Technology And Mechanism Of Cu-Sn Bimetallic Powder In Methyl Sulfonate System

As the advantages of its excellent stability, good electrical conductivity, high corrosion resistance, good electromagnetic shielding, Cu-Sn Bimetallic Powder has broad application prospects in the field of conductive filler and industrial catalysis. In this paper, the technological parameters for preparing Cu-Sn Bimetallic Powder in methyl sulfonate system were explored and optimized with stereo microscope, field emission scanning electron microscopy, X-ray diffraction and electrochemical workstation, by using tin methane sulfonate as main salt, thiourea as complexing agent. The influences of tin ion concentration, thiourea concentration, bath temperature and methyl sulfonic acid on the oxidation resistance, electrical conductivity and corrosion resistance of Cu-Sn Bimetallic Powder were studied.The results show that, due to the effect of thiourea in methyl sulfonate system, copper ions would form complex ions, which would reduce the electrode potential to make the replacement reaction possible to happen. Tin ion concentration, thiourea concentration, methyl sulfonic acid and bath temperature have effects on the morphology of Cu-Sn Bimetallic Powder, in which, the influence of thiourea concentration is the most significant. High concentration of thiourea will make high crystallization overpotential during immersion process, resulting in dull and rough coating surface. Orthogonal test shows that, when tin ion concentration is 0.15mol/L, thiourea concentration is 0.80mol/L, adding amount of methyl sulfonic acid is 50mL/L, and bath temperature is 75℃, a uniform, dense and bright tin coating which distributes as granular can be obtained on the surface of copper powder. The essence of immersion tin onto copper powder in methyl sulfonate system is the replacement reaction between copper and tin, including the following five steps:tin ion diffusion, adsorption, copper atoms complexation with thiourea, Cu-Sn electrochemical reaction, nucleation and growth of tin atoms. In the process of immersion tin onto copper powder, tin ions nucleate instantly in the local position of the copper surface at first; And then coating planar sandwich grows along parallelly to the copper surface; While copper surface is almost covered with tin coating, the replacement reaction is inhibited, and tin coating is arranged into the densification stage, until copper surface is covered with tin coating completely.Conductivity tests indicate that, tin ion concentration, thiourea concentration, methyl sulfonic acid and bath temperature have effects on conductivity of Cu-Sn Bimetallic Powder. Under this experiment conditions, the resistivity of Cu-Sn Bimetallic Powder that average particle size of 50μm is 1.598x×10-3Ω·cm, close to resistivity of silver-plated copper powder in the same size (0.893×10-3Ω·cm), which is expected to become the alternative to silver-plated copper. Oxidation resistance experiments show that performance of Cu-Sn Bimetallic Powder is closely related to the dense degree of tin coating particles arrangement on the surface. The denser tin coating is, the better oxidation resistance of Cu-Sn Bimetallic Powder will be gotten. After 168h oxidation test on Cu-Sn Bimetallic Powder with optimal technical parameters, there is no obvious oxidation and no weight gain phenomenon. EDS analysis shows that it does not detect oxygen element in Cu-Sn Bimetallic Powder after oxidation test, showing good oxidation resistance. Corrosion resistance tests indicate that, tin ion concentration, thiourea concentration, methyl sulfonic acid and bath temperature have effects on the corrosion resistance of Cu-Sn Bimetallic Powder. It is consistent with the influence of these process parameters on the surface morphology of Cu-Sn Bimetallic Powder. It also proves that the dense degree of tin coating directly determines corrosion resistance of Cu-Sn Bimetallic Powder in another way.