Silver-nickel electrical contact material added with lanthanum oxide and its preparation method

Abstract

The application discloses a silver-nickel electric contact material added with lanthanum oxide and a preparation method thereof. The method comprises the following steps: calculating the required amounts of lanthanum oxide, nickel powder and Ag element for preparing the contact, weighing the Ag element as silver nitrate and preparing a silver nitrate solution by adding water; first, reacting the lanthanum oxide with the silver nitrate solution, calculating the total amount of sodium hydroxide required for completely reacting the generated lanthanum nitrate and the unreacted silver nitrate with sodium hydroxide to generate lanthanum hydroxide and silver oxide respectively, weighing the sodium hydroxide and preparing a sodium hydroxide solution by adding water; then, reacting the sodium hydroxide solution with the aforementioned suspension to obtain a composite powder of silver oxide and lanthanum hydroxide; washing the composite powder to neutral, drying and roasting to obtain a silver-lanthanum hydroxide composite powder; and mixing the obtained silver-lanthanum hydroxide composite powder with the nickel powder, and then performing the processes of isostatic pressing, sintering and extrusion to obtain the silver-nickel electric contact material. The method can make the lanthanum oxide more uniformly distributed in the silver matrix, and obtain a uniform metallographic structure.

Description

Technical Field

[0001] This invention relates to the field of silver-based electrical contact materials technology, specifically to a silver-nickel electrical contact material with added lanthanum oxide and its preparation method. Background Technology

[0002] Silver-nickel (AgNi) material is a composite material mainly composed of silver and nickel. Due to its numerous advantages, including good electrical and thermal conductivity, low and stable contact resistance, excellent resistance to arc erosion, fast arc movement speed, excellent processing performance, simple manufacturing process, and low manufacturing cost, it is the preferred material for applications such as photovoltaic relays. However, traditional silver-nickel materials also have some shortcomings in application. For example, when used in photovoltaic relays, the high current carrying capacity and high ambient temperature make it prone to welding, leading to relay control failure. When used in small relays in smart home appliances, the large amount of spatter can damage the insulation withstand voltage performance of these relays in confined spaces after a period of operation, creating safety hazards. When used in push-button switches, the surge current generated when connecting light loads can easily cause welding, leading to premature switch failure. Adding an appropriate amount of high-melting-point, non-decomposing metals or metal oxides to silver-nickel materials is the main method to improve their resistance to welding and arc erosion.

[0003] Lanthanum oxide (La2O3), a rare earth oxide, has a high decomposition temperature (2315℃), higher than CdO and SnO2, and exhibits a high melting point and good stability. During high-temperature processing, the dispersion strengthening effect of La2O3 effectively prevents dislocation climb and grain boundary slip in silver-nickel materials, significantly improving the softening temperature and high-temperature strength of the contact material. Furthermore, La2O3 effectively prevents Ni aggregation during sintering, NiO aggregation under arcing, and spattering of molten Ag, thereby improving the weld resistance, wear resistance, and contact resistance stability of silver-nickel contact materials. In addition, La2O3 is intrinsically stable and not easily reduced, and does not react with H2 in the sintering atmosphere of conventional AgNi production. Therefore, La2O3 is one of the ideal additives for AgNi electrical contact materials.

[0004] The main preparation processes for AgNi electrical contact materials include mechanical powder mixing, mechanical alloying, chemical co-deposition, and chemical coating. The mechanical powder mixing method, with its main steps of "powder mixing—sintering—extrusion," is widely used due to its simple processing, low manufacturing cost, easy control of material composition, and high production efficiency. For example, invention patents such as CN106298293A, CN114058884A, and CN101608272A all provide manufacturing methods for AgNi containing additives using mechanical powder mixing as the main process route, where additives are added through powder mixing. However, due to the small additive content, poor dispersibility, and poor wettability, adding additives through simple powder mixing easily leads to additive segregation and poor interfacial bonding between the additive phase and the silver matrix.

