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CARACTERIZAÇÃO DIMENSIONAL, MORFOLÓGICA E ESTRUTURAL DE PARTÍCULAS DE CALCÁRIO E DOLOMITO COMINUÍDAS EM MOINHO PLANETÁRIO E O ESTUDO DA AGLOMERAÇÃO DE ULTRAFINOS
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The applications of limestone and dolostone in ultrafine size (<10 μm) are related to purity, size distribution and particle morphology. In this granulometry, carbonate rocks are employed, for example, in the production of polymers, pharmaceuticals, paper and cellulose. Milling in high energy mills is used to ensure high size reduction factors without compromising the purity of the particulate state. However, in addition to high energy consumption, ultrafine processing is hampered by agglomeration and structural modifications induced by the mechanical action of grinding. In this context, the aim of this work was to investigate the influence of grinding time on granulometric distribution, structural modifications and thermal decomposition in ultrafine limestone and dolostone particles processed in a planetary ball mill. Samples from two sources were used: metamorphic limestone (Currais Novos, RN), with predominance of calcite (CaCO3), and sedimentary dolostone (Jandaíra, RN), with predominance of dolomite (CaMg(CO3)2). The tests were performed with bawls (250 ml) and zirconia balls (25; 10 mm), at twelve time intervals between 1 and 1920 minutes, at 300 rpm. The techniques of laser scattering, gas absorption-desorption (BET-BJH) and scanning electron microscopy were used to perform the dimensional and morphological characterization of the ground product. The results showed that the apparent grinding limit was reached after 60 minutes for limestone (D50 = 12.33 ± 0.58 μm) and after 480 minutes for dolostone (D50 = 6.35 ± 0.19 μm). Above this limits agglomeration was observed, mainly for dolostone. Structural modifications were analyzed by X-ray diffraction (XRD) and EPR spectroscopy in irradiated samples (5 kGy). The variation of crystallite sizes and plastic deformations showed that the structural modifications were significant in the dolostone, especially above the grinding limits. It was concluded that there was a change from brittle to ductile behavior between 240 and 480 minutes for dolostone, evidenced by the significant increase in plastic deformation and reduction of crystallite size. The EPR spectra of the irradiated samples showed that the mechanical action of the grinding induces the formation of paramagnetic centers in the limestone (g-factor=1.9999) and dolostone (g-factor=2.0026). The thermal decomposition analysis was carried out in a thermodifferential (DTA) and thermogravimetric (TG) equipment under CO2 atmosphere. The limestone did not show a significant variation in the thermal analysis. For dolostone the calcination showed a reduction of ~ 30 °C in the reaction temperature and of ~ 40% in the activation energy with the increase of the grinding time. It was observed that these reductions are associated to the appearance of a new thermal event at the temperature of ~ 650 ° C. This new event is associated with the structural modifications caused by the mechanical action of grinding. The distinct grinding limits observed for limestone and dolostone were explained by the more refined texture of the dolostone. The mechanisms of plastic deformation affected the thermal decomposition of dolostone. However, it was not possible to establish a clear relation between the presence of paramagnetic centers and agglomeration.
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... O método de difração de Raios-X é utilizado para a investigação da estrutura atômica e molecular da matéria e permite a avaliação do tamanho e orientação de microcristais (Barros, 2019). Segundo Costa (2015), essa técnica auxilia na caracterização da micromorfologia do solo e é um estudo importante para compreender a pedogênese e avaliar as práticas agrícolas. ...
