... 7. Kesraou-ouki S., Cheeseman C. and Perry R., Environmental Science and Technology 2 (1993),... more ... 7. Kesraou-ouki S., Cheeseman C. and Perry R., Environmental Science and Technology 2 (1993), 1108. 8. Kurama H. and Kaya M., Proceedings of Treatment Minimization Heavy Metal Containing Water (1995), 113. ... 12. Melis S., Cao G. and Morbidelli M., Ind Eng. Chem. Res. ...
In this work the feasibility of synthesizing MoSi2/Al cermet foam under the combustion mode was s... more In this work the feasibility of synthesizing MoSi2/Al cermet foam under the combustion mode was studied. A halogen containing organic polymer, namely, polytetrafluoroethylene (PTFE) was used as foaming agent. It was shown that the target product reached the maximum porosity, up to 70%, when amount of the foaming agent was 0.04mol. SEM analyses have shown there are two types of
The fabrication by Spark Plasma Sintering (SPS) of bulk high entropy ceramics from powders obtain... more The fabrication by Spark Plasma Sintering (SPS) of bulk high entropy ceramics from powders obtained by Self-propagating High temperature Synthesis (SHS) is addressed in this work. The effect produced by the introduction of 1 wt.% of graphite to the powders before SPS is investigated under different temperature conditions. The final density and composition of sintered (Hf0.2Mo0.2Zr0.2Ti0.2Ta0.2)B2 and (Hf0.2Mo0.2Zr0.2Ti0.2Nb0.2)B2 ceramics are found to be negatively affected by the presence of oxide impurities in the powders. While product composition can be progressively improved when the temperature is increased from 1800 to 1950 °C, residual porosities remain relatively high if using additive-free powders. In contrast, the introduction of 1 wt.%C markedly allows for oxides elimination by carbothermal reduction mechanism. Products consolidation is correspondingly enhanced so that relative densities of about 97% are attained. Other than the latter effect, surface oxides removal also...
The mechonism of the selfpropogating thermite reoction befween aluminum and hemalite or the micro... more The mechonism of the selfpropogating thermite reoction befween aluminum and hemalite or the microstruclure formotion of the reoction products with the some olumino ond silico content in the storling mixture ore investigoted by means of the combustion front quenching technique. lt is found thot the reoclonÍs in powder form are converted into products by possing through different Íronsformatíon zones wîth chonging microstructure ond compositíon. A relotively detoiled structurol tronsformotion mechonism for the cose of olumino os odditive, whose finolsfep is the crystallizotion of olumino and hercynite from o melt, is postuloted. On the other hond, ot leost ot thís stoge, o result of Íhe some lype seems díffícult to obÍoin when consídering silico os odditive.
The synthesis of ZrB2 from elemental reactants via reactive spark plasma sintering (SPS) process ... more The synthesis of ZrB2 from elemental reactants via reactive spark plasma sintering (SPS) process is markedly affected by the heating rate conditions adopted. Specifically, when the temperature during SPS is increased at 500 °C/min or faster, the synthesis reaction proceeds under the combustion regime. On the other hand, if heating rates equal or lower than 200 °C/min are considered, the process is governed by a gradual solid-state diffusion mechanism. Although the route involving the combustion synthesis event permits the obtainment of pure dense products at relatively milder conditions, the gradual evolution of the synthesis reaction is preferable. Indeed, the inconveniences encountered during the process (gas pressure increase, powder expulsion, product inhomogeneity, abrupt sample displacement, die/punches breakage) make its practical exploitation difficult. In contrast, safety conditions are preserved when sufficiently lowering the heating rates to suppress the combustion reacti...
A comparative investigation regarding the consolidation behavior displayed by three commercially ... more A comparative investigation regarding the consolidation behavior displayed by three commercially available hydroxyapatite powders during Spark Plasma Sintering (SPS) is performed in this work. Starting powders are different in terms of purity, particle size, morphology and thermochemical stability. A completely dense product without secondary species is produced by SPS at 900 °C, when starting from highly pure powders with relatively small sized particles and grains. The resulting consolidated material, consisting of sub-micrometer sized hydroxyapatite grains, exhibits optical transparency and good mechanical properties. On the other hand, temperature levels up to 1,200 °C are needed to sinter powders with larger particles. This holds also true when relatively finer powders are used, also containing CaHPO4, are used. In both the latter cases products with coarser microstructures and/or significant amount of β-TCP, as a result of hydroxyapatite decomposition, are obtained. Optical, c...
