A linear negative temperature coefficient thermistor material and a preparation method thereof

Abstract

The application relates to a linear negative temperature coefficient thermistor material. The material takes graphene oxide and a manganese-cobalt-nickel system transition metal oxide as a base material, is doped with urea, melamine, dicyandiamide, thiourea, boric acid or sodium borohydride, and is obtained by hydrothermal synthesis to have the linear negative temperature coefficient thermistor material. The material has obvious NTC performance, and the resistance value thereof changes with temperature in a linear manner. The preparation steps are simple, the process is safe, the cost is low, the performance is stable, and the material is easy to popularize in the industrial field. The material overcomes the process of realizing the compensation of electrical parameters from nonlinearity to linearity by complicated design of a circuit part in the application process of an existing nonlinear thermistor device, and has a larger TCR value compared to a linear negative temperature coefficient thermistor material obtained by only doping modification, and has a good application prospect in the temperature sensing field.

Description

Technical Field

[0001] This invention relates to a linear negative temperature coefficient thermistor material and its preparation method. Background Technology

[0002] In modern society, the importance of accurate temperature measurement and control is self-evident. NTC thermistors, due to their good stability, high sensitivity, simple manufacturing process, and low cost, are currently the most commonly used temperature sensing elements. Most NTC thermistors are made of transition metal composite oxides composed of Mn, Co, Ni, etc., and their resistance-temperature characteristics are non-linear. In practical applications, they first need to be compensated by connecting them in series and parallel with general resistors to linearize them, making their resistance-temperature characteristics linear within a certain temperature range. This process not only increases the complexity of the circuit but also narrows the operating temperature range. To expand the linear temperature range, engineers generally need to use multiple thermistors and "multi-element linearizers" to form a complex linear network, which makes the circuit even more complex.

[0003] To further address existing problems, researchers have undertaken the research and development of linear thermistors. When used for temperature control, the linear thermistor has the same sensitivity at each control point, eliminating the need for proportional adjustments. When used for temperature compensation, the linear thermistor functions the same as the compensated element, enabling wide-range compensation. When used for temperature measurement, the measurement results from the linear thermistor can be compared with a calibration table to ensure uniform dial markings, significantly reducing process complexity and improving reliability.

[0004] Graphene materials have been found to have good NTC thermistor properties in recent years, and their resistance value decreases with increasing temperature [1]. This is mainly due to the thermal excitation of charge carriers inside the graphene material. When graphene is in a high-temperature environment, the internal thermal energy of the material increases, the limited jump of charge carriers from graphene sheets to sheets and the tunneling migration of charge carriers between adjacent reduced graphene oxide sheets increase, because the possibility of charge carriers overcoming the potential barrier is higher. Therefore, the mobility of charge carriers inside the material increases significantly, thus giving the material a smaller resistance value. Conversely, when graphene materials are in a low-temperature environment, the internal carrier mobility decreases, resulting in a larger resistance value of the material. Usually, researchers control the electrical properties of graphene by chemically modifying the functional groups on the surface of graphene. Among these methods, heteroatom doping is one of the effective methods to regulate the electronic structure of graphene. However, studies have found that although modifying graphene materials can indeed obtain NTC thermistors with high linearity, the temperature coefficient of resistance (TCR) of the material is still too low, thus limiting the wide application of the material in the field of temperature detection.

[0005] References:

[0006] [1] Kong Wenwen, Zhu Jianpeng, Chen Long, Chang Aimin. A method for preparing boron, nitrogen and sulfur ternary doped reduced graphene oxide material [P]. 202111343276.6, 2021-11-13.

