To reduce energy losses due to the insufficient thermal insulation is one of the current “hot” topics. Various commercial porous materials are used with the best conductivity around ...0.03–0.04 W/(m·K). Aerogels are the only known materials with “intrinsic” thermal superinsulating properties, i.e. with thermal conductivity below that of air in ambient conditions (0.025 W/(m·K)). The classical thermal superinsulating aerogels are based on silica and some synthetic polymers, with conductivity 0.014–0.018 W/(m·K). Aerogels based on natural polymers are new materials created at the beginning of the 21st century. Can bio-aerogels possess thermal superinsulating properties? What are the bottlenecks in the development of bio-aerogels as new high-performance thermal insulationing materials? We try to answer these questions by analyzing thermal conductivity of bio-aerogels reported in literature.
•Thermal conductivity of bio-aerogels is analysed.•Correlations between thermal conductivity and aerogel density and surface area are built.•A special focus is made on thermal conductivity below that of air.•Prospects of using bio-aerogels for thermal insulation are discussed.
•Porous starches were made via supercritical CO2 and freeze-drying of gels.•The morphology of freeze-dried gels is mainly the replica of sublimated ice crystals.•The properties of starch aerogels ...depend on starch source and retrogradation time.•Specific surface area of aerogels is 20–30 times higher than that of freeze-dried gels.
Porous starch materials with various morphology and properties were made via starch dissolution, retrogradation and drying either with supercritical CO2 (“aerogels”) or lyophilisation (“cryogels”). Their properties were correlated with the rheological response of retrograded starch gels and crystallinity of aerogels and cryogels. All starch cryogels possess very low density (0.07 – 0.16 g/cm3), very large macropores and low specific surface area (around 3–13 m2/g). Their morphology is mainly the replica of sublimated ice crystals. The properties of starch aerogels strongly depend on starch source: the lowest density (around 0.1 g/cm3) and highest specific surface area (170–250 m2/g) was recorded for pea starch aerogels and the highest density (0.3–0.6 g/cm3) and lowest specific surface area (7–90 m2/g) for waxy maize starch aerogels. The morphology and properties of starch aerogels are interpreted by amylose and amylopectin evolution during retrogradation.
High toxicity is the main reason for the limited application of traditional corrosion inhibitors. Herein, it is critical to find a green, efficient, and long-term stable alternative substitute for ...the hazardous and conventional corrosion inhibitor. Ambrosia trifida L is widely distributed in fields and riverside wetlands as an invasive plant in China. According to the concept of turning waste into treasure, the extract of Ambrosia trifida L leaves (ATL) has the potential to address this issue due to its natural origin and abundant presence of heterocyclic organics. Therefore, ATL, as a green corrosion inhibitor, is prepared for the first time via a simple water-based extraction method. FT-IR (Fourier transform infrared spectroscopy) and UV-Vis (UV-visible) indicate that ATL extract contains abundant heterocyclic organics with conjugated structures, which exhibit the potential to become a high-efficiency inhibitor. Notably, the active sites of ATL molecules and their interaction with Q235 steel at the molecular/atomic level are revealed via theoretical calculations. The highest Ebinding value observed for the major components in the ATL extract is 259.66 kcal/mol, implying a significant adsorption capacity. The electrochemical results verify that microdose ATL extract can prominently inhibit steel corrosion, and the highest inhibition efficiency (η) is 97.5% (1000 mg/L). Following immersion for 24 h, the η value is enhanced to 99.0%, indicating a reliable and long-term ATL extract protection film is formed on the steel surface in harsh acidic solutions. The results of the weight loss, SEM (scanning electron microscope), and LSCM (laser scanning confocal microscopy) are consistent with the above conclusions. Finally, this study anticipates providing theoretical support for developing novel green plant extract inhibitors and aiding in their application in industrial pickling environments.
Aerogels with low density and high porosity exhibit outstanding performances as thermal or acoustic insulators. However, most aerogels are mechanically brittle and need further chemical or physical ...surface treatments to obtain elasticity and superhydrophobicity. Structurally new types of polysilsesquioxane (PSQ) aerogels containing thiourethane as their bridging groups are now reported. These novel PSQ aerogels were prepared from thiourethane bridged silsesquioxane through a simple sol-gel process and vacuum-drying method. The PSQ aerogels exhibit inherent superhydrophobicity, excellent mechanical toughness and good thermal insulation properties. Moreover, the morphology and mechanical performance of these aerogels can be tailored by changing the rigidity of the bridging group.
Electroplating is widely exploited in numerous application areas. Understanding the kinetics of electroplating, which is essentially a dynamic phenomenon, is crucial to making use of it appropriately ...in the real world. Currently, there exist a variety of research tools for studying electroplating kinetics, each with its own pros and cons. In this paper, we introduce a novel, immersion ultrasonic testing‐based technique that carries out in situ, direct monitoring of the thickness increase of an electroplated layer. Through careful design and optimization of the measurement setup and the signal processing protocol, the measurement resolution of the technique was able to reach a sub‐micron level. Via a number of demonstrative zinc plating experiments that were performed under different conditions, the measurement accuracy of the technique was thoroughly validated by a number of independent methods. All in all, the technique can become a promising alternative tool for studying the kinetics of different electroplating processes, supplementing the existing toolbox with the capability of providing a new class of information.
An immersion ultrasonic testing‐based technique that carries out in situ, direct monitoring of the thickness increases of electroplated layers is introduced. The technique possesses a sub‐micron measurement resolution and an experimentally proven measurement accuracy. The technique can become a new alternative for studying the kinetics of different electroplating processes.
Biorefinery Approach for Aerogels Budtova, Tatiana; Aguilera, Daniel Antonio; Beluns, Sergejs ...
