阅读说明：本技术 一种镁或镁合金表面自催化降解涂层及其制备方法 (Magnesium or magnesium alloy surface autocatalytic degradation coating and preparation method thereof ) 是由 曾荣昌 殷正正 曾美琪 于晓彤 崔蓝月 李硕琦 张芬 邹玉红 于 2020-06-30 设计创作，主要内容包括：本发明提供了一种镁或镁合金表面自催化降解涂层及其制备方法,以磷酸盐和亚铁盐或铁盐为原料,采用化学转化法,在镁或镁合金基体表面制备具有加速镁合金降解的涂层,所得涂层为铁、亚铁的磷酸盐和氢氧化物。为阴极型多孔涂层,因开路电位高于镁合金基体,同时由于铁或亚铁离子被还原产生的单质铁会和镁合金形成电偶腐蚀,从而起到加速镁合金腐蚀的作用,进而实现对镁合金的自催化降解。本发明开创了一种新的思路,相对于现有技术,具有工艺环保、简单、反应时间短、生产成本低、不损害基体结构和力学性能等特点。所获得的镁合金表面涂层,具有结构多孔、生物可降解性和生物相容性能好等优点,所以既可做结构性材料,又可作可降解生物医用材料。(The invention provides a magnesium or magnesium alloy surface autocatalytic degradation coating and a preparation method thereof, which takes phosphate and ferrous salt or ferric salt as raw materials, adopts a chemical conversion method to prepare the coating with the function of accelerating the degradation of magnesium alloy on the surface of a magnesium or magnesium alloy substrate, and the obtained coating is phosphate and hydroxide of iron and ferrous. The coating is a cathode type porous coating, and because the open-circuit potential is higher than that of the magnesium alloy matrix, simple substance iron generated by reducing iron or ferrous ions can form galvanic corrosion with the magnesium alloy, the effect of accelerating the corrosion of the magnesium alloy is achieved, and the autocatalytic degradation of the magnesium alloy is further realized. Compared with the prior art, the invention creates a new idea and has the characteristics of environment-friendly and simple process, short reaction time, low production cost, no damage to the structure and the mechanical property of the matrix and the like. The obtained magnesium alloy surface coating has the advantages of porous structure, good biodegradability and biocompatibility and the like, so that the magnesium alloy surface coating can be used as a structural material and a degradable biomedical material.)

1. The magnesium or magnesium alloy surface autocatalytic degradation coating is characterized in that the chemical component of the autocatalytic degradation coating comprises Fe₃(PO₄)₂And/or FePO₄(ii) a The open circuit potential and the self-corrosion current density of the autocatalytically degradable coating are both greater than the corresponding open circuit potential and the self-corrosion current density of the magnesium or the magnesium alloy.

2. The magnesium or magnesium alloy surface autocatalytic degradation coating of claim 1, wherein the thickness of the magnesium or magnesium alloy surface autocatalytic degradation coating is greater than 0 and equal to or less than 20 μm.

3. The magnesium or magnesium alloy surface autocatalytic degradation coating of claim 1, wherein the autocatalytic degradation coating has an open circuit potential of-1.56 ± 0.35V/SCE to-1.57 ± 0.04V/SCE after 1 hour of electrochemical test and an autocorrosion current density of 5.69 × 10^-4A/cm²～1.04×10^-5A/cm²(ii) a The hydrogen evolution rate after soaking in 3.5 wt.% NaCl for 78 hours was 0.20. + -. 0.12mL cm^-2·h^-1～0.08±0.01mL·cm^-2·h^-1。

4. A preparation method of a magnesium or magnesium alloy surface autocatalytic degradation coating is characterized by comprising the following steps:

(1) preparation of precursor solution

Weighing phosphate and ferrous salt or ferric salt in a beaker according to the ferrous ion/phosphate ion molar ratio of 8.43-100:100 or the ferric ion/phosphate ion molar ratio of 6-100:100, adding deionized water to prepare a uniform mixed solution;

adjusting the pH value of the mixed solution to 2-5 by using phosphoric acid to obtain a precursor solution;

