CN111701606B - Magnesium or magnesium alloy surface self-catalytic degradation coating and preparation method thereof - Google Patents
Magnesium or magnesium alloy surface self-catalytic degradation coating and preparation method thereof Download PDFInfo
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- CN111701606B CN111701606B CN202010613270.5A CN202010613270A CN111701606B CN 111701606 B CN111701606 B CN 111701606B CN 202010613270 A CN202010613270 A CN 202010613270A CN 111701606 B CN111701606 B CN 111701606B
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- B01J27/185—Phosphorus; Compounds thereof with iron group metals or platinum group metals
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- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
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- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
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- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
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Abstract
The invention provides an autocatalytic degradation coating for magnesium or magnesium alloy surface and a preparation method thereof, wherein phosphate and ferrous salt or ferric salt are used as raw materials, a chemical conversion method is adopted to prepare a coating for accelerating the degradation of magnesium alloy on the magnesium or magnesium alloy substrate surface, and the obtained coating is iron, ferrous phosphate and ferrous hydroxide. The cathode porous coating has higher open circuit potential than the magnesium alloy matrix, and the elementary iron generated by reduction of iron or ferrous ions can form galvanic corrosion with the magnesium alloy, so that the effect of accelerating the corrosion of the magnesium alloy is achieved, and the autocatalysis degradation of the magnesium alloy is further realized. Compared with the prior art, the invention has the characteristics of environment-friendly process, simplicity, short reaction time, low production cost, no damage to the matrix structure and mechanical properties and the like. The obtained magnesium alloy surface coating has the advantages of porous structure, biodegradability, good biocompatibility and the like, so that the magnesium alloy surface coating can be used as a structural material and a degradable biomedical material.
Description
Technical Field
The invention relates to the technical field of magnesium or magnesium alloy surface coatings, in particular to an autocatalytic degradation coating for a magnesium or magnesium alloy surface and a preparation method thereof.
Background
Magnesium is one of the lightest metals and has a density of 1.75g/cm 3 Is one of the elements rich in the resource storage on earth, and the content of the element in the crust can be about 2.7 percent.
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 performance of resisting organic matters and alkaline solution, and the like. In addition, the magnesium alloy has good dimensional stability, electromagnetic shielding property, easy processing property and recycling property. They are therefore used in the fields of structural materials (e.g. automotive, aerospace, 3C products) and functional materials (e.g. biomedical materials). With the progress of technology, the application range 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, magnesium and the alloy thereof also have good biocompatibility and mechanical compatibility. Magnesium ion is intracellular positive ion with the content inferior to potassium, sodium and calcium in human body, can participate in protein synthesis, can activate various enzymes in the body, regulate activities of central nervous system and muscle, and ensure normal contraction of cardiac muscle. As a degradable magnesium alloy material, the material can be rapidly corroded in a human body, and the inconvenience caused by secondary operation is avoided. In addition, the mechanical properties of magnesium alloys are more advantageous than traditional polylactic acid, titanium alloys, stainless steel and other types of degradable implant materials; not only has the capability of promoting the formation of bone cells and accelerating the bone healing; in addition, the elastic modulus similar to that of human bones is possessed, so that the stress shielding effect can be effectively avoided. The degradable magnesium and magnesium alloy are used as biomedical devices, and comprise bone fixing materials such as bone plates, bone nails and the like and stent materials such as vascular stents and the like, and have huge clinical application prospect.
However, because magnesium is very reactive (-2.36V/SHE) in its chemical nature, it is not corrosion resistant in both acidic and neutral solutions. Meanwhile, the oxide film generated on the surface of the magnesium alloy is usually porous, and the film layer cannot effectively protect the matrix. Therefore, corrosion of magnesium alloys is a major bottleneck in general, which limits the application of magnesium alloys, and limits the application of magnesium alloys in many fields. Researchers at home and abroad mainly research from the perspective of improving the corrosion resistance of magnesium alloy, and three basic methods are available:
(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 (5) surface modification. Among them, surface treatment techniques such as micro-arc oxidation (MAO), layer-by-layer assembly (LBL), chemical Conversion Coating (CCC), chemical Vapor Deposition (CVD), hydrotalcite (LDHs) are important means for improving the corrosion resistance of magnesium alloys.
The chemical conversion treatment is one of the common surface treatment processes of the magnesium alloy at present, and a indissolvable film layer with good adhesive force, which is composed of oxide, chromide, phosphide or other compounds, can be formed on the surface of the magnesium alloy through a chemical or electrochemical treatment method. The film has good binding force with the matrix, and prevents the erosion of the corrosive medium to the matrix. Compared with the anodic oxide film, the chemical conversion film is thinner, and has lower hardness and wear resistance. The chemical conversion film process has simple equipment, low investment, easy operation and low cost. As long as the conversion liquid is in contact with the alloy surface, a conversion film having a uniform thickness can be obtained.
The chemical conversion coating is generally used as a primer layer for organic coating to enhance the adhesion of the coating. Is suitable for devices with complex structures and large surface areas and occasions with less severe use environments. The chemical conversion process of the magnesium alloy commonly used at present mainly comprises the following steps: chromate conversion films, rare earth conversion films, phosphate conversion films (including manganese-based, zinc-based phosphating films, zinc-calcium-based phosphating films), and the like.
Chinese patent CN202010002483.4 discloses "a biomedical degradable magnesium alloy bone plate", relates to bone plate technical field, and it contains base plate subassembly, reinforcement subassembly, and several base plate subassembly establishes ties from top to bottom and sets up, and it carries out the concatenation installation through the base plate subassembly of establishing ties for bone plate whole can be installed according to patient's specific injury condition, can obtain the bone plate that accords with patient's operation requirement fast, makes patient can accept the treatment more fast, guarantees that patient's injury condition is stable.
