A low thermal expansion dual-phase ceramic and method of making

Abstract

The application provides a low-thermal expansion dual-phase ceramic and a preparation method, and belongs to the field of ceramic materials.The dual-phase ceramic comprises a negative thermal expansion phase and a positive thermal expansion phase;the positive thermal expansion phase has an isolation layer on the edge;the positive thermal expansion phase accounts for 50-85% of the volume percentage of the dual-phase ceramic;the closer the negative thermal expansion phase is to the positive thermal expansion phase, the smaller the average grain size is.By setting the grains of the negative thermal expansion phase and the positive thermal expansion phase according to a certain rule and setting the isolation layer, the low-thermal expansion dual-phase ceramic which can be applied in engineering and does not produce cracks when the positive thermal expansion phase accounts for more than 50% is prepared.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of ceramic materials, and particularly relates to a low thermal expansion dual-phase ceramic and a preparation method. BACKGROUND

[0002] Due to the influence of non-harmonic vibration potential energy between atoms, the volume of most substances expands with the increase of temperature. Thermal expansion will affect the service life and precision of many large-scale engineering and precision devices, such as electronic packaging, laser detection, satellite antennas, etc. A small part of materials will shrink with the increase of temperature, i.e. negative thermal expansion. People expect to solve the problems caused by thermal expansion through negative thermal expansion or even zero thermal expansion materials. Reducing the thermal expansion of compounds and exploring methods to enhance the negative thermal expansion of compounds are of great significance for the application of solid materials in precision instruments.

[0003] The application of negative thermal expansion materials is limited at present. The method of element substitution is often used in the regulation of material properties. The method of element substitution is easy to affect the performance range, resulting in poor effect after material regulation and not meeting the expectation. In the prior art, low thermal expansion materials are prepared by sintering after mixing of metal or amorphous alloy and negative thermal expansion particles. Since the metal or amorphous material has a larger deformation capacity compared with the ceramic material, cracks are not easy to occur during preparation or subsequent use. However, the dual-phase composite ceramic prepared by using positive thermal expansion ceramic particles and negative thermal expansion ceramic particles is easy to cause large difference in thermal expansion coefficient, resulting in cracks during use, which greatly shortens the service life. Therefore, it is very urgent to develop a method for preparing low thermal expansion dual-phase ceramic with good regulation expectation. SUMMARY

[0004] To solve the above problems, the present application provides a low thermal expansion dual-phase ceramic and a preparation method. The crystal grains of the negative thermal expansion phase and the positive thermal expansion phase are arranged according to a certain rule, and an isolation layer is arranged, so that the low thermal expansion dual-phase ceramic which can be used in engineering application and does not produce cracks when the positive thermal expansion phase accounts for more than 50% of the volume percentage of the dual-phase ceramic is prepared.

[0005] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0006] On the one hand, the present application provides a low thermal expansion dual-phase ceramic, which comprises a negative thermal expansion phase and a positive thermal expansion phase; the edge of the positive thermal expansion phase has an isolation layer; the positive thermal expansion phase accounts for 50% to 85% of the volume percentage of the dual-phase ceramic; and the closer the negative thermal expansion phase is to the positive thermal expansion phase, the smaller the average grain size is.

[0007] Further, the linear thermal expansion coefficient of the negative thermal expansion phase is -15 to -25 ppm / K.

[0008] Further, the linear thermal expansion coefficient of the positive thermal expansion phase is 3-10 ppm / K.

[0009] Further, the density of the dual-phase ceramic is 90-98%.

[0010] Further, the ratio of the average particle size of the negative thermal expansion phase to the positive thermal expansion phase is 1:6-50; and the average particle size of the positive thermal expansion phase is 10-100 μm.

[0011] Further, the thickness of the isolation layer is not more than 200 nm.

[0012] Further, the positive thermal expansion phase is one or more of carbide ceramic, nitride ceramic, boride ceramic and polycrystalline diamond; and the negative thermal expansion phase is a ceramic containing a general formula One of the powders, wherein A and M include at least one element selected from P, Mg, Al, Si, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, La, Ta, W, Bi.

[0013] In another aspect, the present application provides a method for preparing a low thermal expansion dual-phase ceramic, characterized in that it comprises the following steps: preparing a negative thermal expansion ceramic powder and a positive thermal expansion ceramic powder coated with an isolation layer; based on the average particle size of the positive thermal expansion ceramic powder, selecting a first preset average particle size of the negative thermal expansion ceramic powder to mix with the positive thermal expansion ceramic powder, mixing and then pre-sintering, and then vibrating the sintered product; mixing a second preset average particle size of the negative thermal expansion ceramic powder with the pre-sintered product after vibrating according to a ratio and sintering, and then obtaining the product; and the second preset average particle size is greater than the first preset average particle size.

[0014] Further, the first preset average particle size r is calculated as follows:

[0015]

[0016] wherein λ is a correction coefficient, r1 is the average particle size of the positive thermal expansion ceramic powder, and r0 is a reference particle size; the D50 / D10 of the powder with the first preset average particle size is not more than 5; and the volume ratio of the powder with the first preset average particle size to the positive thermal expansion ceramic powder is 1-5%.

[0017] Further, the ratio of the second preset average particle size to the average particle size of the positive thermal expansion ceramic powder is 1:2-30.

