Standard No.:	GB/T 43666-2024
English Name:	Corrosion of metals and alloys-Guidelines for corrosion test by electrochemical noise measurements
Chinese Name:	金属和合金的腐蚀 电化学噪声测量腐蚀试验导则
Chinese Classification:	H25    Metal chemical property test method
Professional Classification:	GB    National Standard
Source Content Issued by:	SAMR; SAC
Issued on:	2024-3-15
Implemented on:	2024-10-1
Status:	valid
Target Language:	English
File Format:	PDF
Word Count:	10000 words
Translation Price(USD):	300.0
Delivery:	via email in 1~3 business day

GB/T 43666-2024 Corrosion of metals and alloys - Guidelines for corrosion test by electrochemical noise measurements 1 Scope This document is intended to assist in corrosion testing by electrochemical noise measurement. It covers test procedures and analysis methods for reliable measurement of electrochemical noise for both uncoated and organically coated metal. 2 Normative references The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 8044 Corrosion of metals and alloys - Basic terms and definitions Note: GB/T 10123-2022, Corrosion of metals and alloys - Vocabulary (ISO 8044:2020, IDT) ISO 17475 Corrosion of metals and alloys - Electrochemical test methods - Guidelines for conducting potentiostatic and potentiodynamic polarization measurements Note: GB/T 24196-2009, Corrosion of metals and alloys - Electrochemical test methods - Guidelines for conducting potentiostatic and potentiodynamic polarization measurements (ISO 17475:2005, IDT) 3 Terms and definitions For the purposes of this document, the terms and definitions given in ISO 8044 and the following apply. 3.1 electrochemical noise; EN fluctuation typically at low frequencies (≤1 HZ) and low amplitude in current and potential generated by electrochemical reactions and other processes on the surface, for example, bubble evolution 3.2 electrochemical potential noise fluctuation in potential (typically in the range of µV to mV) of an electrode relative to a reference electrode or fluctuation in potential between two similar electrodes 3.3 electrochemical current noise fluctuation in current (typically in the range of nA to µA) of one electrode or between two electrodes 3.4 electrochemical noise resistance resistance obtained by dividing the standard deviation of potential noise by the standard deviation of current noise from the time record 3.5 power spectral density of potential PSDE power present in the potential noise as a function of frequency 3.6 power spectral density of current PSDI power present in the current noise as a function of frequency 3.7 electrochemical noise impedance Zn impedance determined as Zn = √(PSD_E/PSD_I ) where all terms are a function of frequency Note 1: The noise impedance is real and positive. 3.8 working electrode electronic conductor in contact with the electrolyte, made out of the investigated material Note 1: This definition differs from that of the same term given in ISO 8044:2015, 6.1.46, “test electrode in an electrochemical cell designed for polarization tests”. 3.9 auxiliary electrode electrode commonly used in applied polarization to balance the current passing to the working electrode Note 1: It is usually made from a non-corroding material. 3.10 Nyquist frequency frequency equal to one half of the sampling frequency (fs/2); maximum frequency about which information can be obtained from the sampled data 3.11 thermal noise noise resulting from thermal vibrations of electrons and charge carriers Note 1: Thermal noise is the absolute minimum of the noise that can be expected; also called Johnson noise. 3.12 shot noise noise due to the quantized nature of the charge carriers that move in very short times causing current peaks 3.13 dummy cell non-electrochemical cell with a well-defined noise level that usually does not deliberately generate noise above normal thermal noise levels 4 Principles 4.1 The source of EN in corrosion might result from partial faradaic currents, adsorption/desorption processes, surface coverage, and, in the case of localized corrosion, the initiation of pits, crevice corrosion, and mechanical effects from cracking and several other processes. Special care has to be taken as a variety of other sources not related to corrosion might cause fluctuations in current and potential. 4.2 Electrochemical noise can be measured potentiostatically, galvanostatically, or at the free corrosion potential (the various methods are described in Clause 5). Examples of two simple tests with EN measurements on aluminium during pitting corrosion and on organically coated carbon steel can be found in Annexes B and C. 4.3 Electrochemical noise data can be analysed in the time and/or frequency domains. Details of data analysis are described in Annex A. 5 Apparatus and measurement methods 5.1 Instrumentation 5.1.1 Accurate measurement of potential and current requires instruments that have appropriate input impedance (much higher than the system being measured in the case of potential and much lower in the case of current) and sensitivity (sufficient to minimize quantization noise). Suggestions are given in the following Clauses but these will not be sufficient for some systems. 5.1.2 Potential measuring instruments The instrument should have an input impedance of at least 109 ohm for bare metal and 1011 ohm for coated metal to minimize current drawn from the system during measurement. The higher input impedance might be necessary for very high impedance systems (e.g. for EN measurements with coated metals). The sensitivity and accuracy of the instrument should be sufficient to detect a change of 10 μV or lower for the typical range of 1 V. 5.1.3 Current measuring instruments The instrument should be capable of measuring current to a resolution of 10−9 A or better with a voltage burden of less than 1 mV. A low voltage burden ammeter is often termed a zero resistance ammeter (ZRA) in corrosion literature. Note 1: The low voltage burden is only required when the current measurement is made between two corroding working electrodes. Note 2: The voltage between the terminals, also known as a voltage drop or burden voltage. 5.1.4 Potentiostat Some measurement configurations use a potentiostat to control the potential of an electrode. The potentiostat shall have low noise characteristics, which should be tested by using a dummy cell with comparable properties to the system under investigation (see Clause 8 or Reference [1]). 5.1.5 Galvanostat Some measurement configurations use a galvanostat to apply a current to an electrode. The galvanostat shall have low noise characteristics, which should be tested by using a dummy cell with comparable properties to the system under investigation (see Clause 8 or Reference [1]). 5.1.6 Grounding, shielding, and isolation It is very important to ensure correct grounding and shielding of the measurement system. In particular, there should be a single well-defined connection to ground in order to avoid ground loops and to minimize induced interference. Isolated or differential measuring devices will commonly be required to avoid short-circuit connections to ground and ground loops, especially in plant monitoring conditions. 5.2 Measurement configurations Schematics of the most important EN measurement configurations can be seen in Figure 1. a) Potentiostatic current noise b) Galvanostatic potential noise c) Open-circuit potential noise d) Current noise at open-circuit potential e) Simultaneous current and potential noise Key 1——potentiostat (see 5.1.4) 2——current measurement device (see 5.1.3, implies connection to PC or other device for recording or analysis) 3——working electrode (WE) 4——reference electrode (RE) 5 auxiliary electrode (AE) 6——galvanostat (see 5.1.5) 7——potential measurement device (see 5.1.2, implies connection to PC or other device for recording or analysis) Figure 1 - Configurations for measurements