Abstract The flotation mechanism of galena with xanthate as the collector is generally explained based on the mixed potential of the pulp, in which an anodic electron transfer reaction from the collector to the mineral is combined with an O2 cathodic reduction. Sodium sulphide, often used as a mineral activator, strongly influences the pulp's mixed potential, and depending on the dosage applied, it can become a galena depressor reagent. In this way, the current study assesses galena flotability in the absence of collector, as well as in the presence of the collector potassium amyl xanthate (PAX) and sodium sulphide. The effect of an extremely cathodic potential was also studied through the addition of hydrogen peroxide. In addition, the effect of different stages in the oxidation of the galena surface on the flotability was investigated. Moreover, the zeta potential was measured and contact angle (wettability) tests were carried out. The contact angle measurements were taken for a distilled water, PAX solution and for a mixture of PAX and sodium sulphide solution on the oxidized and non-oxidized surface of galena. All the results showed that galena could be floated in all the PAX concentrations tested. It was observed that a moderate oxidation in the galena surface may contribute to an improvement of its flotation with PAX. However, extremely anodic and cathodic potentials cause flotability close to zero. The zeta potential results showed that sodium sulphide affected the interaction between PAX and galena. The measurements of the contact angle corroborated the results obtained in the microflotation tests. pulp O reduction activator pulps s applied reagent way (PAX peroxide investigated Moreover wettability (wettability out water nonoxidized non tested However zero

Abstract The cold roller die process increases the tensile strength and decreases the ductility of steel wire. Annealing heat treatment is applied to restore mechanical properties, but this is a costly process. This research shows that it is possible to control the mechanical properties of ultra-low carbon steel wire inducing the Bauschinger effect and relieving residual steel stresses. The present study uses several pulleys to promote and control the Bauschinger effect magnitude through alternated cyclic bending. A Completely Randomized Design, a regression study, and the Akaike Information Criterion were used to understand the relationship between the quantity and diameter of pulleys and the influence on the magnitude of the Bauschinger effect. Statistical models showed that it is possible to have a maximum increase of 103% in uniform elongation and a maximum decrease of 14% in yield strength. An interaction between the factors studied in controlling the Bauschinger effect magnitude was confirmed.

ABSTRACT Neste trabalho é feita uma avaliação da influência do teor de cromo e da combinação do cromo e nióbio em ligas de revestimento duro do tipo Fe-Cr-C, na microestrutura e propriedades que envolvam a resistência ao desgaste microabrasivo. Vários estudos têm sido realizados em busca de informações conclusivas sobre este sistema em condições de desgaste, devido às distintas fases e propriedades apresentadas por estas ligas. As ligas de Fe-Cr-C associam fases duras (carbonetos), com uma matriz metálica, o que lhes proporciona elevada dureza e resistência mecânica. Para realização dos experimentos, foram utilizadas as ligas de Fe-Cr-C comerciais, em forma de consumíveis (eletrodos e arame) e aplicadas em aço carbono ASTM A36 por meio de processos de soldagem SMAW e GMAW, respectivamente, como revestimentos. Neste caso, foram utilizados dois eletrodos com adição de 25 e 45% em peso de cromo e um arame com 20 e 5% em peso de cromo e nióbio, respectivamente. O ensaio de desgaste por microabrasão foi realizado utilizando o teste por esfera rotativa fixa e, como abrasivo, uma suspensão de diamante de granulação 3µm. Para o qual, foram utilizados 4 corpos de prova referentes à cada liga. Para determinar o coeficiente de desgaste foi obtida a perda média de volume de material, em intervalos de tempo de ensaio pré-estabelecidos, relacionando o resultado com a distância de deslizamento. Ao analisar os resultados obtidos, verificou-se que a liga que apresentou combinação de cromo e nióbio em sua composição exibiu melhores resultados de resistência ao desgaste, embora apresentasse menores valores de dureza e percentual de carbonetos em relação às outras duas ligas. Tal fato evidencia a possibilidade de se utilizar tais ligas em aplicações que requerem alto desempenho em relação à resistência ao desgaste.