Due to their inherent chemical complexity and their refractory nature, the obtainment of highly d... more Due to their inherent chemical complexity and their refractory nature, the obtainment of highly dense and single-phase high entropy (HE) diborides represents a very hard target to achieve. In this framework, homogeneous (Hf0.2Nb0.2Ta0.2Mo0.2Ti0.2)B2, (Hf0.2Zr0.2Ta0.2Mo0.2Ti0.2)B2, and (Hf0.2Zr0.2Nb0.2Mo0.2Ti0.2)B2 ceramics with high relative densities (97.4, 96.5, and 98.2%, respectively) were successfully produced by spark plasma sintering (SPS) using powders prepared by self-propagating high-temperature synthesis (SHS). Although the latter technique did not lead to the complete conversion of initial precursors into the prescribed HE phases, such a goal was fully reached after SPS (1950 °C/20 min/20 MPa). The three HE products showed similar and, in some cases, even better mechanical properties compared to ceramics with the same nominal composition attained using alternative processing methods. Superior Vickers hardness and elastic modulus values were found for the (Hf0.2Nb0.2Ta0.2...
Poly(glycerol-sebacate) (PGS) and poly(epsilon caprolactone) (PCL) have been widely investigated ... more Poly(glycerol-sebacate) (PGS) and poly(epsilon caprolactone) (PCL) have been widely investigated for biomedical applications in combination with the electrospinning process. Among others, one advantage of this blend is its suitability to be processed with benign solvents for electrospinning. In this work, the suitability of PGS/PCL polymers for the fabrication of composite fibers incorporating bioactive glass (BG) particles was investigated. Composite electrospun fibers containing silicate or borosilicate glass particles (13-93 and 13-93BS, respectively) were obtained and characterized. Neat PCL and PCL composite electrospun fibers were used as control to investigate the possible effect of the presence of PGS and the influence of the bioactive glass particles. In fact, with the addition of PGS an increase in the average fiber diameter was observed, while in all the composite fibers, the presence of BG particles induced an increase in the fiber diameter distribution, without changing...
An adequate tuning of amorphous calcium phosphates ionic composition and cold sintering condition... more An adequate tuning of amorphous calcium phosphates ionic composition and cold sintering conditions allowed the first successful stabilization of these bioactive compounds. These results show promise for the setup of highly-resorbable bone substitutes.
... 7. Kesraou-ouki S., Cheeseman C. and Perry R., Environmental Science and Technology 2 (1993),... more ... 7. Kesraou-ouki S., Cheeseman C. and Perry R., Environmental Science and Technology 2 (1993), 1108. 8. Kurama H. and Kaya M., Proceedings of Treatment Minimization Heavy Metal Containing Water (1995), 113. ... 12. Melis S., Cao G. and Morbidelli M., Ind Eng. Chem. Res. ...
In this work the feasibility of synthesizing MoSi2/Al cermet foam under the combustion mode was s... more In this work the feasibility of synthesizing MoSi2/Al cermet foam under the combustion mode was studied. A halogen containing organic polymer, namely, polytetrafluoroethylene (PTFE) was used as foaming agent. It was shown that the target product reached the maximum porosity, up to 70%, when amount of the foaming agent was 0.04mol. SEM analyses have shown there are two types of
The fabrication by Spark Plasma Sintering (SPS) of bulk high entropy ceramics from powders obtain... more The fabrication by Spark Plasma Sintering (SPS) of bulk high entropy ceramics from powders obtained by Self-propagating High temperature Synthesis (SHS) is addressed in this work. The effect produced by the introduction of 1 wt.% of graphite to the powders before SPS is investigated under different temperature conditions. The final density and composition of sintered (Hf0.2Mo0.2Zr0.2Ti0.2Ta0.2)B2 and (Hf0.2Mo0.2Zr0.2Ti0.2Nb0.2)B2 ceramics are found to be negatively affected by the presence of oxide impurities in the powders. While product composition can be progressively improved when the temperature is increased from 1800 to 1950 °C, residual porosities remain relatively high if using additive-free powders. In contrast, the introduction of 1 wt.%C markedly allows for oxides elimination by carbothermal reduction mechanism. Products consolidation is correspondingly enhanced so that relative densities of about 97% are attained. Other than the latter effect, surface oxides removal also...
