A varistor dielectric material and a preparation method thereof

Abstract

The present application relates to the technical field of preparation of varistor dielectric materials, and specifically to a varistor dielectric material and a preparation method thereof, the method comprising: mixing the raw materials of the varistor dielectric material, and ball milling, drying, and stirring to obtain a spray slurry, and then spray drying to obtain a powder; filling the powder into a customized mold for dry pressing, placing it in a muffle furnace, heating it sequentially to a preset temperature range at different stage rates, and then keeping it warm, and discharging polyvinyl alcohol; placing the zinc oxide varistor green body after debinding in a high-temperature sintering furnace, and obtaining the heating power of the heater by analyzing the temperature distribution in the high-temperature sintering furnace, so that the zinc oxide varistor green body is evenly heated, and the temperature is raised to the sintering temperature to obtain the varistor dielectric material. The present application aims to ensure the uniformity of the microstructure of the varistor dielectric material.

Description

Technical Field

[0001] The present application relates to the technical field of varistor dielectric material preparation, and in particular to a varistor dielectric material and a preparation method thereof. Background Art

[0002] Varistor dielectric materials are key materials for manufacturing high-performance zinc oxide varistors. As zinc oxide varistors have transient voltage suppression functions, varistors, as an important branch of functional ceramics, are mainly used to make lightning arresters, overvoltage protection devices, surge protectors, etc. Moreover, with the rapid development of the power industry, traditional zinc oxide varistors are difficult to meet the protection needs of new products, and high-performance zinc oxide varistors are more competitive in the market. At present, the dielectric materials of varistors use typical ceramic manufacturing processes. Long-term high-temperature sintering will cause the bismuth oxide in the varistor material to volatilize and diffuse, resulting in high process energy consumption and adverse effects on the electrical properties of the varistor material.

[0003] At present, the sintering temperature of varistor materials is reduced by doping B4C while avoiding complexation reaction with organic binders. However, when the temperature in the high-temperature sintering furnace rises to 500°C, the B4C doped in the zinc oxide varistor green body will undergo an oxidation reaction to generate B2O3, releasing a large amount of heat. It is impossible to accurately obtain the effect of the B4C oxidation reaction on the increase in the temperature of the zinc oxide varistor green body, which easily causes a large difference between the heater heating power and the ideal power. Summary of the invention

[0004] In order to solve the above technical problems, the present application provides a varistor dielectric material and a preparation method thereof, and the technical solutions adopted are as follows:

[0005] In a first aspect, an embodiment of the present application provides a method for preparing a varistor dielectric material, the method comprising the following steps:

[0006] S1 raw material mixing: zinc oxide is used as the main material, and the raw materials of the varistor dielectric material are mixed to form a mixture;

[0007] S2: adding dispersant, ball milling, mixing and drying: putting the mixed material into a ball mill, adding deionized water and dispersant, ball milling to obtain a mixed slurry, and drying to obtain a dried slurry;

[0008] S3 stirring, mixing and spray drying: putting the dried slurry into a stirring container, adding a binder and a defoamer, mixing evenly to obtain a spray slurry, and then spray drying to obtain a powder;

[0009] S4 prepares green body and arranges glue: fills the powder into a customized mold for dry pressing to form a green body of zinc oxide varistor; puts the green body of zinc oxide varistor into a muffle furnace, heats it to a preset temperature range in sequence according to the rate of different stages, and then keeps it warm, and discharges polyvinyl alcohol;

[0010] S5 sintering: placing the zinc oxide varistor green body after debinding in a high-temperature sintering furnace, obtaining the heating power of the heater by analyzing the temperature distribution in the high-temperature sintering furnace, and uniformly heating the zinc oxide varistor green body to the sintering temperature to obtain the varistor dielectric material; wherein, the process of obtaining the heating power of the heater includes:

[0011] Acquire green body sintering images of zinc oxide varistor green body during sintering process;

[0012] Calculate the temperature average of the green body sintering image at all times within the temperature increase adjustment interval; when the temperature average is less than a preset temperature threshold, adjust the heating power according to the expected temperature increase; otherwise, adjust the heating power according to the significance of the auxiliary temperature increase;

[0013] The process of obtaining the significance of auxiliary warming is as follows:

[0014] (1) Divide the green body sintering image into several green body regions;

[0015] (2) Prediction is performed based on a sequence consisting of the difference between the temperature mean of the same green body region at different acquisition times and the temperature mean of the green body sintering image where it is located, and the prediction result is used as the continuous significant temperature rise coefficient of the green body region;

[0016] (3) Based on the distribution of temperature values ​​of the same pixel at different acquisition times, the temperature sudden rise points are screened out; the average value of the total number of temperature sudden rise points of all pixels in the green area at different acquisition times is taken as the cumulative reaction time of the green area;

[0017] (4) The normalized value of the product of the sustained significant temperature rise coefficient and the cumulative reaction time is used to screen out the doping-enriched regions; the degree of auxiliary temperature rise significance in the temperature rise adjustment range is determined by using the chaotic distribution of the distances between the centers of the doping-enriched regions and the sustained significant temperature rise coefficients of all green body regions.

