The Experts below are selected from a list of 273 Experts worldwide ranked by ideXlab platform
Nobumitsu Shohoji - One of the best experts on this subject based on the ideXlab platform.
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low temperature short time nitriding of va group metals v nb and ta in uncracked nh3 gas under heating with concentrated Solar power csp
Ciência & Tecnologia dos Materiais, 2016Co-Authors: Joao Fernandes, Luis Guerra Rosa, Teresa Magalhães, Inmaculada Canadas, Jose Rodriguez, Fernando Costa A Oliveira, Nobumitsu ShohojiAbstract:Abstract Over the last two decades, the authors have been using concentrated Solar Beam as the reaction heat source for synthesizing carbides and nitrides of d -group transition elements in view of usage of ecological renewable energy source in place of conventional heat sources using electricity or natural gas. In recent works, nitriding of VIa-group metals (Cr, Mo, W) and Fe in stream of NH 3 gas with suppressed extent of dissociation (uncracked NH 3 ) was attempted under heating with concentrated Solar Beam. It was demonstrated that mono-nitride δ-MoN of Mo and sub-nitride ɛ-Fe 2 N of Fe that are known to be impossible to synthesize in N 2 gas environment even at elevated N 2 gas partial pressure p (N 2 ) up to 300 bar were successfully synthesized by the reactions of these metals in stream of NH 3 gas under heating with concentrated Solar Beam up to 800 °C. In the present work, nitriding of Va-group metals (V, Nb and Ta) was attempted in stream of NH 3 gas under irradiation of concentrated Solar Beam. After 90 min heating in uncracked NH 3 under concentrated Solar Beam up to 800 °C, X-ray diffraction (XRD) characterization of the reaction products showed certain extent of nitriding progressed for all the specimens in spite of relatively low reaction temperature for short reaction duration.
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nitriding vi group metals cr mo and w in stream of nh3 gas under concentrated Solar irradiation in a Solar furnace at psa plataforma Solar de almeria
Solar Energy, 2015Co-Authors: Fernando Costa A Oliveira, Jorge Cruz Fernandes, Luis Guerra Rosa, Teresa Magalhães, Inmaculada Canadas, Jose Rodriguez, Nobumitsu ShohojiAbstract:Abstract Carbides and nitrides of d -group transition metals are classified as refractory hard material and their industrial importance has been recognized for long. In recent years, unique functionalities including catalytic function and superconductivity are discovered for this group of materials to raise serious attention of materials researchers and engineers to refractory carbides and nitrides as novel functional materials. Synthesis of refractory carbides and nitrides demands high temperature reaction route to consume considerable amount of electricity or gas in conventional industrial process. In view of saving cost of such conventional energy, feasibility of using concentrated Solar Beam as heat source for synthesizing carbide and nitride has been investigated by the authors since 1997. After verifying usefulness of concentrated Solar Beam as heat source for carbide forming reactions, similar attempts of employing concentrated Solar Beam as heat source for nitride synthesis were initiated recently. After brief experimental verification of nitride synthesis for IVa group metal, Ti, and Vg group metals, V, Nb and Ta, in N 2 gas environment under irradiation with concentrated Solar Beam to 2000 °C, the authors decided to undertake nitride synthesis of VIa group metals, Cr, Mo and W, as well as of Fe in stream of ammonia (NH 3 ) gas as a nitriding medium under irradiation of concentrated Solar Beam at temperatures not exceeding 1000 °C. NH 3 gas with suppressed extent of dissociation by flowing is defined empirically as uncracked NH 3 and it is proved to possess very high nitriding power to make synthesis of mono-nitride MoN of Mo coexisting with sub-nitride Mo and higher nitride Fe 2 N of Fe possible under normal pressure condition that are not possible when chemically stable N 2 gas is used as a nitriding agent. VIa-group metals including Cr, Mo and W are known to be highly resistant against nitriding. In the present report, results of nitriding in flowing NH 3 gas at a fixed flow rate 10 l/h (≈167 ml/min) under heating with concentrated Solar Beam for VIa-group metals, Cr, Mo and W, are summarized to demonstrate favorable effect of Solar Beam heating towards further enhancement of nitriding power of flowing NH 3 gas compared with the situation in conventional electric furnace in which visible light components except infra-red (IR) heat wave component are absent in the reaction system.