[0005] Patent documents published under CN103555980A and CN103667767A describe a method for producing AgNi materials by first melting and atomizing metallic elements such as La, Ce, Bi, Cu, In, and Zn with silver to obtain silver powder containing additives, and then mixing it with Ni powder, sintering, and extruding. Adding additives through melting and atomization can improve the problem of additive segregation, but this method is limited to adding metallic elements.

[0006] Patent document CN103710564A discloses a method for preparing silver-nickel electrical contact materials containing additives. Specifically, silver or nickel powder is added to an aqueous or ethanol solution prepared by dissolving salt compounds containing additive elements in water or anhydrous ethanol. The mixture is then wet-mixed, dried, and sintered to uniformly distribute the elemental metal and / or metal oxides on the surface of the silver or nickel powder. This method improves upon the additive segregation phenomenon caused by traditional powder mixing processes. However, the nitrogen-containing gas generated by the decomposition of the added salt additives during subsequent processing can cause problems with the adhesion between the additives and the silver matrix.

[0007] In summary, the existing processing methods for silver-nickel electrical contact materials containing additives have certain limitations. Therefore, how to add lanthanum oxide to silver-nickel to improve the dispersibility of the additives and enhance the metallographic structure, mechanical and physical properties, and electrical life of lanthanum oxide-containing silver-nickel electrical contact materials is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a silver-nickel electrical contact material with uniform structure and lanthanum oxide and its preparation method. The method can make lanthanum oxide more uniformly distributed in silver-nickel and better microscopically bonded to the silver matrix, so that the resulting silver-nickel electrical contact material has better metallographic structure, mechanical and physical properties and electrical life.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution.

[0010] A method for preparing a silver-nickel electrical contact material with added lanthanum oxide includes the following steps:

[0011] 1) Calculate the required amounts of lanthanum oxide, nickel powder, and Ag element according to the material ratio of the silver-nickel electrical contacts to be prepared, weigh them for later use, wherein the Ag element is weighed in the form of silver nitrate, and dissolved in water to prepare a silver nitrate solution.

[0012] 2) React silver nitrate solution with lanthanum oxide to obtain a suspension containing silver nitrate, lanthanum nitrate and silver oxide; calculate the total amount of sodium hydroxide required for them to react completely with sodium hydroxide to produce lanthanum hydroxide and silver oxide based on the amount of lanthanum nitrate generated in the reaction and the amount of unreacted silver nitrate. Weigh the sodium hydroxide solution and prepare it with water for later use.

[0013] 3) Add sodium hydroxide solution to a suspension containing silver nitrate, lanthanum nitrate and silver oxide. After the reaction is complete, filter to obtain a composite powder of silver oxide and lanthanum hydroxide.

[0014] 4) The obtained composite powder of silver oxide and lanthanum hydroxide was washed with water until neutral, dried and then calcined to obtain silver-lanthanum hydroxide composite powder;

[0015] 5) The obtained silver-lanthanum hydroxide composite powder is mixed evenly with nickel powder, and then subjected to isostatic pressing, sintering and extrusion processes to obtain the silver-nickel electrical contact material with added lanthanum oxide; wherein, the sintering adopts a stepped sintering process, specifically: first sintering at 400-600℃ for 2-4 hours, then sintering at 600-800℃ for 1-2 hours, and then sintering at 800-920℃ for 3-6 hours.

[0016] In this application, the composition and ratio of the silver-nickel electrical contact material with added lanthanum oxide to be prepared are the same as in the prior art. Preferably, the lanthanum oxide content is typically 0.5–5 wt%, the silver content is typically 80–90 wt%, and the balance is nickel; more preferably, the lanthanum oxide content is 0.5–3 wt%, the silver content is 84–90 wt%, and the balance is nickel. The nickel powder is typically selected with a particle size of -100 mesh or less (i.e., less than or equal to 150 μm), preferably less than or equal to 300 mesh (i.e., less than or equal to 50 μm). The particle size of the lanthanum oxide is preferably less than or equal to 300 mesh (i.e., less than or equal to 50 μm).