[0018] Preferably, the raw materials in the S1 raw material mixture are composed, by molar parts, of 100 parts of zinc oxide, 0.5-1.5 parts of antimony oxide, 1-2.5 parts of bismuth oxide, 0.5-1.5 parts of cobalt trioxide, 0.5-1.3 parts of manganese dioxide, 0.5-1.5 parts of chromium trioxide, 0.5-1.5 parts of silicon dioxide, 0.05-0.6 parts of silver nitrate, and 0.5-1.5 parts of boron carbide.

[0019] Preferably, the deionized water and the dispersant in the S2 adding the dispersant and performing the ball milling mixing are 1-1.5 times the total weight of the mixture, and the dispersant is polyacrylic acid amine dispersant, and the addition amount of the polyacrylic acid amine dispersant is 0.1wt%-2.0wt% of the mixture.

[0020] Preferably, the binder added in the stirring, mixing and spray drying in S3 is 10wt% of the dried slurry, and the binder is a polyvinyl alcohol solution, and the mass ratio of polyvinyl alcohol to water in the polyvinyl alcohol solution is 1:9; the defoaming agent added is 0.05wt%-1.0wt% of the dried slurry, and the defoaming agent is tributyl phosphate.

[0021] Preferably, the pressure for dry pressing in the step of preparing the green body and performing the debonding and molding in S4 is set to 8-10 MPa.

[0022] Preferably, the method for screening the temperature sudden rise point is: performing mutation point detection on the differential sequence composed of the temperature values ​​of the same pixel at different acquisition times, and taking the mutation point in the differential sequence where the element value is greater than zero as the temperature sudden rise point.

[0023] Preferably, the method for screening the impurity-enriched region is: when the normalized value is greater than a preset impurity content threshold, the green body region where the normalized value is located is regarded as the impurity-enriched region.

[0024] Preferably, the method for determining the significance of the auxiliary heating in the heating adjustment interval includes:

[0025] Calculate the standard deviation of the distances between the centers of all doping-enriched regions;

[0026] Calculate the cumulative sum of the continuous significant temperature rise coefficients of all green body regions;

[0027] The standard deviation and the cumulative sum are reversely fused to obtain the significance of the auxiliary warming in the warming adjustment range.

[0028] Preferably, the method for adjusting the heating power using the auxiliary temperature rise significance is: multiplying the reverse mapping result of the auxiliary temperature rise significance by the power value that needs to be adjusted corresponding to the expected temperature increase, and then summing it with the heating power value obtained in the last temperature rise adjustment interval to obtain the heating power.

[0029] In a second aspect, an embodiment of the present application provides a varistor dielectric material, and the dielectric material is prepared using the method for preparing a varistor dielectric material.

[0030] In the above scheme, the present application avoids the problem of low identification accuracy of doping-enriched regions when the overall temperature difference between doping-enriched regions and ordinary doping regions is small through multi-scale analysis of green regions and green region pixels at different acquisition times, improves the accuracy of distinguishing and identifying doping-enriched regions and ordinary doping regions, evaluates the B4C doping content in each green region, and improves the accuracy of subsequent analysis of the influence of B4C oxidation reaction on auxiliary heating conditions. The present application comprehensively considers the distribution of each doping-enriched region and the intensity of the oxidation reaction of each green region, accurately evaluates the auxiliary heating influence of B4C oxidation reaction, analyzes the influence of B4C oxidation reaction on the adjustment of heater heating power, obtains appropriate heater heating power, and enables the adjustment of heater heating power to adapt to the heat released by the later B4C oxidation reaction, avoiding the traditional method of only analyzing the temperature of zinc oxide varistor green body, resulting in excessive heater heating power, causing sintering temperature to rise too fast, and reducing density and electrical properties. The present application ensures uniform heating of zinc oxide varistor green body and ensures the uniformity of the microstructure of the varistor dielectric material. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present application or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0032] Figure 1 A flowchart of the steps of a method for preparing a varistor dielectric material provided in the present application;

[0033] Figure 2 A flow chart of a process for obtaining the heating power of a heater provided in Example 1 of the present application;

[0034] Figure 3 A partial schematic diagram of a green embryo sintering image provided in Example 1 of the present application;

[0035] Figure 4 A flowchart of the process of obtaining the significance of auxiliary temperature rise provided in Example 1 of the present application;

[0036] Figure 5 A schematic diagram of a uniformly distributed impurity-enriched region provided in Example 1 of the present application;

[0037] Figure 6 A schematic diagram of the unevenly distributed impurity-enriched region provided in Example 1 of the present application;

[0038] Figure 7A flow chart of a method for determining the significance of auxiliary heating in a heating adjustment interval provided in Example 1 of the present application;

[0039] Figure 8 A schematic diagram of the heating condition of the sintering process provided in Example 1 of the present application;

[0040] Fig. 9 A schematic diagram of the heating condition of the sintering process provided in Example 2 of the present application;

[0041] Fig.10 This is a schematic diagram of the temperature rise conditions of the sintering process provided in Example 3 of the present application. DETAILED DESCRIPTION

[0042] In order to further explain the technical means and effects adopted by the present application to achieve the predetermined invention purpose, the following is a detailed description of a varistor dielectric material and its preparation method proposed in the present application, its specific implementation method, structure, characteristics and effects, in combination with the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "another embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures or characteristics in one or more embodiments may be combined in any suitable form.