Chinese patent CN202010041280.6 discloses a high compression resistance and rapid reduction Jie Mei alloy and a preparation method thereof, and the invention improves the material by adding Cu, nd, ca and other alloy elementsCompression resistance, cu and Ni elements increase degradation rate. The prepared magnesium alloy has high compression resistance and rapid drop Jie Mei alloy, and the corrosion rate in 3 percent KC1 solution at 25 ℃ can reach 7.4mg cm -2 ·h -1 The corrosion rate in a 3% KC1 solution at 93 ℃ can reach 88mg cm -2 ·h -1 Meanwhile, the high-strength shale gas oil well has high compressive strength, and is suitable for the field of shale gas exploitation with rapid corrosion requirements.
The Chinese patent CN201911096925.X discloses a method for preparing a degradable magnesium alloy sliding sleeve fracturing ball and controlling degradation rate, which mainly relates to the acceleration of the corrosion rate of magnesium alloy by adding 2% nickel-coated diatomite into molten AZ91D magnesium alloy.
However, the methods mainly rely on alloying by adding Cu and Ni metal elements with high potential to regulate the degradation rate of the magnesium alloy. The alloying process is complex in operation and harsh in condition, and the added components are existed in the magnesium alloy in the form of impurities through a metallurgical bonding method, so that the mechanical properties of the magnesium alloy are adversely affected, and the corrosion rate is uncontrollable.
Disclosure of Invention
Based on the background art, one of the purposes of the present invention is to provide a magnesium or magnesium alloy surface self-catalytic degradation coating; the invention also aims to provide a preparation method of the autocatalytic degradation coating, which is safe and environment-friendly in process, simple in preparation method and has an accelerating effect on degradation of a 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:
a self-catalytic degradation coating for the surface of magnesium or magnesium alloy is characterized in that the chemical components of the self-catalytic degradation coating comprise Fe 3 (PO 4 ) 2 And/or FePO 4 The method comprises the steps of carrying out a first treatment on the surface of the The open circuit potential and the self-corrosion current density of the self-catalytic degradation coating are both greater than those of magnesium or magnesium alloy.
Further, 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 mu m.
Further, autocatalytic descentThe open-circuit potential of the coating after 1 hour of electrochemical test is-1.56+/-0.35V/SCE to-1.57+/-0.04V/SCE; self-etching current density of 5.69×10 -4 A/cm 2 ～1.04×10 -5 A/cm 2 The method comprises the steps of carrying out a first treatment on the surface of the Hydrogen evolution rate after 78 hours of immersion in 3.5wt.% NaCl was 0.21.+ -. 0.06mL cm -2 ·h -1 ～0.08±0.01mL·cm -2 ·h -1 。
Therefore, the magnesium or magnesium alloy surface self-catalytic degradation coating can meet the service life and safety requirements of daily structural products or medical implantable magnesium alloy products.
The preparation method of the self-catalytic degradation coating on the surface of magnesium or magnesium alloy 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, and 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, alkaline washing, second water washing, acid washing and third water washing, and drying to obtain the magnesium or magnesium alloy workpiece with a fresh surface;
(3) Placing the magnesium or magnesium alloy workpiece with the fresh surface into a precursor solution, and immersing the processed magnesium or magnesium alloy workpiece under the liquid surface of the precursor solution;
sealing the mouth of the beaker with a preservative film and placing the beaker into a water bath kettle for water bath reaction;
(4) Taking out the beaker, opening the preservative film, taking out the sample, washing the sample with water, and drying the sample to prepare the self-catalytic degradation coating on the surface of the magnesium or the magnesium alloy.
Further, in the step (1), the ferrous salt is ferrous sulfate, ferrous chloride or ferrous nitrate.
Further, in 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 scheme directly brings the technical effects of simple process, environmental protection and short reaction time; the obtained magnesium alloy surface coating has a porous structure, obvious self-catalytic degradation effect and good biocompatibility.
For a better understanding of the above technical solutions, the reaction principle will now be briefly described:
in the technical scheme, phosphate and ferrous salt or ferric salt are used as nucleating agents.
Taking ferrous sulfate heptahydrate and trisodium phosphate dodecahydrate as examples:
the components in the solution have the following functions: ferrous sulfate heptahydrate and trisodium phosphate dodecahydrate ionize iron ions and phosphate ions in an aqueous solution to provide the required ions for forming the iron-containing coating. Meanwhile, the precursor solution with pH of 2-5 adjusted by phosphoric acid can maintain the pH to change slightly during the reaction by forming hydrogen phosphate and phosphate through the hydrolysis of phosphoric acid.
In performing autocatalytic degradation, the chemical reaction process includes:
Mg→2e - +Mg 2+ (1)
H 2 O→OH - +H + (2)
2H + +2e - →H 2 ↑ (3)
Mg 2+ +2OH - →Mg(OH) 2 ↓ (4)
Fe 2+ +2OH - →Fe(OH) 2 ↓ (5)
Mg 2+ +2H n PO 4 (3-n)- →Mg (3-n) (H n PO 4 ) 2 ↓ (6)
Fe 2+ +2H n PO 4 (3-n)- →Fe (3-n) (H n PO 4 ) 2 ↓ (7)
Fe 2+ +2e - →Fe↓ (8)
4Fe(OH) 2 +O 2 +2H 2 O→4Fe(OH) 3 ↓ (9)
Mg(OH) 2 +CO 2 →MgCO 3 ↓+H 2 O (10)
firstly, in an acidic precursor solution, mg is dissolved and Mg is generated 2+ The reaction consumes water, generates hydrogen gas, and raises the pH of the solution (equations (1) to (3)). Free Mg released 2+ And added Fe 2+ Can be combined with the generated OH - Reaction to give Mg (OH) 2 And Fe (OH) 2 (equations (4) to (5)). H + And OH (OH) - The consumption of (a) accelerates the reaction process of the reaction formula (2), and further accelerates the reactions of the reaction formulae (3) to (5). For H n PO 4 (3-n)- Wherein n is a group selected from the group consisting of PO and 4 3- bound H + Ranging from 0 to 3. When n is 0, H n PO 4 (3-n)- By PO 4 3- Is present in the form of (c). Due to H n PO 4 (3-n)- Is present in some Fe (3-n) (H n PO 4 ) 2 And Mg (magnesium) (3-n) (H n PO 4 ) 2 Precipitated on the substrate (equations (6) to (7)).
