Abstract The pelletizing process agglomerates ore fines previously considered as tailings and makes its application possible in the form of pellets. During the process, the pellets are subjected to various compressive forces and temperature changes, which cause ruptures in their surface. These ruptures (cracks) impair the performance of the pellets in the reduction furnaces and affect their strength. In addition to cracking, the formation of clusters inside the furnaces is also a problem for the reduction process because they compromise the flow of gases inside the furnaces. This bonding phenomenon occurs from the formation of iron bridges between pellets subjected to high temperatures. This problem can be minimized by coating the pellets with a mixture of magnesium oxides that inhibits bridging. The present study considered the importance of characterizing cracks and coating on the pellet surface and developed methodologies for the acquisition, processing and digital analysis of images acquired with a stereoscope. Adjustable sample holders were developed which made it possible to cover most of the surface area of the spherical object avoiding overlapping of analysis regions. The crack analysis routine used semantic segmentation and provided attributes such as mean thickness, area fraction and length. The coating analysis routine used color threshold segmentation and measured the fraction of the area occupied by the coating in the samples. The use of the sample holders was essential for the success of the acquisition procedure. The analysis routines were robust for different samples.

Abstract The discrimination between pores and cracks is an important step in the microstructural analysis of iron ore pellets. While the porosity is fundamental during the reduction process in blast furnaces, cracks are strongly detrimental to the mechanical strength. The usual image processing tools cannot automatically discriminate between these two types of features, especially in 3D images obtained, for instance, with x-ray microtomography (microCT). As pores and cracks have essentially the same x-ray absorbance, they cannot be discriminated by a simple intensity threshold. Given the complex shapes in 3D and the presence of many connections between pores and cracks, shape discrimination is not successful either. Thus, this article proposes the use of Deep Convolutional Neural Networks (DCNN) to discriminate between these 2 classes of discontinuities. The well-known U-NET architecture was employed. The network was trained by manually outlining representative objects of the 2 classes in a few layers of the 3D image. After optimization of the training parameters, the network was applied to the full image, successfully discriminating between pores and cracks. The trained network was then applied to the images of different pellets with good results. However, some residual errors are present. These characteristics are analyzed and possible solutions are proposed.

TiO2 nanorods present good performance as catalysts in the sorption behavior of magnesium hydride. In the present study, the morphology of TiO2 nanorods produced from titanate nanotubes heat-treated at 550 °C (NR550), 650 °C (NR650) and 750 °C (NR750) was characterized and their catalytic role on the sorption kinetics of MgH2 was evaluated. For this, ball-milled MgH2-TiO2 nanocomposites with 5 wt% of additives were prepared and the materials were characterized by X-ray diffraction (XRD), BET surface area and Transmission Electron Microscopy (TEM). The hydrogen sorption kinetics of the composites were evaluated in a Sievert’s apparatus at 350 °C. The results indicated that NR550 and NR650 consisted of a mixture of nanorods and nanoparticles and NR750 of coarser nanoparticles of TiO2-anatase with a small amount of rutile. Composites with NR750 and NR550 presented the best sorption kinetics, suggesting the positive effect of the presence of rutile and of anatase nanorods, respectively, on the sorption properties of the material.

Abstract A correlative approach employing optical microscopy and scanning electron microscopy is proposed for the quantification of phases and pores in iron ore pellets. Combining mosaic images covering the full cross-sections of pellets, obtained with both techniques, it is possible to improve the discrimination of pores, quartz and silicates. First, the images must be carefully registered to show the exact same regions. The procedure for registration, discrimination and quantification was developed with Fiji open source software. A qualitative and quantitative analysis confirmed the advantages of the correlative method as compared to the individual techniques.

This work proposes a three-dimensional methodology to characterize porosity in iron ore pellets by X-ray Microtomography (microCT). An image analysis routine was developed to discriminate and quantify open/closed porosity. The results were compared to the traditional techniques of mercury intrusion porosimetry (MIP) and optical microscopy (OM). As expected, the porosity values obtained from microCT were much lower than those from MIP and OM, due to the lower spatial resolution of the proposed technique. However, the resolution can be optimized to detect the main peak of the pore size distribution, close to 10 µm. MicroCT was also able to discriminate between open and closed porosities, and revealed the volumetric spatial distribution of the pores, parameters that cannot be obtained from the other techniques. Thus, microCT may become a new standard for this analysis, eliminating the need for specimen preparation (as for OM) or the use of toxic materials (as in MIP).