The mechonism of the selfpropogating thermite reoction befween aluminum and hemalite or the micro... more The mechonism of the selfpropogating thermite reoction befween aluminum and hemalite or the microstruclure formotion of the reoction products with the some olumino ond silico content in the storling mixture ore investigoted by means of the combustion front quenching technique. lt is found thot the reoclonÍs in powder form are converted into products by possing through different Íronsformatíon zones wîth chonging microstructure ond compositíon. A relotively detoiled structurol tronsformotion mechonism for the cose of olumino os odditive, whose finolsfep is the crystallizotion of olumino and hercynite from o melt, is postuloted. On the other hond, ot leost ot thís stoge, o result of Íhe some lype seems díffícult to obÍoin when consídering silico os odditive.
The synthesis of ZrB2 from elemental reactants via reactive spark plasma sintering (SPS) process ... more The synthesis of ZrB2 from elemental reactants via reactive spark plasma sintering (SPS) process is markedly affected by the heating rate conditions adopted. Specifically, when the temperature during SPS is increased at 500 °C/min or faster, the synthesis reaction proceeds under the combustion regime. On the other hand, if heating rates equal or lower than 200 °C/min are considered, the process is governed by a gradual solid-state diffusion mechanism. Although the route involving the combustion synthesis event permits the obtainment of pure dense products at relatively milder conditions, the gradual evolution of the synthesis reaction is preferable. Indeed, the inconveniences encountered during the process (gas pressure increase, powder expulsion, product inhomogeneity, abrupt sample displacement, die/punches breakage) make its practical exploitation difficult. In contrast, safety conditions are preserved when sufficiently lowering the heating rates to suppress the combustion reacti...
A comparative investigation regarding the consolidation behavior displayed by three commercially ... more A comparative investigation regarding the consolidation behavior displayed by three commercially available hydroxyapatite powders during Spark Plasma Sintering (SPS) is performed in this work. Starting powders are different in terms of purity, particle size, morphology and thermochemical stability. A completely dense product without secondary species is produced by SPS at 900 °C, when starting from highly pure powders with relatively small sized particles and grains. The resulting consolidated material, consisting of sub-micrometer sized hydroxyapatite grains, exhibits optical transparency and good mechanical properties. On the other hand, temperature levels up to 1,200 °C are needed to sinter powders with larger particles. This holds also true when relatively finer powders are used, also containing CaHPO4, are used. In both the latter cases products with coarser microstructures and/or significant amount of β-TCP, as a result of hydroxyapatite decomposition, are obtained. Optical, c...
Due to their inherent chemical complexity and their refractory nature, the obtainment of highly d... more Due to their inherent chemical complexity and their refractory nature, the obtainment of highly dense and single-phase high entropy (HE) diborides represents a very hard target to achieve. In this framework, homogeneous (Hf0.2Nb0.2Ta0.2Mo0.2Ti0.2)B2, (Hf0.2Zr0.2Ta0.2Mo0.2Ti0.2)B2, and (Hf0.2Zr0.2Nb0.2Mo0.2Ti0.2)B2 ceramics with high relative densities (97.4, 96.5, and 98.2%, respectively) were successfully produced by spark plasma sintering (SPS) using powders prepared by self-propagating high-temperature synthesis (SHS). Although the latter technique did not lead to the complete conversion of initial precursors into the prescribed HE phases, such a goal was fully reached after SPS (1950 °C/20 min/20 MPa). The three HE products showed similar and, in some cases, even better mechanical properties compared to ceramics with the same nominal composition attained using alternative processing methods. Superior Vickers hardness and elastic modulus values were found for the (Hf0.2Nb0.2Ta0.2...
Poly(glycerol-sebacate) (PGS) and poly(epsilon caprolactone) (PCL) have been widely investigated ... more Poly(glycerol-sebacate) (PGS) and poly(epsilon caprolactone) (PCL) have been widely investigated for biomedical applications in combination with the electrospinning process. Among others, one advantage of this blend is its suitability to be processed with benign solvents for electrospinning. In this work, the suitability of PGS/PCL polymers for the fabrication of composite fibers incorporating bioactive glass (BG) particles was investigated. Composite electrospun fibers containing silicate or borosilicate glass particles (13-93 and 13-93BS, respectively) were obtained and characterized. Neat PCL and PCL composite electrospun fibers were used as control to investigate the possible effect of the presence of PGS and the influence of the bioactive glass particles. In fact, with the addition of PGS an increase in the average fiber diameter was observed, while in all the composite fibers, the presence of BG particles induced an increase in the fiber diameter distribution, without changing...
An adequate tuning of amorphous calcium phosphates ionic composition and cold sintering condition... more An adequate tuning of amorphous calcium phosphates ionic composition and cold sintering conditions allowed the first successful stabilization of these bioactive compounds. These results show promise for the setup of highly-resorbable bone substitutes.
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