[0018] The technical scheme provided by the embodiments of the present application has the following beneficial effects:

[0019] (1) through the positive thermal expansion particles and negative thermal expansion particles mixed after sintering to prepare a dual-phase ceramic material, dual-phase ceramic to achieve low thermal expansion effect in order to achieve engineering applications, namely to achieve low thermal expansion effect, need to consider the proportion of negative thermal expansion phase and positive thermal expansion phase, by calculating the positive thermal expansion phase to occupy at least 50%, at this time there are corresponding problems, on the one hand, the positive thermal expansion phase may react with the negative thermal expansion phase, resulting in the negative thermal expansion effect is weakened; on the other hand, the positive thermal expansion phase and the negative thermal expansion phase tear in the grain boundary during thermal cycling, cracks, and the cracks in the ceramic material is easy to expand so that the dual-phase ceramic is broken, in order to solve the above problems, the present application is provided with an insulating layer on the edge of the positive thermal expansion phase, to prevent the positive thermal expansion phase and the negative thermal expansion phase from reacting, and the insulating layer allows a certain elastic slip between the positive thermal expansion phase and the negative thermal expansion phase without cracks.

[0020] (2) a structure is proposed, that is, the negative thermal expansion phase is used to form a framework structure, which is used to coat and limit the positive thermal expansion phase, and the framework structure is limited in particle size, that is, the closer the negative thermal expansion phase is to the positive thermal expansion phase, the smaller the average grain size is, the closer the negative thermal expansion phase is to the positive thermal expansion phase, and the small size of the negative thermal expansion phase is combined with the positive thermal expansion phase uniformly, and is coordinated in the deformation process, combined with the above insulating layer, at least 10 4 orders of magnitude of thermal cycling conditions, the dual-phase ceramic does not produce cracks or cracks.

[0021] (3) the present application limits the positive thermal expansion phase to not more than 85% of the volume percentage of the dual-phase ceramic, that is, when the proportion of the negative thermal expansion phase is not more than 15%, the negative thermal expansion phase is too small, which leads to the inability to effectively constrain the positive thermal expansion phase, and the corresponding low thermal expansion dual-phase ceramic cannot be successfully prepared. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced below, and obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0023] Figure 1 X-ray diffraction pattern of the sample after replacing Ti2O3 ceramic powder with different proportions of SiC ceramic powder in the present application embodiment 1;

[0024] Figure 2 Electron scanning microscope image of the dual-phase ceramic when the addition amount of 75vol% SiC powder in the present application embodiment 1;

[0025] Figure 3 Elemental energy spectrum of the dual-phase ceramic when the addition amount of 75vol% SiC powder in the present application embodiment 1;

[0026] Figure 4 The linear expansion curve diagram of different SiC powder adding amount in the embodiment 1 of the application;

[0027] Figure 5 The linear expansion curve diagram of different TiC powder adding amount in the embodiment 4 of the application;

[0028] Figure 6 The linear expansion curve diagram of different ZrN powder adding amount in the embodiment 5 of the application;

[0029] Figure 7 The linear expansion curve diagram of different HfB2 powder adding amount in the embodiment 6 of the application. DETAILED DESCRIPTION

[0030] In order to make the objects, technical solutions and advantages of the application clearer, the following will further describe the application in detail with reference to the drawings and specific embodiments.

[0031] The application provides a low thermal expansion dual-phase ceramic, which comprises a negative thermal expansion phase and a positive thermal expansion phase; the positive thermal expansion phase has an isolation layer on the edge; the positive thermal expansion phase accounts for 50%-85% of the volume percentage of the dual-phase ceramic; the closer the negative thermal expansion phase is to the positive thermal expansion phase, the smaller the average grain size is.

[0032] The low thermal expansion of the application is the absolute value of the linear expansion coefficient below 2ppm / K. The positive thermal expansion phase and the negative thermal expansion phase are both ceramic phases, the isolation layer is prepared from an inert substance which is difficult to react with the negative thermal expansion phase and the positive thermal expansion phase at high temperature, such as coated with boron nitride material or directly prepared by oxidation, and the isolation layer is beneficial to the small elastic slip between the positive thermal expansion phase and the negative thermal expansion phase, thereby avoiding the generation of cracks.

[0033] The application provides a low-thermal expansion dual-phase ceramic, which is prepared by mixing positive thermal expansion particles and negative thermal expansion particles, and the dual-phase ceramic needs to achieve low thermal expansion effect to realize engineering application, that is, to achieve low thermal expansion effect, the proportion of the negative thermal expansion phase and the positive thermal expansion phase needs to be considered, and the positive thermal expansion phase needs to account for at least 50% through calculation, at this time, there are corresponding problems, on the one hand, the positive thermal expansion phase may react with the negative thermal expansion phase to weaken the negative thermal expansion effect, and on the other hand, the positive thermal expansion phase and the negative thermal expansion phase are torn at the grain boundary in the thermal cycle process, cracks are generated, and the cracks in the ceramic material are easy to expand to make the dual-phase ceramic break, in order to solve the above problems, the application sets an isolation layer on the edge of the positive thermal expansion phase to prevent the positive thermal expansion phase and the negative thermal expansion phase from reacting, and the isolation layer allows a certain degree of elastic slip between the positive thermal expansion phase and the negative thermal expansion phase without generating cracks, secondly, a structure is proposed, that is, the negative thermal expansion phase is used to form a framework structure to coat and limit the positive thermal expansion phase, and the framework structure is limited in particle size, that is, the smaller the average grain size of the negative thermal expansion phase, the closer to the positive thermal expansion phase, and the small-size grain of the negative thermal expansion phase is combined with the positive thermal expansion phase uniformly, and is coordinated in the deformation process, in combination with the above isolation layer, the dual-phase ceramic can be successfully prepared without cracks or cracking under the condition of thermal cycle of at least 10 4 orders of magnitude; finally, the application limits the positive thermal expansion phase to account for not more than 85% of the volume percentage of the dual-phase ceramic, that is, when the proportion of the negative thermal expansion phase is not more than 15%, the positive thermal expansion phase cannot be effectively constrained due to too little negative thermal expansion phase, and the corresponding low-thermal expansion dual-phase ceramic cannot be successfully prepared.

