@article{dosSantos2024d,

title = {Heat treatment of the SAE 9254 spring steel: Influence of cooling rate on the microstructure and microhardness},

author = {Silvano Leal dos Santos and Sydney F. Santos},

url = {https://www.sciencedirect.com/science/article/pii/S2949822824000728},

doi = {10.1016/j.nxmate.2024.100175},

issn = {2949-8228},

year  = {2024},

date = {2024-04-00},

urldate = {2024-04-00},

journal = {Next Materials},

volume = {3},

publisher = {Elsevier BV},

abstract = {Mn-Si spring steels are widely employed for manufacturing automotive components such as helical springs. To develop higher strength spring steels based on the concept of the composition design and heat treatments, the generation ultra-high strength spring steels can reach tensile strength over 2200 MPa increasing the C, Si and Cr concentrations and optimizing heat treatments routes Heat treatments of these steels usually comprise high-temperature austenitization followed by quenching and tempering. A number of heat treatment parameters strongly influence the final microstructures of these steels such as the cooling rate during quenching. In this research, phase transformations in SAE 9254 steel were investigated by quenching dilatometry. The samples were austenitized at 850 °C by 12 minutes followed by quenching with 7 different cooling rates ranging from 0.5 to 40 °C/s. Their microstructures were characterized by microscopy techniques and their mechanical properties assessed by microhardness measurements. The obtained results show that the microstructure was very sensitive to the cooling rate. Low cooling rates promoted the formation microstructures of ferrite and perlite while high cooling rates produced martensitic microstructures. It was demonstrated the intermediate cooling rates can produce multiphase microstructures composed by polygonal ferrite, perlite colonies, martensite islands and retained austenite. The complex microstructures contribute to enhance the mechanical properties of the steels.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{dosSantos2024c,

title = {Investigating the role of the austenitizing temperature and cooling rate on the martensitic transformation kinetics in a SAE 9254 spring steel},

author = {Silvano Leal dos Santos and Felipe Ribeiro Toloczko and Davinson Mariano da Silva and Sydney F. Santos},

url = {https://www.sciencedirect.com/science/article/pii/S2949917824000129},

doi = {10.1016/j.jalmes.2024.100065},

issn = {2949-9178},

year  = {2024},

date = {2024-03-00},

urldate = {2024-03-00},

journal = {Journal of Alloys and Metallurgical Systems},

volume = {5},

publisher = {Elsevier BV},

abstract = {The effect of austenitizing temperature (ranging from 850 to 1050 °C) and cooling rates on the phase transformations were investigated, particularly when a two cooling steps protocol was adopted. It was possible to observe that the heat treatment parameters play a major role on the martensitic transformation kinetics a possible occurrence of bainitic transformation. The results indicate that a microstructure composed by small austenite grains and the formation of bainite prior the athermal martensitic transformation significantly contribute to increase the martensitic transformation rate. The Koistinen-Marburger model was employed to analyze the non-isothermal kinetics, revealing an increase in the KM and k parameters due to an increase in austenite grain size and the presence of bainite in the microstructure. The results herein demonstrate that the optimization of the heat treatment parameters is crucial to the proper control of the phases that will be present in the microstructure of the alloy, as well as the volume fraction of martensite. Thus, the accurate control of the heat treatment process is a promising approach to enhance the properties of SAE 9254 spring steel, which finds extensive use in the automotive industry.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{D3TC03810F,

title = {Interface passivation with Ti3C2Tx-MXene doped PMMA film for highly efficient and stable inverted perovskite solar cells},

author = {João Pedro F. Assunção and Hugo G. Lemos and Jéssica H. H. Rossato and Gabriel L. Nogueira and João V. M. Lima and Silvia L. Fernandes and Rafael K. Nishihora and Ricardo V. Fernandes and Sidney A. Lourenço and Diego Bagnis and Sydney F. Santos and Carlos F. O. Graeff},

