Jhon Jairo Olaya

Potentiodynamic Polarization Studies and Surface Chemical Composition of Bismuth Titanate (BixTiyOz) Films Produced through Radiofrequency Magnetron Sputtering

The applications of Bismuth Titanate (BixTiyOz) materials have been focused on their electronic and optical properties, but with respect to the use of these compounds in applications like corrosion resistance, have been very few or nonexistent. For this reason, in the present investigation BixTiyOz thin films were deposited using RF magnetron sputtering onto silicon wafers, stainless steel 316L, and titanium alloy (Ti6Al4V) substrates, in order to carry out a study of the corrosion behavior of this compound. The structural properties of the coatings were studied through X-ray diffraction (XRD), the morphology was determined using Scanning Electron Microscopy (SEM), the corrosion resistance behavior of the coated and uncoated substrates was evaluated via the Potentiodynamic Polarization technique, and surface chemical composition was evaluated through X-ray photoelectron spectroscopy (XPS). The XRD results indicated that the films were amorphous. The SEM micrographs showed that the deposited films were homogeneous, but in some cases there were cracks. The potentiodynamic polarization technique showed that the corrosion current in the coated substrates decreased by an order of two magnitudes with respect to the uncoated substrates, but in both cases the corrosion mechanism was pitting due to the pores in the film. The XPS analysis shows that the deposited films contain both Bi3+ and Ti4+.

Annealing Effect on the Structural and Optical Properties of Sputter-Grown Bismuth Titanium Oxide Thin Films

The aim of this work is to assess the evolution of the structural and optical properties of BixTiyOz films grown by rf magnetron sputtering upon post-deposition annealing treatments in order to obtain good quality films with large grain size, low defect density and high refractive index similar to that of single crystals. Films with thickness in the range of 220–250 nm have been successfully grown. After annealing treatment at 600 °C the films show excellent transparency and full crystallization. It is shown that to achieve larger crystallite sizes, up to 17 nm, it is better to carry the annealing under dry air than under oxygen atmosphere, probably because the nucleation rate is reduced. The refractive index of the films is similar under both atmospheres and it is very high (n =2.5 at 589 nm). However it is still slightly lower than that of the single crystal value due to the polycrystalline morphology of the thin films.

Production and characterization of niobium carbide coatings produced on tool steels by thermoreactive deposition/diffusion

En este trabajo se depositaron recubrimientos de carburo de niobio sobre aceros AISI M2, H13 y D2, utilizando la tecnica de deposicion por difusion termorreactiva. Los carburos se obtuvieron usando banos de sales compuestos por borax fundido, ferroniobio, ferrovanadio y aluminio a una temperatura de 1.020 °C durante 4 horas. La presencia de los recubrimientos fue observada por microscopia electronica de barrido. Las fases fueron determinadas usando difraccion de rayos X, y se utilizo microdureza para determinar la dureza. El comportamiento electroquimico fue estudiado mediante curvas de polarizacion potenciodinamica para determinar la densidad de corriente de corrosion, y espectroscopia de impedancia electroquimica para determinar la resistencia a la polarizacion. Los resultados fueron comparados con las propiedades del sustrato sin recubrimiento y en general se observo mayor dureza y mejor resistencia a la corrosion en los recubrimientos producidos.

Corrosiveness of biodiesel obtained from different raw materials on gray cast iron

espanolResumen En esta investigacion se estudian los efectos corrosivos del Biodiesel en la fundicion de hierro gris a temperatura ambiente. Los ensayos de inmersion estatica se realizaron mediante tecnicas gravimetricas con ausencia de luz y con cinco diferentes materias primas: sebo vacuno, manteca de cerdo, aceite de girasol, aceite de soya y aceite de coco. La afectacion de los acidos grasos que componen los diferentes Biodiesel fue determinada por medio de la regresion lineal con los datos obtenidos de velocidad de corrosion. Los resultados muestran que el Biodiesel con mayor nivel de insaturacion en su composicion es el que afecta la perdida de masa en el material de manera mas significativa, llevando a procesos mas corrosivos sobre la fundicion gris. portuguesResumo Esta pesquisa estuda os efeitos corrosivos do Biodiesel no ferro fundido cinzento a temperatura ambiente. Os ensaios de imersao estatica foram realizados mediante tecnicas gravimetricas com ausencia de luz e com cinco materias primas diferentes: sebo bovino, gordura suina, oleo de girassol, oleo de soja e oleo de coco. O efeito dos acidos graxos que compoem os diferentes Biodiesel foi determinado atraves da regressao linear com os dados avaliados da taxa de corrosao. Os resultados demonstram que os Biodiesel com maior concentracao de esteres insaturados afetam de forma mais significativa a perda de massa no material, causando processos mais corrosivos sobre o ferro fundido cinzento. EnglishAbstract The corrosive effects of biodiesel on gray cast iron at room temperature were studied. Static immersion tests were carried out through gravimetric techniques and in the absence of light, using five raw materials: beef tallow, lard, sunflower oil, soybean oil, and coconut oil. The influence of fatty acids that make up biodiesel was determined through linear regression with data obtained from the corrosion rate. Results show that biodiesels with a higher degree of unsaturated fats in their composition have a more significant effect on the loss of mass in the material, leading to more corrosive processes in gray cast iron.

