A corrosion-resistant alloy coating for a waste incineration boiler and a method for preparing the same

Abstract

The present application relates to the technical field of anticorrosive coating, and particularly relates to a waste incineration boiler corrosion-resistant alloy coating and a preparation method thereof.A waste incineration boiler corrosion-resistant alloy coating comprises an alloy coating and an oxide film; the alloy coating comprises Ni, Cr and Mo; the oxide film comprises NiO, Cr2O3, MoO2 and NiCr2O4; in the scheme, the elements of Ni, Cr and Mo are used as the alloy coating, and a dense oxide film of NiO, Cr2O3, MoO2 and NiCr2O4 is formed on the alloy coating; the alloy coating and the oxide film jointly form the waste incineration boiler corrosion-resistant alloy coating, which provides double protection for the corrosion resistance of the metal, and improves the corrosion resistance of the metal coating.

Description

Technical Field

[0001] This invention relates to the field of anti-corrosion coating technology, and in particular to an anti-corrosion alloy coating for waste incineration boilers and its preparation method. Background Technology

[0002] Waste incineration has significant volume reduction effects, saves land, and can eliminate various pathogens, converting toxic and harmful substances into harmless ones, making it one of the main methods of urban waste treatment. As the main equipment in a waste incineration system, the corrosion of key heating surfaces in waste incineration boilers is a major problem plaguing most waste incineration plants in China. Key heating surfaces in a waste incineration system include the water-cooled walls, superheaters, boiler tube bundles, economizers, air preheaters, and some heat exchange equipment. The tube bundles in these heat exchange equipment are all pressure components; therefore, once metal corrosion occurs and the tube walls thin, perforation and cracking can easily occur, leading to serious pollutant leakage problems.

[0003] Studies of damaged equipment have revealed that corrosion of heated surfaces is generally related to the presence of elements such as chlorine, sulfur, alkali metals, and heavy metals. Therefore, to improve the corrosion resistance of waste incineration boilers, a C22 alloy coating of a certain thickness is usually applied to achieve corrosion resistance. However, the corrosion resistance effect of this alloy coating alone is limited. After the coating is damaged, it can also cause slagging, intergranular corrosion, and other phenomena, thereby aggravating the corrosion of waste incineration boilers and resulting in poor corrosion resistance of existing waste incineration boilers. Summary of the Invention

[0004] This invention provides an anti-corrosion alloy coating for waste incineration boilers and its preparation method, which is used to improve the anti-corrosion effect of alloy coatings for waste incineration boilers.

[0005] This invention provides an anti-corrosion alloy coating for waste incineration boilers, comprising: an alloy coating and an oxide film;

[0006] The alloy coating comprises: Ni, Cr, and Mo;

[0007] The oxide film includes one or more of NiO, Cr2O3, MoO2, and NiCr2O4.

[0008] Preferably, the oxide film comprises: an outer layer, a middle layer, and an inner layer;

[0009] The outer layer is NiO;

[0010] The intermediate layer is composed of Cr2O3 and NiCr2O4;

[0011] The inner layer is MoO2.

[0012] Preferably, in the alloy coating, the Cr content is more than twice that of Mo, and the Ni content is more than twice that of Cr;

[0013] The weight percentage of Cr is greater than 20%;

[0014] The Mo weight percentage is 8%-10%.

[0015] Specifically, the main alloying elements in the alloy coating of this invention are Ni (nickel) and Cr (chromium), both of which possess excellent corrosion resistance. Ni imparts a fully austenitic structure to the alloy, improving its resistance to chloride stress corrosion, increasing thermal stability and processing performance; Cr imparts resistance to oxidizing media corrosion, increasing resistance to localized corrosion. Experimental studies on stainless steel have shown that a Cr content greater than 13% is required for corrosion resistance, and higher Cr content results in better corrosion resistance. However, in this invention, the primary role of Cr is to generate a dense Cr₂O₃ oxide protective film, thereby further enhancing the corrosion resistance of the alloy coating.

