Method for simultaneous electrochemical measurement of thermodynamic and kinetic parameters of molten magnesium alloys

Abstract

The application provides a synchronous electrochemical measurement method for thermodynamic and kinetic parameters of molten magnesium alloy, comprising the following steps: constructing a three-electrode test system comprising a working electrode, a counter electrode, a reference electrode and a molten salt electrolyte; the molten salt electrolyte is used for conducting magnesium ions at a test temperature; the working electrode is a magnesium alloy to be measured placed in a limiting assembly, the limiting assembly is used for restraining the magnesium alloy to be measured at a preset position in the molten salt electrolyte and making the magnesium alloy to be measured form an electrical contact with the molten salt electrolyte; the electrochemical characteristic potential of magnesium ions in the three-electrode test system is calibrated; a constant current pulse signal is applied to the working electrode, and the potential response information of the working electrode after excitation is obtained; and the thermodynamic activity of magnesium in the magnesium alloy to be measured and the diffusion coefficient of magnesium in the magnesium alloy to be measured are calculated according to the potential response information and the electrochemical characteristic potential. The problems of low-density liquid electrode floating, molten salt complexing interference and synchronous measurement of thermodynamic and kinetic parameters are solved.

Description

Technical Field

[0001] This invention relates to the field of high-temperature thermodynamic and electrochemical testing technology for metals, specifically to a method for simultaneous electrochemical measurement of thermodynamic and kinetic parameters of molten magnesium alloys. Background Technology

[0002] Magnesium alloys, as the lightest metallic structural materials in engineering applications, have broad application prospects. The solid-state microstructure and mechanical properties of high-performance magnesium alloys depend on the intrinsic physicochemical properties of their high-temperature melts. However, the basic melt property data upon which thermodynamic phase diagram (CALPHAD) calculations rely are scarce. Key parameters such as thermodynamic activity and diffusion coefficient are not only the physical source for evaluating phase equilibrium relationships, guiding alloy composition design, and simulating solidification phase transformation paths, but also the foundation for constructing high-precision thermodynamic databases. Currently, obtaining high-precision basic data on magnesium melts faces significant high-temperature technical challenges. Magnesium's extremely high high-temperature chemical activity and its inherent lightweight and low-density characteristics make it extremely difficult to conduct high-precision experimental studies directly. When applied to highly reactive magnesium melts, the electromotive force method based on electrochemical principles faces bottlenecks such as difficulty in selecting suitable electrolytes, easy oxidation at high temperatures, easy drift of reference electrode potential, difficulty in stabilizing and fixing liquid electrodes due to the buoyancy of magnesium's light weight, and high-temperature oxidation and fracture of current collectors. This results in very little accurate experimental data, and a severe shortage of full-composition data that can be used for phase diagram construction and verification. Therefore, there is an urgent need to develop a high-precision synchronous method for measuring the thermodynamic and kinetic parameters of high-temperature magnesium alloy melts that can stably lock the liquid electrode interface, have a highly reliable reference system, and provide oxidation protection. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention proposes a method for simultaneous electrochemical measurement of thermodynamic and kinetic parameters of molten magnesium alloys, aiming to solve the problems of low-density liquid electrode floating, molten salt complexation interference, and simultaneous measurement of thermodynamic / kinetic parameters.

[0004] In a first aspect, embodiments of this application provide a method for simultaneous electrochemical measurement of thermodynamic and kinetic parameters of molten magnesium alloys, including: S1, construct a three-electrode testing system comprising a working electrode, a counter electrode, a reference electrode, and a molten salt electrolyte; the molten salt electrolyte is composed of Mg... 2+ The device comprises at least one molten salt for conducting magnesium ions at a test temperature; the counter electrode is made of a conductive material; the reference electrode is made of a reference material with a stable electrode potential; the working electrode is for placing the magnesium alloy to be tested in a limiting component, the limiting component being used to constrain the magnesium alloy to be tested at a preset position in the molten salt electrolyte and to make the magnesium alloy to be tested and the molten salt electrolyte form an electrical contact. S2, calibrating the electrochemical characteristic potential of the magnesium ions in the three-electrode test system; S3, apply a constant current pulse signal to the working electrode and obtain the potential response information of the working electrode after the excitation ends; S4. Based on the potential response information and the electrochemical characteristic potential, calculate the thermodynamic activity of magnesium in the magnesium alloy to be tested and the diffusion coefficient of magnesium in the magnesium alloy to be tested.

[0005] Optionally, the molten salt electrolyte is composed of a Mg-containing electrolyte. 2+ When a molten salt is composed of a certain amount of salt, the molten salt is in a liquid state at the corresponding temperature. Its melting point can be determined by constructing a molten salt phase diagram using Factsage.

[0006] Optionally, the molten salt electrolyte is composed of Mg 2+ When a multi-component molten salt is composed, mixing multiple molten salts can lower the melting point to ensure it remains liquid. Specifically, the melting point can be determined by constructing a molten salt phase diagram using Factsage. If it contains multiple Mg-containing... 2+ The composition of the molten salt can include substances with a precipitation potential higher than that of Mg. 2+ / Mg cations, such as Na + K + Li + wait.

[0007] Optionally, in S1, the preparation of the working electrode includes: placing the magnesium alloy to be tested in a first container, which is positioned inside a second container, forming a channel between the first and second containers for the permeation of molten salt electrolyte. To prevent the magnesium alloy from being tested from floating, an inverted limiting structure is used—the first container containing the alloy sample is placed upside down inside the second container, with the opening facing downwards. An annular gap is formed between the outer wall of the first container and the inner wall of the second container, serving as a permeation channel for the molten salt electrolyte. This ensures effective contact between the molten salt and the electrode while preventing the electrode from floating or shifting. The spatial position of the liquid electrode is firmly locked by the mechanical limiting structure, eliminating displacement and wandering caused by buoyancy, ensuring a stable ohmic contact between the molybdenum wire current collector and the liquid alloy, thus ensuring that the measured potential truly reflects the equilibrium electrode potential of the alloy.

[0008] Optionally, in S1, the preparation of the counter electrode includes: being constructed by loading an inert metal or alloy into a container. The counter electrode material is at least one of Sn, Pb, and Bi, or an alloy containing the aforementioned metals. Sn has a large relative atomic mass, which can effectively dissolve and stabilize the deposited target metal, preventing it from migrating in the molten salt due to density differences.

[0009] Optionally, in S1, the preparation of the reference electrode includes: loading an alloy formed from a first metal and a second metal into a container, wherein the reference electrode has a stable electrode potential at the test temperature. The reference electrode is a Mg-Sn alloy, a Mg-Pb alloy, or a Mg-Bi alloy, wherein the molar ratio of Mg to other metals is 40:60 to 60:40, most preferably 50:50. Alloys with this ratio have been shown to have excellent potential stability in high-temperature molten salt environments.

