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j.icarus.2018.08.017

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Accepted Manuscript
Simple deceleration mechanism confirmed in the terminal
hypervelocity impacted tracks in SiO2 aerogel
Mingfang Liu , Ai Du , Tiemin Li , Ting Zhang , Zhihua Zhang ,
Guangwei Cao , Hongwei Li , Jun Shen , Bin Zhou
PII:
DOI:
Reference:
S0019-1035(18)30075-7
https://doi.org/10.1016/j.icarus.2018.08.017
YICAR 12992
To appear in:
Icarus
Received date:
Revised date:
Accepted date:
5 February 2018
17 July 2018
17 August 2018
Please cite this article as: Mingfang Liu , Ai Du , Tiemin Li , Ting Zhang , Zhihua Zhang ,
Guangwei Cao , Hongwei Li , Jun Shen , Bin Zhou , Simple deceleration mechanism confirmed in the terminal hypervelocity impacted tracks in SiO2 aerogel, Icarus (2018), doi:
https://doi.org/10.1016/j.icarus.2018.08.017
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Highlights:
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All kinds of A-type tracks were classified into three types based on the conditions of vapor model
proposed by (Dominguez, 2009).
A simple deceleration mechanism was confirmed by the data fitted well with the regular data of
the terminal A-β type track.
Thermal effects happened around and along track was observed by scanning electron microscopy.
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
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Simple deceleration mechanism confirmed in the terminal
hypervelocity impacted tracks in SiO2 aerogel
Mingfang Liu1, 2, Ai Du1, 2 *, Tiemin Li1, 2, Ting Zhang1,2, Zhihua Zhang1,2,
Guangwei Cao3, Hongwei Li3, Jun Shen1, 2, Bin Zhou1, 2
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1. Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, Tongji
University, Shanghai 200092, P. R. China;
2. School of Physics Science and Engineering, Tongji University, Shanghai 200092, P. R. China;
3. National Space Science Center, Chinese Academy of Sciences, Beijing 100190, P. R. China;
Abstract
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As an attractive collector medium for hypervelocity particles, SiO 2 aerogel has been deployed on
outer space missions. Aiming at quantifying the complicated relationship between the penetration
track and the residual grains, many attempts have been made on hypervelocity experiments and
models. However, models were difficult to accord strictly well with experimental data attributed to
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many uncertainties including thermal effects, aerogel accretions and projectile ablation during the
penetration. In this paper, impact experiments were conducted at various density silica aerogels
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(50~120 kg·m-3) with regular soda-lime glass beads as projectiles. Varying degrees of thermal effects
happened around and along track was observed by scanning electron microscopy. That energy
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distribution in the track released by hypervelocity projectile has a decreasing change. The regular
data of the terminal A-β type track (the track with combined features) was found according to A-type
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tracks classification based on the conditions of vapor model (Domínguez, 2009). Just considering for
projectile overcoming the crushing strength with uniform deceleration, the simple mechanism was
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confirmed by the data fitted well with the snowplow model (Domínguez et al., 2004). The result after
tracks classification is due to the terminal track with few thermal effects and aerogel accretions. In
addition, other two types of tracks formation processes were discussed.
Keywords:
Hypervelocity impact; thermal effects; tracks classification; SiO2 aerogel
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1. Introduction
Different from ordinary materials, the unique characteristics and diverse chemical compositions
make the aerogel recognized as a state of matter (Du et al., 2013). Nanoporous and transparent silica
aerogel had previously been proven the suitability as a capture medium for interplanetary dust in the
laboratory (Tsou et al., 1988; Barrett et al., 1992; Tsou, 1995). Comet dust has been successfully
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brought back by SiO2 aerogels in Stardust Mission (Brownlee et al., 2003; Brownlee et al., 2006;
Hörz et al., 2006). Comet dust in the aerogel formed a variety of track morphologies which could be
classified into carrot-like and bulbous shapes (Brownlee et al., 2006; Burchell, 2007). The high
diversity of impactor properties was demonstrated to range from highly porous and friable
aggregates to consolidated monomineralic grains well. The various tracks were classified into three
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broad types (A, B, and C) and subsequently quantified (Hörz et al., 2006; Burchell et al., 2008).
To correctly derive the characteristics of primary grains from their impact tracks, both research of
the morphology and generation on the track are ongoing. To obtain stardust cometary particle
cumulative size distributions, laboratory calibration experiments have provided samples as
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references for composition analysis teams (Hörz et al., 1998; Burchell et al., 2008; Kearsley et al.,
2012).
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Numerous efforts were made in experiment and theory to estimate the impact conditions in aerogel.