[0016] The addition of Mo (molybdenum) to the alloy coating of this invention enhances the stability of the passivation film on the alloy surface, prolongs the incubation period for potential pitting corrosion, and combines with Cl (chloride) ions in the medium to form an insoluble chloride salt film covering the material surface, thereby inhibiting the generation and development of pitting corrosion. This further increases the alloy's resistance to localized corrosion and chloride stress corrosion, and also plays a role in solid solution strengthening. Although adding Mo to the alloy coating can enhance its passivation ability in reducing media, if the Mo content is too high, it will cause more σ phase precipitation. The interface between the σ phase and austenite is an important site for pitting corrosion, which will reduce the alloy's resistance to pitting corrosion.

[0017] The present invention uses a composite oxide film to improve the stability of the oxide film and increase the corrosion resistance, thus avoiding the problem of poor corrosion resistance of individual oxide films, such as a single Cr2O3 oxide film, which has unstable performance.

[0018] Preferably, the Cr content is 20-30% and the Mo content is 13%.

[0019] More preferably, the Cr content is 26% and the Mo content is 13%. The alloy coating in this invention uses powder with a Cr content of 26%, which refines the grains and grain boundaries, resulting in a more stable microstructure.

[0020] Preferably, the alloy coating further includes: Fe, W, Co, Mn, V, and Si.

[0021] Specifically, the addition of W (tungsten) and Co (cobalt) in this invention provides solid solution strengthening, improving the alloy's resistance to localized corrosion. Adding Fe increases the nickel-based alloy's resistance to oxidizing corrosion media, replacing some nickel and reducing costs. However, the iron content in the nickel-based alloy also significantly affects its corrosion resistance; as the iron content increases, the corrosion rate rises. Therefore, the preferred Fe content is 3% by weight. Adding rare earth elements or noble metal elements with corrosion-resistant properties reduces the corrosion current, shifts the corrosion potential positively, and improves the coating's corrosion resistance. The rare earth elements in this invention can be selected from Si (silicon), Ti (titanium), Zr (zirconium), Ta (tantalum), etc.

[0022] Furthermore, since copper improves the corrosion resistance of alloys in reducing media such as seawater, no copper is added in this invention.

[0023] Preferably, the Fe weight percentage is 2.5-3.5%;

[0024] The weight percentage of W is 2.5-3.5%;

[0025] The weight percentage of Co is 2-3%;

[0026] The Mn weight percentage content is 0.1-1%;

[0027] The weight percentage of V is 0.1-0.5%;

[0028] The Si weight percentage is 0.01-0.1%.

[0029] More preferably, the Fe weight percentage is 3%;

[0030] The W content by weight is 3%;

[0031] The Co content by weight is 2.5%;

[0032] The Mn weight percentage is 0.5%;

[0033] The weight percentage of V is 0.35%;

[0034] The Si weight percentage is 0.08%.

[0035] Another aspect of the present invention provides a method for preparing an anti-corrosion alloy coating for a waste incineration boiler, comprising the following steps:

[0036] In an oxidizing atmosphere, the outer surface of the alloy coating is placed in molten salt and heated to melt and corrode, thereby forming an oxide film on the outer surface of the alloy coating.

[0037] Specifically, the oxidizing atmosphere is an oxygen atmosphere or an atmosphere containing oxygen.

[0038] Preferably, before placing the outer surface of the alloy coating in molten salt, the process further includes: mixing metallic Ni, Cr, and Mo to obtain Ni-Cr-Mo alloy powder; and then spraying the Ni-Cr-Mo alloy powder onto the heated surface of the waste incineration boiler to form an alloy coating.

[0039] Preferably, the molten salt is selected from one of KCl, CaCl2, NaCl, and MgCl2.

[0040] Preferably, the spraying method is thermal spraying or plasma spraying.

[0041] Preferably, the thickness of the oxide film is 10. -9 m~10 -10 m.