At the same time, with Fe 2+ Moving in solution, they can contact the substrate and exchange reactions to form elemental Fe (equation (8)). In addition, gases in the air, such as oxygen and carbon dioxide, can dissolve in the solution and react with the components in the coating to form Fe (OH) 3 (equation (9)) and MgCO 3 (reaction (10)). Notably, in theory many metal ions such as Zn 2+ 、Al 3+ 、Cu 2+ Can react with Mg. However, coatings based on these ions can improve magnesiumCorrosion resistance of gold (Study on hydrophobicity and wettability transition of Ni-Cu-SiC coating on Mg-Li alloy. Surface and Coatings Technology,2018,350 (25): 428-435; double-doped Mg-Al-Ce-V) 2 O 74 -LDH composite film on magnesium alloy AZ31for anticorrosion.Journal of Materials Science&Technology (2019) and Bioactivity enhancement by Sr doped Zn-Ca-P coatings on biomedical magnesium alloy journal of Magnesium and Alloys,2019,7 (4): 584-596) due to the tight coating can effectively prevent penetration of solutions. Meanwhile, the dissolution rate of the coating is low, only a very small amount of metal ions are in contact with the magnesium alloy, and the catalytic degradation effect on the magnesium matrix is smaller than the corrosion resistance. The magnesium alloy surface self-catalytic degradation coating prepared by the method has a porous structure, can enable the solution to fully contact with the substrate, and meanwhile, fe in the coating 2+ There are more opportunities to contact with the substrate and generate oxidation-reduction reaction to generate elemental iron, and the formed elemental iron can further form galvanic couple with magnesium to accelerate the corrosion of the magnesium. With time delay, more iron is reduced, thereby forming a more effective degradation accelerating effect.
Namely, trisodium phosphate and ferrous sulfate are utilized to react, a layer of self-catalytic degradation coating is prepared 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 self-catalytic degradation performance of the coating is obviously improved. Meanwhile, the coating has higher potential and higher self-corrosion current density than the magnesium alloy matrix. 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 couples and the acceleration of degradation are a deepened process over time, so that the degradation rate of magnesium alloy can be continuously accelerated.
In the above technical scheme, ferrous ions are mainly used as the core of the catalytic degradation coating, because:
iron is a metal element, is widely distributed in life, accounts for 4.75% of the crust content, is next to oxygen, silicon and aluminum, and has fourth crust content, is industrially called "ferrous metal", and has wide application. In addition, the human body also contains iron element, and ferrous ion with +2 valence is an important constituent component of hemoglobin and is used for transporting oxygen. Iron is an essential component of human cells, and participates in synthesis of hemocytochromes and various enzymes to promote growth. In addition, the corrosion potential of iron and the magnesium alloy have a larger difference, and the formed micro-couple pair can promote the degradation of the magnesium alloy more effectively. Therefore, the iron is used as a nontoxic, safe and environment-friendly element and can be used as a coating to promote the degradation of magnesium and the magnesium alloy.
In addition, based on the part of 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 so as to promote the degradation of the magnesium or magnesium alloy and be used on structural materials.
In the above technical solution, the reason for using phosphate is: p is an essential element in human body, and calcium is an important component for forming bones and teeth; meanwhile, the DNA and RNA are also components; has a vital function in regulating the acid-base balance in the body and maintaining normal osmotic pressure. Therefore, P can be applied to human body, has no toxicity and harm, has good biocompatibility, and provides possibility for further researching the biodegradability and being used as an implantation material.
Moreover, the Fe-containing self-catalytic degradation coating on the surface of the magnesium alloy has the following advantages:
1. the coating has simple preparation process and loose conditions, and does not produce environmental pollution in the preparation process. The cost is low.
2. Good suitability: for degradable medical magnesium alloy, the matching of the implant degradation rate and the new bone growth rate can be achieved; for structural materials, the requirement of degrading the device in corresponding time can be met.
3. The controllable catalytic degradation rate can control the content of iron in the coating by controlling the addition amount of iron or ferrous iron, and further control the reaction rate.
4. The coating is porous, which is beneficial to the contact of the solution, the coating and the matrix and the effect of accelerating degradation.
Further, in step (1), the solution concentrations of phosphate and ferrous or ferric salts are calculated by MEDUSA software from the precipitation dissolution balance of ferrous or ferric phosphate.
In the technical scheme, MEDUSA software is used for dividing the graph according to the advantages drawn by chemical reaction equilibrium, and the concentration of the solution is selected.
For example, fe calculated using MEDUSA software package 2+ Ion at [ PO 4 3- ]＝0.1mol/L，[Fe 2+ ]At 1X 10 - 6 Heat balance dominance area diagram of mol/L-10 mol/L and pH value at 0-12.
Further, the volume ratio of the surface area of the magnesium or magnesium alloy workpiece in the step (3) to the precursor solution is 1cm 2 :4±0.5mL。
Further, the water bath reaction condition is that the water bath reaction is carried out for 2-60min at 20-80 ℃.
Further, the magnesium alloy working device is made of pure Mg or magnesium alloy.