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low temperature nitriding of va group metal powders v nb ta in flowing nh3 gas under heating with concentrated Solar Beam at psa
Ciência & Tecnologia dos Materiais, 2015Co-Authors: Jorge Cruz Fernandes, Luis Guerra Rosa, Teresa Magalhães, F Costa A Oliveira, Inmaculada Canadas, Jose Rodriguez, Nobumitsu ShohojiAbstract:Over the last two decades, we have been using concentrated Solar Beam as the reaction heat source for synthesizing carbides and nitrides of d-group transition elements in view of usage of ecological renewable energy source in place of conventional heat sources using electricity or gas. In recent works [1,2] nitriding of VIa-group metals (Cr, Mo, W) and Fe in stream of NH3 gas with suppressed extent of dissociation (uncracked NH3) was attempted under heating with concentrated Solar Beam. It was demonstrated that mono-nitride -MoN of Mo and sub-nitride -Fe2N of Fe that are known to be impossible to synthesize in N2 gas environment even at elevated pressure p(N2) were successfully synthesized by the reactions of these metals in stream of NH3 gas under heating with concentrated Solar Beam up to 800oC. In the present work, nitriding of Va-group metals (V, Nb and Ta) was attempted in stream of NH3 gas under irradiation of concentrated Solar Beam. By up to 90 min heating in uncracked NH3 under concentrated Solar Beam up to 800oC, reaction products were identified by X-ray diffraction (XRD) analysis to be consisted of mono-nitride MN co-existent with sub-nitride M2N.
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roles of unstable chemical species and non equilibrium reaction routes on properties of reaction product a review
Journal of Surfaces and Interfaces of Materials, 2014Co-Authors: Nobumitsu ShohojiAbstract:Chemical species might be held in a state being away from equilibrium state, at least temporarily, as represented by non-graphitic carbon and gaseous ammonia NH3 with suppressed extent of dissociation by flowing. Such chemical species X in unstable state would possess chemical activity a X considerably higher than that of the same element in equilibrium (reference) state. In case of carbon, a C of amorphous carbon is higher than that of graphite (equilibrium state of C; a C = 1). Thus, when metal M is reacted with excess C, carbon content x ′ in carbide MCx′ in equilibrium with amorphous carbon becomes higher than x in MCx in equilibrium with graphite. In case of uranium carbo-nitride UCxN1−x in equilibrium with excess free C under given conditions of temperature T and N2 gas partial pressure p(N2 , x ′ in UCx′N1−x′ in equilibrium with amorphous carbon was experimentally demonstrated to be higher than x in UCxN1−x in equilibrium with graphite. Gaseous ammonia NH3 with suppressed extent of dissociation by flowing would yield very high nitrogen activity a N and modestly high hydrogen activity a H while NH3 dissociated to N2 and H2 to reach equilibrium state in closed reaction chamber would yield a N and a H to be represented by respective partial pressures, p(N2 1/2 and p(H2 1/2, in the gas phase. Synthesis of mono-nitride MoN of Mo in N2 gas was reported to be impossible even at high pressure up to 300 atm in autoclave but MoN co-existing with sub-nitride Mo2N might be synthesized in flowing NH3 gas at normal pressure. As such, unstable chemical species might allow us to synthesize novel reaction product that cannot be prepared by using stable chemical species alone in the reactant. However, special care must be taken in usage of unstable chemical species. For example, in case of non-graphitic carbon, graphitization might proceed with considerably fast rate when the reaction temperature is set to be well above 2000 K and thence no effect of high a(C) might be gained at reaction temperature exceeding 2000 K. On the other hand, in case of flowing NH3 gas, extent of dissociation of NH3 gas would depend on the position along the flow path of NH3 gas stream (i.e., tends to rise inevitably on going from the up-stream side to the down-stream side) as well as on the NH3 gas flow rate (i.e., at specific position in the flow path tends to rise with diminishing NH3 gas flow rate). On the other hand, rapid solidification processing with cooling rate reaching to 106 K/s has been employed for refinement of microstructure of alloys and for extension of solubility limit as well as for formation of amorphous phases. Rapid solidification is considered as ultra-fast quenching process of high temperature micro structure, or more precisely, retention of atomistic configuration in molten state of multi-component system through extraction of heat with very high rate to inhibit atom diffusion processes to reach inherent equilibrium state defined uniquely as functions of temperature T and alloy composition. On the other hand, under certain mode of operation of Solar furnace using concentrated Solar Beam as the reaction heat source, rapid heating to reach reaction temperature around 2000 K from ambient temperature within order of a second or even less is realized. During carbide synthesis from tungsten (W ) under such operation mode of Solar furnace, the authors detected evidence of formation of WmCn phases that did not correspond to the phase anticipated by referring to available equilibrium binary W–C phase diagram at the processing temperature. This experimental evidence is tentatively appreciated in terms of small energetic differences among WmCn phases with varying m/n ratios. That is, once certain WmCn phase is formed during rapid heating of W/C powder mixture, the formed phase would remain stable at the processing temperature T even if it is not the genuine equilibrium phase at T without being transformed to the genuine equilibrium phase at the specified T due to smallness of driving force for the phase transformation