[0043] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0044] The specific scheme of a varistor dielectric material and a preparation method thereof provided by the present application is described in detail below with reference to the accompanying drawings.

[0045] Example 1

[0046] Example 1 provides a method for preparing a varistor dielectric material. For a preparation flow chart, please refer to Figure 1 , the specific preparation process is as follows:

[0047] S1 Raw material mixing: zinc oxide (ZnO) is used as the main material, and the raw materials of the varistor dielectric material are mixed to form a mixture. Among them, the composition of each raw material, measured by mole, is: 100 parts of zinc oxide (ZnO), 0.5 parts of antimony oxide (Sb2O3), 1.7 parts of bismuth oxide (Bi2O3), 0.5 parts of cobalt trioxide (Co2O3), 0.7 parts of manganese dioxide (MnO2), 0.9 parts of chromium trioxide (Cr2O3), 0.5 parts of silicon dioxide (SiO2), 0.05 parts of silver nitrate (AgNO3), and 0.8 parts of boron carbide (B4C).

[0048] Among them, during the sintering process, SiO2 reacts with Bi2O3 and AgNO3 to produce liquid glass, which can reduce the sintering temperature, improve the degree of structural densification, and at the same time improve the pulse tolerance of the varistor dielectric material; low-melting-point sintering aids such as boron-containing compounds such as B2O3 and H3BO3 are easy to react with organic binders to form complexes. This application utilizes B4C, which does not react with PVA solution. By introducing a low-melting-point sintering aid in the form of B4C into the raw material, low-temperature sintering of the varistor dielectric material is achieved while ensuring the stability and rheological properties of the slurry.

[0049] S2: Add dispersant, perform ball milling, mixing and drying: put the mixture into a ball mill, and add deionized water and dispersant in an amount of 1 times the total weight of the mixture, wherein the dispersant is polyacrylic acid amine dispersant, and the addition amount of the polyacrylic acid amine dispersant is 0.1wt% of the mixture, and the dispersing effect of the dispersant is used to promote uniform dispersion and mixing of the components.

[0050] The ball mill jar after adding deionized water and dispersant is placed in a ball mill for ball milling. The ball milling speed is set to 150-250 r / min, preferably 220 r / min, wherein the ball mill is reversed once every 20 minutes. The ball milling time is 40-60 minutes, preferably 40 minutes.

[0051] After the ball milling is completed, the ball mill jar is taken out to obtain a mixed slurry, and the mixed slurry is placed in an electric blast drying oven, the drying temperature is set to 100-110°C, preferably 110 degrees Celsius, the drying insulation time is set to 7-9h, preferably 8h, and the drying is completed to obtain the dried slurry.

[0052] S3 stirring, mixing and spray drying: the dried slurry is put into a stirring container, and a binder of 10 wt% of the dried slurry is added. Preferably, the binder is a PVA (polyvinyl alcohol) solution, and the mass ratio of PVA to water in the PVA solution is 1:9. Adding a binder is beneficial to the uniform distribution of the dried slurry components and helps to form spherical particle powder during subsequent spray drying.

[0053] Then add 0.05wt% of defoamer into the dried slurry to eliminate the foam generated by stirring the PVA aqueous solution to avoid difficulty in spray granulation. The defoamer is tributyl phosphate, which is stirred until mixed evenly to obtain spray slurry.

[0054] The spray slurry is sent to a centrifugal spray drying tower for spray drying, and the dried powder is granulated through an 80-100 mesh sieve.

[0055] S4 prepares green body and glues: the powder obtained by spray drying is filled into a customized mold and dry pressed by a hydraulic press, wherein the hydraulic pressure is set to 8 MPa to form a green body of zinc oxide varistor.

[0056] The zinc oxide varistor green body is placed in a muffle furnace, heated to 340-360°C at a rate of 1-3°C / min, and then heated to 400-420°C at a rate of 0.5°C / min, and kept warm for 4-6 hours to allow the added polyvinyl alcohol to slowly evaporate and be discharged.

[0057] S5 sintering: placing the zinc oxide varistor green body after debinding in a high-temperature sintering furnace, obtaining the heating power of the heater by analyzing the temperature distribution in the high-temperature sintering furnace, and uniformly heating the zinc oxide varistor green body, raising the temperature to the sintering temperature, the sintering temperature is 800-860°C, preferably 840°C, the sintering holding time is set to 60-150min, preferably 90min, and the varistor dielectric material can be obtained.

[0058] Sintering is the most important process step in preparing varistor dielectric materials. By analyzing the temperature distribution, the high-temperature sintering furnace is controlled to heat up evenly, which makes the free energy of the material in the zinc oxide varistor green body gradually decrease, the grains gradually become larger, and the structure gradually becomes dense, and finally forms the varistor dielectric material. In order to ensure that the components of the zinc oxide varistor green body heat up slowly and evenly, the application obtains the heating power of the heater by analyzing the temperature distribution in the high-temperature sintering furnace, wherein the process of obtaining the heating power of the heater includes:

[0059] In the embodiment of the present application, the process flow chart of obtaining the heating power of the heater is as shown in the attached figure. Figure 2 shown.

