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JSC-1A lunar soil simulant: Characterization, glass formation, and selected glass properties
Journal of Non-Crystalline Solids 356 (2010) 2369–2374
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Journal of Non-Crystalline Solids j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j n o n c r y s o l
JSC-1A lunar soil simulant: Characterization, glass formation, and selected glass properties C.S. Ray a, S.T. Reis a,⁎, S. Sen b, J.S. O'Dell c a b c
Materials Research Center, Missouri University of Science and Technology, Rolla, MO 65409, USA BAE System, Marshall Space Flight Center, National Aeronautics and Space Administration, Huntsville, AL 35812, USA Plasma Processes Inc., 4914 Moores Mill Road, Huntsville, Al 35811, USA
a r t i c l e
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Article history: Received 15 October 2009 Received in revised form 21 April 2010 Available online 9 June 2010 Keywords: Lunar soil simulant; Glass formation; XRD; DTA; Mössbauer
a b s t r a c t The chemical composition of a volcanic ash deposited near Flagstaff, Arizona, USA closely resembles that of the soil from the Maria geological terrain of the Moon. After mining and processing, this volcanic ash was designated as JSC-1A lunar simulant, and made available by NASA to the scientific research community in support of its future exploration programs on the lunar surface. The present paper describes characterization of the JSC-1A lunar simulant using DTA, TGA, XRD, chemical analysis and Mössbauer spectroscopy and the feasibility of developing glass and ceramic materials using in-situ resources on the surface of the Moon. The overall chemical composition of the JSC-1A lunar simulant is close to that of the actual lunar soil collected by Apollo 17 mission, and the total iron content in the simulant and the lunar soil is nearly the same. The JSC-1A lunar simulant contains both Fe2+ (∼ 76%) and Fe3+ (∼ 24%) ions as opposed to the actual lunar soil which contains only Fe2+ ions, as expected. The glass forming characteristics of the melt of this simulant as determined by measuring its critical cooling rate for glass formation suggests that the simulant easily forms glass when melted and cooled at nominal rates between 50 and 55 °C/min. The coefficient of thermal expansion of the glass measured by dilatometry is in close agreement with that of alumina or YSZ, which makes the glass suitable for use as a coating and sealing material on these ceramics. Potential applications envisaged up to this time of these glass/ceramics on the surface of the Moon are also discussed. © 2010 Elsevier B.V. All rights reserved.
1. Introduction A long duration human presence on the surface of the Moon appears to be an important priority of NASA's space exploration vision. For such a vision to be affordable it is imperative to significantly reduce the up mass of essentials from Earth. In this context processing and utilization of in-situ resources on the surface of the Moon becomes an integral part of the exploration vision. Some of the most important lunar resource utilization activities that have been proposed includes extraction of oxygen from the lunar regolith for propellant and human sustenance [1,2], extraction of important metals such as Si to fabricate thin film solar cells for electrical power generation [3], constructions of habitats that provide sufficient protection from radiation hazards [4], and development of lunar glass for structural fibers and spacecraft landing sites to mitigate the hazards of excessive lunar dust migration due to spacecraft plume impact. Development of appropriate techniques that will facilitate such activities begins with our understanding of the resources that are available on the lunar surface.
⁎ Corresponding author. E-mail address: [email protected] (S.T. Reis). 0022-3093/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2010.04.049
The lunar atmosphere is often described as a hard vacuum since the gas concentration varies between 105 and 104 molecules/cm3 [5]. This is approximately 14 order of magnitude less compared to Earth's atmosphere. In the absence of any atmosphere the lunar regolith becomes the primary source for in-situ resources. The term regolith is used to define the first 4–15 m of lunar soil that has been derived from fragmentation of the bedrock by large and small meteoritic impacts [6]. The major components of the lunar regolith consist of fragments of rocks, minerals and glasses. The major group of minerals found on the lunar surface consists of silicate minerals namely, olivine, pyroxene, and plagioclase, and non-silicate minerals such as ilmenite [6,7]. The samples returned from the Apollo and Luna missions were predominantly from two geological terrains of the Moon, namely the Maria or the relatively flat plains and Highlands or heavily cratered mountainous regions [5]. However, there is appreciable diversity in intrinsic and granular properties of the regolith between the different locations. For example, chemically the Highlands are richer in Ca and Al whereas the Maria is enriched in Ti and Fe [7]. Moreover, even within a given location there is variation in regolith particle angularity and size, ranging from a few microns to millimeters. Such diversities in turn lead to differences in properties such as bulk density, thermal conductivity and dielectric constant. Further details on lunar regolith composition can be found elsewhere [5–8] and to some extent will be discussed later in this paper.