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synthesizing higher nitride of molybdenum mo and iron fe in ammonia nh3 gas stream under irradiation of concentrated Solar Beam in a Solar furnace
Materialwissenschaft Und Werkstofftechnik, 2013Co-Authors: Nobumitsu Shohoji, Teresa Magalhães, Almeida Costa F Oliveira, Cruz J Fernandes, Guerra L Rosa, Rodriguez J Garcia, Canadas I Martinez, Ramos C Minarro, F CestariAbstract:Flowing gaseous ammonia NH3 with suppressed extent of dissociation (un-cracked NH3) is acknowledged to function as a powerful nitriding medium to realize formation of metal nitride MNx with considerably high N/M ratio x that cannot be achieved through reaction of M with N2 gas. For example, mono-nitride δ-MoN of Mo and e-FeNx phase of Fe with x = 0.33 ˜ 0.50 (i. e. hypo-stoichiometric sub-nitride e-Fe2N) were reported to be difficult to prepare in N2 gas environment even at elevated pressure but might be synthesized in flowing NH3 gas at normal pressure when reaction temperature and NH3 gas flow rate were set adequately. In the present work, nitriding experiments for Mo and Fe were carried out in flowing NH3 gas under irradiation with concentrated Solar Beam. The acquired experimental evidences demonstrated that temperature range for formation of δ-MoN was somewhat extended in flowing NH3 gas under heating with concentrated Solar Beam compared with that under heating in conventional laboratory or industrial electric furnace. On the other hand, no such merit of extending temperature range for formation of e-Fe2N in flowing NH3 gas was detected in the present work under heating with concentrated Solar Beam.
Nicolas Calvet - One of the best experts on this subject based on the ideXlab platform.
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new concentrating Solar power facility for testing high temperature concrete thermal energy storage
Energy Procedia, 2015Co-Authors: Matthieu Martins, Pål Bergan, Uver Villalobos, Thomas Delclos, Peter R Armstrong, Nicolas CalvetAbstract:Abstract Several thermal energy storage (TES) systems have been developed and tested to be integrated in concentrating Solar power (CSP) systems. Recent studies show that concrete as storage media has the potential to become an interesting solution due to its properties such as relatively high specific heat and thermal conductivity, good mechanical properties, a thermal expansion coefficient similar to that of steel pipe and low cost of a material that is easy to obtain and process. This article outlines a new 100 kW th Solar Beam-down facility for testing high temperature concrete storage at 393°C and the first project to use the facility for TES testing in collaboration with NEST. Initial concrete characterization and testing results which show promising thermal and mechanical performance, are also presented. The CSP hot oil-loop has been modified and instrumented to perform research and testing of TES systems in real Solar radiation conditions. Experimental TES system testing at real scale with a total storage capacity of 1.0 MWh th is planned to begin operation early 2015.
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new concentrating Solar power facility for testing high temperature concrete thermal energy storage
Energy Procedia, 2015Co-Authors: Matthieu Martins, Pål Bergan, Uver Villalobos, Thomas Delclos, Peter R Armstrong, Nicolas CalvetAbstract:Abstract Several thermal energy storage (TES) systems have been developed and tested to be integrated in concentrating Solar power (CSP) systems. Recent studies show that concrete as storage media has the potential to become an interesting solution due to its properties such as relatively high specific heat and thermal conductivity, good mechanical properties, a thermal expansion coefficient similar to that of steel pipe and low cost of a material that is easy to obtain and process. This article outlines a new 100 kW th Solar Beam-down facility for testing high temperature concrete storage at 393°C and the first project to use the facility for TES testing in collaboration with NEST. Initial concrete characterization and testing results which show promising thermal and mechanical performance, are also presented. The CSP hot oil-loop has been modified and instrumented to perform research and testing of TES systems in real Solar radiation conditions. Experimental TES system testing at real scale with a total storage capacity of 1.0 MWh th is planned to begin operation early 2015.