Materiais saprolíticos constituem importantes seções no recorte vertical da paisagem. São materiais ainda pouco conhecidos e demandam maior dedicação. Para caracterização destes materiais pode-se fazer uso de técnicas mineralogia e micromorfologia como a difração de Raios-X (DRX) e o Microscópio Eletrônico de Varredura (MEV). O DRX é uma técnica de caracterização de estruturas cristalinas. O MEV é um tipo de microscópio capaz de produzir imagens de alta resolução da superfície de materiais sólidos. O objetivo é caracterizar amostras de materiais intemperizados de diferentes rochas. Foram selecionados cinco perfis de intemperismo em Juiz de Fora - MG. Os parâmetros utilizados para a análise física e mineralógica foram os seguintes: cor, textura, consistência, rocha de origem e grau de alteração, mineralogia e micromorfologia. A cor é variável entre e intra amostras, é dependente dos minerais constituintes e do grau de alteração. A textura está ligada aos minerais constituintes e seus tamanhos, que são dependentes de seus graus de alteração. A consistência é dependente da resistência dos minerais constituintes e da alteração. As rochas de origem são o quartzito ou o gnaisse. Os principais minerais encontrados foram quartzo, biotita, muscovita e caulinita. Quanto maior a porcentagem de argila, menor a consistência e maior o grau de alteração. A presença de minerais mais resistentes tende a dificultar a pedogênese, resultando em perfis mais arenosos, com poucos minerais de argila e sem atividade biológica. Nos perfis em que predomina o quartzo, apesar da presença desse mineral, o grau de alteração é elevado. Physical and Mineralogical Characterization of Weathering Materials in the Urban Area of Juiz de Fora - MG through Macroscopic Analysis, X-Ray Diffractometer and Scanning Electron Microscope ABSTRACTSaprolitic materials are important sections in the vertical cutout of the landscape. These materials are still little known and demand greater dedication. To characterize these materials, we can use mineral and micromorphological techniques such as X-ray diffraction, a technique for characterizing crystalline structures and the Scanning Electron Microscope, a type of microscope capable of producing high-resolution images of the surface of solid materials. The objective is to characterize weathered colors of different stones. Five weathering profiles were selected in Juiz de Fora - MG. The parameters used for physical and mineralogical analysis were as follows: color, texture, consistency, original rock and degree of change, mineralogy and micromorphology. The color is variable, depends on the constituent minerals and the degree of change. The texture is linked to the constituent minerals and their sizes, which depend on their degree of change. The consistency is dependent on the strength of the constituent minerals and the degree of change. The original rocks are quartzite and gneiss. The main minerals found were quartz, biotite, muscovite and kaolinite. The higher the clay percentage, the lower the consistency and the greater the degree of change. The presence of more resistant mineralsmakes pedogenesis difficult, resulting in more sandy profiles, with few clay minerals and without biological activity. In profiles that predominate quartz, despite the presence of this mineral, the degree of change is high.Keywords: Mineralogy; Micromorphology; Weathering material.
The applications of limestone and dolostone in ultrafine granulometry (<10 μm) are closely connected to the purity, size distribution and morphology of the particles. The processing of these minerals up to the micrometric range is hampered by the presence of agglomeration mechanisms and possible modifications of the crystal structure due to the mechanical action of the grinding. It is believed that a better understanding of the mechanical and microstructural properties of the starting materials may contribute, for example, to clarifying the relationship between the apparent milling limit and the agglomeration process of ultrafine particles. Thus, the objective of this work was to characterize the hardness, fracture toughness and grain size of samples of metamorphic limestone and sedimentary dolostone previously used in ultrafine grinding with a planetary ball mil. The mechanical properties were determined by static indentation tests and the grain size was estimated by microscopy. The texture analysis showed that the average grain size of the limestone (2190±1270 μm) is about 25 times greater than the dolostone (89±27 μm). Static indentation tests showed that the dolostone (3.18±0.16 GPa) is harder than limestone (1.36±0.07 GPa) and has the same fracture toughness (0, 37±0.11 MPa * m0.5 for limestone and 0.49±0.09 MPa * m0.5 for dolostone). These results suggest that the level texture refinement in carbonate rock may have a greater influence on ultrafine milling results than mechanical properties. Palavras-chave: Carbonatic rocks, high energy grinding, grain size, hardness and fracture toughness.
