Gustavo E. Lascalea

The Material Characterization of a Santamarian Ceremonial Axe

The characterization of a ceremonial bronze axe is described. The axe is assigned to the Santamarian culture of north-west Argentina, c. 1000–1470 ad, and was selected to increase presently limited knowledge of prehistoric metallurgy in the Andean region of Argentina. The characterization methods used were electron probe microanalysis, gamma radiography, X-ray diffraction, optical metallography and microhardness testing. The axe was well cast in a bivalve mould, with the only defects in the area of an ancient fracture. The analysis showed that it is made from a tin bronze with a, probably, accidental addition of lead. Arsenic was found as a surface contamination, probably deriving from arsenic in the water of the stream in which the axe was found. The axe shows that Santamarian craftsmen had the skill to decorate the axe in an artistic style with a strong local accent while providing a functional, annealed and cold-worked cutting edge.

Coprecipitation-assisted coacervative extraction coupled to high-performance liquid chromatography: An approach for determining organophosphorus pesticides in water samples

An analytical methodology based on coprecipitation‐assisted coacervative extraction coupled to HPLC‐UV was developed for determination of five organophosphorus pesticides (OPPs), including fenitrothion, guthion, parathion, methidathion, and chlorpyrifos, in water samples. It involves a green technique leading to an efficient and simple analytical methodology suitable for high‐throughput analysis. Relevant physicochemical variables were studied and optimized on the analytical response of each OPP. Under optimized conditions, the resulting methodology was as follows: an aliquot of 9 mL of water sample was placed into a centrifuge tube and 0.5 mL sodium citrate 0.1 M, pH 4; 0.08 mL Al2(SO4)3 0.1 M; and 0.7 mL SDS 0.1 M were added and homogenized. After centrifugation the supernatant was discarded. A 700 μL aliquot of the coacervate‐rich phase obtained was dissolved with 300 μL of methanol and 20 μL of the resulting solution was analyzed by HPLC‐UV. The resulting LODs ranged within 0.7–2.5 ng/mL and the achieved RSD and recovery values were <8% (n = 3) and >81%, respectively. The proposed analytical methodology was successfully applied for the analysis of five OPPs in water samples for human consumption of different locations of Mendoza.

Combustion synthesis of Co-Cu-Mn oxides deploying different fuels

Ternary spinel-like oxides such as CuFeMnO4, CoCuMnOxand CuCr2O4 are attractive materials due to their absorbent properties when used as pigments for selective surfaces thus improving solar heaters efficiency. These materials are obtained through sol-gel and sol-gel-combustion methods. This work proposes the synthesis of mixed oxides of Co, Cu and Mn by means of original one-step stoichiometric combustion methods starting from Mn(NO3)2,Co(NO3)26H2O, Cu(NO3)23H2O and Aspartic acid (Asp) or Lysine( Lys) as fuels. The resulting ashes after the combustion were calcined at 500 °C. The obtained ashes and the calcined powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and by Brunauer-Emmett-Teller method (BET), and TG-DTA analysis. In calcined powders obtained with Lys (CoCuMnOx-Lys), the phase corresponding to CoCuMnOx and others segregated phases were identified. However, in calcined powders obtained with Asp (CoCuMnOx-Asp) only the phase corresponding to CoCuMnOxwas identified. The sample CoCuMnOx-Lys presented an average crystallite size of 44 nm and a specific surface area of 23 m2/g while in CoCuMnOx-Asp, 54 nm and 13 m2/g values were obtained throughout FT-IR vibrational modes associated with spinel metallic oxides for both calcined powders (Asp and Lys) were observed. Additionally, by means of TEM, polyhedral particles with an average size of 20 to 100 nm were observed. In particular, it was determined in CoCuMnOx-Lys an average size of 44nm. According to the different fuels used (Asp and Lys), an evident variation in the obtained phases was observed. However, it was not obtained any difference in crystallite size and specific area surface values. It is of considerable importance the study of further syntheses processes to verify this trend.

X-ray line broadening study of tetragonal zirconia nanopowders synthesized by gel-combustion

Tetragonal zirconia ceramics have excellent electrical and mechanical properties. However, the physical mechanisms involved in the stabilization of the metastable tetragonal phase at room temperature are not well known yet. This phase can be retained in ceramic specimens provided that the grain size is smaller than a critical value (about 1 micron). In the case of powders, it has been established that the crystallite size must be nanometric (the surface free energy has a very important role), but the influence of stresses and defects are not fully understood. The aim of this work was to study the stability of yttria or ceria-doped tetragonal zirconia nanopowders synthesized by different gelcombustion routes. These methods are based on the gelling of a nitrate solution of the desired metals and some organic fuel (glycine, citric acid, etc.) followed by an intense combustion due to the exothermal redox reaction between nitrate ions and the fuel. The powders were characterized by X-ray diffraction applying the Rietveld method. A conjunct analysis of crystallite size and microstrain was carried out employing the multiple-line integral breadth method and assuming Lorentzian and Gaussian components for both effects. The crystallite size profile presented both components, being the Lorentzian the most important. On the contrary, the microstrain profile had a negligible Gaussian component, which is an interesting result since it is generally represented by a Gaussian function. It was also found that both, crystallite size and microstrains, affect the stability of the tetragonal phase.