Abstract
Ni/NiO nanopowders have been prepared by using thermal decomposition of aqua solutions of nickel acetate ammine complexes in air at the annealing temperature range of 300°C to 500°C, time of decomposition from 30 to 180 min, and ammonia content in initial complex 3.6 to 9.55 mol/mol Ni2+. Chemical composition of obtained powders has been characterized by chemical and thermal analysis. Phase analysis and particle size of powders have been investigated by X-ray diffraction method, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The powders’ pore structure has been determinated by low-temperature nitrogen adsorption method.Products of decomposition were represented as agglomerates of nanoparticles of Ni, NiO, and hydroxy-containing precursors. Mean agglomerate size depended on ammonia content in initial complex, annealing temperature, and duration and has grown from 30 to 40 to 400 to 520 nm. Mean nanoparticle size of hydroxy-containing precursors was invariable with ammonia concentration in initial complex, annealing temperature, and duration and has grown 5 nm. Mean nanoparticle size of Ni depended on annealing temperature and has grown from 40 to 60 to 40 to 70 nm at temperatures 400°С and 500°С, respectively. Mean nanoparticle size of NiO increased with temperature rising from 5 nm at 350°С to 20 to 25 nm at 500°С.
Highlights
Nickel powders are widely used as electrode materials in multilayered ceramic capacitors
Annealing temperature effect on powder composition and particle size In accordance with thermal (Figure 1 curve a) and chemical (Figure 1 curve b) analyses, the degree of initial complex decomposition depended on the annealing temperature
In the paper, effect of annealing temperature and duration and ammonia content in initial complex on composition and particle size of Ni/NiO nanopowders obtained by thermal decomposition of aqua solutions of nickel acetate ammines in air has been investigated
Summary
Nickel powders are widely used as electrode materials in multilayered ceramic capacitors. The tendency of ceramic and electrode layers thinning to 100 to 200 nm that is used for increasing of capacitor dielectric capacity leads to the necessity of the powder size decreasing to 10 to 20 nm. These powders used as electrode materials should fulfill the requirements for morphology, particle size distribution, ability to disperse in organic solvents, and impurity composition. Every one of these characteristics effects properties of conductive paste for screen printing, electrode layers obtained from it, and multilayered ceramic capacitor as a whole. Carbon impairs powder conductivity and leads to increasing of the Schottky barrier because of eutectic melting of electrode layers under sintering temperature as a result of Ba/Ti/Ni alloy formation [9]
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