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The different regolith properties and their variations have to be considered before a lunar surface operation is selected and the corresponding hardware is developed. The stockpile of actual lunar regolith from Apollo return missions is not sufficient for comprehensive research activities. Availability of one or more lunar regolith simulants that will allow researchers to develop and optimize their processes is therefore necessary. In 1993 NASA released a lunar regolith simulant, JSC-1 to support studies related to lunar surface operations. The source of this simulant is the south flank of the Merriam Crater near Flagstaff, Arizona. Analysis and characterization of the JSC-1 lunar simulant were conducted and reported elsewhere [9]. Supply of this simulant has been exhausted and recently NASA has released to the research community a lunar Maria simulant material commonly known as JSC-1A. This new simulant is from the same quarry as JSC-1 and some of the physical, chemical and mineralogical characteristics of this simulant are discussed elsewhere [8–12]. Understanding the properties of this newly released lunar simulant and the differences compared to lunar regolith is the first major step before using it to develop and validate potential lunar surface operations. The primary objective of the current work is to quantify certain important properties of the starting raw material, JSC-1A, using standard characterization procedures. This paper reports the results obtained for the JSC-1A lunar simulant as characterized by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), differential thermal and thermo-gravimetric analysis (DTA/TGA), chemical analysis for composition by inductively coupled plasma atomic absorption spectroscopy (ICP-AES), and Mössbauer spectroscopy. Moreover, the abundance of SiO2, the basic constituent of glass, makes the lunar regolith conducive for fabrication of important glass products. Accordingly, another important objective of the present paper is to measure and report the critical cooling rate for glass formation (RC) that determines the ability of a melt to form glass. 2. Experimental procedures The composition for the as-received JSC-1A lunar simulant was determined by ICP-AES chemical analysis. Table 1 shows the composition of JSC-1A lunar simulant along with the compositions reported [9] previously for the JSC-1 lunar stimulant, and the composition of the lunar soil from Apollo 17 sample 70051 [8]. No separate determination was made for FeO in the present ICP-AES analysis, and the total iron oxide content is reported as Fe2O3. The crystalline phases present in this simulant was determined by X-ray diffraction analysis (XRD), Scintag XDS2000, and also by scanning electron microscopy (SEM, model JEOL T330A) operated at 15 to 20 kV and equipped with energy dispersive X-ray analysis (EDS). Differential thermal analysis (DTA) and thermo-gravimetric analysis (TGA) were performed using a Netzch simultaneous DTA/ TGA STA 409 apparatus for the as-received JSC-1A lunar simulant powders with particle size between 50 and 100 μm. The experiments Table 1 Composition (wt.%) of the major constituents in JSC-1A lunar simulants, JSC-1 lunar simulant and from Apollo 17 sample 70051. Constituent oxides
JSC-1 lunar simulant [8]
Apollo 17 sample 70051 [8]
Chemical analysis Present work
SiO2 Al2O3 CaO MgO FeO Fe2O3 Na2O K2O TiO2 P2O5 MnO
47.4 15.0 10.4 9.0 7.4 3.4 2.7 – 1.6 – –
42.2 15.7 11.5 10.3 12.4 – 0.2 0.1 5.1 – 0.2
45.7 16.2 10.0 8.7 – 12.4 3.2 0.8 1.9 0.7 0.2
were conducted in alumina containers (volume 60 mm3) at a heating rate of 10 °C/min in flowing dry nitrogen gas from room temperature to 1300 °C. The purpose of these experiments was to determine the temperatures of any phase transformations such as glass transition and crystallization temperatures occurring in the simulant with increasing temperature as well as any mass loss or gain associated with the transformations. The Mössbauer spectrum for the JSC-1A was obtained at room temperature on a spectrometer provided with a 10 mCi rhodium matrix cobalt-57 source. The amount of iron found at the sample holder was 4 mg/cm2. The velocity of the source was calibrated using a pure iron foil. Dilatometric data was collected in glass samples (25 × 10 mm) using an Orton Dilatometer model 1600D at a heating rate of 10 °C/ min in air to determine the coefficient of thermal expansion (CTE), glass transition (Tg), and dilatometric softening points (Ts) for the glasses prepared from the JSC-1A lunar simulant. Glasses were prepared by melting the simulant at 1450 °C in platinum crucibles in air for about 2 hours. A typical melt size was approximately 50 grams. Melts were quenched on steel plates and glasses were annealed for 6 h near the glass transition temperature (650 °C). 3. Results 3.1. Chemical analysis The chemical composition of JSC-1A lunar soil simulant as determined by ICP is given in Table 1 along with the compositions determined previously for the JSC-1 [8,9] lunar simulant and the actual lunar soil collected during the Apollo 17 mission from the Valley of Taurus–Littrow [8]. Both stimulants, JSC-1 and JSC-1A, contained slightly higher amounts of alkali oxide and smaller amount of TiO2 compared to the Apollo 17 (70051) lunar soil. The total iron content determined by ICP for the JSC-1A is presented as Fe2O3 in Table 1, although a substantial amounts of FeO should be present in the simulant as well. Regardless of presenting Fe as either FeO or Fe2O3, the results in Table 1 show that the total Fe content for the JSC-1A simulant in the present work is very close to that of the previously reported JSC-1 lunar simulant [8,9] and lunar soil procured from the Apollo 17 landing site. 3.2. XRD and SEM The XRD pattern for the JSC-1A lunar simulant is shown in Fig. 1. The presence of major phases, olivine [(Mg, Fe)2SiO4] and pyroxene [(Ca, Mg, Fe) (Si, Al)2O6], and also the minor phase ilmenite [FeTiO3] is observed in the XRD of JSC-1A. Fig. 2 shows the scanning electron microscopy (SEM) backscattered image obtained from the as received JSC-1A powder. The major minerals, such as olivine and pyroxene have also been identified by EDS. The smooth particles whose compositions as measured by EDS (not shown) closely resemble the overall composition of the simulant as measured by ICP and are assumed to be glass. Similar results were observed for the JSC-1 simulant [9,11], confirming that the basic mineralogical characteristics for both JSC-1 and JSC-1A lunar simulants are nearly the same. 3.3. Mössbauer analysis The typical Mössbauer spectrum measured in this study for the JSC-1A lunar simulant is shown in Fig. 3, which has resulted from the presence of iron bearing components olivine [(Mg, Fe)2SiO4], pyroxene [(Ca, Mg, Fe) (Si, Al)2O6], and ilmenite [FeTiO3] in the simulant. The general appearance of the spectra for the JSC-1A is similar to that reported previously for the JSC-1 lunar simulant [9]. In this study three Lorentzian doublets have been used to fit each Mössbauer spectrum and each doublet has been assigned to the iron redox ion, Fe2+ and Fe3+, see Fig. 3. Analyses of the spectra to
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Fig. 1. XRD pattern for the as-received JSC1-A lunar simulant.
determine the Mössbauer parameters such as quadrupole splitting and isomer shift, are continuing to better understand the relative contributions of the iron bearing components (pyroxene, olivine, and ilmenite) to the Mössbauer spectra. At this time, however, the concentration of the Fe2+ and Fe3+ ions in the simulant was calculated from relative areas of the fitted Lorentzian doublets for each ion in the Mössbauer spectra, and is shown in Table 2. As expected, the Fe2+ or Fe3+ concentration in the JSC-1A simulant is close to that of the JSC-1, since both simulants were procured from the same terrestrial source.
The TGA profile in Fig. 5 shows initially a small mass loss (0.30%) which continues up to about 525 °C and which maybe due to evaporation of absorbed moisture. The sample then starts gaining weight, which continues up to about 1030 °C causing a net mass gain of about 1.0%. In any case, the TGA profile does not show either a huge mass gain or a mass loss with increasing temperature which suggests that this JSC-1A lunar simulant does not contain any volatiles or undergoes any phase transformation that is associated with a change of mass with increasing temperature. 3.5. Critical cooling rate for glass formation (RC)
3.4. DTA and TGA The DTA and TGA thermal profiles for the JSC-1A lunar simulant are shown in Figs. 4 and 5, respectively. The DTA profile, Fig. 4, shows the presence of an endothermic peak, at about 670 °C, followed by an exothermic peak, at about 880 °C. The endo- and exothermic peaks correspond to the glass transition (Tg) and glass crystallization (Tc) events, respectively. The appearance of these peaks suggests the presence of a glass phase in the JSC-1A simulant. The endothermic peak (Tm) occurring after the crystallization events, at about 1120 °C, corresponds to melting.