[0017] In step 1) of the preparation method of the present invention, the concentration of the silver nitrate solution is usually 20-50 wt%, preferably 30-50 wt%, and more preferably 40-45 wt%.

[0018] In step 2) of the preparation method of the present invention, the total amount of sodium hydroxide is usually 5.9 / 25 to 8 / 25 of the weight of silver nitrate weighed in step 1), preferably 6 / 25 to 6.5 / 25 of the weight of silver nitrate weighed in step 1). There are no particular requirements for the concentration of the sodium hydroxide solution, but it is preferably 20 to 30 wt%, more preferably 20 to 25 wt%.

[0019] In step 3) of the preparation method described in this invention, sodium hydroxide solution is typically added slowly to a suspension containing silver nitrate, lanthanum nitrate, and silver oxide to carry out the reaction. When a sodium hydroxide solution with a concentration of 20–30 wt% is used, the addition rate of the sodium hydroxide solution is preferably 0.1–1 L / min. The reaction is carried out at room temperature, and according to the applicant's experience, the reaction usually takes 0.3–1 h to complete.

[0020] In step 4) of the preparation method of this invention, calcination is performed to decompose silver oxide into silver. Therefore, the calcination temperature is 400–500°C, and the calcination time is usually 2–6 hours; preferably, calcination is performed at 400–450°C for 4–6 hours. To facilitate better decomposition of silver oxide, it is preferable to perform a crushing operation before calcination after drying. The drying and crushing operations are the same as in the prior art. It is preferable to perform drying at 150–200°C, at which temperature it usually takes 4–8 hours to dry the composite powder of silver oxide and lanthanum hydroxide; after crushing, the powder is first passed through a 100–200 mesh sieve, and the material passing through the sieve is then calcined.

[0021] In step 5) of the preparation method described in this invention, sintering is carried out in a protective atmosphere (such as a hydrogen atmosphere). In a specific stepped sintering process, sintering is first performed at 400–600℃ for 2–4 hours to remove moisture from the compact; then, sintering is performed at 600–800℃ for 1–2 hours to fully decompose lanthanum hydroxide in the compact into lanthanum oxide and water, with the water vaporizing and being discharged; finally, sintering is performed at 800–920℃ for 3–6 hours to fully densify the compact, resulting in a silver-nickel lanthanum oxide ingot. The applicant discovered in experiments that the stepped sintering process can obtain a more uniform metallographic structure, leading to superior mechanical and physical properties in the resulting silver-nickel lanthanum oxide electrical contact material.

[0022] In step 5) of the preparation method of the present invention, the operations of uniformly mixing the silver-lanthanum hydroxide composite powder with nickel powder, static pressing, and extrusion are the same as those in the prior art, and preferably as follows:

[0023] The silver-lanthanum hydroxide composite powder and nickel powder are mixed in a dual-motion mixer to achieve uniform mixing. During the mixing process, the speed of the dual-motion mixer is preferably controlled at 20-50 r / min and the time is 2-4 h.

[0024] The molding pressure of isostatic pressing is usually 80-100 MPa, and the dimensions of isostatic pressing are more preferably Φ(80-110)×(300-500) mm.

[0025] Extrusion is carried out in a protective atmosphere (such as hydrogen atmosphere) at a temperature of 600–700°C, with the extrusion ratio preferably controlled at 150–350. When it is necessary to further extrude the silver-nickel lanthanum oxide ingot into wire, the resulting wire is subjected to multiple drawing and annealing processes in a reducing atmosphere until the desired size of the silver-nickel lanthanum oxide electrical contact material wire product is obtained. This wire product is further processed by a riveting machine to obtain riveted silver-nickel lanthanum oxide electrical contact material.

[0026] The present invention also includes silver-nickel lanthanum oxide electrical contact material prepared by the above method.

