Acid and alkali resistant medium Ni-Cr based alloy, and preparation method and application thereof

Abstract

The application discloses an acid and alkali resistant Ni-Cr based alloy and a preparation method and application thereof, and belongs to the technical field of electric heating functional materials and corrosion resistant alloy. The method comprises the following steps: taking nickel oxide, chromium oxide and aluminum powder as raw materials, introducing Ce or Sb by Cr-Ce or Cr-Sb intermediate alloy, and mixing to obtain precursor powder; pressing into a blank; igniting under vacuum to initiate high-temperature self-propagating reaction, controlling the cooling rate to separate slag and gold; after cooling, removing slag and post-processing, and the acid and alkali resistant Ni-Cr based alloy is obtained. By introducing trace elements through the intermediate alloy, the oxidation and burning loss of the single element addition are avoided, the accurate and uniform distribution of the trace elements is realized, and the micro-alloying modification effect is stably played. The obtained material is uniform in structure, resistant to acid and alkali corrosion, excellent in thermoelectric performance, and suitable for electric heating elements, chemical heating equipment and pipeline heat tracing devices.

Description

Technical Field

[0001] This invention relates to the field of electrothermal functional materials and corrosion-resistant alloys, specifically to a Ni-Cr based alloy resistant to acid and alkali media, its preparation method, and its application. Background Technology

[0002] Nickel-chromium (Ni-Cr) based alloys are widely used in industrial heating elements, corrosion-resistant heating components, heating elements for chemical equipment, and pipeline heat tracing devices due to their excellent resistance heating performance, high-temperature oxidation resistance, good thermal stability, and certain corrosion resistance. Especially for heating elements operating in harsh environments such as acidic media, alkaline media, or alternating acid-alkali media, the materials are required not only to have stable heating performance but also high microstructural stability, phase structure stability, and resistance to media corrosion.

[0003] Currently, the preparation of Ni-Cr based alloys mainly employs methods such as vacuum melting, induction melting, electric arc melting, or conventional powder metallurgy. For example, Chinese patent CN112048631A discloses a method for preparing a nickel-chromium master alloy with a Cr content of 50-60 wt% using vacuum induction melting. This method uses pure nickel and pure chromium as raw materials and significantly reduces the content of gaseous elements and non-metallic impurities through progressively increasing power alloying, high-temperature refining, and deoxidation and desulfurization treatment. However, this type of smelting method generally has the following shortcomings: First, it requires large equipment investment, has a complex process flow, and consumes a lot of energy. Second, due to the large difference in melting points between nickel and chromium (Ni is 1455℃ and Cr is 1907℃), low-melting-point elements are easily burned off and high-melting-point chromium refractory blocks are easily formed during the smelting process, causing the alloy composition to deviate from the design value. Moreover, long-term high-temperature smelting is required to ensure that chromium is completely melted, which further increases energy consumption and the risk of impurity contamination. Third, when introducing trace amounts of modifying elements (such as Ce, Sb, etc.), problems such as uneven element distribution and severe burn-off are likely to occur, resulting in low alloying efficiency and difficulty in achieving precise control of microstructure and properties.

