Overloading Effect on the Fatigue Strength in Resistance Spot Welding

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Contents lists available at ScienceDirect

International Journal of Fatigue

journal homepage: www.elsevier.com/locate/ijfatigue

Overloading eﬀect on the fatigue strength in resistance spot welding joints of a DP980 steel ⁎ J.H. Ordoñeza, R.R. Ambriza, , C. Garcíab,G.Plascenciaa, D. Jaramilloa a Instituto Politécnico Nacional CIITEC-IPN, Cerrada de Cecati S/N, Col. Sta. Catarina, C.P. 02250 Azcapotzalco, Ciudad de México, Mexico b Facultad de Ingeniería, Universidad Autónoma de San Luis Potosí, Av. Dr. Manuel Nava No. 8, Zona Universitaria, C.P. 78290 San Luis Potosí, S.L.P., Mexico

ARTICLE INFO ABSTRACT

Keywords: Dual phase steel DP980 sheets were joined by resistance spot welding (RSW) process. Mechanical resistance of DP980 steel the welds was characterized by microhardness, tensile shear and fatigue tests. A signiﬁcant hardness decreases Resistance spot welding was observed in the RSW lap joints with respect to the base material, which was attributed to phase transfor- Fatigue behavior mations during the heating and cooling of the steel. Fatigue Wöhler curves using a ﬁxed load ratio of 0.1 were Compressive residual stresses obtained. It was found that the spot weld at the nugget interface close to the fusion zone induced a critical stress concentration factor, which decreased the fatigue life of the joints in the as-welded condition. Failure of the welds was initiated at the interface between welded sheets. Two predominant fatigue fracture modes were observed associated with mode I/III cyclic loading, which were correlated with the fatigue crack initiation and propagation stages. Compressive residual stresses were induced by a loading-unloading cycle on the spot welds, which tends to increase the fatigue life of the joints when compared to the as-welded condition.

1. Introduction attributed to the stress concentration effect produced by the nugget zone reducing the fatigue life of the welded joints. Shariati and Nejad Dual-phase steels are composed of a ferrite matrix with martensite [7] studied resistance spot welded U-shape specimens of low carbon as a second phase. This dual microstructure allows to obtain a balance steel subjected to tensile cyclic loading. They observed a stress con- between strength and ductility, which is very attractive to reduce the centration effect at the nugget interface that resulted in either a pull-out weight in automobiles. The manufacture of vehicles requires the use of or a fatigue crack growth failure as a function of the applied load, welding processes, such as the resistance spot welding RSW (a vehicle specimen thickness and nugget diameter. Bandyopadhyay et al. [8], has around three thousand welding spots) [1–3]. However, due to the performed a failure analysis on DP980 joints that were fractured under heat generated during the RSW process, microstructural changes are tensile tests; by SEM images they found void initiation at the interface induced, which affects the mechanical behavior of the welded joints. of ferrite and martensite grains on the necked region. The micro- Some studies have been carried out on this regard [4–8]. The soft zone structural and mechanical properties changes induced by the conven- produced in the heat affected zone (HAZ) by the RSW process on dual- tional RSW process represents a challenge in the use of high strength phase steels (DP600, DP780 and DP980) has been studied by Nayak steels for the automotive industry, because the fatigue strength can be et al. [4]. They observed an increase in the volume of martensite in the seriously affected. Despite the work performed on the RSW joints, re- fusion zone, as well as tempering of the martensite in the HAZ (soft covery mechanisms for the fatigue life had been limited reported in the zone formation). Additionally, these authors reported a reduction of the literature. Fujimoto et al. [9] reported the use of shot blasting proces- mechanical properties in the welded joints because of the micro- sing on RSW lap joints of high strength steel sheets (1.2 mm-thickness). structural changes. Mediratta et al. [5], determined that the decreased The fatigue strength was improved because of high compressive re- hardening occurs when there is a uniform distribution of dislocations sidual stresses induced by the shot blasting to the RSW lap joint. On the due to the dispersion of martensite. Farabi et al. [6] studied the mi- contrary, tensile residual stresses decreased the fatigue strength, but crostructure and mechanical properties in dissimilar welds (DP600- they can be diminished through careful control and optimization of the DP980), they observed that fine grains and continuous martensite heat input in welding processes [10]. In view of the massive usage of around the ferrite grains allowed to obtain the best performance in the the RSW processes by the automobiles manufacturers industry results fatigue life. Also, it has been found that the fatigue failure on RSW was relevant to propose additional operations routes to improve the

⁎ Corresponding author. E-mail address: [email protected] (R.R. Ambriz). https://doi.org/10.1016/j.ijfatigue.2018.12.026 Received 13 November 2018; Received in revised form 20 December 2018; Accepted 27 December 2018 $YDLODEOHRQOLQH'HFHPEHU (OVHYLHU/WG$OOULJKWVUHVHUYHG

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Contents lists available at ScienceDirect

Optical Materials

journal homepage: www.elsevier.com/locate/optmat

Synthesis of luminescent terbium-thenoyltriﬂouroacetone MOF nanorods for green laser application

∗ D.Y. Medina-Velazqueza, , U. Caldiñob, A. Morales-Ramirezc,e, J. Reyes-Mirandaa, R.E. Lopeza, R. Escuderod, R. Ruiz-Guerreroe, M.F. Morales Pereza a Universidad Autónoma Metropolitana-Azcapotzalco, División de Ciencias Básicas e Ingeniería, Av. San Pablo No 180, Col, Reynosa-Tamaulipas, C.P. 02200, CDMX, Mexico b Universidad Autónoma Metropolitana-Iztapalapa, Departamento de Física, P.O. Box 55-534, CDMX, 09340, Mexico c Instituto Politécnico Nacional-ESIQIE, Departamento de Metalurgia y Materiales A.P. 118-431, 07051, CDMX, Mexico d Universidad Nacional Autónoma de México, Instituto de Investigaciones en Materiales, A. Postal 70-360, CDMX, 04510, Mexico e Instituto Politécnico Nacional, CIITEC IPN, Cerrada de Cecati S/N. Col. Santa Catarina, Azcapotzalco, C.P. 02250, CDMX, Mexico

ARTICLE INFO ABSTRACT

Keywords: The metalorganic frameworks (MOFs) with lanthanides ions offer great potential in the optical area because can Luminescent MOF provide properties of flexibility, low density, low-cost methods of synthesis, and insolubility in water, which give Green laser them an advantage over traditional phosphors. In this study, a thenoyltriflouroacetone ligand (TTA) with a Tb3+ Rod-like morphology MOF was synthesized (Tb = 10 and 50% mol) and its structural and luminescent properties were analyzed. The Luminescence metalorganic compound was generated in a simple one-pot reaction from terbium nitrate and 2-thenoyltri- Metalorganic framework fluoroacetone precursors at room temperature. By means of FTIR, it was confirmed the presence of carbon Green emission groups, which made possible the terbium ion chelation, and also the Tb-O bonds vibration modes. 1HNMR results confirm that the complex with 10% mol of Tb3+ contains three coordinates molecules of TTA and two waters molecules. The powders exhibit rod-like morphology with size about 170 nm of diameter and a length about 2 μm; the rod-like nature of powders was confirmed by SEM and TEM analyses. By XRD it was concluded that at higher terbium concentration (TTA-50Tb sample) higher the crystallite size and crystallinity, in fact the 5 7 TTA-10Tb sample shows a partial-amorphous nature. By photoluminescence analyses, the D4→ FJ (J = 3, 4, 5

and 6) emissions were recorded for both synthesized samples (λexc = 376 nm). Furthermore, it was observed that the emission intensity was enhanced in a factor of 3.5 for the TTA-50Tb. The energy transfer efficiency from TTA to Tb3+ (antenna effect) was 0.984 for TTA-10Tb and 0.993 for TTA-50Tb. Decay time analyses indicate effective lifetime of 1.45 and 1.60 m s for the samples doped at 10 and 50%, respectively, indicating that the 5 7 forbidden transition rules are stronger at higher crystallinity. The integrated intensities of the D4 → F5 (green 5 7 at 541 nm) and D4 → F6 (blue at 486 nm) emissions and their intensity ratios IG/IB upon 376 nm excitation have been evaluated for TTA-10Tb andTTA-50Tb samples. The CIE1931 color of the MOFs excited at 376 nm attains a higher green color purity by increasing the terbium concentration. This is in concordance with the

increased IG/IB ratio up for the TTA-10Tb and TTA-50Tb samples. Thus, the TTA-50Tb sample exhibits a green color purity of 67.94% with chromaticity coordinates (0.30, 0.57), being very close to those (0.29, 0.60) of European Broadcasting Union illuminant green. This interesting feature of the TTA-50Tb sample, together with 5 7 an experimental branching ratio of 61.3% for the D4 → F5 green emission, highlights its capability as solid state green laser pumped by GaN (376 nm) LEDs.

