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- Effect of Passivation on the Sintering Behavior of Submicron Nickel Powder Compacts for MLCC Application
- Gi-Young Jo, Kwi-Jong Lee, Suk-Joong L. Kang
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Journal of Korean Powder Metallurgy Institute 2013;20(6):405-410
DOI: https://doi.org/10.4150/KPMI.2013.20.6.405
2LCR Division, Samsung Electro-Mechanics
3Materials Interface Laboratory, Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology
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Abstract
During sintering of Ni-electrode multi-layer ceramic capacitors (MLCCs), the Ni electrode often becomes discontinuous because of its lower sintering temperature relative to that of BaTiO_3. In an attempt to retard the sintering of Ni, we introduced passivation of the Ni powder. To find the optimal passivation conditions, a thermogravimetric analysis (TGA) was conducted in air. After passivation at 250°C for 11 h in air, a nickel oxide shell with a thickness of 4-5 nm was formed on nickel nanoparticles of 180 nm size. As anticipated, densification of the compacts of the passivated Ni/NiO core-shell powder was retarded: the starting temperature of densification increased from sim400°C to sim600°C in a 97N_2-3H_2 (vol %) atmosphere. Grain growth was also retarded during sintering at temperatures of 750 and 1000°C. When the sintering atmosphere was changed from wet 99.93N_2-0.07H_2 to wet 99.98N_2-0.02H_2, the average grain size decreased at the same sintering temperature. The conductivity of the passivated powder sample sintered at 1150°C for 8 h in wet 99.93N_2-0.07H_2 was measured to be 3.9times104S/cm, which is comparable with that, 4.6times104S/cm, of the Ni powder compact without passivation. These results demonstrate that passivation of Ni is a viable means of retarding sintering of a Ni electrode and hence improving its continuity in the fabrication of BaTiO_3-based multi-layer ceramic capacitors.
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