Low-density Aerogels Research Articles

Simulation and experimental analysis of aerogel's attenuation for high-energy alpha particles in fission-fusion fragment rocket applications

Emerging studies are geared toward exploring new methods of nuclear rocket propulsion to provide more efficient space transit beyond Earth's orbit. One method is to employ a Fission Fragment Rocket Engine utilizing fissionable layers embedded in a low-density aerogel. A quantitative understanding of particle attenuation is essential for developing a functional prototype that permits fission fragments to escape the layers and contribute to specific impulse rather than being attenuated and generating waste heat. In this investigation, the MCNP code was used to theoretically analyze the attenuation of alpha particles from 241Am sources within aerogel materials. Simulations were conducted on aerogels with various densities and compositions. These simulations aimed to predict the expected intensity of alpha particles reaching a detector. CR-39 was employed as a Plastic Nuclear Track Detector to assess particle attenuation by the aerogels. The experimental and simulation results show that the threshold areal density of atoms was found to be high 1020 atoms/cm2 for the three materials studied in this project.

Characterization of similar Marshak waves observed at the LMJ

We detail results of two experiments performed at the Laser Mégajoule (LMJ) facility aimed at studying similar supersonic Marshak waves propagating in a low-density SiO2 aerogel enclosed in metallic tubes. Similar means here that these two experiments, driven by the same input radiation temperature history, use purposely very different tubes in terms of length (L = 1200 or 2000 μm), diameter (2R = 1000 or 2000 μm), nature of the wall (gold or copper), and aerogel densities (ρ = 30 or 20 mg/cm3), yet the transit time and the radiation temperature of the fronts at the tube exit are the same for both shots. Marshak waves are characterized at the exit using simultaneously for the first time to our knowledge, a one dimensional soft x-ray imager from which the radiation front transit time and curvature are measured and also a broadband x-ray spectrometer to infer its temperature history. These constraining results are then successfully compared to those from simple analytical models [Cohen et al., Phys. Rev. Res. 2, 023007 (2020) and Hurricane et al., Phys. Plasmas 13, 113303 (2006)] and from the three dimensional Lagrangian radiation-hydrodynamics code TROLL to get information on x-ray energy losses. Controlled compensation effects between the length, diameter, and nature of the tubes (governing these losses) are such that the radiation temperature drop along the tubes is eventually the same for these two similar shots.

A novel reduced thermal conductivity ductility cement-based composite material with containing aerogels: Towards multi-function in buildings

Fully exploring and expanding the performance of building materials has become an important direction for the sustainable development of building materials. In this study, low-density silica aerogel (LSA) with a density of 74.3 kg/m³ and conventional silica aerogel (CSA) with a density of 141.6 kg/m³ were used as partial aggregates to prepare a reduced thermal conductivity ductility cement-based composite material (RTCDCC). Based on this, the effects of LSA and CSA at different contents on the compressive strength, four-point bending performance, water absorption, thermal conductivity, and density of RTCDCC were compared and studied. The results showed that when the aerogel content was the same, the influence of LSA on the mechanical and physical properties of the mixture was more significant compared to CSA. Furthermore, the mixture exhibits good ductility when the content of aerogel was less than 30 %. Additionally, the impact of different density aerogels on the internal pore distribution of the mixture was investigated through low-field nuclear magnetic resonance (NMR) tests, providing further insights into the reasons for the variations in performance between LSA and CSA mixtures. Notably, the RTCDCC prepared in this study not only has good compressive strength but also maintains a lower thermal conductivity, and an average comprehensive performance index (Icp) of 0.63, which promotes the application of aerogel in the realm of multi-function building materials.