Fig. 2. SEM back scattered electron image of JSC-1A lunar simulant.
The critical cooling rate for glass formation (RC) is defined as the slowest rate a melt can be cooled to solid without crystallizing, i.e. the solidified melt becomes a glass. This implies that the melts with increasing values of RC have decreasing ability to form glass on cooling. Since, preparing glass preform and other glass-derived products from the melts of JSC-1A lunar soil simulant is one of the goals of this work; measuring RC for this melt is an important task.
Fig. 3. Mössbauer spectra for the JSC-1A lunar simulant.
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Table 2 Fraction of Fe+ 2 and Fe+ 3 calculated from the Mössbauer spectra at 293 K for JSC-1 and JSC-1A lunar simulants. Component
JSC-1 A (%)
JSC-1 [9] (%)
Fe2+/(Fe2+ + Fe3+) Fe3+/(Fe2+ + Fe3+)
76 ± 2 24 ± 2
72 ± 2 28 ± 2
A previously reported DTA [13] method was used to measure RC for these melts. This method which utilizes the area of crystallization peaks obtained by reheating solidified melts produced at different cooling rates (R), is rapid and easy to perform. The detailed experimental procedure for measuring RC by this DTA method is given in Ref. [13]. In brief, it requires melting the mixture of raw materials (simulant in this case) inside the DTA-7 Perkins Elmer instrument at a temperature about 150 to 200 °C higher than its melting temperature, cooling the melt at a rate R to room temperature, and finally re-heating the solidified melt at a different rate, Φ, until crystallization is complete. This experiment is repeated several times on the same sample by changing R while keeping Φ constant; 15 °C/min in the present experiments. Examples of thermal profiles for a few such heating-cooling cycles for the melts of the JSC1A lunar simulant are shown in Fig. 6. The area of an exothermic DTA peak obtained on re-heating a solidified melt is proportional to the amount of heat evolved during crystallization and, hence, to the amount of residual glass present in the sample after cooling the melt, which, in turn, depends upon R, the prior cooling rate of the melt. Higher is the value of R, larger is the volume fraction of glass present in the solidified melt. A melt which partially crystallizes on cooling (for a slow R, for example) will contain a smaller fraction of glass, and its subsequent rate-heating DTA peak area will be smaller compared to that for a sample prepared by cooling the melt at a faster R. This is clearly shown in Fig. 6 for the JSC-1A lunar simulant, where the rate-heating DTA peak area for the sample increases with increasing R that was used to quench the melt. The DTA peak area for the samples as a function of their prior cooling rate, R, is shown in Fig. 7 for the JSC-1A lunar simulant. A small change (within 6 °C) in both the glass transition temperature and crystallization temperature with changing cooling rate of the melt is observed in Fig. 6. This is probably due to a small change in the overall glass composition with changing cooling rate. With increasing R (below RC), more crystals dissolve in the melt causing the overall composition of the melt and, hence, the glass to change. However, the changes in these temperatures are too small to be considered significant. Fig. 7 shows that the peak area increases initially with increasing R, which is expected per discussion above. However, it attains a plateau
Fig. 4. DTA curve for the JSC-1A lunar simulant.
Fig. 5. TGA curve for the JSC-1A lunar simulant.
as the prior cooling rate of the melt exceeds a certain critical value. The area of the rate-heating DTA peak for the sample which was prepared by cooling its melt at an R = RC, would be the highest, since this sample should not contain any crystal and should be totally glassy. For all samples which were prepared at R ≥ RC, the DTA peak area would, therefore, remain the same, Fig. 7. The value of R for which the subsequent rate-heating DTA peak area attains a maximum value is the critical cooling rate for glass formation RC. From the analysis of Fig. 7, the value of RC for the melt of JSC-1A lunar simulant is determined to be about 52 ± 1 °C/min. 3.6. Coefficient of thermal expansion (CTE) The CTE curve for the glass prepared from glass melted from the JSC-1A lunar simulant is shown in Fig. 8 along with the CTE curve for alumina (Al2O3) for comparison. The CTE for the simulant-derived glass and alumina, which is used as a common ceramic material in many high temperature applications appears to be very similar. The glass transition temperature (Tg ∼ 647 °C) and the softening temperature (T s ∼ 732 °C) for the simulant-derived glass are comparable or higher than those of most commercial glasses. For example, the Tg for a Li2O·2SiO2 glass [14] is about 490 °C. A high Tg for the JSC-1A lunar simulant glass makes it suitable for high temperature applications.
Fig. 6. DTA curves at a heating rate of 15 °C/min for the melt of JSC-1A lunar simulant after quenching the melt at rates (R) shown.
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Fig. 7. DTA peak area as a function of prior cooling rate for the melts of JSC-1A lunar simulant. The solid line is a guide for the eyes.