url = {http://dx.doi.org/10.1039/D3TC03810F},

doi = {10.1039/D3TC03810F},

year  = {2024},

date = {2024-01-01},

urldate = {2024-01-01},

journal = {J. Mater. Chem. C},

volume = {12},

issue = {2},

pages = {562-574},

publisher = {The Royal Society of Chemistry},

abstract = {Achieving inverted perovskite solar cells (PSCs) that combine high efficiency and long-term stability is still challenging due to intrinsic material issues and low tolerance to environmental factors. The use of an ultra-thin poly(methyl methacrylate) (PMMA) layer to passivate interfacial defects as well as working as a physical barrier to extrinsic factors is promising. However, the low electrical conductivity of PMMA may have deleterious effects on charge extraction. Herein, we explored the use of Ti3C2Tx MXene as a PMMA additive (PMMA:MX) to tune the electrical features of the passivation layers. The optimal concentration of MXenes resulted in improvement of the PSC photovoltaic parameters, boosting their efficiency to 21.30 ± 0.51% (22.1% for the benchmark PSC). Electrical characterizations indicate a reduction of trap state densities accompanied by mitigation of non-radiative recombination. These features contributed to an increase in the extraction of photo-generated carriers and a considerable enhancement of Voc. The improved performance may be attributed to the electrical properties of MXenes and the better wettability of the PMMA:MX interface. Furthermore, the combination of hydrophobic characteristics and passivation features of the PMMA:MX layer resulted in more stable PSCs. The PMMA:MX based devices maintained 95% of their original PCE after 3000 h (ISOS-D-1I) and took 3× longer to reach T80 compared to the control PSC under heat and light soaking (ISOS-L-2).},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Alvarenga2023,

title = {Formic acid oxidation on Pd/RuO2: does the RuO2 support enhance the electrocatalytic activity of Pd nanoparticles?},

author = {Gabriel M. Alvarenga and Julio Palombarini and Rosana A. Gonçalves and Olivia M. Berengue and Ronaldo S. Nunes and Sydney F. Santos and Hebe M. Villullas and Eduardo G. Ciapina},

url = {https://link.springer.com/article/10.1007/s10008-023-05524-8},

doi = {10.1007/s10008-023-05524-8},

issn = {1433-0768},

year  = {2023},

date = {2023-09-00},

urldate = {2023-09-00},

journal = {J Solid State Electrochem},

volume = {27},

number = {9},

pages = {2465--2477},

publisher = {Springer Science and Business Media LLC},

abstract = {The aim of this work was to study the effect of a RuO2 support on the activity of Pd nanoparticles for formic acid oxidation, comparing the results with those obtained for Pd/C. In contrast with reports of enhancing effects of RuO2 for other systems, such as methanol oxidation on Pt particles, our data reveal a detrimental effect of the RuO2 support on the activity of Pd nanoparticles for the oxidation of formic acid. FTIR spectra show CO2 formation at potentials as low as 0.10 V and absence of adsorbed CO signals, suggesting that a bifunctional mechanism involving OH species on the oxide support surface does not occur nor has a significant contribution and that formic acid oxidation on Pd/RuO2 and Pd/C takes place by the direct pathway. The unfavorable effect of the RuO2 support on activity seems likely to be due to metal-support interactions that modify the Pd electronic properties.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Yao2023,

title = {Microstructure and corrosion behavior of the Ti-V-Cr-Nb high-entropy alloys in 3.5 wt% NaCl solution},

author = {Jie-Yi Yao and Leandro Bernardes Serrano and Sydney F. Santos and Kátia Regina Cardoso},

url = {https://www.sciencedirect.com/science/article/pii/S0010938X23001919},

doi = {10.1016/j.corsci.2023.111149},

issn = {0010-938X},

year  = {2023},

date = {2023-07-00},

urldate = {2023-07-00},

journal = {Corrosion Science},

volume = {218},

publisher = {Elsevier BV},

abstract = {Novel high-entropy alloys (HEAs) of the Ti(30–x)VCrNb(x) (x = 0, 5, 10, 15, and 20 at%) system were designed, synthesized, and characterized. The microstructural features were investigated by XRD, SEM, and EDS. The corrosion behavior was evaluated in 3.5 wt% sodium chloride (NaCl) solution of pH 5 at 25 °C by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The investigated HEAs exhibited a single-phase BCC solid solution with dendritic microstructures. The polarization curves showed the Ti10V35Cr35Nb20 (Nb20) HEA exhibited the best corrosion resistance with the lowest corrosion current density (2.24 µA/cm2) and corrosion rate (1.15 × 10–2 mm/yr). The interpretation of an equivalent electric circuit (EEC) suggested the formation of a stable passive oxide film on the HEAs, as indicated by good capacitive behavior and high impedance values (>104 Ω cm2) at low frequencies and phase angles close to − 80°. This study demonstrated that an appropriate Nb content can stabilize the BCC phase and significantly enhance the corrosion resistance of the HEAs.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Serrano2023,

