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  • Author or Editor: C. Sepúlveda x
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Abstract  

The aim of the present work is to obtain the separation of233Th from the radioisotopes formed in the irradiation of Mn, U, Ba, Cs, Co and the lanthanide elements with thermal neutrons, because they may interfere in the neutron activation analysis of Th, when the activity of233Th is used. The experiments were performed with the resin Bio-Rad AG 50W X-4 and X-8 (100–200 mesh) in the thorium form. The separation of233Th from the interfering radioisotopes is based on the retention of233Th by the resin (isotope exchange) and the elution of the interfering radioisotopes with a dilute solution of Th in 0.5M HCl. Batch experiments were made in order to determine the equilibrium time for the isotopic ion exchange of thorium and also the distribution coefficients of the interfering elements between the solution and the resin. Column experiments were carried out with the purpose of establishing the conditions that allow the maximum isotope exchange of233Th and the minimum retention of the interfering radioisotopes in the resin. With this purpose, a statistical interpretation of a four variable experimental design is presented.

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Abstract  

Adsorption of Cr(VI) by two tannin sorbents is evaluated using radiotracers. Evaluation of the sorption process shows that the Cr(VI)-tannin molecule binding is the principal responsible for chromium adsorption. High sorption capacities were registered for both sorbents at pH 2. ForEucaliptus Saligna Sm sorbent (ETS) sorption capacity is 0.92±0.03 mmol/g and forLysiloma latisiliqua sorbent (LTS) is 3.8±0.3 mmol/g. Influence of different ions present in water is examined. High sorption capacity is reported for LTS in sea and tap water samples. It represents 90–94% of adsorption in distillated water.

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Metastable effects on martensitic transformation in SMA

Part II. The grain growth effects in Cu-Al-Be alloy

Journal of Thermal Analysis and Calorimetry
Authors: A. Sepulveda, R. Muñoz, F. Lovey, C. Auguet, A. Isalgue, and V. Torra

Abstract  

The efficiency of shape memory alloy (SMA) as damper and/or standard actuator is truly enhanced when the material can be cycled without any relevant accumulation of the permanent deformation (i.e. under 0.5% for several hundreds of cycles). The particular properties of the CuAlBe alloy permit relevant grain growth with reasonable reduction of mechanical properties (from 300–350 to 250–300 MPa at fracture). Samples prepared with an appropriate heat thermal treatment (HTT) and relevant mean diameter of grain avoids accumulative deformation for series of cycles (near 500) up to 3.5% of deformation. The analysis of different wires of CuAlBe alloy shows, in the first part of HTT, a proportionality between the grain surface and the time at 1123 K. In the last part of the HTT the grain growth shows an increased complexity related with interactions between the grain boundaries and the external surface of the samples.

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Metastable effects on martensitic transformation in SMA

Part VIII. Temperature effects on cycling

Journal of Thermal Analysis and Calorimetry
Authors: V. Torra, C. Auguet, A. Isalgue, F. Lovey, A. Sepulveda, and H. Soul

Abstract  

The use of Shape Memory Alloys (SMA) in technical applications as damping in civil engineering structures requires the characterization of the alloy for each specific application. This involves the evolution of the mechanical properties and damping capacity with the number of cycles, frequency, maximum deformation, applied stresses, and the evolution of the alloy with aging time and temperature. In particular, the temperature effects associated to self-heating need to be evaluated. In continuous cycling the effects of latent heat, the associated dissipation induced by the hysteresis, the heat flow to surroundings and the cycling frequency induce different states of temperature in the specimen, which in turn produces changes in the transformation-retransformation stresses. In this article, the temperature effects associated to cycling are outlined for different cycling frequencies. The results show that, for relatively faster frequency the temperature arrives at an oscillatory state superimposed to an exponential increase. For lower frequencies, some parts of the sample attain temperatures below room temperature. The experimental results are represented with an elementary model (the 1-body model or the Tian equation used in calorimetric representation) of heat transfer. For the higher fracture where life requirements are associated to damping in stayed cables for bridges, the results show (for the NiTi alloy) a reduction of the hysteresis width as the frequency increases for deformations up to 8%. For reduced deformation, under 2% appears an asymptotic behavior where the frictional area is practically independent of the cycling frequency (up to 20 Hz). In addition, it is shown that more than 4 million of working cycles can be attained if the maximum applied stress is kept below a threshold of about 200 MPa. Although under this condition the deformation must remain lower than 2% a reasonable damping capacity can still be obtained.

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