Thermal Outgassing Research Articles

Hierarchical Ceramic Nanofibrous Aerogels for Universal Passive Radiative Cooling

AbstractSolar‐induced thermal challenges in buildings, cold chain logistics, and spacecrafts may be overcome by integrating passive radiative cooling (PRC) with aerogels having thermal insulation (TI). Herein, a universal radiative cooling silica aerogel (UCSA) is prepared through the simple regeneration and freeze‐drying of commercial quartz fiber membranes. The optically engineered UCSA with a hybrid structure (silica nanofibers/microbeads) achieves remarkable solar reflectance (RS.E. = 98.1%) and atmospheric transparency window emittance (εATW = 92.1%) under Earth conditions, with a theoretical daytime cooling power of 103.3 W m−2. In the harsh space environment, it exhibits ultrahigh average solar reflectance (RS.E. = 99.1%) and broadband mid‐infrared emittance (εMIR = 90%), achieving a cooling power of 354.1 W m−2. Compared to single‐functional approaches, UCSA synergistically integrates the PRC and TI performance for excellent thermal management capability. Moreover, this ceramic aerogel can resist temperatures up to 830 °C, safeguarding building occupants and spacecraft electronics. Furthermore, UCSA passes environmental aging and thermal vacuum outgassing tests for long‐term viability both on Earth and in space. Finally, a USCA‐covered box achieves an average sub‐ambient cooling of 18.6 °C when exposed to sunlight. In summary, UCSA opens a path for energy‐efficient and sustainable cooling strategy with universal applications.

Investigation of the Thermal Outgassing from P43 Phosphor and Aerogel for Use in the Vacuum System of the SRF SKIF

Investigation of the Thermal Outgassing from P43 Phosphor and Aerogel for Use in the Vacuum System of the SRF SKIF

Investigation on the thermal properties of carbon fibres with silica-based aerogel composites

In this research, thermal protection systems of space hardware have prompted the development and study of silica aerogel composites bonded with a variety of Carbon fibres. Carbon fibres were woven into a matrix of tetra ethoxy silane (Ts) and vinyl tri-methoxy silane (Vs) to create these composites. Many different composites were developed, each with its own set of characteristics and capabilities because to the wide range of fibres used. The measured bulk density values were often relatively low, with the lowest recorded value being only 180 kg m−3. The thermal conductivity was reduced to below 30 mW m−1 K−1 and the stability was maintained up to 600°C. Nanocomposites consisting of longer fibres containing meta-Carbons are superior insulators, while short-fiber composites are stiffer and have lower thermal conductivities. The aerogel composites compliance with Space conditions was evaluated using standard Space materials qualification procedures like thermal cycling and outgassing, proving their fitness for use in this context.

Modeling of intrinsic photon-stimulated desorption yields under readsorption effect

In synchrotron radiation and electron storage rings, photon-stimulated gas desorption is a major contributor to gas load, leading to vacuum degradation and compromising the stability and quality of the beamline. Therefore, it is imperative to investigate the underlying mechanisms of photon-stimulated gas desorption to enhance the reliability of the experiments. In this paper, a theoretical model for analyzing the process of photon-stimulated desorption is presented, and the equations are solved numerically by considering the evacuation, bulk diffusion, thermal outgassing, adsorption, and desorption of surface gas molecules. The modified model can predict the yield of H2 gas desorption induced by photon stimulation when synchrotron radiation is directed vertically onto various sample surfaces, utilizing the coupled multi-physics solution. The calculated results are consistent with the experimental measurements obtained from the Shanghai Synchrotron Radiation Facility. The results show that the photodesorption yield is related to the amount of surface-adsorbed molecules, which explains the observed decrease in the photodesorption yield with increasing accumulated photon dose. Furthermore, the study provides a theoretical approach to predicting the pressure evolution of photon-stimulated desorption.

Improvement of the Mechanical Properties of Silica Aerogels for Thermal Insulation Applications through a Combination of Aramid Nanofibres and Microfibres.

