• Araxá, Brazil
Recent publications
Recrystallization and grain growth during plate rolling are prevented by Nb addition both with the solute drag and the Nb carbide precipitation. Although a fine microstructure is achieved in the base material, welding heat completely changes the microstructure in the heat affected zone (HAZ). In this study, laboratory simulation of the coarse grain HAZ (CGHAZ) thermal cycle of double submerged arc welded linepipe was carried out using low carbon steels containing different Nb contents. Extraction residue analysis of the simulated CGHAZ samples revealed that almost all the Nb remained in solid solution. To clarify the interaction of Nb carbide dissolution and grain growth on overall simulated HAZ microstructure evolution, additional weld HAZ thermal simulations were performed. It was found that Nb carbides remain undissolved at HAZ peak temperatures up to 1200°C and showed significant pinning effect to prevent austenite grain growth. Significant grain growth was seen after continuous fast heating to 1350°C peak temperature, while the higher Nb added steel showed a slower overall austenite grain growth rate, suggesting that grain growth in the HAZ at higher temperature was suppressed by the combined effects of slower coarse Nb carbide dissolution providing some pinning, and the solute drag effect of higher amounts of Nb in solid solution. A pronounced retardation of longer-term isothermal grain growth was identified at 1350°C at higher levels of solute Nb, confirming the influence of Nb solute drag on high temperature resistance to austenite grain coarsening.
Obtaining high levels of mechanical properties in steels is directly linked to the use of special mechanical forming processes and the addition of alloying elements during their manufacture. This work presents a study of a hot-rolled steel strip produced to achieve a yield strength above 600 MPa, using a niobium microalloyed HSLA steel with non-stoichiometric titanium (titanium/nitrogen ratio above 3.42), and rolled on a Steckel mill. A major challenge imposed by rolling on a Steckel mill is that the process is reversible, resulting in long interpass times, which facilitates recrystallization and grain growth kinetics. Rolling parameters whose aim was to obtain the maximum degree of microstructural refinement were determined by considering microstructural evolution simulations performed in MicroSim-SM® software and studying the alloy through physical simulations to obtain critical temperatures and determine the CCT diagram. Four ranges of coiling temperatures (525–550 °C/550–600 °C/600–650 ° C/650–700 °C) were applied to evaluate their impact on microstructure, precipitation hardening, and mechanical properties, with the results showing a very refined microstructure, with the highest yield strength observed at coiling temperatures of 600–650 °C. This scenario is explained by the maximum precipitation of titanium carbide observed at this temperature, leading to a greater contribution of precipitation hardening provided by the presence of a large volume of small-sized precipitates. This paper shows that the combination of optimized industrial parameters based on metallurgical mechanisms and advanced modeling techniques opens up new possibilities for a robust production of high-strength steels using a Steckel mill. The microstructural base for a stable production of high-strength hot-rolled products relies on a consistent grain size refinement provided mainly by the effect of Nb together with appropriate rolling parameters, and the fine precipitation of TiC during cooling provides the additional increase to reach the requested yield strength values.
A new, 19 π-delocalized electrons planar Blatter radical building block was developed and used to obtain paramagnetic bent-core liquid crystals. The mesogens were investigated by optical, thermal, powder XRD and DFT methods in the pure form and as binary mixtures. Comparison of their properties with those of the classical Blatter radical analogues revealed that planarization of the central angular element results in a significantly higher stability of the mesophases and increased molecular organization suitable for the formation of organized banana and columnar mesophases with tighter π-π interactions. These results indicate access to a new, potentially rich class of functional paramagnetic soft materials.
Characterizing the function spaces corresponding to neural networks can provide a way to understand their properties. In this paper we discuss how the theory of reproducing kernel Banach spaces can be used to tackle this challenge. In particular, we prove a representer theorem for a wide class of reproducing kernel Banach spaces that admit a suitable integral representation and include one hidden layer neural networks of possibly infinite width. Further, we show that, for a suitable class of ReLU activation functions, the norm in the corresponding reproducing kernel Banach space can be characterized in terms of the inverse Radon transform of a bounded real measure, with norm given by the total variation norm of the measure. Our analysis simplifies and extends recent results in [45], [36], [37].
