Carbon ceramic linear resistor with spherical graphite as conductive phase

Abstract

This invention discloses a carbon ceramic linear resistor using spherical graphite as the conductive phase, relating to the field of carbon ceramic resistor technology. The carbon ceramic linear resistor is prepared through the following steps: alumina, clay, spherical graphite, adhesive, dispersant, and deionized water are weighed according to a preset ratio and added to a ball mill jar, forming a mixed slurry through ball milling; the mixed slurry is then centrifugally spray-granulated to obtain granulated powder; the granulated powder is sealed and aged to prepare a green body; the green body is then subjected to debinding and sintering to obtain a ceramic body; after grinding the ceramic body into wafers, electrodes are prepared on the end faces. The carbon ceramic linear resistor prepared by this invention exhibits a gradual, controllable, and small abrupt change in resistivity with increasing graphite content, demonstrating excellent resistivity adjustability and significantly expanding the application range and industrialization value of carbon ceramic linear resistors.

Description

Technical Field

[0001] This invention relates to the field of carbon ceramic resistor technology, and more particularly to a carbon ceramic linear resistor using spherical graphite as the conductive phase. Background Technology

[0002] Carbon ceramic linear resistors combine the advantages of ceramic matrices (high temperature resistance, corrosion resistance, structural stability) with the adjustable conductivity of the carbon phase, making them indispensable functional resistive devices in pulse power systems, power electronics, and new energy storage. While meeting linearity requirements, the application and promotion of carbon ceramic linear resistors largely depend on resistivity. Adjustable resistivity means that carbon ceramic linear resistors can be adapted to different operating conditions, cover multiple application fields, and ensure device stability and reliability. For example, they can be matched to different operating voltage, current, and power scenarios, providing corresponding resistance values ​​for high-voltage current limiting, low-voltage voltage regulation, and pulse energy absorption, preventing device breakdown or failure. Alternatively, the same system of resistors can be flexibly used in different fields such as power electronics, pulse power, and new energy storage, significantly expanding the application scope and industrial value. Furthermore, they can be precisely adapted to equipment circuit designs, ensuring resistance linearity and temperature stability, and improving the overall system safety and durability.

[0003] Existing carbon ceramic resistors generally use flake graphite as the conductive phase, which has drawbacks in resistivity control, including drastic abrupt changes, poor controllability, and difficulty in adapting to different operating conditions. Due to the anisotropic morphology of flake graphite, it is prone to agglomeration and uneven distribution. Its resistivity does not decrease slowly with increasing graphite content, but rather changes abruptly within a very narrow content range. The abrupt change near the percolation threshold spans orders of magnitude greater than two units, making it impossible to achieve smooth and precise resistivity adjustment. At the same time, its resistivity fluctuates greatly with increasing graphite content, making it impossible to stably lock in the target resistivity. These characteristics of uncontrollable abrupt changes and steep / fluctuating control ranges make it difficult for carbon ceramic linear resistors to flexibly match resistivity parameters according to the needs of different working conditions, significantly reducing their application scenarios and promotional value. Summary of the Invention

[0004] This invention provides a carbon ceramic linear resistor using spherical graphite as the conductive phase. The carbon ceramic linear resistor comprises a ceramic matrix and a conductive phase dispersed within the ceramic matrix, wherein the conductive phase is spherical graphite. The carbon ceramic linear resistor is prepared through the following steps:

[0005] S1, Weigh alumina, clay, spherical graphite, dispersant, adhesive, and deionized water according to the preset ratio and add them to the ball mill jar to form a mixed slurry through ball milling process;

[0006] S2, the mixed slurry is centrifuged by spray granulation to obtain granulated powder; the granulated powder is then sealed and aged before being used to prepare green bodies by pressing molding process;

[0007] S3, the green body is heated to remove the binder, and then the green body after removing the binder is sintered to obtain a ceramic body;

[0008] S4, the ceramic blank is ground into a wafer, and electrodes are prepared on the two end faces of the ground ceramic blank to obtain a carbon ceramic linear resistor.

