Method for producing a thermosensitive bulk material by means of laser melting

Abstract

The application laser melting method for preparing thermosensitive bulk material belongs to the field of functional oxide ceramic material preparation, and the method first dissolves nickel oxide NiO and manganese dioxide MnO2 raw materials in oxalic acid solution, prepares NiMn2O4 thermosensitive powder material through drying, then anneals in an atmospheric environment to obtain a spinel structure thermosensitive powder material, and finally melts the thermosensitive powder material laid on the substrate into NiMn2O4 bulk material using a laser. By controlling parameters such as energy density of the melting laser, the performance of the prepared NiMn2O4 bulk material can be regulated. The thermosensitive bulk material prepared by the method has the advantages of simple preparation process, high density, good electrical performance and the like.

Description

Technical Field

[0001] This invention belongs to the field of functional oxide ceramic material preparation, specifically relating to a method for preparing thermosensitive bulk materials by laser melting. Background Technology

[0002] Negative temperature coefficient (NTC) thermistors have been extensively studied in recent decades due to their unique characteristic of decreasing resistance with increasing temperature. The conductivity of manganese-based transition metal oxides is influenced by the octahedral Mn content. 3+ and Mn 4+ This is achieved through polaron hopping. Due to its high sensitivity to temperature changes, fast response speed, and low cost, this material is widely used in aerospace, control, temperature monitoring, and other industrial fields. The simplest manganese-based transition metal oxide is NiMn2O4. Furthermore, the physical properties of manganese-based transition metal oxides can be modified by adding various metal ions such as cobalt, iron, and zinc.

[0003] Currently, commonly used methods for synthesizing thermistor materials such as NiMn2O4 include solution methods, solid-state sintering methods, electric field-assisted flash calcination methods, and co-precipitation methods. Patent "CN109534412A" discloses a method for preparing three-dimensional porous NiMn2O4 using a self-sacrificial template method; however, the NiMn2O4 prepared by this method is intended for use in supercapacitors and is not suitable for thermistors. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention proposes a method for preparing thermosensitive bulk materials using laser melting. This invention utilizes chemical solutions and laser melting to prepare NiMn2O4 powder material with a spinel structure using NiO powder, MnO2 powder, and oxalic acid solution as raw materials. The powder is then thermally annealed in an atmospheric atmosphere. Finally, NiMn2O4 thermosensitive bulk materials are prepared on a substrate using different laser energy densities. This material has a simple preparation process, good crystallinity, and excellent electrical properties.

[0005] To achieve the above objectives, the present invention provides a method for preparing thermosensitive bulk materials by laser melting, comprising the following steps:

[0006] Step 1) Place the NiO and MnO2 powder raw materials into a beaker, then add alcohol and stir until homogeneous;

[0007] Step 2) Slowly add oxalic acid solution to the beaker and stir continuously with a glass rod to prevent the generated gas from causing the material in the beaker to overflow;

[0008] Step 3) Place the beaker in an ultrasonic cleaner and vibrate and stir for 30 minutes to allow the powder raw material and oxalic acid to react fully;

[0009] Step 4) Then place the beaker in a constant temperature water bath and heat until the solution in the beaker evaporates into a paste;

[0010] Step 5) Dry the paste prepared in step 4 in a drying oven to obtain the precursor;

[0011] Step 6) Anneal the precursor prepared in step 5) in an atmospheric atmosphere to obtain NiMn2O4 thermistor powder material;

[0012] Step 7) Set the laser parameters of the laser melting equipment and determine the laser energy density that needs to be changed;

[0013] Step 8) Clean and wipe the substrate with alcohol, and then spread the NiMn2O4 powder material evenly on the substrate;

[0014] Step 9) Turn on the laser instrument and set the laser beam to scan and melt along the flat layer of thermistor powder on the substrate to obtain NiMn2O4 thermistor bulk material.

[0015] Furthermore, the purity of both NiO and MnO2 powder raw materials is above 99.99%.