Optimization in machine learning typically deals with the minimization of empirical objectives defined by training data. The ultimate goal of learning, however, is to minimize the error on future data (test error), for which the training data provides only partial information. In this view, the optimization problems that are practically feasible are based on inexact quantities that are stochastic in nature. In this paper, we show how probabilistic results, specifically gradient concentration, can be combined with results from inexact optimization to derive sharp test error guarantees. By considering unconstrained objectives, we highlight the implicit regularization properties of optimization for learning.
Base excision repair (BER) removes damaged bases by generating single‐strand breaks (SSBs), gap‐filling by DNA polymerase β (POLβ), and resealing SSBs. A base‐damaging agent, MMS is widely used to study BER. BER increases cellular tolerance to MMS, anti‐cancer base‐damaging drugs, Temozolomide, Carmustine, and Lomustine, and to clinical poly(ADP ribose)polymerase (PARP) poisons, Olaparib and Talazoparib. The poisons stabilize PARP1/SSB complexes, inhibiting access of BER factors to SSBs. PARP1 and XRCC1 collaboratively promote SSB resealing by recruiting POLβ to SSBs, but XRCC1‐/‐ cells are much more sensitive to MMS than PARP1‐/‐ cells. We recently report that the PARP1 loss in XRCC1‐/‐ cells restores their MMS tolerance and conclude that XPCC1 facilitates the release of PARP1 from SSBs by maintaining its autoPARylation. We here show that the PARP1 loss in XRCC1‐/‐ cells also restores their tolerance to the three anti‐cancer base‐damaging drugs, although they and MMS induce different sets of base damage. We reveal the synthetic lethality of the XRCC1‐/‐ mutation, but not POLβ‐/‐, with Olaparib and Talazoparib, indicating that XRCC1 is a unique BER factor in suppressing toxic PARP1/SSB complex and can suppress even when PARP1 catalysis is inhibited. In conclusion, XRCC1 suppresses the PARP1/SSB complex via PARP1 catalysis‐dependent and independent mechanisms.
Among post-translational modifications of proteins, ADP-ribosylation has been studied for over fifty years, assigning to this post-translational modification (PTM) a large set of functions, including DNA repair, transcription and cell signaling. This review presents an update on the function of a large set of enzyme writers, the readers that are recruited by the modified targets, and the erasers that reverse the modification to the original amino acid residue, removing the covalent bonds formed. In particular, the review provides details on the involvement of the enzymes performing monoADP-ribosylation/ polyADP-ribosylation (MAR/PAR) cycling in cancers. Of note, there is potential for application of the inhibitors developed for cancer also in the therapy of non-oncological diseases such as the protection against oxidative stress, suppression of inflammatory responses, and the treatment of neurodegenerative diseases. This field of studies is not concluded, since novel enzymes are being discovered at a rapid pace.
Annually over 500 million tons worldwide of flat and long commodity grade structural steel products are produced for applications in the construction sector. Major costs to produce these commodity grade structural steels lies in alloys, energy and depending on region labor. Production costs for these commodity grades, which typically have low margins for profits, continue to rise worldwide driven by ferro alloy costs. Improved operational efficiencies (productivity, reduced energy consumption, improved melt to finished yields, reduced consumable consumption, etc.) can be realized along with lowered alloy costs with a proper understanding of a new metallurgical strategy to alloy design. These operational efficiencies along with cost savings can be accomplished with proper alloy design in conjunction with the mills processing capabilities to achieve the desired end metallurgy/mechanical properties. Requirements of strength and ductility for any given structural steel microstructure are obtained from three metallurgical mechanisms or "building blocks": a) grain size refinement, b) solid solution and c) precipitation. Overall operation costs including alloy costs can be minimized if better engineering of these contributions can be realized. The correct use of these factors brings improved process/mechanical property stability. Use of practical metallurgical modeling tools along with mill data to determine process control capabilities can also assist in optimization of the metallurgical designs for cost effective structural steel production.