[0009] Optionally, in step S1, the proportion of alumina, clay, spherical graphite, adhesive, and dispersant by weight is 8-12% alumina: 60-70% clay: 7-25% spherical graphite: 2-3% adhesive: 0.1-0.5% dispersant, with the balance being deionized water.

[0010] Optionally, in step S1, the proportion of alumina, clay, spherical graphite, adhesive, and dispersant by weight is 10% alumina: 65% clay: 7%~25% spherical graphite: 2.5% adhesive: 0.3% dispersant, with the balance being deionized water.

[0011] Optionally, the clay is bentonite.

[0012] Optionally, the adhesive is polyvinyl alcohol, and the dispersant is polyacrylate.

[0013] Optionally, the average particle size of the spherical graphite is 12~18μm, preferably 15μm.

[0014] Optionally, the ball milling process is as follows: using a pot mill at a speed of 450 rpm for 24 hours, with agate balls as the grinding media particles.

[0015] Optionally, the centrifugal spray granulation process is as follows: a high-speed centrifugal spray dryer is used for spray granulation, with an inlet temperature of 220°C and an outlet temperature of 110°C.

[0016] Optionally, the moisture content of the granulated powder is 1.4-1.6%, preferably 1.5%.

[0017] Optionally, the density of the green body is 1.8~2.2 g / cm³. 3 2g / cm 3 .

[0018] Optionally, in step S3, the process parameters for heating and debinding are: debinding temperature 410~450℃, preferably 430℃, and holding time 1.5~2.5h, preferably 2h.

[0019] Optionally, in step S3, the sintering process parameters are: sintering temperature 1000~1100℃, preferably 1050℃, holding time 1.5~2.5h, preferably 2h, and the protective atmosphere during sintering is a mixture of nitrogen and hydrogen; the mixture can be a mixture of nitrogen and hydrogen = 97:3.

[0020] Optionally, the electrode is an aluminum electrode.

[0021] The present invention has the following beneficial effects:

[0022] The carbon ceramic linear resistor prepared by this invention, which uses spherical graphite as the conductive phase, exhibits a gradual and controllable change in resistivity with varying graphite content. In particular, the abrupt change near the percolation threshold only produces a two-unit change, demonstrating excellent resistivity controllability. This allows it to adapt to different operating conditions, cover multiple application fields, and match precision circuit designs, significantly expanding the application range and industrialization value of carbon ceramic linear resistors. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a flowchart of the preparation method of the carbon ceramic linear resistor using spherical graphite as the conductive phase according to the present invention.

[0025] Figure 2 This is a process flow diagram of the carbon ceramic linear resistor using spherical graphite as the conductive phase in this invention.

[0026] Figure 3 The X-ray diffraction pattern of a carbon ceramic linear resistor with spherical graphite as the conductive phase.

[0027] Figure 4 SEM image and EDS spectrum of carbon ceramic linear resistor with spherical graphite as the conductive phase.

[0028] Figure 5 The graph shows the relationship between spherical graphite content, matrix density, and porosity.

[0029] Figure 6 The graph shows the relationship between the resistivity of carbon ceramic linear resistors and the content of spherical graphite.

[0030] Figure 7 Voltage-current curves for carbon ceramic linear resistors with different spherical graphite contents;

[0031] Figure 8 A trend graph of the temperature coefficient of resistance (TCR) for carbon ceramic linear resistors with different spherical graphite contents.

[0032] Figure 9 The graph shows the relationship between the energy density and the spherical graphite content of carbon ceramic linear resistors.

[0033] Figure 10 A graph showing the relationship between resistivity and graphite content for ceramic linear resistors with added flake graphite as a comparative example. Detailed Implementation

[0034] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0035] Experimental methods in the embodiments of this invention that do not specify specific conditions are generally performed under conventional conditions and conditions described in the manual, or under conditions recommended by the manufacturer; the general equipment, materials, reagents, etc. used are commercially available unless otherwise specified.