ABSTRACT This paper presents an evaluation of the influence of chromium content and the blend of chromium and niobium in Fe-Cr-C hardfacing alloys on the microstructure and properties that involve microabrasive wear resistance. Various studies have been carried out searching for conclusive information on this system under wear conditions, due to the different phases and properties presented by these alloys. These alloys associate carbides with a metallic matrix giving them high hardness and mechanical resistance. For the realization of the experiments, commercial Fe-Cr-C alloys were obtained in the form of consumables (electrodes and wire) and applied as coatings on ASTM A36 carbon steel by means of SMAW and GMAW welding processes, respectively. In this case, two electrodes with addition of 25 and 45 percent by weight of chromium and a wire with 20 and 5 percent by weight of chromium and niobium, respectively, were used. The microabrasion wear test was performed using the fixed rotating ball method and, as an abrasive, a diamond suspension of 3μm granulation. For this, four test specimens were used for each alloy. In order to calculate the wear coefficient, the average loss in volume was determined at pre-established time intervals, relating the result to the sliding distance.

ABSTRACT The heat input is the amount of energy supplied per unit length of the welded workpiece. In this study, the effect of two different heat inputs in laser beam welding of a high strength aluminum alloy AA6013-T4 was evaluated from macrostructural and microstructural points of view. The experiments were performed using a continuous wave 2 kW Yb-fiber laser with 100 µm spot size on the upper surface of the workpiece. Keeping the heat input at a given level, 13 or 30 J/mm, the laser power was changed from 650 W to 2 kW and the welding speed from 33 to 150 mm/s. In the condition of higher heat input 30 J/mm it was possible to obtain both cutting and welding processes. For 13 J/mm, welding processes were obtained in conduction and keyhole modes. The equiaxed grain fraction changed with changing speed for the same heat input. The laser processing induced a decrease in the hardness of the weld bead of about 25% due to the solubilization of the precipitates. The estimated absorptivities of the laser beam in the liquid aluminum changed largely with experimental conditions, from 4.6% to 10.5%, being the most significant source of error in measuring the real amount of energy absorbed in the process. For the same heat input the macrostructure of the welded surfaces, i.e., humps and dropouts, changed as well. All these facts indicate that the heat input is not a convenient method to parameterize the laser beam welding parameters aiming the same weld features.

Abstract This work was developed in order to validate a simplified computer simulation method for application in the drawing processes. The results of tensile tests on AISI 1004, AISI 1020 steel and copper were compared to those of computer simulations performed using the Deform-3D TM software. Each specimen was assumed to be an elasto-plastic material and was meshed with 50,000 finite elements. Young's modulus and Poisson's ratio were the only material properties considered in the elastic region; the parameters of Hollomon's equation were used in the plastic region up to constriction. A strain rate of 1x10-3 s-1 was applied during the simulations. In the plastic region, up to the point of constriction, the curves obtained from the simulations showed reasonable correspondence to those determined from physical testing. However, the former diverged from the latter in the elastic and elastic-plastic transition regions. This divergence indicates that microstructural factors may have a greater influence in the transition region than in the plastic region. Moreover, the correlation obtained in the plastic region indicates that the proposed method has the potential to be applied in drawing processes.

Este trabalho faz uma avaliação da influência de parâmetros operacionais utilizados no processo de soldagem a laser do aço inoxidável AISI 316. Os resultados dos experimentos de soldagem realizados com parâmetros ajustados para diversas situações foram avaliados levando em consideração a densidade de potência disponibilizada e o tempo de interação do feixe com o metal base. Essas avaliações foram baseadas nos resultados de microdureza e nos ensaios de corrosão eletrolítica das soldas, auxiliadas pela macrografia do cordão de solda. Buscou-se evidenciar correlações entre os parâmetros operacionais selecionados para os experimentos e os resultados obtidos nos cordões de solda, medindo-se grandezas como largura e profundidade. Concluiu-se que a escolha adequada dos parâmetros operacionais é fundamental para a garantia da qualidade dos cordões de solda. Além disso, validou-se um método rápido de avaliação da susceptibilidade dos cordões de solda à corrosão.

This paper addresses an evaluation of the influence of operational parameters used in the AISI 316 stainless steels laser welding process. The results of the welding experiments performed with parameters adjusted to a variety of situations were evaluated taking into account the power density available and the interaction time of the laser beam with the base metal. These evaluations were based on the results of microhardness and the electrolytic corrosion tests of the solders, assisted by the macrography of the weld bead. It was sought to emphasize correlations between selected operating parameters and the results obtained with weld beads, measuring their width and depth. It was concluded that the proper choice of operating parameters is fundamental to the guarantee of quality of the weld beads. Besides that, a quick method of evaluation of weld beads susceptibility was validated.

