scholarly journals Alloying and Phase Transformation of Fe/FeNi Core/Alloy Nanoparticles at High Temperatures

2021 ◽  
Author(s):  
Tennyson L. Doane ◽  
Laxmikant Pathade ◽  
R. Davon Slaton ◽  
Michael E. Klaczko ◽  
Mathew M. Maye
Keyword(s):  
Photoelectron Spectroscopy ◽  
Elevated Temperatures ◽  
Bulk Diffusion ◽  
Phase Segregation ◽  
Mixing Enthalpy ◽  
Alloy Nanoparticles ◽  
Self Assembled Monolayer ◽  
X Ray ◽  
Self Diffusion ◽  
The Many

This work explores how to form and tailor the alloy composition of Fe/FexNi1-x core/alloy nanoparticles by annealing a pre-formed particle at elevated temperatures between 180 – 325 oC. This annealing allowed for a systematic FeNi alloying at a nanoparticle whose compositions and structure began as a alpha-Fe rich core, and a thin gamma-Ni rich shell, into mixed phases resembling gamma-FeNi3 and gamma-Fe3Ni2. This was possible in part by controlling surface diffusion via annealing temperature, and the enhanced diffusion at the many grain boundaries of the nanoparticle. Lattice expansion and phase change was characterized by powder X-ray diffraction (XRD), and composition was monitored by X-ray photoelectron spectroscopy (XPS). Of interest is that no phase precipitation was observed (i.e., heterostructure formation) in this system and the XRD results suggest that alloying composition or alloy gradient is uniform. This uniform alloying was considered using calculations of bulk diffusion and grain boundary diffusion for Fe and Ni self-diffusion, as well as Fe-Ni impurity diffusion is provided. In addition, alloying was further considered by calculations for Fe-Ni mixing enthalpy (Hmix) and phase segregation enthalpy (HSeg) using the Miedema model, which allowed for the consideration of alloying favorability or core-shell segregation in the alloying, respectively. Of particular interest is the formation of stable metal carbides compositions, which suggest that the typically inert organic self-assembled monolayer encapsulation can also be internalized.

Oxidation of Alloy-X in Subcritical, Transition, and Supercritical Water

CORROSION ◽  
10.5006/3881 ◽  
2021 ◽  
Author(s):  
Zachary Karmiol ◽  
Dev Chidambaram
Keyword(s):  
Supercritical Water ◽  
Photoelectron Spectroscopy ◽  
Focused Ion Beam ◽  
Elevated Temperatures ◽  
Subcritical Water ◽  
Ion Beam ◽  
X Ray Diffraction ◽  
X Ray ◽  
Nickel Based Superalloy ◽  
Before And After

This work investigates the oxidation of a nickel based superalloy, namely Alloy X, in water at elevated temperatures: subcritical water at 261°C and 27 MPa, the transition between subcritical and supercritical water at 374°C and 27 MPa, and supercritical water at 380°C and 27 MPa for 100 hours. The morphology of the sample surfaces were studied using scanning electron microscopy coupled with focused ion beam milling, and the surface chemistry was investigated using X-ray diffraction, Raman spectroscopy, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy before and after exposure studies. Surfaces of all samples were identified to comprise of a ferrite spinel containing aluminum.

scholarly journals The effect of cobalt on morphology, structure, and ORR activity of electrospun carbon fibre mats in aqueous alkaline environments

2021 ◽  
Vol 12 ◽  
pp. 1173-1186
Author(s):  
Markus Gehring ◽  
Tobias Kutsch ◽  
Osmane Camara ◽  
Alexandre Merlen ◽  
Hermann Tempel ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Inductively Coupled Plasma ◽  
Elevated Temperatures ◽  
Current Collector ◽  
Alkaline Media ◽  
Emission Spectrometry ◽  
Free Standing ◽  
X Ray ◽  
Turbostratic Carbon ◽  
Current Densities

An innovative approach for the design of air electrodes for metal–air batteries are free-standing scaffolds made of electrospun polyacrylonitrile fibres. In this study, cobalt-decorated fibres are prepared, and the influence of carbonisation temperature on the resulting particle decoration, as well as on fibre structure and morphology is discussed. Scanning electron microscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, elemental analysis, and inductively coupled plasma optical emission spectrometry are used for characterisation. The modified fibre system is compared to a benchmark system without cobalt additives. Cobalt is known to catalyse the formation of graphite in carbonaceous materials at elevated temperatures. As a result of cobalt migration in the material the resulting overall morphology is that of turbostratic carbon. Nitrogen removal and nitrogen-type distribution are enhanced by the cobalt additives. At lower carbonisation temperatures cobalt is distributed over the surface of the fibres, whereas at high carbonisation temperatures it forms particles with diameters up to 300 nm. Free-standing, current-collector-free electrodes assembled from carbonised cobalt-decorated fibre mats display promising performance for the oxygen reduction reaction in aqueous alkaline media. High current densities at an overpotential of 100 mV and low overpotentials at current densities of 333 μA·cm−2 were found for all electrodes made from cobalt-decorated fibre mats carbonised at temperatures between 800 and 1000 °C.