There seems always be significant scatter of data points in penetration track length normalized to
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residual diameter versus density of silica aerogel in the impact experiments (Burchell and Thomson,
1996; Hörz et al., 1998; Burchell et al., 1999; Burchell et al., 2001; Domínguez et al., 2004; Burchell
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et al., 2008). Penetration process is accompanied by complex physical phenomena (Trucano and
Grady, 1995; Hörz et al., 2009). The thermal history of the terminal particles during capture in
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aerogel was investigated by the theoretical calculation and the designed experiment (target and
projectiles). For example, the thermal history of particles captured in several densities aerogel were
calculated by (Coulson, 2009). Hypervelocity grains were captured by a fluorescent aerogel and that
passively recorded their kinetic energies (Domínguez et al., 2003). Projectiles coated with an
ultrathin organic conducting polymer were fired and analyzed in-situ using Raman Microscopy after
captured (Burchell et al., 2009b). The Magnetic sub-micron hematite particles were selected directly
to measure the temperatures experienced during hypervelocity capture in aerogels (Jones et al., 2013).
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The captured particles typically experienced some degree of thermal ablation before coming to rest
(Noguchi et al., 2007). The kinetic energy of a particle is converted to thermal energy during the
capture process, altering or even destroying components of the particle (Jones et al., 2013).
In addition, there have also been several attempts to model the capture process when fine,
hypervelocity particles are decelerated and stopped in low density media. The energy loss of
projectiles captured in organic foams was focused solely investigated by (Anderson and Ahrens,
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1994). Based on previous experimental results, the vaporization model for impact cratering in low
density foams was proposed by (Kadono, 1999). The snowplow model, a kinetic model of impact
cratering in aerogels were developed and tested in which an outgoing cylindrical shock wave
attenuates was discussed by (Domínguez et al., 2004). Energy loss in aerogel with carrot shaped
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tracks was researched. After then, a general model of track formation was proposed by (Domínguez,
2009). This vapor model includes the presence of partially and completely vaporized aerogel
material that can reduce to the kinetic “snowplow” model. Analyzing experimental data from in-situ
observation, deceleration mechanism of projectiles was provided by (Niimi et al., 2011; Kadono et
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al., 2012). In this simplified penetration model, the deceleration of hard sphere projectiles in aerogel
is described by hydrodynamic and crushing regimes for higher and lower velocities, respectively.
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In this paper, we focus on thermal effect and formation process in terminal type A tracks.
Hypervelocity impactor experiments were conducted in silica aerogel (50~120 kg·m-3) @5 km·s-1
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with glass bead projectiles. The landing stage was designed to place the two samples in the same
impact experiment. Some tracks created on the cylinder surface were observed by scanning electron
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microscope (SEM). The thermal effects were studied by various degrees of damaged microstructure
in aerogel. The dispersion of track classification results was greatly reduced by vapor model. Based
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on the classified track results, the track formation process was briefly discussed. Among them, the
regular data of the terminal A-β type was investigated. The result was fitted well with sample
interaction model, which just considering for projectile overcoming the crushing strength with
uniform deceleration.
2. Experimental Description
2.1 . Experimental Samples
A series of SiO2 aerogel samples (50~120 kg·m-3) were used for hypervelocity impact experiments.
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Combined with ethanol supercritical drying process, they were prepared by acid-base catalyzed
method similar to our previous work (Liu and Zhou, 2013; Liu et al., 2013). All aerogel samples
were monolithic obtained in the shape of 1.5~2.5-cm-long cylinder, 3.2~4.9 cm in diameter. The
apparent density is determined by weighing method. Corresponding number of shots for different
density samples in experiment are listed in Table 1.
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2.2 . Experimental Condition
Laboratory Impacts with Glass Beads
Soda-lime glass beads (density~2.4×103 kg·m-3) were employed as projectiles in the impact
experiments. As shown in figure 1a, these glass beads were adhered nearly as a monolayer on a
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Mylar film for launch. Regular spherical glass beads were used to reduce the uncertain influence of
penetration behavior (SEM in Fig. 1b, c). The projectile diameter range is 60-100μm, mainly
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concentrated in 70-92μm (accounting for 75% of the total) (Fig.1d).
Fig. 1. Images and parameter of glass beads (a) glass beads @Mylar film as projectiles (b, c) regular
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spherical glass solid beads (the scale bar: 100μm, 20μm) (d) distribution range of projectiles size.
Launch Facility
The impact laboratory experiments were conducted by the plasma gun (PG) of plasma dynamic
accelerator (PDA) at Nation Space Science Center (NSSC), the Chinese Academic of Sciences
(CAS). Before the impact experiments, an ablator film is used to load the projectiles (Fig.1a), similar
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to the processes described by (Best and Rose, 1999). In the PDA (Huang et al., 2009), particles were
loaded on Mylar film. The hot plasma is produced by disruptive discharge and rapidly accelerated by
a strong Ampere's force. This plasma then accelerates the Mylar film. The particle cloud is
accelerated by the PG. The device is similar with that mentioned by (Kitazawa et al., 1999).