[0016] Furthermore, in step 6), the annealing temperature of the NiMn2O4 thermistor powder material is 830℃-900℃, and the annealing time is 100min-140min.

[0017] Furthermore, the NiMn2O4 thermistor powder material prepared in step 6) has a spinel structure.

[0018] Furthermore, the substrate material in step 8) is stainless steel, titanium alloy, or aluminum alloy, etc.

[0019] Furthermore, the laser parameters of the laser melting equipment are as follows: laser power not exceeding 2000W, laser scanning speed not exceeding 1cm / s, scanning method being unidirectional single-scan, and powder thickness being 2mm.

[0020] Compared with existing technologies, this invention uses NiO, MnO2 powder materials and oxalic acid as raw materials to produce NiMn2O4 powder material, which is then annealed in an atmospheric atmosphere to form NiMn2O4 powder material with good crystallinity. Finally, molten bulk NiMn2O4 material is obtained on a stainless steel substrate by controlling different laser energy densities. Its advantages are as follows:

[0021] 1. This invention utilizes laser melting technology to manufacture thermistor components with complex shapes and micron-level dimensional accuracy, eliminating the need for molds or tooling and enabling free-form design and customized production. Furthermore, analysis of samples reveals that samples prepared at appropriate energy densities typically exhibit smooth surface quality and high density.

[0022] 2. The laser melting method used in this invention can prepare highly dense point-like, line-like, and planar thermistor bulk materials on various metal substrates (including titanium alloys, stainless steel, aluminum alloys, etc.). Furthermore, the dimensions of the thermistor bulk materials can achieve micrometer-level precision, making them suitable for manufacturing various thermistor components with high requirements for size and shape accuracy. Attached Figure Description

[0023] Figure 1 This is a simplified diagram illustrating the preparation of materials on a stainless steel substrate using laser melting, as part of an embodiment.

[0024] Figure 2 These are XRD patterns of the NiMn2O4 thermistor bulk materials prepared in Examples 1-4.

[0025] Figure 3 This is a surface SEM image of the NiMn2O4 thermosensitive bulk material prepared in Example 1.

[0026] Figure 4 This is a surface SEM image of the NiMn2O4 thermosensitive bulk material prepared in Example 2.

[0027] Figure 5 This is a surface SEM image of the NiMn2O4 thermosensitive bulk material prepared in Example 3.

[0028] Figure 6 This is a surface SEM image of the NiMn2O4 thermosensitive bulk material prepared in Example 4.

[0029] Figure 7 These are the temperature resistance curves and Ln(R / T)-1000 / T graphs of the NiMn2O4 thermistor bulk materials prepared in Examples 1-4.

[0030] Figure 8 These are aging performance diagrams of the NiMn2O4 thermistor bulk materials prepared in Examples 1-4. Detailed Implementation

[0031] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. To better understand the method for preparing thermosensitive bulk materials using the laser melting method of the present invention, the specific steps of the present invention will be briefly introduced first.

[0032] A method for preparing thermosensitive bulk materials by laser melting includes the following steps:

[0033] Step 1) Select nickel oxide (NiO) and manganese dioxide (MnO2) powder raw materials with a purity of 99.99% or higher. Put the NiO and MnO2 powder raw materials into a beaker, and then add alcohol and stir evenly.

[0034] Step 2) Slowly add oxalic acid solution to the beaker and stir continuously with a glass rod to prevent the generated gas from causing the material in the beaker to overflow;

[0035] Step 3) Place the beaker in an ultrasonic cleaner and vibrate and stir for 30 minutes to allow the powder raw material and oxalic acid to react fully;

[0036] Step 4) Then place the beaker in a constant temperature water bath and heat until the solution in the beaker evaporates into a paste;

[0037] Step 5) Dry the paste prepared in step 4 in a drying oven to obtain the precursor;

[0038] Step 6) Anneal the precursor prepared in step 5) in an atmospheric atmosphere at an annealing temperature of 830℃-900℃ for 100min-140min to obtain NiMn2O4 thermistor powder material.

