A method for recycling waste of a positive temperature coefficient thermistor

Abstract

The present invention discloses a method for recycling waste materials of a positive temperature coefficient thermistor, comprising the following steps: mixing waste materials, carbon black and Y2O3 according to a weight ratio of 100:(0.5-1.5):(0.0005-0.0007), loading them into a ball mill and ball milling for 12 to 14 hours to obtain a mixed powder; then drying the mixed powder and carrying out sealed reduction in a reducing gas atmosphere for 2 to 3 hours; then carrying out secondary ball milling on the mixed powder, and then adding a polyvinyl alcohol solution for granulation; pressing the granulated powder into a green body with a dry pressing mold, and then carrying out high-temperature sintering to form a ceramic; spraying electrodes on the surface of the obtained ceramic, and then carrying out low-temperature sintering and curing to obtain a finished product of PTC thermistor ceramic material. The present invention overcomes the deficiencies of the prior art, effectively solves the problem of large resistance caused by secondary sintering of ceramic waste materials, and enables the secondary sintered resistance to return to the level of primary sintering.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic materials, and particularly relates to a method for recycling waste materials of a positive temperature coefficient thermistor. Background Art

[0002] PTC ceramics generally refer to thermistor materials or components with a positive resistance temperature coefficient. PTC ceramics have the advantages of temperature sensitivity, energy saving, no open flame, and safety, and have been widely used in fields such as automobiles, household appliances, communications, and automatic control. The heater made with PTC as the constant temperature heating element has high reliability and safety, and the heat generation can be automatically adjusted according to the ambient temperature. In fields such as current limiting and temperature sensing, due to the unique characteristic of the sudden jump of the PTC resistance with temperature change, these devices have the characteristics of small volume, simple structure, and high reliability.

[0003] The resistance of PTC is determined by the concentration of free electrons and oxygen vacancies; among them, oxygen vacancies will be supplemented by oxygen in the atmosphere during the sintering cooling process. The fired PTC ceramics themselves have undergone a primary oxygen supplementation during the sintering cooling process; the waste materials need to be sintered twice and then undergo another oxygen supplementation, which will greatly reduce the concentration of oxygen vacancies, resulting in the resistance of the PTC ceramics fired from the waste materials reaching as high as megaohms and being unusable. Summary of the Invention

[0004] In view of the deficiencies of the prior art, the present invention provides a method for recycling waste materials of a positive temperature coefficient thermistor, which overcomes the deficiencies of the prior art and effectively solves the problem of high resistance caused by the secondary sintering of ceramic waste materials, enabling the resistance after secondary sintering to return to the level of primary sintering.

[0005] To achieve the above objectives, the present invention is realized through the following technical solutions:

[0006] A method for recycling waste materials of a positive temperature coefficient thermistor includes the following steps:

[0007] Step S1: Mix waste materials: carbon black: Y2O3 in a ratio of 100:(0.5 - 1.5):(0.0005 - 0.0007) according to the weight ratio of raw materials, and load them into a ball mill and ball mill for 12 - 14 hours to obtain a mixed powder; among them, the waste materials include ceramic chips with unqualified resistance and the scraps during the processing of ceramic chips.

[0008] Step S2: After drying the mixed powder obtained in step S1, heat it to 550 - 650 °C in a reducing gas atmosphere and perform airtight reduction for 2 - 3 hours;

[0009] Step S3: Perform secondary ball milling on the mixed powder obtained in step S2, and then add a polyvinyl alcohol solution for granulation;

[0010] Step S4: Press the granulated powder obtained in Step S3 into a green body using a dry pressing mold, and then perform high-temperature sintering to form a ceramic.

[0011] Step S5: Spray electrodes on the surface of the ceramic obtained in Step S4, and then perform low-temperature sintering and curing to obtain a finished PTC thermistor ceramic material.

[0012] Preferably, the waste material is any one or a combination of two of ceramic chips with unqualified resistance or scraps during the processing of ceramic chips.

[0013] Preferably, in Step S3, the added polyvinyl alcohol for granulation accounts for 3.0 - 12.0 wt% of the total weight of the mixed powder, and the concentration of polyvinyl alcohol is 5 - 12 wt%.

[0014] Preferably, in Step S4, the high-temperature sintering is carried out at 1200 - 1400 °C for 1 hour.

