Method for in-situ generation of heating wire gallium-based high-temperature oxidation-resistant composite coating

Abstract

The invention relates to a method for generating a gallium-based high-temperature anti-oxidation composite coating of an electric heating wire in situ, and belongs to the technical field of material preparation. An oxidation film on the surface of the electric heating wire is removed through abrasive paper polishing, and then the pretreated electric heating wire is obtained through polishing, degreasing and acid activation in sequence; gallium and metal A are mixed and smelted to be alloyed to obtain a gallium-based alloy melt, the pretreated electric heating wire is evenly coated with the gallium-based alloy melt, a high-temperature in-situ reaction is conducted for 50-70 min at the temperature of 1000-1400 DEG C to enable the gallium-based alloy to be dealloyed, the metal A is separated out, oxidized and floated on the surface of liquid gallium to form a ceramic layer of metal A oxide, and the gallium-based high-temperature anti-oxidation composite coating is obtained. The composite coating effectively solves the problem that the coefficient of thermal expansion (CTE) of the oxide layer is not matched with the coefficient of thermal expansion (CTE) of the heating wire, and the service life of the heating wire is greatly prolonged.

Description

Technical Field

[0001] The invention relates to a method for in-situ generating a gallium-based high-temperature anti-oxidation composite coating for a heating wire, and belongs to the field of material preparation technology. Background Art

[0002] Self-passivating alloy technology and coating surface technology are two measures to solve the problem of easy oxidation of metals. In the early stage of self-passivating alloy technology, a protective anti-oxidation coating is formed on the surface of the substrate by sacrificing part of the substrate elements. However, the oxides generated by the substrate elements often have a high pilling ratio (PBR), which leads to volume expansion and shedding of the protective layer. At the same time, the addition of multiple alloying elements will also affect the mechanical properties of the alloy. Therefore, self-passivating alloy technology has certain limitations. Surface coating technologies mainly include halide activation cladding method, chemical vapor deposition method, hot dip siliconization method, etc. By forming an anti-oxidation coating on the surface of the substrate, it can avoid oxidation to the greatest extent without affecting the performance of the alloy. It is the mainstream method of pre-oxidation of metals.

[0003] Gallium metal is a non-toxic, non-volatile liquid metal that is liquid at room temperature and has a promising coating application prospect. Pre-oxidized gallium has considerable viscosity and can be directly brushed on the substrate to prevent oxidation. At the same time, the flexibility of liquid gallium itself can effectively solve the CTE coefficient mismatch problem between the substrate and the coating. Hu et al. used pre-oxidized gallium to form a high-temperature anti-oxidation coating on the surface of a tungsten substrate, but the strength of the coating was low and had certain limitations. Summary of the invention

[0004] The present invention aims at the problem of high temperature oxidation of the heating wire, and is different from other traditional methods for preparing high temperature anti-oxidation coatings. A method for in-situ generation of gallium-based high temperature anti-oxidation composite coatings for heating wires is proposed, that is, according to the difference in reduction potential between metal element A and gallium, an oxide ceramic with an outer layer of metal A and a flexible layer of liquid metal gallium can be in-situ precipitated on the surface of the heating wire. If the heating wire is a tungsten wire, the gallium-based high temperature anti-oxidation composite coating is a high temperature anti-oxidation coating with two distinct structures, including a flexible layer of liquid metal gallium and an oxide ceramic of an outer layer of metal A. If the heating wire is a nickel-chromium alloy wire or an iron-chromium-nickel alloy wire, the gallium-based high temperature anti-oxidation composite coating also includes a gallium alloy layer formed by in-situ penetration of the bottom metal gallium into the surface layer of the heating wire, forming a high temperature anti-oxidation coating with three distinct structures. The coating prepared by the present invention has a distinct structure, is uniform and dense, has a simple process, and the oxide layer is well combined with the liquid metal gallium layer, which can effectively improve the service life of the heating wire and is suitable for large-scale industrial production.