The particle cloud was impacted to the two aerogel targets through the middle of the window (Fig.
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2). In this way, impact experiments with improved efficiency provide approximately the same impact
velocity. And it is also convenient for optical imagery to acquire data of tracks without cutting
aerogel into thin slice (the track created near the cylinder surface). In addition, the vacuum of inner
facility is lower than 6×10-3 Pa. The velocity of impactors is controlled by the capacitor discharge.
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The light signal acquisition unit is placed in front of sample stage to measure the flight time of the
particles. The signal was acknowledged that produced by the most group reaching particles. The
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speed was calculated from the flight time and flight distance (6 m). The impact velocity was covered
about 5.0 ± 0.7 km·s-1 (Table 1). Due to the normally large error range of PDA method, some low
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velocity impacts may exist.
Fig. 2. a) Samples placement. Both samples are targeted simultaneously. b) Landing-surface on the targets.
The particles were impacted on the edge of the sample leaving a gray area where the film is carbonized.
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Table 1. List of experimental conditions.
Aerogel density
(kg·m-3)
velocity
(km·s-1)
1
2
3
4
5
6
50,53
64,76
87,108
72,119
52,68
89
4.23
6.06
5.31
——
4.69
5.66
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Shoot number
Image
Based on optical imagery, an industrial vision measuring machine (VMM) was employed to record
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dimensions of tracks and residual grains. By means of side or back green lighting, tracks were
photographed on a glass or transparent plastic surface. The parameters of the tracks (length and the
maximum diameter of penetration tracks) near the side surface were carefully measured.
The morphology of tracks created in the aerogel was observed by Scanning Electron Microscopy
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(SEM, Philips-XL30FEG). Thin slice cut from the surface by a scalpel blade was sputter coated with
gold (33mA current, 450 seconds) before the SEM observation.
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3. Results
As provided in figure 3, the impacted track in the sample was observed morphologically by SEM.
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As a morphological contrast picture, the typical structure of silica aerogel is presented in figure 3b,
like stacked silica spheres and the porous morphology. The opening (entrance hole size ~60μm) into
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the interior of the track is observed vertically (Fig. 3a). The track wall is surrounded by depressed
and spalled region. The entrance hole (point c) shows obvious porous structure that was ablated and
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Compacted. (Fig. 3c). For the same track, the VMM and SEM were employed on its morphology.
The part of the track was left exactly along the side of the sample (Fig. 3d). Four points in the track
were observed separately. Three points (f, g, h) were located at approximately the same penetration
length and one point (i) was from deeper penetration length (Fig. 3e). Compared with figure 3b,
these four points have various degrees signs of high-temperature ablation and compression. The
signs of ablation and squeezing compression on the track wall are most noticeable (Fig. 3g). The
symptom is better outside the track wall (Fig. 3f). Far away from the central axis of the track, the
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point at the track branch seem not so bad. Pores of microstructure are not filled completely (the scale
bar: 200nm, Fig. 3h). The situation at point i (near to the middle track, Fig. 3i) was less severely
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damaged than at the point g (close to impact entrance, Fig. 3g).
Fig. 3. The observation of track by VMM and SEM. (a) Top view of the entrance hole in aerogel (50 kg·m-3)
created by the impactor. (b) Typical porous structure of silica aerogel. (c) The edge-magnification of the hole
indicated by white arrow in figure a. (d) The observation of impacted track obtained by VMM (72 kg·m-3). The
impact direction is from the left to right. (e) The observation of the same track in figure d obtained by SEM. The
white arrows are marked at the point of observation followed by figure f, g, h, i. (f) The point outside of the track
wall. (g) The observation area on the track wall. (h) The point on the branch of the track. (i) The point on to the
track and closed to the terminal track.
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Fig. 4. Hypervelocity particle captured in the silica aerogel (density~52 kg·m-3) with the narrow penetration
track (a) The whole track. (White line indicates the path of penetration) (b) Maximum diameter of the track. (c)
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Captured particle in the terminal track.
Due to the adhesion to the ablator film, not all of the captured particles are mono-disperse particles.
The terminal tracks also find non-spherical grains, irregular fragment, or the spherical glass bead
with the film residue. Conducted by PG with high temperature (Best and Rose, 1999), the projectiles
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may undergo some physical alteration as described by (Kitazawa et al., 1999). In order to study the
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law of interaction between hypervelocity projectile and aerogel, the data with mono-disperse
spherical glass beads at the terminal tracks can be treated as valid data.
