Sol-jel yöntemi ile (Th-Ce)O2 sentezinde katkı maddelerinin pelet özelliklerine etkilerinin incelenmesi
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Tarih
2017
Yazarlar
Dergi Başlığı
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Cilt Başlığı
Yayıncı
Ege Üniversitesi, Fen Bilimleri Enstitüsü
Erişim Hakkı
info:eu-repo/semantics/openAccess
Özet
Bu çalışmada Th(NO3)4.5H2O ve (NH4)2Ce(NO3)6 başlangıç kimyasalları ile, (Th0.95Ce0.05)O2 final mol oranına denk düşecek şekilde hazırlanan nitrat çözeltilerine, düşük nötron tesir kesitine sahip metallerin oksitleri (MgO, CaO, V2O5, Ti2O5, Cr2O3, Al2O3) ilave edilerek, sol-jel yöntemiyle yüksek homojenite ve yoğunlukta, kolay sinterlenebilen ve ortalama tane boyutu 50μm'ye ulaşan iri taneli peletlerin elde edilmesi amaçlanmıştır. Başlangıç metal konsantrasyonu 1.6 M olacak şekilde hazırlanan Th(NO3)4.5H2O ve (NH4)2Ce(NO3)6 karışık çözeltisine, belirlenen oranlarda metal oksit katkısı ile elde edilen ana çözeltinin, sıcaklık ve pH kontrollü sistemde NH4OH ile ön-nötralizasyonu sonucunda sol çözeltileri hazırlanmıştır. Hazırlanan sol çözeltileri vibrasyon-nozül sistemi kullanılarak, jelleşme kolonunda bulunan organik ve sulu fazlar yardımı ile kürecik formunda jelleştirilmiştir. Jel mikroküreciklerinin yaşlandırma, yıkama ve kurutma sonrası, TG/DTA analizleri ile termal davranışları incelenmiş ve ICP-MS/ICP-OES analizleri ile metal içerikleri saptanmıştır. Mikroküreciklere 450˚C, 800˚C ve 1150˚C olmak üzere üç farklı sıcaklıkta ısıl işlem uygulanmış ve kristal parametrelerinin hesaplanması için X-ışınları kırınım analizleri yapılmıştır. Isıl işleme tabi tutulan mikroküreciklerin BET yüzey alanı ve BJH gözeneklilik analizleri gerçekleştirilmiştir. Mikrokürecikler 520 MPa basınç altında hidrolik pres ile peletlenmiş ve peletlerin termo-mekanik analizleri dilatometre cihazı ile 1000˚C, 1100˚C, 1200˚C ve 1300˚C olmak üzere 4 farklı sıcaklıkta incelenmiş, katkısız (Th0.95Ce0.05)O2 ve 6 farklı metal oksit kullanılarak elde edilen katkılı (Th0.95Ce0.05)O2 peletlerinin aktivasyon enerjileri hesaplanmış ve sinterlenme kinetikleri belirlenmiştir. Sinterleme sonrası peletlerin taramalı elektron mikroskop görüntüleri çekilmiş, m-Ksilen daldırma yöntemi ile gerçek yoğunlukları hesaplanmıştır. Katkısız (Th0.95Ce0.05)O2 peletleri için aktivasyon enerjisi 449 kJ/mol, metal oksit katkılı olan; Mg-(Th0.95Ce0.05)O2, Ca-(Th0.95Ce0.05)O2, V-(Th0.95Ce0.05)O2, Ti-(Th0.95Ce0.05)O2, Cr-(Th0.95Ce0.05)O2, Al-(Th0.95Ce0.05)O2 peletleri için aktivasyon enerjileri sırası ile 252 kJ/mol, 202 kJ/mol, 107 kJ/m ol, 90 kJ/mol, 190 kJ/mol, 171 kJ/mol bulunmuştur. Ham pelet yoğunluklarının, teorik yoğunluğun %40-43'ü, sinterlenmiş pelet yoğunluklarının ise teorik yoğunluğun %92-98'i aralığında olduğu belirlenmiştir. Bu çalışmada, metal oksit katkı maddesi eklenerek sol-jel yöntemi ile elde edilen (Th0.95Ce0.05)O2 mikroküreciklerden hazırlanan karışık oksit peletler, yanma oranının yükseltilmesi ve fisyon gazlarının yakıt içersinde daha yüksek oranda tutulabilmesi amacına uygun olarak, katkısız karışık oksit peletlere oranla daha iri taneli malzemeler olarak üretilmiştir.
