Conie Lopez

The hydrogen evolution reaction on nanocrystalline Ni30Mo70, Co30Mo70, Co30Ni70, and Co10Ni20Mo70, metallic powders prepared by mechanical alloying was investigated with linear polarization and ac impedance methods, in 30 wt.% KOH aqueous solution at room temperature. The formation process and structural properties of these nanocrystalline materials were characterized by X-ray diffraction and transmission electron microscopy. Alloyed powders showed the presence of two phases: an fcc solid solution and intermetallic compounds of Ni, Co and Mo. Based on polarization and ac impedance measurements, an improved electrocatalytic activity for hydrogen evolution reaction was observed in mechanically alloyed Co30Ni70 powders, which is slightly higher than milled metallic Ni powders.

Note: This article was originally published with an incorrect version of the Acknowledgments, which appeared on p. 218 of the print version. The correct version of the Acknowledgments appeared on pp. 1–2. The corrected article is available below.

Bimetallic CoNi nanoparticles have been prepared within the apoferritin cavity. The protein shell controls size, prevents aggregation, and makes nanoparticles water-soluble. The CoNi series prepared in this way were structurally and magnetically characterized, the resulting magnetic properties varying accordingly with composition (Co(75)/Ni(25), Co(50)/Ni(50), Co(25)/Ni(75)). Co and Ni metals were associated in each nanoparticle, as demonstrated by high-angle annular dark field scanning electron microscopy and electron energy loss spectroscopy (EELS). After intentional oxidation, the CoNi nanoparticles were characterized by EELS, X-ray absorption near edge structure (XANES), and SQUID measurements to evaluate the importance of the oxidation on magnetic properties.

We describe in this paper different and complementary experimental methods for assessing the adsorption of surfactants on metal particles in oil-based suspensions. Two different kinds of particles are dispersed in mineral oil: iron microparticles and CoNi nanoparticles. The adsorption of oleic acid in the Fe/oil interface in diluted suspensions can be determined by obtaining the adsorption isotherm. In addition, we present a method based on the time evolution of the optical absorbance of suspensions, from which the existence of adsorption can be inferred. For concentrated suspensions, the used of optical methods is not recommended, since they are affected by a significant inaccuracy. We present here a useful alternative based on electromagnetic induction phenomena. The results obtained allow a more comprehensive knowledge of the aggregation process in concentrated suspensions. With the same purpose, a third group of experiments, based on rheological techniques, is carried out in Fe/oil and CoNi/oil concentrated suspensions. In these series of experiments, the effect of three surfactants (oleic acid, aluminum stearate and lecithin) is tested by measuring either the viscosity, or the magnetic field-induced yield stress of the suspensions. The combination of these series of experiments gives us valuable information about the most appropriate surfactant/carrier combination capable of imparting a high stability and a strong magnetorheological response in magnetic colloids.

In a previous article, growth and survival of Argentine and Peruvian Prosopis were measured in a greenhouse hydroponic system in which the salinities were increased from 10 to 45 dS m−1. Twenty-one of the Prosopis alba seedlings that grew at the 45 dS m−1 salinity were propagated by rooting cuttings and a seed orchard/long-term evaluation trial established. To develop predictors and/or correlations between seedling and performance in mature field trials, this study characterized the seedlings for growth, leaf, and thorn morphology and ease in asexual propagation by rooting of cuttings. The percentage rooting of all clones varied from 40 to 100%, the roots per cutting from 0.60 to 67, and the length of the longest root from 1.63 to 6.70 cm. The parent trees were selected from P. alba specimens in a highly saline area of Argentina where P. ruscifolia Griseb (which has larger leaves and 15 cm long spines) was the dominant species. Some progeny were intermediate in spine and morphological characters between P. alba and P. ruscifolia and were locally known as vinalillo (P. vinalillo Stuck). The thorn length varied from 7.7 mm to 53.3 mm for the vinalillo “species” and from 0 thorns to 28 mm for P. alba. There was no correlation between leaf/thorn characters and salinity tolerance. The overwhelmingly greater abundance of spiny P. ruscifolia over P. alba may be due to livestock palatability rather than salinity tolerance. The increasing demand for the high-quality Prosopis lumber for furniture may make recuperation of moderately saline soils (< 30 dS m−1) economically attractive.