1. Introduction doped materials because their high quantum yield, narrow spectral emission and large lifetime, which depend on the host and the crystal Recently, the study of luminescent compounds has grown due to the ﬁeld around lanthanide ions. large number of areas in which these materials can be applied (optics, Among the many research areas of luminescence materials, the medicine, electronics, etc.). Special attention is located on lanthanide- study of rare earth doped organic binders (like β-diketones) is growing

∗ Corresponding author. E-mail address: [email protected] (D.Y. Medina-Velazquez). https://doi.org/10.1016/j.optmat.2018.08.021 Received 5 May 2018; Received in revised form 20 July 2018; Accepted 7 August 2018 $YDLODEOHRQOLQH$XJXVW (OVHYLHU%9$OOULJKWVUHVHUYHG &HUDPLFV6LOLNiW\ ZZZFHUDPLFVVLOLNDW\F] GRLFV

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*Instituto Politécnico Nacional, CIITEC IPN, Cerrada de Cecati S/N, CP 02250, Col. Santa Catarina Azcapotzalco Ciudad de México, México **Universidad Tecnológica de Tecámac, UTTEC, Carretera Federal México, Pachuca Km 37.5, CP 55740, Col. Sierra Hermosa, Tecámac, Estado de México, México

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This paper studies the structural and photoluminescent properties of hydroxyapatite (HA) and europium-doped hydroxyapatite (HA:Eu) synthesised by the hydrothermal method and sintered by the spark plasma sintering (SPS) technique. HA and HA:Eu SRZGHUVV\QWKHVLVHGDWS+RIDQGZHUHFKDUDFWHULVHGE\PHDQVRILQIUDUHGVSHFWURVFRS\;UD\GLৼUDFWLRQVFDQQLQJ electron microscopy, Raman spectroscopy and luminescence spectroscopy. The HA and HA:Eu samples were sintered using the SPS technique at 900 and 1200 °C. It was determined that the HA and HA:Eu powders crystallised in the hexagonal phase, which is stable until 900 °C. The presence of Eu3+ ions tended to stabilise the hexagonal phase of hydroxyapatite at &8QGRSHGK\GUR[\DSDWLWHVLQWHUHGDW&UHYHDOHGDVLJQL¿FDQWDPRXQWRIWULFDOFLXPSKRVSKDWH ȕ7&3 DV 5 7 5 7 DUHVXOWRILWVGHFRPSRVLWLRQ%\LQFUHDVLQJWKHKHDWWUHDWPHQWWHPSHUDWXUHGLৼHUHQWHPLVVLRQOLQHV D0ĺ F0, D0ĺ F1 and 5 7 D0ĺ F2 transitions) were obtained due to calcium site substitution by the europium ions in the HA structure.

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TiO2@SiO2 Nanoparticles Functionalized with Para-Aminobenzoic Acid (PABA) by Fisher Esteriﬁcation Reaction

María L. Carrera-Jota1,+, Margarita García-Hernández2,3, Ernesto Rivera-Becerril4, Jorge H. Luna-Domínguez2, Ángel de J. Morales-Ramírez5, Arturo López-Marure6, Perla Y. López-Camacho3 and Brenely González-Penguelly5

1Posgrado en Ciencias Naturales e Ingeniería, Universidad Autónoma Metropolitana, Unidad Cuajimalpa, Av. Vasco de Quiroga 4871, Col. Santa Fe, Delegación Cuajimalpa de Morelos, CDMX, C.P. 05300, México 2Universidad Autónoma de Tamaulipas, Facultad de Odontología, Boulevard Adolfo López Mateos S/N Col, Universidad, Tampico, Tamaulipas C.P. 89109, México 3Instituto Politécnico Nacional, CECyT 16, Ciudad del Conocimiento y la Cultura, Carretera Pachuca Actopan km 1 + 500 San Agustín Tlaxiaca, Hidalgo C.P. 42162, México 4Departamento de Ciencias Naturales, Universidad Autónoma Metropolitana, Unidad Cuajimalpa, Av. Vasco de Quiroga 4871, Col. Santa Fe, Delegación Cuajimalpa de Morelos, CDMX, C.P. 05300, México 5Instituto Politécnico Nacional, CIITEC, UPALM S/N Col. Lindavista, Gustavo A. Madero CDMX C.P. 07738, México 6Instituto Politécnico Nacional, CICATA Altamira, Carretera Tampico-Puerto Industrial Altamira, Altamira, Tamaulipas, C.P. 89600, México

In this work, hybrid TiO2 nanoparticles embedded in SiO2 were obtained by means of sol-gel process, testing different proportions of the silicon and titanium oxides to obtain TiO2 particles with a high surface content of hydroxyl groups. Anatase crystalline form of TiO2 is a widely used material in active-substance release studies, due to its optimal properties for the transport, distribute and release of different molecules into biological systems. According to the X-ray diffraction analysis, all the proportions of evaluated hybrid systems presented the anatase phase, however, the molar proportion (20:80, TiO2:SiO2) contains a high quantity of hydroxyl groups according to infrared spectroscopy. The spherical morphology of the particles were observed by scanning electron microscopy forming agglomerates. The functionalization of these surfaces was carried out using para-aminobenzoic acid as a drug-binding model that generated a covalent bond between the TiO2@SiO2 system, likewise, thermogravimetric analysis identified the content of functionalized PABA. Dynamic light scattering showed particles and agglomerates around 25609 nm and negative value of zeta (¦)-potential in the molar ratio TiO2:SiO2 20:80-PABA. Finally, we demonstrated that PABA hydrolyzes in the presence of human plasma, recovering the nanoparticularized systems with the hydroxyl groups. The hydroxyl groups on the particle surface promote the incorporation of organic molecules that contain carboxyl groups in their structure. [doi:10.2320/matertrans.M2019085]

(Received March 27, 2019; Accepted June 18, 2019; Published July 22, 2019) Keywords: hybrid nanoparticles, functionalization, PABA, sol-gel

1. Introduction groups. Several authors have demonstrated that TiO2 and SiO2 are chemically inert, with large surface area and non- The nanostructured materials of metal oxides (MO2) toxic, together forming a system of TiO2 embedded in SiO2 embedded in silicon oxide (MO2@SiO2) are very interesting system, formed by two components, where the dispersed for their physicochemical properties. They commonly have a phase consists of nanoscale particles distributed in a host multiple crystalline structure and can be obtained in a variety matrix and it is characterized as the properties of the final of sizes and shapes.1,2) These types of materials have been material are superior to those of the constituent materials widely used in the area of electronics and optics,3,4) however, separately. they have now attracted the attention in biological areas The methods commonly used to synthesize these mixed owing to their low or no toxicity as well as a large surface oxides are: sol-gel, co-precipitation, chemical vapor deposi- area, which allows it to confine drugs, proteins or some tion, amongst others.812) The sol-gel method is the most biological markers,5) and has been described as having widely used due to its ability to control the texture and optimal properties for the transport, distribution and release surface properties of compound oxides.1317) 6,7) of these molecules in biological systems. The TiO2 is one The amorphous silica surfaces can be described by the of most characteristic metallic oxide that has these properties Zhuralev model18) which considers that the determining when is present in anatase phase. factor of surface properties are the silanol groups and However, aspects such as the particle size and poor surface siloxane bridges. The chemical reactions involving these areas have motivated the development of new systems where groups lead to modifications of the surfaces that can be used SiO2 has emerged as an adequate alternative to imbedded to to obtain information about the structure of the surface, such nanostructured particles in order to improve these aspects.1,2) as nanoroughness, chemical fractality, and distribution of Once formed, the TiO2@SiO2 material has been studied as silanol groups, and to achieve a surface with entirely different an active substance release due to its potential bioactivity, properties.4) For any type of completely hydroxylated silica, which is strongly correlated to the presence of SiOH surface regardless of its origin, a number of 4.64.9 OH groups per 2 nm have been established. The simple silanols, (SiO)3Si + Corresponding author, E-mail: [email protected] OH, and geminal, (SiO)2Si (OH)2, act as adsorption Sintering and hot corrosion of yttria silicate tablets in molten salts prepared by spark plasma sintering Merlina A. Navarro Villanueva, Luis A. Soto Hernández, Melquisedec Vicente Mendoza, Ángel de J. Morales Ramírez and Fernando Juárez Lopez CIITEC, Instituto Politécnico Nacional, CIITEC, Cd. de México, Mexico

Abstract Purpose – This paper aims to study the microstructural hot corrosion behaviour of the sintered Y2SiO5 ceramic silicate under a Na2SO4 1 V2O5 mixture at an engine representative temperature of 1150°C. Y2SiO5 is a promising candidate for thermal barrier coatings (TBC) due to its excellent chemical stability at high temperatures. As a continuous source of Y31, it is expected that Y2SiO5 environmental barrier coating may prolong the lifetime of TBC systems by stopping the degradation caused by the loss of the Y2O3 stabilizer. Design/methodology/approach – Two routes were chosen for the yttria silicate powder synthesis by sol-gel from TEOS and APTES precursors as the difference in Si source changed the ratio of Y2SiO5/Y2Si2O7 phases. Hot corrosion studies using Na2SO4 and V2O5 mixtures were conducted on both surfaces of APTES and TEOS tablets at 1150°C for 8 h in atmospheric air. The morphology and microstructure analyses of the silicate samples after hot corrosion tests were carried out using a SEM and X-ray diffraction analyse techniques. Findings – Based on the degradation, the general status of the APTES tablet after hot corrosion presents a better hot corrosion resistance at a temperature of 1150°C than does that of the TEOS tablet. In the TEOS tablet, the crystal morphology of NaY9Si60O26 woodchip shapes with a size of 60 mmis developed on the surface for ﬁnally initiating some cracks. In the APTES case, the crystal morphology of rod-like shapes with a size of 100 mmisdeveloped; hence, a dense thick layer predominately postpones the reaction of V2O5 and Na2SO4 with yttria silicate, and consequently, less damage is observed. Originality/value – Coating yttria silicate preparation is very complicated; the problems of a high synthesis temperature, long production period and low yield still need to be solved. Under these perspectives, ceramics prepared via spark plasma sintering (SPS) can reach theoretical high densities and a ﬁne grain size can be retained after the SPS process; hence, well resistance to the corrosion in molten salts is expected to obtain for the sintered yttria silicate tablets. Keywords Sintering, Molten salts, Yttria-Silicate Paper type Research paper