Reinforcement of silica aerogels, remarkable lightweight mesoporous materials with outstanding insulation performance, is still a challenging research topic. Among the strategies used to overcome their brittleness, one of the most effective is the manufacturing of aerogel composites with embedded fibres. In this work, the incorporation of nanofibres together with microfibres in a tetraethoxysilane-vinyltrimethoxysilane matrix is investigated for the first time for the development of novel aerogel nanocomposites. The nanofibres, synthesized from different aramid fibres, including Kevlar® pulp, Technora®, Teijinconex® and Twaron® fibres, were used in different combinations with microaramids and the resulting nanocomposites were thoroughly investigated for their physicochemical and thermomechanical features. The properties depended on the type and amount of the nano/microfibre used. While the microfibres exhibited low interaction with the silica matrix, the higher surface of the nanofibres ensured increased contact with the gel matrix. A low bulk density of 161 kg m-3 and thermal conductivity of 38.3 mW m-1 K-1 (Hot Disk®) was achieved when combining the nanofibres obtained from Kevlar® pulp with the Technora® or Teijinconex® long fibres. The nanofibres showed higher dispersion and random orientation and in combination with microfibres led to the improvement by a factor of three regarding the mechanical properties of the aerogel nanocomposites reinforced only with microfibres. The scale-up process of the samples and simulated tests of thermal cycling and vacuum outgassing successfully conducted indicate good compliance with space applications.

Observability of silicates in volatile atmospheres of super-Earths and sub-Neptunes

Many of the confirmed short-period super-Earths and smaller sub-Neptunes are sufficiently irradiated for the surface silicates to be sustained in a long-lasting molten state. While there is no direct evidence of magma ocean influence on exoplanets, theory suggests that, due to outgassing and diverse evolution paths, a wide range of resulting atmospheric compositions should be possible. Atmospheric contamination caused by the outgassing of the underlying magma ocean is potentially detectable using low-resolution spectroscopy. The James Webb Space Telescope provides the necessary spectral coverage and sensitivity to characterise smaller planets, including lava worlds. In light of this, we assess the observability of outgassed silicates submerged in volatile atmospheres on the edge of the evaporation valley. By placing a hypothetical 2 R⊕ planet around a Sun-like star, we self-consistently model in 1D a wide range of potential atmospheric compositions, including thermal structure and outgassing. We focus on atmospheres rich in H, C, and N. We assess the diverse chemistry of silicates and volatiles, and what features of outgassed species could be detected via emission spectroscopy using MIRI LRS. Results indicate that even for substantial volatile envelopes, strong in infrared opacity, the presence of silicates causes deep thermal inversions that affect emission. Similar to pure lava worlds, SiO remains the only outgassed species with major infrared bands at 5 and 9 µm. However, even a small amount of volatiles, especially of H2O and H−, may hinder its observability. We also find that the C/O ratio plays a large role in determining the abundance of SiO. Detecting SiO on a strongly irradiated planet could indicate an atmosphere with high metallicity and a low C/O ratio, which may be a result of efficient interaction between the atmosphere and the underlying melt.

Surface, Structural, and Mechanical Properties Enhancement of Cr2O3 and SiO2 Co-Deposited Coatings with W or Be.

Direct current (DC) and radio frequency (RF) magnetron sputtering methods were selected for conducting the deposition of structural materials, namely ceramic and metallic co-depositions. A total of six configurations were deposited: single thin layers of oxides (Cr2O3, SiO2) and co-deposition configurations (50:50 wt.%) as structural materials (W, Be)—(Cr2O3, SiO2), all deposited on 304L stainless steel (SS). A comprehensive evaluation such as surface topology, thermal desorption outgassing, and structural/chemical state was performed. Moreover, mechanical characterization evaluating properties such as adherence, nano indentation hardness, indentation modulus, and deformation relative to yielding, was performed. Experimental results show that, contrary to SiO2 matrix, the composite layers of Cr2O3 with Be and W exhibit surface smoothing with mitigation of artifacts, thus presenting a uniform and compact state with the best microstructure. These results are relevant in order to develop future dense coatings to be used in the fusion domain.

Effect of the film thickness on electron stimulated desorption yield from Ti-Zr-V coating

With the benefits of evenly distributed pumping, low thermal outgassing rate and low photon-/electron-/ion stimulated desorption yields, non-evaporable getter (NEG) coating has been widely used in particle accelerators for many years. Our earlier work has demonstrated the different thickness of Ti-Zr-V coating in the range of 0.1–1 μm affects its pumping properties. In this study, the electron stimulated desorption (ESD) yields were studied for Ti-Zr-V coating deposited from a twisted target with its thickness less than 0.5 μm, while an uncoated sample was also measured as a reference. The ESD yields for H2, CH4, CO and CO2 were measured as a function of electron accumulated dose up to ∼2 × 1024 e-/m2 followed bakeout/activation by heating to 80, 120, 140, 180 and 250°C. After each ESD experiment the samples were full saturated with a mix of H2, CO and CO2. Both NEG coated samples demonstrate lower values in comparison to the uncoated one after heating/activation to temperatures up to 180°C for H2, up to 250°C for CH4, up to 140°C for CO and 120°C for CO2. The activation to 140°C is the most efficient way to reach lower pressure and avoid quick aging of the NEG coating. The thinner NEG coating provides a significantly lower ESD yield in comparison to the thicker one only after activation to 180°C, while their ESD yields are almost identical for each gas at the lower temperature.