Luis Guerra Rosa - One of the best experts on this subject based on the ideXlab platform.
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low temperature short time nitriding of va group metals v nb and ta in uncracked nh3 gas under heating with concentrated Solar power csp
Ciência & Tecnologia dos Materiais, 2016Co-Authors: Joao Fernandes, Luis Guerra Rosa, Teresa Magalhães, Inmaculada Canadas, Jose Rodriguez, Fernando Costa A Oliveira, Nobumitsu ShohojiAbstract:Abstract Over the last two decades, the authors have been using concentrated Solar Beam as the reaction heat source for synthesizing carbides and nitrides of d -group transition elements in view of usage of ecological renewable energy source in place of conventional heat sources using electricity or natural gas. In recent works, nitriding of VIa-group metals (Cr, Mo, W) and Fe in stream of NH 3 gas with suppressed extent of dissociation (uncracked NH 3 ) was attempted under heating with concentrated Solar Beam. It was demonstrated that mono-nitride δ-MoN of Mo and sub-nitride ɛ-Fe 2 N of Fe that are known to be impossible to synthesize in N 2 gas environment even at elevated N 2 gas partial pressure p (N 2 ) up to 300 bar were successfully synthesized by the reactions of these metals in stream of NH 3 gas under heating with concentrated Solar Beam up to 800 °C. In the present work, nitriding of Va-group metals (V, Nb and Ta) was attempted in stream of NH 3 gas under irradiation of concentrated Solar Beam. After 90 min heating in uncracked NH 3 under concentrated Solar Beam up to 800 °C, X-ray diffraction (XRD) characterization of the reaction products showed certain extent of nitriding progressed for all the specimens in spite of relatively low reaction temperature for short reaction duration.
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nitriding vi group metals cr mo and w in stream of nh3 gas under concentrated Solar irradiation in a Solar furnace at psa plataforma Solar de almeria
Solar Energy, 2015Co-Authors: Fernando Costa A Oliveira, Jorge Cruz Fernandes, Luis Guerra Rosa, Teresa Magalhães, Inmaculada Canadas, Jose Rodriguez, Nobumitsu ShohojiAbstract:Abstract Carbides and nitrides of d -group transition metals are classified as refractory hard material and their industrial importance has been recognized for long. In recent years, unique functionalities including catalytic function and superconductivity are discovered for this group of materials to raise serious attention of materials researchers and engineers to refractory carbides and nitrides as novel functional materials. Synthesis of refractory carbides and nitrides demands high temperature reaction route to consume considerable amount of electricity or gas in conventional industrial process. In view of saving cost of such conventional energy, feasibility of using concentrated Solar Beam as heat source for synthesizing carbide and nitride has been investigated by the authors since 1997. After verifying usefulness of concentrated Solar Beam as heat source for carbide forming reactions, similar attempts of employing concentrated Solar Beam as heat source for nitride synthesis were initiated recently. After brief experimental verification of nitride synthesis for IVa group metal, Ti, and Vg group metals, V, Nb and Ta, in N 2 gas environment under irradiation with concentrated Solar Beam to 2000 °C, the authors decided to undertake nitride synthesis of VIa group metals, Cr, Mo and W, as well as of Fe in stream of ammonia (NH 3 ) gas as a nitriding medium under irradiation of concentrated Solar Beam at temperatures not exceeding 1000 °C. NH 3 gas with suppressed extent of dissociation by flowing is defined empirically as uncracked NH 3 and it is proved to possess very high nitriding power to make synthesis of mono-nitride MoN of Mo coexisting with sub-nitride Mo and higher nitride Fe 2 N of Fe possible under normal pressure condition that are not possible when chemically stable N 2 gas is used as a nitriding agent. VIa-group metals including Cr, Mo and W are known to be highly resistant against nitriding. In the present report, results of nitriding in flowing NH 3 gas at a fixed flow rate 10 l/h (≈167 ml/min) under heating with concentrated Solar Beam for VIa-group metals, Cr, Mo and W, are summarized to demonstrate favorable effect of Solar Beam heating towards further enhancement of nitriding power of flowing NH 3 gas compared with the situation in conventional electric furnace in which visible light components except infra-red (IR) heat wave component are absent in the reaction system.