[0060] A1, a green body sintering image of a zinc oxide varistor green body during the sintering process.

[0061] Since the traditional temperature detection method uses thermocouple monitoring, it can only effectively monitor the temperature of the atmosphere in the furnace, and cannot measure the temperature of the zinc oxide varistor green body itself, and the thermocouple monitoring has obvious hysteresis. In the whole process of sintering, the present application uses an infrared high-temperature thermal imaging detection system to collect real-time temperature information of the zinc oxide varistor green body, and obtains the green body sintering image of the zinc oxide varistor green body. In this embodiment, the collection time interval is set to 2s, and 10min is used as the temperature adjustment interval. The temperature rise rate is adjusted once every temperature adjustment interval.

[0062] Among them, the process of collecting real-time temperature information of the zinc oxide varistor green body by using an infrared high-temperature thermal imaging detection system is a well-known technology and will not be described in detail.

[0063] In the embodiment of the present application, a partial schematic diagram of the green embryo sintering image is shown in the attached Figure 3 shown.

[0064] A2, calculate the temperature average of the green body sintering image at all times within the temperature increase adjustment interval; when the temperature average is less than the preset temperature threshold, adjust the heating power according to the expected temperature increase; otherwise, adjust the heating power according to the auxiliary temperature increase significance.

[0065] Calculate the average temperature of the green body sintering image at all times within the temperature adjustment interval. Due to the doping of B4C during the sintering process, when the green body temperature in the high-temperature sintering furnace is lower than 500°C, that is, the average green body temperature in the temperature adjustment interval is lower than 500°C, it is difficult for the doped B4C to undergo redox reaction with oxygen, and the doped B4C does not assist the green body of the zinc oxide varistor to heat up. The green body of the zinc oxide varistor heats up slowly, the sintering degree is more uniform, and it can be sintered according to the preset sintering heating rate. Therefore, in this case, the power is adjusted directly according to the expected temperature increase.

[0066] Specifically, the specific process of adjusting the heating power according to the expected temperature increase is:

[0067] Get the temperature average value. In the embodiment of the present application, the sintering heating rate is set to 60 °C / h, that is, the zinc oxide varistor green body needs to be heated by 10 °C every other temperature adjustment interval. Get the heating power value of the high temperature sintering furnace heater The expression is: ; In the formula, is the heating power value of the high temperature sintering furnace heater, is the heating power value obtained in the last temperature adjustment interval. The heating power value required to increase the green body temperature of zinc oxide varistor by 10℃. As the heating power of high temperature sintering furnace heater.

[0068] In other implementations of the embodiments of the present application, different sintering heating rates can be set, as well as the temperature of the zinc oxide varistor green body that needs to be increased in every temperature adjustment interval, which can be set by the implementer.

[0069] When the temperature of the interval green body in the high-temperature sintering furnace rises to 500℃, the B4C doped in the zinc oxide varistor green body undergoes an oxidation reaction to generate B2O3, releasing a large amount of heat. The auxiliary zinc oxide varistor green body doped with B4C heats up, which easily leads to rapid heating of the zinc oxide varistor green body and poor sintering uniformity, causing uneven changes in the microstructure and phase of the zinc oxide varistor green body, and a decrease in density and electrical properties.

[0070] Specifically, the specific process of adjusting the heating power by utilizing the auxiliary temperature rise significance is as follows:

[0071] Preferably, the reverse mapping result of the auxiliary temperature rise significance is multiplied by the power value that needs to be adjusted corresponding to the expected temperature increase, and then summed with the heating power value obtained in the previous temperature rise adjustment interval to obtain the heating power.

[0072] The larger the reverse-mapped data is, the smaller the result of the reverse mapping of the data is; the smaller the data is, the larger the result of the reverse mapping of the data is. The reverse mapping can be in the form of a reciprocal, an opposite number, or a negative exponent, without specific limitation.

[0073] In the embodiment of the present application, the auxiliary heating significance degree of the current heating adjustment interval is obtained, and the heating power value of the high temperature sintering furnace heater is The expression is: ; In the formula, It is the significance degree of auxiliary warming in this warming adjustment range.

[0074] It should be understood that when the auxiliary temperature rise is more significant, the B4C doped in the zinc oxide varistor green body can generate more heat, and the auxiliary heater is used to heat up. In order to prevent the zinc oxide varistor green body from being heated too quickly, the heating power value is The smaller.

[0075] In other implementations of the embodiments of the present application, it is also possible to use Adjust the heating power, where exp is an exponential function with the natural constant e as the base.

[0076] Specifically, in the embodiment of the present application, the process flow chart of obtaining the significant degree of auxiliary heating is as shown in the attached Figure 4 As shown, the specific process is:

[0077] (1) Divide the green body sintering image into several green body regions;

[0078] Since the doping content of B4C in the zinc oxide varistor green body may be different, preferably, the embodiment of the present application divides the green body sintering image into M green body regions. In this embodiment, the value of M is 16, which can be adjusted by the implementer in the specific implementation process.