The particle sizes are counted and compared before and after impacting (Fig. 5a). The statistical
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individuals are 145 and 95, respectively. It‟s found that the average particle size decreased from
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81.06μm to 78.03μm, indicating a slightly melting or vaporization of projectiles during the capture.
The track lengths () from 11 samples are normalized to projectile diameters ( ), which is plotted
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against target bulk density (Fig. 5b). In addition, the normalized maximum impact track diameter
(/ ) versus aerogel density is potted in figure 5c.
In the low-density range (< 80kg ∙ −3 ), there seems to be no trend that the with normalized track
length against and the density. The discrete data points may be caused influenced by uncertain
interaction between the low-density aerogels and hypervelocity projectiles. The data of the
normalized maximum impact diameter (/ ) against aerogel density is fitted by


∝ −0.35 with
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correlation coefficient  2 = 0.82. This is a manifestation of the mechanical properties of aerogel
(Moner-Girona et al., 1999), and also similar with the results mentioned by (Domínguez et al., 2004).
However, there are some individual points deviate from the overall trend that making it difficult to
obtain sufficiently accurate, quantitative information for our purposes. When hypervelocity
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projectiles penetrates into aerogel, there would be additional complications include build-up and
shedding of caps of compressed or melted aerogel and general fragmentation in track walls
(Domínguez et al., 2004; Brownlee et al., 2006). These formation and loss of such features could
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contribute to the some of the scatter in the results.
This may be related to the complex interaction between hypervelocity projectiles and aerogel,
which is required classification and statistics. The mechanisms that govern development of track
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features and the deceleration in the interior of the aerogel are shown to be different in figure 6.
Fig. 5. (a) Summary of results: original and captured projectiles diameter. (b) The normalized track lengths
(/) against target bulk density (ρ). (c) The normalized maximum impact track diameter (/ ) versus
aerogel density (ρ). Dashed red line indicates fit to data, given by


∝ −0.35 .
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Fig. 6. Classification of tracks. (a) A-α type track with  > 0, (b) A-β type, (c) A-γ type track with  = 0.
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Different from previous work about the kinetic snowplow model (Kitazawa et al., 1999;
Domínguez et al., 2004), a general vapor model of track formation was proposed by (Domínguez,
2009). The existence of partially and completely vaporized aerogel material were considered in track
formation. In this model, the author assumes that  is the proportion of the vapor phase in the
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impact track. Whether the projectile is wrapped with aerogel, the two extreme situations ( = 0 and
 = 1) were explained, respectively. In addition, if  = 0, under certain conditions, the vapor
model reduces to snowplow model.
Based on this vapor model condition and according to the expansion cavity and the extended crack
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in the impact track, we classify the A-type tracks into three types. They are in turn defined as A-α
type, A-β type and A-γ type (Fig. 6). For the track morphology, as shown in figure 6a, this is a
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typical carrot-shaped track which is presumed  > 0. When the hypervelocity projectiles impact on
the silica aerogel, the tracks were created by silica vapor and shock wave during the penetration
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process. The process is accompanied by the high temperature and pressure and the expansion cavity
is significant in Fig. 6a. Figure 6c shows an A-γ type track. There appears to be no apparent
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expansion of the cavity with characteristic cone or skirt shaped fractures distributed around the track.
These fractures look similar to the ones that are observed near the end of type A tracks (see in
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(Burchell et al., 2009a; Hörz et al., 2009; Niimi et al., 2011)). It is indicted that there is no silica
vapor ( = 0) in this scenario. The deceleration of the projectile depends mainly on the strength and
elasticity of the aerogel material. At the same time, the projectile is accompanied by the bow shock
during the penetration process. The track branches are obliquely and forwardly covered around the
track wall along the impact direction. They are similar in shape as pricking aerogel with a needle as
described by (Kitazawa et al., 1999).
A-β type track includes obviously two parts. As shown in Fig. 7, the beginning part L1 has
obviously large and rough track, while the end part L2 has thin and smooth track. The first half track
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(L1) appears to be a hybrid type of the A-α type and or A-γ type (Fig. 6b). L1 track has a clearly
enlarged cavity, indicating a certain amount of silica was vapored on the track ( > 0). The diameter
of track is significantly greater than the residual diameter. Furthermore, L1 of some tracks are also
accompanied by stress relief leading material to cracks like snowplow. However, all A-β type track
shows a consistent and smooth track at the later track (L2). The track is tube-like and slightly smaller
than the diameter of the stopping particles. There are little fine-scale features observed like styli,
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spiraling „petals‟ and short lateral „spikes‟ as described in detail by (Kearsley et al., 2012). According
the conjecture of (Domínguez et al., 2004), there may be absence of aerogel accretion in L2 track.
