CN113820266A - 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 equivalent conversion principle of corrosion of a single metal material and is used for converting the equivalent of the galvanic corrosion of the dissimilar metal materials in contact with each other; the measurement parameter is selected according to the electrochemical principle that metal corrosion (including galvanic corrosion and the like) is mainly caused by electrochemical corrosion, the anode loses electrons to generate oxidation reaction, and the cathode obtains electrons to generate reduction reaction; corrosion current
The influence of the environment on the metal corrosion can be measured accurately, and a strict equivalent relation exists; thus, corrosion current is used herein
Between the environment of service and the laboratory conditions as a measurement parameterEquivalent conversion of (2); the invention can take the contact of dissimilar metal materials as a research object and establish the equivalent accelerated corrosion conversion relation which is feasible in laboratory conditions.
Description
Technical Field
The invention relates to an equivalent acceleration conversion method for galvanic corrosion of dissimilar metal materials, belonging to the technical field of equivalent of galvanic corrosion.
Background
The marine environment is extremely complex, and the temperature, salinity, humidity and frost conditions of various sea areas are different. According to practical experience, tropical marine environments (high salt spray, high temperature, high humidity) accelerate the corrosion rate of metallic materials and components of marine equipment. According to statistics, the failure rate of marine equipment caused by corrosion is up to more than 70%. However, according to the law of corrosion damage of the climate environment in a specific sea area, various domestic research institutes are in the theoretical research stage, and no effective method exists. The section of acidic salt spray and acidic atmosphere of GJB150A-2009 laboratory environmental test method for military equipment belongs to a general environmental test program, and lacks pertinence to corrosion accumulated damage in a specific marine environment. Therefore, scientific research has a great necessity for accurately simulating the corrosion damage effect of the environment on the equipment metal material under the existing laboratory conditions.
The traditional corrosion test research carried out by simulating the service environment of equipment needs to consume a great deal of time, expenditure and the like, and the technology has a bottleneck. In order to obtain the corrosion loss rule of the equipment in the service environment in a short time, a feasible equivalent accelerated corrosion conversion relation in a laboratory condition is established, further, the corrosion damage of the equipment in the service environment is converted into an equivalent accelerated environment spectrum which can be reproduced in the laboratory in an equivalent manner, and the equivalent accelerated environment spectrum is effectively applied to engineering practice.
The environmental acceleration method is a common and effective research method at present, and researchers at home and abroad develop researches in different degrees. In China, many achievements are made in the aspects of establishment of an accelerated environment spectrum of a marine equipment laboratory and research on accelerated corrosion equivalence. Compared with foreign countries, the related research in China is obviously lagged, and most of the related research is in the initial research stage. A few research institutions and scholars also carry out accelerated equivalent technical research, and the test aiming at individual sea areas is compiled to be an environmental acceleration spectrum.
For the existing accelerated quantitative research and analysis, a single metal material or a composite material or a coating is used as a research object to establish an accelerated equivalent relationship between a service environment and a laboratory condition, for example, a patent with the patent number "CN 108256139A" and the patent name "an accelerated environment spectrum compiling method for a dissimilar metal material combined structure", and the method deduces a combined structure environment conversion coefficient formula according to the single metal environment conversion coefficient principle to establish an environment conversion coefficient database. Based on a simulation method, a galvanic corrosion model is established when dissimilar metals are in contact, 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. Selecting a typical dissimilar metal combined contact structure of an airplane for testing, and correcting an accelerated equivalent environment spectrum of the dissimilar metal combined structure according to the corrosion damage characterization quantity. Finally constructing a theory and an engineering method of accelerated corrosion equivalence of the combined structure, wherein although the research on accelerated corrosion equivalence can be carried out, the theory and the engineering method finally take a single metal material or a composite material or a coating as a research object; regarding the contact of dissimilar metal materials as a research object, it is very rare to research the acceleration equivalent relationship between the service environment and the laboratory conditions. However, in the actual service environment of marine equipment, most of the marine equipment is in the condition that dissimilar metal materials are contacted with each other, not only the corrosion of a single metal material is caused, but also the acceleration effect of galvanic corrosion exists. The evaluation, simulation and test of galvanic corrosion of dissimilar metal materials are not only an important problem in the research of the corrosion subject, but also a practical problem to be solved in the marine equipment engineering application. Therefore, there is an urgent need to establish equivalent accelerated corrosion conversion relationship that is feasible in laboratory conditions by using dissimilar metal materials as research objects to be contacted.