[0005] A method for in-situ generation of a gallium-based high-temperature anti-oxidation composite coating for a heating wire, the specific steps of which are as follows:

[0006] (1) The heating wire is grinded to remove the surface oxide film, polished, degreased, and acid activated to obtain a pretreated heating wire; the heating wire is tungsten wire, nickel-chromium alloy wire, or iron-chromium-nickel alloy wire;

[0007] (2) mixing gallium and metal A to alloy them to obtain a gallium-based alloy melt, wherein the metal A is one or more of aluminum, zinc, and magnesium, and the melting temperature is not lower than the melting point of the alloy of gallium and metal A;

[0008] (3) The gallium-based alloy melt is uniformly coated on the pretreated heating wire, and the heating wire is energized to self-heat to a temperature of 1000-1400° C. The gallium-based alloy melt coating layer undergoes a high-temperature in-situ precipitation reaction for 50-70 minutes to dealloy the gallium-based alloy, and the metal A is precipitated and oxidized to float on the surface of the liquid gallium to form a ceramic layer of metal A oxide, thereby obtaining a gallium-based high-temperature anti-oxidation composite coating; the heating wire is a nickel-chromium alloy wire or an iron-chromium-nickel alloy wire, and the gallium-based high-temperature anti-oxidation composite coating also includes a gallium alloy layer formed by the bottom metal gallium in-situ penetrating into the surface of the heating wire.

[0009] The heating wire in step (1) is tungsten wire, nickel-chromium alloy wire, iron-chromium-nickel alloy wire, the degreasing solvent is acetone or ethanol, the acid for acid activation treatment is hydrofluoric acid, the mass concentration of hydrofluoric acid is 35-45%, the acid activation time is 1-2 minutes, and the acid activation temperature is 25-35°C.

[0010] The amount of metal A added in step (2) accounts for 10-30% of the mass of the gallium-based alloy melt.

[0011] The smelting temperature in step (2) is 40 to 700° C., and the smelting time is 30 to 60 minutes.

[0012] The total thickness of the gallium-based high-temperature anti-oxidation composite coating in step (3) is 30 to 60 μm.

[0013] The beneficial effects of the present invention are:

[0014] (1) The gallium-based alloy melt obtained by simple metal smelting in the present invention has good viscosity, and then a simple coating process is used. Then, the gallium alloy is precipitated in situ under the condition of self-heating when the heating wire is powered on, and oxidation reaction can be performed to complete the preparation of the gallium-based high-temperature anti-oxidation composite coating. The preparation process is effective and simple. If the heating wire is a nickel-chromium alloy wire or an iron-chromium-nickel alloy wire, the gallium bottom layer is also infiltrated into the heating wire substrate under the condition of self-heating when the heating wire is powered on, so as to alloy it, thereby further improving the adhesion of the gallium-based high-temperature anti-oxidation composite coating on the surface of the heating wire substrate.

[0015] (2) The present invention utilizes the difference in reduction potential of each element in the gallium-based alloy to in-situ precipitate on the surface of the tungsten heating wire a two-layer gallium-based high-temperature anti-oxidation composite coating with a distinct structure, wherein the outer layer is an oxide ceramic of metal A and the inner layer is a flexible layer of liquid metal gallium. The heating wire is a nickel-chromium alloy wire or an iron-chromium-nickel alloy wire. A three-layer gallium-based high-temperature anti-oxidation composite coating with a distinct structure can also be obtained, wherein the bottom layer is a gallium-based alloy layer infiltrated into the interior of the heating wire to alloy it, thereby effectively regulating the coating structure;

[0016] (3) The gallium-based high-temperature anti-oxidation composite coating formed by the present invention is uniform and dense, the metal A oxide ceramic layer is well bonded with the liquid metal gallium layer, and the liquid metal gallium layer is well bonded with the surface layer of the heating wire, which effectively improves the high-temperature service life of the heating wire. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a SEM image (magnification 2200 times) of the coating surface of the iron-chromium-nickel alloy wire coated with the coating in Example 1 after being energized in air for 1 hour;