[0015] Preferably, in Step S5, the electrode spraying is printing Ag-Zn, or Al, or spraying an aluminum electrode, and the low-temperature sintering is carried out at 450 - 680 °C for low-temperature sintering, keeping warm for 10 minutes to cure the electrode.

[0016] The present invention provides a method for recycling waste materials of a positive temperature coefficient thermistor. It has the following beneficial effects: By reducing the waste materials and carbon black at 600 °C to obtain more oxygen vacancies, and by increasing the concentration of oxygen vacancies, the resistance can be effectively reduced; in addition, by using Y2O3 to replace the A site in ABO3, free electrons can be further obtained; thus effectively solving the problem of large resistance caused by secondary sintering of ceramic waste materials, enabling the secondary sintering resistance to return to the level of primary sintering; in addition, it also solves the environmental protection problem of lead in the waste materials and realizes the recycling of waste materials. Specific Embodiments

[0017] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0018] Embodiment 1, a method for recycling waste materials of a positive temperature coefficient thermistor, includes the following steps:

[0019] Step S1: Mix waste materials: carbon black: Y2O3 in a ratio of 100:(0.5 - 1.5):(0.0005 - 0.0007) according to the weight ratio of raw materials, and load them into a ball mill and ball mill for 12 - 14 hours to obtain a mixed powder; wherein, the waste materials are any one or a combination of two of ceramic chips with unqualified resistance or scraps during the processing of ceramic chips (the waste materials used in the following embodiments are the same as those in this embodiment);

[0020] Step S2: After drying the mixed powder obtained in Step S1, heat it to 550 - 650 °C in a reducing gas atmosphere and perform sealed reduction for 2 - 3 hours;

[0021] Step S3: Then perform secondary ball milling on the mixed powder obtained in Step S2, and then add a polyvinyl alcohol solution for granulation; among them, the polyvinyl alcohol added for granulation accounts for 3.0 - 12.0 wt% of the total weight of the mixed powder, and the concentration of polyvinyl alcohol is 5 - 12 wt%;

[0022] Step S4: Use a dry pressing mold to press the granulated powder obtained in Step S3 into a green body, and then perform high-temperature sintering at 1200 - 1400 °C for 1 hour to form a ceramic;

[0023] Step S5: Spray an electrode on the surface of the ceramic obtained in Step S4, and then perform low-temperature sintering and curing. Among them, the sprayed electrode is printed Ag-Zn, or Al, or a sprayed aluminum electrode, and the low-temperature sintering is performed at 450 - 680 °C for low-temperature sintering and heat preservation for 10 minutes to cure the electrode to obtain a finished product of PTC thermistor ceramic material.

[0024] In the present invention, the waste material and carbon black are reduced at 600 °C to obtain more oxygen vacancies. By increasing the oxygen vacancy concentration, the resistance can be effectively reduced; in addition, by using Y2O3 to replace the A site in ABO3, and doping NbO5 in the original ceramic waste material to replace the B site in ABO3, on the basis of obtaining free electrons, more free electrons can be further obtained; thus effectively solving the problem of large resistance caused by secondary sintering of ceramic waste, and enabling the secondary sintering resistance to return to the level of primary sintering.

[0025] In addition, due to the problem of the existence of lead in the waste material after the product is sintered (the product sintering reaction formula is: 85BaCO3 + 15PbO + 100TiO2 = 85BaPbTiO3 + 15PbTiO3 + 85CO2↑), therefore, after grinding its surface, the ground waste material is a hazardous waste solid of BaTiO3 and PbTiO3. However, in the present invention, by activating the waste material, carbon black and Y2O3 in a certain manner, it can be reused to make a product that meets the functions; through this recycling process, the environmental protection problem of lead-containing solid waste is also effectively solved.

[0026] Example Two

[0027] Mix 100 g of waste material and 0.5 g of carbon black, load them into a ball mill and ball mill for 12 hours to obtain a mixed powder; then dry the mixed powder and carry out airtight reduction for 2 hours in a reducing gas atmosphere at 600 °C; conduct secondary ball milling, and then add a polyvinyl alcohol solution for granulation, wherein the polyvinyl alcohol added for granulation accounts for 8 wt% of the total weight of the mixed powder, and the concentration of the polyvinyl alcohol is 8 wt%.

