Ni-Cu bimetallic colloids prepared in nonaqueous solvents

Colloidal dispersions in nonaqueous media were obtained by simultaneous evaporation of Ni and Cu. The metals were cocondensed at 77 K in an organic matrix of 2-methoxyethanol, 2-propanol or acetone. The metallic dispersions were characterized by transmission electron microscopy, electron diffraction and UV–vis spectroscopy. The stability at room temperature was also measured. The stability of the Ni–Cu bimetallic dispersions is less than that of the Ni and Cu dispersions alone. The presence of more than one phase was observed. It is interesting to note that Ni/Cu ratio does not change the stability of the bimetallic dispersions dramatically. The polarity of the solvent should play a very important role in stabilizing the metal particles by solvatation effects. Transmission electron microscopy studies show the size control effect of Cu with small colloidal size in the bimetal. The electron diffraction studies reveal the presence of amorphous bimetallic particles and particles with crystallinity show typical particles formed for more than one phase (NiO, CuO, Cu, Ni and Cu–Ni). Cu and Ni, for example, are amorphous and crystalline particles, respectively. Differential scanning calorimetry and X-ray spectroscopy characterized the bimetallic solids of Ni–Cu/2-methoxyethanol obtained by evaporation of solvent. The differential scanning calorimetry studies of the solids show transition characteristics of crystalline growth; no glass transitions were observed. The X-ray diffractograms show that the crystallites are too small (less than 100 A), giving rise to low intensity and wide peaks.