Dehydrogenation and reaction pathway of Perovskite-Type NH4Ca(BH4)3

Perovskite-type borohydride, NH_4Ca(BH_4)_3, is considered as a promising hydrogen storage material due to its high gravimetric hydrogen capacity(15.7 wt%). In this work, the dehydrogenation performance and reaction pathway of NH_4Ca(BH_4)_3 have been systematically investigated. It is found that the initial decomposition temperature is only 65 °C, suggesting a low thermodynamic stability of NH4Ca(BH4)3. The desorption kinetics conducted by differential scanning calorimetry(DSC) indicates that the activation energy of decomposition is about 226.1 k J/mol. The dehydrogenation pathway of NH_4Ca(BH_4)_3 characterized by fourier-transform infrared spectroscopy(FTIR) and solid-state nuclear magnetic resonance(NMR) shows a stepwise decomposition process,in which the initial dehydrogenation is due to destabilization of H~+ in NH4 and H-in BH4 followed by the subsequent dehydrogenation steps arising from the decomposition of homologous NH_3BH_3 and the final decomposition of Ca(BH_4)_2 at a high temperature, respectively.     

Efficient and selective recovery of Ni,Cu,and Co from low-nickel matte via a hydrometallurgical process

Low-nickel matte was intensively characterized,and Ni,Cu,and Co were determined to exist mainly as(Fe,Ni)_9S_8 and Fe Ni_3,Cu_5FeS_4,and(Fe,Ni)_9S_8 and Fe_3O_4(in isomorphic form),respectively.The efficient and selective extraction of Ni,Cu,and Co from the low-nickel matte in an(NH_4)_2S_2O_8/NH_3·H_2O solution system was studied.The effects of(NH_4)_2S_2O_8 and NH_3·H_2O concentrations,leaching time,and leaching temperature on the metal extraction efficiency were systematically investigated.During the oxidative ammonia leaching process,the metal extraction efficiencies of Ni 81.07%,Cu 93.81%,and Co 71.74% were obtained under the optimal conditions.The relatively low leaching efficiency of Ni was mainly ascribed to Ni Fe alloy deactivation in ammonia solution.By introducing an acid pre-leaching process into the oxidative ammonia leaching process,we achieved the high extraction efficiencies of 98.03%,99.13%,and 85.60% for the valuable metals Ni,Cu,and Co,respectively,from the low-nickel matte.     

Study on the hydrogen storage property of (TiZr0.1)xCr1.7-yFeyMn0.3 (1.05

Jigang Li  Li Xu  Xiaojing Jiang  Xingguo Li 《自然科学进展(英文版)》2018,28(4):470-477

Ca(BH_4)_3NH_4与Ca(BH_4)_2储氢性能对比分析

采用密度泛函理论(DFT)对Ca(BH_4)_3NH_4和Ca(BH_4)_2两种储氢材料进行分析,并对过程中产生的焓变、熵变、热力学变化及吉普斯函数进行计算。结果表明:Ca(BH_4)_3NH_4和Ca(BH_4)_2能够收敛,结构可以得到优化。Ca(BH_4)_3NH_4与Ca(BH_4)_2相比,Ca(BH_4)_3NH_4对氢的吸附能力较强,但是,两种储氢材料需要在高温下才能完成对氢的吸附。     

Microstructural characterization and hydrogenation performance of Zr_xV_5Fe(x=3-9) alloys

Zr_xV_5 Fe(x=3,5,7,8,9) alloys were designed to investigate the influence of Zr addition on hydrogenation performance.The alloys were prepared by arc melting and then annealed at 1273 K for 168 h.The results showed that the alloys were composed of α-Zr and C15-ZrV2 phases.The cell volume of C15-ZrV_2 phase firstly increased and then decreased as the content of Zr increased,while the reversed trend was found for the cell volume of α-Zr phase,which was related to the stoichiometric ratio of elements.α-Zr phase distributed in C15-ZrV2 phase matrix in Zr_xV_5 Fe(x=5,7,8,9) alloys,among which Zr7 V5 Fe alloy showed the best distribution.The PCT curves of the alloys under 623 K,673 K and 723 K showed that the hydrogen absorption plateau pressure of the phases in different alloys decreased gradually with the increasing content of Zr.However C15-ZrV2 phase in Zr7 V5 Fe alloy had the lowest hydrogen absorption plateau pressure at room temperature,which was consistent with the change tendency of the corresponding cell volume.Moreover,the kinetic curves of hydrogen absorption at 623 K revealed that Zr7 V5 Fe alloy with the smallest average particle size and the largest phase boundary area showed the fastest hydrogen absorption kinetics.Compared with other four alloys(including St707 alloy),Zr_7 V_5 Fe alloy is more suitable for the use of getter.     

