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Scientific Papers in SCI

2018


A direct in situ observation of water-enhanced proton conductivity of Eu-doped ZrO2: Effect on WGS reaction


Garcia-Moncada, N; Bobadilla, LF; Poyato, R; Lopez-Cartes, C; Romero-Sarria, F; Centeno, MA; Odriozola, JA
Applied Catalysis B-Environmental, 231 (2018) 343-356

ABSTRACT

Eu-doped ZrO2 solid solutions have been synthesized in order to prepare proton conductors as water-enhancer additives for the WGS reaction. Elemental characterization has been carried out revealing homogeneous dopant distribution resulting in fluorite-type solid solutions for Eu2O3 contents up to similar to 9 mol.%. Representative samples of the Eu-doped ZrO2 series have been analysed by Impedance Spectroscopy (IS) in inert, oxygen and wet conditions. The solid solution with 5 mol.% of Eu2O3 has presented the highest conductivity values for all tested conditions indicating an optimal amount of dopant. Moreover, the presence of vapour pressure results in an increment of the conductivity at temperatures lower than 300 degrees C, meanwhile at higher temperatures the conductivity is the same than that in inert conditions. To elucidate these results, in situ DRIFTS studies were carried out. These experiments evidenced the existence of water dissociation at oxygen vacancies (band at 3724 cm(-1)) as well as the presence of physisorbed water at temperatures up to similar to 300 degrees C where the band at 5248 cm(-1) characteristic of these species disappeared. These results points to a layer model where the physisorbed water interacts with surface hydroxyls generated by dissociated water that improves the proton conductivity through Grotthuss' mechanism in the RT-300 degrees C temperature range. These samples were successfully tested in WGS reaction as additive to a typical Pt-based catalyst. The presence of the mixed oxide reveals an increase of the catalyst' activity assisted by the proton conductor, since improves the water activation step.


September, 2018 | DOI: 10.1016/j.apcatb.2018.03.001

ZnO and Pt-ZnO photocatalysts: Characterization and photocatalytic activity assessing by means of three substrates


Jaramillo, N; Navio, J.A.; Hidalgo, M.C.; Macías, M.
Catalysis Today, 313 (2018) 12-19

ABSTRACT

ZnO nanoparticles have been previously synthesized by a facile precipitation procedure by mixing aqueous solutions of Zn(II) acetate and dissolved Na2CO3 at pH ca. 7.0 without the addition of a template. The as-prepared ZnO material was anealed at 400 °C in air for 2 h. The Pt-ZnO catalysts (0.5 or 1.0 Pt wt.%) were obtained by photochemical deposition method on the surface of the prepared ZnO sample, using hexachloroplatinic acid (H2PtCl6). It has been shown that Zn2+ is lost from the photocatalyst to the medium and a replacement of the cationic vacancies of Zn2+ by Pt4+ cations occurs during the platinization process of the ZnO samples, regardless of whether the platinum metal photodeposition process. The as-prepared catalysts were characterized by XRD, BET, FE-SEM, TEM, XPS and diffuse reflectance spectroscopy (DRS). Three different probe molecules were used to evaluate the photocatalytic properties under UV-illumination: Methyl Orange and Rhodamine B were chosen as dye substrates and Phenol as a transparent substrate. High conversion values (ca. 100%) and a total organic carbon (TOC) removal of 90–96%, were obtained over these photocatalysts after 160 min of UV illumination. In general, it was observed that the presence of Pt on ZnO affects the lattice parameters and the crystallite size. Although ZnO can completely degrade RhB, MO and Phenol totally in ca. 60 min, the process is more efficient for Pt–ZnO photocatalysts.


September, 2018 | DOI: 10.1016/j.cattod.2017.12.009

Solar pilot plant scale hydrogen generation by irradiation of Cu/TiO2 composites in presence of sacrificial electron donors


Maldonado, MI; Lopez-Martin, A; Colon, G; Peral, J; Martinez-Costa, JI; Malato, S
Applied Catalysis B-Environmental, 229 (2018) 15-23

ABSTRACT

A Cu/TiO2 photocatalyst has been synthesised by reducing a Cu precursor with NaBH4 onto the surface of a sulphate pretreated TiO2 obtained by a sol-gel procedure. The catalyst, that shows a clearly defined anatase phase with high crystallinity and relatively high surface area, and contains Cu2O and CuO deposits on its surface, has been used to produce hydrogen in a solar driven pilot plant scale photocatalytic reactor. Different electron donor aqueous solutions (methanol, glycerol, and a real municipal wastewater treatment plant influent) have been tested showing similar or even higher energy efficiency than those obtained using more expensive noble metal based photocatalytic systems. The glycerol solutions have provided the best reactive environments for hydrogen generation.


