a b s t r a c tThis paper reports a method for producing ␣-Al 2 O 3 at low temperature using a seeding technique. A white product obtained by hydrolyzing aluminum isopropoxide in water at 80 • C was peptized using acetic acid at 80 • C, which transformed the white product to a transparent alumina sol. ␣-Al 2 O 3 particles were added to the alumina sol as seed material; the sol containing ␣-Al 2 O 3 particles was then transformed to an ␣-Al 2 O 3 -seeded alumina gel by drying the sol at room temperature. The non-seeded alumina gel remained boehmite after annealing at 300 • C and crystallized into ␥-Al 2 O 3 and ␣-Al 2 O 3 at temperatures between 300 and 500 • C and between 900 and 1100 • C, respectively. The ␣-Al 2 O 3 seeding promoted crystallization of the alumina gel into ␣-Al 2 O 3 . The promotion of crystallization was significant with an increase in ␣-Al 2 O 3 particle content by weight in the final seeded alumina gel. With an ␣-Al 2 O 3 particle content of 5%, the seeded alumina gel was partially crystallized into ␣-Al 2 O 3 by annealing at a temperature as low as 900 • C.

Precision grinding is one of the important processes for finishing of hardened steel parts. However, the grinding process might be quite costly providing the parts with shape complexity should be finished because a number of production steps are needed. Also, this process has some environmental issues, such as disposal of a large amount of grinding sludge and grinding fluid. Precision cutting would become a better alternative process to reduce cost and environmental burden because process steps can be simplified by use of CNC machine tools with PcBN cutting insert if deterioration of cutting tool edge by wear and chipping can be suppressed for long duration. In this study, to improve performance of a PcBN cutting insert, such as wear resistance and defect resistance by the applying of pulse laser processing to sharpen cutting edge in order to realize substitution of cutting for grinding. Precision cutting experiments for hardened steel are conducted by use of the PcBN insert with sharp and tough edges processed by pulsed laser and, for comparison, by use of the PcBN insert ground with diamond wheel. From the results of cutting experiments, it was found that precision cutting with PcBN insert processed by pulsed laser can provide a steady cutting state for a long cutting duration, and a smooth finished surface comparable to precision grindings.

This paper reports a method for producing α-Al2O3 at low temperature from aluminum alkoxide using a combination of seeding of α-Al2O3 nanocryatallites and adding of inorganic alumina sol. An alkoxide alumina sol was obtained by hydrolyzing aluminum isopropoxide in water at 80°C and then peptizing the hydrolyzed aluminum isopropoxide using acetic acid at 80°C. An inorganic alumina sol was obtained by producing aluminum compound with a homogeneous precipitation method using aluminum nitrate and urea in aqueous solution and then peptizing the aluminum compound using acetic acid at room temperature. α-Al2O3 nanocrystallites were added to the alkoxide alumina sol containing the inorganic alumina sol. The addition of inorganic alumina sol provided successful fabrication of a crack-free α-Al2O3-seded alumina film by a spin-coating technique. The sol containing α-Al2O3 nanocrystallites was transformed to an α-Al2O3-seeded alumina gel by drying the sol at room temperature. The non-seeded alumina gel was crystallized into γ-Al2O3 at a temperature below 900°C. In contrast, the alumina seeded at 1% α-Al2O3 nanocrystallites content began to be transformed to α-Al2O3 by annealing at the temperature. The seeding and the adding promoted crystallization of the alumina gel into α-Al2O3. The promotion of crystallization was significant with an increase in α-Al2O3 nanocrystallites content by weight in the final seeded alumina gel.

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