On the Behavior of Yttria/Yttrium during Mechanical Alloying of a Fe - Y2O3 Model Alloy System

2014 ◽  
Vol 922 ◽  
pp. 598-603
Author(s):  
Gerald Ressel ◽  
Peter Parz ◽  
Alexander Fian ◽  
David Holec ◽  
Sophie Primig ◽  
...  
Keyword(s):  
Mechanical Alloying ◽  
Positron Annihilation ◽  
Photoelectron Spectroscopy ◽  
Atom Probe Tomography ◽  
Elevated Temperatures ◽  
Positron Annihilation Spectroscopy ◽  
Atom Probe ◽  
Model Alloy ◽  
High Temperature Strength ◽  
X Ray

Mechanical alloying (MA) is an established way to prepare nanocrystalline materials and metastable solutions of materials, which normally have no mutual solubility. This is also the case for oxide dispersion strengthened (ODS) steels with improved mechanical properties at elevated temperatures. It is known that a small addition of yttria (Y2O3) has a beneficial effect on high temperature strength and reduces the creep rate in mechanically alloyed ferritic steels by about six orders of magnitude. In this work we present an experimental study using atom probe tomography, X-ray photoelectron spectroscopy, and positron annihilation spectroscopy combined with first principles modeling focusing on the distribution and behavior of yttria in pure iron prepared by mechanical alloying. Atom probe tomography and X-ray photoelectron spectroscopy measurements as well as positron annihilation spectroscopy conducted on powder particles directly after milling have revealed that a predominantly fraction of the yttria powder dissolves in the iron matrix and Y atoms occupy convenient positions, such as vacancies or dislocations. This is supported by ab initio calculations demonstrating that the formation energy for Y substitutional defects in bcc-Fe is significantly lower in the close neighborhood of vacancies.

OBSERVATION OF PHASE TRANSITIONS AT THE (100) SURFACE OF Al-3 at.% Ag

1995 ◽  
Vol 02 (02) ◽  
pp. 141-145 ◽  
Author(s):  
E. WETLI ◽  
M. HOCHSTRASSER ◽  
D. PESCIA ◽  
M. ERBUDAK
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Photoelectron Spectroscopy ◽  
Short Range ◽  
Short Range Order ◽  
Elevated Temperatures ◽  
X Ray ◽  
First Order ◽  
First Order Phase Transition ◽  
First Order Phase

In the bulk binary alloy Al-3 at.% Ag , Ag 2 Al precipitates are formed below 410°C which are reversibly dissolved at elevated temperatures. We have followed this phase transition at a (100) surface as a function of temperature by monitoring the bandwidth of the Ag 4d states in X-ray photoelectron spectroscopy. Since the bandwidth measures the coordination number of the emitting atoms, it directly reveals the short-range order of the Ag atoms at the surface. The measurements show that the dissolution of the Ag -rich clusters starts at temperatures at least 100 K below the bulk transition, and the observed hysteresis behavior is indicative of a first-order phase transition at the surface.

Oxidation Resistance of Multicomponent CrTiAlN Hard Coatings at Elevated Temperatures

2009 ◽  
Vol 75 ◽  
pp. 37-42
Author(s):  
P.L. Tam ◽  
Zhi Feng Zhou ◽  
P.W. Shum ◽  
K.Y. Li
Keyword(s):  
Oxidation Resistance ◽  
Photoelectron Spectroscopy ◽  
High Speed ◽  
Elevated Temperatures ◽  
Oxidation Mechanism ◽  
Hard Coatings ◽  
Closed Field ◽  
X Ray ◽  
Mechanical And Tribological Properties ◽  
Pin On Disc

Quaternary CrTiAlN hard coatings were deposited by closed field unbalanced magnetron sputtering ion plating technique onto steel substrates, and their structural, mechanical, and tribological properties after heat treatment in air at different temperatures (500-900 oC) were studied and compared by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), micro-indentation, and pin-on-disc (POD) tribometer, etc. The onset temperature of oxidation was determined by thermogravimetric analyser (TGA). The compositional depth profiles before and after the heat treatments were examined by X-ray photoelectron spectroscopy (XPS) in order to study the oxidation mechanism. The experimental results indicate that the CrTiAlN coatings have excellent oxidation resistance and thermal stability, and outperform the traditional hard coatings like TiN and TiAlN in terms of higher oxidation temperature, hardness, adhesion, and wear resistance. It is expected that the CrTiAlN coatings with superior properties should have better performance in dry high speed machining.

