Molecular dynamics study of the response of nanostructured Al/Ni clad particles system under thermal loading

Molecular dynamics simulations are used to study the exothermic alloying reactions by imposing a thermal loading on a local area of nanostructured Al/Ni clad particles. The combustion parameters, such as particles size, density, and ignition temperature, are characterized. Reducing the size of Al/Ni clad particles makes the propagation velocity of reaction front increase but lowers both the adiabatic combustion temperature and pressure of the system. However, increasing either mass density or ignition temperature makes the propagation velocity of reaction front increase and raises the adiabatic temperature and pressure as well. We estimate the propagation velocity of the chemical reaction front to range from 35.70 to 44.06 m/s.     

Relationship between transformation temperatures and alloying elements in Cu–Al–Ni shape memory alloys

Cu–Al–Ni shape memory alloys are good candidates for high temperature applications. We have investigated the effects of alloying elements on transformation temperatures, heat-capacity values, and structural properties of Cu–13.73Al–4.3Ni and Cu–13Al–4.3Ni (wt%) shape memory alloys. The evolution of the transformation temperatures was studied by differential scanning calorimetry with different heating/cooling rates. The heat-capacity measurements of the samples were made. It was found that the mass percentage of the alloying element has an important effect on the characteristic transformation temperatures and thermodynamic parameters. The structural changes of the samples were studied by X-ray diffraction measurements and optical microscope observations at room temperature. It is evaluated that the transformation parameters of CuAlNi shape memory alloy can be controlled by the change of the mass percentages of the alloying elements.     

Influence of minor alloying elements on the initial stages of oxidation of austenitic stainless steel materials

Surface oxidation of Fe‐19Cr‐17Ni, Fe‐19Cr‐18Ni‐1Al and TiC‐enriched Fe‐19Cr‐18Ni‐1Al alloys was investigated by photoelectron spectroscopy (PES). The experiments were conducted at 323 K in pure O₂ (2.7 × 10^?6 mbar). Composition and morphology of the nanoscale surface oxides were determined quantitatively by inelastic electron background analysis. Moreover, use of synchrotron radiation facilities were necessary to obtain improved sensitivity for studying minor alloying elements such as Al and Si. The results indicate oxygen‐induced segregation of Al, which significantly hinders the oxidation of the major alloying elements Fe and Cr. Ti remains in its inert carbide form. The relative concentration of Fe within the oxide layer was found to increase with the oxide‐layer thickness, indicating greater mobility of Fe relative to other alloying elements. Copyright © 2008 John Wiley & Sons, Ltd.     

Thermodynamic analysis of (Ni,Fe)3Al formation by mechanical alloying

(Ni, Fe)₃Al intermetallic compound was synthesized by mechanical alloying (MA) of Ni, Fe and Al elemental powder mixtures of composition Ni₅₀Fe₂₅Al₂₅. Phase transformation and microstructure characteristics of the alloy powders were investigated by X-ray diffraction (XRD). The results show that mechanical alloying resulted in a Ni (Al, Fe) solid solution. By continued milling, this structure transformed to the disordered (Ni, Fe)₃Al intermetallic compound. A thermodynamic model developed on the basis of extended theory of Miedema is used to calculate the Gibbs free-energy changes. Final product of MA is a phase having minimal Gibbs free energy compared with other competing phases in Ni–Fe–Al system. However in Ni–Fe–Al system, the most stable phase at all compositions is intermetallic compound (not amorphous phase or solid solution). The results of MA were compared with thermodynamic analysis and revealed the leading role of thermodynamic on the formation of MA product prediction.     

