The duplex stainless steel UNS S32205 was plasma nitrided at 380°C for 10 h using a gas mixture of 25% N 2 -75% H 2 . The thickness of the nitrided layer was 4.5 ± 0.5 lm, composed mainly of nitrogen-expanded austenite and iron nitrides precipitates. There was an increase in surface hardness around 2.6 and 3.8 times in the nitrided layer formed on the austenite and the ferrite phases, respectively, in relation to the untreated samples. The surface texture parameters skewness (S sk ), maximum peak height (S p ) and texture aspect ratio (S tr ) were the most appropriate parameters for studying the topography changes after treatment. An improvement in the localized corrosion properties after the nitriding treatment was revealed by the cyclic polarization curves. The nitrided samples showed higher pitting corrosion and repassivation potentials compared to the untreated material. The ferritic phases and grain boundaries were more susceptible to corrosion in the nitrided samples. The potentiodynamic curves of the nitrided samples exhibited a hillside on the passive-to-transpassive transition. This feature was already observed by other researchers, but it has not been well investigated. Potentiostatic studies demonstrated that metastable pitting took place on this transition.
El trabajo que aquí presentamos, propone una reflexión teórica e histórica de las controversias socio-científicas planteadas como situaciones problematizadores que han venido convirtiéndose en una herramienta eficaz en la enseñanza de las ciencias, ya que permiten el desarrollo de procesos argumentativos, el desarrollo del pensamiento crítico, concepciones más acordes a la ciencia y la actividad científica y permite utilizar la historia y la filosofía. En este sentido, los lectores encontraran un breve recuento histórico del origen de las controversias socio-científicas y una propuesta para trabajar la Educación en Energías Renovables.
Este trabajo presenta algunas perspectivas epistemológicas y teóricas relacionadas con la argumentación científica escolar dese el enfoque pragmático-dialéctico orientado hacia la resistencia, defensa y conservación del medio ambiente. El documento abordará la perspectiva de enfoque territorial y las ontologías relacionales, y cómo estas se articulan con la lucha que han gestado algunas organizaciones ambientales por la conservación de los recursos medioambientales del municipio de Soacha; finalmente, se expone la necesidad de desarrollar procesos de argumentación científica escolar en los estudiantes de educación básica secundaria en el municipio de Soacha -Colombia.
Water care is an imperative duty in industries with effluents loaded with pollutants such as heavy metals, especially chromium (VI), extremely dangerous for humans and the environment. One way of treating water is possible through a continuous system with dry and crushed vegetable biomass of cellulose xanthogenate because it can adsorb heavy metals, especially due to its low production costs. Through continuous systems and with the waste of PET plastics, it is possible to develop a water treatment process adapting this system and biomass. The objective of this research is the development of a treatment for water contaminated with Cr (VI) using cellulose xanthogenate from E. crassipes on a pilot scale. Where a mass balance conducted to determine the adsorption capacity of this heavy metal, corroborating it through the Thomas model. The treatment process eliminated around 95% of Cr (VI) present in the water, in addition, biomass reuse cycles carried out, which maintained a considerable adsorption capacity in all the cycles conducted through EDTA reagent.
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