In-situ electrochemical-based moisture sensor for detecting moisture in composite and bonded structures

• US 6,313,646 B1
• Filed: 02/02/1999
• Issued: 11/06/2001
• Est. Priority Date: 02/02/1999
• Status: Expired due to Fees

• Current Assignee: Dacco SCI, Inc.
• Original Assignee: Dacco SCI, Inc.
• Inventors: Davis, Guy D., Dacres, Chester M.
• Primary Examiner(s): Metjahic, Safet
• Assistant Examiner(s): Nguyen, Vincent Q
• Application Number:
  US09/240,658
• Time in Patent Office: 1,008 Days
• Field of Search: 324/664, 324/693, 324/690, 324/71.2, 205/775.5, 205/776.5, 205/791, 204/404, 204/406
• US Class Current: 324/690
• CPC Class Codes: G01N 17/02 Electrochemical measuring systems for weathering, corrosion or corrosion-protection measurement

Abstract

A hand-held or permanently attached corrosion sensor is described that uses electrochemical impedance spectroscopy (EIS, also known as AC impedance) to detect coating and structural degradation caused by excessive moisture uptake of coated and uncoated composite laminations or honeycomb or adhesively bonded structures. The hand-held sensor is pressed against the surface of the structure or specimen to be inspected. Alternatively, the sensor electrode may be permanently or temporarily attached. An EIS spectrum can then be obtained in the field or under arbitrary conditions and the degree of moisture uptake or coating or material degradation can be determined from the resultant spectrum. There are no restrictions on the configuration of the structure being inspected. The area of detection is controlled by controlling the extent and degree of wetness of the surface. A dry surface will provide a localized measurement; a wet surface will allow inspection of the wetted area.

Claims

1. A method detecting moisture absorption, electrochemical corrosion, and adhesive bond degradation in composite laminations, honeycomb, and adhesively bonded structures comprising steps of:

(a) providing a sensor consisting of a first and a second electrode, said first and second-electrode are pressed against a specific material;

simultaneously an electrical voltage is applied to that material to produce an electrical output correlating to an identifiable impedance spectrum of that specific material;

said first and second electrode serving as a reference and a working electrode responsive to water uptake, incubation, hydration, and corrosion to produce differences in impedance spectra, thus eliminating the need for electrolyte immersion of the composite laminations or honeycomb or adhesively bonded structures being tested;

(b) utilizing the first electrode of the sensor as a counter reference and a second electrode as a working electrode, and pressing electrodes against the top of said material;

applying a small electrical voltage between the two electrodes; and

measuring the resulting current based upon the applied voltage between the electrodes;

(c) converting an analog signal indicative of the measured current to a corresponding ac impedance signal; and

(d) converting the impedance spectrum as a function of accelerated exposure and interpreting said spectrum as a functional expression which correlates to distinctive impedance spectra that are material specific, in order to determine the amount of moisture uptake or the stage of corrosion to that said material has experienced.

2. The method according to claim 1, wherein said sensor is used to detect and evaluate corrosion or coating degradation of the material by wetting the surface of said material with water or other electrolyte.