[0079] (2) Prediction is performed based on a sequence consisting of the difference between the temperature mean of the same green body region at different acquisition times and the temperature mean of the green body sintering image where it is located, and the prediction result is used as the continuous significant temperature rise coefficient of the green body region;

[0080] B4C will undergo an oxidation reaction to generate B2O3, releasing a large amount of heat, causing the overall temperature of the green area to rise. The green area has an extremely high temperature contrast compared to the green sintering image. The higher the B4C doping content in the green area, the longer the green area can continue to heat up.

[0081] Preferably, the embodiment of the present application takes the green body region in the green body sintering image at any time as an example, and calculates the difference between the temperature mean of the green body region and the temperature mean of the green body sintering image as the regional temperature comparison value of the green body region.

[0082] The regional temperature comparison values ​​of the same green body area at all acquisition moments are sorted in ascending order according to the corresponding moments of the green body sintering image as the temperature comparison sequence of the green body area. The temperature comparison sequence of the green body area is used as the input of an exponential moving average (EMA) algorithm, where the smoothing factor of the EMA algorithm is 0.5 in this embodiment, and the predicted value of the temperature comparison sequence is output as the continuous significant temperature rise coefficient of the green body area.

[0083] It should be understood that the higher the sustained significant temperature rise coefficient is, the more intense the B4C oxidation reaction in the green area in the temperature rise adjustment interval is, and the longer the green area can continue to rise in temperature. Among them, the exponential moving average algorithm is a well-known technology and will not be described in detail. In other implementations of the embodiments of the present application, a simple moving average algorithm, a weighted moving average algorithm, etc. can also be used for sequence prediction.

[0084] (3) Based on the distribution of temperature values ​​of the same pixel at different acquisition times, the temperature sudden rise points are screened out; the average value of the total number of temperature sudden rise points of all pixels in the green area at different acquisition times is taken as the cumulative reaction time of the green area;

[0085] During the sintering process, the main way to increase the temperature is the heater inside the high-temperature sintering furnace. The heat generated by the heater is evenly distributed as a whole. The overall temperature difference between different green body areas may be small. A continuous and significant temperature increase coefficient may make it difficult to accurately identify the green body area with a high B4C doping content.

[0086] When a B4C oxidation reaction occurs in the green embryo region, a large amount of heat from the oxidation reaction is suddenly absorbed, which causes a sudden rise in the temperature of the pixels in the green embryo region. Preferably, for each pixel in the green embryo region in the green embryo sintering image, the temperature values ​​of the same pixel at all acquisition times are sorted in ascending order at the corresponding time of the green embryo sintering image to form a temperature sequence, and a first-order difference sequence of the temperature sequence is obtained. The first-order difference sequence is used as the input of the mutation point detection algorithm, and each mutation point is output. The mutation point with an element value greater than 0 in the first-order difference sequence is recorded as a temperature sudden rise point, and each temperature sudden rise point may represent a B4C oxidation reaction in the pixel.

[0087] Among them, the embodiment of the present application adopts the BG sequence segmentation algorithm to detect mutation points in the sequence. The BG sequence segmentation algorithm is a well-known technology and will not be described in detail. In other implementations of the embodiment of the present application, other methods such as Bayesian can also be used to detect mutation points in the sequence.

[0088] In other implementations of the embodiments of the present application, the element values ​​in the temperature sequence of the pixel may be segmented by thresholds, and the pixels of the elements having values ​​in the temperature sequence greater than the segmentation threshold are taken as temperature sudden rise points.

[0089] Preferably, in the embodiment of the present application, the cumulative reaction time of the mth green area is For example, the calculation formula is: ; Where X is the total number of pixels in the green area, It is the total number of temperature rise points of the x-th pixel in the m-th green area at different acquisition times.

[0090] In other implementations of the embodiments of the present application, the average value of the total number of temperature rise points of all pixels in the mth green area at different acquisition times may be used as the cumulative reaction time of the mth green area.

[0091] It should be understood that when more B4C oxidation reactions occur in each pixel in the green area, that is, The larger the value is, the longer the B4C oxidation reaction may occur in the green area, and the higher the B4C doping content in the green area may be.

[0092] (4) Using the normalized value of the product of the sustained significant temperature rise coefficient and the cumulative reaction time, the doping-enriched region is screened out; using the chaotic distribution of the distance between the centers of the doping-enriched regions and the sustained significant temperature rise coefficient of all green body regions, the significance of the auxiliary temperature rise in the temperature rise adjustment range is determined;

[0093] Based on the above analysis, the present application obtains the sustained significant temperature rise coefficient and the cumulative reaction time of each green body area. The sustained significant temperature rise coefficient reflects the severity of the B4C oxidation reaction from a time scale, and the cumulative reaction time reflects the B4C oxidation reaction time from a regional scale. The distinction between the doping-enriched area and the ordinary doping area can be further analyzed based on the sustained significant temperature rise coefficient and the cumulative reaction time.

[0094] Preferably, the normalized result of the product of the continuous significant temperature rise coefficient and the cumulative reaction time of the green body region in the embodiment of the present application is used as the significant coefficient of the doping content of the green body region, reflecting the content of B4C doped in the green body region.