1. Introduction properties of the thermal barrier ceramic have not been clearly explained, although the defects can signiﬁcantly affect the high- Great progress has been achieved in developing functional temperature properties of the ceramics(Kima et al.,2003; Taylor ceramics as thermal barrier coating (TBC) systems (Schulz et al., et al., 1990; McPherson, 1989; Park et al., 2005). Rare earth 1996; Rabiei and Evans, 2000; Ahmaniemi et al.,2004; Cao silicates were recognized as the third generation of et al., 2004; Guo et al., 2016; Wang et al.,2012, 2014). Coating environmental barrier coating (EBC) ceramics (Tian et al., systems have been widely used in the gas turbine industry, 2016; Xu et al., 2015; Heveran et al., 2013; Lee et al., 2005; Sun though the degradation of the ceramic layer is accelerated when et al.,2008, 2009; Zhou et al., 2013). The thermal conductivities ceramics are used in corrosive environments or used with low- quality fuels at high working temperatures. The failure of the of rare earth disilicates have been extensively studied, but few ceramic has a close relationship with impurities such as aspects of the environmental durability have been explored. The ﬁ vanadium, sodium sulphates and vanadate salts condensed on main obstacle is the dif culty in fabricating pure and dense the coating surface. These salts melt above 700°C and penetrate samples of a yttria silicate phase. To promote the high- into the coating, destroying the microstructure of the coating throughput screening of EBC candidates, it is important to and corroding the top-coat and the substrate (Huang et al., bridge the intrinsic relationship between the crystal chemistry 2011; Xu et al.,2012; Liu et al., 2013; Guo et al., 2017; Jones, and the characteristic of the environmental durability of silicates 31 1997; Jones et al., 1985; Siemers and McKee, 1982; Jones and (Sun et al.,2008). As a continuous source of Y , it is expected Williams, 1987). On the other hand, the effects of coating that Y2SiO5 EBC may prolong the lifetime of TBC systems by defects, such as pores or microcracks, on the hot corrosion stopping the degradation caused by the loss of the Y2O3 stabilizer. During engine operation, sodium chloride ingested via The current issue and full text archive of this journal is available on Emerald Insight at: www.emeraldinsight.com/0003-5599.htm The authors acknowledge COFAA, EDI-IPN and SNI-CONACYT for supporting this work. The authors are also indebted to Red de Nanociencias y Nanotecnología of IPN. Anti-Corrosion Methods and Materials 66/6 (2019) 782–790 Received 12 December 2018 © Emerald Publishing Limited [ISSN 0003-5599] Revised 12 December 2018 [DOI 10.1108/ACMM-12-2018-2043] Accepted 22 February 2019

782 0DWHULDOV5HVHDUFK%XOOHWLQ

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Materials Research Bulletin

journal homepage: www.elsevier.com/locate/matresbu

3+ 3+ Eﬀect of NaOH concentration on the 805 nm emission of NaYF4:Yb ,Tm phosphors synthesized by a pressure -assisted hydrothermal method ⁎ J. Reyes Mirandaa,b, F. de J. Carrillo Romoa, A. García Murilloa, , J. Olivac, C.R. Garcíad a Instituto Politécnico Nacional, CIITEC IPN, Cerrada de Cecati S/N. Col. Santa Catarina, Azcapotzalco México D.F. C.P 02250, Mexico b Universidad Autónoma Metropolitana-Azcapotzalco, Departamento de Materiales, Av. San Pablo 180, Col. Reynosa-Tamaulipas, Azcapotzalco, CDMX, 02200, Mexico c CONACYT-Facultad de Ciencias Químicas, Universidad Autónoma de Coahuila, 25000, Saltillo, Mexico d Facultad de Ciencias Físico-Matemáticas, Universidad Autónoma de Coahuila, 25000, Saltillo, Mexico

ARTICLE INFO ABSTRACT

3+ 3+ Keywords: In this work, Yb ,Tm co-doped NaYF4 powders with several morphologies (spheres, micro-needles, and NaOH microrods) were successfully synthesized by varying the NaOH concentration from 0 to 2 M. The synthesis was Hydrothermal carried out with pressure-assisted hydrothermal reactions. XRD diffraction patterns confirmed the presence of a Upconversion pure crystalline hexagonal phase in all the NaYF4 samples. Structural data, crystallite sizes, lattice parameters, Reaction pressure and cell volumes were obtained with the Rietveld method. The up-conversion spectra of the 3+ 3+ NaYF4:Yb (20%),Tm (1%) powders synthesized with different concentration of NaOH were obtained under infrared excitation at λ = 980 nm. These spectra showed the characteristic visible emissions of Tm3+ at 455 1 3 1 3 3 3 ( D2→ F4), 478 nm ( G4→ H6) and 805 nm ( H4→ H6) for NaOH concentrations below 1 M. However, the visible emission was completely quenched for NaOH concentrations from 1 M and only a pure IR emission was

observed at 805 nm. Hence, the NaYF4 powders studied in this work could be candidates as active media of solid state laser at 805 nm, which are currently important for biomedical applications and photothermal therapy.

3+ 3+ 1. Introduction Yb ,Tm co-doped NaYF4 phosphors present a weak NIR emission at 800 nm which is accompanied by blue and UV emissions. Those ma- Up-conversion (UC) phosphors are a current topic of research be- terials are not desirable for phototherapy treatments because the VIS cause of their excellent optical properties, which enable them to con- emission could produce degradation in the cells [17]. Thus, new stra- vert near-infrared (NIR) light to visible (VIS) light. Therefore, these tegies to inhibit the UV and VIS emissions are required to produce phosphors have applications for photocatalysis [1–3], solar cells [4–7], materials with emission only at 800 nm. solid-state lasers [8] and biomedicine [9–12]. Particularly in the bio- The hexagonal NaYF4 has been considered as one of the most effi- medical field, if the UC phosphors are used as biomarkers, they can be cient up-converter hosts, its superior optical properties are attributed to excited with NIR light which do not damage the cells. In contrast, other the multisite character of its crystal lattice. It has two possible different ¯ biomarkers such as quantum dots or organic dyes need to be excited symmetries: NaNdF4, with space group P 6 [18] and the gagarinite with harmful and even carcinogenic UV light. Moreover, the auto- structure, with space group P63/m [19]. In addition, its photostability − fluorescence of many biomolecules is absent under NIR excitation and and low phonon energy (≈360 cm 1) diminishes the non-radiative the penetration depth of NIR light on human skin and tissues is en- relaxation of excited electrons, thereby increasing the light emission hanced in the optical window of 700–900 nm [10,13]. Currently, there intensity [20,21]. One of the most employed methods for the synthesis are advances for the development of materials able to emit single of doped NaYF4 nanoparticles is the hydrothermal method, which emission at 800 nm through the use of Yb3+,Tm3+ dopants, since this produces nanoparticles with good optical properties, but it involves wavelength is resonant with the gold nanoparticles, which are em- complex steps and requires the use of organic additives such as oleic ployed for surface plasmon resonance (SPR) and this effect is used for acid and octadecene for the formation of spherical shapes in almost all photothermal cancer therapy [14,15]. In fact, Abadeer et al. [16] re- cases [22–25]. The hydrothermal method yields a variety of morphol- ported that a ratio (length/width) of 3.7–4.4 for gold nanoparticles, ogies and sizes by controlling synthesis parameters such as surfactants, produces a strong optical absorption of NIR photons at 800 nm. Most of pH, temperature, reaction time, and fluoride sources. The pH has an

⁎ Corresponding author. E-mail address: [email protected] (A. García Murillo). https://doi.org/10.1016/j.materresbull.2019.110531 Received 5 December 2018; Received in revised form 20 May 2019; Accepted 26 June 2019 $YDLODEOHRQOLQH-XQH (OVHYLHU/WG$OOULJKWVUHVHUYHG 226 Send Orders for Reprints to [email protected]

Current Physical Chemistry, 2019, 9, 226-231

RESEARCH ARTICLE

ISSN: 1877-9468 eISSN: 1877-9476 Blue, Green and Red Upconverted Emission of Controlled Hydro- 3+ 3+ thermal Pressure Synthesized Y2O3: Er (1%) Tm (1%) and Dif- ferent Yb3+ Ratio Conditions Nanophosphors

Solange Ivette Rivera Manrique1,*, Felipe de Jesús Carrillo Romo2, Antonieta García Murillo2, Carlos Eduardo Rodríguez García3 and Jorge Roberto Oliva Uc4

1Ingeniería Biomédica, Facultad de Tecnologías de la Información, Universidad de la Salle, Bajío, León, Gto, México; 2Tecnología de Partículas, Instituto Politécnico Nacional-Centro de Investigación e Innovación Tecnológica, CDMX, México; 3Facultad de Físico Matemáticas, Universidad Autónoma de Coahuila, Saltillo, Coahuila, México; 4CONACYT-División de Materiales Avanzados, Instituto Potosino de Investigación Científica y Tecnológica A.C., San Luis Potosí, SLP, México

Abstract: Introduction: Rare earth-doped Upconverting Nanoparticles (UCN's) can con- vert near-infrared photons into visible photons via multiphoton processes, which makes it a good material for generating white light. The production of luminescent materials for technology applications focuses on controlling powder characteristics such as chemical homo- geneity and low impurity levels. Objective: In this research study, we synthesized Er3+ (1%) Tm3+ (1%) Yb3+ (at different percentages) by co-doping Y2O3 NPs, using the Controlled-Pressure Hydrothermal Method (CPHM), with nitrogen. The ratio used was chosen to conduct a detailed photolumniscence analysis. 3+ 3+ 3+ Methods: Samples of Y2O3: Er (1%) Tm (1%) Yb (at 1.5%, 2%, and 2.5%) were prepared using the controlled-pressure hydrothermal method (CPHM). Each solution was A R T I C L E H I S T O R Y transferred into a mini-clave drive Büchiglasuster with an inner Teflon vessel. In this case, the mini-clave was heated at 190°C for 3 h, and nitrogen was used to control the pressure. Received: May 23, 2019 The initial pressure was 20 bars; it was increased during the process to 42 bars. The pow- Revised: June 25, 2019 Accepted: August 16, 2019 ders obtained were washed with distilled water using centrifugation at 4000 rpm for 15 min. The washed product was dried to 120°C, followed by subsequent heat treatment at DOI: 10.2174/1877946809666190830151043 1000°C for 5 h. 3+ 3+ 3+ Results: The representative XRD patterns for the Y2O3: Er (1%) Tm (1%) and Yb (at 1.5%, 2%, 2.5%) doped samples confirms the presence of a cubic Y2O3 crystal structure. Scanning Electron Microscope (SEM) images show that the morphology of these particles 3+ 3+ is spherical. Upconversion photoluminescence spectra of Y2O3:Er (1% mol) Tm (1% mol) Yb3+ (1.5% mol), Yb3+ (2.0% mol), and Yb3+ (2.5% mol), after 908-nm excitation. Blue, green, and red bands are centred at 440 nm, 469 nm, 618 nm, and 678 nm, respectively. Conclusion: The controlled-pressure hydrothermal method is a productive method for syn- 3+ 3+ 3+ thesizing rare earth-doped and codoped Y2O3; when Er , Yb , and Tm ions are introduced into the host matrix, they do not cause any changes in the cubic structure nor influence the crystal structure. This method can used to synthesize any type of nanoparticle, because it involves low pressure (10-20 bars), low temperatures, and short time reactions. Keywords: Controlled pressure, hydrothermal, luminescence, nitrogen, rare earths, upconversion.