[0007] Based on this, this invention proposes a hydrothermal method to composite graphene materials with high linearity and transition metal oxide materials with high sensitivity. Utilizing the cocktail effect and synergistic effect of the composite materials, a linear NTC thermistor material with a high TCR value is obtained. This method is simple, low-cost, and suitable for large-scale production. Summary of the Invention

[0008] The present invention aims to provide a linear negative temperature coefficient (TCR) thermistor material and its preparation method. This material uses graphene oxide and transition metal oxide powders as base materials, and urea, melamine, dicyandiamide, thiourea, boric acid, and sodium borohydride as dopants. The synthesis is achieved through hydrothermal treatment. The dopants are added to deionized water to form a solution, followed by the addition of graphene oxide powder. The resulting solution, after stirring, is mixed with the transition metal oxide powder and placed in a hydrothermal synthesis reactor for hydrothermal treatment, thereby obtaining a linear negative temperature coefficient thermistor material composed of metal oxides and doped graphene. The procedure is simple, the experimental operation is safe, and the preparation cost is low, yet the material exhibits superior performance. The synthesized linear negative temperature coefficient thermistor material displays a lower resistance value. When applied to the field of temperature sensing, the temperature-resistance relationship shows a clear linear relationship, and it has a larger TCR value. It can be widely used in the field of temperature sensing.

[0009] The present invention discloses a linear negative temperature coefficient thermistor material, which is based on graphene oxide and transition metal oxides, and synthesized by a hydrothermal method using urea, melamine, dicyandiamide, thiourea, boric acid or sodium borohydride as dopants. The specific operation is carried out according to the following steps:

[0010] Pretreatment of graphene oxide and transition metal oxide powders:

[0011] a. Graphene oxide is prepared by a modified Hummer method. The prepared graphene oxide is a brown viscous liquid. After freeze-drying for 10-30 hours, it is placed in a mortar and ground for 10-30 minutes to obtain fine and uniform graphene oxide powder for later use.

[0012] b. Pass the transition metal oxide powders MnNi2O4, CoMn2O4, NiMn2O4 or MnCo2O4 through a 200-400 mesh sieve;

[0013] Hydrothermal preparation of composite materials:

[0014] c. Place the dopant urea, melamine, dicyandiamide, thiourea, boric acid, or sodium borohydride in a beaker, add deionized water, and magnetically stir at room temperature for 15-30 minutes to obtain a colorless and transparent solution; then add the graphene oxide powder obtained in step a, and magnetically stir for 20-60 minutes; then add the transition metal oxide powder obtained in step b, and magnetically stir at room temperature for 15-30 minutes to obtain a suspension; wherein the mass ratio of graphene oxide, dopant, and transition metal oxide powder is 1:1-50:1-70.

[0015] d. Transfer the suspension obtained in step c to a hydrothermal synthesis reactor, place it in an oven, set the hydrothermal temperature to 100-300℃, and set the reaction time to 5-30h.

[0016] e. After the hydrothermal reaction is completed, wait for the reactor to cool to room temperature, then remove the reactants and filter them. During the filtration process, wash with deionized water 3-9 times, with a water volume of 5-10 ml each time. Then wash with anhydrous ethanol 2-6 times, with anhydrous ethanol volume of 1-5 ml each time. After the filtration operation is completed, place the product in a vacuum drying oven and dry it at a temperature of 60-120℃ to obtain the linear negative temperature coefficient thermistor material.

[0017] A method for preparing a linear negative temperature coefficient thermistor material, using graphene oxide and transition metal oxides as base materials and urea, melamine, dicyandiamide, thiourea, boric acid, or sodium borohydride as dopants, is synthesized via a hydrothermal method. The specific operation is carried out according to the following steps:

[0018] Pretreatment of graphene oxide and transition metal oxide powders:

[0019] a. Graphene oxide is prepared by a modified Hummer method. The prepared graphene oxide is a brown viscous liquid. After freeze-drying for 10-30 hours, it is placed in a mortar and ground for 10-30 minutes to obtain fine and uniform graphene oxide powder for later use.

[0020] b. Pass the transition metal oxide powders MnNi2O4, CoMn2O4, NiMn2O4 or MnCo2O4 through a 200-400 mesh sieve;

[0021] Hydrothermal preparation of composite materials:

[0022] c. Place the dopant urea, melamine, dicyandiamide, thiourea, boric acid, or sodium borohydride in a beaker, add deionized water, and magnetically stir at room temperature for 15-30 minutes to obtain a colorless and transparent solution; then add the graphene oxide powder obtained in step a, and magnetically stir for 20-60 minutes; then add the transition metal oxide powder obtained in step b, and magnetically stir at room temperature for 15-30 minutes to obtain a suspension; wherein the mass ratio of graphene oxide, dopant, and transition metal oxide powder is 1:1-50:1-70.

