A method for in-situ generating an electrically heated wire gallium-based high-temperature oxidation-resistant composite coating

Abstract

The present application relates to a kind of in-situ generation electric heating wire gallium-based high temperature oxidation-resistant composite coating method, belong to material preparation technical field.The present application is removed by sand paper polishing to remove the oxidation film on the surface of electric heating wire, then in turn by polishing, degreasing, acid activation to obtain pretreated electric heating wire;Gallium is mixed with metal A and is alloyed to obtain gallium-based alloy melt, and the gallium-based alloy melt is uniformly coated on the pretreated electric heating wire, and the gallium-based alloy is de-alloyed at high temperature in-situ reaction for 50-70min at 1000-1400 ℃, and metal A is precipitated and oxidized to form a ceramic layer of metal A oxide on the surface of liquid gallium, to obtain gallium-based high temperature oxidation-resistant composite coating.The composite coating of the present application effectively solves the problem of mismatching of the oxidation layer and the electric heating wire thermal expansion coefficient (CTE), greatly improves the service life of electric heating wire.

Description

Technical Field

[0001] This invention relates to a method for in-situ generation of a gallium-based high-temperature antioxidant composite coating for heating wires, belonging to the field of materials preparation technology. Background Technology

[0002] Self-passivating alloying technology and surface coating technology are two measures to address the easy oxidation of metals. Early self-passivating alloying technology formed a protective anti-oxidation coating on the substrate surface by sacrificing some matrix elements. However, the oxides generated by the matrix elements often have a high balling ratio (PBR), leading to volume expansion and peeling of the protective layer. Furthermore, the addition of multiple alloying elements can affect the mechanical properties of the alloy, thus self-passivating alloying technology has certain limitations. Surface coating technologies mainly include halide activated cladding, chemical vapor deposition, and thermal infiltration of silicon. By forming an anti-oxidation coating on the substrate surface, oxidation can be minimized without affecting the alloy's performance, and this is currently the mainstream method for pre-oxidizing metals.

[0003] Gallium is a non-toxic, non-volatile liquid metal that is liquid at room temperature, making it a promising candidate for coating applications. Pre-oxidized gallium has considerable viscosity, allowing it to be directly brushed onto substrates to prevent oxidation. Furthermore, the flexibility of liquid gallium effectively addresses the CTE (Coefficient of Thermal Expansion) mismatch between the substrate and the coating. Hu et al. used pre-oxidized gallium to form a high-temperature anti-oxidation coating on a tungsten substrate, but the coating exhibited low strength, presenting certain limitations. Summary of the Invention

[0004] This invention addresses the problem of high-temperature oxidation of heating wires. Unlike other traditional methods for preparing high-temperature anti-oxidation coatings, it proposes a method for in-situ generation of a gallium-based high-temperature anti-oxidation composite coating for heating wires. Based on the difference in reduction potential between metal element A and gallium, an outer layer of metal A oxide ceramic and an inner flexible layer of liquid gallium metal can be precipitated in-situ on the surface of the heating wire. If the heating wire is tungsten, the gallium-based high-temperature anti-oxidation composite coating consists of two distinct high-temperature anti-oxidation layers: the flexible layer of liquid gallium metal and the outer layer of metal A oxide ceramic. 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 the in-situ infiltration of the bottom layer of gallium metal into the surface of the heating wire, forming a three-layer high-temperature anti-oxidation coating. The coating prepared by this invention has a distinct, uniform, and dense structure, a simple process, and good bonding between the oxide layer and the liquid gallium metal layer, effectively improving the service life of the heating wire and making it suitable for large-scale industrial production.

[0005] A method for in-situ generating a gallium-based high-temperature oxidation-resistant composite coating for heating wires, comprising the following specific steps:

[0006] (1) The heating wire is pretreated by grinding to remove the surface oxide film, polishing, degreasing and acid activation; the heating wire is tungsten wire, nickel-chromium alloy wire or iron-chromium-nickel alloy wire.