[0034] It should be pointed out that the stability of the positive thermal expansion ceramic phase in the application is higher than that of the negative thermal expansion phase, that is, the thermal stability of the positive thermal expansion ceramic phase is high.

[0035] Specifically, the linear thermal expansion coefficient of the negative thermal expansion phase is -15 to -25 ppm / K, and the linear thermal expansion coefficient of the positive thermal expansion phase is 3 to 10 ppm / K.

[0036] Specifically, the density of the dual-phase ceramic is 95-98%. The density of the dual-phase ceramic affects the thermal expansion performance and the anti-cracking ability of the dual-phase ceramic. On one hand, since the negative thermal expansion phase is used to coat the positive thermal expansion phase in the application, extrusion force is generated between the positive thermal expansion phase and the negative thermal expansion phase during the deformation process of the dual-phase ceramic. The greater the extrusion force, the more likely the cracks are to occur. The negative thermal expansion phase needs to have a certain porosity, and the porosity can absorb the extrusion force between the two phases to prevent the extrusion force from exceeding the compression resistance of the structure itself and causing cracks. On the other hand, if the porosity is too large, the increased volume of the positive thermal expansion phase due to temperature rise will be absorbed by the porosity during the extrusion process, and the effect of the negative thermal expansion phase will dominate, but the strength will be reduced.

[0037] In the application, the density is measured by the existing technology, which will not be described here.

[0038] The ratio of the average particle size of the negative thermal expansion phase to the average particle size of the positive thermal expansion phase is 1:6-50, and the average particle size of the positive thermal expansion phase is 10-100 μm. Due to the size effect of the particle size, the performance of the final product of the dual-phase ceramic is greatly affected. The average particle size of the negative thermal expansion phase is smaller than that of the positive thermal expansion phase, which ensures that the negative thermal expansion phase can form a certain framework structure. On the other hand, the particle size is not too small, which will reduce the porosity and increase the density, and high density will increase the crack tendency of the dual-phase ceramic.

[0039] It should be pointed out that the average particle size of the negative thermal expansion phase and the positive thermal expansion phase is measured by scanning electron microscope pictures.

[0040] The thickness of the isolation layer is not more than 200 nm. The isolation layer prevents the positive thermal expansion phase and the negative thermal expansion phase from generating cracks, and can also generate elastic slip between the positive thermal expansion phase and the negative thermal expansion phase. Therefore, the thickness of the isolation layer should not be too thick, otherwise non-elastic slip may occur between the two phases, thereby increasing the probability of cracks.

[0041] The positive thermal expansion phase is one or more of carbide ceramic, nitride ceramic, boride ceramic and polycrystalline diamond; and the negative thermal expansion phase is a phase containing a general formula One of the powders, wherein A and M include at least one element selected from P, Mg, Al, Si, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, La, Ta, W, Bi.

[0042] The carbide ceramic includes, for example, SiC, TiC, ZrC, TaC, etc.; the nitride ceramic includes AlN, Si3N4, ZrN, HfN, TaN, etc.; the boride ceramic includes TiB2, HfB2, ZrB2, TaB2, etc.; and the polycrystalline diamond (PCD) ceramic.

[0043] The application further provides a preparation method of the low-thermal-expansion dual-phase ceramic.

[0044] S1. Preparing a negative thermal expansion ceramic powder and a positive thermal expansion ceramic powder coated with an isolation layer.

[0045] The negative thermal expansion ceramic powder can be purchased or prepared by using the prior art, and the application uses Ti2O3 for illustration.

[0046] The preparation method of the isolation layer includes coating treatment or high-temperature oxidation treatment; the coating treatment process is as follows: the high-thermal-stable-phase ceramic powder to be treated is put into a powder stirrer, boron nitride is sprayed while stirring, the spraying ratio is 5-20 ml / 100 g, after the spraying is completed, the stirring is continued for 20-40 min, and then the powder is dried in a vacuum drying box;

[0047] The high-temperature oxidation treatment process is as follows: the high-thermal-stable-phase ceramic powder to be treated is put into a crucible, and is kept at a temperature above 1000℃ for 3-5 h.

[0048] S2. Based on the average particle diameter of the positive thermal expansion ceramic powder, the negative thermal expansion ceramic powder with a first preset average particle diameter is selected and mixed with the positive thermal expansion ceramic powder, and then pre-sintering is performed, and the sintering is vibrated and crushed after being completed.

[0049] The calculation method of the first preset average particle diameter r is as follows:

[0050]

[0051] Wherein, λ is a correction factor, r1 is the average particle diameter of the positive thermal expansion ceramic powder, and r0 is a reference particle diameter, and the value of r1 is not greater than r0; the powder with the first preset average particle diameter has a D50 / D10 not greater than 5; and the volume ratio of the powder with the first preset average particle diameter to the positive thermal expansion ceramic powder is 1-5%.

[0052] In the application, the value range of λ is 0.09-0.11, and the value of r0 is 130 μm.

[0053] It should be pointed out that, in addition to the first preset average particle size, the D50 / D10 value of the powder is also limited, the above-mentioned limitation ensures that the proportion of fine powder is large, the fine powder has large surface energy, and the adhesion to the surface of the positive thermal expansion ceramic powder is large, thus having a spontaneous gradient distribution characteristic.