[0028] Press the granulated powder obtained with a dry pressing mold into a green body, and then carry out high-temperature sintering at 1350 °C for 1 hour to form a ceramic; spray electrodes on the surface of the obtained ceramic, and then carry out low-temperature sintering at 500 °C for 10 minutes to cure the electrodes to obtain a finished PTC thermistor ceramic material.

[0029] Example 3

[0030] Mix 100 g of waste material and 1.0 g of carbon black, load them into a ball mill and ball mill for 12 hours to obtain a mixed powder; then dry the mixed powder and carry out airtight reduction for 2 hours in a reducing gas atmosphere at 600 °C; conduct secondary ball milling, and then add a polyvinyl alcohol solution for granulation, wherein the polyvinyl alcohol added for granulation accounts for 8.0 wt% of the total weight of the mixed powder, and the concentration of the polyvinyl alcohol is 8 wt%.

[0031] Press the granulated powder obtained with a dry pressing mold into a green body, and then carry out high-temperature sintering at 1350 °C for 1 hour to form a ceramic; spray electrodes on the surface of the obtained ceramic, and then carry out low-temperature sintering at 500 °C for 10 minutes to cure the electrodes to obtain a finished PTC thermistor ceramic material.

[0032] Example 4

[0033] Mix 100 g of waste material and 1.5 g of carbon black, load them into a ball mill and ball mill for 12 hours to obtain a mixed powder; then dry the mixed powder and carry out airtight reduction for 2 hours in a reducing gas atmosphere at 600 °C; conduct secondary ball milling, and then add a polyvinyl alcohol solution for granulation, wherein the polyvinyl alcohol added for granulation accounts for 8.0 wt% of the total weight of the mixed powder, and the concentration of the polyvinyl alcohol is 8 wt%.

[0034] Press the granulated powder obtained with a dry pressing mold into a green body, and then carry out high-temperature sintering at 1350 °C for 1 hour to form a ceramic; spray electrodes on the surface of the obtained ceramic, and then carry out low-temperature sintering at 500 °C for 10 minutes to cure the electrodes to obtain a finished PTC thermistor ceramic material.

[0035] Number the finished PTC thermistor ceramic materials obtained in Example 2, Example 3, and Example 4 as No. 1, No. 2, and No. 3 respectively, and conduct resistance and withstand voltage tests; the results are shown in Table 1 below:

[0036] Table 1: Influence of Carbon Black Reduction on Resistance

[0037]

[0038] It can be clearly seen from Table 1 above that by adding carbon black reduction, the corresponding PTC resistance is significantly reduced.

[0039] Example Five

[0040] Mix 100 g of waste material, 1.5 g of carbon black and 0.001 g of Y2O3, load them into a ball mill and ball mill for 12 hours to obtain a mixed powder; then dry the mixed powder and carry out sealed reduction at 600 °C in a reducing gas atmosphere for 2 hours; carry out secondary ball milling, and then add a polyvinyl alcohol solution for granulation, wherein the polyvinyl alcohol added for granulation accounts for 8 wt% of the total weight of the mixed powder, and the concentration of polyvinyl alcohol is 8 wt%.

[0041] Press the granulated powder obtained with a dry pressing mold into a green body, and then carry out high-temperature sintering at 1350 °C for 1 hour to form a ceramic; spray electrodes on the surface of the obtained ceramic, and then carry out low-temperature sintering at 500 °C for 10 minutes to cure the electrodes to obtain a finished product of PTC thermistor ceramic material.

[0042] Example Six

[0043] Mix 100 g of waste material, 1.5 g of carbon black and 0.002 g of Y2O3, load them into a ball mill and ball mill for 12 hours to obtain a mixed powder; then dry the mixed powder and carry out sealed reduction at 600 °C in a reducing gas atmosphere for 2 hours; carry out secondary ball milling, and then add a polyvinyl alcohol solution for granulation, wherein the polyvinyl alcohol added for granulation accounts for 8 wt% of the total weight of the mixed powder, and the concentration of polyvinyl alcohol is 8 wt%.

[0044] Press the granulated powder obtained with a dry pressing mold into a green body, and then carry out high-temperature sintering at 1350 °C for 1 hour to form a ceramic; spray electrodes on the surface of the obtained ceramic, and then carry out low-temperature sintering at 500 °C for 10 minutes to cure the electrodes to obtain a finished product of PTC thermistor ceramic material.

