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A través de la historia la aplicación de fundiciones de hierro gris en la industria de combustibles, así como automotriz, ha sido de gran importancia para la sociedad moderna. Los materiales usados en aplicaciones como la fabricación motores han evolucionado, pero las fundiciones de hierro gris han mantenido su vigencia, debido a su durabilidad, resistencia mecánica, facilidad de maquinado y bajo costo. Paralelamente, el contexto mundial de agotamiento de los recursos fósiles y tendencias ambientales más rigurosas, propone el uso de fuentes energéticas sustitutas a los derivados del petróleo y ambientalmente aceptables. Es así, como el biodiesel ha adquirido gran importancia a nivel mundial como combustible suplementario al diesel de origen fósil. La principal ventaja que se asocia a este combustible es su origen renovable y sus beneficios ambientales. Actualmente su aplicación se ve limitada a mezclas de combustible diesel con bajos porcentajes de biodiesel (B2, B5, B10) , debido a que la industria automotriz no garantiza la vida útil de sus componentes. Desde el enfoque de la ingeniería de materiales esto se debe, entre otros, a la incertidumbre relacionada a los procesos degradativos de los materiales que se encuentran en contacto a lo largo su vida útil con el biocombustible, entre los cuales encontramos frecuentemente a las fundiciones grises. Este, es un material versátil ampliamente usado en los procesos industriales de la cadena productiva del biodiesel como carcasas de bombas, válvulas, bridas, collarines, entre otros. La limitante técnica relacionada a la incertidumbre del comportamiento de la fundición de hierro gris a largo plazo, al estar en contacto continuo con combustible biodiesel plantea una incógnita frente a la compatibilidad existente entre el par material-biodiesel, bajo diferentes condiciones térmicas. A fin de responder esta pregunta de investigación, se propone determinar los efectos corrosivos para una fundición de hierro gris comercial, sometida a ensayos de inmersión (bajo diferentes condiciones de temperatura) y corrosión electroquímica en medios no electrolíticos (biodiesel y diesel), con la finalidad de establecer diferencias cualitativas y cuantitativas en los procesos corrosivos entre dos sistemas de combustible. Las fundiciones de hierro gris fueron sometidas al proceso de recubrimiento por la técnica de difusión Termoreactiva (TRD) para obtener capas duras de carburo de niobio y carburo de vanadio. El comportamiento de corrosión de los recubrimientos fue evaluado en condiciones homologas a la fundición de hierro gris a fin de establecer diferencias entre la fundición y los recubrimientos. El análisis de las características físicas, químicas y de corrosión se realizó usando las técnicas de caracterización como microscopia óptica, microscopia electrónica de barrido, difracción de rayos X, pérdida de masa (ensayos gravimétricos), espectroscopia de impedancia electroquímica, espectrometría de emisión óptica entre otras. Abstract. Throughout history the application of gray iron casting in the fuel industry as well as automotive has been of immense importance to modern society. Materials used in applications such as engine manufacturing have evolved, but gray iron cast have remained in place, due to their durability, mechanical strength, ease of machining and low cost. At the same time, the global context of depletion of fossil resources and more stringent environmental trends, proposes the use of substitute energy sources for oil and environmentally acceptable sources. Thus, as biodiesel has acquired significant importance in the world as a supplementary fuel to diesel of fossil origin. The main advantage associated with this fuel is its renewable origin and its environmental benefits. Currently its application is limited to blends of diesel fuel with low percentages of biodiesel (B2, B5, B10), because the automotive industry does not guarantee the useful life of its components. From the materials engineering approach, this is due, among other things, to the uncertainty related to the degradative processes of the materials that are in contact throughout their useful life with the biofuel, among which we often find gray castings. This is a versatile material widely used in the industrial processes of the biodiesel production chain such as casings of pumps, valves, flanges, collars, among others. The technical limitation related to the uncertainty of the behavior of gray iron castings in the long term, being in continuous contact with biodiesel fuel proposes an unknown before the compatibility between the material-biodiesel pair under different thermal conditions. To answer this research question, it is proposed to determine the corrosive effects for a commercial gray iron casting, subjected to immersion tests (under different temperature conditions) and electrochemical corrosion in non-electrolytic media (biodiesel and diesel), with the Purpose of establishing qualitative and quantitative differences in the corrosive processes between two fuel systems. The gray iron smelters were subjected to the coating process by the Thermo-reactive diffusion technique (TRD) to obtain hard layers of niobium carbide and vanadium carbide. The corrosion behavior of the coatings was evaluated under conditions homologous to the gray iron casting to establish differences between the casting and the coatings. The analysis of physical, chemical and corrosion characteristics was performed using characterization techniques such as optical microscopy, scanning electron microscopy, X-ray diffraction, mass loss (gravimetric tests), electrochemical impedance spectroscopy, optical emission spectrometry between others. Doctorado

