Micro-channel continuous flow preparation method of silver tin oxide electrical contact material

Abstract

The invention discloses a micro-channel continuous flow preparation method of a silver tin oxide electrical contact material, and belongs to the technical field of silver-based electrical contact materials. The method specifically comprises the following steps: firstly, calculating the required amounts of tin nitrate, silver nitrate and sodium hydroxide, and respectively preparing into solutions by using water; then the prepared solutions are synchronously conveyed into a micro-channel reactor at the flow speed of 70-90 ml / min for reaction, filtering is conducted, and composite powder of silver oxide and tin hydroxide is obtained; the obtained composite powder is washed, dried and roasted, and silver tin oxide composite powder is obtained; and then carrying out conventional forming, sintering and extruding procedures to obtain the composite material. According to the invention, the microchannel reactor is applied to the preparation of the silver tin oxide electrical contact for the first time, and the particle size distribution of tin oxide is controlled by limiting the flow velocity of the solution on the basis of enhancing mass transfer by using the microchannel reactor to uniformly disperse tin oxide in a matrix; therefore, the obtained electrical contact has a uniform microstructure and can also obtain more excellent mechanical properties at the same time.

Description

Technical Field

[0001] The invention relates to a preparation method of a silver-based electric contact material, and in particular to a microchannel continuous flow preparation method of a silver tin oxide electric contact material. Background Art

[0002] In switching electrical appliances, electrical contacts are directly responsible for disconnecting and connecting circuits and carrying normal operating current or overload current within a certain period of time. The working performance and quality of electrical contacts directly determine the key functions of various switching electrical appliances, such as the switching capacity of distribution electrical appliances, the electrical life of control electrical appliances, and the reliability of relays.

[0003] Silver tin oxide (AgSnO2) electrical contact material is a composite material composed of silver (Ag) and tin oxide (SnO2). Due to its excellent wear resistance, resistance to welding, resistance to arc erosion, conductivity and environmental protection properties, it has become the best alternative to toxic silver cadmium oxide electrical contacts.

[0004] The commonly known methods for preparing silver tin oxide electrical contact materials mainly include internal oxidation, powder metallurgy and chemical co-precipitation. Among them, chemical co-precipitation has attracted the attention of researchers and manufacturers due to its advantages such as simple equipment, convenient operation and low cost. For example, the invention patent with publication number CN116555614A discloses a method for preparing silver tin oxide electrical contact materials using chemical co-precipitation. First, soluble Sn is used to prepare the silver tin oxide electrical contact material. 4+ After the ionic metal salt solution and graphene oxide are evenly mixed, a complexing agent with a pH of 7 to 10 adjusted by ammonia water is added and stirred thoroughly to generate Sn(OH)4, which is then calcined to obtain graphene / tin oxide composite material powder; the composite material powder is then mixed with silver powder and conductive ceramic powder and subjected to hot isostatic pressing, sintering, hot extrusion, hot drawing and other processes to prepare a silver tin oxide electrical contact material. For example, the invention patent with publication number CN104498763A discloses a method for processing silver tin oxide electrical contact materials. After weighing the corresponding amounts of tin oxide powder, oxide powder, silver nitrate, and sodium hydroxide, the silver nitrate and sodium hydroxide are respectively prepared into solutions with water, and then divided into two parts; one part of the silver nitrate solution and one part of the sodium hydroxide solution are mixed with the oxide powder to form a silver oxide and oxide composite powder slurry; the other part of the silver nitrate solution is mixed with tin oxide to form a suspension, which is then mixed with the above composite powder slurry and the other part of the sodium hydroxide solution to react to obtain a silver oxide, oxide, and tin oxide composite powder; the obtained composite powder is washed with water and calcined to obtain a silver tin oxide composite powder; the composite powder is formed, sintered, and hot extruded to obtain. However, during the preparation process of the chemical precipitation method, the mixing of two or more materials is not synchronized. This intermittent reaction can lead to problems such as wide particle size distribution and component segregation in the reaction, which in turn leads to batch inhomogeneity.