纳米颗粒对Ni基复合镀渗层耐冲蚀性能的影响

采用复合镀渗工艺在316L不锈钢表面分别制备了两种纳米颗粒(非晶nano-SiO2颗粒和nano-SiC颗粒)增强的Ni基复合镀渗合金层. 利用扫描电子显微镜(SEM)和透射电子显微镜(TEM)观察了两种复合镀渗合金层的微观组织特征. 通过外加电位(+0.2 V)条件下的电流密度、冲蚀条件下的极化曲线和冲蚀后的交流阻抗谱表征了这两种复合镀渗层在单相流(3.5%(w, 质量分数)NaCl溶液)与料浆流(3.5%NaCl+10%(w)石英砂)中的电化学腐蚀特征, 并采用SEM观察两种复合镀渗层冲蚀后的截面形貌, 探讨这两种纳米颗粒增强的Ni基复合镀渗层在料浆流中的冲蚀机理. 电化学测试结果表明: 静态条件下, 电刷镀含纳米SiO2颗粒的复合镀渗层的耐蚀性能低于单一合金层, 而动态冲蚀条件下, 结果与之相反; 电刷镀含SiC颗粒的复合镀渗层的耐蚀性能在静态和动态冲蚀条件下均低于单一合金层. 对两种复合镀渗层的冲蚀截面形貌观察表明: 弥散分布的纳米SiO2颗粒能明显改善Ni基合金层的耐冲蚀性能; 而添加纳米SiC颗粒在渗金属过程中已完全分解, 导致三元硅化物(Cr6.5Ni2.5Si)和碳化物(Cr23C6)的析出, 而析出相在冲蚀过程易于脱落, 加速了Ni基合金层的质量流失.     

Energy release in the reaction of metal powders with fluorine containing polymers

Fluorine and its derivatives have been used as a substitute to oxygen-containing oxidizers in higher performing propellants and other energetic materials. They typically react rapidly with metals or thin oxide layers of the metals to produce metal fluorides, generally in the gaseous state.Thermal reactions of stoichiometric mixtures of metal (M=Al, Ti) -F containing polymers have been studied using thermal analyzers and their energetics are compared with the metals in other halogen element containing oxidizers. The experimental results indicated that thermal reaction becomes more exothermic as the bond strength between Al-X (X=F, Br, I) becomes stronger. It was also found that oxidation of metal powders is largely affected by the size of metal powders as well as the nature of existing oxide layer.     

Interaction of micas with nickel sulfate solutions

The interaction of natural biotites with dilute nickel sulfate solutions at various pHs are studied by X-ray powder diffraction, thermogravimetric analysis, and chemical analysis. K ? Ni, Mg ? Ni, and to a lesser extent Fe ? Ni ion exchange is shown to occur. Nickel can both enter octahedral layers and act as an interlayer cation. Tetrahedral layers have a virtually invariable composition. The mechanoactivation of biotites enhances exchange reactions.     

Electrochemical characterization of Ni-Co and Ni-Co-Fe for oxidation of methyl alcohol fuel w ith high energetic catalytic surface*简

 Non Pt based metals and alloys as electrode materials for methyl alcohol fuel cells have been investigated with an aim of finding high electrocatalytic surface property for the faster electrode reactions. Electrodes were fabricated by electrodeposition on pure Al foil, from an electrolyte of Ni, Co, Fe salts. The optimum condition of electrodeposition were found out by a series of experiments, varying the chemistry of the electrolyte, pH valve, temperature, current and cell potential. Polarization study of the coated Ni-Co or Ni-Co-Fe alloy on pure Al was found to exhibit high exchange current density, indicating an improved electro catalytic surface with faster charge-discharge reactions at anode and cathode and low overvoltage. Electrochemical impedance studies on coated and uncoated surface clearly showed that the polarization resistance and impedance were decreased by Ni-Co or Ni-Co-Fe coating. X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX) and atomic absorption spectroscopy (AAS) studies confirmed the presence of alloying elements and constituents of the alloy. The morphology of the deposits from scanning electron microscope (SEM) images indicated that the electrode surface was a three dimensional space which increased the effective surface area for the electrode reactions to take place.     