August, 2018 | DOI: 10.1016/j.apcatb.2018.02.005

Effect of milling mechanism on the CO2 capture performance of limestone in the Calcium Looping process


Benitez-Guerrero, M; Valverde, JM; Perejon, A; Sanchez-Jimenez, PE; Perez-Maqueda, LA
Chemical Engineering Journal, 346 (2018) 549-556

ABSTRACT

This work analyzes the relevant influence of milling on the CO2 capture performance of CaO derived from natural limestone. Diverse types of milling mechanisms produce contrasting effects on the microstructure of the CaO formed after calcination of the milled limestone samples, which affects crucially the kinetics of carbonation at conditions for CO2 capture. The capture capacity of CaO derived from limestone samples milled using either shear or impact based mills is impaired compared to as-received limestone. After calcination of the milled samples, the resulting CaO porosity is increased while crystallinity is enhanced, which hinders carbonation. Conversely, if the material is simultaneously subjected to intense impact and shear stresses, CaO porosity is promoted whereas CaO cristanillity is reduced, which enhances carbonation in both the reaction and solid-state diffusion controlled regimes.


August, 2018 | DOI: 10.1016/j.cej.2018.03.146

The effect of vitreous phase on mullite and mullite-based ceramic composites from kaolin wastes as by-products of mining, sericite clays and kaolinite


Sanchez-Soto, PJ; Eliche-Quesada, D; Martinez-Martinez, S; Garzon-Garzon, E; Perez-Villarejo, L; Rincon, JM
Materials Letters, 223 (2018) 154-158

ABSTRACT

Mullite precursors were prepared using kaolin waste, sericite clay containing kaolinite and industrial kaolin with addition of alumina in a wet medium to synthesize mullite (72 wt% Al2O3 and 28 wt% SiO2). Uniaxial pressed bars of the powdered mullite precursors were fired in the range 1400-1600 degrees C with soaking times 30-120 min. The resultant materials were studied by XRD and SEM-EDX. Bulk densities, apparent porosities and flexural strengths in four points were determined in the fired bars at 1500, 1550 and 1600 degrees C. It was concluded that the thermal behaviour of these mullite precursors was influenced by the presence of impurities in the raw materials. These impurities originate a liquid phase forming a glassy phase which produces a progressive and enhanced densification of the mullite materials by reaction sintering at 1500-1600 degrees C. The technical properties were also influenced by the relative proportion of vitreous phase. The microstructure of characteristic mullite crystals was revealed by SEM. It was emphasized the use of kaolin waste by-products of mining and sericite clays as valuable raw materials for mullite preparation.


July, 2018 | DOI: 10.1016/j.matlet.2018.04.037

Comparison of solvent extraction and extraction chromatography resin techniques for uranium isotopic characterization in high-level radioactive waste and barrier materials


Hurtado-Bermudez, S; Villa-Alfageme, M; Mas, JL; Alba, MD
Applied Radiation and Isotopes, 137 (2018) 177-183

ABSTRACT

The development of Deep Geological Repositories (DGP) to the storage of high-level radioactive waste (HLRW) is mainly focused in systems of multiple barriers based on the use of clays, and particularly bentonites, as natural and engineered barriers in nuclear waste isolation due to their remarkable properties. 
Due to the fact that uranium is the major component of HLRW, it is required to go in depth in the analysis of the chemistry of the reaction of this element within bentonites. The determination of uranium under the conditions of HLRW, including the analysis of silicate matrices before and after the uranium-bentonite reaction, was investigated. The performances of a state-of-the-art and widespread radiochemical method based on chromatographic UTEVA resins, and a well-known and traditional method based on solvent extraction with tri-n-butyl phosphate (TBP), for the analysis of uranium and thorium isotopes in solid matrices with high concentrations of uranium were analysed in detail. 
In the development of this comparison, both radiochemical approaches have an overall excellent performance in order to analyse uranium concentration in HLRW samples. However, due to the high uranium concentration in the samples, the chromatographic resin is not able to avoid completely the uranium contamination in the thorium fraction.


