Background
The magnesium alloy has very excellent mechanical properties such as specific strength, specific rigidity and the like as a light alloy, and is widely applied to the fields of aerospace, automobiles, ships and other industries. However, magnesium alloys have poor corrosion resistance, and their bare metal is highly susceptible to localized corrosion leading to component failure.
At present, the corrosion protection measures of magnesium alloy mainly comprise alloy component modification, electrochemical protection, surface coating treatment and direct use of corrosion inhibitor. Wherein, the direct use of the corrosion inhibitor is a simple and easy method with quick effect and low cost. The corrosion inhibitor is a chemical substance which directly acts on the metal surface and can slow down the corrosion reaction of the metal surface. The main action mechanism comprises: complex precipitates are formed on the metal surface, and the metal surface is adsorbed to form a hydrophobic film and oxidized to form a passivation layer. When one corrosion inhibitor is used alone, the requirements of low concentration and high efficiency cannot be met at the same time. The compound corrosion inhibitor is prepared by combining two or more different corrosion inhibitors, wherein if the corrosion inhibition efficiency after compounding is higher than that of each component used alone, the two corrosion inhibitors have synergistic effect, and if the corrosion inhibition efficiency is lower than that of each component used alone, the two corrosion inhibitors have antagonistic effect.
Due to different action mechanisms of different corrosion inhibitors, the corrosion inhibition efficiency can be greatly improved by using the corrosion inhibitors with different corrosion inhibition mechanisms through the synergistic action of the corrosion inhibitors. The compound combination can be divided into organic corrosion inhibitor and inorganic corrosion inhibitor compound, organic matter and organic matter compound and inorganic matter compound according to the substance types. The synergistic effect of the compound corrosion inhibitor is not only related to the selected combination type, but also depends on the concentration of each component and the compounding ratio. The synergistic effect can be obviously embodied only in a certain specific concentration ratio and range, and the combination outside the concentration range can not produce synergistic effect or even produce antagonistic effect on the contrary, so as to promote corrosion.
The Chinese invention patent CN 111690936A discloses a compound corrosion inhibitor of AZ91 magnesium alloy suitable for neutral brine corrosion medium and a preparation method thereof, wherein the compound corrosion inhibitor consists of benzotriazole linseed oleamide derivative, sodium molybdate, an emulsifier OP-21 and isopropanol. Although the slow release efficiency of the compound corrosion inhibitor to magnesium alloy can reach about 98%, the compound corrosion inhibitor has the following defects: (1) has sustained release efficacy only for a unique brand of magnesium alloy AZ 91D; (2) only for neutral saline media; (3) the compound components are complex and are not easy to realize industrialized popularization. In addition, Chinese patent CN 101922009B discloses a corrosion inhibitor formula for inhibiting corrosion of magnesium alloy in automobile engine coolant, which comprises 0.1-20% of sodium fluoride, 0.1-20% of inorganic salts such as sodium molybdate and the like, and 0.1-10% of organic substances such as hexamethylene tetramine, 0.1-5% of benzotriazole, 0.1-5% of sodium dodecyl benzene sulfonate and the like. The invention can well solve the problems of serious environmental pollution and harm to human health caused by toxic and harmful substances such as chromate, phosphate, nitrite and the like added into the prior ethylene glycol type automobile coolant, and greatly reduces the production and use cost. However, as described in the above example, the compound corrosion inhibitor has a complex composition, and is only suitable for magnesium alloy materials serving as ethylene glycol, but not suitable for magnesium alloy parts serving as water-based media. Similarly, chinese patent CN 105369256 a discloses a magnesium alloy corrosion inhibitor in an automobile coolant, which mainly comprises diammonium hydrogen phosphate and sodium lignosulfonate. Although the binary compound component has excellent high-temperature corrosion inhibition performance (99.38%), the service environment of the binary compound component is still ethylene glycol solution, and the introduction of phosphorus in the compound component also has potential threat of causing environmental pollution, so the binary compound component is not suitable for open atmospheric environment.