[0027] Compared with the prior art, the present invention is characterized by:

[0028] 1. This invention first reacts lanthanum oxide with silver nitrate solution to generate a suspension of silver nitrate and lanthanum nitrate containing silver oxide. Then, sodium hydroxide solution reacts with the suspension of silver nitrate and lanthanum nitrate containing silver oxide to obtain a composite powder of silver oxide and lanthanum hydroxide. Since both lanthanum nitrate and silver nitrate are soluble in water, lanthanum ions and silver ions are evenly distributed in the solution, resulting in the formation of a uniform silver oxide and lanthanum hydroxide composite powder during the reaction with sodium hydroxide. After calcination and crushing, the obtained lanthanum hydroxide and silver oxide composite powder yields a uniform silver-lanthanum hydroxide composite powder, which makes the lanthanum element more evenly distributed in the silver matrix, effectively improving the uneven distribution of additives in the prior art and obtaining a uniform metallographic structure.

[0029] 2. A stepped sintering process is used to prepare silver-nickel lanthanum oxide ingots. Sintering is carried out at the optimal temperature during the decomposition stage of lanthanum hydroxide, which allows lanthanum hydroxide to diffuse rapidly into the binder phase silver atoms while generating lanthanum oxide. The lanthanum oxide has a stronger bond with silver in the binder phase silver matrix. Furthermore, the moisture from the decomposition of lanthanum hydroxide is removed before densification of the compact, avoiding metallographic inhomogeneities such as porosity and cracks in the resulting contact material. These two measures result in silver-nickel lanthanum oxide electrical contact materials with superior mechanical and physical properties.

[0030] 3. Furthermore, the sintering, extrusion, drawing and annealing processes are all carried out under a hydrogen atmosphere, which can avoid the oxidation of nickel during the production process and prevent the reduction of lanthanum oxide to metal, thus obtaining pure silver-nickel-lanthanum oxide material. This is difficult to achieve in the preparation process of silver-nickel materials with other silver metal oxide additives. Attached Figure Description

[0031] Figure 1The images shown are metallographic images (1000×) of the silver-nickel lanthanum oxide electrical contact material prepared in Example 1 of this invention; where (a) is a transverse metallographic image of the material and (b) is a longitudinal metallographic image of the material.

[0032] Figure 2 The images shown are metallographic images (1000×) of the silver-nickel lanthanum oxide electrical contact material prepared in Comparative Example 1 of this invention; where (a) is a transverse metallographic image of the material and (b) is a longitudinal metallographic image of the material.

[0033] Figure 3 The images shown are metallographic images (1000×) of the silver-nickel lanthanum oxide electrical contact material prepared in Comparative Example 2 of this invention; where (a) is a transverse metallographic image of the material and (b) is a longitudinal metallographic image of the material. Detailed Implementation

[0034] To better explain the technical solution of the present invention, the present invention will be further described in detail below with reference to the embodiments, but the implementation of the present invention is not limited thereto.

[0035] Example 1: Preparation of Ag-Ni(15)-La2O3(1) by the method described in this invention

[0036] 1) Calculate the required amounts of lanthanum oxide powder, nickel powder and silver nitrate according to the material ratio for preparing 10 kg of Ag-Ni(15)-La2O3(1). Weigh 0.10 kg of lanthanum oxide powder (-300 mesh), 1.48 kg of nickel powder (-300 mesh) and 13.26 kg of silver nitrate for later use. Dissolve the weighed silver nitrate in water to prepare a silver nitrate solution with a concentration of 40 wt%.

[0037] 2) Lanthanum oxide and silver nitrate solutions were placed in a reactor and stirred for 60 minutes to obtain a suspension containing silver nitrate, lanthanum nitrate, and silver oxide. The chemical reaction formula is shown in formula ①.

[0038] 6AgNO3+La2O3=2La(NO3)3+3Ag2O↓ Formula ①

[0039] Then, based on the amount of lanthanum nitrate generated in the reaction of formula ① and the amount of unreacted silver nitrate, calculate the amount of sodium hydroxide required. Weigh 3.13 kg of sodium hydroxide and dissolve it in water to prepare a sodium hydroxide solution with a concentration of 30 wt%.

