Processing Glass Fiber from Moon/Mars Resources

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Processing Glass Fiber from Moon/Mars Resources
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   Tucker 1 Processing Glass Fiber from Moon/Mars Resources Dr. Dennis S. Tucker 1  and Edwin C. Ethridge 2 Abstract Processing of Lunar/Mars raw materials into usable structural and thermalcomponents for use on a Lunar/Mars base will be essential for human habitation. Onesuch component will be glass fiber which can be used in a number of applications. Glassfiber has been produced from two lunar soil simulants. These two materials simulate lunarmare and lunar highlands soil compositions. Short fibers containing recrystallized areaswere produced from the as-received simulants. Doping the highland simulant with 8weight percent boria yielded a material which could be spun continuously. The effects of lunar gravity on glass fiber formation were studied utilizing NASA’s KC135 aircraft.Gravity was found to play a role in crystallization and final fiber diameter. Introduction  With NASA’s commitment to a permanent manned presence in low-Earth orbit(LEO), International Space Station (ISS), and eventual return to the moon, numerousstudies have been undertaken in the areas of microgravity and lunar materials processing(Proceedings 1985; MRS Proceedings 1987). Continuous glass fiber processing is onesuch area of research interest. In LEO, the processing of optical and single crystal fibersmay be enhanced due to the absence of gravity forces (Schlicta and Nerad 1991). In fact,a miniaturized fiber pulling apparatus has been developed (Schlicta 1988). On the lunarsurface, abundant materials exist which can be used to produce structural materials.Similar materials should exist on Mars, but this paper will concentrate on lunarapplications. The use of lunar regolith for the production of structural materials couldgreatly reduce the cost of construction and long-term habitation of a lunar colony. Onelunar product, fiberglass, promises ease of manufacture and wide applicability (Criswell1975). Continuous fiberglass can be utilized as reinforcement in structural composites,including pressure vessels, glass cables and woven-fiber insulation. The chemistry of lunar soils is similar to that of terrestrial basalts (Mackenzie and Claridge 1979; Allton,   1  Marshall Space Flight Center, Space Sciences Laboratory, Huntsville, AL 35812 2  Marshall Space Flight Center, Space Sciences Laboratory, Huntsville, AL 35812   Tucker 2 Galindo, and Watts 1985). Terrestrial basalt has been used to produce continuous glassfiber, with the chemical and mechanical properties similar to that of the standard E-glass(Chemical and Engineering News 1973; Subramanian, Yang, and Austin 1977).Comparable fibers have been produced with simulated basalt (Magoffin and Garvey 1990).This paper describes research which was undertaken to study the production of continuousglass fiber from two lunar soil simulants. Experimental Methods and ResultsMaterial The materials used in this study were supplied by the University of Minnesota andare known as “Minnesota Lunar Simulant-1” (MLS-1) and “Minnesota Lunar Simulant-2”(MLS-2). MLS-1 is a low-titanium basalt (Weiblen, Murawa, and Reid 1990) similar inchemistry to that of Apollo sample 10084. The results of MLS-1 and Apollo sample10084 are given in Table 1. The grain size of MLS-1 is similar to coarser lunar marebasalts (< 1mm) but is more equigranular, perhaps due to recrystallization (Weiblen,Murawa, and Reid 1990). Lunar soils generally contain varying amounts of glass andagglutinates due to micrometeorite impact (Papike, et al.). MLS-1 contains 10-30 weightpercent glass products produced by processing in an in-flight sustained shockwave plasmareactor (ISSP) (Weiblen, Murawa, and Reid 1990). This compares to 10-80 weightpercent found in lunar soil samples.MLS-2 is a highlands simulant containing more silica and less titania than MLS-1.It also contains a great deal more alumina. Average starting compositions of MLS-2 aregiven in Table 2. Differential thermal analysis (DTA) was used to characterize eachsimulant