O tratamento utilizando Radioterapia em Arco Modulado Volumétrico é a modalidade mais moderna de radioterapia conformacional de forma que, com superposição de vários campos, as distribuições de dose forneçam uma perfeita conformação ao tumor, diminuindo a probabilidade de complicações nos tecidos normais adjacentes. Nesse sentido, muitos esforços estão sendo investidos para melhorar a conformidade de distribuição de dose, bem como a integração de técnicas de imagem para rastreamento de tumores e correção de variações inter e intrafração. Para isso, um intenso acompanhamento da qualidade dos processos e um programa de garantia de qualidade são fundamentais para a segurança dos pacientes e o cumprimento da legislação vigente; além do uso de diferentes metodologias de dosimetria para inter comparação e validação dos resultados. Este trabalho tem por objetivo avaliar e comparar o desempenho dos dosímetros OSL de óxido de alumínio (Al2O3:C) fabricados pela Landauer Inc. com os fabricados pela Rexon™ na dosimetria de feixes clínicos de fótons de energias altas empregados em radioterapia com tratamento em arco modulado volumétrico (VMAT) utilizando diferentes objetos simuladores. Os dosímetros foram caracterizados para radiação gama do 60Co e para feixes clínicos de fótons de 6 MV típicos de tratamentos por VMAT em condições de equilíbrio eletrônico e de dose máxima respectivamente. Testes de desempenho das leitoras TL e OSL utilizadas e repetibilidade das amostras foram avaliadas. Após realizados todos os testes, os dosímetros foram irradiados na simulação de diferentes tratamentos radioterápicos por VMAT e suas respostas comparadas ao sistema de planejamento. Todos os tipos de dosímetros apresentaram resultados satisfatórios na verificação das doses desse tipo de simulação de planejamento. Os dosímetros de Al2O3:C apresentaram resultados compatíveis entre si e validados pelos outros dosímetros e câmara de ionização. Em relação a melhor técnica, o sistema comercial OSL InLight apresenta maior praticidade e versatilidade para uso e aplicação na rotina clínica. / Treatment using Volumetric Modulated Arc Radiation Therapy is the most modern modality of conformational radiotherapy so that, with the overlapping of several fields, the dose distributions provide a perfect conformation to the tumor, reducing the probability of complications in adjacent normal tissues. In this sense, many efforts are being invested to improve dose distribution compliance as well as the integration of imaging techniques for tumor screening and correction of inter and intrafraction variations. To this end, an intensive monitoring of the quality of the processes and a quality assurance program are fundamental for patient safety and compliance with current legislation; besides the use of different dosimetry methodologies for intercomparison and validation of the results. The aim of this study is to evaluate and compare the performance of aluminum oxide (Al2O3:C) OSL dosimeters manufactured by Landauer Inc. with those produced by Rexon™ in the dosimetry of high energy photon clinical bundles used in arcuate treatment Modulated volumetric (VMAT) using different simulating objects. The dosimeters were characterized for gamma radiation of the 60Co and for clinical photon beams of 6 MV typical of treatments by VMAT under conditions of electronic equilibrium and maximum dose respectively. Performance tests of the TL and OSL readers used and repeatability of the samples were evaluated. After all tests, the dosimeters were irradiated in the simulation of different radiotherapy treatments by VMAT and their responses compared to the planning system. All types of dosimeters presented satisfactory results in verifying the doses of this type of planning simulation. The Al2O3:C dosimeters presented compatible results and validated by the other dosimeters and ionization chamber. Regarding the best technique, the OSL InLight commercial system presents greater practicality and versatility for use and application in the clinical routine.