[0004] In recent years, high-temperature self-propagating synthesis (also known as aluminothermic reduction) technology has been explored for the preparation of Ni-Cr based alloys due to its advantages such as high reaction temperature, fast synthesis speed, low equipment cost, and simple process. For example, Chinese patent CN118639057A proposes to prepare a nickel-chromium master alloy with a Cr content of 25-60 wt% through an aluminothermic reduction reaction using chromium trioxide, nickel suboxide, and aluminum powder as raw materials, avoiding the burn-off and refractory problems caused by the difference in melting points of the elements, while reducing the cost of raw materials. However, this method still has inherent defects in practical applications: to ensure sufficient reduction of oxides, an excessive amount of aluminum powder is usually added, resulting in 0.5%-1.5% aluminum residue in the final alloy. For Ni-Cr based heating element materials, the residual aluminum will form intermetallic compounds such as Ni3Al with nickel, changing the resistivity and high-temperature oxidation resistance of the alloy, and the segregation of aluminum will affect the long-term stability of the heating element. Furthermore, the aluminothermic reaction rapidly generates a large number of Al2O3 particles. Due to the extremely short time the reaction system remains in a high-temperature liquid state, the Al2O3 inclusions cannot be fully floated and removed, remaining in the alloy as hard and brittle inclusions. This reduces the material's mechanical properties and corrosion resistance, especially in acidic or alkaline media where they easily become preferential corrosion initiation sites. Simultaneously, the separation between the alloy and slag after the reaction is incomplete, often requiring additional mechanical separation or refining, reducing yield and production efficiency. More importantly, when active trace elements such as Ce and Sb are directly added to the aluminothermic reaction system, they are easily burned off due to reaction with oxygen or slag-forming agents, making it difficult to precisely control their content and distribution in the alloy, thus failing to stably achieve the microalloying modification effect.

[0005] Therefore, developing a simple, low-cost, highly alloyed, low-impurity, and uniformly structured Ni-Cr-based heating element material preparation method, and achieving stable and controllable introduction of trace elements such as Ce and Sb to improve the material's corrosion resistance and thermoelectric response characteristics in acidic and alkaline media, has significant engineering value and market prospects. Summary of the Invention

[0006] Therefore, this invention provides a Ni-Cr based alloy resistant to acid and alkali media, its preparation method, and its application, in order to solve the problems in the prior art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: According to a first aspect of the present invention, a method for preparing a Ni-Cr-based alloy resistant to acid and alkali media is provided, the method comprising: S1: Using nickel oxide powder, chromium oxide powder and aluminum powder as raw materials, and introducing Ce or Sb elements in the form of Cr-Ce master alloy or Cr-Sb master alloy, and mixing them evenly to obtain a precursor mixed powder. S2: Press the precursor mixed powder into a compact to obtain a pressed blank; S3: The compact is locally heated and ignited under vacuum conditions to initiate a high-temperature self-propagating reaction, which allows the reaction to propagate on its own. The cooling rate is controlled during the reaction to promote the separation of alumina slag from the alloy melt. S4: After the reaction is completed, cool to room temperature, separate and remove the alumina slag, and perform post-processing on the obtained alloy product to obtain the Ni-Cr based alloy heating element material.

[0008] In step S1, the amount of aluminum powder added is 95%-100% of the theoretical required amount, so as to control the residual aluminum content ≤0.2wt%.

[0009] Furthermore, in step S1, the mixing is performed using a V-type mixer or a ball mill, and the mixing time is 25-35 minutes.

[0010] Furthermore, in step S3, the vacuum degree of the vacuum condition is 10. -1 Pa to 10 -2 Argon gas is introduced after the Pa level is reached.

[0011] Furthermore, in step S3, the cooling rate is 5℃ / min-10℃ / min, and the cooling time is 5h-8h.

[0012] Furthermore, in step S4, the post-treatment includes sandblasting to remove the surface oxide layer, with a sandblasting air pressure of 0.6MPa-0.8MPa.

[0013] The Seebeck coefficient of the Ni-Cr based alloy heating element material is ≥11.5μV / K.

[0014] According to a second aspect of the present invention, an acid- and alkali-resistant Ni-Cr-based alloy heating element material is prepared by the preparation method described above. The Ni-Cr-based alloy heating element material is composed of Ni, Cr and at least one trace element selected from Ce and Sb, wherein the content of Cr is 10-20 at%, the content of the trace element is 0.5-2.0 at%, and the balance is Ni.

[0015] Furthermore, the Cr content is 15 at%, and the trace elements are 1 at% Ce or 1 at% Sb.

[0016] The application of the acid and alkali resistant Ni-Cr based alloy heating element material according to the above-described method in the preparation of electric heating elements, provided by a third aspect of the present invention.

[0017] Furthermore, the heating element is used as a heating component, corrosion-resistant heating component, chemical heating equipment, or pipeline heat tracing device in acidic, alkaline, or alternating acid-alkali environments.