The interaction between the projectile and the aerogel in L2 track is different from the L1 track in
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A-β type track.
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Fig. 7. The normalized track length (/ ) against target bulk density for (a) A-α type and (c) A-γ type,
respectively. The normalized maximum diameter (/ ) against target bulk density for (b) A-α type and (d)
A-γ type, respectively. (e) The normalized track length (2 /) of L2 track versus target bulk density. Dashed
blue line indicates fit to data, given by
2

∝ −0.99 , correlation coefficient  2 = 0.99. (f) The diagram of
A-β type track including two sections named L1 and L2.
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The relevant parameters (/ vs. ρ, / vs. ρ) of the three types of track are shown in figure 6.
There is some scatter of A-α type and A-γ type normalized track length (/ ) against aerogel
density (Fig. 7a, c). Although parameters have been normalized to the track length, the ratio of the
maximum to the minimum is at least close to 5. The scatter in these individual points is large with no
obvious tendency to change with density. The relationship between the normalized maximum
diameter (/ ) of the A-α type and the A-γ type track versus the density (ρ) are displayed in
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figures 7b, d. Likewise, the data points circled in the figure 7b make the data appear more dispersed.
It is noteworthy that the two sets of average data (/ vs. ρ) are 2.55 ± 0.21, 1.85 ± 0.11,
respectively (Points circled in Fig. 7b are excluded). The model and data in the work of (Domínguez,
2009) showed that when  = 0, the track has evolved a radius less than 3 times the radius of the
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projectile. When the radius of a track grows to about 4 times the radius of the projectile
( = 6 km ∙ s −1 ), silica vapor is unworkable in the track. It also shows a first upper limit to
the survival of vapor in hypervelocity tracks. All these coincidences indicate that this method of track
classification is feasible.
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L1 of A-β type track has the maximum diameter of the track expansion cavity near the impact
entrance (Fig. 7f). Then with the penetration process, the projectile is gradually decelerated. The
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effect of thermal and shock wave gets weak. The diameter of the track gradually decreases and even
is smaller than the projectile diameter in L2. As mentioned by (Anderson, 1998), when the
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hypervelocity impactor slowed below the sound speed of the aerogel, the strength and elasticity of
the aerogel become the primary source of deceleration of the projectile.

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In addition, the data ( 2 ∝  −0.99 ,  2 = 0.99) of L2 shows that the data is less discrete and the

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length of L2 have a function of projectile diameter.
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Fig. 8. The proportions of the three types of track in each density of aerogel target.
As shown in figure 8, the proportions of the three types of tracks in each density are counted. It
can be concluded that A-α type tracks are more likely to occur in aerogel samples with density lower
than 80 kg·m-3. A-γ type tracks often appeared in high density aerogel materials. In low-density
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materials, where Accompany with A-α type tracks appear, A-β type tracks appear.
4.1 Data correlation
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4. Discussion
As shown in Fig. 5b, the / data are widely scattered in the low-density range, there is no
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clear trend or relevance. In the high-density range, the / data tends to decrease with increasing
density. The inhomogeneities of aerogels, rotation and shock pressure of projectile may contribute to
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the wide variation of / in the low-density range (Kitazawa et al., 1999). It is also possible that
despite the same impact parameters of PG (voltage, capacitance, degree of vacuum, etc.), there is
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inevitably that the individual particles have different impact velocity. As shown in Fig. 5c, the
double-exponential fitting relationship of the normalized maximum impact diameter (/ ) versus
aerogel density (ρ) have basically agreement with that of (Domínguez et al., 2004), which is related
to the nature of the material itself relationship.
As shown in figures 7a, c, the tracks are classified and statistically analyzed. For A-α type and A-γ
type, the data scatter of / are wider. In particular, the A-α type track does not show a clear trend
with density (Fig. 7a). It is indicated that the generation of this A-α type track is more random. It
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also means that the interaction of hypervelocity particles with low-density range aerogel is affected
by many factors. However, the / data for A-α type track are narrow (Fig. 7b). After removing
two discrete points in the data (circled in the figure 7b), the average range of / is 2.55 ± 0.21.
/ range is close to theoretical prediction (Domínguez, 2009) and narrow dispersion. It proves
that this classification has a certain credibility. In addition, the A-γ type track appears nearly at all
sample densities (Fig. 8) and the / data is 1.85 ± 0.11.