Disclosure of Invention
In order to solve the defects of the prior art, the invention provides a magnesium alloy compound corrosion inhibitor suitable for a chlorine-containing medium and a preparation method thereof. The compound corrosion inhibitor is suitable for pure magnesium and common magnesium alloys such as magnesium-aluminum systems, magnesium-zinc systems, magnesium-rare earth systems and the like, the corrosion inhibition efficiency can reach more than 90 percent and up to 98 percent, the corrosion inhibition efficiency is improved along with the prolonging of the soaking time, and the long-acting corrosion inhibition effect can be provided.
The first purpose of the invention is to provide a magnesium alloy compound corrosion inhibitor suitable for chlorine-containing media.
The second purpose of the invention is to provide a preparation method of the magnesium alloy compound corrosion inhibitor suitable for chlorine-containing media.
The first purpose of the invention can be achieved by adopting the following technical scheme:
the magnesium alloy compound corrosion inhibitor comprises soluble fluoride and soluble dicarboxylate, wherein the soluble fluoride is sodium fluoride or potassium fluoride, and the soluble dicarboxylate is malate, succinate, fumarate or diglycolate.
Further, the molar ratio of the soluble fluoride to the soluble dicarboxylate is the same.
Further, the mixing concentration of the soluble fluoride and the soluble dicarboxylate in the chlorine-containing medium is controlled to be 0.01 to 0.1mol/L, thereby obtaining the corrosion inhibition effect.
Further, the chlorine-containing medium contains water or ethylene glycol.
The second purpose of the invention can be achieved by adopting the following technical scheme:
a preparation method of a magnesium alloy compound corrosion inhibitor suitable for a chlorine-containing medium comprises the following steps:
and sequentially adding the soluble fluoride and the soluble dicarboxylate into a chlorine-containing medium, fully stirring until the soluble fluoride and the soluble dicarboxylate are dissolved, and adjusting the pH value by using sodium hydroxide to obtain a solution containing the magnesium alloy compound corrosion inhibitor.
Further, the pH value is adjusted to 6.8-7.2 by using sodium hydroxide.
Compared with the prior art, the invention has the following beneficial effects:
1. the magnesium alloy compound corrosion inhibitor provided by the invention has a remarkable corrosion inhibition effect on magnesium alloys of various brands in a chlorine-containing solution, can generally reach more than 90 percent and maximally 98 percent, and can realize long-term effectiveness.
2. The total concentration of the magnesium alloy compound corrosion inhibitor provided by the invention is far lower than the use concentration when a single corrosion inhibitor is used to achieve the same efficiency, and the use cost is greatly reduced.
3. The selected compound components are conventional and harmless, are environment-friendly, have low price and very high operability and economic value.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer and more complete, the technical solutions in the embodiments of the present invention will be described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments, and all other embodiments obtained by a person of ordinary skill in the art without creative efforts based on the embodiments of the present invention belong to the protection scope of the present invention. It should be understood that the description of the specific embodiments is intended to be illustrative only and is not intended to be limiting.
Example 1:
the embodiment provides a magnesium alloy compound corrosion inhibitor suitable for a chlorine-containing medium, which is a novel binary environment-friendly compound corrosion inhibitor suitable for magnesium alloy in the chlorine-containing medium, and mainly comprises the following two parts: and (2) component A: soluble fluoride (including, but not limited to, sodium fluoride (NaF) or potassium fluoride (KF)) and component B: soluble dicarboxylic acid (potassium, sodium) salts (including, but not limited to, malate, succinate, fumarate, or diglycolate), and the organic acid molecular structures of malate, fumarate, succinate, and diglycolate are shown in fig. 1.
The binary compound corrosion inhibitor is prepared from a component A (soluble fluoride) and a component B (soluble dicarboxylate) in the same molar ratio. In the process of implementing corrosion protection, the two are sequentially added into a chlorine-containing medium (the chlorine-containing medium contains water or ethylene glycol) to be completely dissolved. Finally, the mixing concentration of the two in the chlorine-containing medium should be controlled between 0.01 and 0.1mol/L to obtain the optimal corrosion inhibition effect. Wherein, when the concentration of the two is 0.05mol/L, the corrosion inhibition efficiency is the highest and reaches 98 percent; when the concentration of the corrosion inhibitor and the concentration of the corrosion inhibitor are both 0.1mol/L, the efficiency of compounding the corrosion inhibitor is 91 percent; when the concentration of the two is reduced by 0.01mol/L at the same time, the corrosion inhibition efficiency is reduced to 60 percent; the corrosion inhibition efficiency is between 60 and 98 percent when the components are mixed according to the rest proportion.