[0018] Figure 2 This is a graph of the oxidation weight gain of the uncoated iron-chromium-nickel alloy wire and the coated iron-chromium-nickel alloy wire in Example 1 within 1 hour;

[0019] Figure 3 This is a SEM image of the coating surface of the nickel-chromium alloy wire coated with the coating in Example 2 after being energized in air for 1 hour (magnification 7500 times);

[0020] Figure 4 This is a graph of the oxidation weight gain of the nickel-chromium alloy wire without coating and the nickel-chromium alloy wire coated with coating in 1 hour in Example 2;

[0021] Figure 5 This is a SEM image of the coating surface of the tungsten wire coated with the coating in Example 3 after being energized in air for 1 hour (magnification 1800 times);

[0022] Figure 6 This is a graph of the oxidation weight gain of the uncoated tungsten wire and the coated tungsten wire in Example 3 within 1 hour. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below in conjunction with specific implementation modes, but the protection scope of the present invention is not limited to the described contents.

[0024] Example 1: A method for in-situ generation of a gallium-based high-temperature anti-oxidation composite coating for a heating wire, the specific steps are as follows:

[0025] (1) using sandpaper to grind and remove the oxide film on the surface of the iron-chromium-nickel alloy wire, and then polishing, degreasing, and acid activation in sequence to obtain a pretreated iron-chromium-nickel alloy wire; the degreasing solvent is acetone, the acid for the acid activation treatment is hydrofluoric acid with a mass concentration of 35%, the acid activation temperature is 25° C., and the time is 2 min;

[0026] (2) at a temperature of 400° C., mixing gallium and metal A (zinc) and smelting for 40 minutes to obtain a gallium-zinc alloy melt; in the gallium-zinc alloy melt, metal A (zinc) accounts for 10 wt.%, and gallium accounts for 90 wt.%;

[0027] (3) The gallium-zinc alloy melt is uniformly coated on the pretreated iron-chromium-nickel alloy wire, and the electric heating wire (iron-chromium-nickel alloy wire) is energized to self-heat to a temperature of 1000° C. The gallium-zinc alloy melt coating layer is subjected to a high-temperature in-situ precipitation reaction for 60 minutes to de-alloy the gallium-based alloy, and the metal A (zinc) is precipitated and oxidized to float on the surface of the liquid gallium to form a ceramic layer of metal A oxide (zinc oxide), and the bottom metal gallium in-situ penetrates into the surface of the electric heating wire to form a gallium alloy layer, thereby obtaining a gallium-based high-temperature anti-oxidation composite coating;

[0028] The preparation process of the high-temperature anti-oxidation composite coating of this embodiment is simple, the coating is dense and crack-free, the oxide ceramic layer (zinc oxide) and the liquid metal gallium layer are well combined, the thickness of the gallium-based high-temperature anti-oxidation composite coating is 30 μm, the surface layer is a ceramic layer of zinc oxide, the interior is gallium liquid metal, the surface layer of the iron-chromium-nickel alloy wire is a gallium alloy layer formed by in-situ infiltration of metal gallium into the surface layer of the heating wire;

[0029] The SEM image (magnification 2200 times) of the coating surface of the Fe-Cr-Ni alloy wire containing the gallium-based high temperature anti-oxidation composite coating in this embodiment after being energized in air for 1 hour is shown in FIG. Figure 1 ,from Figure 1 It can be seen that the coating surface is a dense layer of zinc oxide, without obvious cracks and holes, and the oxide ceramic layer (zinc oxide) is well combined with the liquid metal gallium layer. It can be seen that the gallium-zinc composite coating has a good protective effect on the iron-chromium-nickel alloy wire;

[0030] The oxidation weight gain of the uncoated iron-chromium-nickel alloy wire and the coated iron-chromium-nickel alloy wire in 1 hour is shown in FIG. Figure 2 ,from Figure 2 It can be seen that the uncoated iron-chromium-nickel alloy wire has obvious oxidation weight gain, and the weight gain tends to be stable at 40 minutes. This is because a dense layer of chromium oxide is generated on the surface of the alloy wire. However, the oxidation weight gain of the coated iron-chromium-nickel alloy wire within 60 minutes is not obvious and can be ignored. It can be seen that the gallium-zinc composite coating has a good protective effect on the iron-chromium-nickel alloy wire.