[0054] The mixing process is as follows: an acoustic resonance mixer is used, the instrument model is MixBox-G1, the mixing vibration frequency is 60 Hz, and the mixing time is 4-24 min.

[0055] The pre-sintering is performed by heating in an inert gas atmosphere to 200-300 ℃ below the negative thermal expansion ceramic melting point, and the temperature is kept for at least 20 min. After the temperature keeping is finished, the furnace is cooled, and no pressure treatment is needed during the heating process. After the pre-sintering is completed, the vibration crushing is performed, the positive thermal expansion ceramic particles adhered to the negative thermal expansion phase are separated by vibration, and the positive thermal expansion ceramic particles are prevented from being crushed. In the embodiment of the present application, the vibration frequency of the vibration machine is 20-30 Hz, the vibration amplitude is 2-3 mm, and the vibration time is 10-40 min.

[0056] S3. According to the proportion, the negative thermal expansion ceramic powder with the second preset average particle size is mixed with the pre-sintered powder after vibration crushing and sintered, and the product is obtained. The second preset average particle size is larger than the first preset average particle size. The ratio of the second preset average particle size to the average particle size of the positive thermal expansion ceramic powder is 1:2-30.

[0057] The addition amount of the negative thermal expansion ceramic powder with the second preset average particle size is the theoretical addition amount calculated according to the proportion minus the addition amount of the negative thermal expansion ceramic powder with the first preset average particle size.

[0058] The mixing process is as follows: an acoustic resonance mixer is used, the instrument model is MixBox-G1, the mixing vibration frequency is 60 Hz, and the mixing time is 4-24 min.

[0059] The sintering process is as follows: the discharge plasma sintering is used, the heating rate is 30-200 ℃ / min, the pressure is 30 MPa-80 MPa, the sintering temperature is 200-1000 ℃ but not less than 500 ℃ below the negative thermal expansion ceramic melting point, and the sintering time is 4-24 min. After the furnace is cooled, the final product is obtained.

[0060] The sintering process and the particle size are very critical, and the purpose is to prepare a dual-phase ceramic product with a density of 90-98% to meet the requirements of the present application.

[0061] In order to better illustrate the embodiments of the present application, the present application will be further described in detail through specific examples.

[0062] Example 1

[0063] The embodiment provides a preparation method of low-thermal-expansion dual-phase ceramic, and comprises the following steps:

[0064] S1. preparing negative-thermal-expansion ceramic powder and positive-thermal-expansion ceramic powder coated with an isolation layer.

[0065] The preparation method of the isolation layer is as follows: 100 g of SiC powder with an average particle size of 15 μm is taken, 5 ml of boron nitride solution is added, the boron nitride solution is a commercially available boron nitride high-temperature release agent, after spraying, stirring is continued for 20 min, and then the isolation layer is dried in a vacuum drying box, and the thickness of the isolation layer is measured to be 80 nm.

[0066] S2. Ti2O3 powder with a first preset average particle size is selected according to the average particle size of the positive-thermal-expansion ceramic powder, and is mixed with the SiC powder, and after mixing, pre-sintering is performed, and after sintering is completed, vibration crushing is performed.

[0067] The formula is as follows:

[0068]

[0069] λ is 0.09, r0 is 130 μm, and the first preset average particle size r is calculated to be 1.2 μm;

[0070] The volume ratio of the Ti2O3 powder with the first preset average particle size to the SiC powder is 1%, and then mixing is performed, the mixing vibration frequency is 60 Hz, the mixing time is 4 min, heating is performed to 1100 DEG C in an inert gas, and then vibration is performed for 10 min by using a vibration machine with a vibration frequency of 20-30 Hz and an amplitude of 2-3 mm.

[0071] S3. The SiC ceramic powder is proportioned into 75 vol%, 45 vol% and 0% according to the volume percentage, the second preset average particle size of the Ti2O3 powder is calculated to be 74 vol%, 44 vol% and 0% respectively, the average particle size is 5.2 μm, and the pre-sintered powder after vibration crushing is mixed, the vibration frequency is 60 Hz, and the mixing time is 4 min.

[0072] Discharge plasma sintering is adopted, the heating rate is 30 DEG C / min, the pressure is 30 MPa, sintering is performed at 1130 DEG C for 4 min, and after furnace cooling, the final product is obtained.

[0073] Figure 1 After the Ti2O3 ceramic powder is replaced by the SiC ceramic powder with different proportions, the X-ray diffraction pattern of the sample is obtained, it can be seen that there is no obvious impurity peak except the characteristic peaks of Ti2O3 and SiC, and it is indicated that there is no interface reaction between the two-phase ceramics or the interface reaction is not obvious.

[0074] Figure 2 The electron scanning microscope picture of the dual-phase ceramic for the 75vol% SiC powder addition amount, Figure 3 The elemental energy spectrum for the 75vol% SiC powder addition amount, it can be seen that the SiC phase with a larger area is surrounded by Ti2O3, Ti2O3 forms a skeleton structure to support and constrain the SiC phase, the closer to the surface of the SiC phase, the smaller the size of the Ti2O3 phase.

[0075] Figure 4 The linear expansion curve diagram for different SiC powder addition amounts.

[0076] Through the thermal cycle test of the ceramic, the temperature interval is 0-200℃, the heating rate is 5℃ / s, and the thermal cycle experiment is carried out for 1000 times at the end point temperature for 10min, no crack is found in the three groups of samples with different contents, and the density of the dual-phase ceramic is 90.5%.