Example 2:
in this example, a single-factor and two-factor comparison test is performed on the compound corrosion inhibitor.
The specific process of the experiment is as follows:
(1) magnesium alloy (working electrode) surface pretreatment.
Processing the magnesium alloy sample into a cylinder with the diameter of 12 mm multiplied by 50mm, encapsulating the whole electrode with epoxy resin and exposing only 1.0cm2The working area of (a). And (3) grinding the test surface by using metallographic abrasive paper from 200#, 600#, 800#, 1000# and 1500# step by step, removing oil by using acetone, cleaning by using ethanol, and then placing in cold air for drying for later use.
(2) The novel compound magnesium alloy corrosion inhibitor solution is prepared.
The embodiment provides a preparation method of a magnesium alloy compound corrosion inhibitor suitable for a chlorine-containing medium, which comprises the following specific steps:
preparing sodium fluoride (analytically pure), sodium malate (analytically pure), sodium chloride (analytically pure) and 1mol/L sodium hydroxide medicine, dissolving sodium chloride into deionized water, and preparing a sodium chloride solution with the mass fraction of 0.9 wt.% as a corrosion medium; thereafter, component a (fluoride, in this case sodium fluoride) and component B (soluble dicarboxylate, in this case sodium malate) were added to 0.9 wt.% sodium chloride solution, respectively, stirred to dissolve, pH-adjusted to neutral 6.8-7.2 using 1mol/L sodium hydroxide, and constant volume was made to obtain a solution containing a single component (component a or component B) at a concentration of 0.05 mol/L; similarly, the component A sodium fluoride and the component B sodium malate are sequentially added into the prepared sodium chloride solution, fully stirred until dissolved, the pH value is adjusted to 6.8-7.2 of near neutrality by using 1mol/L sodium hydroxide, and finally the solution of the compound corrosion inhibitor containing 0.05mol/L sodium fluoride and 0.05mol/L sodium malate (the component A and the component B) is obtained by constant volume.
(3) Laboratory apparatus and method.
And evaluating the corrosion inhibition performance of the corrosion inhibitor of the embodiment by adopting an electrochemical test mode.
The electrochemical measuring instrument selects an American Gamry Interface 1010B electrochemical workstation, adopts a three-electrode system, selects an AM50 magnesium alloy as a magnesium alloy sample to be measured, uses the sample to be measured as a working electrode, and has an exposed area of 1cm2The saturated calomel electrode is used as a reference electrode, and the platinum sheet is used as a counter electrode. The electrolyte is the 0.9 wt.% sodium chloride solution prepared in example 1 and containing the component a and the component B dissolved therein, and the blank is the sodium chloride solution containing only 0.9 wt.%. The potential scanning range of the polarization curve test is about-0.30 to +0.30V (vs OCP), and the scanning speed is 0.5 mV/s.
(4) And (5) experimental results.
The slow release effect of the corrosion inhibitor can be calculated by using the corrosion current density corresponding to the polarization curve.
η=(icorr-i’corr/icorr) X 100%, where eta represents corrosion inhibition efficiency of corrosion inhibitor, icorrRepresents the corrosion current density of the metal in the medium without adding the corrosion inhibitor; i'corrThe corrosion current density of the metal in the medium with the corrosion inhibitor added is shown.
As shown in fig. 2, fig. 2 is a polarization curve diagram of no corrosion inhibitor (BGS) added, sodium fluoride (NaF) added alone, sodium malate (DMA) added alone, and a combination of the two (Mix). It can be seen from fig. 1 that after soaking for 24 hours, the polarization curve with the addition of the compound corrosion inhibitor (Mix) drifts significantly toward a smaller current density than the blank BGS without the addition of the corrosion inhibitor.