A combination of “Inner - Outer skeleton” strategy to improve the mechanical properties and heat resistance of polyimide composite aerogels as composite sandwich structures for space vehicles

Low density aerogels with high fatigue resistance are widely used in the manufacturing of core material structures in aircraft fuselage to be able to tolerate the extreme environment of aerospace. However, most organic aerogel materials have poor energy absorption of external impact forces, and are prone to irreversible deformation, such as contracture and collapse in the process of long-term service. In order to solve this problem, a new type of thermosetting-thermoplastic polyimide composite aerogel was prepared, with its microstructure presenting the coexistence of the inner and outer skeletons. The intermolecular forces promoted the assembly of the soft thermoplastic layer and the strong thermosetting layer in the thermodynamic process with 4.63–6.55 μm range. The hard-soft layer structure improved the compressive and the shear load bearing capacities by bending of the panel (Compressive modulus is 1.60 MPa–3.52 MPa, tensile modulus is 1.04 MPa–1.45 MPa). Its permanent degradation less than 1.5 % after 500 cycles at 30 % strain. C–CPIAs also exhibited excellent heat resistance and thermal insulation performances, with a T5% value of 612 °C (C-CPIA-2), Tg of 458 °C (C-CPIA-3). The sandwich materials can be used as outer protective composite material of aircraft fuselage for future deep space missions.

Synthesis and Characterization of Modified Silica Gel from Teff Straw Ash Using Sol-gel Method

Teff straw ash was first converted into sodium silicate solution, then processed via sol-gel, producing low-density silica aerogel (modified silica gel). A one-step modification method was applied to produce modified silica gel from teff straw ash. The method involved the use of trimethylchlorosilane (TMCS), ethanol, and n-hexane as reagents, with a specific molar ratio. Then, we used ambient pressure drying to complete the process. The modified silica gel had improved properties compared to the unmodified one. These chemicals were used to modify the surface properties of the substrate. The surface of the modified silica gel used in the sol-gel method was altered with a TMCS solution. We studied how the properties of silica gel changed when we used different amounts of ethanol, n-hexane, and TMCS to modify it. Using BET, FTIR, XRD, and SEM, the properties of the porous structure of the modified silica gel were identified. The optimal molar ratio of pore (ethanol/TMCS/n-hexane) for modifying silica gel was found to be 25/25/100. This resulted in a modified silica gel with a specific surface area of 909.25 m2/g, a pore size of 0.5422 cm3/g, and a pore volume of 2.670 nm. The functional groups of the modified silica gel were verified by the FTIR analysis. The XRD analysis verified the amorphous and crystalline nature of the silica gel and the modified silica gel, respectively. The SEM images revealed the surface morphology of the modified silica gel.

Exoskeleton-like mechanical enhanced low-density aerogel with electromagnetic interface shielding and infrared stealth

The integrated design and mechanical enhancement of multifunctional electromagnetic interference shielding and infrared stealth aerogels are challenging for the development and application of novel aerogels. Here, inspired by the biological exoskeleton to enhance the body, we develop the exoskeleton-like aramid nanofiber/polyimide/MXene (APM) aerogel through a secondary impregnation strategy. For APM aerogel, the polyimide reinforcement layer makes the aerogel more elastic and tough; the Ti3C2Tx-MXene exoskeleton enhances the strength and stiffness of the aerogel. Importantly, Ti3C2Tx-MXene forms a continuous conductive network on the surface of the airgel backbone, resulting in high-performance electromagnetic interference (EMI) shielding (EMI shielding efficiency reached 55.315 dB at an ultra-low Ti3C2Tx content of 0.58 vol%), high-efficiency infrared radiation (IR) stealth (ultra-low thermal conductivity of 0.0666 W·m−1·K−1 and IR emissivity of 0.566 at 3–5 μm and 0.55 at 8–14 μm). This study provides a way to design robust aerogel materials with infrared stealth and electromagnetic shielding compatibility.

Thermally Insulating and Moisture-Resilient Foams Based on Upcycled Aramid Nanofibers and Nanocellulose.