Estado del arte en biocompatibilidad de recubrimientos

The success of a biocompatible material is intrinsically linked to the improvement on its surface properties since the surface is to be in direct contact with the living system when the material is implanted. For example, it has been shown that, via in vitro cell cultures, factors such as surface roughness or porosity increase cell adhesion on the biomaterial. Consequently, recent research on the design and development of biocompatible materials for implants in living systems must be closely connected to surface modifications and coating manufacturing techniques. The present article describes biocompatibility of surface coatings using, as a point of reference, widely implemented tests, namely cell adhesion, cell viability, biomineralization and corrosion, as well as their fundamental methods.

Obtención y caracterización mecánica de un acero bainítico aleado con boro (10 y 20 ppm)

Los aceros bainiticos se han convertido en uno de los materiales que se han investigado durante la ultima decada, debido a sus excepcionales propiedades mecanicas. La ventaja que ha tenido desarrollar este tipo materiales es particularmente la obtencion de estructuras libres de carburos que combinan una muy buena resistencia mecanica con una excelente tenacidad. Mediante este trabajo se establecieron y controlaron adecuadamente las condiciones metalurgicas para fundir en vacio un acero bainitico aleado con 10 y 20 ppm de Boro y tratamiento termomecanico de laminacion entre 1000 °C y 1200 °C. La caracterizacion microestructural se realizo mediante microscopia optica y microscopia electronica de barrido, y la caracterizacion mecanica mediante pruebas de dureza, traccion y tenacidad a temperatura ambiente. Los resultados obtenidos muestran resistencias ultimas del orden de 1800 MPa y elongaciones de aproximadamente el 16%. Es apreciable el aumento en las propiedades mecanicas con el incremento del contenido de boro en los aceros. El boro posiblemente esta actuando como agente refinador de grano y disminuye la nucleacion de la ferrita en los limites de grano de la austenita, facilitando la formacion de bainita.

Microstructural characterisation of Cr/CrN nano-multilayers produced by unbalanced magnetron sputtering

The production of Cr/CrN nano-multilayers through the unbalanced magnetron sputtering (UBM) technique was presented, and the influence of the unbalance degree on microstructure was studied. X-ray diffraction (XRD) was used to study phase formation in the coatings, and the presence of a multilayer structure was confirmed through transmission electron microscopy (TEM). Total thickness was measured through profilometry and it was assessed using grazing incidence X-ray reflectometry (XRR), which was also used for density, bilayer period and interface roughness measurements. The sin2 ψ method was used to study residual stresses presence. Results showed that the unbalance degree did not significantly influence the orientation of the multilayer planes, but it had an influence on peak positions, which indicated the presence of residual stresses. The density was also influenced by the unbalance degree, mainly due to ionic bombardment variation with each unbalance degree use.

Effect of period and degree of unbalancing on the structure and resistivity of Cr/CrN magnetron sputtered nano-multilayers

Cr/CrN nano-multilayers have been produced by varying the period and the degree of unbalancing in a magnetron sputtering system in order to study the influence of these parameters in the electrical properties. X-ray Diffraction (XRD) was used to investigate the microstructure characteristics of the multilayers and the Four Point Probe (FPP) technique in the Van der Pawn mode was used to evaluate electrical resistivity. The results show that the resistivity strongly depends on the period and the degree of unbalancing of the magnetron. These nano-multilayers are proposed to be used as contacts in Cu metallization and as diffusion barriers between copper and silicon.