Observation of metastable phase separation and amorphous phase in Fe67Co33 alloy thin films synthesized by pulsed laser depositions

Pulsed laser deposition technique has been used to manipulate the structural order of Fe₆₇Co₃₃ films grown at various substrate temperatures. Films deposited at room temperature exhibited two phases including the stable crystalline phase embedded in the amorphous phase. The crystalline phase separated into two distinct bcc phases as evident from the splitting of (110) reflections, as compared to the bulk counterpart which crystalize into the single phase bcc structure. Both crystalline phases and the amorphous phase were metastable. Films prepared at higher substrate temperatures (∼500 °C), crystallized into the single stable equilibrium bcc structure. Orientation dependent magnetic properties are also presented for the films prepared at both room temperature and higher substrate temperatures. As expected, the easy axes lie parallel to the plane of the substrate due to shape anisotropy. Out of plane magnetization for the films which exhibited short range ordering is found to saturate at smaller field compared to films where single phase bcc structure is stabilized.     

The influence of surface energy on stress-free microstructures in shape memory alloys

Certain alloys such as In-Tl, Ni-Ti, Ag-Cd or Cu-Al-Ni display remarkable mechanical properties such as the shape memory effect or pseudo-elasticity. This behaviour is related to a solid-solid phase transformation which leads to a complicated microscopic arrangement of different phases. In recent studies such microstructures have been analyzed by the minimization of elastic energy. We discuss the influence of additional surface energy terms on the existence of stress-free microstructures both in the nonlinear and a geometrically linear setting.

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Sommario Certe leghe come quelle di In-Tl, Ni-Ti, Ag-Cd o Cu-Al-Ni mostrano proprietà meccaniche notevoli quali la memoria di forma o la pseudoelasticità. Questo comportamento è determinato da una trasformazione di fase solido-solido che conduce a complicati arrangiamenti a livelo microscopico. In studi recenti tali microstrutture sono state analizzate attraverso la minimizzazione dell'energia elastica. Noi discutiamo l'influenza di termini addizionali di energia superficiale sull'esistenza di microstrutture in uno stato naturale sia in un contesto lineare che non lineare.

     

Shape inverse problem for Stokes–Brinkmann equations

In this paper, we propose an imaging technique for the detection of porous inclusions in a stationary flow governed by Stokes–Brinkmann equations. We introduce the velocity method to perform the shape deformation, and derive the structure of shape gradient for the cost functional based on the continuous adjoint method and the function space parametrization technique. Moreover, we present a gradient-type algorithm to the shape inverse problem. The numerical results demonstrate the proposed algorithm is feasible and effective for the quite high Reynolds numbers problems.     

New understanding on the memory effect of crystallized iPP

In this study, recovery processes of isotactic polypropylene(iPP) melted spherulites at 135 °C after melting at higher temperatures(170 °C–176 °C) were investigated with polarized optical microscopy and Fourier transform infrared spectroscopy. The recovery temperature was fixed to exclude the interference from heterogeneous nuclei. After melting at temperatures between 170 °C and 174 °C, the melted spherulite could recover back to the origin spherulite at low temperatures. Interestingly, a distinct infrared spectrum from iPP melt and crystal was observed in the early stage of recovery process after melting at low temperatures, where only IR bands resulting from short helices with 12 monomers or less can be seen, which indicates that the presence of crystal residues is not the necessary condition for the polymer memory effect. Avrami analysis further indicated that crystallization mainly took place in melted lamellae. After melting at higher temperatures, melted spherulite cannot recover. Based on above findings, it is proposed that the memory effect can be mainly ascribed to melted lamellae, during which crystalline order is lost but conformational order still exists. These conformational ordered segments formed aggregates, which can play as nucleation precursors at low temperatures.     

