A high-efficiency process for preparing silicon nitride ceramics

Abstract

The present application relates to the field of ceramic preparation technology, and specifically to a process for efficiently preparing silicon nitride ceramics, the process comprising: subjecting silicon nitride ceramic slurry to a light-curing treatment, followed by cleaning and curing; degreasing the cured ceramic formed body to obtain a degreased ceramic body; sintering the degreased ceramic body, collecting the surface temperature matrix of the degreased ceramic body at each moment during the sintering process, and determining the local thermal stress significance at the position corresponding to each temperature value in the surface temperature matrix; forming a thermal stress distribution matrix with the local thermal stress significance of all temperature values in the surface temperature matrix, and determining the thermal effect singularity at the corresponding moment of the thermal stress distribution matrix; adjusting the heating rate at each moment during the sintering process by utilizing the difference in thermal effect singularity between each moment and the previous moment; and maintaining the temperature, cooling, and cooling with the furnace after sintering to obtain silicon nitride ceramics. The present application improves the performance and efficiency of preparing silicon nitride ceramics.

Description

Technical Field

[0001] The present application relates to the technical field of ceramic preparation, and in particular to a process for efficiently preparing silicon nitride ceramics. Background Art

[0002] During the preparation of silicon nitride ceramics, a sintering process is typically used to sinter the ceramic body to improve the density of the silicon nitride ceramic and obtain silicon nitride ceramics with better performance. However, to avoid thermal stress cracking during the sintering process and to ensure the production efficiency of silicon nitride ceramics, the heating rate during the sintering process must be strictly controlled to achieve high-efficiency and high-quality production of silicon nitride ceramics.

[0003] Since there are likely to be certain differences in the composition of different positions on the surface of the ceramic degreased green body, the surface temperature of the ceramic degreased green body is prone to complex thermal stress changes during the sintering process. The existing technology usually uses a single fixed heating rate to achieve the sintering of the ceramic degreased green body. It is impossible to accurately control and adjust the heating rate during the sintering process according to the thermal stress changes of the surface temperature of the ceramic degreased green body during the sintering process, which easily leads to higher thermal stress inside the ceramic degreased green body material during the sintering process, thereby affecting the quality of silicon nitride ceramics. Summary of the Invention

[0004] In order to solve the above technical problems, the present application provides a process for efficiently preparing silicon nitride ceramics to solve the existing problems.

[0005] A high-efficiency process for preparing silicon nitride ceramics in this application adopts the following technical solution:

[0006] One embodiment of the present application provides a process for efficiently preparing silicon nitride ceramics, the process comprising:

[0007] The polysilane liquid, silicon nitride powder, and sintering aid are mixed, and then a light-curing resin and a photoinitiator are added, and ball milling is performed to obtain a silicon nitride ceramic slurry;

[0008] placing the silicon nitride ceramic slurry in a photocuring machine for photocuring to obtain a ceramic formed body;

[0009] cleaning the ceramic formed body and then curing it;

[0010] Degreasing the solidified ceramic formed body to obtain a degreased ceramic body;

[0011] Sintering a degreased ceramic body, collecting a surface temperature matrix of the degreased ceramic body at each moment during the sintering process, and constructing a local temperature difference vector for each temperature value in the surface temperature matrix based on the difference between each temperature value in the surface temperature matrix and the rest of the temperature values in its neighborhood window;

[0012] Analyzing the distribution of differences between adjacent elements in the local temperature difference vector and the degree of disorder of all elements in the local temperature difference vector to determine the local thermal stress significance of each temperature value in the surface temperature matrix at a corresponding position of the degreased ceramic body;

[0013] The local thermal stress significance of all temperature values in the surface temperature matrix is used to form a thermal stress distribution matrix, and based on the similarity between each row vector in the thermal stress distribution matrix and the remaining row vectors, and the distribution of the rate of change of the difference between adjacent elements in each row vector, the lateral thermal effect singularity of each row vector in the thermal stress distribution matrix is determined;

[0014] Accordingly, the longitudinal thermal effect singularity of each column vector in the thermal stress distribution matrix is obtained, and combined with the transverse thermal effect singularity, the thermal effect singularity of the thermal stress distribution matrix at the corresponding moment is obtained; the difference in the thermal effect singularity at each moment and the previous moment is used to adjust the heating rate at each moment in the sintering process;

[0015] After sintering is completed, the process is carried out by heat preservation, temperature reduction, and furnace cooling to obtain silicon nitride ceramics.

[0016] In one embodiment, the mixing mass ratio of the polynitrosilane liquid, silicon nitride powder, sintering aid, photocurable resin, and photoinitiator is 30:20~80:4~8:12~40:0.2~0.6g, the photocurable resin is a mixture of 1,6-hexanediol diacrylate HDDA and pentaerythritol tetraacrylate PETTA in a mass ratio of 1:1, the sintering aid is one of magnesium oxide and aluminum oxide, and the photoinitiator is phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide.