Made available in DSpace on 2017-07-21T20:43:49Z (GMT). No. of bitstreams: 1 Dis_Ariel_final.pdf: 5083548 bytes, checksum: acac140ede5eeafdd769aa58a612e863 (MD5) Previous issue date: 2016-08-25 This work aims to study the electrochemical steel ASTM A285 Grade C and the same welded with coated electrode AWS E 7018 in the solution of industrial white liquor used in pulp and paper industry by the Kraft method. Samples were withdrawn by electroerosion into three regions: the base metal (BM), the heat affected zone (HAZ) and at the weld metal (WM). Corrosion rates of the three metal regions were determined in 8°C, 16°C, 24°C, 35°C, 42°C, 50°C and 60°C temperature. The values of corrosion rates were compared with the BM, ZTA and WM corrosion rates in electrolytic solutions of the main chemical components of the industrial white liquor in the same temperature range. These solutions were 0,1 mol/L of Na2SO4; 2.276 mol/L of NaOH; 0.126 mol/L of Na2S; 0.128 mol/L of Na2CO3 and simulated white liquor composed of the above solutions with the same molar concentrations. The BM to 24°C, industrial white liquor aerated presented corrosion rate of 0.022 mm/year, 0.045 mm/year for the HAZ and 0.032 mm/year for the WM. It was observed that the HAZ corrosion rates were higher than BM and WM in all solutions studied. Lower corrosion rates were in Na2CO3, followed by NaOH, Na2S, simulated white liquor and finally with the highest corrosion rates in white liquor industry. All solutions are presented alkaline, except sodium sulfate, and it was observed that the three regions are passivated when compared to a reference solution of 0.1 mol/L Na2SO4, and aerated with a pH between 6.0 to 6.5. This passivation film are complex chemical composition due to the presence in solution of OH- HS- ion. From the corrosion potentials of BM in each solution and the pH values it was found that the BM region is passivated according iron Pourbaix diagram in water. Chronoamperometry and voltammetric studies showed that these passivation films that promote greater protection against corrosion, they are solubilized in NaOH solution, simulated white liquor and industrial white liquor when submitted to anodic polarization in potential near at +2.0 V versus saturated calomel electrode. In Na2S and Na2CO3 solution was observed the formation of thick deposits on the surface of BM and when analyzed by EDS was observed the presence of phases such as oxides, sulfides and possibly iron carbonate. Este trabalho tem como objetivo o estudo eletroquímico do aço ASTM A285 Grau C soldados com eletrodo revestido AWS E 7018 em meio de licor branco industrial empregado na indústria de papel e celulose pelo método Kraft. As amostras foram retiradas por eletroerosão em três regiões: metal base (MB), região termicamente afetada pela soldagem (ZTA) e pelo metal de solda (MS). As taxas de corrosão das três regiões metálicas foram determinadas em temperaturas de 8°C a 60°C. Os valores das taxas de corrosão foram comparados com as taxas de corrosão do MB, ZTA e MS em soluções eletrolíticas dos principais componentes químicos do licor branco industrial, no mesmo intervalo de temperatura. Estas soluções foram de 0,1 mol/L de Na2SO4; 2,276 mol/L de NaOH; 0,126 mol/L de Na2S; 0,128 mol/L de Na2CO3 e em um licor branco simulado composto pelas soluções acima com as mesmas concentrações molares. O MB, a 24°C, em licor branco industrial, aerado, apresentou taxa de corrosão de 0,022 mm/ano, 0,045 mm/ano para a ZTA e 0,032 mm/ano par o MS. Observou-se que as taxas de corrosão da ZTA foram superior a do MB e MS em todas as soluções estudadas. As taxas de corrosão mais baixas foram em Na2CO3, seguido pela solução de NaOH, Na2S, licor branco simulado e finalmente, com as maiores taxas de corrosão, em licor branco industrial. Todas as soluções apresentaram-se alcalinas, exceto a de sulfato de sódio, e constatou-se que as três regiões encontravam-se passivadas quando comparada a uma solução de referência de 0,1 mol/L de Na2SO4,aerada e com pH entre 6,0 a 6,5. Estes filmes de passivação são de composição química complexa devido a presença em solução de íon OH- e HS-. A partir dos potenciais de corrosão do MB em cada solução e dos valores do pH foi verificado que a região do MB encontra-se passivado segundo o diagrama de Pourbaix de ferro em água. Estudos voltamétricos e de cronoamperometria mostraram que estes filmes de passivação, que promovem uma maior proteção contra a corrosão, são solubilizados em meio de NaOH, licor branco simulado e no licor branco industrial quando submetidos a polarizações anódicas em potenciais próximos de +2,0 V versus eletrodo de calomelano saturado. Em solução de Na2S e Na2CO3 foi observado à formação de depósitos espessos sobre a superfície do MB e quando analisados por EDS, observou-se a presença de fases como de óxidos, sulfetos e possivelmente carbonato de ferro.