Alloying in an Intercalation Host: Metal Titanium Niobates as Anodes for Rechargeable Alkali‐Ion Batteries

We discuss here a unique flexible non‐carbonaceous layered host, namely, metal titanium niobates (M‐Ti‐niobate, M: Al³⁺, Pb²⁺, Sb³⁺, Ba²⁺, Mg²⁺), which can synergistically store both lithium ions and sodium ions via a simultaneous intercalation and alloying mechanisms. M‐Ti‐niobate is formed by ion exchange of the K⁺ ions, which are specifically located inside galleries between the layers formed by edge and corner sharing TiO₆ and NbO₆ octahedral units in the sol‐gel synthesized potassium titanium niobate (KTiNbO₅). Drastic volume changes (approximately 300–400 %) typically associated with an alloying mechanism of storage are completely tackled chemically by the unique chemical composition and structure of the M‐Ti‐niobates. The free space between the adjustable Ti/Nb octahedral layers easily accommodates the volume changes. Due to the presence of an optimum amount of multivalent alloying metal ions (50–75 % of total K⁺) in the M‐Ti‐niobate, an efficient alloying reaction takes place directly with ions and completely eliminates any form of mechanical degradation of the electroactive particles. The M‐Ti‐niobate can be cycled over a wide voltage range (as low as 0.01 V) and displays remarkably stable Li⁺ and Na⁺ ion cyclability (>2 Li⁺/Na⁺ per formula unit) for widely varying current densities over few hundreds to thousands of successive cycles. The simultaneous intercalation and alloying storage mechanisms is also studied within the density functional theory (DFT) framework. DFT expectedly shows a very small variation in the volume of Al‐titanium niobate following lithium alloying. Moreover, the theoretical investigations also conclusively support the occurrence of the alloying process of Li ions with the Al ions along with the intercalation process during discharge. The M‐Ti‐niobates studied here demonstrate a paradigm shift in chemical design of electrodes and will pave the way for the development of a multitude of improved electrodes for different battery chemistries.     

MoNiP/Al2O3加氢脱氮催化剂的研究:金属分散状态对催化剂活性的影响

采用ＰＡＳＣ Ａ，ＸＰＳ，ＳＴＥＭ和微型反应色谱等技术，研究了一系列ＭｏＮｉＰ／Ａｌ２Ｏ３催化剂表面活性组分的分散状态及其对催化剂ＨＤＮ反应活性的影响。     

Controlling carbon surface chemistry by alloying: carbon tolerant reforming catalyst

Steam reforming is a process where a hydrocarbon is converted into hydrogen and oxygenated carbon species. Ni is often used as catalyst for the reaction. Long term stability of steam reforming catalysts is governed by their ability to selectively oxidize C atoms while preventing C-C bond formation. In this communication we demonstrate that C atom chemistry over Ni surfaces can be controlled by surface alloying. We show that bimetallic Sn/Ni catalyst is much more carbon-tolerant that monometallic Ni. The main reason for this is that Sn alloying results in dramatically lower rates of C-C bond formation as compared to C-oxidation. The bimetallic catalyst was identified in quantum computational studies of the underlying atomic-scale phenomena that govern C atom surface chemistry. The catalysts were also characterized with various electron- and X-ray-based microscopies and spectroscopies.     

甲烷部分氧化制合成气Pt-Ni/Al~2O~3催化剂的研究

研究了Ni/Al~2O~3,Pt/Al~2O~3和一系列Pt-Ni/Al~2O~3催化剂对甲烷部分氧化制合成气的催化作用,发现Pt-Ni/Al~2O~3催化剂显示了比Ni/Al~2O~3和Pt/Al~2O~3更高的活性和稳定性。H~2-TPR,CO-TPD,CO~2-TPD,SEM,XPS和XRD等结果证明:Pt和Ni之间存在较强的相互作用,Pt和部分Ni形成固溶体合金并且Pt在催化剂表面富集。Pt和Ni之间的相互作用提高了催化剂的活性和稳定性,甲烷在Pt-Ni/Al~2O~3上的催化部分氧化具有不同于在Pt/Al~2O~3和Ni/Al~2O~3上的反应性能。     

Reaction mechanisms of dissociative chemisorption of HI, I2, and CH3I on a magic cluster Al13-