基于催化应用调控氧化铈纳米材料的形貌

催化剂的设计、合成和结构调控是获得优异性能的关键.传统的策略主要是尽量减小催化剂颗粒尺寸以增加活性中心的数目,即尺寸效应.近年来,材料科学的快速发展使得在纳米尺度上调变催化剂的尺寸和形貌成为可能,特别是通过形貌调控可暴露更多的高活性晶面,大幅度提高催化性能,即纳米催化中的形貌效应.因此,调节催化剂的尺寸与形貌可以单独或协同优化材料的性能.氧化铈作为催化剂的重要组分与结构、电子促进剂被广泛应用于多相催化剂体系.本文总结了近期氧化铈材料形貌可控合成的进展,包括主要的合成策略和表征方法; 进而分析了氧化铈和金-氧化铈催化材料的形貌效应,指出金-氧化铈之间独特的相互作用与载体形貌密切相关; 阐述了氧化铈纳米材料因暴露晶面的差异而获得不同催化性能的化学机制.     

Electrochemical characterization of poly 3-thiopheneacetonitrile: Technique,solvent and relaxation effects

Characterization and electosynthesis of 3-thiopheneacetonitrile (TA) on a platinum electrode have been studied. Different solvents such as Nitrobenzene (NB), 1,2-Dichloroethane (DCE), Dichloromethane (DCM) and Acetonitrile (AN) were used. Many techniques were used for the electrodeposition of films such as potentiodynamic, chronoamperometric and galvanostatic techniques. Poly 3-thiopheneacetonitrile PTA has been subjected to relaxation effect. When the polymer is left at a potential value in its insulating state for some time, the reverse peak in the voltammetric profile during the first positive run differs from the steady state wave. The effect of solvent on the relaxation of the polymer has been studied. A weak or no relaxation was found by using different solvents such as NB, DCE, and DCM.     

Experimental study of thermal oxidation of nanoscale alloys of aluminium and zinc (nAlZn)

Aluminium-based alloys have wide applications but little is known about the thermal-chemical kinetics of nanoalloys. This work investigated the thermal oxidation of Zn and Al nanoalloys (nAlZn) with a BET equivalent diameter of 141 nm through the simultaneous TGA/DSC method. The thermal analysis was combined with elemental, morphology and crystalline structure analysis to elucidate the reaction mechanisms. It was found that the complete oxidation of nAlZn in air can be characterised by a three-stage process, including two endothermic and three exothermic reactions. With the help of ex-situ XRD, different reaction pathways were proposed for different stages, forming the end products of ZnO and ZnAl₂O₄. The reactivity comparison between Al and nAlZn suggested that different criteria should be used for different applications.     

Exploring Variation in Three-Dimensional Shape Data

A variety of very useful methods of statistical shape analysis are available for landmark data. In particular, standard methods of multivariate analysis can often be applied after suitable alignment and transformation of the data. An important example is the use of principal components analysis to provide a convenient route to graphical exploration of the main modes of variation in a sample. Where there are many landmarks or shape information is extracted in the form of curves or surfaces, the dimensionality of the resulting data can be very high and it is unlikely that substantial proportions of variability will be captured in one or two principal components. Issues of graphical exploration are explored in this setting, including random tours of a suitable low-dimensional subspace, the comparison of different groups of data, longitudinal changes and the identification of the features which distinguish individual cases from a group of controls. A suitable software environment for handling these methods with three-dimensional data is outlined. Issues of comparing principal components across time are also tackled through appropriately constructed permutation tests. All of these techniques are illustrated on a longitudinal study of facial development in young children, with particular interest in the identification of differences in facial shape between control children and those who have undergone surgical repair of a cleft lip and/or palate.     

Synthesis routes for the growth of complex nanostructures

The interest in research on inorganic colloidal nanoparticles has moved to more complex structures, such as anisotropically shaped particles and branched objects. Recently, schemes for the synthesis of heterostructures have also been presented. In this article we discuss the synthesis conditions for spherical and branched nanoparticles. The influence of parameters as temperature and composition of the mixture of surfactants on the shape of the growing particles is discussed. Also, an overview on different approaches for the formation of heterostructures is presented briefly.     

Variational approach to shape derivatives for a class of Bernoulli problems

The shape derivative of a functional related to a Bernoulli problem is derived without using the shape derivative of the state. The gradient information is combined with level set ideas in a steepest descent algorithm. Numerical examples show the feasibility of the approach.