An Experimental Study of Submerged Entry Nozzles (SEN) Focusing on Decarburization and Clogging

The submerged entry nozzle (SEN) is used to transport the molten steel from a tundish to a mould. The main purpose of its usage is to prevent oxygen and nitrogen pick-up by molten steel from the gas. Furthermore, to achieve the desired flow conditions in the mould. Therefore, the SEN can be considered as a vital factor for a stable casting process and the steel quality. In addition, the steelmaking processes occur at high temperatures around 1873 K, so the interaction between the refractory materials of the SEN and molten steel is unavoidable. Therefore, the knowledge of the SEN behaviors during preheating and casting processes is necessary for the design of the steelmaking processes  The internal surfaces of modern SENs are coated with a glass/silicon powder layer to prevent the SEN graphite oxidation during preheating. The effects of the interaction between the coating layer and the SEN base refractory materials on clogging were studied. A large number of accretion samples formed inside alumina-graphite clogged SENs were examined using FEG-SEM-EDS and Feature analysis. The internal coated SENs were used for continuous casting of stainless steel grades alloyed with Rare Earth Metals (REM). The post-mortem study results clearly revealed the formation of a multi-layer accretion. A harmful effect of the SENs decarburization on the accretion thickness was also indicated. In addition, the results indicated a penetration of the formed alkaline-rich glaze into the alumina-graphite base refractory. More specifically, the alkaline-rich glaze reacts with graphite to form a carbon monoxide gas. Thereafter, dissociation of CO at the interface between SEN and molten metal takes place. This leads to reoxidation of dissolved alloying elements such as REM (Rare Earth Metal). This reoxidation forms the “In Situ” REM oxides at the interface between the SEN and the REM alloyed molten steel. Also, the interaction of the penetrated glaze with alumina in the SEN base refractory materials leads to the formation of a high-viscous alumina-rich glaze during the SEN preheating process. This, in turn, creates a very uneven surface at the SEN internal surface. Furthermore, these uneven areas react with dissolved REM in molten steel to form REM aluminates, REM silicates and REM alumina-silicates. The formation of the large “in-situ” REM oxides and the reaction of the REM alloying elements with the previously mentioned SEN´s uneven areas may provide a large REM-rich surface in contact with the primary inclusions in molten steel. This may facilitate the attraction and agglomeration of the primary REM oxide inclusions on the SEN internal surface and thereafter the clogging. The study revealed the disadvantages of the glass/silicon powder coating applications and the SEN decarburization. The decarburization behaviors of Al2O3-C, ZrO2-C and MgO-C refractory materials from a commercial Submerged Entry Nozzle (SEN), were also investigated for different gas atmospheres consisting of CO2, O2 and Ar. The gas ratio values were kept the same as it is in a propane combustion flue gas at different Air-Fuel-Ratio (AFR) values for both Air-Fuel and Oxygen-Fuel combustion systems. Laboratory experiments were carried out under nonisothermal conditions followed by isothermal heating. The decarburization ratio (α) values of all three refractory types were determined by measuring the real time weight losses of the samples. The results showed the higher decarburization ratio (α) values increasing for MgO-C refractory when changing the Air-Fuel combustion to Oxygen-Fuel combustion at the same AFR value. It substantiates the SEN preheating advantage at higher temperatures for shorter holding times compared to heating at lower temperatures during longer holding times for Al2O3-C samples. Diffusion models were proposed for estimation of the decarburization rate of an Al2O3-C refractory in the SEN. Two different methods were studied to prevent the SEN decarburization during preheating: The effect of an ZrSi2 antioxidant and the coexistence of an antioxidant additive and a (4B2O3 ·BaO) glass powder on carbon oxidation for non-isothermal and isothermal heating conditions in a controlled atmosphere. The coexistence of 8 wt% ZrSi2 and 15 wt% (4B2O3 ·BaO) glass powder of the total alumina-graphite refractory base materials, presented the most effective resistance to carbon oxidation. The 121% volume expansion due to the Zircon formation during heating and filling up the open pores by a (4B2O3 ·BaO) glaze during the green body sintering led to an excellent carbon oxidation resistance. The effects of the plasma spray-PVD coating of the Yttria Stabilized Zirconia (YSZ) powder on the carbon oxidation of the Al2O3-C coated samples were investigated. Trials were performed at non-isothermal heating conditions in a controlled atmosphere. Also, the applied temperature profile for the laboratory trials were defined based on the industrial preheating trials. The controlled atmospheres consisted of CO2, O2 and Ar. The thicknesses of the decarburized layers were measured and examined using light optic microscopy, FEG-SEM and EDS. A 250-290 μm YSZ coating is suggested to be an appropriate coating, as it provides both an even surface as well as prevention of the decarburization even during heating in air. In addition, the interactions between the YSZ coated alumina-graphite refractory base materials in contact with a cerium alloyed molten stainless steel were surveyed. The YSZ coating provided a total prevention of the alumina reduction by cerium. Therefore, the prevention of the first clogging product formed on the surface of the SEN refractory base materials. Therefore, the YSZ plasma-PVD coating can be recommended for coating of the hot surface of the commercial SENs.

