Silica Aerogel

Increasing the sustainability of existing buildings is being motivated by reduction of their energy demands. It is the above all the building envelope and its refurbishment by substitution or addition of new materials that makes the opportunity for reduction of energy consumption. A special type of refurbishment is conservation of historical buildings. Preservation of historic buildings permits also application of innovative methods and materials in addition to the original materials if their effects are known and the gained experience ensures their beneficial effect. On the market, there are new materials with addition of silica aerogel in various forms of products. They are also potentially useful in conservation of monuments. However, the effects of aerogel application in these cases are not known. For refurbishment is commercially available additional transparent insulation paint-Nansulate Clear Coat which is containing aerogel and can be used for structured surfaces such as bri...

Už niekoľko rokov sa aj na Slovensku zdôrazňuje potreba šetrenia energiami, v dôsledku čoho sa pri starších budovách pristupuje k zatepľovaniu obvodových plášťov budov. Klasické zatepľovacie systémy však nie je vhodné použiť vo všetkých prípadoch. Existujú budovy, napríklad pamiatkové objekty, kde sa tradičné zatepľovacie systémy neodporúčajú použiť najmä preto, že menia štruktúru aj proporcie budov. Preto sa hľadala alternatíva využitia pre nový potenciálny materiál. Aerogél. Látka s viacerými výhodnými vlastnosťami, ktorá skĺbuje pozitíva rozličných súčasných materiálov a prináša ďalšie. Svojimi minimálnymi rozmermi môže pomôcť pri rekonštrukciách stavieb, a to najmä tam, kde dimenzie pridaných materiálov hrajú kľúčovú rolu pri zachovaní výrazu a charakteru stavby: pri kultúrnych pamiatkach.

The objective of this paper is to evaluate the effect of silica aerogel on the thermal conductivity of cement paste for the construction of concrete buildings in sustainable cities. Samples consisting of Ordinary Portland Cement (OPC), free water and different volumes of silica aerogel were prepared and cured for three (3), seven (7) and 28 days. Compressive strength tests were performed on samples at three (3), seven (7) and 28 days of curing. Porosity and thermal conductivity tests were conducted on samples at 28 days of curing. The lowest thermal conductivity measured was 0.076 W/mK, which was achieved by sample mix with 20 ml of silica aerogel (M20), which represents a 93.58% reduction in thermal conductivity relative to the control mix. The highest permeable porosity measured for cement paste incorporated with silica aerogel was 25.6%, which was also obtained by sample M20. However, the highest compressive strength measured was 54.33 MPa, which was obtained by sample mix with 10 ml of silica aerogel (M10) at 28 days of curing. The addition of silica aerogel as filler in cement paste can reduce the thermal conductivity of cement paste at the expense of reduced compressive strength and increased permeable porosity.

Excessive usage of sand in construction industries has generated many environmental issues. Silica aerogel, is able to minimise environmental issues while providing thermal resistance for building materials. Silica aerogel has properties such as lightweight, nano-porous and very low thermal conductivity compared to sand in the mortar matrix. This paper studied the compression and flexural strengths of mortar with silica aerogel as a sand replacement. Cement to sand ratio of 1:3 was used and sand was replaced with silica aerogel in the volumes of 15%, 20% and 25%. 15% volume of sand replacement with silica aerogel powder was the optimum ratio as it possessed the highest strength during experimental work. All the specimens were able to achieve the minimum strength for Type N non load bearing wall with the optimum ratio of 15% volume silica aerogel powder. In conclusion, silica aerogel mortar achieved the minimum strength of type N mortar.

This paper reviews the synthesis and the absorbing properties of the wide variety of porous sorbent materials that have been studied for application in the removal of organics, particularly in the area of oil spill cleanup. The discussion is especially focused on hydrophobic silica aerogels, zeolites, organoclays and natural sorbents many of which have been demonstrated to exhibit (or show potential to exhibit) excellent oil absorption properties. The areas for further development of some of
these materials are identified.

