Gabriel A. López

Universidad del País Vasco / Euskal Herriko Unibertsitatea | UPV/EHU · Physics

New metal matrix composites were developed with a view to elaborating high-damping materials. These composites were produced by infiltrating a relatively high amount of Cu–Al–Ni shape memory alloy particles with soft metallic matrices. Details on the processing method as well as on the composite microstructure are given in the present paper. An inv...

Severe plastic deformation (SPD) frequently induces phase transformations like decomposition of su-persaturated solid solution, dissolution of precipitates, amorphization, nanocrystallization etc. Such diffusive phase transitions are combined with SPD-driven accelerated mass transfer. Displacive (or martensitic) phase transitions can also take plac...

This paper shows a systematic experimental and theoretical study on the temperature dependence of the infrared optical properties of pyrolytic boron nitride (pBN), from 390 to 1050 °C for wavelengths between 4 and 16 μm. The temperature dependence of these properties has never been analyzed before. The measured emissivity spectra were fitted to a d...

The stability of solar selective absorber coatings in hostile environments (e.g., humid condition, corrosive medium, longer exposure at elevated temperature) needs to be critically assessed to ensure durability of such coatings. In the present work, magnetron sputtered W/WAlN/WAlON/Al2O3-based absorber coating with a high absorptance (0.958) and lo...

The directional spectral emissivities of two V-4Cr-4Ti family alloys, candidate structural materials for fusion first wall/blanket applications, were measured between 200 ºC and their working temperatures (700−750 ºC), with and without a high-temperature treatment. Besides showing the typical metallic behavior, an increase in the emissivity after t...

Understanding thermal emissivity at high temperatures is crucial for developing efficient materials for solar thermal applications. We present a new approach for creating an efficient material for solar absorbers by developing a modified Si surface on stainless steel substrate through annealing. We prepare five samples by annealing them at five tem...

The emissivity of two unencapsulated photovoltaic cells has been measured by a direct radiometric method, between 30 and 50 °C, and indirectly at room temperature. The advantages of the angle-resolved direct method for the determination of the emissivity of the bare cell, and the challenge of using direct measurements around room temperature, are d...

A method based on infrared (IR) micro-reflectance measurements for the structural characterization of glassy nanomaterials is presented. Near-specular reflectance spectra of pressed pellets can be analyzed using a model relating the structure of silicate glasses to their dielectric response and an effective medium approximation to account for the e...

Flexible nanoporous materials are of great interest for applications in many fields such as sensors, catalysis, material separation, and energy storage. Of these, metal–organic frameworks (MOFs) are the most explored thus far. However, tuning their flexibility for a particular application remains challenging. In this work, we explore the effect of...

The present study proposes a computational fluid dynamics (CFD) modelling framework to accomplish a successful representation of combustion and heat transfer phenomena in the 2D representative radiation section of an industrial top-fired steam methane reforming (SMR) furnace containing 64 reforming tubes, 30 burners and 3 flue-gas tunnels. The fram...

Reducing the economic and environmental impact of industrial process may be achieved by the smartisation of different components. In this work, tube smartisation is presented via direct fabrication of a copper (Cu)-based resistive temperature detector (RTD) on their outer surfaces. The testing was carried out between room temperature and 250 °C. Fo...

Material amorfoen arloan nanomaterial beirakaren inguruko ikerketak ardatz nagusietako bat osatzen du. Material horien propietate optikoak eta egitura molekularra aztertzeko, erabilgarria suertatzen da erreflektantzia infragorriko neurketak burutzea, izaera kualitatiboa izan ohi dutenak. Silizearen sare amorfoan rol garrantzitsua jokatzen dute Q3 e...

Hypothesis: The behavior of Heterogeneous Lyophobic Systems (HLSs) comprised of a lyophobic porous material and a corresponding non-wetting liquid is affected by a variety of different structural parameters of the porous material. Dependence on exogenic properties such as crystallite size is desirable for system tuning as they are much more facile...

