Carlos Otávio Petter

Optical influence of the type of illuminant, substrates and thickness of ceramic materials

OBJECTIVES The present study is an instrumental evaluation of the optical influence of the type of illuminant, substrate and different thickness on the color of dental ceramics. METHODS Thirty ceramic disks were prepared from IPS-Empress and IPS-Empress2 in three different thicknesses (1.5, 2.0 and 2.5mm). Disks made of composite resin; silver-palladium alloy and gold were used as substrates. The disks with a 1.5mm thickness were placed on a neutral gray photographic paper and measured with a spectrophotometer under three illuminants: daylight (D65), incandescent light (A) and fluorescent light (F6). All ceramic disks were combined with the substrate disks and a spectrophotometer was used to measure the coordinates of lightness (L*) and chromaticity (a* and b*). Two-way ANOVA (p<0.05) was used to analyze the combinations of ceramics, substrates and illuminants tested considering the coordinates of lightness (L*) and chromaticity (a* and b*), and also differences of color (DeltaE), lightness (DeltaL*), chromaticity values (Deltaa* and Deltab*). RESULTS For the illuminants tested, the results present significant differences for coordinates of chromaticity a* and b*, suggesting a metamerism effect. In combination with the substrates, the results present statistical differences in all the tested conditions, especially where there is no ceramic substructure. SIGNIFICANCE The presence of discolored tooth remnants or metallic posts and cores can interfere with the desired aesthetic result, based on the selection of color aided by a single luminous source. Thus, the substrate color effect, thickness of the ceramic materials and type of illuminant are important factors to be considered during the clinical application of the ceramic systems.

Avaliação da perda da coloração artificial de ágatas

O Rio Grande do Sul e um dos principais produtores de geodos de agatas do mundo. As agatas da regiao de Salto do Jacui permitem a introducao de alguns corantes em seus poros, tornando-as coloridas. O objetivo do presente trabalho foi estudar a perda de cor de agatas tingidas artificialmente, considerando diferentes ambientes de exposicao. Estudaram-se agatas coloridas pelos procedimentos classicos (verde, vermelho, azul e preto) e coloridas com corantes orgânicos (verde, vermelho, rosa e roxo). O procedimento experimental consistiu em expor as chapas de agatas em tres ambientes com luminosidades distintas: escuro, domestico e ao ar livre. A evolucao da cor foi avaliada pela tecnica de colorimetria diferencial, usando o sistema colorimetrico CIE L*a*b*. Os resultados obtidos demonstram que os metodos classicos de tingimento proporcionam cores permanentes, enquanto que os corantes orgânicos promovem cores instaveis. Dependendo do grau de luminosidade e tempo de exposicao, a perda de cor pode ser praticamente total.

Quantification of Hematite and Goethite Concentrations in Kaolin Using Diffuse Reflectance Spectroscopy: A New Approach to Kubelka-Munk Theory

Kaolin ores are usually contaminated by some Fe-bearing minerals, the strong colors of which degrade the quality of the final product. A spectroscopic technique is sought to quantify the content of hematite and goethite, the main contaminant minerals in the kaolin from Capim River in Brazil, was the focus of this study. The total Fe content obtained through X-ray fluorescence showed a poor correlation with the brightness of kaolin, due to the inability to differentiate between the Fe contained in the (oxyhydr)oxides and the Fe present in the crystalline structure of kaolinite, especially when the Fe-bearing minerals occur in small quantities. Here, a new generic technique to quantify Fe (oxyhydr)oxides in kaolin, based on the Kubelka-Munk theory, is presented. A new interpretation of the theory was made that enables its use without the need to measure thin layers of material. The results with synthetic goethite and hematite were very positive (R2pred ≈ 0.99) and experiments with contaminants from the mine are already underway.

Purification of north Brazilian kaolin by selective flocculation

Abstract The main kaolin deposits in north Brazil present are contaminated with colored titanous impurities. Conventional beneficiation processes do not completely remove TiO 2 . The difficulty in separation is mainly due to the ultra-fine size of the minerals. This work presents a study of an alternative kaolin purification method based on selective adsorption of soluble polymers. In the process, flocs were generated by interaction of anionic polyacrylamide with titanous impurities and were separated from the kaolin suspension through sedimentation.

Teoria de Kubelka-Munk aplicada na indústria de minerais industriais: predição do teor de contaminantes em caolim

For most industrial minerals, the economic value of the product is directly associated to its optical properties, like color, brightness, etc. These optical properties can also be used as auxiliary tools in the mine planning and mineral processing. In this work, the Kubelka-Munk Theory was used in an attempt to create a method for the determination of contaminant concentration in kaolin. Due to practical difficulties, it was necessary to develop some mathematical relations involving the model to obtain the two constants needed for each material. The obtained results were satisfactory, making possible the realization of more detailed studies about the application of these mathematical relations, as much for the kaolin as for industrial minerals in general.

