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- Processamento de materiais termoelétricos baseados na tetraedrite usando minério de tetraedrite-tenantitePublication . Esperto, Luís; Figueira, Isabel; Mascarenhas, João; Salgueiro, Rute; Silva, Teresa; Lopes, E.B.; Gonçalves, António Pereira; Correia, J.B.; de Oliveira, Daniel Pipa Soares; Almeida, P.; Neves, FilipeRESUMO: O desenvolvimento e implementação de tecnologias com baixo potencial de aquecimento global e energeticamente eficientes requer uma contínua inovação na área dos materiais para a energia. Nesta estratégia insere-se a pesquisa sobre o processamento de materiais termoelétricos baseados na tetraedrite. No presente trabalho procede-se à avaliação da viabilidade da incorporação direta, sem qualquer pré-tratamento, de minério da série tetraedrite-tenantite no processamento de materiais à base de tetraedrite por síntese mecanoquímica. Para tal prepararam-se misturas de pós contendo diferentes rácios de amostras de tetraedrite sintética, também obtida por síntese mecanoquímica, e de amostras de minério, recolhidas na mina de Neves-Corvo e na escombreira da mina do Barrigão. A caraterização estrutural e microestrutural dos materiais processados após 1 h e 2 h de síntese mecanoquímica permitiu verificar a formação de um composto constituído por tetraedrite-tenantite-(Fe) como fase principal, independentemente do minério de origem. Estes resultados são uma indicação do sucesso da abordagem seguida.
- Mechanochemical synthesis of tetrahedrite materials using mixtures of synthetic and ore samples collected in the Portuguese zone of the Iberian Pyrite BeltPublication . Neves, Filipe; Esperto, Luís; Figueira, Isabel; Mascarenhas, João; Salgueiro, Rute; Silva, Teresa; Correia, J.B.; Carvalho, Patricia Almeida; de Oliveira, Daniel Pipa SoaresABSTRACT: Considering that the synthesis of tetrahedrite-based materials usually uses high purity elements, the evaluation of the direct application of ore samples as raw materials for their synthesis is a pertinent issue. In the present study, multiphase synthetic tetrahedrite samples were mixed with tetrahedrite-tennantite ore samples (in weight ratios of 0.8/0.2, 0.5/0.5 and 0.2/0.8) to produce tetrahedrite-based materials by solid-state mechanochemical syn-thesis. The ore samples were obtained from the abandoned Barrig ̃ao mine dumps and from the Neves Corvo mine, both located in the Portuguese zone of the Iberian Pyrite Belt, whose main constituents were found to be As-rich tetrahedrite and tennantite-(Fe), respectively. Depending on the ore sample and on the mixture ratios, the displacement reactions occurring during the synthesis process gave rise to different phase transformation paths. For the ratios of 0.5/0.5 and 0.2/0.8, the mixtures with the Barrig ̃ao ore were found to consist of a single sulfide phase, tetrahedrite-tennantite-(Fe), plus quartz, while famatinite was also observed in the 0.8/0.2 mixture. Tetrahedrite-tennantite-(Fe) phase was the main constituent of all mixtures with the Neves Corvo ore, but in all of them other sulfide phases, famatinite-luzonite and pyrite, were also present in addition to quartz. Despite being dissimilar, these results are very promising and encouraging, by confirming the possible direct usage of ore samples and of dump material for the synthesis of tetrahedrite-based materials with all the potential environmental-economic gains that can be obtained.
- Thermoelectric Properties of Tetrahedrites Produced from Mixtures of Natural and Synthetic MaterialsPublication . Santos, Beatriz; Esperto, Luís; Figueira Vasques, Isabel; Mascarenhas, João; Lopes, E.B.; Salgueiro, Rute; Silva, Teresa; Correia, Jose B.; de Oliveira, Daniel Pipa Soares; Pereira Gonçalves, Antonio; Neves, FilipeABSTRACT: Thermoelectric materials have considerable potential in the mitigation of the global energy crisis, through their ability to convert heat into electricity. This study aims to valorize natural resources, and potentially reduce production costs, by incorporating tetrahedrite-tennantite (td) ores from the Portuguese Iberian Pyrite Belt into synthetic samples. The ore samples were collected in a mine waste at Barrig & atilde;o and as "dirty-copper" pockets of ore from the Neves Corvo mine. Subsequently, high-energy ball milling and hot pressing were employed in the production of thermoelectric materials. These are characterized by XRD, SEM/EDS, and thermoelectrical properties. The complete dissolution of the dump material sulfides with the synthetic tetrahedrite constituents led to an increase in the amount of the tetrahedrite-tennantite phase, which was made up of a tetrahedrite-tennantite-(Fe) solid solution. The thermoelectric characterization of these materials is provided, revealing that most of the combined synthetic ore samples displayed better results than the pristine tetrahedrite, mostly due to higher Seebeck coefficient values. Furthermore, the best thermoelectric performance is achieved with 10% of ore, where a power factor of 268 mu W.K-2.m-1 is reached at room temperature.
- Processing of tetrahedrite-based thermoelectric materials using tetrahedrite-tennantite copper oresPublication . Neves, Filipe; Esperto, Luís; Figueira, Isabel; Mascarenhas, João; Salgueiro, Rute; Silva, Teresa; Correia, J.B.; de Oliveira, Daniel Pipa Soares; Almeida, P.ABSTRACT: Tetrahedrite-based compounds are considered a promising thermoelectric material. The tetrahedrite-tennantite series, that can be generically expressed as Cu6[Cu4(Fe,Zn)2](Sb,As)4S13, is one of the most abundant sulfosalt minerals in the earth’s crust. The Iberian Pyrite Belt (IPB), located in southern Portugal and Spain, is the host of the largest concentration of massive sulfide deposits worldwide, where the tetrahedrite-tennantite series mineral is one of the constituents. In this work we evaluate the effectiveness of combining synthetic tetrahedrite (ST) with tetrahedritetennantite ore samples (TTOS) in the mechanochemical synthesis (MCS) process of tetrahedrite based compounds. The ore samples were collected from two distinct deposits within the Portuguese part of the IPB, the Neves Corvo mine and the abandoned Barrigão copper mine. The ST, also produced by MCS, were mixed with the TTOS in different mass ratios ranging from 20-80%. The influence of the chemical composition and phase constitution of the ore samples and of the mixing ratios will be presented in relation to the micro-structural properties of the obtained materials. The results here described are part of a broader study dedicated to the development of energy-harvesting applications based on tetrahedrite.