*Address correspondence to this author at the Ingeniería Biomédica, Facultad de Tecnologías de la Información, Universidad de la Salle, Bajío, León, Gto, México; Tel: +1525510245130; E-mails: [email protected]; [email protected]

RESEARCH

3+ Sol-gel synthesis of red phosphor GdPO4-Gd3PO7:Eu : luminescence and morphology

A. Rosas Camacho1 & F. Carrillo Romo1 & A. García Murillo 1 & J. Oliva Uc2

Received: 17 September 2018 /Revised: 9 March 2019 /Accepted: 19 March 2019 # Australian Ceramic Society 2019

Abstract 3+ A down-conversion luminescent material GdPO4-Gd3PO7:Eu has been synthesized by Pechini sol-gel process. The XRD patterns indicated that the obtained powders have a mixed crystalline phase. An intense luminescent red emission was obtained 5 7 upon excitation 275 nm. The influence of different synthesis conditions on morphology and the PL emission ratio I( D0 → F2)/ 5 7 I( D0 → F1) was established.

Keywords GdPO4-Gd3PO7 . Pechini sol-gel . Europium

Introduction its valence and ionic radii [6]. The monoclinic or monazite structure is well known as the matrix of the lanthanide ions The useful applications of rare earth element compounds, es- to give rise to doped phosphates [7]. It is well known that the 3+ pecially lanthanide phosphate doped with rare earth elements, photoluminescence emission of Eu -activated GdPO4 is have wide applications in display industry, optoelectronics, more dominant in the orange region (corresponding to the 5 7 3+ sensors, and nanoelectronic devices [1] due to its characteris- magnetic dipole D0 → F1 transition of Eu ions) than that 5 7 tic physical and chemical properties. of the red region (corresponding to electric dipole D0 → F2 Pechini method consists of the formation of a polymeric transition of Eu3+ ions) [8]. The strong red–emitting intensity 5 7 resin between a metallic acid chelate and polyhydroxide alco- peaking at 614–620 nm originates the D0 → F2 transition hol by polyesterification. Some authors have reported the re- and is observed upon 275-nm UV irradiation, indicating that 3+ markable influence of surfactants on structural and optical Eu ions in Gd3PO7 mainly occupied non-centrosymmetry 3+ 3+ 3+ characteristics of LaPO4:Eu and GdPO4:Ce /Tb nano- sites [9–11]. particles obtained by hydrothermal process [2, 3]. In this process, metal nitrates or carbonates are used as the starting materials, which avoid the problem of handling moisture- Experimental sensitive alkoxides. In addition; different cations can be mixed to the quasiatomic level that allows precise control of the 3+ chemical composition [4, 5]. The microcrystalline powders of GdPO4-Gd3PO7:Eu were synthesized by the sol-gel Pechini type reaction [12, 13]. The GdPO4 is a very important matrix to host lanthanide ions since its great thermal and chemical stability, due to the 4f full starting reagents were stoichiometric mixture of analytical orbital of Gd3+ with a stable structure. The Gd3+ ions are grade Gd2O3,Eu2O3,(NH4)2HPO4. easily replaced by the lanthanide ions due to the equality of Citric acid (C6H8O7), ammonium hydroxide (NH4OH), glycerol (C3H8O3), ethylene glycol (C2H6O2), nitric acid (HNO3, 96%), and ethanol (CH3CH2OH) were used as * A. García Murillo solvents. [email protected] Firstly, Re2O3 (Gd, Eu) was dissolved with dilute HNO3 (160 °C). A solution of C6H8O7:H2O-EtOH = (7:1) was incor- 1 Instituto Politécnico Nacional, CIITEC, Cerrada CECATI S/N Col. porated into RE solution. Secondly, NH4OH was diluted in Sta. Catarina, Alcaldía Azcapotzalco CDMX C.P. 02250, México RE solution was diluted to adjust the pH. Thirdly, 2 P CONACYT-Facultad de Ciencias Químicas, Universidad Autónoma (NH4)2HPO4 was dissolved into last solution with a Gd: = de Coahuila, 25000 Saltillo, Mexico 1.5 M ratio. An appropriate volume of glycerol or &HUDPLFV,QWHUQDWLRQDO ²

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Ceramics International

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Magnetoelectric coupling in multiferroic BiFeO3 by co-doping with strontium and nickel

F. Pedro-Garcíaa, L.G. Betancourt-Canteraa, A.M. Bolarín-Miróa, C.A. Cortés-Escobedob, ∗ A. Barba-Pingarrónc, F. Sánchez-De Jesúsa, a Área Académica de Ciencias de la Tierra y Materiales, Universidad Autónoma del Estado de Hidalgo Mineral de la Reforma, 42184, Hidalgo, Mexico b Instituto Politécnico Nacional, Centro de Investigación e Innovación Tecnológica, 02250, Ciudad de México, Mexico c Centro de Ingeniería de Superﬁcies y Acabados (CENISA), Facultad de Ingeniería, UNAM. Circuito Exterior, Ciudad Universitaria, 04510, Ciudad de México, Mexico

ARTICLE INFO ABSTRACT

2+ 2+ Keywords: We report the eﬀects of the Sr and Ni co-doping of BiFeO3 on the crystal structure and multiferroic

Magnetodielectric coupling properties of Bi1−xSrxFe1-yNiyO3 (x = 0.05, 0.0 ≤ y ≤ 0.10, and Δy = 0.05) that is synthesized using assisted SreNi co-doping high-energy ball milling. The mixtures of Bi2O3,Fe2O3, SrO and NiO were milled for 5 h, pressed at 900 MPa, and BiFeO3 co-doped sintered at 800 °C in order to obtain cylindrical test pieces. X-ray diffraction and Rietveld refinement elucidated High-energy ball milling the effects of Sr2+ and Ni2+ on the crystal structure. Co-doping with SreNi in suitable proportions stabilizes Multiferroic 2+ rhombohedral BiFeO3. High contents of Ni promote the precipitation of secondary phases in the forms of

NiFe2O4 and Bi25FeO40. The magnetic behavior was examined by means of vibrating sample magnetometry. The results showed a change in the magnetic order from antiferromagnetic for the undoped sample to the ferromagnetic order for the co-doped samples. This change is attributed to the modulations in the magnetic moment due to crystal structure distortions. All samples show high relative permittivity values, which were enhanced by doping with Sr2+.Ni2+ cations increase the dielectric dissipation factor; this enhancement is related to their interactions with cations of a diﬀerent oxidation state, such as Fe3+,Fe2+,Ni2+,Bi3+ and Sr2+ in the crystal

structure of BiFeO3. The magnetoelectric coupling that was evaluated using magnetodielectric measurements was above 4% at 1 kHz for the higher applied magnetic ﬁeld of 18 kOe.

1. Introduction cycloid, where the Fe3+ electron spins and aligns in a canted G-type antiferromagnetic arrangement with an extended propagation length of

Multiferroic materials with magnetoelectric coupling present an 62–64 nm [7–9]. While the synthesis of BiFeO3 is subject to the oc- interesting phenomenon by allowing a wide range of technological currence of secondary phases, such as sillenite (Bi25FeO40) and mullite applications, such as storage devices, sensors, and controllers [1]. In (Bi2Fe4O9)[10], the low volatilization temperature of Bi produces addition, semiconductor magnetic nanoparticles could provide a new oxygen vacancies, which lead to a valence change from Fe3+ to Fe2+, type of conduction control in devices due to the combination of the resulting in high conductivity and an increase in the leakage current ferromagnetism order and the semiconductor behavior [2–6]. However, [11]. To improve the multiferroic properties and minimize the sec- ferroelectric and ferromagnetic coupling in a single-phase material is ondary phase formation, ion substitution in both positions, A and B, is diﬃcult to obtain. Bismuth ferrite, BiFeO3 (BFO), is a rhombohedrally one of the most common approaches for bismuth ferrite. For example, distorted ABO3-type perovskite material with the R3c space group, substitutions at the A site can strongly modify the ferroelectric prop- which presents the possibility to achieve magnetoelectric coupling. In erties and slightly modify the magnetic properties [12–14]. Dopants, 2+ addition, BiFeO3 exhibits ferroelectricity and antiferromagnetism above such as Sr , have been shown to increase the dielectric properties, room temperature with a high ferroelectric transition temperature, or thus reducing the occurrence of secondary phases and slightly in-

Curie temperature (TC = 830 °C), and magnetic ordering temperature, creasing the magnetization of bismuth ferrite. Hegab et al. [15] re- 2+ or Néel temperature (TN = 370 °C). The ferroelectric properties are at- ported the results of doping with diﬀerent concentrations of Sr , tributed to the A position and are caused by the free electron pair 6s2 of showing a high solubility in the structure of bismuth ferrite and an Bi3+. Antiferromagnetism results from the long period of the spin increase in magnetization due to the doping element that distorted the

∗ Corresponding author. E-mail address: [email protected] (F. Sánchez-De Jesús). https://doi.org/10.1016/j.ceramint.2019.02.058 Received 13 November 2018; Received in revised form 15 January 2019; Accepted 10 February 2019 $YDLODEOHRQOLQH)HEUXDU\ (OVHYLHU/WGDQG7HFKQD*URXS6UO$OOULJKWVUHVHUYHG Journal of Alloys and Compounds 792 (2019) 694e701