Temperature-assisted densification methods are typically used in oxide-based solid-state batteries to suppress resistive interfaces. However, chemical reactivity among the different cathode components (which include a catholyte, the conducting additive, and the electroactive material) still represents a major challenge and processing parameters nee...

Pool boiling of liquid water has many practical applications in daily life and industry, including steam accumulators. Thus, pool boiling on polymeric surface coatings with nanoporous microparticle addition for boiling heat transfer coefficient (HTC) enhancement and potential for solid-solid phase change material (PCM) encapsulation have been studi...

In the research of potential solid-solid Phase Change Materials (PCMs) for their use in latent heat storage applications, tris(hydroxymethyl)aminomethane (TRIS) is pointed out as a strong candidate due to the high energetic transition that it undergoes. However, calorimetric studies demonstrate the strong subcooling at which this transition is subj...

Directional spectral emissivity measurements on a rolled aluminum sheet are reported between 423 and 823 K in vacuum. The results are compared to available literature data and to theoretical predictions, revealing the crucial role of the surface state in explaining the observed scatter of values. In particular, it is argued that the cold-rolling pr...

The multicomponent alloys with nearly equal concentration of components, also known as high entropy alloys (HEAs), were first proposed 22 years ago. The HEAs quickly became very important in materials science due to their unique properties. Nowadays, the HEAs are frequently used in energy conversion and storage applications. HEAs can consist of fiv...

High-entropy alloys (HEAs) are called also alloys without a main component or multiprincipal alloys. They consist of five, six or more components in more or less equal proportions and possess unique properties. Several dozens of thousands of publications have already been devoted to bulk HEAs, while HEA coatings are just beginning to develop. More...

Non-contact temperature measurement is very important for the control and inspection in different sectors of industry involving harsh environments, and an accurate measurement depends crucially on the emissivity determination. This work compares two possible methodologies to obtain accurate temperatures. Firstly, the emissivity is rigorously charac...

Petronor aims to monitor the surface temperature of the tubes inside a high temperature reforming furnace to avoid failures that could result in unplanned plant shutdowns. For this purpose, a thermographic camera has been installed in the furnace wall. However, the temperature readings obtained from the images provided by the camera include several...

In this review, we analyze the structure of multicomponent alloys without principal components (they are also called high entropy alloys-HEAs), containing not only metals but also hydrogen, nitrogen, carbon, boron, or silicon. In particular, we discuss the phenomenon of grain boundary (GB) wetting by the melt or solid phase. The GB wetting can be c...

In this review, the phenomenon of grain boundary (GB) wetting by the second solid phase is analyzed for the high entropy alloys (HEAs). Similar to the GB wetting by the liquid phase, the GB wetting by the second solid phase can be incomplete (partial) or complete. In the former case, the second solid phase forms in the GB of a matrix, the chain of...

In this review, the phenomenon of grain boundary (GB) wetting by melt is analyzed for multicomponent alloys without principal components (also called high-entropy alloys or HEAs) containing titanium. GB wetting can be complete or partial. In the former case, the liquid phase forms the continuous layers between solid grains and completely separates...

Shape memory alloys (SMAs), in comparison to other materials, have the exceptional ability to change their properties, structures, and functionality, depending on the thermal, magnetic, and/or stress fields applied[...]

The NPG–TRIS binary system (NPG = (CH3)2C(CH2OH)2 = 2,2-dimetyl-1,3-propanodiol; TRIS = NH2C(CH2OH)3 = 2-Amino-2-(hydroxymethyl)-1,3-propanediol) was intensively investigated as a thermal energy storage system, due to the reversibility of its phase transitions and their associated energy. An adapted methodology was applied to precisely quantify its...

