Resumo For the determination of the coating to be used, corrosion-resistant alloys were tested in comparison with material employed in the pipes of heat exchangers, ASTM 178A. The selection of the most resistant coating was made by means of accelerated corrosion test in SO2 chamber and also by testing polarization. It was found that the aluminum coating had the best results in the tests when compared with materials currently used in the heat exchangers (ASTM 178A). Key-words:Coal. Corrosive wear. Coating. Aluminum. IntroduçãoO histórico de manutenção dos aquecedores tubulares do tipo recuperativo de fluxo cruzado, do Complexo Termoelétri-co Jorge Lacerda (CTJL), relatam constantes paradas por conta da corrosão dos tubos. A corrosão se deve à natureza do carvão utilizado, uma vez que o tipo empregado possui elevado teor de enxofre em sua composição. Os compostos de enxofre quando dissociados com a queima do carvão resultam numa elevada formação de gases SO 2 . [10] O problema se agrava com a condensação dos vapores d'água sobre a superfície dos tubos, pois estes sofrem ininterruptos ataques de compostos químicos altamente corrosivos, os quais estão contidos no condensado, como o ácido sulfúrico (H 2 SO 4 ). Este desgaste químico avança até que os tubos sejam furados, ou mesmo desconectando-os do sistema (falha total). Os gestores da usina termoelétrica entendem que, o problema da corrosão dos tubos tem influência direta, na queda de eficiência da planta geradora de energia elétrica. [7,10] A corrosão pode ser definida como a deterioração de um corpo sólido, por meio de ação química ou eletroquímica provocada pelo meio ambiente ou agente agressor. Estima-se que uma parcela superior a 30% do aço produzido no mundo seja usada para reposição de peças e partes de equipamentos, ou ainda instalações deterioradas pela corrosão. [13]
The aim of this paper was to determine the influence of machining parameters on the surface layer, and consequently on the electrochemical properties, of ASTM F138 austenitic stainless steels. Eight different surface conditions were generated in cylindrical samples by turning and polishing. The surface was characterized by surface roughness R a and R t , Vickers microhardness and microstructural characteristics. Cyclic voltammetric tests were performed to evaluate the potential of repassivation and pitting. The surfaces were analyzed by Scanning Electron Microscopy after the electrochemical tests were performed. The cutting parameters were identified to have a significant influence, and the feed rate was as influential as the depth of cut. The use of polishing alone is not sufficient to ensure that a surface has good surface integrity. Even with the polishing application, usually used to produce prostheses, a significant reduction in corrosion resistance occurs if care is not taken to minimize surface machining damage. Corrosion resistance is lower and pitting nucleation is higher in the samples with no polishing and with more severe machining parameters. The tests indicated that softer machining parameters can contribute to an increase in the life of implantable components, reducing the probability of localized corrosion, as well as improving the mechanical properties of prostheses.
Glasses containing metallic nanoparticles are promising materials that should also possess the best spectroscopic, chemical, mechanical and thermal characteristics for technological applications in optics and photonics. For this reason it was chosen to synthesize and characterize the pure silver doped borosilicate glasses and silver nitrate. The present work investigates the generation of silver nanoparticles on the surface and the mass of a borosilicate glass in which it was directed to the synthesis process in which it was consisted: in the stoichiometric calculations, in the determination of the melting temperature, in the choice of reagents with high degree of purity, in the manufacture of the samples, in the appropriate polishes and in the determination of heat treatments close to Tg of the glass in question. From this phase, the research followed the application of techniques of differential thermal analysis (ATD) and transmission electron microscopy (MET). Thus, from the results and analyzes obtained, it was possible to observe that the borosilicate glass samples of this work will obtain satisfactory experimental results, in which it was possible to prove its optical and structural properties similar to those recognized in literature, thus making it a promising material in area of vitreous materials applied to nanotechnology borosilicate glasses are obtained from the combination of silicon dioxide (SiO2) with boron oxide (B2O3) and the resulting samples were annealed at various temperatures. Due to the structural shape, these glasses have a high resistance to thermal shock, good chemical durability and excellent electrical resistivity compared to other glasses on the market today. Therefore, based on these important structural, physical and chemical characteristics and also in the variety of applications, this study was chosen for the synthesis and characterization of pure borosilicate glass and doped with silver nitrate. We verified the formation of silver nanoparticles, after the heat treatment, by transmission electron microscopy.
Refletindo sobre nossa atuação profissional em meio à sociedade contemporânea, surgiu o questionamento: Afinal, por que sou educador? E a partir disso: Para quem, para quê e por que a educação, que está posta, serve? Enquanto educadores de escola pública federal, percebemos o quanto nossa prática ainda é tecnicista e empobrecida das reflexões cruciais sobre o processo civilizatório. Desse modo, este artigo objetiva estabelecer o papel do educador frente às variáveis contemporâneas. Para tal, realizou-se uma pesquisa de cunho bibliográfico, pautando-se na literatura sobre a temática, balizando as discussões e reflexões. Na tentativa de responder à problemática de pesquisa, o artigo foi dividido em três seções: o papel do educador; o processo educativo como uma variável contemporânea; e, a imbricação da equação civilizatória com a Educação. Alcançar o objetivo da pesquisa, mostrou-se uma reflexão complexa, contudo, evidenciamos que o educador possui inúmeras possibilidades de incorporar as variáveis contemporâneas no processo educativo.
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