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 establish a feasible equivalent accelerated corrosion conversion relation in a laboratory condition by taking the contact of dissimilar metal materials as a research object, and can overcome the defects of the prior art.
The technical scheme of the invention is as follows: a equivalent acceleration conversion method for galvanic corrosion of dissimilar metal materials is based on the principle of equivalent conversion of corrosion of a single metal material, the equivalent conversion of the galvanic corrosion of the dissimilar metal materials in contact is inferred, and the equivalent conversion of the galvanic corrosion consisting of a pure anode and a pure cathode and the equivalent conversion of the galvanic corrosion consisting of a non-pure anode and a pure cathode are distinguished at the same time, and the specific conversion method comprises the following steps:
I. based on the principle of equivalent conversion of single metal material corrosion;
(1) selecting measurement parameters: as known from the electrochemical principle, metal corrosion (including galvanic corrosion and the like) is mainly caused by electrochemical corrosion, the anode loses electrons to generate an oxidation reaction, and the cathode obtains the electrons to generate a reduction reaction. Corrosion current IcThe influence of the environment on the metal corrosion can be measured accurately, and a strict equivalent relation exists; thus, corrosion current I is used hereincAnd performing equivalent conversion between a service environment and a laboratory condition as a measurement parameter.
(2) Equivalent conversion principle: assuming the action time t of the service environment of the equipment, the metal electric quantity in the time t is as follows:
Q＝Ic·t (1)
due to the influence of service environment factors, the corrosion of metal is that the time intensity changes in a spectrum shape, and the corrosion current IcAlso over time; therefore, under the service environment, in combination with faraday's law, the corrosion electric quantity Q of the metal in the time from t1 to t2 can be expressed in the form of integral:
in the formula (2), F is a Faraday constant.
Under laboratory conditions, the same metal component was tested by a selected accelerated environmental spectrum, with a corrosion current of I'cThe corrosion charge Q ' of the metal over the test time t1 ' to t2 ' can be expressed in the form of an integral:
according to the corrosion loss equivalence 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, and the equivalent relation under two environments can be established, namely:
to simplify the problem, the corrosion current I is adjustedcAnd l'cAs a constant discussion, and assuming t is t1-t2, t ' is t1 ' -t2 ', equation (4) can be written as:
Ic·t＝I′C·t′ (5)
from formula (5):
from the formula (6), it is found that the corrosion current I 'can be increased by changing the test conditions, for example, the temperature, humidity, salt spray, etc'cThe test time t 1' is shortened, and the aim of accelerating under the laboratory condition is achieved;
(3) equivalent conversion factor
Order to
Equation (6) may be rewritten as:
t′＝α·t (7)
alpha is defined as an equivalent conversion coefficient, after the equivalent conversion of the environmental spectrum for equivalent damage, the test time is shortened by alpha times under the action of the laboratory accelerated environmental spectrum, and the purpose of the accelerated test of the corrosion damage of the service environment and the like can be realized;
no matter a single metal material or a contacted dissimilar metal material is used, the metal corrosion amount is always closely related to the corrosion current according to Faraday's law, so the equivalent conversion principle is used;
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 couple, the metal material with lower corrosion potential is corroded by the metal material, and the anode is dissolved under the action of a short-circuited galvanic cell formed by the metal material with higher corrosion potential; according to the principle of corrosion electrochemistry, a galvanic cell formed by contacting a metal material with high corrosion potential essentially accelerates the self corrosion of the metal material with low corrosion potential, but does not cause new corrosion; therefore, galvanic corrosion caused by contact of dissimilar metals is accelerated in the corrosion of the anode metal material itself, as compared with a single metal;
as described above, the corrosion current I when galvanic corrosion occurs in contact with dissimilar metalscSelf-corrosion current I of the anode equal to K timessNamely:
Ic＝K·Is (8)
in the formula (8), IcFor corrosion current, IsSelf-corrosion current for metal anodes (not before coupling); k is the galvanic corrosion increasing effect, and the numerical value is related to the environmental conditions (temperature, humidity, salt fog and the like).