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low temperature nitriding of va group metal powders v nb ta in flowing nh3 gas under heating with concentrated Solar Beam at psa
Ciência & Tecnologia dos Materiais, 2015Co-Authors: Jorge Cruz Fernandes, Luis Guerra Rosa, Teresa Magalhães, F Costa A Oliveira, Inmaculada Canadas, Jose Rodriguez, Nobumitsu ShohojiAbstract:Over the last two decades, we have been using concentrated Solar Beam as the reaction heat source for synthesizing carbides and nitrides of d-group transition elements in view of usage of ecological renewable energy source in place of conventional heat sources using electricity or gas. In recent works [1,2] nitriding of VIa-group metals (Cr, Mo, W) and Fe in stream of NH3 gas with suppressed extent of dissociation (uncracked NH3) was attempted under heating with concentrated Solar Beam. It was demonstrated that mono-nitride -MoN of Mo and sub-nitride -Fe2N of Fe that are known to be impossible to synthesize in N2 gas environment even at elevated pressure p(N2) were successfully synthesized by the reactions of these metals in stream of NH3 gas under heating with concentrated Solar Beam up to 800oC. In the present work, nitriding of Va-group metals (V, Nb and Ta) was attempted in stream of NH3 gas under irradiation of concentrated Solar Beam. By up to 90 min heating in uncracked NH3 under concentrated Solar Beam up to 800oC, reaction products were identified by X-ray diffraction (XRD) analysis to be consisted of mono-nitride MN co-existent with sub-nitride M2N.
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synthesising carbo nitrides of some d group transition metals using a Solar furnace at psa
Materials Science Forum, 2012Co-Authors: Nobumitsu Shohoji, Luis Guerra Rosa, Teresa Magalhães, Inmaculada Canadas, Jose Rodriguez, Fernando Costa A Oliveira, Jose Cruz Fernandes, Manuel Caldeira Coelho, Carlos Ramos, Diego MartinezAbstract:Carbo-nitride synthesis was undertaken using a Solar furnace at PSA in flowing N2/Ar gas mixture under total pressure 1 atm and processing temperature T = 1600°C for some d-group transition elements (Ti; Zr, V, Nb, Mo, W) starting from 1.5G/M (graphite/metal powder mixture with mole ratio 1.5:1) compact to ensure co-presence of free carbon with the reaction product. Clear X-ray diffraction (XRD) evidence of formation of carbo-nitride was detected for Ti (IVa group metal) showing higher N content in the carbo-nitride synthesised in N2 gas environment at partial pressure p(N2) = 1 atm than that at p(N2) = 0.5 atm. For M = V and Nb (Va group metals), formation of mono-carbide MC single-phase was detected in the N2 environment showing no evidence of formation of carbo-nitride in spite of presence of N2 in the environment. For M = Mo and W (VIa group metals), formation of higher carbide, among several options of carbide phases, appeared to be promoted in the N2 gas environment although, like in cases with the Va group metals, no evidence of dissolution of N into the reaction product was detected. As such, at T = 1600°C in N2 gas environment up to p(N2) = 1 atm under concentrated Solar Beam, carbo-nitride formed from the 1.5G/M mixture only for IVa group metal (Ti) but not for Va and VIa group metals. Anyway, it seemed certain that N2 gas affected somehow the reaction path between G and M to yield the carbide phase for M = V, Nb, Mo and W.