(2) pretreatment of coated substrates

Mechanically polishing the magnesium or magnesium alloy workpiece to remove burrs on the surface of the magnesium or magnesium alloy workpiece, sequentially washing with first water, alkali washing, washing with second water, acid washing and washing with third water, and drying to obtain a magnesium or magnesium alloy workpiece with a fresh surface;

(3) putting the magnesium or magnesium alloy workpiece with the fresh surface into a precursor solution, and immersing the processed magnesium or magnesium alloy workpiece below the liquid level of the precursor solution;

sealing the mouth of the beaker by using a preservative film and placing the beaker in a water bath kettle for water bath reaction;

(4) and taking out the beaker, opening the preservative film, taking out the sample, washing the sample with water, and drying to finish the preparation of the magnesium or magnesium alloy surface autocatalytic degradation coating.

5. The method for preparing the autocatalytic degradation coating on the surface of magnesium or magnesium alloy according to claim 4, wherein in the step (1), the ferrous salt is ferrous sulfate, ferrous chloride or ferrous nitrate; the ferric salt is ferric sulfate, ferric chloride or ferric nitrate.

6. The method for preparing the magnesium or magnesium alloy surface autocatalytically degradable coating according to claim 4, wherein said phosphate is trisodium phosphate dodecahydrate, disodium hydrogen phosphate, sodium dihydrogen phosphate, ammonium phosphate or ammonium hydrogen phosphate.

7. The method for preparing the autocatalytically degradable coating on the surface of magnesium or magnesium alloy according to claim 4, wherein in the step (1), the concentration of the solution of phosphate and ferrous or ferric salt is calculated by MEDUSA software according to the precipitation and dissolution balance of ferrous or ferric phosphate.

8. The method for preparing the autocatalytic degradation coating on the surface of the magnesium or magnesium alloy as claimed in claim 4, wherein the volume ratio of the surface area of the magnesium or magnesium alloy workpiece to the precursor solution in the step (3) is 1cm²:4±0.5mL。

9. The method for preparing the magnesium or magnesium alloy surface autocatalytic degradation coating according to claim 4, wherein the water bath reaction condition is 20-80 ℃ for 2-60 min.

10. The method for preparing the autocatalytic degradation coating on the surface of magnesium or magnesium alloy according to claim 4, wherein the phosphate, ferrous salt or ferric salt is analytically pure.

Technical Field

The invention relates to the technical field of magnesium or magnesium alloy surface coatings, in particular to a magnesium or magnesium alloy surface autocatalytic degradation coating and a preparation method thereof.

Background

Magnesium is one of the lightest metals and has a density of 1.75g/cm³It is one of the elements rich in resource storage on earth, and the content in the earth crust can be about 2.7%.

The magnesium alloy also has the advantages of high specific strength, high specific rigidity, large elastic modulus, good damping property, good thermal conductivity, good vibration damping property, good organic matter and alkaline solution resistance and the like. In addition, the magnesium alloy also has good dimensional stability, electromagnetic shielding property, easy processing property and recycling property. Therefore, they are used in the fields of structural materials (e.g., automobiles, aerospace, 3C products) and functional materials (e.g., biomedical materials). With the technological progress, the range of application of magnesium alloy is gradually expanded, and the magnesium alloy is expanded to a plurality of non-traditional fields, such as pressure balls.

As a degradable biomedical metal material, the magnesium and the magnesium alloy also have good biocompatibility and mechanical compatibility. Magnesium ions are intracellular positive ions with contents second to potassium, sodium and calcium in human bodies, can participate in protein synthesis, can activate various enzymes in vivo, regulate the activities of central nervous systems and muscles, and ensure the normal contraction of cardiac muscles. As a degradable magnesium alloy material, the material can be quickly corroded in a human body, and inconvenience caused by secondary operation is avoided. In addition, the mechanical property of the magnesium alloy is more advantageous than that of the traditional polylactic acid, titanium alloy, stainless steel and other types of degradable implant materials; not only has the capacity of promoting the formation of bone cells and accelerating the healing of bones; moreover, the elastic modulus similar to that of human skeleton can effectively avoid stress shielding effect. The degradable magnesium and the magnesium alloy can be used as biomedical devices, including bone fixing materials such as bone plates and bone nails, and stent materials such as vascular stents, and have great clinical application prospect.