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Journal of Alloys and Compounds

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Multiferroic properties of nanostructured BiFeO3 tailored by milling and sintering by SPS

F. Pedro-García a,F.Sanchez-De Jesús a, C.A. Cortes-Escobedo b, J.A. Patino-Pineda~ b, A.M. Bolarín-Miro a, * a Area Academica de Ciencias de la Tierra y Materiales, Universidad Autonoma del Estado de Hidalgo Mineral de la Reforma, 42184, Hidalgo, Mexico b Instituto Politecnico Nacional, Centro de Investigacion e Innovacion Tecnologica, 02250, Ciudad de Mexico, Mexico article info abstract

Article history: We report the magnetic and dielectric behavior of multiferroic bismuth ferrites synthesized using Received 30 November 2018 milling-annealing processes and tailored through the crystallite size reduction and the microstrain Received in revised form generated by mechanical milling. For synthesis, stoichiometric mixtures of Bi2O3 and Fe2O3 were mixed 6 March 2019 and milled for 5 h using a ball to powder weight ratio of 10:1 by high-energy ball milling and annealed at Accepted 9 April 2019 650 C. Subsequently, was carried out the Crystallite Size Reduction by Milling-Process at different Available online 10 April 2019 milling times, in a range of 0e60 min, using a ball to powder weight ratio of 50:1 adding 5% wt. of methanol. X-ray diffraction and Rietveld analysis were used to evaluate the crystallite size and micro- Keywords: strain of the crystal structure. Morphology was studied by scanning electron microscopy, and magnetic Multiferroic BiFeO3 Mechanochemical processing behavior was evaluated using vibrating sample magnetometry. The powders obtained from Crystal Size Reduced crystallite size Reduction by Milling-Process were sintered using spark plasma sintering in a 10 mm diameter graphite Bi2Fe4O9 die at 750 C. The effect of spark plasma sintering was evaluated by X-ray diffraction, Rietveld analysis, High-energy ball milling vibrating sample magnetometry and broadband dielectric spectroscopy. The results show a transformation from BiFeO3 phase to Bi2Fe4O9 phase for longest Crystallite Size Reduction by Milling Process time. Relationships between microstructural transformation and oxidation-reduction reactions, as well as antiferromagnetic-ferromagnetic changes, are discussed. Dielectric properties were found to decrease with high Crystallite Size Reduction by Milling-Process. Also, an unusual ratio was observed in magnetodielectric coupling which increases with Crystallite Size Reduction by Milling-Process time. © 2019 Elsevier B.V. All rights reserved.

1. Introduction exchange coupling to a ferromagnetic (FM) [3]. Bismuth ferrite is a Type-I multiferroic with perovskite crystal structure distorted Currently, substantial reports have been done to synthesize rhombohedrally in the axis [111] with space group R3c and Gold- multiferroic magnetoelectric materials. It is very important for the schmidt tolerance factor (t) of 0.88. It is calculated from the ratio of development of future electronics and information technologies the ionic radii following the expression: t ¼ (rBi þ rO)/√2(rFe þ rO), 3þ 2 3þ because of their unique properties and diverse application ranges where rBi, rO and rFe are the ionic radii of Bi ,O and Fe , such as in memories and tunnel junctions, aiming to apply in de- respectively. Using the ionic radii reported by Shannon [4], t is vices such as low-power-consumption memory devices [1]. calculated for BiFeO3 compound, obtaining 0.88. In bulk has Although some of them, as bismuth ferrite (BiFeO3, BFO) exhibit ferroelectricity and antiferromagnetism. It is known that ferro- þ þ signiﬁcant magnetoelectric effects at room temperature [2], the electricity properties are due to Fe3 and Bi3 ions, which are dis- main effort in BiFeO3 studies has been devoted to understand the placed from their centrosymmetric positions resulting in internal magnetoelectric coupling between ferroelectric (FE) and spontaneous polarization along the direction [111] [5]. Antiferro- antiferromagnetic (AFM) behaviors, motivated by interest in magnetic behavior is governed by the Dzyaloshinskii-Moriya (DM) interaction, which is described below: the magnetic structure is organized as G-type antiferromagnetism, it means, for each parallel 3þ * Corresponding author. spin its nearest neighbors are antiparallel. Also, the Fe ions are E-mail addresses: [email protected], [email protected] (A.M. Bolarín- hosted in oxygen octahedra, it buckles in order to ﬁt in a small Miro). https://doi.org/10.1016/j.jallcom.2019.04.106 0925-8388/© 2019 Elsevier B.V. All rights reserved. materials

Article Enhanced Multiferroic Properties of YFeO3 by + Doping with Bi3

Omar Rosales-González 1,Félix Sánchez-De Jesús 1, Fernando Pedro-García 1, Claudia Alicia Cortés-Escobedo 2 ,Màrius Ramírez-Cardona 1 and Ana María Bolarín-Miró 1,* 1 Área Académica de Ciencias de la Tierra y Materiales, Universidad Autónoma del Estado de Hidalgo Mineral de la Reforma, Hidalgo 42184, Mexico 2 Instituto Politécnico Nacional, Centro de Investigación e Innovación Tecnológica, Ciudad de Mexico 02250, Mexico * Correspondence: [email protected] Received: 31 May 2019; Accepted: 25 June 2019; Published: 26 June 2019

+ + Abstract: Tthe present work studied the cationic substitution of Y3 by Bi3 on the crystal structure ff of orthorhombic YFeO3 and its e ect over magnetic, dielectric and electric properties of multiferroic yttrium orthoferrite. Stoichiometric mixtures of Y2O3,Fe2O3 and Bi2O3 were mixed and milled for 5 h using a ball to powder weight ratio of 10:1 by high-energy ball milling. The obtained powders ◦ were pressed at 1500 MPa and sintered at 700 C for 2 h. The test samples were characterized at room temperature by X-ray diffraction (XRD), vibrating sample magnetometer (VSM), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and impedance spectroscopy + (IS). The X-ray diffraction patterns disclosed a maximum solubility of 30 % mol. of Bi3 into the orthorhombic YFeO3. For higher concentrations, a transformation from orthorhombic to garnet 3+ 3+ structure was produced, obtaining partially Y3Fe5O12 phase. The substitution of Bi in Y sites promoted a distortion into the orthorhombic structure and modified Fe-O-Fe angles and octahedral tilt. In addition, it promoted a ferromagnetic (FM) order, which was attributed to both the crystal distortion and Dzyaloshinskii-Moriya interaction. For doped samples, an increase in real permittivity values was observed, and reduced with the increase of frequency. This in good agreement with the Maxwell-Wagner effect.

Keywords: YFeO3; Bismuth doped YFeO3; high-energy ball milling; ferromagnetic; dielectric; multiferroic

1. Introduction Multiferroic materials are those that exhibit at least two of three ferroic orders: Ferroelectricity, ferromagnetism, and ferroelasticity [1]. Multiferroic that combines ferromagnetic and ferroelectric behaviors, also known as magnetoelectric multiferroic, is quite rare compared to other multiferroic materials., However, there has been considerable scientiﬁc interest for its potential applications in electronic systems, especially in storage devices for recording and reading information [2–4]. However, there are still many design challenges for multiferroics materials, highlighting that this behavior is exhibited only at low temperature [5]. Bismuth ferrite (BiFeO3) is the ﬁrst generation of multiferroic materials that combine in a single phase ferroelectric and antiferromagnetic behavior at room temperature [6,7]. Furthermore, it presents many issues due to the formation of secondary phases that provide a high leakage current [8,9]. The second generation of multiferroic materials is = composed by perovskites with the general formula RFeO3 where R Y, Ho, Lu, Er or Sc. [10] YFeO3 is a second-generation multiferroic material. This material crystallizes in two polymorphic forms:

Materials 2019, 12, 2054; doi:10.3390/ma12132054 www.mdpi.com/journal/materials Journal of Alloys and Compounds 808 (2019) 151700

Contents lists available at ScienceDirect

Journal of Alloys and Compounds

journal homepage: http://www.elsevier.com/locate/jalcom

Magnetic and dielectric characterization of xBiFeO3:(1-x)SrFe12O19 multiferroic composites

J.P. Martínez-Perez a, A.M. Bolarín-Miro a, F. Pedro-García a, C.A. Cortes-Escobedo b, A. Barba-Pingarron c,F.Sanchez-De Jesús a, * a Area Academica de Ciencias de la Tierra y Materiales, Universidad Autonoma del Estado de Hidalgo Mineral de la Reforma, 42184, Hidalgo, Mexico b Instituto Politecnico Nacional, Centro de Investigacion e Innovacion Tecnologica, 02250, Ciudad de Mexico, Mexico c Centro de Ingeniería de Superﬁcies y Acabados (CENISA), Facultad de Ingeniería. UNAM, Circuito Exterior, Ciudad Universitaria, 04510, Ciudad de Mexico, Mexico article info abstract

Article history: Multiferroic composites xBiFeO3:(1-x) SrFe12O19 (0.5 x 1, Dx ¼ 0.1) were produced by mixing pow- Received 3 April 2019 ders of BiFeO3 and SrFe12O19 obtained by high energy ball milling assisted with heat treatment. To study Received in revised form their multiferroic properties, the ferromagnetic, dielectric and magnetodielectric behavior was evaluated 30 July 2019 for each composite. The composites were produced using powders of BiFeO and SrFe O that were Accepted 4 August 2019 3 12 19 mixed, pressed at 800 MPa, and sintered at 700 C for 4 h. XRD analysis confirms the presence of both Available online 5 August 2019 ferroic phases, BiFeO3 and SrFe12O19, and small amounts of the secondary phase, Bi2Fe4O9 (mullite). The quantity of this secondary phase increases with the concentration of strontium hexaferrite. The rema- Keywords: ¼ ¼ Bismuth ferrite nent magnetization values are 17.9 emu/g and 2.54 emu/g for x 0.5 and x 0.9, respectively. The co- fi Strontium hexaferrite ercive eld does not change with the composition; it exhibits a nearly constant value of 5.5 kOe for all the Magnetoresistance samples containing strontium hexaferrite. The addition of strontium hexaferrite produces diminution of Dielectric the relative permittivity (xr) and dielectric losses (tan d). At 5 MHz, the composite with x ¼ 0.9 shows the Multiferroic highest relative permittivity (16.78), and a diminution of dielectric loses of 43.88% due to the higher Composite resistivity of the strontium hexaferrite. The magnetodielectric measurements showed an increase in the relative permittivity of the composites due to a reduction of the resistivity in agreement with the Maxwell-Wagner behavior when a magnetic field was applied. This study show evidence for magne- toresistive behavior by pure bismuth ferrite at room temperature, which has not been previously reported. © 2019 Elsevier B.V. All rights reserved.