Thus, α can be rewritten as:
in the formula (9), Ic、IsK is the corrosion current of the solution 1, the self-corrosion current of the metal anode (before coupling), and the factors related to the environmental conditions (temperature, humidity, salt fog, and the like); i'c、I′sK' is the corrosion current of the solution 2, the self-corrosion current of the metal anode (before coupling), and the factors related to the environmental conditions (temperature, humidity, salt fog, etc.);
a. galvanic corrosion of pure anode and pure cathode
After the dissimilar metals are contacted, the anodic metal mainly undergoes an anodic oxidation (dissolution) reaction, on the surface thereofThe speed of the cathode reduction reaction of the upper depolarizer is negligibly small; meanwhile, the cathodic reduction reaction of the depolarizer is mainly performed on the surface of the cathode metal, and the anodic oxidation (dissolution) reaction rate is negligibly small. Corrosion current IcI.e. the dissolution current of the metal anode corroding the anode of the galvanic couple and the current I measured in the external circuit contacting the corroding galvanic couplegEqual;
Ic＝K·Is＝Ig (10)
in the formula (10), IgIs the current measured in an external circuit contacting the corroding couple; k is a galvanic corrosion increase effect, and the numerical value is related to environmental conditions (temperature, humidity, salt fog and the like);
therefore, equation (9) can be rewritten as:
in the formula (11), IgThe current measured in the external circuit of the contact corrosion couple of solution 1; i'gThe current measured in the external circuit of the contact corrosion couple of solution 2;
b. galvanic corrosion of non-pure anodes and pure cathodes
Impurities exist on the surfaces of the anode metal and the cathode metal, and under the condition that the impurity content is not negligible, the cathode reduction reaction of the depolarizer on the surface of the anode metal is not negligible, and the cathode reduction reaction speed is controlled by diffusion; in this case, the dissolution current density of the anode metal after contact with the dissimilar metal is larger than the anode current density measured in the external circuit contacting the corrosion couple, that is, the corrosion current I when the areas of the anode metals are equalcGreater than the current I measured in an external circuit contacting a corroding coupleg；
In the formula (12), A1Is the anode metal area; a. the2Is the cathode metal area;
therefore, equation (9) can be rewritten as:
in summary, in the case of galvanic corrosion consisting of a pure anode and a pure cathode, the equivalent weight conversion factor α is the ratio of the currents measured in the external circuit contacting the corroded galvanic couple under two different solutions or environmental conditions; under the condition of galvanic corrosion consisting of a non-pure anode and a pure cathode, the equivalent weight conversion coefficient alpha is the ratio of self-corrosion currents (before coupling) of the metal anode under two different solutions or environmental conditions; the equivalent conversion factor α can be expressed as:
in the formula (14), a is the galvanic corrosion condition formed by a pure anode and a pure cathode; b is galvanic corrosion condition composed of non-pure anode and pure cathode; i isg、I′gThe current measured in an external circuit contacting and corroding a galvanic couple under two different solutions or environmental conditions; i iss、I′sIs the self-corrosion current of the metal anode in two different solutions or ambient conditions (not before coupling).
Compared with the prior art, the equivalent accelerated conversion method for the galvanic corrosion of the dissimilar metal materials deduces the conversion relation between the service environment and the laboratory environment of the galvanic corrosion generated by the contact of the dissimilar metals, measures the self corrosion current and the galvanic current by adopting an electrochemical test method, namely the conversion coefficient undetermined term of the contact of the dissimilar metals in different environments, determines the value of a conversion coefficient, establishes a conversion coefficient a database, establishes the equivalent accelerated corrosion conversion relation which is feasible in the laboratory condition, converts the corrosion damage and the like of the equipment in the service environment into an equivalent accelerated environment spectrum which can be reproduced in the laboratory in an equivalent manner, and effectively applies the equivalent accelerated environment spectrum to engineering practice, so that the equivalent accelerated conversion method can replace the traditional corrosion test research which simulates the service environment of the equipment to develop, and avoids consuming a large amount of time, expenditure and the like; meanwhile, a conversion coefficient a database is established by determining the value of the conversion coefficient a, and a basis is also provided for compiling a laboratory acceleration environment spectrum.
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In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in 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 illustrative of the invention only and are not limiting upon the scope of the invention.