However, magnesium is very reactive by its chemical nature (-2.36V/SHE) and does not resist corrosion in both acidic and neutral solutions. Meanwhile, an oxide film generated on the surface of the magnesium alloy is usually porous, and the film layer cannot effectively protect a substrate. Therefore, the corrosion of magnesium alloy generally becomes a bottleneck limiting the application of magnesium alloy, and limits the application of magnesium alloy in many fields. Researchers at home and abroad mainly research from the perspective of improving the corrosion resistance of magnesium alloy, and the basic methods are three types:

(1) purifying and reducing the concentration of impurity elements (iron, silicon, nickel and cobalt);

(2) alloying (adding elements such as aluminum, manganese, zinc, rare earth and the like) and post-treatment (rolling, extrusion, heat treatment and the like);

(3) and (4) surface modification. The surface treatment technologies such as micro-arc oxidation (MAO), layer-by-layer assembly (LBL), Chemical Conversion Coating (CCC), Chemical Vapor Deposition (CVD), hydrotalcite (LDHs) and the like are important means for improving the corrosion resistance of the magnesium alloy.

The chemical conversion treatment is one of the common surface treatment processes of the magnesium alloy at present, and a layer of insoluble film layer which is composed of oxides, chromium compounds, phosphorus compounds or other compounds and has good adhesion can be formed on the surface of the magnesium alloy by a chemical or electrochemical treatment method. The film has good bonding force with the substrate, and can prevent the corrosion medium from corroding the substrate. The chemical conversion coating is thin, and has low hardness and wear resistance, as compared to the anodic oxide coating. The chemical conversion film process needs simple equipment, less investment, easy operation and low cost. As long as the conversion solution is in contact with the alloy surface, a conversion coating with uniform thickness can be obtained.

The chemical conversion coating is generally used as an undercoat of organic coating to enhance the adhesion of the coating. The method is suitable for devices with complex structures and large surface areas and occasions with less severe use environments. The currently common chemical conversion process of magnesium alloy mainly comprises the following steps: chromate conversion films, rare earth conversion films, and phosphate conversion films (including manganese-based, zinc-calcium-based phosphate films).

Chinese patent CN202010002483.4 discloses "a biomedical degradable magnesium alloy coaptation board", relates to coaptation board technical field, and it contains base plate subassembly, reinforcement subassembly, and several base plate subassembly is established ties from top to bottom and is set up, and its base plate subassembly through establishing ties splices the installation for the coaptation board is whole to be installed according to patient's concrete wound, can obtain the coaptation board that accords with patient operation requirement fast, makes the patient can accept the treatment sooner, guarantees that the patient wound is stable.

Chinese patent CN202010041280.6 discloses a high-compression-resistance and rapid-degradation magnesium alloy and a preparation method thereof, the invention improves the compression resistance of the material by adding alloy elements such as Cu, Nd, Ca and the like, and the Cu and Ni elements improve the degradation rate. The prepared magnesium alloy has high compression resistance and can be rapidly degraded, the corrosion rate in a 3 percent KC1 solution at 25 ℃ can reach 7.4mg cm^-2·h^-1The corrosion rate in a 3 percent KC1 solution at 93 ℃ can reach 88mg cm^-2·h^-1And meanwhile, the shale gas has higher compressive strength, and is suitable for the field of shale gas exploitation with rapid corrosion requirements.

Chinese patent CN201911096925.X discloses a method for preparing degradable magnesium alloy sliding sleeve fracturing balls and controlling degradation rate, and mainly relates to the acceleration of magnesium alloy corrosion rate by adding 2% of nickel-coated diatomite into a molten AZ91D magnesium alloy.