[0018] The present invention has the following advantages: This invention significantly reduces the residual aluminum content (≤0.2wt%) and alumina inclusion content in the product by controlling the amount of aluminum powder added to 95%-100% of the theoretical required amount, combined with high-temperature self-propagating reaction under vacuum conditions and cooling rate control, thereby improving the purity and uniformity of the material and overcoming the technical defects of high residual aluminum and many inclusions in the traditional aluminothermic reduction method.

[0019] This invention introduces Ce or Sb elements in the form of Cr-Ce or Cr-Sb master alloys, avoiding compositional deviations caused by oxidation and burn-off when directly adding elemental elements. This achieves precise and uniform distribution of trace elements in the alloy, thereby stabilizing the microalloying modification effect.

[0020] By introducing trace elements Ce or Sb, the Seebeck coefficient of the Ni-Cr based alloy heating element material prepared by this invention is ≥11.5 μV / K. Compared with the binary Ni-Cr alloy without trace elements, the Seebeck coefficient can be increased by 17.9%-26.6%, indicating that the thermoelectric response characteristics of the material are significantly improved, which is beneficial to improving the temperature control accuracy and energy efficiency of the heating element.

[0021] Due to the significant reduction in the content of residual aluminum and alumina inclusions, the corrosion resistance of the material in acidic, alkaline, and alternating acid-alkali environments is significantly improved, avoiding the problem of preferential local corrosion caused by inclusions and extending the service life of the heating element.

[0022] This invention employs a high-temperature self-propagating synthesis technology. Compared to traditional methods such as vacuum melting and induction melting, it eliminates the need for large-scale melting equipment and prolonged high-temperature heating, resulting in lower equipment investment, lower energy consumption, and faster synthesis speed. Furthermore, by using oxides as raw materials instead of high-purity elemental metals, it further reduces raw material costs, making it suitable for large-scale industrial production.

[0023] The high-temperature self-propagating reaction of this invention has a high temperature and rapid reaction, which is conducive to the rapid in-situ alloying of Ni, Cr and trace elements. The product has a uniform structure and no refractory blocks or element segregation, which ensures the structural stability and performance consistency of the heating element material during long-term service.

[0024] The Ni-Cr based alloy heating element material prepared by this invention is particularly suitable for electric heating elements in acidic, alkaline, or alternating acid-base environments. It can be widely used in chemical heating equipment, corrosion-resistant electric heating components, pipeline heat tracing devices, and other fields, filling the gap in existing corrosion-resistant heating element materials. Attached Figure Description

[0025] To more clearly illustrate the embodiments of the present invention or the technical solutions in 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 merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0026] The structures, proportions, sizes, etc. illustrated in this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0027] Figure 1 This is a microstructure diagram of the Ni-Cr-Ce alloy provided in Example 1 of the present invention;

[0028] Figure 2 This is a microstructure image of the Ni-Cr-Sb alloy provided in Example 2 of the present invention;

[0029] Figure 3 The image shows the microstructure of the Ni-Cr alloy provided in Comparative Example 1 of this invention.

[0030] Figure 4 The XRD spectra of Example 1, Example 2 and Comparative Example 1 provided for Experimental Example 1 of the present invention. Detailed Implementation

[0031] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Unless otherwise specified in the embodiments of this invention, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available products; different manufacturers and models of raw materials do not affect the implementation of the technical solution or the achievement of the technical effect of this invention.

[0033] Nickel oxide powder: nickel content ≥76.5% by mass, particle size 100-200 mesh; Chromium oxide powder: Cr2O3 purity ≥99.0%, particle size 300-500 mesh; Aluminum powder: purity ≥99.0%, particle size 80-200 mesh; Cr-Ce master alloy: Ce content 5wt%-20wt%, balance Cr, particle size 100-200 mesh; Cr-Sb master alloy: Sb content 5wt%-20wt%, balance Cr, particle size 100-200 mesh.

