Electroreactivity of isopropanol on platinum in acids studied by DEMS and FTIRS

The reactivity of isopropanol on polycrystalline Pt in acid solutions was investigated using in-situ Fourier transform IR spectroscopy (FTIRS) and on-line differential electrochemical mass spectrometry (DEMS). The electro-oxidation products are acetone and CO2; the former is observed when isopropanol is present in the bulk of the solution, and the latter is produced from strongly adsorbed species. Both bulk and adsorbed isopropanol electro-reduction yield propane. H-D exchange is observed during propane formation when the reaction takes place in a D2O + DCIO4 solution. This observation suggests the formation of adsorbates bonded to the surface through the C ∝ atom of the isopropanol molecule. FTIR spectra of adsorbed species show the presence of -CH3 and -COH groups. The most probable adsorbate structures are (CH3-C-CH3)Pt, (CH3-CH-CH3)Pt and (CH3-COH-CH3)Pt, presumably accompanied by (CH3-CO-CH3)Pt.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Electroreactivity of isopropanol on platinum in acids studied by DEMS and FTIRS

The reactivity of isopropanol on polycrystalline Pt in acid solutions was investigated using in-situ Fourier transform IR spectroscopy (FTIRS) and on-line differential electrochemical mass spectrometry (DEMS). The electro-oxidation products are acetone and CO2; the former is observed when isopropanol is present in the bulk of the solution, and the latter is produced from strongly adsorbed species. Both bulk and adsorbed isopropanol electro-reduction yield propane. H-D exchange is observed during propane formation when the reaction takes place in a D2O + DCIO4 solution. This observation suggests the formation of adsorbates bonded to the surface through the C ∝ atom of the isopropanol molecule. FTIR spectra of adsorbed species show the presence of -CH3 and -COH groups. The most probable adsorbate structures are (CH3-C-CH3)Pt, (CH3-CH-CH3)Pt and (CH3-COH-CH3)Pt, presumably accompanied by (CH3-CO-CH3)Pt.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Kinetics of copper passivation and pitting corrosion in Na2SO4 containing dilute NaOH aqueous solution

The electrochemical behaviour of Cu in alkaline solutions containing Na2SO4 was studied using potentiodynamic and potentiostatic techniques complemented by scanning electron microscopy. The presence of Na2SO4 enhances Cu electrodissolution through the passive layer and decreases the breakdown potential. There is a critical OH-/sulphate concentration ratio for the onset of localized corrosion. The competitive interaction between OH- and sulphate ions at the passive layer can explain the experimental data. Pit initiation fits the point defect model for passivity breakdown. Pit growth involves a number of current contributions which can be distinguished through the analysis of current transients at constant potential by using nucleation and growth models.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Lightweight Carbon Fiber Mirrors for Solar Concentrator Applications

Lightweight parabolic mirrors for solar concentrators have been fabricated using carbon fiber reinforced polymer (CFRP) and a nanometer scale optical surface smoothing technique. The smoothing technique improved the surface roughness of the CFRP surface from ~3 {\mu}m root mean square (RMS) for as-cast to ~5 nm RMS after smoothing. The surfaces were then coated with metal, which retained the sub-wavelength surface roughness, to produce a high-quality specular reflector. The mirrors were tested in an 11x geometrical concentrator configuration and achieved an optical efficiency of 78% under an AM0 solar simulator. With further development, lightweight CFRP mirrors will enable dramatic improvements in the specific power, power per unit mass, achievable for concentrated photovoltaics in space.Comment: IEEE Photovoltaic Specialist Conference (PVSC), DC, USA, 201

La irrupción de las tecnologías electrónicas y de la información

Entendemos por agricultura de precisión el conjunto de prácticas agrícolas que se centran en áreas concretas del campo en momentos particulares del tiempo. Las prácticas de manejo agrícola tradicionales, como por ejemplo el riego o la aplicación de fertilizantes o pesticidas, habitualmente se han realizado de forma uniforme en todo el campo, sin tener en cuenta la heterogeneidad intraparcelaria, es decir, la variación natural o las diferentes necesidades que puedan existir dentro de una parcela. Los avances en nuevas tecnologías, así como el desarrollo de nuevos sensores cada vez más especializados y económicos, permiten su incorporación en el sector agrícola (Cubero et al., 2016). Uno de los principales usos y posibilidades de la agricultura de precisión es la detección temprana de plagas y enfermedades o de deficiencias nutricionales e hídricas, a partir del análisis de los datos proporcionados por los sensores sobre la energía reflejada o emitida por las plantas. Los sensores utilizados en teledetección como las cámaras multiespectrales, hiperespectrales o térmicas permiten estimar algunos parámetros relacionados con el estado del cultivo tales como escasez de agua, clorosis e incluso la deficiencia de nutrientes como nitrógeno, fósforo o potasio, debido a la relación entre los compuestos químicos y determinadas longitudes de onda donde se absorben

