J. Lira

Electroless nickel-boron coatings on metal carbides

Abstract Electroless deposition is a very simple process which can be used to obtain amorphous metallic coatings of uniform thickness on metallic or non-metallic substrates. In this work, nickel-boron coatings were deposited by electroless plating on WC and VC powders and sintered substrates. Two electrolyte solutions for the deposition of Ni-B coatings were developed: an alkaline and an acidic bath, both based on nickel chloride. Coating characterization was carried out by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Auger electron spectroscopy (AES) and X-ray diffraction (XRD). Both electrolytes produced continuous firms of uniform thickness on sintered carbide substrates; the acidic bath showed a higher deposition rate. Furthermore on the carbide powders it produced crack-free Ni-B continuous coatings. Ni was detected by EDS and the coating purity was confirmed by AES. XRD proved that amorphous coatings were obtained in all cases.

Zirconia coatings by spray pyrolysis

Abstract Zirconia coatings were obtained with the spray pyrolysis process, using a precursor solution of zirconium n-propoxide in 1-propanol. An investigation was undertaken into the influence of carrier gas (air, He, N2 and Ar), temperature (450 and 600 °C), time (1 and 2 h) and substrate composition (borosilicate glass, alumina, stainless steel and carbon steel) on coating characteristics. The most important deposition parameters were found to be the atomic or molecular weight of the carrier gas and the pyrolysis temperature. Cubic ZrO2 thin films, with dense and homogeneous nanostructrure were obtained using He and N2 as carrier gas, at 600 °C, on ceramic substrates.

A novel photocrosslinkable and cytocompatible chitosan coating for Ti6Al4V surfaces

Background In this work, chitosan (CH) was used to produce a novel coating for Ti6Al4V, the most widely used alloy in orthopedic implants, so as to improve the biological tissue response at the metallic surface. Methods The Ti6Al4V surface was sandblasted with alumina particles. CH was chemically modified, via carbodiimide chemistry, using lactobionic and 4-azidebenzoic acid to make it soluble at physiological pH and photocrosslinkable, respectively. The reaction was verified by FTIR, NMR and UV/vis spectroscopy. Ti6Al4V surfaces were coated with solutions of the modified CH and exposed to UV light, causing polymer crosslinking and formation of a hydrogel on the surface. The crosslinking reaction was monitored by FTIR at different exposure times. Coating morphology was observed by SEM. The coatings cytocompatibility was determined in vitro through the culture of rat bone marrow mesenchymal stem cells, using an MTT assay, with their morphology assessed by SEM. Results The developed coating behaved as a hydrogel on the Ti6Al4V and was stable on the surface. FTIR and NMR confirmed the crosslinking mechanism, based on an arile ring expansion, and subsequent reaction with the CH amine groups. Furthermore, the coating was able to support cell proliferation and osteogenic differentiation. Conclusions UV crosslinking of CH is easy to apply and has potential for future metallic implant surface modifications. Due to its nature as a hydrogel, the coating could be used for further studies in the encapsulation of bioactive molecules to improve osteogenic potential at the tissue–implant interface.

The Stability of Cermet Coatings and their Dependence on the Distribution of Elements

The wear and corrosion of carbon steel parts can be reduced by-coating them with an appropriate alloy. It would be even more desirable to design a cermet with toughness imparted by the metal matrix and hardness or strength by the ceramic reinforcement thus more closely approximating the industrial requirement for the sintered or coated parts. Investigation of the electrochemical and tribological behavior of commercial metal matrix composites and cermets has drawn attention to the chemical and mechanical behavior and characteristics of metal-ceramic interfaces.

Study of Sol-Gel Transition in Ceramic Systems by High Resolution Refractometry

Sol-gel methods are used to synthesize ceramic oxides for a wide range of applications in coatings, powders and monolithic pieces. The early stages of sol reactions, up to gelation, play an important role in the nanoscale microstructure, morphology and density of gels. This paper presents a recently developed interferometric method. A spectroscopic analysis of interferograms of white light passing through samples of sols, permits the precise measurement of gelation time up to 10 -7 s, and the geometrical positioning of the initial stage of the gel in the solution.