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This paper studies the structural and photoluminescent properties of hydroxyapatite (HA) and europium-doped hydroxyapatite (HA:Eu) synthesised by the hydrothermal method and sintered by the spark plasma sintering (SPS) technique. HA and HA:Eu powders, synthesised at pH of 10, 11 and 12, were characterised by means of infrared spectroscopy, X-ray diffraction, scanning electron microscopy, Raman spectroscopy and luminescence spectroscopy. The HA and HA:Eu samples were sintered using the SPS technique at 900 and 1200 °C. It was determined that the HA and HA:Eu powders crystallised in the hexagonal phase, which is stable until 900 °C. The presence of Eu3+ ions tended to stabilise the hexagonal phase of hydroxyapatite at 1200 °C. Undoped hydroxyapatite sintered at 1200 °C revealed a significant amount of tricalcium phosphate (β-TCP) as a result of its decomposition. By increasing the heat treatment temperature, different emission lines (⁵D₀→ ⁷F₀, ⁵D₀→ ⁷F₁ and ⁵D₀→ ⁷F₂ transitions) were obtained due to calcium site substitution by the europium ions in the HA structure.

Lanthanum chromite nano-particles, with a composition of La0.9Ca0.1CrO3 and La0.8Ca0.2CrO3, were produced by 1 h of hydrothermal reaction at 400 and 425°C respectively. The sintering of the powders was conducted using a spark plasma apparatus over the temperature range 1300-1550ºC for 1 min with a constant loading pressure of 45 MPa. Additional sintering experiments using conventional firing were carried out for comparison. Fully densified (98 % r.d.) lanthanum chromite pellets with fine equiaxial grains 2.3 μm in size were obtained using the SPS (spark plasma sintering) method. In contrast, a maximum relative density of 97 % was produced using La0.8Ca0.2CrO3 sintered conventionally at 1400ºC for 300 min, and the average grain size of the resulting sintered sample was 6 μm.Partículas ultrafinas de cromita de lantano, con una composición de La0.9Ca0.1CrO3 y La0.8Ca0.2CrO3, se obtuvieron después de 1 hora de síntesis hidrotermal a las temperaturas de 400 y 425°C respectivamente. Los compuestos obtenidos, con un tamaño de partícula de ~ 200 nm, se caracterizaron utilizando las técnicas de DRX, MEB y MET. La sinterización de estos polvos se efectuó en un equipo de chispa de plasma en el rango de temperatura de 1300-1500°C durante 1 min, y a una presión de compactación de 45 MPa. Ambos polvos también se sinterizaron siguiendo un tratamiento térmico convencional, en aire, con el propósito de comparar ambos métodos de sinterización. Las muestras de cromita de lantano sinterizadas por plasma presentaban una densidad relativa del 98 % (/t); y una microestructura monofásica con granos equaxiales con un tamaño medio de grano menor de 2.3 μm. En contraste, la composición La0.8Ca0.2CrO3, sinterizada a 1400°C/300 min, por métodos convencionales alcanzó una densidad relativa máxima del 97 % y su microestructura estaba formada por una sola fase con un tamaño medio de grano de 6 μm.

This work focused in the study of the effect of the conforming process on the transformation of the alumina during the conventional sintering of spherical γ-alumina powders with a 35 nm of the average particle. We made compacts by three different method; slip casting, axial and isostatic compaction. Then sintering was carried out at 1500 ºC with an isothermal plateau of 1 hour in a vertical dilatometer. Samples were evaluated by SEM and XRD in order to observe the final microstructures, the final grain size was assessed by image analysis. Results show that sintering was activated earlier for the compacts produced by compaction either axial or isostatic, however maximal densification was observed for the slip casting. The smaller final grain size was obtained when isostatic compaction is used. In the other hand the evolution into the α-alumina was promoted by the slip casting.El presente trabajo se enfoca a estudiar efecto del proceso de conformado en la transformación y evolución de la microestructura de alúmina durante el sinterizado convencional de polvos esféricos de γ-alúmina con tamaño promedio de partícula de 35 nm. Las muestras fueron preparadas por tres diferentes rutas de conformado; colada por barbotina, prensado axial e isostático. Los compactos fueron sinterizados a 1500 ºC durante una hora en un dilatómetro vertical. Las muestras fueron evaluadas usando MEB y DRX con el propósito de observar la microestructura final, el tamaño de grano se obtuvo por análisis de imágenes. Los resultados revelaron que el sinterizado es activado, inicialmente en los compactos hechos mediante prensado ya sea axial o isostático, sin embargo, la máxima densificación se obtiene en muestras fabricadas por colada continua. El tamaño de grano más pequeño fue obtenido cuando la compactación isostática fue utilizada. Por el contrario la evolución a la fase α-alúmina se incrementa en muestras formadas por colada de barbotina.

Hydroxyapatite (HAp) nanoparticles with a homogeneous rod morphology were successfully synthesized using the hydrothermal method. The powders were characterized using Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. The antibacterial and dermal irritation analyses of the samples were performed and discussed. The use of cationic and anionic surfactants, namely, cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS), respectively, at a low concentration (2.5 mol%) modified the length/diameter (L/D) ratio of the HAp rods. Structural characterizations of hydroxyapatite synthesized without surfactant (HA), with 2.5 and 5 mol% of SDS (SDS- and SDS+, respectively), and with 2.5 and 5 mol% of CTAB (CTAB- and CTAB+, respectively) revealed well-crystallized samples in the hexagonal phase. The CTAB- sample presented antibacterial activity against Pseudomonas aeruginosa , Escherichia coli , Streptococcus anginosus , Staphylococcus aureus , Micrococcus luteus , and Klebsiella pneumoniae , suggesting that antimicrobial susceptibility was promoted by the bacterial nature and the use of the surfactant. Dermal irritation showed no clinical signs of disease in rabbits during the study, where there was neither erythema nor necrosis at the inoculation sites.

The present work studies the microstructure and mechanical performance of tricalcium phosphate (TCP) based cermet toughened by iron particles. A novelty arises by the employment of spark plasma sintering for fabrication of the cermet. Results showed partial transformation of initial alpha TCP matrix to beta phase and the absence of oxidation of iron particles, as well as a lack of chemical reaction between TCP and iron components during sintering. The values of compressive and tensile strength of TCP/Fe cermet were 3.2 and 2.5 times, respectively, greater than those of monolithic TCP. Fracture analysis revealed the simultaneous action of crack-bridging and crack-deflection microstructural toughening mechanisms under compression. In contrast, under tension the reinforcing mechanism was only crack-bridging, being the reason for smaller increment of strength. Elastic properties of the cermet better matched values reported for human cortical bone. Thereby the new TCP/Fe cermet has potential for eventual use as a material for bone fractures fixation under load-bearing conditions., (Copyright © 2018 Elsevier Ltd. All rights reserved.)