Abrasion resistant steel plates with hardness equal to or greater than 360 BHN and high strength structural steel plates/coils with yield strength requirements equal to or greater than 690 MPa are typically produced by the quench and tempering (Q&T) process. The Q&T microstructures thus produced by either reheating, quench or tempering (RQT) or direct quench and/or tempering (DQ and/or DQT) lead to very high hardness and strength levels as a result of tempered martensite/bainite or auto-tempered and/or lower bainite microstructures. Using these steels in the earth moving, mining equipment and in the general materials processing industry, in addition to strength and toughness other major requirements are weldability (low CE), good elongation and formability. Hence, to achieve optimum balance of properties in these steels, it is very important to understand the microstructural evolution from the interaction of thermo-mechanical control rolling of plate/coil followed by the RQT/DQ/DQT processes. It is shown in the present paper that with careful design of the steel chemistry (C, Mn, Si, Cr, Mo) while utilising optimized microalloying, especially niobium, titanium and boron complemented by proper rolling, cooling, and Q&T process design, uniform cross sectional microstructure and optimum balance of strength, hardness, toughness, ductility and weldability are achieved.
The objective of this work was to observe the significant factors for the dehydration reaction of xylose to furfural and to optimize the processes using experimental design. The studied variables were temperature, time, initial percentage of xylose mass, and catalyst/xylose ratio. Temperature and initial percentage of xylose mass were considered statistically significant, while the maximum point for furfural selectivity was at 160 °C and 2% of initial xylose mass. Using niobic acid and niobium phosphate (1:1) (NbP/NbA), 44.05% xylose conversion and 74.71% furfural selectivity were obtained. The results showed that the mixture of catalysts with Brönsted acid and Lewis acid sites improved the selectivity of furfural from the xylose dehydration reaction. NbP/NbA catalysts were very stable under the investigated condition after 5 continuous recycles.
5-Hydroxymethylfurfural (HMF) production from fructose was studied by using niobium phosphate as solid acid catalyst. HMF selectivity was optimized in a water-acetone system and compared to a water system. The HMF optimal selectivity for process carried out in the water-acetone system was 62.94%. When the process was performed in water, the HMF selectivity achieved 55.73%. These results were used in a large-scale simulation and economic analysis of the two processes. The higher selectivity of system water-acetone affected the HMF minimum selling price (MSP). The MSP value was 2.21 USD/kg for process performed in water-acetone and 3.05 USD/kg for process in water. In the sensitivity analysis, we have found that in addition to process selectivity, the fructose cost was the most significant factor affecting HMF price.
PdxNby/C binary electrocatalysts supported on Vulcan carbon XC72 were prepared by the sol-gel method. The materials are characterized by transmission electron microscopy, X-ray diffraction analysis, inductively coupled plasma–mass spectrometry and contact angle measurements. The electrocatalytic activity for ethanol electrooxidation reaction was studied by cyclic voltammetry, chronoamperometry, Tafel slope and accelerated durability testing. The direct ethanol performance and the products after the experiments were studied by Fourier transform infrared spectroscopy. Pd1Nb1/C (50:50 wt%) shows superior activity for ethanol oxidation compared to the other electrocatalysts prepared in this work. All electrocatalysts containing Nb show the highest current exchange density. The Tafel slope results suggest that the Nb modified the Pd-electrocatalyst to obtain a reaction path with high selectivity with only a single determining step with low production of the intermediates for the ethanol oxidation reaction. The best performance is obtained using Pd1Nb1/C 18.11 mW cm⁻². The Pd1Nb1/C electrocatalyst displays the highest production of CO2 and the lowest production of acetaldehyde. Pd1Nb1/C shows the highest peak current density during 1000 cycles of the experiment and the lowest mass loss of Pd after the cycling test. We find that the Nb modifies the Pd electrocatalysts from the bifunctional mechanism and reduces the loss of Pd during the accelerated durability test.
Resumo Os aços de alta resistência microligados ao nióbio têm mostrado ser uma boa opção para fabricação de perfis estruturais, utilizando os conceitos já desenvolvidos para a indústria de gás e óleo. Entretanto, a definição das reais necessidades em termos de soldagem desta família de aços não está bem descrita nas normas de soldagem mais utilizadas pelo setor. Este trabalho demonstra a construção e avaliação de um Atlas de Soldagem produzido através de simulações físicas (Gleeble e dilatometria) e ensaios mecânicos de amostras simuladas. O objetivo é que o atlas de soldagem seja uma ferramenta orientativa para melhor definição das faixas de parâmetros para soldagem desta classe de material. A metodologia proposta foi aplicada a um aço ARBL bainítico da classe 65 ksi. Foi possível determinar com mais segurança a faixa de energia de soldagem recomendada, inclusive quanto à necessidade ou não do uso de pré-aquecimento, e evidenciar que as simulações são comparáveis a soldas reais. Esta abordagem mostrou trazer benefícios, como redução de custos com processo de pré-aquecimento desnecessário.