Resumo O objetivo deste estudo foi comparar a porcentagem de área não-instrumentada de canais radiculares preparados com diferentes ampliações utilizando sistemas reciprocantes de lima única (Reciproc e WaveOne) e um sistema rotatório convencional de múltiplas limas (BioRaCe) usando a análise da micro tomografia computadorizada. Trinta raízes mesiais de molares inferiores com curvatura moderada (10º a 20º) apresentando a configuração classe II de Vertucci e semelhança de volume do canal foram selecionadas e escaneadas em uma resolução isotrópica de 14,16 µm. A amostra foi dividida em 3 grupos (n=10) de acordo com o sistema utilizado para a preparação do canal radicular: grupo Reciproc, grupo WaveOne e grupo BioRaCe. Segundo e terceiro escaneamentos foram realizados após os canais serem preparados com instrumentos tamanhos 25 e 40, respectivamente. As imagens registradas de voxels da área de superfície dos canais, antes e após o preparo, foram examinadas desde o nível da furca até o ápice para quantificar a superfície não instrumentada. Os dados foram comparados estatisticamente através de GLM para medidas repetidas com um nível de significância de 5%. Os sistemas de instrumentação não influenciaram o percentual de superfícies não tocadas dos canais radiculares (p=0,690), enquanto que uma redução significativa no percentual de voxels estáticos foi observada após o alargamento do canal radicular (p=0,010) em todos os grupos (p=0,507). Nenhum dos sistemas foi capaz de preparar toda a área de superfície do canal mesial dos molares inferiores. O aumento do tamanho final apical resultou num efeito positivo significativo sobre a capacidade de modelar dos sistemas testados.

The aim of this study was to compare the percentage of non-instrumented area of root canals prepared with different enlargements using single-file reciprocating systems (Reciproc and WaveOne) and a conventional multi-file rotary (BioRaCe) system by micro-computed tomographic analysis. Thirty mesial roots of mandibular molars with moderate curvature (10° to 20°) presenting a type II Vertucci canal configuration and similar internal volume were chosen and scanned at an isotropic resolution of 14.16 µm. The sample was assigned to 3 groups (n=10) according to the system used for root canal preparation: Reciproc, WaveOne, and BioRaCe groups. Second and third scans were taken after the canals were prepared with instruments sizes 25 and 40, respectively. The recorded images of the surface area voxels of the canals, before and after preparation were examined from the furcation level to the apex to quantify the non-instrumented surface. Statistical data were compared using GLM for repeated-measures with a significance level set at 5%. Instrumentation systems did not influence the percentage of untouched root canal surfaces (p=0.690) whilst a significant reduction in the percentage of static voxels was observed after the enlargement of the root canal (p=0.010) in all groups (p=0.507). None of the systems was able to prepare the entire surface area of the mesial root canal of mandibular molars. The increased final apical size resulted in a significant positive effect on the shaping ability of the tested systems.

<sec><title>Aim:</title><p>To evaluate enamel microhardness and morphology after bleaching with hydrogen peroxide containing calcium in different concentrations.</p></sec><sec><title>Methods:</title><p>One hundred specimens of human teeth were ground and polished and had the initial microhardness evaluated. The specimens were randomly assigned into five groups (n=20): Group 1 - Control group (no treatment); Group 2 - Home Peroxide 6% (without calcium); Group 3 - Home Peroxide 7.5% (without calcium); Group 4 - White Class 6% (with calcium); Group 5 - White Class 7.5% (with calcium). For each group, the bleaching was performed according to the manufacturer's specifications. The specimens were bleached once a day for 5 days and subjected to pH cycling. Microhardness and scanning electron microscopy (SEM) analysis were performed before and after bleaching.</p></sec><sec><title>Results:</title><p>The results showed that groups submitted to bleaching treatment presented hardness loss compared to the control group. The group of 7.5% hydrogen peroxide with calcium showed a lower percentage of hardness loss in relation to other groups.</p></sec><sec><title>Conclusion:</title><p>Calcium in association with a higher hydrogen peroxide concentration may decrease microhardness changes on enamel.</p></sec>