[0005] A microchannel reactor (MCR) is a device that enables continuous flow chemical reactions based on a micron-scale channel structure (channel diameters typically range from tens of microns to several millimeters). Its core feature is the enhanced mass and heat transfer through microscale fluid dynamics. It boasts extremely high mixing efficiency (radial complete mixing in the millisecond range), strong heat exchange capacity, and a narrow residence time distribution (virtually no backmixing, essentially approaching plug flow). It is widely used in fine chemicals, pharmaceuticals, nanomaterial synthesis, and other fields. Patent publication number CN106391002A discloses a method for preparing a nanosilver / graphene oxide composite dispersion, employing a high-gravity rotating packed bed or microchannel reactor as the reaction apparatus. This significantly enhances the mass transfer and microscopic mixing involved in the reverse process. Currently, there are no reports on the use of a microchannel reactor to prepare silver-tin oxide electrical contact materials. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a microchannel continuous flow preparation method for silver tin oxide electrical contact material. This method uses a microchannel reactor to enhance mass transfer so that the tin oxide is uniformly dispersed in the matrix. At the same time, the particle size distribution of the tin oxide is controlled by limiting the flow rate of the solution entering the microchannel reactor, so that the obtained electrical contact material has a uniform microstructure and also obtains better mechanical properties.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] A microchannel continuous flow preparation method for silver tin oxide electrical contact material comprises the following steps:

[0009] 1) Calculating and weighing the required amounts of tin nitrate, silver nitrate, and sodium hydroxide according to the material ratio for preparing the silver tin oxide electrical contact, and preparing solutions thereof with water to obtain tin nitrate solution, silver nitrate solution, and sodium hydroxide solution;

[0010] 2) Synchronously conveying the tin nitrate solution, the silver nitrate solution, and the sodium hydroxide solution to a microchannel reactor for reaction, filtering the resulting material, and collecting the precipitate to obtain a composite powder of silver oxide and tin hydroxide; wherein the flow rates of the tin nitrate solution, the silver nitrate solution, and the sodium hydroxide solution are controlled to be 70 to 90 ml / min;

[0011] 3) washing the obtained composite powder of silver oxide and tin hydroxide with water until neutral, drying and then roasting to obtain a silver tin oxide composite powder;

[0012] 4) The obtained silver tin oxide composite powder is subjected to the steps of forming, sintering and extrusion to obtain the silver tin oxide electrical contact material.

[0013] In this application, the flow rates of the tin nitrate solution, silver nitrate solution, and sodium hydroxide solution entering the microchannel reactor have a crucial impact on the mechanical properties of the subsequent contact material and the distribution range of the tin oxide particle size therein. The applicant has found in experiments that only when the flow rates of the tin nitrate solution, silver nitrate solution, and sodium hydroxide solution are all controlled at 70-90 ml / min does the resulting contact material not only have a very uniform microstructure (the tin oxide particles are very evenly distributed in the matrix), but also have uniform size (particle size distribution ranges from 0.4 to 2.0 μm, with the absolute value of the particle size difference less than or equal to 1.2 μm, and in preferred embodiments, less than or equal to 0.4 μm). More importantly, the resulting contact material exhibits superior mechanical properties. When the flow rates of the tin nitrate solution, silver nitrate solution and sodium hydroxide solution are not particularly limited (such as a flow rate of 30-65 ml / min or 95-110 ml / min), although the distribution of the particle size of the tin oxide particles in the obtained contact material is relatively uniform in some cases (such as in some cases the generated tin oxide particle size distribution range is 0.8-1.8 μm, and the absolute value of the particle size difference is less than or equal to 1.0 μm; in more cases the tin oxide particle size distribution range is 0.3-2.2 μm, and the absolute value of the particle size difference is greater than or equal to 1.6 μm), the mechanical properties of the obtained contact material are significantly reduced.

[0014] In the present application, the silver tin oxide electrical contact material to be prepared has a tin oxide content of 8-15 wt %, with the remainder being silver, more preferably a tin oxide content of 10-12 wt %, with the remainder being silver.

[0015] In step 1) of the above method, the required amount of sodium hydroxide is calculated based on the determined amounts of silver nitrate and tin nitrate. The concentrations of the tin nitrate solution, silver nitrate solution, and sodium hydroxide solution are the same as those in the prior art. Specifically, the concentration of the tin nitrate solution is limited to 20-40 wt%, preferably 25-35 wt%; the concentration of the silver nitrate solution is limited to 20-40 wt%, preferably 25-35 wt%; and the concentration of the sodium hydroxide solution is limited to 10-30 wt%, preferably 15-25 wt%.