[0034] Example 1 This embodiment provides a Ni-Cr based alloy heating element material resistant to acid and alkali media, with a target composition of: Ni (84-x)at%, Cr 15at%, Ce 1at%, where x is a slight offset adjusted according to the actual ratio, and the balance is Ni.

[0035] The preparation method is as follows: S1: Weigh out nickel oxide powder, chromium oxide powder, and aluminum powder according to the target composition, and introduce Ce element in the form of a Cr-Ce master alloy (Ce content 10wt%). The amount of aluminum powder added is 98% of the theoretical requirement (the theoretical requirement is calculated based on the stoichiometric ratio of the oxide reduction reaction). Pour the weighed raw materials into a V-type mixer and mix at 50 r / min for 30 min to obtain the precursor mixed powder.

[0036] S2: The precursor mixed powder is loaded into the mold and molded under a pressure of 20MPa-50MPa to obtain a cylindrical compact with a size of Φ50mm×50mm.

[0037] S3: Place the compact into the aluminothermic reduction reaction equipment and start the vacuum system to bring the internal pressure of the equipment to 10. -1 After reaching the Pa level, argon gas was introduced to atmospheric pressure, and then the vacuum system was shut off. A nickel-chromium resistance wire was used for localized heating and ignition at one end of the compact, initiating a high-temperature self-propagating reaction. The reaction propagated self-sustainingly throughout the compact in the form of a combustion wave. During the reaction, the cooling rate was controlled at 8°C / min by adjusting the flow rate of the cooling medium, and the cooling time was 6 hours to promote the complete separation of the alumina slag from the alloy melt.

[0038] S4: After the reaction is completed, the furnace is cooled to room temperature. The obtained nickel-chromium alloy block is mechanically separated from the alumina-based slag and the base slag. Then, the surface oxide layer is removed by grinding with a pressurized sandblasting machine at an air pressure of 0.7 MPa to obtain the Ni-Cr-Ce alloy heating element material.

[0039] Microstructure diagram of Ni-Cr-Ce alloy as shown in Figure 1 Figure 1 As shown, by Figure 1It can be seen that after the high-temperature self-propagating reaction, the sample formed a relatively continuous microstructure. Compared with the Ni-Cr alloy without Ce, the microstructure of the alloy changed after the addition of Ce, indicating that trace Ce elements have a regulatory effect on the microstructure evolution of Ni-Cr based alloys.

[0040] The alloy obtained in this embodiment was tested and found to have the following composition: Cr 14.8at%, Ce 0.95at%, residual Al 0.08wt%, O content 0.05wt%, and Seebeck coefficient of 12.8μV / K.

[0041] Example 2 This embodiment provides a Ni-Cr based alloy heating element material resistant to acid and alkali media, with the target composition being: Ni (84-x)at%, Cr 15at%, Sb 1at%, and the balance being Ni.

[0042] The preparation method is as follows: S1: Weigh out nickel oxide powder, chromium oxide powder, and aluminum powder according to the target composition, and introduce Sb element in the form of Cr-Sb master alloy (Sb content 10wt%). The amount of aluminum powder added is 97% of the theoretical requirement. Pour all raw materials into a ball mill and ball mill them together at a speed of 60 r / min for 25 min to obtain the precursor mixed powder.

[0043] S2-S4: Same as Example 1.

[0044] The microstructure of the Ni-Cr-Sb alloy is as follows: Figure 2 As shown, after the high-temperature self-propagating reaction, the sample formed a relatively continuous microstructure. Compared with the Ni-Cr alloy without Ce, the microstructure distribution characteristics of the sample changed after the addition of Sb, indicating that Sb also has a significant impact on the microstructure of Ni-Cr based alloys.

[0045] The alloy obtained in this embodiment was tested and found to have the following composition: Cr 15.1 at%, Sb 0.92 at%, residual Al 0.10 wt%, O content 0.06 wt%, and Seebeck coefficient of 11.9 μV / K.

[0046] Example 3 This embodiment provides a Ni-Cr based alloy heating element material resistant to acid and alkali media, with a target composition of: Cr 18at%, Ce 1.5at%, and the balance being Ni.

