Impact of High Temperature and Pressure to Steel Passivation in CO2 Atmosphere

The corrosion behaviour of AISI 347 in 0.1 M sulfuric acid at temperatures 50 and 75 °C and pressures up to 300 bar in a CO2 atmosphere was studied by surface analysis and electrochemical methods. Corrosion reactions in which CO2 is present accelerate the formation of a protective FeCO3 layer, but the success of such a passivation depends on the saturation concentration and the corresponding temperature. Significantly better results compared to untreated steels were obtained at lower temperatures by increasing the pressure. To explain the differences in corrosion rates between samples, the activation energy for the layer dissolution was also discussed. It can be assumed that the compressibility of the CO2 at different pressures has an influence on the formation of the protective iron carbonate layer and its properties and thus to on the corrosion behaviour.

Stability of an abandoned siderite mine: A case study in northern Spain

Bodovalle is an iron carbonate mine located in Gallarta (near Bilbao, northern Spain), which is currently in the closure stage. The deposit was first exploited as an open-pit mine and later as an underground mine. The underground mine currently has 40 large rooms with rib pillars, occupying an area of 2,000 m long by 600 m wide. Room depth is around 200 m. The main geotechnical incident occurred in the NW1N zone, where an over-exploited rib pillar in poor condition was partially removed, leaving a 70-m roof span that eventually collapsed in 1999, resulting in a surface crater measuring 60 m in diameter. The collapse was preceded by noises and movements detected outside the mine. The subsidence was improved by means of infilling and monitoring. In 2014, residents living in homes built over the abandoned mine rooms detected very loud noises similar to those of 1999. The article describes a stability review carried out using advanced numerical methods (finite element method and boundary element method) and the geomechanical parameters obtained from a back analysis of the 1999 collapse.

Influence of Acetic Acid on the Integrity and Protectiveness by an Iron Carbonate (FeCO3) Corrosion Product Layer

ABSTRACT The effect of undissociated acetic acid on the integrity of iron carbonate (FeCO3) layer formed on platinum and X65 steel substrates is investigated. Experiments were conducted using buffered solutions with 0.8 - 5 mM undissociated acetic acid. For the platinum substrates, changes in the FeCO3 layer were monitored via in-situ electrochemical quartz crystal microbalance (EQCM) measurements. This investigation was supported by performing electrochemical experiments, under comparable conditions, on the X65 steel specimens, linking the integrity of FeCO3 layer to its corrosion protection effect. The EQCM measurements revealed that the addition of acetic acid, at all concentrations tested here, caused partial dissolution of the FeCO3 layer. The dissolution occurred selectively, with the outer layer dissolving first, leaving behind an inner FeCO3 layer at the end of the immersion experiment. The electrochemical results revealed that introducing the acetic acid caused a sudden increase in the corrosion rate, which over time returned to a lower value similar in magnitude to that seen before addition of the acetic acid. This was attributed to the protection provided by the inner FeCO3 layer, which was only mildly affected by the addition of acetic acid and was able to repair over time. It was proven that the dissolution of the protective FeCO3 layer in the presence of acetic acid was not due to a small pH change but rather due to the formation of ferrous acetate complexes and changes in ionic strength, which decreases the FeCO3 saturation values.

Effects of feeding increasing levels of iron from iron sulfate or iron carbonate on nursery pig growth performance and hematological criteria

A total of 140 weanling pigs (241 × 600, DNA, Columbus, NE; initially 5.5 ± 0.79 kg body weight) were used in a 32-d study evaluating the effects of increasing dietary Fe from either iron sulfate (FeSO4) or iron carbonate (FeCO3) on nursery pig growth performance and blood Fe status. The pigs used for this trial did not receive an Fe injection after birth in order to increase the sensitivity to added dietary Fe after weaning. Pigs were weaned at approximately 21 d and allotted to pens based on the initial weight in a completely randomized block design with five pigs in each pen and four pens per treatment. Experimental treatments were arranged as a 2 × 3 + 1 factorial with main effects of dietary Fe source (FeSO4 vs. FeCO3) and level (10, 30, or 50 mg/kg of added Fe) plus a negative control with no additional dietary Fe. The basal diet contained 40 mg/kg total dietary Fe based on ingredient contributions and was formulated with an Fe-free trace mineral premix. Experimental diets were formulated below the pigs recommended Fe requirement based on NRC (2012) estimates. Experimental diets were fed in pellet form in a single phase for the duration of the trial. From day 0 to 32, there was no evidence for source × level interactions for growth performance, hemoglobin (Hb), or hematocrit (Hct) values. There was no evidence for a difference (P > 0.10) in dietary Fe source. Providing increasing Fe levels in the diet from either FeSO4 or FeCO3 improved (P < 0.05) average daily gain, average daily feed intake, gain-to-feed ratio, and increased (P < 0.05) Hb and Hct values. A day effect (P = 0.001) was observed for both Hb and Hct with values increasing throughout the study. Increasing dietary Fe levels in the diet from either FeSO4 or FeCO3 increased (linear; P < 0.05) Hb and Hct values on days 14, 21, and 32. In summary, these data suggest that the micronized form of FeCO3 is a source of Fe that can be added to nursery diets to yield similar responses to those observed from FeSO4 supplementation. Similar to previous research, increasing dietary Fe improved the growth performance and increased Hb and Hct values when pigs have low Fe status at weaning.