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crystal grain morphology evolution over ti v nb and ta surface heated in n2 gas environment to 2000 c by filtered concentrated Solar Beam in a Solar furnace at promes cnrs
Materials Transactions, 2012Co-Authors: Fernando Costa A Oliveira, Jorge Cruz Fernandes, Luis Guerra Rosa, Teresa Magalhães, Gilles Peraudeau, Bernard Granier, Nobumitsu ShohojiAbstract:In recent attempts of reacting d-group transition metals with N2 gas under irradiation of concentrated Solar Beam at temperatures around 2000°C using a standard setup with graphite specimen holder, reaction products obtained were carbo-nitrides rather than targeted nitrides on account of yield of C2 radical plume from the graphite crucible. To suppress the interference of C2 radical possessing high carbon chemical activity a(C) in nitriding d-group transition elements in Solar furnace, we investigated effectiveness of inserting colour filters in the Solar Beam path. Two readily available colour filters, Sky blue and Medium yellow filters, were tested for this purpose. As reported in our earlier publications, XRD (X-ray diffraction) phase identification results indicated that insertion of the Sky blue filter was effective for suppressing C2 radical yield under Solar Beam radiation to synthesize carbo-nitride with comparatively high N content. On the other hand, insertion of the Medium yellow filter did not result in so remarkable effect for suppressing carburization as the one detected with the Sky blue filter. In the present work, aspects of microstructures developed for Ti, V, Nb and Ta surfaces heated to 2000°C under exposure to colour-filtered Solar Beam in N2 gas environment are reviewed. The present experimental evidences indicated that, by insertion of the Sky blue filter, appreciable crystallite grain size refinement was realized for the synthesized M(C,N) with high N content while, by insertion of the Medium yellow filter, certain extent of influence on the morphological development, that varied depending on the substrate material, was unmistakably discernible. [doi:10.2320/matertrans.M2011299]
Matthieu Martins - One of the best experts on this subject based on the ideXlab platform.
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new concentrating Solar power facility for testing high temperature concrete thermal energy storage
Energy Procedia, 2015Co-Authors: Matthieu Martins, Pål Bergan, Uver Villalobos, Thomas Delclos, Peter R Armstrong, Nicolas CalvetAbstract:Abstract Several thermal energy storage (TES) systems have been developed and tested to be integrated in concentrating Solar power (CSP) systems. Recent studies show that concrete as storage media has the potential to become an interesting solution due to its properties such as relatively high specific heat and thermal conductivity, good mechanical properties, a thermal expansion coefficient similar to that of steel pipe and low cost of a material that is easy to obtain and process. This article outlines a new 100 kW th Solar Beam-down facility for testing high temperature concrete storage at 393°C and the first project to use the facility for TES testing in collaboration with NEST. Initial concrete characterization and testing results which show promising thermal and mechanical performance, are also presented. The CSP hot oil-loop has been modified and instrumented to perform research and testing of TES systems in real Solar radiation conditions. Experimental TES system testing at real scale with a total storage capacity of 1.0 MWh th is planned to begin operation early 2015.
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new concentrating Solar power facility for testing high temperature concrete thermal energy storage
Energy Procedia, 2015Co-Authors: Matthieu Martins, Pål Bergan, Uver Villalobos, Thomas Delclos, Peter R Armstrong, Nicolas CalvetAbstract:Abstract Several thermal energy storage (TES) systems have been developed and tested to be integrated in concentrating Solar power (CSP) systems. Recent studies show that concrete as storage media has the potential to become an interesting solution due to its properties such as relatively high specific heat and thermal conductivity, good mechanical properties, a thermal expansion coefficient similar to that of steel pipe and low cost of a material that is easy to obtain and process. This article outlines a new 100 kW th Solar Beam-down facility for testing high temperature concrete storage at 393°C and the first project to use the facility for TES testing in collaboration with NEST. Initial concrete characterization and testing results which show promising thermal and mechanical performance, are also presented. The CSP hot oil-loop has been modified and instrumented to perform research and testing of TES systems in real Solar radiation conditions. Experimental TES system testing at real scale with a total storage capacity of 1.0 MWh th is planned to begin operation early 2015.
Fernando Costa A Oliveira - One of the best experts on this subject based on the ideXlab platform.
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low temperature short time nitriding of va group metals v nb and ta in uncracked nh3 gas under heating with concentrated Solar power csp
Ciência & Tecnologia dos Materiais, 2016Co-Authors: Joao Fernandes, Luis Guerra Rosa, Teresa Magalhães, Inmaculada Canadas, Jose Rodriguez, Fernando Costa A Oliveira, Nobumitsu ShohojiAbstract:Abstract Over the last two decades, the authors have been using concentrated Solar Beam as the reaction heat source for synthesizing carbides and nitrides of d -group transition elements in view of usage of ecological renewable energy source in place of conventional heat sources using electricity or natural gas. In recent works, nitriding of VIa-group metals (Cr, Mo, W) and Fe in stream of NH 3 gas with suppressed extent of dissociation (uncracked NH 3 ) was attempted under heating with concentrated Solar Beam. It was demonstrated that mono-nitride δ-MoN of Mo and sub-nitride ɛ-Fe 2 N of Fe that are known to be impossible to synthesize in N 2 gas environment even at elevated N 2 gas partial pressure p (N 2 ) up to 300 bar were successfully synthesized by the reactions of these metals in stream of NH 3 gas under heating with concentrated Solar Beam up to 800 °C. In the present work, nitriding of Va-group metals (V, Nb and Ta) was attempted in stream of NH 3 gas under irradiation of concentrated Solar Beam. After 90 min heating in uncracked NH 3 under concentrated Solar Beam up to 800 °C, X-ray diffraction (XRD) characterization of the reaction products showed certain extent of nitriding progressed for all the specimens in spite of relatively low reaction temperature for short reaction duration.
