Role of B2O3 on the Viscosity and Structure in the CaO-Al2O3-Na2O-Based System
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The effect of B2O3 on the viscosity and structure in the calcium-aluminate melt flux system containing Na2O was studied. An increase in the B2O3 content at fixed CaO/Al2O3 ratio lowered the viscosity. Higher CaO/Al2O3 ratio at fixed B2O3 content also decreased the viscosity. The alumino-borate structures were confirmed through Fourier transformed infrared (FTIR) and Raman spectroscopy and consisted of [AlO4]-tetrahedral structural units, [BO3]-triangular structural units, and [BO4]-tetrahedral structural units, which could be correlated to the viscosity. At fixed CaO/Al2O3 ratio, B2O3 additions decreased the [AlO4]-tetrahedral structural units and transformed the 3-D network structures such as pentaborate and tetraborate into 2-D network structures of boroxol and boroxyl rings by breaking the bridged oxygen atoms (O0) to produce non-bridged oxygen atoms (O−) leading to a decrease in the molten flux viscosity. At fixed B2O3 contents and higher CaO/Al2O3 ratio, 3-D complex network structures become 3-D simple and 2-D isolated network structures, resulting in lower viscosities. The apparent activation energy for viscous flow varied from 132 to 249 kJ/mol according to the composition of B2O3 and CaO/Al2O3 ratio.
KeywordsB2O3 Mold Flux Slag System B2O3 Content Boroxol Ring
This study was partially supported by the Brain Korea 21 (BK21) Project at the Division of the Humantronics Information Materials and by the Priority Research Centers Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2009-0093823). Partial funding was also provided by the National Science Foundation of Korea Project No. 2012-8-0486.
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