[0042] Specifically, the thickness of the oxide film in this invention is 10. -9 m~10 -10 The thickness of the oxide film is in the nanometer range, which cannot be obtained by thermal spraying or plasma spraying (the thickness of thermal spraying or plasma spraying is in the millimeter range). Therefore, in order to form a thin film with good oxidation resistance on the Ni-Cr-Mo alloy coating, this application adopts a high-temperature molten salt oxidation method to form a composite oxide film. Although this method is time-consuming, it is necessary to use this process to further improve the corrosion resistance for parts with high corrosion resistance requirements.

[0043] Preferably, the thickness of the alloy coating is greater than 3 mm.

[0044] Preferably, the heating temperature is 700–900°C, and the heating time is 50–350 h.

[0045] More preferably, the heating temperature is 900°C and the heating time is 50 hours.

[0046] As can be seen from the above technical solutions, the present invention has the following advantages:

[0047] This invention provides an anti-corrosion alloy coating for waste incineration boilers, comprising: an alloy coating and an oxide film; the alloy coating comprises: Ni, Cr, and Mo; the oxide film comprises: NiO, Cr2O3, MoO2, and NiCr2O4. In this design, Ni, Cr, and Mo are used as the alloy coating elements, resulting in the formation of a dense NiO, Cr2O3, MoO2, and NiCr2O4 oxide film on the alloy coating. The alloy coating and the oxide film together form an anti-corrosion alloy coating for waste incineration boilers, providing dual protection for the metal's corrosion resistance and improving the corrosion resistance performance of the anti-corrosion alloy coating for waste incineration boilers. Attached Figure Description

[0048] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0049] Figure 1 This is a layered structure diagram of an anti-corrosion alloy coating for a waste incineration boiler provided in Embodiment 6 of the present invention;

[0050] Figure 2 The corrosion rate variation curves of the alloy coatings prepared in Examples 1 to 5 of this invention are shown.

[0051] Figure 3 The corrosion rate curves of the alloy coating samples provided in Examples 6-9 of this invention in molten salt are shown.

[0052] Figure 4 The images show the oxide film detection results of the alloy coating samples provided in Examples 6-9 of this invention. Detailed Implementation

[0053] Damaged waste incineration equipment is typically covered with a thick layer of deposits. Studies of the damaged equipment revealed a layer of concentrated chloride FeCl2 at the metal / oxide film interface, indicating chloride enrichment. Furthermore, the oxide film above the chloride precipitates became porous and loose, rendering it ineffective as a protective layer against corrosion. This demonstrates that whether corrosion occurs under high-temperature HCl or Cl2 gases, or when chloride salts are applied to the metal surface, the final result is a loose, porous oxide film that separates from the metal substrate. This also indicates that the current technology of applying a certain thickness of alloy coating to achieve corrosion resistance has limited effectiveness, and that damage to the coating can lead to more severe corrosion problems in waste incineration boilers.

[0054] In view of this, the present invention provides an anti-corrosion alloy coating for waste incineration boilers and its preparation method, which improves the anti-corrosion performance of the anti-corrosion alloy coating for waste incineration boilers through dual protection, and solves the problem of poor anti-corrosion effect of existing anti-corrosion alloy coatings.

[0055] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0056] In the following examples, all raw materials or reagents used are commercially available or self-made.

[0057] Example 1

[0058] This embodiment provides a first alloy coating, which is prepared by the following method:

[0059] An alloy coating is formed using Ni-Cr-Mo alloy powder through thermal spraying or plasma spraying. The coating thickness is greater than 3 mm, and the particle size of the Ni-Cr-Mo powder is between 140 mesh and 300 mesh. The mass percentage of each component in the Ni-Cr-Mo alloy powder is shown in Table 1.

[0060] The alloy coating prepared in this embodiment has good corrosion resistance, and its corrosion resistance can be further improved by further surface treatment to form various oxide films.

[0061] Example 2

[0062] This embodiment provides a second alloy coating, which is prepared using the same method as in Example 1, except that the amount of Cr in the alloy is 24%. The specific composition is shown in Table 1.

[0063] Example 3

[0064] This embodiment provides a third alloy coating, which is prepared in the same way as in Example 1, except that the amount of Cr in the alloy is 26%, and the specific composition is shown in Table 1.