[0040] 3) Under stirring conditions, sodium hydroxide solution was added dropwise to a suspension containing silver nitrate, lanthanum nitrate, and silver oxide (dropping rate of 1 L / min). The reaction was stirred for 0.6 h, filtered, and a composite powder of silver oxide and lanthanum hydroxide was obtained. The chemical reaction formulas are shown in formulas ②, ③, and ④.

[0041] La(NO3)3+3NaOH=3NaNO3+La(OH)3↓ Formula ②

[0042] AgNO3 + NaOH = AgOH + NaNO3 (Equation ③)

[0043] 2AgOH=Ag2O↓+H2O (Equation ④)

[0044] 4) The obtained composite powder of silver oxide and lanthanum hydroxide was washed with deionized water until neutral, and then dried in an oven at 150°C for 6 hours. After removal, it was crushed in a double-motion mixer (25 r / min, 1 hour). The resulting powder was then calcined in a muffle furnace at 400°C for 4 hours. After removal, it was crushed again in a double-motion mixer (25 r / min, 1 hour). The powder was then passed through a 100-mesh sieve, and the undersize was collected to obtain the silver-lanthanum hydroxide composite powder. The chemical reaction formula is shown in formula ⑤:

[0045] 2Ag₂O=4Ag+O₂↑ Equation ⑤

[0046] 5) The obtained silver-nickel lanthanum hydroxide composite powder and nickel powder were mixed in a double-motion mixer (25 r / min for 2 h) to obtain a silver-nickel lanthanum hydroxide mixed powder; the mixed powder was formed on an isostatic press (forming pressure 80 MPa) to obtain a silver-nickel lanthanum hydroxide compact; the obtained silver-nickel lanthanum hydroxide compact was sintered in a hydrogen atmosphere using a stepped sintering process (first sintering at 500℃ for 3 h, then sintering at 700℃ for 1.5 h, and then sintering at 880℃ for 3 h) to obtain a silver-nickel lanthanum oxide ingot, the chemical reaction formula of which is shown in formula ⑥:

[0047] 2La(OH)3=La2O3+3H2O↑ Formula ⑥

[0048] The obtained silver-nickel lanthanum oxide billet was then hot-extruded into wire in a hydrogen atmosphere (hot extrusion temperature was 650℃, extrusion cylinder preheating temperature was 480℃, and extrusion ratio was 350); the obtained wire was repeatedly drawn and annealed in a hydrogen atmosphere to the required wire product, and then the obtained wire was processed into riveted silver-nickel lanthanum oxide (Ag-Ni(15)-La2O3(1)) electrical contact material using a riveting machine.

[0049] Metallographic analysis was performed on the wire product obtained in this embodiment, such as... Figure 1 As shown. By Figure 1 It can be seen that in the Ag-Ni(15)-La2O3(1) material prepared by the method described in this invention, lanthanum oxide is uniformly distributed in the silver-nickel matrix material.

[0050] Comparative Example 1: Preparation of Ag-Ni(15)-La2O3(1) by conventional powder mixing-extrusion method

[0051] 1) Calculate the required amounts of lanthanum oxide powder, nickel powder and silver powder according to the material ratio for preparing 10 kg of Ag-Ni(15)-La2O3(1). Weigh out 0.10 kg of lanthanum oxide powder (-300 mesh), 1.48 kg of nickel powder (-300 mesh) and 8.42 kg of silver powder (-200 mesh) for later use.

[0052] 2) Weigh out lanthanum oxide powder, nickel powder, and silver powder and put them into a double-motion mixer to mix them (speed 25 r / min, time 2 h) to obtain silver-nickel lanthanum oxide mixed powder; the obtained mixed powder is formed on an isostatic press (forming pressure 80 MPa) to obtain silver-nickel lanthanum oxide compact; the obtained silver-nickel lanthanum oxide compact is placed in a hydrogen atmosphere for sintering (heated to 880℃ and sintered for 4 h) to obtain silver-nickel lanthanum oxide ingot.

