Tirole Research Articles

From Economics of the Welfare to Economics for the “Common Goods”: the contribution of Jean Tirole

From Economics of the Welfare to Economics for the “Common Goods”: the contribution of Jean Tirole

Regulating electronic structure of anionic oxygen by Ti4+ doping to stabilize layered Li-rich oxide cathodes for Li-ion batteries

Abstract Layered Li-rich oxide cathodes enable to activate lattice oxygen anions redox in the charge compensation process and provide superior high specific capacity over 250 mAh g−1 due to their unique configuration, and thus attracting great attentions as promising cathode candidates for Li-ion batteries. However, how to better stabilize the bulk lattice oxygen framework and surface structure, and slow down the release of oxygen, is still major bottleneck to develop high performance Li-rich materials. Transition metal ions with outer d0 electronic configuration have distortable configuration, which can accommodate the local structure and chemical environment of the material, and then improve structural stability. Herein this work, the d0 transition metal Ti4+ is used as doping element to improve the chemical and structural stability, capacity retention and lithium ion diffusion kinetics of Li-rich material. The role of Ti in the material modification is revealed through synchrotron-based soft x-ray absorption spectroscopy, XRD, XPS and electrochemical tests. The improvement in structural stability can be attributed to that Ti doping can adjust the hybridization of O2p and TM3d to regulate the local electronic structure of both bulk lattice oxygen and surface oxygen vacancies. It is hoped that this work should shed light on the development of high-performance cathode materials for Li-ion Batteries.

Stabilizing Ti3C2Tx MXene flakes in air by removing confined water

MXenes have demonstrated potential for various applications owing to their tunable surface chemistry and metallic conductivity. However, high temperatures can accelerate MXene film oxidation in air. Understanding the mechanisms of MXene oxidation at elevated temperatures, which is still limited, is critical in improving their thermal stability for high-temperature applications. Here, we demonstrate that Ti[Formula: see text]C[Formula: see text]T[Formula: see text] MXene monoflakes have exceptional thermal stability at temperatures up to 600[Formula: see text]C in air, while multiflakes readily oxidize in air at 300[Formula: see text]C. Density functional theory calculations indicate that confined water between Ti[Formula: see text]C[Formula: see text]T[Formula: see text] flakes has higher removal energy than surface water and can thus persist to higher temperatures, leading to oxidation. We demonstrate that the amount of confined water correlates with the degree of oxidation in stacked flakes. Confined water can be fully removed by vacuum annealing Ti[Formula: see text]C[Formula: see text]T[Formula: see text] films at 600[Formula: see text]C, resulting in substantial stability improvement in multiflake films (can withstand 600[Formula: see text]C in air). These findings provide fundamental insights into the kinetics of confined water and its role in Ti[Formula: see text]C[Formula: see text]T[Formula: see text] oxidation. This work enables the use of stable monoflake MXenes in high-temperature applications and provides guidelines for proper vacuum annealing of multiflake films to enhance their stability.

The role of Ti in mitigating thermal expansion of silica from molecular dynamics simulations

AbstractMolecular dynamics simulations are performed to investigate the structural response of titania silicate glass to temperature. The coefficient of thermal expansion is computed for two titania silicate glasses with 0 and 10 mol% titania content, the structures of which are presented in terms of radial and angular distributions. Revealed by the different changing rates of intertetrahedra bond angles and bond lengths with respect to the Ti and Si atoms, the glass structures tend to exhibit a nonvectorized expansion process at elevated temperatures, leading to inconsistent expansion rates of the structures in different scales. While the average length of TiO and Si‐O bonds both increases with temperature, the decrease in the coefficient of thermal expansion by the addition of Ti atoms is associated with the different expansion rate of tetrahedra. Arising from the gradual decrease in atomic overlapping, decrease in free volume inside the glass with temperature is also identified.

The role of Ti in the phase transformation and microstructure manipulation of ZrCu alloys with excellent mechanical properties

The effect of Ti content on the phase composition, microstructure manipulation and work-hardening behavior of ZrCu alloys during compression was investigated in this work. The results show that the phase composition, microstructure, mechanical properties and work-hardening ability of ZrCu alloys are very sensitive to Ti content. The introduction of Ti enhances the stability of the austenite phase and the amorphous forming ability of ZrCu alloys. The Zr45Cu50Ti5 alloy exhibited best comprehensive mechanical properties, its yield strength, ultimate compressive strength and fracture strain are 981 MPa, 1922 MPa and 16.9%, respectively. Zr49Cu50Ti1 and Zr47Cu50Ti3 alloys have the best work hardening ability under low strain, and the Zr43Cu50Ti7 alloy has the best work hardening ability under high strain. Finally, the austenite stabilization mechanism, strengthening mechanism and work hardening mechanism are revealed.