Low-density foams and aerogels based on upcycled and bio-based nanofibers and additives are promising alternatives to fossil-based thermal insulation materials. Super-insulating foams are prepared from upcycled acid-treated aramid nanofibers (upANFA ) obtained from Kevlar yarn and tempo-oxidized cellulose nanofibers (CNF) from wood. The ice-templated hybrid upANFA /CNF-based foams with an upANFA content of up to 40wt% display high thermal stability and a very low thermal conductivity of 18-23mW m-1 K-1 perpendicular to the aligned nanofibrils over a wide relative humidity (RH) range of 20% to 80%. The thermal conductivity of the hybrid upANFA /CNF foams is found to decrease with increasing upANFA content (5-20wt%). The super-insulating properties of the CNF-upANFA hybrid foams are related to the low density of the foams and the strong interfacial phonon scattering between the very thin and partially branched upANFA and CNF in the hybrid foam walls. Defibrillated nanofibers from textiles are not limited to Kevlar, and this study can hopefully inspire efforts to upcycle textile waste into high-performance products.

A multi-scale model for use in hydrodynamic simulations of impacts and hypervelocity penetrations into porous silica aerogel

Low-density silica aerogel is an ideal material for capturing hypervelocity interplanetary dust. To investigate the behavior of hypervelocity shock waves at different particle velocities using silica aerogel densities ranging from 80 kg/m3 to 320 kg/m3, a multi-scale Smooth Particle Hydrodynamics (SPH) approach is employed. The simulation results demonstrate a good agreement with the macroscopic experimental findings across a wide range of particle velocities, from 0.5 km/s to 20 km/s, while considering the shock wave velocities of the porous material and their linear variation. In addition, simulations of pressure-specific volume curves were conducted using the microscopic model. According to the simulation results, we present a novel compression model of silica aerogel materials regarding the classical form of the P−V relationship for porous materials. Building upon the microscopic model, we propose a macroscopic equivalent model for dynamic compression of low-density aerogel, which is subsequently incorporated into the hydrodynamic calculation of interplanetary dust hypervelocity penetration into aerogel. The results of the simulation of hypervelocity penetration indicate that the multi-scale model presented in this work can be used to simulate the macroscopic mechanical behavior of aerogels in a non-uniform field.

Multifunctional nanocomposites reinforced by aligned graphene network via a low-cost lyophilization-free method

Compared with a disordered network, the ordered framework is more beneficial to improving the multifunctional properties (including thermal, electrical, and mechanical properties) of epoxy-based composites. However, current methods for building aligned structures are both energy and time-consuming on account of the tedious and lengthy lyophilization process. Herein, a new strategy is proposed to obtain low-density graphene aerogels (GAs) with long-range oriented structures through a lyophilization-free processes. Due to the minimum thermal boundary resistance, the prepared aligned graphene/epoxy composite exhibits an ultrahigh thermal conductivity of ∼11.6 W/(m·K) at a graphene content of 1.84 vol%, i.e., an enhancement efficiency of 3640% per 1 vol%. In addition, the compressive strength of the composite is increased by 2.6 times compared to epoxy (from 0.29 MPa to 0.76 MPa). Because the composite shows a modulus as low as 0.5–1.0 MPa, it has excellent deformability and compression performance. Moreover, the obtained 3-mm-thick composite achieves an electromagnetic interference shielding effectiveness (EMI SE) of 40 dB due to the interconnected graphene network structure, which meets the requirements of commercial EMI shielding applications. Hence, this strategy can be used to synthesize aligned graphene/epoxy composites with excellent multifunctional performances, which can be simultaneously used as elastic thermal interface materials (TIMs) and EMI shielding materials in the fields of advanced electronic packaging.