[0036] This invention provides a carbon ceramic linear resistor using spherical graphite as the conductive phase. The carbon ceramic linear resistor using spherical graphite as the conductive phase includes a ceramic matrix and a conductive phase dispersed in the ceramic matrix, wherein the conductive phase is spherical graphite; see reference. Figure 1 , 2 In this embodiment of the invention, the carbon ceramic linear resistor is prepared by the following steps:

[0037] S1. Weigh alumina, clay, spherical graphite, adhesive, dispersant, and deionized water according to the preset ratio and add them to the ball mill jar. The mixture is then formed by ball milling.

[0038] In this embodiment of the invention, the proportions of alumina, clay, spherical graphite, dispersant, and adhesive, by weight, are: 8-12% alumina, 60-70% clay, 7-25% spherical graphite, 2-3% adhesive, 0.1-0.5% dispersant, with the balance being deionized water. For example, alumina can be selected from 8%, 9%, 10%, 11%, 12%, or any value within that range; clay can be selected from 60%, 65%, 70%, or any value within that range; adhesive can be selected from 2%, 2.5%, 3%, or any value within that range; and dispersant can be selected from 0.1%, 0.3%, 0.5%, or any value within that range.

[0039] In this embodiment of the invention, alumina and clay are used to construct an insulating ceramic matrix; spherical graphite is a conductive phase; adhesive is used to bond the powder and ensure molding; and dispersant is used to improve the interaction force between powders and prevent agglomeration.

[0040] In some preferred embodiments, bentonite is selected as the clay; bentonite has strong binding properties and is key to green body forming. During sintering, it reacts with alumina to form mullite and cristobalite, which together with the corundum formed by alumina constitute the insulating matrix and are the main crystalline phase of the resistor.

[0041] The embodiments of the present invention do not limit the adhesive and dispersant. For example, the adhesive may be polyvinyl alcohol, acrylate, carboxymethyl cellulose, hydroxypropyl methyl cellulose, etc., and the dispersant may be polyacrylate, sodium tripolyphosphate, sodium hexametaphosphate, sodium citrate, organosilicon dispersant, etc.

[0042] In some specific embodiments, polyvinyl alcohol (PVA) is selected as the adhesive and polyacrylate (e.g., sodium polyacrylate, ammonium polyacrylate) is selected as the dispersant. Polyvinyl alcohol and polyacrylate are the most widely used adhesives and dispersants in the field of carbon ceramic resistors, respectively, and their processes are the most mature and reliable.

[0043] In this embodiment of the invention, spherical graphite is a conductive phase, and the average particle size of the spherical graphite is selected to be 12~18μm, for example 12μm, 15μm, 18μm or any value within the range.

[0044] S2, the mixed slurry is granulated by centrifugal spraying to obtain granulated powder; after the granulated powder is sealed and aged, it is used to prepare green blanks by compression molding process.

[0045] Specifically, this step uses a high-speed centrifugal spray dryer for spray granulation. Different processing temperatures and parameters can be set depending on the type of centrifugal spray dryer, ensuring a stable formation of granulated powder. Sealing and aging ensures that moisture is evenly dispersed among the granulated powder particles. The moisture content of the granulated powder is 1.4~1.6%, preferably 1.5%; the density of the green body is 1.8~2.2 g / cm³. 3 .

[0046] S3 involves heating the green body to remove the binder, followed by sintering the green body to obtain a ceramic body.

[0047] In this step, the process parameters for heating and debinding are: debinding temperature 410~450℃, holding time 1.5~2.5h, preferably 2h; the process parameters for sintering are: sintering temperature 1000~1100℃, preferably 1050℃, holding time 1.5~2.5h, preferably 2h; the protective atmosphere during sintering is a mixture of nitrogen and hydrogen; the mixture can be a nitrogen:hydrogen = 97:3 mixture.

[0048] S4. The ceramic blank is ground into a wafer, and electrodes are prepared on the two end faces of the ground ceramic blank to obtain a carbon ceramic linear resistor.

[0049] The electrode materials are not limited to various metals, alloys, and carbon materials with good conductivity; the methods for preparing the electrodes include, but are not limited to, physical vapor deposition, chemical vapor deposition, spraying, inkjet printing, and heating and curing of low-melting-point metals, etc., and the present invention does not limit these methods.