Malaysia is located in the equator, with a hot and humid climate. The highest temperature recorded during the day was 39 °C, which leads to discomfort among building occupants, in particular, residential buildings, where indoor thermal comfort is of a higher priority compared to other types of buildings. Hence, the thermal performance of the residential roof assembly needs to be improved to lower the indoor temperature and, accordingly, maintain the level of indoor thermal comfort. In view of the need to improve the thermal performance, a silica-aerogel-incorporated rigid board roof insulation material for residential buildings was developed using kapok fibre, high density polyethylene (HDPE) and silica aerogel. The thermal conductivity of the material was measured. The sample with 4 wt. % and 5 wt. % of silica aerogel content obtained the lowest thermal conductivity of 0.04 W/mK. Silica aerogel content of above 4 wt. % did not result in further reduction of the thermal conductivity. Therefore, it can be concluded that the optimum silica aerogel content for the sample was 4 wt. %. Building-Information-Modelling (BIM)based thermal-energy performance evaluation of the material was performed by generating temperature and cooling load data using Integrated Environmental Solution-Virtual Environment to validate the thermal-energy performance of the material, by installing the material within the roof assembly of a residential BIM. Findings indicate that the material can potentially be employed in the future as a roof insulation material to maintain the level of indoor thermal comfort among residential building occupants.

Novel lightweight and highly thermal insulative aerogel-doped poly(vinyl chloride)-coated fabric composites were prepared on woven fabrics made of polyester fibres using knife coating method, and their performances were compared with neat composite. The composites were prepared by incorporating a commercial aerogel to a ‘green’ poly(vinyl chloride) (PVC) plastisol. The effect of aerogel-content, thermal insulating property, thermal degradation, surface characteristics, tensile and physical properties of the composites were investigated. Results revealed that aerogel could reduce thermal conductivity, density and hydrophilicity of the composites dramatically without significant decrease in other properties. Experimental results showed that thermal insulation properties were enhanced by ∼26% (from 205 to 152 mW/m-K), density decreased by ∼17% (from 1.132 to 0.941 g/cm3) and hydrophobicity increased by 16.4% (from 76.02 to 88.67 ± 1.48°) with respect to the unmodified coated fabric. An...

Thermal insulation is the reduction of the heat transfer between objects in thermal contact area. The act of insulation is accomplished by encasing an object in material with low thermal conductivity. Thermal insulation provides a region of insulation in which thermal conduction is reduced. Low thermal conductivity is equivalent to high insulating capability. Thermal insulation is mainly used in where the heat transfer rate is high. Thermal industries generally use cotton ropes, mineral wool, glass wool, polyethylene, saw dust as insulators etc.... From the literature survey it has been found that there are other insulators which are more effective than the conventional insulators. Silica aerogel which act as good insulator. It has a low density, low thermal conductivity of 0.017W/m K. It is equivalent to high insulating capability. Coconut fiber is a natural fiber extracted from the husk of coconut. Coconut fiber has a thermal conductivity ranging from 0.046 to 0.068W/m K which was close to those conventional insulation materials such as cellulose fiber and mineral wool. In this experimental work the effectiveness of steam pipe insulation with silica aerogel and coconut fiber as insulators are compared with that of cotton rope. Silica aerogel and coconut fiber are expected to be a promising insulator for steam pipe insulation.

Silica aerogels are excellent thermal and acoustic insulators because of interconnected open nanopores with more than 90% porosity and higher surface area. Sil-ica aerogel is derived by sol‐gel process and dried under super‐critical, sub‐ critical or ambient pressure conditions. Thin silica aerogel sheets could be effective thermal insulators but high fragility hinders the wider applications. We have successfully developed a synthesis method for thin, flexible, and non‐fragile aerogel sheets with excellent hydrophobicity, lower thermal conductivity, and non‐combustible properties via ambient drying method. The silica aerogel sheets prepared compose of silica aerogel powder, fiber glass chopped strands, and solvent‐based binder. Aerogel thin insulation sheets of thickness 164 μm were prepared by pressing through rollers using aerogel paste composed of aerogel powder, fiber glass strands, and binders. The thermal conductivity values obtained were between 0.02~0.63 W/mK at temperature 25~400°C, contact angle θ = 121' , weight loss 3.91% when heated up to 800°C in air, dielectric voltage breakdown 3.67 kV, dielectric strength 6.37 kV/mm and tensile strength of 2.65 N/mm². The overall thermal, electrical, and mechanical evaluation of aerogel thin insulation sheet showed they have higher potential to replace existing thick and bulky aerogel composites as thermal and electrical insulators in aviation, automobiles, electronics, and high power batteries.