[0017] In one embodiment, the photocuring process is performed with a layer thickness of 20 μm and an exposure dose of 100-200 mJ / cm².

[0018] In one embodiment, the cleaning followed by curing is to immerse the ceramic formed body in anhydrous alcohol, clean the uncured resin on the surface by ultrasonic cleaning, and then place it in a UV light box for curing for 3 to 5 hours.

[0019] In one embodiment, the degreasing comprises:

[0020] The solidified ceramic formed body is placed in a nitrogen atmosphere, heated to 280°C at a rate of 1~2°C / min and kept warm for 1~3 hours, then heated to 600°C at a rate of 1~2°C / min and kept warm for 1~3 hours, and then heated to 1000°C at a rate of 0.5~1°C / min and kept warm for 3~5 hours to obtain a ceramic degreased body.

[0021] In one embodiment, the sintering comprises:

[0022] The degreased ceramic body was heated to 1700-1850°C in a nitrogen environment with a pressure of 5-10 MPa, wherein the initial heating rate was 5°C / min.

[0023] In one embodiment, the local temperature difference vector is obtained by arranging the differences between each temperature value in the surface temperature matrix and all other temperature values in its neighborhood window in ascending order;

[0024] The local thermal stress significance is the product of the mean of the absolute values of all elements in the first-order difference vector of the local temperature difference vector of each temperature value and the permutation entropy of the local temperature difference vector.

[0025] In one embodiment, determining the transverse thermal effect singularity includes:

[0026] The average value of the similarity between each row vector and all other row vectors in the thermal stress distribution matrix is calculated, and the inverse of the average value is used as an exponential function with a natural constant as the base. The discreteness of all elements in the second-order difference vector of each row vector in the thermal stress distribution matrix is calculated, and the lateral thermal effect singularity is the product of the discreteness and the calculation result of the exponential function.

[0027] In one embodiment, adjusting the heating rate at each moment during the sintering process includes:

[0028] The normalized result of the mean of the longitudinal thermal effect singularity of all column vectors and the mean of the transverse thermal effect singularity of all row vectors in the thermal stress distribution matrix is taken as the thermal effect singularity of the thermal stress distribution matrix at the corresponding moment;

[0029] The difference between the thermal effect singularity at each moment and the previous moment is calculated and recorded as the first difference. The multiplication result of the first difference and the heating rate at each moment is calculated. The adjusted heating rate at each moment is the difference between the heating rate at each moment and the multiplication result.

[0030] In one embodiment, the insulation time is 1-3 hours, the cooling rate is 1-2°C / min, and the temperature is lowered to 800°C and then cooled in the furnace.

[0031] This application has at least the following beneficial effects:

[0032] The present application constructs a thermal stress distribution matrix for a degreased ceramic body by analyzing the local thermal stress on the surface of the degreased ceramic body. The thermal stress distribution matrix reflects the distribution characteristics of the thermal stress on the surface of the degreased ceramic body during the sintering process, which is conducive to more accurate control and adjustment of the heating rate during the sintering process, thereby reducing the accumulation of thermal stress on the ceramic surface and improving the density of silicon nitride ceramics. Furthermore, the thermal effect singularity on the surface of the degreased ceramic body in the horizontal and vertical directions is analyzed by the thermal stress distribution matrix, and combined with the change of the singularity of the thermal stress on the surface of the degreased ceramic body in the horizontal and vertical directions, the variation characteristics of the thermal stress distribution singularity on the surface of the degreased ceramic body during the sintering process are more comprehensively and accurately measured, which facilitates the subsequent accurate control and adjustment of the heating rate during the sintering process to avoid the accumulation of thermal stress inside the degreased ceramic body material during the sintering process. Furthermore, by the change characteristics of the thermal effect singularity at each moment during the sintering process, the heating rate during the sintering process is accurately controlled and adjusted, thereby avoiding the generation of high thermal stress inside the degreased ceramic body material during the sintering process, and improving the performance and efficiency of preparing silicon nitride ceramics. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions and advantages of the embodiments of the present application or the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. 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 any creative work.

[0034] Figure 1 A flowchart of the steps of a process for efficiently preparing silicon nitride ceramics provided in this application;

[0035] Figure 2 Flow chart for adjusting the heating rate during the sintering stage of silicon nitride ceramics. DETAILED DESCRIPTION

[0036] To further illustrate the technical means and effects employed by this application to achieve the intended invention objectives, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effects of a high-efficiency process for preparing silicon nitride ceramics proposed in this application. In the following description, references to different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics of one or more embodiments may be combined in any suitable manner.

[0037] 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.

