Hydriding behavior in Zr-based AB2 alloy by gas atomization process

The hydriding characteristics of Zr-based AB₂ alloy produced by gas atomization have been investigated during its absorption–desorption reaction with hydrogen gas. Its gas-phase hydrogenation properties are different from those of specimens prepared by conventional methods. For the particle morphology of the as-cast and gas-atomized powders, it can be seen that the mechanically crushed powders are irregular, while the atomized powder particles are spherical. In PCT (Pressure–Composition–Temperature) measurements, for the gas-atomized particles smaller than 50 μm, the hydrogen storage capacity is dramatically decreased and the hysteresis loop becomes larger than that of the gas-atomized particles larger than 50 μm. In addition, the increase of jet pressure of gas atomization results in the decrease of hydrogen storage capacity and the slope of plateau pressure significantly increases. TEM and EDS studies showed the increase of jet pressure in the atomization process accelerated the phase separation within grain of the gas-atomized alloy, which brought about a poor hydrogenation property. In the measurements of hydrogen absorption–desorption kinetics, the improvement of desorption kinetics of gas-atomized AB₂ alloys was mainly caused by the higher plateau pressure, which is attributed to the smaller grain size and higher site energy for hydrogen in the gas-atomized alloys.     

The influence of aluminum powder dispersity on composite solid propellants ignitability by laser radiation

The results of experimental study of ignition process of composite solid propellants based on ammonium nitrate and energetic binder containing aluminum powders of various particle sizes by CO₂-laser radiation in air (with ambient pressure) are presented. Partial or complete replacement of micron-sized aluminum powder on Alex ultrafine powder as part of composite solid propellants leads to the reduction of ignition time by decrease the temperature of burning surface, thickness of reaction layer and by increase of the heating rate in condensed phase. It was found that the efficiency of ultrafine aluminum powder additives in formulations increasing with decreasing of laser radiation intensity. The temperature of the formulation’s burning surface at the ignition moment was measured by usage of the thermal imager. The temperature of burning surface under ignition by radiant heat flux was 545–660 °C (formulations containing ultrafine aluminum powder) and 713–820 °C (formulations with micron-sized aluminum powder) for the radiation intensity 60 W/cm².     

A metal hydride–polymer composite for hydrogen storage applications

To address the issue of the breakdown into fine powders that occurs in the practical use of metal hydrides, the possibility of using a polymeric material as a matrix that contains the active metal particles was experimentally assessed. A ball milling approach in the tumbling mode was used to develop a metal hydride–polymer composite with a high metal to polymer weight ratio. The alloy powder was blended with the polymer and a coating of the metal particles was obtained. The composite was consolidated by hot pressing and the pellets were characterized in terms of their hydriding–dehydriding properties. The materials did not show significant losses in either loading capacity or kinetic properties. The polymeric matrix resulted as being stable under hydrogen cycling. Further, from SEM observation it was confirmed that the metal powders remained embedded in the polymeric matrix even after a number of cycles and that the overall dimensional integrity was retained.     

The heat and mass transfer performance of facile synthesized silica gel/carbon-fiber based consolidated composite adsorbents developed by freeze-drying method

A series of experimental investigations had been performed to analyze the heat and mass transfer performance for two novel types of silica-based consolidated composite adsorbents developed by the freeze-drying method. The first type of adsorbent is silica gel consolidated with carboxymethyl cellulose (CMC) (SC), while the other is silica gel consolidated with CMC and carbon fiber powder (SCC). Results indicate that the thermal conductivity of consolidated composite adsorbents increases with the mass proportion of carbon fiber powder, while it decreases with the increasing moisture content in the preparation process of the adsorbents. When the mass ratio of silica gel, CMC, and carbon fiber powder is 4:1:4, the highest thermal conductivity of consolidated composite adsorbent obtained from experiments reaches 1.66 W m^?1 K^?1, which is 13.4 times greater than that of pure silica gel. Furthermore, the results of macroporous properties analysis of typical samples including SC20 and SCC20 (where the 20 means that the undried samples have a water content of 20% by mass during the preparation process) show that heat transfer additives effectively improve the macroporous porosity and permeability of the consolidated composite adsorbents. The study on adsorption dynamic performance indicates that the freeze-drying method helps to improve the adsorption performance including adsorption rate and equilibrium water uptake. The experimental results also show that the mass transfer coefficient K of the two typical samples are approximately stable at 5 × 10^?3 s^?1 when the adsorption temperature is ranged between 30 and 40°C, which are almost twice the corresponding values of the samples developed by heating–drying method. Therefore, the proposed approach which is the consolidation with heat transfer additives combined with freeze-drying method is effective for simultaneously enhancing the heat and mass transfer performance of the silica gel adsorbents.     