A logística, ao longo do tempo, tornou-se processo determinante para a sobrevivência das empresas em função dos seus aspectos. Os aspectos logísticos são responsáveis pelo fluxo de materiais e de informações, desde o fornecedor até o consumidor, e impactam, diretamente, no desempenho das empresas, bem como no custo dos produtos e serviços que oferecem. Isso é razão suficiente para sugerir a adição dos aspectos logísticos nas ferramentas de análise e seleção de materiais. Esse estudo tem como objetivo apresentar o desenvolvimento de um modelo de seleção de materiais metálicos que considera os aspectos logísticos no processo de decisão. Para isso, utilizou-se uma adaptação da rede PERT (Program Evaluation and Review Technique), relacionando-se indicadores da variável seleção de materiais com os da variável logística. Implementamos o nosso modelo e apresentamos a especialistas de empresas do setor minerometalúrgico com fins de validação. Esses relataram que não possuem sistema gerencial que realize processo de seleção utilizando informações do material com informações logísticas. Assim, consideraram o modelo proposto um importante instrumento de tomada de decisão gerencial.

Logistics has become a decisive process for the survival of companies. Logistic aspects are responsible for the flow of materials and information from the supplier to the consumer, and have a direct impact on the performance of companies, as well as on the costs of the products and services they offer. This is enough to justify the addition of logistic aspects as tools for analysis and material selection. This work aims at presenting the development of a model for the selection of metallic material, which considers the logistic aspects on the decision process. For this reason, we have used an adaptation of the PERT net (Program Evaluation and Review Technique), relating indicators of variables from material selection with those from logistics. For the purpose of validation, we then implemented the model and presented it to experts of the mining-metallurgical sector. These experts had previously reported a lack of management systems that support the selection process relating to material and logistic information. As a result, they considered the proposed model to be an important instrument for undertaking managerial decisions.

Óxidos de ferro (goethita e hematita) pulverizados foram irradiados com pulsos laser objetivando verificar o resultado da interação desses pós com a radiação infravermelha concentrada em pulsos de curta duração e altamente energéticos. Esses experimentos se justificam diante da utilização desses pós, em obras de arte, como pigmentos, desde as épocas mais remotas. Na atualidade, tornou-se frequente recorrer a pulsos laser como ferramenta de limpeza de obras de arte, o que justifica a necessidade do desenvolvimento de conhecimentos relacionados à interação laser-pigmentos. Evitar danos às obras de arte, recentes ou não, é uma exigência inevitável. Os resultados mostraram que os pulsos laser Nd:YAG fornecem energia suficiente para promover, instantaneamente, mudanças químicas e estruturais nos pigmentos minerais estudados. Material vitrificado (amorfo) foi identificado nas amostras irradiadas e sua formação deveu-se à solidificação ultra-rápida ocorrida no locais onde a energia disponibilizada pelos pulsos laser foi suficiente para fundir as partículas do pó. Em consequência das mudanças químicas e estruturais induzidas, houve alteração da cor original do material irradiado. Essas alterações cromáticas foram quantificadas por intermédio de um método desenvolvido para tal finalidade e que é baseado na variação da intensidade das componentes RGB das cores digitais.

Laser irradiation of powdered iron oxides (goethite and hematite) was performed in order to obtain information about their interaction with short duration near-infrared pulses. Results have shown that under some conditions, Nd:YAG laser provides enough energy to induce fast chemical and structural transformations of the goethite and hematite. This kind of information is of great interest for professionals working with artwork conservation because this technique is used in the conservation of cultural heritage. Depending on the laser's working conditions, glassy (amorphous) material was detected and its presence was related to areas of fast solidification where the energy delivered was enough to melt the powder particles. Color changes were observed and quantified by means of an RGB color measurement method developed to show the evolution of each color component.

O Museu de Ciência e Técnica da Escola de Minas da Universidade Federal de Ouro Preto possui um fragmento de meteorito metálico com 110,76g denominado Itumirim, encontrado próximo a Itutinga, cidade do interior de Minas Gerais, distante 228km de Belo Horizonte. Realizando-se análises ao microscópio eletrônico de varredura (MEV), determinou-se a classificação estrutural do fragmento Itumirim como octaedrito médio, Om. As fases mineralógicas presentes foram determinadas recorrendo-se às análises com o detector de energia dispersiva de raios X (EDS) acoplado ao MEV e com o espectrômetro Mössbauer miniaturizado, MIMOS II. Esses resultados somados à correlação existente entre classificação estrutural e química permitiram classificar o fragmento Itumirim como pertencente ao grupo IIIAB, a mesma classificação do meteorito Itutinga.