However, the methods mainly rely on alloying by adding high-potential Cu and Ni metal elements to regulate the degradation rate of the magnesium alloy. The alloying process is complex in operation and harsh in condition, and the added components exist in the magnesium alloy in the form of impurities through a metallurgical bonding method, which has adverse effect on the mechanical property of the magnesium alloy and uncontrollable corrosion rate.

Disclosure of Invention

Based on the above background, one of the objectives of the present invention is to provide a magnesium or magnesium alloy surface autocatalytically degradable coating; the invention also aims to provide a preparation method of the autocatalytic degradation coating, which has safe and environment-friendly process, simple preparation method and accelerating effect on the degradation of the magnesium or magnesium alloy matrix. So that the material can be used as a structural material and a medical material.

The invention adopts the following technical scheme:

the magnesium or magnesium alloy surface autocatalytic degradation coating is characterized in that the chemical component of the autocatalytic degradation coating comprises Fe₃(PO₄)₂And/or FePO₄(ii) a The open circuit potential and the self-corrosion current density of the autocatalytically degradable coating are both greater than the corresponding open circuit potential and the self-corrosion current density of the magnesium or the magnesium alloy.

Furthermore, the thickness of the autocatalytic degradation coating on the surface of the magnesium or magnesium alloy is more than 0 and less than or equal to 20 μm.

Furthermore, the open circuit potential of the autocatalytically degraded coating after 1 hour of electrochemical test is-1.56 +/-0.35V/SCE to-1.57 +/-0.04V/SCE, and the autogenous corrosion current density is 5.69 × 10^-4A/cm²～1.04×10^-5A/cm²(ii) a The hydrogen evolution rate after soaking in 3.5 wt.% NaCl for 78 hours was 0.21. + -. 0.06mL cm^-2·h^-1～0.08±0.01mL·cm^-2·h^-1。

Therefore, the magnesium or magnesium alloy surface autocatalytic degradation coating can meet the service life and safety use requirements of daily structural products or medical implantable magnesium alloy products.

A preparation method of a magnesium or magnesium alloy surface autocatalytic degradation coating comprises the following steps:

(1) preparation of precursor solution

Weighing phosphate and ferrous salt or ferric salt in a beaker according to the ferrous ion/phosphate ion molar ratio of 8.43-100:100 or the ferric ion/phosphate ion molar ratio of 6-100:100, adding deionized water to prepare a uniform mixed solution;

adjusting the pH value of the mixed solution to 2-5 by using phosphoric acid to obtain a precursor solution;

(2) pretreatment of coated substrates

Mechanically polishing the magnesium or magnesium alloy workpiece to remove burrs on the surface of the magnesium or magnesium alloy workpiece, sequentially washing with first water, alkali washing, washing with second water, acid washing and washing with third water, and drying to obtain a magnesium or magnesium alloy workpiece with a fresh surface;

(3) putting the magnesium or magnesium alloy workpiece with the fresh surface into a precursor solution, and immersing the processed magnesium or magnesium alloy workpiece below the liquid level of the precursor solution;

sealing the mouth of the beaker by using a preservative film and placing the beaker in a water bath kettle for water bath reaction;

(4) and taking out the beaker, opening the preservative film, taking out the sample, washing the sample with water, and drying to finish the preparation of the magnesium or magnesium alloy surface autocatalytic degradation coating.

Further, in the step (1), the ferrous salt is ferrous sulfate, ferrous chloride or ferrous nitrate.

Further, in the step (1), the iron salt is ferric sulfate, ferric chloride or ferric nitrate.

Further, in the step (1), the phosphate is trisodium phosphate dodecahydrate, disodium hydrogen phosphate, sodium dihydrogen phosphate, ammonium phosphate or ammonium hydrogen phosphate.

The technical effect directly brought by the technical scheme is that the process is simple and environment-friendly, and the reaction time is short; the obtained magnesium alloy surface coating has a porous structure, obvious autocatalytic degradation effect and good biocompatibility.