[0038] The specific scheme of a process for efficiently preparing silicon nitride ceramics provided by the present application is described in detail below with reference to the accompanying drawings.

[0039] Example 1

[0040] See also Figure 1 , which shows a flow chart of the steps of a process for efficiently preparing silicon nitride ceramics provided in Example 1 of the present application, the process comprising:

[0041] S1, prepare slurry: mix 30g of polynitrosilane liquid, 20g of silicon nitride powder and 4g of sintering aid, then add 12g of photocurable resin and 0.2g of photoinitiator and place them in a ball mill for ball milling to obtain silicon nitride ceramic slurry, wherein the photocurable resin is a mixture of 1,6-hexanediol diacrylate HDDA and pentaerythritol tetraacrylate PETTA, with a mass ratio of 1:1, the sintering aid is aluminum oxide, and the photoinitiator is phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide (819).

[0042] S2, molding: Add silicon nitride ceramic slurry into the light-curing molding machine, set the layer thickness to 20μm, and the exposure dose to 100mJ / cm². Expose, cure and stack layer by layer according to the slice outline of the part drawing to obtain the ceramic molding body.

[0043] S3, curing after cleaning: immerse the ceramic formed body in anhydrous alcohol, clean the uncured resin on the surface by ultrasonic cleaning, and then place it in a UV light box for curing for 3 hours.

[0044] S4, degreasing; placing the solidified ceramic formed body in a nitrogen atmosphere, heating it to 280°C at a rate of 1°C / min and keeping it warm for 1 hour, then heating it to 600°C at a rate of 1°C / min and keeping it warm for 1 hour, and then heating it to 1000°C at a rate of 0.5°C / min and keeping it warm for 3 hours to obtain a ceramic degreased body.

[0045] S5, sintering: heating the degreased ceramic body to 1700°C in a nitrogen environment with a pressure of 5 MPa, wherein the initial heating rate is 5°C / min. The implementer can set the initial heating rate according to the actual situation, and this embodiment does not limit it.

[0046] S501, collecting a surface temperature matrix of a degreased ceramic body at each moment during the sintering process, and constructing a local temperature difference vector for each temperature value in the surface temperature matrix based on the difference between each temperature value in the surface temperature matrix and the rest of the temperature values in its neighborhood window.

[0047] During the heating process of the sintering process, this embodiment uses an ultra-high temperature infrared thermal imager equipped with a high-temperature resistant pinhole lens to collect temperature data on the surface of the ceramic degreased blank at time intervals of 1 minute to obtain a surface temperature matrix of the ceramic degreased blank at each collection moment. Each position in the surface temperature matrix represents each temperature measurement position on the surface of the ceramic degreased blank, and the value of each position in the surface temperature matrix represents the temperature size of each measurement position on the surface of the ceramic degreased blank. The implementer can set the size of the collection time interval according to actual conditions, and this embodiment does not impose any restrictions here.

[0048] Furthermore, in order to improve the accuracy of temperature measurement on the surface of the ceramic degreased body and reduce the interference of external noise on the temperature data collection, the surface temperature matrix is filtered using filtering technology. This embodiment uses mean filtering technology for filtering to obtain the filtered surface temperature matrix of the ceramic degreased body at each collection moment. The implementer can use other existing feasible filtering technologies, and this embodiment does not make specific restrictions on this.

[0049] Because compositional variations can occur at different locations on the surface of a degreased ceramic body, the surface temperature can experience complex variations. These variations can lead to high thermal stresses in certain locations, and in severe cases, can even create the risk of thermal stress cracking. To reduce the high thermal stresses within the degreased ceramic body, the heating rate during sintering must be accurately controlled and adjusted based on the complex surface temperature variations during sintering to avoid any subsequent degradation of the silicon nitride ceramic's quality.

[0050] To analyze the cumulative thermal stress characteristics of local areas on a degreased ceramic body at each acquisition moment, the surface temperature matrix of the degreased ceramic body at acquisition moment t is used as an example. An m×m neighborhood window is set with each temperature value in the surface temperature matrix as the center. In this embodiment, m is set to 9. The implementer can set the value of m according to actual conditions. If the temperature values within the neighborhood window are incomplete, a mean filling technique is used to complete them. Mean filling is a well-known technique, and the specific process is not described in detail here.

[0051] Furthermore, based on the difference between each temperature value in the surface temperature matrix and the rest of the temperature values within its neighborhood window, a local temperature difference vector is constructed for each temperature value in the surface temperature matrix. It should be noted that the difference represents the degree of difference between two variables and can be calculated using methods such as difference, absolute value of difference, square of difference, and ratio.

