Titanium and its alloys are reference materials in biomedical applications because of their desirable properties. However, one of the most important concerns in long-term prostheses is bone resorption as a result of the stress-shielding phenomena. Development of porous titanium for implants with a low Young’s modulus has accomplished increasing scientific and technological attention. The aim of this study is to evaluate the viability, industrial implementation and potential technology transfer of different powder-metallurgy techniques to obtain porous titanium with stiffness values similar to that exhibited by cortical bone. Porous samples of commercial pure titanium grade-4 were obtained by following both conventional powder metallurgy (PM) and space-holder technique. The conventional PM frontier (Loose-Sintering) was evaluated. Additionally, the technical feasibility of two different space holders (NH4HCO3 and NaCl) was investigated. The microstructural and mechanical properties were assessed. Furthermore, the mechanical properties of titanium porous structures with porosities of 40% were studied by Finite Element Method (FEM) and compared with the experimental results. Some important findings are: (i) the optimal parameters for processing routes used to obtain low Young’s modulus values, retaining suitable mechanical strength; (ii) better mechanical response was obtained by using NH4HCO3 as space holder; and (iii) Ti matrix hardening when the interconnected porosity was 36–45% of total porosity. Finally, the advantages and limitations of the PM techniques employed, towards an industrial implementation, were discussed.

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Spinel LiMn2O4 is a promising cathode material for lithium-ion batteries. However, bulk LiMn2O4 commonly suffers from capacity fading due to the dissolution of Mn into the electrolyte during cycling. Moreover, bulk LiMn2O4 exhibits a low Li+ diffusion coefficient that limits the volume available to Li+ storage. Herein, we report the synthesis of small hollow porous LiMn2O4 nanostructures with a mean size of 51 nm exhibiting exposed (111) planes, assembled by nanoparticles of about 6 nm in size. The morphological features of these nanostructures ensure a large contact area between the material and the electrolyte, shorten the pathways for Li+ diffusion and provide effective accommodation of the volume change during cycling. Therefore, these hollow nanostructures exhibit improved discharge capacity retention (nearly 82% after 200 cycles) and a greater Li+ diffusion coefficient (3.46 × 10−7 cm s−1) compared with that of bulk LiMn2O4.

A series of Ni/γ-Al 2 O 3 samples were prepared by the sol-gel method using a solution of nickel nitrate as gelation agent. The Ni content of the samples was in the range 7-39 wt%. High specific BET areas, from 150 to 200 m 2 /g, were determined in samples after 4 h calcination at 600 ºC. As the metal was incorporated into the alumina during formation of the porous structure, high metal-support interaction and nickel dispersion were expected. To investigate the extent of these effects, reducing treatments were carried out and monitored by Thermogravimetry (TG), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and X-ray Diffractrometry (XRD). All XRD spectra from calcined samples showed patterns corresponding to NiO and spinellike NiAl 2 O 4 structures. Reducing treatments at 400ºC were performed in a TG set up, in 10% H 2 /Ar flow, until no mass change was detected. XRD spectra recorded afterwards showed Niº diffraction peaks corresponding to 20nm metal particles but also NiO and NiAl 2 O 4 patterns consistent with smaller particles of 4-7 nm in size. Subsequent treatments at 700ºC also in H 2 /Ar flow allowed accomplishing the metal reduction. XRD spectra indicated that reduction was complete in all samples after 30 min plateau. This time proved short enough to avoid introducing much distortion in the alumina matrix as confirmed by BET area. All samples showed particles of 20-30 nm in size under TEM, indicating that this method allows the obtention of high dispersed Ni particles even for very high Ni contents.

-Acero Eutectoide: Es un acero al carbono con una composición muy cercana al punto Eutectoide de 0.77 % en peso de Carbono. Para obtener esta microestructura se ha realizado un Normalizado que consiste en un tratamiento térmico calentado la muestra a 800 ͦC y realizando un enfriamiento al aire. Mientras permanecía a alta temperatura la estructura era monofásica de Austenita (solución sólida de carbono en hierro gamma). Al enfriarse los granos se ha transformado en láminas alternas de Ferrita y de Cementita que se denominan Perlita. Estas láminas están muy próximas unas a otras y sólo se resuelven en el microscopio óptico a grandes aumentos. -Acero Hipoeutectoide: Es un acero al carbono con una composición de 0.35 % en peso de Carbono. Para obtener esta microestructura se ha dejado enfriar lentamente la muestra desde 870 ͦC donde su estructura era de Austenita (monofásica) hasta situarse en el campo bifásico de Austenita y Ferrita. Esos granos de Ferrita proeutectoide, donde el carbono está en muy baja proporción, al seguir bajando la temperatura hacen que la Austenita se enriquezca cada vez más en carbono hasta alcanzar la composición eutectoide de 0.77 %C. Al continuar el enfriamiento, esa Austenita se transforma en Perlita (láminas alternas de Ferrita y Cementita). Esa es la estructura que se observa granos de Perlita rodeados de granos de Ferrita. -Acero Hipereutectoide: Es un acero al carbono con una composición de 1.3 % en peso de Carbono. La microestructura que se observa se ha conseguido enfriando lentamente el acero desde 970 ͦC donde su estructura es Austenita (monofásica) hasta situarse en el campo bifásico de Austenita y Cementita. Esta Cementita precipita en los bordes de granos de Austenita rodeándolos. Al seguir enfriando, la Austenita se empobrece cada vez más en carbono hasta alcanzar la composición eutectoide de 0.77 %C. Disminuyendo la temperatura, los granos de Austenita se transforman en Perlita (láminas alternas de Ferrita y Cementita). Esa es la estructura que se observa granos de Perlita rodeados de Cementita.