Dosímetros Luminescentes Opticamente Estimulados (OSL) vêm sendo testados como alternativa dosimétrica no controle da qualidade e verificação de tratamentos por possuir características adequadas para esse fim, como elevada sensibilidade à radiação ionizante, alta resolução espacial e facilidade de leitura. Neste trabalho, o óxido de alumínio, dopado com diferentes concentrações de carbono (Al2O3:C), foi estudado como material dosimétrico OSL. Nanotubos de carbono de paredes simples também foi avaliado como dopante, associados ao mesmo material, Al2O3:NTC, em alguns testes preliminares de resposta em função da dose em feixes de fótons de 50 kVp. O presente trabalho apresenta o processo de fabricação do dosímetro OSL, além de testes dosimétricos envolvendo metodologia experimental e por simulação Monte Carlo com o código PENELOPE para avaliação da resposta dosimétrica do Al2O3:C em função da concentração do carbono dopante. Neste trabalho foi investigada a resposta do dosímetro OSL para doses entre 50 cGy e 1000 cGy, em um amplo intervalo de energia de feixes de fótons. Foi analisada também, a interferência do uso do dosímetro OSL de Al2O3:C nas doses superficial e profunda em tratamentos radioterápicos. O dosímetro Al2O3:C(1%) apresentou diferença percentual máxima de 12% na homogeneidade de resposta em um grupo de 100 dosímetros e linearidade de resposta entre as doses de 50 cGy e 800 cGy para feixes de fótons de alta energia de 1,25 MV, 6 MV e 15 MV. Já para feixes de fótons de baixas energias, de 50 kVp, 120 kVp e 200 kVp, o dosímetro apresentou diferença significativa entre as respostas, evidenciando dependência com a energia. Além disso, foi investigada a estabilidade do sinal OSL em função do tempo e estipulado um tempo mínimo de armazenamento do dosímetro, entre a exposição e a leitura. O dosímetro Al2O3:NTC apresentou um aumento de sensibilidade de até 30% em relação ao dosímetro Al2O3:C(1%). Os resultados encontrados neste trabalho sugerem o uso do material dosimétrico OSL estudado como ferramenta em controle da qualidade em procedimentos clínicos de rotina na Radioterapia. / Optically Stimulated Luminescent dosimeters (OSL) have been tested as a dosimetric alternative in quality control and treatment verification since they have suitable characteristics for this purpose, such as high sensitivity to ionizing radiation, high spatial resolution and readability. In this work the aluminum oxide, doped with different concentrations of carbon (Al2O3:C), was studied as OSL dosimetric material. Single-walled carbon nanotubes were also evaluated as a dopant associated with the same material, Al2O3:NTC, and preliminary tests of response to dose in photon beams of 50 kVp were performed. This work presents the fabrication process of the OSL dosimeter, and dosimetric tests involving experimental methodology and Monte Carlo simulation with PENELOPE code to evaluate the response of the dosimetric Al2O3:C as a function of the concentration of carbon dopant. In this study we investigated the response of the OSL dosimeter for doses ranging from 50 cGy to 1000 cGy in a wide range of energy of photon beams. The interference of the OSL dosimeter Al2O3:C in superficial and deep doses in Radiotherapy treatments was also analyzed. The dosimeter Al2O3:C (1%) had a maximum percentage difference of 12% in the homogeneity of a group of 100 dosimeters and presented linearity of response in a dose range of 50 cGy and 800 cGy for photon beams of high energy of 1.25 MV, 6 MV and 15 MV. As for photon beams of low energies of 50 kVp, 120 kVp and 200 kVp, the dosimeter showed a significant difference between responses, indicationg dependence on energy. In addition, we investigated the stability of the OSL signal as a function of time and set a minimum time of storage of the dosimeter, between exposure and reading. The dosimeter Al2O3:NTC showed an increased sensitivity of up to 30% over the dosimeter Al2O3:C (1%). The findings on this study suggest the use of the material studied as OSL dosimeter as a tool in quality control in routine clinical procedures in Radiotherapy.