The article offers an analysis of the use of nanotechnological insulation materials (NIMs) for energy upgrading of buildings, illustrating the possibility of their integration into the building envelope and the benefits achievable in terms of architectural quality, comfort and energy saving, within the new framework of European legislation aimed at achieving
Zero energy buildings. Particular reference is given to Fibre Reinforced Aerogel Blankets for the building envelope, especially interesting for their wide possible applications even combined with phase change materials.

This article will address autoclave design considerations and
manufacturing working with high pressure low temperature
supercritical drying technique to produce silica aerogel. The design
elects carbon dioxide as a supercritical fluid (31.7 oC and 72.3 bar).
Both temperature and pressure have independently controlling
facility through present design. The autoclave was light weight (4.5
kg) and factory-made from stainless steel. It contains a high pressure
window for monitoring both transfer carbon dioxide gas to liquid
carbon dioxide and watching supercritical drying via aerogel
preparation process. In this work aerogel samples were prepared and
the true apparent densities, total pore volume and pore size
distribution, BET surface area, spectroscopic refractive index,
structure and thermal properties have been systematically
investigated characteristic.

Iron oxide (Fe 2 O 3) aerogel powders were prepared by solvent exchange method using n-butanol without a supercritical fluid drying. The obtained aerogel powders have a porosity of 94%, a BET specific surface area of 421.1 m 2 /g, and an average pore size of 7.9 nm. The aerogel powders possessed a BET specific surface area of 51.8 m 2 /g even after calcination at 500 C for 2 h despite the effect of pore shrinkage and particle coagulation. Initially, the Fe 2 O 3 aerogel was amorphous, but some parts of it were changed to a crystalline structure after heat treatment. Introduction Highly porous metal oxide (HPMO) aerogels with nano-sized pores have recently drawn attention in the industries due to their physicochemical, thermal and light weight properties. These aerogel materials have been being used in various fields such as thermal insulators, catalysts, electrochemical, and electric and electronic industries [1-4]. Many kinds of aerogels have been prepared using a supercritical fluid drying method [5-13], which causes the high cost and safety issues in the production of aerogels. In general, the preparation of metal oxide aerogel starts with a precursor synthesized from precipitation of metal salts in water or alcohol-based solution. To date, many studies have been also carried out through the solvent exchange process mainly using some solvents like methanol, ethanol, and propanol as a solvent to prevent pore shrinking during the drying process illustrated in Fig. 1 [14-20]. The advantage of using these solvent is that they have large solubility in water and can easily penetrate into the pores which are filled with water in the gel structure. But this process also has a disadvantage of difficulties in the recovery of the alcohols from the alcohol-water solution, which originates from their large mutual solubility. So it is very important to select an appropriate solvent for the process and recover it from the solution. The solvents for the solvent exchange method have to possess the appropriate hydrophilicity so that it can easily mix with water-based precipitate particles then the solvent could be exchanged with the water in the precipitates while penetrating into the pores of the water-based precipitates. In addition, the solvent should be also with some degree of hydrophobicity for easy recovery of the alcohol from the water-solvent mixed system via physical separation. Another important aspect of aerogel preparation is that it must be economically competitive. Since a large volume of solvent is used in the preparation of aerogel by the solvent exchange method, the solvent needs to be cheaper and to be recovered easily from the mixture. In the present study, the iron-oxide aerogel was obtained by the solvent exchange method using n-butanol without a supercritical fluid drying process which is conventionally used to synthesize highly porous aerogel materials. In this study our focus is to prepare iron oxide aerogel through different drying route and eliminating multiple solvent exchange steps through single solvent exchange step by utilizing suitable solvent minimizing pore shrinkage. The novelty of this study is the utilization of n-butanol as solvent and boiling the metal oxide hydrogel together to facilitate convenient exchange of water from the hydrogel with n-butanol. The final iron oxide aerogel obtained showed relatively lower specific gravity along with higher specific surface area. The

