Construction of plate-like magnetic heterostructure for synergistic microwave absorption

The dramatically dropped permeability of magnetic materials at gigahertz frequencies, known as the Snoek's limit, has severely constrained the microwave absorbing performance of magnetic materials. To break the Snoek's limit at high frequencies, a plate-like magnetic heterostructure composed of Ni-Fe ferrite, nitride, and Permalloy is fabricated through nitridation of Ni-Fe layered double hydroxide. It has been found that single-phase magnetic flakes or the multi-phase heterostructure with extraordinarily linked magnetic nanoplates can be obtained by simply adjusting the temperature of nitridation. Due to the highly anisotropic morphology and synergistic effect at abundant heterogeneous interfaces, the magnetic heterostructure shows enhanced imaginary permeability that is even higher than that of single-phase Permalloy. Accordingly, the magnetic loss in C and X bands is improved, leading to significant enhancement of attenuation constant in this novel microwave absorber. Combined with the moderate permittivity, the impedance matching of the heterostructure is superior compared to every single component, as well as the mixture of these components. As a result, the minimum reflection loss of −59.30 dB at a thickness of 2.02 mm and effective absorption bandwidth (RL<−10 dB) of 2.44 GHz is realized. These findings provide a novel path to designing high-performance microwave absorbers based on magnetic materials.     

Aromatic volatile organic compounds absorption with phenyl-based deep eutectic solvents: A molecular thermodynamics and dynamics study

The suitability of phenyl-based deep eutectic solvents (DESs) as absorbents for toluene absorption was investigated by means of thermodynamic modeling and molecular dynamics (MD). The thermodynamic models perturbed-chain statistical associating fluid theory (PC-SAFT) and conductor-like screening model for real solvents (COSMO-RS) were used to predict the vapor–liquid equilibrium of DES–toluene systems. PC-SAFT yielded quantitative results even without using any binary fitting parameters. Among the five DESs studied in this work, [TEBAC][PhOH] consisting of triethyl benzyl ammonium chloride (TEBAC) and phenol (PhOH), was considered as the most suitable absorbent. Systems with [TEBAC][PhOH] had lowest equilibrium pressures of the considered DES–toluene mixtures, the best thermodynamic characteristics (i.e., Henry's law constant, excess enthalpy, Gibbs free energy of solvation of toluene), and the highest self-diffusion coefficient of toluene. The molecular-level mechanism was explored by MD simulations, indicating that [TEBAC][PhOH] has the strongest interaction of DES–toluene compared to the other DESs under study. This work provides guidance to rationally design novel DESs for efficient aromatic volatile organic compounds absorption.     

SiCnw@SiC foam prepared based on vapor-solid mechanism for efficient microwave absorption

A SiC_nw@SiC foam with highly efficient microwave absorption (MA) performance was successfully synthesized based on Vapor-Solid (V–S) growth mechanism. SiC nanowire (SiC_nw) and SiC foam skeleton efficiently form a double network coupling structure, which gives additional interface polarization and dielectric loss for the SiC foam, significantly enhancing the MA capacity of the foam. In this study, the SiC_nw@SiC foam has a minimum reflection loss (RL_min) of ?86.31 dB and an effective absorption bandwidth (EAB) of 12.55 GHz in room-temperature environment. However, the MA performance of SiC_nw@SiC foam decreases with increasing temperature, which may be due to the thickening of the SiO₂ layer in the SiC_nw at high temperature. At 600 °C, it has no effective absorption bandwidth, while at 1000 °C, the EAB and RL_min were 0.6 GHz and ?13.04 dB, respectively. As the temperature reaches 1000 °C, the defects in the material further increase, leading to a recovery in the MA performance.     

Hierarchically porous networks structure based on flexible SiO2 nanofibrous aerogel with excellent low frequency noise absorption

Environmental noise has been regarded as major noise pollution with severe hazards to human physical and mental health. The common commercial fiber sound-absorption materials have insufficient low frequencies wave absorbing and fire-resistant ability, limiting their wide application. To solve these problems, a novel strategy combining flexible nanofibers and rGO/MXene nanosheets was proposed to fabricate rGO/MXene/SiO₂ nanofibers composite aerogel with hierarchically porous structure, which possessed an extremely low density of 9.8 mg/cm³ and superior low-frequency sound absorption ability (NRC value of 0.51). The obtained composite aerogel possessed a large deformation up to 80% (corresponding compressive stress of 17 kPa) and quickly recovered. In addition, the as-prepared aerogel could be easily produced on a large scale, providing a reference for the development of new generation of sound-absorbing products.     

Magnetic hierarchically porous biomass carbon for realizing broadband and strong absorption of electromagnetic wave

Hierarchically porous carbon materials provide favorable conditions for electromagnetic wave loss enhancement due to the superimposed positive influence of multilevel pores. However, high production costs and complex preparation limit their large-scale production. Biomass carbon with a natural hierarchically porous structure offers an alternative; however, the impedance mismatch and single-loss mechanism prevent biomass carbon from being an ideal absorbent for broadband and strong absorption. In this study, a series of magnetic hierarchically porous biomass carbons were prepared using a facile adsorption-inert calcination method. The natural hierarchical porous structure of the loofah sponge provides numerous adsorption sites for ferric ions, which are transformed in situ into Fe₃O₄ during calcination to regulate the conductivity. The impedance matching and electromagnetic loss properties of the biomass carbon/Fe₃O₄ composites were adjusted by varying the amount of ferric nitrate. Optimal performance occurs when ferric nitrate weighs 0.8 g, and the calcination temperature is 600 °C. Under these conditions, the effective absorption bandwidth reaches 5.28 GHz (11.84–17.12 GHz, 2.5 mm), and the minimum reflection loss (RL_min) is as low as −52.54 dB (4.5 mm), which is achieved by superior impedance matching and strong conduction loss together with polarization loss due heterogeneous interfaces and carbon defects. Our work provides a new perspective and a simple method for the large-scale production of high-efficiency biomass-based electromagnetic wave absorbents.     