[0065] Example 4

[0066] This embodiment provides a fourth alloy coating, which is prepared in the same way as in Example 1, except that the amount of Cr in the alloy is 28%, and the specific composition is shown in Table 1.

[0067] Example 5

[0068] This embodiment provides a fifth alloy coating, which is prepared in the same way as in Example 1, except that the amount of Cr in the alloy is 30%, and the specific composition is shown in Table 1.

[0069] Table 1. Composition of Ni-Cr-Mo alloy powder in Examples 1-5

[0070]

[0071] Test Example 1

[0072] This embodiment tests the corrosion resistance of the alloy coatings prepared in Examples 1-5. The test results are as follows: Figure 2 As shown.

[0073] With the increase of Cr content, the corrosion rate and polarization potential of the Ni-Cr-Mo alloy coating corrosion cladding layer both exhibit a parabolic distribution, and reach the optimal value when the Cr content is 26%, indicating that the corrosion resistance is best when the Cr content is 26%.

[0074] Example 6

[0075] This embodiment provides a first type of anti-corrosion alloy coating for waste incineration boilers. By subjecting the surface of the Ni-Cr-Mo alloy coating prepared in Example 1 to melt corrosion treatment, a second layer of anti-corrosion protection—an oxide film—is further formed on the surface of the Ni-Cr-Mo alloy coating.

[0076] In this embodiment, KCl high-temperature molten salt is used to prepare the oxide film. The specific preparation steps are as follows:

[0077] (1) Select a 15mm×15mm×1.5mm sample, and coat the sample with a 5mm Ni-Cr-Mo alloy coating. The preparation method of the Ni-Cr-Mo alloy coating is the same as that in Example 1.

[0078] (2) The sample was fixed and suspended in a graphite crucible with nickel wire, and then 160g of eutectic salt was added. After that, the sealed reaction crucible was placed in a muffle furnace and kept at 900℃ for 50 hours to form an anti-corrosion alloy coating oxide film, thus obtaining an anti-corrosion alloy coating for waste incineration boilers.

[0079] It should be noted that the same oxide film can also be formed by heat preservation corrosion at 700℃ for 350 hours, but this process is time-consuming, energy-intensive, and not conducive to industrial production.

[0080] Testing revealed that the layered structure of the corrosion-resistant alloy coating for waste incineration boilers prepared in this embodiment is shown in the diagram below. Figure 1 As shown, the outermost layer 11 of the oxide film 1 of the anti-corrosion alloy coating for waste incineration boilers forms a NiO oxide film, the middle layer 12 forms NiCr2O4 and Cr2O3 oxide films, and the innermost layer 13 forms a MoO2 oxide film, which is tightly connected to the alloy coating 2. The anti-corrosion alloy coating for waste incineration boilers prepared in this embodiment effectively slows down the rate of further oxidation of the waste incineration boiler in a corrosive environment through the three-layer oxide film, and this multi-layered oxide film further ensures the overall integrity of the oxide film, thus achieving a good anti-oxidation effect.

[0081] The NiO, Cr2O3, MoO2, and NiCr2O4 composite oxide film prepared in this embodiment has good protective properties. The oxide film is intact and relatively dense, with no obvious interface between it and the alloy coating. It covers the surface of the alloy coating and protects the base metal from further oxidation.

[0082] The principle of oxide film formation in this embodiment is as follows:

[0083] During molten corrosion, NiO forms first on the outer layer. Then, during NiO growth, Cr2O3 and MoO2 also form rapidly. This is because the rapid outward diffusion of Ni increases the Cr and Mo content in its vicinity, further promoting the formation of Cr2O3 and MoO2. Therefore, in the initial stage of corrosion in KCl molten salt, the oxide film is a mixed oxide film with NiO as the main component and Cr2O3 and MoO2 coexisting. Cr2O3 exhibits the best oxidation resistance, while NiO lacks oxidation resistance and provides poor protection. As oxidation continues, oxygen gradually diffuses through the NiO layer into the interior of the compound, causing the oxides to increase continuously. The oxide layer gradually covers the entire alloy coating surface. Furthermore, during the molten corrosion process in this embodiment, a certain amount of nodular oxide appears on the oxide film surface. These oxide particles are mainly composed of spinel, and while the particle size is uneven, their distribution is relatively regular. These spinels undergo a solid-state reaction between NiO and Cr2O3 particles as oxidation time increases: NiO + Cr2O3 → NiCr2O4. The NiCr2O4 composite oxide formed in the middle layer, along with the outer oxide layer, can inhibit the outward diffusion rate of various metal elements and the inward diffusion rate of O, thus slowing down the oxidation rate. In the oxidation kinetic curve, this is shown as a slow increase in oxidation weight until it tends to stabilize. This results in an oxide film with NiO as the outermost layer, NiCr2O4 and Cr2O3 as the middle layer, and MoO2 as the innermost layer.

