Emulsion-templated, hydrophilic-oleophobic aerogels with flexibility, stretchability and recyclability
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Aerogels are highly porous (up to 99%), nanostructured materials with low density (0.01-0.3 g/cm³), high surface area (200-1000 m²/g) and low thermal conductivity (< 0.03 W/m.K). They are prepared via a sol-gel process and are obtained after a suitable drying of the gel, e.g. under supercritical (CO2) or ambient conditions depending on the materials chemistry. Due to the excellent properties aerogels are suitable to be used as ultralight thermal insulation material for example in building construction, in vehicles or elsewhere. The challenge is to produce large plates or a similar shape of aerogel material adapted to the application. Mostly, aerogels are very sensitive concerning inhomogeneous stresses during all steps of preparation and tend to break due to the high porosity. In our study we fixed silica aerogel (SiO2) granulate fabricated by industry with resorcinol-formaldehyde (RF) aerogel which is an organic aerogel synthesized via a sol-gel reaction of resorcinol (R, 1,3-dihydroxybenzol) and formaldehyde (F) in deionized water (W) with Na2CO3 as the catalyst (C). The composite aerogel is prepared by mixing the hydrophobic silica aerogel granulate into the already highly viscous RF-solution. The mass can then be cast in any mold for gelation and aging and the gel can finally be dried under ambient conditions. The molar ratios used for RF were R/F = 0.7, R/W = 0.04 and R/C = 1500 leading to a less sensitive RF-aerogel. The silica aerogel granulate grain size was between 0.5 and 4 mm in which the choice of size influences the mechanical properties. Properties like density, surface area and thermal conductivity are dependent of the content of silica. A content of 60 vol.-% silica was practicable and we obtained a density of 0.215 g/cm³, a surface area of 306 m²/g and a thermal conductivity at room temperature of 0.023 W/m.K.
Supercritical drying
Resorcinol
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Aerogel is known as one of today's 10 advanced structures that have earned a special place in industry or research based on its very high porosity, high active surface area, and low density. There are various methods that can be used to produce it as well as make it easily produced in bulk as subtopics in this paper in Section 2.0. At present, aerogels are widely used in catalytic applications, energy storage, photocatalysts, membrane separation, and fuel cells. Aerogel application in fuel cell has been discussed in Section 3.0 which include carbon-based aerogel, graphene-based aerogel, other aerogel based, and non-noble catalyst with aerogel. This article is a reference for researchers to identify the advantages and opportunities available to lower costs and improve the performance of fuel cell systems that rely heavily on cost-rich catalysts such as platinum. Opportunities and challenges in developing aerogel structures in the future are also explained in Section 5.0 in this paper.
Carbon fibers
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This work investigates the influence of processing parameters and aerogel pore structure on the physical properties and hydrophobicity of aerogel blankets. Aerogel blankets were produced by in situ synthesis of nanostructured silica aerogel on a polyester nonwoven substrate. Nitrogen adsorption-desorption analysis, contact angle test and FE-SEM images were used to characterize both the aerogel particles and the blankets. The results showed that the weight and thickness of the blanket were reduced when the low amount of catalyst was used. A decrease in the aerogel pore size from 22 to 11 nm increased the weight and thickness of the blankets. The xerogel particles with high density and pore size of 5 nm reduced the blanket weight. Also, the blanket weight and thickness were increased due to increasing the sol volume. It was found that the hydrophobicity of aerogel blankets is not influenced by sol volume and pore structure of silica aerogel.
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Abstract Aerogel are synthetic light weight material obtained in a gel form with gas without any shrinkage. The first form of aerogel is produced by using Silica gels. There are several other types of aerogels such as carbon-Based aerogel, clay-Based aerogel and silica-Based aerogel. Aerogel are mostly in solid form with extremely low conductivity and possess very low density and high porosity ( < 100nm). Aerogel are water repellent material. In recent years, Aerogel have attracted towards various sectors, including building construction based on their promising properties and surprising applications in wide range of technical spaces. Aerogel based materials are prepared for its high-performance thermal insulation applications in building sectors. Despite, it also used in manufacture of chemical products, Electronics, thermal and acoustic insulations, energy absorbers, space suits and in building systems. This paper reviews the properties, formation and applications of aerogel in various sectors and its abundant utilization in building construction.