[0023] d. Transfer the suspension obtained in step c to a hydrothermal synthesis reactor, place it in an oven, set the hydrothermal temperature to 100-300℃, and set the reaction time to 5-30h.

[0024] e. After the hydrothermal reaction is completed, wait for the reactor to cool to room temperature, then remove the reactants and filter them. During the filtration process, wash with deionized water 3-9 times, with a water volume of 5-10 ml each time. Then wash with anhydrous ethanol 2-6 times, with anhydrous ethanol volume of 1-5 ml each time. After the filtration operation is completed, place the product in a vacuum drying oven and dry it at a temperature of 60-120℃ to obtain the linear negative temperature coefficient thermistor material.

[0025] The linear negative temperature coefficient (TCR) thermistor material and its preparation method provided by this invention are simple to prepare, safe to prepare, and inexpensive, yet the material exhibits superior performance. The synthesized composite material displays an even lower resistance value. When applied to the field of temperature sensing, its temperature-resistance relationship is linear, resulting in a larger TCR value, and it can be widely used in temperature sensing applications.

[0026] This invention discloses a linear negative temperature coefficient (TCR) thermistor material and its preparation method. The material is synthesized using a hydrothermal method, resulting in a linear negative temperature coefficient thermistor material with low resistivity and high carrier mobility. When used in temperature sensing, this material overcomes the need for complex circuit design in existing nonlinear thermistor devices to achieve linear electrical parameters through nonlinear compensation. Furthermore, compared to reduced graphene oxide obtained through mere doping modification, this material exhibits a higher TCR value, thus showing promising application prospects in temperature sensing. Attached Figure Description

[0027] Figure 1 A scanning electron microscope (SEM) image of the composite material prepared in Example 1 of the present invention;

[0028] Figure 2 X-ray diffraction (XRD) image of the composite material prepared in Example 2 of this invention;

[0029] Figure 3 The resistance-temperature relationship of the composite material MnNi2O4 / N-rGO prepared in Example 3 of this invention in the temperature range of 20-80℃ is shown.

[0030] Figure 4 The resistance-temperature relationship of the composite material MnNi2O4 / N-rGO prepared in Example 3 of this invention is shown in the temperature range of 35-37.5℃. Detailed Implementation

[0031] The present invention and its effective technical effects will be further described in detail below with reference to the embodiments and accompanying drawings. However, the implementation of the invention is not limited thereto. Any modifications or equivalent substitutions to the technical solutions of the present invention that do not depart from the spirit and scope of the technical solutions of the present invention should be covered within the protection scope of the present invention.

[0032] Example 1

[0033] Pretreatment of graphene oxide and transition metal oxide powders:

[0034] a. Graphene oxide was prepared using a modified Hummer method. The prepared graphene oxide was a brown viscous liquid. After freeze-drying for 10 hours, it was placed in a mortar and ground for 10 minutes to obtain fine and uniform graphene oxide powder for later use.

[0035] b. Pass the transition metal oxide MnNi2O4 powder through a 200-mesh sieve;

[0036] Hydrothermal preparation of composite materials:

[0037] c. Place the dopant urea in a beaker, add deionized water, and magnetically stir at room temperature for 15 minutes to obtain a colorless and transparent solution; then add the graphene oxide powder obtained in step a, and magnetically stir for 20 minutes; then add the transition metal oxide MnNi2O4 powder obtained in step b, and magnetically stir at room temperature for 15 minutes to obtain a suspension; wherein the mass ratio of graphene oxide, dopant, and transition metal oxide MnNi2O4 powder is 1:30:5.

[0038] d. Transfer the suspension obtained in step c to a hydrothermal synthesis reactor, place it in an oven, set the hydrothermal temperature to 100℃, and set the reaction time to 5h.

[0039] e. After the hydrothermal reaction is completed, the reaction vessel is cooled to room temperature. The reactants are then removed and filtered. During the filtration process, the product is washed three times with deionized water, each time using 5 ml of water. Then, it is washed twice with anhydrous ethanol, each time using 1 ml of anhydrous ethanol. After the filtration operation is completed, the product is placed in a vacuum drying oven and dried at 60°C to obtain the linear negative temperature coefficient thermistor material.

