We present observations from the laboratory capture of particles in aerogel. The paper focuses on a possible extraction technique and the bulk mineral characterization of the captured material using non-destructive analytical techniques

Bland, P.A.

Burchell, M.J.

Butterworth, A.L.

Creighton, J.A.

Cressey, G.

Grady, M.M.

Graham, G.A.

Jones, C.G.

Kearsley, A.T.

Mann, J.

Wright, I.P.

English

Graham, GA

Butterworth, AL

Burchell, MJ

Kearsley, AT

Creighton, JA

Mann, J

Bland, PA

Cressey, G

Jones, CG

Grady, MM

Wright, IP

Spiral - Imperial College Digital Repository

LABORATORY CAPTURE, ISOLATION AND ANALYSIS OF MICROPARTICLES IN AEROGEL:PREPARATION FOR THE RETURN OF STARDUST  G. A. Graham1,3,4, A. L. Butterworth1,  M. J. Burchell2,A. T. Kearsley3, J. A. Creighton2, J. Mann2, P. A. Bland1, G. Cressey4, C. G. Jones4 , M. M. Grady4 and I. P.Wright1, 1Planetary and Space Sciences Research Institute (PSSRI), The Open University, Milton Keynes MK76AA, U.K  (g.a.graham@open.ac.uk), 2School of Physical Sciences, University of Kent, Canterbury CT2 7NR, U.K,3Space Science Research , School of BMS, Oxford Brookes University, Oxford OX3 0BP, U.K, 4Department ofMineralogy, Natural History Museum, London SW7 5BD, U.K.Introduction:  Over the past 30 years geochemicalstudies of cosmic dust have focused on material re-trieved or captured from terrestrial locations, e.g. thestratosphere and Antarctic ice [1,2] and from low Earthorbit (LEO) [3-4].  Extensive investigation, using awide range of analytical techniques [5] has resulted insubstantial data on mineralogical and chemical proper-ties of particles [e.g. 6].  Yet, despite detailed studies[7] it is generally not possible to state unambiguouslythe parent body origin (in terms of cometary versusasteroidal) for a given class of particle [8]. In 2006dust particles collected from Comet Wild 2 should bereturned by NASA’s Stardust spacecraft [9].  Aerogelis the primary capture cell media [9], however othersurfaces on the spacecraft will also preserve particleremnants.  Laboratory simulations and LEO exposure[10-12] have shown that particles impacting into aero-gel at hypervelocity (e.g. 6 km s-1) can be preserved asalmost intact pristine material.  After recovery and pre-liminary investigations of Stardust at the NASA John-son Space Center curation facility, samples will bemade available to the international community foranalysis [9].  It is therefore essential that groups pre-pare for the return of samples, in particular developingextraction techniques and analytical strategies so thatthe maximum yield of information can be obtainedfrom every particle examined.  Herein we discuss ob-servations made during laboratory experiments focus-sing on a possible extraction technique and in-situ min-eralogical analysis.Experimental:  Impact experiments were carried outusing a two stage light-gas-gun (LGG).  The aerogeltargets had a density of 96 kg m-3. A range of projectilecompositions were used, from individual, homogene-ous minerals (e.g. olivine, pyroxene, etc.), to complex,crushed meteorite powders (matrix material from Mur-chison, Allende and Orgueil carbonaceous chondrites).In a ‘buck-shot’ technique [13] projectiles were sabot-mounted and accelerated to approximately 5.1km s-1 toimpact the aerogel targets.Raman spectroscopy was carried out on an Instru-ments SA (now Jobin Yvon) model HR640 spectro-graph with a liquid nitrogen cooled CCD detector,linked to an Instruments SA Raman scattering modulebased on an Olympus BX40 microscope.  The analyti-cal conditions for the work were: spot size of approxi-mately 25µm; a He-Ne laser (wavelength 632.8 nm) at20 mW power. A full description of the technique isgiven in [14].Electron microscopy was carried out using a Jeol840 scanning electron microscope with an Oxford In-struments eXL energy-dispersive spectrometer micro-analyser (EDS).  Samples were carbon coated. Typicalanalytical conditions were 32 mm working distance, 2nA beam current and 20 kV.  High resolution imagingwas carried out using a Philips XL FEG-SEM with anaccelerating voltage of 5-7 kV and a working distanceof 10mm.Ablation of aerogel was carried out using a 266 nmquadrupled Nd-YAG laser operated at 10 Hz.  Theaerogel block was subjected to pulses of variable en-ergy (e.g. 0.5 to 6 mJ/pulse) over variable exposuretimes (e.g. 5 to 30 seconds).Discussion:Simulation of Impact Features.  The LGG shotsproved to be highly successful in generating both trackfeatures and capturing the projectile particles at impactvelocities similar to those of the encounter velocities ofthe stardust collectors with Comet Wild 2 [9].Extraction Technique.  Probably the most signifi-cant challenge to overcome before the actual return ofstardust samples is the extraction procedure of particlesfrom the aerogel.  Several novel techniques have pre-viously been applied [15-16] with varying degrees ofsuccess.  We have carried out preliminary experimentsusing a Nd-YAG laser to ablate aerogel, with the aimof either cutting a captured particle out of the aerogel,or removing excess aerogel so that in-situ analysis canbe achieved.  Our initial experiments have shown thatdifferent combinations of pulse energy and durationallow fine control of ablation by moving the samplerelative to the fixed beam on a computer controlled x-ystage, creating ‘pits’ (nm to µm in depth) and ‘tracks’(µm in depth).  