[0039] Step 7) Set the laser parameters of the laser melting equipment. The laser power should not exceed 2000W, the laser scanning speed should not exceed 1cm / s, the scanning mode should be unidirectional single scan, the powder thickness should be 2mm, and determine the laser energy density that needs to be changed. The laser energy density is the ratio of laser power to scanning speed, scanning distance and powder thickness.

[0040] Step 8) Clean and wipe the substrate with alcohol, and then spread NiMn2O4 powder material on the substrate. The substrate material is stainless steel, titanium alloy, aluminum alloy, etc.

[0041] Step 9) Turn on the laser instrument and set the laser beam to scan and melt along the flat layer of thermistor powder on the substrate to obtain NiMn2O4 thermistor bulk material.

[0042] The preparation method of the NiMn2O4 thermosensitive bulk material of the present invention has been briefly introduced above. The following specific examples and analysis of the prepared samples are used to verify the effectiveness of the present invention.

[0043] Example 1

[0044] A chemical solution method was used to mix nickel oxide, manganese dioxide, and oxalic acid solution. After thorough reaction, the mixture was dried to obtain a precursor. This precursor was then annealed at 850°C in an atmospheric atmosphere for 120 minutes to obtain NiMn2O4 powder material with a spinel structure. Finally, the NiMn2O4 powder material was spread evenly on a stainless steel substrate and scanned and melted using a 1000W laser beam to obtain NiMn2O4 thermistor bulk material.

[0045] Example 2

[0046] A chemical solution method was used to mix nickel oxide, manganese dioxide, and oxalic acid solution. After thorough reaction, the mixture was dried to obtain a precursor. This precursor was then annealed at 850°C in an atmospheric atmosphere for 120 minutes to obtain NiMn2O4 powder material with a spinel structure. Finally, the NiMn2O4 powder material was spread evenly on a stainless steel substrate and scanned and melted using a 1200W laser beam to obtain NiMn2O4 thermistor bulk material.

[0047] Example 3

[0048] A chemical solution method was used to mix nickel oxide, manganese dioxide, and oxalic acid solution. After thorough reaction, the mixture was dried to obtain a precursor. This precursor was then annealed at 850°C in an atmospheric atmosphere for 120 minutes to obtain NiMn2O4 powder material with a spinel structure. Finally, the NiMn2O4 powder material was spread evenly on a stainless steel substrate and scanned and melted using a 1500W laser beam to obtain NiMn2O4 thermistor bulk material.

[0049] Example 4

[0050] A chemical solution method was used to mix nickel oxide, manganese dioxide, and oxalic acid solution. After thorough reaction, the mixture was dried to obtain a precursor. This precursor was then annealed at 850°C in an atmospheric atmosphere for 120 minutes to obtain NiMn₂O₄ powder material with a spinel structure. Finally, the NiMn₂O₄ powder material was spread evenly on a stainless steel substrate and scanned and melted using a 2000W laser beam to obtain NiMn₂O₄ thermistor bulk material.

[0051] The four samples prepared in Examples 1-4 were analyzed using X-ray diffraction and scanning electron microscopy. The results are shown in the figure. Figure 2-7 See Table 1.

[0052] Figure 2 The results showed that the peaks of all four samples were of the spinel phase NiMn2O4 with good crystallinity, and no diffraction peaks of other impurity phases were observed. The main diffraction peak orientations were (311), (400), (422), (511), and (440), with the characteristic peak (400) being the strongest at a laser power of 2000W.

[0053] Figure 3-6 The results showed that when the laser power was 1500W, the sample surface corresponding to Example 3 was smooth and free of pores, exhibiting higher density. Other samples, however, showed defects such as pores and cracks. This is because when the laser power is too low, the amount of liquid formed by the melting of the powder material decreases, resulting in a high concentration of the liquid-solid mixture, which hinders liquid flow and particle rearrangement. Consequently, adjacent spherical powder materials are not effectively bonded, and molten pores and spheroidization are prone to occur during scanning. Furthermore, excessive laser power leads to a large temperature gradient; the extremely high temperature gradient and the thermal shock effect of the laser cause internal stress in the sample, resulting in surface cracks and reduced density.

[0054] Figure 7 The results in Table 1 show that the resistance values ​​of the four samples decrease with increasing temperature, consistent with the characteristics of NTC thermistors. The Ln(R) of the four samples exhibits a linear relationship with 1000 / T, demonstrating a typical small polaron hopping mechanism. Furthermore, the B value is highest at a laser power of 1500W, indicating the best electrical performance. Overall, the electrical performance of the samples is enhanced.

[0055] Figure 8 The graph shows the aging performance parameters of four samples annealed at 125℃ for 600 hours. It can be seen that the aging performance is best at a laser power of 1500W, with a failure rate of only about 10%. The poor aging performance of the other three samples can be attributed to their poor densification. A dense microstructure can stabilize the distribution of cations and inhibit the oxidation and diffusion of cation vacancies between grains and grain boundaries. The poor microstructure of the other three samples enhances atmospheric oxygen adsorption, leading to increased Mn content on the tetrahedra. 2+ It is easily oxidized to Mn 3+ This makes the structure of cation distribution unstable and easier to migrate, resulting in poor aging performance.

[0056] The method of this invention can obtain bulk NiMn2O4 thermistor material; the obtained sample has good crystallinity, good density and excellent electrical properties.

[0057] Table 1. Electrical performance parameters of the NiMn2O4 thermistor bulk materials prepared in Examples 1-4

[0058] Power / W <![CDATA[R 315 (MΩ)]]> <![CDATA[R 345 (MΩ)]]> <![CDATA[B 315 / 345 (K)]]> <![CDATA[E a (eV)]]> 1000 5.5 2.37 3049.6 0.6746 1200 4.95 2.18 29707. 0.6571 1500 6.52 2.55 3400.7 0.7523 2000 1.76 0.72 3237.9 0.7162

[0059] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing thermosensitive bulk materials by laser melting, characterized in that: Includes the following steps: Step 1) Place the NiO and MnO2 powder raw materials into a beaker, then add alcohol and stir until homogeneous; Step 2) Slowly add oxalic acid solution to the beaker while continuously stirring with a glass rod; Step 3) Place the beaker in an ultrasonic cleaner and vibrate and stir for 30 minutes to allow the powder raw materials and oxalic acid to react fully; Step 4) Then place the beaker in a constant temperature water bath and heat until the solution in the beaker evaporates into a paste; Step 5) Dry the paste prepared in step 4 in a drying oven to obtain the precursor; Step 6) Anneal the precursor prepared in step 5) in an atmospheric atmosphere to obtain NiMn2O4 thermistor powder material; The annealing temperature of NiMn2O4 thermistor powder material is 830℃-900℃, and the annealing time is 100min-140min; Step 7) Set the laser parameters of the laser melting equipment and determine the laser energy density that needs to be changed; Step 8) Clean and wipe the substrate with alcohol, and then spread the NiMn2O4 powder material evenly on the substrate; Step 9) Turn on the laser instrument and set the laser beam to scan and melt along the flat layer of thermistor powder on the substrate to obtain NiMn2O4 thermistor bulk material.

2. The method for preparing thermosensitive bulk materials by laser melting according to claim 1, characterized in that: The purity of both NiO and MnO2 powder raw materials is above 99.99%.

3. The method for preparing thermosensitive bulk materials by laser melting according to claim 2, characterized in that: The NiMn2O4 thermistor powder material prepared in step 6) has a spinel structure.

4. The method for preparing thermosensitive bulk materials by laser melting according to claim 1, characterized in that: The substrate material in step 8) is stainless steel, titanium alloy, or aluminum alloy.

5. The method for preparing thermosensitive bulk materials by laser melting according to claim 1, characterized in that: The laser parameters of the laser melting equipment are as follows: laser power not exceeding 2000W, laser scanning speed not exceeding 1cm / s, scanning method is unidirectional single scan, and powder thickness is 2mm.

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