We have investigated the transition-state structures and reaction mechanisms for the dissociative chemisorption reactions of HI, I(2), and CH(3)I on the magic cluster Al(-) (13). The HI, I(2), and CH(3)I molecules approach Al(-) (13) with an end-on orientation rather than a side-on orientation because of the more effective orbital overlap in the end-on orientation. The reactions of Al(-) (13) with HI and I(2) would produce Al(13)HI(-) and Al(13)I(2) (-), respectively, because of large exothermic energy changes and relatively small activation energies. The reaction of Al(-) (13) with CH(3)I is unlikely to take place because of the low mobility of CH(3) on Al(-) (13) and the high activation barrier for the S(N)2-type reaction. The dissociative chemisorption reactions are preferred thermodynamically to the abstractive chemisorption reactions.     

Addition of water, methanol, and ammonia to Al3O3- clusters: reaction products, transition states, and electron detachment energies

Products of reactions between the book and kite isomers of Al3O3- and three important molecules are studied with electronic structure calculations. Dissociative adsorption of H2O or CH3OH is highly exothermic and proton-transfer barriers between anion-molecule complexes and the products of these reactions are low. For NH3, the reaction energies are less exothermic and the corresponding barriers are higher. Depending on experimental conditions, Al3O3- (NH3) coordination complexes or products of dissociative adsorption may be prepared. Vertical electron detachment energies of stable anions are predicted with ab initio electron propagator calculations and are in close agreement with experiments on Al3O3- and its products with H2O and CH3OH. Changes in the localization properties of two Al-centered Dyson orbitals account for the differences between the photoelectron spectra of Al3O3- and those of the product anions.     

硫化态NiW/Al2O3催化剂加氢脱硫活性相的研究Ⅰ.XPS和HREM表征

 采用孔饱和共浸法制备了一系列具有相同W含量和不同Ni含量的NiW/Al2O3催化剂,并对相应的硫化态催化剂进行了XPS和HREM表征. 结果表明,引入的助剂Ni优先修饰WS2晶粒的边角位置,形成高活性的NiWS相. 催化剂中助剂Ni在噻吩加氢脱硫反应中的显著促进效应(活性提高了约30倍)与形成的NiWS活性相数量有关. 同时,助剂Ni的引入使得催化剂表面WS2晶粒的堆叠程度略有增加,晶片长度略有减小;而且引入助剂后WOx相的硫化度提高了近20%. 但相比之下,活性相织构的变化和硫化度的增大对催化脱硫活性的贡献较小,不是Ni产生助剂效应的主要原因.     

Ni-Mo-B非晶态合金纳米颗粒的抗氧化性能研究

在水溶液体系中用化学还原法制备Ni-B和Ni-Mo-B非晶态合金纳米颗粒.SEM测试表明,样品的颗粒形貌呈球形或类球形,平均粒径约10nm.XPS分析结果表明,Ni-Mo-B非晶态合金中钼元素主要以氧化态形成于合金的表面,并导致合金表面合金化硼原子浓度显著增加,氧化态硼（B3＋）的原子浓度显著减少,氧的原子浓度明显减少,合金化镍的原子浓度显著增加,氧化态镍（Ni3＋）的原子浓度显著减少.因此,Ni-Mo-B合金的抗氧化性能显著高于Ni-B合金.XPS谱图分析还表明,在Ni-B和Ni-Mo-B非晶态合金中,存在Ni和B的合金化物Ni2B,其中B失去部分电子,而Ni则富余电子.Ni2B的氧化产生副产物Ni2O3和B2O3.     

Chemical and icosahedral short-range orders in liquid and undercooled Al80Mn20 and Al80Ni20 alloys: a first-principles-based approach

Atomic structures of stable liquid and undercooled liquid Al(80)Mn(20) and Al(80)Ni(20) alloys have been calculated by first-principles molecular-dynamics simulations. For both alloys, the local structure as defined by the Faber-Ziman pair-correlation functions is characterized by a strong Al-transition-metal affinity, which leads to a well-pronounced chemical short-range order which is more temperature dependent for Al(80)Mn(20) than for Al(80)Ni(20). In addition, a structural analysis using three-dimensional pair analysis techniques has been performed in details. More particularly, we find that the fivefold local symmetry around Mn atoms is predominant in both stable and undercooled Al(80)Mn(20) alloys and displays no significant variation with temperatures. On the contrary, in Al(80)Ni(20), a strong variation of the topological short-range order is observed since in the undercooled state, the local environment of Ni atoms is characterized by the predominance of the fivefold symmetry over the close-packed local symmetry which is opposed to what occurs in the stable liquid phase.     