[0010] Optionally, in S1, the molten salt electrolyte is prepared by mixing at least one alkali metal chloride with a magnesium chloride. A KCl-MgCl2 mixed molten salt is used, wherein the molar percentage of MgCl2 is 10 at.% to 30 at.%, most preferably 20 at.%. This ratio ensures complete liquefaction of the molten salt while avoiding excessively high MgCl2 concentrations that could induce a strong Mg-Cl complexing effect and reduce ion migration capacity.

[0011] Optionally, S1 can be used for the fabrication of the three-electrode testing system and electrodes: Working electrode (WE): A plate-shaped Mg-X binary alloy polished to a mirror finish is placed in a small magnesium oxide crucible and an inverted limiting structure is adopted, that is, the small magnesium oxide crucible containing the Mg-X alloy is placed upside down at the bottom of the large magnesium oxide crucible and fixed by molybdenum wire. Counter electrode (CE): Consists of 3 g of pure Sn loaded in a small magnesium oxide crucible; Reference electrode (RE): consisting of 4 g of Mg-Sn alloy in a 50:50 molar ratio loaded in a small magnesium oxide crucible; Molten salt electrolyte: composed of a mixture of KCl and 20 at.% MgCl2 molten salt, contained in an alumina crucible; The working electrode, counter electrode, and reference electrode are heated to melt and inserted into a molybdenum wire. After cooling and solidification, a pre-fabricated electrode is formed and placed in a dehydrated molten salt electrolyte.

[0012] Optionally, in S1, the Mg-X binary alloy sample is a rectangular sheet with a shape of 10mm × 10mm × 5mm, and its surface is polished to a mirror finish. Polishing the surface of the magnesium alloy to be tested to a mirror finish removes the oxide film on the surface, reducing the obstruction of electron transfer by the surface oxide layer. If the oxide film is not sufficiently removed, it will affect the alloy composition and thus the accuracy of the final data.

[0013] Optionally, in S1, the molybdenum wire inserted into the electrode has a diameter of 1.5 mm and is fitted with an alumina tube with an inner diameter of 2 mm. Pre-melting the inserted wire ensures excellent electrical contact between the metal and the molybdenum wire after complete melting at high temperatures, avoiding poor contact during measurement. The alumina tube prevents the molybdenum wire from breaking due to oxidation by trace amounts of oxygen. This effectively blocks the oxidation path of the molybdenum wire, ensuring that the current collector maintains structural integrity and good conductivity throughout the entire multi-stage GITT long-cycle test, preventing data incompleteness due to breakage during the test.

[0014] Optionally, the crucible for loading the electrodes is made of magnesium oxide with a purity of ≥99%; the small magnesium oxide crucible has an inner diameter of 12mm, an outer diameter of 16mm, and an outer height of 27mm; the large magnesium oxide crucible has an inner diameter of 21mm, an outer diameter of 27mm, and a height of 32mm; when inverted, an annular gap is formed between the outer wall of the small crucible and the inner wall of the large crucible, with an effective cross-sectional area of ​​1.45cm². 2 The gap.

[0015] Since the density of the magnesium alloy was not significantly greater than that of the molten salt at the experimental temperature, the working electrode needed to be inverted to prevent it from floating. A molybdenum wire was used as a support structure to ensure effective contact between the molten salt and the electrode. Pure Sn was used as the counter electrode because its relatively large atomic mass effectively dissolved and stabilized the deposited magnesium, preventing it from migrating in the molten salt due to density differences. A 50:50 molar ratio Mg-Sn alloy was used as the reference electrode because it has been proven stable under the corresponding conditions. The reference electrode potential remained highly stable during long-term GITT multi-pulse-relaxation cycles, ensuring that the equilibrium potential read from each pulse was based on the same reference, eliminating the interference of reference drift on the accuracy of activity calculations.

[0016] Because the electrode composition contains highly reactive magnesium, the crucible used to hold it must be made of magnesium oxide to prevent them from reacting. The dimensions of both the large and small crucibles must be such that they remain at least 1 cm wide after being inverted. 2 The gaps mentioned above.

[0017] Optionally, the preparation and drying steps of the molten salt electrolyte in S1 are as follows: KCl with a purity ≥99.5% and MgCl2 are mixed at a molar ratio of 80:20. Under the protection of high-purity argon, the temperature is increased to 700℃ at a heating rate of 5℃ / min and held for 12 hours. The crucible containing the molten salt is an alumina crucible with a purity ≥99%, and the dimensions are an inner diameter of 80mm, an outer diameter of 90mm, and a height of 163mm.

[0018] KCl-MgCl2 molten salt is used to ensure the liquid phase and conductivity of the system at 700℃. MgCl2 can lower the melting point, but excessive amounts will enhance the Mg-Cl complexation effect, reduce ion migration ability, and affect Mg... 2+Transport kinetics. Therefore, the MgCl2 content was controlled at 20 at.% to balance liquid phase stability and transport performance. FactSage calculations showed that this composition was a completely liquid phase at 700 °C. Literature measured the density of the eutectic binary KCl-MgCl2 in the range of 450-800 °C, obtaining a linear relationship of 1.9037-5.52 × 10⁻⁶. -4 Based on T(°C), the density of KCl-32at.%MgCl2 at 700℃ is 1.5173 g / cm³. 3 Because the higher density MgCl2 content is higher, the actual density of KCl-20at.%MgCl2 will be lower, but still not significantly lighter than magnesium alloy. Therefore, as mentioned earlier, an inverted buckle device needs to be designed. The heating rate is controlled (5℃ / min) to prevent crucible cracking caused by rapid heating, and the temperature is held for 12 hours to completely remove trace moisture. The MgCl2 content is precisely controlled at 20 at.%, and calculations using the FactSage phase diagram confirm that this composition is a completely liquid phase at 700℃. Simultaneously, the MgCl2 concentration is controlled below the threshold for a sudden increase in the complexation effect, ensuring that Mg... 2+ It mainly exists in a relatively simple ionic form and maintains a high ionic mobility.

[0019] Since the crucible containing molten salt does not involve direct contact with the electrode alloy, an alumina crucible, which is more economical, can be selected.

[0020] Alternatively, S2 can be Mg 2+ Calibration of the electrochemical deposition potential of Mg and the reference electrode potential: Cyclic voltammetry (CV) tests were performed under a protective atmosphere and at 700°C, using a smooth molybdenum wire as the temporary working electrode and a graphite rod as the temporary counter electrode, to calibrate the reference electrode potential and Mg. 2+ / Mg electrochemical deposition potential.