title = {Development of Ti-V-Nb-Cr-Mn high entropy alloys for hydrogen storage},

author = {Leandro Serrano and Maria Moussa and Jie-Yi Yao and Gilbert Silva and Jean-Louis Bobet and Sydney F. Santos and Kátia Regina Cardoso},

url = {https://www.sciencedirect.com/science/article/pii/S0925838823005923},

doi = {10.1016/j.jallcom.2023.169289},

issn = {0925-8388},

year  = {2023},

date = {2023-06-00},

urldate = {2023-06-00},

journal = {Journal of Alloys and Compounds},

volume = {945},

publisher = {Elsevier BV},

abstract = {The development of novel high entropy alloys (HEA) of the TiVNbCrMn system for hydrogen storage is reported. The CALPHAD method was used to design alloys with a body centered cubic structures. Three alloy compositions, Ti35V35Nb20Cr5Mn5; Ti32V32Nb18Cr9Mn9; Ti27.5V27.5Nb20Cr12.5Mn12.5, were fabricated by the arc melting process and characterized by X-ray diffraction (XRD) and SEM techniques. The activation behavior during the 1st hydrogen absorption of these alloys was investigated at room temperature and 2 MPa of H2 pressure. These alloys absorb hydrogen forming FCC hydrides with high capacities of 2.47, 2.09 and 3.38 wt%, respectively. Activation kinetics and incubation times were distinct for each alloy’s composition. Hydrogen absorption/desorption cycles were performed for two alloys showing promising results since the maximum capacity of the alloys has been maintained despite a reduction in absorption kinetics.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ronchi2023c,

title = {Tribology of polymer-based nanocomposites reinforced with 2D materials},

author = {Rodrigo Mantovani Ronchi and Hugo Gajardoni de Lemos and Rafael Kenji Nishihora and Márcio Gustavo Di Vernieri Cuppari and Sydney F. Santos},

url = {https://www.sciencedirect.com/science/article/pii/S2352492823000879},

doi = {10.1016/j.mtcomm.2023.105397},

issn = {2352-4928},

year  = {2023},

date = {2023-03-00},

urldate = {2023-03-00},

journal = {Materials Today Communications},

volume = {34},

publisher = {Elsevier BV},

abstract = {The study of friction and wear of different materials have gained increased attention due to their influence in the component lifetime and on the energy efficiency of the systems. In order to optimize tribological properties in different applications, from gears to medical implants, the use of 2D materials into polymer matrices has attracted interest due to their intrinsic properties, including high mechanical properties, high surface area and even superlubricity features. Graphene and its derivatives, Transitional Metal Dicalcogenides (TMDs), Boron Nitride (BN), and, more recently, MXenes, stand out as the most researched 2D nanomaterials used for polymer nanocomposites. This review aims to describe experimental and computational researches of these 2D polymer nanocomposites regarding tribological properties and applications, evidencing the main mechanisms involved on their enhanced anti-friction performances. Furthermore, an overview and the remaining issues in the area are highlighted, which may serve as a reference for future studies.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Portugal2023c,

title = {Composition-dependent photocatalytic activity and high-mobility carrier gas in NaTaO3/BaBiO3 heterojunctions},

author = {Guilherme Ribeiro Portugal and Rodrigo Mantovani Ronchi and Sydney F. Santos and Jeverson Teodoro Arantes},

