CN113820266B - Equivalent acceleration conversion method for galvanic corrosion of dissimilar metal materials - Google Patents
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Abstract
The invention discloses an equivalent acceleration conversion method for galvanic corrosion of dissimilar metal materials, which is based on the conversion principle of corrosion equivalent of single metal material to the conversion principle of contact galvanic corrosion equivalent of dissimilar metal material; the measurement parameters are selected, namely, according to an electrochemical principle, metal corrosion (including galvanic corrosion and the like) is mainly caused by electrochemical corrosion, electrons are lost from an anode to generate oxidation reaction, and electrons from a cathode generate reduction reaction; corrosion currentThe influence of the environment on metal corrosion can be accurately measured, and a strict equivalent relation is achieved; thus, the corrosive current is employed hereinEquivalent conversion between service environment and laboratory conditions is carried out as a measurement parameter; the invention can establish a feasible equivalent accelerated corrosion conversion relationship in laboratory conditions by taking the contact of dissimilar metal materials as a research object.
Description
Technical Field
The invention relates to an equivalent acceleration conversion method for galvanic corrosion of dissimilar metal materials, and belongs to the technical field of the equivalent of galvanic corrosion.
Background
The ocean environment is extremely complex, and the conditions of temperature, salinity, humidity and frost are different from sea area to sea area worldwide. According to practical experience, the tropical marine environment (high salt mist, high temperature, high humidity) accelerates the corrosion rate of marine equipment metallic materials and components. It is counted that the failure of marine equipment due to corrosion is up to more than 70%. However, aiming at the corrosion damage rule of the climate environment of a specific sea area, at present, each national institute is in a theoretical research stage, and no effective method exists. The GJB150A-2009 "environmental test method in military equipment laboratory" is a general environmental experiment program for acid salt fog and acid atmosphere chapter, and lacks the pertinence of corrosion and accumulated damage in specific marine environment. Therefore, scientific research has quite necessity to accurately simulate the problem of the corrosion damage effect of the environment on equipment metal materials under the existing laboratory conditions.
The corrosion test research conducted by the traditional simulation equipment service environment needs to consume a great deal of time, expense and the like, and the technology has a bottleneck. In order to obtain the corrosion loss law of equipment in a service environment in a short time, an equivalent accelerated corrosion conversion relation which is feasible in laboratory conditions is established, and further, the corrosion damage of the equipment in the service environment is converted into an equivalent accelerated environment spectrum which can be reproduced in a laboratory in an equivalent way, and the equivalent accelerated environment spectrum is effectively applied to engineering practice.
The environment acceleration method is a common and effective research method at present, and researchers at home and abroad have conducted researches to different degrees. Many achievements are achieved in the aspects of compiling accelerated environmental spectrums and accelerating corrosion equivalent research of marine equipment laboratories. Compared with foreign countries, domestic related researches are obviously lagged, and most of the related researches are in the primary research stage. There are also few research institutions and scholars who have conducted accelerated equivalence technology research to develop an environmental acceleration profile for an individual sea area.