Technological characterization of riacho dos machados gold ore for cyanide leaching and study of the utilization of oxidising agents

This work evaluates the behavior in the cyanide leaching of primary gold ore from Riacho dos Machados, central Brazil. The parameters studied were: extraction of gold/silver in different ore sizes to determine the exposition of precious metals; rate of extraction in bottle roll tests with crushed and ground ores; and the effect of addition of oxidising agents (air, oxygen and hydrogen peroxide) on gold/silver leaching. The run of mine ore contains about 7 ppm of gold and 2 ppm of silver. The gold/silver particles are of microscopic and submicroscopic sizes and 90% of the gold was extractable. The use of oxygen and hydrogen peroxide mixed with air increased the rate of gold dissolution.

Espectrocolorimetria de variedades de caulim da Jazida Ipixuna, no Estado do Pará

Varieties of kaolin ore were sampled from a sedimentary deposit in Para state and processed in a pilot plant for spectrocolorimetry studies. The aim was to provide a tool for the mining and processing operations. Ores like that contain textural and mineralogical variations that define whether the ore blocks may or may not be processed. The decision making depends, first, on the ore color subjective analysis: reddish blocks are inappropriate, but the whitish ones are appropriate. The ore color depends on the mineral paragenesis contaminant. Fifteen representative samples of five varieties of kaolin were analyzed under different parameters. These samples were visually defined by the ore color. The reflectance curves of the sandless product defined seven spectrocolorimetric groups, four of which were appropriate for generating a quality product for the market. This study presents both the analyses and the results for each group, what they represent as a tool to support the mining and processing operations, and some considerations about the blending among the kaolin groups.

Report: the current situation of sanitary landfills in Brazil and the importance of the application of economic models

We present the development stage of the sanitary landfills in Brazil in the context of urban solid residue management, demonstrating the necessity and importance of the employment of economic models. In the article, a cost estimate model is proposed as the basis for studies to be applied by sector management, including the city council, companies, consultants and engineers, contributing to the choice of new areas, public bids, municipal consortia and private public partnerships.

FILTRO ANAERÓBIO: USO DE RESÍDUOS DE CONSTRUÇÃO COMO MATERIAL SUPORTE.

O trabalho avalia o desempenho de residuos da construcao civil como cerâmica vermelha e cimenticios (argamassa) para o enchimento de filtro anaerobio. A pesquisa foi realizada em escala de laboratorio utilizando filtros ascendentes com capacidade de 730 ml. Os materiais suporte testados foram os seguintes: brita (material padrao), residuo de cerâmica vermelha, e este misturado com material cimenticio. A agua a ser tratada foi coletada na etapa intermediaria de uma estacao de tratamento. Os filtros foram alimentados de forma continua e por gravidade, com a vazao de alimentacao controlada atraves do gotejamento. Os materiais empregados foram caracterizados quanto a granulometria, absorcao de agua e detencao hidraulica. A eficiencia de filtragem dos materiais foi avaliada mediante parâmetro de DQO (demanda quimica de oxigenio). Os resultados mostraram eficiencias compativeis e pouco superiores a da brita. A utilizacao desses residuos justifica-se principalmente pela facilidade, disponibilidade e quantidade e valor em relacao a brita. Palavras-chave: filtro anaerobio; material suporte; residuo de construcao. ABSTRACT Anaerobic treatment: use with filter of recycle material from construction. The work, proposes to evaluate the accomplishment of residues generated by civil construction, such as: ceramics and cement, as a support material of biofilm in the anaerobe filtration. The research is utilizing models of anaerobe filters with a capacity of 730ml. In one of the filters will be used a pattern material (mineral rock crunching) that will serve as a comparative element on the efficiency of the other filters. The filters are fed in a continuous way and by gravity. The materials used were characterized: size and water absorption and hydraulic detention. The efficiency of the materials will be measured through the variability of the parameters: CDO (Chemical demand of oxygen). The utilization of these residuals is supported mostly by the easiness, availability, quantity and quality related to the aggregate of rock. Key words: anaerobe filters, support material of biofilm, civil construction

Factors and competitiveness analysis in rare earth mining, new methodology: case study from Brazil

Rare earths are increasingly being applied in high-tech industries, such as green energy (e.g. wind power), hybrid cars, electric cars, permanent high-performance magnets, superconductors, luminophores and many other industrial sectors involved in modern technologies. Given that China dominates this market and imposes restrictions on production and exports whenever opportunities arise, it is becoming more and more challenging to develop business ventures in this sector. Several initiatives were taken to prospect new resources and develop the production chain, including the mining of these mineral assets around the world, but some factors of uncertainties, including current low prices, increased the challenge of transforming the current resources into deposits or productive mines. Thus, analyzing the competitiveness of advanced projects becomes indispensable. This work has the objective of introducing a new methodology of competitiveness analysis, where some variables are considered as main factors that can contribute strongly to make unfeasible a mining enterprise for the use of rare earth elements (REE) with this methodology, which is quite practical and reproducible, it was possible to verify some real facts, such as: the fact that the Lynas Mount Weld CLD (AUS) Project is resilient to the uncertainties of the RE sector, at the same time as the Molycorp Project is facing major financial difficulties (under judicial reorganization). It was also possible to verify that the Araxá Project of CBMM in Brazil is one of the most competitive in this country. Thus, we contribute to the existing literature, providing a new methodology for competitiveness analysis in rare earth mining.