The Thermal Outgassing Rate of Materials Used in High-Vacuum Systems

The Thermal Outgassing Rate of Materials Used in High-Vacuum Systems

Oxidant generation in the ice under electron irradiation: Simulation and application to Europa

Electron irradiation of ice is an important process in the Solar System, especially for icy satellites (e.g., Europa) whose tenuous atmospheres originate from the thermal and radiation-induced outgassing of their icy surfaces. Laboratory experiments have been performed on the electron irradiation of water ice to study the volatile gases (e.g., H2 and O2) that leave the surface and the chemical compounds (e.g., H2O2) that are produced inside the ice. Semi-empirical models have also been developed to estimate the production of the chemical species in the ice during irradiation as functions of electron energy and ice temperature. In this study, we build a chemistry-transport model to simulate chemical processes occurring in the ice during irradiation by 10 keV electrons and to describe how the chemical species of interest are formed, transported, and distributed in the ice. The simulated H2O2 mixing ratio agrees well with experiments performed by Hand and Carlson (2011). Our model can be applied to the surfaces of icy satellites (e.g., Europa) to estimate the oxidant generation in the ice and to evaluate the potential habitability of those satellites. This study calls for further experimental studies on ice under electron irradiation to constrain critical parameters such as rate coefficients and diffusion coefficients of volatile species produced by radiation in the ice.

The Thermal Outgassing Rate of Materials Used in Vacuum Systems

The Thermal Outgassing Rate of Materials Used in Vacuum Systems

Fluorocarbon Rubber-Based Inert Dry Adhesive for Applications under Harsh Conditions

Artificial dry adhesives have been developed based on materials and production methods by many researchers. Nowadays, extensive research has attempted to apply dry adhesives to various industrial fields, such as glass transportation systems, with admirable performance. However, most artificial dry adhesives consist of polymers such as thermosetting polymers, ultraviolet curable polymers, and water-based polymers. These polymers exhibit low thermal resistance and outgassing under high-vacuum conditions. Hence, the usage of dry adhesives under high-temperature and vacuum conditions, such as semiconductor manufacturing processes, is critically limited. In this study, based on the contact mechanism, a dry adhesive for use under high-temperature and vacuum conditions is developed using fluorocarbon rubber with excellent thermal resistance and low outgassing properties. The fluorocarbon rubber dry adhesive (FDA) material shows a high pull-off strength of up to 24.1 N cm–2 and its performance is verified through various experiments. Glass transportation experiments using a robot arm and custom-built equipment are also conducted and the results confirm the feasibility of using FDA in industrial applications. The FDA is expected to be a useful alternative under high-temperature and vacuum conditions, such as those in the aerospace industry and display manufacturing processes.

Silica-based aerogel composites reinforced with different aramid fibres for thermal insulation in Space environments

Silica aerogel composites reinforced with different aramid fibres have been synthesized and compared considering their potential use in thermal protection systems of Space devices. These composites were prepared from tetraethoxysilane and vinyltrimethoxysilane and the network was strengthened with aramid fibres. The results showed that the physical and chemical properties of the fibres were relevant, leading to composites with different properties/performance. In general, the obtained values for bulk density were low, down to 150 kg m−3. Very good thermal properties were achieved, reaching thermal conductivities bellow 30 mW m−1 K−1, and thermal stability up to 550 °C in all cases. Short length fibres produce stiffer composites with lower thermal conductivities, while among longer fibres, meta-aramid-containing fibres lead to nanocomposites with best insulation performance. Standard tests for Space materials qualification, as thermal cycling and outgassing, were conducted to assess the compliance with Space conditions, confirming the suitability of these aerogel composites for this application.

Surface roughness of asteroid (162173) Ryugu and comet 67P/Churyumov–Gerasimenko inferred fromin situobservations

