•Nb2O5/SiO2 were formed in the initial oxidation of FeCrAl-Nb/Si thin films.•Niobium and Silicon promoted the formation of Cr-rich and Al-rich oxides.•Niobium and Silicon enhanced anti-oxidation ...properties of FeCrAl thin films.
FeCrAl thin films are considered optimal candidates for protecting surfaces in harsh environments, with potential for improvement in their anti-oxidation properties by incorporating beneficial dopants such as Nb and Si. However, the thermodynamic mechanism responsible for this improvement remains unknown. This study investigates the impact of Nb and Si additions on the growth mechanism of oxide formation during the initial stage of 1000°C air exposure. Spectroscopic analyses indicate the inception stage is characterized by the formation of α-Al2O3, accompanied by the generation of Cr-, Nb-, and Si-containing oxides. Thermodynamic calculations reveal that the additions of both Nb and Si can stabilize the phase structure of the thin films before oxide scale formation occurs, slowing down oxidation rates. Nb is shown to increase Cr activity, while Si enhances Al activity, promoting the formation of Cr-rich and Al-rich oxides respectively. This contributes to improvements in the thin films’ anti-oxidation properties. Overall, this research sheds light on the origin of the improved oxidation resistance of FeCrAl thin films containing Nb and Si.
Incorporation of additional carbides into the widely-used Ti(C, N)-based cermets constitutes an important aspect of materials optimization strategy to impart better service properties for mining and ...machining applications. In this work, Ti(C, N)-WC-Mo2C–TaC-(Ni, Co) cermets with the WC content varying from 5.77 wt% to 19.68 wt% were specifically designed based on thermodynamic calculations, and their mechanical and tribological properties were subsequently examined. The results show that the increase of WC content brought about a higher fraction of the white core phase, which also induced a rise in hardness (by ∼10%) but a decline in toughness (by ∼20%). In addition, decreased wear rates (by ∼80%) at both 25 °C and elevated temperatures (400 and 750 °C) were also noted on the cermets containing the highest WC concentration. The wear behavior was found to be controlled by the surface hardness at 25 °C whereas the extent of oxide tribolayer formation at high temperatures. Micro-Raman spectroscopic and transmission electron microscopic observations suggested that the favorable generation of oxide tribolayers consisting of TiO2 and WO3 nano-crystals contributed to the improved high-temperature tribological properties.
Heat flow was calculated from XRD data and compared with measured heat flow from calorimetric experiments. It was shown that the heat released during the hydration of a commercial Ordinary Portland ...Cement can be assigned mainly to three mechanisms, the silicate reaction (sum of dissolution of alite and precipitation of C-S-H-phase and portlandite), the dissolution of C
3A, and the precipitation of ettringite. The contributions made by anhydrite dissolution and gypsum dissolution to the heat released during hydration turned out to be quite small. It is possible to explain, on the basis of the data produced, the origin of the heat flow curve of the cement used.
This paper reports a study of ternary blends composed of calcium aluminate cement, calcium sulfate hemihydrate and limestone. Compressive strength tests and hydration kinetics were studied as a ...function of limestone and calcium sulfate content. The phase evolution and the total porosity were followed and compared to thermodynamic simulation to understand the reactions involved and the effect of limestone on these binders. The reaction of limestone leads to the formation of hemicarboaluminate and monocarboaluminate. Increasing the ratio between sulfate and aluminate decreases the extent of limestone reaction.
One of the main challenge in belite, ye'elimite and ferrite cement is the control of the belite phase reactivity. We propose to study two mechanisms that impact belite hydration kinetic: the first ...mechanism is linked to available space for hydration products and can be seen as a decrease of water accessibility to cement surface and the second concerns the cement fineness. We used a thermodynamic model that can predict phase assemblage and we found good correlations between this model and the results obtained with XRD measurement and Rietveld refinement.
