Revistas
Autores:
Pérez, B. (Autor de correspondencia); Bergara, A.; Bre, A.; et al.
Revista:
NUCLEAR MATERIALS AND ENERGY
ISSN:
2352-1791
Año:
2022
Vol.:
30
Págs.:
101124
Flow Channel Inserts (FCIs) are key elements in the high temperature DCLL blanket concept since they provide the required thermal insulation between the He-cooled structural steel and the hot PbLi flowing at a maximum temperature of 700 ?, and the necessary electrical insulation to minimize magnetohydrodynamic (MHD) effects. In this paper, the use of SiC-sandwich material for FCIs consisting of a porous SiC core (thermal and electrical insulator) covered by a dense Chemical Vapor Deposition (CVD) SiC layer (protection against PbLi infiltration) has been studied. Lab-scale FCI prototypes were produced by the gel casting method and characterized in terms of thermal and electrical conductivities (the latter before and after exposure to ionizing radiation) and flexural strength. Corrosion tests under flowing PbLi at 500-700 ?& nbsp;in presence of a magnetic field up to 5 T were performed obtaining promising results regarding the reduction of MHD pressure drop and the compatibility of SiC and PbLi under dynamic conditions. Additionally, thermomechanical finite elements simulations were performed in a 3D channel geometry to identify black spots regarding thermal stresses.
Autores:
Bocanegra-Bernal, M. H.; García-Reyes, A.; Domínguez-Ríos, C.; et al.
Revista:
JOURNAL OF ALLOYS AND COMPOUNDS
ISSN:
0925-8388
Año:
2020
Vol.:
818
Págs.:
152840
Zirconia (ZrO2) and alumina (Al2O3) ceramics are used in technical and biomedical applications. The great challenge in ZrO2-based ceramics, to improve their mechanical properties, is to take control of the stress-activated t -> m martensitic transformation, since this transformation causes accelerated low-temperature degradation (LTD) under ambient conditions, leading to premature failure by the presence of water or its vapor. Dispersion of Al2O3 in a ZrO2 matrix, the so-called alumina toughened zirconia (ATZ), can restrain LTD of mechanical properties of zirconia, however exposure of zirconia to moisture must be avoided to suppress the t -> m transformation. In this paper, the in-situ formation of an alumina layer surrounding ATZ pieces, during sintering under the presence of graphitic compounds and a low oxygen atmosphere, is reported. The layer formation mechanism consists of the reaction of CO with Al2O3 during the heating of the specimens, where a volatile species of aluminum forms, which, on contact with the specimen surface and due to the presence of CO2, is oxidized to the non-volatile Al2O3, thus forming the surface layer. This approach improves the hydrothermal stability and enhances the possibility of applying ATZ in ceramic implants, solid oxide fuel cells, and thermal barrier coatings. (C) 2019 Elsevier B.V. All rights reserved.
Revista:
FUSION ENGINEERING AND DESIGN
ISSN:
0920-3796
Año:
2019
Vol.:
146
N°:
Part.B
Págs.:
1983 - 1987
Flow Channel Inserts (FCIs) are key elements in the high-temperature Dual Coolant Lead Lithium (DCLL) blanket, since they insulate electrically the flowing PbLi to avoid MHD effects and protect the steel structure from the hot liquid metal. SiC-based materials are main candidates for high-temperature FCIs, being a denseporous SiC-based sandwich material an attractive option. The present work is focused on the development of such a SiC-based material. On the one hand, in order to assess the suitability of the concept for FCIs, the main results of a stress analysis, MHD and heat transfer simulations are summarized. On the other hand, the experimental production of the SiC-based material is addressed, where the porous SiC core is manufactured from SiC powder by two different techniques: uniaxial pressing and gelcasting. The porosity is introduced using graphite spherical powder as a sacrificial template. After the production of the porous SiC core, a dense SiC coating of similar to 200 mu m thickness is deposited by Chemical Vapor Deposition (CVD); the coated material was tested against hot PbLi in corrosion experiments. The properties of the material in terms of thermal and electrical conductivities, flexural strength and elastic modulus were measured, with promising results for high-temperature FCIs.