Role of Ti and Cr on microstructure and hydrogen embrittlement of welded joint of low-alloy steel used for armor layer

Welded joints suffer from hydrogen embrittlement (HE) owing to the internal stress generated during welding. Alloying elements play a vital role in the metallurgical behavior of welded joints. In this study, the influence of chromium (Cr) and titanium (Ti) on the HE behavior of welded joints in low-alloy steel was investigated by examining the microstructural morphology, grain characteristics, precipitate particles, engineering stress–strain curves, and fracture modes. The experimental results indicated that, compared with the addition of Cr, the addition of Ti promoted the formation of acicular ferrite in the lower fusion zone (FZ) via Ti-bearing oxides, and refined the grains of the FZ. The strength and elongation of the Ti joint were superior to those of the Cr joint in both air- and hydrogen-containing environments. Furthermore, compared with the addition of Cr, the addition of Ti improved the HE sensitivity. The fracture modes of both the Cr and Ti welded joints changed from ductile to brittle when the prepared joints were exposed to an H-containing environment.

Threshold Switching of ALD-NbOx Films for Neuromorphic Applications

Neuromorphic architecture has been suggested as an alternative to the existing von Neumann counterpart. The neuromorphic approach allows massively parallel processing and asynchronous timing schemes with low power consumption. This work presents ALD- NbOx thin films as a potential material for neuromorphic computation. NbO2 shows metal-insulator transition which is the desired property for threshold switching (TS). However, direct forming of NbO2 is rather difficult and deposited NbOx tends predominantly to result in Nb2O5. To obtain NbO2 we used an oxygen scavenger layer of Ti to alter Nb2O5 to NbO2. After a proper electroforming process, the device with a Ti insert showed metal-insulator transition above a specific voltage, i.e., a threshold voltage, and a stable threshold switching characteristics with wide operation range, characteristics not observed in the absence of a Ti insert. The well-defined TS characteristics clearly indicated the Ti role in controlling the oxidation state of NbOx.To verify the oxidation state of NbOx, XPS depth profile analyses were used. The presence of a Ti insertion layer resulted in an increase of 10~30% in Nb4+ states, depending on the total thickness of the NbOx films, while Nb5+ states decreased. Bearing in mind practical applications, we used only CMOS-compatible materials and processes to fabricate TS devices. Our approach suggests a reliable method to fabricate NbO2 neurons.Acknowledgment: This work was supported by Electronics and Telecommunications Research Institute (ETRI) grant funded by the Korean government under grant " Non-CMOS Neuromorphic Device Basic Technology." (22BB1110).

Role of Ti on the microstructure and mechanical properties of MoNbTi medium-entropy alloy

Equiatomic MoNb and MoNbTi alloys are synthesized by arc melting. Ti addition resulted in a significant grain refinement (from 115 μm to 34 μm) of MoNb alloy. Exposure to high temperature for considerably longer duration (24 h at 1673 K) did not alter the beneficial effect of grain refinement imparted by Ti addition. Also, addition of Ti (33 at. %) significantly reduces the overall density without effecting the hardness of MoNbTi alloy, which is one of the key findings of the present study (MoNb - 4.06 ± 0.01 GPa, MoNbTi - 4.10 ± 0.01 GPa). MoNbTi also showed an exceptionally high "density-normalized" hardness when compared to various high-entropy alloys of similar family. Finally, from a simple analysis it is found that extraordinarily high "density-normalized" hardness can be obtained in just two/three element equiatomic systems, suggesting that developing new concentrated alloy systems with more than 3 elements in equiatomic proportion may not be offering any benefits with respect to hardness (strength) in single phase material systems where the beneficial effect of solid solution strengthening is exhausted.