Because the open circuit potential, the self-corrosion current and the hydrogen evolution rate of the prepared self-catalytic degradation coating are all higher than those of pure Mg and various magnesium alloy matrixes. Therefore, the technical scheme has universality and universality. Thus, the method of the technical scheme can be used for not only structural tools/materials, but also medical magnesium alloy tools. 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, both trisodium phosphate dodecahydrate and ferrous sulfate heptahydrate are analytically pure.
Ferrous sulfate heptahydrate and trisodium phosphate dodecahydrate are taken as examples, and ferrous salt and phosphate are all analytically pure, mainly because of special requirements of target products on purity (preventing generation or introduction of other harmful foreign matter components).
In addition, based on the requirement of the self-catalytic degradation coating on the surface of the magnesium or the magnesium alloy, the invention can also provide a self-catalytic degradation coating on the surface of the magnesium or the magnesium alloyA catalytic degradation coating, the chemical composition of the self-catalytic degradation coating comprising Fe (OH) 2 And/or Fe (OH) 3 The method comprises the steps of carrying out a first treatment on the surface of the The open circuit potential and the self-corrosion current density of the self-catalytic degradation coating are both greater than those of magnesium or magnesium alloy.
The self-catalytic degradation coating forms Fe (OH) on the surface of magnesium or magnesium alloy through iron or ferrous salt under weak acid or alkaline condition 2 And/or Fe (OH) 3 And (3) coating.
In conclusion, the invention creates a new thought, and 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, the safety and environment friendliness are realized, and the excellent characteristics of good biocompatibility and the like are realized. Without adversely affecting the mechanical properties of the magnesium or magnesium alloy and the internal structure. Therefore, the coating can be used as a structural material coating and a degradable biomedical magnesium alloy coating. Provides an effective strategy for the wide application of degradable magnesium or magnesium alloy.
Drawings
Fig. 1 is a layout of the component advantage areas of examples 1, 2, and 3 drawn using the MEDUSA software.
FIG. 2 is a microscopic morphology SEM (FIGS. 2a,2c and 2 e), cross-sectional view (FIGS. 2b,2d and 2 f), EDS profile (FIG. 2 g), X-ray diffraction pattern (XRD, FIG. 2 h), fourier infrared profile (FTIR, FIG. 2 i) of the surface of the autocatalytically degraded coating prepared in examples 1, 2, 3;
FIG. 3 shows the X-ray photoelectron spectroscopy (XPS) results of the autocatalytically degraded coating prepared in example 1.
FIG. 4 is a graph showing the open circuit potential (OCP, FIG. 4 c) polarization curve (PDP, FIG. 4 d) of electrochemical impedance spectra (FIGS. 4 a-b) of the autocatalytically degraded coatings and magnesium alloy substrates prepared in examples 1, 2, and 3 in NaCl 3.5% solution;
FIG. 5 is a graph showing the hydrogen evolution change of the autocatalytically degradable coatings and magnesium alloy substrates prepared in examples 1, 2 and 3 after being immersed in a NaCl 3.5% solution for 78 hours.
FIG. 6 is a graph showing the results of the detection of the binding force of the autocatalytically degradable coatings prepared in examples 1, 2 and 3.
FIG. 7 is an analysis of the autocatalytic mechanism of the autocatalytically degradable coatings prepared in examples 1, 2 and 3
Detailed Description
The present invention will be described in detail with reference to examples.
Description: in the examples below, the phosphate, ferrite or iron salt are commercially available products, rated analytically pure.
Example 1
Magnesium alloy tool: the material composition is Mg-3AlLi-1Zn (AZ 31).
The preparation method comprises the following steps:
first, preparing a precursor solution
Respectively taking ferrous sulfate heptahydrate and trisodium phosphate dodecahydrate, and adding deionized water to prepare a mixed aqueous solution; wherein FeSO 4 ·7H 2 O is 100mmol/L, na 3 PO 4 ·12H 2 O is 100mmol/L;
adjusting the pH value of the mixed solution to 3.27 by using phosphoric acid to obtain a precursor solution;
second step, pretreatment of the coated substrate
Mechanically polishing the magnesium alloy workpiece to remove burrs on the surface of the magnesium alloy workpiece, and sequentially washing the magnesium alloy workpiece with first water, alkaline washing, second water washing, acid washing and third water washing, and drying to obtain the magnesium alloy workpiece with fresh surface;
third, surface coating treatment of magnesium alloy workpiece
The volume ratio of the surface area of the work device to the precursor solution is 1cm 2 Measuring a precursor solution by using a measuring cylinder under the condition of 4+/-0.5 mL, pouring the precursor solution into a beaker, and putting the magnesium alloy workpiece with the fresh surface into the beaker so that the processed magnesium alloy workpiece is immersed below the liquid level of the precursor solution;
then, sealing the beaker mouth by using a preservative film, placing the beaker mouth into a water bath kettle, and carrying out water bath reaction for 30min at 25 ℃;
and step four, taking out the beaker, opening the preservative film, taking out the sample, washing the sample with water, and drying the sample to obtain the magnesium alloy surface self-catalytic degradation coating, wherein the coating is marked as a coating I.
Detecting and checking products:
the thickness of the self-catalytic degradation coating is 4.1-10 mu m, the film layer is relatively uniform, the coating can be observed to take on petal-shaped structures after being amplified 10000 times, and the open circuit potentials of the coating I and the substrate are respectively-1.56+/-0.35V/SCE and-1.59+/-0.25V/SCE; self-etching current density of 5.69×10 -4 A/cm 2 ～5.80×10 -4 A/cm 2 . The hydrogen evolution rates of the coating I and the magnesium alloy after being soaked in 3.5wt.% NaCl for 78 hours are respectively 0.21+/-0.06 mL cm -2 ·h -1 And 0.07.+ -. 0.01mL cm -2 ·h -1 Coating I is 2.96 times that of the magnesium alloy substrate. These can prove that the coating can provide better catalytic degradation function for the magnesium alloy matrix.