[0040] Example 2

[0041] Pretreatment of graphene oxide and transition metal oxide powders:

[0042] a. Graphene oxide was prepared using a modified Hummer method. The prepared graphene oxide was a brown viscous liquid. After freeze-drying for 15 hours, it was placed in a mortar and ground for 15 minutes to obtain fine and uniform graphene oxide powder for later use.

[0043] b. Pass the transition metal oxide CoMn2O4 powder through a 250-mesh sieve;

[0044] Hydrothermal preparation of composite materials:

[0045] c. Place the dopant melamine in a beaker, add deionized water, and magnetically stir at room temperature for 20 minutes to obtain a colorless and transparent solution; then add the graphene oxide powder obtained in step a, and magnetically stir for 60 minutes; then add the transition metal oxide CoMn2O4 powder obtained in step b, and magnetically stir at room temperature for 20 minutes to obtain a suspension; wherein the mass ratio of graphene oxide, dopant, and transition metal oxide CoMn2O4 powder is 1:1:1.

[0046] d. Transfer the suspension obtained in step c to a hydrothermal synthesis reactor, place it in an oven, set the hydrothermal temperature to 150℃, and set the reaction time to 10h.

[0047] e. After the hydrothermal reaction is completed, the reaction vessel is cooled to room temperature. The reactants are then removed and filtered. During the filtration process, the product is washed five times with deionized water, using 8 ml of water each time. Then, it is washed three times with anhydrous ethanol, using 2 ml of anhydrous ethanol each time. After the filtration is completed, the product is placed in a vacuum drying oven and dried at 0°C to obtain the linear negative temperature coefficient thermistor material.

[0048] Example 3

[0049] Pretreatment of graphene oxide and transition metal oxide powders:

[0050] a. Graphene oxide was prepared using a modified Hummer method. The prepared graphene oxide was a brown viscous liquid. After being freeze-dried for 20 hours, it was placed in a mortar and ground for 20 minutes to obtain fine and uniform graphene oxide powder for later use.

[0051] b. Pass the transition metal oxide NiMn2O4 powder through a 300-mesh sieve;

[0052] Hydrothermal preparation of composite materials:

[0053] c. Place the dopant dicyandiamide in a beaker, add deionized water, and magnetically stir at room temperature for 25 minutes to obtain a colorless and transparent solution; then add the graphene oxide powder obtained in step a, and magnetically stir for 30 minutes; then add the transition metal oxide NiMn2O4 powder obtained in step b, and magnetically stir at room temperature for 30 minutes to obtain a suspension; wherein the mass ratio of graphene oxide, dopant, and transition metal oxide powder is 1:10:20.

[0054] d. Transfer the suspension obtained in step c to a hydrothermal synthesis reactor, place it in an oven, set the hydrothermal temperature to 250℃, and the reaction time to 25h.

[0055] e. After the hydrothermal reaction is completed, the reaction vessel is cooled to room temperature. The reactants are then removed and filtered. During the filtration process, the product is washed 6 times with deionized water, with 10 ml of water used each time. After that, it is washed 4 times with anhydrous ethanol, with 3 ml of anhydrous ethanol used each time. After the filtration operation is completed, the product is placed in a vacuum drying oven and dried at a temperature of 70°C to obtain the linear negative temperature coefficient thermistor material.

[0056] Example 4

[0057] Pretreatment of graphene oxide and transition metal oxide powders:

[0058] a. Graphene oxide was prepared using a modified Hummer method. The prepared graphene oxide was a brown viscous liquid. After being freeze-dried for 30 hours, it was placed in a mortar and ground for 30 minutes to obtain fine and uniform graphene oxide powder for later use.

[0059] b. Pass the transition metal oxide MnCo2O4 powder through a 400-mesh sieve;

[0060] Hydrothermal preparation of composite materials:

[0061] c. Place the dopant thiourea in a beaker, add deionized water, and magnetically stir at room temperature for 30 minutes to obtain a colorless and transparent solution; then add the graphene oxide powder obtained in step a, and magnetically stir for 50 minutes; then add the transition metal oxide MnCo2O4 powder obtained in step b, and magnetically stir at room temperature for 30 minutes to obtain a suspension; wherein the mass ratio of graphene oxide, dopant, and transition metal oxide MnCo2O4 powder is 1:40:50.

