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 admittan ce spectra of the piezoelectric quartz crystal (PQC) resonator. The conduct ance (G) and susceptance (B) data are acquired synchronously by QCIS and us ed to obtain the maximum conductance (G(max)), the half bandwidth (Delta f( whh)) 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 visc oelasticity changes of zinc phosphate coatings can be assessed by the varia tions of these parameters during the phosphating. The effects of an acceler ator (NaNO2) on the viscoelasticity change of zinc phosphate coatings are a lso discussed in detail. It is shown to be found that the viscoelasticity o f zinc phosphate coatings decreases with phosphating time and the concentra tion of NaNO2. (C) 2000 Elsevier Science S.A. All rights reserved.