[0050] The carbon ceramic linear resistor prepared by the embodiments of the present invention, which uses spherical graphite as the conductive phase, exhibits a gradual and controllable change in resistivity with graphite content. In particular, the abrupt change near the percolation threshold only produces a change of two units, demonstrating excellent resistivity controllability. This allows it to adapt to different working conditions, cover multiple application fields, and match precision circuit designs, significantly expanding the application range and industrialization value of carbon ceramic linear resistors.

[0051] Based on the above embodiments, the present invention also proposes the following specific embodiments. It should be noted that the following specific embodiments are merely exemplary and are not intended to limit the scope of protection of the present invention in any way.

[0052] Example 1

[0053] Process flow reference Figure 2 .

[0054] Raw material ratio: alumina (10%), bentonite (65%), spherical graphite (average particle size 15μm, 7%), PVA (2.5%), polyacrylate (0.3%), with the balance being deionized water. All percentages are by mass.

[0055] First, alumina, bentonite, spherical graphite, and agate balls are poured into a ball mill jar in a certain proportion using an electronic balance. Appropriate amounts of dispersant, binder, and deionized water are added. Then, a GMJ-8-5 ball mill is used at 450 r / min. -1 The mixture was ball-milled at a certain speed for 24 hours, and then the ball-milled slurry was taken out and sieved to obtain the total slurry.

[0056] The total slurry was spray-granulated using an LZG-5 high-speed centrifugal spray dryer to obtain granulated material. The inlet temperature of the spray dryer was 220℃ and the outlet temperature was 110℃.

[0057] Take a portion of the granulated material and use an HB43-S Halogen moisture analyzer to determine the moisture content of the granulated material. Using a final moisture content of 1.5% as the standard, calculate whether deionized water needs to be added and the amount of deionized water to be added. Mix it evenly with 0.7% of the mass of the granulated material powder as a release agent, spray it evenly on the granulated material, and then seal and age the granulated material powder for 20 hours to allow the moisture to be evenly dispersed between the granulated material powder.

[0058] The aged, water-containing granulated material was pressed into shape using a Y79-25 bidirectional counter-pressure powder hydraulic press to obtain a size of [missing value]. The cylindrical green body was formed, and the density of the green body was controlled to be 2.00 g·cm³ by adjusting the forming pressure. -3 The prepared carbon ceramic linear resistance green body was placed in an ECF1-6-13 high-temperature electric furnace for debinding. The maximum debinding temperature was 430℃, and the holding time was 2 hours. The debinded green body was then embedded in graphite and placed in an OFS-12-17 high-temperature experimental atmosphere furnace for sintering. The sintering temperature was 1050℃, and the holding time was 2 hours. The protective atmosphere was a nitrogen-hydrogen mixture of 97:3.

[0059] The sintered blank was placed on a UPINOL-802 precision grinding and polishing machine to grind the two end faces of the cylindrical blank. After the blank was dried, aluminum electrodes were sprayed onto the two end faces of the ceramic blank using a DPL-IZ aluminum spraying machine to obtain a sample of carbon ceramic linear resistor, which was designated as "SG-7".

[0060] Example 2

[0061] The raw material ratio and process flow are the same as in Example 1, except that the amount of spherical graphite added in the raw material is 9%, and the prepared sample is designated as "SG-9".

[0062] Example 3

[0063] The raw material ratio and process flow are the same as in Example 1, except that the amount of spherical graphite added in the raw material is 11%, and the prepared sample is designated as "SG-11".

[0064] Example 4

[0065] The raw material ratio and process flow are the same as in Example 1, except that the amount of spherical graphite added in the raw material is 13%, and the prepared sample is designated as "SG-13".

[0066] Example 5

[0067] The raw material ratio and process flow are the same as in Example 1, except that the amount of spherical graphite added in the raw material is 15%, and the prepared sample is designated as "SG-15".

[0068] Example 6

[0069] The raw material ratio and process flow are the same as in Example 1, except that the amount of spherical graphite added in the raw material is 17%, and the prepared sample is designated as "SG-17".

