GB/T 40299-2021 English PDF (GBT40299-2021)

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GB/T 40299-2021: Corrosion of metals and alloys -- Conventions applicable to electrochemical measurements in corrosion testing
GB/T 40299-2021
Corrosion of metals and alloys - Conventions applicable to electrochemical measurements in corrosion testing
ICS 77.060
CCSH25
National Standards of People's Republic of China
Metal and alloy corrosion corrosion test electrochemistry
Conventions applicable to measurement methods
(ISO 17474.2012, IDT)
Released on 2021-08-20
2022-03-01 implementation
State Administration for Market Regulation
Issued by the National Standardization Management Committee
Metal and alloy corrosion corrosion test electrochemistry
Conventions applicable to measurement methods
Warning. This document is not intended to solve all safety issues (if any) related to its use. The user of this document is responsible
Determine appropriate safety and health practices, and determine the applicability of regulatory restrictions before use.
1 Scope
This document specifies the common methods for reporting and displaying electrochemical corrosion data, including potential, current density, electrochemical impedance and the above data.
Graphical representation of data.
2 Normative references
The content of the following documents constitutes an indispensable clause of this document through normative references in the text. Among them, dated quotations
Only the version corresponding to the date is applicable to this document; for undated reference documents, the latest version (including all amendments) is applicable to
This document.
ISO 8044 Corrosion of metals and alloys basic terms and definitions (Corrosionofmetalsandaloys-Basicterms
anddefinitions)
3 Terms and definitions
The terms and definitions defined in ISO 8044 apply to this document.
4 Significance and use
This document provides guidance for the reporting, display and drawing of electrochemical corrosion data, and proposes suggestions on symbols and conventions. Pick
Using the method specified in this document, the corrosion electrochemical data can be reported in a standard format, which is convenient to compare the data obtained in different laboratories or at different time points.
data. The recommendations given in this document can be used to record and report corrosion data obtained from electrochemical tests, which include potentiostatic electrodes.
Electrochemical and dynamic potential polarization, polarization resistance, electrochemical impedance, galvanic corrosion and open circuit potential measurement.
5 Electrode potential symbol
5.1 In this document, the positive direction of the electrode potential represents an increase in the oxidation condition of the electrode surface in question. Positive direction also means precious metal side
Because the corrosion potential of most precious metals (such as platinum) is more positive than that of other non-passivated metals. On the other hand, the negative direction means that the electrode surface is still
The original condition is enhanced, and it also indicates the direction of the active metal, because the corrosion potential of the active metal (such as potassium) is more negative than other commonly used metals.
In 1953, the International Union of Theoretical and Applied Chemistry unanimously adopted this convention as the standard practice for characterizing electrode potential.
5.2 In order to measure the potential of the working electrode in the aqueous electrolyte solution, the experimental device consists of a potentiometer, a reference electrode, an electrolytic cell, and an electrolyte, see
figure 1.If the reading of the potentiometer is negative, the potential of the working electrode is negative relative to the reference electrode. Conversely, if the potentiometer reading is positive, the working electrode
The potential is positive relative to the reference electrode.
If the polarity of the measuring instrument is in doubt, simple verification can be carried out in the following way. Connect the measuring instrument to a dry battery, which will
Connect the wire connecting the reference electrode to the negative terminal of the battery, and connect the wire connecting the working electrode to the positive terminal of the battery. The pointer of the potentiometer should be positive
The potential direction is shifted. For example, a silver/silver chloride electrode (KCl(sat.)/AgCl/Ag.sat.SSCE) saturated with KCl is used as a reference electrode to measure
The corrosion potential of magnesium or zinc in 1mol/L NaCl solution should be negative.
To ensure the accuracy of potential measurement, the input impedance of the potentiometer should be greater than 1011Ω.
6 Current and current density symbols
The current and current density symbols recommended in this document, the anode and cathode values are designated as positive and negative, respectively. When plotting potential and current density
In the logarithmic relationship diagram, only the absolute value of the cathode current density can be drawn. In the logarithmic chart, if the cathode value and the anode value exist at the same time,
A clear distinction should be made between the cathode value and the anode value.
7 Polarization data representation
7.1 Symbols
This document recommends the use of standard mathematical plots to represent corrosion electrochemical data. In this mapping method, the positive value should be drawn in the vertical position
In the area formed by above the origin of the mark (y-axis) and to the right of the origin of the abscissa (x-axis). In a logarithmic chart, the abscissa value increases from left to right,
The ordinate value increases from bottom to top.
7.2 Current density-potential diagram
This document recommends that when plotting current density and potential data, the ordinate represents the current density and the abscissa represents the potential. In current density
In the degree-potential diagram, the current density can be plotted on the linear or logarithmic axis. Usually, the logarithmic chart is used to display a wide range of current density data and table
Show Tafel (Tafel) relationship. The linear graph is used to study the situation where the current density or potential range is very small, or to evaluate the current density from the positive
The case where the pole becomes a partial area of the cathode. The linear graph is also used to determine the polarization resistance Rp. Polarization resistance Rp is defined as the corrosion potential Ecor
The reciprocal of the slope of the current density-potential curve. The relationship between the polarization resistance Rp and the corrosion current density icor is as shown in formula (1) [2], [3].
