Fábio C.S. da Silva

Disponibilidade de fósforo em solos avaliada por diferentes extratores

The objective of this paper was the comparative study of the most important extractors of soil phosphorus. It presents a literature review of papers that deal with methods of extraction for the evaluation of phosphorus availability in soils. The methods considered were: anion exchange resin, Olsen, Bray 1, Bray 2, Mehlich 1, Troug, Egner, water, 0,01M CaCl2, iron hydroxide impregnated filter paper (Pi) and the determinations of the E and L values. The comparison between results of soil analysis by different methods of phosphorus extraction in soils and phosphorus uptake by plants was initially made considering the coefficient of determination (r2) for several extractants. The following average values and corresponding numbers of articles in which the method was considered were obtained: resin, 70% (34); E value, 68% (16); L value, 65% (8); Olsen, 54% (48); Bray 1, 50% (42); Mehlich 1, 46% (25); Egner, 44% (9); Bray 2, 42% (19); Water, 42% (15); Truog, 38% (13); CaCl2, 36% (13), and Morgan, 32% (13). The comparison of several methods, considering the pairs of results (r2) obtained for the extractants, that were tested together through linear correlation and average contrasts (t student test), indicated that the resin method was statistically superior to the other methods. The resin method presents the following favorable features: (a) highest values for the determinations coefficients for the correlations between P uptake by plants and soil P by the different methods, as reviewed in 72 papers; (b) it can be used in both acid and alkaline soils, which is not the case for the other most commonly used methods; (c) it reveals adequately the effect of liming on the increase of P availability in soils for crops, which is not the case of Mehlich 1, Bray 1 and Olsen; (d) it does not overestimate P availability in soils treated with rock phosphates, as is the case of acid extractans; (e) it is the method with the best theoretical background.

Quasicrystalline Phase Formation on Glassy ZrAINiCuPd Alloys by Linear Varying Joule Heating

Linear varying current Joule heating was employed to perform thermal treatments on bulk amorphous samples. Using this method it is possible to monitor the evolution of the materials structure through the on-line measurement of the samples electrical resistance. Therefore, it is possible to interrupt the treatment at any desired point. Using this method, we have succeeded to obtain icosaedral phases in some glassy alloys. The quasicristallization results in an increase of the samples resistance, which is visible in the Joule heating curves.

Controlled Crystallization of Metallic Glasses Through Joule Heating

This work reviews the basic aspects of an alternative thermal treatment of metallic glasses by Joule heating, which explores the heat produced by an electrical current flowing through samples. The advantages of this annealing method are discussed, and a brief description of available models in a variety of materials is given. The experimental procedures are discussed in detail, with emphasis in a new variant of Joule heating, known as “linear varying current Joule heating”. This method allows one to precisely monitor the structural transformations that take place during annealing, by interrupting the thermal treatment at any desired point, leading to samples with controlled micro and/or nanostructures. Some examples of Joule heating curves in novel bulk amorphous samples are shown, to illustrate the excellent perspectives of this annealing technique.