[0070] Example 7

[0071] The raw material ratio and process flow are the same as in Example 1, except that the amount of spherical graphite added in the raw material is 19%, and the prepared sample is designated as "SG-19".

[0072] Example 8

[0073] The raw material ratio and process flow are the same as in Example 1, except that the amount of spherical graphite added in the raw material is 21%, and the prepared sample is designated as "SG-21".

[0074] Example 9

[0075] The raw material ratio and process flow are the same as in Example 1, except that the amount of spherical graphite added in the raw material is 23%, and the prepared sample is designated as "SG-23".

[0076] Example 10

[0077] The raw material ratio and process flow are the same as in Example 1, except that the amount of spherical graphite added in the raw material is 25%, and the prepared sample is designated as "SG-25".

[0078] Comparative Example 1

[0079] The raw material ratio and process flow are the same as in Example 1, except that flake graphite is added to the raw materials. The average size of the flake graphite is 13μm. Carbon ceramic linear resistor samples with flake graphite addition of 7%, 9%, 10%, 11%, 13% and 15% are prepared respectively. The sample prepared in this comparative example is denoted as "FG-L".

[0080] Comparative Example 2

[0081] The raw material ratio and process flow are the same as in Example 1, except that flake graphite is added to the raw materials. The average size of the flake graphite is 4.5 μm. Carbon ceramic linear resistor samples with flake graphite addition of 7%, 8%, 9%, 11%, 13%, and 15% are prepared respectively. The sample prepared in this comparative example is denoted as "FG-M".

[0082] Comparative Example 3

[0083] The raw material ratio and process flow are the same as in Example 1, except that flake graphite is added to the raw materials. The average size of the flake graphite is 1.6 μm. Carbon ceramic linear resistor samples with flake graphite addition of 1%, 3%, 5%, 7%, 9%, 11%, 13%, and 15% are prepared respectively. The sample prepared in this comparative example is denoted as "FG-S".

[0084] After the above samples were prepared, their morphology was characterized and their performance was tested.

[0085] See Figure 3 , Figure 3 The X-ray diffraction (XRD) patterns of the carbon ceramic resistor samples prepared in each embodiment are shown. The XRD results indicate that the main phase composition of the carbon ceramic linear resistors consists of corundum (PDF#10-0173), mullite (PDF#15-0776), carbon (PDF#26-1076), and cristobalite (PDF#27-0605). With the increase of spherical graphite content, no new peaks were generated in the XRD pattern. The change in spherical graphite content did not change the crystal phase types of the carbon ceramic linear resistors, indicating that spherical graphite did not participate in the ceramic sintering reaction. At the same time, it can be seen from the figure that with the increase of spherical graphite content, the peak intensities of corundum, mullite, and cristobalite gradually weakened, indicating that the content of these crystal phases decreased. Excessive spherical graphite is not conducive to crystal growth.

[0086] See Figure 4 , Figure 4 SEM images and EDS spectra of the linear resistivity of ceramics with different spherical graphite contents are shown. From left to right, the spherical graphite content increases sequentially (graphite contents are 9%, 17%, and 25%, respectively). The images show that with increasing spherical graphite content, the porosity and grain boundary number of the ceramic body gradually increase. Simultaneously, the SEM images show that with increasing spherical graphite content, their distribution in the matrix becomes more dispersed, and the aggregation of crystals into large ceramic masses gradually decreases. The EDS spectra clearly show the distribution of spherical graphite. Distribution: Spherical graphite is embedded and coated on crystals such as corundum and mullite. Since the size of the spherical graphite is similar to that of the framework, most of the spherical graphite forms the framework of the matrix, and only a small number of broken spherical graphite are pushed to the grain boundaries by the crystals. When the content of spherical graphite is very low, the spherical graphite particles are far apart, isolated and cannot connect with each other, which macroscopically manifests as a high resistivity. When the content of spherical graphite increases to a certain extent, the spherical graphite particles connect and overlap with each other, forming a conductive network, which macroscopically manifests as a rapid decrease in resistivity.

