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Carmine Dagostino - One of the best experts on this subject based on the ideXlab platform.

  • effect of Al Content on the strength of terminAl silanol species in zsm 5 zeolite catAlysts a quantitative drifts study without the use of molar extinction coefficients
    Physical Chemistry Chemical Physics, 2018
    Co-Authors: Pierre Brauer, Olivia Situmorang, Carmine Dagostino
    Abstract:

    The strength of terminAl hydroxyl Si-OH groups (silanols) in zeolites is important for many non-size-selective catAlytic reactions occurring onto the externAl surface of the zeolite crystAls and may often be responsible for catAlyst deactivation, e.g., coke formation. A quantitative anAlysis of Si–OH strength and its link with the Al Content, hence varying silica-to-Alumina ratio (SAR = SiO2/Al2O3), has not been established yet. Various hypotheses have been proposed in the literature; nonetheless, the role of Al Content in determining silanol strength remains still unclear and the object of speculation. In this work, we have systematicAlly investigated the effect of the Al Content on the strength of terminAl silanol sites in ZSM-5 zeolite catAlysts with varying SAR using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) at variable temperatures without molar extinction coefficients. Two base probe molecules with different proton affinity vAlues, pyridine and collidine, were used. To quantify the strength of terminAl silanol sites the change of the terminAl silanol peak in the OH stretching region, together with data on elementAl anAlysis, was used. With this experimentAl protocol, unlike most IR studies, the use of molar extinction coefficients, often difficult to obtain, is not needed for quantification. The results reported here show for the first time that for ZSM-5 zeolite catAlysts the fraction of occupied terminAl silanol acid sites for both pyridine and collidine increases with increasing concentration of externAl Bronsted acid sites, hence establishing a clear link between the two types of acid sites. In summary, this work shows that the use of DRIFTS without molar extinction coefficients is able to quantitatively probe the strength of terminAl silanol acid sites and establishes a link between the externAl Bronsted Al Content and the strength of terminAl silanol species in ZSM-5 zeolites with varying SAR at elevated temperatures.

  • effect of Al Content on number and location of hydroxyl acid species in zeolites a drifts quantitative protocol without the need for molar extinction coefficients
    RSC Advances, 2017
    Co-Authors: Pierre Brauer, Olivia Situmorang, Iain Hitchcock, Carmine Dagostino
    Abstract:

    In this work, we have systematicAlly investigated the effect of the Al Content on the number and location of bridging hydroxyls (Bronsted acid sites) and terminAl hydroxyls (terminAl silanol sites) in ZSM-5 zeolites with varying silica-Alumina ratio (SAR = SiO2/Al2O3) using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) without molar extinction coefficients. Two base probe molecules with different kinetic diameters, pyridine (5.7 A) and collidine (7.4 A), were used. The totAl Content of Bronsted acid sites is obtained by elementAl anAlysis of the proton form and sodium exchanged form of ZSM-5. To quantify the number of internAl and externAl Bronsted acid sites the change in area of the Bronsted acid site peak in the O–H stretching region is then used; thus, the need for molar extinction coefficients to quantify Bronsted acid sites is thereby eliminated. The results reported here show that for ZSM-5 the number of externAl Bronsted sites, in absolute terms, increases with increasing totAl Al Content, as evidenced by collidine adsorption. The number of terminAl silanol acid sites was found to be proportionAl to the externAl surface area probed by argon sorption experiments. In summary, this work shows that the use of DRIFTS in conjunction with elementAl anAlysis is a vAlid Alternative to quAlitatively and quantitatively probe the number and location of hydroxyl acid sites without the use of molar extinction coefficients and gives a comprehensive picture of the effect of Al Content on number and location of hydroxyl acid species in ZSM-5 zeolites with varying SAR. The work contributes to advancing the range of characterisation protocols for solid acid catAlysts.

R Kainuma - One of the best experts on this subject based on the ideXlab platform.

  • effect of Al Content on abnormAl grain growth and superelasticity in fe mn Al cr ni shape memory Alloys with near zero temperature dependence of transformation stress
    Shape Memory and Superelasticity, 2021
    Co-Authors: Ji Xia, Toshihiro Omori, Toru Hoshi, R Kainuma
    Abstract:

    The solvus temperature of face-centered cubic (FCC) phase in Fe–34Mn–xAl–4Cr–7.5Ni (x = 13, 14, and 15) shape memory Alloys with different Al Contents, and their abnormAl grain growth and superelasticity at various temperatures were evAluated. With increasing Al Content, the solvus temperature of the FCC phase decreased and the FCC precipitates became finer. Whereas cyclic heat treatment induced abnormAl grain growth (AGG) in All samples, large grains were obtained more easily in the Alloys with higher Al Content. The criticAl stress for martensitic transformation increased with increasing Al Content. The x = 14 Alloy is the optimAl composition considering grain growth and superelasticity. The newly developed Fe–34Mn–14Al–4Cr–7.5Ni Alloy, in which single-crystAl can easily be fabricated by AGG, exhibited superelasticity at temperatures ranging from − 263 °C (10 K) to 27 °C (300 K), with a very smAll temperature-dependence of the criticAl stress, comparable to that of conventionAl Fe–34Mn–13.5Al–3Cr–7.5Ni Alloy.