[0021] Optionally, in S2, the CV test has a scan rate of 50 mV / s, a potential window of -0.7V to 1.3V, and an immersion depth of the temporary working electrode molybdenum wire ≤ 5 mm. This is for calibrating Mg. 2+ The / Mg potential requires cyclic voltammetry testing. A smooth molybdenum wire is used as the temporary working electrode, and the immersion depth must be controlled to ≤5mm to prevent excessive current. Pure Sn cannot be used as the counter electrode because Sn will be present during the scanning process. 2+ This can interfere with the measurement of Mg precipitation potential and contaminate the molten salt, therefore a graphite rod is needed as a temporary counter electrode. A scan rate of 50 mV / s was used for CV testing to obtain a clear redox response and reduce the impact of molten salt temperature fluctuations and electrode interface evolution during long-term testing. The potential window was set to -0.7V to 1.3V to cover Mg precipitation potential. 2+The reduction deposition process, while avoiding excessively high positive potentials for Cl - Oxidation leads to the decomposition of molten salt.

[0022] Optionally, S3 can be used for galvanostatic intermittent titration (GITT) testing and equilibrium potential acquisition: A constant current pulse was applied to the working electrode using the GITT method to induce an electrochemical response. After the pulse ended, the electrode was allowed to relax, and the potential-time response curve was recorded and the equilibrium potential E was extracted. eq ; Optionally, the GITT test described in S3 applies a current of 50 mA, corresponding to a current density ≤ 50 mA / cm². 2 The relaxation time after each pulse is 3000 s. The effective surface area of ​​the crucible is approximately 1.13 cm². 2 Setting the current to 50mA ensures that the applied current density is less than or equal to 50mA / cm². 2 This ensures that the Mg extraction process in the working electrode is diffusion-controlled, so that the potential change mainly reflects the diffusion behavior of Mg in the Mg-X alloy, rather than electrochemical polarization or interfacial reactions. A relaxation time of 3000 s ensures that the system fully reaches thermodynamic equilibrium.

[0023] Optionally, S4 can be used to derive thermodynamic and kinetic parameters: Calculate the thermodynamic activity a of Mg in Mg-X alloy using the Nernst equation. Mg Based on Fick's second law, the diffusion coefficient D of Mg in the alloy was derived according to the relaxation potential response. Mg .

[0024] Optionally, the electrochemical characteristic potential includes the calibration reference electrode potential. and electrochemical deposition potential.

[0025] Optionally, the potential response information includes the potential-time response curve and the equilibrium potential. .

[0026] Optionally, the limiting component includes a first container and a second container, the magnesium alloy to be tested is placed in the first container, the first container is disposed inside the second container, and a fluid channel for the molten salt electrolyte to permeate is formed between the first container and the second container.

[0027] Optionally, the first container is a small magnesium oxide crucible. The second container is a large magnesium oxide crucible.

[0028] Optionally, the density of the magnesium alloy to be tested is less than or close to the density of the molten salt electrolyte, and the first container is disposed inside the second container with its opening facing downwards.

[0029] Optionally, at least a portion of the surface of the limiting component in contact with the molten salt electrolyte is made of a high-temperature resistant insulating material, wherein the high-temperature resistant insulating material is selected from at least one of oxide ceramics, nitride ceramics, or carbide ceramics.

[0030] Optionally, the counter electrode is constructed by loading an inert metal into a container or by loading an inert alloy into a container; the material of the counter electrode is a high-density metal or a high-density alloy, wherein the high-density metal is selected from at least one of Sn, Zn, Bi, Al, Pb, Ga, In, Cd, and Tl, or has a density exceeding 1.6 g / cm³. 3 alloy.

[0031] Optionally, the reference electrode is composed of an alloy of magnesium and other metals loaded in a container; the molar percentage of magnesium in the alloy of magnesium and other metals is 40% to 60%.

[0032] Optionally, the molten salt electrolyte comprises an alkali metal chloride and magnesium chloride, wherein the molar percentage of magnesium chloride is 5 at.% to 30 at.%.

[0033] Optionally, the alkali metal chloride is KCl or NaCl.

[0034] Optionally, the electrochemical characteristic potential is calibrated using a transient electrochemical testing method, which includes cyclic voltammetry, linear sweep voltammetry, square wave voltammetry, or differential pulse voltammetry.

[0035] Optionally, the electrochemical characteristic potential includes a calibration potential, and the potential response information includes a potential-time response curve and an equilibrium potential; based on the potential response information and the electrochemical characteristic potential, the thermodynamic activity of magnesium in the magnesium alloy to be tested and the diffusion coefficient of magnesium in the magnesium alloy to be tested are calculated, including: The thermodynamic activity of magnesium in the magnesium alloy under test is calculated based on the Nernst equation using the calibration potential in the electrochemical characteristic potential and the equilibrium potential in the potential response information. Based on the potential-time response curve, the pulse duration, the potential change of the working electrode during the excitation of the constant current pulse signal, and the equilibrium potential change of the working electrode before and after relaxation are obtained. The chemical diffusion coefficient of magnesium in the magnesium alloy under test is calculated based on Fick's diffusion law, according to the pulse duration, the potential change of the working electrode during the excitation of the constant current pulse signal, and the equilibrium potential change of the working electrode before and after relaxation.

[0036] Optionally, the step of calculating the chemical diffusion coefficient of magnesium in the magnesium alloy under test based on Fick's diffusion law, according to the pulse duration, the potential change of the working electrode during the excitation of the constant current pulse signal, and the equilibrium potential change of the working electrode before and after relaxation, includes: The molar volume of the magnesium alloy to be tested, the mass of magnesium in the magnesium alloy to be tested, and the effective contact area between the working electrode and the molten salt electrolyte are obtained. The chemical diffusion coefficient of magnesium in the magnesium alloy under test is calculated based on Fick's diffusion law, taking into account the molar volume of the magnesium alloy under test, the mass of magnesium in the magnesium alloy under test, the effective contact area between the working electrode and the molten salt electrolyte, the pulse duration, the potential change of the working electrode during the excitation of the constant current pulse signal, and the equilibrium potential change of the working electrode before and after relaxation.

[0037] Optionally, based on the molar volume of the magnesium alloy to be tested, the mass of magnesium in the magnesium alloy to be tested, the effective contact area between the working electrode and the molten salt electrolyte, the pulse duration, the potential change of the working electrode during the excitation of the constant current pulse signal, and the change of the equilibrium potential of the working electrode before and after relaxation, the chemical diffusion coefficient of magnesium in the magnesium alloy to be tested is calculated according to Fick's diffusion law, including: ; Where τ is the pulse duration; S is the effective contact area of ​​the electrode; The molar volume of the alloy; This represents the mass of Mg in the alloy. This represents the molar mass of Mg in the alloy; This represents the change in equilibrium potential before and after a single pulse. This represents the total change in potential during the pulse after deducting the ohmic voltage drop.

