This paper describes a novel experiment on surface modification for alumina plates. Polycarbosilane (PCS), an organosilicon polymer, was used in this experiment as a precursor. Tiny cracks on an alumina surface caused by grain boundaries and introduced by rough grinding were filled by PCS, and PCS was transformed into silicon oxycarbide (SiCO, silicon carbide including several mass percents of oxygen) by thermal oxidation curing at 453 K and pyrolysis at 1273 K. Moreover, Al 6 Si 2 O 13 (mullite) layer was made from alumina and SiCO and prevented exfoliation of the alumina and SiCO during pyrolysis. In addition, the wettability between samples and molten aluminum was investigated in order to make sure the effect of surface modification. This experiment confirms that surface modification of alumina with a SiCO membrane can be successfully.

This study demonstrated that a long silicon nitride pipe of several meters with adequately strong joints can be fabricated by a local-heating joining technique. Commercially available silicon nitride ceramic pipes sintered with Y 2 O 3 and Al 2 O 3 additives were used for parent material, and powder slurry of Si 3 N 4 -Y 2 O 3 -Al 2 O 3 -SiO 2 system was brush-coated on the rough or uneven end faces of the pipes. Joining was carried out by locally heating the joint region at different temperatures from 1500°C to 1650°C for 1 h with a mechanical pressure of 5 MPa in N 2 flow; using a horizontal electrical furnace specially designed for this experiment. The silicon nitride pipe 3-m long was successfully fabricated without voids or cracks in the joint region, and the microstructure of the joint region was similar to that of the parent one. The joint strength was examined in flexure using specimens cut from the joined pipes, and those joined at 1600°C and 1650°C indicated the highest strength of about 680 MPa, which was almost the same as that of the parent material. This study also indicated that the slurry brushcoating technique is advantageous to easily joining ceramic pipes with rough or uneven end faces, which is essentially important for practical use.

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