The technique will now be used to at-tempt isolation of impact-captured olivine particles.Bulk Analysis.  It is important to ascertain whichanalytical techniques should be used following extrac-tion of captured particles, and especially, in what se-quence.  Stable isotopic measurements on extraterres-trial materials are clearly of major importance, as dem-onstrated by the long-established record of the PSSRI[e.g. 17].  However, whilst such analyses provide valu-Lunar and Planetary Science XXXII (2001) 1637.pdfLaboratory capture, isolation and analysis of microparticles in aerogel:  G. A. Graham et al.able information on light elements, they are by theirvery nature essentially destructive.  Clearly, suchmeasurements must be acquired at the end of a se-quence of analytical protocols.  The first fundamentaltask is identification of bulk chemistry and mineralogy.Analytical SEM and electron microprobe analysis arethe usual workhorse techniques [5].  Unfortunately,both require that samples be given a conductive carboncoat, contaminating the sample surface and precludingthe reliable use of stable isotopic mass spectrometry.Advances in microscopy have removed the need for theconductive coat in some circumstances, see discussionin [5].  Notwithstanding the potential contaminationissue, conventional SEM does enable imaging and de-tailed X-ray microanalysis of impact tracks and cap-tured projectiles.  Nevertheless, initial characterizationof particles needs a non-destructive, and non-contaminating technique.Raman Spectroscopy.  We have used Raman spec-troscopy.  The technique obtains a vibrational spectrumof the crystal lattice of the sample by illuminating itwith a laser, and collecting the spectrum of inelasticallyscattered photons.  The detected spectrum contains asuite of peaks that are characteristic of the chemicalstructure of the sample.  As each component of thesample that is illuminated by the laser may contributeto the spectrum seen, it is fortunate that the aerogeldoes not significantly absorb or scatter the laser light.Consequently, only the selected impacted particle ma-terial is analyzed (Figure 1).Figure 1. The Dispersive raman spectra for a pristinepyroxene grain and a grain captured in aerogel.Our experience suggests that Raman spectroscopy is anextremely powerful technique for the non-destructiveanalysis of particles trapped in aerogel, especially as itallows the differentiation of materials of similar com-position but widely differing states of shock deforma-tion, not possible by X-ray microanalysis. This is animportant ability as a previous investigation [18] hasindicated that impacted particles may be subject tothermal and mechanical alteration.  However there areseveral drawbacks with the technique. Localized small-scale thermal heating of the sample can occur, as ob-served during our analysis of matrix material from Al-lende.  Also many Raman systems have relativelybroad analytical spot size, resulting in spectra frommore than one fine-grained mineral component.  Therecent purchase of a new Jobin Yvon LabRam HR Ra-man microscope gives a spot size down to 2 µm whichwill hopefully enable us to distinguish between thedifferent fine-grained mineral components presentwithin the captured particles.  Furthermore Raman onlyworks on samples that contain covalent bonds [5], so itis necessary to carry out complementary investigations,such as synchrotron X-ray microprobe studies [19].We propose to use a new type of X-ray source micro-probe [20].  Bland and Cressey, with industrial partnersBede Scientific, are developing a high-brightness X-rayprobe that will allow both rapid phase identificationand quantification of abundance in-situ for small sam-ples, and has the potential for automated phase map-ping, imaging and analysis of polished sections.  Pre-liminary results [20] show that patterns can be acquiredfrom 50 µm areas of carbonaceous chondrite matrix,and can identify individual phases.  Improvements inresolution to 10 µm, and a higher X-ray flux, are an-ticipated when the instrument is completed.Summary:  Laboratory experiments have shownthat we have made substantial steps toward isolationand characterization of aerogel-captured material.  Thetechniques will now be applied to an aerogel blockexposed in LEO [11].References: [1] Bradley J. P. and Brownlee D. E.(1986) Science, 231, 1542-1544. [2] Maurette M. et al.(1991) Nature, 351, 44-47. [3] Zolensky M. E. (1994)AIP Conf. Proc 310, 291-204. [4] Graham G. A. et al.(2000) Adv. Space Res., 25, 2, 303-307. [5] ZolenskyM. E. et al. (2000) Meteorit. Planet. Sci., 35, 9-29. [6]Messenger S. (2000) Nature, 404, 968. [7] MessengerS. and Walker R. M. (1998) LPS XXIX, #1906. [8]Kelm K. et al. (1999) LPS XXX, #1999. [9] BrownleeD. E. et al. (2000) Meteorit. Planet. Sci., 35, A35. [10]Tsou P. (1995) J. Non-Crystalline Solids, 186, 415-427. [11] Hörz F. et al. (1998) LPS XXIX, #1773. [12]Burchell M. J. et al. (1999) Planet. Space Sci., 47, 189-204. [13] Burchell M. J. et al. (1999) Meas. Sci. Tech-nol., 10, 41-50. [14] Burchell M. J. et al. (2001) Mete-orit. Planet. Sci., 36. [15] Raynal P. I. et al. (2000)LPS XXXI, #1319. [16] Stadermann F. J. and Floss C.(2000) LPS XXXI, #1372. [17] Graham G. A. et al.(1996) Meteorit. Planet. Sci., 31, A53-54. [18] BunchT. E. et al. (1991) Icarus, 91, 76-92. [19] Flynn G. J. etal. (2000) LPS XXXI, #1457. [20] Bland P. A. et al.(2000) Meteorit. Planet. Sci., 35, A27.Lunar and Planetary Science XXXII (2001) 1637.pdf