To better understand the above technical scheme, the reaction principle is briefly explained:

in the technical scheme, phosphate and ferrous salt or ferric salt are used as nucleating agents.

Ferrous sulfate heptahydrate, trisodium phosphate dodecahydrate are taken as examples:

the components in the solution have the following functions: ferrous sulfate heptahydrate ionizes iron and phosphate ions in an aqueous solution with trisodium phosphate dodecahydrate to provide the desired ions for forming the iron-containing coating. Meanwhile, the precursor solution with the pH value of 2-5 regulated by phosphoric acid can form hydrogen phosphate radicals and phosphate radicals through the hydrolysis of phosphoric acid to maintain the pH value to change in a small range in the reaction process.

In the case of autocatalytic degradation, the chemical reaction process comprises:

Mg→2e^-+Mg²⁺(1)

H₂O→OH^-+H⁺(2)

2H⁺+2e^-→H₂↑ (3)

Mg²⁺+2OH^-→Mg(OH)₂↓ (4)

Fe²⁺+2OH^-→Fe(OH)₂↓ (5)

Mg²⁺+2H_nPO₄ ^(3-n)-→Mg_(3-n)(H_nPO₄)₂↓ (6)

Fe²⁺+2H_nPO₄ ^(3-n)-→Fe_(3-n)(H_nPO₄)₂↓ (7)

Fe²⁺+2e^-→Fe↓ (8)

4Fe(OH)₂+O₂+2H₂O→4Fe(OH)₃↓ (9)

Mg(OH)₂+CO₂→MgCO₃↓+H₂O (10)

firstly, in an acid precursor solution, Mg is dissolved and Mg is generated²⁺The reaction consumes water, generates hydrogen gas, and raises the pH of the solution (reaction formulas (1) to (3)). Liberated free Mg²⁺And added Fe²⁺Can react with the OH formed^-Reaction to form Mg (OH)₂And Fe (OH)₂(reaction formulae (4) to (5)). H⁺And OH^-The consumption of (3) accelerates the reaction process of the reaction formula (2), and further accelerates the reactions of the reaction formulas (3) to (5). For H_nPO₄ ^(3-n)-Wherein n is and PO₄ ^3-Bound H⁺In the range of 0 to 3. When n is 0, H_nPO₄ ^(3-n)-By PO₄ ^3-Exist in the form of (1). Due to H_nPO₄ ^(3-n)-In the presence of some Fe_(3-n)(H_nPO₄)₂And Mg_(3-n)(H_nPO₄)₂And precipitated on the substrate (reaction formulae (6) to (7)).

At the same time, with Fe²⁺Moving in the solution, they can contact the substrate and undergo displacement reaction to form elemental Fe (equation (8)). In addition, air gases, such as oxygen and carbon dioxide, may dissolve in the solution and react with the components of the coating to form Fe (OH)₃(reaction formula (9)) and MgCO₃(reaction formula (10)). It is noteworthy that, in theory, many metal ions such as Zn²⁺、Al³⁺、Cu²⁺Can react with Mg. However, Coatings based on these ions can improve the corrosion resistance of magnesium alloys (Study on hydrobicity and comfort transition of Ni-Cu-SiC coating on Mg-Li alloy. surface and Coatings Technology,2018,350(25):428-₂O₇₄-LDH composite film on magnesium alloyAZ31for anticorrosion.Journal of Materials Science&Technology (2019) and biological enhancement by Sr doped Zn-Ca-P coatings on biological magnetic metals alloy.journal of Magnesium and Alloys,2019,7(4):584-596), due to the fact that dense coatings can effectively prevent the penetration of solutions. Meanwhile, the coating has low dissolution speed, only a very small amount of metal ions contact with the magnesium alloy, and the catalytic degradation effect on the magnesium substrate is less than the corrosion resistance. The magnesium alloy surface autocatalytic degradation coating prepared by the method has a porous structure, can ensure that a solution is fully contacted with a substrate, and simultaneously Fe in the coating²⁺More chances are provided for contacting with the matrix and oxidation reduction reaction is carried out to generate elementary substance iron, and the formed elementary substance iron can further form a galvanic couple with the magnesium matrix to accelerate corrosion of magnesium. More iron is reduced with time, thereby forming more effective effect of accelerating degradation.