According to the existing quantitative research and analysis about acceleration, a single metal material or composite material or coating is taken as a research object, the equivalent relation between the service environment and laboratory condition acceleration is established, for example, the patent number is CN108256139A, the patent name is a patent of a heterogeneous metal material combined structure acceleration environment spectrum preparation method, an environment conversion coefficient formula of a combined structure is deduced according to a single metal environment conversion coefficient principle, and an environment conversion coefficient database is established. Based on a simulation method, a galvanic corrosion model is established when dissimilar metals are contacted, information such as potential distribution, total current and the like of galvanic corrosion is obtained, the correctness of the galvanic corrosion model is verified, and a combined metal structure environment conversion coefficient database is supplemented. And selecting a typical dissimilar metal combined contact structure of the airplane for testing, and correcting an acceleration equivalent environment spectrum of the dissimilar metal combined structure according to the corrosion damage characterization quantity. Finally, a combined structure accelerated corrosion equivalent theory and an engineering method are constructed, and although the accelerated corrosion equivalent can be studied, a single metal material or a composite material or a coating is used as a research object; regarding the contact of dissimilar metal materials, it is very rare to study the relationship of acceleration equivalent in service environment and laboratory conditions. However, in the actual service environment of marine equipment, most of the marine equipment is in contact with dissimilar metal materials, and the marine equipment is not only self-corrosion of single metal materials, but also has acceleration effect of galvanic corrosion. The evaluation, simulation and test of galvanic corrosion of dissimilar metal materials are not only an important problem in research of corrosion disciplines, but also practical problems to be solved in marine equipment engineering application. Therefore, there is an urgent need to establish equivalent accelerated corrosion conversion relationships that are viable in laboratory conditions, with dissimilar metal materials in contact as the subject of investigation.
Disclosure of Invention
The technical problem to be solved by the invention is to provide an equivalent accelerated conversion method for galvanic corrosion of dissimilar metal materials, which can take the contact of dissimilar metal materials as a research object, establish a feasible equivalent accelerated corrosion conversion relationship in laboratory conditions and overcome the defects in the prior art.
The technical scheme of the invention is as follows: the method is characterized in that the method is based on a single metal material corrosion equivalent conversion principle, and is inferred to be equivalent conversion of dissimilar metal material contact galvanic corrosion, and the equivalent conversion of galvanic corrosion consisting of a pure anode and a pure cathode and galvanic corrosion consisting of a non-pure anode and a pure cathode is distinguished at the same time, and the specific conversion method is as follows:
I. based on the single metal material corrosion equivalent conversion principle;
(1) And (3) selecting measurement parameters: according to the electrochemical principle, the metal corrosion including galvanic corrosion is mainly caused by electrochemical corrosion, electrons are lost from an anode to generate oxidation reaction, and electrons from a cathode generate reduction reaction; corrosion current I c The influence of the environment on metal corrosion can be accurately measured, and a strict equivalent relation is achieved; thus, the corrosion current I is adopted c Equivalent conversion between service environment and laboratory conditions is carried out as a measurement parameter;
(2) Equivalent conversion principle: assuming an action time t of the equipment service environment, the metal electric quantity in the time t is as follows:
Q＝I c ·t(1)
due to the influence of service environment factors, the corrosion of metal is strong and weak, and the corrosion current I changes in a spectrum shape c Also over time; therefore, in the service environment, the corrosion electric quantity Q of the metal in the time t1 to t2 is expressed as an integral form by combining Faraday law:
in the formula (2), F is Faraday constant;
under laboratory conditions, the same metal component was tested from a selected accelerated environmental spectrum with a corrosion current of I' c The corrosion charge Q ' of the metal over the test time from t1' to t2' is expressed in integral as:
according to the corrosion loss equivalent principle, for the same metal material component, the corrosion electric quantity Q in the service environment condition is equal to the corrosion electric quantity Q' under the laboratory condition, so that the equivalent relation between the two environments can be established, namely:
to simplify the problem, the corrosion current I is c And I' c As a constant discussion, and assuming t=t1-t 2, t ' =t1 ' -t2', then equation (4) can be written as:
I c ·t＝I′ C ·t′(5)
from formula (5):
as can be seen from the formula (6), the corrosion current can be increased to I 'by changing the test conditions, including changing the temperature, humidity and salt mist' c Shortening the test time t1' to achieve the purpose of acceleration under laboratory conditions;