1. Introduction dielectric properties and limit its performance as a multiferroic material. In this sense, the interest in producing multiferroic Bismuth ferrite (BiFeO3, BFO) has a perovskite crystal structure composites, combining ferroelectric and ferromagnetic materials, distorted in the [111] direction and crystallizes in the rhombohedral has grown. These composites are usually high energy density ma- space group R3c. Moreover, to the best of our knowledge, is the only terials that can be configured to store and release energy (electrical, single phase material which shows multiferroic behavior above magnetic and mechanical) in a well-regulated manner, making room temperature, specifically, presenting ferroelectricity and them highly useful in sensors, actuators and signal processing de- antiferromagnetism [1e3]. However, the antiferromagnetic order vices [7,8]. limits their potential applications [4]. To overcome this problem, It is worth mentioning that the strontium hexaferrite (SrFe12O19, doping with magnetic cations such as Ni or Co has been proposed HFS) phase is a known hard magnetic material with high values of [5,6]. Nevertheless, high doping concentrations destabilize its saturation magnetization (MS z 64 emu/g), coercive field rhombohedral crystal structure and, consequently, reduce its (Hc z 5 kOe) and remanent magnetization (Mr z 45 emu/g) [9]. In addition, it has a high resistivity (2 108 Ucm) [10] and high relative permittivity (εr > 100). Recently, hexaferrites have been reported as multiferroics with coexisting spontaneous electric and * Corresponding author. E-mail address: [email protected] (F. Sanchez-De Jesús). magnetic polarizations characterized by a large magnetoelectric https://doi.org/10.1016/j.jallcom.2019.151700 0925-8388/© 2019 Elsevier B.V. All rights reserved. 1708 IEEE JOURNAL OF PHOTOVOLTAICS, VOL. 9, NO. 6, NOVEMBER 2019

Effect of the TiO2 Anchoring of a Hydrophobic Ionic Liquid in a Fully Aqueous DSSC Kisiev Salgado-Castro , Irina V. Lijanova , David Jaramillo-Vigueras , and Jazmin N. Castillo-Cervantes

Abstract—This article describes the effect on the efficiency of a An example of an IL that is typically used in DSSCs is 1-Hexyl- fully aqueous dye-sensitized solar cell (DSSC) after the anchoring 3-methylimidazolium iodide (HMImI), which works at the same of the hydrophobic and halogen-free ionic liquid (IL) trioctyl- time as a solvent and as iodide supplier for the redox couple [4]. methyl ammonium dodecanedioate (DTMA) on its titanium oxide (TiO2) photo-anode surface. In comparison with nontreated Nevertheless, ILs display generally high viscosity, which lowers DTMA DSSCs, efficiency increments of 137% and 176% were the ionic mobility in comparison with organic solvents and water observed when azo dye Red Reactive 2 and N3 dye were employed as [5]; and given that redox species are the electron carriers, this in sensitizers, respectively. Since VOC and ISC were increased, it was photovoltaic terms means a reduction in the DSSC short circuit concluded that DTMA reinforced the dye-TiO2 anchoring, shifted current (ISC), and in the cell efficiency, which varies inversely negatively the levels of photo-anode conduction bands, improved electron injection, and reduced recombination losses. with the IL viscosity [4]. Regarding the laboratory fabrication process, DSSCs consist Index Terms—Aqueous dye-sensitized solar cell (DSSC), azo, traditionally of a nanosized semiconductor material of titanium ionic liquid (IL), photo-anode, surface treatment. oxide (TiO2) in the anatase phase with particle sizes generally I. INTRODUCTION below 100nm; these characteristics have given the best results concerning the dye loading process (sensitization) and electron ONIC liquids (ILs) are materials with a wide range of appli- mobility along the TiO2 film [6]–[8], which, in turn, is deposited I cations within the energetic field, where they are employed on an electrical conductive glass substrate better known as in batteries, supercapacitors, thermo-electrochemistry cells [1] indium-tin oxide (ITO) substrate or fluorine doped tin oxide and, as in the case of this article, in dye-sensitized solar cells (FTO) substrate. The deposited films are subsequently dyed or, (DSSCs), which are also known as Grätzel solar cells in honor in more precise terms, sensitized using organic or organometallic of Michael Grätzel who invented them in 1991 [2]. dyes, the later mainly based on ruthenium [9], [10]. In this consist ILs consist of cationic and anionic parts capable of remaining the photo-anode (working electrode) of the cell; on the other in the liquid phase at room or even higher temperatures, this hand, or rather, electrode, is the counter-electrode, which is made characteristic is the main reason for their wide range of appli- by platinating an ITO or FTO substrate, for example, by means cations, since their ionic nature gives them the capability of of the thermal decomposition of a hexachloroplatinic (H2PtCl6) dissolving ionic or polar compounds without displaying evapo- acid solution. For this case, platinum works as the catalyst ration nor high toxicity levels as in the case of organic solvents of the redox reactions taking place on the counter electrode [1]. Then, ILs can dissolve electro-active species (redox species) (CE) [11]. and become, for example, the electrolyte of a battery, remaining To complete the description of the cell components, the liquid at its working temperature. The electro-chemical stability medium which internally unites both electrodes, is the elec- is another advantage of the ILs, keeping their original chemi- trolyte, which consists of the solvent and the redox couple cal structure within a wide range of voltages, avoiding either (I–/ –) salts, the latter is usually iodide-triiodide molecules 3 3I reduction or oxidation, thus resisting self-degradation a higher obtained from potassium iodide (KI) or lithium iodide (LiI) number of working cycles [3]. and elemental iodide (I2) when dissolved in a solution [12]; As for DSSCs, ILs are typically used inside the electrolyte the former could be an IL, an organic solvent or water, which cell, being used as additive, solvent, and solvent-redox couple. has been used more often in DSSC during the past decade [13] and that features advantages such as no toxicity, lower cost with Manuscript received March 5, 2019; revised July 26, 2019 and August 21, respect to IL and organic solvents and better ionic mobility in 2019; accepted September 20, 2019. Date of publication October 8, 2019; comparison with ILs. However, the main drawbacks of using date of current version October 28, 2019. This article was supported in part water as a solvent are the dye desorption effect from the film by the Instituto Politécnico Nacional (IPN), SIP 20196319 and by the Center of Research and Technological Innovation. (Corresponding author: Irina V. and the reduction of dye excited-state time, which affects the Lijanova.) electron injection process, by lowering the transfer of electrons The authors are with the Instituto Politécnico Nacional CIITEC, Colonia from the dye to the TiO2 film [14], [15]. Santa Catarina de Azcapotzalco, México CP 02250, México (e-mail: kisiev@ hotmail.com; [email protected]; [email protected]; jcastilloc91@ In order to reduce the undesirable effects of water when used outlook.com). as a solvent, Murakami et al. [16] employed the hydrophobic Color versions of one or more of the figures in this article are available online compound tert-butylpyridine (TBP) dissolved in solution with at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JPHOTOV.2019.2943619 the sensitizing dye (ruthenium-based dye); increments in cell

2156-3381 © 2019 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. Materials Research. 2019; 22(3):e20180623 DOI: http://dx.doi.org/10.1590/1980-5373-MR-2018-0623

3+ F-127-Assisted Sol-Gel Synthesis of Gd2O3:Eu Powders and Films

Antonieta García Murilloa* , Víctor Hugo Colín Calderona , Felipe de Jesús Carrillo Romoa , Dulce Yolotzin Medina Velázquezb

D,QVWLWXWR3ROLWpFQLFR1DFLRQDO&HQWURGH,QYHVWLJDFLyQH,QQRYDFLyQ7HFQROyJLFD&,,7(&&HUUDGDGH &HFDWL61&RO6DQWD&DWDULQD$]FDSRW]DOFR&'0;')0p[LFR b'LYLVLyQGH&LHQFLDV%iVLFDVH,QJHQLHUtD8QLYHUVLGDG$XWyQRPD0HWURSROLWDQD$]FDSRW]DOFR$Y 6DQ3DEOR1R&3&RO5H\QRVD7DPDXOLSDV0p[LFR

Received: September 18, 2018; Revised: February 08, 2019; Accepted: February 20, 2019

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Keywords: Gd2O33OXURQLF)VROJHOSRZGHUV¿OPVHXURSLXP

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5HVHDUFK 3XEOLVKHG$SULO 3+ Sol-gel synthesis of red phosphor GdPO4-Gd3PO7:Eu : luminescence and morphology

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Journal of the Australian Ceramic Society ££² $FFHVVHV 0HWULFV

Abstract

3+ A down-conversion luminescent material GdPO4-Gd3PO7:Eu has been synthesized by Pechini sol-gel process. The XRD patterns indicated that the obtained powders have a mixed crystalline phase. An intense luminescent red emission was obtained upon excitation 275 nm. The influence of different synthesis conditions on morphology and the PL emission ratio 5 7 5 7 I( D0ௗĺௗ F2)/I( D0ௗĺௗ F1) was established.

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Acknowledgments

A. Rosas acknowledges the Conacyt (Consejo Nacional de Ciencia y Tecnología) Ph.D. scholarship.

Funding

The authors received financial support of this work from the Secretaría de Investigación y Posgrado-Instituto Politécnico Nacional projects 20180530 and 20180531 and from Centro de Nanociencias y Micro y Nanotecnologías-Instituto Politécnico Nacional experimental support.