Example 2
Ferrous sulfate heptahydrate and trisodium phosphate dodecahydrate are removed respectively at 34.4mmol/L and 100mmol/L; carrying out water bath reaction for 30min at 25 ℃; adjusting the pH value of the mixed solution to 3.77 by using phosphoric acid to obtain a precursor solution;
the remainder was the same as in example 1. The prepared magnesium alloy surface self-catalytic degradation coating is marked as coating II.
Detecting and checking products:
the thickness of the coating is 15-20 mu m, the whole film layer is of a porous structure, the coating is unevenly distributed and is scattered and piled on the surface of the substrate.
The open circuit potential was-1.56.+ -. 0.01V/SCE, which was higher than the substrate but lower than example 1, and tended to accelerate corrosion relative to the substrate; the self-etching current was 2.20X10 -4 A/cm 2 ～2.40×10 -4 A/cm 2 About 1/3 of the current of example 1 also has a certain effect of accelerating corrosion.
Example 3
Ferrous sulfate heptahydrate and trisodium phosphate dodecahydrate are removed to be 8.43mmol/L and 100mmol/L respectively; carrying out water bath reaction for 30min at 25 ℃;
adjusting the pH value of the mixed solution to 4.27 by using phosphoric acid to obtain a precursor solution;
the remainder was the same as in example 1. The prepared magnesium alloy surface self-catalytic degradation coating is marked as coating III.
Detecting and checking products:
the thickness of the film layer is 7-8 mu m, the film is compact and uniform, and a plurality of dry and dry river-shaped cracks are formed on the surface of the film.
The open circuit potential and current were respectively: -1.56.+ -. 0.04V/SCE, 1.04X 10 -5 A/cm 2 ～1.30×10 -5 A/cm 2 Is 1/2 of the self-etching current density of the matrix. Meanwhile, the hydrogen evolution rate after 3.5wt.% NaCl is soaked for 78 hours is 0.08+/-0.01 mL cm -2 ·h -1 . The coating III has a certain protection effect on the matrix after being soaked for 78 hours, mainly because the coating is compact and can prevent the contact between the aqueous solution and the matrix. And simultaneously, the adjustability of the catalytic degradation rate of the coating can be demonstrated.
Example 4
Except that the selected magnesium alloy workpiece material is pure magnesium, the water bath reaction is carried out for 30min at 25 ℃; the rest is the same as in example 1
Detecting and checking products:
the thickness of the film layer is 3-10 μm, and the self-corrosion current density is 5.78X10 -4 A/cm 2 ～5.85×10 -4 A/cm 2 After soaking in 3.5% NaCl for 78 hr, the hydrogen evolution rate is maintained at 0.29+ -0.22 mL cm -2 ·h -1 . The hydrogen evolution rate is faster than that in Mg-3Al-1 Zn. The effect of the coating on pure magnesium is better.
Example 5
Except that the selected magnesium alloy workpiece material components are Mg-1Li-1Ca; carrying out water bath reaction for 30min at 25 ℃; the rest is the same as in example 1
Detecting and checking products:
the morphology of the film layer was similar to that of example 1, the thickness was 2-11 μm, and the self-etching current density was 5.64×10 -4 A/cm 2 ～5.80×10 -4 A/cm 2 After soaking in 3.5% NaCl for 78 hr, the hydrogen evolution rate is maintained at 0.24+ -0.03 mL cm -2 ·h -1 . The hydrogen evolution rate is faster than that in Mg-3Al-1 Zn. Description of the coating on Mg-1The autocatalytic degradation effect on the Li-1Ca magnesium alloy is better than example 1, but less effective than the coating in example 4.
Principle and influencing factor analysis of coating self-catalysis:
first, the autocatalytic effect of a coating depends primarily on two aspects:
1. content of ferrous ions in the coating: the iron content of the coating was further affected by the varying degree of reaction during the formation of the coating due to the non-uniform ferrous content and pH of the three solutions of examples 1-3. In general, the concentration of ferric ions in solution I is highest, the reaction process is more severe, and a large number of bubbles are generated. The overflow of a large number of bubbles is also a major cause of porosity in the coating. In the reaction process of the embodiment 1, more ferrous ions are deposited on the surface of the matrix after being reduced due to the higher ferrous ion concentration of the solution I, and a galvanic couple is formed with the magnesium alloy matrix, so that the degradation of the magnesium alloy is accelerated; meanwhile, the coating has more excellent self-catalytic degradation function.
2. Loose porous structure: the structure of the coating plays a critical role in its autocatalytic degradation effect. The coating in example 3 was relatively dense and uniform, but the solution was almost impermeable to the coating and substrate contact due to the physical barrier effect of the dense coating; although the coating also contains a small amount of iron element, the iron element cannot be connected with the solution and the matrix, so that oxidation-reduction reaction cannot be performed, a magnesium-ferroelectric couple cannot be formed, and the self-catalytic effect of the coating is greatly reduced. So that the porous coating structure is one of the requirements for preparing the self-catalytic coating.
Secondly, the effect of different magnesium or alloy on the coating is not great, as in the examples 4 and 5, pure magnesium and Mg-1Li-1Ca are respectively adopted as matrixes, and the morphology of the obtained coating is not greatly different from that of the examples 1 and 2; the self-corrosion current and hydrogen evolution rate change are smaller and are more influenced by the corrosion resistance of the substrate itself.
Thirdly, the reaction time is prolonged, the reaction temperature is increased, the reaction degree in the coating preparation process is increased, and more hydrogen is generated; meanwhile, the thickness of the coating is thicker, the self-catalytic effect is improved, but too fast reaction rate can cause the coating to be too loose, and the binding force of the coating is poor. .