[0047] The preparation method is as follows: S1: Weigh out nickel oxide powder, chromium oxide powder, and aluminum powder according to the target composition, and introduce Ce element in the form of Cr-Ce master alloy (Ce content 15wt%). The amount of aluminum powder added is 96% of the theoretical requirement. Pour all raw materials into a V-type mixer and mix at a speed of 40 r / min for 35 min to obtain the precursor mixed powder.

[0048] S2-S4: Same as Example 1.

[0049] The alloy obtained in this embodiment was tested and found to have the following composition: Cr 17.8 at%, Ce 1.42 at%, residual Al 0.12 wt%, O content 0.07 wt%, and Seebeck coefficient of 12.1 μV / K.

[0050] Example 4 This embodiment provides a Ni-Cr based alloy heating element material resistant to acid and alkali media, with a target composition of: Cr 12at%, Sb 0.8at%, and the balance being Ni.

[0051] The preparation method is as follows: S1: Weigh out nickel oxide powder, chromium oxide powder, and aluminum powder according to the target composition, and introduce Sb element in the form of Cr-Sb master alloy (Sb content 8wt%). The amount of aluminum powder added is 99% of the theoretical requirement. Pour all raw materials into a V-type mixer and mix at a speed of 55 r / min for 28 min to obtain the precursor mixed powder.

[0052] S2-S4: Same as Example 1.

[0053] The alloy obtained in this embodiment was tested and found to have the following composition: Cr 11.9at%, Sb 0.75at%, residual Al 0.07wt%, O content 0.04wt%, and Seebeck coefficient of 11.6μV / K.

[0054] Comparative Example 1 The difference between this comparative example and Example 1 is that no Cr-Ce master alloy is added, i.e., a binary Ni-15Cr alloy is prepared. The amount of aluminum powder added is 98% of the theoretical requirement, and the cooling rate is controlled at 8°C / min. The remaining steps are the same as in Example 1.

[0055] The microstructure of Ni-Cr alloy is as follows: Figure 3 As shown, after a high-temperature self-propagating reaction, the sample formed a relatively continuous tissue structure.

[0056] The alloy obtained in this comparative example was found to have a residual Al content of 0.16 wt%, an O content of 0.10 wt%, and a Seebeck coefficient of 10.0 μV / K, which is lower than the Seebeck coefficients of Examples 1-4 of this invention (all ≥11.5 μV / K).

[0057] Comparative Example 2 The difference between this comparative example and Example 1 is that the amount of aluminum powder added is 110% of the theoretical required amount, and the reaction is allowed to cool naturally (cooling rate of approximately 20°C / min-30°C / min), without controlling the cooling rate. The remaining steps are the same as in Example 1.

[0058] Testing revealed that the alloy obtained in this comparative example had a residual Al content of 0.45 wt%, an O content of 0.28 wt%, a Seebeck coefficient of 9.5 μV / K, and a corrosion weight loss rate significantly higher than that in Example 1 in both acidic and alkaline media.

[0059] Comparative Example 3 The difference between this comparative example and Example 1 is that pure metallic Ce powder (99.5% purity, 200 mesh particle size) was added directly instead of the Cr-Ce master alloy. The remaining steps are the same as in Example 1.

[0060] Testing revealed that the Ce yield in the alloy obtained in this comparative example was only 45%, with an actual Ce content of approximately 0.45 at%, and the distribution was uneven. The Seebeck coefficient was 10.8 μV / K, which is lower than the 12.8 μV / K of Example 1.

[0061] Comparative Example 4 The difference between this comparative example and Example 1 is that the amount of aluminum powder added is 92% of the theoretically required amount. The remaining steps are the same as in Example 1.

[0062] During the reaction, the propagation speed of the combustion wave slowed significantly after ignition, and the flame went out in the middle of the compact, failing to complete the self-propagating reaction of the entire compact. Ultimately, only a partial alloy product was obtained, with an alloy yield of only 38%, and unreacted chromium oxide powder remained in the product. Testing revealed that the obtained alloy block had an oxygen content as high as 0.45 wt% and a Cr content of only 10.2 at%, with the composition significantly deviating from the design values.