Radiation characteristics of an aerogel-supported fission fragment rocket engine for crewed interplanetary missions

The ionizing radiation properties of a fission fragment rocket engine concept are described in the context of a crewed Mars mission. This propulsion system could achieve very high specific impulses (>106 s) at a high power density (>kW/kg), utilizing micron-sized fissile fuel particles suspended in an aerogel matrix. The fission core is located within the bore of an electromagnet and external neutron moderator material. The low-density aerogel allows for radiative cooling of fuel particles while minimizing collisional losses with the fission fragments, leading to a more efficient use of fissile fuel in producing thrust compared to previous concepts. This paper presents the estimates of the steady-state ionizing radiation equivalent dose to the astronaut crew from both external (e.g., galactic cosmic rays) and internal (reactor) sources. The spacecraft design includes a centrifugation concept where the transit habitation module rotates around the spacecraft’s center of mass, providing artificial gravity to the crew and the separation distance to the nuclear core. We find that the fission fragment propulsion system combined with centrifugation could lead to reduced transit time, reduced equivalent radiation doses, and a reduced risk of long-term exposure to micro-g environments. Such a high-specific impulse propulsion system would enable other crewed fast transit, high delta-V interplanetary missions with payload mass fractions much greater than those of alternative propulsion architecture (chemical and solar electric).

Non-supercritical drying synthesis of hydrophobic, low-density, and high surface area silica aerogel using a sonication technique

Replacing the solvent in silica aerogel production with air is critical in getting the desired physical properties. Even though drying by evaporation under ambient pressure is thought to be the simplest way, it shrinks and collapses the gel network. In this research, uniform sol was prepared by sonication at room temperature. The surface of the developed wet gel was modified with trimethylchlorosilane (TMCS) after solvent exchange. The prepared aerogels underwent various characterization techniques to evaluate their functional, structural, morphological, surface, and thermal properties. The textural and physical characteristics of prepared silica aerogel were examined in relation to the precursor concentration, catalysts that affect the density of silica aerogel, volumetric shrinkage, and gelation time. The silica aerogel was found thermally stable up to 800 °C while hydrophobicity retained up to 350 °C. The contact angle of prepared aerogels confirms their hydrophobic nature. Field emission scanning electron microscopy (FE-SEM) and X-Ray Diffraction (XRD) results demonstrate the porous nature of silica aerogel. The Brunauer-Emmett-Teller (BET) surface area analysis revealed that the surface area and the pore radius were 784 m2/g and 36 Å, respectively.

Density-Induced Joule-Heating Characteristics of Nanocarbon Aerogels: Implications for Tunable Electrothermal Behaviors

An in-depth understanding of the electrothermal characteristics and behaviors of nanocarbon aerogels is crucial for optimizing their Joule-heating performance and expanding their applications. Modifying a single parameter of nanocarbon aerogels can reveal potential variations in Joule heating, which makes it a valuable area for investigation. This study explores reduced graphene oxide aerogels and reduced graphitized nanofiber aerogels with varying densities (14.9–31.7 mg·cm–3), fabricated using the hydrothermal method and polymer-assisted cross-linking method, to elucidate density-induced Joule-heating discrepancies. The critical step in aerogel preparation is the freeze-drying process, which yields structurally intact nanocarbon aerogels for Joule-heating experiments. Aerogels with higher densities displayed enhanced electrical and thermal conductivities (up to 24.9 S·m–1 and 0.882 W·m–1·K–1, respectively) compared to their lower-density counterparts, owing to the increased number of pathways available for electron/phonon transportation. The low-density aerogels exhibited more pronounced features in the heating temperature range (up to 117 °C) and efficiency (up to 46.5 °C·W–1), making them more suitable for energy-efficient applications. Despite variations in the density, all of the fabricated aerogels showed efficient electron hopping between the interconnected nanocarbons, which enabled uniform resistive heating throughout the aerogel entity. This work highlighted the importance of density control in altering the Joule-heating performance of nanocarbon aerogels for specific applications, which has far-reaching implications for optimizing the properties of other electrically conducting aerogel materials.

