Influence of pores on wetting of alumina- and zirconia-base ceramics by molten manganese
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N. SHINOZAKI, Associate Professor, K. MUKAI, Professor, Department of Materials Science and Engineering, Faculty of Engineering, and T. NOBORITATE, Graduate Student, Department of Materials Science and Engineering, are with the Kyushu Institute of Technology, Tobata, Kitakyushu, 804-8550, Japan. Contact e-mail: [email protected] H. KAKU, formerly Graduate Student, Department of Materials Science and Engineering, Kyushu Institute of Technology, is Engineer, Sankyu Co. Ltd., Tobata, Kita-kyushu, 804-8538, Japan. Manuscript submitted March 12, 2002. METALLURGICAL AND MATERIALS TRANSACTIONS A
surface roughness measuring device is unsuitable for porous materials. Owing to the pores, Ra was a high value of 1.4 m. Also, two types of zirconia-base substrates were prepared. A dense ZrO2-Y2O3-MnO substrate was prepared using the same procedure as that for making dense MnAl2O4 substrate, in which ZrO2-3 mol pct (5.1 mass pct)Y2O3 substrate and molten manganese were reacted. Figure 2(a) shows a scanning electron (SE) micrograph of the surface with no pore. The manganese concentration was 7.7 mass pct, i.e., 9.9 mass pct as MnO, in a region near the free surface. The substrate surface was smooth and the surface roughness Ra was in a range from 0.1 to 0.2 m. Another type of porous ZrO2-4.6 mass pct Y2O3-9.9 mass pct MnO substrate was made from ZrO2-5.1 mass pct Y2O3 and manganese carbonate powders: those powders were mixed and sintered at 1673 K for 2 hours followed by polishing with no. 1500 emery paper. Pores of size 1 to 5 m exist, as shown in Figure 2(b), and the apparent porosity fraction, p, is 0.10. The surface roughness Ra was 0.3 m, slightly higher than that of the dense substrate. These zirconia-base substrates consisted of cubic phase. Several thin plates of electrolytic manganese were piled high on the substrate before heating, as shown in Figure 3(a). The manganese plates were molten by heating and the molten manganese spread over the substrate. A photograph of manganese droplet immediately after melting is shown in Figure 3(b): the contact angle between molten manganese and substrate was high, about 120 deg for any substrate prepared here. It took several minutes to reach the measurement temperature of 1573 K after melting of manganese. Figure 4 shows contact angles measured at 1573 K using two types of MnAl2O4 spinel substrates. There is an apparent difference in contact angle depending on the surface condition, and the contact angle shows high values when the substrate has a large amount of porosity. The MnAl2O4 spinel substrate having a little pore was further densified after the experiment, resulting in a surface with no pore and larger grains of 5 to 10 m. On the other hand, the surface conditions of porous MnAl2O4 substrates before and after the measurement were similar to one another. Figure 5 shows contact angles for ZrO2-4.6 mass pct Y2O3-9.9 mass pct MnO substrates. The contact angle for the dense substrate is constant, being about 79 deg, although it slightly decreases in an early stage
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