(3) Equivalent conversion coefficient
Order theFormula (6) can be rewritten as:
t′＝α·t(7)
alpha is defined as an equivalent calculation coefficient, after the equivalent damage of the environmental spectrum is converted, the test time is shortened by alpha times under the action of the laboratory accelerated environmental spectrum, and the aim of the corrosion damage acceleration test with the service environment and the like can be fulfilled;
whether for a single metal material or a dissimilar metal material in contact, the metal corrosion amount is always closely related to the corrosion current according to Faraday's law, so the equivalent conversion principle is applicable;
II. Equivalent acceleration conversion of galvanic corrosion of dissimilar metals
When two metals with different corrosion potentials are contacted with each other to form a galvanic couple, the metal material with lower corrosion potential is corroded by itself, and the anode is dissolved under the action of a short-circuit primary cell formed by contacting the metal material with high corrosion potential; according to the corrosion electrochemical principle, the galvanic cell formed by contacting the metal material with high corrosion potential is used for accelerating the self corrosion of the metal material with low corrosion potential, but not causing new corrosion; thus, galvanic corrosion, which is formed by contact of dissimilar metals relative to single metals, is corrosion that accelerates the anodic metal material itself;
in summary, the corrosion current I is generated when dissimilar metals contact each other to generate galvanic corrosion c Self-etching current I of anode equal to K times s The method comprises the following steps:
I c ＝K·I s (8)
in the formula (8), I c For corrosion current, I s Self-corrosion current before the metal anode is not coupled; k is a couple corrosion increasing effect, and the numerical value is related to environmental conditions including temperature, humidity and salt mist.
Therefore, α can be rewritten as:
in the formula (9), I c 、I s K is the corrosion current of the solution 1, the self-corrosion current before the metal anode is uncoupled, and factors related to environmental conditions including temperature, humidity and salt mist; i' c 、I′ s K' is the corrosion current of solution 2, the self-corrosion current before the metal anode is uncoupled, factors related to environmental conditions including temperature, humidity, salt spray;
a. galvanic corrosion of pure anode and pure cathode composition
After the dissimilar metals are contacted, the anodic metal mainly undergoes anodic oxidation dissolution reaction, and the depolarizer cathode reduction reaction on the surface of the anodic metal is slow enough to be able to performNeglecting; meanwhile, the cathode reduction reaction of the depolarizer is mainly carried out on the surface of the cathode metal, and the anodic oxidation dissolution reaction speed is negligibly low; corrosion current I c That is, the metal anode dissolution current of the corrosion couple anode and the current I measured in the external circuit of the contact corrosion couple g Equal;
I c ＝K·I s ＝I g (10)
in the formula (10), I g A current measured in an external circuit for contacting the corrosion couple; k is a couple corrosion increasing effect, and the numerical value is related to environmental conditions including temperature, humidity and salt mist;
therefore, the formula (9) can be rewritten as:
in the formula (11), I g The current measured in the external circuit of the contact corrosion couple for solution 1; i' g The current measured in the external circuit of the contact corrosion couple for solution 2;
b. galvanic corrosion of non-pure anode and pure cathode composition
Under the conditions that impurities are arranged on the surfaces of the anode and the cathode metal and the impurity content is not negligible, the cathode reduction reaction of a depolarizer on the surface of the anode metal is not negligible, and the speed of the cathode reduction reaction is controlled by diffusion; in this case, after the dissimilar metals are contacted, the anodic metal has a higher dissolution current density than the anodic current density measured in the external circuit of the contact corrosion couple, i.e. the corrosion current I is equal in the case of the anodic metal areas c Greater than the current I measured in the external circuit of the contact corrosion couple g ；
In the formula (12), A 1 Is the anode metal area; a is that 2 Is the cathode metal area;
therefore, the formula (9) can be rewritten as:
in summary, in the case of galvanic corrosion consisting of pure anode and pure cathode, the equivalent calculation coefficient α is the ratio of the currents measured in the external circuit of the contact corrosion galvanic couple in two different solutions or under ambient conditions; under the condition of galvanic corrosion consisting of a non-pure anode and a pure cathode, the equivalent calculation coefficient alpha is the ratio of self-corrosion currents before the metal anode is not coupled under two different solutions or environmental conditions; the equivalent conversion coefficient α is expressed as:
in the formula (14), a is the galvanic corrosion condition consisting of a pure anode and a pure cathode; b is the galvanic corrosion condition consisting of an impure anode and a pure cathode; i g 、I′ g The current measured in the external circuit of the contact corrosion couple for two different solutions or ambient conditions; i s 、I′ s Is a self-etching current before the metal anode is uncoupled in two different solutions or under ambient conditions.