Revista:
HELIYON
ISSN:
2405-8440
Año:
2019
Vol.:
5
N°:
8
Págs.:
e02311
In this study, the influence of abrasives (size and morphology) and graphite on the processing and properties of friction materials were investigated. Friction materials based on bronze matrix, graphite as solid lubricant and different abrasives (silica, mullite and zircon) were prepared following two routes. On the one hand, following the traditional P/M technology (pressing-sintering) and on the other hand, using an alternative P/M route, which consists on sintering a powder blend free deposited in a mold and subsequently cold pressing. Sinterability, microstructure and physical-mechanical properties of the processed friction materials have been studied. Tribological and wear tests were carried out on a pin-on-disc system at different loads and sliding speeds using samples of 20 mm in diameter. Results show that the influence of abrasives size is especially relevant in the alternative P/M route, where materials including fine abrasives present unsuitable properties. Graphite also plays an important role on tribological behavior, in this work it has been found that friction materials with 4 wt.% graphite have better tribological properties than those with 2 wt.% graphite, despite having lower density and mechanical resistance.
Revista:
JOURNAL OF THE EUROPEAN CERAMIC SOCIETY
ISSN:
0955-2219
Año:
2019
Vol.:
39
N°:
14
Págs.:
3949 - 3958
Porous silicon carbide (SiC) is a promising ceramic for high-temperature applications due to its unique combination of properties. In the present work, a fabrication route for porous SiC is presented using graphite spherical powder as sacrificial phase to introduce porosity. By varying the initial amount of sacrificial phase, high-performance SiC materials with porosities in the range 30-50% were manufactured and characterized in terms of microstructure, density, thermal conductivity and flexural strength. The materials were fabricated by liquid phase sintering in presence of 2.5 wt.% Al2O3 and Y2O3 as sintering additives. The results indicate that the SiO2 present in the starting SiC powders interacts with the sintering additives forming liquid phases that promote densification and weight loss. Besides, an Al-Si liquid phase is formed at higher sintering temperatures, whose contribution to densification is inhibited in presence of graphite due to the formation of Al-rich carbides.
Revista:
IEEE TRANSACTIONS ON PLASMA SCIENCE
ISSN:
0093-3813
Año:
2018
Vol.:
46
N°:
5
Págs.:
1561 - 1569
Flow channel inserts (FCIs) are the key elements in the high-temperature dual-coolant lead-lithium blanket, since in this concept the flowing PbLi reaches temperatures near 700 degrees C and FCIs should provide the necessary thermal and electrical insulations to assure a safe blanket performance. In this paper, the use of a SiC-sandwich material for FCIs consisting of a porous SiC core covered by a dense chemical vapor deposition-SiC layer is studied. A fabrication procedure for porous SiC is proposed and the resulting materials are characterized in terms of thermal and electrical conductivities (the latter before and after being subjected to ionizing radiation) and flexural strength. SiC materials with a wide range of porosities are produced; in addition, preliminary results using an alternative route based on the gel-casting technique are also presented, including the fabrication of hollow samples to be part of future lab-scale FCI prototypes. Finally, to study the corrosion resistance of the material in hot PbLi, corrosion tests under static PbLi at 700 degrees C and under flowing PbLi at similar to 10 cm/s and 550 degrees C, with and without a 1.8-2T magnetic field, were performed to materials coated with a 200-400-mu m-thick dense SiC layer, obtaining promising results.