Laboratory capture, isolation and analysis of microparticles in aerogel: Preparation for the return of Stardust.

Open Research Online (The Open University)

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsLaboratory capture, isolation and analysis ofmicroparticles in aerogel: Preparation for the return ofStardustConference or Workshop ItemHow to cite:Graham, G.A.; Butterworth, A.L.; Burchell, M.J.; Kearsley, A.T.; Creighton, J.A.; Mann, J.; Bland, P.A.;Cressey, G.; Jones, C.G.; Grady, M.M. and Wright, I.P. (2001). Laboratory capture, isolation and analysis ofmicroparticles in aerogel: Preparation for the return of Stardust. In: 32nd Lunar and Planetary Science Conference,12-16 Mar 2001, Houston, Texas, USA.For guidance on citations see FAQs.c© [not recorded]Version: [not recorded]Link(s) to article on publisher’s website:http://www.lpi.usra.edu/meetings/lpsc2001/pdf/1637.pdfCopyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.ukLABORATORY CAPTURE, ISOLATION AND ANALYSIS OF MICROPARTICLES IN AEROGEL:PREPARATION FOR THE RETURN OF STARDUST  G. A. Graham1,3,4, A. L. Butterworth1,  M. J. Burchell2,A. T. Kearsley3, J. A. Creighton2, J. Mann2, P. A. Bland1, G. Cressey4, C. G. Jones4 , M. M. Grady4 and I. P.Wright1, 1Planetary and Space Sciences Research Institute (PSSRI), The Open University, Milton Keynes MK76AA, U.K  (g.a.graham@open.ac.uk), 2School of Physical Sciences, University of Kent, Canterbury CT2 7NR, U.K,3Space Science Research , School of BMS, Oxford Brookes University, Oxford OX3 0BP, U.K, 4Department ofMineralogy, Natural History Museum, London SW7 5BD, U.K.Introduction:  Over the past 30 years geochemicalstudies of cosmic dust have focused on material re-trieved or captured from terrestrial locations, e.g. thestratosphere and Antarctic ice [1,2] and from low Earthorbit (LEO) [3-4].  Extensive investigation, using awide range of analytical techniques [5] has resulted insubstantial data on mineralogical and chemical proper-ties of particles [e.g. 6].  Yet, despite detailed studies[7] it is generally not possible to state unambiguouslythe parent body origin (in terms of cometary versusasteroidal) for a given class of particle [8]. In 2006dust particles collected from Comet Wild 2 should bereturned by NASA’s Stardust spacecraft [9].  Aerogelis the primary capture cell media [9], however othersurfaces on the spacecraft will also preserve particleremnants.  Laboratory simulations and LEO exposure[10-12] have shown that particles impacting into aero-gel at hypervelocity (e.g. 6 km s-1) can be preserved asalmost intact pristine material.  After recovery and pre-liminary investigations of Stardust at the NASA John-son Space Center curation facility, samples will bemade available to the international community foranalysis [9].  It is therefore essential that groups pre-pare for the return of samples, in particular developingextraction techniques and analytical strategies so thatthe maximum yield of information can be obtainedfrom every particle examined.  Herein we discuss ob-servations made during laboratory experiments focus-sing on a possible extraction technique and in-situ min-eralogical analysis.Experimental:  Impact experiments were carried outusing a two stage light-gas-gun (LGG).  The aerogeltargets had a density of 96 kg m-3. A range of projectilecompositions were used, from individual, homogene-ous minerals (e.g. olivine, pyroxene, etc.), to complex,crushed meteorite powders (matrix material from Mur-chison, Allende and Orgueil carbonaceous chondrites).In a ‘buck-shot’ technique [13] projectiles were sabot-mounted and accelerated to approximately 5.1km s-1 toimpact the aerogel targets.Raman spectroscopy was carried out on an Instru-ments SA (now Jobin Yvon) model HR640 spectro-graph with a liquid nitrogen cooled CCD detector,linked to an Instruments SA Raman scattering modulebased on an Olympus BX40 microscope.  