The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Fernando Guiberteau - One of the best experts on this subject based on the ideXlab platform.
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effect of the sintering Additive Content on the protective passive oxidation behaviour of pressureless liquid phase sintered sic
Journal of The European Ceramic Society, 2012Co-Authors: Fernando Rodriguezrojas, Angel L Ortiz, Oscar Borrerolopez, Fernando GuiberteauAbstract:Abstract The long-term oxidation behaviour in air of pressureless liquid-phase-sintered SiC was investigated as a function of the sintering-Additive Content (a mixture of Y2O3 and Al2O3 in the 3:5 molar ratio) at oxidizing temperatures in the interval 1100–1300 °C. It is shown that oxidation under these mild conditions is always passive, and with formation of protective oxide scales. However, the oxidation kinetics cannot be described appropriately by the parabolic-rate law. Instead, due to the gradual crystallization of the oxide scales during oxidation, it is more complex, exhibiting two different stretches given respectively by the arctan- and parabolic-rate laws. Furthermore, it was found that the rate-limiting mechanism of the initial arctan oxidation is the outward diffusion of metal cations from the secondary intergranular phase into the oxide scale, with the activation energy of the oxidation being very high and decreasing from 545 to 432 kJ/mol with increasing sintering-Additive Content from 5 to 20 wt%. The rate-limiting mechanism of the subsequent parabolic oxidation is however the inward diffusion of oxygen through the multicomponent oxide scale, with the activation energy being lower than before and also decreasing from 345 to 205 kJ/mol as the sintering-Additive Content increases from 5 to 20 wt%. It is also shown that the oxidation resistance decreases with increasing sintering-Additive Content, but that while the decrease is moderate up to 10 wt%, it is very marked for greater Contents.
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microstructural evolution and contact mechanical properties of sic ceramics prepared colloidally with low Additive Content
Ceramics International, 2012Co-Authors: Oscar Borrerolopez, Angel L Ortiz, Fernando Rodriguezrojas, Esther Ciudad, Fernando GuiberteauAbstract:Abstract The microstructural evolution and contact-mechanical properties of liquid-phase sintered (LPS) SiC ceramics processed colloidally with low loads of sintering Additives was investigated as a function of the sintering duration, and was compared with the case of their counterparts processed conventionally. The two processing routes differ in the preparation of the powder batch, which in the colloidal method is done by covering the SiC particles with an oxide nano-film synthesized by the sol–gel method, whereas in the conventional method it is done by mixing mechanically the SiC powder with the oxide powders. It was found that the colloidal processing route offers clear benefits in terms of densification and contact-mechanical properties (stiffness, hardness, and damage and wear resistances) over the conventional processing route when the sintering times are short, but not when the sintering times are moderate or prolonged. Furthermore, no differences were found in the microstructural evolution with the sintering duration between the two types of ceramics. Based on the results, it is proposed that the more sophisticated colloidal processing route is certainly the appropriate choice for short sintering times, whereas in other cases its use would be justified if the goal is to incorporate into the microstructure new homogeneous multi-component oxide Additives with tailored stoichiometry.
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a route for the pressureless liquid phase sintering of sic with low Additive Content for improved sliding wear resistance
Journal of The European Ceramic Society, 2012Co-Authors: Angel L Ortiz, Oscar Borrerolopez, M Z Quadir, Fernando GuiberteauAbstract:Abstract A colloidal processing route has been developed for the pressureless sintering of dense SiC with a low Content of sintering Additives. In this route, a sol–gel solution precursor of the sintering Additives is deposited onto the surface of the SiC particles, achieving a uniform distribution of the sintering Additives in the green compact. This in turn promotes complete densification at short sintering times, which is not otherwise achievable when the batch is prepared by the standard method of mechanically mixing powders. It is also shown that the resulting ceramic has improved sliding-wear resistance compared to its counterpart prepared by the classical method, with essentially the same rate of mild and severe wear but a notably delayed transition from the mild to the severe wear regimes. This improvement is attributed to the reduction in the microstructural defect size achieved by the colloidal processing. Implications for the fabrication of low-cost SiC ceramics for wear-resistance applications are discussed.
