BS-SEM evaluation of the tisular interactions between cortical bone and calcium-phosphate covered titanium implants

The improvement of the reliability of the contact between the osseous tissues and the implant materials has been tested by recovering the metallic implants with ceramic materials, usually calcium phosphates. In our study, the calcium phosphate recovering layers were deposited by means of a pulsed-laser deposition technique. Our aim was to to evaluate the tissue interactions established between cortical bone and titanium implants covered by five different layers, ranging from amorphous calcium phosphate to crystalline hydroxyapatite, obtained by altering the parameters of the laser ablation process. The surgical protocol of the study consisted in the simultaneous implantation of the five types of implants in both the tibial dyaphisis of three Beagle dogs, sacrificed respectively one, two and three months after the last surgical procedures. After the sacrifice, the samples were submitted to a scheduled procedure of embedding in plastic polymers without prior decalcification, in order to perform the ultrastructural studies: scanning microscopy with secondary and backscattered electrons (BS-SEM). Our observations show that both in terms of the calcified tissues appearing as a response to the presence of the different coatings and of time of recovering, the implants coated with crystalline calcium phosphate layers by laser ablation present a better result than the amorphous-calcium-phosphate-coated implants. Moreover, the constant presence of chondroid tissue, related with the mechanical induction by forces applied on the recovering area, strongly suggests that the mechanisms implied in osteointegration are related to endomembranous, rather than endochondral ossification processes

Tribologia de Recubrimientos de Cermet/NiCrBSi Aplicables a la Obtencion de Recubrimientos y Conformados Resistentes al Desgaste

El trabajo consta de un completo estudio tribológico del sistema WX que consiste en la mezcla mecánica de WC-12Co y NiCrBSi en diferentes proporciones: 20% NiCrBSi (W2), 40% NiCrBSi (W4) y 60% NiCrBSi (W6). Los recubrimientos se han obtenido por proyección térmica de alta velocidad (HVOF). Para todos los sistemas, el coeficiente de fricción es menor que 0.5 y la energía intercambiada entre el par friccionante y el recubrimiento es inferior a 10 KJ. Para cuantificar el desgaste por fricción se han utilizado la profundidad de la huella y el volumen perdido durante el ensayo, obtenidos mediante Interferometría de Barrido de Luz Blanca (SLWI) y SEM. La profundidad de la huella sigue una evolución directamente proporcional al contenido en NiCrBSi. Un mayor contenido en WC-12Co aumenta la resistencia al desgaste por fricción y disminuye la velocidad de desgaste por abrasión (ensayo Rubber Wheel). En los recubrimientos obtenidos, no se observa difusión entre las fases, la adherencia con el sustrato es excelente, la porosidad menor al 2% y se produce un incremento de la dureza del recubrimiento debido al endurecimiento por trabajo de la matriz causada por impacto.

Catalytic gasification of glycerol in supercritical water

The conversion of glycerol in supercritical water (SCW) was studied at 510-550 °C and a pressure of 350 bars using both a bed of inert and non-porous ZrO2 particles (hydrothermal experiments), and a bed of a 1% Ru/ZrO2 catalyst. Experiments were conducted with a glycerol concentration of 5 wt% in a continuous isothermal fixed-bed reactor at a residence time between 2 and 10 s. Hydrothermolysis of glycerol formed water-soluble products such as acetaldehyde, acetic acid, hydroxyacetone and acrolein, and gases like H2, CO and CO2. The catalyst enhanced the formation of acetic acid, inhibited the formation of acrolein, and promoted gasification of the glycerol decomposition products. Hydrogen and carbon oxides were the main gases produced in the catalytic experiments, with minor amounts of methane and ethylene. Complete glycerol conversion was achieved at a residence time of 8.5 s at 510 °C, and at around 5 s at 550 °C with the 1 wt% Ru/ZrO2 catalyst. The catalyst was not active enough to achieve complete gasification since high yields of primary products like acetic acid and acetaldehyde were still present. Carbon balances were between 80 and 60% in the catalytic experiments, decreasing continuously as the residence time was increased. This was attributed partially to the formation of methanol and acetaldehyde, which were not recovered and analyzed efficiently in our set-up, but also to the formation of carbon deposits. Carbon deposition was not observed on the catalyst particles but on the surface of the inert zirconia particles, especially at high residence time. This was related to the higher concentration of acetic acid and other acidic species in the catalytic experiments, which may polymerize to form tar-like carbon precursors. Because of carbon deposition, hydrogen yields were significantly lower than expected; for instance at 550 °C the hydrogen yield potential was only 50% of the stoichiometric value.