O tratamento utilizando Radioterapia em Arco Modulado Volumétrico é a modalidade mais moderna de radioterapia conformacional de forma que, com superposição de vários campos, as distribuições de dose forneçam uma perfeita conformação ao tumor, diminuindo a probabilidade de complicações nos tecidos normais adjacentes. Nesse sentido, muitos esforços estão sendo investidos para melhorar a conformidade de distribuição de dose, bem como a integração de técnicas de imagem para rastreamento de tumores e correção de variações inter e intrafração. Para isso, um intenso acompanhamento da qualidade dos processos e um programa de garantia de qualidade são fundamentais para a segurança dos pacientes e o cumprimento da legislação vigente; além do uso de diferentes metodologias de dosimetria para inter comparação e validação dos resultados. Este trabalho tem por objetivo avaliar e comparar o desempenho dos dosímetros OSL de óxido de alumínio (Al2O3:C) fabricados pela Landauer Inc. com os fabricados pela Rexon™ na dosimetria de feixes clínicos de fótons de energias altas empregados em radioterapia com tratamento em arco modulado volumétrico (VMAT) utilizando diferentes objetos simuladores. Os dosímetros foram caracterizados para radiação gama do 60Co e para feixes clínicos de fótons de 6 MV típicos de tratamentos por VMAT em condições de equilíbrio eletrônico e de dose máxima respectivamente. Testes de desempenho das leitoras TL e OSL utilizadas e repetibilidade das amostras foram avaliadas. Após realizados todos os testes, os dosímetros foram irradiados na simulação de diferentes tratamentos radioterápicos por VMAT e suas respostas comparadas ao sistema de planejamento. Todos os tipos de dosímetros apresentaram resultados satisfatórios na verificação das doses desse tipo de simulação de planejamento. Os dosímetros de Al2O3:C apresentaram resultados compatíveis entre si e validados pelos outros dosímetros e câmara de ionização. Em relação a melhor técnica, o sistema comercial OSL InLight apresenta maior praticidade e versatilidade para uso e aplicação na rotina clínica. / Treatment using Volumetric Modulated Arc Radiation Therapy is the most modern modality of conformational radiotherapy so that, with the overlapping of several fields, the dose distributions provide a perfect conformation to the tumor, reducing the probability of complications in adjacent normal tissues. In this sense, many efforts are being invested to improve dose distribution compliance as well as the integration of imaging techniques for tumor screening and correction of inter and intrafraction variations. To this end, an intensive monitoring of the quality of the processes and a quality assurance program are fundamental for patient safety and compliance with current legislation; besides the use of different dosimetry methodologies for intercomparison and validation of the results. The aim of this study is to evaluate and compare the performance of aluminum oxide (Al2O3:C) OSL dosimeters manufactured by Landauer Inc. with those produced by Rexon™ in the dosimetry of high energy photon clinical bundles used in arcuate treatment Modulated volumetric (VMAT) using different simulating objects. The dosimeters were characterized for gamma radiation of the 60Co and for clinical photon beams of 6 MV typical of treatments by VMAT under conditions of electronic equilibrium and maximum dose respectively. Performance tests of the TL and OSL readers used and repeatability of the samples were evaluated. After all tests, the dosimeters were irradiated in the simulation of different radiotherapy treatments by VMAT and their responses compared to the planning system. All types of dosimeters presented satisfactory results in verifying the doses of this type of planning simulation. The Al2O3:C dosimeters presented compatible results and validated by the other dosimeters and ionization chamber. Regarding the best technique, the OSL InLight commercial system presents greater practicality and versatility for use and application in the clinical routine.