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nitriding vi group metals cr mo and w in stream of nh3 gas under concentrated Solar irradiation in a Solar furnace at psa plataforma Solar de almeria
Solar Energy, 2015Co-Authors: Fernando Costa A Oliveira, Jorge Cruz Fernandes, Luis Guerra Rosa, Teresa Magalhães, Inmaculada Canadas, Jose Rodriguez, Nobumitsu ShohojiAbstract:Abstract Carbides and nitrides of d -group transition metals are classified as refractory hard material and their industrial importance has been recognized for long. In recent years, unique functionalities including catalytic function and superconductivity are discovered for this group of materials to raise serious attention of materials researchers and engineers to refractory carbides and nitrides as novel functional materials. Synthesis of refractory carbides and nitrides demands high temperature reaction route to consume considerable amount of electricity or gas in conventional industrial process. In view of saving cost of such conventional energy, feasibility of using concentrated Solar Beam as heat source for synthesizing carbide and nitride has been investigated by the authors since 1997. After verifying usefulness of concentrated Solar Beam as heat source for carbide forming reactions, similar attempts of employing concentrated Solar Beam as heat source for nitride synthesis were initiated recently. After brief experimental verification of nitride synthesis for IVa group metal, Ti, and Vg group metals, V, Nb and Ta, in N 2 gas environment under irradiation with concentrated Solar Beam to 2000 °C, the authors decided to undertake nitride synthesis of VIa group metals, Cr, Mo and W, as well as of Fe in stream of ammonia (NH 3 ) gas as a nitriding medium under irradiation of concentrated Solar Beam at temperatures not exceeding 1000 °C. NH 3 gas with suppressed extent of dissociation by flowing is defined empirically as uncracked NH 3 and it is proved to possess very high nitriding power to make synthesis of mono-nitride MoN of Mo coexisting with sub-nitride Mo and higher nitride Fe 2 N of Fe possible under normal pressure condition that are not possible when chemically stable N 2 gas is used as a nitriding agent. VIa-group metals including Cr, Mo and W are known to be highly resistant against nitriding. In the present report, results of nitriding in flowing NH 3 gas at a fixed flow rate 10 l/h (≈167 ml/min) under heating with concentrated Solar Beam for VIa-group metals, Cr, Mo and W, are summarized to demonstrate favorable effect of Solar Beam heating towards further enhancement of nitriding power of flowing NH 3 gas compared with the situation in conventional electric furnace in which visible light components except infra-red (IR) heat wave component are absent in the reaction system.
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synthesising carbo nitrides of some d group transition metals using a Solar furnace at psa
Materials Science Forum, 2012Co-Authors: Nobumitsu Shohoji, Luis Guerra Rosa, Teresa Magalhães, Inmaculada Canadas, Jose Rodriguez, Fernando Costa A Oliveira, Jose Cruz Fernandes, Manuel Caldeira Coelho, Carlos Ramos, Diego MartinezAbstract:Carbo-nitride synthesis was undertaken using a Solar furnace at PSA in flowing N2/Ar gas mixture under total pressure 1 atm and processing temperature T = 1600°C for some d-group transition elements (Ti; Zr, V, Nb, Mo, W) starting from 1.5G/M (graphite/metal powder mixture with mole ratio 1.5:1) compact to ensure co-presence of free carbon with the reaction product. Clear X-ray diffraction (XRD) evidence of formation of carbo-nitride was detected for Ti (IVa group metal) showing higher N content in the carbo-nitride synthesised in N2 gas environment at partial pressure p(N2) = 1 atm than that at p(N2) = 0.5 atm. For M = V and Nb (Va group metals), formation of mono-carbide MC single-phase was detected in the N2 environment showing no evidence of formation of carbo-nitride in spite of presence of N2 in the environment. For M = Mo and W (VIa group metals), formation of higher carbide, among several options of carbide phases, appeared to be promoted in the N2 gas environment although, like in cases with the Va group metals, no evidence of dissolution of N into the reaction product was detected. As such, at T = 1600°C in N2 gas environment up to p(N2) = 1 atm under concentrated Solar Beam, carbo-nitride formed from the 1.5G/M mixture only for IVa group metal (Ti) but not for Va and VIa group metals. Anyway, it seemed certain that N2 gas affected somehow the reaction path between G and M to yield the carbide phase for M = V, Nb, Mo and W.