[0062] d. Transfer the suspension obtained in step c to a hydrothermal synthesis reactor, place it in an oven, set the hydrothermal temperature to 180℃, and set the reaction time to 30h.

[0063] e. After the hydrothermal reaction is completed, the reaction vessel is cooled to room temperature. The reactants are then removed and filtered. During the filtration process, the product is washed 7 times with deionized water, with 10 ml of water used each time. After that, it is washed 6 times with anhydrous ethanol, with 5 ml of anhydrous ethanol used each time. After the filtration operation is completed, the product is placed in a vacuum drying oven and dried at 100°C to obtain the linear negative temperature coefficient thermistor material.

[0064] Example 5

[0065] Pretreatment of graphene oxide and transition metal oxide powders:

[0066] a. Graphene oxide was prepared using a modified Hummer method. The prepared graphene oxide was a brown viscous liquid. After freeze-drying for 18 hours, it was placed in a mortar and ground for 30 minutes to obtain fine and uniform graphene oxide powder for later use.

[0067] b. Pass the transition metal oxide MnNi2O4 powder through a 200-mesh sieve;

[0068] Hydrothermal preparation of composite materials:

[0069] c. Place the dopant boric acid in a beaker, add deionized water, and magnetically stir at room temperature for 15 minutes to obtain a colorless and transparent solution; then add the graphene oxide powder obtained in step a, and magnetically stir for 60 minutes; then add the transition metal oxide MnNi2O4 powder obtained in step b, and magnetically stir at room temperature for 15 minutes to obtain a suspension; wherein the mass ratio of graphene oxide, dopant, and transition metal oxide MnNi2O4 powder is 1:50:10.

[0070] d. Transfer the suspension obtained in step c to a hydrothermal synthesis reactor, place it in an oven, set the hydrothermal temperature to 260℃, and set the reaction time to 15h.

[0071] e. After the hydrothermal reaction is completed, the reaction vessel is cooled to room temperature. The reactants are then removed and filtered. During the filtration process, the product is washed 8 times with deionized water, with 10 ml of water used each time. After that, it is washed 2 times with anhydrous ethanol, with 1 ml of anhydrous ethanol used each time. After the filtration operation is completed, the product is placed in a vacuum drying oven and dried at a temperature of 110°C to obtain the linear negative temperature coefficient thermistor material.

[0072] Example 6

[0073] Pretreatment of graphene oxide and transition metal oxide powders:

[0074] a. Graphene oxide was prepared using a modified Hummer method. The prepared graphene oxide was a brown viscous liquid. After being freeze-dried for 30 hours, it was placed in a mortar and ground for 10 minutes to obtain fine and uniform graphene oxide powder for later use.

[0075] b. Pass the transition metal oxide CoMn2O4 powder through a 400-mesh sieve;

[0076] Hydrothermal preparation of composite materials:

[0077] c. Place the dopant sodium borohydride in a beaker, add deionized water, and magnetically stir at room temperature for 30 minutes to obtain a colorless and transparent solution; then add the graphene oxide powder obtained in step a, and magnetically stir for 20 minutes; then add the transition metal oxide CoMn2O4 powder obtained in step b, and magnetically stir at room temperature for 30 minutes to obtain a suspension; wherein the mass ratio of graphene oxide, dopant, and transition metal oxide CoMn2O4 powder is 1:50:70.

[0078] d. Transfer the suspension obtained in step c to a hydrothermal synthesis reactor, place it in an oven, set the hydrothermal temperature to 200℃, and set the reaction time to 30h.

[0079] e. After the hydrothermal reaction is completed, the reaction vessel is cooled to room temperature. The reactants are then removed and filtered. During the filtration process, the product is washed 9 times with deionized water, with 10 ml of water used each time. After that, it is washed 6 times with anhydrous ethanol, with 5 ml of anhydrous ethanol used each time. After the filtration operation is completed, the product is placed in a vacuum drying oven and dried at a temperature of 120°C to obtain the linear negative temperature coefficient thermistor material.