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The A-β type track seems to more complicated, which has two sections of tracks. L1 of the A-β
type track (Figs. 4a, 6b) is similar to A-α type and A-γ type track. As shown in figure 4a, left the
initial part of the carrot shaped track (L1), with a certain critical state and a small angle of deflection,
the penetration results in a tubular track (L2) (Fig. 4c). The maximum diameter of the L2 is slightly
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smaller than and close to the diameter of the stopping projectile.
Compared with A-α type, A-γ type, L2 track has a completely different track morphology. The
track morphology of L2 is a smooth, thin tubular track left by “squeezing” into the aerogel. The L2
track is free from the obvious fine-scale features of L1, like the fine branches created by shock waves
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and thermal effects and the styli structure on the surface of wide track walls. That means that aerogel
accretion may be absence of in L2 track. The reason for the formation of L2 is no longer complicated.
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It can be found that the fitted correlation coefficients are improved with classification (Fig. 7e). The
fitting coefficient is r2 = 0.99. In the high-density range, fewer data points are presented due to A-β
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type individuals were formed difficultly in the high-density aerogel (Fig. 8).
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4.2 Interactions in three types of tracks
When the a hypervelocity projectile impacts the a target, not all the kinetic energy is coupled back
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into the particle; some is partitioned into the target and ~50% of the total kinetic energy is typically
converted into thermal energy at high velocities (Domínguez et al., 2004; Trigo-Rodriguez et al.,
2008). The shock wave is generated in the radial direction of the track. The aerogel is compressed by
the expand outward shock wave. The energy of the shock wave in the material weakens until it
cannot overcome the strength of the aerogel, leaving an impact track (Domínguez et al., 2004).
A simple, semi-analytical model was developed by (Coulson, 2009). It suggests that the majority
of the kinetic energy lost from the particle goes into heating the aerogel and the particle. With the
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impacting track length longer, the temperatures of impactor through frictional heating is lower in
aerogel. Molten aerogel within and immediately adjacent to tracks was observed in figure 3. The
porous structure at point g is more severely damaged than point i on the impact track wall (Fig. 3g, i).
The porous destruction shows the signs of ablation and compression company with high-temperature
and shock wave in the radial direction of the track (Figs. 3g, f, h). That means the energy distribution
released by the projectile also has a decreasing change.
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A-α type track is a typical carrot shaped penetration. The expansion of the track wall is caused by
the shock wave with the instantaneous high temperature and the vaporization (Domínguez, 2009).
This process is accompanied by the complex energy, thermal effects and vaporization behavior in
capture material. The narrow distribution of data (/ ) from a statistical point reflects this
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phenomenon (Fig. 7a).
A-γ type track with many branches around the track wall are observed similar with description in
(Niimi et al., 2011), which marked the velocity was as lower than 3~4km/s in his work. Compared
with A-α type track, A-γ type track is mainly created by hydrodynamic force with energy loss of
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material fracture. The thermal effect of track expansion accompanying is not obvious in A-γ type
track.
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L1 of A-β type track have similar morphology with both A-α and A-γ. However, L2 of A-β type
track seems to be different from the other two types of tracks. The normalized track length and

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density of L2 is close to -1 exponentiations ( 2 ∝ −0.99 ,  2 = 0.99), agreed with the experiments

in (Burchell et al., 2009a). The ratio of track length to diameter is in the range of 50 to 500 at the
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figure 5 in his paper. This expression is very close to the track length scales of snowplow model (see


∝ −1 (  is the
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the expression (24) in (Domínguez et al., 2004)), which could be simplified to
penetration depth,  is projectile of radius). Moreover, L2 is located in the terminal of the total A-β
type track, which means that L2 track may only be caused by a simple material resistance, few other
complicated factors. The deceleration mechanism of hard projectiles in aerogel could be described by
crushing regimes for lower velocities (Niimi et al., 2011).
For simplicity, we consider a spherical projectile (diameter- , density- ) creates L2 track.
Assuming  is constant. The crushing strength of the aerogel (density-0 ) is the dominant force
that keeps the particles decelerated. Ignoring viscous drag and thermal effects, we suppose the
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deceleration process of the projectile is a linear motion of uniform deceleration. The initial speed ()
is the instantaneous speed at the junction of L1 and L2. The final speed ( ) is the critical velocity for
aerogel crushing. The equation of motion for the deceleration process is given by:
 2 −  2 = 22
(1)

The acceleration value is  = . Similar to (Domínguez et al., 2004), the force ( ) exerted by
 =  
where A is the cross sectional area of the projectile,
(2)
=
 2
.
2
aerogel is given by:
4
The mass of the projectile is  = 3
1
 2
2 0 
The crushing pressure ( ) of the
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 =
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the aerogel resisting compression is given by:
 3
.