url = {https://www.sciencedirect.com/science/article/pii/S2468023022007453},

doi = {10.1016/j.surfin.2022.102486},

issn = {2468-0230},

year  = {2023},

date = {2023-02-00},

urldate = {2023-02-00},

journal = {Surfaces and Interfaces},

volume = {36},

publisher = {Elsevier BV},

abstract = {Perovskite oxide heterostructures have been extensively investigated for their excellent nanoelectronics and photocatalytic properties. Herein, the general features of monoclinic (001) NaTaO3/BaBiO3 heterojunctions are theoretically investigated, exploring how the interface creation affects their physicochemical properties. Density functional theory results reveal that a superlattice with 24 wt.% of BaBiO3 displays a typically desired electronic structure for photocatalytic reactions, with an intermediate band gap and highly dispersive energy levels. Hybrid functional calculations provide a band gap of 1.85 eV, with optical absorption peaks inside the visible light spectrum and band-edge potentials better aligned with water splitting levels when compared with the pristine NaTaO3 phase. Upon increasing the number of BaBiO3 layers a semiconductor-to-metal transition is observed and described based on electrostatic and polarization arguments, leading to the formation of a high-mobility two-dimensional electron gas (2DEG) at the interface. The presented results highlight the importance of such nanojunctions not only for photocatalytic but also for nanoelectronics applications.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ronchi2023b,

title = {Interfacial properties of polyethylene/Ti3C2Tx mxene nanocomposites investigated by first-principles calculations},

author = {Rodrigo M. Ronchi and Sydney F. Santos and Roberto G.A. Veiga},

url = {https://www.sciencedirect.com/science/article/pii/S0169433222028720},

doi = {10.1016/j.apsusc.2022.155344},

issn = {0169-4332},

year  = {2023},

date = {2023-01-00},

urldate = {2023-01-00},

journal = {Applied Surface Science},

volume = {609},

publisher = {Elsevier BV},

abstract = {MXenes have recently emerged as promising candidates for reinforcements in polymer-based nanocomposites, due to their combination of mechanical and electronic properties with the presence of functional groups at the surface. These terminations, may dramatically affect their intrinsic electronic properties, as well as MXene dispersion and interfacial bonding in composites. Therefore, in order to provide a deeper understanding of the functional groups influence in polymer nanocomposites, we addressed the interfacial interaction between polyethylene (PE) and Ti3C2Tx MXene with different functional groups (Tx=O, F or OH) using the Density Functional Theory (DFT) framework. The cohesion at the interface followed the order O > F > OH, as a result of the formation of hydrogen bonds and lower amount of charge transfer. Moreover, this simulation enabled to predict conductive PE-MXene composites that could be used in different applications, such as Electromagnetic Interference Shielding (EMI) or artificial muscles. Finally, the findings in this work point towards the relevance of tailoring MXenes’ surface chemistry in order to tailor MXenes/polymers properties in nanocomposites.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ciapina2021,

title = {On the lattice dilation of palladium nanoparticles and a new methodology for the quantification of interstitials},

author = {Eduardo G. Ciapina and Monica L. dos Santos and Rayana M.I.S. Santos and Julio Palombarini and Osvaldo P. Almeida Júnior and Jéssica C.C. de Castro Santana and Diego A. Modesto and Alexandre J.C. Lanfredi and Sydney F. Santos},

url = {https://www.sciencedirect.com/science/article/pii/S0925838821020375},

doi = {10.1016/j.jallcom.2021.160628},

issn = {0925-8388},

year  = {2021},

date = {2021-11-00},

urldate = {2021-11-00},

journal = {Journal of Alloys and Compounds},

volume = {881},

publisher = {Elsevier BV},

abstract = {In contrast to the expected behavior for metallic nanoparticles (NPs) where a contraction of the lattice parameter occurs as the crystal size decreases, palladium NPs experience both lattice contraction and dilation. Such dual behavior has not been discussed in detail so far but it is of paramount importance given Pd is widely used in catalysis, electrocatalysis, gas sensors, and many other areas, and all these applications are strongly affected by structural change at the NP surface. Herein, we address the issue investigating both lattice contraction and dilation of Pd NPs synthesized by chemical reduction and also by compiling several results already published in the literature. It was found that when the synthesis is carried out in the absence of a substrate, dilation of the unit cell was detected; in contrast, if the synthesis is carried out in the presence of a substrate (carbon and RuO2), lattice contraction is observed. Lattice dilation was ascribed by the incorporation of interstitial atoms, such as H, C, O, which is suppressed on supported catalysts likely by a spillover effect from the metallic phase to the substrate, thus yielding to lattice contraction. Furthermore, we propose a new methodology to assess the total variation of the lattice parameter in the case of lattice dilation taking into consideration the expected contracted values for nanosized particles. To illustrate the importance of such new approach, it was possible to show a particle-size dependence of the carbon solubility on Pd nanostructures based on literature data.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}