July, 2018 | DOI: 10.1016/j.apradiso.2018.04.008

Room temperature synthesis of water-dispersible Ln(3+):CeF3 (Ln = Nd, Tb) nanoparticles with different morphology as bimodal probes for fluorescence and CT imaging


Gonzalez-Mancebo, D; Becerro, AI; Rojas, TC; Olivencia, A; Corral, A; Balcerzyk, M; Cantelar, E; Cusso, F; Ocana, M
Journal of Colloid and Interface Science, 520 (2018) 134-144

ABSTRACT

The singular properties of lanthanide-based inorganic nanoparticles (NPs) has raised the attention of the scientific community in biotechnological applications. In particular, those systems with two or more functionalities are especially interesting. In this work, an effective and commercially attractive procedure has been developed that renders uniform, water-dispersible Ln(3+):CeF3 (Ln = Tb, Nd) NPs with different shapes and size. The method consists of the homogeneous precipitation, in a mixture of polyol and water, of cations and anions using precursors that allow the controlled release of the latter. The advantages of the reported method are related to the absence of surfactants, dispersing agents or corrosive precursors as well as to the room temperature of the process. The obtained Tb:CeF3 NPs produce an intense emission after excitation through the Ce-Tb energy transfer band located in the UV spectral region, thus being potentially useful as phosphors for in-vitro imaging purposes. On the other hand, the synthesized Nd:CeF3 NPs are good candidates for in-vivo imaging because their excitation and emission wavelengths lie in the biological windows. Finally, the excellent X-ray attenuation efficacy of the Nd:CeF(3)NPs is shown, which confers double functionality to this material as both luminescence bioprobe and contrast agent for X-ray computed-tomography. 


June, 2018 | DOI: 10.1016/j.jcis.2018.03.007

Effects of milling time, sintering temperature, Al content on the chemical nature, microhardness and microstructure of mechanochemically synthesized FeCoNiCrMn high entropy alloy


Alcala, MD; Real, C; Fombella, I; Trigo, I; Cordoba, JM
Journal of Alloys and Compounds, 749 (2018) 834-843

ABSTRACT

FeCoNiCrMn(Al)-based powdered high entropy alloys were synthesized by a short time mechanical alloying process in a high energy planetary ball milling from mixtures of elemental powders, and subsequently sintered by a pressureless procedure. The composition and microstructure of the HEA phases before and after the sintering process were studied by X-ray diffraction, energy dispersive X-ray analysis (EDX) and scanning electron microscopy. The microhardness and tensile strength values for Fe1,8Co1,8Ni1,8Cr1,8Mn1,8Al1,0 HEA sintered at 1400 degrees C sample were 3,7 GPa and 1011 MPa, respectively. Statistical Fisher-Pearson coefficient of skewness and kurtosis were played to determine the optimum synthesis milling time. The use of NaCl as additive led on to a reduction of the as-milled grain size. After sintering, SEM study confirmed a segregation of the initial HEA phase directly related to the melting temperature of the elements. Three melting temperature groups were described (Cr, FeCoNi and Mn) and they agree with the observation in the elemental mapping study. The presence of Al favored the segregation of Cr. 


June, 2018 | DOI: 10.1016/j.jallcom.2018.03.358

Heteroatom framework distribution and layer charge of sodium Taeniolite


Perdigon, AC; Pesquera, C; Cota, A; Osuna, FJ; Pavon, E; Alba, MD
Applied Clay Science, 158 (

ABSTRACT

The most advanced applications of clays depend crucially on their hydration state and swelling is probably the most important feature of expandable 2:1 layered silicate. Sodium Taeniolite, Na-TAE, a swelling trioctahedral fluormica, has been synthesized and studied using thermogravimetric analysis, X-ray diffraction, scanning electron microscopy and infrared and solid state NMR spectroscopies. The results indicated the formation of a swelling 2:1 phyllosilicate with actual layer charge lower than the nominal one. Herein, a new heteroatom distribution and more accurate composition could be deduced.