We propose a new lightweight, slim,
high energy efficient, light-transmitting
envelope system using VIP technology,
providing for seamless, free-form designs
for use in architectural projects. The
research is based on envelope components
already existing on the market, especially
components implemented with
aerogel insulation, as this is the most
effective translucent thermal insulation
there is today. This research revealed
that no other insulation has all the features
required of the proposed new envelope
model. Even so, some systems,
namely, VIP technology, monolithic
aerogel used for insulation purposes,
and polymethyl methacrylate (PMMA)
barriers, do have properties that could
be exploited to generate this envelope.
Using these design elements, data from
tests and independent studies, we have
defined a new, variable geometry, envelope
insulation system with excellent
energy-saving levels.

In this study, classical molecular dynamics with the well-known van Beest, Kramer and van Santen potential are used for the first time to investigate the solid thermal conductivity of silica aerogel. Aerogel samples at various densities are obtained through negative pressure rupturing of dense silica samples, and reverse non-equilibrium molecular dynamics is employed to determine the thermal conductivity at each density. Results indicate that a power-law fit of the thermal conductivity obtained varies almost linearly with density, where decreasing density and increasing porosity led to an almost linear decrease in thermal conductivity. This is reflective of the trend observed in experimental bulk sintered silica aerogel. The results also showed that the thermal conductivity is of the same order of magnitude as bulk sintered aerogel. The power-law fit of the results also accurately reflected the variation found in bulk sintered aerogel.

Aerogels are open-porous, high-performance thermal insulation materials that can be used for very thin building insulation. So far, the application conditions of these materials and their potential in heritage buildings have not yet been described comprehensively. This review shows the technical properties of commercially available aerogel materials – such as blankets, boards and renders – and their use scenarios in heritage buildings, taking into account the heritage criteria of authenticity, integrity, reversibility and compatibility. Additionally, historic buildings that were refurbished using aerogels are presented. The study by theoretical evaluations and calculated U-values indicates that superinsulating aerogel materials have an exceptional potential in the refurbishment of heritage buildings. The presented examples show the feasibility of refurbishments with aerogel and the resulting improvements in terms of both comfort and thermal properties. Hence, aerogel materials are well suited to be used in preservation of heritage objects according to generally known rules and conditions of heritage preservation, thus contributing to the reduction of energy consumption in the building sector.

Currently, numerous studies are devoted to the pursuit of thermal conductivity enhancement of phase change materials (PCMs). On the contrary, few researches are reported to reduce the thermal conductivity of PCMs. Generally, the PCMs with reduced thermal conductivity have great potential in thermal protection application. Herein, we propose a novel in situ one-step strategy to facilely prepare monolithic silica aerogel-based composite PCMs. The silica aerogels possess low thermal conductivity and are used to encapsulate PCMs to prepare composite PCMs, such as polyethylene glycol (PEG) or octadecanol. Compare with PEG2000@silica aerogel, the resulting monolithic octadecanol@silica aerogel have low thermal conductivity (0.12 W m 1 K 1), high latent heat (127.73 J/g), large compressive strength (11 MPa), good hydrophobicity (contact angle 124�) and superior thermal cycling stability. This monolithic silica aerogel-based composite PCMs could prolong heat preservation duration due to the synergistic effect between low thermal conductivity and high latent heat of composite PCMs, showing potential promise for direct application to the thermal insulation and thermal protection device. More importantly, this in situ one-step synthesis strategy is universal for different types of PCMs.