2
(3)
Simultaneous above equations, we can get the
expression for normalized length of track versus density of silica aerogel:
2

∝ 0 −1 . This expression is similar to expression (24) in (Domínguez et al.,
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After simplification,
(4)
M
2 2
2
=  2 − 1 0 −1
 3

2004). It is noteworthy that this model is only a simplified expression of the process for the L2, there
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are some variables need to be further explored. For example, the critical velocity for crushing ( ) is
relate to the mechanical properties of aerogel. Different densities may mean different values  .
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Similarly, the instantaneous speed () at the junction of L1 and L2 is possibly relate to the
mechanical properties rather than the velocity impact by PG. The speed () may be the transition
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between hydrodynamic and crushing regimes for higher and lower velocities, which is mentioned by
(Niimi et al., 2011). It could be avoided that inconsistent effects of impact velocities are accelerated
by plasma in A-β type track.
5. Conclusion
Impact experiments were performed to investigate the interaction between spherical hypervelocity
glass particles and silica aerogel. First, We found the destruction of porous morphology by SEM and
varying degrees of thermal effects happened around and along the track. The results imply that the
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kinetic energy lost from the particle goes into heating the aerogel.
Second, The dispersion of experimental data means that the tracks were created by impacted by
projectile with many uncertain factors, including different impact velocities, thermal effects and the
inhomogeneities of capture medium, etc. All kinds of A-type tracks were classified according to the
conditions of vapor model. The average of normalized maximum diameter is close to theoretical
prediction. Three types of tracks show the different interaction in each type track. The hydrodynamic
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effect at high speed and the crushing strength under low speed were observed in the same track.
Third, The regular A-β type data effectively slowly show terminal tracks created show by few
thermal effects and aerogel accretions, excluding different impact velocities caused by plasma
accelerating. The simple deceleration mechanism was confirmed by L2 track. After simplification,
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Our results approximately in accordance with simplified snowplow theory of (Domínguez et al.,
2004).
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Acknowledgement
We are thankful for financial support from National Key Research and Development Program of
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China (2017YFA0204600), Science and Technology Innovation Fund of Shanghai Aerospace, China
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CE
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(SAST201469) and the Natural Science Foundation of China (No. 11404213).
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References
Anderson, W. W., 1998. Physics of interplanetary dust collection with aerogel.
Anderson, W. W., Ahrens, T. J., 1994. Physics of interplanetary dust capture via impact into organic polymer foams.
Journal of Geophysical Research E. 99, 2063-2071.
Barrett, R., Zolensky, M., Horz, F., Lindstrom, D., Gibson, E., 1992. Suitability of silica aerogel as a capture medium for
CR
IP
T
interplanetary dust. Lunar and Planetary Science Conference Proceedings, Vol. 22, pp. 203-212.
Best, S. R., Rose, M. F., 1999. A plasma drag hypervelocity particle accelerator (HYPER). International Journal of
Impact Engineering. 23, 67-76.
Brownlee, D., et al., 2006. Comet 81P/Wild 2 under a microscope. science. 314, 1711-1716.
Brownlee, D. E., et al., 2003. Stardust: Comet and interstellar dust sample return mission. Journal of Geophysical
Research: Planets. 108.
Burchell, M., 2007 Stardust and comets. In: R. B. Hoover, G. V. Levin, A. Y. Rozanov, P. C. W. Davies, (Eds.),
AN
US
Instruments, Methods, and Missions for Astrobiology X.
Burchell, M. J., Creighton, J. A., Cole, M. J., Mann, J., Kearsley, A. T., 2001. Capture of particles in hypervelocity
impacts in aerogel. Meteoritics & Planetary Science. 36, 209-221.
Burchell, M. J., Fairey, S. A. J., Foster, N. J., Cole, M. J., 2009a. Hypervelocity capture of particles in aerogel:
Dependence on aerogel properties. Planetary and Space Science. 57, 58-70.
Burchell, M. J., et al., 2008. Characteristics of cometary dust tracks in Stardust aerogel and laboratory calibrations.
M
Meteoritics & Planetary Science. 43, 23-40.
Burchell, M. J., Foster, N. J., Ormond‐ Prout, J., Dupin, D., Armes, S. P., 2009b. Extent of thermal ablation suffered by
model organic microparticles during aerogel capture at hypervelocities. Meteoritics & planetary science. 44,
ED
1407-1419.
Burchell, M. J., Thomson, R., 1996. Intact hypervelocity particle capture in aerogel in the laboratory. AIP Conference
Proceedings, Vol. 370. AIP, pp. 1155-1158.
PT
Burchell, M. J., Thomson, R., Yano, H., 1999. Capture of hypervelocity particles in aerogel: in ground laboratory and low
earth orbit. Planetary and Space Science. 47, 189-204.