[0031] Example 2: A method for in-situ generation of a gallium-based high-temperature anti-oxidation composite coating for a heating wire, the specific steps are as follows:

[0032] (1) using sandpaper to grind and remove the oxide film on the surface of the nickel-chromium alloy wire, and then polishing, degreasing, and acid activation in sequence to obtain a pretreated nickel-chromium alloy wire; the degreasing solvent is ethanol, the acid for the acid activation treatment is hydrofluoric acid with a mass concentration of 40%, the acid activation temperature is 30° C., and the time is 1.5 min;

[0033] (2) Mixing gallium and metal A (aluminum) and smelting them at a temperature of 40° C. for 50 minutes to obtain a gallium-aluminum alloy melt; the gallium-aluminum alloy melt contains 20 wt.% of metal A (aluminum) and 80 wt.% of gallium;

[0034] (3) The gallium-aluminum alloy melt is uniformly coated on the pretreated nickel-chromium alloy wire, and the electric heating wire (nickel-chromium alloy wire) is energized to self-heat to a temperature of 1100° C. The gallium-aluminum alloy melt coating layer is subjected to a high-temperature in-situ precipitation reaction for 50 minutes to de-alloy the gallium-based alloy, and the metal A (aluminum) is precipitated and oxidized to float on the surface of the liquid gallium to form a ceramic layer of metal A oxide (aluminum oxide), and the bottom metal gallium in-situ penetrates into the surface of the electric heating wire to form a gallium alloy layer, thereby obtaining a gallium-based high-temperature anti-oxidation composite coating;

[0035] The preparation process of the high-temperature anti-oxidation composite coating of this embodiment is simple, the coating is dense and crack-free, the oxide ceramic layer (aluminum oxide) and the liquid metal gallium layer are well combined, the thickness of the gallium-based high-temperature anti-oxidation composite coating is 50 μm, the surface layer is a ceramic layer of aluminum oxide, the interior is gallium liquid metal, and the surface layer of the nickel-chromium alloy wire is a gallium alloy layer formed by in-situ infiltration of metal gallium into the surface layer of the heating wire;

[0036] The SEM image (magnification 7500 times) of the coating surface of the nickel-chromium alloy wire containing the gallium-based high-temperature anti-oxidation composite coating in this embodiment after being energized in air for 1 hour is shown in FIG. Figure 3 ,from Figure 3 It can be seen that the aluminum oxide on the coating surface presents a flake morphology, with no obvious cracks and holes. The oxide ceramic layer (aluminum oxide) is well combined with the liquid metal gallium layer, and the coating has good density. It can be seen that the gallium-aluminum composite coating has a good protective effect on the nickel-chromium alloy wire.

[0037] The oxidation weight gain of the nickel-chromium alloy wire without coating and the nickel-chromium alloy wire coated with coating in 1 hour is shown in FIG. Figure 4 ,from Figure 4 It can be seen that the uncoated nickel-chromium alloy wire has a significant weight gain in the initial stage of oxidation, and the oxidation weight gain tends to be stable near 60 minutes. This is because the chromium on the surface of the nickel-chromium alloy wire is oxidized to form a dense layer of chromium oxide; while the nickel-chromium alloy wire coated with the coating has no significant oxidation weight gain within 60 minutes and can be ignored. It can be seen that the gallium-aluminum coating has a good protective effect on the nickel-chromium alloy wire.

