Summary The ordering behavior of quenched Cu-12 at% Mn was investigated by differential scanning calorimetry (DSC) under increasing temperature conditions. The ordering process can be better explained in terms of a homogeneous short-range-order (SRO) rather than a disperse-short-range-order (DSRO) model as for concentrated Cu-γMn solid solutions. At the employed high quench rates ordering is established in one stage here termed stage 1, assisted by excess vacancies. This stage obeys a first order kinetics law, being the effective activation energy consistent with a weighed average sum of the activation energy for migration of free and bound vacancies. An estimated solute-vacancy binding energy of 15 kJ mol-1 seems quite reasonable for this alloy together with the assessed activation energy for complex migration of 92.6 kJ mol-1. By adopting a first SRO order parameter based in quasi-chemical theory in pair approximation and using boundary values calculated from displayed features of DSC traces, the retained degree of quenched-in order at room temperature was calculated. This procedure also enabled to estimate an ordering energy of -2.7 kJ mol-1. The effect of quenching temperature demonstrate that for smaller vacancy sink densities, the retained degree of order at room temperature goes through a minimum.
The precipitation process for a concentration of CoTi of super-saturated solutions of Cu-0.50 at.% Co-0.45 at.% Ti (Cu-1 at.%
CoTi) was studied through differential scanning calorimetry (DSC) and microhardness measurements. The analysis of the calorimetric
curves between the environmental temperature and 900 K shows the presence of only one exothermic reaction attributed to the
formation of CoTi particles in the matrix of copper. The energy of activation estimated by using the modified Kissinger method
came out much lower than the corresponding to the diffusion of the cobalt and titanium in copper. We may attribute this fact
to the strong contribution of the vacancies introduced by quenching.
We used the formalism of Johnson-Mehl-Avrami (JMA) to assess the kinetic parameters. The energetic and kinetic evaluations
and the molar heats of precipitation obtained from the isochor of van’t Hoff allow us to infer that the reaction corresponds
to the formation of CoTi precipitates. The isothermal kinetics of precipitation reaction could be represented satisfactory
by an overall kinetic function based in a macroscopic parameter (Vickers hardness). The kinetic parameters obtained from microhardness
model are in agreements with those obtained from DSC traces.
Authors:C. Díaz Romero, S. Tort, E. Díaz, and J.P. Pérez-Trujillo
Samples of sweet wines from the Canary Islands belonging to the Denominations of Origin of La Palma and Lanzarote islands were analysed in relation to chemical parameters. The main chemical parameters analysed demonstrated that these wines fulfil all the legal requirements, since the content of all components tested falls below the maximum concentration admissible. Applying techniques of multivariate analysis (principal component, discriminant and cluster analysis), a complete differentiation could be achieved between the wines according to the island of production using only alcohol degree and isobutanol, which are chemical parameters related to the elaboration process.
From 1994 to 1996 we have studied a number of radioactive (total b and residual b-activity levels and 3H activity) and physico-chemical (pH, conductivity, and natural potassium content) parameters in the water of two Alcántara and Guadiloba reservoirs, which are artificially connected by interbasin transfers. The analysis of the results showed the existence of major correlations between the two systems for tritium activity, conductivity, and stable potassium content. A model based on the water balance in the Guadiloba reservoir was also elaborated which allowed us to forecast its effective surface area monthly, which varied extraordinarily between 0.405 and 135 km2.
Authors:E. De Amo, R. Del Campo, and M. Díaz Carrillo
We study the integration theory for general integral metrics when restricted to upper integrals q, finding improvements in the relation between the classes of the q-integrable and the ql-integrable functions. We give new results and notions which lead to the desirable characterizations of q-integrable functions as ql-integrable f with q(|f|) < ∞, and of ql-integrable functions via the integrability of their upper truncations, under natural conditions which are fulfilled in most
finitely additive integration theories.
Authors:J. Griffith, R. Rosenberg, O. Díaz-Rizo, and E. González
Thermal and epithermal non-destructive activation analyses have been performed on samples of final molasses from 14 different sugar factories, covering the most important regions in Cuba. From the first measurement after irradiation at the Triga Mark reactor (VTT), the concentration of more than 15 elements is reported. The almost constant elemental composition shows that they can be used equally for different purposes as animal foodstuff and for the manufacture of biotechnological products. This work is part of a research project developed in order to establish a complete characterization of Cuban sugar molasses.