[0016] In step 2) of the above method, the microchannel reactor is preferably a sleeve-type microchannel reactor, wherein the channel diameter is preferably ≤1 mm. After the tin nitrate solution, silver nitrate solution, and sodium hydroxide solution are prepared, they are placed in different containers and synchronously transported to the microchannel reactor via different injection pumps for reaction. The reaction time is generally 5 to 10 minutes. The resulting material precipitates, which are collected to form a composite powder of silver oxide and tin hydroxide. The flow rates of the tin nitrate solution, silver nitrate solution, and sodium hydroxide solution are preferably controlled at 75 to 85 ml / min.

[0017] In steps 3) and 4) of the above method, the operations of drying, calcining, forming, sintering, extrusion, etc. are the same as those in the prior art, and are preferably as follows:

[0018] In step 3), drying is carried out at 100-150°C and usually takes 12-18 hours. The dried silver oxide and tin hydroxide composite powder is usually crushed (passed through a 100-200 mesh sieve) and then calcined. Calcination is preferably carried out at 400-500°C for 2-6 hours. After calcination, the resulting powder is crushed (passed through a 100 mesh sieve) before entering the next step.

[0019] In step 4), the forming is isostatic pressing, and the forming pressure is controlled at 80-100 MPa. The pressed green sheet obtained by isostatic pressing is placed in an air atmosphere and sintered at 880-920° C. for 4-8 hours to obtain a silver tin oxide ingot. Extrusion is carried out at 750-900° C., and the extrusion ratio is controlled at 10-200, preferably 100-200. When the silver tin oxide ingot is extruded into a strip, the obtained strip is rolled and compounded multiple times, annealed to the desired size, and then punched by a punch to obtain a sheet-like silver tin oxide electrical contact material. When the silver tin oxide ingot is extruded into a wire, the obtained wire is drawn and annealed to the desired size multiple times and then processed by a rivet machine to obtain a rivet-type silver tin oxide electrical contact material.

[0020] Compared with the existing technology, the present invention applies a microchannel reactor to the preparation of silver tin oxide electrical contact materials for the first time. On the basis of using the microchannel reactor to enhance mass transfer so that the tin oxide is evenly dispersed in the matrix, the particle size distribution of the tin oxide is controlled by limiting the flow rate of the solution entering the microchannel reactor, so that the obtained electrical contact material has a uniform microstructure and can also obtain better mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the microchannel reactor in the method of the present invention.

[0022] Figure 2 This is a microstructure diagram (×1000) of the electrolytic head material prepared in Example 1 of the present invention.

[0023] Figure 3 This is the microstructure diagram (×1000) of the electrolytic head material prepared in Comparative Example 1-1 of the present invention.

[0024] Figure 4 This is the microstructure diagram (×1000) of the electrolytic head material prepared in Comparative Example 1-2 of the present invention.

[0025] Figure 5Microstructure diagram (×1000) of the electrolytic head material prepared in Comparative Examples 1-3 of the present invention.

[0026] Figure 6 Microstructure diagram (×1000) of the electrolytic head materials prepared in Comparative Examples 1-4 of the present invention.

[0027] Figure 7 This is the microstructure diagram (×1000) of the electrolytic head material prepared in Example 2 of the present invention.

[0028] Figure 8 This is the microstructure diagram (×1000) of the electrolytic head material prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0029] In order to better explain the technical solution of the present invention, the present invention is further described in detail below with reference to examples, but the embodiments of the present invention are not limited thereto.