Automated Detection of Tetranychus urticae Koch in Citrus Leaves Based on Colour and VIS/NIR Hyperspectral Imaging

etranychus urticae Koch is an important citrus pest that produces chlorotic spots on the leaves and scars on the fruit of affected trees. It is detected by visual inspection of the leaves. This work studies the potential of colour and hyperspectral imaging (400–1000 nm) under laboratory conditions as a fast and automatic method to detect the damage caused by this pest. The ability of a traditional vision system to differentiate this pest from others, such as Phyllocnistis citrella, and other leaf problems such as those caused by nutritional deficiencies, has been studied and compared with a more advanced hyperspectral system. To analyse the colour images, discriminant analysis has been used to classify the pixels as belonging to either a damaged or healthy leaves. In contrast, the hyperspectral images have been analysed using PLS DA. The rate of detection of the damage caused by T. urticae with colour images reached 92.5%, while leaves that did not present any damage were all correctly identified. Other problems such as damage by P. citrella were also correctly discriminated from T. urticae. Moreover, hyperspectral imaging allowed damage caused by T. urticae to be discriminated from healthy leaves and to distinguish between recent and mature leaves, which indicates whether it is a recent or an older infestation. Furthermore, good results were achieved in the discrimination between damage caused by T. urticae, P. citrella, and nutritional deficiencies

Electrochemical behaviour of copper in aqueous moderate alkaline media, containing sodium carbonate and bicarbonate, and sodium perchlorate

The voltammetric polarization of Cu specimens in Na2CO3, NaHCO3 and NaClO4 solutions (8-12pH range) has been investigated. Voltammetry data were complemented with SEM and electron microprobe analysis. Results are found to be in agreement with the passivation model developed for Cu in plain NaOH solutions. For the latter the process can be described in terms of two steps, namely, at low potentials the initial formation of a Cu2O thin layer followed by the growth of a massive Cu2O layer, and at higher potentials the appearance of a CuO-Cu(OH)2 layer. These processes are accompanied by the formation of soluble Cu species. Beyond a certain potential which increases with the solution pH, copper pitting takes place. This model can be extended to Cu in carbonate/bicarbonate containing solutions by considering that Cu carbonates precipitate as long as soluble ionic Cu species are produced, without interfering appreciably with the formation of Cu oxides. The appearance of copper carbonate species is enhanced when pitting corrosion sets in. The precipitation of Cu carbonates occurs principally around pits. Cu pitting, although it is observed for all solutions, becomes more noticeable at the lowest pH values. At a constant pH, the density of pits increases in the order NaClO4 > NaHCO3 > Na2CO3. The influence of the electrolyte composition on Cu pitting is closely related to the blockage capability for pit nucleation and growth of the corresponding copper salts. Passivation in the Cu2O-Cu(OH)2 region hinders pitting corrosion.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta

Distribución del género Tityus Koch, 1836 (Scorpiones: Buthidae) en la ciudad de La Plata (Argentina)