[0095] The identification of whether the green body region is a doping-enriched region is achieved by a preset doping content threshold. Preferably, the green body region whose doping content significant coefficient is greater than the preset doping content threshold is recorded as a doping-enriched region, and the green body region whose doping content significant coefficient is not greater than the doping content threshold is recorded as a common doping region. The doping content threshold is 0.7 in this embodiment and can be set by the implementer according to actual conditions.

[0096] In other implementations of the present application, the significant coefficients of the impurity content of all green body regions are segmented by thresholds, and the green body regions where the significant coefficients of the impurity content are greater than the segmentation threshold are recorded as impurity-rich regions. The algorithm for performing threshold segmentation can be the Otsu method or the clustering algorithm.

[0097] Due to heat transfer, the B4C oxidation reaction will assist the heater of the high-temperature sintering furnace and synergistically increase the green body temperature of the zinc oxide varistor. The more uniform the distribution of the doping-enriched area is, the more uniform the auxiliary heating can be.

[0098] In the embodiment of the present application, a schematic diagram of a uniformly distributed dopant-enriched region is shown in the attached Figure 5 The schematic diagram of unevenly distributed impurity enrichment areas is shown in the attached Figure 6 shown.

[0099] Figure 5 The impurity-enriched regions in the are evenly distributed; Figure 6 The doping-enriched areas in the figure are unevenly distributed; the black area represents the doping-enriched area, the white area represents the common doping area, and the arrow is the schematic direction of heat transfer. The stronger the B4C oxidation reaction, the more obvious the temperature rise, and the more significant the auxiliary heating effect of the B4C oxidation reaction in the zinc oxide varistor green body.

[0100] Preferably, the standard deviation of the distances between the centers of all doping-enriched regions is calculated; the cumulative sum of the continuous significant temperature rise coefficients of all green regions is calculated; the standard deviation and the cumulative sum are reversely merged to obtain the auxiliary temperature rise significance of the temperature rise adjustment interval. The standard deviation can also be replaced by the variance.

[0101] It can be understood that reverse fusion is a fusion method such as subtraction and division between data. The specific reverse fusion method is determined by the implementer according to the actual situation, and this application does not impose any special restrictions.

[0102] In addition, in one implementation of the embodiment of the present application, the auxiliary heating significance degree of the heating adjustment interval is obtained by the following formula: : ; In the formula, is the doping uniformity, which is obtained by calculating the standard deviation of the distances between the centers of all doping-enriched regions. is the intensity of the oxidation reaction, which is obtained by calculating the cumulative sum of the continuous and significant temperature rise coefficients of all green areas. Norm is the normalization function. It is a preset parameter adjustment factor, which is used to prevent the denominator from being 0. In this embodiment, it is set to 0.01.

[0103] It should be understood that the more uniform the distribution between the doping-enriched regions, the better the doping uniformity. The smaller the value is, the more uniform the oxidation reaction of B4C in the doping-enriched area can provide heat for the green body of the zinc oxide varistor. At the same time, when the temperature of each green body area rises higher, the oxidation reaction of B4C is stronger, that is, the intensity of the oxidation reaction is The larger the value, the more significant the auxiliary heating effect of the B4C oxidation reaction in the green body of the zinc oxide varistor within the temperature adjustment range. The bigger. The larger the value, the less the heating power of the heater needs to be in order to prevent the zinc oxide varistor green body from being heated too quickly.

[0104] In the embodiment of the present application, a flow chart of a method for determining the significance of auxiliary heating in the heating adjustment interval is shown in the attached Figure 7 shown.

[0105] In the embodiment of the present application, the schematic diagram of the heating condition of the sintering process is as shown in the attached Figure 8 The temperature rise condition in the high-temperature sintering furnace obtained by using the present embodiment 1 is shown in the solid line of the present embodiment 1, and the temperature rise condition in the high-temperature sintering furnace not obtained by using the present embodiment 1 is shown in the dotted line of the comparative example 1.

[0106] Example 2

[0107] Example 2 provides a method for preparing a varistor dielectric material. For a preparation flow chart, please refer to Figure 1 , the specific preparation process is as follows:

[0108] S1 Raw material mixing: zinc oxide (ZnO) is used as the main material, and the raw materials of the varistor dielectric material are mixed to form a mixture. Among them, the composition of each raw material, measured by mole, is: 100 parts of zinc oxide (ZnO), 1.5 parts of antimony oxide (Sb2O3), 1 part of bismuth oxide (Bi2O3), 1.5 parts of cobalt trioxide (Co2O3), 1.3 parts of manganese dioxide (MnO2), 1.5 parts of chromium trioxide (Cr2O3), 1.5 parts of silicon dioxide (SiO2), 0.6 parts of silver nitrate (AgNO3), and 1.5 parts of boron carbide (B4C).

[0109] S2: adding dispersant, ball milling, mixing and drying: putting the mixture into a ball mill, adding deionized water and dispersant in an amount of 1.5 times the total weight of the mixture, wherein the dispersant is polyacrylic acid amine dispersant, and the addition amount of the polyacrylic acid amine dispersant is 1.2wt% of the mixture.

[0110] S3 stirring, mixing and spray drying: the dried slurry is put into a stirring container, and 10 wt% of a binder is added to the dried slurry, and then 1.0 wt% of a defoamer is added to the dried slurry.