[0084] Example 7

[0085] This embodiment provides a second type of anti-corrosion alloy coating for waste incineration boilers. The preparation steps of this embodiment are the same as those of Embodiment 6, except that CaCl2 molten salt is used to corrode the alloy coating to form an oxide film.

[0086] Testing revealed that the oxide film of the corrosion-resistant alloy coating for the waste incineration boiler prepared in this embodiment mainly consists of Cr2O3 and NiCr2O4. The alloy coating exhibits minimal weight loss during complete melting of the corrosive agent, and its solubility with oxygen in high-temperature liquids is significantly reduced, thereby inhibiting active oxidation. Consequently, the corrosion products of both components also correspondingly generate Ni. 1.12 Cr 2.88 .

[0087] Example 8

[0088] This embodiment provides a third type of corrosion-resistant alloy coating for waste incineration boilers. The preparation steps of this embodiment are the same as those of Embodiment 2, except that NaCl molten salt is used to corrode the alloy coating to form an oxide film.

[0089] The oxide film formed by the corrosion of the alloy coating by NaCl molten salt is similar to that formed by CaCl2 molten salt. Diffraction peaks show that the products of corrosion in CaCl2 molten salt include not only most of Cr2O3, but also NiCr2O4.

[0090] Example 9

[0091] This embodiment provides a fourth type of anti-corrosion alloy coating for waste incineration boilers. The preparation steps of this embodiment are the same as those of Embodiment 2, except that this embodiment uses MgCl2 molten salt corrosion alloy coating to form an oxide film.

[0092] When using MgCl2 molten salt to corrode the alloy coating, no Cr2O3 was detected in the corrosion products of the sample in MgCl2 molten salt. This may be because Cr2O3 did not appear on the sample being tested, or because the oxide film prepared in this embodiment is relatively sparse and has pores, and is easily washed away by the salt layer during the water bath process.

[0093] Test Example 2

[0094] The composition and performance of the oxide films prepared under the conditions described in the above examples were tested as follows:

[0095] (1) Corrosion rate detection:

[0096] In Examples 6-9 above, when preparing oxide films by molten salt corrosion of alloy coatings, the molten salts used were KCl, CaCl2, NaCl, and MgCl2, respectively. Experimental testing revealed that the corrosion rates in Examples 6-9 differed, specifically as follows: Figure 3 As shown. From Figure 3 It can be seen that the corrosion rates of the samples in molten salts KCl, CaCl2, NaCl, and MgCl2 are different. Among them, CaCl2 and MgCl2 have the fastest corrosion rates, while KCl and NaCl molten salts have slower corrosion rates and are more suitable for preparation.

[0097] (2) Oxide film composition detection

[0098] Since the film formed on a 15mm×15mm×1.5mm sample cannot be detected, this invention uses a gradient temperature rise test of 400~900℃ to perform XRD detection on the composition of the oxide film prepared by KCl, CaCl2, NaCl and MgCl2 molten salt corrosion of the Ni-Cr-Mo alloy coating at the temperature. The results of the oxide film composition detection of each embodiment are shown in Table 2.