[0038] Optionally, the thermodynamic activity of magnesium in the magnesium alloy under test is calculated based on the Nernst equation according to the calibration potential and the equilibrium potential, including:

[0039] in, For calibration potential; This is the equilibrium potential.

[0040] Optionally, the calculation of the thermodynamic activity further includes: The activity coefficient of magnesium is calculated based on the thermodynamic activity and the mole fraction of magnesium in the magnesium alloy to be tested. Based on the activity coefficient of magnesium, the activities and activity coefficients of other components in the magnesium alloy to be tested, excluding magnesium, are calculated using the Gibbs-Duhem integral formula.

[0041] Optionally, based on the activity coefficient of magnesium, and in conjunction with the Gibbs-Duhem integral relation, the activities and activity coefficients of other components in the magnesium alloy to be tested, excluding magnesium, are calculated, including: ; in, ; Activity coefficient, Thermodynamic activity; The mole fraction of magnesium in the magnesium alloy to be tested.

[0042] Optionally, the current density of the constant current pulse is 10 mA / cm². 2 Up to 100mA / cm 2 The relaxation time is 600s to 7200s. Controlling the current density within a reasonable range can ensure that the extraction process of the target metal in the working electrode is in a diffusion-controlled state, so that the potential change mainly reflects the diffusion behavior of the target metal in the alloy.

[0043] Optionally, the thermodynamic activity is calculated using the Nernst equation; the diffusion coefficient is derived from the potential response information based on Fick's diffusion law. Based on the dissolution equilibrium reaction and the Nernst equation, and substituting the Faraday constant, gas constant, absolute temperature, calibration potential, and measured equilibrium potential, the thermodynamic activity and activity coefficient of the target metal in the liquid alloy at different composition points are calculated. Furthermore, the activities and activity coefficients of other components in the alloy are calculated using the Gibbs-Duhem integral relationship. Simultaneously, based on the potential relaxation behavior during constant current intermittent perturbation, and combined with Fick's second law to describe the diffusion relaxation process of the target metal component inside the liquid alloy, the chemical diffusion coefficient of the target metal in the alloy is obtained.

[0044] Optionally, the three-electrode testing system and testing process are carried out under a protective atmosphere.

[0045] Optionally, the entire experiment is conducted in a well-type experimental resistance furnace filled with high-purity argon gas, with the gas flow rate maintained at 400 mL / min. Maintaining a continuous flow of high-purity argon gas effectively isolates the Mg alloy from air, preventing reactions at high temperatures and oxidation failure of the molten salt.

[0046] This application has the following beneficial effects: (1) This application effectively solves the problem of low-density liquid metal electrodes floating and shifting in molten salt due to buoyancy by combining the inverted limiting structure with the optimized molten salt, ensuring stable and effective contact between the electrode and the molten salt and accurate acquisition of electrical signals.

[0047] (2) This application uses an alloy with a specific composition as a reference electrode in combination with an optimized molten salt, which avoids the problem of easy fluctuation and potential drift of pure metal reference electrodes in high-temperature molten salt, and provides a long-term stable reference potential.

[0048] (3) By optimizing the content of MgCl2 in the molten salt electrolyte, this application avoids the problem of reduced ion migration ability caused by complexation effect due to excessively high concentration of MgCl2 while ensuring the stability of the molten salt liquid phase.

[0049] (4) This application integrates the electromotive force method activity measurement and the GITT diffusion coefficient measurement into the same test system, realizing high-precision synchronous in-situ determination of thermodynamic activity and kinetic diffusion coefficient, avoiding systematic errors between multiple experiments, and significantly improving the internal consistency and comparability of the data.

[0050] (5) This application ensures the integrity of the current collector during long-cycle high-temperature testing through the synergy of the conductive wire protective sleeve and the overall atmosphere protection, so that multi-stage GITT cycle testing can be carried out continuously until the full composition range data is obtained, effectively preventing the current collector from oxidizing and breaking at high temperature, and ensuring the integrity of the test and the reliability of the data. Attached Figure Description

[0051] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0052] Figure 1 This is a schematic flowchart illustrating a method for simultaneous electrochemical measurement of thermodynamic and kinetic parameters of molten magnesium alloys, provided as an embodiment of this application.

[0053] Figure 2 The overall flowchart of a method for simultaneous electrochemical measurement of thermodynamic and kinetic parameters of molten magnesium alloy provided in an embodiment of this application is shown.

[0054] Figure 3 A schematic diagram of the prefabricated three-electrode assembly in Example 1 of a method for simultaneous electrochemical measurement of thermodynamic and kinetic parameters of molten magnesium alloy provided in an embodiment of this application; Figure 4 (a) In Example 1 of a simultaneous electrochemical measurement method for thermodynamic and kinetic parameters of molten magnesium alloy provided in an embodiment of this application, the reference electrode and Mg are calibrated using the CV method. 2+ / voltammetric curve of Mg deposition potential; Figure 4(b) Potential / current-time response curve obtained by GITT test in a simultaneous electrochemical measurement method for thermodynamic and kinetic parameters of molten magnesium alloy provided in an embodiment of this application. Figure 5 (a) A graph showing the changes in magnesium activity and alloy element activity with alloy element composition in Example 1 of a method for simultaneous electrochemical measurement of thermodynamic and kinetic parameters of molten magnesium alloy provided in an embodiment of this application; Figure 5 (b) A graph showing the variation of excess Gibbs free energy and mixed Gibbs free energy with alloy element composition in Example 1 of a synchronous electrochemical measurement method for thermodynamic and kinetic parameters of molten magnesium alloy provided in an embodiment of this application; Figure 5 (c) A graph showing the variation of the diffusion coefficient of magnesium with the alloy element composition in Example 1 of a method for simultaneous electrochemical measurement of thermodynamic and kinetic parameters of molten magnesium alloy provided in an embodiment of this application; Figure 5 (d) is a graph showing the variation of partial molar excess Gibbs free energy with alloy element composition in Example 1 of a synchronous electrochemical measurement method for thermodynamic and kinetic parameters of molten magnesium alloy provided in an embodiment of this application. Figure 6 (a) In Example 2 of a simultaneous electrochemical measurement method for thermodynamic and kinetic parameters of molten magnesium alloy provided in an embodiment of this application, the reference electrode and Mg are calibrated using the CV method. 2+ / voltammetric curve of Mg deposition potential; Figure 6 (b) Potential / current-time response curve obtained by GITT test in Example 2 of a method for simultaneous electrochemical measurement of thermodynamic and kinetic parameters of molten magnesium alloy provided in an embodiment of this application; Figure 7 (a) In Example 3 of a simultaneous electrochemical measurement method for thermodynamic and kinetic parameters of molten magnesium alloy provided in an embodiment of this application, the reference electrode and Mg are calibrated using the CV method. 2+ / voltammetric curve of Mg deposition potential; Figure 7 (b) Potential / current-time response curve obtained from GITT test in Example 3 of a method for simultaneous electrochemical measurement of thermodynamic and kinetic parameters of molten magnesium alloy provided in an embodiment of this application; Figure 8 The potential / current-time response curve obtained by GITT test in Comparative Example 1 is shown in the simultaneous electrochemical measurement method for thermodynamic and kinetic parameters of molten magnesium alloy provided in an embodiment of this application. Figure 9The potential / current-time response curve obtained by GITT test in Comparative Example 2 is shown in the simultaneous electrochemical measurement method of thermodynamic and kinetic parameters of molten magnesium alloy provided in an embodiment of this application. Figure 10 The potential / current-time response curve obtained by GITT test in Comparative Example 3 is shown in the simultaneous electrochemical measurement method of thermodynamic and kinetic parameters of molten magnesium alloy provided in an embodiment of this application. Figure 11 A schematic diagram illustrating the change in chemical potential energy in a simultaneous electrochemical measurement method for thermodynamic and kinetic parameters of a molten magnesium alloy, provided in an embodiment of this application. Figure 12 (a) Potential / current-time response curve obtained by GITT test in Comparative Example 4 in a simultaneous electrochemical measurement method for thermodynamic and kinetic parameters of molten magnesium alloy provided in an embodiment of this application; Figure 12 (b) Potential / current-time response curve obtained by GITT test in Comparative Example 5 in a simultaneous electrochemical measurement method for thermodynamic and kinetic parameters of molten magnesium alloy provided in an embodiment of this application. Detailed Implementation