Revista:
FUSION ENGINEERING AND DESIGN
ISSN:
0920-3796
Año:
2017
Vol.:
124
Págs.:
958 - 963
Flow Channel Inserts (FCIs) are key elements in a DCLL blanket concept for DEMO, since they provide the required thermal insulation between the He cooled structural steel and the hot liquid PbLi flowing at approximate to 700 degrees C, and the necessary electrical insulation to minimize MHD effects. In this work a SiC-based sandwich material is proposed for FCIs, consisting of a porous SiC core covered by a dense CVD-SiC layer. A method to produce the porous SiC core is presented, based on combining a starting mixture of SiC powder with a spherical carbonaceous sacrificial phase, which is removed after sintering by oxidation, in such a way that a microstructure of spherical pores is achieved. Following this technique, a porous SiC material with low thermal and electrical conductivities, but enough mechanical strength was produced. Samples were covered by a 200 mu m thick CVD-SiC coating to form a SiC-sandwich material. Finally, corrosion tests under static PbLi were performed, showing that such a dense layer offers a reliable protection against static PbLi corrosion. (C) 2017 Elsevier B.V. All rights reserved.
Revista:
CERAMICS INTERNATIONAL
ISSN:
0272-8842
Año:
2016
Vol.:
42
N°:
14
Págs.:
16417 - 16423
Zirconia-based ceramics are prone to transformation from the tetragonal phase to the monoclinic phase in the presence of moisture at low temperatures. Here, we report the formation of a protective alumina layer after conventional sintering in air for alumina toughened zirconia (ATZ) composites at 1520 degrees C using graphite as a powder bed. Alumina layers with thicknesses of 1.7 and 2.20 mu m were formed after sintering at 0 h for ATZ+15 wt% Al2O3 and ATZ+30 wt% Al2O3, respectively. A sintering time of 10 h increased the thickness of this Al2O3 layer, allowing its retention after the inevitable final polishing step in the production of real ceramic bodies. This could lead to a dramatic retardation of the t -> m ZrO2 phase transformation via the presence of alumina grains that can isolate the zirconia grains in the lattice structure, which prevents the propagation process under the most hostile hydrothermal conditions by taking advantage of the combined high hardness of alumina with the high fracture toughness of zirconia. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Revista:
CERAMICS INTERNATIONAL
ISSN:
0272-8842
Año:
2016
Vol.:
42
N°:
1
Págs.:
2054 - 2062
Multi-walled carbon nanotube (MWCNT), single-double walled carbon nanotube (SDWCNT) and single-walled carbon nanotube (SWCNT) were dispersed for the first time into alumina matrix using conventional mixing/sonication for dispersion of pristine CNTs followed by spark plasma sintering (SPS) process. The resultant composites displayed an increase of the grain size, a decrease in fracture toughness from 8% to 40% over monolithic Al2O3 and the hardness values did not change significantly with the addition of CNTs. In the light of the observed fracture surfaces in different CNT reinforced alumina composites, poor dispersion of these into ceramic matrix will lead to a decrease in fracture toughness. On the other hand, the lower ratio aspects, large surface areas of CNTs, as well as large grain size could be unfavorable to achieve high fracture toughness and the results are worse than for pure alumina questioning whether worth the effort to reinforce alumina with CNTs to obtain marginal improvement under the present conditions, although the literature has reported significant improvement of mechanical properties with alumina and other ceramics systems reinforced with CNTs, resulting from different testing techniques adopted. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Revista:
WEAR
ISSN:
0043-1648
Año:
2016
Vol.:
348
Págs.:
27 - 42
During braking, high temperatures can be generated on the contact surfaces and inside the brake pads. Solid lubricants, i.e., metal sulphides, play an important role in brake performance, but they can react, oxidise or decompose with exposure to temperature, modifying their tribological properties. This paper investigates the chemical reactions between different metal powders (Cu, Fe, Sn and Zn) and Sb2S3 that take place in a low-metallic brake pad during braking in conditions were high temperature is generated. The reaction products were characterised by SEM-EDS and the glancing XRD technique. Moreover, thermal treatments (in air and argon) of binary mixtures, containing the same weight ratio of these metal powders and Sb2S3 contained in the brake pad, were carried out and analysed via DSC-TGA and XRD techniques. The paper finds that the reaction features and reaction products depend on the temperature generated during braking, the specific combination of metal/lubricant and the atmosphere conditions (oxidant or inert). In general, the reaction products are a combination of an intermetallic (metallic antimonide) and a metal sulphide (from the metal powder), which can be found both on the surface and inside the brake pad. (C) 2015 Elsevier B.V. All rights reserved.