Upconversion materials, capable of energy-shifting light, have direct application in devices where the
tunability of the optical spectrum can result in higher performance. Due to the low transparency of
upconversion nanomaterials, it is beneficial to disperse them in a medium with a low optical attenuation
coefficient in order to allow light to reach and increase the contributions from each individual particle.
Silica aerogels, with their high transparency and open porosity, are ideal media for the dispersion of
the nanomaterials throughout a volume. NaYF4–based nanocrystals with differing dopants were incorporated
into silica xerogels and aerogels to observe the effect of the composites on the properties of
each. It was observed that, while the average surface area of the aerogel decreased in the composite,
the shape and phase of the nanocrystals were preserved during xerogel processing. The luminescence
of the nanoparticles increased upon incorporation into the xerogel composites. By accounting for effects
emerging from collection geometry and the composite morphology, it is argued that the increase in the
composite luminescent intensity is due to the nanoparticles being shielded from quenching effects by
the silica matrix.

This article examines, from the energy viewpoint, a new lightweight, slim, high energy efficient, light-transmitting envelope system, providing for seamless, free-form designs for use in architectural projects. The research was based on envelope components already existing on the market, especially components implemented with granular silica aerogel insulation, as this is the most effective translucent thermal insulation there is today. The tests run on these materials revealed that there is not one that has all the features required of the new envelope model, although some do have properties that could be exploited to generate this envelope, namely, the vacuum chamber of vacuum insulated panels (VIP), the monolithic aerogel used as insulation in some prototypes, and reinforced polyester barriers. By combining these three design components — the high-performance thermal insulation of the vacuum chamber combined with monolithic silica aerogel insulation, the free-form design potential provided by materials like reinforced polyester and epoxy resins—, we have been able to define and test a new, variable geometry, energy-saving envelope system.

In this study, water glass was synthesized from bamboo leaf as a precursor to produce silica aerogel. Bamboo leaf was combusted to produce bamboo leaf silica (BLS) and reacted with sodium hydroxide to form a water glass solution. The effects of the processing parameters such as the temperature, the time, and the agitation speed on the silica yield in water glass were studied. These processing parameters were optimized based on the regressed correlation to synthesize water glass. It was found that bamboo leaf contains approximately 20 wt.% of silica, which is higher than the silica content in rice husk. Characterizations of BLS confirmed that it has identical purity, amorphicity and chemical nature as rice husk silica. Optimization study also showed that BLS can be completely dissolved in NaOH in at least 2 h at 30 °C and an agitation speed of 20 rpm, depending on the combination of the parameters.

This study presents the development of large-area (18 × 18 × 2 cm3), high refractive index (n ~1.05) hydrophobic silica aerogel tiles for use as Cherenkov radiators. These transparent aerogel tiles will be installed in a Cherenkov detector for the next-generation accelerator-based particle physics experiment Belle II, to be performed at the High Energy Accelerator Research Organization (KEK) in Japan. Cracking has been eliminated from the prototype aerogel tiles by improving the supercritical carbon dioxide (scCO2) extraction procedure when drying the wet gel tiles. Finally, a method of mass-producing aerogel tiles for the actual detector was established. It was confirmed that the experimentally manufactured aerogel tiles meet the required optical and hydrophobic characteristics and have a uniform tile density.

Silica aerogel, a nanoporous material, was produced by using rice husk ash via sol–gel method. The aim of the study is to examine effects of the acid type (acetic, hydrochloric, nitric, oxalic and sulfuric acid), dryer type (air, freeze, oven and vacuum) and the addition of tetraethyl orthosilicate on the structural and physical properties of aerogels produced from rice husk ash. In addition, this is the first study investigating the effect of vacuum oven drying on the structure of rice husk based silica aerogel. Specific surface area and pore size of obtained silica aerogels have been analyzed by the N2 adsorption and desorption measurements at 77 K via Brunauer–Emmett–Teller (BET) and Barrett–Joiner–Halenda (BJH) methods, respectively. Surface functional groups were determined with fourier transform infrared spectroscopy (FTIR). Surface morphology was examined with scanning electron microscopy (SEM). Moreover, density was calculated by tapping method. The results showed that all o...