[0055] The present invention will be further described in detail below with reference to specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0056] When a quantity, concentration, or other value or parameter is described as a range, preferred range, or preferred upper and lower limits, it should be understood that it is equivalent to specifically disclosing any range by combining any pair of upper or preferred values ​​with any lower or preferred values, regardless of whether the range is specifically disclosed. Unless otherwise stated, the numerical range values ​​listed herein include the endpoints of the range and all integers and fractions within that range.

[0057] Unless otherwise stated, all percentages, parts, ratios, etc. in this document are by weight.

[0058] The materials, methods, and embodiments described herein are exemplary and should not be construed as limiting unless otherwise stated.

[0059] This application discloses a method for simultaneous electrochemical measurement of thermodynamic and kinetic parameters of molten magnesium alloys, which specifically includes the following steps: S1, construct a three-electrode testing system comprising a working electrode, a counter electrode, a reference electrode, and a molten salt electrolyte; the molten salt electrolyte is composed of Mg... 2+The device comprises at least one molten salt for conducting magnesium ions at a test temperature; the counter electrode is made of a conductive material; the reference electrode is made of a reference material with a stable electrode potential; the working electrode is for placing the magnesium alloy to be tested in a limiting component, the limiting component being used to constrain the magnesium alloy to be tested at a preset position in the molten salt electrolyte and to make the magnesium alloy to be tested and the molten salt electrolyte form an electrical contact. S2, calibrating the electrochemical characteristic potential of the magnesium ions in the three-electrode test system; S3, apply a constant current pulse signal to the working electrode and obtain the potential response information of the working electrode after the excitation ends; S4. Based on the potential response information and the electrochemical characteristic potential, calculate the thermodynamic activity of magnesium in the magnesium alloy to be tested and the diffusion coefficient of magnesium in the magnesium alloy to be tested.

[0060] Example 1: Measurement of thermodynamic activity and chemical diffusion coefficient of Mg-Zn binary molten alloy It mainly consists of four steps: 1. Electrode preparation (1) Preparation of working electrode (WE): High-purity Mg (purity ≥99.99%) and high-purity Zn (purity ≥99.99%) were weighed according to the set atomic ratio and smelted into a Mg-Zn binary alloy ingot. After cooling, it was machined into rectangular sheet samples with dimensions of 10mm × 10mm × 5mm. The sample surface was then polished to thoroughly remove the surface oxide film and impurities, ensuring that the surface oxide layer did not hinder electron transfer.

[0061] The polished Mg-Zn sheet sample was placed flat on the bottom of a small MgO crucible. This small MgO crucible was then placed upside down on the inner bottom surface of a large MgO crucible. Because the inner diameter of the large crucible (21 mm) is larger than the outer diameter of the small crucible (16 mm), an annular gap was left between the small crucible and the inner wall of the large crucible after inversion. Based on the inner diameter of the small crucible, the effective contact area between the electrode and the molten salt was calculated to be approximately 1.13 cm². 2 High-purity molybdenum wire (1.5mm in diameter) is knotted, punched, and wrapped around the outside of crucibles of different sizes to form a tightly secured inverted limiting electrode assembly, preventing the Mg-Zn alloy electrode, whose density is close to that of molten salt at 700℃, from floating or shifting.

[0062] (2) Preparation of counter electrode (CE) and reference electrode (RE) Counter electrode: Weigh 3g of high-purity Sn particles (purity ≥99.99%) and place them in a small magnesium oxide crucible.

[0063] Reference electrode: Accurately weigh 4g of high-purity Mg and high-purity Sn (molar ratio of Mg:Sn=50:50) and put them into a small magnesium oxide crucible.

[0064] (3) Electrode wire pre-embedding and curing Three crucible assemblies containing the aforementioned WE, CE, and RE materials were placed in a preheating furnace and heated to 750°C under high-purity Ar protection to completely melt the metal. High-purity molybdenum wires with a diameter of 1.5 mm and a smooth surface polished with sandpaper were vertically inserted into the bottom of the liquid metal in each of the three crucibles. After maintaining their stable position, they were cooled to room temperature to solidify, thus obtaining a prefabricated three-electrode assembly. Figure 3 As shown.

[0065] 2. Preparation and dehydration of molten salt electrolytes Weigh out KCl and MgCl2 powders with a purity ≥99.5%, and mix them evenly at a molar ratio of 80:20 (i.e., KCl-20 at.%MgCl2), with a total mass of 400g. Place the mixed salt into a high-purity alumina crucible and put it at the bottom of the sealed reaction chamber of a well-type experimental resistance furnace. Pass high-purity argon gas through the crucible at a flow rate of 400mL / min, and raise the temperature to 700℃ at a programmed heating rate of 5℃ / min. Hold the temperature at this level for 12 hours to completely evaporate and remove trace amounts of water and water of crystallization adsorbed in the molten salt.