Compared with the prior art, the equivalent acceleration conversion method of dissimilar metal material galvanic corrosion of the invention derives the conversion relation of galvanic corrosion generated by contact of dissimilar metal in service environment and laboratory environment, adopts electrochemical test method to measure self corrosion current and galvanic current, namely conversion coefficient undetermined item of contact of dissimilar metal in different environments to determine conversion coefficient a value, establishes conversion coefficient a database, establishes feasible equivalent acceleration corrosion conversion relation in laboratory condition, further converts corrosion damage equipping in service environment into equivalent acceleration environment spectrum which can be reproduced in laboratory, and effectively applies the equivalent acceleration environment spectrum to engineering practice, thus being capable of replacing corrosion test research developed by traditional simulation equipment service environment and avoiding consuming a great amount of time, cost and the like; meanwhile, a conversion coefficient a value is determined, a conversion coefficient a database is established, and a foundation is provided for compiling a laboratory acceleration environment spectrum.
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For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings, in which:
fig. 1 is a schematic view of the connection structure of the present invention.
Detailed Description
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be understood that the preferred embodiments are presented by way of illustration only and not by way of limitation.
Embodiment 1. As shown in FIG. 1, the method is characterized in that based on the principle of equivalent conversion of corrosion of a single metal material, the method is inferred to be equivalent conversion of galvanic corrosion of a dissimilar metal material in contact with the metal material, and the equivalent conversion of galvanic corrosion consisting of a pure anode and a pure cathode and galvanic corrosion consisting of a non-pure anode and a pure cathode is distinguished simultaneously, and the specific conversion method is as follows:
I. based on the single metal material corrosion equivalent conversion principle;
(1) And (3) selecting measurement parameters: according to the electrochemical principle, the metal corrosion including galvanic corrosion is mainly caused by electrochemical corrosion, electrons are lost from an anode to generate oxidation reaction, and electrons from a cathode generate reduction reaction; corrosion current I c The influence of the environment on metal corrosion can be accurately measured, and a strict equivalent relation is achieved; thus, the corrosion current I is adopted c Equivalent conversion between service environment and laboratory conditions is carried out as a measurement parameter;
(2) Equivalent conversion principle: assuming an action time t of the equipment service environment, the metal electric quantity in the time t is as follows:
Q＝I c ·t(1)
due to the influence of service environment factors, the corrosion of metal is strong and weak, and the corrosion current I changes in a spectrum shape c Also over time; therefore, under the service environment, faraday law is combinedThe corrosion capacity Q of the metal in the time t1 to t2 is expressed in integral form as:
in the formula (2), F is Faraday constant;
under laboratory conditions, the same metal component was tested from a selected accelerated environmental spectrum with a corrosion current of I' c The corrosion charge Q ' of the metal over the test time from t1' to t2' is expressed in integral as:
according to the corrosion loss equivalent principle, for the same metal material component, the corrosion electric quantity Q in the service environment condition is equal to the corrosion electric quantity Q' under the laboratory condition, so that the equivalent relation between the two environments can be established, namely:
to simplify the problem, the corrosion current I is c And I' c As a constant discussion, and assuming t=t1-t 2, t ' =t1 ' -t2', then equation (4) can be written as:
I c ·t＝I′ C ·t′(5)
from formula (5):
as can be seen from the formula (6), the corrosion current can be increased to I 'by changing the test conditions, including changing the temperature, humidity and salt mist' c Shortening the test time t1' to achieve the purpose of acceleration under laboratory conditions;
(3) Equivalent conversion coefficient
Order theCan be rewritten as:
t′＝α·t(7)
alpha is defined as an equivalent calculation coefficient, after the equivalent damage of the environmental spectrum is converted, the test time is shortened by alpha times under the action of the laboratory accelerated environmental spectrum, and the aim of the corrosion damage acceleration test with the service environment and the like can be fulfilled;
whether for a single metal material or a dissimilar metal material in contact, the metal corrosion amount is always closely related to the corrosion current according to Faraday's law, so the equivalent conversion principle is applicable;