Authors:N. Garcia-Gonzalez, E. Ordóñez-Regil, E. Simoni, and C. Barrera-Díaz
Hydration of zirconium diphosphate (ZrP2O7) conduced to formation of active sites in solid/liquid interface. In ZrP2O7/NaClO4 0.5 M suspensions, active sites and their acidity constants are quite determined but the presence of some impurities is now
studied. This work was conducted to determine the surface properties changes produced by oxalic and citric acid during the
hydration process. Moreover the presence of organic acids with ZrP2O7 modified reveals an increase in uranium sorption constants. The zirconium diphosphate has been characterized using X-ray
powder diffraction (XRD), Scanning electron microscopy (SEM) and Particle induced X-ray emission and Neutron (PIXE). Furthermore,
the specific surface area, measured by the BET method, was 3.5 m2/g. The pH corresponding to the isoelectric point, determined by Zeta Potential measurements and mass titration was 3.6. The
sites density calculated using titration curves was around of 5.37 s/nm2 for NaClO4 0.5 M, 13.71 s/nm2 for NaClO4 0.5 M/citric acid 0.1 M and 7.33 s/nm2 NaClO4 0.5 M/oxalic acid 0.1 M. The surface acidity constants and species distribution in surface were calculated by means of simulation
of the titration curves with the FITEQL code (constant capacitance model), for ZrO and PO amphoteric sites of ZrP2O7. The uranyl sorption edge was determined for NaClO4 0.5 M. It spreads between pH 3 and 4.5 for complete sorption according to the previously published results. In the ZrP2O7–citrate modified surface, the uranyl sorption edge begin at pH 2 and was almost complete at pH 3.2 while ZrP2O7–oxalate modified surface edge started at 50% of sorption at pH of 1.5 and was complete at pH 3.
Authors:O. Díaz Rizo, M. Manso Guevara, E. Herrera Peraza, I. Alvarez Pellón, and M. López Reyes
Using the facilities of the Triga Mark III reactor at the NNRI, Mexico and the HAV-1 multipurpose monitor, the reactor power dependency for thek0-standardization essential neutron flux parameters as: epithermal shape factor (), thermal to epithermal ratio (f) and neutron temperature (Tn) were experimentally obtained. Evaluation of the obtained dependencies shows that it is unnecessary to analyze the possible introduction of correction factors in thek0-INAA experimental results. A single experimental procedure to determine throughf is suggested.
Authors:L. Hernández Rodríguez, D. Afonso Morales, E.M. Rodríguez-Rodríguez, and C. Díaz Romero
Proximate composition was determined in 19 wheat cultivars from the Canary Islands in order to establish differences between them and contribute to their characterization. All parameters analysed showed significant differences between cultivars; and also many parameters were affected by the species and subspecies of wheat. Triticum aestivum had higher mean moisture, protein, and fibre and lower mean starch, sucrose, and amylose concentrations than Triticum turgidum. Low starch content and high fibre content could be due to the transformation of starch into resistant starch during desiccation process. An important contribution of complex carbohydrates, including fibre as well as protein and phenolic compounds, was observed for the consumption of wheat.
Authors:R. Casañas Rivero, P. Suárez Hernández, E. Rodríguez Rodríguez, and C. Díaz Romero
Moisture, protein, starch, amylose, ash, ascorbic acid and fibre contents were determined in potato samples harvested in Tenerife belonging to eight cultivars and three species/subspecies:
chaucha, Solanum tuberosum
. There were several significant differences among the means of various chemical compounds according to cultivar, species or subspecies, local and recently imported potatoes. Mean values of moisture contents were often significantly different concerning the three species/subspecies considered. Local potatoes presented lower moisture and higher content of chemical compounds than the recently imported potatoes. After Varimax rotation, the first component was related to starch, and in a lesser extent to moisture (negatively), the second and the third components were associated to ash. Applying discriminant analysis on potato samples belonging to the spp.
, adequate separation according to the cultivars was obtained.