Guo-jun Li

Preparation and characteristics of nanocrystalline NiO by organic solvent method

Nanocrystalline nickel oxide (NiO) powder was prepared by thermal decomposition of the precursor of NiC2O4·2H2O obtained via the reaction between Ni(NO3)·6H2O and H2C2O4·2H2O in ethanol solvent. The products were characterized using X-ray diffraction, infrared absorption spectroscopy, thermogravimetric analysis_differential thermal analysis, and transmission electron microscopy. The particle sizes of the as-calcined NiO increased with increase in temperature. The as-calcined NiO at 400°C for 1 h was of narrow distribution, weak agglomeration and small particle size (average=8 nm). The reason for weak agglomeration was explained.

Microstructure, texture, grain boundaries in recrystallization regions in pure Cu ECAE samples

By means of equal channel angular extrusion (ECAE), pure Cu single crystal samples were processed down to the submicron scale. In some parts of the samples, recrystallization occurs at room temperature. The recrystallization mechanism was analyzed by SEM-EBSP and SEM-ECC techniques. The grain boundary character distribution (GBCD) and orientation distribution function (ODF) of the regions undergoing recrystallization were computed. The results show that the nuclei can be formed at the intersections of two different shear bands, and the microstructures and the grain boundary characters in these locations contribute to growth of recrystallized nuclei. The recrystallized grains had grown according to the Felthams mechanism

Scanning electron microscopy-electron channelling contrast investigation of recrystallization during cyclic deformation of ultrafine grained copper processed by equal channel angular pressing

Cyclic deformation has been performed at ambient temperature on ultrafine-grained copper processed by equal channel angular pressing. Observations by electron channelling contrast in a scanning electron microscope revealed that pronounced recrystallization occurred and several distinct dislocation configurations such as dislocation walls and labyrinth structures were found within the recrystallized regions. A model is proposed to account for the evolution of recrystallization, emphasizing that its development results from an interaction between the cyclic deformation and the growth of recrystallized regions. The formation of recrystallized regions of different sizes is discussed.

Fabrication of Ni-coated Al2O3 powders by the heterogeneous precipitation method

Abstract Ni-coated Al 2 O 3 powders were prepared by the heterogeneous precipitation method using Al 2 O 3, Ni(NO 3 ) 2 ·6H 2 O and NH 4 HCO 3 as the starting materials. The amorphous NiCO 3 ·2Ni(OH) 2 ·2H 2 O was uniformly coated on the surface of Al 2 O 3 particles with the thickness of 20 nm. The amorphous coating layer was crystallized to NiO with the size of about 15 nm at 500°C for 2 hours in air, meantime, the dispersant was eliminated. NiO was completely reduced to Ni at 700°C for 4 hours in hydrogen atmosphere. Ni with the size of about 20 nm in the coating layer was spherical and weakly agglomerated. The continuous coating layer became discontinuous during heating treatment.