LiMn2O4/λ-MnO2 redox couple, possessing the advantage of high selectivity and intercalation capacity, is the most promising candidate for efficient electrochemically switched ion exchange (ESIX) from ...salt-lake brines. Currently Eh-pH diagrams are the main means for studying the dissolution mechanism of LiMn2O4/λ-MnO2 redox couple, however, the dissolution behavior obtained from experiments deviates significantly from the thermodynamic calculations. By introducing ionic strength correction into the thermodynamic calculation matrix of high salinity system, precise species distributions of Mn3+/Mn2+ are successfully predicted, which are in good accordance with the experimental results. Based on the novel thermodynamic calculations, the strong dependence between pH and the dominant species of Mn3+/Mn2+ is clarified, which in return determines the manganese dissolution (MD) behavior and intercalation capacity of the redox couple. The MD behavior differentiation between LiMn2O4 and λ-MnO2 electrodes is induced by the electrode potential and pH. At pH > 5, high capacity (>30 mg/g) and low MD ratio (<0.1 %) can be achieved. This research sheds light on the existence status of Mn3+ on the MD behavior and suggests the reasonable application range of ESIX with LiMn2O4/λ-MnO2 redox couple.
•Novel thermodynamic calculations for high salinity system were proposed and verified.•A new manganese dissolution mechanism was revealed with thermodynamic calculations.•Eh-pH diagram for Mn-H2O in high salinity system was corrected.•One electron transfer during the electroredox was clarified for the first time.
Austenitic Fe-13.50Mn-3.98Si-9.54Cr-4.51Ni shape memory alloyed with (0.18, 0.42 and 0.96 wt%) Ce was exposed in air at 800 °C. Both 0.18 and 0.42 wt% Cerium additions yielded protective kinetics, ...while the 0.96 wt% Ce content did not change the oxidation resistance. Increased oxidation resistance was related to the growth of a fine-grained oxide layer, slightly wrinkled with a higher Cr content. Cerium also acted as a S scavenger, suppressing its interfacial segregation. In the Ce-free alloy, fast oxide growth occurred in regions where S segregated at the interface, leading to severe wrinkling of the layer, resulting in lower oxidation resistance.
•Mn oxysulfide inclusions within FeMnSiCrNi contributed to poor oxidation resistance.•Interfacial S segregation accelerated the scale growth, causing wrinkling of the oxide.•Cerium acted as a S scavenger, suppressing its interfacial segregation.•Small Cerium levels yielded protective oxidation kinetics.•High cerium content did not positively affect the oxidation resistance.
This work focuses on the challenging task of joining high-strength steels and titanium alloys, which are extensively utilized in the defense and aerospace industries. The study presented the ...fabrication of bimetals comprising high-strength steel (HSS)and Ti6Al4V (TC4) using laser-directed energy deposition (LDED) technology. The research elucidated the interface bonding mechanism of LDEDed HSS/TC4 bimetals and analyzed various bonding strategies for achieving superior properties of steel/titanium joints based on thermodynamic calculations. Due to the limited compatibility between Fe and Ti, a large amount of Fe-Ti intermetallics, especially Fe2Ti, were formed at the interface of LDEDed HSS/TC4 bimetals. The presence of Fe2Ti intermetallics caused a significant enhancement in interfacial hardness, ultimately leading to the fracture of tensile specimens during the wire cutting. Thermodynamic calculations indicated that utilizing a composition gradient processing strategy does not yield a high-quality metallurgical bonding interface between HSS and TC4. Interlayer engineering is an effective building strategy to obtain high-performance LDEDed HSS/TC4 bimetals. Moreover, these compatible interlayers should ensure a reasonable match of thermophysical properties and have a certain thickness. The findings provide valuable insights into bonding and failure behavior, building strategies, and potential future directions for joining high-strength steels and titanium alloys.
•The HSS/TC4 bimetals with defect-free interfaces were successfully fabricated via LDED.•The interface bonding mechanism and failure behavior of LDEDed HSS/TC4 bimetals were comprehensively elucidated.•Various building strategies for achieving high-performance LDEDed HSS/TC4 bimetals were analyzed.
Thermodynamic modeling was used to predict the stable hydrate phase assemblages in a ternary CSA-OPC-anhydrite system. On the basis of this modeling, five systems with diverging expected hydrate ...phases were chosen for experimental examination via QXRD and TGA. The aim of this study was to examine whether and to which extent the predicted equilibrium states are reached after 28 days of hydration. Qualitatively the predicted hydrate phase assemblages were reached for all five systems after 28 d of hydration. When the reaction degrees of the anhydrous phases are taken into account the experimental data fits remarkably well to the thermodynamic model. Additionally, C2S dissolution was found to be the most rapid in straetlingite forming environments.
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