Alfredo Flores

Cerium extraction by metallothermic reduction using cerium oxide powder injection

Abstract This work presented the feasibility of cerium recovery by Al-Mg alloy through the metallothermic reduction of CeO 2 to obtain a master alloy Al-4%Ce. The master alloy obtained in this investigation was for the grain refinement and modification of Al-Si alloys. The reagent was incorporated into a molten alloy using the submerged powder injection technique, and metallic samples were obtained during injection. Chemical and microstructural analyses (by inductively coupled plasma (ICP) and scanning electron microscopy (SEM), respectively) confirmed the possibility of Ce uptake in the bath (0 to 4 wt.%), as CeO 2 was reduced through metallothermic reactions in the molten alloys. Based on the characterization of reaction products, the sequence of the reaction was proposed.

Effect of magnesium on the aluminothermic reduction rate of zinc oxide obtained from spent alkaline battery anodes for the preparation of Al–Zn–Mg alloys

The aluminothermic reduction of zinc oxide (ZnO) from alkaline battery anodes using molten Al may be a good option for the elaboration of secondary 7000-series alloys. This process is affected by the initial content of Mg within molten Al, which decreases the surface tension of the molten metal and conversely increases the wettability of ZnO particles. The effect of initial Mg concentration on the aluminothermic reduction rate of ZnO was analyzed at the following values: 0.90wt%, 1.20wt%, 4.00t%, 4.25wt%, and 4.40wt%. The ZnO particles were incorporated by mechanical agitation using a graphite paddle inside a bath of molten Al maintained at a constant temperature of 1123 K and at a constant agitation speed of 250 r/min, the treatment time was 240 min and the ZnO particle size was 450-500 mesh. The results show an increase in Zn concentration in the prepared alloys up to 5.43wt% for the highest initial concentration of Mg. The reaction products obtained were characterized by scanning electron microscopy and X-ray diffraction, and the efficiency of the reaction was measured on the basis of the different concentrations of Mg studied.

Microstructure Formation of Al-Fe-Mn-Si Aluminides by Pressure-Assisted Reactive Sintering of Elemental Powder Mixtures

This paper presents the results of an investigation aimed at understanding microstructure formation of Al-Fe-Mn-Si intermetallics during pressure-assisted reactive sintering of elemental powders. The proportion of elements was selected such that the composition of the product was 55 wt % Al, 17 wt % Si, 14 wt % Mn, and 14 wt % Fe. Experiments were conducted at temperatures between 600 and 800°C, using compaction stresses of up to 20 MPa. Rietveld analysis of x-ray diffraction patterns of fully processed samples showed that the powders were transformed into a mixture of Al9FeMnSi and Al9FeMn2Si phases. However, as temperature and pressure were increased, the Al9FeMnSi phase was transformed into the Al9FeMn2Si phase. Differential Thermal Analysis, as well as microstructural characterization by scanning electron microscopy and x-ray diffraction, showed that these intermetallics do not form directly from the powder mixtures. Rather, they are the result of metallurgical reactions between a molten Al-Si solution and various intermediate phases formed during reactive sintering.

Kinetic study on the metallothermic reduction of chromite ore using magnesium scrap

A study on the metallothermic reduction of chromite ore is presented and discussed, using magnesium scrap as reducing agent. Microstructural analysis corroborated the distribution of phases inside the particles, where Fe and Cr were located at the centre surrounded by layers of reaction products, mainly MgO. The maximum conversion efficiency of Fe and Cr was 38% at 1050°C, after a reaction time of 3 hours, using 75% excess of magnesium scrap. A kinetic study was performed fitting the experimental data to available kinetic models, where the data adjusted to the chemical reaction model, especially at the beginning of reaction. A second reaction stage was confirmed once the experimental data was adjusted to the Jander diffusion model. For the chemical reaction model, the constant rate and the activation energy were 0.32 h−1 and 60.12 kJ mol−1, respectively. For the diffusion model, the rate constant was 0.20 h−1 and the activation energy 47.04 kJ mol−1.

Characterization by EBSD of antimony-calcium rich phases formed during purification of aluminum scrap

We studied the influence of antimony on the modification rate of the silicon eutectic with sodium and/or strontium for casting of Al-Si alloys, and introduced controlled Ca and Sb to the system and studied the resulting compounds, which were determined to be Ca2Sb and AlSb. Scanning electron microscopy together with the complementary technique of electron backscatter diffraction (EBSD) were used to characterize the materials. The experimental results provided the basis for us to establish that antimony removal from Al occurs mainly through the reaction (Sb)Al + 2Ca = Ca2Sb + Al.

New Approaches to Reaction Kinetics during Molten Aluminum Refining Using Electron Backscatter Diffraction (EBSD)

The use of aluminium scrap to produce different alloys has increased considerably at the start of the current century because of the low amount of energy required for its melting, in comparison to the energy required to produce aluminium from bauxite. However, contamination problems can arise if the different kinds of scrap with several chemical compositions are not separated using appropriate methods. In this way, contamination with elements such as Fe, Sb, Mg, Na, K, Pb, and Sn is quite common, so melt treatment practices have been recommended. Of these contaminants, antimony is considered to be among the most harmful because of its high potential toxicity, which is of special concern for products intended for handling of food and drink. Also, modification with sodium and/or strontium is not effective because of the formation of intermetallic compounds that remove these elements from solution, preventing any effect of this modification on the eutectic silicon phase. The negative effects of antimony on the rate of modification of the silicon eutectic with sodium and/or strontium in casting Al-Si alloys have been broadly studied by (Wang & Gruzleski, 1990), (Wang & Gruzleski, 1992), (Garant et al., 1992), and (Tuttle et al., 1991). The general problem in mixing antimony with sodium and/or strontium is the formation of high melting temperature compounds that are difficult to remove. Moreover, it is possible to generate phases with harmful morphologies that affect the mechanical properties of this type of alloy. These compounds eliminate sodium and/or strontium from the solution, preventing the effect of sodium/strontium modification on the silicon eutectic phase. On the other hand, antimony has been shown to possess a great chemical affinity for calcium, forming stable compounds that can be removed through dross. However, to study the mechanism of reaction, it is first necessary to define the stoichiometry of the reaction. Different techniques have been proposed to hinder the effects of antimony, including dilution with pure aluminium, separation of polluted scrap, addition of an excess of the modifier agent, or removal by means of chemical agents, as described by (Castrejon, 1995). However, no effective method has yet been developed at the cast shop facility level. Antimony, among other elements, possesses great affinity for calcium, as demonstrated long ago by (Hardy, 1941), who established that Ca3Sb2 or AlSb phases could form when these elements are present in molten aluminium. Nevertheless, the mechanism of reaction outside of molten aluminium scrap has not been determined.

Microstructural feature of As-cast A-356 alloy modifiers with the addition of SrO

To explore the effect of strontium on the structure of as-cast A356 alloy, the strontium was incorporated to the alloy by metallothermic reduction of SrO where the mineral was added to the melt through the submerged powders injection technique. The evaluation of the modification of the eutectic silicon and the chemical analysis of samples were done using optical microscopy (OP) and inductively coupled plasma (ICP), respectively, while microstructural analyses by scanning electron microscopy (SEM), and the injection time was variable. Magnesium was added to the melt to increase the reactivity and reduce the surface tension of the molten aluminum. It was possible to increase the strontium content from 0 to 0.027% after 20 minutes treatment. This concentration was sufficient to bring about full modification structure of eutectic silicon of as cast alloy A 356 and the acceptable quality metallurgical of alloy.