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effect of the sintering Additive Content on the non protective oxidation behaviour of pressureless liquid phase sintered α sic in air
Journal of The European Ceramic Society, 2010Co-Authors: Fernando Rodriguezrojas, Angel L Ortiz, Oscar Borrerolopez, Fernando GuiberteauAbstract:Abstract The long-term oxidation resistance of pressureless liquid-phase-sintered (PLPS) α-SiC was investigated as a function of the Content of sintering Additive (in particular, YAG) at 1500 °C in air. It is shown that, regardless of the vol.% YAG, the oxidation is passive at that high temperature, with a kinetics given by the paralinear-rate law. This is because the oxide scales grow due to oxidation of the SiC grains, but recede due to the formation of a eutectic phase and to the carbothermal reduction of YAG. It is also shown that the oxidation resistance of PLPS SiC decreases markedly with increasing vol.% YAG, an effect that is especially marked above 7.3 vol.% YAG where a change in oxidation behaviour occurs. Thus, while up to 7.3 vol.% YAG the PLPS SiC ceramics gain mass during the entire oxidation process (500 h) because the oxide scales are at least semi-protective, from 11.1 vol.% YAG onwards the PLPS SiC ceramics first gain mass and then lose mass linearly over oxidizing time because the oxide scales are non-protective. Finally, implications for the design of PLPS SiC ceramics that can tolerate prolonged exposures at high temperatures in air are discussed.
Angel L Ortiz - One of the best experts on this subject based on the ideXlab platform.
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liquid phase assisted flash sintering of sic from powder mixtures prepared by aqueous colloidal processing
Journal of The European Ceramic Society, 2017Co-Authors: Victor M Candelario, Rodrigo Moreno, Richard I Todd, Angel L OrtizAbstract:The effects were investigated of the starting particle size (i.e., nanometer or submicrometer powders), Content of Y3Al5O12 Additives (YAG; in the range 5–20 wt.%), and difference of size scales between the two particle types on the liquid-phase assisted flash sintering of SiC from powder mixtures prepared by aqueous colloidal processing. It was found that flash sintering benefits from the refinement of the particles size, the increase in Additive Content, and the smaller size scale of the particulate Additive. It was also found that under the present flash sintering conditions (i.e., 900 °C furnace temperature, 13 A current, and 50 s in flash state) the resulting ceramics are, despite the formation of liquid phase, porous to a greater or lesser extent, and exhibit decreasing porosity gradients from their surface to the centre. These observations are rationalized to extract guidelines for powder batch design contributing to the pressureless ultrafast sintering of non-oxide advanced ceramics.
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effect of the sintering Additive Content on the protective passive oxidation behaviour of pressureless liquid phase sintered sic
Journal of The European Ceramic Society, 2012Co-Authors: Fernando Rodriguezrojas, Angel L Ortiz, Oscar Borrerolopez, Fernando GuiberteauAbstract:Abstract The long-term oxidation behaviour in air of pressureless liquid-phase-sintered SiC was investigated as a function of the sintering-Additive Content (a mixture of Y2O3 and Al2O3 in the 3:5 molar ratio) at oxidizing temperatures in the interval 1100–1300 °C. It is shown that oxidation under these mild conditions is always passive, and with formation of protective oxide scales. However, the oxidation kinetics cannot be described appropriately by the parabolic-rate law. Instead, due to the gradual crystallization of the oxide scales during oxidation, it is more complex, exhibiting two different stretches given respectively by the arctan- and parabolic-rate laws. Furthermore, it was found that the rate-limiting mechanism of the initial arctan oxidation is the outward diffusion of metal cations from the secondary intergranular phase into the oxide scale, with the activation energy of the oxidation being very high and decreasing from 545 to 432 kJ/mol with increasing sintering-Additive Content from 5 to 20 wt%. The rate-limiting mechanism of the subsequent parabolic oxidation is however the inward diffusion of oxygen through the multicomponent oxide scale, with the activation energy being lower than before and also decreasing from 345 to 205 kJ/mol as the sintering-Additive Content increases from 5 to 20 wt%. It is also shown that the oxidation resistance decreases with increasing sintering-Additive Content, but that while the decrease is moderate up to 10 wt%, it is very marked for greater Contents.