II. Equivalent acceleration conversion of galvanic corrosion of dissimilar metals
When two metals with different corrosion potentials are contacted with each other to form a galvanic couple, the metal material with lower corrosion potential is corroded by itself, and the anode is dissolved under the action of a short-circuit primary cell formed by contacting the metal material with high corrosion potential; according to the corrosion electrochemical principle, the galvanic cell formed by contacting the metal material with high corrosion potential is used for accelerating the self corrosion of the metal material with low corrosion potential, but not causing new corrosion; thus, galvanic corrosion, which is formed by contact of dissimilar metals relative to single metals, is corrosion that accelerates the anodic metal material itself;
in summary, the corrosion current I is generated when dissimilar metals contact each other to generate galvanic corrosion c Self-etching current I of anode equal to K times s The method comprises the following steps:
I c ＝K·I s (8)
in the formula (8), I c For corrosion current, I s Self-corrosion current before the metal anode is not coupled; k is a couple corrosion increasing effect, and the numerical value is related to environmental conditions including temperature, humidity and salt mist.
Therefore, α can be rewritten as:
in the formula (9), I c 、I s K is the corrosion current of the solution 1, the self-corrosion current before the metal anode is uncoupled, and factors related to environmental conditions including temperature, humidity and salt mist; i' c 、I′ s K' is the corrosion current of solution 2, the self-corrosion current before the metal anode is uncoupled, factors related to environmental conditions including temperature, humidity, salt spray;
a. galvanic corrosion of pure anode and pure cathode composition
After the dissimilar metals are contacted, the anodic metal mainly performs anodic oxidation dissolution reaction, and the speed of the depolarizer cathode reduction reaction on the surface of the anodic metal is negligibly small; meanwhile, the cathode reduction reaction of the depolarizer is mainly carried out on the surface of the cathode metal, and the anodic oxidation dissolution reaction speed is negligibly low; corrosion current I c That is, the metal anode dissolution current of the corrosion couple anode and the current I measured in the external circuit of the contact corrosion couple g Equal;
I c ＝K·I s ＝I g (10)
in the formula (10), I g A current measured in an external circuit for contacting the corrosion couple; k is a couple corrosion increasing effect, and the numerical value is related to environmental conditions including temperature, humidity and salt mist;
therefore, the formula (9) can be rewritten as:
in the formula (11), I g The current measured in the external circuit of the contact corrosion couple for solution 1; i' g The current measured in the external circuit of the contact corrosion couple for solution 2;
b. galvanic corrosion of non-pure anode and pure cathode composition
Under the condition that impurities are arranged on the surfaces of the anode and the cathode metal and the impurity content is not negligible, removing impurities on the surface of the anode metalThe cathode reduction reaction of the polarizer is not negligible, and the cathode reduction reaction speed is controlled by diffusion; in this case, after the dissimilar metals are contacted, the anodic metal has a higher dissolution current density than the anodic current density measured in the external circuit of the contact corrosion couple, i.e. the corrosion current I is equal in the case of the anodic metal areas c Greater than the current I measured in the external circuit of the contact corrosion couple g ；
In the formula (12), A 1 Is the anode metal area; a is that 2 Is the cathode metal area;
therefore, the formula (9) can be rewritten as:
in summary, in the case of galvanic corrosion consisting of pure anode and pure cathode, the equivalent calculation coefficient α is the ratio of the currents measured in the external circuit of the contact corrosion galvanic couple in two different solutions or under ambient conditions; under the condition of galvanic corrosion consisting of a non-pure anode and a pure cathode, the equivalent calculation coefficient alpha is the ratio of self-corrosion currents before the metal anode is not coupled under two different solutions or environmental conditions; the equivalent conversion coefficient α is expressed as:
in the formula (14), a is the galvanic corrosion condition consisting of a pure anode and a pure cathode; b is the galvanic corrosion condition consisting of an impure anode and a pure cathode; i g 、I′ g The current measured in the external circuit of the contact corrosion couple for two different solutions or ambient conditions; i s 、I′ s Is a self-etching current before the metal anode is uncoupled in two different solutions or under ambient conditions.