Revista:
CERAMICS INTERNATIONAL
ISSN:
0272-8842
Año:
2015
Vol.:
41
N°:
3
Págs.:
4569 - 4580
Zirconia-based ceramics have been introduced in biomedical applications, for example, in hip implants. Certain zirconia composites are prone to spontaneously transform from the tetragonal phase to the monoclinic phase during long-term storage in the presence of moisture at low temperatures. This phenomenon is time-dependent and can be accelerated by water or water vapour. Herein, we report strong experimental evidence of a delayed t -> m ZrO2 phase transformation in alumina-toughened zirconia (ATZ) and ATZ/multi-walled carbon nanotube (MWCNT) composites when pressureless sintered in air in a graphite powder bed. The m-ZrO2 phase in ATZ and ATZ/MWCNT composites sintered in a graphite powder bed after hydrothermal ageing for 20 h at 134 degrees C decreased by 81% and 87%, respectively, compared to an ATZ sample sintered in an alumina powder bed. The enhanced hydrothermal stability could be attributed to the formation of a thin continuous alumina protective layer covering the surface of the ceramic composites. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Revista:
JOURNAL OF MATERIALS CHEMISTRY A
ISSN:
2050-7488
Año:
2013
Vol.:
1
N°:
35
Págs.:
10173 - 10183
An innovative ionic liquid (IL)-based synthesis route was developed to obtain ZnO-based hybrid nanostructured films with a modified surface. In particular, ZnO-IL hybrid films, with thickness from 1.5 to 4.5 mu m and an appealing sponge-like morphology, were obtained from the electrochemical reduction of NO3- in ionic liquid-based electrolytes containing Zn2+. The presence of the ionic liquid moieties and/or derivatives in the as-deposited films was demonstrated by Fourier transform infra-red spectroscopy and energy dispersive X-ray spectroscopy. However, a relatively soft thermal annealing (i.e. 1 hour in air at 350 degrees C) was proved to be an effective way to remove the ionic liquid content from the samples, leading to porous ZnO films with high specific surface area. In comparison to ionic liquid-free samples, a blue shift of similar to 40 meV in the absorption onset is detected for the ZnO-PYR14TFSI hybrid films, which suggests a modification of the bandgap. Both kind of films (i.e. ZnO-IL and ZnO) were sensitized with an indoline dye, coded D358, and evaluated as photoanodes in Dye-sensitized Solar Cells (DSCs). Although less D358 was adsorbed onto ZnO-IL samples (suggesting co-adsorption of the IL and D358), a clear enhancement (by a factor of ca. 2) of the power conversion efficiency was detected in DSC based on ZnO-IL hybrid films. This improvement was mainly due to a huge increase (similar to 180 mV) in the photovoltage, which reaches values of up to 780 mV. The DSC characterization, by electrochemical impedance spectroscopy and open circuit voltage decay techniques, indicates that the photovoltage improvement is likely due to a negative displacement of the conduction band in hybrid films. Therefore, the use of metal oxide-IL hybrid anodes appears to be a promising strategy to increase the open circuit voltage of the DSCs.
Revista:
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY
ISSN:
1533-4880
Año:
2012
Vol.:
12
N°:
9
Págs.:
7529 - 7534
Nanoparticles of Co10Cu90 alloy have been prepared by sonochemical wet method. According to transmission electron microscopy, bimetallic particles with typical diameter of 50-100 nm consisting of nanocrystallites with average diameter of 15-20 nm were obtained. The samples were annealed at 300 degrees C and 450 degrees C. Zero field cooled and field cooled temperature dependences of magnetization in the temperature range of 5-400 K at 50 Oe, as well as magnetization hysteresis loops at 15, 100 and 305 K were measured by vibrating sample magnetometry. Presence of antiferromagnetic phase, most probably of the oxide Co3O4, was observed in as-prepared sample. The lowest coercivity was found for the CoCu sample annealed at 300 degrees C, whereas for as prepared sample and the one annealed at 450 degrees C it was significantly higher. The samples were additionally probed by continuous wave ferromagnetic resonance at room temperature using a standard X-band electron spin resonance spectrometer. A good correspondence between evolution of the coercivity and the microwave resonance fields with annealing temperature was observed.