Namely, trisodium phosphate and ferrous sulfate are reacted to prepare an autocatalytic degradation coating on the surface of magnesium and magnesium alloy, and the coating is of a porous structure and contains a large amount of iron ions, so that the autocatalytic degradation performance of the coating is remarkably improved. Meanwhile, the coating has higher potential and higher self-corrosion current density than the magnesium alloy matrix. The iron ions contained in the film layer play a core role in accelerating the degradation of the magnesium alloy. More importantly, the reduction of iron ions, the formation of galvanic couple and the accelerated degradation of iron ions are a deepened process along with the time, so that the degradation rate of the magnesium alloy is accelerated continuously.

In the above technical solution, ferrous ions will be mainly used as the core of the catalytic degradation coating, because:

iron is a metal element, has wide distribution in life, occupies 4.75 percent of the shell content, is second to oxygen, silicon and aluminum, has the fourth content in the local shell, is called as ferrous metal in industry, and has wide application. In addition, the human body also contains iron element, and ferrous ions with the valence of +2 are important components of hemoglobin and are used for oxygen transportation. Iron is an essential component of human cells, and is involved in the synthesis of hemocytochrome and various enzymes to promote growth. In addition, the corrosion potential of iron is different from that of magnesium alloy, and the formed micro-couple pair can promote the degradation of magnesium alloy more effectively. Therefore, iron, as a non-toxic, safe, environmentally friendly element, can be used as a coating to promote degradation of magnesium and its alloys.

In addition, for the reasons, the invention can also select iron ions as the core of the catalytic degradation coating, prepare the coating on the surface of magnesium or magnesium alloy to promote the degradation of magnesium or magnesium alloy, and use the coating on structural materials.

In the above technical solution, the reason why phosphate is used is that: p is an essential element in a human body, and calcium is an important component for forming bones and teeth; meanwhile, the DNA and RNA are also components; has the important functions of regulating acid-base balance in vivo and maintaining normal osmotic pressure. Therefore, P can be applied to human bodies, has no toxicity and harm, has good biocompatibility, and provides possibility for further researching the biodegradability of the P and serving as an implant material.

In addition, the Fe-containing autocatalytic degradation coating on the surface of the magnesium alloy has the following advantages:

1. the coating preparation process is simple, the conditions are loose, and no environmental pollution is generated in the preparation process. The cost is low.

2. Good suitability: for degradable medical magnesium alloy, the matching of the degradation rate of an implant and the growth rate of new bones can be achieved; the structural material can meet the requirement of degrading the device within corresponding time.

3. The controllable catalytic degradation rate can control the content of iron in the coating by controlling the addition of iron or ferrous iron, and further control the reaction rate.

4. The coating is porous, which is beneficial to the contact of solution-coating-matrix and is more beneficial to the effect of accelerating degradation.

Further, in the step (1), the concentrations of the phosphate and the ferrous salt or ferric salt solution are calculated by MEDUSA software according to the precipitation and dissolution equilibrium of the ferrous phosphate or ferric phosphate.

In the technical scheme, MEDUSA software is used for distributing the map according to the advantage area drawn by the chemical reaction balance, and the concentration of the solution is selected.

For example, Fe calculated using MEDUSA software package²⁺Ion in [ PO ]₄ ^3-]＝0.1mol/L，[Fe²⁺]At 1 × 10^{- 6}A heat balance advantage area diagram when the mol/L is between 10 and 10mol/L and the pH value is between 0 and 12.

Further, the ratio of the surface area of the magnesium or magnesium alloy device to the volume of the precursor solution in the step (3) is 1cm²:4±0.5mL。

Further, the water bath reaction condition is that the water bath reaction is carried out for 2-60min at the temperature of 20-80 ℃.