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Abstract A hydrophobic, CF3-functionalized silica aerogel has been applied to water-oil mixtures to determine oil absorbing capacity of the solid aerogel. Preliminary tests on Prudhoe Bay crude oil mixed with salt water, using the aerogel in powder form, show three regimes for absorbing based on oil to aerogel wt ratios (O/A):1) all oil is absorbed and the aerogel is dry, O/A 0?3.5; 2) all oil is involved in an oil?aerogel? water emulsion, O/A 4.6?14; and 3) some oil is involved in an oil?aerogel?water emulsion, but free-phase oil is seen, O/A > 16. For comparison, a silica aerogel that has not been functionalized shows maximum absorbing capacity without the appearance of free-phase oil at O/A < 0.1. Separation and extraction studies showed good aerogel recovery and moderate oil recovery. Extraction studies at O/A of 2.3 showed that the aerogel could be reused at least two times. Infrared studies show that the oil recovered from the absorbing material and the starting oil are structurally similar. These results indicate that the CF3-functionalized aerogel as a powder has the potential of cleanly separating oil from oil?water mixtures up to 14 times the weight of the aerogel. Keywords: Oil Spill Aerogels Absorbing Materials Hydrophobic Aerogels Oil-SPILL Remediation
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Abstract Aerogel fibers, which combine the lightweight and multimesoporous properties of aerogel with the flexible and slender characteristics of the fiber, have received growing attention in the fields of smart fabrics, flexible electronic devices, and transparency‐determined optics. Herein a pure Ti 3 C 2 T x MXene aerogel fiber, showing an intriguing oriented mesoporous structure, ultrahigh electrical conductivity, and electrothermal/photothermal dual‐responsiveness, is fabricated via a simple dynamic sol–gel spinning and subsequent supercritical CO 2 drying. MXene aerogel fibers exhibit tunable porosity (96.5–99.3%), high specific surface area (up to 142 m 2 g −1 ), and low density (down to 0.035 g cm −3 ). Benefiting from the metal‐like conductive MXene nanosheets and their high orientation induced by dynamic sol–gel wet spinning, the resultant Ti 3 C 2 T x MXene aerogel fibers display ultrahigh conductivity up to 10 4 S m −1 , which far surpasses the known aerogel materials (including aerogel monoliths, aerogel fibers, and aerogel films) reported in the literature. In addition, MXene aerogel fibers also have excellent electrothermal/photothermal dual‐responsiveness due to high electrical conductivity and remarkable light absorption ability. The combination of these characteristics makes MXene aerogel fibers with encouraging potential in flexible wearable devices, smart fabrics, and portable equipment applications.
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Ambient pressure
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Rigid Polyurethane foam (RPUF)은 우수한 단열성을 가진 화합물로서 단열재로 사용되고 있다. 하지만 단열재의 성능 규정이 강화됨에 따라 PUF의 내열성, 단열성, 기계적 물성 등의 개선이 필요한 실정이다. Silica aerogel은 나노크기의 입자들이 망목구조를 형성하고 있으며, 90 % 이상의 기공도와 낮은 밀도로 20 mW/mK 이하의 낮은 열전도도를 가지고 있다. 또한 Silica aerogel은 불연성 무기화합물로서 내열성 및 난연성이 뛰어나다. 하지만 Silica aerogel은 취약한 기계적 물성으로 일정 이상의 강도를 요구하는 분야의 사용에 제한이 있다. 본 연구에서는 RPUF 시스템에 Silica aerogel을 첨가하여 Silica aerogel의 저열전도도 특성을 이용해 RPUF의 단열성을 높이고 Silica aerogel의 취약한 기계적 물성을 RPUF의 높은 강도로 보완하는 연구를 진행하였다.
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Hydrophobic silica
Carbon fibers
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