Self-corrosion current I s Couple electricityStream I g The measurement and conversion factor a were measured as follows:
self-corrosion current I s And (3) measuring: respectively selecting a service environment and specific laboratory conditions, using an electrochemical workstation, adopting a classical three-electrode system, wherein a reference electrode is a saturated calomel electrode, measuring a material polarization curve, and acquiring and processing data to obtain self-corrosion current;
couple current I g And (3) measuring: respectively selecting a service environment and specific laboratory conditions, building a galvanic couple model, and acquiring and processing data by using an electrochemical workstation or a potentiostat to obtain galvanic couple current;
calculating a conversion coefficient alpha: according to the corrosion potential difference of two dissimilar metals, calculating an equivalent conversion coefficient alpha according to a formula (14), and on the basis, establishing an equivalent conversion coefficient alpha database of galvanic corrosion generated by contact of the dissimilar metals in a service environment and a laboratory environment.
The equivalent conversion coefficient is applied to the establishment of a laboratory acceleration environment spectrum, and the basic technical thought (see figure 1) is as follows:
step 1: collecting environmental data of equipment in service environment, including annual temperature, humidity, salt fog and condensation, and preparing an environmental spectrum of the equipment in service environment according to the basis of the existing literature research method; step 2: selecting a laboratory accelerated environment test mode and basic conditions; step 3: calculating the equivalent of the laboratory acceleration environment according to the conversion coefficient alpha of the dissimilar metal equivalent or a database, and compiling a laboratory acceleration environment spectrum; step 4: and respectively testing under the service environment spectrum and the laboratory acceleration environment spectrum, mutually verifying test results, and further optimizing a heterogeneous metal equivalent conversion relation algorithm and the laboratory acceleration environment spectrum.
Finally, it is noted that the above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications and equivalents may be made thereto without departing from the spirit and scope of the present invention, which is intended to be covered by the claims of the present invention.
