Method of monitoring constituents in conversion coating baths
First Claim
1. A method for monitoring the constituents present in a conversion coating solution used in a non-electrolytic conversion coating process wherein a conversion coating is applied to a metal substrate, said method comprising the steps of:
- (a) applying a selected dc potential to a working electrode which has been subjected to annealing and anodic pretreatment, said working electrode being positioned within said solution containing said constituents, said dc potential producing a dc current; and
wherein hydrogen gas is produced at said working electrode and said conversion coating precipitates at said working electrode;
(b) superimposing a constant ac voltage on said dc potential applied to said working electrode, said ac voltage having an amplitude and a frequency and producing an ac current;
(c) varying said dc potential at a chosen sweep rate over a chosen range; and
(d) measuring said dc and/or said ac current or a harmonic of ac current at one or more reference phase angles with respect to said constant ac voltage between said working electrode and a reference electrode positioned within said solution as said dc potential is varied over said range, said measurement of dc and/or ac current in relation to varying dc potential being expressed as a dc and/or an ac current spectra which is used to determine and monitor said constituents in said solution.
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Abstract
A method for monitoring the constituents present in conversion coating bath solutions. The method involves using specific ac and dc voltammetry and using platinum or other noble metal working electrodes. First, a selected dc potential is applied to a working electrode which has been subjected to pretreatment and which is present as an in-tank sensor in the bath being analyzed. A constant ac signal is superimposed on the dc potential. The dc potential is then swept over a chosen range at a selected sweep rate. The various constituents in the bath are then monitored by measuring dc current and the ac current at one or more reference phase angles with respect to the constant ac signal between the working electrode and a reference electrode as the dc potential is varied. The resulting dc and ac spectra provide a useful measurement of the make-up of the constituents in the bath solutions.
28 Citations
18 Claims
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1. A method for monitoring the constituents present in a conversion coating solution used in a non-electrolytic conversion coating process wherein a conversion coating is applied to a metal substrate, said method comprising the steps of:
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(a) applying a selected dc potential to a working electrode which has been subjected to annealing and anodic pretreatment, said working electrode being positioned within said solution containing said constituents, said dc potential producing a dc current; and
wherein hydrogen gas is produced at said working electrode and said conversion coating precipitates at said working electrode;(b) superimposing a constant ac voltage on said dc potential applied to said working electrode, said ac voltage having an amplitude and a frequency and producing an ac current; (c) varying said dc potential at a chosen sweep rate over a chosen range; and (d) measuring said dc and/or said ac current or a harmonic of ac current at one or more reference phase angles with respect to said constant ac voltage between said working electrode and a reference electrode positioned within said solution as said dc potential is varied over said range, said measurement of dc and/or ac current in relation to varying dc potential being expressed as a dc and/or an ac current spectra which is used to determine and monitor said constituents in said solution. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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Specification