EPD Technology for Functionalizing 3D Printing Scaffolds

Please click Additional Files below to see the full abstract

Mechanics and mechanisms of fatigue in a WC-Ni hardmetal and a comparative study with respect to WC-Co hardmetals

There is a major interest in replacing cobalt binder in hardmetals (cemented carbides) aiming for materials with similar or even improved properties at a lower price. Nickel is one of the materials most commonly used as a binder alternative to cobalt in these metal-ceramic composites. However, knowledge on mechanical properties and particularly on fatigue behavior of Ni-base cemented carbides is relatively scarce. In this study, the fatigue mechanics and mechanisms of a fine grained WC-Ni grade is assessed. In doing so, fatigue crack growth (FCG) behavior and fatigue limit are determined, and the attained results are compared to corresponding fracture toughness and flexural strength. An analysis of the results within a fatigue mechanics framework permits to validate FCG threshold as the effective fracture toughness under cyclic loading. Experimentally determined data are then used to analyze the fatigue susceptibility of the studied material. It is found that the fatigue sensitivity of the WC-Ni hardmetal investigated is close to that previously reported for Co-base cemented carbides with alike binder mean free path. Additionally, fracture modes under stable and unstable crack growth conditions are inspected. It is evidenced that stable crack growth under cyclic loading within the nickel binder exhibit faceted, crystallographic features. This microscopic failure mode is rationalized on the basis of the comparable sizes of the cyclic plastic zone ahead of the crack tip and the characteristic microstructure length scale where fatigue degradation phenomena take place in hardmetals, i.e. the binder mean free path. (C) 2014 Elsevier Ltd. All rights reserved.Peer ReviewedPostprint (author’s final draft

Protective nature of nano-TiN coatings shaped by EPD on Ti substrates

The hardness and corrosion resistance of TiN coatings, processed by Electrophoretic Deposition (EPD) to cover polished and unpolished Ti substrates, have been evaluated. A deposition time of 5 min has been enough to obtain a cohesive layer of 7–8 μm in thickness. The coatings were thermally treated in vacuum atmosphere at 1200 °C for 1 h with heating and cooling rates of 5 °C min−1. The surfaces have been covered homogeneously optimizing the properties of the Ti substrates. Uniform and dense TiN coatings have been obtained onto polished substrates, while on unpolished Ti the nitrogen diffuses toward the substrate, moderately dissolving TiN coating. The nanohardness values of the polished samples have been increased from 2.8–4.8 GPa up to 6.5–8.5 GPa. Besides, the corrosion current density has been reduced more than one order of magnitude obtaining a protective efficiency of 82%. These values have been compared with other works in literature where authors used complex and costly processing techniques, demonstrating the strong impact of the colloidal processing over the specific properties of the material

Functionalizing Ti-Surfaces through the EPD of Hydroxyapatite/NanoY₂O₃

Ceramic materials for skeletal repair and reconstruction are expanding to a number of different applications. Present research is addressing new compositions and performances to promote osseo-integration through metal coatings. Nanotechnology plays a key role in this research because nanostructures can be introduced into implants to functionalize them and/or to enhance their properties, such as the thermal or mechanical response. In this work, the insertion of Y₂O₃ nanoparticles into a hydroxyapatite (HA) coating of Ti using colloidal processing technology was developed. The suspensions of HA and Y₂O₃ nanoparticles were formulated with a focus on zeta potential, particle size distribution, and viscosity for the codeposition of both phases by electrophoresis. The microstructure of the nanocomposite coating was optimized by adjusting the main parameters of the electrophoretic deposition process. A threshold value of the applied electric field for the composite shaping was identified. The results demonstrate that the Y₂O₃ nanoparticles are homogeneously distributed in the coating and decrease in concentration as the distance from the substrate increases. As a consequence of the presence of the Y₂O₃, delays in the HA thermal decomposition and the improvement of metal–ceramic joining were observed.This work has been supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under contracts MAT2009 14448 C02 01, MAT2012 38650 C02 02, and IPT 310000 2010 12

Effect of highly dispersed yttria addition on thermal stability of hydroxyapatite