29 Synopsis: Since the erection of the first modern cable-stayed bridge in 1956 in Sweden structural engineers have always looked for improved material performance, especially for the steel wire rod. This type of long-span bridge is increasing in popularity across the world and in particular in South East Asia and China. The world's longest cable-stay bridge is the 10 km (main span) JaiShao Bridge, completed in 2013 in China. In general, the steel used for stay-cables and pre-stressed concrete is characterised by its high carbon content which imparts tensile strengths nearing 1,800 MPa, however, this high carbon approach negatively impacts the desired elongation. This paper presents and provides metallurgical analysis on experimental data demonstrating that microalloying using niobium imparts significant microstructural refinement of high carbon steel wire rods; effectively reducing pearlite colony size and inter-lamellar spacing. This refinement not only leads to improvements in strength allowing for example, light-weighting of cables, but moreover and importantly improvements in ductility, %RA, and drawability for cold drawn wire. The overriding conclusion is that through very small additions of niobium to high carbon steel wire rod, notable product and operational cost benefits can be created for steelmakers, rod and wire rope producers generating improved productivity and quality in the cold drawing process and better final performance of the strand in applications such as wire rope for cable-stayed bridges.
Mathematical models have been used extensively in the optimization of hot rolling schedules. They are cost effective tools in reducing mill trials and give guidance in the directions to follow when either schedule parameters or chemical compositions are changed. However, the existing models were usually derived from laboratory parametric equations, obtained with the inherent limitations of attainable processing variables, in particular strain rates. The present paper introduces a model for austenite grain size evolution during thermomechanical processing in which the focus is hot deformation schedule optimization with lean chemistry designs. Very often, nowadays, expensive elements such as Cr, Mo and Ni, among others, have been used to promote adequate microstructure and mechanical properties. By using the model presented in this paper, a hot rolling schedule can be examined from the point of view of the fundamentals of physical metallurgy and, if possible, optimized both in terms of processing parameters and chemical composition. The model has been used to design a lean microalloyed chemistry which was then tested in an industry trial. Results showed that reasonable mechanical properties can be obtained and that the model can be used for the purpose of industry scale alloy designing.
This paper reports the synthesis of a new class of catalysts based on niobium using Filter Cake (FC) as precursor, which is more affordable economically than other niobium sources commonly used. FC is obtained before the necessary purification to obtain niobic acid (Nb2O5.nH2O), making the catalyst synthesis process less costly. Its modification by hydrothermal treatment in the presence of different agents (oxalic acid or hydrogen peroxide) allowed the obtention of nanostructured materials in the form of rods or spheres with larger BET area, crystallinity and acidity than the precursor. Their catalytic potential were evaluated in fructose dehydration reaction in aqueous media, aiming the obtention of 5-hydroxymethylfurfural (5-HMF). The production of furan compounds from sugars has become a process of great interest in recent years because it is related to the search for more sustainable sources of energy, since carbohydrates are the predominant part of biomass. In optimum conditions, it was possible to obtain 22% yield of 5-HMF in aqueous medium and 47% yield of 5-HMF using DMSO as solvent.
Institution pages aggregate content on ResearchGate related to an institution. The members listed on this page have self-identified as being affiliated with this institution. Publications listed on this page were identified by our algorithms as relating to this institution. This page was not created or approved by the institution. If you represent an institution and have questions about these pages or wish to report inaccurate content, you can contact us here.
24 members
Luanna Silveira Parreira
  • Battery Products Executive Management
Fabio D’Aiuto
Córrego da Mata, s/n, 38183-903, Araxá, Brazil
+55 11 3371-9222 / +55 34 3669-3131
+55 (34) 3669-3100