[0087] See Figure 5 , Figure 5The graph shows the relationship between spherical graphite content, matrix density, and porosity. As the spherical graphite content increases, the matrix density gradually decreases, while porosity initially increases and then decreases. The porosity is highest when the spherical graphite content is 17%, while the density is lowest. The gradual decrease in density is due to two main reasons: firstly, the density of spherical graphite is inherently much lower than that of alumina and silicon dioxide; the more spherical graphite, the lower the matrix density. Secondly, XRD patterns show that spherical graphite does not participate in the sintering reaction of the ceramic matrix. Excessive spherical graphite hinders the microscopic fluidity of the ceramic matrix at high temperatures, inhibits crystal movement, and thus reduces density.

[0088] The increase in porosity with the increase in spherical graphite content can be understood as follows: During the sintering process of the ceramic matrix, the spherical graphite inhibits the sintering reaction. The more spherical graphite there is, the more obvious the inhibition of sintering. Since the linear expansion coefficients of spherical graphite are different from those of mullite, corundum, and cristobalite, once the sintering temperature decreases, mullite and corundum, which have larger expansion coefficients, will generate a large number of pores and cracks due to shrinkage, which is macroscopically manifested as an increase in porosity. The reason for the subsequent decrease in porosity may be that after the spherical graphite content increases to a certain extent (e.g., 17%), when the temperature decreases, defects such as cracks and fissures generated by the shrinkage of alumina and silica are filled by spherical graphite with strong self-lubrication and higher fluidity, which is macroscopically manifested as a decrease in porosity.

[0089] Figure 6 The figures show the relationship between the resistivity of the carbon ceramic linear resistor and the content of spherical graphite in each embodiment. As can be seen from the figures, the resistivity of the carbon ceramic linear resistor decreases with increasing spherical graphite content, eventually stabilizing. Simultaneously, a small abrupt change in resistivity occurs when the spherical graphite content is between 13% and 15%, with the resistivity decreasing from 7 × 10⁻⁶. 6 Ω·cm decreased to 1.5×10 4The resistivity changes by only two units (Ω·cm). The critical value at which resistivity undergoes a sudden change is called the percolation threshold. When the content of spherical graphite in the material is less than the percolation threshold, the distance between graphite particles is large, and they are dispersed. Corundum, mullite, and cristobalite are all insulators. When the content of spherical graphite exceeds the percolation threshold, the graphite particles connect to form a conductive network, thus the resistivity decreases rapidly. As the content of spherical graphite further increases, the spacing between graphite particles further shortens. At this point, the voltage-current relationship exhibits ohmic characteristics, and the resistivity eventually hardly decreases with the increase of the spherical graphite content. This smaller change in resistivity is of great significance. As an electronic component, the application and promotion of carbon ceramic linear resistors largely depend on resistivity. If the resistivity is adjustable, it means that carbon ceramic linear resistors can be selected according to the needs of different working conditions, which greatly enhances the possibility of carbon ceramic linear resistors being used in different fields. The carbon ceramic linear resistors prepared from spherical graphite exhibit excellent resistance control.

[0090] See Figure 7 , Figure 7 The voltage-current curves of carbon ceramic linear resistors with different spherical graphite contents are shown in Table 1. Table 1 shows the correlation coefficient R after linear fitting of the voltage-current curves of the carbon ceramic linear resistors. 2 Value (R) 2 The closer the value is to 1, the closer the curve is to a straight line, and the higher the linearity of the ceramic linear resistor. Figure 7 and R in Table 1 2 The values ​​all show that the carbon ceramic linear resistor prepared in the embodiments of the present invention has a high linearity, and the change in the content of spherical graphite does not affect the linearity of the carbon ceramic linear resistor.