Claims

1. A linear negative temperature coefficient thermistor material, characterized in that... This material is synthesized using a hydrothermal method with graphene oxide and transition metal oxides as base materials and urea, melamine, dicyandiamide, thiourea, boric acid, or sodium borohydride as dopants. The specific operation is carried out according to the following steps: Pretreatment of graphene oxide and transition metal oxide powders: a. Graphene oxide is prepared by a modified Hummer method. The prepared graphene oxide is a brown viscous liquid. After freeze-drying for 10-30 hours, it is placed in a mortar and ground for 10-30 minutes to obtain fine and uniform graphene oxide powder for later use. b. Pass the transition metal oxide powders MnNi2O4, CoMn2O4, NiMn2O4 or MnCo2O4 through a 200-400 mesh sieve; Hydrothermal preparation of composite materials: c. Place the dopant urea, melamine, dicyandiamide, thiourea, boric acid, or sodium borohydride in a beaker, add deionized water, and magnetically stir at room temperature for 15-30 minutes to obtain a colorless and transparent solution; then add the graphene oxide powder obtained in step a, and magnetically stir for 20-60 minutes; then add the transition metal oxide powder obtained in step b, and magnetically stir at room temperature for 15-30 minutes to obtain a suspension; wherein the mass ratio of graphene oxide, dopant, and transition metal oxide powder is 1:1-50:1-70. d. Transfer the suspension obtained in step c to a hydrothermal synthesis reactor, place it in an oven, set the hydrothermal temperature to 100-300℃, and set the reaction time to 5-30h. e. After the hydrothermal reaction is completed, wait for the reactor to cool to room temperature, then remove the reactants and filter them. During the filtration process, wash with deionized water 3-9 times, with a water volume of 5-10 ml each time. Then wash with anhydrous ethanol 2-6 times, with anhydrous ethanol volume of 1-5 ml each time. After the filtration operation is completed, place the product in a vacuum drying oven and dry it at a temperature of 60-120℃ to obtain the linear negative temperature coefficient thermistor material.

2. A method for preparing a linear negative temperature coefficient thermistor material, characterized in that... This method uses graphene oxide and transition metal oxides as base materials, and urea, melamine, dicyandiamide, thiourea, boric acid, or sodium borohydride as dopants. It employs a hydrothermal synthesis method, and the specific operation is carried out according to the following steps: Pretreatment of graphene oxide and transition metal oxide powders: a. Graphene oxide is prepared by a modified Hummer method. The prepared graphene oxide is a brown viscous liquid. After freeze-drying for 10-30 hours, it is placed in a mortar and ground for 10-30 minutes to obtain fine and uniform graphene oxide powder for later use. b. Pass the transition metal oxide powders MnNi2O4, CoMn2O4, NiMn2O4 or MnCo2O4 through a 200-400 mesh sieve; Hydrothermal preparation of composite materials: c. Place the dopant urea, melamine, dicyandiamide, thiourea, boric acid, or sodium borohydride in a beaker, add deionized water, and magnetically stir at room temperature for 15-30 minutes to obtain a colorless and transparent solution; then add the graphene oxide powder obtained in step a, and magnetically stir for 20-60 minutes; then add the transition metal oxide powder obtained in step b, and magnetically stir at room temperature for 15-30 minutes to obtain a suspension; wherein the mass ratio of graphene oxide, dopant, and transition metal oxide powder is 1:1-50:1-70. d. Transfer the suspension obtained in step c to a hydrothermal synthesis reactor, place it in an oven, set the hydrothermal temperature to 100-300℃, and set the reaction time to 5-30h. e. After the hydrothermal reaction is completed, wait for the reactor to cool to room temperature, then remove the reactants and filter them. During the filtration process, wash with deionized water 3-9 times, with a water volume of 5-10 ml each time. Then wash with anhydrous ethanol 2-6 times, with anhydrous ethanol volume of 1-5 ml each time. After the filtration operation is completed, place the product in a vacuum drying oven and dry it at a temperature of 60-120℃ to obtain the linear negative temperature coefficient thermistor material.

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