Dosímetros Luminescentes Opticamente Estimulados (OSL) vêm sendo testados como alternativa dosimétrica no controle da qualidade e verificação de tratamentos por possuir características adequadas para esse fim, como elevada sensibilidade à radiação ionizante, alta resolução espacial e facilidade de leitura. Neste trabalho, o óxido de alumínio, dopado com diferentes concentrações de carbono (Al2O3:C), foi estudado como material dosimétrico OSL. Nanotubos de carbono de paredes simples também foi avaliado como dopante, associados ao mesmo material, Al2O3:NTC, em alguns testes preliminares de resposta em função da dose em feixes de fótons de 50 kVp. O presente trabalho apresenta o processo de fabricação do dosímetro OSL, além de testes dosimétricos envolvendo metodologia experimental e por simulação Monte Carlo com o código PENELOPE para avaliação da resposta dosimétrica do Al2O3:C em função da concentração do carbono dopante. Neste trabalho foi investigada a resposta do dosímetro OSL para doses entre 50 cGy e 1000 cGy, em um amplo intervalo de energia de feixes de fótons. Foi analisada também, a interferência do uso do dosímetro OSL de Al2O3:C nas doses superficial e profunda em tratamentos radioterápicos. O dosímetro Al2O3:C(1%) apresentou diferença percentual máxima de 12% na homogeneidade de resposta em um grupo de 100 dosímetros e linearidade de resposta entre as doses de 50 cGy e 800 cGy para feixes de fótons de alta energia de 1,25 MV, 6 MV e 15 MV. Já para feixes de fótons de baixas energias, de 50 kVp, 120 kVp e 200 kVp, o dosímetro apresentou diferença significativa entre as respostas, evidenciando dependência com a energia. Além disso, foi investigada a estabilidade do sinal OSL em função do tempo e estipulado um tempo mínimo de armazenamento do dosímetro, entre a exposição e a leitura. O dosímetro Al2O3:NTC apresentou um aumento de sensibilidade de até 30% em relação ao dosímetro Al2O3:C(1%). Os resultados encontrados neste trabalho sugerem o uso do material dosimétrico OSL estudado como ferramenta em controle da qualidade em procedimentos clínicos de rotina na Radioterapia. / Optically Stimulated Luminescent dosimeters (OSL) have been tested as a dosimetric alternative in quality control and treatment verification since they have suitable characteristics for this purpose, such as high sensitivity to ionizing radiation, high spatial resolution and readability. In this work the aluminum oxide, doped with different concentrations of carbon (Al2O3:C), was studied as OSL dosimetric material. Single-walled carbon nanotubes were also evaluated as a dopant associated with the same material, Al2O3:NTC, and preliminary tests of response to dose in photon beams of 50 kVp were performed. This work presents the fabrication process of the OSL dosimeter, and dosimetric tests involving experimental methodology and Monte Carlo simulation with PENELOPE code to evaluate the response of the dosimetric Al2O3:C as a function of the concentration of carbon dopant. In this study we investigated the response of the OSL dosimeter for doses ranging from 50 cGy to 1000 cGy in a wide range of energy of photon beams. The interference of the OSL dosimeter Al2O3:C in superficial and deep doses in Radiotherapy treatments was also analyzed. The dosimeter Al2O3:C (1%) had a maximum percentage difference of 12% in the homogeneity of a group of 100 dosimeters and presented linearity of response in a dose range of 50 cGy and 800 cGy for photon beams of high energy of 1.25 MV, 6 MV and 15 MV. As for photon beams of low energies of 50 kVp, 120 kVp and 200 kVp, the dosimeter showed a significant difference between responses, indicationg dependence on energy. In addition, we investigated the stability of the OSL signal as a function of time and set a minimum time of storage of the dosimeter, between exposure and reading. The dosimeter Al2O3:NTC showed an increased sensitivity of up to 30% over the dosimeter Al2O3:C (1%). The findings on this study suggest the use of the material studied as OSL dosimeter as a tool in quality control in routine clinical procedures in Radiotherapy.