Coulson, S. G., 2009. On the deceleration of cometary fragments in aerogel. International Journal of Astrobiology. 8,
CE
9-17.
Domínguez, G., 2009. Time evolution and temperatures of hypervelocity impact-generated tracks in aerogel. Meteoritics
& Planetary Science. 44, 1431-1443.
AC
Domínguez, G., Westphal, A. J., Jones, S. M., Phillips, M. L. F., 2004. Energy loss and impact cratering in aerocyels:
theory and experiment. Icarus. 172, 613-624.
Domínguez, G., Westphal, A. J., Phillips, M. L. F., Jones, S. M., 2003. A fluorescent aerogel for capture and identification
of interplanetary and interstellar dust. Astrophysical Journal. 592, 631-635.
Du, A., Zhou, B., Zhang, Z., Shen, J., 2013. A Special Material or a New State of Matter: A Review and Reconsideration
of the Aerogel. Materials. 6, 941-968.
Hörz, F., et al., 2006. Impact features on Stardust: Implications for comet 81P/Wild 2 dust. Science. 314, 1716-1719.
Hörz, F., Cintala, M. J., See, T. H., Nakamupa-Messenger, K., 2009. Penetration tracks in aerogel produced by Al2O3
spheres. Meteoritics & Planetary Science. 44, 1243-1264.
Hörz, F., et al., 1998. Capture of hypervelocity particles with low-density aerogel.
Huang, J., et al., 2009. Mechanism and operation parameters of a plasma-driven micro-particle accelerator. Chinese
ACCEPTED MANUSCRIPT
Science Bulletin. 54, 616-622.
Jones, S. M., Anderson, M. S., Dominguez, G., Tsapin, A., 2013. Thermal calibrations of hypervelocity capture in aerogel
using magnetic iron oxide particles. Icarus. 226, 1-9.
Kadono, T., 1999. Hypervelocity impact into low density material and cometary outburst. Planetary and Space Science.
47, 305-318.
Kadono, T., Niimi, R., Okudaira, K., Hasegawa, S., Tabata, M., Tsuchiyama, A., 2012. Penetration into low-density
media: In situ observation of penetration process of various projectiles. Icarus. 221, 587-592.
Kearsley, A. T., et al., 2012. Experimental impact features in Stardust aerogel: How track morphology reflects particle
structure, composition, and density. Meteoritics & Planetary Science. 47, 737-762.
CR
IP
T
Kitazawa, Y., Fujiwara, A., Kadono, T., Imagawa, K., Okada, Y., Uematsu, K., 1999. Hypervelocity impact experiments
on aerogel dust collector. Journal of Geophysical Research-Planets. 104, 22035-22052.
Liu, G., Zhou, B., 2013. Synthesis and characterization improvement of gradient density aerogels for hypervelocity
particle capture through co-gelation of binary sols. Journal of Sol-Gel Science and Technology. 68, 9-18.
Liu, G., Zhou, B., Du, A., Shen, J., Yu, Q., 2013. Effect of the thermal treatment on microstructure and physical
properties of low-density and high transparency silica aerogels via acetonitrile supercritical drying. Journal of
AN
US
Porous Materials. 20, 1163-1170.
Moner-Girona, M., Roig, A., Molins, E., Martinez, E., Esteve, J., 1999. Micromechanical properties of silica aerogels.
Applied Physics Letters. 75, 653-655.
Niimi, R., et al., 2011. In situ observation of penetration process in silica aerogel: Deceleration mechanism of hard
spherical projectiles. Icarus. 211, 986-992.
Noguchi, T., Nakamura, T., Okudaira, K., Yano, H., Sugita, S., Burchell, M. J., 2007. Thermal alteration of hydrated
minerals during hypervelocity capture to silica aerogel at the flyby speed of Stardust. Meteoritics & Planetary
M
Science. 42, 357-372.
Trigo-Rodriguez, J. M., Domínguez, G., Burchell, M. J., Hoerz, F., Llorca, J., 2008. Bulbous tracks arising from
hypervelocity capture in aerogel. Meteoritics & Planetary Science. 43, 75-86.
ED
Trucano, T. G., Grady, D. E., 1995. Impact shock and penetration fragmentation in porous media. International Journal of
Impact Engineering. 17, 861-872.
Tsou, P., 1995. Silica aerogel captures cosmic dust intact. Journal of Non-Crystalline Solids. 186, 415-427.
PT
Tsou, P., Brownlee, D., Laurance, M., Hrubesh, L., Albee, A., 1988. Intact capture of hypervelocity micrometeoroid
AC
CE
analogs. Lunar and Planetary Science Conference, Vol. 19.
ACCEPTED MANUSCRIPT
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CE
PT
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US
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