Abnormal magnetic behaviour of powder metallurgy austenitic stainless steels sintered in nitrogen

The magnetic response of AISI 304L and AISI 316L obtained through powder metallurgy and sintered in nitrogen were studied. AISI 304L sintered in nitrogen showed a ferromagnetic behaviour in as-sintered state while AISI 316L was paramagnetic. After solution annealing both were paramagnetic. Magnetic behaviour was analysed by using a vibrating sample magnetometer, a magnetic ferritscope and magnetic etching. A microstructural characterization was performed by means of optical metallography, X-ray diffraction, scanning electron microscopy (SEM) and energy dispersive analysis of X-rays (EDS). Some samples when needed were submitted to aged heat treatments at 675 and 875 °C for 90 min, 4, 6, 8 or 48 h. The main microstructural feature found was the presence of a lamellar constituent formed by nitride precipitates and an interlamellar matrix of austenite and/or ferrite. The abnormal magnetic response was explained based on this.Dirección General de Programas y Transferencia de Conocimiento, Ministerio de Ciencia e Innovación, España, MAT2008-0278

Analysis of musts and wines by means of a bio-electronic tongue based on tyrosinase and glucose oxidase using polypyrrole/gold nanoparticles as the electron mediator

Producción CientíficaA bioelectronic tongue (bioET) based on combinations of enzymes (tyrosinase and glucose oxidase) and polypyrrole (Ppy) or polypyrrole/AuNP (Ppy/AuNP) composites was build up and applied to the analysis and discrimination of musts and wines. Voltammetric responses of the array of sensors demonstrated the effectiveness of polymers as electron mediators and the existence of favorable synergistic effects between Ppy and the AuNPs. Using Principal Component Analysis and Parallel Factor Analysis it was possible to discriminate musts according to the °Brix and TPI (Total Polyphenol Index), and wines according to the alcoholic degree and TPI. Partial Least Squares provided good correlations between the bioET output and traditional chemical parameters. Moreover, Support Vector Machines permitted to predict the TPI and the alcoholic degree of wines, from data provided by the bioET in the corresponding grapes. This result opens the possibility to predict wine characteristics from the beginning of the vinification process.Ministerio de Economía, Industria y Competitividad - Fondo Europeo de Desarrollo Regional (project AGL2015-67482-R)Junta de Castilla y León - Fondo Europeo de Desarrollo Regional (project VA275P18)Junta de Castilla y León (grant BOCYL-D-4112015-9

Biosensors Platform Based on Chitosan/AuNPs/Phthalocyanine Composite Films for the Electrochemical Detection of Catechol. The Role of the Surface Structure

Producción CientíficaBiosensor platforms consisting of layer by layer films combining materials with different functionalities have been developed and used to obtain improved catechol biosensors. Tyrosinase (Tyr) or laccase (Lac) were deposited onto LbL films formed by layers of a cationic linker (chitosan, CHI) alternating with layers of anionic electrocatalytic materials (sulfonated copper phthalocyanine, CuPcS or gold nanoparticles, AuNP). Films with different layer structures were successfully formed. Characterization of surface roughness and porosity was carried out using AFM. Electrochemical responses towards catechol showed that the LbL composites efficiently improved the electron transfer path between Tyr or Lac and the electrode surface, producing an increase in the intensity over the response in the absence of the LbL platform. LbL structures with higher roughness and pore size facilitated the diffusion of catechol, resulting in lower LODs. The [(CHI)-(AuNP)-(CHI)-(CuPcS)]2-Tyr showed an LOD of 8.55∙10−4 μM, which was one order of magnitude lower than the 9.55·10−3 µM obtained with [(CHI)-(CuPcS)-(CHI)-(AuNP)]2-Tyr, and two orders of magnitude lower than the obtained with other nanostructured platforms. It can be concluded that the combination of adequate materials with complementary activity and the control of the structure of the platform is an excellent strategy to obtain biosensors with improved performances.Ministerio de Ciencia, Innovación y Universidades - Fondo Europeo de Desarrollo Regional (project RTI2018-097990-B-100)Junta de Castilla y Leon - Fondo Europeo de Desarrollo Regional (project VA275P18)Infraestructuras Red de Castilla y León (grant UVA01

