Real-time monitoring of zinc phosphating process by quartz crystal impedance system

The zinc phosphating process in manganese-modified low-zinc phosphating bat hs has been monitored firstly by an in situ quartz crystal impedance system (QCIS) which allows rapid and simultaneous measurements of admittance spec tra of the zinc-coated piezoelectric quartz crystal (PQC) resonator. The el ectrical equivalent circuit parameters are obtained by non-linear least squ are regression analysis of synchronously acquired conductance and susceptan ce data. The experimental results show that the kinetic growth process of z inc phosphate coating can be monitored on-line by measuring the equivalent circuit parameters and frequency shifts of the zinc-coated PQC resonator. A ccording to the motional inductance (L-m) change of zinc-coated PQC during zinc phosphating treatment, the whole process can be divided into four regi ons: pickling reaction, exponential growth, linear growth and exponential d ecay growth, respectively. And effects of inorganic additives (Ni2+ and/or Mn2+) on the properties and performance of zinc phosphating coatings as wel l as the variations of equivalent circuit parameters of zinc-coated PQC dur ing the phosphating treatment are also investigated. (C) 2001 Elsevier Scie nce B.V. All rights reserved.