Claims (3)
1. The method is characterized in that the method is based on a single metal material corrosion equivalent conversion principle, and is inferred to be equivalent conversion of dissimilar metal material contact galvanic corrosion, and the equivalent conversion of galvanic corrosion consisting of a pure anode and a pure cathode and galvanic corrosion consisting of a non-pure anode and a pure cathode is distinguished at the same time, and the specific conversion method is as follows:
I. based on the single metal material corrosion equivalent conversion principle;
(1) And (3) selecting measurement parameters: according to the electrochemical principle, the metal corrosion including galvanic corrosion is mainly caused by electrochemical corrosion, electrons are lost from an anode to generate oxidation reaction, and electrons from a cathode generate reduction reaction; corrosion current I c The influence of the environment on metal corrosion can be accurately measured, and a strict equivalent relation is achieved; thus, the corrosion current I is adopted c Equivalent conversion between service environment and laboratory conditions is carried out as a measurement parameter;
(2) Equivalent conversion principle: assuming an action time t of the equipment service environment, the metal electric quantity in the time t is as follows:
Q＝I c ·t(1)
due to the influence of service environment factors, the corrosion of metal is strong and weak, and the corrosion current I changes in a spectrum shape c Also over time; therefore, in the service environment, the corrosion electric quantity Q of the metal in the time t1 to t2 is expressed as an integral form by combining Faraday law:
in the formula (2), F is Faraday constant;
under laboratory conditions, the same metal component was tested from a selected accelerated environmental spectrum with a corrosion current of I' c The corrosion charge Q ' of the metal over the test time from t1' to t2' is expressed in integral as:
according to the corrosion loss equivalent principle, for the same metal material component, the corrosion electric quantity Q in the service environment condition is equal to the corrosion electric quantity Q' under the laboratory condition, so that the equivalent relation between the two environments can be established, namely:
to simplify the problem, the corrosion current I is c And I' c As a constant discussion, and assuming t=t1-t 2, t ' =t1 ' -t2', then equation (4) can be written as:
I c ·t＝I′ C ·t′(5)
from formula (5):
as can be seen from the formula (6), the corrosion current can be increased to I 'by changing the test conditions, including changing the temperature, humidity and salt mist' c Shortening the test time t1' to achieve the purpose of acceleration under laboratory conditions;
(3) Equivalent conversion coefficient
Order theFormula (6) can be rewritten as:
t′＝α·t(7)
alpha is defined as an equivalent calculation coefficient, after the equivalent damage of the environmental spectrum is converted, the test time is shortened by alpha times under the action of the laboratory accelerated environmental spectrum, and the aim of the corrosion damage acceleration test with the service environment and the like can be fulfilled;
whether for a single metal material or a dissimilar metal material in contact, the metal corrosion amount is always closely related to the corrosion current according to Faraday's law, so the equivalent conversion principle is applicable;
II. Equivalent acceleration conversion of galvanic corrosion of dissimilar metals
When two metals with different corrosion potentials are contacted with each other to form a galvanic couple, the metal material with lower corrosion potential is corroded by itself, and the anode is dissolved under the action of a short-circuit primary cell formed by contacting the metal material with high corrosion potential; according to the corrosion electrochemical principle, the galvanic cell formed by contacting the metal material with high corrosion potential is used for accelerating the self corrosion of the metal material with low corrosion potential, but not causing new corrosion; thus, galvanic corrosion, which is formed by contact of dissimilar metals relative to single metals, is corrosion that accelerates the anodic metal material itself;
in summary, the corrosion current I is generated when dissimilar metals contact each other to generate galvanic corrosion c Self-etching current I of anode equal to K times s The method comprises the following steps:
I c ＝K·I s (8)
in the formula (8), I c For corrosion current, I s Self-corrosion current before the metal anode is not coupled; k is a couple corrosion increasing effect, and the numerical value is related to environmental conditions including temperature, humidity and salt mist;
therefore, α can be rewritten as:
in the formula (9), I c 、I s K is the corrosion current of the solution 1, the self-corrosion current before the metal anode is uncoupled, and factors related to environmental conditions including temperature, humidity and salt mist; i' c 、I′ s K' is the corrosion current of solution 2, the self-corrosion current before the metal anode is uncoupled, factors related to environmental conditions including temperature, humidity, salt spray;
a. galvanic corrosion of pure anode and pure cathode composition