Fabricating Novel Geometries of GA-CH Aerogels Through Wax Infiltration and Leaching of Fused Quartz

General Atomics-Carbon Hydrogen (GA-CH) and General Atomics-Carbon Deuterium (GA-CD) aerogels have applications as inertial confinement fusion (ICF) targets at the National Ignition Facility, Omega Laser Facility, and Z Pulsed Power Facility. However, fusion experiments at these facilities require the fabrication of precise geometries of aerogels, achievable only by machining. Unfortunately, machining low-density (<50 mg/cm3) GA-CH aerogels is difficult, given their fragile structure. Higher-density GA-CH aerogels, although easier to machine, are left with a small nub after machining. This work investigates filling the GA-CH gel pores with wax to increase their machinability. The wax was added by exchanging the solvent of the GA-CH gel with melted wax. In addition, 1- to 2-mm spherical voids were created within the aerogels using fused quartz beads that were leached with hydrofluoric acid. Samples were characterized for contaminants, structural damage, dopant loss, and surface roughness using size measurements, scanning electron microscopy, Fourier transform infrared spectroscopy, micro-computed tomography imaging, and optical profilometry. Through advances in aerogel fabrication techniques, progress is made toward testing new ICF target designs.

Low-density, high-strength and large-scaled monolithic carbon aerogels fabricated via modified ambient pressure drying

Low-density, high-strength and large-scaled monolithic carbon aerogels fabricated via modified ambient pressure drying

Atomistic mechanisms underlying plastic flow at ultralow yield stress in ductile carbon aerogels.

We investigated carbon aerogel samples with super low densities of 0.013 g cm-3 (graphite is 2.5) and conducted compression experiments showing a very low yield stress of 5-8 kPa. To understand the atomistic mechanisms operating in these super low density aerogels, we present a computational study of the mechanical response of very low-density amorphous carbonaceous materials. We start from our previously derived atomistic models (based on the DynReaxMas method) with a density of 0.16 g cm-3 representing the core regions of carbon aerogels. We considered three different phases exhibiting either a fiber-like clump morphology interconnected with string-like units or a more reticulated framework. We subjected these phases to compression and shear deformations and analyzed the resulting plastic response via an inherent-structure protocol. Strikingly, we find that these materials possess shear plastic relaxation modes with extremely low values of yield stress, negligible with respect to the finite values predicted outside this "zero-stress" region. This is followed by a succession of two additional regimes with increasing yield stress values. Our analysis of the atomistic relaxation mechanisms finds that these modes have a collective and cooperative character, taking the form of nanoscopic shear bands within the clumps. These findings rationalize our experimental observations of very low-stress plastic deformation modes in carbon aerogels, providing the first steps for developing a predictive multi-scale modeling of the mechanical properties of aerogel materials.

Extensive characterization of Marshak waves observed at the LIL laser facility

We detail results of an experiment performed at the Ligne d'Intégration Laser facility aimed at studying supersonic and diffusive radiation front propagation in low-density SiO2 aerogel (20 and 40 mg/cm3) enclosed in a gold tube, driven by thermal emission from a laser-heated spherical gold cavity. The evolution of the front is studied continuously by measuring its self-emission with a 1D (one-dimensional) time-resolved soft x-ray imager. Measurement is performed along (through a 200-μm-wide observation slit) and at the exit of the tube giving access to the dynamics and the curvature of the front. Experimental results are then compared successfully to results from the 3D (three-dimensional) radiation hydrodynamics code TROLL, which shows that if continuous tracking of the front position is accessible with this experimental scheme, measurement of its maximum radiation temperature is on the contrary affected by radiation closure of the observation slit. 3D simulations also indicate that this effect can even be worsened if one includes pointing errors of the x-ray imager. Radiation temperature along the tube was then inferred by combining results from the imager to a wall shock breakout time measurement using a velocity interferometer system for any reflector and results from a broadband x-ray spectrometer used to determine the temperature at the exit of the tube. A decrease in the radiation temperature along the tube is observed, the decrease being more important for the higher SiO2 aerogel density.

Polyvinylidene Fluoride Aerogels with Tailorable Crystalline Phase Composition.

