Homogenous Silver-Tungsten Composite Production for Electrical Contacts

Abstract

Silver-tungsten composite materials have been widely used as medium duty electrical contacts since they offer the advantages of both refractory tungsten (welding and erosion resistance) and silver (efficient electro-thermal conductivities). Since there is no alloying between the two elements (Ag and W), the properties of the composite depends on their composition. So for any particular application, a balance must be struck between the desirable properties of the two metals. Both welding and erosion resistance properties of silver-tungsten contacts depend on particle size, morphology and distribution of both elements within the composite, with finer W particles in Ag matrix give better performance. The main objective of this study is to produce an intimately mixed silver-tungsten powder with homogeneous distribution of both phases (silver and tungsten) in the composite. Thus, to produce homogenous elemental silver-tungsten powder, the reduction behavior of each tungstate is studied at various reduction temperatures using TGA technique. Based on the results obtained from TGA, the reduction of silver tungstate carried out in two stage reduction process for producing elemental silver-tungsten powder with controlled particle size of tungsten. Also, small quantities of Fe and Co as sinter aids are introduced into tungstates by coprecipitation technique. However, the precipitated Fe and Co doped silver tungstates are reduced to yield Iron and cobalt doped silver-tungsten powders. The effect of Fe and Co on the morphology and particle size of the tungsten is studied using SEM. The reduced products will be used for subsequent sintering experiments to produce high density sintered compact for contact fabrication.

Sintering Characteristics of Iron and Cobalt Doped Silver-tungsten Metal-matrix Composites

“…Silver tungstate: The analysis of the precipitated silver tungstate is made by atomic absorption spectroscopy and the molecular formula for precipitated silver tungstate (Ag 2 WO 4 ) is obtained (Calculated Formula = Ag 1.96 WO 4.01 ), Azhar and Es-Saheb (2013) and Es-Saheb and . It is evident from the formula that the silver/tungsten ratio is very close to the theoretical value 2:1 and the oxygen content calculated from the total mass of specimen also agrees with the theoretical value for silver tungstate.…”

Kinetic Highlights of the Reduction of Silver Tungstate by Mg + C Combined Reducer

“…This is further complicated by the limited mutual solubility of the metals in both the solid and liquid states [13,14] and the associated extensive segregation of silver. The powder metallurgy [15], hydrogen reduction of silver tungstate [16], explosive consolidation [17], press-sinter infiltration [18] and combustion synthesis [19] are reported as W-Ag preparation methods. However, a huge challenge still lies in the lack of sufficient quality materials (high relative density, homogeneous dispersion of phases, etc.)…”