[0052] This embodiment calculates the temperature difference between each temperature value in the surface temperature matrix and all the remaining temperature values in its neighborhood window, and organizes all the temperature differences into vectors in ascending order, which are recorded as the local temperature difference vectors of each temperature value in the surface temperature matrix. The local temperature difference vectors reflect the temperature difference changes in the local area on the surface of the ceramic degreased body. If the consistency and continuity of the temperature difference changes in the local area are worse and the degree of chaos of the temperature difference changes is higher, it can more effectively reflect the phenomenon of local thermal stress generated on the surface of the ceramic degreased body under temperature regulation, which is likely to affect the density of the surface of the ceramic degreased body. At this time, it is necessary to accurately control and adjust the heating rate during the sintering process in order to reduce the effect of thermal stress accumulation on the ceramic surface.

[0053] S502, analyzing the distribution of differences between adjacent elements in the local temperature difference vector and the degree of disorder of all elements in the local temperature difference vector, and determining the local thermal stress significance of each temperature value in the surface temperature matrix at the corresponding position of the ceramic degreased body.

[0054] Through the above analysis, the first-order difference vector of the local temperature difference vector of each temperature value in the surface temperature matrix is calculated. The first-order difference vector reflects the consistent continuity characteristics of the temperature difference change in the local area, and the mean of the absolute values of all elements in the first-order difference vector is calculated. The product of this mean and the permutation entropy of the local temperature difference vector is recorded as the local thermal stress significance of each temperature value in the surface temperature matrix at the corresponding position of the ceramic degreased body.

[0055] It should be understood that the local thermal stress significance reflects the significant characteristics of the local thermal stress on the surface of the ceramic degreased body. The greater the significant characteristics of the local thermal stress, the higher the degree of chaos of the temperature difference change in the local area and the worse the consistency and continuity, which is prone to thermal stress cracking defects. It is necessary to accurately control and adjust the heating rate during the sintering process. Among them, the calculation of the first-order difference vector and the permutation entropy are well-known technologies and will not be elaborated on in detail.

[0056] It should be noted that, based on the measurable degree of disorder in the distribution of the local temperature difference vector, implementers may choose other feasible calculation methods.

[0057] In another embodiment, the first-order difference vector of the local temperature difference vector of each temperature value in the surface temperature matrix is calculated, and the mean of the absolute values of all elements in the first-order difference vector is calculated. The product of the mean and the information entropy of the local temperature difference vector is recorded as the local thermal stress significance of each temperature value in the surface temperature matrix at the corresponding position of the ceramic degreased body.

[0058] S503, forming a thermal stress distribution matrix with the local thermal stress significance of all temperature values in the surface temperature matrix, and determining the lateral thermal effect singularity of each row vector in the thermal stress distribution matrix based on the similarity between each row vector in the thermal stress distribution matrix and the remaining row vectors, and the rate of change of the difference between adjacent elements in each row vector.

[0059] Furthermore, in order to accurately analyze the distribution characteristics of thermal stress on the surface of the ceramic degreased body in the future, the temperature values corresponding to all data points in the surface temperature matrix are replaced one by one with the local thermal stress significance, and the thermal stress distribution matrix of the ceramic degreased body at each acquisition moment is obtained. The thermal stress distribution matrix reflects the distribution characteristics of thermal stress on the surface of the ceramic degreased body during the sintering process, which is conducive to more accurate control and adjustment of the heating rate during the sintering process, thereby reducing the phenomenon of thermal stress accumulation on the ceramic surface and improving the preparation quality of silicon nitride ceramics.

[0060] During the sintering process of a degreased ceramic body, the greater the variation in the singularity of the thermal effect in different directions on the surface of the degreased ceramic body, the more it indicates the accumulation of singular thermal effects on the body surface during sintering. Furthermore, the more severe this accumulation of singular thermal effects on the body surface, the more effective the control and adjustment of the heating rate during sintering should be, thereby achieving accurate control and adjustment of the heating rate.

[0061] Furthermore, the second-order difference vectors of each row vector in the thermal stress distribution matrix are calculated. The second-order difference vectors reflect the change rate characteristics of the lateral thermal effect in the thermal stress distribution matrix. If the degree of discreteness of the change rate of the lateral thermal effect is higher and the similarity between the row vector and other row vectors is lower, the singularity change of the lateral thermal effect on the row vector can be more reflected.

[0062] Therefore, for each moment, the mean of the similarity between each row vector and all other vectors in the thermal stress distribution matrix is calculated. In this embodiment, cosine similarity is used to measure the similarity between row vectors. In another embodiment, the Jaccard similarity coefficient is used as a method for calculating the similarity. The larger the mean of the similarity, the higher the similarity between each row vector and all other vectors. The calculation method of cosine similarity is a well-known technology, and the specific process is not repeated here.