Effect of ageing heat treatments on the microstructure and intergranular corrosion of powder metallurgy duplex stainless steels

The influence of ageing heat treatments (675 and 875 °C for 1.5 to 48 h) on the microstructure and intergranular corrosion resistance of sintered in nitrogen duplex stainless steels was investigated. The materials were obtained by sintering mixtures of austenitic AISI 316L and ferritic AISI 430L powders. Corrosion behaviour was evaluated by using electrochemical techniques. The beneficial effect of nitrogen on corrosion behaviour of solution annealed samples was established. During ageing, secondary phases were precipitated and the intergranular and transgranular corrosion resistance significantly decreased though repassivation was observed in specimens aged at 875 °C for times up to 8 h.Ministerio de Ciencia e Innovación, Dirección General de Programas y Transferencia de Conocimiento, Proyectos I+D, MAT2008-0278

Characterization of porous nickel-free austenitic stainless steel prepared by mechanical alloying

Nickel-free austenitic powder metallurgy stainless steels were prepared and characterized. The main issue was to obtain potential biocompatible materials. Mechanical alloying in a nitrogen atmosphere was used to obtain these powders. The main factor to be controlled was the milling time. Powder metallurgy was the technique to obtain massive samples from alloyed powders. Two sintering processes were applied by controlling the sinter-cooling rate (furnace and water-cooling). The sintering atmosphere applied was nitrogen because of its gammagenic effect. Samples made of powders milled for 48 h, sintered in nitrogen and water-cooled showed a clean austenitic microstructure, which is a suitable microstructure for biological applications. A complete microstructural characterization, including optical metallography, image analysis, Scanning Electron Microscopy with X-ray microanalysis, X-Ray diffraction and Vickers hardness and microhardness, was carried out. The electrochemical behaviour in a simulated body fluid, phosphate buffered saline, was also studied. The biocorrosion behaviour was evaluated in terms of anodic polarization measurements.2020-07-102020-07-1

Improved corrosion behavior and biocompatibility of porous Titanium samples coated with bioactive Chitosan-based nanocomposites

Producción CientíficaPorous titanium implants can be a good solution to solve the stress shielding phenomenon. However, the presence of pores compromises mechanical and corrosion resistance. In this work, porous titanium samples obtained using a space-holder technique are coated with Chitosan, Chitosan/AgNPs and Chitosan/Hydroxyapatite using only one step and an economic electrodeposition method. The coatings’ topography, homogeneity and chemical composition were analyzed. A study of the effect of the porosity and type of coating on corrosion resistance and cellular behavior was carried out. The electrochemical studies reveal that porous samples show high current densities and an unstable oxide film; therefore, there is a need for surface treatments to improve corrosion resistance. The Chitosan coatings provide a significant improvement in the corrosion resistance, but the Chitosan/AgNPs and Chitosan/HA coatings showed the highest protection efficiency, especially for the more porous samples. Furthermore, these coatings have better adherence than the chitosan coatings, and the higher surface roughness obtained favors cell adhesion and proliferation. Finally, a combination of coating and porous substrate material with the best biomechanical balance and biofunctional behavior is proposed as a potential candidate for the replacement of small, damaged bone tissues.Ministerio de Ciencia, Innovación y Universidades (grants RTI2018-097990-B-I00 and PID2019-109371GB-I00)Junta de Andalucía - Fondo Europeo de Desarrollo Regional (project US-1259771)Junta de Castilla y León (projects VA275P18 and VA044G19

Corrosion properties of a low-nickel austenitic porous stainless steel in simulated body fluids

Producción CientíficaNickel can cause severe allergic reactions. Therefore, efforts are made to reduce the content of nickel in austenitic stainless steels (SS). Powder metallurgy (PM) techniques can produce this steel in a highly affordable way. A novel low-nickel high-nitrogen austenitic powder metallurgy PM stainless steel is investigated in terms of corrosion behavior. Nitrogen, because of its gammagenic effect, is the applied sintering atmosphere. Two sintering processes are applied by controlling the sinter-cooling rate (furnace- and water-cooling). This material shows an austenitic microstructure free of precipitates only after the water-cooling process. The electrochemical behavior in two simulated body fluids—phosphate buffered saline (PBS) solution and Ringer solution—are studied. Corrosion behavior is evaluated by means of anodic polarization measurements and cyclic polarization curves. In addition, Electrochemical Impedance Spectroscopy is used to evaluate the corrosion resistance of this steel in PBS at open circuit potential and at 100 mV above corrosion potential. The water-cooling process promotes better corrosion behavior in simulated body fluids for high nitrogen and low nickel than a conventional (high nickel) austenitic PM SS 316LN type