and the glasses processed from each. The melting point for MLS-1 wasdetermined to be1200 ° C (Figure 1). This was confirmed by heating a small amount of MLS-1 in aplatinum boat at 1200 ° C in a tube furnace and observing the material. Glassy MLS-1 wasmade by firing the simulant to 1450 ° C for 24 hours in a box furnace, then pouring themelt on an aluminum quench block. This material was crushed and DTA performed. Theresult is shown in Figure 2. The exotherm noted at approximately 800 ° C could beinterpreted as recrystallization of the basalt material.The DTA trace for MLS-2 yields a more complex situation. There is no clearevidence of distinct melting, but rather peaks indicating reactions and possiblepolymorphic transformations. DTA of glassy MLS-2 yields a trace with three exothermsand one endotherm (Figure 3). The exotherms likely represent recrystallization, while theendotherm may be due to structural transformation of the recrystallized material.Viscosity measurements (Theta Industries, Port Washington, NY) of the MLS-1and MLS-2 yielded the curves shown in Figures 4 and 5, respectively. The curves areplotted as log viscosity versus temperature. A curve for E-glass is shown for reference inFigure 6. This curve was plotted from tabulated viscosity data (Bansal and Doremus1986). As can be seen from Figure 4, the viscosity of MLS-1 does not provide evidencethe gradual decrease in viscosity with temperature as E-glass does. This implies that thereis little or no working range to MLS-1. A comparative plot between MLS-1 and MLS-2   Tucker 3 can be seen in Figure 7. In this case, viscosity in centipoise versus temperature is plotted.It can be seen from this plot that the MLS-2 has a higher viscosity at higher temperaturesand a gentler slope. This implies a more stable working range. Fiber Processing In order to produce continuous fibers of MLS-1 and MLS-2, the apparatus shownin Figure 8 was constructed. It consisted of a platinum-wound furnace containing a single-hole platinum bushing, a power supply, and take-up reel. The furnace was mounted twofeet above the take-up reel. The take-up reel was driven by an ordinary laboratory stirringmotor. Vitrified simulant was placed into the bushing through the top of the furnace andheated to a temperature which allowed fiber spinning. Fiber spinning is initiated by handdrawing the fiber from the bushing orifice to the take-up reel using an alumina rod. Fiberwas wound continuously until the bushing was empty of simulant.Only short fiber segments were drawn from MLS-1. Ideal viscosity for fiberpulling is approximately 10,000 poise. For MLS-1, this viscosity lies well below themelting point and within the recrystallization range. It was observed that the simulantwould recrystallize in the bushing below 1205 ° C. Above this temperature moltensimulant would run freely from the bushing orifice. This agrees with the viscosity data inFigure 4. The fibers which were successfully pulled showed small crystallites visibleunder a low-power microscope.Longer segments of MLS-2 could be pulled; however, the same type of problemsassociated with MLS-1 occurred. In order to enhance the viscosity range of MLS-2, 8weight percent of boric oxide was added to the raw simulant. Boric oxide is a glass formerwith low viscosity as compared to other glass-forming oxides (Doremus 1973). However,boric oxide shows anomalous viscosity behavior when mixed with glass modifiers. Thatis, the viscosity increases with additions of modifiers rather than decrease as seen withsilicon dioxide. This has been attributed to the change in coordination number of oxygenwith boron (Doremus 1973). Vitrified material was produced in the same manner as thetwo raw simulants. The doped simulant was pulled continuously at 1300 ° C. Fibers assmall as 30 microns in diameter were produced. Evidence of recrystallization was notobserved using optical microscopy. Additions of boric oxide to MLS-1 did not enhancefiber pulling behavior.Twenty-eight specimens from the wound fiber package of the doped MLS-2 werecut to 4-inch lengths and tested for tensile strength. The average fiber diameter was 45microns. The mean