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The present work is focused on developing Ti-xTa porous alloys processed by the space holder method and solid-state sintering. The volume fraction of Ta ranged between 20 and 30 wt.%. The sintering kinetics was evaluated by dilatometry tests. Sintered materials were characterized by SEM, XRD and computed tomography. Porosity features and permeability were determined from 3D images, and their mechanical properties were evaluated from microhardness and compression tests. The sintering behavior and the final microstructure are driven by the Ta diffusion into the Ti, slowing down the densification and modifying the transition temperature of α-to-β. Due to β-stabilization, martensite α′ was obtained after sintering. Mechanical properties are reduced because of the β-stabilization and pore addition, being predominantly the pore effect. Permeability depended on the pore characteristics, finding values close to the human bones. It was concluded that powder metallurgy generates highly TixTa alloys with a combination of α, β and α′ Ti phases as well as remaining Ta particles that are beneficial to improve the biocompatibility and osseointegration of such materials. Being the Ti25Ta40salt alloy the most suitable for orthopedic implants because of its characteristics and properties. [ABSTRACT FROM AUTHOR]

We present a novel Ti64/20Ag highly porous composite fabricated by powder metallurgy for biomedical applications and provide an insight into its microstructure and mechanical proprieties. In this work, the Ti64/20Ag highly porous composites were successfully fabricated by the space holder technique and consolidated by liquid phase sintering, at lower temperatures than the ones used for Ti64 materials. The sintering densification was evaluated by dilatometry tests and the microstructural characterization and porosity features were determined by scanning electron microscopy and computed microtomography. Permeability was estimated by numerical simulations on the 3D real microstructure. Mechanical properties were evaluated by simple compression tests. Densification was achieved by interparticle pore filling with liquid Ag that does not drain to the large pores, with additional densification due to the macroscopical deformation of large pores. Pore characteristics are closely linked to the pore formers and the permeability was highly increased by increasing the pore volume fraction, mainly because the connectivity was improved. As expected, with the increase in porosity, the mechanical properties decreased. These results permitted us to gain a greater understanding of the microstructure and to confirm that we developed a promising Ti64/20Ag composite, showing E of 7.4 GPa, σy of 123 MPa and permeability of 3.93 × 10−11 m2. Enhanced adaptability and antibacterial proprieties due to Ag were obtained for bone implant applications. [ABSTRACT FROM AUTHOR]

Ignimbrites' facies are key for interpreting the dynamics of explosive eruptions. Furthermore, they provide evidence of the physicochemical processes that acted during and after their deposition. Nevertheless, ignimbrites commonly present complex facies associations that require an integrative analytical methodology over a robust stratigraphic framework for their proper characterization. This work presents a facies characterization of the caldera-forming Xáltipan ignimbrite at Los Humeros Volcanic Complex, by integrating a combination of petrophysical and geochemical analyses aimed at its outflows (exposed) and intracaldera (buried) deposits. Based on the petrophysical properties, a three-facies association is identified controlled by welding and secondary mineralization effects: (1) The basal facies, characterized in the outflows by highly welded deposits (ranks V-VI), with low porosity (~4–8%), and practically impermeable conditions (<0.01–0.05 mD). In the intracaldera deposits, this facies shows pervasive geothermal-related propylitic mineralization that can reduce porosity up to ca. 80%. (2) A middle facies, with moderately welded deposits (ranks III-IV) and porous conditions consisting of a combination of intershard, vesicular, and fracture spaces, partially filled by secondary minerals, which reduce the porosity (6–11.5% in the outflows; 16–28% for the intracaldera), resulting in semi-permeable conditions (6.11–46.38 mD). (3) The upper facies are defined by being not to poorly welded deposits (ranks I-II), and characterized by being highly porous (dominated by intershard spaces) and permeable (310–1557 mD), and barely affected by secondary mineralization. The geochemical results (major and trace element) indicate that the Xáltipan ignimbrite shows a vertical compositional zonation, from rhyolitic (70.9–76.2 wt% SiO 2) in the lower flow unit to rhyolitic-trachydacitic (67–70.7 wt% SiO 2) composition in its upper flow unit. This last unit shows a geochemical affinity with the subsequent pyroclastic deposits. Geochemical analyses of intercalated lavas from well logs also provided evidence of unprecedented breccias formed during the caldera collapse, discarding the existence of previously assumed thick lava flows. Facies correlation, among other well logs, shows that the facies distribution is directly controlled by the ignimbrite thickness. Where the ignimbrite is > 400 m thick, the entire facies association is observed, while when the thickness is < 400 m, the upper and middle facies occurs preferentially. This facies analysis may contribute to the overall model of Los Humeros subsurface stratigraphy, by defining the Xáltipan ignimbrite distribution and its porosity-permeability-based zones, which are of particular interest for geothermal purposes. Finally, this work provides the first example of a caldera-forming ignimbrite that presents analog facies associations between its outflows and intracaldera deposits that may be applied for other ignimbrites worldwide. • The Xáltipan ignimbrite shows petrophysical and geochemical variations. • Three petrophysical facies are identified in both outflows and intracaldera deposits. • Welding and secondary mineralization are porosity-permeability changing factors. • In the highly-welded basal facies, the Xáltipan ignimbrite is impermeable. • Unprecedented coarse, lithic-rich, intracaldera breccias are identified. [ABSTRACT FROM AUTHOR]