The infrared emittance of single-crystal rutile TiO2 has been measured from room temperature to 2000 K in dry air for two polarization states. A very strong thermally induced opacification phenomenon has been found, with the sample being completely opaque in the near-infrared range several hundred K before its melting point. A large contribution fr...

The present study proposes an optimized computational fluid dynamics (CFD) modelling framework to provide a complete and accurate representation of combustion and heat transfer phenomena in the radiation section of an industrial top-fired steam methane reforming (SMR) furnace containing 64 reforming tubes, 30 burners and 3 flue-gas tunnels. The fra...

Estimating the temperature of hot emissive samples (e.g. liquid slag) in the context of harsh industrial environments such as steelmaking plants is a crucial yet challenging task, which is typically addressed by means of methods that require physical contact. Current remote methods require information on the emissivity of the sample. However, the s...

Aluminioaren propietate optikoen inguruko ezagutza garatzea beharrezkoa da termografia eta pirometria tekniketan, zeinak aluminioaren ekoizpena eta saiakuntzak optimizatzeko funtsezkoak diren. Hori dela eta, aluminioaren emisibitatearen neurketa direkzionalak egin dira espektro infragorrian, hainbat tenperaturatarako. Metalen erradiazio teoriarekin...

Neopentylglycol (NPG) and tris(hydroxymethyl)aminomethane (TRIS) are promising phase change materials (PCMs) for thermal energy storage. These latent-heat based materials undergo reversible solid-solid phase transitions characterized by high enthalpy change (119,4 J/g for NPG and 280,7 J/g for TRIS). However, a desirable property of latent heat sto...

The spectral directional emissivity of Eurofer 97 is reported between 423 and 873 K for two surface states. Total hemispherical data has been calculated by numerical integration of the measured data and compared to the theoretical predictions based on electrical resistivity data. A semi-quantitative agreement between measured emissivity data and pr...

Phase Change Materials (PCM) are nowadays in the state-of-the-art of the Thermal Energy field since they are able to store/release energy isothermally. Within the PCMs, solid-solid transitions are becoming promising solutions for storing energy with the advantage over the solid-liquid transitions of not to deal with liquids in the up-scale prototyp...

Phase Change Materials (PCMs) are nowadays key solutions for thermal energy storage (TES). These latent heat-based storage materials have high storage density and an isothermal operation temperature. Globular-shape polyols as neopentylglycol, pentaerythritol or pentaglycerol have been studied as potential TES systems due to the different phase tran...

This work addresses the thermographic temperature monitoring in a high temperature industrial environment (800-1000 ºC). Specifically, Petronor Innovación aims to monitor the tube surface temperature of a reforming furnace to avoid failures that could result in unplanned plant shutdowns. The main drawback lies in the current absence of algorithms o...

We present pygiftgenerator , a python module for systematically preparing a large number of numerical and multiple-choice questions for Moodle-based quizzes oriented to students’ formative evaluation. The use of the module is illustrated by means of examples provided with the code and drawn from different topics, such as mechanics, electromagnetism...

This work reports on the upgrades made to the direct emissivity measurement facility of the University of the Basque Country (UPV/EHU). The instrumental improvements consist of, among others, a high-vacuum system and a wider temperature range (300−1273 K). Methodological developments include a refined measurement equation with updated parameters an...

We present pygiftgenerator, a python module for systematically preparing a large number of numerical and multiple-choice questions for Moodle-based quizzes oriented to students' formative evaluation. The use of the module is illustrated by means of examples provided with the code and they cover topics from Mechanics, Electromagnetism, Thermodynamic...

Neopentylglycol (NPG) and tris(hydroxymethyl)aminomethane (TRIS) are promising phase change materials (PCMs) for thermal energy storage (TES) applications. These molecules undergo reversible solid-solid phase transitions that are characterized by high enthalpy changes. This work investigates the NPG-TRIS binary system as a way to extend the use of...