Furthermore, the material of the magnesium alloy device is pure Mg or magnesium alloy.

The open circuit potential, the self-corrosion current and the hydrogen evolution rate of the prepared autocatalytically degradable coating are all higher than those of a magnesium alloy substrate made of pure Mg and various magnesium alloys. Therefore, the technical scheme has universality and universality. Therefore, the method of the technical scheme can be used for structural devices/materials and medical magnesium alloy devices. Meanwhile, the degradation speed controllability of the matrix can be realized by preparing coatings with different iron contents and different thicknesses.

Further, the phosphate, ferrous salt or ferric salt is analytically pure.

Further, the trisodium phosphate dodecahydrate and ferrous sulfate heptahydrate are both analytically pure.

Taking ferrous sulfate heptahydrate and trisodium phosphate dodecahydrate as examples, both ferrous salts and phosphates are analytically pure, mainly due to the special requirements of the target product for purity (preventing the generation or introduction of other harmful foreign components).

In addition, based on the appeal of the magnesium or magnesium alloy surface autocatalytic degradation coating, the invention also can provide an autocatalytic degradation coating based on the magnesium or magnesium alloy surface, and the chemical composition of the autocatalytic degradation coating comprises Fe (OH)₂And/or Fe (OH)₃(ii) a The open circuit potential and the self-corrosion current density of the autocatalytically degradable coating are both greater than the corresponding open circuit potential and the self-corrosion current density of the magnesium or the magnesium alloy.

The autocatalytic degradation coating forms Fe (OH) on the surface of magnesium or magnesium alloy through iron or ferrous salt under the weak acid or alkaline condition₂And/or Fe (OH)₃And (4) coating.

In conclusion, the invention creates a new idea, compared with the prior art, the invention has the advantages of environment-friendly process, simple preparation method and porous structure of the obtained coating; the reaction rate is controllable, the coating is degradable, no heavy metal pollution is caused, and the coating is safe and environment-friendly and has excellent characteristics of good biocompatibility and the like. Without adversely affecting the mechanical properties and internal organization of the magnesium or magnesium alloy. Therefore, the coating can be used as a structural material coating and a degradable biomedical magnesium alloy coating. Provides an effective strategy for wide application of degradable magnesium or magnesium alloy.

Drawings

FIG. 1 is a composition dominant region plot of examples 1, 2, 3 using MEDUSA software.

FIG. 2 is a surface-enlarged 10000 microtopography SEM (FIGS. 2a, 2c and 2e), cross-sectional view (FIGS. 2b, 2d and 2f), EDS energy spectrum (FIG. 2g), X-ray diffraction pattern (XRD, FIG. 2h), Fourier infrared spectrum (FTIR, FIG. 2i) of the autocatalytically degradable coatings prepared in examples 1, 2, 3;

FIG. 3 shows the X-ray photoelectron spectroscopy (XPS) results of the autocatalytically degraded coating obtained in example 1.

FIG. 4 is the electrochemical impedance spectrum (FIG. 4a-b) open circuit potential (OCP, FIG. 4c) polarization curve diagram (PDP, FIG. 4d) of the autocatalytically degradable coatings and magnesium alloy substrates prepared in examples 1, 2, 3 in NaCl 3.5% solution;

FIG. 5 is a graph showing the change of hydrogen evolution of the autocatalytically degradable coatings and the magnesium alloy substrates prepared in examples 1, 2 and 3 after immersion in NaCl 3.5% solution for 78 hours.

FIG. 6 is a graph showing the results of measuring the bonding force of the autocatalytic degradation coatings prepared in examples 1, 2 and 3.

FIG. 7 is an analysis chart of the autocatalysis mechanism of the autocatalysis degradation coatings prepared in examples 1, 2 and 3

Detailed Description

The present invention will be described in detail with reference to examples.

Description of the drawings: in the following examples, the phosphate, ferrous or ferric salts are all commercially available in the grade of analytical grade.