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High‐Thermal‐Conductivity Aluminum Nitride Ceramics: The Effect of Thermodynamic, Kinetic, and Microstructural Factors
Author(s) -
Jackson T. Barrett,
Virkar Anil V.,
More Karren L.,
Dinwiddie Ralph B.,
Cutler Raymond A.
Publication year - 1997
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1997.tb03000.x
Subject(s) - materials science , sintering , nitride , ceramic , thermal conductivity , grain boundary , annealing (glass) , dopant , lanthanide , chemical engineering , microstructure , composite material , metallurgy , mineralogy , doping , chemistry , ion , optoelectronics , organic chemistry , layer (electronics) , engineering
Improvement in the thermal conductivity of aluminum nitride (AlN) can be realized by additives that have a high thermodynamic affinity toward alumina (Al 2 O 3 ), as is clearly demonstrated in the aluminum nitride‐yttria (AlN‐Y 2 O 3 ) system. A wide variety of lanthanide dopants are compared at equimolar lanthanide oxide:alumina (Ln 2 O 3 : Al 2 O 3 , where Ln is a lanthanide element) ratios, with samaria (Sm 2 O 3 ) and lutetia (Lu 2 O 3 ) being the dopants that give the highest‐ and lowest‐thermal‐conductivity AlN composites, respectively. The choice of the sintering aid and the dopant level is much more important than the microstructure that evolves during sintering. A contiguous AlN phase provides rapid heat conduction paths, even at short sintering times. AlN contiguity decreases slightly as the annealing times increase in the range of 1–1000 min at 1850°C. However, a substantial increase in thermal conductivity results, because of purification of AlN grains by dissolution‐reprecipitation and bulk diffusion. Removal of grain‐boundary phases, with a concurrent increase in AlN contiguity, occurs at high annealing temperatures or at long times and is a natural consequence of high dihedral angles (poor wetting) in liquidphase‐sintered AlN ceramics.