[0063] Through the above analysis, the lateral thermal effect singularity of each row vector in the thermal stress distribution matrix at each moment is calculated. The specific calculation method is:

[0064] Where, is the transverse thermal effect singularity of the j-th row vector in the thermal stress distribution matrix, is the mean of the cosine similarity between the jth row vector and all other row vectors in the thermal stress distribution matrix, exp() is an exponential function with a natural constant as the base, is the degree of dispersion of all elements in the second-order difference vector of the j-th row vector in the thermal stress distribution matrix. The measurement method of the degree of dispersion can be standard deviation, variance or dispersion coefficient. This implementation uses standard deviation as the calculation method of the degree of dispersion. Implementers can choose other existing feasible calculation methods of the degree of dispersion.

[0065] It should be noted that reflects the rate of change of the thermal effect in the lateral direction in the thermal stress distribution matrix. In another embodiment, The calculation method is as follows: calculate the first-order difference vector of the j-th row vector in the thermal stress distribution matrix, and use the least squares method to perform nonlinear fitting on the first-order difference vector of the j-th row vector to obtain a fitting curve, and calculate the slope of each element in the first-order difference vector of the j-th row vector on the fitting curve. is the degree of dispersion of the slopes of all elements in the first-order difference vector of the j-th row vector, wherein the degree of dispersion is calculated using the standard deviation. The least squares method is a well-known technique, and the specific process is not described in detail.

[0066] It should be understood that the singularity of the lateral thermal effect reflects the singular change characteristics of the lateral thermal effect at different positions on the surface of the ceramic degreased body. The greater the singular change characteristics of the lateral thermal effect, the more serious the singular phenomenon of the accumulated thermal effect on the surface of the ceramic degreased body is. At this time, it is more necessary to timely control and adjust the heating rate during the sintering process to reduce the risk of thermal stress cracking of the ceramic degreased body during the sintering process.

[0067] S504, accordingly, obtain the longitudinal thermal effect singularity of each column vector in the thermal stress distribution matrix, and combine it with the transverse thermal effect singularity to obtain the thermal effect singularity of the thermal stress distribution matrix at the corresponding moment; use the difference in thermal effect singularity at each moment and the previous moment to adjust the heating rate at each moment in the sintering process.

[0068] In order to analyze the singular variation characteristics of the longitudinal thermal effect at different positions on the surface of the degreased ceramic body, the thermal stress distribution matrix is transposed to obtain the transposed matrix of the thermal stress distribution matrix. The thermal stress changes in the row vectors of the transposed matrix of the thermal stress distribution matrix can reflect the singular variation characteristics of the thermal stress in the longitudinal direction in the thermal stress distribution matrix.

[0069] Furthermore, the same calculation method of the transverse thermal effect singularity is used to calculate each row vector in the transposed matrix of the thermal stress distribution matrix to obtain the longitudinal thermal effect singularity of each row vector in the transposed matrix of the thermal stress distribution matrix, which is used as the longitudinal thermal effect singularity of each column vector in the thermal stress distribution matrix. The longitudinal thermal effect singularity reflects the singular change characteristics of the longitudinal thermal effect at different positions on the surface of the ceramic degreased blank. At the same time, combined with the singular changes in the thermal stress in the transverse and longitudinal directions on the surface of the ceramic degreased blank, it can more accurately reflect the singular phenomenon of thermal stress accumulation on the surface of the ceramic degreased blank, which is conducive to more accurate control and adjustment of the heating rate during the sintering process.

[0070] Therefore, for each moment, the mean of the transverse thermal effect singularity of all row vectors in the thermal stress distribution matrix is calculated, and the mean of the longitudinal thermal effect singularity of all column vectors in the thermal stress distribution matrix is calculated. The normalized result of the sum of the mean of the transverse thermal effect singularity and the mean of the longitudinal thermal effect singularity is recorded as the thermal effect singularity of the degreased ceramic body at each acquisition moment. The thermal effect singularity reflects the singularity characteristics of the thermal stress distribution in the transverse and longitudinal directions on the surface of the degreased ceramic body, and can more comprehensively and accurately reflect the singular change characteristics of the thermal stress distribution on the surface of the degreased ceramic body during the sintering process. It can accurately control and adjust the heating rate during the sintering process to avoid the accumulation of thermal stress inside the degreased ceramic body during the sintering process. Among them, the normalization method in this embodiment adopts the Sigmoid function. The implementer can choose other existing feasible normalization methods at will, and this embodiment does not limit it here.

[0071] Generally speaking, if the singularity of the thermal stress distribution continues to increase during the sintering process, that is, the thermal effect singularity continues to increase, it means that the heating rate of the sintering process is relatively large, which makes the thermal stress distribution show more significant singular changes, and even causes the risk of thermal stress cracking on the surface of the ceramic degreased body. At this time, the heating rate of the sintering process should be reduced; on the contrary, if the thermal effect singularity continues to decrease during the sintering process, it means that the heating rate of the sintering process is relatively small, which makes the temperature distribution on the surface of the ceramic degreased body uniform. In order to improve the efficiency of preparing silicon nitride ceramics, the heating rate of the sintering process should be increased at this time.

