A study of the viscoelasticity of zinc phosphate coatings using a quartz crystal impedance system

Zinc phosphating processes in manganese-modified low-zinc phosphating baths have been studied firstly by employing an in-situ quartz crystal impedance system (QCIS) which allows rapid and simultaneous measurements of admittance spectra of the piezoelectric quartz crystal (PQC) resonator. The conductance (G) and susceptance (B) data are acquired synchronously by QCIS and used to obtain the maximum conductance (Gmax), the half bandwidth (Δfwhh) of the curve of G and scanning frequency (f), and thereby the quality factor (Q) of zinc-coated PQC. The experimental results show that the viscoelasticity changes of zinc phosphate coatings can be assessed by the variations of these parameters during the phosphating. The effects of an accelerator (NaNO2) on the viscoelasticity change of zinc phosphate coatings are also discussed in detail. It is shown to be found that the viscoelasticity of zinc phosphate coatings decreases with phosphating time and the concentration of NaNO2.