Example 1. as shown in fig. 1, an equivalent acceleration conversion method for galvanic corrosion of dissimilar metal materials is based on the equivalent conversion principle of corrosion of a single metal material, which is to infer the equivalent conversion of galvanic corrosion of dissimilar metal materials in contact with each other, and to distinguish the equivalent conversion of galvanic corrosion of pure anode and pure cathode from galvanic corrosion of non-pure anode and pure cathode, and the specific conversion method is as follows:
I. based on the principle of equivalent conversion of single metal material corrosion;
(1) selecting measurement parameters: as known from the electrochemical principle, metal corrosion (including galvanic corrosion and the like) is mainly caused by electrochemical corrosion, the anode loses electrons to generate an oxidation reaction, and the cathode obtains the electrons to generate a reduction reaction. Corrosion current IcThe influence of the environment on the metal corrosion can be measured accurately, and a strict equivalent relation exists; thus, corrosion current I is used hereincAnd performing equivalent conversion between a service environment and a laboratory condition as a measurement parameter.
(2) Equivalent conversion principle: assuming the action time t of the service environment of the equipment, the metal electric quantity in the time t is as follows:
Q＝Ic·t (1)
due to the influence of service environment factors, the corrosion of metal is that the time intensity changes in a spectrum shape, and the corrosion current IcAlso over time;therefore, under the service environment, in combination with faraday's law, the corrosion electric quantity Q of the metal in the time from t1 to t2 can be expressed in the form of integral:
in the formula (2), F is a Faraday constant.
Under laboratory conditions, the same metal component was tested by a selected accelerated environmental spectrum, with a corrosion current of I'cThe corrosion charge Q ' of the metal over the test time t1 ' to t2 ' can be expressed in the form of an integral:
according to the corrosion loss equivalence 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, and the equivalent relation under two environments can be established, namely:
to simplify the problem, the corrosion current I is adjustedcAnd l'cAs a constant discussion, and assuming t is t1-t2, t ' is t1 ' -t2 ', equation (4) can be written as:
Ic·t＝I′C·t′ (5)
from formula (5):
from the formula (6), it is found that the corrosion current I 'can be increased by changing the test conditions, for example, the temperature, humidity, salt spray, etc'cThe test time t 1' is shortened, and the aim of accelerating under the laboratory condition is achieved;
(3) equivalent conversion factor
Order to
Equation (6) may be rewritten as:
t′＝α·t (7)
alpha is defined as an equivalent conversion coefficient, after the equivalent conversion of the environmental spectrum for equivalent damage, the test time is shortened by alpha times under the action of the laboratory accelerated environmental spectrum, and the purpose of the accelerated test of the corrosion damage of the service environment and the like can be realized;
no matter a single metal material or a contacted dissimilar metal material is used, the metal corrosion amount is always closely related to the corrosion current according to Faraday's law, so the equivalent conversion principle is used;
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 couple, the metal material with lower corrosion potential is corroded by the metal material, and the anode is dissolved under the action of a short-circuited galvanic cell formed by the metal material with higher corrosion potential; according to the principle of corrosion electrochemistry, a galvanic cell formed by contacting a metal material with high corrosion potential essentially accelerates the self corrosion of the metal material with low corrosion potential, but does not cause new corrosion; therefore, galvanic corrosion caused by contact of dissimilar metals is accelerated in the corrosion of the anode metal material itself, as compared with a single metal;
as described above, the corrosion current I when galvanic corrosion occurs in contact with dissimilar metalscSelf-corrosion current I of the anode equal to K timessNamely:
Ic＝K·Is (8)
in the formula (8), IcFor corrosion current, IsSelf-corrosion current for metal anodes (not before coupling); k is the galvanic corrosion increasing effect, and the numerical value is related to the environmental conditions (temperature, humidity, salt fog and the like).