Thermodynamics of ultrarefractory condensates: Implications for the high-temperature limit of the inner dust rim of the early solar protoplanetary disk

Ultrarefractory (UR) condensates found in refractory inclusions in chondrites contain records of the early nebular thermochemistry that prevailed in the high-temperature region close to the protosun. Recent reports of the UR phases such as allendeite (Sc4Zr3O12), tazheranite ((Zr,Ti,Ca)O2−x), and kangite ((Sc,Ti,Al,Zr,Mg,Ca,□)2O3) imply, respectively, nebular condensation temperatures and origins higher than and inward of those previously deduced from calcium-aluminum-rich inclusions. However, knowledge gaps on their thermochemistry have precluded a quantitative understanding of temperatures and chemical pathways that led to their origins in the early solar protoplanetary disk. Here we use density functional theory to determine the thermochemistry of these materials for the first time. We find that allendeite is a stable phase under equilibrium conditions with its condensation temperature (1643 K at 10−4 bar) in the same range as that of nominal hibonite (CaAl12O19, 1637 K at 10−4 bar). Among the UR oxides, tetragonal ZrO2 exhibits the highest condensation temperature (1739 K at 10−4 bar) and potentially reveals the high-temperature limits at which solid dust could have survived in the inner region of the disk. In comparison, we find that pure cubic ZrO2 does not form from a cooling gas of solar composition undergoing equilibrium condensation. Similarly, we find that the stoichiometric endmember of kangite, Sc2O3 does not condense under equilibrium conditions, and moreover, the role of Ti and Zr as solutes is crucial to modeling its stability and origins.

Nano-precipitation behavior and mechanical properties of Ti-containing Fe–12Mn–9Al–3Cr-1.4C medium-Mn lightweight steel

The role of Ti in lightweight steel has been widely concerned due to its influence on the precipitation of nano-particle and its inherent low density. In this work, the nano-precipitation behavior and mechanical properties of Ti-containing Fe–12Mn–9Al–3Cr-1.4C-xTi (wt.%, x = 0.02/0.04) medium-Mn lightweight steels were systematically investigated. It was found that the increase of 0.02 wt% Ti content had little influence on the two-phase structure of ferrite and austenite. TEM characterization revealed that Ti could suppress the precipitation and growth of κ-carbide in austenite while promoting the precipitation of TiC particle. Based on thermodynamics and first-principles calculations, the suppression of κ-carbide precipitation by the Ti element resulted from the increased formation energy of κ-carbide and the decreased diffusion coefficient of C in austenite. The reduction of κ-carbide decreased the precipitation strengthening in lightweight steels. However, the precipitation of TiC particle not only resulted in additional strength, but also refined the austenite grain and introduced a large number of dislocations, improving the grain boundary strengthening and dislocation strengthening. For the aged lightweight steels at 450–550 °C for 3 h, the increase of 0.02 wt% Ti content mainly affected the precipitation strengthening of κ-carbide and dislocation strengthening. Especially, when the ageing temperature exceeded 500 °C, the precipitation strengthening of κ-carbides became the primary factor contributing to the reinforcement of lightweight steels.

Effect of Ti additive and preparation procedure on the temperature and decomposition kinetics of the MgH2 phase in the synthesized mechanicals alloys

The mechanical alloy Mg + 10 wt.% Ti and two mechanical alloys MgH2 + 10 wt.% Ti were synthesized by a reactive mechanical alloying (RMA) method, but in different ways. The influence of doping and the preparation procedure of mechanical alloys (MAs) on thehydrogen sorption properties, temperature and decomposition kinetics of their MgH2 phase was investigated by isobaric thermodesorption spectroscopy at a constant hydrogen pressure of 0.1 MPa. The desorption kinetics of the milled MgH2 + 10 wt.% Ti are faster than in the case of the ball milled Mg + 10 wt.% Ti. It was found that the manner of obtaining a mechanical alloys by reactive milling of MgH2 +10 wt. % Ti powder mixture rather than Mg +10 wt. % Ti powder mixture to improve the kinetic characteristics. The role of Ti as an alloying element in improving the hydrogen desorption kinetics of МAs obtained by various preparation procedures was studied. The stabilizing effect of Ti on the nanocrystalline structure and growth of the crystallites (grains) of the MgH2 phase during the cycling was also evaluated. It has been established the practical absence of the influence of Ti additive and the manner of obtaining MAs on the its thermodynamic stability.

Oxidation behaviors of low carbon MgO‐C refractories: Roles of Ti2AlC and Ti2AlN

AbstractIn this study, Ti2AlC/Ti2AlN powders were first incorporated to fabricate low‐carbon MgO‐C refractories, and their oxidation behaviors were investigated. Computed tomography (CT) results indicated that stress cracks only occurred in the Ti2AlC‐added sample after exposure to 1100°C, and the anomalous oxidation behavior of Ti2AlC powder at 578°C worsened the oxidation result at 1100°C for MgO‐C refractories with Ti2AlC. At 1500°C, the oxidation behaviors of MgO‐Ti2AlC/Ti2AlN‐C samples revealed a slight mass gain due to the disintegration of Ti2AlC/Ti2AlN, and their oxidation resistances increased by 18% as compared to their counterparts. In addition, the role of Ti2AlC/Ti2AlN was elucidated. The oxidation process was comprehensive and was mainly determined by the deterioration of carbon and MAX phases. The obtained results indicated that Ti2AlN was more suitable for fabricating low‐carbon MgO‐C refractories as compared with Ti2AlC.