[0053] 3) The silver-nickel lanthanum oxide billet obtained above is hot-extruded into wire in a hydrogen atmosphere (hot extrusion temperature is 650℃, extrusion cylinder preheating temperature is 480℃, extrusion ratio is 350); the obtained wire is drawn and annealed multiple times in a hydrogen atmosphere to the required wire product, and then the obtained wire is processed into riveted silver-nickel lanthanum oxide (Ag-Ni(15)-La2O3(1)) electrical contact material by a riveting machine.

[0054] Comparative Example 2: Preparation of Ag-Ni(15)-La2O3(1) by single-temperature sintering

[0055] Repeat Example 1, except that in step 5), the sintering process adopts conventional sintering, that is, sintering at 880°C for 7.5 hours.

[0056] Example 2: Preparation of Ag-Ni(15)-La2O3(3) by the method described in this invention

[0057] 1) Calculate the required amounts of lanthanum oxide, nickel powder and silver nitrate according to the material ratio for preparing 10 kg of Ag-Ni(15)-La2O3(3). Weigh 0.30 kg of lanthanum oxide powder (-300 mesh), 1.28 kg of nickel powder (particle size -300 mesh) and 13.26 kg of silver nitrate for later use. Dissolve the weighed silver nitrate in water to prepare a silver nitrate solution with a concentration of 30 wt%.

[0058] 2) Place lanthanum oxide and silver nitrate solution in a reactor and stir for 40 min to obtain a suspension containing silver nitrate, lanthanum nitrate and silver oxide. Calculate the required amount of sodium hydroxide based on the amount of lanthanum nitrate generated in the reaction and the amount of unreacted silver nitrate. Weigh 3.13 kg of sodium hydroxide and dissolve it in water to prepare a 20 wt% sodium hydroxide solution.

[0059] 3) Under stirring conditions, sodium hydroxide solution was added dropwise to a suspension containing silver nitrate, lanthanum nitrate and silver oxide (dropping rate of 0.5 L / min), the mixture was stirred for 1 h, filtered, and the composite powder of silver oxide and lanthanum hydroxide was obtained.

[0060] 4) The obtained composite powder of silver oxide and lanthanum hydroxide was washed with deionized water until neutral, and then dried in an oven at 200℃ for 6 hours. After being removed, it was crushed in a double-motion mixer (50 r / min, time 2 hours). The resulting powder was calcined in a muffle furnace at 450℃ for 6 hours. After being removed, it was crushed again in a double-motion mixer (speed 40 r / min, time 1 hour). The powder was passed through a 100-mesh sieve, and the sieve residue was collected to obtain the silver-lanthanum hydroxide composite powder.

[0061] 5) The obtained silver-nickel lanthanum hydroxide composite powder and nickel powder were mixed in a double-motion mixer (30 r / min for 4 h) to obtain a silver-nickel lanthanum hydroxide mixed powder; the mixed powder was formed on an isostatic press (forming pressure 100 MPa) to obtain a silver-nickel lanthanum hydroxide compact; the obtained silver-nickel lanthanum hydroxide compact was sintered in a hydrogen atmosphere using a stepped sintering process (first sintering at 400℃ for 4 h, then raising the temperature to 600℃ for 1 h, and then raising the temperature further). The silver-nickel lanthanum oxide billet was sintered at 800℃ for 5 hours to obtain a silver-nickel lanthanum oxide billet. The silver-nickel lanthanum oxide billet was then hot-extruded into wire in a hydrogen atmosphere (hot extrusion temperature was 700℃, extrusion cylinder preheating temperature was 480℃, and extrusion ratio was 300). The obtained wire was repeatedly drawn and annealed in a hydrogen atmosphere to the required size wire product. The obtained wire was then processed into riveted silver-nickel lanthanum oxide (Ag-Ni(15)-La2O3(3)) electrical contact material using a riveting machine.

[0062] Example 3: Preparation of Ag-Ni(15)-La2O3(3) by the method described in this invention

[0063] Repeat Example 2, except that in step 5), the specific process of stepped sintering is as follows: first sinter at 600°C for 2 hours, then sinter at 700°C for 2 hours, and then sinter at 900°C for 4 hours.