After the dissimilar metals are contacted, the anodic metal mainly performs anodic oxidation dissolution reaction, and the speed of the depolarizer cathode reduction reaction on the surface of the anodic metal is negligibly small; meanwhile, the cathode reduction reaction of the depolarizer is mainly carried out on the surface of the cathode metal, and the anodic oxidation dissolution reaction speed is negligibly low; corrosion current I c That is, the metal anode dissolution current of the corrosion couple anode and the current I measured in the external circuit of the contact corrosion couple g Equal;
I c ＝K·I s ＝I g (10)
in the formula (10), I g A current measured in an external circuit for contacting the corrosion couple; k is a couple corrosion increasing effect, and the numerical value is related to environmental conditions including temperature, humidity and salt mist;
therefore, the formula (9) can be rewritten as:
in the formula (11), I g The current measured in the external circuit of the contact corrosion couple for solution 1; i' g The current measured in the external circuit of the contact corrosion couple for solution 2;
b. galvanic corrosion of non-pure anode and pure cathode composition
Under the conditions that impurities are arranged on the surfaces of the anode and the cathode metal and the impurity content is not negligible, the cathode reduction reaction of a depolarizer on the surface of the anode metal is not negligible, and the speed of the cathode reduction reaction is controlled by diffusion; in this case, after the dissimilar metals are contacted, the anodic metal has a higher dissolution current density than the anodic current density measured in the external circuit of the contact corrosion couple, i.e. the corrosion current I is equal in the case of the anodic metal areas c Greater than the current I measured in the external circuit of the contact corrosion couple g ；
In the formula (12), A 1 Is the anode metal area; a is that 2 Is the cathode metal area;
therefore, the formula (9) can be rewritten as:
in summary, in the case of galvanic corrosion consisting of pure anode and pure cathode, the equivalent calculation coefficient α is the ratio of the currents measured in the external circuit of the contact corrosion galvanic couple in two different solutions or under ambient conditions; under the condition of galvanic corrosion consisting of a non-pure anode and a pure cathode, the equivalent calculation coefficient alpha is the ratio of self-corrosion currents before the metal anode is not coupled under two different solutions or environmental conditions; the equivalent conversion coefficient α is expressed as:
in the formula (14), a is the galvanic corrosion condition consisting of a pure anode and a pure cathode; b is the galvanic corrosion condition consisting of an impure anode and a pure cathode; i g 、I′ g The current measured in the external circuit of the contact corrosion couple for two different solutions or ambient conditions; i s 、I′ s Is a self-etching current before the metal anode is uncoupled in two different solutions or under ambient conditions.
2. The equivalent accelerated conversion method of dissimilar metal material galvanic corrosion according to claim 1, wherein: self-corrosion current I s Couple current I g The measurement and conversion coefficient α were measured as follows:
self-corrosion current I s And (3) measuring: respectively selecting service environment and specific laboratory conditions, using an electrochemical workstation, adopting a classical three-electrode system, wherein a reference electrode is a saturated calomel electrode, measuring a material polarization curve, collecting and processing data to obtain self-corrosionEtching current;
couple current I g And (3) measuring: respectively selecting a service environment and specific laboratory conditions, building a galvanic couple model, and acquiring and processing data by using an electrochemical workstation or a potentiostat to obtain galvanic couple current;
calculating a conversion coefficient alpha: according to the corrosion potential difference of two dissimilar metals, calculating an equivalent conversion coefficient alpha according to a formula (14), and on the basis, establishing an equivalent conversion coefficient alpha database of galvanic corrosion generated by contact of the dissimilar metals in a service environment and a laboratory environment.
3. The equivalent accelerated conversion method of dissimilar metal material galvanic corrosion according to claim 1, wherein: the equivalent conversion coefficient is applied to the establishment of a laboratory acceleration environment spectrum, and the basic steps are as follows:
step 1: collecting environmental data of equipment in service environment, including annual temperature, humidity, salt fog and condensation, and preparing an environmental spectrum of the equipment in service environment according to the basis of the existing literature research method;
step 2: selecting a laboratory accelerated environment test mode and basic conditions;
step 3: calculating the equivalent of the laboratory acceleration environment according to the conversion coefficient alpha of the dissimilar metal equivalent or a database, and compiling a laboratory acceleration environment spectrum;
step 4: and respectively testing under the service environment spectrum and the laboratory acceleration environment spectrum, mutually verifying test results, and further optimizing a heterogeneous metal equivalent conversion relation algorithm and the laboratory acceleration environment spectrum.
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