[0066] 3. Potential calibration of the reference electrode Before conducting the formal activity measurement, it is necessary to analyze the Mg content. 2+ The deposition potential of Mg and the reference electrode potential were accurately calibrated. A smooth molybdenum wire with a diameter of 1.0 mm was set as a temporary working electrode (the immersion depth of the wire in the molten salt was controlled to be ≤5 mm), a graphite rod (diameter of 5 mm) was used as a temporary counter electrode, and a prefabricated Mg-Sn (50:50 mol%) electrode was used as a reference electrode.

[0067] Connect the electrochemical workstation, set the cyclic voltammetry (CV) scan rate to 50 mV / s, and the potential scan window to -0.7 V to 1.3 V. The results are as follows: Figure 4 (a) shows the CV-voltaic response curve. Clear Mg was observed in the negative potential scan segment. 2+ The reduction deposition cathode peak and subsequent anodic dissolution peak were observed. Based on the cathode deposition initiation point, the Mg content was precisely determined. 2+ / The characteristic deposition potential E of Mg relative to this Mg-Sn reference electrode at 700℃ ⊙ (Mg 2+ / Mg)=-0.137V.

[0068] 4. GITT Testing and Data Recording The temporary electrode was removed, and the system was switched to the Mg-Zn working electrode and the pure Sn counter electrode. The electrochemical workstation was set to GITT mode. The effective response area was approximately 1.13 cm². 2 A constant current pulse of magnitude I = 50 mA (actual current density j = 44.2 mA / cm²) was applied to the Mg-Zn working electrode. 2 The pulse duration is set to 3000s, and this tiny current pulse drives a trace amount of magnesium to undergo an oxidative release reaction at the interface.

[0069] After each current pulse, the current output is turned off, allowing the working electrode to enter a long-term resting relaxation phase, with the relaxation time set to τ = 3000 s. During this time, due to the concentration gradient between the surface and the interior, Mg atoms spontaneously diffuse within the alloy matrix until the concentration at the electrode surface returns to thermodynamic equilibrium. Multiple pulse-relaxation cycles are continuously performed, and the data are recorded as follows: Figure 4 (b) shows the potential-time response curve. The plateau potential is accurately read from the end of the relaxation curve (the 3000s endpoint), which is the equilibrium electromotive force E of the alloy under the current composition. eq .

[0070] 5. Derivation of Thermodynamic and Kinetic Parameters (1) Calculation of thermodynamic activity The known dissolution equilibrium reaction is Mg (alloy). Mg 2+ (solution) + 2e - (Number of electrons transferred in the reaction n=2).

[0071] Since Mg dissolves at the working electrode, the mass (g) of dissolved Mg can be calculated using Faraday's first law:

[0072] Where z is the number of electrons transferred by a single atom (Mg 2+ (2), F is the Faraday constant (96485 C / mol), M is the relative atomic mass of Mg (24.305 g / mol), and Q is the amount of charge transferred (Q=It, unit A). Then, based on the initial mass of Zn, the alloy composition x after each cycle can be obtained. Zn Here's an example of the calculation after the first loop:

[0073] In other words, after one cycle, 0.0189g of Mg dissolves. Combined with the initial alloy containing 0.15g of Zn, X can be calculated. Zn Activity calculations are based on the Nernst equation and thermodynamic derivations:

[0074] Substituting the Faraday constant F = 96485 C / mol, the gas constant R = 8.314 J / (mol·K), the absolute temperature T = 973 K, and the CV calibration potential... = -0.137 V and the measured equilibrium potential .

[0075] The calculation of the first activity point is based on the first static equilibrium voltage, substituted into the formula: The same principle applies to the remaining points; the thermodynamic activity of Mg in the liquid Mg-Zn alloy at different composition points is calculated. and activity coefficient Furthermore, combining this with the Gibbs-Duhem integral relation:

[0076] The activity and activity coefficient of the alloying element Zn were calculated, and then the curve of thermodynamic activity versus alloy composition was plotted (e.g., Figure 5 (a) shows the calculated values, which are shown in Table 1. Combining the Redlich-Kister (RK) polynomial model, the excess Gibbs free energy G... E and the mixed Gibbs free energy ΔG mix The calculation formula is as follows (e.g. Figure 5 (b) shows:

[0077]

[0078] In the formula, L k These are the interaction parameters for the RK model. Furthermore, taking the partial derivative with respect to the total excess Gibbs free energy yields the partial molar excess Gibbs free energy of component i (Mg or Zn). (like Figure 5 (c) shows:

[0079] according to The variation pattern can be used to directly and quantitatively assess the strength of the mutual attraction between Mg and alloying elements in the melt and its stability in liquid magnesium.

[0080] (2) Calculation of kinetic diffusion coefficient Based on the local Mg concentration gradient generated by GITT current perturbation, and combined with Fick's second law, the diffusion relaxation process of Mg components inside the liquid Mg-X alloy is described, and the chemical diffusion coefficient D of Mg is obtained. Mg :

[0081] In the formula, τ is the pulse duration (s); S is the effective contact area of ​​the electrode, determined according to the inner diameter of the crucible (cm). 2 ); Molar volume of alloy (cm³) 3 The density ( / mol) was calculated based on the alloy composition and density, with density data derived from literature or theoretical mixing principles. and The values ​​are the mass (g) and molar mass (g / mol) of Mg in the alloy, respectively. , , It should be changed according to the specific composition and quality of the working electrode; The change in equilibrium potential before and after a single pulse is the potential change term, which is the change in potential of the working electrode during the excitation of the constant current pulse signal. It reflects the change in the chemical potential of Mg and the change in the thermodynamic equilibrium potential of the total amount of ions removed in a single pulse. This represents the total change in potential during the pulse after deducting the ohmic voltage drop (iRdrop), which is also the change in equilibrium potential of the working electrode before and after relaxation. Its physical significance lies in the fact that during pulsed energization, ions are rapidly embedded only on the surface of the electrode particles, forming an ion concentration gradient within the particles. This continuous accumulation of concentration polarization leads to a slow potential drift, entirely caused by the restricted diffusion of ions in the solid phase. A schematic diagram is shown below. Figure 11 As shown.

[0082] Among them, the first point (X) Zn The specific steps for calculating (=13.3) are as follows:

[0083] The second point (X) Zn The specific steps for calculating (=13.9) are as follows:

[0084] The same applies to the other points, as shown in Table 1.

[0085] The Mg activity coefficient was calculated using a liquid alloy thermodynamic model, while the Redlich-Kister model was used to fit and describe the thermodynamic properties. The Gibbs-Duhem relationship ensures thermodynamic consistency among the activity coefficients of each component.