4. Discussion The chemical composition of the JSC-1A lunar soil simulant characterized in the present investigation is very close (Table 1) to that of the JSC-1 simulant studied previously, which is consistent with the fact that both simulants were procured from the same geological location (Flagstaff Arizona). A higher TiO2 content for the Apollo 17 lunar soil compared to that of JSC-1 and JSC-1A simulants may be due to the reason that the Apollo 17 soil sample was collected from the Maria terrain region of Moon, which is reported [8] to be rich in Ti. Like the chemical composition, no difference in the mineralogical characteristics as evaluated by XRD and SEM was observed for the JSC-1A and JSC-1 simulants. Both simulants contained olivine, pyroxene, and ilmenite minerals along with some volcanic glasses, which are also the constituents of Apollo 17 lunar soil. However, the lunar soil contained the mineral plagioclase, which could not be identified either by XRD or SEM in the JSC-1A or JSC-1 simulants. This is the major difference between the characteristics of the Apollo 17 lunar soil from the Maria terrain and the present stimulants. The absence of a gaseous atmosphere in the environment of moon leaves the iron ions in its soil to exist as 0 (elemental) and 2+ states,
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but not in 3+ states. On the contrary, due to presence of oxygen in the environment of earth, it is nearly impossible for an iron bearing soil on earth's surface to be completely free from Fe2O3. Thus, the presence of both Fe2+ and Fe3+, as determined by Mössbauer analysis (Table 2), in the JSC-1A simulant which was developed from a soil on earth is an expected result. The simulant may contain elemental iron, but its presence in the simulant could not be detected by Mössbauer analysis at this time. Once again, the relative concentration of Fe2+ and Fe3+ ions in the JSC-1A simulant is in excellent agreement with that of the JSC-1 simulant (Table 2) due to their same mining location. Thermogravimetric analysis of the JSC-1A simulant does not show any appreciable mass loss upon heating suggesting this simulant does not contain any volatile component. However, a small, but consistent mass gain (about 1%) is an interesting result. This simulant contains about 12.4% iron oxide (Table 1), of which about 76% exist as FeO (Mössbauer results, Table 2). An oxidation of all these FeO to Fe2O3 should cause a mass gain of 1.09%, which is consistent with the observed 1% mass gain in the TGA. Thus, the small mass gain observed in the present TGA data (Fig. 5) may have been due to oxidation of Fe2+ to Fe3+. This simulant when melted and cooled forms an excellent glass. The critical cooling rate for glass formation (RC) for the melt as determined by DTA is about 52 °C/min, which is close to that (42 °C/min) of the melt for JSC-1 simulant measured previously using the same method [9]. A melt of a lithium disilicate composition (Li2O·2SiO2) which has commercial importance for developing glass-ceramic products, has an RC of about 60 °C/min [14,15]. By this standard, the melt of the JSC-1A lunar soil simulant can be described as a reasonably good glass forming melt. A close match of the coefficient of thermal expansion (CTE) of the glass prepared from this simulant with that of the commercial alumina ceramics (Fig. 8) makes the glass useful in many practical applications such as for coating on alumina substrates. The yttriastabilized zirconia (YSZ) ceramics, which are used in solid oxide fuell cell (SOFC) technology have similar CTE [16] as that of alumina, and, hence, that of the simulant-derived glass. Thus, this glass can also be used as sealing material in SOFCs. The melt of the JSC-1A simulant appears to have a viscositytemperature characteristic that is appropriate for fabricating various types glass preforms such as bulk glass of appreciable quantity, glass fibers, rods, tubes, microspheres, etc. Typical examples of continuous glass fibers and hollow glass shells prepared from this melt are shown in Fig. 9. Hollow glass shells can be used for storing hydrogen or other important gases for future use on Moon using in-situ resources. Glass fibers reinforced light weight composite materials can be developed for use as structural components in habitat construction on Moon. Since, the lunar soil appears to have the ability to form glass easily, many more applications that use glass as the core material can be envisaged. 5. Summary
Fig. 8. Thermal expansion curve for the glass prepared from JSC-1A lunar simulant. CTE: Coefficient of thermal expansion; Tg: Glass transition temperature; Ts: Softening temperature.
Various results that characterize the JSC-1A lunar simulant have been obtained using DTA, TGA, XRD, SEM, Mossbauer spectroscopy, and ICP. The overall chemical composition of the JSC-1A lunar simulant is close to that of the actual lunar soil collected by Apollo 17 mission. While the total iron content in the simulant and the lunar soil is nearly the same, the JSC-1A lunar simulant contains both Fe2+ and Fe3+ ions as opposed to the lunar soil which contains only Fe2+ ions, as expected. With the exception of plagioclase, all other minerals (olivine, pyroxene, ilmenite) present in the lunar soil are also present in the simulant. The absence of plagioclase in the simulant is considered a major mineralogical difference between the lunar soil and the simulant. Like the lunar soil, the simulant also contains a glassy phase whose glass transition temperature is about 670 °C, and which crystallizes at about 880 °C when re-heated. No major volatile
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Fig. 9. (a) Glass fibers prepared from JSC-1 lunar simulant and (b) hollow glass microspheres produced from JSC-1A lunar simulant.
component is detectable in the simulant, which melts completely at about 1120 °C. The simulant easily forms glass when melted and cooled at nominal rates between 50 and 55 °C/min. Glass preforms of various shapes and sizes (glass fibers and rods, microspheres) can be easily fabricated because of the appropriate viscosity of the melt at its forming temperatures. The coefficient of thermal expansion of the simulant-derived glass is in close agreement with that of alumina or YSZ, which makes the glass suitable for use as a coating and sealing material on these ceramics. Acknowledgments The authors wish to acknowledge the NASA Small Business Innovative Research (SBIR) program for funding this effort. The authors wish to thank Dr. J. B. Yang of the University of Missouri-Rolla for analyzing the Mössbauer spectra. Thanks are also due to Dr C.W. Kim of MO-SCI Corporation, Rolla, MO, USA for fabricating the hollow glass shells. References [1] P.A. Curreri, E.C. Ethridge, S.B. Hudson, Process Demonstration for Lunar In-Situ Resource Utilization – Molten Oxide Electrolysis, NASA Technical Report 214600, 2006. [2] M.A. Gibson, C.W. Knudsen, in: W.W. Mendell (Ed.), Proceeding of the Lunar Bases and Space Activities of the 21st Century, Lunar and Planetary Institute, 1985, pp. 543–550.