[0063] Comparative Example 5 The difference between this comparative example and Example 1 is that the reaction is carried out in an atmospheric pressure air environment (without vacuum), while the other steps are the same as in Example 1.

[0064] Testing revealed that the alloy obtained in this comparative example had a residual Al content of 0.35 wt%, an O content of 0.24 wt%, and an Al2O3 inclusion content of approximately 0.45 wt%, significantly higher than the 0.08 wt% and 0.05 wt% of Example 1, respectively. Simultaneously, the Seebeck coefficient decreased to 9.8 μV / K.

[0065] Comparative Example 6 The difference between this comparative example and Example 1 is that the reaction was allowed to cool naturally after completion (cooling rate approximately 25°C / min), without controlling the cooling rate. The remaining steps are the same as in Example 1.

[0066] Testing revealed that the alloy obtained in this comparative example had a residual Al content of 0.28 wt%, an O content of 0.18 wt%, and an Al2O3 inclusion content of approximately 0.35 wt%, which were significantly higher than those in Example 1.

[0067] Test Example 1 XRD phase analysis was performed on the alloys obtained in Examples 1, 2, and Comparative Example 1. An X-ray diffractometer (Cu target, Kα radiation, λ = 0.15406 nm, scanning range 2θ = 20°–90°, step size 0.02°, scanning rate 2° / min) was used.

[0068] The results are as follows Figure 4 As shown. By Figure 4 It can be seen that the XRD spectra of the three samples all show three strong diffraction peaks near 2θ≈44.0°, 51.5° and 75.5°, corresponding to the (111), (200) and (220) crystal planes of the face-centered cubic (FCC) structure, respectively, which are highly consistent with the standard PDF card (PDF#04-0850, Ni-Cr solid solution). This indicates that the main phase of all samples is Ni-Cr solid solution, and Cr and Ni are completely alloyed. After adding Ce or Sb (Examples 1 and 2), no obvious new diffraction peaks appeared in the spectra, and no intermetallic compounds such as Al3Ni and AlCr2 or oxide impurities such as CeO2, Sb2O3 and Al2O3 were detected. This indicates that the introduction of trace modifying elements did not destroy the main phase structure of Ni-Cr solid solution, and Ce and Sb entered the lattice in solid solution form (or segregated at the grain boundaries), and did not form independent crystalline phases with a content exceeding the XRD detection limit (usually 3~5 wt%). By slowly scanning and magnifying the main peak (111), it can be observed that Example 1 is shifted to a lower angle by about 0.08° compared to Comparative Example 1, and Example 2 is shifted by about 0.04°, confirming that Ce and Sb solid solutions cause lattice expansion.

[0069] Test Example 2 Corrosion resistance test: Alloy samples obtained from each example and comparative example were processed into 10mm×10mm×2mm test pieces, and polished sequentially with 600#, 1000#, and 2000# sandpaper. They were then immersed in 1mol / L H2SO4 solution (pH≈0.3), 1mol / L NaOH solution (pH≈14), and an alternating medium (H2SO4 immersion for 24h, followed by NaOH immersion for 24h, repeated 3 times) at 80℃ for a total immersion time of 72h. The weight was recorded before and after the test (accuracy 0.1mg), and the corrosion weight loss rate (mg / cm³) was calculated. 2 ·h). Simultaneously, scanning electron microscopy (SEM) was used to observe the surface morphology after corrosion.

[0070] The results are shown in Table 1.

[0071] Table 1 Corrosion weight loss rate of each embodiment and comparative example Example 1 0.038 0.030 0.042 Example 2 0.044 0.036 0.048 Example 3 0.042 0.034 0.046 Example 4 0.040 0.032 0.044 Comparative Example 1 0.085 0.062 0.098 Comparative Example 2 0.098 0.075 0.112 Comparative Example 3 0.052 0.042 0.062 Comparative Example 4 — — — Comparative Example 5 0.078 0.058 0.092 Comparative Example 6 0.072 0.054 0.086

[0072] Note: Comparative Example 4 did not obtain a complete alloy and was not tested. Subsequent related tests excluded Comparative Example 4.