And fourthly, the corrosion of the magnesium alloy is realized by preparing a coating on the surface, and the influence of alloying on the structure and mechanical properties of the matrix can be effectively avoided.
Fifth, the film forming characteristics, the structural characteristics, the film thickness, the self-catalytic degradation performance, the economic factors and the like of the film are combined, so that the optimal different proportion and conditions can be obtained.
The invention will be described in detail below with reference to the accompanying drawings for better understanding of technical features of the invention.
Examples 1 to 3 were selected as representative examples, and the obtained sacrificial anode conversion film coatings were subjected to scanning electron microscope observation, hydrogen evolution rate detection, electrochemical detection, and X-ray photoelectron spectroscopy (XPS), X-ray diffraction pattern (XRD), and fourier infrared spectroscopy (FTIR) analysis, respectively, to obtain the following fig. 1 to 6. Meanwhile, the mechanism of the self-catalytic degradation of the coating was derived from the above detection analysis and is shown in fig. 7. Wherein:
FIG. 1 shows Fe calculated using MEDUSA software package for examples 1-3 2+ Ion at [ PO 4 3- ]＝0.1mol/L，[Fe 2+ ]At 1X 10 -6 Heat balance dominance area diagram of mol/L-10 mol/L and pH value at 0-12. As shown in FIG. 1, the concentration and pH of the solution required to produce the coating should be selected to produce Fe 3 (PO 4 ) 2 ·8H 2 O or the area on the boundary line to the left thereof.
FIG. 2 is an SEM image and a cross-sectional view of the auto-catalytic degradation coating prepared in examples 1 to 3 at 10000 times; EDS, XRD, and FTIR results plots.
The coatings of examples 1-3 shown in fig. 2 were fully covered on the substrate with a pronounced morphology. Coatings I (fig. 2 a) and II (fig. 2 c) have a relatively rough surface with an irregular and granular microstructure. In contrast, for coating III (FIG. 2 e), the surface was smoother, with dry riverbed or dry mud cracks. The particles on the surface of the coating I are obviously larger than the coating II, which is the reason that the coating I reacts more severely and the coating is accumulated more thoroughly; both have porous structures, which provide more channels for the penetration of the solution, facilitating the acceleration of the degradation of the matrix. The coating III has a relatively dense microstructure, which impedes penetration of corrosive media and protects the substrate to some extent.
Fig. 2 (g) specifies the elemental composition of the coating. The coating consisted essentially of O, P, fe and Mg. The atomic percentage of O is very high, in particular, coating II and coating III, 66.93% and 43.44%, respectively. However, the atomic percent of iron of coating I was high, 83.82%, indicating the presence of substantial amounts of elemental iron.
Fig. 2 (h) verifies by XRD the crystalline solids present in the coatings prepared in examples 1-3. The only crystals detected at the surface of coatings I, II and III were Mg. Fe designed in FIG. 1 3 (PO 4 ) 2 Not detected, possibly due to amorphous Fe 3 (PO 4 ) 2/3 Is formed of (a) and Mg 2+ And a competing reaction with phosphate.
FIG. 2 (i) is the FTIR spectra, mg (OH), of the coatings obtained in examples 1-3 2 、Fe(OH) 2/3 、CO 3 2- 、PO 4 3- 、H 2 PO - Is present.
FIG. 3 is a graph showing the result of XPS analysis of the self-catalyzed degradation coating prepared in example 1.
As shown in FIG. 3, from the full spectrum (FIG. 3 a), one or more peaks of C1s, O1s, mg1s, P2P and Fe2P can be found. The relative atomic percentages of coating I were c=36.73%, o= 44.65%, mg=5.51%, p=9.83%, fe=3.26%.
FIG. 4 is a graph of electrochemical results for the autocatalytically degradable coatings prepared in examples 1-3, with (a), (b), (c) and (d) being Nyquist, enlarged Nyquist, bode and PDP results, respectively.
As shown in fig. 4, the coatings I and II prepared in examples 1 to 3 can effectively increase the self-corrosion effect of the magnesium alloy. The inductive reactance arcs of the coatings of examples 1-3 in the Nyquist diagram are significantly smaller than that of the substrate, wherein the inductive reactance arc of the coating I prepared in example 1 is 1/70 of that of the substrate, and the catalytic degradation effect is more obvious; while in Bode, coatingI. The values of |Z| for II and III were 25.19.+ -. 0.56. Omega. Cm, respectively 2 、31.49±0.86Ω·cm 2 And 32.60+ -0.15 Ω cm 2 Is far lower than 96.39 +/-1.48 omega cm of the AZ31 matrix 2 . The substrate obtained by the potential polarization curve and the self-etching currents of examples 1 to 3 were I in order from the large to the small>II>AZ31 matrix>III, the autocatalytic effect of coatings I and II was further demonstrated.
FIG. 5 is a graph showing the results of hydrogen evolution experiments for the self-catalyzed degradation coatings prepared in examples 1-3.
As shown in FIG. 5, the hydrogen evolution rates of the coatings and substrates of examples 1 to 3 after soaking for 78 hours were 0.21.+ -. 0.06 mL. Cm, respectively -2 ·h -1 、0.20±0.12mL·cm -2 ·h -1 And 0.08+ -0.01 mL cm -2 ·h -1 。
FIG. 6 is a graph showing the results of the nano scratch test of the self-catalyzed degradation coating prepared in examples 1 to 3.
The critical loads of the coatings I, II and III shown in FIG. 6 are 5590+ -30 mN, 5246+ -86 mN and 4960+ -68 mN, respectively, indicating good bonding of the three coatings to the substrate.
