Low temperature crystalline Ag–Ni alloy formation from silver and nickel nanoparticles entrapped in a fatty acid composite film

Abstract

Nanoparticles of silver and nickel were grown in thermally evaporated fatty acid (stearic acid) films by immersion of the film sequentially in solutions containing Ag+ ions and Ni2+ ions. Attractive electrostatic interaction between the metal cations and the carboxylate ions in the fatty acid film leads to entrapment of the cations in the film. Thereafter, the metal ions were reduced in situ to yield nanoparticles of Ag and Ni of ∼30 nm diameter within the fatty acid matrix. Thermal treatment of the stearic acid-(silver+nickel) nanocomposite films led to the formation of a Ni–Ag alloy at ∼100 °C. Prolonged heat treatment at this temperature resulted in the phase separation of the alloy and the reformation of individual Ag and Ni nanoparticles.

Study of Ni–Ag/SiO2 catalysts prepared by reduction in aqueous hydrazine

“…Moreover, one has to get in mind that Ni and Ag do not form stable alloys [21,22]. Therefore, we may infer that some metastable supported NiAg alloy, of high metal surface area, arose in the hydrazine media but were not detected by the tools we used to characterize the catalysts.…”

“…Indeed, only metastable NiAg alloys have been observed in specific conditions [21,22]. These alloys give rise to phase separation and reformation of Ni and Ag particles with time on stream [21]. Our study aimed to re-investigate this system in preparation conditions not reported before, namely the hydrazine media and using silica as a support.…”

“…Indeed, nickel and silver do not form stable solid solutions. Metastable NiAg alloys have been observed in specific conditions [21,22]. These metastable alloys give rise to phase separation and reformation of Ni and Ag particles with time on stream [21].…”

“…Metastable NiAg alloys have been observed in specific conditions [21,22]. These metastable alloys give rise to phase separation and reformation of Ni and Ag particles with time on stream [21]. Only few studies were devoted to supported NiAg systems as catalysts [38,39].…”

“…Recently, increasing interest has been shown in preparing metal alloys such as Au/Pd [15], Au/Pt [16], Fe/Ni [17], Ni/Cu [18,19] and Ni/Ag [20][21][22][23]. It has been demonstrated that even with small particles bimetallic clusters are vastly superior to their monometallic counterparts [1,15].…”