Formation Process of AIN Through Precursors and Its Application to Joining AIN Ceramics

摘要

Formation process of AIN from urea and aluminum chloride hexa-hydrate (N/Al = 60) under nitrogen is investigated. An aluminum hexa-urea complex crystallizes on mixing the two raw materials at room temperature. The complexes react with excess urea and/or its decomposed products, such as biuret above 160℃, and form an amorphous phase containing Al, N, C, and O around 400℃ after releasing volatile products. The resultant amorphous phase undergoes changes as the temperature increases, and then crystalline carbon with a fullerene-like XRD pattern forms at 850℃. AIN crystallization follows the decomposition of the fullerene-like crystals. At the AIN precursor stage, a large number of radicals (g = 2.0029 and S = 1/2) are detected by ESR. The radicals are assumed to be due to dangling bonds with an unpaired electron in amorphous carbon. Joining AIN ceramics is conducted using the 850℃ product at the AIN precursor stage as the filler material, and is successfully achieved at temperatures above 1000℃. The shear strengths of the joints formed at 1500℃ are 88 ± 29 MPa.