Revista:
CARBON
ISSN:
0008-6223
Año:
2012
Vol.:
50
N°:
2
Págs.:
706 - 717
It is demonstrated that 0.1 wt% of multi-walled carbon nanotubes (MWCNTs) or single-walled carbon nanotubes (SWCNTs) added to zirconia toughened alumina (ZTA) composites is enough to obtain high hardness and fracture toughness at indentation loads of 1, 5, and 10 kg. ZTA composites with 0.01 and 0.1 wt% of MWCNTs or SWCNTs were densified by spark plasma sintering (SPS) at 1520 degrees C resulting in a higher hardness and comparable fracture toughness to the ZTA matrix material. The observed toughening mechanisms include crack deflection, pullout of CNTs as well as bridged cracks leading to improved fracture toughness without evidence of transformation toughening of the ZrO2 phase. Scanning electron microscopy showed that MWCNTs rupture by a sword-in-sheath mechanism in the tensile direction contributing to an additional increase in fracture toughness. (C) 2011 Elsevier Ltd. All rights reserved.
Revista:
CHEMICAL COMMUNICATIONS
ISSN:
1359-7345
Año:
2012
Vol.:
48
N°:
66
Págs.:
8255 - 8257
Thiol-functionalised silicone-oils were crosslinked with silver nanoparticles to give mechanically consistent elastomers with high self-healing power. The materials were broken into small pieces and put together in intimate contact for 24 hours at room temperature, observing a complete macroscopic healing and a quantitative recovery of compression-stress and strain.
Autores:
Bocanegra-Bernal, M.H.; Reyes-Rojas, A.; Aguilar-Elguezabal, A.; et al.
Revista:
INTERNATIONAL JOURNAL OF REFRACTORY METALS AND HARD MATERIALS
ISSN:
0263-4368
Año:
2012
Vol.:
35
Págs.:
315 - 318
We have demonstrated by X-ray diffraction a transformation from the t-ZrO2 phase into the m-ZrO2 phase by the presence of multiwall carbon nanotubes (MWCNTs) and graphite powder (GP) in zirconia toughened alumina composites sintered in air. The phase transformation does not occur in sintering under an argon atmosphere. The quantitave phase analysis was carried out by fitting the X-ray diffraction profile with the Rietveld method making use of the FullProf software. The obtained amounts of m-ZrO2 phase by the presence of GP and MWCNTs were 5% and 2.2%, respectively, at a sintering temperature of 1520 degrees C for 1 h. (C) 2012 Elsevier Ltd. All rights reserved.
Revista:
CARBON
ISSN:
0008-6223
Año:
2011
Vol.:
49
N°:
5
Págs.:
1599 - 1607
The use of multi-wall carbon nanotubes (MWCNTs) or single-wall carbon nanotubes (SWCNTs) as filler in ceramic matrices could create composites with exceptional mechanical properties. We have prepared dense monolithic alumina (Al2O3) and zirconia-toughened alumina (ZTA) composites with additions of 0.01 wt% of MWCNTs or 0.01 wt% of SWCNTs by conventional sintering and have demonstrated that the mechanical properties depend on (a) the distribution of CNTs in the matrix and (b) the interaction between the ceramic phases and CNTs. The fracture toughness of Al2O3 ceramics reinforced with SWCNTs was significantly better than those reinforced with MWCNTs. However, fracture toughness in MWCNT-reinforced ZTA increased 41% over ZTA free of the toughening agent and 44% over ZTA reinforced with SWCNTs. A well dispersed and small amount of MWCNTs was enough to produce an increase of fracture toughness in ZTA composites. (C) 2010 Elsevier Ltd. All rights reserved.