[0038] Example 3: A method for in-situ generation of a gallium-based high-temperature anti-oxidation composite coating for a heating wire, the specific steps are as follows:

[0039] (1) using sandpaper to polish and remove the oxide film on the surface of the tungsten wire, and then polishing, degreasing, and acid activation in sequence to obtain a pretreated tungsten wire; the degreasing solvent is acetone, the acid for the acid activation treatment is hydrofluoric acid with a mass concentration of 45%, the acid activation temperature is 35° C., and the time is 1 min;

[0040] (2) at a temperature of 700° C., gallium and metal A (aluminum) are mixed and smelted to obtain a 70-min gallium-aluminum alloy melt; the gallium-aluminum alloy melt contains 30 wt.% of metal A (aluminum) and 70 wt.% of gallium;

[0041] (3) The gallium-aluminum alloy melt is uniformly coated on the pretreated tungsten wire, and the electric heating wire (tungsten wire) is energized to self-heat to a temperature of 1200° C. The gallium-aluminum alloy melt coating layer is subjected to a high-temperature in-situ precipitation reaction for 65 minutes to de-alloy the gallium-based alloy, and the metal A (aluminum) is precipitated and oxidized to float on the surface of the liquid gallium to form a ceramic layer of metal A oxide (aluminum oxide), thereby obtaining a gallium-based high-temperature anti-oxidation composite coating;

[0042] The preparation process of the high-temperature anti-oxidation composite coating in this embodiment is simple, and the coating is dense and crack-free; the oxide ceramic layer (aluminum oxide) is well combined with the liquid metal gallium layer, and the thickness of the gallium-based high-temperature anti-oxidation composite coating is 38 μm, the surface layer is a ceramic layer of aluminum oxide, and the interior is gallium liquid metal. The metal gallium on the surface of the tungsten wire increases in viscosity when the electric heating wire (tungsten wire) is energized and self-heated, and the adhesion to the surface of the tungsten wire increases;

[0043] The SEM image (magnification 1800 times) of the coating surface of the tungsten wire containing the gallium-based high temperature anti-oxidation composite coating in this embodiment after being energized in air for 1 hour is shown in FIG. Figure 5 ,from Figure 5 It can be seen that the coating surface is a dense flaky aluminum oxide ceramic layer with no obvious cracks and holes, and the oxide ceramic layer (aluminum oxide) is well combined with the liquid metal gallium layer. It can be seen that the gallium-aluminum composite coating has a good protective effect on the tungsten wire.

[0044] The oxidation weight gain of the tungsten wire without coating and the tungsten wire coated with coating in this embodiment within 1 hour is shown in Figure 6 ,from Figure 6 It can be seen that the tungsten wire without coating has obvious oxidation weight gain and melted at 17 minutes; while the tungsten wire coated with coating has no obvious oxidation weight gain and can be ignored. It can be seen that the gallium-aluminum composite coating has a good protective effect on the tungsten wire.

[0045] Example 4: A method for in-situ generation of a gallium-based high-temperature anti-oxidation composite coating for a heating wire, the specific steps are as follows:

[0046] (1) using sandpaper to polish and remove the oxide film on the surface of the iron-chromium-nickel alloy wire, and then polishing, degreasing, and acid activation in sequence to obtain a pretreated iron-chromium-nickel alloy wire; the degreasing solvent is acetone, the acid for the acid activation treatment is hydrofluoric acid with a mass concentration of 45%, the acid activation temperature is 30° C., and the time is 1 min;

[0047] (2) at a temperature of 60° C., gallium and metal A (magnesium) are mixed and smelted to obtain a gallium-magnesium alloy melt for 45 min; the gallium-magnesium alloy melt contains 2 wt.% of metal A (magnesium) and 98 wt.% of gallium;