strength was 60,000 psi with a standard deviation of 17,500 psi. Toincrease strength, the continuous doped fiber was produced with a polyvinyl alcoholsizing. The sizing was a 5 percent aqueous solution. The sizing was applied by pullingthe fiber between two saturated pieces of felt. Each piece of felt was attached to areservoir of polyvinyl alcohol solution. A hot-air gun was directed onto the fiber to drythe sizing before the fiber was wound on the take-up reel. Thirty-eight samples weretested for tensile strength. Average fiber diameter was measured to be 30 microns. Themean strength was 102,000 psi with a standard deviation of 40,000 psi. For comparison,E-glass fiber can have strengths as high as 500,000 psi.   Tucker 4 Discussion Using E-glass as an ideal glass-fiber forming material, the two raw simulants testeddo not compare well. Both exhibit nonglass-like viscosity behavior and a strong tendencyto recrystallization when the vitrified materials are heated to just below the melting point.Composition, of course, dictates these characteristics. The ability to produce continuousfiber from the doped MLS-2 indicates that the composition of the material was adjustedsuch that recrystallization tendencies were inhibited at the pulling temperature.The strength of the doped material was seen to increase by 40,000 psi when coated.Since glass fails primarily from surface flaws, the coating acted to protect the as-spunfiber. It is felt that decreasing the fiber diameter to 10 to 15 microns will enhance strength. Conclusions It was concluded from this study that lunar simulants MLS-1 and MLS-2 in the as-received state were unsuitable for producing continuous glass fibers with the presentcapabilities. This was attributed to recrystallization near the melting point and a narrowviscosity range from which to pull the fibers. Doping MLS-2 with boric oxide yielded amaterial which could be pulled continuously. This is most likely due to compositionalchanges resulting in a wider viscosity pulling range and suppression of recrystallization.Breaking strength of doped MLS-2 was increased by coating the fiber with polyvinylalcohol during the spinning operation. The decrease in fiber diameter from 45 microns to30 microns could also account for some of the strength increase.   Tucker 5 References Allton, J.H., Galindo, C. Jr., and Watts, L.A. “Guide to Using Lunar Soil and SimulantsforExperimentation.” Lunar Bases and Space Activities of the 21 st  CenturyProceedings, 1985. p. 497.Bansal, N.P., and Doremus, R.H., eds.  Handbook of Glass Properties . 1986. p. 34. Chemical and Engineering News . June 4, 1973, p.49; April 29, p. 18.Criswell, D.R. “Lunar Materials.” Second Princeton Conference on Space ManufacturingFacilities-Space Colonies, 1975.Doremus, R.H. Glass Science . New York: John Wiley and Sons, 1973.Magoffin, M. and Garvey, J. “Lunar Glass Production Using Concentrated Solar Energy.”AIAA Space Programs and Technological Conference, Huntsville, AL, Sept. 25-28, 1990.“Materials Processing in the Reduced Gravity Environment of Space.” Materials ResearchSociety Proceedings. Vol. 1557, 1991.McKenzie, J.D. and Claridge, R.C. “Glass and Ceramics from Lunar Materials.” AIAAProceedings, 1979. pp. 135-140.Papike, J.J., Hodges, F.N., Bence, A.E., Cameron, M., and Rhodes, J.M. “Mare Basalts:Crystal Chemistry, Mineralogy, and Petrology.”  Review of Geophysics and SpacePhysics . Vol. 14 (4), 1976. pp.475-540.Proceedings of Lunar Bases and Space Activities of the 21 st  Century. Washington, DC,1985.Schlicta, P.J. “Miniaturized Fiber Pulling Apparatus for Producing Single-Crystal-CoreGlass Fibers in Microgravity.” Final Report, contract NAS3-25400, 1988.Schlicta, P.J. and Nerad, B.A. “Advantages of Drawing Crystal-Core Fibers inMicrogravity.” SPIE Proceedings. Vol. 1557, 1991.Subramanian, R.V., Yang, T.J.Y. and Austin, H.F. “Reinforcement of Polymers byBalsaltFibers.” SAMPE Quarterly . July 1977. pp.1-10.Weiblen, P.W., Murawa, M.J. and Reid, K.J. “Preparation of Simulants for Lunar SurfaceMaterials.” Proceedings of Space ’90. Aerospace/ASCE, Albuquerque, NM.April 22-26, 1990.
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