Controllable layer-by-layer assembly based on brucite and alginates with the assistance of spray drying and flame retardancy influenced by gradients of alginates

With the aim of tailoring and controlling surface assembly, multifunctional flame retardants (FRs) were obtained based on depositing alginates and silane coupling agents on brucite via the spray-drying-assisted layer-by-layer assembly technique. The assembly was controllable in both structure and gradient mass. Two series of FRs were named CuFR1-3 and NiFR1-3 based on the assembly content of metal alginates. With the assistance of spray drying, good compatibility between FRs and ethylene-vinyl acetate (EVA) was obtained, resulting in better mechanical properties. Meanwhile, the FRs improved flame retardancy and smoke suppression when used in EVA composites. With 55 wt % loading, composites with CuFR3 and NiFR1 passed UL 94 V-0 rating, while those with brucite were not rated. The peak of heat release rate decreased by 51.7 and 49.3% while the residue increased by 9.8 and 11.9%, respectively. The FRs also reduced the smoke and CO production rates. For the two series of FRs, the relationship between FR efficiency and alginate contents is different. The CuFRs assembled more copper alginates and exerted better flame retardancy caused by lower catalytic graphitization. NiFRs exerted a higher catalyzing efficiency at low assembly content. However, at high assembly content, the catalytic graphitization effect would decrease by thermally oxidized degradation leading to excess nickel alginates. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 47570.     

Turbulent flame structure characteristics of hydrogen enriched natural gas with CO2 dilution

This paper investigated the hydrogen enriched methane/air flames diluted with CO₂. The turbulent premixed flame was stabilized on a Bunsen type burner and the two dimensional instantaneous OH profile was measured by Planar Laser Induced Fluorescence (PLIF). The flame front structure characteristics were obtained by extracting the flame front from OH-PLIF images. And the turbulence-flame interaction was analyzed through the statistic parameters. The role of hydrogen addition as well as CO₂ dilution on the features of turbulent flame were revealed by those parameters. In this work, hydrogen fractions of 0, 0.2 and CO₂ dilution ratios of 0, 0.05 and 0.1 were studied. Results showed that hydrogen addition can enhance turbulent burning velocity ST/S_L through decreasing the scale of the finer structure of the wrinkled flame front, caused by the smaller flame instability scale. In contrast, CO₂ dilution decreased turbulent burning velocity S_T/S_L due to its inactive response to turbulence perturbation and larger flame wrinkles. For all flames, the probability density function (PDF) profile of the local curvature radius R shows a bias to positive value, resulted from the flame intrinsic instability. The PDF profile of R decreases with CO₂ dilution, while the value of local curvature radius corresponding to the peak PDF is larger. This indicates that larger wrinkles structure was generated due to CO₂ dilution, which leads to the decrease in S_T/S_L as a consequence. Hydrogen addition increases the flame volume and results in more intense combustion. CO₂ dilution has a decrease effect on flame volume for both X_H2 = 0 and X_H2 = 0.2 while the decrease is obvious at X_H2 = 0.2, Z_CO2 = 0.1. In all, hydrogen enrichment improves the combustion while CO₂ can moderate combustion. Therefore, adding hydrogen and CO₂ in natural gas can be a potential method for adjusting the combustion intensity in combustion chamber during the combustor design.     

Surface sedimentation and adherence of Nano‐SiO2 to improve thermal stability and flame resistance of melamine‐formaldehyde foam via sol‐gel method

Melamine‐formaldehyde foam possesses intrinsic flame retardance; however, relative poor thermal stability and a certain amount of heat release rate restrict its applications in heated environment to a degree. In the present research, sol‐gel method has been adopted to precipitate nano‐SiO₂ particles on the surface of the melamine‐formaldehyde foam's fibers to construct a protective inorganic gel layer. Taking advantages of the shielding effects of the gel layer, the thermal‐oxygen degradation of the foam can be greatly retarded during heating; hence, the thermal stability is remarkably improved, and the flame retardance is further enhanced. In addition, introducing a small amount of membrane‐forming agent in the sol‐gel system can make the depositional nano‐SiO₂ particles well adhered to avoid dusting.     

Synergistic flame retardant effects of activated carbon and molybdenum oxide in poly(vinyl chloride)

The synergistic effects of activated carbon (AC) and molybdenum oxide (MoO₃) in improving the flame retardancy of poly(vinyl chloride) (PVC) were investigated. The effects of AC, MoO₃ and their mixture with a mass ratio of 1:1 on the flame retardancy and smoke suppression properties of PVC were studied using the limiting oxygen index and cone calorimeter tests. It was found that the flame retardancy of the relatively cheaper AC was slightly weaker than that of MoO₃. In addition, the incorporation of AC and MoO₃ greatly reduced the total heat release and improved smoke suppressant property of PVC composites. When the total content of AC and MoO₃ was 10 phr, PVC/AC/MoO₃ had the lowest peak heat release rate and peak smoke production rate values of 173.80 kW m^?2 and 0.1472 m² s^?1, which represented reductions of 47.3 and 59.9%, respectively, compared with those of PVC. Furthermore, thermogravimetric analysis and gel content tests were used to analyze the flame retardant mechanism of AC and MoO₃, with results showing that AC could promote early crosslinking in PVC. Char residue left after heating at 500 °C was analyzed using scanning electron microscopy and Raman spectroscopy, and the results showed that MoO₃ produced the most compact char, with the smallest and most organized carbonaceous microstructures. © 2017 Society of Chemical Industry     