June, 2018 | DOI: 10.1016/j.clay.2018.03.036

Chemical CO2 recycling via dry and bi reforming of methane using Ni-Sn/Al2O3 and Ni-Sn/CeO2-Al2O3 catalysts


Stroud, T; Smith, TJ; Le Sache, E; Santos, JL; Centeno, MA; Arellano-Garcia, H; Odriozola, JA; Reina, TR
Applied Catalysis B-Environmental, 224 (2018) 125-135

ABSTRACT

Carbon formation and sintering remain the main culprits regarding catalyst deactivation in the dry and bi-reforming of methane reactions (DRM and BRM, respectively). Nickel based catalysts (10 wt.%) supported on alumina (Al2O3) have shown no exception in this study, but can be improved by the addition of tin and ceria. The effect of two different Sn loadings on this base have been examined for the DRM reaction over 20 h, before selecting the most appropriate Sn/Ni ratio and promoting the alumina base with 20 wt.% of CeO2. This catalyst then underwent activity measurements over a range of temperatures and space velocities, before undergoing experimentation in BRM. It not only showed good levels of conversions for DRM, but exhibited stable conversions towards BRM, reaching an equilibrium H-2/CO product ratio in the process. In fact, this work reveals how multicomponent Ni catalysts can be effectively utilised to produce flexible syngas streams from CO2/CH4 mixtures as an efficient route for CO2 utilisation.


May, 2018 | DOI: 10.1016/j.apcatb.2017.10.047

Carbonation of Limestone Derived CaO for Thermochemical Energy Storage: From Kinetics to Process Integration in Concentrating Solar Plants


Ortiz, C; Valverde, JM; Chacartegui, R; Perez-Maqueda, LA
ACS Sustainable Chemistry & Engineering,

ABSTRACT

Thermochemical energy storage (TCES) is considered as a promising technology to accomplish high energy storage efficiency in concentrating solar power (CSP) plants. Among the various possibilities, the calcium-looping (CaL) process, based on the reversible calcination–carbonation of CaCO3 stands as a main candidate due to the high energy density achievable and the extremely low price, nontoxicity, and wide availability of natural CaO precursors such as limestone. The CaL process is already widely studied for CO2 capture in fossil fuel power plants or to enhance H2 production from methane reforming. Either one of these applications requires particular reaction conditions to which the sorbent performance (reaction kinetics and multicycle conversion) is extremely sensitive. Therefore, specific models based on the conditions of any particular application are needed. To get a grip on the optimum conditions for the carbonation of limestone derived CaO in the CaL-CSP integration, in the present work is pursued a multidisciplinary approach that combines theoretical modeling on reaction kinetics, lab-scale experimental tests at relevant CaL conditions for TCES, process modeling, and simulations. A new analytic equation to estimate the carbonation reaction rate as a function of CO2 partial pressure and temperature is proposed and validated with experimental data. Using the kinetics analysis, a carbonator model is proposed to assess the average carbonation degree of the solids. After that, the carbonator model is incorporated into an overall process integration scheme to address the optimum operation conditions from thermodynamic and kinetics considerations. Results from process simulations show that the highest efficiencies for the CaL-CSP integration are achieved at carbonator absolute pressures of ∼3.5–4 bar, which leads to an overall plant efficiency (net electric power to net solar thermal power) around 41% when carbonation is carried out at 950 °C under pure CO2


May, 2018 | DOI: 10.1021/acssuschemeng.8b00199

Influence of gold particle size in Au/C catalysts for base-free oxidation of glucose


Megias-Sayago, C; Santos, JL; Ammari, F; Chenouf, M; Ivanova, S; Centeno, MA; Odriozola, JA
Catalysis Today, 306 (2018) 183-190

ABSTRACT

A series of gold colloids were prepared and immobilized on commercial activated carbon. The influence of the colloid preparation and stability were studied and related to the gold particle size in the final catalyst. The catalysts show an important activity in the glucose to gluconic acid oxidation reaction, leading to gluconic acid yield close to 90% in base free mild conditions (0.1 MPa O-2 and 40 degrees C). The size-activity correlation and probable mechanism were also discussed. Finally, the viability of the catalyst was tested by recycling it up to four times. 


May, 2018 | DOI: 10.1016/j.cattod.2017.01.007

Development of a novel TiNbTa material potentially suitable for bone replacement implants


Chicardi, E; Gutierrez-Gonzalez, CF; Sayagues, MJ; Garcia-Garrido, C
Materials & Design, 145 (2018) 88-96

ABSTRACT

A novel (beta + gamma)-TiNbTa alloy has been developed by a combined low energy mechanical alloying (LEMA) and pulsed electric current sintering process (PECS). Microstructurally, this material presents interesting characteristics, such as a submicrometric range of particle size, a body-centered phase (beta-TiNbTa) and, mainly, a novel face-centered cubic Ti-based alloy (gamma-TiNbTa) not previously reported. Related to mechanical performance, the novel (beta + gamma)-TiNbTa shows a lower E (49 +/- 3 GPa) and an outstanding yield strength (sigma(y) 1860 MPa). This combination of original microstructure and properties makes to the (beta + gamma)-TiNbTa a novel material potentially suitable as biomaterial to fabricate bone replacement implants, avoiding the undesirable and detrimental stressshielding problem and even the usual damage on the mechanical strength of Ti-based foams biomaterials. 