[0048] (3) The gallium-magnesium alloy melt is uniformly coated on the pretreated iron-chromium-nickel alloy wire, and the electric heating wire (iron-chromium-nickel alloy wire) is energized to self-heat to a temperature of 1300° C. and a high-temperature in-situ precipitation reaction is carried out for 70 minutes to dealloy the gallium-based alloy, and metal A (magnesium) is precipitated and oxidized to float on the surface of the liquid gallium to form a ceramic layer of metal A oxide (magnesium oxide), and the bottom metal gallium in-situ penetrates into the surface of the electric heating wire to form a gallium alloy layer, thereby obtaining a gallium-based high-temperature anti-oxidation composite coating;

[0049] The preparation process of the high-temperature anti-oxidation composite coating in this embodiment is simple, and the coating is dense and crack-free; the oxide ceramic layer (magnesium oxide) is well combined with the liquid metal gallium layer, and the thickness of the gallium-based high-temperature anti-oxidation composite coating is 60 μm, the surface layer is a magnesium oxide ceramic layer, the interior is gallium liquid metal, and the surface layer of the iron-chromium-nickel alloy wire is a gallium alloy layer formed by in-situ infiltration of metal gallium into the surface layer of the heating wire;

[0050] After the iron-chromium-nickel alloy wire containing the gallium-based high-temperature anti-oxidation composite coating in this embodiment was energized in the air for 1 hour, the surface of the coating was a dense layer of magnesium oxide without obvious cracks and holes, and the oxide ceramic layer (magnesium oxide) was well combined with the liquid metal gallium layer. It can be seen that the gallium-magnesium composite coating has a good protective effect on the iron-chromium-nickel alloy wire.

[0051] The specific implementation modes of the present invention are described in detail above, but the present invention is not limited to the above implementation modes, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A method for in-situ generation of a gallium-based high-temperature anti-oxidation composite coating for a heating wire, characterized in that: The specific steps are as follows: (1) The heating wire is grinded to remove the surface oxide film, polished, degreased, and acid activated to obtain a pretreated heating wire; the heating wire is tungsten wire, nickel-chromium alloy wire, or iron-chromium-nickel alloy wire; (2) Gallium and metal A are mixed and smelted to alloy them to obtain a gallium-based alloy melt, wherein the metal A is one or more of aluminum, zinc, and magnesium, and the smelting temperature is not lower than the melting point of the alloy of gallium and metal A; (3) The gallium-based alloy melt is uniformly coated on the pretreated heating wire, and the heating wire is energized to self-heat to a temperature of 1000-1400°C. The gallium-based alloy melt coating layer is subjected to a high-temperature in-situ precipitation reaction for 50-70 minutes to dealloy the gallium-based alloy, and the metal A is precipitated and oxidized to float on the surface of the liquid gallium to form a ceramic layer of metal A oxide, thereby obtaining a gallium-based high-temperature anti-oxidation composite coating; the heating wire is a nickel-chromium alloy wire or an iron-chromium-nickel alloy wire, and the gallium-based high-temperature anti-oxidation composite coating also includes a gallium alloy layer formed by the bottom metal gallium in-situ penetrating the surface of the heating wire.

2. The method for preparing the in-situ generated gallium-based high-temperature anti-oxidation composite coating for heating wires according to claim 1, characterized in that: The solvent for degreasing in step (1) is acetone or ethanol, the acid for acid activation treatment is hydrofluoric acid, the mass concentration of hydrofluoric acid is 35-45%, the acid activation time is 1-2 min, and the acid activation temperature is 25-35°C.

3. The method for preparing the in-situ generated gallium-based high-temperature anti-oxidation composite coating for heating wire according to claim 1, characterized in that: In the step (2), the amount of metal A added is 10-30% of the mass of the gallium-based alloy melt.

4. The method for preparing the in-situ generated gallium-based high-temperature anti-oxidation composite coating for heating wires according to claim 1, characterized in that: The smelting temperature in step (2) is 40-700° C., and the smelting time is 30-60 min.

5. The method for preparing the in-situ generated gallium-based high-temperature anti-oxidation composite coating for heating wires according to claim 1, characterized in that: The thickness of the gallium-based high-temperature anti-oxidation composite coating in step (3) is 30-60 μm.

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