ABSTRACTAlteration processes on asteroid and comet surfaces, such as thermal fracturing, (micrometeorite) impacts or volatile outgassing, are complex mechanisms that form diverse surface morphologies and roughness on various scales. These mechanisms and their interaction may differ on the surfaces of different bodies. Asteroid Ryugu and comet 67P/Churyumov–Gerasimenko, both, have been visited by landers that imaged the surfaces in high spatial resolution. We investigate the surface morphology and roughness of Ryugu and 67P/Churyumov–Gerasimenko based on high-resolution in situ images of 0.2 and 0.8 mm pixel resolution over an approximately 25 and 80 cm wide scene, respectively. To maintain comparability and reproducibility, we introduce a method to extract surface roughness descriptors (fractal dimension, Hurst exponent, joint roughness coefficient, root-mean-square slope, hemispherical crater density, small-scale roughness parameter, and Hapke mean slope angle) from in situ planetary images illuminated by LEDs. We validate our method and choose adequate parameters for an analysis of the roughness of the surfaces. We also derive the roughness descriptors from 3D shape models of Ryugu and orbiter camera images and show that the higher spatially resolved images result in a higher roughness. We find that 67P/Churyumov–Gerasimenko is up to 6 per cent rougher than Ryugu depending on the descriptor used and attribute this difference to the different intrinsic properties of the materials imaged and the erosive processes altering them. On 67P/Churyumov–Gerasimenko sublimation appears to be the main cause for roughness, while on Ryugu micrometeoroid bombardment as well as thermal fatigue and solar weathering may play a significant role in shaping the surface.

Single metal zirconium non-evaporable getter coating

Non-evaporable getter (NEG) coating has been used for years in many particle accelerator facilities due to its evenly distributed pumping speed, low thermal outgassing, and low photon and electron stimulated desorption yields. In our earlier work, it has been demonstrated that quaternary Ti–Zr-Hf-V coating deposited from an alloy target in a form of a rod has the lowest desorption yields, the highest sticking probability and sorption capacity. In this paper, a single element Zr target has been explored. This type of target is widely available and produced in a form of a wire that is easy to apply for a uniform coating of various shapes of vacuum chambers. Two samples coated with Zr film of dense and columnar structure were analysed and results of the pumping properties and electron stimulated desorption results are reported. The results show that pure Zr coating could be an economic solution, despite not being as effective as can be achieved with a quaternary NEG film. It shows that columnar Zr coating can be activated and reaches full pumping capacity at 160 °C. This is close to the activation temperature of Ti–Zr-Hf-V film and lower than that for the widely used ternary Ti–Zr–V film. Single metal Zr coatings demonstrated that it could be a more efficient and inexpensive way of producing the NEG-coated vacuum chambers.

Compression and thermal conductivity tests of Cryogel® Z for use in the ultra-transparent cryostats of FCC detector solenoids

The Future Circular Collider (FCC) study includes the design of the detector magnets for the FCC-ee+ (electron-positron) collider, requiring a 2 T solenoid for particle spectrometry, and for the FCC-hh (proton-proton) collider, with a 4 T detector solenoid. For both solenoids and their cryostats, CERN is developing an innovative and challenging design in which the solenoids are positioned inside the calorimeters, directly surrounding the inner tracker. For this purpose, the cryostats must be optimized to have maximum radiation transparency. They are structured as a sandwich of thinnest possible metallic shells for achieving vacuum tightness, supported by layers of low density and highly radiation transparent insulation material, still providing sufficient mechanical resistance and low thermal conductivity. In this respect, thermal and mechanical analysis of innovative insulation materials are currently being carried out. The first material of interest, Cryogel® Z, is shaped as a flexible composite blanket, which combines silica aerogel with reinforcing fibers and a density of 160 kg/m3. It allows a 4 m bore, 6 m long FCC-ee+ detector solenoid cryostat with a total thickness of 250 mm. CERN has investigated the compression of Cryogel® Z under 1 bar equivalent mechanical load and its thermal conductivity between 10 K and room temperature, as well as the critical phenomena of thermal shrinkage and outgassing. We present the test results, as a first overview on the material.

Impact of divertor configuration on recycling neutral fluxes for ITER-like wall in JET H-mode plasmas

In recent years it has been well known that in JET, with the ITER-like wall, the performance of high-power H-mode plasmas depends strongly on the magnetic topology of the divertor. This is generally attributed to the effect of the magnetic field shaping on the neutral flux transport and pumping, which—in high density H-mode plasmas—determine the pedestal properties and the global confinement. In this work we have analysed the spatial distribution and the dynamic behaviour of the Dα-emission for different magnetic configurations. Experimental observations indicate that for certain configurations, the surface temperature and the Dα—emission anomalously increase on top of the inner divertor, which points to thermal outgassing there. This is also the region where most beryllium co-deposits accumulate and most deuterium becomes trapped. The overheating at this region far from the strike point (SP) is observed to happen in magnetic configurations with reduced distance between the divertor material surface and the separatrix (clearance). The neutral flux that appears at the upper inner divertor during a few milliseconds after the ELM-crash, is more than an order of magnitude larger than the gas puffing rate and dominates over all other regions. Finally, a preliminary study describes how this thermal fuel outgassing from the co-deposited layers could be used intentionally as a wall-conditioning in JET technique with plasmas that focus their particle and heat flux there. This could be used as a complementary wall isotope control technique and more specifically for tritium recovery from the upper inner divertor where most fuel-trapping beryllium co-deposits accumulate in JET ITER-like wall.

