Composite Nitride Nanoceramics in the System Titanium Nitride (TiN)-Aluminum Nitride (AlN) through High Pressure and High Temperature Sintering of Synthesis-Mixed Nanocrystalline Powders

Abstract

Presented is a study on the original preparation of individual and in situ intimately mixed composite nanocrystalline powders in the titanium nitride-aluminum nitride system, Ti:Al = 1:1 (at.), which were used in high pressure (7.7 GPa) and high temperature (650 and 1200 °C) sintering with no binding additives for diverse individual and composite nanoceramics. First, variations in precursor processing pathways and final nitridation temperatures, 800 and 1100 °C, afforded a pool of mixed in the nanosized regime cubic TiN (c-TiN) and hexagonal AlN (h-AlN) composite nanopowders both with varying average crystallite sizes. Second, the sintering temperatures were selected either to preserve initial powder nanocrystallinity (650 °C was lower than both nitridation temperatures) or promote crystal growth and recrystallization (1200 °C was higher than both nitridation temperatures). Potential equilibration towards bimetallic compounds upon solution mixing of the organometallic precursors to nanopowders, monomeric Ti[N(CH3)2]4 and dimeric {Al[N(CH3)2]3}2, was studied with 1H and 13C NMR in C6D6 solution. The powders and nanoceramics, both of the composites and individual nitrides, were characterized if applicable by powder XRD, FT-IR, SEM/EDX, Vicker’s hardness, and helium density. The Vicker’s hardness tests confirmed many of the composite and individual nanoceramics having high hardnesses comparable with those of the reference h-AlN and c-TiN ceramics. This is despite extended phase segregation and, frequently, closed microsized pore formation linked mainly to the AlN component. No evidence was found for metastable alloying of the two crystallographically different nitrides under the applied synthesis and sintering conditions. The high pressure and high temperature sintering of the individual and in situ synthesis-mixed composite nanopowders of TiN-AlN was demonstrated to yield robust nanoceramics.

New Nitride Nanoceramics from Synthesis-Mixed Nanopowders in the Composite System Gallium Nitride GaN–Titanium Nitride TiN

“…The 13 C-NMR spectrum for pure Ti-tetrakis(dimethylamide) ( Figure 2 , bottom) is consistent with its monomeric character, resulting in the single signal at 44.38 ppm [ 32 ]. On the other hand, the spectrum for pure Ga-tris(dimethylamide) confirms its dimeric character in the solution with four terminal and two bridging –N(CH 3 ) 2 groups to yield two nonequivalent carbon sites at 44.40 and 44.68 ppm with the intensity ratio 2:1 [ 20 ].…”

“…For the theoretical Ti-imide Ti(NH) 2 , the deamination is accompanied by redox reactions as approximated by {Ti(IV)(NH) 2 } → Ti(III)N + 1/2 NH 3 + 1/4 H 2 + 1/4 N 2 . The general transamination/deamination chemistry was precedented in the 1980s [ 29 , 30 ] and, specifically, it was detailed by us for the dimethylamide derivatives of gallium [ 19 , 20 ], manganese-doped gallium [ 28 ], aluminum [ 20 ], mixtures of gallium and aluminum [ 20 , 31 ], and mixtures of aluminum and titanium [ 32 ]. It was also demonstrated to work for some trimethylsilylamides as reported for the preparation of manganese nitride η -Mn 3 N 2 from Mn-bis(trimethylsilyl)amide [ 35 ].…”

“…In the actual bimetallic system of dimeric Ga-tris(dimethylamide) and monomeric Ti-tetrakis(dimethylamide), the formation of the mixed bimetallic Ga/Ti-tris/tetrakis/(dimethylamide) seems unlikely due to steric factors, although the possibility cannot be excluded. In the recently reported by us and very closely related bimetallic system of dimeric Al-tris(dimethylamide) and monomeric Ti-tetrakis(dimethylamide), no equilibration in hexane solution toward mixed bimetallic molecular species was observed, which was reflected by no solid solution formation in that system made at the end of the individual nitrides of cubic TiN and hexagonal AlN [ 32 ].…”

“…Upon ampoule opening, the powders were removed and briefly handled in air prior to high-pressure and high-temperature sintering, as described earlier [ 27 , 28 , 31 , 32 ]. Specifically, the powders were sintered for 3 min in a high-pressure torroid cell at 650, 1000, and 1200 °C under pressure of 7.7 GPa, yielding dark brown/golden or gray ceramic pellets, D = 4 mm, thickness ca.…”

“…Such a system of intimately mixed monometallic and bimetallic dimers, when subjected to further ammonolysis reactions with ammonia, afforded a complex solid amide-imide precursor already containing –N–Al–N–Ga–N– linkages that later favored the Al x Ga 1−x N solid solution formation. In the system TiN–AlN [ 32 ], no solid solution of the crystallographically different component nitrides was detected at any of the processing stages including sintering, whereas the latter stage was characteristic of the pronounced individual nitride phase segregation on the micrometer scale. This was paralleled this time by no metal-dimethylamide interactions in the hexane solution, even under reflux conditions, as confirmed by a relevant NMR study.…”