[0072] Through the above analysis, the heating rate at each moment in the sintering process is adjusted. The specific calculation method is:

[0073] Where VT is the adjusted heating rate at each acquisition moment during the sintering process, V is the actual heating rate at each moment during the sintering process, and C is the thermal effect singularity at each moment during the sintering process. is the singularity of the thermal effect at the previous acquisition moment during the sintering process. Recorded as the first difference, the flow chart of the temperature rise rate adjustment in the sintering stage of silicon nitride ceramics is as follows: Figure 2 shown.

[0074] During the sintering process of the degreased ceramic body, if the singularity of the thermal effect at adjacent sampling moments during the sintering process increases, in order to avoid the accumulation of thermal stress inside the degreased ceramic body material during the sintering process, the heating rate during the sintering process is reduced; if the singularity of the thermal effect at adjacent sampling moments during the sintering process decreases, in order to improve the efficiency of preparing silicon nitride ceramics, the heating rate during the sintering process is increased.

[0075] This embodiment utilizes a PID (Proportion Integration Differentiation) controller to intelligently control the heating rate during sintering based on the adjusted heating rate at each sampling point during the sintering process. This prevents thermal stress accumulation within the degreased ceramic body during sintering and improves the efficiency of silicon nitride ceramic production. The PID controller is well-known technology, and the specific process is not described in detail here.

[0076] S6, after the sintering is completed, the heat is kept, the temperature is lowered, and the furnace is cooled to obtain silicon nitride ceramics.

[0077] Finally, after sintering is completed, the temperature is raised to 1700°C, kept at this temperature for 1 hour, then cooled to 800°C at a rate of 1°C / min and cooled in the furnace to obtain silicon nitride ceramics.

[0078] Example 2

[0079] See also Figure 1 , which shows a flow chart of the steps of a process for efficiently preparing silicon nitride ceramics provided in Example 2 of the present application, the process comprising:

[0080] S1, prepare slurry: mix 30g of polynitrosilane liquid, 50g of silicon nitride powder and 6g of sintering aid, then add 30g of photocurable resin and 0.4g of photoinitiator and place them in a ball mill for ball milling to obtain silicon nitride ceramic slurry, wherein the photocurable resin is a mixture of 1,6-hexanediol diacrylate HDDA and pentaerythritol tetraacrylate PETTA, with a mass ratio of 1:1, the sintering aid is aluminum oxide, and the photoinitiator is phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (819).

[0081] S2, molding: Add silicon nitride ceramic slurry into the light-curing molding machine, set the layer thickness to 20μm, and the exposure dose to 150mJ / cm². Expose, cure and stack layer by layer according to the slice outline of the part drawing to obtain the ceramic molding body.

[0082] S3, curing after cleaning: immerse the ceramic formed body in anhydrous alcohol, clean the uncured resin on the surface by ultrasonic cleaning, and then place it in a UV light box for curing for 4 hours.

[0083] S4, degreasing; placing the solidified ceramic formed body in a nitrogen atmosphere, heating it to 280°C at a rate of 2°C / min and keeping it warm for 2h, then heating it to 600°C at a rate of 2°C / min and keeping it warm for 2h, and then heating it to 1000°C at a rate of 1°C / min and keeping it warm for 4h to obtain a ceramic degreased body.

[0084] S5, sintering: heating the degreased ceramic body to 1800°C in a nitrogen environment at a pressure of 8 MPa, wherein the initial heating rate is 5°C / min. The implementer can set the initial heating rate according to the actual situation, and this embodiment does not limit it.

[0085] Then, the heating rate during the sintering process is adjusted using the same method as steps S501 to S504 in Example 1 of the present application.

[0086] S6, after the sintering is completed, the heat is kept, the temperature is lowered, and the furnace is cooled to obtain silicon nitride ceramics.

[0087] Finally, after sintering is completed, the temperature is raised to 1800°C, kept at this temperature for 2 hours, then cooled to 800°C at a rate of 2°C / min and cooled in the furnace to obtain silicon nitride ceramics.

[0088] Example 3

[0089] See also Figure 1 , which shows a flow chart of the steps of a process for efficiently preparing silicon nitride ceramics provided in Example 3 of the present application, the process comprising:

[0090] S1, prepare slurry: mix 30g of polynitrosilane liquid, 80g of silicon nitride powder and 8g of sintering aid, then add 40g of photocurable resin and 0.6g of photoinitiator and place them in a ball mill for ball milling to obtain silicon nitride ceramic slurry, wherein the photocurable resin is a mixture of 1,6-hexanediol diacrylate HDDA and pentaerythritol tetraacrylate PETTA, with a mass ratio of 1:1, the sintering aid is aluminum oxide, and the photoinitiator is phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide (819).