[0073] As shown in Table 1, the corrosion weight loss rates of Examples 1-4 of the present invention in acid, alkali, and alternating media were significantly lower than those of all comparative examples. Among them, the acidic weight loss rate of Example 1 was only 44.7% of that of Comparative Example 1. This indicates that the reduction of residual aluminum and alumina inclusions, as well as Ce / Sb microalloying, significantly improved corrosion resistance.

[0074] Test Example 3 Temperature coefficient of resistance (TCR) test: The resistivity change of each example and comparative sample in the range of 25℃-500℃ was measured using the four-probe method, with records taken every 50℃. The temperature coefficient of resistance (TCR) was calculated as follows: TCR = (R2-R1) / [R1×(T2-T1)]×10 6 (Unit: ppm / ℃). The smaller the absolute value of TCR, the smaller the resistance fluctuation with temperature, and the higher the temperature control accuracy.

[0075] The results are shown in Table 2.

[0076] Table 2 Temperature coefficients of resistance (25-500℃) for each embodiment and comparative example Example 1 95 Example 2 112 Example 3 108 Example 4 105 Comparative Example 1 185 Comparative Example 2 320 Comparative Example 3 156 Comparative Example 5 210 Comparative Example 6 198

[0077] As shown in Table 2, Example 1 has the lowest absolute TCR value (95 ppm / ℃), compared to 185 ppm / ℃ in Comparative Example 1 and a high of 320 ppm / ℃ in Comparative Example 2. A lower TCR is beneficial for the heating element to maintain stable heating power over a wide temperature range, improving temperature control accuracy and energy efficiency.

[0078] Test Example 4 Long-term thermal stability test: The samples of Example 1 and Comparative Example 1 were subjected to high-temperature aging treatment at 800℃ (typical operating temperature of Ni-Cr heating element) for 100h, 500h and 1000h respectively. The samples were taken out at each time point, and their Seebeck coefficient and resistivity were tested. The phase and microstructure changes were observed by XRD and SEM.

[0079] The results are shown in Table 3.

[0080] Table 3. Changes in Seebeck coefficient and resistivity after high-temperature aging

[0081] Example 1 0 12.8 — — Ni-Cr solid solution Example 1 100 12.6 1.6 1.2 Ni-Cr solid solution Example 1 500 12.5 2.3 1.9 Ni-Cr solid solution Example 1 1000 12.3 3.9 2.8 Ni-Cr solid solution Comparative Example 1 0 10.0 — — Ni-Cr solid solution Comparative Example 1 100 9.5 5.0 4.2 Ni-Cr solid solution Comparative Example 1 500 8.4 16.0 12.5 Ni-Cr solid solution with trace precipitates Comparative Example 1 1000 7.6 24.0 18.3 Increased grain boundary precipitates

[0082] As shown in Table 3, after aging for 1000 hours, the Seebeck coefficient of Example 1 decreased by only 3.9%, the resistivity changed by 2.8%, XRD showed that it was still a single Ni-Cr solid solution, and SEM showed no obvious grain coarsening or precipitates. In Comparative Example 1, after aging for 500 hours, the Seebeck coefficient decreased by 16.0%, the resistivity changed by 12.5%, XRD showed trace amounts of precipitates, and fine particles were present at the grain boundaries. This indicates that the material of the present invention has excellent long-term structural stability and performance consistency.

[0083] Test Example 5 Microscopic morphology analysis after corrosion: SEM observation was performed on the sample from Test Example 2 after corrosion by acidic medium, and the microstructure of the sample per unit area (mm²) was statistically analyzed. 2 The number of corrosion pits and the maximum depth of corrosion pits within the pit were determined; the elemental composition at the bottom of the corrosion pits was analyzed using EDS.

[0084] The results are shown in Table 4.