A técnica de soldagem subaquática molhada com eletrodos revestidos apresenta um crescente potencial de aplicação para reparos submarinos em elementos estruturais de unidades flutuantes de produção de petróleo (profundidade até 20 m). Porém, ela apresenta problemas tais como o maior risco de fissuração a frio e de formação acentuada de porosidade. O presente trabalho tem como objetivo melhorar a resistência mecânica do metal de solda de um eletrodo experimental do tipo oxi-rutílico. Foram estudadas as influências de adições de Mo (até 0,4% no metal de solda) na microestrutura e em propriedades mecânicas. As soldas foram realizadas em simulador de soldagem subaquática em profundidade equivalente de 10m utilizando um sistema de soldagem por gravidade. As análises das micrografias mostrou que o aumento do teor de Mo no metal de solda diminui significantemente o tamanho médio de grão da região reaquecida de grãos finos. O aumento do teor de Mo no metal de solda resultou, ainda, em aumento do limite de resistência à tração sem perdas de tenacidade e ductilidade até aproximadamente 0,25%Mo.

the underwater wet welding with coated electrodes technique is undergoing an important use growth in underwater repairs of oil production floating unit's structural elements (up to 20 m depth). However, it presents problems such as increased risk of cold cracking and sharp porosity formation. This work aims to improve the weld metal's mechanical strength through the addition of molybdenum to experimental oxy-rutilic type electrodes. Both the microstructure and the mechanical properties of weld metals were studied while electrodes would receive additional Mo (up to 0.4%). The welds were done using a gravity welding system placed in an underwater welding simulator with an equivalent depth of 10 m. Analyses of micrographics shown that the increased level of Mo in weld metal (a) decreases significantly the average grain size of fine-grained reheated region while (b) increases tensile strength limit without loss of toughness and ductility up to 0,25% Mo approximately.

Com o objetivo de fornecer subsídios para a seleção de consumíveis para a soldagem molhada foram determinadas algumas propriedades do metal de solda a partir de juntas soldadas em água doce com eletrodos revestidos comerciais específicos para este fim. As soldas foram realizadas em tanque a 0,5m de profundidade por dispositivo de soldagem por gravidade. Foram levantados dados que auxiliem a eleger os consumíveis de melhor desempenho para serem testados em maiores profundidades. Foram realizados os seguintes testes e avaliações: caracterização microestrutural, análise e quantificação das inclusões, composição química do metal de solda, dureza Vickers, hidrogênio difusível e avaliação da soldabilidade. Os resultados obtidos permitem classificar os consumíveis testados em dois grupos com características bem distintas. No primeiro grupo está o único eletrodo do tipo oxidante e no segundo grupo estão os quatro eletrodos do tipo rutílico testados. Quanto às propriedades mecânicas e às características operacionais, os eletrodos do tipo rutílico apresentaram os melhores resultados. Por outro lado, o eletrodo oxidante testado produziu soldas com mais baixo teor de hidrogênio difusível e, portanto, menor risco potencial de provocar trincas a frio. As diferenças de propriedades entre os eletrodos testados são evidenciadas e discutidas no presente trabalho.

With the objective to supply subsidies to select ferritic electrodes for underwater wet welding, some weld metal characteristics of commercial electrodes were determined. The welding trials were carried out at 0.5m fresh water depth in an aquarium, using a gravity device for welding. The study aimed also to obtain data to help to elect the consumables of best performance to be tested in higher depths. The following characterizations were performed: microstructural analysis, quantification of inclusions, weld metal and inclusions chemical composition, mechanical properties, diffusible hydrogen and weldability evaluation. The obtained results helped to classify the tested consumables in two groups with quite different characteristics. The first group is composed of one oxidizing type electrode and the second one is composed of four rutile type electrodes. Regarding to hydrogen in the weld metal, the obtained results show that the oxidizing electrode is able to produce welds with considerable low diffusible hydrogen content. As a consequence, smaller potential risk of cold cracking is expected when using this electrode. Meantime, regarding to the arc stability and other operational indicators, the oxidizing electrode presented inferior performance. Considering mechanical properties, the rutile electrodes presented the best results. The properties differences among the electrodes tested are shown and discussed in the present work.