[0111] S4 preparation of green body and adhesive bonding: the powder obtained by spray drying is filled into a customized mold and dry pressed by a hydraulic press, wherein the hydraulic pressure is set to 9 MPa to form a zinc oxide varistor green body.

[0112] S5 sintering: placing the zinc oxide varistor green body after debinding in a high-temperature sintering furnace, obtaining the heating power of the heater by analyzing the temperature distribution in the high-temperature sintering furnace, and uniformly heating the zinc oxide varistor green body to the sintering temperature to obtain the varistor dielectric material. The process of obtaining the heating power of the heater in this embodiment 2 is the same as that in embodiment 1.

[0113] In the embodiment of the present application, the schematic diagram of the heating condition of the sintering process is as shown in the attached Fig. 9 The temperature rise condition in the high-temperature sintering furnace obtained by using the present embodiment 2 is shown in the solid line of the present embodiment 2, and the temperature rise condition in the high-temperature sintering furnace not obtained by using the present embodiment 2 is shown in the dotted line of the comparative example 2.

[0114] Example 3

[0115] Example 3 provides a method for preparing a varistor dielectric material. For a preparation flow chart, please refer to Figure 1 , the specific preparation process is as follows:

[0116] S1 Raw material mixing: Take zinc oxide (ZnO) as the main material, and mix the raw materials of the varistor dielectric material to form a mixture. Among them, the composition of each raw material by mole is: 100 parts of zinc oxide (ZnO), 1 part of antimony oxide (Sb2O3), 2.5 parts of bismuth oxide (Bi2O3), 1 part of cobalt trioxide (Co2O3), 0.5 parts of manganese dioxide (MnO2), 0.5 parts of chromium trioxide (Cr2O3), 1 part of silicon dioxide (SiO2), 0.3 parts of silver nitrate (AgNO3), and 0.5 parts of boron carbide (B4C).

[0117] S2: adding dispersant, ball milling, mixing and drying: putting the mixture into a ball mill, adding deionized water and dispersant in an amount of 1.25 times the total weight of the mixture, wherein the dispersant is polyacrylic acid amine dispersant, and the addition amount of the polyacrylic acid amine dispersant is 2.0wt% of the mixture.

[0118] S3 stirring, mixing and spray drying: the dried slurry is put into a stirring container, and a binder of 10 wt% of the dried slurry is added, and then a defoamer of 0.07 wt% of the dried slurry is added.

[0119] S4 preparation of green body and adhesive bonding: the powder obtained by spray drying is filled into a customized mold and dry-pressed by a hydraulic press, wherein the hydraulic pressure is set to 10 MPa to form a zinc oxide varistor green body.

[0120] S5 sintering: placing the zinc oxide varistor green body after debinding in a high-temperature sintering furnace, obtaining the heating power of the heater by analyzing the temperature distribution in the high-temperature sintering furnace, and uniformly heating the zinc oxide varistor green body to the sintering temperature to obtain the varistor dielectric material. The process of obtaining the heating power of the heater in this embodiment 3 is the same as that in embodiment 1.

[0121] In the embodiment of the present application, the schematic diagram of the heating condition of the sintering process is as shown in the attached Fig.10 The temperature rise condition in the high-temperature sintering furnace obtained by using the present embodiment 3 is shown in the solid line of the present embodiment 3, and the temperature rise condition in the high-temperature sintering furnace not obtained by using the present embodiment 3 is shown in the dotted line of the comparative example 3.

[0122] Based on the above method, an embodiment of the present application further provides a varistor dielectric material, and the dielectric material is prepared using the above method for preparing a varistor dielectric material.

[0123] The various embodiments in the present application are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0124] It should be noted that, unless otherwise specified and limited, terms such as "include", "comprises" or any other variants thereof are intended to cover non-exclusive inclusion, so that a circuit structure, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such article or device. In the absence of further restrictions, an element defined by the sentence "including one..." does not exclude the existence of other identical elements in the article or device including the element. In addition, the term "and\or" used herein includes any and all combinations of one or more related listed items.

[0125] Those skilled in the art will readily appreciate other embodiments of the present application after considering the specification and practicing the invention herein. The present application is intended to cover any variations, uses or adaptations of the present application, which follow the general principles of the present application and include common knowledge or customary technical means in the art that are not invented by the present application.

[0126] It will be appreciated that the present application is not limited to the exact construction that has been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof.