Installation of stone wool as thermal insulation in the roof assembly can be adopted to store heat in the living space, if the building is exposed to cold weather, and, inversely, to retard heat from entering the living space, if it is exposed to hot weather. In spite of the effectiveness of stone wool as a roof insulation material, during installation, it can cause irritation to the skin and can be hazardous to the lungs. Therefore, incorporation of stone wool with other materials to form a rigid board, without compromising its effectiveness as a roof insulation material, is imperative. Strength properties of a stone-wool-fibre-reinforced high-density polyethylene (HDPE) composite roof insulation material were studied. Granular silica aerogel, which possesses an ultra-low thermal conductivity, was added as filler to reduce the thermal conductivity of the composite. Hot compression moulding was performed to prepare samples of the composite with varying silica aerogel content of 0, 1, 2, 3, 4, and 5 wt. %. Findings suggest that 2 wt.% is the optimum silica aerogel content as it resulted in the highest flexural strength and modulus, which is 24.4 MPa and 845.85 MPa, respectively, even though it reduced the tensile strength and modulus by 10% and 4.45% respectively, relative to 0 wt. %, which can be considered as inconsequential. Higher silica aerogel content above 2 wt. % may result in poor interfacial adhesion and low compatibility to the stone wool fibre and HDPE, which further reduces the tensile and flexural strengths and moduli of the composite.

TEOS aerogel a is the most commonly used. a Aerogel has attracted increasing attention from both academic and industries due to its extraordinary performance and potentials. We have systematically studied the relationship between the densification temperature of the synthesis environment of silica aerogels on their resulting morphological, optical and thermal properties. SEM and BET measurements were employed as structural probes to ascertain the structural differences. Lee's disc apparatus was used for determining the thermal conductivity coefficient. There is a systematic correlation between the annealing temperature and the aerogel surface area, porosity, as well as pore size. The implemented autoclave was able to produce aerogel monolith of surface area reaching to 998.25 g/m2 and low electric conductivity arrive to of 1.17*10-4(s/m), associated with density of 0.047 g/cm3.The calculated thermal conductivities were (0.0063, 0.016 and 0.0053 mW m-1 0 C-1) for pH1, pH7 and pH8 samples respectively. The microstructure observed is categorized into three types, namely, open cellular foam (the substance that is formed by trapping pockets of gas in solid), fractal (the structural features it's clearly show the hierarchical repetition) and isotropic morphology (visible spectrum scale). The aerogel properties were are remarkably varied. While the influence of annealing temperature the reaction setting has gradually influence on the final aerogel properties, h However, it is obviously requested for achieving desirable optically and nano-featured products.

This article examines, from the energy viewpoint, a new lightweight, slim, high energy efficient, light-transmitting envelope system, providing for seamless, free-form designs for use in architectural projects. The research was based on envelope components already existing on the market, especially components implemented with granular silica gel insulation, as this is the most effective translucent thermal insulation there is today. The tests run on these materials revealed that there is not one that has all the features required of the new envelope model, although some do have properties that could be exploited to generate this envelope, namely, the vacuum chamber of vacuum insulated panels (VIP), the monolithic aerogel used as insulation in some prototypes, reinforced polyester barriers. By combining these three design components — the high-performance thermal insulation of the vacuum chamber combined with monolithic silica gel insulation, the free-form design potential provided by materials like reinforced polyester and epoxy resins—, we have been able to define and test a new, variable geometry, energy-saving envelope system.

The objective of this paper is to evaluate the effect of silica aerogel on the thermal conductivity of cement paste for the construction of concrete buildings in sustainable cities. Samples consisting of Ordinary Portland Cement (OPC), free water and different volumes of silica aerogel were prepared and cured for three (3), seven (7) and 28 days. Compressive strength tests were performed on samples at three (3), seven (7) and 28 days of curing. Porosity and thermal conductivity tests were conducted on samples at 28 days of curing. The lowest thermal conductivity measured was 0.076 W/mK, which was achieved by sample mix with 20 ml of silica aerogel (M20), which represents a 93.58% reduction in thermal conductivity relative to the control mix. The highest permeable porosity measured for cement paste incorporated with silica aerogel was 25.6%, which was also obtained by sample M20. However, the highest compressive strength measured was 54.33 MPa, which was obtained by sample mix with 10 ml of silica aerogel (M10) at 28 days of curing. The addition of silica aerogel as filler in cement paste can reduce the thermal conductivity of cement paste at the expense of reduced compressive strength and increased permeable porosity.