Study on the hydrogen storage properties of core–shell structured Mg–RE (RE = Nd,Gd, Er) nano-composites synthesized through arc plasma method

Mg based Mg–Rare earth (RE) hydrogen storage nano-composites were prepared through an arc plasma method and their composition, phase components, microstructure and hydrogen sorption properties were carefully investigated. It is shown that the Mg–RE composites have special metal-oxide type core–shell structure, that is, ultrafine Mg(RE) particles are covered by nano-sized MgO and RE₂O₃. In comparison to pure Mg powders prepared using the same method, the hydrogen absorption kinetics can be significantly improved through minor addition of RE to Mg. In addition, the Mg–RE composite powders show better anti-oxidation ability than pure Mg powders, resulting in the increased hydrogen storage capacity of Mg–RE powders over pure Mg powders. In particular, the hydrogenation enthalpy can be increased and the dehydriding temperature can be reduced through minor addition of Er. The experimental results show that both the RE in solid solution state in Mg and the RE₂O₃ nano-grains covered on Mg particles contribute to the improved hydrogen storage thermodynamic, kinetic and anti-oxidation properties of Mg ultrafine particles.     

水煤膏冷态雾化试验装置和测量系统的研究

建立了一套垂直式水煤膏雾化试验装置，提出了通过采用PIV技术及二将开发的图像处理软件来测量水煤膏雾化颗粒的平均粒径与分布的方法，分析了水煤膏雾化颗粒测量的影响因素，为进一步研究水煤膏喷嘴雾化性能提供了保证。     

TiO2超声光催化降解荧光增白剂-CBW

均匀沉淀法制备了纳米TiO2，TEM，xRD分别进行了表征。以该纳米TiO2为光催化剂，对超声光催化降解荧光增白剂CBw的反应进行了研究。结果表明，超声波的引入提高了纳米TiO2光催化降解CBw的反应效率；反应符合Langmuir-Hinshelwood动力学模型，表观反应速率常数k1为0．0266min^-1；反应受超声波功率的影响；溶液中添加少量的Fe^3 ，H3PW12O40、H2O2均能够明显地强化CBw的降解反应。     

Impact of waste cooking oil in biodiesel blends on particle size distributions from a city-car engine

Using biodiesel as a blending component in diesel engine has demonstrated to reduce hydrocarbon and particulate matter emissions. Literature showed that biodiesel type, engine architecture and test conditions deeply affect performance and emission characteristics. Among suitable biodiesel fuels, waste cooking oil (WCO) is considered very attractive due to the reduced environmental impact without sacrificing engine performance.This paper aims at investigating how mixing ratio of biodiesel from WCO and mineral diesel affects the particle size distributions of a current state of art small displacement diesel engine.Experimental tests have been performed on an up-to date light common rail diesel engine. Its complete operative field has been investigated. The results obtained show that the use of biodiesel blends from WCO reduces the total number of particles emitted from the engine with respect to the diesel fuel; the reduction is more evident as the percentage of biodiesel in the blend increases. The number of particles in WCO biodiesel soot with diameter smaller than 10 nm is reduced as compared to diesel fuel; the same trend is observed for diameters larger than 200 nm; comparable particle numbers were obtained in the ultrafine range (Dp < 100 nm).     

