COMPARISON OF THE PROPERTIES OF CoW AND CoMo ALLOYS DEPOSITED BOTH FROM ALKALINE CITRATE AND CITRATE-PYROPHOSPHATE ELECTROLYTES

Abstract

The chemical composition, current efficiency and some properties of galvanic binary CoMo and CoW alloys, deposited from both alkaline citrate and citrate-pyrophosphate electrolytes, were studied. It is shown that the main difference between mono- and polyligand electrolytes is the mechanism of the electrodeposition process and the rate of passage of limiting stages preceding the formation of an electrochemically active complex. During electrolysis in a citrate solution, the limiting step is the mass transfer of [CoCit2]4– complexes, while in the citrate-pyrophosphate one, the process proceeds with kinetic control, and the hydrodynamic regime does not significantly affect the content of metals and the rate of their deposition. The use of a polyligand electrolyte makes it possible to increase the current efficiency for CoW alloys from 32.1 to 45.5% in the convective mass transfer mode and from 5.9 to 35.7% in the diffusion transfer mode. During electrodeposition from citrate-pyrophosphate electrolytes of the same composition of alloys of two different refractory metals, it was found that the current efficiency of the CoMo alloy is on average 20% higher than that of CoW. It has been found that at a close value of the content of the refractory component in X-ray amorphous alloys, the differences in the magnetic and corrosion properties of the coatings are determined by the nature of the refractory metal. Thus, during electrodeposition from a polyligand electrolyte, CoMo alloys have Ms 300–380 emu·cm-3 and Hc 60–72 Oe, while CoW alloys have Ms 22–45 emu·cm-3 and Hc 50–70 Oe. Both types of alloys are characterized by Mr/Ms – 0.2-0.3. The properties of CoW alloys deposited from a monoligand citrate electrolyte approach hard magnetic materials with Mr/Ms – 0.6–0.7.