| 1. |
- Alvarado Ávila, María Isabel, et al.
(author)
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Cellulose as sacrificial agents for enhanced photoactivated hydrogen production
- 2023
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In: Sustainable Energy & Fuels. - : Royal Society of Chemistry (RSC). - 2398-4902. ; 7:8, s. 1981-1991
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Journal article (peer-reviewed)abstract
- The search for new energy sources together with the need to control greenhouse gas emissions has led to continued interest in low-emitting renewable energy technologies. In this context, water splitting for hydrogen production is a reasonable alternative to replace fossil fuels due to its high energy density producing only water during combustion. Cellulose is abundant in nature and as residuals from human activity, and therefore a natural, ecological, and carbon-neutral source for hydrogen production. In the present work, we propose a sustainable method for hydrogen production using sunlight and cellulose as sacrificial agents during the photocatalytic water splitting process. Platinum (Pt) catalyst activates hydrogen production, and parameters such as pH of the system, cellulose concentration, and Pt loading were studied. Using different biomasses, we found that the presence of hemicellulose and xyloglucan as part of the molecular composition considerably increased the H-2 production rate from 36 mu mol L-1 in one hour for rapeseed cellulose to 167.44 mu mol L-1 for acid-treated cellulose isolated from Ulva fenestrata algae. Carboxymethylation and TEMPO-oxidation of cellulosic biomass both led to more stable suspensions with higher rates of H-2 production close to 225 mu mol L-1, which was associated with their water solubility properties. The results suggest that cellulosic biomass can be an attractive alternative as a sacrificial agent for the photocatalytic splitting of water for H-2 production.
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| 2. |
- Alvarado Ávila, María Isabel, et al.
(author)
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Cerium Oxide on a Fluorinated Carbon-Based Electrode as a Promising Catalyst for Hypochlorite Production
- 2022
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In: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 7:42, s. 37465-37475
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Journal article (peer-reviewed)abstract
- Sodium hypochlorite (NaOCl) is widely used as a disinfectant agent for water treatment and surface cleaning. A straightforward way to produce NaOCl is by the electrolysis of an aqueous sodium chloride (NaCl) solution. This process presents several side reactions decreasing its efficiency with hypochlorite reduction on the cathode surface being one of the main detrimental reactions. In this work, we have studied carbon-based electrodes modified with cerium oxide (CeO2), fluorine, and platinum nanoparticles as cathodes for hypochlorite production. Fluorination was carried out electrochemically; the polyol method was used to synthesize platinum nanoparticles; and the hydrothermal process was applied to form a CeO2 layer. Scanning electron microscopy, FTIR, and inductively coupled plasma (ICP) indicated the presence of cerium oxide as a film, fluorine groups on the substrate, and a load of 3.2 mg/cm2 of platinum nanoparticles and 2.7 mg/cm2 of CeO2. From electrochemical impedance spectroscopy, it was possible to demonstrate that incorporating platinum and fluorine decreases the charge transfer resistance by 16% and 28%, respectively. Linear sweep voltammetry showed a significant decrease in hypochlorite reduction when the substrate was doped with fluorine from -16.6 mA/cm2 at -0.6 V to -9.64 mA/cm2 that further reduced to -8.78 mA/cm2 with cerium oxide covered fluorinated electrodes. The performance of the cathode materials during hypochlorite production improved by 80% compared with pristine activated carbon cloth (ACC) electrodes. The improvement toward hindering NaOCl reduction is probably caused by the incorporation of a partial negative charge upon doping with fluorine.
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| 3. |
- Alvarado Ávila, María Isabel, et al.
(author)
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Improved chlorate production with platinum nanoparticles deposited on fluorinated activated carbon cloth electrodes
- 2020
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In: Cleaner Engineering and Technology. - : Elsevier BV. - 2666-7908. ; 1
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Journal article (peer-reviewed)abstract
- Sodium chlorate is one of the main oxidizing agents used in the wood industry due to their capability of use as an elemental chlorine-free (CEF) bleaching. A simple way to produce chlorates is by the electrolysis of an aqueous sodium chloride (NaCl) solution. In the present study activated carbon cloth electrodes (ACC) modified with fluorine and platinum nanoparticles (Pt–F/ACC and Pt/ACC) were used as one of the electrodes. Electrofluorination was used for fluorination of the anodes and polyol method was used for the synthesis of platinum nanoparticles. Chlorate production using a typical solution of 100 g/l of sodium chloride (NaCl) and 2 g/l sodium chromate (Na2Cr2O7) and an applied current of 0.540 A was studied. Prior to the electrolysis assays, the microstructural properties of the electrodes were characterized by scanning electron microscopy and surface modifications and bonding using infra-red (FTIR) spectroscopy. Electrochemical properties were determined using cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. Interaction between fluorine (F) and platinum (Pt) on the electrode leads to an improvement of the electrocatalytic properties for chlorine evolution as observed from the increase in the current efficiency from 37.5% at 78.5% after 150 min of continuous electrolysis using Pt–F/ACC anodes. The results suggest that modified activated carbon material is an attractive and economical alternative as electrodes for chlorate production.