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Instituto Politécnico Nacional, CIITEC, Cerrada CECATI S/N Col. Sta. Catarina, Alcaldía Azcapotzalco, CDMX C.P. 02250, México A. Rosas Camacho, F. Carrillo Romo & A. García Murillo

CONACYT-Facultad de Ciencias Químicas, Universidad Autónoma de Coahuila, 25000, Saltillo, Mexico J. Oliva Uc

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Correspondence to A. García Murillo.

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GH SP Sintering and hot corrosion of yttria silicate tablets in molten salts prepared by spark plasma sintering Merlina A. Navarro Villanueva, Luis A. Soto Hernández, Melquisedec Vicente Mendoza, Ángel de J. Morales Ramírez and Fernando Juárez Lopez CIITEC, Instituto Politécnico Nacional, CIITEC, Cd. de México, Mexico

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Contents lists available at ScienceDirect

Journal of Luminescence

journal homepage: www.elsevier.com/locate/jlumin

Preparation of luminescent Eu-doped yttria-silicate coupons by spark plasma sintering: Reduction from Eu3+ to Eu2+

∗ Merlina A. Navarro Villanueva, Angel de J. Morales Ramirez, Fernando Juarez Lopez

Instituto Politécnico Nacional-CIITEC, México D.F., Postal Code 02250. Mexico

ARTICLE INFO ABSTRACT

Keywords: Spark plasma sintering technique was used to densify both Eu-doped and Un-doped yttria silicate powders at Yttria-silicate temperatures in the range between 1300 and 1400 °C. Shrinkage behavior was investigated for sintering powders Sintering into a full-consolidated matrix for both undoped and doped Eu+3 yttria silicates powder. Maximum shrinkage Luminescence rate at sintering temperature of 1000 °C was determined when Eu content is present. Sintering process induced Eu2+ blue emission phase transition from X1 to X2 in both undoped and Eu-doped powder. On yttrium silicate powders, only has Eu3+ to Eu2+ reduction been observed the typical reddish emission of Eu3+ ions (centered at 612 nm), however, after the SPS process, the Eu3+ has been reduced to Eu2+, showing the typical bluish emission, at 404 and 445 nm, corresponding to the two diﬀerent atomic positions of Eu2+ at the X2 phase.

1. Introduction provides a very intense and sharp luminescence spectrum when doped into the host material. Yttria silicate ceramics are important materials due to their low In the same sense, the preparation of single-phase and fully dense thermal conductivity, low density, and good thermal shock resistance as Y2SiO5 bulk material is very diﬃcult. The synthesis of Y2SiO5 is always well at high temperature as thermal insulator is one of their outstanding accompanied with the presence of undesired compounds such as Y4.67 applications [1–9]. Recently, Y2SiO5 ceramics, as a new developed (SiO4)3O, Y2Si2O7, etc., as well as incomplete polymorph transforma- porous ceramic attracts attention as a promising high temperature tion between the low temperature phase (X1 - Y2SiO5) and high-tem- thermal protection material [10–13]. In addition to the common merits perature phase (X2 - Y2SiO5). Thus there have been number studies on of porous ceramics, Y2SiO5 also posses the advantages of ceramics, the preparation process of Si-base ceramics but the problems of the high which shows high melting point, good thermal stability, and good synthesis temperature, long production period, and low yield still need erosion resistance. Y2SiO5 has low thermal conductivity, which is lower to be solved [14–16]. In these perspectives a number plausible of stu- than most well known low thermal conductivity materials such as YSZ dies indicate that ceramics prepared via spark plasma sintering (SPS) and La2Zr2O7 [13]. Besides, there is no phase transformation can reach theoretical high densities and grain size can be retained after throughout the full operating temperature range for Y2SiO5. As for the SPS process thanks to much lower sintering temperatures than typically previous works on processing of porous Y2SiO5 ceramic, Y2SiO5 pow- are used [31–34]. SPS has allowed to sintering with excellent properties ders are generally used as the starting material [13–16]. Moreover most and to produce near-net shape turbine blades in a single step, both research activities are related to Rare Earth (Ce 3+,Eu3+, etc.) doped without subsequent thermal treatments [35,36]. Due to the inherent

Y2SiO5 crystals to be used as eﬃciently improve the high temperature simplicity of the process, this cost-eﬀective technology represents a performance of silicon-based ceramics. In the idea of luminescence breakthrough in the use of SPS to improve the performance of aircraft sensing for high temperature performance, luminescence sublayers engines [37]. However, there is a lack of literature on sintering of Yttria (doped europium or doped terbium sublayers) have been used to self- silicate [38]. To the best of our knowledge, no systematic investigation indicate the delamination or the spallation in TBCs (Thermal Barriers has yet been reported in this matter. The process being investigated is to Coating) [17–22]. Recently, Rare Earth oxides have been introduced prepare of yttria silicate powder by sol-gel technique and subsequently into ceramics as a temperature sensor indicator [23–29]. The emission sintering via SPS. Initial results introducing the sol-gel process have 3+ spectrum of Eu has been used to monitor the phase structure of ZrO2 been presented in Ref. [39] and the present work is only devotes to the 3+ [30]. Eu ion is one of the most typical luminescent Rare Earth which study of sintering behavoir of Y2SiO5 ceramic in the range temperature

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%HQHPpULWD8QLYHUVLGDG$XWyQRPDGH3XHEOD)DFXOWDGGH,QJHQLHUtD4XtPLFD$Y6DQ&ODXGLR\ 6XU&LXGDG8QLYHUVLWDULD&RO6DQ0DQXHO3XHEOD3XH0p[LFR ,QVWLWXWR0H[LFDQRGHO3HWUyOHR*HUHQFLDGH,QJHQLHUtDGH5HFXSHUDFLyQ$GLFLRQDO(MH&HQWUDO /i]DUR&iUGHQDV1R&RO6DQ%DUWROR$WHSHKXDFDQ&LXGDGGH0p[LFR0p[LFR ,QVWLWXWR3ROLWpFQLFR1DFLRQDO&,,7(&&HUUDGD&HFDWL61&RORQLD6DQWD&DWDULQD$]FDSRW]DOFR 0p[LFR')0p[LFR ,QVWLWXWRGH&LHQFLDV%HQHPpULWD8QLYHUVLGDG$XWyQRPDGH3XHEODVXU3XHEOD 0p[LFR (PDLOQYLFWRUR#LPSP[ 19/LNKDQRYD R[RFWDYLR#\DKRRFRPP[ 22OLYDUHV;RPHWO Received: $SULO Accepted: -XQH Published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ο ιୟୢୱ ο ιୟୢୱDQGοιୟୢୱሻ7KHVXUIDFHFKDUDFWHUL]DWLRQRIWKHVDPSOHVSURWHFWHGZLWK&,VZDVFDUULHGRXWE\ PHDQVRIWKH0|VVEDXHUWHFKQLTXHZKLFKKHOSHGWRFRQFOXGHWKDWWKHPDLQFRUURVLRQSURGXFWVZHUH UR]HQLWHJRHWKLWHDQGDNDJDQHLWHOHSLGRFURFLWH)LQDOO\WKHFRUURVLRQLQKLELWLRQPHFKDQLVPSHUIRUPHG E\WKH,/VLVSURSRVHG .H\ZRUGV ,RQLF OLTXLG $,6, FDUERQ VWHHO 6XUIDFH DQDO\VLV (OHFWURFKHPLFDO WHFKQLTXHV 0|VVEDXHU Received: 9 May 2018 | Revised: 31 July 2019 | Accepted: 8 August 2019 DOI: 10.1111/cote.12429

ORIGINAL ARTICLE

Extraction of reactive dyes from aqueous solutions by halogen‐ free ionic liquids

1CIITEC, Instituto Politécnico Abstract Nacional, Cerrada Cecati S/N, Colonia Santa Catarina de Azcapotzalco, CDMX, Dyes are commonly used in various industries and unfortunately many of them are México discharged into water bodies, causing environmental problems. In the current study, 2 Programa de Investigación y three hydrophobic, halogen‐free ionic liquids were synthesised and their capability Posgrado, Instituto Mexicano del Petróleo, CDMX, México as extracting agents was evaluated using four reactive dyes (CI Reactive Blue 4, CI 3Facultad de Ingeniería Reactive Black 5, CI Reactive Orange 16 and CI Reactive Red 2). The ionic liquids, Química, Benemérita Universidad immiscible with the aqueous phase, could extract the reactive dyes from aqueous so- Autónoma de Puebla, Ciudad Universitaria, lutions, withdrawing the same amount of weight. The effects of pH and temperature Puebla, México on the extraction process were also studied. Trioctylmethyl ammonium ethylenedi- Correspondence aminetetraacetate displayed a high extraction efficiency (99%), where only 33 mg Irina Victorovna Lijanova, CIITEC, Instituto Politécnico Nacional, Cerrada of ionic liquids extracted 50 mg of CI Reactive Blue 4. Fourier Transform–infra- Cecati S/N, Colonia Santa Catarina de red spectroscopy was used to screen the interaction between the ionic liquid and CI Azcapotzalco, CDMX 02250, México. Reactive Blue 4 during the extraction stage. Email: [email protected]