Um método dosimétrico para avaliação da exposição à radiação ultravioleta foi estabelecido com os detectores Al2O3:C InLight e com o sistema leitor OSL microStar e software, da Landauer, associados às técnicas de Luminescência Opticamente Estimulada (OSL) e Luminescência Opticamente Estimulada Fototransferida (PTOSL). As etapas principais do trabalho foram: caracterização dos detectores Al2O3:C InLight, sem pré-condicionamento, em relação às fontes de RUV solar e artificial, utilizando a técnica OSL; caracterização dos detectores Al2O3:C InLight, pré-condicionados, em relação às fontes de RUV solar e artificial, utilizando a técnica PTOSL; e aplicações práticas dos detectores Al2O3:C InLight, sem pré-condicionamento e pré-condicionados, em locais de exposição à RUV solar e RUV artificial proveniente de processos de soldagens elétrica e TIG (Tungsten Inert Gas). Os detectores Al2O3:C InLight apresentaram respostas OSL e PTOSL satisfatórias em relação aos parâmetros: comprimento de onda, tempo de iluminação UV, irradiância, exposição radiante e dependência angular, quando expostos à RUV. Esses detectores mostraram estimulação máxima OSL e PTOSL para o comprimento de onda de 330 nm, o que os torna uma opção viável para detecção e dosimetria da radiação na faixa UVA. / A dosimetric method for the exposure evaluation to ultraviolet radiation was established with Al2O3:C InLight detectors and an OSL microStar reader and software, of Landauer, associated to the techniques of Optically Stimulated Luminescence (OSL) and Phototransferred Optically Stimulated Luminescence (PTOSL). The main phases of this work were: characterization of the Al2O3:C InLight detectors, without pre-conditioning, exposed to ultraviolet radiation (RUV) of solar and artificial sources, using the OSL technique; characterization of the Al2O3:C InLight detectors, pre-conditioned, exposed to RUV solar and artificial sources, using the PTOSL technique; practical applications of the Al2O3:C InLight detectors to the solar and artificial RUV, originating from TIG (Tungsten Inert Gas) and electric welding. The Al2O3:C InLight detectors presented satisfactory OSL and PTOSL responses in relation to the parameters: wavelength, UV illumination time, irradiance, radiance exposure and angular dependence to the RUV. Those detectors presented maximum OSL and PTOSL stimulation for the wavelength of 330 nm, showing that they are may be useful for UVA radiation detection and dosimetry.

Um método dosimétrico para avaliação da exposição à radiação ultravioleta foi estabelecido com os detectores Al2O3:C InLight e com o sistema leitor OSL microStar e software, da Landauer, associados às técnicas de Luminescência Opticamente Estimulada (OSL) e Luminescência Opticamente Estimulada Fototransferida (PTOSL). As etapas principais do trabalho foram: caracterização dos detectores Al2O3:C InLight, sem pré-condicionamento, em relação às fontes de RUV solar e artificial, utilizando a técnica OSL; caracterização dos detectores Al2O3:C InLight, pré-condicionados, em relação às fontes de RUV solar e artificial, utilizando a técnica PTOSL; e aplicações práticas dos detectores Al2O3:C InLight, sem pré-condicionamento e pré-condicionados, em locais de exposição à RUV solar e RUV artificial proveniente de processos de soldagens elétrica e TIG (Tungsten Inert Gas). Os detectores Al2O3:C InLight apresentaram respostas OSL e PTOSL satisfatórias em relação aos parâmetros: comprimento de onda, tempo de iluminação UV, irradiância, exposição radiante e dependência angular, quando expostos à RUV. Esses detectores mostraram estimulação máxima OSL e PTOSL para o comprimento de onda de 330 nm, o que os torna uma opção viável para detecção e dosimetria da radiação na faixa UVA. / A dosimetric method for the exposure evaluation to ultraviolet radiation was established with Al2O3:C InLight detectors and an OSL microStar reader and software, of Landauer, associated to the techniques of Optically Stimulated Luminescence (OSL) and Phototransferred Optically Stimulated Luminescence (PTOSL). The main phases of this work were: characterization of the Al2O3:C InLight detectors, without pre-conditioning, exposed to ultraviolet radiation (RUV) of solar and artificial sources, using the OSL technique; characterization of the Al2O3:C InLight detectors, pre-conditioned, exposed to RUV solar and artificial sources, using the PTOSL technique; practical applications of the Al2O3:C InLight detectors to the solar and artificial RUV, originating from TIG (Tungsten Inert Gas) and electric welding. The Al2O3:C InLight detectors presented satisfactory OSL and PTOSL responses in relation to the parameters: wavelength, UV illumination time, irradiance, radiance exposure and angular dependence to the RUV. Those detectors presented maximum OSL and PTOSL stimulation for the wavelength of 330 nm, showing that they are may be useful for UVA radiation detection and dosimetry.

