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1.
Lun Feng William G. Fahrenholtz Gregory E. Hilmas Frédéric Monteverde 《Journal of the European Ceramic Society》2021,41(1):92-100
Dense high-entropy (Hf,Zr,Ti,Ta,Nb)B2 ceramics with Nb contents ranging from 0 to 20 at% were produced by a two-step spark plasma sintering process. X-ray diffraction indicated that a single-phase with hexagonal structure was detected in the composition without Nb. In contrast, two phases with the same hexagonal structure, but slightly different lattice parameters were present in compositions containing Nb. The addition of Nb resulted in the presence of a Nb-rich second phase and the amount of the second phase increased as the Nb content increased. The relative densities were all >99.5 %, but decreased from ~100 % to ~99.5 % as the Nb content increased from 0 to 20 at%. The average grain size decreased from 13.9 ± 5.5 μm for the composition without Nb additions to 5.2 ± 2.0 μm for the composition containing 20 at% Nb. The reduction of grain size with increasing Nb content was due to the suppression of grain growth by the Nb-rich second phase. The addition of Nb increased Young’s modulus and Vickers hardness, but decreased shear modulus. While some Nb dissolved into the main phase, a Nb-rich second phase was formed in all Nb-containing compositions. 相似文献
2.
Bataillou Léa Martinelli Laure Desgranges Clara Bosonnet Sophie Ginestar Kevin Miserque Frédéric Wouters Yves Latu-Romain Laurence Pugliara Alessandro Proietti Arnaud Monceau Daniel 《Oxidation of Metals》2020,93(3-4):329-353
Oxidation of Metals - The oxidation of a Ni–30Cr alloy at 700 °C in impure argon was studied in order to provide new elements of understanding on chromia scale growth in low... 相似文献
3.
Paweł Maciąg Paweł Malczyk Janusz Frączek 《International journal for numerical methods in engineering》2020,121(22):5082-5100
The design of multibody systems involves high fidelity and reliable techniques and formulations that should help the analyst to make reasonable decisions. Given that constrained equations of motion for the simplest of multibody systems are highly nonlinear, determining the sensitivity terms is a computationally intensive and complex process that requires the application of special procedures. In this article, two novel Hamiltonian-based approaches are presented for efficient sensitivity analysis of general multibody systems. The developed direct differentiation and the adjoint methods are based on constrained Hamilton's canonical equations of motion. This formulation provides solutions, which are more stable as compared to the results of direct integration of equations of motion expressed in terms of accelerations due to a reduced differential index of the underlying system of differential-algebraic equations and explicit constraint imposition at the velocity level.The proposed Hamiltonian based methods are both capable of calculating the sensitivity derivatives and keeping the growth of constraint violation errors at a reasonable rate. The Hamiltonian-based procedures derived herein appear to be good alternatives to existing methods for sensitivity analysis of general multibody systems. 相似文献
4.
AbstractThe objective of this study was to compare spray-dried and freeze-dried extracts of Sennae fructus regarding the stability of the sennosides. Therefore, the influence of the addition of maltodextrin (MD) not only before the drying processes but also during fluidized bed granulation was investigated. Analysis of the hygroscopicities, the simultaneous TGA-DSC-MS data, and the influence of storage revealed that spray-dried extracts are more stable than freeze-dried extracts. The addition of MD led to an even better stability of the extracts. Lower amounts of MD are sufficient if applied onto the surface of the native extract during fluidized bed granulation. 相似文献
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6.
Céline Mallet Jérôme Fortin Yves Guéguen Fréric Bouyer 《Mechanics of Time-Dependent Materials》2015,19(2):117-133
We investigate pore fluid effects due to surface energy variation or due to chemical corrosion in cracked glass. Both effects have been documented through experimental tests on cracked borosilicate glass samples. Creep tests have been performed to investigate the slow crack propagation behavior. We compared the dry case (saturated with argon gas), the nonreactive water saturated case (commercial mineralized water), and the distilled and deionized water saturated case (pure water). Chemical corrosion effects have been observed and evidenced from pH and water composition evolution of the pure water. Then, the comparison of the dry case, the mineral water saturated case, and the corrosion case allow to (i) evidence the mechanical effect of the presence of a pore fluid and (ii) show also the chemical effect of a glass dissolution. Both effects enhance subcritical crack propagation. 相似文献
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8.
Saint Martin Marie-Judith Orlhac Fanny Akl Pia Khalid Fahad Nioche Christophe Buvat Irène Malhaire Caroline Frouin Frédérique 《Magma (New York, N.Y.)》2021,34(3):355-366
Magnetic Resonance Materials in Physics, Biology and Medicine - Quantitative analysis in MRI is challenging due to variabilities in intensity distributions across patients, acquisitions and... 相似文献
9.
Florian Weyland Thorsten Eisele Sebastian Steiner Till Frömling George A. Rossetti Jürgen Rödel Nikola Novak 《Journal of the European Ceramic Society》2018,38(2):551-556
The stability of the electrocaloric effect under electric field cycling is an important consideration in the development of solid-state cooling devices. Here we report measurements carried out on Ba(Zr0.2Ti0.8)O3 ceramics which reveal that the adiabatic temperature change, polarization-electric field hysteresis loops and dielectric permittivity/loss show stable behavior up to 105 cycles. We further demonstrate that the loss in electrocaloric response observed after 105 cycles is associated with the migration of oxygen vacancies. As a result, the electrical properties of the material are changed leading to an increase in leakage current and Joule heating. Reversing the polarity of the electric field after every 105 cycles changes the migration direction of oxygen vacancies, thereby preventing charge accumulation at grain boundaries and electrodes. By doing so, the electrocaloric stability is improved and the adiabatic temperature remains constant even after 106 cycles, much higher than achieved in commercially available barium titanate ceramics. 相似文献
10.
A general model is proposed in order to describe the growth of a deposit by heterogeneous reactions. The hydrodynamics in the fluid is described by a multicomponent transport model for ionic species diluted in a solvent and heat transfer is taken into account in both liquid and solid domains. The boundary condition at the interface where the reaction takes place is described thoroughly. It involves the reaction kinetics and gives access to the velocity of the interface, ie, the mass rate of the solid deposit. The model is then applied to the case of barite crystallization in a heat exchanger. The liquid phase is therefore composed of two ionic species Ba2+ and SO42− diluted in water. The solid phase is modelled as a homogeneous barite deposit. The fully dynamic CFD simulation of the model is made using Comsol Multiphysics, in a cylindrical pipe. The solid growth is analyzed over time and space in terms of the relevant variables of the model. 相似文献