[0091] Table 1. R0 of carbon ceramic linear resistors with different spherical graphite contents 2 value

[0092]

[0093] See Figure 8 , Figure 8 This is a trend graph of the temperature coefficient of resistance (TCR) of carbon ceramic linear resistors with different spherical graphite contents. As can be seen from the graph, the absolute value of the temperature coefficient of resistance of carbon ceramic linear resistors decreases with increasing graphite content. The more negative the temperature coefficient of resistance, the more sensitive the carbon ceramic linear resistor is to temperature, which is less conducive to the application of the material. The more positive the temperature coefficient of resistance, the less affected the carbon ceramic linear resistor is by temperature and the better its performance.

[0094] The variation of the temperature coefficient of resistance (TCR) of carbon ceramic linear resistors with graphite content can be understood as follows: When the content of spherical graphite is low, although a conductive network has been formed inside the ceramic body, the number of conductive chains is relatively small. As the temperature rises, the thermal vibration of the spherical graphite particles and the transfer of hot electrons are intensified. At the same time, the thermal expansion of insulators such as mullite and corundum compresses the graphite at the framework and grain boundaries, making the contact between the spherical graphite particles closer. Macroscopically, this promotes a decrease in resistivity, resulting in a larger absolute value of the TCR. When the content of spherical graphite is high, the number of conductive chains is greater than before, given the existing conductive network. Although the thermal expansion of the insulating crystal compresses the spherical graphite as the temperature rises, causing thermal vibration and electron thermal migration in the spherical graphite particles, the effect on the numerous conductive networks is not so significant. The compression of the spherical graphite by the insulating crystal, as well as the thermal vibration and hot electron transfer of the spherical graphite, are limited, thus the degree of resistance reduction is somewhat mitigated. Macroscopically, this is manifested as a smaller rate of change in resistance and a smaller absolute value of the TCR.

[0095] See Figure 9 , Figure 9 The graph shows the relationship between the energy density of carbon ceramic linear resistors and the content of spherical graphite. As the content of spherical graphite increases, the energy density increases. However, when the content exceeds a certain value, it decreases. Energy density is closely related to the uniformity and density of the ceramic body. SEM and EDS images show that as the content of spherical graphite increases, the graphite distribution becomes more uniform, the distribution of crystal particles in the carbon ceramic linear resistor becomes more uniform, and the crystal aggregation is improved. Simultaneously, the number of pores gradually decreases. This change in composition and structure has a greater impact on energy density, resulting in a higher energy density. Finally, when the content of spherical graphite exceeds a certain value, excessive spherical graphite is detrimental to the strength and toughness of the ceramic body, causing a rapid decrease in energy density. Based on practical application requirements, the preferred addition range of spherical graphite in this invention is 7% to 25%.

[0096] When the spherical graphite content is 23%, the resistivity of the carbon ceramic resistor is 12 Ω·cm, and the temperature coefficient of resistance is -8.9 × 10⁻⁶. -4 The energy density obtained from long-term low-power testing is 1500 J·cm³. -3 It has the best overall performance.

[0097] See Figure 10 , Figure 10 The resistivity and graphite content of ceramic linear resistors with added flake graphite are shown as comparative examples. It can be seen that the resistivity changes abruptly when the flake graphite size is 4.5 μm and 1.6 μm. For the carbon ceramic linear resistor with a flake graphite size of 1.6 μm, the resistivity increases from 2 × 10⁻⁶ to 7% when the graphite content increases from 5% to 7%.5 The resistivity of a carbon ceramic linear resistor with 4.5 μm flake graphite decreased from 2.7 × 10⁻⁶ Ω·cm to 50 Ω·cm, a change of four units. This meant the resistivity of the linear resistor decreased from 2.7 × 10⁻⁶ Ω·cm to 50 Ω·cm. 6 The resistivity decreased to 115 Ω·cm, a change of four units; while the resistivity of the carbon ceramic linear resistor with 13 μm flake graphite increased from 1.1 × 10⁻⁶ to 115 μm with an increase in graphite content from 7% to 9%. 6 It decreased to 5500 Ω·cm, a change of three units.