[0086] The application of the formula for calculating the chemical diffusion coefficient of Mg requires the satisfaction of the semi-infinite diffusion condition, i.e., the duration of a single constant current pulse is much shorter than the time required for complete diffusion homogenization. According to Fick's second law, the characteristic diffusion time is:

[0087] Where L is the characteristic length of diffusion, i.e. the thickness of the working electrode; and D is the diffusion rate.

[0088] Thus, high-precision simultaneous in-situ determination of thermodynamic activity and kinetic diffusion coefficient was completed in the same test system. The calculation results are shown in the figure. Figure 5 As shown in (d).

[0089] Table 1. Experimental results and related data processing in Example 1

[0090] Example 2: Measurement of thermodynamic activity and chemical diffusion coefficient of Mg-Sn binary molten alloy Unlike Example 1, 0.69g of a Mg-8.1 at.%Sn alloy, smelted from high-purity Mg (≥99.99%) and high-purity Sn (≥99.99%), was used as the working electrode. 4.5g of a Mg-Sn alloy (molar ratio 45:55) was used as the reference electrode, and 5g of high-purity Sn was used as the counter electrode. The electrolyte composition was KCl-20 at.%MgCl2. The CV curve results are shown below. Figure 6 As shown in (a), due to the decrease in Mg content of the reference electrode, the deposition potential of Mg becomes more negative, at -0.192V. Figure 6 In (b), due to the change in the composition of the working electrode, the GITT curve is somewhat different from that in Example 1.

[0091] Example 3: Measurement of thermodynamic activity and chemical diffusion coefficient of Mg-Al binary molten alloy Unlike Example 2, this example uses a 0.59g Mg-10.5at.%Al alloy, smelted from high-purity Mg (≥99.99%) and high-purity Al (≥99.99%), as the working electrode. A 4.5g Mg-Sn alloy (50:50 molar ratio) is used as the reference electrode, and 5g high-purity Zn is used as the counter electrode. The electrolyte composition is KCl-10at.%LiCl-5at.%MgCl2, with a further reduction in MgCl2 content. The role of LiCl is to lower the melting point of the molten salt. Figure 7 (a) shows the CV curves of the test and Figure 7 (b) shows the GITT curves of the test. At the same electrode insertion depth, the decrease in current in the CV curve is due to the presence of Mg in the molten salt. 2+With the reduction of Mg content, the deposition potential of Mg remained almost identical to that in Example 1, indicating that the reference electrodes of both exhibited high stability. Even after replacing the counter electrode with pure Zn, the GITT curve remained relatively stable, indicating that Mg did not exhibit any floating interference during the test, demonstrating that Zn effectively adsorbed Mg. The change in the working electrode composition resulted in some differences in the shape of the GITT curve, reflecting the differences in the thermodynamic and kinetic properties of different binary magnesium alloys.

[0092] Comparative Example 1 Unlike Example 1, this comparative example uses pure Mg as the reference electrode and a KCl-50 at.% MgCl2 mixed molten salt as the electrolyte. Since the densities of both the pure Mg reference electrode and the Mg-Zn working electrode are lower than that of this high-concentration molten salt, both employ an inverted limiting structure. Figure 8 As shown, two problems are evident. First, the pure Mg reference electrode is prone to severe fluctuations and interfacial disturbances in high-temperature molten salt, resulting in significant irregular shifts and drifts in the potential response, failing to provide a stable reference potential. Second, excessively high MgCl2 concentrations induce strong Mg-Cl complexation effects, reducing the Mg content in the molten salt. 2+ The migration rate. This leads to a significant increase in the potential polarization difference during the GITT test, resulting in dramatic fluctuations in the potential response curve and a substantial increase in the overall polarization impedance.

[0093] Comparative Example 2 Unlike Comparative Example 1, this comparative example optimizes the molten salt ratio to KCl-20at.%MgCl2 as in Example 1, but the reference electrode remains pure Mg, and the 1.5mm molybdenum wire electrode is not protected with a high-temperature resistant sheath. Figure 9 As shown, the potential polarization difference narrowed significantly during the GITT pulse process, but potential drift and instability remained due to the continued use of a pure Mg reference electrode. In the later stages of the experiment, the lack of sheathing protection for the molybdenum wire allowed trace amounts of residual oxygen in the reaction chamber at high temperatures to cause oxidation and eventual breakage of the wire surface, resulting in severe distortion and abrupt changes in the later test curves.

[0094] Comparative Example 3 Unlike Example 1, this comparative example replaced the reference electrode with a stable Mg-Sn (50:50 molar ratio) alloy, but used a small, upright magnesium oxide crucible (opening upwards) for the polished sheet-like Mg-2.5at.%Zn working electrode. The test results are as follows: Figure 10As shown, the measured potential is very close to the bare potential when the current collector molybdenum wire is directly inserted into the molten salt, and it shows a slow downward trend overall. This is because the liquid Mg-Zn working electrode undergoes local floating and migration under the combined effect of surface tension and density difference, resulting in local detachment or poor contact between the liquid alloy and the molybdenum current collector, failing to form a good equipotential body, and thus making it impossible to measure the correct alloy electrode potential.

[0095] Comparative Example 4 Unlike Example 1, this comparative example uses an upright crucible. The molten salt composition is KCl-10 at.% LiCl-5 at.% MgCl2, which has a relatively low density. The working electrode is Mg-40 at.% Zn, whose density is much greater than that of the molten salt; therefore, an inverted crucible is unnecessary. The GITT test curve is shown below. Figure 12 (a) shows that the test curve is normal. This more clearly defines the applicable scope of the inverted structure—specifically for low-density magnesium alloys.

[0096] Comparative Example 5 Unlike Example 2, this comparative example adjusts the constant current pulse time and relaxation time to 1000 s. The GITT test curve is shown below. Figure 12 (b) shows that the test results are relatively normal.

[0097] Conclusions of the comparative experiment: As can be seen from Comparative Examples 1-3, only by simultaneously employing a Mg-Sn alloy reference electrode, KCl-20at.%MgCl2 to optimize the molten salt ratio, molybdenum wire sheath protection, and an inverted limiting structure for the working electrode can the structural stability and good electrical contact of the high-temperature liquid electrode interface be ensured, thereby obtaining high-precision thermodynamic and kinetic test data. This solves the problems of low-density liquid electrode floating, molten salt complexation interference, and simultaneous measurement of thermodynamic / kinetic parameters.