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| 4. |
- Onate, Angelo, et al.
(author)
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Characterization of Nb-Si-doped low-carbon steel treated by quenching and partitioning : Thermic treatment in two stages supported by computational thermodynamical simulation and controlled sample dimensions
- 2023
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In: Materials Today Communications. - : Elsevier BV. - 2352-4928. ; 34
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Journal article (peer-reviewed)abstract
- Quench and partition steels find wide use in the automotive industry because of their high capability of energy absorption. Industrial demands have prompted the expansion of this research field because of the influence these materials have on components that can absorb high energy of impact to reduce passenger damage, for example. The partition process's difficulties lie mainly in controlling the thermodynamics and the kinetics of the phase transformation. Both affect achieving adequate austenite retention and optimal mechanical properties. Many researchers have attempted to increase these materials' energy absorption efficiency by incorporating micro -alloying elements that control phase transformation during the partitioning process, typically done in three steps. However, no research has been carried out on this topic using Nb and Si microalloying on low-carbon steels in two stages. Therefore, an alloy was designed and modelled with mechanical reinforcement by precipitation and transformation-induced plasticity (TRIP), doping the steel with Nb and Si in a two-stage quenching and parti-tioning process. Then, steel samples were fabricated to validate the model. There were two groups of samples with different dimensions to evaluate the sensitivity of austenite retention concerning the sample thickness. The main results showed that 10.75% of retained austenite allows an energy absorption of 30.55 GPa% with a two -stage quenching and partitioning heat treatment. Sample thickness influences austenite retention due to diffusion kinetics during the partitioning process. Finally, virtual tests quantified the unit strain energy absorption of the retained austenite at 1.9 mJ at 25 degrees C.
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| 5. |
- Oñate, A., et al.
(author)
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Production of Nb-doped super duplex stainless steel based on recycled material : A study of the microstructural characterization, corrosion, and mechanical behavior
- 2023
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In: Materials Chemistry and Physics. - : Elsevier BV. - 0254-0584 .- 1879-3312. ; 308
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Journal article (peer-reviewed)abstract
- The corrosion behavior of a new Nb-doped stainless steel (SDSS-Nb) designed by the CALPHAD method, produced using an open atmosphere process based on recycled materials, was investigated to improve the circular economy. Three heat-treatment conditions were evaluated to assess the sensitization effects of the precipitates and inclusions. XRD and SEM-EDS were used for phase identification, and sensitization was analyzed by cyclic polarization and Scanning Kelvin Probe Force Microscopy (SKPFM). The thermodynamic stability predicted by Thermo-Calc agrees with that observed by SEM-EDS. It was observed by cyclic polarization that the corrosion sensitization was mainly provided by the σ phase, which was deduced from the results obtained by SEM-EDS, XRD, and Thermo-Calc simulations. Furthermore, it was obtained that the sensitization due to Cr2N precipitates and nonmetallic inclusions was low, and the mechanical response is comparable to commercial UNS32750 super duplex stainless steel, which allows a good performance in severe environments and an efficient industrial application. Additionally, it has been obtained by SKPFM that the shear potential between the σ phase and the austenite is between 210 mV and 241 mV and that its value depends on the stability and equilibrium reached by the σ phase during thermal cycling.
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| 6. |
- Sanhueza, J. P., et al.
(author)
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Computational modeling of the effect of B and W in the phase transformation of M23C6 carbides in 9 to 12 pct Cr martensitic/ferritic steels
- 2019
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In: Materials Research Express. - : IOP PUBLISHING LTD. - 2053-1591. ; 6:11
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Journal article (peer-reviewed)abstract
- The effect of B and W in the precipitation kinetic of M23C6 carbides in martensitic/ferritic steels were studied assisted by ThermoCalc and TC-PRISMA. The simulation predicts that B has low solubility in the austenitic and ferritic matrix, thus promoting the formation of M2B borides and (Cr, Fe)(23)(C, B)(6) carbides. Furthermore, calculation carried out in ThermoCalc shown that M2B borides are stable even at austenization temperature (1100 degrees C). This suggests that in martensitic/ferritic steels M2B precipitates first, hence consuming most of available B. Additionally, the precipitation kinetics of (Cr, Fe)(23)C-6, (Cr, Fe, W)(23)C-6 and (Cr, Fe)(23)(C, B)(6) were simulated in TC-PRISMA, results obtained predict a higher steady nucleation rate for the latter. When B atoms incorporate to (Cr, Fe)(23)C-6 reduces the interfacial energy from 0.26 J/m(2) to 0.17 J m(-2), which indicates a smaller misfit between (Cr, Fe)(23)(C, B)(6) carbides and matrix. On the other hand, B and W reduce the coarsening rate of M23C6 carbides by decreasing the interfacial energy and reducing diffusivities, respectively. Theoretical results compared with experimental data of the coarsening rate of (Cr, Fe, W)(23)(C, B)(6) shown that it is one order of magnitude lower than the predicted by TC-PRISMA. This suggests that B can be the rate-controlling element of the coarsening of (Cr, Fe, W)(23)(C, B)(6) carbides instead of W.
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