[0007] (2) Gallium is mixed and smelted with metal A to alloy it to obtain gallium-based alloy melt, wherein metal A is one or more of aluminum, zinc, and magnesium, and the smelting temperature is not lower than the alloy melting point temperature of gallium and metal A;

[0008] (3) The gallium-based alloy melt is uniformly coated on the pretreated heating wire. The heating wire is energized and self-heated to a temperature of 1000-1400℃. 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. Metal A precipitates and oxidizes, floating on the surface of liquid gallium to form a ceramic layer of metal A oxide, thus 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. The gallium-based high-temperature anti-oxidation composite coating also includes a gallium alloy layer formed by the in-situ infiltration of the bottom metal gallium into the surface of the heating wire.

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

[0010] In step (2), the amount of metal A added is 10-30% of the mass of the gallium-based alloy melt.

[0011] The melting temperature in step (2) is 40-700℃ and the melting time is 30-60min.

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

[0013] The beneficial effects of this invention are:

[0014] (1) The gallium-based alloy melt obtained by the present invention through simple metal smelting has good viscosity. Then, by using a simple coating process, the gallium alloy can be precipitated and oxidized in situ under the condition of self-heating by energizing the heating wire, and the preparation of the gallium-based high-temperature anti-oxidation composite coating can be completed. 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 can be penetrated into the heating wire substrate under the condition of self-heating by energizing the heating wire to alloy it, which further improves the adhesion of the gallium-based high-temperature anti-oxidation composite coating on the surface of the heating wire substrate.

[0015] (2) This invention utilizes the difference in reduction potential of each element in the gallium-based alloy to generate a gallium-based high-temperature anti-oxidation composite coating with two distinct layers: an outer layer of metal A oxide ceramic and an inner layer of liquid metal gallium. The heating wire is a nickel-chromium alloy wire or an iron-chromium-nickel alloy wire. It can also obtain a gallium-based high-temperature anti-oxidation composite coating with three distinct layers: a gallium-based alloy layer with gallium penetrating into the heating wire and alloying it. This effectively controls the coating structure.

[0016] (3) The present invention forms a uniform and dense gallium-based high-temperature anti-oxidation composite coating, with good bonding between the metal A oxide ceramic layer and the liquid metal gallium layer, and good bonding between the liquid metal gallium layer and the surface layer of the heating wire, which effectively improves the high-temperature service life of the heating wire. Attached Figure Description

[0017] Figure 1 The image shows a SEM image (magnification 2200x) of the coated iron-chromium-nickel alloy wire in Example 1 after it has been energized in air for 1 hour.

[0018] Figure 2 The graph shows 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 The image shows a SEM image (7500x magnification) of the coated nickel-chromium alloy wire in Example 2 after it has been energized in air for 1 hour.

[0020] Figure 4 The graph shows the oxidation weight gain of the uncoated nickel-chromium alloy wire and the coated nickel-chromium alloy wire in Example 2 within 1 hour.

[0021] Figure 5 The image shows a SEM image (magnification 1800x) of the coated tungsten filament in Example 3 after it has been energized in air for 1 hour.

[0022] Figure 6 The graph shows the oxidative weight gain of the uncoated tungsten wire and the coated tungsten wire in Example 3 within 1 hour. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

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

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

[0026] (2) Gallium and zinc were mixed and smelted at 400°C for 40 min to obtain a gallium-zinc alloy melt; in the gallium-zinc alloy melt, zinc accounted for 10 wt.% and gallium accounted for 90 wt.%.

[0027] (3) The gallium-zinc alloy melt is uniformly coated on the pretreated iron-chromium-nickel alloy wire. The heating wire (iron-chromium-nickel alloy wire) is energized and self-heated to a temperature of 1000℃. The gallium-zinc alloy melt coating layer reacts in situ at high temperature for 60 minutes to de-alloy the gallium-based alloy. Metal A (zinc) is precipitated and oxidized, floating on the surface of liquid gallium to form a ceramic layer of metal A oxide (zinc oxide). The bottom layer of metal gallium is in situ diffused into the surface of the heating wire to form a gallium alloy layer, thus obtaining a gallium-based high-temperature anti-oxidation composite coating.