The electrochemical data corresponding to the polarization curves are shown in table 1, and it can be seen from table 1 that the corrosion inhibition efficiency is-75% with malate alone, 74% with sodium fluoride alone, and 94% with the compound 1 corrosion inhibitor. The corrosion inhibition efficiency of the compound corrosion inhibitor provided by the invention is obviously improved and is higher than the efficiency of each component when the components are used singly, and the obvious synergistic corrosion inhibition effect among the components is embodied.
TABLE 1 polarization curve fitting parameter of AM50 magnesium alloy in single factor and two compounding in three corrosion inhibitors
Example 3:
in this example, a single-factor and two-factor comparison test is performed on the compound corrosion inhibitor.
The magnesium alloy (working electrode) surface pretreatment, corrosion inhibitor solution preparation scheme and experiment are the same as those in example 2, in this example, the corrosion inhibitor is tested by electrochemical impedance spectroscopy, and the test frequency range is 105Hz-10-2Hz, the alternating current excitation signal is a sine wave of 10 mV.
As shown in fig. 3, fig. 3 is a Nyquist impedance spectrum curve of a magnesium alloy in various corrosion inhibitor solutions, after a compound corrosion inhibitor (Mix) is added, the system presents two obvious capacitive arc characteristics, and the radius of the capacitive arc is continuously increased along with the extension of the soaking time, which shows that the corrosion resistance is continuously improved along with the extension of the soaking time. And (4) evaluating the corrosion resistance of the system by calculating the total impedance value of the system, and comparing the total impedance value with a blank group to calculate the corrosion inhibition efficiency. The calculation result shows that the corrosion inhibition efficiency is-90% when the malic acid is singly used, 35% when the sodium fluoride is singly used, and 98% when the compound 1 corrosion inhibitor is used. The data of the electrochemical impedance spectrum also prove that the compound corrosion inhibitor provided by the invention has a more excellent corrosion inhibition effect, and a very obvious synergistic corrosion inhibition effect exists between the two.
Example 4:
in this example, a single-factor and two-factor comparison test is performed on the compound corrosion inhibitor.
(1) The magnesium alloy (working electrode) surface pretreatment and the corrosion inhibitor solution preparation schemes are the same as in examples 2 and 3.
(2) Experimental methods.
A resin-inlaid AM50 magnesium alloy sample (with the surface exposed area of 1cm2) is soaked in 200ml of blank 0.9. wt% NaCl solution (BGS), 0.9 wt% NaCl solution (BGS) +0.05mol/L sodium malate, 0.9 wt% NaCl solution (BGS) +0.05mol/L sodium fluoride and 0.9 wt% NaCl solution (BGS) +0.05mol/L sodium fluoride +0.05mol/L sodium malate solution, the coverage condition of a surface product after the sample is continuously soaked for 24 hours is observed by using a scanning electron microscope, and the effect of different corrosion inhibitors is evaluated.
(3) And (5) experimental results.
As shown in fig. 4, fig. 4 is a scanning electron microscope image of the surface corrosion morphology of the magnesium alloy after being soaked in different corrosion inhibitor solutions for 24 hours. It was observed that the blank surface without added corrosion inhibition had clearly localized, whereas with the addition of a single component corrosion inhibitor the degree of corrosion was reduced and with the use of NaF alone cubic precipitated product particles were formed on the surface forming a protective film. In the solution using the compound corrosion inhibitor (Mix), the precipitated particles generated on the surface are changed into a sphere-like shape from a cubic shape, the generated particles are increased in number, smaller in size and more compact in accumulation, and a more protective film is formed to provide corrosion protection for the magnesium substrate. The compound corrosion inhibitor is mainly used for inhibiting corrosion by forming a compact precipitated particle layer on the surface, and the transformation of the particle morphology also reflects the synergistic corrosion inhibition and mutual influence between the two components.
The above description is only for the preferred embodiments of the present invention, but the protection scope of the present invention is not limited thereto, and any person skilled in the art can substitute or change the technical solution and the inventive concept of the present invention within the scope of the present invention.