[0077] Example 2

[0078] The embodiment provides a preparation method of a low-thermal expansion dual-phase ceramic, comprising the following steps:

[0079] S1. Prepare a negative thermal expansion ceramic powder and a positive thermal expansion ceramic powder coated with an isolation layer.

[0080] The preparation method of the isolation layer is as follows: 100g of SiC powder with an average particle size of 45μm is weighed, 10ml of boron nitride solution is added, the boron nitride solution is a commercially available boron nitride high-temperature release agent, after spraying, continue to stir for 30min, after stirring, put into a vacuum drying box for drying, and the thickness of the isolation layer is measured to be 120nm.

[0081] S2. Based on the average particle size of the positive thermal expansion ceramic powder, Ti2O3 powder with a first preset average particle size is selected and mixed with the SiC powder, then mixed and pre-sintered, and then vibrated and crushed after sintering.

[0082] Through the formula:

[0083]

[0084] λ is 0.09, r0 is 130μm, and the first preset average particle size r is calculated to be 2.9μm;

[0085] The D50 / D10 of the first pre-set average particle size Ti2O3 powder is 3.8; the volume ratio of the first pre-set average particle size Ti2O3 powder to the SiC powder is 2%. Then, mixing is performed at a vibration frequency of 60 Hz for 10 min, heating to 1250°C in an inert gas for 20 min, and then vibration is performed using a vibration machine at a vibration frequency of 20-30 Hz and an amplitude of 2-3 mm for 20 min.

[0086] S3. The SiC powder is prepared in a volume percentage of 85 vol%, and the second pre-set average particle size Ti2O3 powder is calculated to be 83 vol% based on the average particle size of the SiC powder. The pre-sintered powder after vibration is mixed with the Ti2O3 powder having an average particle size of 10 μm at a vibration frequency of 60 Hz for 10 min.

[0087] The final product is obtained by sintering using a spark plasma sintering method at a heating rate of 80°C / min and a pressure of 50 MPa at 1300°C for 10 min, and then cooling in the furnace.

[0088] No interfacial reaction or obvious interfacial reaction is observed between the two-phase ceramics. The SiC phase with a large area is surrounded by Ti2O3, and the Ti2O3 forms a skeleton structure to support and constrain the SiC phase. The size of the Ti2O3 phase is smaller as it is closer to the surface of the SiC phase.

[0089] The ceramic is subjected to a thermal cycle test at a temperature range of 0-200°C at a heating rate of 5°C / s, and the sample is kept at the end point temperature for 10 min. The sample does not show any cracks after 1000 thermal cycle tests, and the density of the two-phase ceramic is 93.2%.

[0090] Example 3

[0091] The present embodiment provides a method for preparing a low thermal expansion two-phase ceramic, comprising the following steps:

[0092] S1. A negative thermal expansion ceramic powder and a positive thermal expansion ceramic powder with a barrier layer are prepared.

[0093] The barrier layer is prepared by weighing 100 g of SiC powder with an average particle size of 100 μm, adding 20 ml of boron nitride solution, and stirring for 40 min after spraying. The barrier layer has a thickness of 190 nm after drying in a vacuum drying box.

[0094] S2. Based on the average particle size of the positive thermal expansion ceramic powder, the first pre-set average particle size Ti2O3 powder is selected and mixed with the SiC powder. After mixing, pre-sintering is performed, and the sintered powder is crushed.

[0095] By the formula:

[0096]

[0097] λ takes the value of 0.09, r0 takes the value of 130 μm, and the first preset average particle size r is calculated to be 4.1 μm;

[0098] The D50 / D10 of the Ti2O3 powder of the first preset average particle size is 3.4; and the volume ratio of the Ti2O3 powder of the first preset average particle size to the SiC powder is 5%. Then, the mixing is performed, the mixing vibration frequency is 60 Hz, the mixing time is 24 min, heating is performed to 1500 ℃ in an inert gas, and the temperature is kept for 24 min, then a vibration machine with a vibration frequency of 20-30 Hz and an amplitude of 2-3 mm is used to vibrate for 40 min.

[0099] S3. The SiC powder is prepared according to the volume percentage of 85 vol%, the second preset average particle size Ti2O3 powder is calculated to be 80 vol%, the average particle size is 8 μm, and the pre-sintered powder after vibration is mixed, the vibration frequency is 60 Hz, and the mixing time is 24 min.

[0100] The discharge plasma sintering is used, the heating rate is 200 ℃ / min, the pressure is 80 MPa, sintering is performed at 1450 ℃ for 24 min, and the final product is obtained after the furnace is cooled.

[0101] No interfacial reaction or obvious interfacial reaction is obtained between the two-phase ceramics. The SiC phase with a large area is surrounded by Ti2O3, Ti2O3 forms a skeleton structure, supports and constrains the SiC phase, and the size of the Ti2O3 phase is smaller and smaller as it is closer to the surface of the SiC phase.

[0102] The thermal cycle test is performed on the ceramic, the temperature interval is 0-200 ℃, the heating rate is 5 ℃ / s, the temperature is kept at the end point for 10 min, 1000 thermal cycle experiments are performed, no crack is found in the sample, and the density of the two-phase ceramic is 97.8%.

[0103] Example 4

[0104] The embodiment provides a preparation method of a low-thermal-expansion two-phase ceramic, and the method comprises the following steps:

[0105] S1. A negative thermal expansion ceramic powder and a positive thermal expansion ceramic powder with a barrier layer are prepared.