När det inte blir som man har tänkt sig : - En fallstudie av undervisningssituationer med elever med behov av särskilt stöd

Fallstudien beskriver och diskuterar några lektioner med elever som har specifika inlärnings-svårigheter, utifrån skolverkets Allmänna råd, och belyser vilka pedagogiskt svårhanterliga problem och dilemman som kan uppstå när det inte blir som läraren har planerat. Teorin om den proximala utvecklingszonen åskådliggörs. Aktivitetens betydelse för inlärning belyses. Komplexiteten kring lärarskap och ledarskap illustreras. Skolverkets teori om kunskap genom progression, enligt givna årskurser med givet innehåll, stämmer inte alltid med erfarenheterna hos några av verklighetens elever. Samspelet mellan lärare och elever belyses i studien. Be-skrivningar av utvecklingsrelaterade funktionsnedsättningar och psykiskt sårbara barn visar ytterligare hur elevers individuella förutsättningar kan ge konsekvenser för inlärning.

Risk of recurrent stroke and death after first stroke in long-distance ski race participants

Background: Physical activity is of benefit for primary prevention of cardiovascular diseases, but it appears to increase the risk for atrial fibrillation. We aimed to study a cohort of patients following a first stroke in individuals with previous high physical activity, compare them to the general population with respect to recurrent stroke and death, and relate these to atrial fibrillation. Methods and results: From the participants of the Vasaloppet, the world's largest ski-race, and matched individuals from the general population (n=708 604), we identified 5964 patients hospitalized with a first-time stroke between 1994 and 2010. Individuals with severe diseases were excluded. One half percent of skiers and 1% of nonskiers were hospitalized due to stroke. The incidence rate was 8.3 per 100 person-years among skiers and 11.1 among nonskiers. The hazard ratio (HR) for recurrent stroke or death between the 2 groups was 0.76 (95% CI 0.67 to 0.86). The result was consistent in subgroups. The HR for death was 0.66 (95% CI 0.56 to 0.78) and for recurrent stroke 0.82 (95% CI 0.70 to 0.96). After adjustment for smoking and socioeconomic factors, the HR for death was consistent at 0.70 (95% CI 0.56 to 0.87) while the HR for recurrent stroke was not statistically significant. Outcomes for skiers with atrial fibrillation tended to show a lower risk than for nonskiers. Conclusions: This large cohort study supports the hypothesis that patients with a stroke and with prior regular physical activity have a lower risk of death, while their risk for recurrent stroke is similar to that of nonskiers. The skiers had a higher incidence of atrial fibrillation, but still no increased risk of recurring stroke.

Older people's experience of utilisation and administration of medicines in a health- and social care context

BACKGROUND: People living at home who lack ability to manage their medicine are entitled to assistance to improve adherence provided by a home care assistant employed by social care. AIM: The aim was to describe how older people with chronic diseases, living at home, experience the use and assistance of administration of medicines in the context of social care. DESIGN: A qualitative descriptive study. METHODS: Ten participants (age 65+) living at home were interviewed in the participants' own homes. Latent content analysis was used. FINDINGS: The assistance eases daily life with regard to practical matters and increases adherence to a medicine regimen. There were mixed feelings about being dependent on assistance; it interferes with self-sufficiency at a time of health transition. Participants were balancing empowerment and a dubious perception of the home care assistants' knowledge of medicine and safety. Physicians' and district nurses' professional knowledge was a safety guarantee for the medicine process. CONCLUSIONS: Assistance eases daily life and medicine regimen adherence. Dependence on assistance may affect self-sufficiency. Perceived safety varied relating to home care assistants' knowledge of medicine. RELEVANCE TO CLINICAL PRACTICE: A well-functioning medicine assistance is crucial to enable older people to remain at home. A person-centred approach to health- and social care delivery is efficient and improve outcome for the recipient of care.

Lärares ledarskap som möjliggörande och begränsande i mötet med ’alla’ barn : En deltagarorienterad studie

The aim of this thesis is to, based on teachers’ experiences, describe and analyse meanings of teachers’ leadership in general, and in relation to children in need of special support in particular. The study was carried out within the tradition of participatory-oriented research, a research circle. The dialogues in the circle were based on the participants’ questions, experiences, interests, and knowledge. The circle included a researcher and nine teachers from the following types of schools: preschool, preschool class, compulsory school, and compulsory school for pupils with learning disabilities. The study is based on an understanding of leadership as a relational practice. Leadership is practised in the interaction between teacher and child. Both parties exert influence over the practice of leadership. A central assumption in the study is that knowledge can develop through and in interactions between people, that knowledge and power are connected, and that knowledge and actions are intertwined. Another central assumption is that learning is a complex phenomenon. In the analysis of the research circle’s dialogues, the following meanings of teachers’ leadership emerge: to facilitate learning and discipline, and to promote different interests. The practice of leadership involves teachers handling complex situations in their interactions with ‘all’ children, i.e. children in need of special support and children without such needs. Leadership is practised between teachers and children, and the teachers have to consider the group of children as a collective in relation to the individual children. At the same time, the teachers have to consider their intentions versus what happens during the interactions. In addition, the teachers have to pay heed to the fact that their own actions and the children’s actions influence one another. Finally, the teachers have to consider the individual child’s ‘best interest’ in relation to the requirements of the policy documents. Furthermore, the results indicate that the practice of leadership is perceived as both unpredictable and, to some extent, predictable at the same time, which adds to the complexity of leadership. The teachers cannot know for sure what the children understand or if the children’s actions facilitate learning. However, the teachers can make certain assumptions about how to practice leadership in order to facilitate learning and discipline in children with different needs. The meanings of leadership were expressed in different ways in the circle’s dialogues; both as enabling and limiting in interactions with children in need of special support. One of the study’s conclusions is that leadership seems to be particularly complex in interactions with children in need of special support. The research circle’s dialogues served to promote a democratic knowledge process. The dialogues were characterised by respect for the participants’ different opinions; however, this does not mean that they were free from power structures.