Search results for "engineering.material"

Integrative analysis of the mineralogical and chemical composition of modern microbialites from ten Mexican lakes: What do we learn about their forma…

2021

International audience; Interpreting the environmental conditions under which ancient microbialites formed relies upon comparisons with modern analogues. This is why we need a detailed reference framework relating the chemical and mineralogical compositions of modern microbialites to the physical and chemical parameters prevailing in the environments where they form. Here, we measured the chemical, including major and trace elements, and mineralogical composition of microbialites from ten Mexican lakes as well as the chemical composition of the surrounding waters. Saturation states of lakes with different mineral phases were systematically determined and correlations between solution and so…

Migration kinetics of ion-implanted beryllium in glassy carbon

2008

Abstract Migration kinetics of low-concentration implanted 7 Be in glassy carbon has been studied by the modified radiotracer technique at temperatures 1285 °C and 1340 °C. The annealed sample concentration profiles show two distinctive components: (i) Main profile broadening assigned to beryllium trapping in defects during annealing. (ii) Tail parts on both sides of the profile maximum related to faster migration. Of the latter the profile representing bulk diffusion lies on the region free of defect influence and is well described by concentration-independent diffusivity. The features of the concentration profile broadening towards the sample surface indicate partial Be trapping in defect…

Batch-to-Melt Conversion Kinetics in Sodium Aluminosilicate Batches Using Different Alumina Raw Materials

2016

The batch-to-melt conversion in batches of sand, soda ash and corundum (C), alumina spinel (A), boehmite (B), or gibbsite (G) as Al2O3 carrier are studied using thermal analysis, X-ray diffraction, and 27Al nuclear magnetic resonance spectroscopy. Laboratory-scaled batches are either heated continuously or quenched from 1600°C in a series of increasing dwell times. The results show that the conversion from the raw materials to the fresh melt proceeds in two kinetic stages. During the first stage (3–5 min), fast conversion of nearly 95% by mass occurs and the conversion coefficient increases in the order G < C ≈ A < B. The second stage is controlled by the slow dissolution of intermediate cr…

Insights into Intrinsic Defects and the Incorporation of Na and K in the Cu2ZnSnSe4 Thin-Film Solar Cell Material from Hybrid-Functional Calculations

2016

We have performed density functional theory calculations using the HSE06 hybrid functional to investigate the energetics, atomic, and electronic structure of intrinsic defects as well as Na and K impurities in the kesterite structure of the Cu2ZnSnSe4 (CZTSe) solar cell material. We found that both Na and K atoms prefer to be incorporated into this material as substitutional defects in the Cu sublattice. At this site highly stable (Na–Na), (K–K), and (Na–K) dumbbells can form. While Na interstitial defects are stable in CZTSe, the formation of K interstitial defects is unlikely. In general, the calculated formation energies for Na-related defects are always lower compared to their K-related…

Large Zero-Field Cooled Exchange-Bias in BulkMn2PtGa

2013

We report a large exchange-bias (EB) effect after zero-field cooling the new tetragonal Heusler compound Mn2PtGa from the paramagnetic state. The first-principle calculation and the magnetic measurements reveal that Mn2PtGa orders ferrimagnetically with some ferromagnetic (FM) inclusions. We show that ferrimagnetic (FI) ordering is essential to isothermally induce the exchange anisotropy needed for the zero-field cooled (ZFC) EB during the virgin magnetization process. The complex magnetic behavior at low temperatures is characterized by the coexistence of a field induced irreversible magnetic behavior and a spin-glass-like phase. The field induced irreversibility originates from an unusual…

A half-metallic half-Heusler alloy having the largest atomic-like magnetic moment at optimized lattice constant

2016

For half-Heusler alloys, the general formula is XYZ, where X can be a transition or alkali metal element, Y is another transition metal element, typically Mn or Cr, and Z is a group IV element or a pnicitide. The atomic arrangements within a unit-cell show three configurations. Before this study, most of the predictions of half-metallic properties of half-Heusler alloys at the lattice constants differing from their optimized lattice constant. Based on the electropositivity of X and electronegativity of Z for half-Heusler alloys, we found that one of the configurations of LiCrS exhibits half-metallic properties at its optimized lattice constant of 5.803Å, and has the maximum atomic-like magn…

Cold gas dynamic spray additive manufacturing today: Deposit possibilities, technological solutions and viable applications

2017

This paper reports the current potentials of cold gas dynamic spraying (CGDS). CGDS has been significantly developed to produce several functional solutions categorized as follows: deposits with a single powder nature, composites-based deposits, nanotechnological deposits and hybrid coating/substrate assemblies. CGDS process has improved in proficiency and is still gaining attention from scientists and industry. Covering a wide range of materials, both standard and advanced, this additive manufacturing process offers substantial applications for surface functionalization, structural or dimensional restoration, bulk production providing specific material properties, and art/decoration. Progr…

2020

Recent experiments have demonstrated the formation of free-standing Au monolayers by exposing the Au–Ag alloy to electron beam irradiation. Inspired by this discovery, we used semi-empirical effective medium theory simulations to investigate monolayer formation in 30 different binary metal alloys composed of late d-series metals such as Ni, Cu, Pd, Ag, Pt, and Au. In qualitative agreement with the experiment, we find that the beam energy required to dealloy Ag atoms from the Au–Ag alloy is smaller than the energy required to break the dealloyed Au monolayer. Our simulations suggest that a similar method could also be used to form Au monolayers from the Au–Cu alloy and Pt monolayers from Pt–…

Structural and morphological characterization of the Cd-rich region in Cd1-xZnxO thin films grown by atmospheric pressure metal organic chemical vapo…

2019

Abstract We have analysed the growth, morphological and structural characterization of Cd1-xZnxO thin films grown on r-sapphire substrates by atmospheric pressure metal organic chemical vapour deposition, mainly focusing on the Cd-rich rock-salt phase for its promising optical and technological applications. The evolution of the surface morphology and crystalline properties as a function of Zn content has been studied by means of high resolution x-ray diffraction and electron microscopy techniques. Monocrystalline (002) single-phase cubic films were obtained with Zn contents up to 10.4%, and with a low density of dislocations as a consequence of the optimized crystal growth process. Particu…

Influence of spray trajectories on characteristics of cold-sprayed copper deposits

2021

Abstract Industrial robots are widely used in cold spray (CS) as well as thermal spray to produce various coatings by precisely controlling kinematic parameters during the process. However, the robot trajectory and its effect on the characteristics of CS deposits are important, but not fully studied. This article introduces four typical spray trajectories, including zigzag path, cross path, parallel path, and spiral path, to elaborate thick CS Cu deposits, and characterizes the corresponding Cu deposits, respectively. The experimental results revealed that the spray trajectories have a major influence on the associated thermal history and the residual stress distribution. However, no signif…