[3] A. Freundlich, T. Kubricht, A. Ignatiev, in: M.S. El - Genk (Ed.), Proceedings of the Space Technology & Applications International Forum, Am. Inst. Physics, 1998, pp. 660–665. [4] J.W. Wilson, L.W. Towsend, W. Schimmerling, et al., Transport Methods and Interactions for Space Radiation, NASA Langley Technical Report, 2003, pp. 500–503, Chapter 12. [5] D. Vaniman, R. Reedy, G. Heiken, G. Olhoeft, and W. Mendell, Chapter 3: The Lunar Environment in Lunar Sourcebook – A User's Guide to the Moon, G.H. Heiken, D.T. Vaniman, and B.M. French, eds., Lunar and Planetary Institute, Cambridge University Press, 2nd edition, (1993), pp. 27–60. [6] M.B. Duke, in: P. Eckart (Ed.), The Lunar Base Handbook, The McGraw Hill Companies Inc., 1999, pp. 105–151. [7] D. Vaniman, J. Dietrich, G. J. Taylor and G. Heiken, “Chapter 2: Exploration, Samples, and Recent Concepts of the Moon” in Lunar Sourcebook – A User's Guide to the Moon, G.H. Heiken, D.T. Vaniman, and B.M. French, eds., Lunar and Planetary Institute, Cambridge University Press, 2nd edition, (1993), pp. 7–25. [8] E. Hill, M.J. Mellin, B. Deane, Y. Liu, L.A. Taylor, J. Geophys. Res. 112 (2007) E02006. [9] C.S. Ray, S.T. Reis, S. Sen, in: M.S. El-Genk (Ed.), Proceedings of the Space Technology & Applications International Forum, Am. Inst. Phys., 2008, pp. 208–216. [10] R.J. Gustafson, B.C. White, M.A. Gustafson, in: M.S. El-Genk (Ed.), Proceedings of the Space Technology & Applications International Forum, Am. Inst. Phys., 2008, pp. 213–220. [11] Zheng Yongchun, Wang Shijie, Ouyang Ziyuan, Zou Yongliao, Liu Jianzhong, Li. Chunlai, Li. Xiongyao, Feng Junming, CAS-1 lunar soil simulant, Adv. Space Res. 43 (2009) 448–454. [12] S. Sen, C.S. Ray, R. Reddy, Mat. Sci. Eng. A 413–414 (2005) 592–597. [13] C.S. Ray, S.T. Reis, R.K. Brow, J. Non-Cryst, Solids 351 (2005) 1350–1358. [14] C.S. Ray, W. Huang, D.E. Day, J. Am, Ceram. Soc. 70 (1987) 599–603. [15] R. Ota, N. Soga, Glastech. Ber. 56K (1983) 776. [16] S.T. Reis, R.K. Brow, Mater. Eng. Perform. 15 (4) (2006) 410–413.
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Journal of Non-Crystalline Solids j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j n o n c r y s o l
JSC-1A lunar soil simulant: Characterization, glass formation, and selected glass properties C.S. Ray a, S.T. Reis a,⁎, S. Sen b, J.S. O'Dell c a b c
Materials Research Center, Missouri University of Science and Technology, Rolla, MO 65409, USA BAE System, Marshall Space Flight Center, National Aeronautics and Space Administration, Huntsville, AL 35812, USA Plasma Processes Inc., 4914 Moores Mill Road, Huntsville, Al 35811, USA
a r t i c l e
i n f o
Article history: Received 15 October 2009 Received in revised form 21 April 2010 Available online 9 June 2010 Keywords: Lunar soil simulant; Glass formation; XRD; DTA; Mössbauer
a b s t r a c t The chemical composition of a volcanic ash deposited near Flagstaff, Arizona, USA closely resembles that of the soil from the Maria geological terrain of the Moon. After mining and processing, this volcanic ash was designated as JSC-1A lunar simulant, and made available by NASA to the scientific research community in support of its future exploration programs on the lunar surface. The present paper describes characterization of the JSC-1A lunar simulant using DTA, TGA, XRD, chemical analysis and Mössbauer spectroscopy and the feasibility of developing glass and ceramic materials using in-situ resources on the surface of the Moon. The overall chemical composition of the JSC-1A lunar simulant is close to that of the actual lunar soil collected by Apollo 17 mission, and the total iron content in the simulant and the lunar soil is nearly the same. The JSC-1A lunar simulant contains both Fe2+ (∼ 76%) and Fe3+ (∼ 24%) ions as opposed to the actual lunar soil which contains only Fe2+ ions, as expected. The glass forming characteristics of the melt of this simulant as determined by measuring its critical cooling rate for glass formation suggests that the simulant easily forms glass when melted and cooled at nominal rates between 50 and 55 °C/min. The coefficient of thermal expansion of the glass measured by dilatometry is in close agreement with that of alumina or YSZ, which makes the glass suitable for use as a coating and sealing material on these ceramics. Potential applications envisaged up to this time of these glass/ceramics on the surface of the Moon are also discussed. © 2010 Elsevier B.V. All rights reserved.
1. Introduction A long duration human presence on the surface of the Moon appears to be an important priority of NASA's space exploration vision. For such a vision to be affordable it is imperative to significantly reduce the up mass of essentials from Earth. In this context processing and utilization of in-situ resources on the surface of the Moon becomes an integral part of the exploration vision. Some of the most important lunar resource utilization activities that have been proposed includes extraction of oxygen from the lunar regolith for propellant and human sustenance [1,2], extraction of important metals such as Si to fabricate thin film solar cells for electrical power generation [3], constructions of habitats that provide sufficient protection from radiation hazards [4], and development of lunar glass for structural fibers and spacecraft landing sites to mitigate the hazards of excessive lunar dust migration due to spacecraft plume impact. Development of appropriate techniques that will facilitate such activities begins with our understanding of the resources that are available on the lunar surface.
⁎ Corresponding author. E-mail address: [email protected] (S.T. Reis). 0022-3093/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2010.04.049
The lunar atmosphere is often described as a hard vacuum since the gas concentration varies between 105 and 104 molecules/cm3 [5]. This is approximately 14 order of magnitude less compared to Earth's atmosphere. In the absence of any atmosphere the lunar regolith becomes the primary source for in-situ resources. The term regolith is used to define the first 4–15 m of lunar soil that has been derived from fragmentation of the bedrock by large and small meteoritic impacts [6]. The major components of the lunar regolith consist of fragments of rocks, minerals and glasses. The major group of minerals found on the lunar surface consists of silicate minerals namely, olivine, pyroxene, and plagioclase, and non-silicate minerals such as ilmenite [6,7]. The samples returned from the Apollo and Luna missions were predominantly from two geological terrains of the Moon, namely the Maria or the relatively flat plains and Highlands or heavily cratered mountainous regions [5]. However, there is appreciable diversity in intrinsic and granular properties of the regolith between the different locations. For example, chemically the Highlands are richer in Ca and Al whereas the Maria is enriched in Ti and Fe [7]. Moreover, even within a given location there is variation in regolith particle angularity and size, ranging from a few microns to millimeters. Such diversities in turn lead to differences in properties such as bulk density, thermal conductivity and dielectric constant. Further details on lunar regolith composition can be found elsewhere [5–8] and to some extent will be discussed later in this paper.
