MOF-derived xPd-NPs@ZnO porous nanocomposites for ultrasensitive ppb-level gas detection with photoexcitation: Design, diverse-scenario characterization, and mechanism.

Metal-organic frameworks (MOFs) have been regarded as a potential candidate with great application prospects in the field of gas sensing. Although plenty of previous efforts have been made to improve the sensitivity of MOF-based nanocomposites, it is still a great challenge to realize ultrafast and high selectivity to typical flammable gases in a wide range. Herein, porous xPd-NPs@ZnO were prepared by optimized heat treatment, which maintained the controllable morphology and high specific surface area of 471.08 m2g-1. The coupling effects of photoexcitation and thermal excitation on the gas-sensing properties of nanocomposites were systematically studied. An ultrafast high response of 88.37 % towards 200 ppm H2 was realized within 1.2 s by 5.0Pd-NPs@ZnO under UV photoexcitation. All xPd-NPs@ZnO exhibited favorable linearity over an extremely wide range (0.2-4000 ppm H2) of experimental tests, indicating the great potential in quantitative detection. The photoexcited carriers enabled the nanocomposites a considerable response at lower operating temperatures, which made diverse applications of the sensors. The mechanisms of high sensing performances and the photoexcitation enhancement were systematically explained by DFT calculations. This work provides a solid experimental foundation and theoretical basis for the design of controllable porous materials and novel photoexcited gas detection.

A collaborative emergency decision making approach based on BWM and TODIM under interval 2-tuple linguistic environment.

Emergencies require various emergency departments to collaborate to achieve timely and effective emergency responses. Thus, the overall performance of emergency response is influenced not only by the efficiency of each department alternative but also by the coordination effect among different department alternatives. This paper proposes a collaborative emergency decision making (CEDM) approach considering the synergy among different department alternatives based on the best-worst method (BWM) and TODIM (an acronym in Portuguese of interactive and multiple attribute decision making) method within an interval 2-tuple linguistic environment. First, the evaluation information provided by decision makers (DMs) is represented by interval 2-tuple linguistic variables to reflect and model the underlying diversity and uncertainty. On the basis of the DMs' evaluations, the individual and collaborative performance evaluations of multi-alternative combinations composed of different department alternatives are constructed. Then, the BWM is extended into interval 2-tuple linguistic environment to obtain the weights of evaluation criteria, where the group decision making is taken into account in an interval fuzzy mathematical programming model. Furthermore, to derive more practical and accurate decision results, an interval 2-tuple linguistic TODIM (ITL-TODIM) method is proposed by considering the DMs' psychological behaviours. In the developed ITL-TODIM method, both the gain and loss degrees of one alternative relative to another are simultaneously computed. Finally, a numerical example is presented to illustrate the applicability of the proposed method. Sensitivity and comparative analyses are also provided to demonstrate the effectiveness and advantages of the proposed approach.

Ignition temperature and mechanism of carbonaceous dust clouds: The roles of volatile matter, CH4 addition, O2 mole fraction and diluent gas.

Minimum ignition temperature of dust clouds (MITC) was studied experimentally and theoretically in different atmospheres. Three carbonaceous dusts were tested in both air and O2/CO2 atmospheres with CH4 mole fraction from 0% to 2%. Results showed that the ignition risk of the three dusts significantly increases (decrease of MITC by ~100 â„ƒ) with increasing XO2 from 21% to 50%, but significantly decreases replacing N2 in air with CO2. The inhibition effect of CO2 on MITCs could be diminished by increasing XO2 or adding CH4. The addition of small amount of CH4 has different effects on the MITCs of different dust samples, following the opposite order of volatile matter content: anthracite>bituminous coal>starch. Two modified steady-state ignition models, considering the density of mixture gas and dust cloud, XO2 and its diffusivity, were developed to interpret the experimental observations. The analysis revealed that the global heterogeneous ignition model suits well for the hybrid mixtures of anthracite or bituminous coal dusts. In contrast, the proposed global homogeneous ignition model was found to be only valid for the pure starch dust, and the extra CH4 addition could strongly affect the ignition process of starch, particularly in O2/CO2 atmospheres with higher XO2.

Experimental study of the effect of typical halides on pyrolysis of ammonium nitrate using model reconstruction.

The energetic material ammonium nitrate (AN) is used as an industrial raw material; however, it presents a pyrolysis and explosion hazard during transportation and storage, especially when mixed with impurities. To study the effects of typical halides on the thermal decomposition kinetics of AN, a series of precision thermogravimetric analysis experiments at four heating rates were carried out in a nitrogen atmosphere. Based on derivative thermogravimetric analysis, the addition of sodium halides was found to change the kinetic reaction mechanism of AN pyrolysis. The activation energies were obtained using the isoconversional method, and the pre-exponential factor was derived from the kinetic compensation effect. Models of the kinetic reaction mechanism were reliably reconstructed by combining composite kinetic data processing methods, namely, model-free method, model-fitting method, and parameter simulation. A comprehensive analysis showed that the addition of sodium halides shifts the kinetic mechanism of the pyrolysis of AN toward different dominant reaction models (such as reaction order models, power law models, or phase boundary control models) than those of the original reaction model. The results are helpful as a reference and provide guidance for the determination of AN pyrolysis behavior and the simulation of parameters.

Experimental investigation on the thermal runaway and its propagation in the large format battery module with Li(Ni1/3Co1/3Mn1/3)O2 as cathode.