[0099] Table 2. Composition of oxide films prepared by molten salt corrosion alloy coatings in Examples 6-9

[0100] Example The molten salt used Oxidation film components 6 KCl <![CDATA[NiO、Cr2O3、MoO2、NiCr2O4]]> 7 <![CDATA[CaCl2]]> <![CDATA[NiCr2O4、Cr2O3、Ni 1.12 Cr 2.88 ]]> 8 NaCl <![CDATA[Cr2O3、NiCr2O4]]> 9 <![CDATA[MgCl2]]> <![CDATA[MgCr2O4、NiCr2O4]]>

[0101] As shown in Table 2, the oxide film composition of the samples in molten salts KCl, CaCl2, NaCl, and MgCl2 is different. Among them, the oxide film produced in molten salt KCl has the most types and is more dense, and has the best corrosion resistance.

[0102] The composition of the oxide films prepared by Ni-Cr-Mo alloy coatings by molten salt corrosion with KCl, CaCl2, NaCl, and MgCl2 was determined by XRD at 900℃. The results of the oxide film composition analysis for each example are as follows: Figure 4 As shown. From Figure 4 It can be seen that for oxide films produced by different molten salts, KCl oxide film is more dense, while NaCl and MgCl2 oxide films are more sparse and have pores. Among them, the oxide film prepared by KCl molten salt in Example 6 is more dense and has the best corrosion resistance.

[0103] It should be noted that, Figure 4 The KCl molten salt test showed no MoO2 because MoO2 dissolves at 900℃, hence no MoO2 was detected at that temperature. However, in actual oxide film preparation, the entire molten corrosion process first raises the temperature from a lower level (room temperature) to 900℃. Therefore, during the heating process, MoO2 is first formed internally, and then NiO, Cr2O3, and NiCr2O4 oxide films are slowly formed on the surface. Although the surface MoO2 dissolves, the internal MoO2 oxide film is protected by the external NiO, Cr2O3, and NiCr2O4 oxide films, so it does not affect the internal MoO2 oxide film.

[0104] The above provides a detailed description of the anti-corrosion alloy coating for waste incineration boilers and its preparation method provided by the present invention. For those skilled in the art, based on the ideas of the embodiments of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A corrosion-resistant alloy coating for a waste incineration boiler, characterized in that, include: Alloy coatings and oxide films; The alloy coating comprises: Ni, Cr, and Mo; wherein the weight percentage of Cr in the alloy coating is greater than 20%; the weight percentage of Mo is 8%-10%; the content of Cr is more than twice that of Mo; and the content of Ni is more than twice that of Cr. The oxide film includes one or more of NiO, Cr2O3, MoO2, and NiCr2O4; The method for preparing the corrosion-resistant alloy coating for the waste incineration boiler includes the following steps: In an oxidizing atmosphere, the outer surface of the alloy coating is placed in molten salt and heated to molten corrosion, thereby forming an oxide film on the outer surface of the alloy coating; The molten salt includes one of KCl and NaCl.

2. The anti-corrosion alloy coating for waste incineration boilers according to claim 1, characterized in that, The oxide film is divided into: an outer layer, a middle layer, and an inner layer; The outer layer is NiO; The intermediate layer is composed of Cr2O3 and NiCr2O4; The inner layer is MoO2.

3. The anti-corrosion alloy coating for waste incineration boilers according to claim 1, characterized in that, The alloy coating also includes: Fe, W, Co, Mn, V, and Si.

4. The anti-corrosion alloy coating for waste incineration boilers according to claim 3, characterized in that, The Fe weight percentage is 2.5-3.5%; The W content by weight is 2.5-3.5%; The Co content by weight percentage is 2-3%; The Mn weight percentage content is 0.1-1%; The weight percentage of V is 0.1-0.5%; The Si weight percentage content is 0.01-0.1%.

5. The anti-corrosion alloy coating for waste incineration boilers according to claim 1, characterized in that, The thickness of the oxide film is 10. -9 m~10 -10 m.

6. The anti-corrosion alloy coating for waste incineration boilers according to claim 1, characterized in that, The thickness of the alloy coating is greater than 3 mm.

7. The anti-corrosion alloy coating for waste incineration boilers according to claim 1, characterized in that, The heating temperature is 700~900℃, and the heating time is 50~350h.

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