Free Opening Performance of Steel Ladle as a Function of Filler Sand Properties

The secondary steel refining process uses filler sand as a thermal insulating barrier that separates the liquid metal from direct contact with slide-gate system of the steel ladle. The effective use of this practice must provide a high free opening rate, impacting on increased productivity and quality of steel, reducing the number of stops, thermal loss and even the steel re-oxidation. Both operational parameters and material properties have influence on the free opening rate. In the present work, two chromite-silica sands were analyzed, and some composition changes were proposed. The properties of these materials and the relevant process parameters were evaluated according to the free opening rate under normal operational conditions. The increases in carbon content and in particle size were considered the main factors relating to the filler sand. The percentage of free opening is also strongly influenced by time and temperature of the steel contact

Water-induced modulation of Helicobacter pylori virulence properties

While the influence of water in Helicobacter pylori culturability and membrane integrity has been extensively studied, there are little data concerning the effect of this environment on virulence properties. Therefore, we studied the culturability of water-exposed H. pylori and determined whether there was any relation with the bacterium’s ability to adhere, produce functional components of pathogenicity and induce inflammation and alterations in apoptosis in an experimental model of human gastric epithelial cells. H. pylori partially retained the ability to adhere to epithelial cells even after complete loss of culturability. However, the microorganism is no longer effective in eliciting in vitro host cell inflammation and apoptosis, possibly due to the non-functionality of the cag type IV secretion system. These H. pylori-induced host cell responses, which are lost along with culturability, are known to increase epithelial cell turnover and, consequently, could have a deleterious effect on the initial H. pylori colonisation process. The fact that adhesion is maintained by H. pylori to the detriment of other factors involved in later infection stages appears to point to a modulation of the physiology of the pathogen after water exposure and might provide the microorganism with the necessary means to, at least transiently, colonise the human stomach.FCT (SFRH/BD/24579/2005) (to NMG

Evaluation of oxidation resistance of MgO‐C bricks in oxy‐combustion and air‐combustion

There are important advantages in oxy-fuel technology over conventional combustion, such as the reduction in fuel consumption and gaseous emissions. However, before its use in the steel industry, it is essential to know that the alteration of the firing system can lead to an increase in the wear of the oxide-carbon refractories. In the present work, four types of MgO-C bricks were fired under oxy-fuel and air-fuel conditions in a semi-industrial furnace, simulating the heating of a steelmaking ladle. The fired bricks were evaluated in terms of weight loss, thickness of the decarburized layer, and phases and microstructure formed in this layer. The results indicated few differences in the properties of the bricks fired in the two systems. The brick with 12% carbon and Al antioxidant showed the highest oxidation resistance among all bricks investigated. The most important factor for the use of the oxy-fuel system was the correct selection of the refractory microstructural properties, including the utilization of antioxidant additives