Thus, α can be rewritten as:
in the formula (9), Ic、IsK is the corrosion current of the solution 1, the self-corrosion current of the metal anode (before coupling), and the factors related to the environmental conditions (temperature, humidity, salt fog, and the like); i'c、I′sK' is the corrosion current of the solution 2, the self-corrosion current of the metal anode (before coupling), and the factors related to the environmental conditions (temperature, humidity, salt fog, etc.);
a. galvanic corrosion of pure anode and pure cathode
After the dissimilar metals are contacted, the anode metal mainly carries out anodic oxidation (dissolution) reaction, and the speed of the depolariser cathode reduction reaction on the surface of the anode metal is negligibly small; meanwhile, the cathodic reduction reaction of the depolarizer is mainly performed on the surface of the cathode metal, and the anodic oxidation (dissolution) reaction rate is negligibly small. Corrosion current IcI.e. the dissolution current of the metal anode corroding the anode of the galvanic couple and the current I measured in the external circuit contacting the corroding galvanic couplegEqual;
Ic＝K·Is＝Ig (10)
in the formula (10), IgIs the current measured in an external circuit contacting the corroding couple; k is a galvanic corrosion increase effect, and the numerical value is related to environmental conditions (temperature, humidity, salt fog and the like);
therefore, equation (9) can be rewritten as:
in the formula (11), IgThe current measured in the external circuit of the contact corrosion couple of solution 1; i'gThe current measured in the external circuit of the contact corrosion couple of solution 2;
b. galvanic corrosion of non-pure anodes and pure cathodes
Impurities are on the metal surfaces of the anode and the cathodeUnder the condition that the content is not negligible, the cathode reduction reaction of the depolarizer on the metal surface of the anode is not negligible, and the cathode reduction reaction speed is controlled by diffusion; in this case, the dissolution current density of the anode metal after contact with the dissimilar metal is larger than the anode current density measured in the external circuit contacting the corrosion couple, that is, the corrosion current I when the areas of the anode metals are equalcGreater than the current I measured in an external circuit contacting a corroding coupleg；
In the formula (12), A1Is the anode metal area; a. the2Is the cathode metal area;
therefore, equation (9) can be rewritten as:
in summary, in the case of galvanic corrosion consisting of a pure anode and a pure cathode, the equivalent weight conversion factor α is the ratio of the currents measured in the external circuit contacting the corroded galvanic couple under two different solutions or environmental conditions; under the condition of galvanic corrosion consisting of a non-pure anode and a pure cathode, the equivalent weight conversion coefficient alpha is the ratio of self-corrosion currents (before coupling) of the metal anode under two different solutions or environmental conditions; the equivalent conversion factor α can be expressed as:
in the formula (14), a is the galvanic corrosion condition formed by a pure anode and a pure cathode; b is galvanic corrosion condition composed of non-pure anode and pure cathode; i isg、I′gThe current measured in an external circuit contacting and corroding a galvanic couple under two different solutions or environmental conditions; i iss、I′sIs the self-corrosion current of the metal anode in two different solutions or ambient conditions (not before coupling).
Self-corrosion current IsGalvanic couple current IgThe measurement and conversion coefficient a were determined as follows:
self-corrosion current IsAnd (3) determination: respectively selecting a service environment and a specific laboratory condition, utilizing an electrochemical workstation (such as PARSTAT4000 model) and 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; galvanic couple current IgAnd (3) determination: respectively selecting a service environment and a specific laboratory condition, 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 a: according to the magnitude of the corrosion potential difference of the two dissimilar metals, the equivalent conversion coefficient a is calculated according to a formula (14), and on the basis, an equivalent conversion coefficient a database of the galvanic corrosion generated by the contact of the dissimilar metals in a service environment and a laboratory environment is established.
The equivalent conversion coefficient is applied to the compilation of a laboratory acceleration environment spectrum, and the basic technical idea (see figure 1) is as follows:
step 1: collecting environmental data (such as annual temperature, humidity, salt fog, condensation and the like) of the equipment in the service environment, and making an environmental spectrum of the service environment according to the basis of the existing literature research methods; step 2: selecting an accelerated environmental test mode and basic conditions of a laboratory, wherein the accelerated environmental test mode and the basic conditions can be selected according to GJB1720-93 'Corrosion and protection of dissimilar metals', GJB150 'environmental test method for military preparations laboratory'; and step 3: according to the equivalent conversion coefficient a or the database of the dissimilar metal, the equivalent calculation of the laboratory accelerated environment is carried out, and a laboratory accelerated environment spectrum is compiled; and 4, step 4: and respectively carrying out tests under the service environment spectrum and the laboratory acceleration environment spectrum, mutually verifying the test results, and further optimizing the equivalent conversion relation algorithm of the dissimilar metal and the laboratory acceleration environment spectrum.
Finally, the above embodiments are only intended to illustrate the technical solutions of the present invention and not to limit the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions, and all of them should be covered by the claims of the present invention.