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The different regolith properties and their variations have to be considered before a lunar surface operation is selected and the corresponding hardware is developed. The stockpile of actual lunar regolith from Apollo return missions is not sufficient for comprehensive research activities. Availability of one or more lunar regolith simulants that will allow researchers to develop and optimize their processes is therefore necessary. In 1993 NASA released a lunar regolith simulant, JSC-1 to support studies related to lunar surface operations. The source of this simulant is the south flank of the Merriam Crater near Flagstaff, Arizona. Analysis and characterization of the JSC-1 lunar simulant were conducted and reported elsewhere [9]. Supply of this simulant has been exhausted and recently NASA has released to the research community a lunar Maria simulant material commonly known as JSC-1A. This new simulant is from the same quarry as JSC-1 and some of the physical, chemical and mineralogical characteristics of this simulant are discussed elsewhere [8–12]. Understanding the properties of this newly released lunar simulant and the differences compared to lunar regolith is the first major step before using it to develop and validate potential lunar surface operations. The primary objective of the current work is to quantify certain important properties of the starting raw material, JSC-1A, using standard characterization procedures. This paper reports the results obtained for the JSC-1A lunar simulant as characterized by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), differential thermal and thermo-gravimetric analysis (DTA/TGA), chemical analysis for composition by inductively coupled plasma atomic absorption spectroscopy (ICP-AES), and Mössbauer spectroscopy. Moreover, the abundance of SiO2, the basic constituent of glass, makes the lunar regolith conducive for fabrication of important glass products. Accordingly, another important objective of the present paper is to measure and report the critical cooling rate for glass formation (RC) that determines the ability of a melt to form glass. 2. Experimental procedures The composition for the as-received JSC-1A lunar simulant was determined by ICP-AES chemical analysis. Table 1 shows the composition of JSC-1A lunar simulant along with the compositions reported [9] previously for the JSC-1 lunar stimulant, and the composition of the lunar soil from Apollo 17 sample 70051 [8]. No separate determination was made for FeO in the present ICP-AES analysis, and the total iron oxide content is reported as Fe2O3. The crystalline phases present in this simulant was determined by X-ray diffraction analysis (XRD), Scintag XDS2000, and also by scanning electron microscopy (SEM, model JEOL T330A) operated at 15 to 20 kV and equipped with energy dispersive X-ray analysis (EDS). Differential thermal analysis (DTA) and thermo-gravimetric analysis (TGA) were performed using a Netzch simultaneous DTA/ TGA STA 409 apparatus for the as-received JSC-1A lunar simulant powders with particle size between 50 and 100 μm. The experiments Table 1 Composition (wt.%) of the major constituents in JSC-1A lunar simulants, JSC-1 lunar simulant and from Apollo 17 sample 70051. Constituent oxides
JSC-1 lunar simulant [8]
Apollo 17 sample 70051 [8]
Chemical analysis Present work
SiO2 Al2O3 CaO MgO FeO Fe2O3 Na2O K2O TiO2 P2O5 MnO
47.4 15.0 10.4 9.0 7.4 3.4 2.7 – 1.6 – –
42.2 15.7 11.5 10.3 12.4 – 0.2 0.1 5.1 – 0.2
45.7 16.2 10.0 8.7 – 12.4 3.2 0.8 1.9 0.7 0.2
were conducted in alumina containers (volume 60 mm3) at a heating rate of 10 °C/min in flowing dry nitrogen gas from room temperature to 1300 °C. The purpose of these experiments was to determine the temperatures of any phase transformations such as glass transition and crystallization temperatures occurring in the simulant with increasing temperature as well as any mass loss or gain associated with the transformations. The Mössbauer spectrum for the JSC-1A was obtained at room temperature on a spectrometer provided with a 10 mCi rhodium matrix cobalt-57 source. The amount of iron found at the sample holder was 4 mg/cm2. The velocity of the source was calibrated using a pure iron foil. Dilatometric data was collected in glass samples (25 × 10 mm) using an Orton Dilatometer model 1600D at a heating rate of 10 °C/ min in air to determine the coefficient of thermal expansion (CTE), glass transition (Tg), and dilatometric softening points (Ts) for the glasses prepared from the JSC-1A lunar simulant. Glasses were prepared by melting the simulant at 1450 °C in platinum crucibles in air for about 2 hours. A typical melt size was approximately 50 grams. Melts were quenched on steel plates and glasses were annealed for 6 h near the glass transition temperature (650 °C). 3. Results 3.1. Chemical analysis The chemical composition of JSC-1A lunar soil simulant as determined by ICP is given in Table 1 along with the compositions determined previously for the JSC-1 [8,9] lunar simulant and the actual lunar soil collected during the Apollo 17 mission from the Valley of Taurus–Littrow [8]. Both stimulants, JSC-1 and JSC-1A, contained slightly higher amounts of alkali oxide and smaller amount of TiO2 compared to the Apollo 17 (70051) lunar soil. The total iron content determined by ICP for the JSC-1A is presented as Fe2O3 in Table 1, although a substantial amounts of FeO should be present in the simulant as well. Regardless of presenting Fe as either FeO or Fe2O3, the results in Table 1 show that the total Fe content for the JSC-1A simulant in the present work is very close to that of the previously reported JSC-1 lunar simulant [8,9] and lunar soil procured from the Apollo 17 landing site. 3.2. XRD and SEM The XRD pattern for the JSC-1A lunar simulant is shown in Fig. 1. The presence of major phases, olivine [(Mg, Fe)2SiO4] and pyroxene [(Ca, Mg, Fe) (Si, Al)2O6], and also the minor phase ilmenite [FeTiO3] is observed in the XRD of JSC-1A. Fig. 2 shows the scanning electron microscopy (SEM) backscattered image obtained from the as received JSC-1A powder. The major minerals, such as olivine and pyroxene have also been identified by EDS. The smooth particles whose compositions as measured by EDS (not shown) closely resemble the overall composition of the simulant as measured by ICP and are assumed to be glass. Similar results were observed for the JSC-1 simulant [9,11], confirming that the basic mineralogical characteristics for both JSC-1 and JSC-1A lunar simulants are nearly the same. 3.3. Mössbauer analysis The typical Mössbauer spectrum measured in this study for the JSC-1A lunar simulant is shown in Fig. 3, which has resulted from the presence of iron bearing components olivine [(Mg, Fe)2SiO4], pyroxene [(Ca, Mg, Fe) (Si, Al)2O6], and ilmenite [FeTiO3] in the simulant. The general appearance of the spectra for the JSC-1A is similar to that reported previously for the JSC-1 lunar simulant [9]. In this study three Lorentzian doublets have been used to fit each Mössbauer spectrum and each doublet has been assigned to the iron redox ion, Fe2+ and Fe3+, see Fig. 3. Analyses of the spectra to
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Fig. 1. XRD pattern for the as-received JSC1-A lunar simulant.
determine the Mössbauer parameters such as quadrupole splitting and isomer shift, are continuing to better understand the relative contributions of the iron bearing components (pyroxene, olivine, and ilmenite) to the Mössbauer spectra. At this time, however, the concentration of the Fe2+ and Fe3+ ions in the simulant was calculated from relative areas of the fitted Lorentzian doublets for each ion in the Mössbauer spectra, and is shown in Table 2. As expected, the Fe2+ or Fe3+ concentration in the JSC-1A simulant is close to that of the JSC-1, since both simulants were procured from the same terrestrial source.
