can be present.* The other liquid of the immiscible pair, called high-iron melt, contains considerable phosphorous (~ 1.5%^3% P2O5), and crystals of apatite or whitlockite (calcium phosphates) from its crystallization are commonly found around the edges of the masses of high-potassium glass. If even an impure concentrate of this high-potassium, high-phosphorous material could be made, as a byproduct of material handling for other products, it might be valuable to an SPS program in several ways. (However, no evidence now indicates that it can be separated.) First, any permanent lunar base will presumably grow food hydroponically. The early results on Apollo 11 soil showed that plants grew better if lunar soil was added to the water. I suggest that this improved growth was probably a result of the added potassium (and phosphorous?), which should dissolve more readily from the potassium-rich glass than might be expected from the overall low concentrations present. Even if all biological wastes at such a base are recycled, use of potassium and phosphorous hydroponic “fertilizer” from lunar soil would mean that much less material to be transported from Earth. Second, this high-potassium glass could be an important additive in several types of ceramic mixtures. Most ceramics consist of crystals of various phases, bonded together by glass. The properties of both are important in controlling the properties of the ceramic, but the one most important property of the glass is its viscosity at a given temperature. Potassium aluminum silicate melts such as this melt have extremely high viscosities, and hence such material should be useful for increasing the viscosity of various glasses, whether they are to be used with crystals in ceramics or for pure glass products. They would also be useful in lowering the melting temperatures of nonrefractory ceramics. Figure 1 shows the relationship between viscosity and temperature for various silicate melts. The high-potassium lunar glasses would presumably have viscosities in the general range of curve 2, for anhydrous obsidian. Note that the viscosity of obsidian at 1100 °C is about nine orders of magnitude higher than that of some basaltic lunar rocks. The actual viscosity of the potassium glass will probably be less than the viscosities shown for obsidian, because the viscosities of alkalialuminosilicate melts show a sharp maximum at a 1:1 mole ratio of alkalies to alumina, as in many obsidians (7), but the lunar glasses are deficient in alkali. Silica Another phase present in lunar soils derived from mare basalt that might be useful in ceramic products is silica. A relatively pure silica phase, either tridymite or cristobalite, is present in many mare basalts in amounts as great as ~ 6%. Anyone who has ever tried to transfer carefully weighed aliquots of powdered cristobalite knows that it is positively devilish in the way in which it takes on a static charge on even minor handling. After extensive handling under low humidity conditions (e.g., on pouring the powder after screening) lumps of the powder commonly levitate from the paper and plaster themselves on the outside on the container into which it is being poured. Electrostatic processes have considerable potential for the separation of plagioclase and ilmenite from lunar soils (3), hence a silica separate might also be obtained as a byproduct of these processes. Such a concentrate would be of considerable value for the manufacture of silica glass or fibers (8), and even large shapes *The exact amounts cannot be simply calculated from these numbers as some K2O also enters the structure of plagioclase.
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