The submerged entry nozzle (SEN) has been used to transport the molten steel from tundish to the mould. The main purpose of the SEN usage is both to prevent oxygen and nitrogen pick-up by molten steel and to achieve the desired flow condition in the mould. Therefore, the SEN can be considered as a vital factor for a stable casting process and the steel quality. Furthermore, 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 pre-heating and casting 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 pre-heating. The effects of the interaction between the coating layer and the SEN base refractory materials on clogging were studied in supplement 1. The results of the study indicated the penetration of the formed alkaline-rich glaze into the Alumina/graphite base refractory during pre-heating. More specifically, the alkaline-rich glaze reacts with graphite to form carbon monoxide gas. Thereafter, dissociation of CO at the SEN/molten metal interface takes place. This leads to reoxidation of dissolved REM (Rare Earth Metal), which form 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 a formation of a high-viscous alumina-rich glaze during the SEN pre-heating process. This in turn, creates a very uneven surface at the SEN internal surface. The “In Situ” formation of the REM oxides together with the uneven internal surface of the SEN may facilitate the accumulation of the primary inclusions. Supplement 1 revealed the disadvantages of the glass/silicon powder layer. On the other hand the carbon oxidation is a main industrial problem for un-coated Alumina/Graphite Submerged Entry Nozzles (SEN) during pre-heating. This led to the proposal of a new refractory material for the SEN. In supplement 2, the effect of ZrSi2 antioxidant and the coexistence of antioxidant additive and (4B2O3 ·BaO) glass powder on carbon oxidation were investigated at simulated non-isothermal heating conditions in a  controlled atmosphere. Also, the effect of ZrSi2 antioxidant on carbon oxidation was investigated at isothermal temperatures at 1473 K and 1773 K. The specimens’ weight losses and temperatures were plotted versus time and compared to each others. The thickness of the oxide areas were measured and also examined using XRD, FEG-SEM and EDS. The coexistence of 8 wt% ZrSi2 and 15 wt% (4B2O3 ·BaO) glass powder of the total alumina/Graphite base refractory 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 (4B2O3 ·BaO) glaze during green body sintering led to an excellent carbon oxidation resistance. In supplement 3, decarburization behaviors of Al2O3-C, ZrO2-C and MgO-C refractory materials constituting a commercial Submerged Entry Nozzle (SEN), have been investigated in different gas atmosphere consisting of CO2, O2 and Ar. The (CO2/O2) ratio values were kept the same as it is in propane combustion flue gas at Air Fuel Ratio (AFR) values equal to 1.5 and 1 for both Air-fuel and Oxygen-fuel combustions. Laboratory experiments were carried out non-isothermally in the temperature range 873 K to 1473 K at 15 K/min followed by isothermal heating at 1473 K for 60 min. The decarburization ratio (α) values of the three refractory types were determined by measuring the weight losses of the samples. The results showed that the decarburization ratio (α) values of the MgO-C refractory became 3.1 times higher for oxygen-fuel combustion compared to air-fuel combustion both at AFR equal to 1.5 in the temperature range 873 K to 1473 K. The decarburization ratio (α) values for Al2O3-C samples were the same as for the isothermal heating at 1473 K and non-isothermal heating in the temperature range 473  to 1773 K with a 15 K/min heating rate. It substantiates the SEN preheating advantage at higher temperatures for shorter holding times instead of heating at lower temperatures for longer holding times. Jander’s diffusion model was proposed for estimating the decarburization rate of Al2O3-C refractory in the SEN. The activation energy for Al2O3-C samples heated at AFR equal to 1.5, for air-fuel and oxygen-fuel combustions were found to be 84.5 KJ/mol and 95.5 KJ/mol respectively during non-isothermal heating in the temperature range 873 K to 1473 K. / QC 20101008

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. / <p>QC 20111014</p>

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.