Efficiency is a critical parameter for a solar cell to be successful and is closely related to the working temperature of the cell. In turn, the temperature can be related to the infrared emissivity, the parameter that governs the thermal radiative properties of a body. In particular, the importance of infrared emissivity in a solar cell is essenti...

The total hemispherical emissivity of materials used in the solar energy industry is a critical parameter in the calculation of the radiative thermal losses and material efficiency, especially in solar thermal collector absorbing surfaces. This is because the radiative heat losses have a significant economic impact on the final cost of the electric...

Phase Change Materials (PCMs) are nowadays key solutions for the thermal energy storage (TES) deficiencies. These latent heat-based storage materials have high storage density and an isothermal operation temperature. Globular-shape polyols as neopentylglycol, pentaerythritol or pentaglycerol have been studied as potential TES systems due to the dif...

This work reports on the upgrades made to the direct emissivity measurement facility of the UPV/EHU. The instrumental improvements consist of, among others, a high-vacuum system and wider temperature range (300-1273 K). Methodological developments include a refined measurement equation with updated parameters and a reworked ISO-compliant uncertaint...

Going one step further in the use and impact measurement of new strategies to improve the teaching-learning process during lecturing General Physics courses, the current contribution reports the last results/observations obtained by the authors on the combination of simple classroom experiments with active methodologies and new technologies (media)...

In this study, the effect of isothermal aging on the thermoelastic martensitic transformation and microstructure of the as-quenched Cu–12Al–3.5Ni–0.7Ti–0.05RE (RE = Ce, La) high temperature shape memory alloy was studied. The results showed that the alloy microstructure and martensitic transformation are strongly influenced by the aging temperature...

We report an experience where first year students of the subject “General Physics” must model a leisure event observable in daily life using simple concepts already studied. Considering students’ different backgrounds, one of the aims of this activity is to motivate and engage them by showing that the Physics they learn is able to explain many simp...

La radiometría o termografía infrarroja se postula desde hace tiempo como ensayo no destructivo muy interesante por su capacidad de automatización, control del 100 % del proceso, independencia del operario, etc. Sin embargo, hay varios factores de gran influencia en los efectos térmicos a registrar que deberán ser tenidos en cuenta a la hora de dis...

The directional spectral emissivities of four new copper-alloyed spinel coatings for concentrated solar power applications were measured up to 800 °C and compared Pyromark 2500 ® , deposited in the same conditions on Inconel 625. Reproducible results were found for all coatings at all temperatures, with similar spectral features at working temperat...

In this study a Cu–12wt%Al–3wt%Ni–0.6wt%Ti + RE high temperature shape memory alloy, where RE denotes the rare earth doping elements, was prepared by vacuum arc melting and characterized by means of scanning electron microscopy, field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction at room and elevated tem...

The mid-infrared (3-22 μm) emissivity of high-purity Ni has been studied in its pure state, during an isothermal oxidation in air at 730 °C and in the fully oxidized state. Measurements in pure Ni were performed in Ar between 200 and 800 °C and a change of slope in the temperature dependence of the total normal emissivity around its Curie temperatu...

CSP (Concentrated Solar Power) plants technologies use the concentration of solar energy on a receiver to produce heat and then electricity by a thermodynamical process. A solar absorber material is used to convert the energy carried by light into heat. This type of material works at high temperatures (up to 1000 °C) under a highly concentrated sol...

High-accuracy thermal emission spectroscopy offers certain advantages over other infrared surface spectroscopic techniques. This paper demonstrates the sensitivity and versatility of this method in the study of structural phase transitions. To that end, the Zn-3%Mg-4%Al (mass %) alloy has been used, as it possesses a first-order structural phase tr...

Emisibitate infragorria da materialen propietate termofisikoa. Erradiazio elektromagnetikoa igortzeko materialek daukaten ahalmena adierazten du parametro horrek. Eguzki-energiaren industrian erabiltzen diren materialen emisibitatea neurtzea oso garrantzitsua da materialen eraginkortasuna handitzeko; erradiazio bidez gertatzen diren bero-galeren ka...

