Vapor-Phase Synthesis of Fine Ag Powder and its Application to the Production of Fine Grained Sintered Ag-C Compacts

• Main Authors: Helson Toku, Oskar Wessel Bender, Alex Clift Doring, Antonio Carlos da Cruz, Pedro K. Kiyohara, Aurelindo Leme Silva
• Format: Article
• Language: English
• Published: Hosokawa Powder Technology Foundation 2014-03-01
• Series: KONA Powder and Particle Journal
• Online Access: https://www.jstage.jst.go.jp/article/kona/21/0/21_2003019/_pdf/-char/en

An experimental investigation was carried out on the production of silver powder based on a vapor phase synthesis process. The main objective of the work was to investigate the feasibility of producing fine metal particles in a lab scale basis, which would lead to a fine grained microstructure of compacts produced from a mixture of these powders with graphite. Using a thermal plasma high temperature reactor, fine silver particles were produced at a rate of 500 g/h, with the thermal plasma power rated at 15 kW. The powders produced were characterized for particle size and size distribution by laser scattering technique, and particle size and morphology using scanning electron microscopy. Sintering experiments of compacted bodies obtained from a mixture of the powders produced and graphite powder demonstrated the feasibility of producing a material presenting a homogeneous microstructure suitable to the fabrication of high performance electrical switch contacts. Metallographic preparations of Ag/C compacts were used for the microstructure analysis using optical microscopy. The experimental apparatus involved the use of a transferred arc plasma evaporator coupled with a tubular cooling section in which the hot gases carrying the metal vapor are quenched to produce fine particles. A study was carried out to provide theoretical support to the experimental investigation. Applied to the tubular gas quenching section, a 2-D model was used to determine the temperature, velocity and species concentration fields. Fluid-dynamics was combined with a model for the nucleation and growth of particles based on the moments of particle size distribution.