Review of principles and methods of severe plastic deformation for producing ultrafine-grained tubes

Severe plastic deformation (SPD) is known to be the best method for producing bulk ultrafine-grained and nanostructured materials with excellent properties. Different SPD methods were developed that are suitable for sheet and bulk solid materials. During the past decade, efforts have been made to create effective SPD processes suitable for producing cylindrical tubes. In this paper, we review SPD processes intended to produce ultrafine-grained and nanostructured tubes, and their effects on material properties. The paper will focus on introduction of the tube SPD processes, and then comparison of them based on their advantages and disadvantages from the viewpoints of processing and properties.     

MgH2 with different morphologies synthesized by thermal hydrogenolysis method for enhanced hydrogen sorption

Magnesium hydride (MgH₂) with a range of morphologies has been synthesized via a simple hydrogenolysis route involving the decomposition of di-n-butylmagnesium. As the synthetic medium evolved from an inert atmosphere of argon to hydrogen pressure, the morphology shifted from rod like to small particles (25–170 nm). In cyclohexane, a solvent relative inert toward magnesium, smaller particles (15–50 nm) were formed. However in diethyl ether, which is more reactive toward magnesium, flakes organized in large microstructures were obtained. Remarkably in all cases β-MgH₂ was readily obtained with some residual carbon contamination. Hydrogen release from these structures occurred at a relatively low temperature (300 °C), with desorption kinetics faster or equivalent to that of ball milled magnesium. In particular, hydrogen desorption from the smallest particles of MgH₂ produced via the hydrogenolysis of di-n-butylmagnesium under hydrogen pressure or cyclohexane was impressive with the full desorption achieved in less than 10 min without any catalyst. These remarkable hydrogen storage properties are believed to result from an appropriate stabilization of the nanoparticles generated.     

燃烧超细颗粒声波团聚的谱分布数值模拟

在简要介绍声波团聚超细颗粒物的动力学机理的基础上，利用区域算法求解超细颗粒声波团聚的动力学方程(GDE)，数值模拟了声波团聚前后的超细颗粒的谱分布变化，并同相关实验数据和数值算法进行了比较和分析．区域算法结果和实验数据以及数值解之间吻合较好，并且利用该算法研究了颗粒质量浓度、声波频率和声波强度对超细颗粒团聚效果的影响，结果表明颗粒质量浓度和声强的增加均有利于颗粒的团聚，而声波频率则存在一个最佳值．     

Hydrogen absorption and electrocatalytic properties of ultrafine LaNi5 powders

The different conditions of milling LaNi₅ have been investigated. The hydrogen absorption characteristics and electrocatalytic properties of the ultrafine powders obtained are described and discussed. An anomalously high value of the exchange current in the reaction of hydrogen cathode deposition for some ultrafine powders has been observed.     

Universal drying rate constant of seedless grapes: A review

Drying kinetics of materials may be described completely using their transport properties together with those of the drying medium. In the case of food drying, the drying rate constant ‘k’ was used instead of transport properties. The drying rate constant combines all the transport properties and may be defined by the thin layer equation. A large number of investigators have worked on solar drying of grapes and the drying rate constant has been calculated through conditions of drying product temperature, equilibrium relative humidity, equilibrium moisture content and drying time. Several mathematical models have been proposed to describe the moisture movement in the drying product. Among the thin layer models, the exponential model is found to be simple and most suitable to describe drying characteristics of grapes. The exponential model considers only the surface resistance, implying that all the resistance is concentrated in a layer at the surface of the drying product. Drying characteristics obtained from experimental results of some investigators were taken into consideration to estimate the value of drying rate constant for grapes. The best fit for drying rate constant value was selected from among the various drying curves obtained experimentally by investigators till date.     