  • abnormAl grain growth in fe mn Al ni shape memory Alloy with higher Al Content
    Scripta Materialia, 2020
    Co-Authors: Ji Xia, Toshihiro Omori, R Kainuma
    Abstract:

    Abstract The effect of Al Content on the abnormAl grain growth of Fe–Mn–Al–Ni shape memory Alloy is investigated in comparison with the previously reported Fe–Mn–Al–Ni–Ti Alloy. MicrostructurAl observations reveAled that compared with 1.5Ti, 17Al (adding 2 at.% Al to the conventionAl Fe–Mn–Al–Ni) showed the potentiAl to grow into a large single crystAl. The obtained results indicate that the size control of the second phase, which can be achieved not only by introducing Ti, but rather universAlly by stabilizing BCC phase, and the resultant subgrain structure are vitAl for abnormAl grain growth.

Arnab Bhattacharya - One of the best experts on this subject based on the ideXlab platform.

  • distorted wurtzite unit cells determination of lattice parameters of nonpolar a plane Algan and estimation of solid phase Al Content
    Journal of Applied Physics, 2011
    Co-Authors: Masihhur R Laskar, Nirupam Hatui, Tapas Ganguli, Azizur A Rahman, Amlan Mukherjee, M R Gokhale, Arnab Bhattacharya
    Abstract:

    Unlike c-plane nitrides, “nonpolar” nitrides, e.g., those grown in the a-plane or m-plane orientation encounter anisotropic in-plane strain due to the anisotropy in the lattice and thermAl mismatch with the substrate or buffer layer. Such anisotropic strain results in a distortion of the wurtzite unit cell and creates difficulty in accurate determination of lattice parameters and solid phase group-III Content (xsolid) in ternary Alloys. In this paper we show that the lattice distortion is orthorhombic, and outline a relatively simple procedure for measurement of lattice parameters of nonpolar group III-nitrides epilayers from high resolution x-ray diffraction measurements. We derive an approximate expression for xsolid taking into account the anisotropic strain. We illustrate this using data for a-plane AlGaN, where we measure the lattice parameters and estimate the solid phase Al Content, and Also show that this method is applicable for m-plane structures as well.

  • distorted wurtzite unit cells determination of lattice parameters of non polar a plane Algan and estimation of solid phase Al Content
    arXiv: Materials Science, 2010
    Co-Authors: Masihhur R Laskar, Tapas Ganguli, Azizur A Rahman, Amlan Mukherjee, M R Gokhale, Arnab Bhattacharya
    Abstract:

    Unlike c-plane nitrides, ``non-polar" nitrides grown in e.g. the a-plane or m-plane orientation encounter anisotropic in-plane strain due to the anisotropy in the lattice and thermAl mismatch with the substrate or buffer layer. Such anisotropic strain results in a distortion of the wurtzite unit cell and creates difficulty in accurate determination of lattice parameters and solid phase group-III Content (x_solid) in ternary Alloys. In this paper we show that the lattice distortion is orthorhombic, and outline a relatively simple procedure for measurement of lattice parameters of non-polar group III-nitrides epilayers from high resolution x-ray diffraction measurements. We derive an approximate expression for x_solid taking into account the anisotropic strain. We illustrate this using data for a-plane AlGaN, where we measure the lattice parameters and estimate the solid phase Al Content, and Also show that this method is applicable for m-plane structures as well.

Bin Yang - One of the best experts on this subject based on the ideXlab platform.

  • in situ electrochemicAl afm study of locAlized corrosion of Al x cocrfeni high entropy Alloys in chloride solution
    Applied Surface Science, 2018
    Co-Authors: Yunzhu Shi, P K Liaw, Liam Collins, Nina Balke, Bin Yang
    Abstract:

    Abstract In-situ electrochemicAl (EC)-AFM is employed to investigate the locAlized corrosion of the AlxCoCrFeNi high-entropy Alloys (HEAs). Surface topography changes on the micro/sub-micro scAle are monitored at different applied anodizing potentiAls in a 3.5 wt% NaCl solution. The microstructurAl evolutions with the increased Al Content in the Alloys are characterized by SEM, TEM, EDS and EBSD. The results show that by increasing the Al Content, the microstructure changes from single solid-solution to multi-phases, leading to the segregations of elements. Due to the microstructurAl variations in the AlxCoCrFeNi HEAs, locAlized corrosion processes in different ways after the breakdown of the passive film, which changes from pitting to phase boundary corrosion. The XPS results indicate that an increased Al Content in the Alloys/phases corresponds to a decreased corrosion resistance of the surface passive film.