Role of Ti and W in the Ni-based ohmic contacts to n-type 4H-SiC

The paper investigated the influence mechanism of Ti and W on the electrical and structural properties of the Ni-based ohmic contacts to n-type 4H-SiC. The variation of specific contact resistances (SCRs) with different contact structures was found to be correlated to the relative proportion of the total contact area occupied by the (220) plane than that of the (301) plane at the contact interface for the polycrystalline and textured δ-Ni2Si films characterized by the X-ray diffraction (XRD). Due to the formation of metal carbides, the W layer was found to be beneficial for a higher relative proportion contributing to a reduction of SCR. In contrast, the Ti layer was detrimental owing to the incorporation of metal oxides and carbides. Therefore, W is considered a better candidate to improve the thermal stability of Ni-based ohmic contacts to n-type 4H-SiC while maintaining a low specific contact resistance. Moreover, it was found that the free carbon atoms were immobilized or blocked by the W or Ti layer, and a greater distance of free carbon away from the contact surface led to a smoother and more uniform surface morphology. We believe that this discovery provides a valuable insight into the tuning of surface morphology for the wire bonding challenge.

Improved microstructure and mechanical properties of ODS-CoCrFeNiMn high entropy alloys by different Ti, Zr and Y2O3 addition

Four ODS-CoCrFeNiMn high entropy alloys (HEAs) with different Ti/Zr/Y2O3 addition were produced by powder metallurgy. The role of Ti, Zr, Y2O3 on improving microstructure and mechanical properties of ODS-CoCrFeNiMn HEAs was studied. The type of nanoscale oxides is effectively changed from Y2O3 (1Y alloy), Y2TiO5, YTiO3 and Y2Ti2O7 (1YT), Y4Zr3O12 and Y2Zr2O7 (1YZ) to YTiO3, Y2TiO5, Y2Ti2O7, Ti2O3 (1YTZ) by introducing different addition. The joint addition of Ti, Zr and Y2O3 in 1YTZ has the most significant refinement on grain size and increases number density of nanoscale oxides, which reach 130 nm and 2.01 × 1021/m3, respectively. The well refined grains and high density of nanoscale oxides in 1YTZ alloy lead to the highest hardness and compressive yield strength, which are 449 HV and 1309 MPa, respectively. The different formation mechanisms of nanoscale oxides due to different addition and its influence on mechanical properties in ODS-CoCrFeNiMn HEAs are disclosed. Data availability statementAll data included in this study are available upon request by contact with the corresponding author.

The role of Ti in cavitation erosion and corrosion behaviours of NAB alloy in 3.5 % NaCl solution

The influence of titanium on the cavitation erosion and corrosion behaviors of a NAB alloy in 3.5 % NaCl solution is investigated using tensile test, mass loss, SEM, Tafel plots, electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS). The results show that the NAB alloy consists of the α phase, β phase and κ phase, in which titanium will enter the κ phase to form the titanium-rich κ phase. With the increment of titanium, the titanium-rich κ phase changes from mainly distributed at grain boundaries to more dispersed at grain boundaries and inside grains. In the case of high titanium content, the κ phase rich in titanium grows and produces an obvious segregation phenomenon, resulting in a decrease in the mechanical property and corrosion resistance of the substrate. The mass loss experiment shows that the mass loss caused by cavitation erosion decreases with increasing titanium content, and it increases with increasing titanium content when titanium content is over 0.478 %. The electrochemical experiments show that the corrosion resistance of NAB alloy in 3.5 % NaCl solution increases with increasing titanium content and reaches a maximum when titanium content is 0.478 %. The reason for the increased corrosion resistance of a NAB alloy containing titanium in 3.5 % NaCl solution is related to the appearance of TiO2 in the passive film automatically formed on a NAB alloy in air.