The TGA profile in Fig. 5 shows initially a small mass loss (0.30%) which continues up to about 525 °C and which maybe due to evaporation of absorbed moisture. The sample then starts gaining weight, which continues up to about 1030 °C causing a net mass gain of about 1.0%. In any case, the TGA profile does not show either a huge mass gain or a mass loss with increasing temperature which suggests that this JSC-1A lunar simulant does not contain any volatiles or undergoes any phase transformation that is associated with a change of mass with increasing temperature. 3.5. Critical cooling rate for glass formation (RC)
3.4. DTA and TGA The DTA and TGA thermal profiles for the JSC-1A lunar simulant are shown in Figs. 4 and 5, respectively. The DTA profile, Fig. 4, shows the presence of an endothermic peak, at about 670 °C, followed by an exothermic peak, at about 880 °C. The endo- and exothermic peaks correspond to the glass transition (Tg) and glass crystallization (Tc) events, respectively. The appearance of these peaks suggests the presence of a glass phase in the JSC-1A simulant. The endothermic peak (Tm) occurring after the crystallization events, at about 1120 °C, corresponds to melting.
Fig. 2. SEM back scattered electron image of JSC-1A lunar simulant.
The critical cooling rate for glass formation (RC) is defined as the slowest rate a melt can be cooled to solid without crystallizing, i.e. the solidified melt becomes a glass. This implies that the melts with increasing values of RC have decreasing ability to form glass on cooling. Since, preparing glass preform and other glass-derived products from the melts of JSC-1A lunar soil simulant is one of the goals of this work; measuring RC for this melt is an important task.
Fig. 3. Mössbauer spectra for the JSC-1A lunar simulant.
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Table 2 Fraction of Fe+ 2 and Fe+ 3 calculated from the Mössbauer spectra at 293 K for JSC-1 and JSC-1A lunar simulants. Component
JSC-1 A (%)
JSC-1 [9] (%)
Fe2+/(Fe2+ + Fe3+) Fe3+/(Fe2+ + Fe3+)
76 ± 2 24 ± 2
72 ± 2 28 ± 2
A previously reported DTA [13] method was used to measure RC for these melts. This method which utilizes the area of crystallization peaks obtained by reheating solidified melts produced at different cooling rates (R), is rapid and easy to perform. The detailed experimental procedure for measuring RC by this DTA method is given in Ref. [13]. In brief, it requires melting the mixture of raw materials (simulant in this case) inside the DTA-7 Perkins Elmer instrument at a temperature about 150 to 200 °C higher than its melting temperature, cooling the melt at a rate R to room temperature, and finally re-heating the solidified melt at a different rate, Φ, until crystallization is complete. This experiment is repeated several times on the same sample by changing R while keeping Φ constant; 15 °C/min in the present experiments. Examples of thermal profiles for a few such heating-cooling cycles for the melts of the JSC1A lunar simulant are shown in Fig. 6. The area of an exothermic DTA peak obtained on re-heating a solidified melt is proportional to the amount of heat evolved during crystallization and, hence, to the amount of residual glass present in the sample after cooling the melt, which, in turn, depends upon R, the prior cooling rate of the melt. Higher is the value of R, larger is the volume fraction of glass present in the solidified melt. A melt which partially crystallizes on cooling (for a slow R, for example) will contain a smaller fraction of glass, and its subsequent rate-heating DTA peak area will be smaller compared to that for a sample prepared by cooling the melt at a faster R. This is clearly shown in Fig. 6 for the JSC-1A lunar simulant, where the rate-heating DTA peak area for the sample increases with increasing R that was used to quench the melt. The DTA peak area for the samples as a function of their prior cooling rate, R, is shown in Fig. 7 for the JSC-1A lunar simulant. A small change (within 6 °C) in both the glass transition temperature and crystallization temperature with changing cooling rate of the melt is observed in Fig. 6. This is probably due to a small change in the overall glass composition with changing cooling rate. With increasing R (below RC), more crystals dissolve in the melt causing the overall composition of the melt and, hence, the glass to change. However, the changes in these temperatures are too small to be considered significant. Fig. 7 shows that the peak area increases initially with increasing R, which is expected per discussion above. However, it attains a plateau
Fig. 4. DTA curve for the JSC-1A lunar simulant.
Fig. 5. TGA curve for the JSC-1A lunar simulant.
as the prior cooling rate of the melt exceeds a certain critical value. The area of the rate-heating DTA peak for the sample which was prepared by cooling its melt at an R = RC, would be the highest, since this sample should not contain any crystal and should be totally glassy. For all samples which were prepared at R ≥ RC, the DTA peak area would, therefore, remain the same, Fig. 7. The value of R for which the subsequent rate-heating DTA peak area attains a maximum value is the critical cooling rate for glass formation RC. From the analysis of Fig. 7, the value of RC for the melt of JSC-1A lunar simulant is determined to be about 52 ± 1 °C/min. 3.6. Coefficient of thermal expansion (CTE) The CTE curve for the glass prepared from glass melted from the JSC-1A lunar simulant is shown in Fig. 8 along with the CTE curve for alumina (Al2O3) for comparison. The CTE for the simulant-derived glass and alumina, which is used as a common ceramic material in many high temperature applications appears to be very similar. The glass transition temperature (Tg ∼ 647 °C) and the softening temperature (T s ∼ 732 °C) for the simulant-derived glass are comparable or higher than those of most commercial glasses. For example, the Tg for a Li2O·2SiO2 glass [14] is about 490 °C. A high Tg for the JSC-1A lunar simulant glass makes it suitable for high temperature applications.
Fig. 6. DTA curves at a heating rate of 15 °C/min for the melt of JSC-1A lunar simulant after quenching the melt at rates (R) shown.
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Fig. 7. DTA peak area as a function of prior cooling rate for the melts of JSC-1A lunar simulant. The solid line is a guide for the eyes.