The capability of the colloidal method to produce yttria (Y₂O₃) dispersed hydroxyapatite (HA) has been investigated as an alternative method to the conventional method of mechanical mixing and sintering for developing HA-based materials that could exhibit controllable and enhanced functional properties. A water based colloidal route to produce HA materials with highly dispersed Y₂O₃ has been applied, and the effect of 10 wt.% Y₂O₃ addition to HA investigated by thermal analysis, X-ray diffraction and Fourier transform infrared spectroscopy. These measurements evidence a remarkable effect of this Y₂O₃ addition on decomposition mechanisms of synthetic HA. Results show that incorporation of Y₂O₃ as dispersed second phase is beneficial because it hinders the decomposition mechanisms of HA into calcium phosphates. This retardation will allow the control of the sintering conditions for developing HA implants with improved properties. Besides, substitution of Ca⁻2+ with Y⁻3+ ions appears to promote the formation of OH- vacancies, which could improve the conductive properties of HA favorable to osseointegration.This work has been supported by the Ministry of Science and Innova tion of Spain (MICINN) under contracts MAT2009 14448 C02 01 and IPT 310000 2010 12, and Regional Government of Madrid through the ESTRUMAT CM program (MAT 1585).Publicad

Semiconductor-metal core-shell nanostructures by colloidal heterocoagulation in aqueous medium

In contrast to complex syntheses for the preparation of colloidal nanocomposites in a core-shell structure proposed in the literature, we present herein a facile colloidal route based on a heterocoagulation process promoted by the electrostatic interaction among ceramic NiO nanoplatelets and metallic Ni nanoparticles (NPs). Before the heterocoagulation process, NiO and Ni were synthetized separately in presence of ultrasound, by chemical precipitation and chemical reduction of the same nickel precursor, respectively. After that, NiO-Ni core-shell nanostructures were prepared forcing the electrostatic interaction among surfaces in aqueous medium. The surface charge balances of both types of particles were tuned effectively by adjusting the pH in a free-additives suspension. For the surface modification of NiO by Ni, the ceramic suspensions maintain a positive zeta potential at pH 9, while the surface of metallic particles is negatively charged. Then the uniform coating of NiO platelets, by the electrostatically induced coagulation with Ni NPs, was favors. The degree of coverage and the formation of NiO-Ni core-shell nanostructures were followed referring the evolution of zeta potential with the geometric calculation in terms of size and morphology of both nanoparticles, and then corroborated by field emission scanning electron microscopy (FESEM).The authors acknowledge the support of the projects S2013/MIT-2862 and MAT2012–38650-02–01, MAT2012–38650-C02–02. M. de Dios acknowledges MINECO through the grant FPI-2013 and Dr. Z González acknowledges to MINECO through the grant PTQ-13–05985

Effect of surface modifiers on the nanoparticles electro-driven assembly

Understanding the colloidal behavior of particles is mandatory to prepare stable and disperse suspensions suitable for EPD. Up today, most of the proposed models for the EPD kinetics have been formulated considering the electrophoresis process, where depositing features are quantified by the sticking factor, a probabilistic and empiric parameter. Proposed models have demonstrated that interparticles forces are also the clue to understand the way in which particles compact on the electrode under the influence of an electric field in an electrostatically stabilized suspension. Please click on the link below for the full content

Effect of surface modifiers on the nanoparticles electro-driven assembly

Understanding the colloidal behavior of particles is mandatory to prepare stable and disperse suspensions suitable for EPD. Up today, most of the proposed models for the EPD kinetics have been formulated considering the electrophoresis process, where depositing features are quantified by the sticking factor, a probabilistic and empiric parameter. Proposed models have demonstrated that interparticles forces are also the clue to understand the way in which particles compact on the electrode under the influence of an electric field in an electrostatically stabilized suspension. Empirically in those systems, the morphology, the crystallography and the reactivity of the particles, determine the charge distribution in their surfaces, while the ionic strength modulates the charge density. However, new perspectives of particles assembly verified that in suspensions stabilized by an electrosteric mechanism, under similar electric conditions, changes in nature, length and ionization strength of surface modifiers or ligands determine the interaction forces among nanoparticles, resulting in an effective tool to manage nanoparticles flocculation and hence kinetics and ordering during the film growth. This fact has been specifically proved in the electrophoretic deposition of nanoplatelets or in the spatial orientation of nanocrystals. In this paper, we will discuss the literature that evidences how the surface modifiers not only define the deposition rate, but they also determine the deposition behavior and the final microstructure of the coating. Particularly the Layer-by-Layer (LbL) technology, understood as the alternate absorption of cationic and anionic polymers onto the particle surface, will be shown as an example of the compaction tailoring in 3D ceramic electrodes for supercapacitor manufacturing