In-situ formation of Cu–Al2O3 nano-scale composites by chemical routes and studies on their microstructures

Abstract Copper–alumina composite briquettes have been prepared by hydrogen (pH 2 =0.1 atm) reduction of a homogeneous mixture of finely divided CuO and Al 2 O 3 formed by two chemical processes. In these processes, the Al 2 O 3 of the desired pct. has been formed in-situ by (1) addition of Al(NO 3 ) 3 solution to CuO; or (2) by addition of stoichiometric amount of ammonia to a slurry of CuO in Al(NO 3 ) 3 solution, followed by filtration, and then heating the mixture in both the cases, at 850°C for 2 h. The Cu–Al 2 O 3 composites thus formed, are sintered at 975°C for 2 h in H 2 atmosphere (composites C-1 and C-2). Composite samples have also been prepared by H 2 reduction of the briquette, made out of; (3) the mixture of Al 2 O 3 and CuO powders; or (4) by direct addition of Al 2 O 3 to Cu powder, followed by sintering at 975°C for 2 h (composites C-3 and C-4), in order to compare their homogeneity and microstructures with those (C-1 and C-2), made by the above two chemical processes. The characterization of the composite samples has been done by metallography, SEM and TEM techniques. The distribution of Al 2 O 3 particles in the Cu matrix, is found to be improved when the Cu is produced in-situ by reduction of CuO by H 2 and very significant improvements in this regard, are noticed in case of composites prepared by the chemical methods, particularly the one through Al(NO 3 ) 3 decomposition. In this case (C-1), besides the grain refinement of Cu (50–250 nm) and homogeneous distribution of Al 2 O 3 in it (about 10 nm in size), an appreciable amount of a third phase is found to appear. The existence of the third phase has been indicated by SEM, TEM and EDS analyses. The third phase is suggested to be possibly CuAlO 2 .