[0106] The preparation method of the insulation layer is as follows: 100 g of TiC powder with an average particle size of 20 μm is taken, 10 ml of boron nitride solution is added, the boron nitride solution is a commercially available boron nitride high-temperature release agent, after spraying, continue to stir for 40 min, after stirring, put into a vacuum drying box for drying, and the thickness of the insulation layer is measured to be 128 nm.

[0107] S2. Based on the average particle size of the positive thermal expansion ceramic powder, Ti2O3 powder with a first preset average particle size is selected and mixed with the TiC powder, and after mixing, pre-sintering is performed, and after sintering is completed, vibration crushing is performed.

[0108] By the formula:

[0109]

[0110] λ is 0.09, r0 is 130 μm, and the first preset average particle size r is calculated to be 1.5 μm;

[0111] The Ti2O3 powder with the first preset average particle size has a D50 / D10 of 4.5, and the volume ratio of the Ti2O3 powder to the TiC powder is 3%. Then, mixing is performed, the mixing vibration frequency is 60 Hz, the mixing time is 24 min, heating to 1500℃ in an inert gas for 24 min, and then vibration is performed using a vibration machine with a vibration frequency of 20-30 Hz and an amplitude of 2-3 mm for 40 min.

[0112] S3. According to the volume percentage of the TiC powder, the Ti2O3 powder with a second preset average particle size is added in an amount of 72 vol%, 42 vol% and 0% respectively, the average particle size is 5.2 μm, and the pre-sintered powder after vibration crushing is mixed, the vibration frequency is 60 Hz, and the mixing time is 4 min.

[0113] Discharge plasma sintering is used, the heating rate is 200℃ / min, the pressure is 80 MPa, sintering is performed at 1450℃ for 24 min, and after furnace cooling, the final product is obtained.

[0114] No interfacial reaction or obvious interfacial reaction is observed between the two-phase ceramics. The TiC phase with a large area is surrounded by Ti2O3, Ti2O3 forms a skeleton structure, supports and constrains the TiC phase, and the size of the Ti2O3 phase becomes smaller as it approaches the surface of the TiC phase.

[0115] Figure 5 The linear expansion curve diagram of different TiC powder addition amounts.

[0116] The ceramic is subjected to a thermal cycle test, the temperature interval is 0-200℃, the temperature rising rate is 5℃ / s, and the sample is kept at the end point temperature for 10 min, 1000 times of thermal cycle test is carried out, no crack is found in the sample, and the density of the dual-phase ceramic is 96.3%.

[0117] Example 5

[0118] The embodiment provides a preparation method of a low-thermal-expansion dual-phase ceramic, and comprises the following steps:

[0119] S1. preparing a negative-thermal-expansion ceramic powder and a positive-thermal-expansion ceramic powder coated with an isolation layer.

[0120] The preparation method of the isolation layer is as follows: 100 g of ZrN powder with an average particle size of 15 μm is weighed, the ZrN powder is placed in a crucible, and the ZrN powder is kept at 1000℃ or above for 3 h, and the thickness of the isolation layer is measured as 65 nm.

[0121] S2. based on the average particle size of the positive-thermal-expansion ceramic powder, Ti2O3 powder with a first preset average particle size is selected and mixed with the ZrN powder, and after mixing, pre-sintering is carried out, and the sintered product is vibrated and crushed.

[0122] The formula is as follows:

[0123]

[0124] λ is 0.09, r0 is 130 μm, and the first preset average particle size r is calculated as 1.2 μm;

[0125] The volume ratio of the Ti2O3 powder with the first preset average particle size to the ZrN powder is 4%, and then the mixing is carried out, the mixing vibration frequency is 60 Hz, the mixing time is 24 min, the inert gas is heated to 1500℃ and kept for 24 min, and then a vibration machine with a vibration frequency of 20-30 Hz and an amplitude of 2-3 mm is vibrated for 40 min.

[0126] S3. the ZrN powder is proportioned into 75 vol%, 45 vol% and 0% according to the volume percentage, the second preset average particle size of the Ti2O3 powder is calculated as 71 vol%, 41 vol% and 0% respectively, the average particle size is 3.2 μm, and the pre-sintered powder after vibration and crushing is mixed, the vibration frequency is 60 Hz, and the mixing time is 4 min.

[0127] The discharge plasma sintering is adopted, the temperature rising rate is 60℃ / min, the pressure is 70 MPa, the sintering is carried out at 1530℃ for 24 min, and after the furnace is cooled, the final product is obtained.

[0128] There is no interfacial reaction or the interfacial reaction is not obvious between the two-phase ceramics. The ZrN phase with a large area is surrounded by the Ti2O3 phase, and the Ti2O3 phase forms a framework structure to support and constrain the ZrN phase. The closer to the surface of the ZrN phase, the smaller the size of the Ti2O3 phase.

[0129] Figure 6 The linear expansion curve diagram of different ZrN powder addition amounts.

[0130] Through the thermal cycle test of the ceramic, the temperature interval is 0-200℃, the heating rate is 5℃ / s, and the sample is not found to have cracks after 1000 thermal cycle experiments at the end point temperature for 10min, and the density of the two-phase ceramic is 95.2%.

[0131] Example 6

[0132] The embodiment provides a preparation method of a low-thermal expansion two-phase ceramic, and the method comprises the following steps:

[0133] S1. Prepare a negative thermal expansion ceramic powder and a positive thermal expansion ceramic powder coated with an isolation layer.

[0134] The preparation method of the isolation layer is as follows: 100g of HfB2 powder with an average particle size of 20μm is weighed, ZrN powder is put into a crucible, and the ZrN powder is kept at 1000℃ or above for 5h. The thickness of the isolation layer is measured to be 120nm.