The aim of the present study is to obtain easily sinterable pellets with high homogeneity and density, coarse grained attaining an average dimension of 50 µm, via sol-gel method by the addition of metal oxides (such as MgO, CaO, V2O5, Ti2O5, Cr2O3, Al2O3 having low neutron sections) to nitrate solutions of the initial chemical materials of Th(NO3)4.5H2O and (NH4)2Ce(NO3)6 conveniently prepared to satisfy (Th0.95Ce0.05)O2 final mole ratio. The sols have been prepared as a result of NH4OH pre-neutralisation of the mother liqueur obtained with the addition of predetermined amount of metal oxide additives to 1.6 M of Th(NO3)4.5H2O and (NH4)2Ce(NO3)6 mixed solution, in a temperature and pH controlled system. By using vibration-nozzle system, prepared sols have been gelled to spheres in a gelation column with the help of organic and aqueous phases. Following of aging, washing and drying processes, thermal behaviors of the microspheres were determined with TG/DTA analyses and the metal compositions of the microspheres were determined with ICP-MS/ICP-OES analyses. Three different heat treatments such as 450˚C, 800˚C and 1150˚C have been applied to microspheres and X-rays diffraction patterns were taken to calculate the crystal parameters. BET surface area and BJH porosity analyses also have been realized for heat treated microspheres. The microspheres were pelletized with a hydraulic press under a pressure of 520 MPa and thermo-mechanical analyses of pellets were realized for 4 different temperatures such as 1000˚C, 1100˚C, 1200˚C and 1300˚C. The activation energies of additives free (Th0.95Ce0.05)O2 and with additives (Th0.95Ce0.05)O2 pellets including 6 different metal oxide additives, were calculated and their sintering kinetics was determined. After sintering, SEM images of the pellets were taken with a scanning electron microscope and the real densities of the microspheres derived pellets were calculated with m-Ksilen immersion method. The activation energies were calculated as 449 kj/mol for additive-free (Th0.95Ce0.05)O2 pellets and 252 kJ/mol, 202 kJ/mol, 107 kJ/mol, 90 kJ/mol, 190 kJ/mol, 171 kJ/mol for Mg-(Th0.95Ce0.05)O2, Ca-(Th0.95Ce0.05)O2, V-(Th0.95Ce0.05)O2, Ti-(Th0.95Ce0.05)O2, Cr-(Th0.95Ce0.05)O2, Al-(Th0.95Ce0.05)O2 pellets, respectively. Green densities of pellets were determined as around 40-43% of the theoretical density. The densities after sintering were around 92-98% of the theoretical density. In this study, in comparaison of additive-free pellets, mixed oxide pellets including additives, prepared via sol-gel microspheres process, were coarse grained materials being able to keep the fission gasses at higher rate in the fuel to increase the burning rate
The aim of the present study is to obtain easily sinterable pellets with high homogeneity and density, coarse grained attaining an average dimension of 50 µm, via sol-gel method by the addition of metal oxides (such as MgO, CaO, V2O5, Ti2O5, Cr2O3, Al2O3 having low neutron sections) to nitrate solutions of the initial chemical materials of Th(NO3)4.5H2O and (NH4)2Ce(NO3)6 conveniently prepared to satisfy (Th0.95Ce0.05)O2 final mole ratio. The sols have been prepared as a result of NH4OH pre-neutralisation of the mother liqueur obtained with the addition of predetermined amount of metal oxide additives to 1.6 M of Th(NO3)4.5H2O and (NH4)2Ce(NO3)6 mixed solution, in a temperature and pH controlled system. By using vibration-nozzle system, prepared sols have been gelled to spheres in a gelation column with the help of organic and aqueous phases. Following of aging, washing and drying processes, thermal behaviors of the microspheres were determined with TG/DTA analyses and the metal compositions of the microspheres were determined with ICP-MS/ICP-OES analyses. Three different heat treatments such as 450˚C, 800˚C and 1150˚C have been applied to microspheres and X-rays diffraction patterns were taken to calculate the crystal parameters. BET surface area and BJH porosity analyses also have been realized for heat treated microspheres. The microspheres were pelletized with a hydraulic press under a pressure of 520 MPa and thermo-mechanical analyses of pellets were realized for 4 different temperatures such as 1000˚C, 1100˚C, 1200˚C and 1300˚C. The activation energies of additives free (Th0.95Ce0.05)O2 and with additives (Th0.95Ce0.05)O2 pellets including 6 different metal oxide additives, were calculated and their sintering kinetics was determined. After sintering, SEM images of the pellets were taken with a scanning electron microscope and the real densities of the microspheres derived pellets were calculated with m-Ksilen immersion method. The activation energies were calculated as 449 kj/mol for additive-free (Th0.95Ce0.05)O2 pellets and 252 kJ/mol, 202 kJ/mol, 107 kJ/mol, 90 kJ/mol, 190 kJ/mol, 171 kJ/mol for Mg-(Th0.95Ce0.05)O2, Ca-(Th0.95Ce0.05)O2, V-(Th0.95Ce0.05)O2, Ti-(Th0.95Ce0.05)O2, Cr-(Th0.95Ce0.05)O2, Al-(Th0.95Ce0.05)O2 pellets, respectively. Green densities of pellets were determined as around 40-43% of the theoretical density. The densities after sintering were around 92-98% of the theoretical density. In this study, in comparaison of additive-free pellets, mixed oxide pellets including additives, prepared via sol-gel microspheres process, were coarse grained materials being able to keep the fission gasses at higher rate in the fuel to increase the burning rate
Açıklama
Anahtar Kelimeler
Toryum, Seryum, Sol-Jel, Sinterleme, Thorium, Cerium, Sol-Gel, Sintering