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microstructural evolution and contact mechanical properties of sic ceramics prepared colloidally with low Additive Content
Ceramics International, 2012Co-Authors: Oscar Borrerolopez, Angel L Ortiz, Fernando Rodriguezrojas, Esther Ciudad, Fernando GuiberteauAbstract:Abstract The microstructural evolution and contact-mechanical properties of liquid-phase sintered (LPS) SiC ceramics processed colloidally with low loads of sintering Additives was investigated as a function of the sintering duration, and was compared with the case of their counterparts processed conventionally. The two processing routes differ in the preparation of the powder batch, which in the colloidal method is done by covering the SiC particles with an oxide nano-film synthesized by the sol–gel method, whereas in the conventional method it is done by mixing mechanically the SiC powder with the oxide powders. It was found that the colloidal processing route offers clear benefits in terms of densification and contact-mechanical properties (stiffness, hardness, and damage and wear resistances) over the conventional processing route when the sintering times are short, but not when the sintering times are moderate or prolonged. Furthermore, no differences were found in the microstructural evolution with the sintering duration between the two types of ceramics. Based on the results, it is proposed that the more sophisticated colloidal processing route is certainly the appropriate choice for short sintering times, whereas in other cases its use would be justified if the goal is to incorporate into the microstructure new homogeneous multi-component oxide Additives with tailored stoichiometry.
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a route for the pressureless liquid phase sintering of sic with low Additive Content for improved sliding wear resistance
Journal of The European Ceramic Society, 2012Co-Authors: Angel L Ortiz, Oscar Borrerolopez, M Z Quadir, Fernando GuiberteauAbstract:Abstract A colloidal processing route has been developed for the pressureless sintering of dense SiC with a low Content of sintering Additives. In this route, a sol–gel solution precursor of the sintering Additives is deposited onto the surface of the SiC particles, achieving a uniform distribution of the sintering Additives in the green compact. This in turn promotes complete densification at short sintering times, which is not otherwise achievable when the batch is prepared by the standard method of mechanically mixing powders. It is also shown that the resulting ceramic has improved sliding-wear resistance compared to its counterpart prepared by the classical method, with essentially the same rate of mild and severe wear but a notably delayed transition from the mild to the severe wear regimes. This improvement is attributed to the reduction in the microstructural defect size achieved by the colloidal processing. Implications for the fabrication of low-cost SiC ceramics for wear-resistance applications are discussed.
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effect of the sintering Additive Content on the non protective oxidation behaviour of pressureless liquid phase sintered α sic in air
Journal of The European Ceramic Society, 2010Co-Authors: Fernando Rodriguezrojas, Angel L Ortiz, Oscar Borrerolopez, Fernando GuiberteauAbstract:Abstract The long-term oxidation resistance of pressureless liquid-phase-sintered (PLPS) α-SiC was investigated as a function of the Content of sintering Additive (in particular, YAG) at 1500 °C in air. It is shown that, regardless of the vol.% YAG, the oxidation is passive at that high temperature, with a kinetics given by the paralinear-rate law. This is because the oxide scales grow due to oxidation of the SiC grains, but recede due to the formation of a eutectic phase and to the carbothermal reduction of YAG. It is also shown that the oxidation resistance of PLPS SiC decreases markedly with increasing vol.% YAG, an effect that is especially marked above 7.3 vol.% YAG where a change in oxidation behaviour occurs. Thus, while up to 7.3 vol.% YAG the PLPS SiC ceramics gain mass during the entire oxidation process (500 h) because the oxide scales are at least semi-protective, from 11.1 vol.% YAG onwards the PLPS SiC ceramics first gain mass and then lose mass linearly over oxidizing time because the oxide scales are non-protective. Finally, implications for the design of PLPS SiC ceramics that can tolerate prolonged exposures at high temperatures in air are discussed.
Oscar Borrerolopez - One of the best experts on this subject based on the ideXlab platform.