制备工艺对聚氨酯酰亚胺泡沫性能的影响

以均苯四甲酸二酐(PMDA)、多苯基多亚甲基多异氰酸酯(PAPI)、聚醚多元醇为主要原料,分别采用聚酰亚胺(PI)预聚法、聚氨酯(PU)预聚法和一步法制备聚氨酯酰亚胺泡沫,从微观形貌、力学性能、热稳定性能以及阻燃性能方面对上述3种制备工艺进行对比和评估。实验结果表明,采用一步法制备PUI泡沫时,PU链段和PI链段同时增长,容易造成泡孔缺陷,导致泡沫的力学性能较差;在采用PU预聚法制备的PUI泡沫中,PU链段含量较高,因此,泡孔孔径分布较宽且平均泡孔直径较大,对应的热稳定性和阻燃性能较差;采用PI预聚法制备的PUI泡沫的泡孔孔径分布窄且平均泡孔直径较小,对应的压缩性能、热稳定性以及阻燃性能均达到最佳。     

Effect of shock structure on stabilization and blow-off of hydrogen jet flames

Under-expanded hydrogen jet has characteristic shock structure immediately downstream of the nozzle exit. The shock structure depends on the ratio p_EX/p_A, i.e. the ratio of nozzle exit to ambient pressure, and the distributions of velocity and concentration in an under-expanded hydrogen jet depend on characteristics of the shock structure. Therefore, the shock structure should affect the blow-off behaviour of under-expanded hydrogen jet flame. Since this issue has not been investigated in detail, this study aims to close this knowledge gap. The effect of changes in shock structure on lift-off length and blow-off conditions for non-premixed turbulent hydrogen free jet flame has been experimentally investigated. The shock structure was varied by using three types of nozzles: convergent, straight and divergent nozzles. Inlet diameters of nozzles change from 0.31 to 1.04 mm and outlet diameters from 0.34 to 1.7 mm. The static pressure and the ratio of cross-section area at the nozzle inlet to that at the outlet were varying parameters in this study. Hydrogen was horizontally spouted through a nozzle to atmosphere. The maximum static pressure in a nozzle was 13.2 MPa. The experiments revealed that when the hydrogen jet had sequential shock cell structures, which occurred in the range of p_EX/p_A smaller than 2.45, a higher mass flow rate of hydrogen was needed for the stabilization of a jet flame than that for p_EX/p_A larger than 2.45 and that when closed to the ideal expansion (p_EX/p_A = 1), the mass flow rate for stable flame became maximum. In addition, it was observed that the lift-off length of stable flames followed with sequential shock cell structures were almost the same when the minimum cross-section area of used nozzles was constant. However, when hydrogen jet had a shock structure with single Mach disk, the lift-off lengths and the minimum mass flow rate required for the stable jet flame were decreasing with the decrease of the cross-sectional area ratio of the nozzle exit to inlet.     

Potential of the Electronic Nose for the Detection of Respiratory Diseases with and without Infection

Respiratory tract infections are common, and when affecting the lower airways and lungs, can result in significant morbidity and mortality. There is an unfilled need for simple, non-invasive tools that can be used to screen for such infections at the clinical point of care. The electronic nose (eNose) is a novel technology that detects volatile organic compounds (VOCs). Early studies have shown that certain diseases and infections can result in characteristic changes in VOC profiles in the exhaled breath. This review summarizes current knowledge on breath analysis by the electronic nose and its potential for the detection of respiratory diseases with and without infection.     

电子计价秤示值误差测量结果不确定度评定

本文介绍ACS-15电子计价秤示值误差测量结果不确定度的评定方法,并通过实际测量,计算出7.5kg秤量点的标准不确定度、合成标准不确定度及扩展不确定度。     

Review of composite cathodes for intermediate-temperature solid oxide fuel cell applications

A composite cathode exhibits low activation polarisation by spreading its electrochemically active area within its volume. Composite cathodes enable the development of high-performance electrodes for solid oxide fuel cells (SOFCs) at intermediate temperatures (600 °C – 800 °C) because of their significant role in determining the kinetics of oxygen reduction reaction (ORR). Few anions O²⁻ are transferred through the electrolyte component when the ORR is low, thereby lowering the reaction with cation H⁺ from an anode side to transfer electrons along the outer circuit to the cathode side to participate in ORR. The resistance to the ORR at the cathode is minimised, thereby contributing to performance degradation and efficiency loss in existing SOFCs, especially at intermediate temperatures. The suitability and compatibility of the cathode and electrolyte are crucial in the development of cathodes and electrochemical reactions. The intercomponent compatibility is important to ensure the robustness and durability of SOFCs, especially at an operating temperature around 800 °C, at which the components experience extreme thermal and mechanical stresses. Composite cathodes are used to improve cathode performance. These composite cathodes help enhance the properties of mixed electronic–ionic conductors and the intercomponent compatibility. Herein, we reviewed historical data of composite-cathode development for SOFCs, including its basic principle and criteria. The overall performance of as-synthesised composite cathodes in terms of microstructure, electrochemical reaction and intercomponent compatibility is briefly discussed.     

Magneto-polaron induced intersubband optical transition in a wide band gap II–VI semiconductor quantum dot

Effects of LO-phonon contribution on the electronic and the optical properties are investigated in a Cd_0.8Zn_0.2Se/ZnSe quantum dot in the presence of magnetic field strength. The magneto-polaron induced hydrogenic binding energy as a function of dot radius in the wide band gap quantum dot is calculated. The oscillator strength and the spontaneous lifetime are studied taking into account the spatial confinement, magnetic field strength and the phonon contribution. Numerical calculations are carried out using variational formulism within the single band effective mass approximation. The optical properties are computed with the compact density matrix method. The magneto-polaron induced optical gain as a function of photon energy is observed. The results show that the optical telecommunication wavelength in the fiber optic communications can be achieved using CdSe/ZnSe semiconductors and it can be tuned with the proper applications of external perturbations.