The solid line in Figure 2 is the relationship curve of the current density i near the corrosion potential Ecor to the potential E, where the corrosion potential Eco is
The reciprocal of the slope of the same curve is determined as the polarization resistance Rp.
7.3 Relative value of potential
On the graph showing the electrode potential, the conversion relationship between the indicated potential value and the standard hydrogen electrode (SHE) should be marked. Recommended Use
The format of "E(V)vs.1MKCl(1MKCl/AgCl/Ag)" indicates the reference electrode used. The electrode potential can be plotted on the abscissa
The scale value of the upper and bottom abscissas can be displayed relative to the value of the reference electrode used, and the scale value of the top abscissa can be displayed relative to the standard hydrogen
Electrode (SHE) conversion value. If the latter is not displayed, according to Appendix A, the conversion relationship shown in equation (2) can be used to perform
Conversion.
7.4 Unit
The recommended potential unit is volts (V). If the potential range is relatively small, millivolts (mV) or microvolts (μV) can be used.
The international standard unit of current density is ampere per square meter (A/m2) or ampere per square centimeter (A/cm2), or milliampere per square meter
Centimeters (mA/cm2), microamperes per square centimeter (μA/cm2).
7.5 Example of polarization curve
The polarization curve of the sample drawn by the above recommended method is shown in Figure 2~Figure 6.Figures 3 and 4 respectively show the anode activation line
It is a schematic curve of activation-passivation transition behavior. Figure 5 and Figure 6 are the measured anode polarization of 430 stainless steel (UNS43000)
Data curve [4] and measured cathodic polarization curve of 2024-T3 aluminum alloy [5]. The function of Figure 3 and Figure 4 is to illustrate the use of corrosion electrochemical
Learn the location of the points discussed in the test data. The function of Figure 5 and Figure 6 is to show how to draw various types of electrodes according to this document.
化 curve.
8 Representation of electrochemical impedance data
8.1 Overview
The two graphs commonly used to represent electrochemical impedance data are the Nyquist graph and the Bode graph. A simple electricity
The equivalent circuit of the pole system is shown in Figure 7.
According to the convention, impedance Z is defined as.
The magnitude or modulus of impedance is defined as Z = ReZ 2 ImZ 2, for the equivalent circuit shown in Figure 7, the imaginary part of the impedance table
Shown as.
ImZ=
2πfC
(-j) (4)
Where.
f ---frequency, in Hertz (Hz), where the angular frequency ω=2πf, in radians per second;
C ---Capacitance, the unit is Faraday (F).
The phase angle θ is defined as.
θ=arctan(-ImZ/ReZ) (5)
8.2 Nyquist diagram (complex plane)
8.2.1 Plot the real part of the impedance on the abscissa and the negative value of the imaginary part on the ordinate. The positive of the real part of the impedance
The value is drawn on the right side of the origin parallel to the abscissa, and the negative value of the imaginary component of the impedance is drawn on the upper side of the origin parallel to the ordinate.
8.2.2 Figure 8 shows the Nyquist diagram of the equivalent circuit (Figure 7). The frequency response of the data is not shown on this type of graph
Indeed displayed. The frequency of selected data points can also be annotated directly, as shown in Figure 8.The magnitude of the impedance is the distance between the data point and the origin.
Higher frequency data points are usually located near the origin, while lower frequency points are far away from the origin.
8.2.3 The recommended unit for the two coordinate axes is ohm square centimeter (Ω·cm2). The impedance value in Ω·cm2 can be measured by
The impedance value of is multiplied by the exposed area of the sample to obtain. For the equivalent circuit of resistors, capacitors or virtual components, the area is assumed to be 1cm2.about
The equivalent circuit of Figure 7, in the impedance data shown in Figure 8, the distance from the origin to the first (high frequency) intersection of the data curve and the abscissa corresponds to
Rs, the distance from the first (high frequency) intersection of the data curve and the abscissa to the second (low frequency) intersection corresponds to Rp.
8.3 Bode diagram
8.3.1 The electrochemical impedance data can be represented by a Bode diagram, which consists of a set of two types of curves, one of which is.
The abscissa is the logarithm of the frequency base 10, and the ordinate is the logarithm of the impedance magnitude or modulus |Z| base 10.The right side of the origin is the frequency
The value above the origin is the impedance modulus value, and the origin can be selected at the appropriate non-zero value of the impedance modulus and frequency.
8.3.2 Another type of curve mentioned in 8.3.1 is. plot the logarithm of the frequency with a base of 10 on the abscissa, and line it on the ordinate
The phase angle or phase shift is plotted. The negative value of the phase angle increases and is plotted downward along the ordinate, and the capacitor phase angle is plotted at -90°.
8.3.3 Figure 9a) and Figure 9b) show a set of typical drawing formats for the equivalent circuit model shown in Figure 7.Frequency-independent high-frequency impedance
The value corresponds to Rs. The frequency-independent low-frequency impedance value corresponds to Rs Rp. The difference between the low-frequency impedance value and the high-frequency impedance value corresponds to
Rp. These resistances are the same as those shown in Figure 8.
8.3.4 The unit of frequency in Figure 9 is Hertz (Hz) or cycles per second or radians per second (rad/s). The unit of impedance modulus is ohm square centimeter
Meter (Ω·cm2). The impedance per unit area is obtained by multiplying the measured impedance by the exposed area of the sample. The unit of phase angle is degree or
Radian, the former is more commonly used.