In the city of La Plata occurs the genus Tityus with records dating back to 1943. The territorial distribution of the genus Tityus in this city and its expansion was studied based on inquiries received at the CEPAVE Arachnology Laboratory from individuals and public and private institutions. 189 inquiries were received from 2005 to 2020. The QGIS program was used to geolocate each scorpion with urban layout layers and storm drains. For the spatial analysis of distribution, a home range of one hectare per individual was considered to calculate the area and in the cases of areas of overlapping influences during the same year, the area was considered as their union. The genus Tityus in the city of La Plata is represented by the species T. carrilloi and T. confluens, both of health interest and of synanthropic habits, which occupy two different well-defined areas. The analysis of the independent dispersion in the two zones would indicate that they could use the drains to disperse, and since they are unconnected there would be no flow of scorpions between both zones. The colonization of these species in the study area was strengthened for T. confluens as of 2005 and for T. carrilloi as of 2011. The highest records are in the warm months, from January to April, the latter being of higher value. September is the only month without complaints. The expansion rate calculated was 4.42 ha/year.En la ciudad de La Plata se encuentra el género Tityus con registros desde 1943. Se estudió la distribución territorial del género Tityus en esta ciudad y su expansión en los últimos 15 años a partir de las consultas recibidas en el Laboratorio de Aracnología del CEPAVE, provenientes de particulares e instituciones públicas y privadas. Se recibieron 189 consultas desde el año 2005 al 2020. Se utilizó el programa QGIS para geolocalizar cada escorpión con capas de trazado urbano y desagües pluviales. Para el análisis espacial de distribución se consideró un home range de una hectárea por individuo para el cálculo de área y en los casos de áreas de influencias solapadas durante el mismo año se consideró el área como la unión de las mismas. El género Tityus en la ciudad de La Plata está representado por las especies T. carrilloi y T. confluens ambas de interés sanitario y de hábitos sinantrópicos, que ocupan dos zonas diferentes bien definidas. El análisis de la dispersión independiente en las dos zonas indicaría que podrían usar los desagües para dispersarse, y al ser inconexos estos no habría flujo de escorpiones entre ambas zonas. La colonización de estas especies en la zona en estudio se vio afianzada para T. confluens a partir del año 2005 y para T. carrilloi a partir del 2011. Los mayores registros son en los meses cálidos, desde enero a abril, siendo este último el de mayor valor. Septiembre es el único mes sin denuncia. La tasa de expansión calculada fue de 4.42 ha/año

A comparative study on the passivation and localized corrosion of α, β, and α + β brass in borate buffer solutions containing sodium chloride—I. Electrochemical data

The passivation and localized corrosion of α-, β-, and (α + β)-brass in borate-boric acid buffer solutions (pH 9) containing different NaCl concentrations (cNaCl) were studied comparatively using conventional electrochemical techniques at 25 °C. The passivation of brass in borate-boric acid buffer was due to the electroformation of a complex passive layer consisting of ZnO · xH2O and Cu2O—CuO. In NaCl-containing borate-boric acid buffer the breakdown of the passive layer occurs leading to pitting corrosion when the applied potential exceeds a certain critical value, Eb. For a given type of brass, the value of Eb is shifted negatively as cNaCl is increased. At a constant cNaCl the localized corrosion resistance of brass increases in the following order (α + β)-brass ≅ β-brass < α-brass. For all brass the localized corrosion resistance was lower than that of polycrystalline Cu, but considerably greater than that of polycrystalline Zn. Passive film composition and de-alloying can account for the localized corrosion resistance of these alloys.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Electrochemical behaviour of copper in aqueous moderate alkaline media, containing sodium carbonate and bicarbonate, and sodium perchlorate

The voltammetric polarization of Cu specimens in Na2CO3, NaHCO3 and NaClO4 solutions (8-12pH range) has been investigated. Voltammetry data were complemented with SEM and electron microprobe analysis. Results are found to be in agreement with the passivation model developed for Cu in plain NaOH solutions. For the latter the process can be described in terms of two steps, namely, at low potentials the initial formation of a Cu2O thin layer followed by the growth of a massive Cu2O layer, and at higher potentials the appearance of a CuO-Cu(OH)2 layer. These processes are accompanied by the formation of soluble Cu species. Beyond a certain potential which increases with the solution pH, copper pitting takes place. This model can be extended to Cu in carbonate/bicarbonate containing solutions by considering that Cu carbonates precipitate as long as soluble ionic Cu species are produced, without interfering appreciably with the formation of Cu oxides. The appearance of copper carbonate species is enhanced when pitting corrosion sets in. The precipitation of Cu carbonates occurs principally around pits. Cu pitting, although it is observed for all solutions, becomes more noticeable at the lowest pH values. At a constant pH, the density of pits increases in the order NaClO4 > NaHCO3 > Na2CO3. The influence of the electrolyte composition on Cu pitting is closely related to the blockage capability for pit nucleation and growth of the corresponding copper salts. Passivation in the Cu2O-Cu(OH)2 region hinders pitting corrosion.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta