Preparation method of bismuth-doped modified silver tin oxide electric contact material

Abstract

The invention discloses a preparation method of a bismuth-doped modified silver tin oxide electric contact material, and relates to a preparation method of a modified silver tin oxide electric contact material. The invention aims to solve the problems that the contact resistance of an Ag / SnO2 series electric contact material is increased and the dispersibility of SnO2 in an Ag matrix is poorer due to poor wettability of an existing Ag / SnO2 phase interface. The Bi element doped SnO2 transparent conductive oxide is prepared through a coprecipitation method, the Bi element is introduced to improve the wettability of the Ag / SnO2 phase interface while the high thermal stability of SnO2 is reserved, and collaborative optimization of the electrical life and the contact resistance is achieved. The Bi element doped Ag / SnO2 electric contact material provided by the invention can assist in replacing Ag / CdO to be used on a low-voltage electric appliance.

Description

Technical Field

[0001] The present invention relates to a preparation method of a modified silver tin oxide electrical contact material. Background Art

[0002] Low-voltage electrical contact components are in service under alternating load conditions such as mechanical shock and local arc ablation. Therefore, the arc ablation resistance characteristics of electrical contact materials will directly affect the stability of low-voltage electrical equipment. Ag / CdO electrical contact materials are known as "universal contact materials" due to their good thermal stability, electrical conductivity, thermal conductivity, anti-welding property, and arc erosion resistance. However, from the perspectives of environmental protection and safety, the Cd element is somewhat toxic and can easily cause certain harm to the environment and users during the preparation, use, and recycling of contacts. Silver tin oxide Ag / SnO2 is an environmentally friendly electrical contact material most likely to replace Ag / CdO. It not only has good physical properties, anti-welding property, and arc erosion resistance but also meets environmental protection requirements, so it is considered one of the most promising electrical contact materials. However, there are still certain problems with Ag / SnO2 as an electrical contact material, which restricts its further development and application: 1) Poor wettability at the Ag / SnO2 phase interface: During the operation of electrical contact materials, the opening and closing of the contact pair will trigger short-term arc discharges. Under the combined action of local high temperature and Lorentz force in the arc, the matrix silver will melt and splash, resulting in mass loss. If the refractory oxide has good wettability with the matrix, the oxide can play a role in stabilizing the silver molten pool and slowing down its splash, thereby reducing the amount of arc ablation. For Ag / SnO2-based electrical contact materials, under long-term arc erosion, SnO2 is prone to accumulate on the surface of the Ag matrix. In severe cases, it will lead to the interruption of local current conduction. Moreover, as the number of ablation times increases, the contact resistance of the contact increases, resulting in a shortened service life; 2) The SnO2 particles themselves are prone to agglomeration and are difficult to disperse uniformly on the surface of the Ag matrix during the preparation process, resulting in the contact being unable to exert its optimal performance and a reduced service life. Over the years, researchers have attempted to optimize and improve Ag / SnO2 electrical contact materials from aspects such as preparation process, second-phase modification, and reinforcement phase regulation in order to improve their comprehensive performance and service life. Regarding the problem of poor wettability between Ag and SnO2, it has been found that adding specific oxides, such as Bi2O3 and CuO, can effectively improve the wettability between Ag and SnO2, thereby increasing the viscosity in the molten pool and reducing arc ablation. Among them, Bi2O3, as an oxide with a low saturation vapor pressure, has properties similar to CdO. As an additive, it has been introduced into Ag / SnO2-based contacts and has been widely used. However, the melting point of Bi2O3 is relatively low, lower than the sintering temperature for preparing Ag-based contacts by powder metallurgy. Directly introducing Bi2O3 makes it difficult to densify the contact during the preparation process. Compared with introducing additives, doping modification with metal elements is a direct and effective means to improve the physical properties of oxides. A large amount of calculation data shows that doping SnO2 with metal elements can increase the interface separation work between Ag and SnO2, thereby improving its interface wettability. However, there is less experimental verification because SnO2 belongs to the rutile structure and it is difficult for metal elements to be doped.Therefore, preparing metal element-doped SnO2 powder, optimizing the process to improve the dispersibility of SnO2 powder in the Ag matrix, and developing a new Ag / SnO2:Bi electrical contact material with comprehensive properties such as anti-welding and stable contact resistance have important research value and application prospects. Summary of the Invention

[0003] The present invention aims to solve the problems of poor wettability at the Ag / SnO2 phase interface, resulting in an increase in the contact resistance of Ag / SnO2-based electrical contact materials and poor dispersibility of SnO2 in the Ag matrix, and proposes a preparation method for a bismuth element-doped modified silver tin oxide electrical contact material.

[0004] The preparation method of the bismuth element-doped modified silver tin oxide electrical contact material of the present invention is carried out according to the following steps:

[0005] Step 1: Dissolve BiCl3 and SnCl4·5H2O powders together in a mixed solution of absolute ethanol and dilute hydrochloric acid, and stir magnetically to mix.

[0006] The volume ratio of the absolute ethanol to the dilute hydrochloric acid is (20 - 6):1.

[0007] The molar amount of Bi element in BiCl3 is 1% - 10% of the molar amount of Sn element in SnCl4·5H2O.

[0008] Step 2: Slowly drop concentrated ammonia water into the mixed solution obtained in Step 1 and continuously stir. When the pH reaches 10 - 10.5, stop dropping concentrated ammonia water and keep stirring for 30 min - 35 min. Then, centrifuge the stirred solution, and wash the solid product obtained by centrifugation 5 - 7 times to obtain a tin dioxide precursor doped with Bi ions. Then, put it into a drying oven for drying and then into a muffle furnace, and calcine it at 500°C - 550°C for 2 h - 2.5 h to obtain a bismuth element-doped tin dioxide powder.

[0009] Step 3: Ball-mill and mix the bismuth element-doped tin dioxide powder prepared in Step 2 with elemental silver powder to obtain a mixed powder; the content of the bismuth element-doped tin dioxide powder in the mixed powder is 10 wt% - 15 wt%.

[0010] Step 4: Press the mixed powder prepared in Step 3 into a blank at a pressure of 300 MPa - 310 MPa, and then place the blank in a muffle furnace and sinter it at 830°C - 850°C in an air environment for 3 h - 3.5 h.

[0011] Step 5: Re-press the billet sintered in Step 4 under a pressure of 1200 MPa to 1250 MPa, and then place the billet in a muffle furnace. Sinter it at 830 °C to 850 °C in an air environment for 3 h to 3.5 h to obtain a bismuth element-doped and modified silver tin oxide material.

[0012] The present invention prepares a Bi element-doped SnO2 transparent conductive oxide by a co-precipitation method. While retaining the high thermal stability of SnO2, Bi elements are introduced to improve the wettability of the Ag / SnO2 phase interface, realizing the synergistic optimization of electrical life and contact resistance. The Bi element-doped Ag / SnO2 electrical contact material proposed by the present invention can help replace the use of Ag / CdO in low-voltage electrical appliances.

[0013] In the present invention, the doping of bismuth elements increases the viscosity of the silver molten pool in the solid tin dioxide phase with good thermal stability at high temperatures, and its viscous force hinders the splashing of silver droplets, thereby reducing the mass loss of the contacts during the ablation process.

[0014] The work of separation (W sep ) is used to measure the wettability and bonding property of the two-phase interface. It is defined as the work done to separate the interface into two free surfaces, and the expression is as follows:

[0015]

[0016] In the formula, E A / B —The total energy (J / m 2 ) of the interface formed by the combination of A / B;

[0017] —The total energy of the free surface of A (J / m 2 );

[0018] —The total energy of the free surface of B (J / m 2 );

[0019] A——The interface area (m).

[0020] The present invention discovers the influence of metal element doping on the interface separation work and electronic structure of the Ag / MeO interface model from aspects such as the bonding analysis and density of states of the interface model after structural optimization through DFT calculation. Through first-principles calculation, the separation work after the structural optimization of the Ag / MeO interface model is: Bi2O3 < SnO2 < Bi:SnO2, indicating that Bi doping enhances the bonding ability of the Ag and SnO2 two-phase interfaces, and the doping enhances the Ag-O bonding ability at the Ag and SnO2 two-phase interfaces, thereby improving the interface wettability.

[0021] In the present invention, there is good wettability between the bismuth element-doped SnO2 and Ag. During the arc ablation process, it can increase the viscosity of the Ag molten pool, reduce the flow and splash of liquid Ag, and at the same time, it can also slow down the enrichment of SnO2 on the surface of the electrical contact material from the Ag molten pool, thereby avoiding excessive contact resistance caused by local oxide enrichment and improving the arc ablation resistance of the Ag / SnO2 electrical contact material.

[0022] In the present invention, the doping of bismuth element can improve the wettability of the tin oxide and silver phase interface. Combining high-speed stirring to mix the powder and powder metallurgy process can ensure the high-efficiency densification of the material, and further reduce the contact resistance and mass loss during service. The present invention is applicable to the preparation of silver tin oxide electrical contact materials. Brief Description of the Drawings

[0023] Figure 1 XRD pattern of the bismuth element-doped tin dioxide powder prepared in Step 2 of Experiment 1;

[0024] Figure 2 XPS full spectrum of the bismuth element-doped tin dioxide powder prepared in Step 2 of Experiment 1;

[0025] Figure 3 XPS Bi 4f orbital diagram of the bismuth element-doped tin dioxide powder prepared in Step 2 of Experiment 1;

[0026] Figure 4 Photo of the wetting angle of the phase interface;

[0027] Figure 5 Curve of the change of the contact resistance R of the symmetric contact pair with the number of ablation times;

[0028] Figure 6 Curve of the change of the mass loss G of the electrical contact of the symmetric contact pair of different materials with the number of ablation times. Detailed Embodiments

[0029] Detailed Embodiment 1: This embodiment is a preparation method of a bismuth element-doped and modified silver tin oxide electrical contact material, and the specific steps are as follows:

[0030] Step 1: Dissolve BiCl3 and SnCl4·5H2O powders together into a mixed solution of absolute ethanol and dilute hydrochloric acid, and stir and mix with a magnetic stirrer;

[0031] The volume ratio of the absolute ethanol to the dilute hydrochloric acid is (20 - 6):1;

[0032] The molar amount of Bi element in the BiCl3 is 1% - 10% of the molar amount of Sn element in the SnCl4·5H2O;

[0033] Step 2: Slowly drop concentrated ammonia water into the mixed solution obtained in Step 1 and continuously stir. When the pH reaches 10 - 10.5, stop dropping the concentrated ammonia water and keep stirring for 30 - 35 minutes. Then, centrifuge the solution after stirring ends, and wash the solid product obtained by centrifugation 5 - 7 times to obtain a tin dioxide precursor doped with Bi ions. Then, place it in a drying oven for drying and then put it into a muffle furnace, and calcine it at 500°C - 550°C for 2 - 2.5 hours to obtain a tin dioxide powder doped with Bi element;

[0034] Step 3: Ball-mill and mix the tin dioxide powder doped with Bi element prepared in Step 2 with elemental silver powder to obtain a mixed powder; the content of the tin dioxide powder doped with Bi element in the mixed powder is 10wt% - 15wt%;

[0035] Step 4: Initially press and sinter the powder to obtain a blank: Press the mixed powder prepared in Step 3 into a blank at a pressure of 300MPa - 310MPa, and then place the blank in a muffle furnace and sinter it at 830°C - 850°C in an air environment for 3 - 3.5 hours;

[0036] Step 5: Re-press and re-sinter to obtain the final contact: Re-press the blank sintered in Step 4 at a pressure of 1200MPa - 1250MPa, and then place the blank in a muffle furnace and sinter it at 830°C - 850°C in an air environment for 3 - 3.5 hours to obtain a bismuth element-doped and modified silver tin oxide material.

[0037] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that: the molar amount of Bi element in BiCl3 in Step 1 is 5% of the molar amount of Sn element in SnCl4·5H2O. Others are the same as Specific Embodiment 1.

[0038] Specific Embodiment 3: The difference between this embodiment and Specific Embodiment 1 or 2 is that: the concentration of the dilute hydrochloric acid in Step 1 is 0.2mol / L. Others are the same as Specific Embodiment 1 or 2.

[0039] Specific Embodiment 4: The difference between this embodiment and any one of Specific Embodiments 1 to 3 is that: in Step 2, slowly drop concentrated ammonia water into the mixed solution obtained in Step 1 and continuously stir. When the pH reaches 10, stop dropping the concentrated ammonia water and keep stirring for 30 minutes. Others are the same as any one of Specific Embodiments 1 to 3.

[0040] Specific Embodiment 5: The difference between this embodiment and Specific Embodiment 4 is that: the drying temperature in Step 2 is 75°C and the drying time is 4 hours. Others are the same as Specific Embodiment 4.

[0041] Specific Embodiment Six: The difference between this embodiment and Specific Embodiment Five is that: in Step 3, the ball milling speed is 200 rad / min to 300 rad / min, and the ball milling time is 4 h. Others are the same as Specific Embodiment Five.

[0042] Specific Embodiment Seven: The difference between this embodiment and Specific Embodiment Six is that: in Step 3, the ball-to-material ratio during ball milling is 5:1; the balls are composed of a mixture of large balls, medium balls, and small balls. The diameters of the large balls, medium balls, and small balls are 10 mm, 5 mm, and 2 mm in sequence, and the mass ratio of the large balls, medium balls, and small balls is 1:2:2. Others are the same as Specific Embodiment Six.

[0043] Specific Embodiment Eight: The difference between this embodiment and Specific Embodiment Seven is that: in Step 4, the mixed powder prepared in Step 3 is pressed into a green body under a pressure of 300 MPa and held for 60 s to 65 s, and then the green body is placed in a muffle furnace and sintered at 830 °C in an air environment for 3 h. Others are the same as Specific Embodiment Seven.

[0044] Specific Embodiment Nine: The difference between this embodiment and Specific Embodiment Eight is that: in Step 5, the green body sintered in Step 4 is repressed under a pressure of 1200 MPa and held for 60 s. Others are the same as Specific Embodiment Eight.

[0045] Specific Embodiment Ten: The difference between this embodiment and Specific Embodiment Nine is that: in Step 5, it is sintered at 830 °C in an air environment for 3 h to obtain a bismuth element-doped modified silver tin oxide material. Others are the same as Specific Embodiment Nine.

[0046] The present invention is verified by the following tests:

[0047] Test One: This test is a preparation method of a bismuth element-doped modified silver tin oxide electrical contact material, and the molar amount of Bi element is 5% of the molar amount of Sn element. Specifically, it is carried out according to the following steps:

[0048] Step 1: Dissolve 0.27 g of BiCl3 and 3 g of SnCl4·5H2O powders together into a mixed solution of 200 mL of absolute ethanol and 10 mL of dilute hydrochloric acid, and magnetically stir and mix for 5 min;

[0049] The concentration of the dilute hydrochloric acid is 0.2 mol / L;

[0050] Step 2: Slowly drip concentrated ammonia water into the mixed solution obtained in Step 1 and continuously stir. When the pH reaches 10, stop dripping concentrated ammonia water and keep stirring for 30 min. Then, centrifuge the solution after stirring ends, and wash the solid product obtained by centrifugation 7 times to obtain a tin dioxide precursor doped with Bi ions. Then, place it in a drying oven for drying. The drying temperature is 75 °C, and the drying time is 4 h. Then, place it in a muffle furnace and calcine it at 500 °C for 2 h to obtain a tin dioxide powder doped with Bi element;

[0051] Step 3: Ball-mill and mix the tin dioxide powder doped with Bi element prepared in Step 2 with elemental silver powder to obtain a mixed powder. The content of the tin dioxide powder doped with Bi element in the mixed powder is 15 wt%;

[0052] The rotation speed of the ball milling is 250 rad / min, and the ball milling time is 4 h; the ball-to-material ratio during ball milling is 5:1; the balls are composed of a mixture of large balls, medium balls, and small balls. The diameters of the large balls, medium balls, and small balls are 10 mm, 5 mm, and 2 mm in sequence, and the mass ratio of the large balls, medium balls, and small balls is 1:2:2;

[0053] Step 4: Initially press and sinter the powder to obtain a blank: Press the mixed powder prepared in Step 3 into a blank at a pressure of 300 MPa, and keep the pressure for 60 s. Then, place the blank in a muffle furnace and sinter it at 830 °C in an air environment for 3 h;

[0054] Step 5: Re-press and re-sinter to obtain the final contact: Re-press the blank sintered in Step 4 at a pressure of 1200 MPa, and keep the pressure for 60 s. Then, place the blank in a muffle furnace and sinter it at 830 °C in an air environment for 3 h to obtain a bismuth element-doped and modified silver tin oxide material.

[0055] Comparative experiment: The difference between this experiment and Experiment 1 is that BiCl3 was not added in Step 1. Others are the same as Experiment 1.

[0056] Figure 1 It is the XRD pattern of the tin dioxide powder doped with Bi element prepared in Step 2 of Experiment 1, which proves that there are only SnO2 diffraction peaks in the XRD of the prepared powder, no other impurity oxide phases, and it is relatively pure. The Bi element is in the crystal lattice of tin dioxide, and the doping maintains the original phase.

[0057] Figure 2 It is the XPS full spectrum of the tin dioxide powder doped with Bi element prepared in Step 2 of Experiment 1, which proves that there are characteristic peaks of bismuth element in the prepared powder, indicating that bismuth atoms already exist in the tin dioxide lattice and the doping is successful.

[0058] Figure 3XPS Bi 4f orbital diagram of the Bi-doped tin dioxide powder prepared in Step 2 of Experiment 1. Compared with the undoped pure tin dioxide powder prepared in the comparative experiment, the Bi 4f characteristic peak is obvious, proving the success of doping.

[0059] The following performance tests were carried out on the two kinds of contact materials prepared in Experiment 1 and the comparative experiment:

[0060] The measurement of the two-phase wettability uses a high-temperature sessile drop experiment. The Bi-doped tin dioxide powder prepared in Step 2 of Experiment 1 and the pure tin dioxide powder prepared in Step 2 of the comparative experiment are respectively made into large substrates, and then an Ag block is placed on the substrate, and the temperature is raised above the melting point of Ag (900 °C) under high vacuum. Subsequently, a high-definition camera is used to record the spreading situation of Ag on different substrates during the dissolution process, and the trend of the wetting angle at the phase interface between the two and the Ag block is compared. As Figure 4 shown, Figures a and c are for the comparative experiment, Figures b and d are for Experiment 1. Figures a and b are wetting angle photos, and Figures c and d are physical photos after high-temperature cooling. It can be seen from the figure that the doping of bismuth elements reduces the wetting angle at the phase interface between tin dioxide and silver from 73° to 64°, a decrease of 12.3%, indicating that the doping of bismuth elements can significantly improve the interfacial wettability between tin dioxide and silver.

[0061] Arc ablation test: It is carried out using the contact material electrical performance simulation system independently developed by Harbin Institute of Technology for cyclic ablation experiments. The test conditions are as follows: I = 60 A, U = 380 V, The on-off ratio is 2 s:2 s. After 5000 AC cyclic ablations, the symmetrical contact pair contact resistance R and the electrical contact mass loss G of the final products of Experiment 1 and the comparative experiment are compared. Figure 5 is the change curve of the symmetrical contact pair contact resistance R with the number of ablations. The black line is the silver tin oxide material prepared in the comparative experiment, and the pink line is the bismuth element-doped and modified silver tin oxide material prepared in Experiment 1. It can be seen from the figure that during the 5000 ablation cycles, the contact resistance of the bismuth element-doped and modified silver tin oxide contacts is lower than that of the silver tin oxide contacts. This is because there is better wettability between SnO2 and Ag after the doping of bismuth elements, which can increase the viscosity of the Ag molten pool during the arc ablation process, reduce the flow and splash of liquid Ag, and at the same time can also slow down the enrichment of SnO2 on the surface of the electrical contact material from the Ag molten pool, thus avoiding excessive contact resistance caused by local oxide enrichment and improving the arc ablation resistance of the Ag / SnO2 electrical contact material.

[0062] Figure 6The figure shows the variation curve of the mass loss G of the symmetrical contact pair of electrical contacts made of different materials with the number of ablation times. The black line represents the silver tin oxide material prepared by the comparative test, and the pink line represents the bismuth element-doped and modified silver tin oxide material prepared in Experiment 1. It can be seen from the figure that during the 5000 ablation cycles, the mass loss of the bismuth element-doped and modified silver tin oxide contacts is lower than that of the silver tin oxide contacts. This is because the doping of bismuth elements increases the viscosity of the silver molten pool by improving the solid tin dioxide phase with good thermal stability at high temperatures, and its viscous force hinders the splashing of silver droplets, thereby reducing the mass loss of the contacts during the ablation process.

Claims

1. A preparation method of a bismuth element-doped and modified silver tin oxide electrical contact material, characterized in that The preparation method of bismuth - doped modified silver tin oxide electrical contact material is carried out according to the following steps: Step 1: Dissolve BiCl3 and SnCl4·5H2O powders together into a mixed solution of absolute ethanol and dilute hydrochloric acid, and stir magnetically for mixing; The volume ratio of the absolute ethanol to the dilute hydrochloric acid is (20 - 6):1; The molar amount of Bi element in BiCl3 is 1% - 10% of the molar amount of Sn element in SnCl4·5H2O; Step 2: Slowly drip concentrated ammonia water into the mixed solution obtained in Step 1 and keep stirring. When the pH reaches 10 - 10.5, stop dripping concentrated ammonia water and keep stirring for 30 min - 35 min. Then centrifuge the solution after stirring ends, and wash the solid product obtained by centrifugation 5 - 7 times to obtain a tin dioxide precursor doped with Bi ions. Then put it into a drying oven for drying and then into a muffle furnace, and calcine at 500℃ - 550℃ for 2 h - 2.5 h to obtain bismuth - doped tin dioxide powder; Step 3: Ball - mill and mix the bismuth - doped tin dioxide powder prepared in Step 2 with elemental silver powder to obtain a mixed powder; the content of the bismuth - doped tin dioxide powder in the mixed powder is 10wt% - 15wt%; Step 4: Initially press and sinter the powder to obtain a blank: Press the mixed powder prepared in Step 3 into a blank at a pressure of 300 MPa - 310 MPa, and then place the blank in a muffle furnace and sinter at 830℃ - 850℃ in an air environment for 3 h - 3.5 h; Step 5: Re - press and re - sinter to obtain the final contact: Re - press the blank sintered in Step 4 at a pressure of 1200 MPa - 1250 MPa, and then place the blank in a muffle furnace and sinter at 830℃ - 850℃ in an air environment for 3 h - 3.5 h to obtain bismuth - doped modified silver tin oxide material.

2. The preparation method of a bismuth element-doped and modified silver tin oxide electrical contact material according to claim 1, wherein The molar amount of Bi element in BiCl3 described in Step 1 is 5% of the molar amount of Sn element in SnCl4·5H2O.

3. The preparation method of a bismuth element-doped and modified silver tin oxide electrical contact material according to claim 1, characterized in that The concentration of the dilute hydrochloric acid described in Step 1 is 0.2 mol / L.

4. The preparation method of a bismuth element-doped and modified silver tin oxide electrical contact material according to claim 1, characterized in that In Step 2, slowly drip concentrated ammonia water into the mixed solution obtained in Step 1 and keep stirring. When the pH reaches 10, stop dripping concentrated ammonia water and keep stirring for 30 min.

5. The preparation method of a bismuth element-doped and modified silver tin oxide electrical contact material according to claim 1, characterized in that In Step 2, the drying temperature is 75℃ and the drying time is 4 h.

6. The preparation method of a bismuth element-doped and modified silver tin oxide electrical contact material according to claim 1, characterized in that In Step 3, the ball - milling speed is 200 rad / min - 300 rad / min and the ball - milling time is 4 h.

7. The preparation method of a bismuth element-doped and modified silver tin oxide electrical contact material according to claim 6, characterized in that In Step 3, the ball - to - material ratio during ball - milling is 5:1; the balls are composed of a mixture of large balls, medium balls and small balls. The diameters of the large balls, medium balls and small balls are 10 mm, 5 mm and 2 mm in sequence, and the mass ratio of the large balls, medium balls and small balls is 1:2:

2.

8. The preparation method of a bismuth element-doped and modified silver tin oxide electrical contact material according to claim 1, characterized in that In Step 4, press the mixed powder prepared in Step 3 into a blank at a pressure of 300 MPa and hold the pressure for 60 s - 65 s, and then place the blank in a muffle furnace and sinter at 830℃ in an air environment for 3 h.

9. The preparation method of a bismuth element-doped and modified silver tin oxide electrical contact material according to claim 1, characterized in that In Step 5, re - press the blank sintered in Step 4 at a pressure of 1200 MPa and hold the pressure for 60 s.

10. The preparation method of a bismuth element-doped and modified silver tin oxide electrical contact material according to claim 9, characterized in that In Step 5, sinter at 830℃ in an air environment for 3 h to obtain bismuth - doped modified silver tin oxide material.

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