Hydrogen absorption properties of amorphous (Ni0.6Nb0.4−yTay)100−xZrx membranes

Ni based amorphous materials have great potential as hydrogen purification membranes. In the present work the melt spun(Ni_(0.6)Nb_(0.4-y)Ta_y)_(100-x)Zr_x with y=0, 0.1 and x=20, 30 was studied. The result of X-ray diffraction spectra of the ribbons showed an amorphous nature of the alloys. Heating these ribbons below T 400 °C, even in a hydrogen atmosphere(1-10 bar), the amorphous structure was retained. The crystallization process was characterized by differential thermal analysis and the activation energy of such process was obtained. The hydrogen absorption properties of the samples in their amorphous state were studied by the volumetric method,and the results showed that the addition of Ta did not significantly influence the absorption properties, a clear change of the hydrogen solubility was observed with the variation of the Zr content. The values of the hydrogenation enthalpy changed from ~37 k J/mol for x=30 to ~9 k J/mol for x=20. The analysis of the volumetric data provides the indications about the hydrogen occupation sites during hydrogenation, suggesting that at the beginning of the absorption process the deepest energy levels are occupied, while only shallower energy levels are available at higher hydrogen content, with the available interstitial sites forming a continuum of energy levels.     

The influence of molar ratios of Ce/Zr on the selective catalytic reduction of NOx with NH3 over Fe2O3-WO3/CexZrl-xO2 （0 〈 x 〈 1） monolith catalyst

A series of CexZrl_xO2 （0 ≤ x ≤ 1） with dif- ferent molar ratios of Ce/Zr were syhthesized via coprecip- itation method, and Fe2O3-WO3/CexZrl-xO2 monolithic catalysts were prepared, for selective catalytic reduction of nitrogen oxides by ammonia （NH3-SCR）. The structural properties and redox behavior of the catalysts were com- prehensively characterized by N2 physisorption, X-ray diffraction （XRD）, X-ray photoelectron spectra （XPS）, H2-temperature programmed reduction （H2-TPR） and activity measurement for NH3-SCR. The results showed that the NH3-SCR activities of the catalysts were gradually enhanced by increasing the molar ratios of Ce/Zr, especially the low- temperature catalytic activity and the reaction temperature window. Fe2O3-WO3/Ceo.68Zro.3202 monolithic catalyst presented the best NH3-SCR activity among the investigated catalysts, more than 90 % NOx could be removed in the temperature range of 247-454 ℃ on the catalyst under the gas hourly space velocities of 30,000 h- 1. And it always held more than 99 % N2 selectivity and less than 20 ppm （1 ppm =10-6 L/L ） N20 generation concentration between 200 and 500 ℃, the catalyst also displayed its strong resistance of H20 and SO2. Good textural and structural properties, more surface Fe, Ce and active oxygen were together contributed to the excellent NH3-SCR performance of Fe2O3-WO3/ Ce0.68Zr0.32O2 catalyst.     

Effect of Mg substitution for La on microstructure, hydrogen storage and electrochemical properties of La1−xMgxNi3.5 (x=0.20, 0.23, 0.25 at%) alloys

The effect of Mg substitution for La on microstructure, hydrogen storage and electrochemical properties of the annealed La_(1-x) Mg_x Ni_3.5(x=0.20, 0.23, 0.25 at%) alloys have been studied. All the samples were mainly composed of(LaMg)_2Ni_7,(LaMg)Ni_3, and LaNi_5 phases. Mg substitution for La changed the phase abundance, but did not change the constitution of all phases, which is con fi rmed by the results of backscattered SEM images and EDS analysis. The P–C isotherms indicated that the La_(1-x) Mg_x Ni_3.5alloys reversibly absorbed and desorbed hydrogen smoothly at 298 K. The hydrogen absorption cyclic stabilities of La_(1-x) Mg_x Ni_3.5alloy after 5 hydrogen absorption/desorption cycles reached the maximum values of91.9% and 96.0% at 298 K and 323 K, respectively. The hydrogen desorption capacity and plateau pressure for the La_(1-x) Mg_x Ni_3.5alloy reached the maximum values of 1.055 H/M and 0.074 MPa, respectively. The desorption capacities of La_(1-x) Mg_x Ni_3.5reached 0.193 H/M and 0.565 H/M in the fi rst minute at 298 K and 323 K, respectively. Electrochemical property measurement indicated that La_(1-x) Mg_x Ni_3.5(x=0.20,0.23, 0.25 at%) alloys possessed excellent activation capability and were completely activated within3 cycles. Discharge capacities of La_(1-x) Mg_x Ni_3.5alloys reached 378.2 m A h/g(x = 0.20 at%), 342.7 m A h/g(x = 0.23 at%), and 369.6 m A h/g(x = 0.25 at%), respectively. Moreover, energy density of La_(1-x) Mg_x Ni_3.5alloy was much larger than that of La_0.80Mg_0.20Ni_3.5 alloy and nearly approaches the maximum value of La0.75Mg0.25Ni3.5. Thus, the La_(1-x) Mg_x Ni_3.5alloy exhibits optimum comprehensive properties of hydrogen storage and electrochemistry.     