Revista:
INTERNATIONAL JOURNAL OF COMPUTER INTEGRATED MANUFACTURING
ISSN:
0951-192X
Año:
2011
Vol.:
24
N°:
4
Págs.:
338 - 351
Equipment efficiency can be measured and improved by the availability, performance and quality rates provided by the overall equipment effectiveness (OEE) metric. Because today's managers operate in a complex manufacturing scenario, measurement systems play an important role in transforming data into decisions, and this task needs to be strengthened. Although sophisticated equipment and information technology systems are available, a methodology is required for understanding and managing data in order to make timely decisions regarding improvement. Thus, improvement needs to be supported by an easy-to-understand measurement system and a cutting-edge data-collecting technique. In order to assist not only managers and operators but also students and academia, this article presents a Plug&Lean system supported by a core element, the Plug&Lean wireless device, based on total productivity maintenance (TPM) and Lean methodology for providing a reliable diagnosis of the current state of equipment, to display graphical information about the equipment performance constraints towards to direct improvements activities. The aim of the Plug and Lean wireless device is to collect accuracy data with less effort from production equipment Two case studies are discussed to illustrate the applicability of the system.
Autores:
Velasco, F.; Guzman, S.; Rabanal, M.E.; et al.
Revista:
POWDER METALLURGY
ISSN:
0032-5899
Año:
2011
Vol.:
54
N°:
1
Págs.:
59 - 66
The effect of milling on different properties of a petroleum coke has been evaluated. The material was subjected to planetary milling at two different rates (400 and 600 rev min(-1)) for different times up to 48 h. The milled material was characterised by scanning electron microscopy, X-ray diffraction, sieve analysis, thermal analysis, chemical analysis, specific surface area and compressibility has been undertaken. The results show that the milling produces a very quick loss of the crystal structure of the coke and a rapid comminution, which lead to large increases in specific surface area and compressibility losses. The coke has shown a high activity through the milling process, absorbing a great quantity of oxygen. The increase in milling time shifts its thermal decomposition to lower temperatures.
Revista:
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY
ISSN:
1533-4880
Año:
2010
Vol.:
10
N°:
7
Págs.:
4246 - 4251
Co10Cu90 nanopowder alloys have been prepared by the sonochemical wet method. In this way, Cu/Co bimetallic nanocrystallites with average diameter of 10-20 nm, presenting a homogeneous metastable solid solution of Co in Cu, were produced. Their structural characterization by X-ray diffraction, transmission electron microscopy and inductive coupled plasma-atomic emission spectrometry techniques has been used. Temperature dependences of the sample magnetization show two characteristic (blocking) temperatures associated to the typical deviation of the zero-field cooling and field-cooling magnetization curves at T, 15 and T, 310 K, respectively. This effect can be attributed to the fact that the samples consist of either superparamagnetic and/or ferromagnetic nanoparticles of different sizes. The samples were annealed at 300 degrees C and 450 degrees C and the observed evolution of their magnetic properties was explained in relation to decomposition of the metastable Co/Cu solid solution.
Revista:
INTERNATIONAL JOURNAL OF REFRACTORY METALS AND HARD MATERIALS
ISSN:
0263-4368
Año:
2010
Vol.:
28
N°:
3
Págs.:
399 - 406
This work describes the microstructure and fracture toughness of zirconia toughened alumina (ZTA) nanocomposite in which multi-wall carbon nanotubes (MWCNTs) and nanosized ZrO2 particles were used as reinforcement. The ZTA nanocomposites with additions of 0, 0.005, and 0.01 wt.% MWCNTs and 2 wt.% nanosized ZrO2 particles were pressureless sintered in an anti-oxidant sagger with graphite powder bed at 1520 degrees C during 1 h in air and then HIPed at 1475 degrees C in argon atmosphere 1 h at a pressure of 150 MPa. Relative densities ranging 94-98% were reached. In HIPed composites the hardness and fracture toughness values were increased up to similar to 17% and similar to 37%, respectively, compared to the "as sintered" composites free of carbon nanotubes. A combined fracture mode, crack deflection, pull-outs of a small amount of carbon nanotubes, and bridging effect were the mechanisms leading to the improvement in fracture toughness. (C) 2009 Elsevier Ltd. All rights reserved.