Hierarchical Ti3C2T@MoS2 heterostructures: A first principles calculation and application in corrosion/wear protection

• The interface interactions between Ti 3 C 2 T x and MoS 2 were elaborately investigated using first-principles calculations based on DFT. • The van der waals forces play a crucial role in Ti 3 C 2 T x @MoS 2 heterostructures. • Ti 3 C 2 T x @MoS 2 heterostructure composites with 2D hierarchical structures were prepared via a facile one-step hydrothermal method. • The as-prepared epoxy composite coating showed enhanced anticorrosion and antiwear properties. Surface and interface engineering plays a crucial role in modulating the properties of materials, especially two-dimensional (2D) materials. Hence, a strategy, forming heterostructures with MoS 2 , is proposed to overcome the natural agglomeration of Ti 3 C 2 T x MXene nanosheets. Most importantly, the interactions between Ti 3 C 2 T x and MoS 2 were elaborately investigated by first-principles calculations based on density functional theory (DFT) for the first time. The calculations demonstrate that van der Waals forces dominate the interface interactions of Ti 3 C 2 T x and MoS 2 , rendering Ti 3 C 2 T x @MoS 2 heterostructures favorable stability. The Ti 3 C 2 T x @MoS 2 heterostructure composites were synthesized through a facile one-step hydrothermal method and exhibit a 2D hierarchical structure. Furthermore, the corrosion and tribological properties of epoxy composite coatings with varying proportions of Ti 3 C 2 T x @MoS 2 composites were studied in detail. As a result, the epoxy composite coating with 0.1 wt.% Ti 3 C 2 T x @MoS 2 composites (Ti 3 C 2 T x @MoS 2 -0.1) exhibits excellent corrosion protection and antiwear performances. The Ti 3 C 2 T x @MoS 2 -0.1 keeps the largest low-frequency impedance modulus (| Z | 0. 01 Hz) and coating resistance ( R c ) during the whole immersion period. Its wear rate is 0.09 μm 3 /(N μm) under the load of 10 N, one half of that of pure epoxy coating (EP). This work further broadens the application of MXene-based heterostructure composites.

Inclusion Agglomeration on Ultra-Low C Liquid Steel Surface: Roles of Ti in the Steel and the Oxygen Potential

Inclusion Agglomeration on Ultra-Low C Liquid Steel Surface: Roles of Ti in the Steel and the Oxygen Potential

Different Renal Function Patterns in Patients With Acute Heart Failure: Relationship With Outcome and Congestion.

BackgroundThe role of worsening renal function during acute heart failure (AHF) hospitalization is still debated. Very few studies have extensively evaluated the renal function (RF) trend during hospitalization by repetitive measurements.ObjectivesTo investigate the prognostic relevance of different RF trajectories together with the congestion status in hospitalized patients.MethodsThis is a post hoc analysis of a multi-center study including 467 patients admitted with AHF who were screened for the Diur-AHF Trial. We recognized five main RF trajectories based on serum creatinine and estimated glomerular filtration rate (eGFR) behavior. According to the RF trajectories our sample was divided into 1-stable (S), 2-transient improvement (TI), 3-permanent improvement (PI), 4-transient worsening (TW), and 5-persistent worsening (PW). The primary outcome was the combined endpoint of 180 days including all causes of mortality and re-hospitalization.ResultsWe recruited 467 subjects with a mean congestion score of 3.5±1.08 and a median creatinine value of 1.28 (1.00–1.70) mg/dl, eGFR 50 (37–65) ml/min/m2 and NTpro B-type natriuretic peptide (BNP) 7,000 (4,200–11,700) pg/ml. A univariate analysis of the RF pattern demonstrated that TI and PW patterns were significantly related to poor prognosis [HR: 2.71 (1.81–4.05); p < 0.001; HR: 1.68 (1.15–2.45); p = 0.007, respectively]. Conversely, the TW pattern showed a significantly protective effect on outcome [HR:0.34 (0.19–0.60); p < 0.001]. Persistence of congestion and BNP reduction ≥ 30% were significantly related to clinical outcome at univariate analysis [HR: 2.41 (1.81–3.21); p < 0.001 and HR:0.47 (0.35–0.67); p < 0.001]. A multivariable analysis confirmed the independently prognostic role of TI, PW patterns, persistence of congestion, and reduced BNP decrease at discharge.ConclusionsVarious RF patterns during AHF hospitalization are associated with different risk(s). PW and TI appear to be the two trajectories related to worse outcome. Current findings confirm the importance of RF evaluation during and after hospitalization.

Role of Ti on the Growth of Coarse Columnar Austenite Grain During Nb-Bearing Peritectic Steel Solidification

Role of Ti on the Growth of Coarse Columnar Austenite Grain During Nb-Bearing Peritectic Steel Solidification

Role of Ti in direct active bonding of SiC substrate using Sn–Ag–Ti alloy filler

Role of Ti in direct active bonding of SiC substrate using Sn–Ag–Ti alloy filler