Particle radiation effects on shape memory alloy couplers for ultra-high vacuum sealing: a preliminary study

A new shape memory alloy (SMA)-based coupling system for ultra-high vacuum (UHV) applications in particle in accelerators is currently under investigation at the European organization for nuclear research (CERN). The use of such technology in some restricted-access radioactive areas within CERN accelerators could result in noticeable advantages, especially during maintenance operations. Bolt-free SMA couplers, can be activated remotely by temperature changes, resulting in significant reduction of the radiation doses collected by the technical personnel. The functional performance of SMA-based prototype systems, in terms of leak tightness, thermal mounting/dismounting and thermal outgassing properties, has been already verified. Radiation-induced microstructural damages usually cause losses in the mechanical properties, such as embrittlement in conventional engineering metals. The particle radiation effects on the functional characteristics of SMAs, in terms of microstructural transition mechanisms, represent a key issue for their application in critical accelerators areas. To this aim, specific research activities are being carried out at CERN for capturing the evolution of SMA mechanical and functional properties during and/or after particle irradiation. In this preliminary study, a few selected SMA-based prototype UHV chambers, have been exposed to a high-energy mixed particle field (up to ∼140 kGy of absorbed dose) at the CERN high-energy accelerator mixed-field (CHARM) facility. The results, in terms of post-irradiation measurements, have revealed that leak tightness and thermal dismounting are unaffected by irradiation.

Habitability of Earth-like Stagnant Lid Planets: Climate Evolution and Recovery from Snowball States

Abstract Coupled models of mantle thermal evolution, volcanism, outgassing, weathering, and climate evolution for Earth-like (in terms of size and composition) stagnant lid planets are used to assess their prospects for habitability. The results indicate that planetary CO2 budgets ranging from ≈3 orders of magnitude lower than Earth’s to ≈1 order of magnitude larger, along with radiogenic heating budgets as large or larger than Earth’s, allow for habitable climates lasting 1–5 Gyr. The ability of stagnant lid planets to recover from potential snowball states is also explored; recovery is found to depend on whether atmosphere–ocean chemical exchange is possible. For a “hard” snowball with no exchange, recovery is unlikely, as most CO2 outgassing takes place via metamorphic decarbonation of the crust, which occurs below the ice layer. However, for a “soft” snowball where there is exchange between atmosphere and ocean, planets can readily recover. For both hard and soft snowball states, there is a minimum CO2 budget needed for recovery; below this limit, any snowball state would be permanent. Thus, there is the possibility for hysteresis in stagnant lid planet climate evolution, where planets with low CO2 budgets that start off in a snowball climate will be permanently stuck in this state, while otherwise identical planets that start with a temperate climate will be capable of maintaining this climate for 1 Gyr or more. Finally, the model results have important implications for future exoplanet missions, as they can guide observations to planets most likely to possess habitable climates.

Si-Ge Heterostructures Fabricated by Room Temperature Wafer Bonding

The newly developed technology EVG® ComBond® was used for the fabrication of Si-Ge heterostructures. In this technology, an ion beam bombardment is used to clean and to activate the Ge- and Si-surfaces at room temperature by removing the native oxides as well as organic contaminants without deteriorating chemical composition and microroughness of the surfaces. After surface activation, the wafers were brought into contact at room temperature under high vacuum, which resulted in a wafer bond extending over the entire area. The successful room temperature covalent bonding of Ge/Si with high bond strength (measured by the crack opening method), no micro-voids, and no thermal outgassing (inspection with scanning acoustic microscopy) was achieved. Cross-sectional transmission electron microscopy (TEM) of the bonded Ge/Si-interface revealed that the wafers bonded without damaging the crystal lattice except for a thin amorphous layer of <0.9 nm. This amorphous layer was completely removed by thermal annealing at 400°C for two hours. Current-voltage measurements on 1 cm2 samples made from p-Si/n-Ge wafer bonds revealed diode behavior with a ratio of forward to reverse current of >4 and a threshold voltage of around 0.3V. The forward current yields an ideality factor of 1.1 after correcting for the series resistance which consists of a contact and interface resistance. Figure : High-resolution TEM image of Ge/Si interface after thermal annealing at 400°C for 2 hours shows no obvious oxide layer and amorphous layer between the wafers. Figure 1