[0091] S2, molding: Add silicon nitride ceramic slurry into the light-curing molding machine, set the layer thickness to 20μm, and the exposure dose to 200mJ / cm². Expose, cure and stack layer by layer according to the slice outline of the part drawing to obtain the ceramic molding body.

[0092] S3, curing after cleaning: immerse the ceramic formed body in anhydrous alcohol, clean the uncured resin on the surface by ultrasonic cleaning, and then place it in a UV light box for curing for 5 hours.

[0093] S4, degreasing; placing the solidified ceramic formed body in a nitrogen atmosphere, heating it to 280°C at a rate of 2°C / min and keeping it warm for 3 hours, then heating it to 600°C at a rate of 2°C / min and keeping it warm for 3 hours, and then heating it to 1000°C at a rate of 1°C / min and keeping it warm for 5 hours to obtain a ceramic degreased body.

[0094] S5, sintering: heating the degreased ceramic body to 1850°C in a nitrogen environment with a pressure of 10 MPa, wherein the initial heating rate is 5°C / min. The implementer can set the initial heating rate according to the actual situation, and this embodiment does not limit it.

[0095] Then, the heating rate during the sintering process is adjusted using the same method as steps S501 to S504 in Example 1 of the present application.

[0096] S6, after the sintering is completed, the heat is kept, the temperature is lowered, and the furnace is cooled to obtain silicon nitride ceramics.

[0097] Finally, after sintering is completed, the temperature is raised to 1850°C, kept at this temperature for 3 hours, then cooled to 800°C at a rate of 2°C / min and cooled in the furnace to obtain silicon nitride ceramics.

[0098] In order to verify the performance of the silicon nitride ceramics prepared in this application, this application sets various comparative examples, specifically:

[0099] Comparative Example 1

[0100] Comparative Example 1 follows exactly the same process steps and parameters as Example 1 of the present application, except that in the S5 sintering step, the heating rate remains unchanged from the initial heating rate, that is, the heating rate is not dynamically adjusted, to obtain the silicon nitride ceramic prepared in Comparative Example 1.

[0101] Comparative Example 2

[0102] Comparative Example 2 follows exactly the same process steps and parameters as Example 2 of the present application, except that in the S5 sintering step, the heating rate remains unchanged from the initial heating rate, that is, the heating rate is not dynamically adjusted, to obtain the silicon nitride ceramic prepared in Comparative Example 2.

[0103] Comparative Example 3

[0104] Comparative Example 3 follows exactly the same process steps and parameters as Example 3 of the present application, except that in the S5 sintering step, the heating rate remains unchanged from the initial heating rate, that is, the heating rate is not dynamically adjusted, to obtain the silicon nitride ceramic prepared in Comparative Example 3.

[0105] The performance comparison results of the silicon nitride ceramics prepared in the examples of the present application and the comparative examples are shown in Table 1.

[0106] Table 1 Comparison of silicon nitride ceramic properties

[0107]

[0108] It can be seen from Table 1 that the performance of the silicon nitride ceramics finally prepared can be improved by adjusting the heating rate in the sintering stage during the preparation process of silicon nitride ceramics.

