Extent of thermal ablation suffered by model organic microparticles during aerogel capture at hypervelocities

Abstract

Abstract-New model organic microparticles are used to assess the thermal ablation that occurs during aerogel capture at speeds from 1 to 6 km s −1 . Commercial polystyrene particles (20 µm diameter) were coated with an ultrathin 20 nm overlayer of an organic conducting polymer, polypyrrole. This overlayer comprises only 0.8% by mass of the projectile but has a very strong Raman signature, hence its survival or destruction is a sensitive measure of the extent of chemical degradation suffered. After aerogel capture, microparticles were located via optical microscopy and their composition was analyzed in situ using Raman microscopy. The ultrathin polypyrrole overlayer survived essentially intact for impacts at ~1 km s −1 , but significant surface carbonization was found at 2 km s −1 , and major particle mass loss at ≥3 km s −1 . Particles impacting at ~6.1 km s −1 (the speed at which cometary dust was collected in the NASA Stardust mission) were reduced to approximately half their original diameter during aerogel capture (i.e., a mass loss of 84%). Thus significant thermal ablation occurs at speeds above a few km s −1 . This suggests that during the Stardust mission the thermal history of the terminal dust grains during capture in aerogel may be sufficient to cause significant processing or loss of organic materials. Further, while Raman D and G bands of carbon can be obtained from captured grains, they may well reflect the thermal processing during capture rather than the pre-impact particle's thermal history.

Aerogel dust collection for in situ mass spectrometry analysis

“…Since the size and composition of the captured particles have been found to directly influence the heating and ablation during the capture process, smaller single grained projectiles should also be tested. Burchell, et al, found that at an impact speed of 6.1 km s À1 in aerogel, 54% of 20 lm polypyrrole coated, polystyrene particles survived (Burchell et al, 2009a). This is taken to indicate that even when smaller particles are capture in aerogel, there would be sufficient captured material from each particle to then test for organics with DART-MS.…”

“…Laboratory impact experiments firing glycine grains into aerogel (Nixon et al, 2012) showed that in impacts at 6 km s À1 the captured grains had lost the majority of their pre-impact mass in the capture process, but no tests were carried out on the aerogel to determine where the missing material had gone or how it may have been processed in the impact event. Similarly, impacts on aerogel by polystyrene microparticles show that 84% of the mass is lost during capture at speeds of 6 km s À1 (Burchell et al, 2009a).…”

The proposed Caroline ESA M3 mission to a Main Belt Comet

“…(the Stardust speed) to 4.5 km s À1 (as here) would have increased the surviving mass fraction from 16% to 49% (Burchell et al, 2009b). This method of dust collection (Tsou et al, 2003) on Stardust returned to Earth a cargo of dust with a very high scientific yield Burchell et al, 2009a).…”

“…There are issues with contamination during manufacture and handling (see Tsou et al, 2003). Thermal modification and ablation during capture can however also present issues, with thin surface coatings lost for example (see Burchell et al, 2009b). Stardust did successfully collect indigenous organic material from the comet for analysis on Earth (see Keller et al, 2006;Sandford et al, 2006).…”

A simple route to synthesize conductive stimuli-responsive polypyrrole nanocomposite hydrogel particles with strong magnetic properties and their performance for removal of hexavalent chromium ions from aqueous solution

“…But to overcome these critical limitations, core@shell composite particles with conductive PPy shells coated on inorganic [10][11][12][13][14][15][16][17][18][19][20][21][22][23] or polymeric cores have been the subject of numerous research works from the late 1980s. These PPycoated particles allow the creation of new polymeric materials have enormous scientific and technological interests following the development of visual biomedical diagnostics [12,38], conductive composites [19,24], conductive paints [46], anticorrosion coatings [34], stationary phase in liquid chromatography [47], conductive pigments [20] and hypervelocity experiments with microprojectiles of PPy mimicking solar dusts [27][28][29][30][31]. Addtionally PPy can be prepared in the form of reactive and functional copolymers for the immobilization of metallic nanoparticles and other nano-objects [12,14,48].…”