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    Effects of solid loading on joining and thermal cycling performance of glass-ceramic sealing pastes for solid oxide fuel cells
    (Elsevier Ltd, 2019) Timurkutluk B.; Celik S.; Ucar E.
    The variation of the joining performance of glass-ceramic sealants in the form of a paste as a function of the solid powder content in the sealing paste after the formation and a number of thermal cycles are experimentally studied. Three different sealing pastes having 40, 50 and 60 wt % solid loadings are prepared and tested for this purpose. The pastes are applied between two metallic interconnector plates and subjected to a glass formation step for the joining. The fracture strengths of 24 samples prepared for each case are determined via tensile tests. Similarly, the mechanical performances of the sealants after 3, 6 and 9 thermal cycles are also obtained. The results reveal that the joining strength tends to increase with the amount of solid powder content in the paste. This can be attributed to increased number of crystalline phases in the sealants with increasing the solid loading. The thermal cycles, on the other hand, are shown to have an adverse effect on the joining performance regardless of the solid loading. However, the rate of decrease in the fracture strengths is found to decrease with the solid powder contents in the pastes. This can be elucidated by the amount of glassy phases in the sealants, which can be expected to increase with the solid loading and provide self-healing ability. The microstructures of the fracture surfaces of all samples are also investigated by a scanning electron microscopy. The obtained images confirm the tensile test results. © 2019 Elsevier Ltd and Techna Group S.r.l.
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    Influence of doctor blade gap on the properties of tape cast NiO/YSZ anode supports for solid oxide fuel cells
    (Elsevier Ltd, 2019) Timurkutluk B.; Celik S.; Ucar E.
    In this study, various tape cast NiO/YSZ anode support layers with similar geometric properties are fabricated by varying the doctor blade from 100 µm to 200 µm with an increment of 25 µm. The mechanical properties of the anode support layers are investigated by three point bending tests of 30 samples for each doctor blade gap. The reliability curves of the flexural strength data are also obtained via two-parameter Weibull distribution method. The effects of the doctor blade gap on the microstructure and the electrochemical performance of the anode support layers are determined via SEM investigations and single cell performance-impedance tests, respectively. The apparent porosities of the samples are also measured by Archimedes’ principle. The results indicate that the doctor blade gap or the resultant tape thickness influences the microstructure of tape cast NiO/YSZ anode supports significantly, yielding different mechanical and electrochemical characteristics. At a reliability level of 70%, the highest flexural strength of 110.20 MPa is obtained from the anode support layer with a doctor blade gap of 175 µm and the 16 cm2 active area cell with this anode support layer also exhibits the highest peak performance of 0.483 W/cm2 at an operating temperature of 800 °C. Thus, a doctor blade gap of 175 µm is found to have such a microstructure that provides not only better mechanical strength but also higher electrochemical performance. © 2018 Elsevier Ltd and Techna Group S.r.l.