Digital image analysis was used to fully characterize the microstructure of human dentin. With the automatic routine implemented, field and region parameters related to human dentin characterization were obtained in significant statistical quantities. The results obtained for the density, area fraction, distance between neighbors, tilt angle, area and average diameter of the dentinary tubules are presented for unerupted third molars. The results, grouped per class of dentin or per tooth, are discussed in the light of the previous data found on the literature.

Um tubo fabricado com material compósito de matriz polimérica reforçado por fibras de vidro foi caracterizado através de microscopia eletrônica digital. Uma seção circunferencial do tubo foi observada em um microscópio eletrônico de varredura com captura digital de imagem. Um mosaico com imagens em alta magnificação foi gerado para que fosse possível uma caracterização que abrangesse desde as fibras individualmente até a distribuição espacial das camadas de fibras. Através do desenvolvimento de uma seqüência de processamento, dados como o diâmetro das fibras e ângulo de enrolamento foram obtidos, bem como foi realizada a identificação das várias camadas de fibras presentes.

A tube made with a glass-fiber reinforced polymer-matrix composite material was characterized through digital microscopy. A circumferential section of the tube was observed in a Scanning Electron Microscopy with digital image acquisition. A mosaic of high magnification images was created in order to allow complete characterization of the material. Through the development of an image analysis method, the fiber diameters, the winding angles and the discrimination of the layers were obtained.

O presente trabalho apresenta um procedimento de análise digital de imagem para a quantificação de mercúrio, baseado no desenvolvimento de uma cor derivada de uma reação de "spot test", utilizando-se um scanner comercial. A análise digital de imagem da cor desenvolvida foi usada para estabelecer uma relação quantitativa entre os componentes da cor e a concentração de mercúrio, sendo a sua intensidade relacionada à concentração na amostra original. Diferentes modelos de separação de cor foram comparados quanto à sensibilidade frente à variação da concentração de mercúrio. O modelo HLS (Hue-Lightness-Saturation) apresentou os melhores resultados, mostrando a relação linear mais sensível entre o valor da componente H (Hue) e a concentração de mercúrio. O procedimento, quando aplicado a amostras de peixes de exercícios interlaboratoriais, apresentou boa correspondência entre os valores encontrados e aqueles relatados. Os limites de detecção foram estimados em função dos intervalos de confiança das curvas analíticas obtidas, mostrando-se fortemente dependentes da faixa de calibração e apresentando um valor de 0,007 µg g-1 na amostra original (peso úmido), para um intervalo de calibração de 100 a 600 ng.

A digital image analysis procedure for mercury quantification based on the analysis of the color developed in a spot-test derived reaction using a commercial scanner is described. The color intensity is related to the concentration in the original sample. Digital image analysis of the developed color was used to establish a quantitative relationship between the color components and the mercury concentration. Different color separation models were compared and their sensitivity to the variation of the mercury concentration was evaluated. The Hue-Lightness-Saturation (HLS) model provided the best results, showing a linear relationship between the Hue value and the mercury concentration. The procedure was used for the analysis of interlaboratorial fish samples and good concordance between found and reported values was found. The detection limits were estimated from the confidence bands of the analytical curves. For a calibration interval of 100 to 600 ng, a detection limit of 0.007 µg g-1 (wet weight) was found.

In this study, the MAXIM technique was used in an attempt to clarify the phase transformation sequence that occurs during in situ annealing of galvanized samples. A diffractometer equipped with a novel imaging system comprising a Micro-Channel Plate in front of a CCD camera was used. The galvanized samples were produced under typical industrial conditions, with effective aluminum content at 0.147wt.%. In situ experiments were performed and the phase evolution was recorded in real time. It can be concluded that, coupled to in situ thermal treatment, MAXIM is an efficient method to observe the evolution of the phases present in galvannealed samples. This technique has enough sensitivity to detect the evolution of the involved phases with good spatial resolution.