Ni3Al箔在甲烷重整反应中的催化性能

研究了以冷轧工艺制备的Ni₃Al单晶箔(Ni-24at% Al), 以及表面预处理(873 K下蒸汽氧化后还原处理)后的Ni₃Al箔, 在甲烷重整制氢反应中的催化性能. 首先, 采用逐步升温法研究了873～1173 K下Ni₃Al箔的催化活性与温度的关系; 然后, 采用等温法研究了973 K下Ni₃Al箔的催化稳定性. 根据催化反应和扫描电镜显微观察的结果得出: 未经预处理和经过预处理的Ni₃Al箔, 在反应中均显示出一定的催化活性和稳定性; 表面预处理对Ni₃Al箔的催化活性有显著的增强作用, 原因是经过该预处理后的Ni₃Al箔形成了富Ni表面; Ni₃Al箔在甲烷重整反应的气氛中, Ni原子从Ni₃Al基体向表面的移动, 是维持催化活性的主要原因.     

Simultaneous operation of dibenzothiophene hydrodesulfurization and methanol reforming reactions over Pd promoted alumina based catalysts

In the current study simultaneous reactions of hydrodesulfurization(HDS) of dibenzothiophene(DBT) and reforming of methanol in a micro-autoclave reactor were studied over bi-metallic(Co-Mo/Al2O3 and Ni-Mo/Al2O3) and tri-metallic(Pd-Co-Mo/Al2O3 and Pd-Ni-Mo/Al2O3) catalyst systems which were prepared by incipient impregnation method.In situ hydrogen utilization and low Pd loadings were the major targets of this study.For comparison purpose,catalytic activity was separately determined for both the methanol reforming and HDS of DBT reactions as well.Ni based catalysts were confirmed with better activity than Co ones for both the reactions with Pd promoted ones ranking at the top i.e.Pd-Ni-Mo/Al2O3 > Ni-Mo/Al2O3 > Pd-Co-Mo/Al2O3 > Co-Mo/Al2O3 where Pd-Ni-Mo/Al2O3 showed 91% DBT conversion at 380 ℃ and 12 h reaction time.Some of the selected organic additives on catalytic activity were tested for their effect toward HDS reaction which was unique with close relation to their chemical nature.Reaction products were quantitatively and qualitatively analyzed via HPLC and GC-MS techniques respectively which helped in elucidating reaction mechanism.     

Ultrafast shock compression of PDMS‐based polymers

The shock response of polymers is important for a number of commercial and defense‐related applications, but it is difficult to obtain empirical shock response data over the wide range of preparations and aging conditions typically found in such applications. Ultrafast compression is useful to characterize polymer shock response over a wide range of polymer initial conditions due to the high throughput of this method. To establish greater confidence in ultrafast compression experiments and to characterize the detailed shock response of several variations in a single base polymer, the results of sub‐nanosecond shock compression experiments in ∼5 μm thick layers of the polydimethylsiloxane (PDMS)‐based elastomeric rubbers Sylgard‐184, SE1700, and an unfilled, end‐linked model PDMS network are presented. The results of conventional ultrafast shock etalon measurements to time‐of‐flight measurements for similar thickness layers of irradiated and unirradiated SE1700 are compared. Good agreement between the shock response measured by these two ultrafast shock methods, as well as consistency between ultrafast data and long time scale gas gun data is found. From measurements across a variety of PDMS formulations, a statistically significant variation in the shock response with the quasistatic elastic modulus is presented. Published 2018.^† J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 827–832