The School of Mines Museum of Science and Technology of the Federal University of Ouro Preto has, in its collection a fragment of an iron meteorite weighing 110.76g named Itumirim. It was found near Itutinga, a village distant 228km from Belo Horizonte in the state of Minas Gerais. SEM analysis, coupled with EDS (Energy Dispersive Spectrometry) showed that the structural class of the studied Itumirim fragment is medium octahedrite, Om. The mineralogical phases were determined using EDS and Mössbauer Spectroscopy (Miniaturized Mössbauer Spectrometer - MIMOS II). Theses studies provided information for classifying the meteorite as belonging to the IIIAB group, the same classification as the Itutinga meteorite.

Esse trabalho decorre das inúmeras atividades desenvolvidas no âmbito do projeto "Organização, Restauração e Difusão do Acervo Técnico-Científico da UFOP: Novos Elementos para a História da Ciência no Brasil". O referido projeto iniciou-se com a restauração de antigos instrumentos científicos pertencentes ao acervo da Escola de Minas de Ouro Preto, inaugurando, assim, uma fase de pesquisas dedicadas a aspectos inusitados da trajetória daquela Instituição, de seus membros e ex-alunos. A pesquisa documental que desenvolvemos forneceu-nos informações preciosas sobre a EMOP e, nesse artigo, apresentamos alguns aspectos da sua atuação na organização das "Seções de Geologia", que objetivavam apresentar o cenário da pesquisa e da indústria mineral do Brasil nas Exposições Universais.

This article is in accordance with several activities developed under the project "Organização, Restauração e Difusão do Acervo Técnico Científico da UFOP: Novos Elementos para a História da Ciência no Brasil". Initially, antique scientific equipment was cleaned and restored. Found then, were documents revealing unknown features of Ouro Preto School of Mines, its members and former students. These documents provide a better understanding of the role played by OPSM in the organization of the "Geology Sections" where the state of the art of our mining industry and research activities were displayed at the Universal Expositions.

Esse artigo reúne informações oriundas do acervo documental do arquivo da Escola de Minas de Ouro Preto. O trabalho sistemático de análise dessa documentação iniciou-se há pouco mais de um ano e essa atividade insere-se no projeto "Organização, restauração e difusão do acervo técnico-científico da UFOP: novos elementos para a história da ciência no Brasil", apoiado pelo CNPq. Depreende-se do título desse artigo o propósito de retomar as Exposições Universais como eventos catalisadores de ações programadas visando à divulgação de conquistas atribuídas ao progresso técnico-científico. O papel desempenhado pela EMOP, na coordenação e condução dessas ações, na Província e depois no Estado de Minas Gerais, será descrito com destaque para a "Sociedade de Geographia Econômica de Minas Geraes".

This article assembles information obtained from the documental library of the Escola de Minas de Ouro Preto (School of Mines, Ouro Preto). This paper systematically analyzes these documents. This study was begun a little more than a year ago and belongs to the project "Organização, restauração e difusão do acervo técnicao científico da UFOP: novos elementos para história de ciência no Brasil" (Organization, restauration and disclosure of the technical scientific library at UFOP: new elements of Brazil's scientific history) sponsered by CNPq. As can be inferred from the title of this article, the proposal is to go back to Universal Expositions as catalystic events of programed actions with the disclosure of conquests attributed to technical scientific progress. The work coordinated and performed by the Escola de Minas de Ouro Preto (EMOP), both in the Province and later in the State of Minas Gerais, will be written with emphasis on the "Sociedade de Geographia Econômic de Minas Geraes" (The Minas Gerais Society of Geographic Economy).

Laser treatment technologies have been widely used to modify superficial layers of different materials. In this work we prepare Nb and Cr rich coatings according to laser alloying technique using cast iron as substrate material. Nb and Cr are intensive used in order to overcome challenges like good chemical and mechanical performance at high temperatures. Following laser alloying the surface-modified samples were submitted to an "in situ" XRD analysis under controlled high temperature and atmosphere. The phase transitions registered point to transformations that do not implies formation of fragile phases or cracks induced by high volumes modifications.