[0109] It should be noted that the order in which the embodiments of the present application are presented is for illustrative purposes only and does not necessarily represent the superiority or inferiority of the embodiments. Furthermore, the foregoing descriptions of specific embodiments of this specification are provided. Furthermore, the processes depicted in the accompanying drawings do not necessarily require the specific order or sequential sequence shown to achieve the desired results. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0110] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0111] The above-described embodiments are only used to illustrate the technical solutions of the present application, and not to limit them. Modifications to the technical solutions described in the aforementioned embodiments, or equivalent replacements of some of the technical features therein, do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A process for efficiently preparing silicon nitride ceramics, characterized in that: The process includes: The polysilane liquid, silicon nitride powder, and sintering aid are mixed, and then a light-curing resin and a photoinitiator are added, and ball milling is performed to obtain a silicon nitride ceramic slurry; placing the silicon nitride ceramic slurry in a photocuring machine for photocuring to obtain a ceramic formed body; cleaning the ceramic formed body and then curing it; Degreasing the solidified ceramic formed body to obtain a degreased ceramic body; Sintering a degreased ceramic body, collecting a surface temperature matrix of the degreased ceramic body at each moment during the sintering process, and constructing a local temperature difference vector for each temperature value in the surface temperature matrix based on the difference between each temperature value in the surface temperature matrix and the rest of the temperature values in its neighborhood window; Analyzing the distribution of differences between adjacent elements in the local temperature difference vector and the degree of disorder of all elements in the local temperature difference vector to determine the local thermal stress significance at the corresponding position of the degreased ceramic body for each temperature value in the surface temperature matrix; wherein the local thermal stress significance reflects the significant characteristics of the local thermal stress on the surface of the degreased ceramic body; the greater the significant characteristics of the local thermal stress, the higher the degree of disorder and the worse the consistency and continuity of the temperature difference change in the local area; The local thermal stress significance of all temperature values in the surface temperature matrix is used to form a thermal stress distribution matrix, and based on the similarity between each row vector in the thermal stress distribution matrix and the remaining row vectors, and the distribution of the rate of change of the difference between adjacent elements in each row vector, the lateral thermal effect singularity of each row vector in the thermal stress distribution matrix is determined; Accordingly, the longitudinal thermal effect singularity of each column vector in the thermal stress distribution matrix is obtained, and combined with the transverse thermal effect singularity, the thermal effect singularity of the thermal stress distribution matrix at the corresponding moment is obtained; the difference in the thermal effect singularity at each moment and the previous moment is used to adjust the heating rate at each moment in the sintering process; After sintering is completed, the temperature is kept, the temperature is lowered, and the furnace is cooled to obtain silicon nitride ceramics; The adjusting of the heating rate at each moment during the sintering process includes: The normalized result of the sum of the mean of the longitudinal thermal effect singularity of all column vectors and the mean of the transverse thermal effect singularity of all row vectors in the thermal stress distribution matrix is taken as the thermal effect singularity of the thermal stress distribution matrix at the corresponding moment; The difference between the thermal effect singularity at each moment and the previous moment is calculated and recorded as the first difference. The multiplication result of the first difference and the heating rate at each moment is calculated. The adjusted heating rate at each moment is the difference between the heating rate at each moment and the multiplication result.

2. A process for efficiently preparing silicon nitride ceramics according to claim 1, characterized in that: The mixing mass ratio of the polynitrosilane liquid, silicon nitride powder, sintering aid, photocurable resin, and photoinitiator is 30:20~80:4~8:12~40:0.2~0.6g, the photocurable resin is a mixture of 1,6-hexanediol diacrylate HDDA and pentaerythritol tetraacrylate PETTA in a mass ratio of 1:1, the sintering aid is one of magnesium oxide and aluminum oxide, and the photoinitiator is phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide.

3. A process for efficiently preparing silicon nitride ceramics according to claim 1, characterized in that: The photocuring process is performed with a layer thickness of 20 μm and an exposure dose of 100-200 mJ / cm².

4. A process for efficiently preparing silicon nitride ceramics according to claim 1, characterized in that: The curing after cleaning is performed by immersing the ceramic formed body in anhydrous alcohol, cleaning the uncured resin on the surface by ultrasonic cleaning, and then curing it in a UV light box for 3 to 5 hours.

5. A process for efficiently preparing silicon nitride ceramics according to claim 1, characterized in that: The degreasing comprises: The solidified ceramic formed body is placed in a nitrogen atmosphere, heated to 280°C at a rate of 1~2°C / min and kept warm for 1~3 hours, then heated to 600°C at a rate of 1~2°C / min and kept warm for 1~3 hours, and then heated to 1000°C at a rate of 0.5~1°C / min and kept warm for 3~5 hours to obtain a ceramic degreased body.

6. A process for efficiently preparing silicon nitride ceramics according to claim 1, characterized in that: The sintering comprises: The degreased ceramic body was heated to 1700-1850°C in a nitrogen environment with a pressure of 5-10 MPa, wherein the initial heating rate was 5°C / min.

7. A process for efficiently preparing silicon nitride ceramics according to claim 1, characterized in that: The local temperature difference vector is obtained by arranging the differences between each temperature value in the surface temperature matrix and all other temperature values in its neighborhood window in ascending order; The local thermal stress significance is the product of the mean of the absolute values of all elements in the first-order difference vector of the local temperature difference vector of each temperature value and the permutation entropy of the local temperature difference vector.

8. A process for efficiently preparing silicon nitride ceramics according to claim 1, characterized in that: The determination of the transverse thermal effect singularity includes: The average value of the similarity between each row vector and all other row vectors in the thermal stress distribution matrix is calculated, and the inverse of the average value is used as an exponential function with a natural constant as the base. The discreteness of all elements in the second-order difference vector of each row vector in the thermal stress distribution matrix is calculated, and the lateral thermal effect singularity is the product of the discreteness and the calculation result of the exponential function.

9. A process for efficiently preparing silicon nitride ceramics according to claim 1, characterized in that: The holding time is 1-3 hours, the cooling rate is 1-2°C / min, and the temperature is lowered to 800°C before cooling with the furnace.

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