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crystal grain morphology evolution over ti v nb and ta surface heated in n2 gas environment to 2000 c by filtered concentrated Solar Beam in a Solar furnace at promes cnrs
Materials Transactions, 2012Co-Authors: Fernando Costa A Oliveira, Jorge Cruz Fernandes, Luis Guerra Rosa, Teresa Magalhães, Gilles Peraudeau, Bernard Granier, Nobumitsu ShohojiAbstract:In recent attempts of reacting d-group transition metals with N2 gas under irradiation of concentrated Solar Beam at temperatures around 2000°C using a standard setup with graphite specimen holder, reaction products obtained were carbo-nitrides rather than targeted nitrides on account of yield of C2 radical plume from the graphite crucible. To suppress the interference of C2 radical possessing high carbon chemical activity a(C) in nitriding d-group transition elements in Solar furnace, we investigated effectiveness of inserting colour filters in the Solar Beam path. Two readily available colour filters, Sky blue and Medium yellow filters, were tested for this purpose. As reported in our earlier publications, XRD (X-ray diffraction) phase identification results indicated that insertion of the Sky blue filter was effective for suppressing C2 radical yield under Solar Beam radiation to synthesize carbo-nitride with comparatively high N content. On the other hand, insertion of the Medium yellow filter did not result in so remarkable effect for suppressing carburization as the one detected with the Sky blue filter. In the present work, aspects of microstructures developed for Ti, V, Nb and Ta surfaces heated to 2000°C under exposure to colour-filtered Solar Beam in N2 gas environment are reviewed. The present experimental evidences indicated that, by insertion of the Sky blue filter, appreciable crystallite grain size refinement was realized for the synthesized M(C,N) with high N content while, by insertion of the Medium yellow filter, certain extent of influence on the morphological development, that varied depending on the substrate material, was unmistakably discernible. [doi:10.2320/matertrans.M2011299]
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influence of colour filter on reaction products from mo and w heated to 2000 c by concentrated Solar Beam in n 2 gas environment in a Solar furnace at promes cnrs
Materials Transactions, 2011Co-Authors: Gilles Peraudeau, Jorge Cruz Fernandes, Luis Guerra Rosa, Teresa Magalhães, Fernando Costa A Oliveira, Bernard Granier, Nobumitsu ShohojiAbstract:In a preceding work, we reported attempts of synthesizing nitride of d-group transition metals including Ti, V, Nb and Ta using a Solar furnace at PROMES-CNRS. In standard Solar furnace experimental setup, graphite crucible is used as the sample holder on account of its resistance against high temperature and thermal shock. Plume of C2 radical with high chemical activity a(C) of C was reported to yield from graphite crucible under irradiation of concentrated Solar Beam. Thus, synthesis of pure metal nitride MN was not successful in the preceding work done in N2 gas environment heated by Solar Beam irradiation under standard experimental setup. To overcome this problem of undesired carburization in Solar furnace, insertion of colour filter in the path of Solar Beam was tried and it was found that the C2 radical yield from the graphite crucible was effectively suppressed by insertion of Sky blue filter and carbo-nitride M(C,N) with comparatively low C-content was synthesized for Ti, V, Nb and Ta at 2000°C in N2 gas environment while, without the Sky blue filter, M(C,N) with high C-content and low N-content was synthesized under the otherwise comparable conditions of temperature and nitrogen partial pressure. These evidences appeared to suggest that nitride synthesis might be realized in standard Solar furnace experimental setup using standard sample holder made of graphite by insertion of Sky blue filter. In the present work, reaction products from Mo and W in N2 gas environment under Solar heating to 2000°C were characterized and effectiveness of the Sky blue filter for suppression of C2 radical yield from the graphite crucible was ascertained.