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effect of the sintering Additive Content on the protective passive oxidation behaviour of pressureless liquid phase sintered sic
Journal of The European Ceramic Society, 2012Co-Authors: Fernando Rodriguezrojas, Angel L Ortiz, Oscar Borrerolopez, Fernando GuiberteauAbstract:Abstract The long-term oxidation behaviour in air of pressureless liquid-phase-sintered SiC was investigated as a function of the sintering-Additive Content (a mixture of Y2O3 and Al2O3 in the 3:5 molar ratio) at oxidizing temperatures in the interval 1100–1300 °C. It is shown that oxidation under these mild conditions is always passive, and with formation of protective oxide scales. However, the oxidation kinetics cannot be described appropriately by the parabolic-rate law. Instead, due to the gradual crystallization of the oxide scales during oxidation, it is more complex, exhibiting two different stretches given respectively by the arctan- and parabolic-rate laws. Furthermore, it was found that the rate-limiting mechanism of the initial arctan oxidation is the outward diffusion of metal cations from the secondary intergranular phase into the oxide scale, with the activation energy of the oxidation being very high and decreasing from 545 to 432 kJ/mol with increasing sintering-Additive Content from 5 to 20 wt%. The rate-limiting mechanism of the subsequent parabolic oxidation is however the inward diffusion of oxygen through the multicomponent oxide scale, with the activation energy being lower than before and also decreasing from 345 to 205 kJ/mol as the sintering-Additive Content increases from 5 to 20 wt%. It is also shown that the oxidation resistance decreases with increasing sintering-Additive Content, but that while the decrease is moderate up to 10 wt%, it is very marked for greater Contents.
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microstructural evolution and contact mechanical properties of sic ceramics prepared colloidally with low Additive Content
Ceramics International, 2012Co-Authors: Oscar Borrerolopez, Angel L Ortiz, Fernando Rodriguezrojas, Esther Ciudad, Fernando GuiberteauAbstract:Abstract The microstructural evolution and contact-mechanical properties of liquid-phase sintered (LPS) SiC ceramics processed colloidally with low loads of sintering Additives was investigated as a function of the sintering duration, and was compared with the case of their counterparts processed conventionally. The two processing routes differ in the preparation of the powder batch, which in the colloidal method is done by covering the SiC particles with an oxide nano-film synthesized by the sol–gel method, whereas in the conventional method it is done by mixing mechanically the SiC powder with the oxide powders. It was found that the colloidal processing route offers clear benefits in terms of densification and contact-mechanical properties (stiffness, hardness, and damage and wear resistances) over the conventional processing route when the sintering times are short, but not when the sintering times are moderate or prolonged. Furthermore, no differences were found in the microstructural evolution with the sintering duration between the two types of ceramics. Based on the results, it is proposed that the more sophisticated colloidal processing route is certainly the appropriate choice for short sintering times, whereas in other cases its use would be justified if the goal is to incorporate into the microstructure new homogeneous multi-component oxide Additives with tailored stoichiometry.
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a route for the pressureless liquid phase sintering of sic with low Additive Content for improved sliding wear resistance
Journal of The European Ceramic Society, 2012Co-Authors: Angel L Ortiz, Oscar Borrerolopez, M Z Quadir, Fernando GuiberteauAbstract:Abstract A colloidal processing route has been developed for the pressureless sintering of dense SiC with a low Content of sintering Additives. In this route, a sol–gel solution precursor of the sintering Additives is deposited onto the surface of the SiC particles, achieving a uniform distribution of the sintering Additives in the green compact. This in turn promotes complete densification at short sintering times, which is not otherwise achievable when the batch is prepared by the standard method of mechanically mixing powders. It is also shown that the resulting ceramic has improved sliding-wear resistance compared to its counterpart prepared by the classical method, with essentially the same rate of mild and severe wear but a notably delayed transition from the mild to the severe wear regimes. This improvement is attributed to the reduction in the microstructural defect size achieved by the colloidal processing. Implications for the fabrication of low-cost SiC ceramics for wear-resistance applications are discussed.