[0135] S2. Based on the average particle size of the positive thermal expansion ceramic powder, Ti2O3 powder with a first preset average particle size is selected and mixed with the HfB2 powder. After mixing, pre-sintering is performed, and the sintered product is crushed.

[0136] The first preset average particle size r is calculated by the formula:

[0137]

[0138] The value of λ is 0.09, the value of r0 is 130μm, and the first preset average particle size r is calculated to be 1.5μm;

[0139] The volume ratio of the Ti2O3 powder with the first preset average particle size to the HfB2 powder is 2%. Then, the Ti2O3 powder with the first preset average particle size is mixed with the HfB2 powder. The mixing vibration frequency is 60Hz, the mixing time is 24min, the mixture is heated to 1650℃ in an inert gas, and then the mixture is vibrated for 40min by using a vibration machine with a vibration frequency of 20-30Hz and an amplitude of 2-3mm.

[0140] S3. The HfB2 powder was proportioned according to the volume percentage of 75 vol%, 45 vol% and 0 vol%, and the Ti2O3 powder was added according to the second preset average particle size of 73 vol%, 43 vol% and 0 vol% respectively, the average particle size was 4.2 μm, and the pre-sintered powder after vibration was mixed, the vibration frequency was 60 Hz, and the mixing time was 4 min.

[0141] The final product was obtained by spark plasma sintering at a heating rate of 90 ℃ / min, a pressure of 80 MPa, and a sintering temperature of 1480 ℃ for 24 min, and then the furnace was cooled.

[0142] There was no interfacial reaction or obvious interfacial reaction between the two-phase ceramics. The larger HfB2 phase was surrounded by Ti2O3, and Ti2O3 formed a skeleton structure to support and constrain the HfB2 phase. The closer to the surface of the HfB2 phase, the smaller the size of the Ti2O3 phase.

[0143] Figure 7 The linear expansion curve of the ceramic with different HfB2 powder addition amounts.

[0144] The ceramic was subjected to a thermal cycle test, the temperature range was 0-200 ℃, the heating rate was 5 ℃ / s, and the sample was kept at the end point temperature for 10 min. The sample did not crack after 1000 thermal cycle tests, and the density of the two-phase ceramic was 96.3%.

[0145] Comparative Example 1

[0146] Compared with Example 1, the difference between the comparative example was that the first preset average particle size in step S2 was 2.4 μm, and the D50 / D10 of the Ti2O3 powder with the first preset average particle size was 5.2; in step S3, the SiC powder was proportioned according to the volume percentage of 45 vol%.

[0147] The ceramic was subjected to a thermal cycle test, the temperature range was 0-200 ℃, the heating rate was 5 ℃ / s, and the sample was kept at the end point temperature for 10 min. The sample did not crack after 1000 thermal cycle tests, and the density of the two-phase ceramic was 96.3%.

[0148] Comparative Example 2

[0149] Compared with Example 1, the difference between the comparative example was that the first preset average particle size in step S2 was 0.8 μm, and the D50 / D10 of the Ti2O3 powder with the first preset average particle size was 5.1; in step S3, the SiC powder was proportioned according to the volume percentage of 45 vol%.

[0150] The ceramic is subjected to thermal cycle test, the temperature interval is 0-200℃, the temperature rising rate is 5℃ / s, and 1000 thermal cycle experiments are conducted at the end point temperature for 10 min, respectively. The dual-phase ceramic appears cracks, and the density of the dual-phase ceramic is 91.5%.

[0151] Comparative Example 3

[0152] Compared with Example 1, the difference of the comparative example is that in step S1, the preparation method of the insulation layer is: 100g of SiC powder with an average particle size of 15μm is weighed, 25ml of boron nitride solution is added, the boron nitride solution is a commercially purchased boron nitride high-temperature release agent, and after spraying, stirring is continued for 20min. After stirring, it is placed in a vacuum drying box for drying, and the thickness of the insulation layer is measured to be 210nm; in step S3, the SiC powder is proportioned according to the volume percentage of 45vol%.

[0153] The ceramic is subjected to thermal cycle test, the temperature interval is 0-200℃, the temperature rising rate is 5℃ / s, and 1000 thermal cycle experiments are conducted at the end point temperature for 10 min, respectively. The dual-phase ceramic appears cracks, and the density of the dual-phase ceramic is 92.5%.

[0154] Comparative Example 4

[0155] Compared with Example 1, the difference of the comparative example is that in step S3, the SiC powder is proportioned according to the volume percentage of 45vol%, and the average particle size of the second pre-set average particle size Ti2O3 powder is 1.0μm.

[0156] The ceramic is subjected to thermal cycle test, the temperature interval is 0-200℃, the temperature rising rate is 5℃ / s, and 1000 thermal cycle experiments are conducted at the end point temperature for 10 min, respectively. The dual-phase ceramic appears cracks, and the density of the dual-phase ceramic is 92.8%.

[0157] Comparative Example 5

[0158] Compared with Example 1, the difference of the comparative example is that in step S3, the SiC powder is proportioned according to the volume percentage of 45vol%. The final product is obtained by using spark plasma sintering, the temperature rising rate is 40℃ / min, the pressure is 25MPa, sintering is carried out at 1130℃ for 4min, and the furnace is cooled after sintering.

[0159] Through measurement, the density of the dual-phase ceramic is 91.8%, and the thermal expansion coefficient between 125℃ and 250℃ is-7.8ppm / K.

[0160] Comparative Example 6

[0161] The difference between the comparative example and example 1 is that in step S3, the SiC powder is proportioned at 45 vol% by volume percentage. The final product is obtained by using a spark plasma sintering process, a heating rate of 40°C / min, a pressure of 90 MPa, sintering at 1130°C for 4 min, and furnace cooling.

