ISO 17463-2022 pdf free download – Paints and varnishes — Guidelines for the determination of anticorrosive properties of organic coatings by accelerated cyclic electrochemical technique.|
4.4 Potential relaxation
The purpose of the relaxation process is to allow the formation of a new stable equilibrium before thenext ElS measurement is performed.By recording the potential during the relaxation process, valuableadditional information about the coating and the coating-metal interface can be obtained.
5 Apparatus
Use the electrochemical equipment specified in IS0 16773-2.
6 Specimens
6.1Samples preparation
Proper preparation and preconditioning of coated specimens is critical for successful and reliableexperimental data.
6.2 Environmental control
The coating should be applied and cured in accordance with the manufacturer’s recommendationunless otherwise agreed upon between the parties involved.The film thickness should be as uniform aspossible.The exact film thickness should be measured and reported (e.g. in accordance with ISO 2808).Temperature and humidity control during the application, curing, conditioning and measurement oforganic coatings is crucial for a proper determination of the coating resistance.
For reliable measurements, temperature controlshould be equal to or better than±1 °C.For conditioningprior to measurement, an accuracy of ±2 °C is sufficient for most cases. Each specimen should be keptunder controlled conditions in order to prevent post-curing, degradation or anyunintended irreversiblemodification of the coating.
The temperature of the specimens during measurements should be maintained constant towithin 2°C, preferably within±1°C, at 23 °C, if not otherwise specified.Relative values for comparisonbetween specimens outside these guidelines are acceptable if all the specimens are run under the sameconditions. When the coating capacitance is the main parameter of interest, control of relative humidityduring specimen conditioning is very important. To ensure accurate conditioning,the humidity shouldbe (50 ±5) % in accordance with lso 327o, if not otherwise agreed.
6.3 Number of specimens and repeatability of results
Coatings are materials with certain inherent properties: holidays,inhomogeneous film thickness,and non-uniform distribution of pigments,fillers and other constituents. It is therefore necessaryto test more than one panel. In most cases, a minimum of three replicate specimens is necessary forreliable results. It should be checked whether the uniformity between the different specimen plates issufficient. It is quite common to find repeatability better than 10 % between the capacitance of replicate specimens, but it depends on the type of coating and the conditions of measurement.More replicatesmight be necessary to overcome uniformity problems.
Such checks should be the responsibility of the operator and should also be agreed between the partiesinvolved.
Specimens undergoing a rapid change, caused by weathering or other effects producing degradation,can show a larger fluctuation and therefore a lower repeatability.
7 Procedure
7.1 EIS measurement
Perform the ElS measurement as specified in ISO 16773-2.
7.2Cathodic polarization
Set a more negative d.c. potential (see Figure 1) that allows the hydrolysis of the water at the pH ofthe electrolyte e.g. approximately -1 v (SCE [saturated calomel electrode]) at pH 7.Additionally, thispotential should be fixed depending on the impedance of the coating; the larger it is the larger should bethe magnitude of the applied cathodic potential. In general, potentials are applied in the range of -2 vto -4 V.
The cathodic polarization time varies depending on the quality of the coating.For high quality coatingswith long term anticorrosive properties polarization time is typically between 20 min and 60 min.
7.3Relaxation process
Disconnect the potentiostat and measure the relaxation potential over the time. The time is typicallybetween 160 min and 180 min.
lf the time of relaxation is too short, the equilibrium will not be reached and ElS measurement istherefore not valid. If this time is too long, the system will evolve due to the migration of ions and theelectrochemical reactions at the metallic substrate.
The study of the potential relaxation over time can provide useful information about the quality of thecoating system, e.g.whether the cathodic reaction producing hydrogen (H2) has taken place during thepolarization. Hydrogen production can indicate a poor coating quality.
For interpretation of the plots,see References [3] and [6].
7.4Number of cycles
The cycle involving cathodic polarization/relaxation/EIS can be repeated either up to the degradationof the coating or it is possible to apply a given number of cycles.The number of cycles commonly usedis 6.If no differences can be detected with 6 cycles, their number should be increased.ISO 17463 pdf download.