In this work, polyvinylidene fluoride (PVDF) aerogels with a tailorable phase composition were prepared by following the crystallization-induced gelation principle. A series of PVDF wet gels (5 to 12 wt.%) were prepared from either PVDF-DMF solutions or a mixture of DMF and ethanol as non-solvent. The effects of the non-solvent concentration on the crystalline composition of the PVDF aerogels were thoroughly investigated. It was found that the nucleating role of ethanol can be adjusted to produce low-density PVDF aerogels, whereas the changes in composition by the addition of small amounts of water to the solution promote the stabilization of the valuable β and γ phases. These phases of the aerogels were monitored by FTIR and Raman spectroscopies. Furthermore, the crystallization process was followed by in-time and in situ ATR-FTIR spectroscopy. The obtained aerogels displayed specific surface areas &gt; 150 m2 g-1, with variable particle morphologies that are dependent on the non-solvent composition, as observed by using SEM and Synchrotron Radiation Computed micro-Tomography (SR-μCT).

Blown Composite Films of Low-Density/Linear-Low-Density Polyethylene and Silica Aerogel for Transparent Heat Retention Films and Influence of Silica Aerogel on Biaxial Properties.

Blown films based on low-density polyethylene (LDPE)/linear low-density polyethylene (LLDPE) and silica aerogel (SA; 0, 0.5, 1, and 1.5 wt.%) were obtained at the pilot scale. Good particle dispersion and distribution were achieved without thermo oxidative degradation. The effects of different SA contents (0.5–1.5 wt.%) were studied to prepare transparent-heat-retention LDPE/LLDPE films with improved material properties, while maintaining the optical performance. The optical characteristics of the composite films were analyzed using methods such as ultraviolet–visible spectroscopy and electron microscopy. Their mechanical characteristics were examined along the machine and transverse directions (MD and TD, respectively). The MD film performance was better, and the 0.5% composition exhibited the highest stress at break. The crystallization kinetics of the LDPE/LLDPE blends and their composites containing different SA loadings were investigated using differential scanning calorimetry, which revealed that the crystallinity of LDPE/LLDPE was increased by 0.5 wt.% of well-dispersed SA acting as a nucleating agent and decreased by agglomerated SA (1–1.5 wt.%). The LDPE/LLDPE/SA (0.5–1.5 wt.%) films exhibited improved infrared retention without compromising the visible light transmission, proving the potential of this method for producing next-generation heat retention films. Moreover, these films were biaxially drawn at 13.72 MPa, and the introduction of SA resulted in lower draw ratios in both the MD and TD. Most of the results were explained in terms of changes in the biaxial crystallization caused by the process or the influence of particles on the process after a systematic experimental investigation. The issues were strongly related to the development of blown nanocomposites films as materials for the packaging industry.

Fabrication of boehmite nanofiber aerogels by a phosphate gelation process for optical applications

A transparent wet gel was obtained in a few minutes at room temperature by adding an aqueous phosphoric acid solution of appropriate concentration to boehmite nanofiber sol. After room temperature aging and supercritical carbon dioxide drying, low bulk density aerogels with visible light transmittance of over 90% at 10 mm thickness were obtained. These aerogels exhibited high Young’s modulus and visible light transmittance, while having the same bulk density as the samples obtained by a conventional gelation process using a base. The high optical transmittance of the aerogel were hardly lost even at high humidity because the phosphorylation of the skeletal surface reduced the percentage of hydroxyl groups. The three-dimensional imaging inspection of the exterior and interior of the aerogel was carried out. The various developments reported in this paper make aerogels with ultralow bulk density (<0.01 g cm−3) and high visible light transmission even more promising for applications in the physical field. Graphical abstract

Vacuum-dried, low-density and robust hydrophobic bridged silsesquioxane aerogels for oil–water separation

Vacuum-dried, low-density and robust hydrophobic bridged silsesquioxane aerogels for oil–water separation