4. Discussion The chemical composition of the JSC-1A lunar soil simulant characterized in the present investigation is very close (Table 1) to that of the JSC-1 simulant studied previously, which is consistent with the fact that both simulants were procured from the same geological location (Flagstaff Arizona). A higher TiO2 content for the Apollo 17 lunar soil compared to that of JSC-1 and JSC-1A simulants may be due to the reason that the Apollo 17 soil sample was collected from the Maria terrain region of Moon, which is reported [8] to be rich in Ti. Like the chemical composition, no difference in the mineralogical characteristics as evaluated by XRD and SEM was observed for the JSC-1A and JSC-1 simulants. Both simulants contained olivine, pyroxene, and ilmenite minerals along with some volcanic glasses, which are also the constituents of Apollo 17 lunar soil. However, the lunar soil contained the mineral plagioclase, which could not be identified either by XRD or SEM in the JSC-1A or JSC-1 simulants. This is the major difference between the characteristics of the Apollo 17 lunar soil from the Maria terrain and the present stimulants. The absence of a gaseous atmosphere in the environment of moon leaves the iron ions in its soil to exist as 0 (elemental) and 2+ states,
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but not in 3+ states. On the contrary, due to presence of oxygen in the environment of earth, it is nearly impossible for an iron bearing soil on earth's surface to be completely free from Fe2O3. Thus, the presence of both Fe2+ and Fe3+, as determined by Mössbauer analysis (Table 2), in the JSC-1A simulant which was developed from a soil on earth is an expected result. The simulant may contain elemental iron, but its presence in the simulant could not be detected by Mössbauer analysis at this time. Once again, the relative concentration of Fe2+ and Fe3+ ions in the JSC-1A simulant is in excellent agreement with that of the JSC-1 simulant (Table 2) due to their same mining location. Thermogravimetric analysis of the JSC-1A simulant does not show any appreciable mass loss upon heating suggesting this simulant does not contain any volatile component. However, a small, but consistent mass gain (about 1%) is an interesting result. This simulant contains about 12.4% iron oxide (Table 1), of which about 76% exist as FeO (Mössbauer results, Table 2). An oxidation of all these FeO to Fe2O3 should cause a mass gain of 1.09%, which is consistent with the observed 1% mass gain in the TGA. Thus, the small mass gain observed in the present TGA data (Fig. 5) may have been due to oxidation of Fe2+ to Fe3+. This simulant when melted and cooled forms an excellent glass. The critical cooling rate for glass formation (RC) for the melt as determined by DTA is about 52 °C/min, which is close to that (42 °C/min) of the melt for JSC-1 simulant measured previously using the same method [9]. A melt of a lithium disilicate composition (Li2O·2SiO2) which has commercial importance for developing glass-ceramic products, has an RC of about 60 °C/min [14,15]. By this standard, the melt of the JSC-1A lunar soil simulant can be described as a reasonably good glass forming melt. A close match of the coefficient of thermal expansion (CTE) of the glass prepared from this simulant with that of the commercial alumina ceramics (Fig. 8) makes the glass useful in many practical applications such as for coating on alumina substrates. The yttriastabilized zirconia (YSZ) ceramics, which are used in solid oxide fuell cell (SOFC) technology have similar CTE [16] as that of alumina, and, hence, that of the simulant-derived glass. Thus, this glass can also be used as sealing material in SOFCs. The melt of the JSC-1A simulant appears to have a viscositytemperature characteristic that is appropriate for fabricating various types glass preforms such as bulk glass of appreciable quantity, glass fibers, rods, tubes, microspheres, etc. Typical examples of continuous glass fibers and hollow glass shells prepared from this melt are shown in Fig. 9. Hollow glass shells can be used for storing hydrogen or other important gases for future use on Moon using in-situ resources. Glass fibers reinforced light weight composite materials can be developed for use as structural components in habitat construction on Moon. Since, the lunar soil appears to have the ability to form glass easily, many more applications that use glass as the core material can be envisaged. 5. Summary
Fig. 8. Thermal expansion curve for the glass prepared from JSC-1A lunar simulant. CTE: Coefficient of thermal expansion; Tg: Glass transition temperature; Ts: Softening temperature.
Various results that characterize the JSC-1A lunar simulant have been obtained using DTA, TGA, XRD, SEM, Mossbauer spectroscopy, and ICP. The overall chemical composition of the JSC-1A lunar simulant is close to that of the actual lunar soil collected by Apollo 17 mission. While the total iron content in the simulant and the lunar soil is nearly the same, the JSC-1A lunar simulant contains both Fe2+ and Fe3+ ions as opposed to the lunar soil which contains only Fe2+ ions, as expected. With the exception of plagioclase, all other minerals (olivine, pyroxene, ilmenite) present in the lunar soil are also present in the simulant. The absence of plagioclase in the simulant is considered a major mineralogical difference between the lunar soil and the simulant. Like the lunar soil, the simulant also contains a glassy phase whose glass transition temperature is about 670 °C, and which crystallizes at about 880 °C when re-heated. No major volatile
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Fig. 9. (a) Glass fibers prepared from JSC-1 lunar simulant and (b) hollow glass microspheres produced from JSC-1A lunar simulant.
component is detectable in the simulant, which melts completely at about 1120 °C. The simulant easily forms glass when melted and cooled at nominal rates between 50 and 55 °C/min. Glass preforms of various shapes and sizes (glass fibers and rods, microspheres) can be easily fabricated because of the appropriate viscosity of the melt at its forming temperatures. The coefficient of thermal expansion of the simulant-derived glass is in close agreement with that of alumina or YSZ, which makes the glass suitable for use as a coating and sealing material on these ceramics. Acknowledgments The authors wish to acknowledge the NASA Small Business Innovative Research (SBIR) program for funding this effort. The authors wish to thank Dr. J. B. Yang of the University of Missouri-Rolla for analyzing the Mössbauer spectra. Thanks are also due to Dr C.W. Kim of MO-SCI Corporation, Rolla, MO, USA for fabricating the hollow glass shells. References [1] P.A. Curreri, E.C. Ethridge, S.B. Hudson, Process Demonstration for Lunar In-Situ Resource Utilization – Molten Oxide Electrolysis, NASA Technical Report 214600, 2006. [2] M.A. Gibson, C.W. Knudsen, in: W.W. Mendell (Ed.), Proceeding of the Lunar Bases and Space Activities of the 21st Century, Lunar and Planetary Institute, 1985, pp. 543–550.
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