Eduardo de Albuquerque Brocchi

Synthesis and characterisation of nanostructured Ni–Co alloy Part 1: NiO reduction kinetics

Abstract Nanostructured materials have been receiving distinguished interest in recent scientific investigations due to their particular properties, which may not be present in the same material in bulk. This work is part one of a whole investigation which presents an alternative route for the synthesis of nanostructured nickel–cobalt alloy. The route begins with the coprecipitation of the NiO–Co3O4 from dissociation of the respective nitrates followed by a hydrogen reduction of these oxides. Preliminary thermodynamic studies have been carried out to evaluate the viability of the process as well as to select experimental conditions for the individual reductions. The reduction reactions were studied in the range from 200 to 500°C. This work is then related to the production of isolated NiO from a Ni(NO3)2.6H2O dissociation, followed by its reduction. The reaction showed an autocatalytic behaviour with E a=28·7 kJ mol−1. Transmission electron microscopy has been used to observe the morphology and size of the nickel oxide. This material presents some particles even smaller than 5 nm while its particle size distribution has an average of 20 nm. The obtained oxide and metallic nickel were both analysed by X-ray diffraction in which was confirmed the presence of these crystallised species.

Synthesis and characterisation of nanostructured Ni–Co alloy Part 3: NiO and Co3O4 coformed reduction kinetics

Abstract This work is the third part of an investigation dedicated to produce a Ni–Co nanostructured alloy. The route begins with the coprecipitation of the NiO–Co3O4 from dissociation of the respective nitrates followed by a hydrogen reduction of these oxides. Preliminary thermodynamic studies have been carried out in order to evaluate the viability of the process as well as to select experimental conditions for the individual reductions. The oxides reduction was studied in the range from 300 to 500°C. This paper is then related to the production of NiO–Co3O4, from a solution containing both Ni(NO3)2.6H2O and Co(NO3)2.6H2O, followed by its hydrogen reduction, which showed a good agreement with the topochemical model. The apparent active tion energy was found to be 29·7 kJ mol−1. Transmission electron microscopy has been used to observe the morphology and size of the obtained materials (Ni–Co co-oxides and Ni–Co alloy). These materials were also analysed by X-ray diffraction in which was confirmed the presence of the crystallised species. Such analyses showed that coformed oxides particles could already be found in the range from 10 to 50 nm while the average particle size of the alloy was ∼40 nm with the smallest ones of ∼20 nm.

Nitration Effect on the Yield and Chemical Composition of Humic Acids Obtained from South Brazil Coal Samples

The use of coal tailings as a source for humic substances (HS) may represent a promising alternative for the sustainable fate of the carbonaceous materials. The main objective of this work was to evaluate the potential use of coal samples from South Brazil as a source for HS, after treating the samples with nitric acid solution. The chemical composition of four coal samples and of extracted humic acids was determined before and after nitration (11 and 25% HNO3 at 70°C) by elemental analyses and FTIR spectroscopy. The HNO3 treatment promoted an increase of the N content in all samples, and the greatest values were found for the 25% HNO3-treated samples. Consequently, C/N ratio decreased with the increase of HNO3 concentration, varying from 11 to 20. The C/N ratio in the HA extracted from nitrated samples was around 16, and in addition to the N insertion, an increase of the proportion of COOH groups occurred.

Chemical Processing of a High Carbon FeCr Alloy Fine Powder

The steelmaking process requires the input of ferro-alloys to implement the adjustment of some elements composition in the final product. In the particular case of stainless steel production, the high carbon FeCr alloy stands out as one important precursor. However in the production of this material a certain quantity of fine powder with remarkable chromium and carbon content is also generated, which, in turn, could be processed through alkaline roasting in order to selectively recovery this element in a subsequent aqueous route. In the present work, this process is investigated, using excess of NaOH as oxidizing agent, and H2O2 for precipitating chromium as Cr(OH)3, which is next calcinated to Cr2O3. According to the results, the global achieved recovery has shown to be around 98%, suggesting that the proposed route can be seen as a potential process for chromium oxide production from the mentioned fine powder.