Electrochemical sensors modified with combinations of sulfur containing phthalocyanines and capped gold nanoparticles: A study of the influence of the nature of the interaction between sensing materials

Producción CientíficaVoltametric sensors formed by the combination of a sulfur-substituted zinc phthalocyanine (ZnPcRS) and gold nanoparticles capped with tetraoctylammonium bromide (AuNPtOcBr) have been developed. The influence of the nature of the interaction between both components in the response towards catechol has been evaluated. Electrodes modified with a mixture of nanoparticles and phthalocyanine (AuNPtOcBr/ZnPcRS) show an increase in the intensity of the peak associated with the reduction of catechol. Electrodes modified with a covalent adduct-both component are linked through a thioether bond-(AuNPtOcBr-S-ZnPcR), show an increase in the intensity of the oxidation peak. Voltammograms registered at increasing scan rates show that charge transfer coefficients are different in both types of electrodes confirming that the kinetics of the electrochemical reaction is influenced by the nature of the interaction between both electrocatalytic materials. The limits of detection attained are 0.9 × 10−6 mol∙L−1 for the electrode modified with the mixture AuNPtOcBr/ZnPcRS and 1.3 × 10−7 mol∙L−1 for the electrode modified with the covalent adduct AuNPtOcBr-S-ZnPcR. These results indicate that the establishment of covalent bonds between nanoparticles and phthalocyanines can be a good strategy to obtain sensors with enhanced performance, improving the charge transfer rate and the detection limits of voltammetric sensors.Ministerio de Economía, Industria y Competitividad - Fondo Europeo de Desarrollo Regional (projects RTI2018-097990-B-I00 / CTQ2017-87102-R)Junta de Castilla y Leon - Fondo Europeo de Desarrollo Regional (project VA275P18

Nanocomposites of conductive polymers and nanoparticles deposited on porous material as a strategy to improve its corrosion resistance

Producción CientíficaA strategy for the corrosion protection of porous materials using conductive polymers and nanocomposites of polymers and nanoparticle is presented. Several conductive polymers, various dopants and different electropolymerization conditions are studied to select the films with the highest corrosion resistance on porous and non-porous materials. It is found that nanocomposite films prepared from two different methods i.e., the co-generation of Au nanoparticles and the dispersion of TiO2 nanoparticles inside the selected polymer coating give rise to an excellent corrosion resistance. Coated porous samples have the most noble corrosion potentials, the lowest stable passive current densities and the highest polarization resistances.Ministerio de Educación y Formación Profesional (project RTI2018-097990-B-I00)Junta de Castilla y León (projects VA275P18 and VA044G19

Development of a bioelectronic tongue modified with gold nanoparticles for dairy analysis

Producción CientíficaThe objective of this work was to create an all-solid-state potentiometric bioelectronic tongue with an array of polymeric membrane-based sensors, which could then be used in the dairy sector. Membranes were modified with gold nanoparticles, and enzymes were covalently linked to the sensor’s surface to create an array of sensors with greater sensitivity. The responses of the sensors modified with gold nanoparticles and covalently associated enzymes, showed higher sensitivities. Moreover, the developed bioelectronic tongue was able to perform the discrimination of milks with different nutritional characteristics by applying principal component analysis. In addition, the results obtained showed that by applying partial least squares analysis, the system could be used as a prediction system for different chemical parameters (such as acidity, proteins, lactose, etc.).Ministerio de Ciencia, Innovación y Universidades - Fondo Europeo de Desarrollo Regional (FEDER) - (Project RTI2018-097990-B-100)Junta de Castilla y León y Fondo Europeo de Desarrollo Regional (FEDER) - (Project VA275P18