[0098] contrast Figure 6 and Figure 10 It can be observed that, with the increase of spherical graphite content, the resistivity of the carbon ceramic resistor using spherical graphite as the conductive phase in the embodiments of the present invention decreases more slowly and smoothly compared to the comparative sample using flake graphite as the conductive phase. When the spherical graphite content is near the percolation threshold of 13-15%, the resistivity decreases from 7×10⁻⁶. 6 Ω·cm decreased to 1.5×10 4 The change in resistivity is only two units per Ω·cm; this smaller abrupt change in resistivity is of great significance: as an electronic component, the application and promotion of carbon ceramic linear resistors largely depend on resistivity. If the resistivity can be adjusted, it means that carbon ceramic linear resistors can be selected according to the needs of different working conditions, which greatly enhances the possibility of carbon ceramic linear resistors being used in different fields; carbon ceramic linear resistors prepared from spherical graphite have excellent resistivity controllability.

[0099] In summary, the systematic characterization and testing results show that the carbon ceramic linear resistor prepared by this invention, which uses spherical graphite as the conductive phase, not only has excellent linear performance, but also exhibits a gradual and controllable change in resistivity with graphite content. In particular, the abrupt change near the percolation threshold only produces a two-unit change, demonstrating excellent resistivity controllability. This allows it to adapt to different operating conditions, cover multiple application fields, and match precision circuit designs, significantly expanding the application range and industrialization value of carbon ceramic linear resistors.

[0100] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A carbon ceramic linear resistor using spheroidal graphite as a conductive phase, characterized by, The carbon ceramic linear resistor comprises a ceramic matrix and a conductive phase dispersed in the ceramic matrix, wherein the conductive phase is spherical graphite; the carbon ceramic linear resistor is prepared by the following steps: S1, Weigh alumina, clay, spherical graphite, adhesive, dispersant and deionized water according to the preset ratio and add them to the ball mill jar, and form a mixed slurry through ball milling process; S2, the mixed slurry is centrifuged by spray granulation to obtain granulated powder; the granulated powder is then sealed and aged before being used to prepare green bodies by pressing molding process; S3, the green body is heated to remove the binder, and then the green body after removing the binder is sintered to obtain a ceramic body; S4, the ceramic blank is ground into a wafer, and electrodes are prepared on the two end faces of the ground ceramic blank to obtain a carbon ceramic linear resistor.

2. The carbon ceramic linear resistor with spheroidal graphite as the electrically conductive phase according to claim 1, characterized in that, In step S1, by weight, the proportions of alumina, clay, spherical graphite, adhesive, and dispersant are 8-12% alumina, 60-70% clay, 7-25% spherical graphite, 2-3% adhesive, 0.1-0.5% dispersant, with the balance being deionized water.

3. The carbon ceramic linear resistor with spheroidal graphite as the electrically conductive phase according to claim 1, characterized in that, The clay is bentonite.

4. The carbon ceramic linear resistor with spheroidal graphite as the electrically conductive phase according to claim 1, characterized in that, The adhesive is polyvinyl alcohol, and the dispersant is polyacrylate.

5. The carbon ceramic linear resistor with spheroidal graphite as the electrically conductive phase according to claim 1, characterized in that, The average particle size of the spherical graphite is 12~18μm.

6. The carbon ceramic linear resistor with spheroidal graphite as the electrically conductive phase according to claim 1, characterized in that, The moisture content of the granulated powder is 1.4~1.6%.

7. The carbon ceramic linear resistor with spheroidal graphite as the electrically conductive phase according to claim 1, characterized in that, The density of the green body is 1.8-2.2 g / cm 3 .

8. The carbon ceramic linear resistor with spheroidal graphite as the electrically conductive phase according to claim 1, characterized in that, In step S3, the process parameters for heating and debinding are: debinding temperature 410~450℃, and holding time 1.5~2.5h.

9. The carbon ceramic linear resistor with spheroidal graphite as the electrically conductive phase according to claim 1, characterized in that, In step S3, the sintering process parameters are: sintering temperature 1000~1100℃, holding time 1.5~2.5h, and the protective atmosphere during sintering is a mixture of nitrogen and hydrogen.

10. The carbon ceramic linear resistor with spheroidal graphite as the electrically conductive phase according to claim 1, characterized in that, The electrode is an aluminum electrode.

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