blacic and Pletka report on the mechanical properties of these materials produced from lunar simulants.

Soils rich in iron oxide (FeO) produce dark but mechanically strong glass-ceramics, whereas "colorless glass windows can be produced from basically anorthite alone or with small additions of CaO and/or SiO₂. The expansion coefficient of such glasses is likely to be less than that of common window glass. This should be an asset for windows which will esperience large changes in temperature."

Clear, pure silica glass (SiO₂) is readily manufacturable from lunar materials. Due to the lack of hydrogen, superior optical fibers can be readily produced.

Glasses, as opposed to glass ceramics, are produced by cooling the melted material faster to create a different crystalline structure. Good coverage of the field, including cooling rates required for different Apollo lunar compositions, is given by Pletka, as well as DeLa'O, Hellawell, Pletka and Rose.

There has also been discussed the prospects of foamed glass structural beams reinforced with asteroid nickel-iron steel so that the structural members could withstand a wide range of both tension and compression.

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