Fibrous porous mullite ceramics modified by mullite whiskers for thermal insulation and sound absorption

In order to meet the demand for thermal insulation and sound absorption, fibrous porous mullite ceramics (FPMC) with high porosity and an interconnected pore structure were prepared, followed by a pore structure modification with in situ grown mullite whiskers on the three-dimensional framework of the FPMC. The resultant hierarchical material exhibited superior sound absorption performance in the low-to-medium frequency to most reported sound-absorbing materials, as well as a sufficient compressive strength of 1.26 MPa with low thermal conductivity of 0.117 W·m^?1·K^?1. Moreover, the effects of solid content and mullite whiskers on the microstructure and physical properties of the material were analyzed. The increase of solid content led to increased compressive strength and thermal conductivity and decreased frequency corresponding to the first sound absorption peak. The thermal conductivity and compressive strength of the material increased as the mullite whiskers grew, while the median pore size decreased.     

Effect of B4C content and annealing on complex permittivity and microwave-absorption properties of B4C/Al2O3 coatings

The B₄C/Al₂O₃ coatings were fabricated by air plasma spraying technology, and their complex permittivity and microwave absorption properties in the X-band were investigated before and after annealing (500 °C/2 h). Both the real and imaginary parts of the complex permittivity of the coatings decreased after annealing, which can be attributed to the weakening of polarization relaxation intensity and the reduction of electrical conductivity caused by the escape of carbon atoms. In addition, the density of B₄C/Al₂O₃ coatings decreased from 3.01 to 2.16 g/cm³ with increasing B₄C content. The B₄C/Al₂O₃ coatings exhibit a minimum reflection loss (RL) value of ?39.58 dB and the effective absorption bandwidth (RL＜?10 dB, EAB) covers 1.9 GHz at a thickness of 1.6 mm. After annealing, the above coatings still had an EAB of 1 GHz. Therefore, the B₄C/Al₂O₃ coatings can be considered as a promising microwave-absorption candidate with good high-temperature microwave-absorbing performance and low density.     

A physico-chemical properties based model for estimating evaporation and absorption rates of perfumes from skin

Because of their potential for inducing allergic contact dermatitis (ACD) if used improperly, perfumes are carefully assessed for dermal safety prior to incorporation into cosmetic products. Exposure assessment for these materials often involves the conservative assumption of 100% absorption of each component. This report describes an improved method to estimate the absorption and evaporation of perfume ingredients from skin, based on their physico-chemical properties. The effect of environmental variables such as temperature and wind velocity can be accounted for in a logical way. This was accomplished using a first-order kinetic approach expected to be applicable for small doses applied to skin. Skin penetration rate was calculated as a fraction of the maximum flux estimated from the compound's lipid solubility, S(lip) (represented by the product of octanol/water partition coefficient, K(octt), and water solubility, S(w)), and molecular weight, MW. Evaporation rates were estimated from a modified Henry's Law approach with a stagnant boundary layer whose thickness is a function of surface airflow, v. At a given value of v, evaporation rate was assumed proportional to the ratio P(vp)/S(lip), where P(vp) is the vapour pressure of the ingredient at skin temperature, T. The model predicts a relationship for total evaporation from skin of the form %evap = 100x/(k+x) where x = P(vp)MW(2.7)/(K(oct)S(w)) and k is a parameter which depends only on v and T. Comparison with published data on perfume evaporation from human skin in vivo showed good agreement between theory and experiment for two closely related perfume mixtures (r(2) = 0.52-0.74, s = 12-14%, n = 10). Thus, the method would seem to have a good prospect of providing skin absorption estimates suitable for use in exposure assessment and improved understanding of dose-related contact allergy.     

速溶豆粉微结构的研究

速溶豆粉微结构研究是理解豆粉速溶性的基础；SEM观察表明，速溶豆粉颗粒是中空凹凸不平的球体．壁厚度在5000～20000nnl之间，具有多微孔的内外表面，微孔随机连通，直径50～300nm；XPS测定表明，速溶豆粉颗粒表面由蛋白质、18碳脂肪酸钠和皂甙构成，3种物质重量比约32：41：27；N2吸附法测定表明，对孔径大于70nm的大孔、大于3nm的微孔和小于3nm的超微孔来说，速溶豆粉的比表面积和孔隙体积都超过普通豆粉10倍。     

污水厂剩余污泥对染料吸附的试验

研究了污水厂剩余污泥在不同pH、SS时对染料吸附的影响。结果显示pH值是决定染料吸附的最重要的因素，随着pH值的降低吸附量明显增大。在SS小于1g／L时，吸附量较大；但在SS大于1g／L时，吸附量则相对变化不大。应用多层吸附模型可计算吸附吉布斯焓变和单层吸附量，进而可以求算不同污泥颗粒的比表面积。