[0085] Table 4. Statistics of corrosion pits on the surface after corrosion.

[0086] Example 1 3 4 none Example 2 5 5 none Example 3 4 5 none Example 4 4 4 none Comparative Example 1 28 18 Al, O Comparative Example 2 65 35 Al, O Comparative Example 3 18 12 Ce Comparative Example 5 42 22 Al, O Comparative Example 6 35 20 Al, O

[0087] As shown in Table 4, Example 1 showed only a few shallow, uniform corrosion pits with low density and shallow depth, and no Al or O enrichment was detected at the bottom of the pits. Comparative Example 2 showed numerous deep corrosion pits, with Al and O elements clearly detected at the bottom of the pits, corresponding to the locations of Al2O3 inclusions. The corrosion pit density on the surface of Comparative Example 3 was between that of Example 1 and Comparative Example 2, but Ce enrichment (rather than Al and O) was detected at the bottom of the pits, indicating that Ce segregation caused by the direct addition of elemental Ce can also induce localized corrosion, but its mechanism is different from that of corrosion caused by inclusions. Comparative Example 1 had a higher corrosion pit density, and Al and O were detected at the bottom of the pits, indicating that inclusions were its main source of corrosion initiation.

[0088] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a Ni-Cr based alloy resistant to acid and alkali media, characterized in that, The method includes: S1: Using nickel oxide powder, chromium oxide powder and aluminum powder as raw materials, and introducing Ce or Sb elements in the form of Cr-Ce master alloy or Cr-Sb master alloy, and mixing them evenly to obtain a precursor mixed powder. S2: Press the precursor mixed powder into a compact to obtain a pressed blank; S3: The compact is locally heated and ignited under vacuum conditions to initiate a high-temperature self-propagating reaction, which allows the reaction to propagate on its own. The cooling rate is controlled during the reaction to promote the separation of alumina slag from the alloy melt. The cooling rate is 5℃ / min-10℃ / min. S4: After the reaction is complete, cool to room temperature, separate and remove the alumina slag, and perform post-processing on the obtained alloy product to obtain the Ni-Cr based alloy heating element material. In step S1, the amount of aluminum powder added is 95%-100% of the theoretical requirement, so as to control the residual aluminum content ≤0.2wt%; the theoretical requirement is calculated based on the stoichiometric ratio of the oxide reduction reaction. The acid and alkali resistant Ni-Cr based alloy is composed of Ni, Cr and at least one trace element selected from Ce and Sb, wherein the Cr content is 10-20 at%, the trace element content is 0.5-2.0 at%, and the balance is Ni.

2. The preparation method according to claim 1, characterized in that, In step S1, the mixing is performed using a V-type mixer or a ball mill, and the mixing time is 25 min to 35 min.

3. The preparation method according to claim 1, characterized in that, In step S3, the vacuum level of the vacuum condition is 10. -1 Pa to 10 -2 Argon gas is introduced after the Pa level is reached.

4. The preparation method according to claim 1, characterized in that, In step S4, the post-treatment includes sandblasting to remove the surface oxide layer, with a sandblasting air pressure of 0.6MPa-0.8MPa.

5. A Ni-Cr based alloy heating element material resistant to acid and alkali media, prepared by the preparation method according to any one of claims 1-4, characterized in that, The Ni-Cr based alloy heating element material is composed of Ni, Cr and at least one trace element selected from Ce and Sb, wherein the Cr content is 10-20 at%, the trace element content is 0.5-2.0 at%, and the balance is Ni.

6. The acid and alkali resistant Ni-Cr based alloy heating element material according to claim 5, characterized in that, The Cr content is 15 at%, and the trace elements are 1 at% Ce or 1 at% Sb.

7. The application of the acid and alkali resistant Ni-Cr based alloy heating element material according to claim 5 or 6 in the preparation of electric heating elements.

8. The application according to claim 7, characterized in that, The heating element is used as a corrosion-resistant heating component, chemical heating equipment, or pipeline heat tracing device in acidic, alkaline, or alternating acid-alkali environments.

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