[0098] In the same three-electrode system, the reference potential was first calibrated using the CV method, and then a constant current pulse was applied and the relaxation process was monitored using the GITT method. According to GITT theory, the potential change during the pulse contains information about the diffusion of Mg in the alloy, and the equilibrium potential difference before and after relaxation reflects the thermodynamic potential change caused by the change in composition. After processing the same set of experimental data using different mathematical models, the activity and diffusion coefficient can be extracted separately, realizing the integrated measurement of thermodynamic and kinetic parameters in the same system, under the same state, and at the same time. This eliminates systematic errors between multiple experiments and significantly improves the internal consistency of the data.

[0099] This application addresses several key challenges: ensuring contact through an inverted structure, optimizing the molten salt to avoid mass transfer interference, utilizing the Mg-Sn reference for stability, and employing an alumina tube for protection. These challenges resolve the need for a stable electron conduction path during pulsed reactions, the requirement to reflect pure diffusion behavior during relaxation, the need for a long-term potential reference during multi-cycle experiments, and the need for an unbroken current collector during long-term experiments. A problem in any of these components would prevent the reliable chemical diffusion coefficient from being resolved from GITT data. This synergistic effect enables the high-precision simultaneous determination of the thermodynamic and kinetic parameters of highly reactive, low-density magnesium alloy melts.

[0100] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for simultaneous electrochemical measurement of thermodynamic and kinetic parameters of molten magnesium alloys, characterized in that, include: A three-electrode testing system comprising a working electrode, a counter electrode, a reference electrode, and a molten salt electrolyte was constructed. The molten salt electrolyte is composed of Mg 2+ The device comprises at least one molten salt for conducting magnesium ions at a test temperature; the counter electrode is made of a conductive material; the reference electrode is made of a reference material with a stable electrode potential; the working electrode is for placing the magnesium alloy to be tested in a limiting component, the limiting component being used to constrain the magnesium alloy to be tested at a preset position in the molten salt electrolyte and to make the magnesium alloy to be tested and the molten salt electrolyte form an electrical contact. The electrochemical characteristic potential of the magnesium ions in the three-electrode test system was calibrated. A constant current pulse signal is applied to the working electrode to obtain the potential response information recorded by the working electrode after the excitation ends and it is allowed to relax. Based on the potential response information and the electrochemical characteristic potential, the thermodynamic activity of magnesium in the magnesium alloy to be tested and the diffusion coefficient of magnesium in the magnesium alloy to be tested are calculated.

2. The method for simultaneous electrochemical measurement of thermodynamic and kinetic parameters of molten magnesium alloys according to claim 1, characterized in that, The limiting component includes a first container and a second container. The magnesium alloy to be tested is placed in the first container, the first container is disposed inside the second container, and a fluid channel for the molten salt electrolyte to permeate is formed between the first container and the second container.

3. The method for simultaneous electrochemical measurement of thermodynamic and kinetic parameters of molten magnesium alloys according to claim 2, characterized in that, The density of the magnesium alloy to be tested is less than or close to the density of the molten salt electrolyte, and the first container is disposed inside the second container with its opening facing downwards.

4. The method for simultaneous electrochemical measurement of thermodynamic and kinetic parameters of molten magnesium alloys according to claim 1, characterized in that, At least a portion of the surface of the limiting component that is in contact with the molten salt electrolyte is made of a high-temperature resistant insulating material, wherein the high-temperature resistant insulating material is selected from at least one of oxide ceramics, nitride ceramics, or carbide ceramics.

5. The method for simultaneous electrochemical measurement of thermodynamic and kinetic parameters of molten magnesium alloys according to claim 1, characterized in that: The counter electrode is constructed by loading an inert metal or an inert alloy into a container; the material of the counter electrode is a high-density metal or a high-density alloy, wherein the high-density metal is selected from at least one of Sn, Zn, Bi, Al, Pb, Ga, In, Cd, and Tl, or has a density exceeding 1.6 g / cm³. 3 alloy.

6. The method for simultaneous electrochemical measurement of thermodynamic and kinetic parameters of molten magnesium alloys according to claim 1, characterized in that, The reference electrode is composed of an alloy of magnesium and other metals loaded in a container; the molar percentage of magnesium is 40% to 60%. The molten salt electrolyte comprises an alkali metal chloride and magnesium chloride, wherein the molar percentage of magnesium chloride is 5 at.% to 20 at.%.

7. The method for simultaneous electrochemical measurement of thermodynamic and kinetic parameters of molten magnesium alloys according to claim 1, characterized in that, The electrochemical characteristic potential is calibrated using transient electrochemical testing methods, including cyclic voltammetry, linear sweep voltammetry, square wave voltammetry, or differential pulse voltammetry.

8. The method for simultaneous electrochemical measurement of thermodynamic and kinetic parameters of molten magnesium alloys according to claim 1, characterized in that, The electrochemical characteristic potential includes the calibration potential, and the potential response information includes the potential-time response curve and the equilibrium potential; Based on the potential response information and the electrochemical characteristic potential, the thermodynamic activity of magnesium in the magnesium alloy to be tested and the diffusion coefficient of magnesium in the magnesium alloy to be tested are calculated, including: Based on the calibration potential and the equilibrium potential, the thermodynamic activity of magnesium in the magnesium alloy to be tested is calculated using the Nernst equation. Based on the potential-time response curve, the pulse duration, the potential change of the working electrode during the excitation of the constant current pulse signal, and the equilibrium potential change of the working electrode before and after relaxation are obtained. The chemical diffusion coefficient of magnesium in the magnesium alloy under test is calculated based on Fick's diffusion law, according to the pulse duration, the potential change of the working electrode during the excitation of the constant current pulse signal, and the equilibrium potential change of the working electrode before and after relaxation.

9. The method for simultaneous electrochemical measurement of thermodynamic and kinetic parameters of molten magnesium alloys according to claim 8, characterized in that, The calculation of the chemical diffusion coefficient of magnesium in the magnesium alloy under test, based on Fick's diffusion law, according to the pulse duration, the potential change of the working electrode during the constant current pulse signal excitation, and the equilibrium potential change of the working electrode before and after relaxation, includes: The molar volume of the magnesium alloy to be tested, the mass of magnesium in the magnesium alloy to be tested, and the effective contact area between the working electrode and the molten salt electrolyte are obtained. The chemical diffusion coefficient of magnesium in the magnesium alloy under test is calculated based on Fick's diffusion law, taking into account the molar volume of the magnesium alloy under test, the mass of magnesium in the magnesium alloy under test, the effective contact area between the working electrode and the molten salt electrolyte, the pulse duration, the potential change of the working electrode during the excitation of the constant current pulse signal, and the equilibrium potential change of the working electrode before and after relaxation.

10. The method for simultaneous electrochemical measurement of thermodynamic and kinetic parameters of molten magnesium alloys according to claim 1, characterized in that, The three-electrode testing system and testing process were carried out under a protective atmosphere.

Images