Significantly enhanced hydrogen desorption properties of Mg(AlH4)2 nanoparticles synthesized using solvent free strategy

Mg(AlH_4)_2 nanoparticles with a particle size less than 10 nm have been successfully synthesized by mechanochemical method using LiAlH_4 and MgCl_2 as raw materials together with Li Cl buffering additive. In comparison to Mg(AlH_4)_2 microparticles, Mg(AlH_4)_2 nanoparticles exhibit a faster hydrogen desorption kinetics and lower desorption temperature. The hydrogen desorption temperatures of the first and second dehydrogenation steps are 80 and 220 °C for the Mg(AlH_4)_2 nanoparticles, which are about 65 and 60 °C, respectively, lower than those of Mg(AlH_4)_2 microparticles. The decomposition activation energy is reduced from 135 k J/mol for Mg(AlH_4)_2 microparticles to 105.3 k J/mol for Mg(AlH_4)_2 nanoparticles. It is proposed that the shortened diffusion distance and enhanced diffusivity of Mg(AlH_4)_2/MgH_2 nanoparticles provide an energy destabilization for lowering the dehydrogenation temperature, and thus being the key factor for promoting the hydrogen desorption kinetics. More importantly, it is demonstrated that the dehydrided nano MgH_2 hydride with a particle size below 10 nm can be formed after rehydrogenation process, resulting in the good cycling hydrogen desorption performance of nano MgH_2.     

Improved hydrogenation-dehydrogenation characteristics of nanostructured melt-spun Mg-10Ni-2Mm alloy pr ocessed by rapid solidification

The as-cast Mg-10Ni-2Mm (mole fraction, %) alloy was prepared by a simple and low-cost two-step method of pre-alloying and vacuum induction melting. The nanocrystalline alloy was obtained by the melt-spun process with the surface velocity of copper wheel of 10.5 m/s. The hydrogen storage properties were examined by PCT measurement. The enthalpy ( ΔH) and entropy ( ΔS) of the alloy determined by van’t Hoff plots indicate that the thermodynamic performance of the nanocrystalline alloy is improved by fast diffusion ability of hydrogen in the nanocrystalline microstructure embedding nano-particles of intermetallics compounds Mg2Ni and MmMg12. The reaction kinetics of the melt-spun alloy is greatly improved due to short diffusion path of hydrogen in the nanocrystalline microstructure, resulting in bett er overall hydrogen storage properties. The hydrogen storage capacity is 5.09% (mass fraction, hereinafter the same), and the amount of hydrogen desorption is 4.86%. The hydrogen desorption rate of 95.5% in the alloy is available.     

Crystal structure and surface photo-electric property of Mn（Ⅱ） coordination supramolecules

Two Mn（Ⅱ） coordination supramolecules, [Mn2（C8HTO2）4（phen）2（p-H20）] （1） and [Mn2（btec）（phen）2（H2O）6]·2H2O （2） （phen=1,10-phenanthroline, H4btec=1,2,4,5-benzenetetracarboxylic acid）, were synthesized by hydrothermal method. The crystal structures of the complexes were determined by X-ray single crystal diffraction. The result indicates that （1） and （2） are both binuclear Mn（Ⅱ） complexes. The existence of hydrogen bonds makes the binuclear complexes become further connected to coordination supramolecules, which possess 1D and 3D infinite structures respectively. The complexes were identified by IR, UV-Vis, surface photovoltage spectrum （SPS） and field-induced surface photovoltage spectrum （FISPS）. The results of SPS for the complexes indicate that they both exhibit positive surface photovoltage response bands in the range of 300-600 nm. The SPS phase spectrum and FISPS of complexes indicate that they show certain p-type semiconductor characteristic. However, the intensity, position and number of the SPV response bands are different obviously. The difference of the SPV response bands is mainly attributed to the different structures of the complexes and the different coordination environment of Mn（ll） in the two complexes. This paper discusses the action of hydrogen bonds in the construction of the supramolecule and the change on the surface photovoltage of complex in different coordination environment.     