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

[0029] The SEM image (magnification 2200x) of the iron-chromium-nickel alloy wire with a gallium-based high-temperature anti-oxidation composite coating after energizing it in air for 1 hour is shown in this embodiment. Figure 1 ,from Figure 1 It can be seen that the coating surface is a dense zinc oxide layer, with no obvious cracks or holes, and the oxide ceramic layer (zinc oxide) is well bonded to the liquid metal gallium layer. It is evident that the gallium-zinc composite coating has a good protective effect on the iron-chromium-nickel alloy wire.

[0030] The oxidation weight gain diagram of the uncoated and coated iron-chromium-nickel alloy wires in this embodiment within 1 hour is shown below. Figure 2 ,from Figure 2 It can be seen that the uncoated iron-chromium-nickel alloy wire showed significant oxidation weight gain, which tended to stabilize after 40 minutes. This is because a dense layer of chromium oxide was formed on the surface of the alloy wire. However, the iron-chromium-nickel alloy wire with coating did not show significant oxidation weight gain within 60 minutes, which can be ignored. This shows 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 heating wires, the specific steps of which are as follows:

[0032] (1) The oxide film on the surface of the nickel-chromium alloy wire is removed by sandpaper, and then polished, degreased and acid activated in sequence to obtain the pretreated nickel-chromium alloy wire; the solvent for degreasing is ethanol, the acid for acid activation treatment is hydrofluoric acid with a mass concentration of 40%, the acid activation temperature is 30℃ and the time is 1.5min.

[0033] (2) Gallium and aluminum metal A are mixed and melted at 40°C for 50 min to obtain a gallium-aluminum alloy melt; in the gallium-aluminum alloy melt, aluminum metal A accounts for 20 wt.% and gallium accounts for 80 wt.%.

[0034] (3) The gallium-aluminum alloy melt is uniformly coated on the pretreated nickel-chromium alloy wire. The heating wire (nickel-chromium alloy wire) is energized and self-heated to a temperature of 1100℃. The gallium-aluminum alloy melt coating layer reacts in situ at high temperature for 50 minutes to de-alloy the gallium-based alloy. Metal A (aluminum) is precipitated and oxidized, floating on the surface of liquid gallium to form a ceramic layer (alumina) of metal A oxide. The bottom layer of metal gallium is in situ penetrated into the surface of the heating wire to form a gallium alloy layer, thus obtaining a gallium-based high-temperature anti-oxidation composite coating.

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

[0036] The SEM image (7500x magnification) of the nickel-chromium alloy wire with a gallium-based high-temperature anti-oxidation composite coating after energizing it in air for 1 hour is shown in this embodiment. Figure 3 ,from Figure 3 It can be seen that the alumina on the coating surface has a plate-like morphology, with no obvious cracks or holes. The alumina layer and the liquid gallium layer are well bonded, and the coating is dense. It is evident that the gallium-aluminum composite coating has a good protective effect on the nickel-chromium alloy wire.

[0037] The oxidation weight gain diagram of the uncoated and coated nickel-chromium alloy wires in this embodiment within 1 hour is shown below. Figure 4 ,from Figure 4 It can be seen that the uncoated nickel-chromium alloy wire showed significant weight gain in the early stage of oxidation, while the weight gain tended to stabilize after about 60 minutes. This is because the chromium on the surface of the nickel-chromium alloy wire oxidized to form a dense layer of chromium oxide. However, the weight gain of the coated nickel-chromium alloy wire was not significant within 60 minutes and could be ignored. This shows 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 heating wires, the specific steps of which are as follows:

[0039] (1) The oxide film on the surface of the tungsten wire is removed by sandpaper, and then the tungsten wire is obtained by polishing, degreasing and acid activation in sequence; the solvent for degreasing is acetone, the acid for acid activation treatment is hydrofluoric acid with a mass concentration of 45%, the acid activation temperature is 35℃ and the time is 1min.

[0040] (2) Gallium and aluminum metal A were mixed and smelted at a temperature of 700℃ to obtain a gallium-aluminum alloy melt for 70 min; in the gallium-aluminum alloy melt, aluminum metal A accounted for 30 wt.% and gallium accounted for 70 wt.%.

