Corrosion Resistance of Porous AlN Polytypoid in Aqueous Solution

Abstract

There are many types of polytypoids with layered crystal structure in the vicinity of AlN in the phase diagram of the system Si₃N₄-Al₂O₃-AlN-SiO₂. We have developed porous AlN polytypoid ceramics with plate-like grain structure based on its anisotropy by firing a powder compact of AlN-SiO₂ at 1900°C for 6h in a Si₃N₄crucible. Corrosion behavior of AlN polytypoid with 10mass% SiO₂addition was examined in H₂SO₄ solution and ion-exchange water. Weight changes per surface area, phases present and microstructures before and after testing were evaluated. Sintered specimens were mainly composed of 27R AlN polytypoids and their relative density was about 50%. The weight changes were found to be much smaller than commercialized AlN ceramics. Although pore size distributions were slightly changed, phases present and microstructures after corrosion test were almost the same as those before test. Consequently, it was shown that AlN polytypoid had excellent corrosion resistance.