  • corrosion of Al xcocrfeni high entropy Alloys Al Content and potentiAl scan rate dependent pitting behavior
    Corrosion Science, 2017
    Co-Authors: Bin Yang, Jamieson Brechtl, Karin A Dahmen, P K Liaw
    Abstract:

    Abstract The present work investigates the influence of Al-Content and potentiAl-scan-rate on stable/metastable pitting of Al x CoCrFeNi high-entropy Alloys in a 3.5 wt.% NaCl solution. The increased Al Content causes the volume fraction of the Cr-depleted phase to increase, resulting in thicker/dispersive passive films that degrade the locAlized corrosion resistance. The varied stable/metastable pitting behavior under different potentiAl scan rates indicates that pit generation is influenced by the properties of passive films and the interactions between chloride ions and the active sites. Furthermore, a mean-field theory is employed to predict the scan-rate dependent, power-law distribution of current fluctuations.

  • the effect of Al Content on the gAlvanic corrosion behaviour of coupled ni graphite and ni Al coatings
    Corrosion Science, 2011
    Co-Authors: C. Xu, Lingzhong Du, Bin Yang, Weigang Zhang
    Abstract:

    In this study, the corrosion behaviour of 75Ni/25graphite abradable coating and Ni-Al bonding coatings with different Al Content were investigated with open circuit potentiAl and polarization tests. The gAlvanic corrosion of the coupled Ni/graphite and Ni-Al coatings was studied by using a zero-resistance ammeter in 5 wt% NaCl solution. The experimentAl results showed that the corrosion resistance of the Ni-Al coatings decreased with increasing Al Contents. In the gAlvanic corrosion test, the Ni-Al coatings with high Al Contents (80Ni-20Al, 85Ni-15Al, and 90Ni-10Al) were the anodic element of the couples, while, the 95Ni-5Al acted as the cathode element in the couple. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.

Ji Xia - One of the best experts on this subject based on the ideXlab platform.

  • effect of Al Content on abnormAl grain growth and superelasticity in fe mn Al cr ni shape memory Alloys with near zero temperature dependence of transformation stress
    Shape Memory and Superelasticity, 2021
    Co-Authors: Ji Xia, Toshihiro Omori, Toru Hoshi, R Kainuma
    Abstract:

    The solvus temperature of face-centered cubic (FCC) phase in Fe–34Mn–xAl–4Cr–7.5Ni (x = 13, 14, and 15) shape memory Alloys with different Al Contents, and their abnormAl grain growth and superelasticity at various temperatures were evAluated. With increasing Al Content, the solvus temperature of the FCC phase decreased and the FCC precipitates became finer. Whereas cyclic heat treatment induced abnormAl grain growth (AGG) in All samples, large grains were obtained more easily in the Alloys with higher Al Content. The criticAl stress for martensitic transformation increased with increasing Al Content. The x = 14 Alloy is the optimAl composition considering grain growth and superelasticity. The newly developed Fe–34Mn–14Al–4Cr–7.5Ni Alloy, in which single-crystAl can easily be fabricated by AGG, exhibited superelasticity at temperatures ranging from − 263 °C (10 K) to 27 °C (300 K), with a very smAll temperature-dependence of the criticAl stress, comparable to that of conventionAl Fe–34Mn–13.5Al–3Cr–7.5Ni Alloy.

  • abnormAl grain growth in fe mn Al ni shape memory Alloy with higher Al Content
    Scripta Materialia, 2020
    Co-Authors: Ji Xia, Toshihiro Omori, R Kainuma
    Abstract:

    Abstract The effect of Al Content on the abnormAl grain growth of Fe–Mn–Al–Ni shape memory Alloy is investigated in comparison with the previously reported Fe–Mn–Al–Ni–Ti Alloy. MicrostructurAl observations reveAled that compared with 1.5Ti, 17Al (adding 2 at.% Al to the conventionAl Fe–Mn–Al–Ni) showed the potentiAl to grow into a large single crystAl. The obtained results indicate that the size control of the second phase, which can be achieved not only by introducing Ti, but rather universAlly by stabilizing BCC phase, and the resultant subgrain structure are vitAl for abnormAl grain growth.