Simulación numérica de ensayos de compresión diametral para la evaluación de discos cerámicos porosos

Se estudió el comportamiento mecánico de materiales porosos de cordierita mediante ensayos en compresión diametral. La solución analítica que permite la medición indirecta de la resistencia mecánica a tracción en compresión diametral se formula bajo ciertas condiciones que no suelen satisfacerse en la práctica. Con el objetivo de analizar desviaciones de las condiciones ideales se simuló el ensayo con técnicas computacionales. Los discos porosos de cordierita se obtuvieron por calcinación (650 °C, 2h) y reacción-sinterización (1330 °C, 4h) de cuerpos en verde preparados por consolidación térmica (85 °C, 4h) de suspensiones acuosas de una mezcla precursora de cordierita (caolín, talco y alúmina) con almidón nativo de papa. Los ensayos mecánicos se realizaron en una máquina servohidráulica en control por desplazamiento (0,2 mm/min). A partir de la relación aparente tensión-deformación se determinaron los parámetros mecánicos: módulo de Young aparente, resistencia mecánica y límite elástico. Sobre los discos ensayados se analizaron las características de la fractura. La influencia de las desviaciones geométricas más frecuentes identificadas en la práctica (desviación de la circularidad y no paralelismo entre las caras del disco) sobre la distribución de tensiones se estudió mediante la simulación por elementos finitos, tomando como referencia la ecuación de Hertz para problemas de contacto.Peer reviewe

Soldadura cerámica: método de reparación de revestimientos refractarios de equipamientos industriales

The ceramic welding process is a unique hot repair technique for refractory linings in industrial equipments. This process consists of projecting a weld mix in powder by means of a current of oxygen or oxygen/air onto the refractory surface to be restored. The weld mix content refractory particles chemically compatible with the refractory to be repaired and a solid combustible (oxidizable fine particles, metallic and/or non metallic) as exotermic agent. When the combustible particles ignites at contact with the hot face (1000-1500°C), an exotermic reaction with oxygen occurs developing temperatures of the order of 2000-2500°C. The heat generated from this reaction is enough to melt the surface to be repaired and allowing a very close bond to be formed between the repaired area and the deposited material. There are limited data in literature about ceramic welding and the larger part of the information is protected by patents. Several differences between the available patents were detected. In this work, the principal aspects of researches about ceramic welding that had been relieved are present, including results and conclusions from a study accomplished about ceramic welding (design and set up of a test in laboratory, and evaluation of the reparations) for the reparation of silica bricks employed to build coke ovens.<br><br>El proceso de soldadura cerámica es un atractivo método para la reparación en caliente de revestimientos refractarios de equipamientos industriales. Consiste en la proyección a alta temperatura de una mezcla de soldadura en polvo mediante una corriente rica en oxígeno sobre el material refractario dañado. La mezcla contiene agregados refractarios gruesos compatibles con el sustrato a reparar y un combustible sólido (finas partículas oxidables, metálicas y/o no metálicas) que actúa como agente exotérmico en el proceso. Cuando las partículas combustibles impactan en la superficie caliente del sustrato (1000-1500°C), reaccionan con el oxígeno liberando calor y alcanzando localmente temperaturas de 2000-2500ºC. Estas temperaturas producen la fusión parcial tanto del sustrato como de la carga de soldadura formándose una unión cerámica entre ambos. Existe muy escasa bibliografía sobre el tema y la mayor parte de la información está protegida por patentes, existiendo ciertas discrepancias entre las disponibles. En este trabajo se presentan los principales aspectos de las investigaciones sobre el tema que han sido relevadas, incluyendo resultados y conclusiones de un estudio desarrollado sobre soldadura cerámica a escala laboratorio para la reparación de ladrillos de sílice de uso siderúrgico