Thermal runaway (TR) and its propagation behavior in the large format lithium-ion battery (LIB) with various states of charge (SOC) are experimentally investigated in this work. Thermal runaway feature of the cell under thermal abuse condition is characterized using extended volume accelerating rate calorimeter. Based on the experimental results, the modules with five LIBs are built to analyze TR propagation mechanism and further discuss the impact of SOC on TR propagation behavior. It is found that the TR is firstly triggered on the layer near the front surface of the LIB, and then spread to the whole battery. The average propagation time inside the single LIB is 10 s in the module with 100% SOC while 39 s in the module with 50% SOC. Moreover, the module with 100% SOC shows intense combustion behavior, which is replaced by a considerable amount of smoke in the module with 50% SOC. Besides, the average propagation time between adjacent LIBs is significantly delayed from 87 s in 100% SOC module to 307 s in 50% SOC module. This work details TR propagation feature in large format LIB pack, and can provide the guidelines for the safety design of lithium-ion battery module.

An experimental and theoretical study of optimized selection and model reconstruction for ammonium nitrate pyrolysis.

Ammonium nitrate (AN) is a commonly-used industrial raw material in industrial explosives and fertilizers areas. However, as an energetic material, its danger exists during the production, transportation, and storage, resulting in a large number of accidents involving personal injury and property loss. To obtain the accurate kinetic triplet parameters of AN thermal decomposition, a series of thermogravimetry analysis (TGA) experiments was conducted with four different heating rates. Activation energies were calculated by different isoconversional methods Then the kinetic triplet of AN pyrolysis was optimized using a combination of experimental and simulant methods. Combined with the traditional model-free and model-fitting approaches, the experimental kinetic model for AN pyrolysis was optimized and then reconstructed. Through the pyrolysis reaction of AN, a reliable methodology for processing TGA data of hazardous material is proposed in the paper, and the kinetic parameters can be accurately obtained by using such a kinetics method.

Experimental study on the efficiency of dodecafluoro-2-methylpentan-3-one on suppressing lithium-ion battery fires.

Currently, the effective and prompt suppression of lithium-ion battery fires is still challenging. Herein, a 38 A h prismatic ternary (Li(Ni1/3Co1/3Mn1/3)O2/graphite) battery with the size of 150 × 92 × 27 mm3 was adopted to investigate the suppression efficiency of dodecafluoro-2-methylpentan-3-one (C6F12O) in high capacity lithium-ion battery fires. Five doses of C6F12O agent including 0, 0.5, 1.0, 1.5 and 2.0 kg were adopted. It was concluded that as the dose of C6F12O agent increased, the peak temperature of the long surface and bottom of the cells first increased slowly and then decreased rapidly. The results indicated that the C6F12O agent first shows a negative inhibitory effect, which is then transformed into an inhibitory effect as the dose increases. This inhibitory effect grew distinct gradually with an increase in dose. It was found that in a 47.5 × 21.5 × 16 cm3 module box, the appropriate dose of C6F12O agent was 9.42 g W-1 h-1. Accordingly, these results have implications in the fire suppression design for lithium-ion batteries.

Experimental study on a comparison of typical premixed combustible gas-air flame propagation in a horizontal rectangular closed duct.

Research surrounding premixed flame propagation in ducts has a history of more than one hundred years. Most previous studies focus on the tulip flame formation and flame acceleration in pure gas fuel-air flame. However, the premixed natural gas-air flame may show different behaviors and pressure dynamics due to its unique composition. Natural gas, methane and acetylene are chosen here to conduct a comparison study on different flame behaviors and pressure dynamics, and to explore the influence of different compositions on premixed flame dynamics. The characteristics of flame front and pressure dynamics are recorded using high-speed schlieren photography and a pressure transducer, respectively. The results indicate that the compositions of the gas mixture greatly influence flame behaviors and pressure. Acetylene has the fastest flame tip speed and the highest pressure, while natural gas has a faster flame tip speed and higher pressure than methane. The Bychkov theory for predicting the flame skirt motion is verified, and the results indicate that the experimental data coincide well with theory in the case of equivalence ratios close to 1.00. Moreover, the Bychkov theory is able to predict flame skirt motion for acetylene, even outside of the best suitable expansion ratio range of 6

Experimental investigation of spontaneous ignition and flame propagation at pressurized hydrogen release through tubes with varying cross-section.

An experimental investigation of spontaneous ignition and flame propagation at high-pressure hydrogen release via cylindrical tubes with varying cross-section is presented. Tubes with different transverse cross-sections are considered in the experiments: (1) local contraction, (2) local enlargement, (3) abrupt contraction, and (4) abrupt enlargement. The results show that the presence of the varying cross-section geometries can significantly promote the occurrence of spontaneous ignition. Compared to the tube with constant cross-section, the minimum pressure release needed for spontaneous ignition for the varying cross-sections tubes is considerably lower. Moreover, the initial ignition location is closer to the disk in the presence of varying cross-section geometries in comparison with straight channel. As the flame emerges from the outlet of the tube, the velocity of the flame front in the vicinity of the nozzle increases sharply. Then, a deflagration develops across the mixing zone of hydrogen/air mixture. The maximum deflagration overpressure increases linearly with the release pressure. Subsequently, a hydrogen jet flame is produced and evolves different shapes at different release stages. A fireball is formed after the jet flame spouts in the open air. Later, the fireball develops into a jet flame which shifts upward and continues to burn in the vertical direction.