[0041] (3) The gallium-aluminum alloy melt is uniformly coated on the pretreated tungsten wire. The heating wire (tungsten wire) is energized and self-heated to a temperature of 1200℃. The gallium-aluminum alloy melt coating layer reacts in situ at high temperature for 65 minutes to de-alloy the gallium-based alloy. Metal A (aluminum) precipitates and oxidizes, floating on the surface of liquid gallium to form a ceramic layer (alumina) of metal A oxide, thus obtaining a gallium-based high-temperature anti-oxidation composite coating.

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

[0043] The SEM image (magnification 1800x) of the tungsten filament containing a gallium-based high-temperature anti-oxidation composite coating after energizing it in air for 1 hour is shown in this embodiment. Figure 5 ,from Figure 5 It can be seen that the coating surface is a dense sheet-like alumina ceramic layer, without obvious cracks and pores, and the alumina ceramic layer is well bonded to the liquid gallium metal layer, indicating that the gallium-aluminum composite coating has a good protective effect on the tungsten wire.

[0044] The oxidation weight gain diagram of the uncoated tungsten wire and the coated tungsten wire in this embodiment within 1 hour is shown below. Figure 6 ,from Figure 6 It can be seen that the uncoated tungsten wire showed significant oxidation and weight gain, and melted after 17 minutes; while the coated tungsten wire showed negligible oxidation and weight gain, indicating 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 heating wires, the specific steps of which are as follows:

[0046] (1) The oxide film on the surface of the iron-chromium-nickel alloy wire is removed by sanding with sandpaper, and then the wire is polished, degreased and acid activated in sequence to obtain the pretreated iron-chromium-nickel alloy wire; the solvent for degreasing is acetone, the acid for acid activation treatment is hydrofluoric acid with a mass concentration of 45%, the acid activation temperature is 30℃ and the time is 1min.

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

[0048] (3) The gallium-magnesium alloy melt is uniformly coated on the pretreated iron-chromium-nickel alloy wire. The heating wire (iron-chromium-nickel alloy wire) is energized and self-heated to a temperature of 1300℃. The high-temperature in-situ precipitation reaction is carried out for 70 minutes to de-alloy the gallium-based alloy. Metal A (magnesium) is precipitated and oxidized and floats on the surface of liquid gallium to form a ceramic layer of metal A oxide (magnesium oxide). The bottom layer of metal gallium is in-situ diffused into the surface of the heating wire to form a gallium alloy layer, thus obtaining a gallium-based high-temperature anti-oxidation composite coating.

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

[0050] In this embodiment, after the iron-chromium-nickel alloy wire containing a gallium-based high-temperature anti-oxidation composite coating is energized in air for 1 hour, the coating surface is a dense layer of magnesium oxide, with no obvious cracks or pores. Furthermore, the oxide ceramic layer (magnesium oxide) and the liquid metal gallium layer are well bonded, indicating that the gallium-magnesium composite coating has a good protective effect on the iron-chromium-nickel alloy wire.

[0051] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for in-situ generation of a gallium-based high-temperature antioxidant composite coating for heating wires, characterized in that, The specific steps are as follows: (1) The heating wire is pretreated by grinding to remove the surface oxide film, polishing, degreasing and acid activation; the heating wire is tungsten wire, nickel-chromium alloy wire or iron-chromium-nickel alloy wire; (2) Gallium is mixed and smelted with metal A to alloy it and obtain a gallium-based alloy melt, wherein metal A is one or more of aluminum, zinc, and magnesium, and the smelting temperature is not lower than the alloy melting point temperature of gallium and metal A; the smelting temperature is 40~700℃, the smelting time is 30~60min; the amount of metal A added accounts for 10~30% of the mass of the gallium-based alloy melt; (3) The gallium-based alloy melt is uniformly coated on the pretreated heating wire. The heating wire is energized and self-heated to a temperature of 1000~1400℃. The gallium-based alloy melt coating layer undergoes a high-temperature in-situ precipitation reaction for 50~70 minutes to de-alloy the gallium-based alloy. Metal A is precipitated and oxidized, floating on the surface of liquid gallium to form a ceramic layer of metal A oxide, thus obtaining a gallium-based high-temperature anti-oxidation composite coating. When 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 the in-situ infiltration of the bottom metal gallium into the surface of the heating wire.

2. The method for preparing the in-situ generated gallium-based high-temperature antioxidant composite coating for heating wire 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 ℃.

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

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