[0162] Through measurement, the density of the dual-phase ceramic is 98.8%; through a thermal cycle test on the ceramic, the temperature interval is 0-200°C, the heating rate is 5°C / s, and the ceramic is kept at the end point temperature for 10 min, respectively, and 1000 thermal cycle experiments are performed, and the dual-phase ceramic cracks.

[0163] Through comparison of example 1, comparative examples 1 and 2, when the first preset average particle size r is greater than or less than 1.2 μm, cracks occur in both samples in the thermal cycle experiment, and the reason is that the mismatch of particle sizes leads to a large stress gradient, and the local stress is greater than the maximum elastic deformation at the site, and then cracks occur, when the particle size is less than 1.2 μm, the first preset average particle size of Ti2O3 powder is easy to produce a larger local stress between the second preset average particle size of Ti2O3 powder; and when the particle size is greater than 1.2 μm, the SiC powder is easy to produce a larger local stress between the first preset average particle size of Ti2O3 powder due to uneven stress.

[0164] Through comparison of example 1 and comparative example 3, it can be seen that the thickness of the insulating layer also affects the thermal cycle number of the dual-phase ceramic, when the thickness of the insulating layer is greater than 200 nm, the insulating layer between the SiC phase and the Ti2O3 phase is easy to produce non-elastic deformation, leading to the generation and expansion of cracks.

[0165] Through comparison of example 1 and comparative example 4, it can be seen that when the average particle size of the second preset average particle size of Ti2O3 powder is smaller than the first preset average particle size of Ti2O3 powder, a larger stress gradient occurs between the Ti2O3 powders of different particle sizes, which is easy to produce a larger local stress, leading to the generation of cracks.

[0166] Through comparison of example 1 and comparative example 5, it can be seen that a smaller pressure is used in the plasma sintering process, the density between the ceramic particles is lower, and in the expansion process of the dual-phase ceramic, the increased volume of SiC in the positive thermal expansion phase with the increase of temperature is absorbed by the gap between the negative thermal expansion phase Ti2O3, leading to a larger negative thermal expansion effect of the dual-phase ceramic, and more positive thermal expansion materials need to be added to adapt to engineering applications.

[0167] Through comparison of example 1 and comparative example 6, it can be seen that a larger pressure is used in the plasma sintering process, which makes the density of the dual-phase ceramic larger, and in the heating process, the coordination between the positive thermal expansion phase and the negative thermal expansion phase is poor, leading to the generation of cracks.

[0168] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A low thermal expansion dual-phase ceramic, characterized in that, The dual-phase ceramic comprises a negative thermal expansion phase and a positive thermal expansion phase; The edge of the positive thermal expansion phase has an insulating layer; The positive thermal expansion phase accounts for 50% to 85% of the volume percentage of the duplex ceramic. The closer the negative thermal expansion phase is to the positive thermal expansion phase, the smaller the average grain size. The preparation method of the low thermal expansion dual-phase ceramic includes the following steps: Prepare negative thermal expansion ceramic powder and positive thermal expansion ceramic powder with an insulating layer coating; Based on the average particle size of the positive thermal expansion ceramic powder, the negative thermal expansion ceramic powder with the first preset average particle size is selected and mixed with the positive thermal expansion ceramic powder. After mixing, it is pre-sintered and then crushed after sintering. According to the formula, the negative thermal expansion ceramic powder with the second preset average particle size is mixed with the crushed pre-sintered powder and then sintered to obtain the final product. The second preset average particle size is greater than the first preset average particle size; The first preset average particle size r is calculated as follows: ； in, r1 is the average particle size of the positive thermal expansion ceramic powder, and r0 is the reference particle size. Furthermore, the powder with the first preset average particle size D50 / D10 is not greater than 5; The sintering process employs spark plasma sintering, with a pressure of 30MPa~80MPa during the sintering process. The insulating layer is made of an inert material that is difficult to react with negative and positive thermal expansion phases, and the thickness of the insulating layer does not exceed 200 nm.

2. The low thermal expansion dual-phase ceramic according to claim 1, characterized in that, The linear thermal expansion coefficient of the negative thermal expansion phase is -15 to -25 ppm / K.

3. The low thermal expansion dual-phase ceramic according to claim 2, characterized in that, The linear thermal expansion coefficient of the positive thermal expansion phase is 3~10ppm / K.

4. The low thermal expansion dual-phase ceramic according to claim 1, characterized in that, The density of the dual-phase ceramic is 90-98%.

5. The low thermal expansion dual-phase ceramic according to claim 1, characterized in that, The ratio of the average particle size of the negative thermal expansion phase to the positive thermal expansion phase is 1:6~50; The average particle size of the positively thermally expanding phase is 10~100μm.

6. The low thermal expansion dual-phase ceramic according to claim 1, characterized in that, The positive thermal expansion phase is one or more of carbide ceramics, nitride ceramics, boride ceramics, and polycrystalline diamond; the negative thermal expansion phase contains a general formula. , , One of the powders, wherein A and M comprise at least one element selected from P, Mg, Al, Si, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, La, Ta, W, and Bi.

7. The low thermal expansion dual-phase ceramic according to claim 1, characterized in that, The volume ratio of the powder with the first preset average particle size to the positive thermal expansion ceramic powder is 1~5%.

8. The low thermal expansion dual-phase ceramic according to claim 7, characterized in that, The ratio of the second preset average particle size to the average particle size of the positively thermally expanded ceramic powder is 1:2~30.

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