Hydrogen storage properties of Mg–TM–La (TM = Ti,Fe, Ni) ternary composite powders prepared through arc plasma method

For the first time, Mg based Mg–Transition metal (TM) –La (TM = Ti, Fe, Ni) ternary composite powders were prepared directly through arc plasma evaporation of Mg–TM–La precursor mixtures followed by passivation in air. The composition, phase components, microstructure and hydrogen sorption properties of the composite powders were carefully investigated. Composition analyses revealed a reduction in TM and La contents for all powders when compared with the compositions of their precursors. It is observed that the composites are all mainly composed of ultrafine Mg covered by nano La₂O₃ introduced during passivation. Based on the Pressure–Composition–Temperature measurements, the hydrogenation enthalpies of Mg are determined to be −68.7 kJ/mol H₂ for Mg–Ti–La powder, −72.9 kJ/mol H₂ for Mg–Fe–La powder and −82.1 kJ/mol H₂ for Mg–Ni–La powder. Meantime, the hydrogen absorption kinetics can be significantly improved and the hydrogen desorption temperature can be reduced in the hydrogenated ternary Mg–TM–La composites when compared to those in the binary Mg–TM or Mg–RE composites. This is especially true for the Mg–Ni–La composite powder, which can absorb 1.5 wt% of hydrogen at 303 K after 3.5 h. Such rapid absorption kinetics at low temperatures can be attributed to the catalytic effects from both Mg₂Ni and La₂O₃. The results gathered in this study showed that simultaneous addition of 3d transition metals and 4f rare earth metals to Mg through the arc plasma method can effectively alter both the thermodynamic and kinetic properties of Mg ultrafine powders for hydrogen storage.     

前置碱雾发生器内气液固多相流动的测量研究

根据两相流相似模化原理建立了前置碱雾发生器烟气脱硫颗粒图像测速技术多相流动实验台,运用颗粒图像测速(PIV)技术对前置碱雾发生器内气液固三相流动进行测量,得到不同工况条件下喷雾射流与固体颗粒的流动结构和流场信息.结果表明:由于雾化液滴射流的卷吸作用,大部分固体颗粒被卷吸进雾化锥内,在喷嘴出口一定区域固体颗粒与雾化液滴具有较大的速度差,在雾化锥内固体颗粒与雾化液滴发生剧烈的碰撞形成浆液,此为形成碱雾的主要区域.合理设计边壁风量有利于抑制甚至防止雾化液滴以及碰撞形成的浆滴可能的粘壁现象.     

Using hydrogen for the production of Fe-Nd-Bsystem permanent magnets

The gas atomized powders of the Fe–TM–Nd–REM–B system have ahydrogen absorption capacity of the same order as that of a cast alloy of identical chemicalcomposition. This paper presents a theoretical explanation of a value of tetrahedral pores in thelattice of Fe₁₄Nd₂B phase. In the volume of these pores we selected thepolyhedrons. Their distribution explains sorption capacity, kinetics to sorption and symmetry ofdistorting a lattice of Fe₁₄Nd₂B phase during the absorption of hydrogen.We have found that a cyclical hydride processing of the GAP raises the residual magneticinduction of magnetoplasts produced from them. This occurs as a consequence of hydrogenembrittlement of GAP. Disintegration of powder during production of magnetoplasts brings aboutsuch consequences. The GAP (in contrast to powder obtained by mechanical size reduction) havea more pronounced effect of form preservation during a cyclical hydride processing.     

Effects of particle size and type of conductive additive on the electrode performances of gas atomized AB5-type hydrogen storage alloy