FIG. 7 is a graph showing the mechanism of catalytic degradation of the autocatalytic degradation coatings prepared in examples 1 to 3.
Example 6
Except that ferrous salt is ferrous chloride and phosphate is disodium hydrogen phosphate, deionized water is added to prepare a mixed aqueous solution. The remainder was the same as in example 2. Finally preparing the self-catalytic degradation coating on the surface of the magnesium alloy.
Example 7
Preparing a precursor solution:
respectively taking ferrous sulfate and trisodium phosphate dodecahydrate, and adding deionized water to prepare a mixed aqueous solution; wherein, the ferrous sulfate is 8.43mmol/L, na 3 PO 4 ·12H 2 O is 100mmol/L;
adjusting the pH value of the mixed solution to 5 by using phosphoric acid to obtain a precursor solution;
taking a magnesium alloy work device substrate, and preprocessing the magnesium alloy work device substrate:
mechanically polishing the magnesium alloy workpiece to remove burrs on the surface of the magnesium alloy workpiece, and sequentially washing the magnesium alloy workpiece with first water, alkaline washing, second water washing, acid washing and third water washing, and drying to obtain the magnesium alloy workpiece with fresh surface;
and (3) surface coating treatment of a substrate:
the volume ratio of the surface area of the work device to the precursor solution is 1cm 2 Measuring a precursor solution by using a measuring cylinder under the condition of 4+/-0.5 mL, pouring the precursor solution into a beaker, and putting the magnesium alloy workpiece with the fresh surface into the beaker so that the processed magnesium alloy workpiece is immersed below the liquid level of the precursor solution;
then, sealing the beaker mouth by using a preservative film, placing the beaker mouth into a water bath kettle, and carrying out water bath reaction for 2min at 80 ℃;
taking out the beaker, opening the preservative film, taking out the sample, washing the sample with water, and drying the sample to obtain the self-catalytic degradation coating on the surface of the magnesium alloy.
Example 8
Preparing a precursor solution:
respectively taking ferrous nitrate and ammonium hydrogen phosphate, and adding deionized water to prepare a mixed aqueous solution; wherein, ferrous nitrate is 30mmol/L, and ammonium hydrogen phosphate is 100mmol/L;
adjusting the pH value of the mixed solution to 3.27 by using phosphoric acid to obtain a precursor solution;
taking a magnesium alloy work device substrate, and preprocessing the magnesium alloy work device substrate:
mechanically polishing the magnesium alloy workpiece to remove burrs on the surface of the magnesium alloy workpiece, and sequentially washing the magnesium alloy workpiece with first water, alkaline washing, second water washing, acid washing and third water washing, and drying to obtain the magnesium alloy workpiece with fresh surface;
and (3) surface coating treatment of a substrate:
the volume ratio of the surface area of the work device to the precursor solution is 1cm 2 Measuring a precursor solution by using a measuring cylinder under the condition of 4+/-0.5 mL, pouring the precursor solution into a beaker, and putting the magnesium alloy workpiece with the fresh surface into the beaker so that the processed magnesium alloy workpiece is immersed below the liquid level of the precursor solution;
then, sealing the beaker mouth by using a preservative film, placing the beaker mouth into a water bath kettle, and carrying out water bath reaction for 60min at 20 ℃;
taking out the beaker, opening the preservative film, taking out the sample, washing the sample with water, and drying the sample to obtain the self-catalytic degradation coating on the surface of the magnesium alloy.
Example 9
Preparing a precursor solution:
respectively taking ferric sulfate and ammonium phosphate, and adding deionized water to prepare a mixed aqueous solution; wherein, the ferric sulfate is 40mmol/L, and the ammonium phosphate is 100mmol/L;
adjusting the pH value of the mixed solution to 2.5 by using phosphoric acid to obtain a precursor solution;
taking a magnesium alloy work device substrate, and preprocessing the magnesium alloy work device substrate:
mechanically polishing the magnesium alloy workpiece to remove burrs on the surface of the magnesium alloy workpiece, and sequentially washing the magnesium alloy workpiece with first water, alkaline washing, second water washing, acid washing and third water washing, and drying to obtain the magnesium alloy workpiece with fresh surface;
and (3) surface coating treatment of a substrate:
the volume ratio of the surface area of the work device to the precursor solution is 1cm 2 Measuring a precursor solution by using a measuring cylinder under the condition of 4+/-0.5 mL, pouring the precursor solution into a beaker, and putting the magnesium alloy workpiece with the fresh surface into the beaker so that the processed magnesium alloy workpiece is immersed below the liquid level of the precursor solution;
then, sealing the beaker mouth by using a preservative film, placing the beaker mouth into a water bath kettle, and carrying out water bath reaction for 2min at 80 ℃;
taking out the beaker, opening the preservative film, taking out the sample, washing the sample with water, and drying the sample to obtain the self-catalytic degradation coating on the surface of the magnesium alloy.
Example 10
Preparing a precursor solution:
respectively taking ferric nitrate and ammonium phosphate, and adding deionized water to prepare a mixed aqueous solution; wherein, the ferric nitrate is 6mmol/L, and the ammonium phosphate is 100mmol/L;
adjusting the pH value of the mixed solution to 2 by using phosphoric acid to obtain a precursor solution;
taking a magnesium alloy work device substrate, and preprocessing the magnesium alloy work device substrate:
mechanically polishing the magnesium alloy workpiece to remove burrs on the surface of the magnesium alloy workpiece, and sequentially washing the magnesium alloy workpiece with first water, alkaline washing, second water washing, acid washing and third water washing, and drying to obtain the magnesium alloy workpiece with fresh surface;
and (3) surface coating treatment of a substrate:
the volume ratio of the surface area of the work device to the precursor solution is 1cm 2 Measuring a precursor solution by using a measuring cylinder under the condition of 4+/-0.5 mL, pouring the precursor solution into a beaker, and putting the magnesium alloy workpiece with the fresh surface into the beaker so that the processed magnesium alloy workpiece is immersed below the liquid level of the precursor solution;
then, sealing the beaker mouth by using a preservative film, placing the beaker mouth into a water bath kettle, and carrying out water bath reaction for 30min at 60 ℃;
taking out the beaker, opening the preservative film, taking out the sample, washing the sample with water, and drying the sample to obtain the self-catalytic degradation coating on the surface of the magnesium alloy.