Gold-leaching performance and mechanism of sodium dicyanamide

In this work, sodium dicyanamide(SD) was used as a leaching reagent for gold recovery, and the effects of the SD dosage and solution pH on the gold-leaching performance were investigated. A gold recovery of 34.8% was obtained when SD was used as the sole leaching reagent at a dosage of 15 kg/t. In the presence of a certain amount of potassium ferrocyanide(PF) in the SD solution, the gold recovery was found to increase from 34.8% to 57.08%. Using the quartz crystal microbalance with dissipation(QCM-D) technique, the leaching kinetics of SD with and without PF were studied. The QCM-D results indicate that the gold-leaching rate increased from 4.03 to 39.99 ng·cm~(–2)·min~(–1) when the SD concentration was increased from 0 to 0.17 mol/L, and increased from 39.99 to 272.62 ng·cm~(–2)·min~(–1) when 0.1 mol/L of PF was used in combination with SD. The pregnant solution in the leaching tests was characterized by X-ray photoelectron spectroscopy and electrospray mass spectrometry, which indicated that Au and(N(CN)_2)~– in the SD solution formed a series of metal complex ions, [Au Nax(N(CN)_2)_(x+2)]~–(x = 1, 2, 3, or 4).     

Microstructure and mechanical properties of the welding joint filled with microalloying 5183 aluminum welding wires

In this study, 7A52 aluminum alloy sheets of 4 mm in thickness were welded by tungsten inert gas welding using microalloying welding wires containing traces of Zr and Er. The influence of rare earth elements Zr and Er on the microstructure and mechanical properties of the welded joints was analyzed by optical microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, hardness testing, and tensile mechanical properties testing. Systematic analyses indicate that the addition of trace amounts of Er and Zr leads to the formation of fine Al₃Er, Al₃Zr, and Al₃(Zr,Er) phases that favor significant grain refinement in the weld zone. Besides, the tensile strength and hardness of the welded joints were obviously improved with the addition of Er and Zr, as evidenced by the increase in tensile strength and elongation by 40 MPa and 1.4%, respectively, and by the welding coefficient of 73%.     

Electrochemical properties and structure of MlNi5-xSnx system

The electrochemical properties and structure of MlNiSnx (x=0-0.5) hydrogen storage alloys were investigated by pressure-composition isotherms, electrochemical measurements, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and atomic parameters. With a small amount of tin substitution, the cycle life increases by 52% (0.5C) and 42% (1.0C), but maximum discharge capacity decreases only by 3.0% and 3.5%, respectively. The cycle life is obviously improved by the low volume expansion and the formed SnO2 surface layers upon electrochemical cycling. The substitution of Ni by Sn leads to an increase of theunit cell volume and charge-discharge cycle life and decrease of the plateau pressure, hysteresis and the hydrogen storage capacity. The standard enthalpy of hydride formation decreases with increasing tin substitution. The main factor that influences the standard enthalpy of the hydriding reaction is the number of the outer orbit electrons and not the atomic size factor.     

Revisiting Al-Ni-Zr bulk metallic glasses using the ＇cluster-resonance＇ model

Six series of alloys,namely,Ni3Zr6Alx,Ni3Zr7Alx,Ni4Zr9Alx,Ni3Zr8Alx,Ni3Zr9Alx and Ni3Zr10Alx (x=1,1.5,2,3) were designed in this work and the bulk metallic glass (BMG) formation of these compositions was investigated by copper mold suction casting. A centimeter-scale BMG sample was obtained for the Ni4Zr9Al2 (Al13.3Ni26.7Zr60 in atomic percent) composition. The thermal glass parameters for this BMG were determined to be ΔTx = 68 K,Trg = 0.579,and γm = 0.689. Using the ’cluster-resonance’ model for glass formation an optimal BMG composition was determined using the cluster formula [Ni3Zr9](Al2Ni1).     