X-Ray Photoelectron Spectroscopy Study of a Self-Assembled Monolayer of Thiophene Thiol

2000 ◽  
Vol 39 (Part 1, No. 1) ◽  
pp. 252-255 ◽  
Author(s):  
Haruki Okawa ◽  
Tatsuo Wada ◽  
Hiroyuki Sasabe ◽  
Kotaro Kajikawa ◽  
Kazuhiko Seki ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Spectroscopy Study ◽  
Self Assembled Monolayer ◽  
X Ray ◽  
Self Assembled

scholarly journals Breaking Simple Scaling Relations Through Metal-Oxide Interactions: Understanding Room Temperature Activation of Methane on M-CeO2 (M= Pt, Ni or Co) Interfaces

2020 ◽  
Author(s):  
Pablo Lustemberg ◽  
Feng Zhang ◽  
Ramón A. Gutiérrez ◽  
Pedro J. Ramírez ◽  
Sanjaya D. Senanayake ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Density Functional ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Ambient Pressure ◽  
Scaling Relations ◽  
Time Resolved ◽  
X Ray ◽  
Metal Support ◽  
Simple Scaling

The clean activation of methane at low temperatures remains an eminent challenge and a field of competitive research. In particular, on late transition metal surfaces such as Pt(111) or Ni(111), elevated temperatures are necessary to activate the hydrocarbon molecule, but a massive deposition of carbon makes the metal surface useless for catalytic activity. However, on very low-loaded M/CeO2 (M= Pt, Ni, or Co) surfaces, the dissociation of methane occurs at room temperature, which is unexpected considering simple linear scaling relationships. This intriguing phenomenon has been studied using a combination of experimental techniques (ambient-pressure X-ray photoelectron spectroscopy, time-resolved X-ray diffraction and X-ray absorption spectroscopy) and density functional theory-based calculations. The experimental and theoretical studies show that the size and morphology of the supported nanoparticles together with strong metal-support interactions are behind the deviations from the scaling relations. These findings point toward a possible strategy to circumvent scaling relations, producing active and stable catalysts which can be employed for methane activation and conversion. <br>

In situ investigation of water on MXene interfaces

2021 ◽  
Vol 118 (49) ◽  
pp. e2108325118
Author(s):  
Wahid Zaman ◽  
Ray A. Matsumoto ◽  
Matthew W. Thompson ◽  
Yu-Hsuan Liu ◽  
Yousuf Bootwala ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Water Adsorption ◽  
Elevated Temperatures ◽  
Ambient Pressure ◽  
Transition Metal Carbide ◽  
Water Removal ◽  
Water Mobility ◽  
Level Control ◽  
X Ray ◽  
In Situ Investigation

A continuum of water populations can exist in nanoscale layered materials, which impacts transport phenomena relevant for separation, adsorption, and charge storage processes. Quantification and direct interrogation of water structure and organization are important in order to design materials with molecular-level control for emerging energy and water applications. Through combining molecular simulations with ambient-pressure X-ray photoelectron spectroscopy, X-ray diffraction, and diffuse reflectance infrared Fourier transform spectroscopy, we directly probe hydration mechanisms at confined and nonconfined regions in nanolayered transition-metal carbide materials. Hydrophobic (K+) cations decrease water mobility within the confined interlayer and accelerate water removal at nonconfined surfaces. Hydrophilic cations (Li+) increase water mobility within the confined interlayer and decrease water-removal rates at nonconfined surfaces. Solutes, rather than the surface terminating groups, are shown to be more impactful on the kinetics of water adsorption and desorption. Calculations from grand canonical molecular dynamics demonstrate that hydrophilic cations (Li+) actively aid in water adsorption at MXene interfaces. In contrast, hydrophobic cations (K+) weakly interact with water, leading to higher degrees of water ordering (orientation) and faster removal at elevated temperatures.

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