Electrodeposited copper-tin alloys were prepared using a tripolyphosphate electrolyte. MBssbauer spectra revealed that a Sn(IV) compound and &II&I were components of the alloys obtained in the deposition range. -250 to -550mV (us nhe). At -770 mV (us nhe) a Sn(IV) species j-Cu-Sn alloy, q-Cu,Sn, and &Sn were formed. It seems that there is a close correlation between the shape of the cathodic Polarization curve and the chemical structure of the deposit.
iNTRODUCTION Electrodeposited bronze has many applications due to its excellent wear properties, attractive appearance, good corrosion resistance, excellent machinability and solderability. Different electrolytes have been tabulated by Bennett[l], but cyanide-stannate electrolytes are the most widely used for the codeposition of copper-tin alloys at any ratio [Z]. Kudra and Galinker[3, suggested a nonpoisonous and inexpensive plating solution for bronze formation using sodium tripolyphosphate as complexing agent. In this plating solution, the current efficiency is W-90%. In the absence of organic additives, the current density is less than 0.6-0.7A dm-', but in their presence, the current density can reach 1.2 A dm-'.
The phase structure of electrodeposited bronzes is highly dependent on the operation conditions. X-ray studies on electrodeposits obtained from perchlorate and sulfate electrolytes showed the formation of a supersaturated copper based solid solution . At potentials more negative than 130mV, there appears the high temperature S-C&, Sn, alloy. Efremova and Kholmyanskii[6] observed that etectrodeposits obtained from sulfate electrolytes were supersaturated solutions in the concentration range 5-25 "/, Sn and, at 25 % Sn, the S-phase is present. After heat treatment in H2 at 830°C for 5min. the deposit with 22% Sn has both the&phaseand a-solid solution, and the one with 25 % has an e-Cu$n phase in addition. q-Cu$ns and &phase, or q-Cu,Sn, and b-solid solution were observed in the X-ray studies of Fedyshkina and Pomosov['l] when the molar concentration of tin in their sulfamate electrolytes exceeded that of copper.
Mdssbauer spectroscopy has also been used [d] to investigate electrodeposited copper-tin alloy. The authors concluded that the as-plated deposit was a modification of the Cu,Sn, structure onto a composition of Cu,Sn, and this was the compound to ' This sample showed a quadrupole splitting of 0.53 * 0.01 mm s-l.