[0030] Example 1: Preparation of Ag-SnO2(12) by the method of the present invention

[0031] 1) Calculate the required amounts of tin nitrate and silver nitrate according to the material ratio for preparing 10 kg of Ag-SnO2 (12), and determine the required amount of sodium hydroxide based on the determined amounts of tin nitrate and silver nitrate, and weigh 2.920 kg of tin nitrate, 13.857 kg of silver nitrate, and 4.535 kg of sodium hydroxide, respectively, for later use; dissolve the weighed tin nitrate, silver nitrate, and sodium hydroxide in water to prepare solutions with concentrations of 30 wt%, 30 wt%, and 20 wt%, respectively;

[0032] 2)Reference Figure 1 , the prepared tin nitrate solution, silver nitrate solution and sodium hydroxide solution are placed in container A, container B and container C respectively, and the liquid in each container is transported to the sleeve microchannel reactor for reaction through the sampling pump A, sampling pump B and sampling pump C connected thereto; after completing the preparatory work, the flow rate of each sampling pump is set to 80 ml / min, and then the sampling pumps are simultaneously turned on to synchronously transport the tin nitrate solution, silver nitrate solution and sodium hydroxide solution to the sleeve microchannel reactor at a flow rate of 80 ml / min for reaction, and the reaction time is 8 minutes. After the reaction is completed, there is a precipitate in the material flowing out of the sleeve microchannel reactor outlet, and the precipitate is collected to obtain a composite powder of silver oxide and tin hydroxide;

[0033] 3) The obtained composite powder of silver oxide and tin hydroxide was washed with water until neutral, and then placed in an oven at 120° C. for 15 h, and then taken out and placed in a double-cone mixer for crushing (25 r / min, time 1 h). The obtained powder was placed in a muffle furnace at 400° C. for 4 h (under air atmosphere), and then taken out and placed in a double-motion mixer for crushing (speed 25 r / min, time 1 h), and passed through a 200-mesh sieve. The sieve underflow was collected to obtain a silver-tin oxide composite powder;

[0034] 4) The obtained silver-tin oxide composite powder is formed on an isostatic press (forming pressure is 150 MPa), and the formed compact is sintered at 880°C in an air atmosphere for 4 hours to obtain a silver-tin oxide ingot; the obtained ingot is processed into a strip by hot extrusion (hot extrusion temperature is 850°C, mold preheating temperature is 150°C, and extrusion ratio is 160); the obtained strip is subjected to multiple rolling and compounding, annealing to the required size, and then punched by a punch to obtain a sheet-like silver-tin oxide (Ag-SnO2(12)) electrical contact material.

[0035] The microstructure of the contact material prepared in this example was analyzed. Figure 2 As shown. Figure 2 It can be seen that the tin oxide particles are uniform in size, with a size distribution of 0.4 to 0.8 μm, and the fine tin oxide particles are evenly distributed in the silver matrix.

[0036] Comparative Example 1-1: Preparation of Ag-SnO2 (12) by conventional chemical precipitation method without using a double-tube microchannel reactor

[0037] 1) Calculate the amount of tin oxide powder and silver nitrate required according to the material ratio for preparing 10 kg of Ag-SnO2 (12), and determine the amount of sodium hydroxide required based on the determined amount of silver nitrate; weigh 1.2 kg of tin oxide (average particle size of 2 to 3 μm), 13.857 kg of silver nitrate, and 3.261 kg of sodium hydroxide, respectively, and set aside; dissolve the weighed silver nitrate and sodium hydroxide in water to prepare solutions with concentrations of 30 wt% and 20 wt%, respectively;

[0038] 2) evenly dispersing the weighed tin oxide powder in the prepared silver nitrate solution to obtain a suspension of silver nitrate and tin oxide powder; dripping the prepared sodium hydroxide solution into the suspension at a drop rate of 0.1 L / min, stirring and reacting for 1 hour, and collecting the precipitate to obtain a composite powder of silver oxide and tin hydroxide;

[0039] 3) Same as Example 1;

[0040] 4) Same as Example 1.

[0041] The microstructure of the contact material prepared in this example was analyzed. Figure 3 As shown. Figure 3 It can be seen that the tin oxide particles are of different sizes, ranging from 0.3 to 4.0 μm, and the distribution of the tin oxide particles in the silver matrix is ​​not very uniform.

[0042] Comparative Example 1-2: Preparation of Ag-SnO2(12) using a double-tube microchannel reactor

[0043] Example 1 was repeated, except that in step 2), the tin nitrate solution, the silver nitrate solution, and the sodium hydroxide solution were all simultaneously delivered to the double-tube microchannel reactor at a flow rate of 65 ml / min for reaction.

[0044] The microstructure of the contact material prepared in this example was analyzed. Figure 4 As shown. Figure 4 It can be seen that although the distribution of tin oxide particles in the silver matrix is ​​relatively uniform, the sizes of the tin oxide particles are different, ranging from 0.8 to 1.8 μm.