[0064] The contact materials prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to performance testing, and the results are shown in Table 1 below.

[0065] Table 1:

[0066] Project Name Material Tensile strength (MPa) Elongation after fracture (%) Resistivity (μΩ·cm) Example 1 <![CDATA[Ag-Ni(15)-La2O3(1)]]> 245～255 25～30 1.95 Comparative Example 1 <![CDATA[Ag-Ni(15)-La2O3(1)]]> 260～270 8～10 2.10 Comparative Example 2 <![CDATA[Ag-Ni(15)-La2O3(1)]]> 250～260 10～15 2.15 Example 2 <![CDATA[Ag-Ni(15)-La2O3(3)]]> 290～300 15～20 2.20 Example 3 <![CDATA[Ag-Ni(15)-La2O3(3)]]> 280～290 20～25 2.18

[0067] Depend on Figure 1As shown in Table 1, the metallographic structure and properties of the silver-nickel lanthanum oxide contact material prepared by the method of the present invention are significantly better than those of the lanthanum oxide-containing silver-nickel contact material prepared by the conventional powder mixing-extrusion method in Comparative Example 1. In contrast, Comparative Example 2 uses conventional one-stage temperature sintering in the sintering step. On the one hand, the moisture in the isostatically pressed compact cannot be fully discharged. On the other hand, the compact is densified prematurely at a higher temperature, which further prevents the moisture from being discharged. Both of these factors cause the resulting contact material to have metallographic inhomogeneities such as pores and cracks, which further leads to unstable mechanical and physical properties.

Claims

1. A method for preparing a silver-nickel electrical contact material with added lanthanum oxide, comprising the following steps: 1) Calculate the required amounts of lanthanum oxide, nickel powder, and Ag element according to the material ratio of the silver-nickel electrical contacts to be prepared, and weigh them for later use; wherein, the Ag element is weighed in the form of silver nitrate, and dissolved in water to prepare a silver nitrate solution. 2) React silver nitrate solution with lanthanum oxide to obtain a suspension containing silver nitrate, lanthanum nitrate and silver oxide; calculate the total amount of sodium hydroxide required for them to react completely with sodium hydroxide to produce lanthanum hydroxide and silver oxide based on the amount of lanthanum nitrate generated in the reaction and the amount of unreacted silver nitrate. Weigh the sodium hydroxide solution and prepare it with water for later use. 3) Add sodium hydroxide solution to a suspension containing silver nitrate, lanthanum nitrate and silver oxide. After the reaction is complete, filter to obtain a composite powder of silver oxide and lanthanum hydroxide. 4) The obtained composite powder of silver oxide and lanthanum hydroxide was washed with water until neutral, dried and then calcined to obtain silver-lanthanum hydroxide composite powder; 5) The obtained silver-lanthanum hydroxide composite powder is mixed evenly with nickel powder, and then subjected to isostatic pressing, sintering and extrusion processes to obtain the silver-nickel electrical contact material with added lanthanum oxide; wherein, the sintering adopts a stepped sintering process, specifically: first sintering at 400-600℃ for 2-4 hours, then sintering at 600-800℃ for 1-2 hours, and then sintering at 800-920℃ for 3-6 hours.

2. The preparation method according to claim 1, characterized in that, In step 1), the silver-nickel electrical contact material to be prepared contains 0.5-5 wt% lanthanum oxide, 80-90 wt% silver, and the balance is nickel.

3. The preparation method according to claim 1, characterized in that, In step 1), the concentration of the silver nitrate solution is 20–50 wt%.

4. The preparation method according to claim 1, characterized in that, In step 2), the total amount of sodium hydroxide used is 5.9 / 25 to 8 / 25 of the weight of silver nitrate weighed in step 1).

5. The preparation method according to claim 1, characterized in that, In step 2), the concentration of the sodium hydroxide solution is 20–30 wt%.

6. The preparation method according to claim 1, characterized in that, In step 4), calcination is carried out at 400–500°C.

7. The silver-nickel lanthanum oxide electrical contact material prepared by the method according to any one of claims 1 to 6.

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