The phase composition, morphology, structure, and state of the surface of gas atomized LaNi_4.5Al_0.5 alloy powders constituting a fine (≤50 μm), a medium (160–316 μm), and a coarse (630–1000 μm) fraction have been investigated. The electrochemical and storage characteristics of electrodes made from these powders with addition of electrolytic copper powder or a carbon composite (1 wt.% carbon nanotubes + 7 wt.% nanosized carbon black) as a conductive additive have been studied. In the work, X-ray diffraction, scanning electron microscopy, electron-probe microanalysis, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and several electrochemical methods have been used. It has been established that, in the initial state, the coarse-fraction gas atomized powders show a better kinetics of the hydrogen exchange reactions and higher discharge capacity (∼300 mA h/g). It is shown that electrodes made from the powders of all the fractions have a good high-rate discharge capability. Hydrogen diffusion coefficients during discharge of the electrodes made from the alloy powders of all the fractions and conductive additives have been calculated. It is shown that, for LaNi_4.5Al_0.5 alloy electrodes with the composite carbon additive, the hydrogen diffusion coefficients during discharge computed from data obtained by the electrochemical impedance spectroscopy method agree well with those calculated from cyclic current–voltage curves (2–4 × 10⁻⁹ cm²/s).     

Modeling of ammonium dinitramide (ADN) monopropellant combustion with coupled condensed and gas phase kinetics

A comprehensive multi-phase combustion model has been developed to study the physiochemical processes involved in the combustion of ammonium dinitramide (ADN). The numerical model is based on the conservation equations of mass, species concentration, and energy, and takes into account finite-rate chemical kinetics in both condensed and gas phases. Based on an extensive review of the literature on ADN thermal decomposition, three global decomposition reactions in the condensed phase of ADN are included. A detailed chemical kinetics scheme involving 34 species and 165 reactions is employed in the gas phase. Detailed combustion-wave structures and burning rate characteristics of ADN are described. The optimized gas-phase kinetics mechanism was able to predict the multi-stage flame structure. Good agreements between the predicted and measured profiles of temperature and species mole fractions were obtained at different pressures. Reasonable agreements between calculated and measured values of propellant burning rates and surface temperatures were obtained over a broad range of pressure from 0.7 to 350 atm. The burning rate increases with pressure, except in the mid range of ∼60–100 atm. The coupled condensed- and gas-phase analysis employed in the current model is able to capture this irregular/unstable combustion behavior in the mid range, where the burning rate decreases with the increase in pressure.     

超细粒度拜尔法赤泥氢还原动力学实验

通过超细粒度拜尔法赤泥的氢还原实验考察了800～1000℃还原温度条件下还原时间对还原率的影响,并根据实验结果对超细粒度铁氧化物还原动力学模型进行了计算分析。研究结果表明,还原时间长、还原温度高对应的还原率高,在1000℃条件下还原70 min还原率高达99%以上,还原过程中赤泥颗粒间未发生烧结,有利于将铁元素与其他杂质元素分离;对于超细粒度拜尔法赤泥的还原,影响反应进行的限制性因素为界面反应;常用未反应核模型不能精确描述超细粒度铁氧化物的还原率和还原时间的变化关系,研究修正了未反应核模型,使之适用于描述超细粒度下铁氧化物的还原过程。     

Multimodal ultrafine particles from pulverized coal combustion in a laboratory scale reactor

Particle size distribution functions have been measured in a ethanol fueled flame reactor fed with a low amount of pulverized coal particles. The reactor is operated in low (5.0 vol.%) and high (76.5 vol.%) oxygen concentrations using two high volatile bituminous Colombian and Indonesian coals. A carbon black powder is also oxidized in the same conditions. Generated particles are sampled using rapid-dilution probes and the size distribution functions are measured on-line by a high resolution Differential Mobility Analyzer. Results clearly show that ultrafine particles, those with sizes lower than 100 nm, have a multimodal size distribution function. These particles have huge number concentrations in both investigated conditions whereas their formation is enhanced in the oxygen enriched condition. Ultrafine particles are almost totally dominated in number by the fraction having sizes below 30 nm. Nanoparticles also account for a significant fraction of total particle mass and slowly coagulate in the reactor. The shape of the size distribution functions is not affected by the coal type, at least for the two investigated coals. Results suggest that ultrafine particles form through the vaporization-nucleation-growth pathway involving inorganic ashes. Moreover the contribution of carbonaceous particles seems particularly important for size smaller than 5 nm.