茂名市涂料检测、油漆性能测试

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茂名市涂料检测、油漆性能测试:

You can use the REAP parameters to estimate the relative time to failure (TTF) of coatings and rank coatings in
terms of their expected long term performance. Another application of REAP testing is the quality control of coated
products. You can follow the variation of the REAP parameters over time, as a measure of coating quality.
Painted Metal Specimens
Experiments Performed
Unscribed Sample Scribed Sample
3. Cathodic Disbonding
for 24 hours

1. Corrosion Potential


2. EIS at 0 hours
4. EIS at 24 hours
REAP Parameter Measured
Rcor dx/dt
CC,0, CC,24 ? %v
Overview of REAP Testing. 
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Measurement of the REAP parameters involves tests on at least two painted metal samples. One of the samples is
scribed with a 2x2 cm right angle cross.3
 Both samples are exposed to a 0.5M aqueous NaCl test solution at room
temperature for 24?2 hours. An overview of the testing process with two samples is illustrated above.
Immediately after filling the cells, the corrosion potential of the unscribed painted sample is measured. The
measured potential determines the DC potential used in the electrochemical impedance spectroscopy (EIS)
experiments on the sample. An EIS experiment is run immediately after the corrosion potential experiment. A
second EIS experiment is run after soaking the unscribed sample in the NaCl test solution for 24 hours.
In between the two EIS tests, a 24-hour potentiostatic experiment is run on the scribed sample. A cathodic
potential (-1.05V vs. SCE) is used to accelerate disbonding of the coating. This test measures one of the REAP
parameters, the disbond rate of the coating (dx/dt), in units of mm per hour. Typical rates measured via cathodic
disbonding are 0.1mm/hr or lower.
Comparison of the results of the two EIS experiments allows you to evaluate the second REAP parameter, water
uptake by the coating. Water uptake is expressed as an apparent volume fraction, %v. % v is calculated from the
change in the measured capacitance of the coating (CC
) over the 24 hour period. These capacitance values are
obtained via analysis of the EIS data using an equivalent circuit model (shown in simplified form below).
Equivalent circuit (simplified) used in EIS data analysis.
The third REAP parameter is obtained from the EIS data recorded after 24 hours. It is the corrosion resistance (Rcor)
of the underlying steel and results directly from the equivalent circuit analysis of the EIS data.
Background
The procedure described in this application note is a condensed summary of a proposed method being considered
by the American Society for Testing Materials (ASTM). The ASTM G01.11 subcommittee on Electrochemical
Measurements in Corrosion Testing used an article by Kendig et. al.1
 as the basis of the proposed method for
testing painted steel.
Kendig’s paper studied the correlation of various electrochemically-measured parameters with the long-term time
to failure (TTF) of painted carbon steel samples. TTF was evaluated by exposure to a salt fog.2
 The three
parameters mentioned above were found to correlate well with the TTF. The rapid electrochemical assessment
method does not attempt to measure the time to failure directly. Instead it relies on the correlation of the TTF with
REAP parameters as demonstrated in the Kendig paper. 
3
This application note is a description of the REAP testing process using Gamry’s products rather than a detailed
review of the original paper or the proposed ASTM method. More information can be obtained from the paper or
the ASTM proposal. You might consider joining the ASTM committee considering this proposal. For information
concerning ASTM, see the endnotes.
Cell Design & Setup

Each REAP measurement requires two electrochemical cells.
The proposed REAP method calls for five replicate tests requiring the use of 10 samples. In most cases, you will
want to run the replicate tests simultaneously, so ten cells are needed.
If you wish to build your own cells, the proposed REAP method describes a cell that holds a flat painted metal
sample. This cell exposes 56 cm2
 of the specimen to the electrolyte. The reference electrode is a saturated
calomel electrode (SCE), while the counter electrode can be platinum, gold, graphite, nickel or passivated stainless
steel. Graphite rods are probably the most economical choice. As mentioned above the test solution used is a 0.5
M NaCl solution in water and the experiments are performed at room temperature.
If you wish to make use of a ready made cell kit, you can consider commercial cell kits from a number of vendors.
Depending on your budget, the need for multiple cells can limit your choices. Gamry’s PTC1 (Paint Test Cell) is
designed to be inexpensive and easy to use.z89g88l5ysqw
Gamry’s PTC1 Cell Kit.
The PTC1 is shown above. It consists of a simple glass tube that clamps onto a flat metal specimen. A rubber Oring
is used to create a watertight seal. The top is a rubber stopper with holes suitably sized for the reference &
counter electrodes. The base is polypropylene. The PTC1 comes with an SCE reference electrode & a graphite rod
counter electrode. The sample exposed in the PTC1 is 4.3 cm in diameter for an area of 14.6 cm2
.
Although neither the REAP paper or proposed method mentions it, you will also want to run your EIS tests in a
Faraday cage. A Faraday cage is a metal enclosure that shields the cell from noise. Shielding is required for 
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accurate EIS tests on very good coatings. A Faraday cage can be as simple as a cardboard box lined with aluminum
foil. Make sure that the Faraday cage does not come in contact with any of the cell electrodes. You must also
connect the black ground lead from the cell cable to the cage.
Needed Files
The experiments are standard techniques, which can be carried out using Gamry’s CMS100/105/300 software and
any of Gamry’s potentiostats. Note that Gamry’s FAS1 Femtostat hardware is very well suited for EIS on high
impedance coatings. The PC4 Potentiostat, while it is less sensitive, is also a good choice. The PC3, on the other
hand, may have difficulty making EIS measurements on thick coatings.
Independent of whether you are using CMS100/CMS300 with a PC3 or with a Femtostat, you will also want to get
REAP.SET and REAP.MDL from Gamry’s Web site. REAP.SET contains experimental setups that can be recalled
when setting up the experiments. REAP.MDL is the model file used in the analysis of the EIS data.
Experiments