The multistage martensitic phase transformation of a polycrystalline NiTi shape-memory alloy (50.3 at. %Ni–49.7 at. % Ti) has been studied by means of calorimetric measurements. After a conventional thermal treatment followed by successive thermal cycles, the initial two-step forward transformation splits into four-overlapping stages. However, the...

The microstructure and phase composition of Al/Ti/Al interfaces with respect to their localization were investigated. An aluminum-flyer plate exhibited finer grains located close to the upper interface than those present within the aluminum-base plate. The same tendency, but with a higher number of twins, was observed for titanium. Good quality bon...

Please get a copy of the full text at the publisher's website (http://scripts.iucr.org/cgi-bin/paper?S2052520617001652). A mullite single crystal with composition Al 4.84 Si 1.16 O 9.58 (2) exhibiting sharp satellite reflections was investigated by means of X-ray diffraction. For the refinement of a superspace model in the superspace group Pbam (α0...

We describe an experimental method and a theoretical framework for the study of the optical properties of ceramics at high temperature. We show the capability of this method by measuring and interpreting the infrared emissivity of two boron nitride (BN)-based materials. Knowledge of the infrared optical properties of these materials is necessary fo...

The Moodle platform has been used to put into practice an ongoing evaluation of the students’ Physics learning process. The evaluation has been done on the frame of the course General Physics, which is lectured during the first year of the Physics, Mathematics and Electronic Engineering Programmes at the Faculty of Science and Technology of the Uni...

Cu-Al-based shape memory alloys are firm candidates to be used up to 473 K. The main limiting aspect is the activation of diffusion processes in the metastable austenite phase, which drive the alloy decomposition. In the present work the study of short-distance diffusion processes has been approached by internal friction. A relaxation peak has been...

High pressure torsion (HPT) has been used for the severe plastic deformation (SPD) treatment of molten Fe–12.3 at% Nd–7.6 at% B alloy (5 GPa, 1 rpm, 5 rot, room temperature). After HPT the microstructure contained the nanograins of the ferromagnetic Nd2Fe14B phase embedded in the amorphous matrix with uniform composition. It is different to the com...

A 4x4 array of square cross-section micro-pillars was milled by focused ion beam technique on an [001] Cu-Al-Ni shape memory alloy single crystal. All pillars in the array were tested in nano-compression using an instrumented nanoindenter. The micro-pillars superelastic response was tested over hundreds cycles on all pillars and over thousands on t...

High-pressure torsion has been successfully applied to polycrystalline Cu–Al–Ni shape memory alloys that had been prepared by a powder metallurgy methodology. The samples before and after high-pressure torsion were characterized by optical and electron microscopy and differential scanning calorimetry. After high-pressure torsion the alloys became u...

In the present work we have studied a high temperature Ru-50Nb (at.%) shape memory alloy using a mechanical spectrometer able to work in the temperature range from 473 to 1723K. We have investigated two internal friction peaks, as well as the dynamic modulus variation, linked to the martensitic transformations in the range from 573K to 1473K. In ad...

Powder La2CoMnO6 double perovskite was synthesized by the solid-state reaction method, and its crystal structure was investigated by (mode-crystallography) Rietveld analysis using X-ray and neutron powder diffraction data. La2CoMnO6 material is monoclinic perovskite at room temperature , adopting the space group P21/n (a − a − b +), a ≈ b ≈ √ 2a p...

Na0.5K0.5NbO3 has been synthesized by the conventional solid-state reaction process. The crystal structures and phase transitions, at low and high temperature, determined from the Rietveld refinements of X-ray and neutron powder diffraction data are reported. The structure evolution of Na0.5K0.5NbO in the temperature range from 2 to 875K shows the...