[0045] Comparative Example 1-3: Preparation of Ag-SnO2(12) using a double-tube microchannel reactor

[0046] Example 1 was repeated, except that in step 2), the tin nitrate solution, the silver nitrate solution, and the sodium hydroxide solution were all simultaneously delivered to the double-tube microchannel reactor at a flow rate of 40 ml / min for reaction.

[0047] The microstructure of the contact material prepared in this example was analyzed. Figure 5 As shown. Figure 5 It can be seen that although the distribution of tin oxide particles in the silver matrix is ​​relatively uniform, the sizes of the tin oxide particles vary, ranging from 0.8 to 2.2 μm.

[0048] Comparative Example 1-4: Preparation of Ag-SnO2(12) using a double-tube microchannel reactor

[0049] Example 1 was repeated, except that in step 2), the tin nitrate solution, the silver nitrate solution, and the sodium hydroxide solution were all simultaneously delivered to the double-tube microchannel reactor at a flow rate of 95 ml / min for reaction.

[0050] The microstructure of the contact material prepared in this example was analyzed. Figure 6 As shown. Figure 6 It can be seen that although the distribution of tin oxide particles in the silver matrix is ​​relatively uniform, the sizes of the tin oxide particles vary, ranging from 0.3 to 2.1 μm.

[0051] Example 2: Preparation of Ag-SnO2 (10) by the method of the present invention

[0052] 1) Calculate the required amounts of tin nitrate and silver nitrate according to the material ratio for preparing 10 kg of Ag-SnO2 (10), and determine the required amount of sodium hydroxide based on the determined amounts of tin nitrate and silver nitrate, and weigh 2.434 kg of tin nitrate, 14.172 kg of silver nitrate, and 4.397 kg of sodium hydroxide, respectively, for later use; dissolve the weighed tin nitrate, silver nitrate, and sodium hydroxide in water to prepare solutions with concentrations of 35 wt%, 35 wt%, and 15 wt%, respectively;

[0053] 2)Reference Figure 1 , the prepared tin nitrate solution, silver nitrate solution and sodium hydroxide solution are placed in container A, container B and container C respectively, and the liquid in each container is transported to the double-tube microchannel reactor for reaction through its corresponding sampling pump A, sampling pump B and sampling pump C. After completing the preparatory work, the flow rate of each sampling pump is set to 90 ml / min, and then the sampling pumps are simultaneously turned on to synchronously transport the tin nitrate solution, silver nitrate solution and sodium hydroxide solution to the double-tube microchannel reactor at a flow rate of 90 ml / min for reaction. The reaction time is 10 minutes. After the reaction is completed, there is a precipitate in the material flowing out of the outlet of the double-tube microchannel reactor. The precipitate is collected to obtain a composite powder of silver oxide and tin hydroxide;

[0054] 3) Same as Example 1;

[0055] 4) Same as Example 1.

[0056] The microstructure of the contact material prepared in this example was analyzed. Figure 7 As shown. Figure 7 It can be seen that the tin oxide particles are uniform in size, with a size distribution of 0.4 to 1.6 μm, and the fine tin oxide particles are evenly distributed in the silver matrix.

[0057] Example 3: Preparation of Ag-SnO2(8) by the method of the present invention

[0058] 1) Calculate the required amounts of tin nitrate and silver nitrate according to the material ratio for preparing 10 kg of Ag-SnO2(8), and determine the required amount of sodium hydroxide based on the determined amounts of tin nitrate and silver nitrate, and weigh 1.947 kg of tin nitrate, 14.487 kg of silver nitrate, and 4.259 kg of sodium hydroxide, respectively, for later use; dissolve the weighed tin nitrate, silver nitrate, and sodium hydroxide in water to prepare solutions with concentrations of 20 wt%, 20 wt%, and 30 wt%, respectively;

[0059] 2)Reference Figure 1, the prepared tin nitrate solution, silver nitrate solution and sodium hydroxide solution are placed in container A, container B and container C respectively, and the liquid in each container is transported to the double-tube microchannel reactor for reaction through its corresponding sampling pump A, sampling pump B and sampling pump C. After completing the preparatory work, the flow rate of each sampling pump is set to 70 ml / min, and then the sampling pumps are simultaneously turned on to synchronously transport the tin nitrate solution, silver nitrate solution and sodium hydroxide solution to the double-tube microchannel reactor at a flow rate of 70 ml / min for reaction. The reaction time is 5 minutes. After the reaction is completed, there is a precipitate in the material flowing out of the outlet of the double-tube microchannel reactor. The precipitate is collected to obtain a composite powder of silver oxide and tin hydroxide;

[0060] 3) Same as Example 1;

[0061] 4) Same as Example 1.