In the processing of industrial minerals such as quartz, gypsum and limestone, the main specifications refer to purity, size and morphology of particles. When used in ultrafine size (<10 micrometers) for the production of high performance ceramics, polymers, pharmaceutics, pulp and paper, the processing of these minerals is affected by agglomeration mechanisms and possible structural changes resulting from the mechanical grinding action. This study aimed to investigate the influence of particle size on the thermal properties of limestone samples from two different sources, as follows: metamorphic (Currais Novos, RN) with a predominance of calcite (CaCO3); sedimentary (Jandaíra, RN), especially formed by dolomite (CaMg(CO3)2). Grinding tests were conducted in a planetary mill with pots (250 ml) and balls (25 and 10 mm diameter) of zirconia in twelve time intervals (between 1 and 1920 minutes) at 300 rpm. The wet grain size analyzes were performed with a laser particle size analyzer. The thermal decomposition curves were obtained with thermal differential analysis (DTA) and thermogravimetric (TG) analysis to 1200 °C (10°C / min) under an inert atmosphere (N2). By DTA curves, it was found that the decomposition temperature of the metamorphic (CaCO3) sample was not affected. For the sedimentary sample, it was found that the calcination temperature of CaMg(CO3)2 roughly decrease with the particle size decreasing. This behavior was modified when the grinding limit of the sedimentary sample (480 minutes) was achieved corresponding to a specific surface area of 0.70 m2/g. Although showing a high amount of agglomerates, the aliquot ground at 1920 minutes showed the highest reduction in calcination temperature (~ 30 °C). This suggests that other effects such as structural changes induced by the grinding action in high energy milling during high times is occurring together with the agglomeration process.
Among the industrial minerals limestone has one of the largest application spectra. In ultrafine
sizes (<10 µm), its main use is in the production of pulp and paper. The production of ultrafine
particles is limited by high energy consumption and agglomeration mechanisms. Thus, the aim of
this study was to characterize the product of ultrafine grinding of two different varieties of
limestone, metamorphic and sedimentary, using the infrared (IR) spectroscopy. For this, aliquots
in the size range of 450x850 µm were comminuted in a planetary ball mill between 1 and 1920
minutes at 300 rpm. The mineralogical characterization showed that the mayor constituent of
metamorphic and sedimentary samples is calcite (CaCO3) and dolomite (Ca,Mg(CO3)2),
respectively. The particle size analysis showed the grinding limit was reached at different time for
each sample, as follows: 120 minutes (12 µm) to the metamorphic sample; 480 minutes (7 µm) to
the sedimentary sample. Intense agglomeration was produced above these limits. By IR
spectroscopy, it was be seen that the intensities of the absorption bands of calcite and dolomite
(stretching and bending of CO3-2 anions) increased up to reaching the grinding limit due to the
fitting of particle size to measurement conditions. Above these limits, the intensity of the IR bands
decreased. Additional measurements using only the agglomerated particles made clear that the
decrease in IR intensity bands is mainly related to particle size.
This book surveys the broad field of mechanical alloying from a scientific and technological perspective to form a timely and comprehensive resource valuable to both students and researchers. The treatment progresses from the historical background through a description of the process, the different metastable effects produced, and the mechanisms of phase formation to applications of mechanically alloyed products. The presentation is straightforward and easy to understand but does not compromise the scientific accuracy. It includes an unusually extensive listing of the results of different metastable effects obtained in various alloy systems along with thorough references in each chapter.
It has been the aim of this paper to know the factors that most affect to the process of obtaining the quicklime in traditional lime kilns. To this end, a comparative study has been carried out between two quicklime types, one obtained in traditional lime kiln and another obtained in an industrial lime kiln. On the other hand, two limestone types, commonly used in the production of lime in these kilns, have been calcination in the laboratory. They correspond to an oosparite and oomicritic limestones, traditionally used in the elaboration of limes in the Morón de la Frontera region, Seville (Spain). The samples have been analyzed from the chemical, physical and mineralogical points of view. The calcination process of the limestones and the optimum heating temperature depends of the porosity and crystalline structure original of the limestones. The calcination temperatures, longer residence time and CO2 and steam pressure in the kilns affects the size and porosity of the CaO crystals. The quicklimes with greater volume of pores allow faster access of water to the interior of the material and consequently the lime slaking reaction is less exothermic. The size of the particles CaO affects the rate of the lime slaking reaction, accelerating the reaction when the particles are smaller. The quicklimes calcined in traditional kilns are characterized by greater particle and pore size and greater volume of mesopores.
The main reasons for selecting the powder metallurgy route are outlined and several examples of specific products which results are identified. The constraints which arise during each process stage lead to a general comprehension of the scope of powder metallurgy. In particular, the basic mechanism of the sintering operation is explained as are the technological developments and trends over recent decades.