The analyti-cal conditions for the work were: spot size of approxi-mately 25µm; a He-Ne laser (wavelength 632.8 nm) at20 mW power. A full description of the technique isgiven in [14].Electron microscopy was carried out using a Jeol840 scanning electron microscope with an Oxford In-struments eXL energy-dispersive spectrometer micro-analyser (EDS).  Samples were carbon coated. Typicalanalytical conditions were 32 mm working distance, 2nA beam current and 20 kV.  High resolution imagingwas carried out using a Philips XL FEG-SEM with anaccelerating voltage of 5-7 kV and a working distanceof 10mm.Ablation of aerogel was carried out using a 266 nmquadrupled Nd-YAG laser operated at 10 Hz.  Theaerogel block was subjected to pulses of variable en-ergy (e.g. 0.5 to 6 mJ/pulse) over variable exposuretimes (e.g. 5 to 30 seconds).Discussion:Simulation of Impact Features.  The LGG shotsproved to be highly successful in generating both trackfeatures and capturing the projectile particles at impactvelocities similar to those of the encounter velocities ofthe stardust collectors with Comet Wild 2 [9].Extraction Technique.  Probably the most signifi-cant challenge to overcome before the actual return ofstardust samples is the extraction procedure of particlesfrom the aerogel.  Several novel techniques have pre-viously been applied [15-16] with varying degrees ofsuccess.  We have carried out preliminary experimentsusing a Nd-YAG laser to ablate aerogel, with the aimof either cutting a captured particle out of the aerogel,or removing excess aerogel so that in-situ analysis canbe achieved.  Our initial experiments have shown thatdifferent combinations of pulse energy and durationallow fine control of ablation by moving the samplerelative to the fixed beam on a computer controlled x-ystage, creating ‘pits’ (nm to µm in depth) and ‘tracks’(µm in depth).  The technique will now be used to at-tempt isolation of impact-captured olivine particles.Bulk Analysis.  It is important to ascertain whichanalytical techniques should be used following extrac-tion of captured particles, and especially, in what se-quence.  Stable isotopic measurements on extraterres-trial materials are clearly of major importance, as dem-onstrated by the long-established record of the PSSRI[e.g. 17].  However, whilst such analyses provide valu-Lunar and Planetary Science XXXII (2001) 1637.pdfLaboratory capture, isolation and analysis of microparticles in aerogel:  G. A. Graham et al.able information on light elements, they are by theirvery nature essentially destructive.  Clearly, suchmeasurements must be acquired at the end of a se-quence of analytical protocols.  The first fundamentaltask is identification of bulk chemistry and mineralogy.Analytical SEM and electron microprobe analysis arethe usual workhorse techniques [5].  Unfortunately,both require that samples be given a conductive carboncoat, contaminating the sample surface and precludingthe reliable use of stable isotopic mass spectrometry.Advances in microscopy have removed the need for theconductive coat in some circumstances, see discussionin [5].  Notwithstanding the potential contaminationissue, conventional SEM does enable imaging and de-tailed X-ray microanalysis of impact tracks and cap-tured projectiles.  Nevertheless, initial characterizationof particles needs a non-destructive, and non-contaminating technique.Raman Spectroscopy.  We have used Raman spec-troscopy.  The technique obtains a vibrational spectrumof the crystal lattice of the sample by illuminating itwith a laser, and collecting the spectrum of inelasticallyscattered photons.  The detected spectrum contains asuite of peaks that are characteristic of the chemicalstructure of the sample.  