Rheology of aqueous mullite-starch suspensions

One of the forming methods developed for the manufacture of porous materials by direct consolidation, in which a ceramic suspension consolidates into non-porous molds (e.g. metal molds) by thermogelation of an organic agent, uses starch as both consolidator/binder of the ceramic suspension and pore former at high temperature. Changes in the rheological behavior of the aqueous suspensions are produced by starch gelatinization thermal process. This process as well as the presence of both the ceramic particles and added processing additives, influences the kinetics of green ceramic body formation and its microstructural features. In this work, the thermogelling behavior of mullite aqueous suspensions (40 vol.%; 0.45 wt.% of a polyacrylic polyelectrolyte as dispersant) containing 10 vol.% of different native starches (potato, cassava, and corn) was studied by dynamic rheology in order to determine the experimental conditions that must be used for forming mullite green bodies by thermal consolidation. Viscoelastic properties (G′ and G″) as a function of temperature (30–95 °C) and deformation (0.1–625.0% at 40 °C) were determined by temperature sweep tests and dynamic strain sweep tests, respectively. From these tests, and considering previous results of the rheological behavior of starch suspensions, we analyzed the influence of ceramic particles on the starch gelatinization process and the strength of the developed gels. On the other hand, shear flow properties of aqueous mullite–starch suspensions were also analyzed to obtain information on the rheological behavior of the suspensions at room temperature.Fil: Talou, Mariano Hernán. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; ArgentinaFil: Villar, M. A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Planta Piloto de Ingeniería Química (i); ArgentinaFil: Camerucci, Maria Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; ArgentinaFil: Moreno, R.. Instituto de Ceramica y Vidrio de Madrid; Españ

Microwave sintering of cordierite precursor green bodies prepared by starch consolidation

This paper reports on a study of the microwave sintering behavior of green disks prepared by the starch consolidation forming method to produce cordierite-based porous materials. Green disks were formed by thermogelling the aqueous suspensions of talc, kaolin and alumina (29.6 vol.%) and potato starch (11.5 vol.%) at 75 and 85 ºC for 4 h, drying and calcining. They were characterized by bulk density and apparent porosity measurements, and SEM. Microwave sintering was carried out at 1300 and 1330 ºC for 15, 20 and 25 min, applying 50 ºC/min. For purposes of comparison, an analysis of green disks prepared and calcined in the same conditions and conventionally sintered (1330 ºC for 4 h) was also made. The materials were characterized by XRD, bulk density and apparent porosity measurements, and microstructurally analyzed SEM. The results were analyzed considering the behavior of starch in aqueous suspension at varying temperatures, and the experimental conditions of consolidation and sintering.Fil: Sandoval, María Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; ArgentinaFil: Talou, Mariano Hernán. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; ArgentinaFil: De Souto P. M.. Universidade Federal do Sao Carlos; BrasilFil: Kiminami, R. H. G. A.. Universidade Federal do Sao Carlos; BrasilFil: Camerucci, Maria Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; Argentin

Prevalence of chronic pancreatitis:Results of a primary care physician-based population study

Background:Data on chronic pancreatitis prevalence are scanty and usually limited to hospital-based studies. AIM: Investigating chronic pancreatitis prevalence in primary care. METHODS: Participating primary care physicians reported the prevalence of chronic pancreatitis among their registered patients, environmental factors and disease characteristics. The data were centrally reviewed and chronic pancreatitis cases defined according to M-ANNHEIM criteria for diagnosis and severity and TIGAR-O classification for etiology. RESULTS: Twenty-three primary care physicians participated in the study. According to their judgment, 51 of 36.401 patients had chronic pancreatitis. After reviewing each patient data, 11 turned out to have definite, 5 probable, 19 borderline and 16 uncertain disease. Prevalence was 30.2/100.000 for definite cases and 44.0/100.000 for definite plus probable cases. Of the 16 patients with definite/probable diagnosis, 8 were male, with mean age of 55.6 (±16.7). Four patients had alcoholic etiology, 5 post-acute/recurrent pancreatitis, 6 were deemed to be idiopathic. Four had pancreatic exocrine insufficiency, 10 were receiving pancreatic enzymes, and six had pain. Most patients had initial stage and non-severe disease. CONCLUSIONS: This is the first study investigating the prevalence of chronic pancreatitis in primary care. Results suggest that the prevalence in this context is higher than in hospital-based studies, with specific features, possibly representing an earlier disease stage.recurrent pancreatitis, 6 were deemed to be idiopathic. Four had pancreatic exocrine insufficiency, 10 were receiving pancreatic enzymes, and six had pain. Most patients had initial stage and non-severe disease.CONCLUSIONS-This is the first study investigating the prevalence of chronic pancreatitis in primary care. Results suggest that the prevalence in this context is higher than in hospital-based studies, with specific features, possibly representing an earlier disease stage