In this work, silica aerogels crack free monoliths of proper properties were simply and
successfully prepared through homemade autoclave. We have systematically studied
the relationship between the densification temperature of the synthesis environment of
silica aerogels on their resulting morphological, optical and electrical properties. SEM
and BET measurements were employed as structural probes to ascertain the structural
differences. There is a systematic correlation between the annealing temperature and
aerogel surface area, porosity, as well as pore size. The implemented autoclave was
able to produce aerogel monolith of surface area reach to 998.25 g/m2 and low
electric conductivity arrive to 1.17*10P
-4
P(s/m), associated with density of 0.047 g/cm3.
The microstructure observed is categorized into three types, namely, open cellular
foam (the substance that is formed by trapping pockets of gas in solid), fractal
(showing a hierarchical repetition of structural features) and isotropic morphology (at
the scale of the visible spectrum). the aerogel properties were remarkably varied.
While the influence of annealing temperature the reaction setting has gradually
influence on the final aerogel properties, however, it is obviously requested for
achieving desirable optically and nano-featured products

The U.S. Department of Energy is currently investigating alternative sorbents for the removal and
immobilization of radioiodine from the gas streams in a nuclear fuel reprocessing plant. One of these new
sorbents, Ag0
-functionalized silica aerogels, shows promise as a potential replacement for Ag-bearing
mordenites because of its high selectivity and sorption capacity for iodine. Moreover, a feasible
consolidation of iodine-loaded Ag0
-functionalized silica aerogels to a durable SiO2-based waste form
makes this aerogel an attractive choice for sequestering radioiodine.
This report provides a preliminary assessment of the methods that can be used to consolidate iodineloaded
Ag0
-functionalized silica aerogels into a final waste form. In particular, it focuses on experimental
investigation of densification of as-prepared Ag0
-functionalized silica aerogel powders, with or without
an organic moiety and with or without a sintering additive (colloidal silica), with three commercially
available techniques: 1) hot uniaxial pressing (HUP), 2) hot isostatic pressing (HIP), and 3) spark plasma
sintering (SPS). Since there are no studies reported in literature on the sintering of aerogels with HIP and
SPS, the preliminary experiments were performed without iodine-loaded aerogels and were focused on
investigating feasibility of these methods to produce a fully dense product. Iodine was excluded from
these initial studies to avoid potential damage to vendor equipment due to the potential release of iodine
during consolidation. The densified products were evaluated with a helium gas pycnometer for apparent
density, with the Archimedes method for apparent density and open porosity, and with high-resolution
scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) for the extent of
densification and distribution of individual elements.
The preliminary investigation of HUP, HIP, and SPS showed that these sintering methods can be used to
effectively consolidate powders of Ag0
-functionalized silica aerogel into products of near-theoretical
density. Also, removal of the organic moiety and adding 5.6 mass% of colloidal silica to Ag0
-
functionalized silica aerogel powders before processing resulted in denser products. Furthermore, the ram
travel data for SPS indicated that rapid consolidation of powders with SPS can be performed at
temperatures below 950 °C.

Porous structures of silica aerogels are generated using classical molecular dynamics, with the Tersoff potential, which has been re-parametrized for modeling silicon dioxides. This work demonstrates that this potential is superior to the widely used BKS potential in terms of characterizing the thermal conductivities of amorphous silica, by comparing the vibrational density of states with previous experimental studies. Aerogel samples of increasing densities are obtained through an expanding, heating and quenching process. Reverse non-equilibrium molecular dynamics is applied at each density to determine the thermal conductivity. A power-law fit of the results is found to accurately reflect the power-law variation found in experimental bulk aerogels. The results are also of the same order of magnitude as experimental bulk aerogels, but they are consistently higher. By analyzing the pore size distribution on different simulation length scales, we show that such a disparity is due to finite sizes of pores that can be represented, where increasing simulation length scales lead to an increase in the largest pore size that can be modeled.