Claims

1. A method for preparing a varistor dielectric material, characterized in that: The method comprises the following steps: S1 raw material mixing: zinc oxide is used as the main material, and the raw materials of the varistor dielectric material are mixed to form a mixed material; wherein the raw materials include B4C; S2: adding dispersant, ball milling, mixing and drying: putting the mixed material into a ball mill, adding deionized water and dispersant, ball milling to obtain a mixed slurry, and drying to obtain a dried slurry; S3 stirring, mixing and spray drying: putting the dried slurry into a stirring container, adding a binder and a defoamer, mixing evenly to obtain a spray slurry, and then spray drying to obtain a powder; S4 prepares green body and arranges glue: fills the powder into a customized mold for dry pressing to form a green body of zinc oxide varistor; puts the green body of zinc oxide varistor into a muffle furnace, heats it to a preset temperature range in sequence according to the rate of different stages, and then keeps it warm, and discharges polyvinyl alcohol; S5 sintering: placing the zinc oxide varistor green body after debinding in a high-temperature sintering furnace, obtaining the heating power of the heater by analyzing the temperature distribution in the high-temperature sintering furnace, and uniformly heating the zinc oxide varistor green body to the sintering temperature to obtain the varistor dielectric material; wherein, the process of obtaining the heating power of the heater includes: Acquire green body sintering images of zinc oxide varistor green body during sintering process; Calculate the temperature average of the green body sintering image at all times within the temperature increase adjustment interval; when the temperature average is less than a preset temperature threshold, adjust the heating power according to the expected temperature increase; otherwise, adjust the heating power according to the significance of the auxiliary temperature increase; The process of obtaining the significance of auxiliary warming is as follows: (1) Divide the green body sintering image into several green body regions; (2) Prediction is performed based on a sequence consisting of the difference between the temperature mean of the same green body region at different acquisition times and the temperature mean of the green body sintering image where it is located, and the prediction result is used as the continuous significant temperature rise coefficient of the green body region; (3) Based on the distribution of temperature values ​​of the same pixel at different acquisition times, the temperature sudden rise points are screened out; the average value of the total number of temperature sudden rise points of all pixels in the green area at different acquisition times is taken as the cumulative reaction time of the green area; (4) Using the normalized value of the product of the continuous significant temperature rise coefficient and the cumulative reaction time, the doping-enriched region is screened out; using the chaotic distribution of the distance between the centers of the doping-enriched regions and the continuous significant temperature rise coefficient of all green body regions, the significance of the auxiliary temperature rise in the temperature rise adjustment interval is determined; The process of obtaining the sustained significant temperature rise coefficient is as follows: calculating the difference between the temperature mean of the green body area and the temperature mean of the green body sintering image as the regional temperature comparison value of the green body area; taking a sequence composed of the regional temperature comparison values ​​of the same green body area at all acquisition times as the temperature comparison sequence of the green body area, taking the temperature comparison sequence of the green body area as the input of the exponential moving average algorithm, and outputting the predicted value of the temperature comparison sequence as the sustained significant temperature rise coefficient of the green body area.

2. The method for preparing a varistor dielectric material according to claim 1, characterized in that: The raw materials in the S1 raw material mixture are composed, by mole, of 100 parts of zinc oxide, 0.5-1.5 parts of antimony oxide, 1-2.5 parts of bismuth oxide, 0.5-1.5 parts of cobalt trioxide, 0.5-1.3 parts of manganese dioxide, 0.5-1.5 parts of chromium trioxide, 0.5-1.5 parts of silicon dioxide, 0.05-0.6 parts of silver nitrate, and 0.5-1.5 parts of boron carbide.

3. The method for preparing a varistor dielectric material according to claim 1, characterized in that: The deionized water and dispersant in the S2 adding dispersant and ball milling mixing are 1-1.5 times the total weight of the mixture, and the dispersant is polyacrylic acid amine dispersant, and the addition amount of polyacrylic acid amine dispersant is 0.1wt%-2.0wt% of the mixture. 。 4. The method for preparing a varistor dielectric material according to claim 1, characterized in that: The binder added in the stirring, mixing and spray drying of S3 is 10wt% of the dried slurry, and the binder is a polyvinyl alcohol solution, and the mass ratio of polyvinyl alcohol to water in the polyvinyl alcohol solution is 1:9; the defoamer added is 0.05wt%-1.0wt% of the dried slurry, and the defoamer is tributyl phosphate.

5. The method for preparing a varistor dielectric material according to claim 1, characterized in that: The pressure for dry pressing in the green body preparation and side-by-side bonding in S4 is set to 8-10 MPa.

6. The method for preparing a varistor dielectric material according to claim 1, characterized in that: The method for screening the temperature sudden rise point is: performing mutation point detection on the differential sequence composed of the temperature values ​​of the same pixel at different acquisition times, and taking the mutation point in the differential sequence where the element value is greater than zero as the temperature sudden rise point.

7. The method for preparing a varistor dielectric material according to claim 1, characterized in that: The method for screening the doping-enriched region is: when the normalized value is greater than a preset doping content threshold, the green body region where the normalized value is located is regarded as the doping-enriched region.

8. The method for preparing a varistor dielectric material according to claim 1, characterized in that: The method for determining the significance of auxiliary heating in the heating adjustment interval includes: calculating the standard deviation of the distances between the centers of all doping-enriched regions; calculating the cumulative sum of the continuous significant heating coefficients of all green body regions; and reversely fusing the standard deviation and the cumulative sum to obtain the significance of auxiliary heating in the heating adjustment interval.

9. The method for preparing a varistor dielectric material according to claim 1, characterized in that: The method for adjusting the heating power using the auxiliary temperature rise significance degree is as follows: multiplying the reverse mapping result of the auxiliary temperature rise significance degree by the power value that needs to be adjusted corresponding to the expected temperature increase, and then summing it with the heating power value obtained in the last temperature rise adjustment interval to obtain the heating power.

10. A varistor dielectric material, characterized in that: The dielectric material is prepared by the method for preparing a varistor dielectric material as claimed in claim 1.

Images