Structure and second-order NLO property of the molecules bridged through n-vertex bis-substituted carborane （n=5, 6, 7）

Density functional theory (DFT) B3LYP at 6-31G* level is employed to optimize the structures of the molecules bridged through n-vertex bis-substituted carborane (n=5, 6, 7) and combined with finite field (FF) formalism to calculate the second-order NLO properties. The results indicate that the structures of n-vertex bis-substituted carborane (n=5, 6, 7) are changed due to bridged donor and acceptor moieties. The distances between two C atoms are becoming longer. And the stability and dipole moment are in- fluenced by changing substituted positions of C atoms. The isomers with the substituents connecting with C atoms of lower coordination number have better stability and larger values of polarizability. One-dimensional structure of the molecules bridged through n-vertex bis-substituted carborane (n=5, 6, 7) is in favor of intramolecular charge-transfer. Meanwhile, the isomer with a larger change of dipole moment has larger value of second-order NLO properties during the charge-transfer process.     

Plasma Modification of Wool: The Effect of Plasma Gas on the Properties of the Wool Fabric

The wool fabrics were treated with low temperature plasma (LTP) using three different gases, namely (ⅰ) oxygen, (ⅱ) nitrogen and (ⅲ) 25％ hydrogen/75％ nitrogen gas mixture. After LTP treatment, the low stress mechanical properties, surface properties and thermal properties of the fabrics were investigated by kES-F (Kawabata Evaluation System) Instruments composing of KES-FBI for tensile and shear property measurement, KES-FB2 for pure bending measurement, kES-FB3 for compression measurement, KES-FB4 for surface friction and surface roughness measurement, and KES-F7 for thermal property measurement. The first four instruments were used for investigating the charaeterlstlc aspect related to fabrle hand while the last one was mainly for the fabric comfort. The properties of LTP treated fabrics under the effect of different gases were compared with the untreated fabric quantitatively.     

Effects of Sc and Zr microalloying on the microstructure and mechanical properties of high Cu content 7xxx Al alloy

The effects of Sc and Zr microalloying on the microstructure and mechanical properties of a 7 xxx Al alloy with high Cu content(7055) during casting, deformation, and heat treatment were investigated. The addition of Sc and Zr not only refined the grains but also transformed the θ-phase into the W-phase in the 7055 alloy. Minor Sc and Zr additions enhanced the hardness and yield strength of the 7055-T6 alloy by strengthening the grain boundaries and Al_3(Sc,Zr) precipitates. However, a further increase in the Sc and Zr fractions did not refine the grains but instead resulted in the formation of the large-sized W-phase and primary coarse Al_3(Sc,Zr) phase and subsequently deteriorated the mechanical properties of the alloys. The 7055 alloy with 0.25 Sc addition exhibited the best mechanical property among the prepared alloys.     

Alkaline Hydrolysis of PP/EHDPET Blend Fibers

Polypropylene superfine fibers or cell porous fibers were prepared from the bi-component blend fibers of polypropylene/easlly hydro-degraded polyester(PP/EHDPET)by alkaline hydrolysis process. EHDPET is a kind of copolyester that can be rapidly hydro-degraded in the hot alkaline solution. This paper discussed the kinetics of alkaline hydrolysis of EHDPET, and the effect of catalyst, bulk ratio and the content of polypropylene grafted maleic anhydride (PP-g-MAH) on the alkaline hydrolysis process. Meanwhile, the morphological change of the outer surface of blend fibers during this process was also investigated by the technology of scanning electron microscope (SEM).     

Hydrogen Adsorption on Metal-Organic Framework MOF-177

This review summarizes the recent literature on the synthesis, characterization, and adsorption properties of meal-organic framework MOF-177. MOF-177 is a porous crystalline material that consists of Zn4O tetrahedrons connected with benzene tribenzoate (BTB) ligands. It is an ideal adsorbent with an exceptionally high specific surface area (BET4500 m2/g), a uniform micropore size distribution with a median pore diameter of 12.7 ?, a large pore volume (2.65 cm3/g), and very promising adsorption properties for hydrogen storage and other gas separation and purification applications. A hydrogen adsorption amount of 19.6 wt.% on MOF-177 at 77 K and 100 bar was observed, and a CO2 uptake of 35 mmol/g on MOF-177 was measured at 45 bar and an ambient temperature. Other hydrogen properties (kinetics and heat of adsorption) along with adsorption of other gases including CO2, CO, CH4, and N2O on MOF-177 were also be discussed. It was observed in experiments that MOF-177 adsorbent tends to degrade or decompose when it is exposed to moisture. Thermogravimetric analysis showed that the structure of MOF-177 remains intact at temperatures below 330℃ under a flow of oxygen, but decomposes to zinc oxide at 420℃.