Example 11
Preparing a precursor solution:
respectively taking ferric chloride and disodium hydrogen phosphate, and adding deionized water to prepare a mixed aqueous solution; wherein, the ferric chloride is 100mmol/L, and the disodium hydrogen phosphate is 100mmol/L;
adjusting the pH value of the mixed solution to 3 by using phosphoric acid to obtain a precursor solution;
taking a magnesium alloy work device substrate, and preprocessing the magnesium alloy work device substrate:
mechanically polishing the magnesium alloy workpiece to remove burrs on the surface of the magnesium alloy workpiece, and sequentially washing the magnesium alloy workpiece with first water, alkaline washing, second water washing, acid washing and third water washing, and drying to obtain the magnesium alloy workpiece with fresh surface;
and (3) surface coating treatment of a substrate:
the volume ratio of the surface area of the work device to the precursor solution is 1cm 2 4+/-0.5 mL of precursor solution is measured by a measuring cylinder, poured into a beaker, and the magnesium alloy workpiece with the fresh surface is put in, so that the processed magnesium alloy workpiece is immersed in the precursor solutionSubsurface;
then, sealing the beaker mouth by using a preservative film, placing the beaker mouth into a water bath kettle, and carrying out water bath reaction for 60min at 20 ℃;
taking out the beaker, opening the preservative film, taking out the sample, washing the sample with water, and drying the sample to obtain the self-catalytic degradation coating on the surface of the magnesium alloy.
It should be understood that the above description is not intended to limit the invention to the particular embodiments disclosed, but to limit the invention to the particular embodiments disclosed, and that the invention is not limited to the particular embodiments disclosed, but is intended to cover modifications, adaptations, additions and alternatives falling within the spirit and scope of the invention.
Claims (6)
1. A process for preparing the autocatalytic degradation coating on the surface of Mg or Mg alloy features that the autocatalytic degradation coating is made up of phosphate and ferrite or ferric salt as nucleator, and has porous structure and chemical components including Fe and Fe 3 (PO 4 ) 2 And/or FePO 4 Factors influencing the autocatalytic effect of the coating include: the content of ferrous ions in the coating and the loose porous structure of the coating; the elemental iron formed by the self-catalytic degradation coating can further form a galvanic couple with magnesium to accelerate the degradation of magnesium or magnesium alloy, and the open circuit potential and the self-corrosion current density of the self-catalytic degradation coating are both greater than those of the magnesium or magnesium alloy; wherein, the open circuit potential of the self-catalytic degradation coating after 1 hour of electrochemical test is-1.56+/-0.35V/SCE to-1.57+/-0.04V/SCE; self-etching current density of 5.69×10 -4 A/cm 2 ～1.04×10 -5 A/cm 2 The method comprises the steps of carrying out a first treatment on the surface of the Hydrogen evolution rate after 78 hours of immersion in 3.5wt.% NaCl was 0.20.+ -. 0.12mL cm -2 ·h -1 ～0.08±0.01mL·cm -2 ·h -1 ；
The preparation method 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 34.4-100:100 or the ferric ion/phosphate ion molar ratio of 40-100:100, and adding deionized water to prepare a uniform mixed solution;
adjusting the pH value of the mixed solution to 2-3.77 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, alkaline washing, second water washing, acid washing and third water washing, and drying to obtain the magnesium or magnesium alloy workpiece with a fresh surface;
(3) The magnesium or magnesium alloy work piece with the fresh surface is put into a precursor solution, so that the treated magnesium or magnesium alloy work piece is immersed under the liquid level of the precursor solution, and the volume ratio of the surface area of the magnesium or magnesium alloy work piece to the precursor solution is 1cm 2 :4±0.5mL；
Sealing the mouth of the beaker with a preservative film and placing the beaker into a water bath kettle for water bath reaction; the water bath reaction condition is that the water bath reaction is carried out for 30-60min at 20-80 ℃;
(4) Taking out the beaker, opening the preservative film, taking out the sample, washing the sample with water, and drying the sample to prepare the self-catalytic degradation coating on the surface of the magnesium or the magnesium alloy.
2. The method for preparing the magnesium or magnesium alloy surface self-catalyzed degradation coating according to claim 1, wherein the thickness of the magnesium or magnesium alloy surface self-catalyzed degradation coating is more than 0 and less than or equal to 20 μm.
3. The method for preparing the autocatalytic degradation coating on the surface of magnesium or magnesium alloy according to claim 1, 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.
4. The method for preparing the autocatalytic degradation coating on the surface of magnesium or magnesium alloy according to claim 1, wherein the phosphate is trisodium phosphate dodecahydrate, disodium hydrogen phosphate, sodium dihydrogen phosphate, ammonium phosphate or ammonium hydrogen phosphate.
5. The method for preparing an autocatalytic degradation coating on a magnesium or magnesium alloy surface according to claim 1, wherein in the step (1), the solution concentrations of phosphate and ferrous salt or ferric salt are calculated by MEDUSA software according to the precipitation dissolution balance of ferrous phosphate or ferric phosphate.
6. The method for preparing an autocatalytic degradation coating on a magnesium or magnesium alloy surface according to claim 1, wherein the phosphate, ferrite or ferric salt is analytically pure.
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