Claims (3)
1. A method for equivalent accelerated conversion of galvanic corrosion of dissimilar metal materials is characterized in that the method is based on the principle of equivalent conversion of corrosion of single metal materials, the equivalent conversion of the galvanic corrosion of dissimilar metal materials in contact is inferred, and the equivalent conversion of the galvanic corrosion consisting of a pure anode and a pure cathode and the equivalent conversion of the galvanic corrosion consisting of a non-pure anode and a pure cathode are distinguished at the same time, and the specific conversion method is as follows:
I. based on the principle of equivalent conversion of single metal material corrosion;
(1) selecting measurement parameters: as known from the electrochemical principle, metal corrosion (including galvanic corrosion and the like) is mainly caused by electrochemical corrosion, the anode loses electrons to generate an oxidation reaction, and the cathode obtains the electrons to generate a reduction reaction. Corrosion current IcThe influence of the environment on the metal corrosion can be measured accurately, and a strict equivalent relation exists; thus, corrosion current I is used hereincAnd performing equivalent conversion between a service environment and a laboratory condition as a measurement parameter.
(2) Equivalent conversion principle: assuming the action time t of the service environment of the equipment, the metal electric quantity in the time t is as follows:
Q＝Ic·t (1)
due to the influence of service environment factors, the corrosion of metal is that the time intensity changes in a spectrum shape, and the corrosion current IcAlso over time; therefore, under the service environment, in combination with faraday's law, the corrosion electric quantity Q of the metal in the time from t1 to t2 can be expressed in the form of integral:
in the formula (2), F is a Faraday constant.
Under laboratory conditions, for the same metal piece, from a selected accelerated environmental spectrumThe test was carried out with the corrosion current I'cThe corrosion charge Q ' of the metal over the test time t1 ' to t2 ' can be expressed in the form of an integral:
according to the corrosion loss equivalence 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, and the equivalent relation under two environments can be established, namely:
to simplify the problem, the corrosion current I is adjustedcAnd l'cAs a constant discussion, and assuming t is t1-t2, t ' is t1 ' -t2 ', equation (4) can be written as:
Ic·t＝I′C·t′ (5)
from formula (5):
from the formula (6), it is found that the corrosion current I 'can be increased by changing the test conditions, for example, the temperature, humidity, salt spray, etc'cThe test time t 1' is shortened, and the aim of accelerating under the laboratory condition is achieved;
(3) equivalent conversion factor
Order to
Equation (6) may be rewritten as:
t′＝α·t (7)
alpha is defined as an equivalent conversion coefficient, after the equivalent conversion of the environmental spectrum for equivalent damage, the test time is shortened by alpha times under the action of the laboratory accelerated environmental spectrum, and the purpose of the accelerated test of the corrosion damage of the service environment and the like can be realized;
no matter a single metal material or a contacted dissimilar metal material is used, the metal corrosion amount is always closely related to the corrosion current according to Faraday's law, so the equivalent conversion principle is used;
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 couple, the metal material with lower corrosion potential is corroded by the metal material, and the anode is dissolved under the action of a short-circuited galvanic cell formed by the metal material with higher corrosion potential; according to the principle of corrosion electrochemistry, a galvanic cell formed by contacting a metal material with high corrosion potential essentially accelerates the self corrosion of the metal material with low corrosion potential, but does not cause new corrosion; therefore, galvanic corrosion caused by contact of dissimilar metals is accelerated in the corrosion of the anode metal material itself, as compared with a single metal;
as described above, the corrosion current I when galvanic corrosion occurs in contact with dissimilar metalscSelf-corrosion current I of the anode equal to K timessNamely:
Ic＝K·Is (8)
in the formula (8), IcFor corrosion current, IsSelf-corrosion current for metal anodes (not before coupling); k is the galvanic corrosion increasing effect, and the numerical value is related to the environmental conditions (temperature, humidity, salt fog and the like).