[0045] Example Seven

[0046] Mix 100 g of waste material, 1.5 g of carbon black and 0.003 g of Y2O3, load them into a ball mill and ball mill for 12 hours to obtain a mixed powder; then dry the mixed powder and carry out sealed reduction at 600 °C in a reducing gas atmosphere for 2 hours; carry out secondary ball milling, and then add a polyvinyl alcohol solution for granulation, wherein the polyvinyl alcohol added for granulation accounts for 8 wt% of the total weight of the mixed powder, and the concentration of polyvinyl alcohol is 8 wt%.

[0047] The granulated powder obtained by a dry pressing die is pressed into a green body, and then sintered at a high temperature of 1350 °C for 1 hour to form a ceramic; an electrode is sprayed on the surface of the obtained ceramic, and then sintered at a low temperature of 500 °C for 10 minutes to cure the electrode to obtain a finished PTC thermistor ceramic material.

[0048] The finished PTC thermistor ceramic materials obtained in Example Five, Example Six and Example Seven are numbered 4, 5, and 6 respectively, and resistance and withstand voltage tests are carried out; the results are shown in Table 2 below:

[0049] Table 2: Influence of Y2O3 doping on resistance

[0050]

[0051] It can be clearly seen from Table 2 above that with the increase of the content of Y2O3 doping, the corresponding PTC resistance first decreases and then increases, and 0.2% wt is the best ratio.

[0052] Therefore, in the present invention, carbon black is added for reduction to obtain more oxygen vacancies, and by increasing the oxygen vacancy concentration, the resistance is effectively reduced; in addition, Y2O3 is used to replace the A site in ABO3, so that free electrons can be further obtained; thus, the problem of high resistance caused by the secondary sintering of ceramic waste is effectively solved, enabling the secondary sintering resistance to return to the level of primary sintering; in addition, the environmental protection problem caused by the lead content in the waste is also solved, and the recycling of the waste is realized.

[0053] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for recycling waste of a positive temperature coefficient thermistor, characterized in that: It includes the following steps: Step S1: Mix three raw materials, namely waste materials, carbon black and Y2O3, according to a weight ratio of 100:(0.5 - 1.5):(0.0005 - 0.003), load them into a ball mill and ball mill for 12 - 14 hours to obtain a mixed powder; Step S2: After drying the mixed powder obtained in Step S1, raise the temperature to 550 - 650 °C in a reducing gas atmosphere and perform airtight reduction for 2 - 3 hours; Step S3: Perform secondary ball milling on the mixed powder obtained in Step S2, and then add a polyvinyl alcohol solution for granulation; Step S4: Use a dry pressing mold to press the granulated powder obtained in Step S3 into a green body, and then perform high-temperature sintering to form a ceramic; Step S5: Spray or print electrodes on the surface of the ceramic obtained in Step S4, and then perform low-temperature sintering and curing to obtain a finished PTC thermistor ceramic material.

2. The waste recycling method of a positive temperature coefficient thermistor according to claim 1, characterized in that: The waste materials are any one or a combination of two of ceramic chips with unqualified resistance or scraps during the processing of ceramic chips.

3. A method for recycling waste of a positive temperature coefficient thermistor according to claim 1, characterized in that: In Step S3, the polyvinyl alcohol added for granulation accounts for 3.0 - 12.0 wt% of the total weight of the mixed powder, and the concentration of polyvinyl alcohol is 5 - 12 wt%.

4. A method for recycling waste materials of a positive temperature coefficient thermistor according to claim 1, characterized in that: In Step S4, the high-temperature sintering is carried out at 1200 - 1400 °C for 1 hour.

5. A method for recycling waste materials of a positive temperature coefficient thermistor according to claim 1, characterized in that: In Step S5, the sprayed electrode is an aluminum-sprayed electrode, and the low-temperature sintering is carried out at 450 - 680 °C, with heat preservation for 10 minutes to cure the electrode.

6. A method for recycling waste materials of a positive temperature coefficient thermistor according to claim 1, characterized in that: In Step S5, the printed electrode is printed with Ag-Zn or Al, and the low-temperature sintering is carried out at 450 - 680 °C, with heat preservation for 10 minutes to cure the electrode.

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