固-液界面での化学反応による自己結合型ホウ酸アルミニウム(9Al_2O_3・2B_2O_3)針状結晶の成長機構

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Self-bonding aluminum borate (9Al_2O_3・2B203) needle-like crystals were synthesized by the reaction of aluminum hydroxide (Al(OH)_3) with boric acid (H_3BO_3). The powders were mixed (B/Al=4/9) and fired at 1250℃ to obtain self-bonding needle-like crystals of 3-20 pμm in length and 0.4-0.8 μm in diameter and to form frame-work of needle-like crystals. Amorphous aluminum oxide (Al_2O_3) were coated with melted boron oxide (B_2O_3) at high temperature. The seeds of needle-like crystals were formed on the surface of Al_2O_3 particles, namely solid-liquid interface. Then the seeds grew as needle-like crystals. In this way boric acid act not only as a reactant, but also as a fiux. In this reaction, nickel oxide (NiO) act as an additive so that the surface of Al_2O_3 had been well wetted by flux. Excess of H_3BO_3 in the raw materials caused by-products in XRD patterns. The B_2O_3 were removed by water. Needle-like crystals grew on the single crystal surface in the Al_2O_3 particles. On the large particles, several needle-like crystals grew on one plane. On the other hand, a needle-like crystal grew on one plane in the small particles. Then needle-like crystals grew in random directions from each plane.
社団法人日本セラミックス協会の論文
1998-04-01