May, 2018 | DOI: 10.1016/j.matdes.2018.02.042

Multicomponent Au/Cu-ZnO-Al2O3 catalysts: Robust materials for clean hydrogen production


Santos, JL; Reina, TR; Ivanov, I; Penkova, A; Ivanova, S; Tabakova, T; Centeno, MA; Idakiev, V; Odriozola, JA
Applied Catalysis A-General, 558 (2018) 91-98

ABSTRACT

Clean hydrogen production via WGS is a key step in the development of hydrogen fuel processors. Herein, we have designed a new family of highly effective catalysts for low-temperature WGS reaction based on gold modified copper-zinc mixed oxides. Their performance was controlled by catalysts' composition and the Au-Cu synergy. The utilization of hydrotalcite precursors leads to an optimal microstructure that ensures excellent Au and Cu dispersion and favors their strong interaction. From the application perspective these materials succeed to overcome the major drawback of the commercial WGS catalysts: resistance towards start/stop operations, a mandatory requisite for H-2-powered mobile devices.


May, 2018 | DOI: 10.1016/j.apcata.2018.04.002

Multicomponent Ni-CeO2 nanocatalysts for syngas production from CO2/CH4 mixtures


le Sache, E.; Santos, J. L.; Smith, T. J.; Centeno, M. A.; Arellano-Garcia, H.; Odriozola, J. A.; Reina, T. R.
Journal of CO2 utilization, 25 (2018) 68-78

ABSTRACT

The dry reforming of methane with CO2 is a common route to transform CO2/CH4 mixtures into added value syngas. Ni based catalysts are highly active for this goal but suffer from deactivation, as such promoters need to be introduced to counteract this, and improve performance. In this study, mono- and bi-metallic formulations based on 10 wt.% Ni/CeO2-Al2O3 are explored and compared to a reference 10 wt.% Ni/gamma-Al2O3. The effect of Sn and Pt as promoters of Ni/CeO2-Al2O3 was also investigated. The formulation promoted with Sn looked especially promising, showing CO2 conversions stabilising at 65% after highs of 95%. Its increased performance is attributed to the additional dispersion Sn promotion causes. Changes in the reaction conditions (space velocity and temperature) cement this idea, with the Ni-Sn/CeAl material performing superiorly to the mono-metallic material, showing less deactivation. However, in the long run it is noted that the mono- metallic Ni/CeAl performs better. As such the application is key when deciding which catalyst to employ in the dry reforming process.


May, 2018 | DOI: 10.1016/j.jcou.2018.03.012

Engineering of III-Nitride Semiconductors on Low Temperature Co-fired Ceramics


Manuel, JM; Jimenez, JJ; Morales, FM; Lacroix, B; Santos, AJ; Garcia, R; Blanco, E; Dominguez, M; Ramirez, M; Beltran, AM; Alexandrov, D; Tot, J; Dubreuil, R; Videkov, V; Andreev, S; Tzaneva, B; Bartsch, H; Breiling, J; Pezoldt, J; Fischer, M; Muller, J
Scientific Reports, 8 (2018) art. 6879

ABSTRACT

This work presents results in the field of advanced substrate solutions in order to achieve high crystalline quality group-III nitrides based heterostructures for high frequency and power devices or for sensor applications. With that objective, Low Temperature Co-fired Ceramics has been used, as a non-crystalline substrate. Structures like these have never been developed before, and for economic reasons will represent a groundbreaking material in these fields of Electronic. In this sense, the report presents the characterization through various techniques of three series of specimens where GaN was deposited on this ceramic composite, using different buffer layers, and a singular metal-organic chemical vapor deposition related technique for low temperature deposition. Other single crystalline ceramic-based templates were also utilized as substrate materials, for comparison purposes.