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effect of the sintering Additive Content on the non protective oxidation behaviour of pressureless liquid phase sintered α sic in air
Journal of The European Ceramic Society, 2010Co-Authors: Fernando Rodriguezrojas, Angel L Ortiz, Oscar Borrerolopez, Fernando GuiberteauAbstract:Abstract The long-term oxidation resistance of pressureless liquid-phase-sintered (PLPS) α-SiC was investigated as a function of the Content of sintering Additive (in particular, YAG) at 1500 °C in air. It is shown that, regardless of the vol.% YAG, the oxidation is passive at that high temperature, with a kinetics given by the paralinear-rate law. This is because the oxide scales grow due to oxidation of the SiC grains, but recede due to the formation of a eutectic phase and to the carbothermal reduction of YAG. It is also shown that the oxidation resistance of PLPS SiC decreases markedly with increasing vol.% YAG, an effect that is especially marked above 7.3 vol.% YAG where a change in oxidation behaviour occurs. Thus, while up to 7.3 vol.% YAG the PLPS SiC ceramics gain mass during the entire oxidation process (500 h) because the oxide scales are at least semi-protective, from 11.1 vol.% YAG onwards the PLPS SiC ceramics first gain mass and then lose mass linearly over oxidizing time because the oxide scales are non-protective. Finally, implications for the design of PLPS SiC ceramics that can tolerate prolonged exposures at high temperatures in air are discussed.
Manuel Belmonte - One of the best experts on this subject based on the ideXlab platform.
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enhanced particle rearrangement during liquid phase spark plasma sintering of silicon nitride based ceramics
Ceramics International, 2011Co-Authors: P Miranzo, Jesus Gonzalezjulian, M I Osendi, Manuel BelmonteAbstract:Abstract Densification evolution has been analysed in liquid phase assisted spark plasma sintering (SPS) of silicon nitride (Si3N4)-based materials. Monolithic ceramics with variable amounts of Al2O3/Y2O3 sintering Additives, and carbon nanotubes (CNTs) containing Si3N4 composites have been considered. The shrinkage behaviour of SPSed monolithic Si3N4 showed a noticeable enhancement of the particle rearrangement stage, exhibiting a complete wetting of the grain boundary phase even for the lowest Additive Content (1.70 vol.%), unlike the corresponding hot pressed (HPed) material. An improvement of the liquid phase wetting by the presence of electromechanical forces is proposed to explain the enhanced densification occurring in the particle rearrangement stage of the SPS process. Furthermore, the addition of CNTs seems to increase the efficiency of this mechanism, decreasing the particle rearrangement temperature.
Choonhyun Park - One of the best experts on this subject based on the ideXlab platform.
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microstructure electrical properties and degradation behavior of praseodymium oxides based zinc oxide varistors doped with y2o3
Journal of Materials Science, 2000Co-Authors: Choonwoo Nahm, Choonhyun ParkAbstract:The microstructure, electrical properties, and degradation behavior of Pr-based zinc oxide varistors, which are composed of Zn-Pr-Co-Cr-Y oxides were investigated according to Y2O3 Additive Content in the range 0.5–4.0 mol%. The majority of the Sadded Y2O3 were segregated at the multiple ZnO grain junctions and grain boundaries. The average grain size was markedly decreased in the range 27.3–8.6 μm with increasing Y2O3 Additive Content. Y2O3 acted as an inhibitor of grain growth. Additions of Y2O3 increased the varistor voltage in the range 36.90–686.58 V/mm, increased the nonlinear exponent in the range 3.75–87.42, decreased the leakage current in the range 115.48–0.047μA, increased the barrier height in the range 1.06–2.16 eV, and decreased the donor concentration in the rang 1.87 × 1018–0.19 × 1018 cm−3. Y2O3 acted as an acceptor, as a result of the decrease of donor concentration. All Pr-based ZnO varistors doped with Y2O3 exhibited very predominant degradation characteristics, which show a nearly symmetric I-V after the stress. In particular, since 4.0 mol% Y2O3-added ZnO varistor has not only very excellent non-ohmicity, but also very stable degradation behavior, it is estimated to be sufficiently used to various application fields.