Thus, α can be rewritten as:
in the formula (9), Ic、IsK is the corrosion current of the solution 1, the self-corrosion current of the metal anode (before coupling), and the factors related to the environmental conditions (temperature, humidity, salt fog, and the like); i'c、I′sK' is the corrosion current of the solution 2, the self-corrosion current of the metal anode (not coupled)Before, environmental conditions (temperature, humidity, salt spray, etc.);
a. galvanic corrosion of pure anode and pure cathode
After the dissimilar metals are contacted, the anode metal mainly carries out anodic oxidation (dissolution) reaction, and the speed of the depolariser cathode reduction reaction on the surface of the anode metal is negligibly small; meanwhile, the cathodic reduction reaction of the depolarizer is mainly performed on the surface of the cathode metal, and the anodic oxidation (dissolution) reaction rate is negligibly small. Corrosion current icI.e. the dissolution current of the metal anode corroding the anode of the galvanic couple and the current I measured in the external circuit contacting the corroding galvanic couplegEqual;
Ic＝K·Is＝Ig (10)
in the formula (10), IgIs the current measured in an external circuit contacting the corroding couple; k is a galvanic corrosion increase effect, and the numerical value is related to environmental conditions (temperature, humidity, salt fog and the like);
therefore, equation (9) can be rewritten as:
in the formula (11), IgThe current measured in the external circuit of the contact corrosion couple of solution 1; i'gThe current measured in the external circuit of the contact corrosion couple of solution 2;
b. galvanic corrosion of non-pure anodes and pure cathodes
Impurities exist on the surfaces of the anode metal and the cathode metal, and under the condition that the impurity content is not negligible, the cathode reduction reaction of the depolarizer on the surface of the anode metal is not negligible, and the cathode reduction reaction speed is controlled by diffusion; in this case, the dissolution current density of the anode metal after contact with the dissimilar metal is larger than the anode current density measured in the external circuit contacting the corrosion couple, that is, the corrosion current I when the areas of the anode metals are equalcGreater than the current I measured in an external circuit contacting a corroding coupleg；
In the formula (12), A1Is the anode metal area; a. the2Is the cathode metal area;
therefore, equation (9) can be rewritten as:
in summary, in the case of galvanic corrosion consisting of a pure anode and a pure cathode, the equivalent weight conversion factor α is the ratio of the currents measured in the external circuit contacting the corroded galvanic couple under two different solutions or environmental conditions; under the condition of galvanic corrosion consisting of a non-pure anode and a pure cathode, the equivalent weight conversion coefficient alpha is the ratio of self-corrosion currents (before coupling) of the metal anode under two different solutions or environmental conditions; the equivalent conversion factor α can be expressed as:
in the formula (14), a is the galvanic corrosion condition formed by a pure anode and a pure cathode; b is galvanic corrosion condition composed of non-pure anode and pure cathode; i isg、I′gThe current measured in an external circuit contacting and corroding a galvanic couple under two different solutions or environmental conditions; i iss、I′sIs the self-corrosion current of the metal anode in two different solutions or ambient conditions (not before coupling).
2. The equivalent accelerated conversion method of galvanic corrosion of dissimilar metal materials according to claim 1, wherein: self-corrosion current IsGalvanic couple current IgThe measurement and conversion coefficient a were determined as follows:
self-corrosion current IsAnd (3) determination: respectively selecting a service environment and a specific laboratory condition,measuring a material polarization curve by using an electrochemical workstation (such as a Costet CS2350H model) and adopting a classical three-electrode system, wherein a reference electrode is a saturated calomel electrode, and acquiring and processing data to obtain self-corrosion current;
galvanic couple current IgAnd (3) determination: respectively selecting a service environment and a specific laboratory condition, 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 a: according to the magnitude of the corrosion potential difference of the two dissimilar metals, the equivalent conversion coefficient a is calculated according to a formula (14), and on the basis, an equivalent conversion coefficient a database of the galvanic corrosion generated by the contact of the dissimilar metals in a service environment and a laboratory environment is established.
3. The equivalent accelerated conversion method of galvanic corrosion of dissimilar metal materials according to claim 1, wherein: the equivalent conversion coefficient is applied to the compilation of a laboratory acceleration environment spectrum, and the basic steps are as follows:
step 1: collecting environmental data (such as annual temperature, humidity, salt fog, condensation and the like) of the equipment in the service environment, and making an environmental spectrum of the service environment according to the basis of the existing literature research methods;
step 2: selecting an accelerated environmental test mode and basic conditions of a laboratory, wherein the accelerated environmental test mode and the basic conditions can be selected according to GJB1720-93 'Corrosion and protection of dissimilar metals', GJB150 'environmental test method for military preparations laboratory';
and step 3: calculating the equivalent of the laboratory accelerated environment according to the equivalent conversion coefficient a of the dissimilar metal or a database, and compiling a laboratory accelerated environment spectrum;
and 4, step 4: and respectively carrying out tests under the service environment spectrum and the laboratory acceleration environment spectrum, mutually verifying the test results, and further optimizing the equivalent conversion relation algorithm of the dissimilar metal and the laboratory acceleration environment spectrum.
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