Polymers,
11/2020, Letnik:
12, Številka:
12
Journal Article
Recenzirano
Odprti dostop
According to the International Energy Agency, biorefinery is "the sustainable processing of biomass into a spectrum of marketable bio-based products (chemicals, materials) and bioenergy (fuels, ...power, heat)". In this review, we survey how the biorefinery approach can be applied to highly porous and nanostructured materials, namely aerogels. Historically, aerogels were first developed using inorganic matter. Subsequently, synthetic polymers were also employed. At the beginning of the 21st century, new aerogels were created based on biomass. Which sources of biomass can be used to make aerogels and how? This review answers these questions, paying special attention to bio-aerogels' environmental and biomedical applications. The article is a result of fruitful exchanges in the frame of the European project COST Action "CA 18125 AERoGELS: Advanced Engineering and Research of aeroGels for Environment and Life Sciences".
Abstract
We present an ultrasonic research technique that can carry out in situ, direct monitoring of the 3D morphologies of corrosion substrates. The technique has a customizable lateral resolution, ...an ultra-high axial resolution of 100 nm, and an experimentally proven measurement accuracy. In using the technique to monitor the localized corrosion processes of carbon steel under constant DCs, it was observed that during each of the experiments conducted in alkaline environments, iron dissolution accelerated for a certain period of time and then slowed down. Based on the various features of the ultrasonic signals acquired and the XRD spectra of the corrosion products obtained, it was deduced that an increase in iron dissolution rate as such was accompanied by the depositing of solid corrosion products onto the substrate used and driven by the formation of Fe
3
O
4
, which consumed electrons. After a while, the corrosion product layer collapsed and the formation of Fe
3
O
4
was halted.
We propose a 2D hybrid spectral/finite element scheme for numerically resolving crack-induced contact acoustic nonlinearity in solid structures. While the high-order spectral element method (SEM) is ...much more efficient than the classical low-order finite element method (FEM), the fact that spectral elements are relatively large renders the SEM ineffective in discretizing microscopic cracks. The classical FEM, on the other hand, is good at modelling complex geometries. However, the computation of large-scale structures by the classical FEM can be extremely expensive. In this work, the coupling between high-order spectral elements and low-order finite elements is formulated by the Lagrange multipliers method. The nonlinear contact between crack surfaces is modelled using a penalty method. The aim of the proposed hybrid method is to simultaneously reduce the degrees of freedom (DOFs) in systems and ensure high numerical accuracy. A comprehensive mesh convergence study has been conducted to demonstrate the high convergence rate of the proposed method in modelling ultrasonic wave propagation, and its capability to converge for weak crack-induced contact acoustic nonlinearity. Through a series of numerical experiments on generation and propagation of nonlinear ultrasonic wave modes, the proposed method has been shown to possess a high accuracy and geometric flexibility, and require significantly less computational resources than the classical FEM. The proposed hybrid method will provide an efficient, accurate and robust numerical approach for studying crack-induced contact acoustic nonlinearity which nowadays is being widely exploited by non-destructive testing applications.
Transparent photothermal coatings based on plasmonic noble metals often face a trade‐off between achieved temperatures and transmittances. This challenge arises from the fact that plasmonic ...nanoparticles (NPs), which rely on their size and structures, selectively absorb light of various wavelengths and convert it into heat. In the cases of randomly arranged plasmonic NPs, absorbances are predominantly in the visible range, leading to lowered transmittances. In this work, the self‐assembly behavior of a biotemplate containing flexible potato virus A (PVA) is used to produce network‐like surface patterns with controllable intermittent vacancies. These templates effectively anchor silver nanoparticles (AgNPs), forming dense arrays of plasmonic hotspots interspersed with vacant regions. With this approach, a temperature increase of 21 °C above ambient temperature under 1‐sun radiation is achieved while maintaining a visible light transmittance as high as 78% measured at 550 nm wavelength. The PVA biotemplated AgNPs show excellent potential as antifogging coating, exhibiting 2–3 times faster defogging rates compared to uncoated samples in both indoor and outdoor conditions. Overall, a platform is presented for biotemplating metal NPs, the development of long‐range surface patterns with controlled vacancies, and the demonstration of transparent photothermal activity with an antifogging application.
In this study, a glass substrate patterned with dense arrays of silver nanoparticles templated on an interconnected network of flexible virus nanoparticles is developed. The templated substrate demonstrates outstanding photothermal performance without compromising excellent light transmittance. Additionally, it displays highly efficient defogging capabilities in various environmental conditions, including both indoor and outdoor settings.
Starch is one of the most abundant and biodegradable natural polysaccharides; it has been widely used in pharmaceutics in tablets, as a disintegrant, or as a porous carrier. In this work, starches in ...different formsalcogels, aerogels, and low-vacuum-dried materials (named xerogels)were designed and tested as carriers of theophylline. The influence of the starch amylose/amylopectin ratio, concentration in solution, retrogradation time, and drying method (supercritical CO2 drying for aerogels, low-vacuum drying for xerogels) on materials’ density, specific surface area, and morphology was investigated. The precursors before drying were starch alcogels made by water-to-ethanol exchange in retrograded hydrogels. Starch alcogels were loaded with theophylline via impregnation. Loading capacities and efficiencies of alcogels, aerogels, and xerogels were determined, and release of the drug from xerogels and aerogels was evaluated. Two remarkable phenomena were obtained: (1) The low-vacuum drying method resulted in starch aerogel-like materials; i.e., xerogels with low densities and specific surface areas above 100 m2/g. (2) Starch alcogels adsorbed theophylline from ethanol resulting in loading efficiency as high as 250%. The results obtained show a new pathway in making aerogel-like polysaccharide materials without drying in supercritical conditions for potential use as drug carriers.
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