Funding information SIP IPN, Grant/Award Number: 20196319

1 | INTRODUCTION photosynthetic activity.12,13 Some of the degradation products are aromatic rings and aryl amides, which are frequently more Dyes are extensively used in the food, cosmetics, textiles and carcinogenic and toxic than basic compounds.14-17 paper industries with the purpose of adding colour to prod- Different methods are employed to remove azo dyes from ucts.1-3 These compounds are part of the wastewater problem aqueous solutions: biological and physical (including membrane because most dyes are synthetic and based on complex aro- filtration, adsorption, coagulation, flocculation, precipitation, matic structures that make them stable and resistant to bio- reverse osmosis and ion exchange), chemical (oxidation and degradation; they may also be toxic, in addition to the huge ozonation) and electrochemical processes.18-20 For example, in water volumes used in the dyeing process.4,5 2014, Adebayo et al modified lignin aluminum and manganese It has been estimated that more than 10 000 commercial chemically, and the obtained compounds were used for the ab- dyes are turned to account and close to 0.7 million tons of sorption of Procion Blue MX‐R (CI Reactive Blue 4), where the these substances are synthesised yearly,6,7 of which almost maximum amounts of Procion Blue adsorbed by carboxy‐meth- 50% are azo dyes.8 In the textiles industry, of the total dye in- ylated lignin (CML), CML‐aluminium and CML‐manganese at take, ca. 10 to 15% of used dyes remain in the dyebaths, and 25°C were 73.52 and 55.16 mg/g, respectively.12 Another ex- are eventually discharged along with wastewater effluents.9-11 ample is the study by Akar in 2010, where fungal biomass was The presence of dyes in natural aquatic recipients can affect modified with cetyltrimethyl ammonium bromide (CTAB) in a water transparency, and it has been demonstrated that they affect biosorption application for the decolorisation of CI Reactive Red

Coloration Technology. 2019;135:417–426. wileyonlinelibrary.com/journal/cote © 2019 The Authors. Coloration Technology © 2019 | 417 Society of Dyers and Colourists Journal of Molecular Liquids 279 (2019) 267–278

Contents lists available at ScienceDirect

Journal of Molecular Liquids

journal homepage: www.elsevier.com/locate/molliq

Effect of organic anions on ionic liquids as corrosion inhibitors of steel in sulfuric acid solution

Natalya V. Likhanova a, P. Arellanes-Lozada b, O. Olivares-Xometl b,⁎, H. Hernández-Cocoletzi b, Irina V. Lijanova c, Janette Arriola-Morales b, J.E. Castellanos-Aguila d a Instituto Mexicano del Petróleo, Gerencia de Ingeniería de Recuperación Adicional, Eje Central Lázaro Cárdenas No. 152, Col. San Bartolo Atepehuacan, 07730 Ciudad de México, Mexico b Benemérita Universidad Autónoma de Puebla, Facultad de Ingeniería Química, Av. San Claudio y 18 Sur, Ciudad Universitaria. Col. San Manuel, 72570 Puebla, Pue, Mexico c Instituto Politécnico Nacional, CIITEC, Cerrada Cecati S/N, Colonia Santa Catarina, Azcapotzalco, México D.F. 02250, Mexico d Universidad Autónoma de Guanajuato, Departamento de Estudios Multidisciplinarios, Av. Yacatitas, S/N Col. Yacatitas, Yuriria, 36940 Guanajuato, Mexico article info abstract

Article history: Two new ionic liquids (ILs), N-ethyl-N,N,N-trihexylammonium adipate (CPA6) and N-ethyl-N,N,N- Received 25 September 2018 trioctylammonium ethyl sulfate (ESA8), were synthesized and their chemical structures were determined by Received in revised form 4 December 2018 1 13 Hand C NMR. The corrosion inhibition effect of the ILs on API-X60 steel in 1 M H2SO4 was studied by weight Accepted 23 January 2019 loss, Tafel polarization curves and polarization resistance. The experimental results show that the ILs were Available online 25 January 2019 adsorbed on API-X60 steel and blocked surface active sites, reducing the corrosion rate of the metallic substrate. The ILs behaved as mixed-type corrosion inhibitors and their adsorption process obeyed the Langmuir isotherm Keywords: Corrosion inhibitor model. The adsorption phenomenon was studied by means of the XPS, DRIFT and SEM/EDS techniques. Quantum Ionic liquid chemical parameters were obtained from the studied ILs, calculated in vacuum and water systems, and correlated Carbon steel with the experimental results. The effect of organic anions on the ILs was analyzed and it was concluded that the

Sulfuric acid ethyl sulfate anion presented better corrosion inhibition properties than the adipate anion; therefore, ESA8 was a

1. Introduction that does not provide information on the inhibition mechanism. On the other hand, environmental regulations aimed at limiting the use of In the oil industry, the use of aqueous acid media is necessary for dif- chemical substances due to their toxic and/or harmful effect on nature ferent ends such as the restoration and maximization of the productiv- have promoted the development and use of green CIs [9,10]. In the pres- ity of mature oil wells through an acidification process and the ent work, encouraged by the problem described before, ionic liquids elimination of muds by using acid solutions in recently drilled wells be- (ILs) were synthesized and evaluated as alternative green CIs [11]. fore their exploitation [1–3]. Notwithstanding, these acid media pro- ILs are salts with low melting points and unique physicochemical voke an excessive corrosion attack of metal structures, especially properties that have made possible their outstanding application in dif- hydrochloric and sulfuric acids [1,2]. For decades, this sector has imple- ferent scientific fields [12–15]. More specifically, their use as CIs has mented diverse control methods against corrosion in order to diminish been an important subject matter due to the desired properties that the damage of metal structures, thus reducing direct and indirect costs these compounds can possess: high inhibition efficiency, chemical and [4]. The extreme acidic corrosion conditions present in this sector thermal stability, low toxicity, and good chemical solubility, among have encouraged the development of corrosion control technology others [11,16]. The design of new ILs for their application as CIs takes that has been transferred to other industrial sectors where corrosion ef- place according to the chemical properties of functional groups such fects are not that serious such as acid pickling, industrial cleaning and as high electronegativity heteroatoms, long alkyl chains and double acid descaling [5–7]. In this sense, a corrosion control method that is and triple bonds [17]. in general economical, feasible and easy-to-be-applied is the use of cor- On the other hand, quaternary ammonium derivatives used to in- rosion inhibitors (CIs) [8]. Despite the wide research field devoted to the hibit the corrosion of ferrous materials in acid media have drawn special use of CIs, their application is in most cases a trial-and-error practice attention due to high inhibition efficiency values (η), as shown in Table 1. Studies on this matter state that ammonium derived com- η ⁎ Corresponding author. pounds inhibit corrosion very effectively, reaching values above E-mail address: [email protected] (O. Olivares-Xometl). 90%; such effectivity is related to the adsorption capacity displayed by

Effect of the TiO2 Anchoring of a Hydrophobic Ionic Liquid in a Fully Aqueous DSSC Kisiev Salgado-Castro , Irina V. Lijanova , David Jaramillo-Vigueras , and Jazmin N. Castillo-Cervantes

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Contents lists available at ScienceDirect

Optical Materials

journal homepage: www.elsevier.com/locate/optmat

Synthesis of luminescent terbium-thenoyltriﬂouroacetone MOF nanorods for green laser application

ARTICLE INFO ABSTRACT

sensors

Article System for Face Recognition under Different Facial Expressions Using a New Associative Hybrid Model Amαβ-KNN for People with Visual Impairment or Prosopagnosia

MoisésMárquez-Olivera 1, Antonio-Gustavo Juárez-Gracia 1,*, Viridiana Hernández-Herrera 2,*, Amadeo-José Argüelles-Cruz 3,* and Itzamá López-Yáñez 4 1 CICATA Unidad Legaria, Instituto Politécnico Nacional, Av. Legaria No. 694 Col. Irrigación, CDMX 11500 Mexico City, México; [email protected] 2 CIITEC, Instituto Politécnico Nacional, Cerrada Cecati s/n Col. Sta. Catarina, Azc., CDMX 02250 Mexico City, México 3 CIC, Instituto Politécnico Nacional, Av. Juan de Dios Bátiz, Esq. Miguel Othón de Mendizábal, Col. Nueva Industrial Vallejo, CDMX 07738 Mexico City, México 4 CIDETEC, Instituto Politécnico Nacional, Av. Juan de Dios Bátiz, Esq. Miguel Othón de Mendizábal, Col. Nueva Industrial Vallejo, CDMX 07700 Mexico City, México; [email protected] * Correspondence: [email protected] (A.-G.J.-G.); vherná[email protected] (V.H.-H.); [email protected] (A.-J.A.-C.); Tel.: +44-55-7178-8986 (A.-G.J.-G.); +44-55-2420-5110 (V.H.-H.); +44-55-2855-8602 (A.-J.A.-C.) Received: 16 November 2018; Accepted: 10 January 2019; Published: 30 January 2019

Abstract: Face recognition is a natural skill that a child performs from the ﬁrst days of life; unfortunately, there are people with visual or neurological problems that prevent the individual from performing the process visually. This work describes a system that integrates Artiﬁcial Intelligence which learns the face of the people with whom the user interacts daily. During the study we propose a new hybrid model of Alpha-Beta Associative memories (Amαβ) with Correlation Matrix (CM) and K-Nearest Neighbors (KNN), where the Amαβ-CMKNN was trained with characteristic biometric vectors generated from images of faces from people who present different facial expressions such as happiness, surprise, anger and sadness. To test the performance of the hybrid model, two experiments that differ in the selection of parameters that characterize the face are conducted. The performance of the proposed model was tested in the databases CK+, CAS-PEAL-R1 and Face-MECS (own), which test the Amαβ-CMKNN with faces of subjects of both sexes, different races, facial expressions, poses and environmental conditions. The hybrid model was able to remember 100% of all the faces learned during their training, while in the test in which faces are presented that have variations with respect to those learned the results range from 95.05% in controlled environments and 86.48% in real environments using the proposed integrated system.

Keywords: face recognition; assistive technologies; facial expressions; impaired vision; alpha-beta associative memories; correlation matrix; k-nearest neighbors (KNN); associative memory

1. Introduction It is estimated that more than a billion people in the world live with some type of disability; that is, around 15% of the population, additionally, according to the World Health Organization (WHO) statistics [1] the percentage of people with disabilities is growing. This is mainly due to the aging of a sector of the population and the increase in chronic degenerative problems, hence the importance and impact of developing technological tools that improve aspects such as [2]:

Sensors 2019, 19, 578; doi:10.3390/s19030578 www.mdpi.com/journal/sensors