[0062] The microstructure of the contact material prepared in this example was analyzed. Figure 8 As shown. Figure 8 It can be seen that the tin oxide particles are uniform in size, with a size distribution of 0.8 to 2.0 μm, and the fine tin oxide particles are evenly distributed in the silver matrix.

[0063] The contact materials prepared in Example 1 and Comparative Examples 1-1 to 1-4 were subjected to performance tests, and the results are shown in Table 1 below.

[0064] Table 1 Performance of products prepared in Example 1 and comparative examples

[0065]

[0066]

[0067] As can be seen from Table 1, the mechanical properties of the silver tin oxide contact material prepared according to the present invention are significantly better than those of the comparative example.

[0068] The Ag-SnO2(12) wires prepared in Example 1 and Comparative Examples 1-1 to 1-4 were processed into 3×0.8+1.5×1.5R8 and 3×0.8+1.5×1.5F rivet contacts, which were respectively assembled as dynamic and static contacts on a simulated electrical performance testing machine for a relay simulated electrical life test. The test conditions are shown in Table 2, and the test results are shown in Table 3.

[0069] Table 2 Simulated electrical performance test conditions

[0070]

[0071] Table 3 Simulated electrical performance test results

[0072]

Claims

1. A microchannel continuous flow preparation method for silver tin oxide electrical contact material, comprising the following steps: 1) Calculating and weighing the required amounts of tin nitrate, silver nitrate, and sodium hydroxide according to the material ratio for preparing the silver tin oxide electrical contact, and preparing solutions thereof with water to obtain tin nitrate solution, silver nitrate solution, and sodium hydroxide solution; 2) Synchronously conveying the tin nitrate solution, the silver nitrate solution, and the sodium hydroxide solution to a microchannel reactor for reaction, filtering the resulting material, and collecting the precipitate to obtain a composite powder of silver oxide and tin hydroxide; wherein the flow rates of the tin nitrate solution, the silver nitrate solution, and the sodium hydroxide solution are controlled to be 70 to 90 ml / min; 3) washing the obtained composite powder of silver oxide and tin hydroxide with water until neutral, drying and then roasting to obtain a silver tin oxide composite powder; 4) The obtained silver tin oxide composite powder is subjected to the steps of forming, sintering and extrusion to obtain the silver tin oxide electrical contact material.

2. The microchannel continuous flow preparation method of silver tin oxide electrical contact material according to claim 1, characterized in that: In step 1), the concentration of the tin nitrate solution is 20-40 wt %, the concentration of the silver nitrate solution is 20-40 wt %, and the concentration of the sodium hydroxide solution is 10-30 wt %.

3. The microchannel continuous flow preparation method of silver tin oxide electrical contact material according to claim 1, characterized in that: In step 3), calcination is carried out at 400-500°C.

4. The microchannel continuous flow preparation method of silver tin oxide electrical contact material according to claim 1, characterized in that: In step 4), sintering is carried out at 880-920°C.

5. The microchannel continuous flow preparation method of silver tin oxide electrical contact material according to claim 1, characterized in that: In step 4), the extrusion is carried out at 750-900°C.

6. The microchannel continuous flow preparation method of silver tin oxide electrical contact material according to any one of claims 1 to 5, characterized in that: In step 1), the content of tin oxide in the silver tin oxide electrical contact material to be prepared is 8-15 wt %, and the balance is silver.

7. The microchannel continuous flow preparation method of silver tin oxide electrical contact material according to any one of claims 1 to 5, characterized in that: In step 2), the flow rates of the tin nitrate solution, silver nitrate solution and sodium hydroxide solution are controlled to be 75-85 ml / min.

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