Superelastic behavior at nano-scale has been studied along cycling in Cu-Al-Ni shape memory alloy micropillars. Arrays of square micropillars were produced by focused ion beam milling, on slides of [001] oriented Cu-Al-Ni single crystals. Superelastic behavior of micropillars, due to the stress-induced martensitic transformation, has been studied b...

Grain boundary and surface segregation of Bi in Cu were investigated under identical conditions. Cu bicrystals containing deliberately made internal cavities at the interfaces were doped with Bi, annealed at different temperatures, and broken in an Auger microprobe. The segregation level at the free surfaces was found to be higher than that at the...

The effect of TiO2 nanoparticle addition on mechanical properties of low carbon steel and the phases originated from this inoculation were investigated. Equilibrium phases were estimated by means of thermodynamic modeling and the results were compared with further microscopy characterization. Both techniques confirmed the dissolution of TiO2 nanopa...

In the last decades, issues on absorption of vibration energy have attracted much attention in several technological sectors like vibration isolation in high-precision electronics, building protection in civil engineering, etc.. In the past, mainly polymers were used as high-damping materials, but the increasingly demanding working conditions (e.g....

Shape memory alloys offer the highest workout per unit of volume, in comparison with other functional materials. As a consequence they become more competitive when decreasing the size of the device, and then they are targeted for potential applications as sensors and actuators in Micro Electro-Mechanical Systems (MEMS). Recently it has been shown t...

Ferric precipitates in the water column at the San Telmo acidic mine pit lake in the Iberian Pyrite Belt, southwest Spain, have been studied by scanning electron microscopy, energy dispersive X-ray spectrometry, X-ray diffraction, X-ray fluorescence, inductively coupled plasma mass spectrometry and other complementary techniques. These Fe(III) prec...

Small grains of an intermetallic phase with an approximate composition Cu(In,Sn) 2 were observed in a metal matrix composite obtained from powders of a Cu–Al–Ni shape-memory alloy and an In–Sn matrix alloy. Samples of this composite were prepared for transmission electron microscopy and the crystal structure of the intermetallic phase was carefully...

Materials able of changing their own properties in response to certain external stimulation are known as "intelligent materials". Shape Memory Alloys (SMAs) are included in these materials due to their thermo-mechanical properties of super-elasticity, pseudo-elasticity, and one-or two-way shape memory effects, which are consequence of a thermo-elas...

@font-face { "Times"; }p.MsoNormal, li.MsoNormal, div.MsoNormal { margin: 0cm 0cm 0.0001pt; font-size: 12pt; ""; }div.Section1 { page: Section1; } Now a day, high damping materials have attracted the scientific and technological interest, because of their useful applications. Indeed, the use of high damping materials may allow to decrease the aco...

Single crystals of the mixed valence compound Pb3Ni1.5Mn5.5O15 were successfully grown. Polarized Raman spectroscopy revealed that they belong to the point group D3d, in accordance with single-crystal x-ray diffraction data which were refined within the trigonal space group (No. 165), with lattice parameters a = 9.941(3) Å and c = 13.543(3) Å. Str...

New high-damping metal matrix composites have been developed, by embedding powders of Cu–Al–Ni shape memory alloys with two different metallic matrices (In–10 wt.%Sn and In–Sn eutectic alloys). The damping properties have been characterized using a sub-resonant torsion pendulum. High damping values were obtained in a wide range of temperature. In t...

High-damping materials have attracted much attention to solve problems such as acoustic pollution, nano-scale vibration isolations in electronic industry, vibration damping in civil engineering, etc. Shape memory alloys (SMAs), which intrinsically present high-damping capacity, are considered as alternative materials to the traditionally used polym...

Recently, absorption of vibration energy by mechanical damping has attracted much attention in several fields such as vibration reduction in aircraft and automotive industries, nanoscale vibration isolations in high-precision electronics, building protection in civil engineering, etc. Typically, the most used high-damping materials are based on pol...