May, 2018 | DOI: 10.1038/s41598-018-25416-6

Crystallization Kinetics of Nanocrystalline Materials by Combined X-ray Diffraction and Differential Scanning Calorimetry Experiments


Gil-Gonzalez, E; Perejon, A; Sanchez-Jimenez, PE; Medina-Carrasco, S; Kupcik, J; Subrt, J; Criado, JM; Perez-Maqueda, LA
Crystal Growth & Design, 18 (2018) 3107-3116

ABSTRACT

Crystallization is one key aspect in the resulting properties of nanocrystalline functional materials, and much effort has been devoted to understanding the physical mechanisms involved in these processes as a function of temperature. The main problems associated with crystallization kinetic studies come from the limitations of the employed techniques, and the obtained results may vary significantly depending on the choice of the measurement method. In this work, a complete description of the thermal crystallization event of nanocrystalline BiFeO3 has been performed by combining the information obtained from three different experimental techniques: in situ high-temperature X-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. Interestingly, the kinetic analysis of the X-ray diffraction and differential scanning calorimetry data yields almost identical results, although the physical properties measured by both techniques are different. This allows the unambiguous determination of the kinetic parameters. The importance of a proper definition of the conversion degree, which is limited by the employed measurement technique, is also highlighted.


May, 2018 | DOI: 10.1021/acs.cgd.8b00241

High-temperature compressive creep of novel fine-grained orthorhombic ZrO2 ceramics stabilized with 12 mol% Ta doping


Sponchia, G; Moshtaghioun, BM; Riello, P; Benedetti, A; Gomez-Garcia, D; Dominguez-Rodriguez, A; Ortiz, AL
Journal of the European Ceramic Society, 38 (2018) 2445-2448

ABSTRACT

A novel fine-grained orthorhombic ZrO2 ceramic stabilized with 12 mol% Ta doping was fabricated by spark plasma sintering from home-made powders, and its high-temperature mechanical properties evaluated for the first time by compressive creep tests in both Ar and air. It was found that the high-temperature plasticity of the ceramic deformed in Ar, under which the Ta-doped orthorhombic ZrO2 is a black suboxide with abundant oxygen vacancies in its crystal structure, is controlled by grain boundary sliding (stress exponent similar to 2, and activation energy similar to 780-800 kJ/mol). However, the high-temperature plasticity of the ceramic deformed in air, under which the Ta-doped orthorhombic ZrO2 is a white oxide due to the elimination in situ of oxygen vacancies, is controlled by recovery creep (stress exponent 3, and activation energy similar to 750 kJ/mol). It was also observed that black Ta-doped orthorhombic ZrO2 is more creep resistant than its white counterpart with the same grain size, and that the former deforms as the more conventional Y2O3-stabilized ZrO2 does.


May, 2018 | DOI: 10.1016/j.jeurceramsoc.2017.12.055

Fabrication and characterization of WC-HEA cemented carbide based on the CoCrFeNiMn high entropy alloy


Velo, IL; Gotor, FJ; Alcala, MD; Real, C; Cordoba, JM
Journal of Alloys and Compounds, 746 (2018) 1-8

ABSTRACT

A high entropy alloy (HEA, CoCrFeNiMn) synthesized by mechanical alloying was used as the binder for the densification of WC by a pressureless high temperature procedure. Three different WC were used by modifying its microstructure with a high energy ball milling treatment. The alloy content in the HEA-WC mixture was varied from 10 to 30% vol. The microstructure and properties of the sintered composites were studied by X-ray diffraction, scanning electron microscopy and microindentation.


May, 2018 | DOI: 10.1016/j.jallcom.2018.02.292

Influence of the Mn content on the TiNbxMn alloys with a novel fcc structure


Chicardi, E; Aguilar, C; Sayagues, MJ; Garcia-Garrido, C
Journal of Alloys and Compounds, 746 (2018) 601-610

ABSTRACT

This work studies the structural evolution of TiNbxMn alloys (x: 0-12 wt%) synthetized by mechanical alloying in a planetary ball mill with different milling times between 1 h and 120 h. The specimens were characterized by X-ray diffraction patterns, scanning and transmission electron microscopies and Energy-dispersive X-ray spectroscopy. It was observed an evolution of the alloys developed from the raw Ti, Nb and Mn elements to bcc-TiNbxMn alloys and, finally, novel fcc-TiNbxMn alloys, with Fm3m space group symmetry, not previously observed. The presence of Mn promotes other interesting effects: a) the decreasing of the crystallite and the particle sizes, reaching values close to 4 nm and 400 nm, respectively, b) the partial amorphization of the fcc-TiNbxMn alloys due to the combined effect of the Mechanical Alloying and the difference of Mn atomic size in comparison with Ti and Nb and c) the presence of Mn that decreases the Fe amount (from milling media) in the as-milled powders. 


May, 2018 | DOI: 10.1016/j.jallcom.2018.02.306

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