Eudésio Oliveira Vilar

Preliminary investigation of some commercial alloys for hydrogen evolution in alkaline water electrolysis

Abstract The electrolytical behavior of 16 commercial alloys was investigated as cathodic material to hydrogen evolution. The results were compared with SAE1020 and NI200, used as standards. The electrolytic experiments were carried out in controlled current (240 and 345 mA cm −2 ), intercalated by polarization at undercurrent condition. The analysis of the potential stability during the electrolytic process shows that the following alloys are advantageous to substitute the mild steel currently used: 2RK65, SAF2304, SAF2507, C22 and MONELK500. Surprisingly, SAF2205 alloy showed as far as 250 mV less cathodic to hydrogen evolution reaction, becoming a very promising material for hydrogen evolution.

A Mass Transfer Study with Electrolytic Gas Production

In general, tall vertical electrolyzers are used industrially to produce only gases like chlorine, hydrogen and oxygen, or gases and products such as soda and chlorine. Moreover, these electrolyzers usually have a very short cathode-anode distance and often operate under forced convection. For many electrochemical processes mass transfer in electrolytic cells, in particular to electrodes, must be optimized to operate economically. Many electrochemical reactions involve a gaseous component and a great deal of research has been devoted to the study of the specific features of these reactions. Three main areas have been investigated such as: the bubble formation (Chirkov & Psenichnikov, 1986), the mass transfer and hydrodynamic instabilities at gas-evolving surfaces (Kreysa & Kuhn, 1985), and the behavior of gas in porous electrodes in fuel cells (White & Twardoch, 1988). Many works were developed up to the present about gas-evolving electrodes (St-Pierre & Wragg, 1993a, 1993b; Vogt, 1979, 1984a, 1984b, 1984c, 1989a, 1989b, 1992, 1994, 1997; Czarnetzki & Janssen, 1989; Boissonneau & Byrne, 2000; Ellis et al., 1992; Janssen et al. 1984; Lastochkin & Favelukis, 1998; Wongsuchoto et al., 2002; Buwa & Ranade, 2002; Gabrielli et al., 2002; Correia & Machado, 1998; Lasia, 1998; Iwasaki et al., 1998; Fahidy & Abdo, 1982; Lasia, 1998, 1997; Barber et al., 1998; Eigeldinger & Vogt, 2000; Solheim et al., 1989; Elsner & Coeuret, 1985; Dykstra et al., 1989; Khun & Kreysa, 1989; Lubetkin, 1989; Martin & Wragg, 1989; Lantelme & Alexopoulos, 1989; Gijsbers & Janssen, 1989; Chen, 2001; Lasia & Rami, 1990; Kienzlen et al., 1994; Saleh, 1999; Janssen, 1978) but, few data on mass transfer with different cathode geometries under flow-by or flowthrough electrolyte conditions with gas-evolving have been studied (Fouad & Sedahmed, 1974; Rousar et al., 1975;; Janssen & Barendrecht, 1979, Mohanta & Fahidy, 1977; Sedahmed, 1978; Sedahmed & Shemilt, 1981; Elsner & Marchiano, 1982; Albuquerque et. al., 2009). This chapter does not intend to explore in detail the mechanism during the bubbles formed electrolytically but only show an comparative study about the effect of hydrodynamic condition over mass transfer gas-electrodes for two cathodes geometries, during the hydrogen production at chlor-alkali cell by diaphragm process in laboratory scale.

Experimental Characterization of Hydrogen Embrittlement in API 5L X60 and API 5L X80 Steels

The present work aims to study the hydrogen embrittlement process in API 5L X60 and API 5L X80 steels. The tests were performed using two kinds of hydrogen sources to work with two conditions of hydrogen damage: environmental hydrogen embrittlement and internal hydrogen embrittlement. The mechanical behavior of API 5L X60 and API 5L X80 steels in tensile tests, with and without hydrogen, were studied. Under environmental hydrogen embrittlement conditions, the API 5L X60 steel presented a softening process observed by the decrease in yield strength and increase in its deformation. The API 5L X80 steel was more susceptible to the phenomenon due the deformation decrease of hydrogenated samples. In notched samples, both steels were susceptible to embrittlement as shown by the decrease in elongation. Under internal hydrogen embrittlement conditions, in both steels the changes in deformation were significant and can be attributed to changes in the hydrogen trapping due to the hydrogenation process used, the chemical composition and microstructure. It was observed that the fracture surface morphology of hydrogenated samples of both steels was ductile by microvoids coalescence, and that the distribution of dimples per unit area was higher in the API 5L X60 steel. It can be concluded, as reported in the literature, that the reversible hydrogen trapping observable in environmental hydrogen embrittlement is more damaging than irreversible hydrogen trapping, observable in internal hydrogen embrittlement.

Evaluation of the diffusivity and susceptibility to hydrogen embrittlement of API 5L X80 steel welded joints

This paper presents a study of susceptibility to hydrogen embrittlement of API 5L X80 steel welded joints by SMAW and GTAW processes. By varying the consumables used and the use of the same interpass temperature three different welded joints were obtained. Tests of hydrogen embrittlement susceptibility were performed according to ASTM G129-2006 with an aqueous solution (Solution A - TM0177/2005 NACE) sodium thiosulfate (Na 2 S 2 O 3 ) replacing the bubbling of H 2 S. From the elongation values was observed that the joint obtained in all welding conditions showed susceptibility to hydrogen embrittlement, which was determined by the elongation ratio. The joints that showed higher levels of hardness showed higher susceptibility to hydrogen embrittlement. The joints obtained with higher welding speeds for the same amount of heat input presented a reduction in the rate of hydrogen embrittlement. All joints tested in solution showed fracture surfaces with quasi cleavage zones.

Fragilización por Hidrógeno de los Aceros API 5L X60 y API 5L X80

Se ha determinado el comportamiento mecanico de los aceros API 5L grados X60 y X80, fragilizados por hidrogeno ambiental y por hidrogeno interno. El potencial y la densidad de corriente para la generacion del hidrogeno fueron determinados por polarizacion potenciodinamica, y el tiempo de saturacion estimado a partir de datos de difusividad y solubilidad obtenidos en ensayos de permeacion con una celula electroquimica. La carga de hidrogeno para reproducir las condiciones de la fragilizacion por hidrogeno ambiental y fragilizacion por hidrogeno interno fue realizada generando un gradiente de concentracion para el primer caso, y generando gradientes de concentracion y de tensiones para el segundo. Luego de los ensayos de traccion se verifico que, en las condiciones definidas en este trabajo, el modo de fractura en ambos tipos de fragilizacion fue predominantemente ductil. Ademas, los dos aceros mostraron una susceptibilidad baja o moderada a la fragilizacion por hidrogeno ambiental, no siendo susceptibles a la fragilizacion por hidrogeno interno.