As each component of thesample that is illuminated by the laser may contributeto the spectrum seen, it is fortunate that the aerogeldoes not significantly absorb or scatter the laser light.Consequently, only the selected impacted particle ma-terial is analyzed (Figure 1).Figure 1. The Dispersive raman spectra for a pristinepyroxene grain and a grain captured in aerogel.Our experience suggests that Raman spectroscopy is anextremely powerful technique for the non-destructiveanalysis of particles trapped in aerogel, especially as itallows the differentiation of materials of similar com-position but widely differing states of shock deforma-tion, not possible by X-ray microanalysis. This is animportant ability as a previous investigation [18] hasindicated that impacted particles may be subject tothermal and mechanical alteration.  However there areseveral drawbacks with the technique. Localized small-scale thermal heating of the sample can occur, as ob-served during our analysis of matrix material from Al-lende.  Also many Raman systems have relativelybroad analytical spot size, resulting in spectra frommore than one fine-grained mineral component.  Therecent purchase of a new Jobin Yvon LabRam HR Ra-man microscope gives a spot size down to 2 µm whichwill hopefully enable us to distinguish between thedifferent fine-grained mineral components presentwithin the captured particles.  Furthermore Raman onlyworks on samples that contain covalent bonds [5], so itis necessary to carry out complementary investigations,such as synchrotron X-ray microprobe studies [19].We propose to use a new type of X-ray source micro-probe [20].  Bland and Cressey, with industrial partnersBede Scientific, are developing a high-brightness X-rayprobe that will allow both rapid phase identificationand quantification of abundance in-situ for small sam-ples, and has the potential for automated phase map-ping, imaging and analysis of polished sections.  Pre-liminary results [20] show that patterns can be acquiredfrom 50 µm areas of carbonaceous chondrite matrix,and can identify individual phases.  Improvements inresolution to 10 µm, and a higher X-ray flux, are an-ticipated when the instrument is completed.Summary:  Laboratory experiments have shownthat we have made substantial steps toward isolationand characterization of aerogel-captured material.  Thetechniques will now be applied to an aerogel blockexposed in LEO [11].References: [1] Bradley J. P. and Brownlee D. E.(1986) Science, 231, 1542-1544. [2] Maurette M. et al.(1991) Nature, 351, 44-47. [3] Zolensky M. E. (1994)AIP Conf. Proc 310, 291-204. [4] Graham G. A. et al.(2000) Adv. Space Res., 25, 2, 303-307. [5] ZolenskyM. E. et al. (2000) Meteorit. Planet. Sci., 35, 9-29. [6]Messenger S. (2000) Nature, 404, 968. [7] MessengerS. and Walker R. M. (1998) LPS XXIX, #1906. [8]Kelm K. et al. (1999) LPS XXX, #1999. [9] BrownleeD. E. et al. (2000) Meteorit. Planet. Sci., 35, A35. [10]Tsou P. (1995) J. Non-Crystalline Solids, 186, 415-427. [11] Hörz F. et al. (1998) LPS XXIX, #1773. [12]Burchell M. J. et al. (1999) Planet. Space Sci., 47, 189-204. [13] Burchell M. J. et al. (1999) Meas. Sci. Tech-nol., 10, 41-50. [14] Burchell M. J. et al. (2001) Mete-orit. Planet. Sci., 36. [15] Raynal P. I. et al. (2000)LPS XXXI, #1319. [16] Stadermann F. J. and Floss C.(2000) LPS XXXI, #1372. [17] Graham G. A. et al.(1996) Meteorit. Planet. Sci., 31, A53-54. [18] BunchT. E. et al. (1991) Icarus, 91, 76-92. [19] Flynn G. J. etal. (2000) LPS XXXI, #1457. [20] Bland P. A. et al.(2000) Meteorit. Planet. Sci., 35, A27.Lunar and Planetary Science XXXII (2001) 1637.pdf

Laboratory capture, isolation and analysis of microparticles in aerogel: Preparation for the return of Stardust

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Laboratory capture, isolation and analysis of microparticles in aerogel: Preparation for the return of Stardust

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