Ceramic composite powder, preparation method and application thereof

Abstract

The present application relates to the technical field of ceramic composite powder, and particularly relates to a ceramic composite powder, a preparation method and application thereof. The powder comprises coarse-grained alumina, a zirconium oxide shell layer on the surface of the coarse-grained alumina, a first part of fine-grained alumina fixed by the shell layer, and a second part of fine-grained alumina in free state. The dry base feeding mass of the first part of fine-grained alumina accounts for 20% to 30% of the dry base feeding mass of all fine-grained alumina. During preparation, a zirconium hydroxide precursor shell layer is formed on the surface of the coarse-grained alumina, the wet coated powder is dried to a dry loss on drying rate of 6.0% to 9.0% at 120 DEG C, the first part of fine-grained alumina is added within 30 minutes and mechanical fusion is carried out at a net mechanical specific energy of 0.10 to 0.16 kWh / kg, the shell layer is converted by calcination and the first part of fine-grained alumina is fixed, and the second part of fine-grained alumina is additionally added. The powder is used for hydroxyl-terminated polydimethylsiloxane-based ceramicized refractory composite material, and is beneficial to improving the continuity of the ceramic layer after being subjected to fire.

Description

Technical Field

[0001] This invention relates to the field of ceramic technology, specifically to a ceramic composite powder, its preparation method, and its application. Background Technology

[0002] Ceramicized organosilicon materials need to balance room temperature processing performance with the integrity of ceramic formation after firing. Larger-diameter ceramic particles are beneficial for forming a load-bearing skeleton, while smaller-diameter particles are beneficial for filling gaps and shortening the sintering diffusion distance. However, after ordinary mixing of coarse and fine particles, the fine particles are prone to separation or aggregation during transportation, metering, and high-viscosity mixing. The particle contact network formed during firing may also affect the formation of the ceramic layer and the escape of pyrolysis gases if it is too loose or too dense.

[0003] Patent CN104725051A discloses a method for producing zirconium oxide-coated alumina powder by using alumina as the main material, forming a zirconium hydroxide coating layer on the alumina surface using zirconium oxychloride and urea, and then spray drying and calcining the resulting powder. Patent CN102361694A discloses a method for forming core-shell composite particles by mechanically fusing coarse and fine particles based on their size difference, followed by drying and calcination. Patent WO2024029464A1 discloses a method for forming surface and interstitial distributions of alumina with large and small particle sizes through high-speed mixing, which can be used in silicone rubber or silicone resin. These technologies respectively relate to inorganic coating, mechanical particle composites, and the use of coarse and fine alumina in resins.

[0004] However, keeping all fine particles in a free state makes it difficult to maintain the intended contact relationship between coarse and fine particles during subsequent mixing; excessive fixation of fine particles or causing them to form continuous agglomerates may weaken their gap-filling ability and hinder gas escape during the firing process. Current technology still needs to address the trade-off between the retention of fine particles and their gap-filling and venting capabilities to ensure that the combination of coarse and fine particles remains in a suitable state during both processing and firing stages. Summary of the Invention

[0005] Purpose of the invention: To solve the problem that when fine particles are not properly fixed during the mixing and firing process of ceramic composite powders with organosilicon, they are prone to detachment or aggregation. However, excessive fixation or aggregation can weaken the gap-filling and degassing capabilities, making it difficult to maintain the contact relationship between coarse and fine particles and the integrity of the ceramic layer.

[0006] Based on the above-mentioned objective, this invention provides a ceramic composite powder, comprising coarse alumina particles, a zirconium oxide shell on the surface of the coarse alumina particles, a first portion of fine alumina particles fixed by the zirconium oxide shell, and a second portion of free fine alumina particles coexisting with the coarse alumina particles having the zirconium oxide shell on their surface; the ceramic composite powder is prepared by a method comprising the following steps: forming a zirconium hydroxide precursor shell on the surface of the coarse alumina particles, drying the resulting wet-coated powder to 120°C with a drying weight loss of 6.0%~9.0%, and after reaching the 120°C drying weight loss, 30 min... The first portion of fine alumina is added and mechanically fused. The net mechanical energy of the mechanical fusion is 0.10~0.16 kWh / kg, based on the total dry weight of the materials added in this mechanical fusion. Then, it is calcined in air at 650~750℃ for 1~3 hours to convert the zirconium hydroxide precursor shell into the zirconium oxide shell and fix the first portion of fine alumina. After the calcination, the second portion of fine alumina is added. The dry weight of the first portion of fine alumina accounts for 20%~30% of the total dry weight of the first portion of fine alumina and the second portion of fine alumina.

[0007] Preferably, the coarse alumina particles, the first portion of fine alumina particles, and the second portion of fine alumina particles are all α-Al2O3 with a purity of not less than 99.99%, the D50 of the coarse alumina particles is 20.3 μm, and the D50 of the first portion of fine alumina particles and the second portion of fine alumina particles are both 0.88 μm.

[0008] Preferably, no organic binder is used in the preparation of the ceramic composite powder, and the second part of fine alumina particles is not coated after calcination.

[0009] Furthermore, the present invention also provides a method for preparing ceramic composite powder, comprising the following steps: S1. Disperse coarse alumina particles in water, add zirconium oxychloride solution and urea solution in sequence, react at 90~98℃ for 4~8h to form a zirconium hydroxide precursor shell on the surface of the coarse alumina particles, filter and wash the reaction slurry to obtain wet coated powder. S2. Dry the wet coated powder at 50~70℃ under negative pressure until the weight loss of the wet coated powder at 120℃ is 6.0%~9.0%. Within 30 minutes after reaching the weight loss at 120℃, add the first part of fine alumina particles and perform mechanical fusion. The net mechanical energy of the mechanical fusion is based on the total dry weight of the materials added in this mechanical fusion, and is 0.10~0.16kWh / kg. S3. The powder obtained by mechanical fusion is pre-dried at 100~120℃, and then heated to 650~750℃ at 2~5℃ / min, and kept in air for 1~3h to convert the zirconium hydroxide precursor shell into a zirconium oxide shell and fix the first part of fine alumina particles. S4. Add the second part of fine alumina to the calcined powder obtained in step S3 and mix. The dry weight of the first part of fine alumina accounts for 20% to 30% of the total dry weight of the first part of fine alumina and the second part of fine alumina.

[0010] Preferably, the coarse alumina particles, the first portion of fine alumina particles, and the second portion of fine alumina particles are all α-Al2O3 with a purity of not less than 99.99%, the D50 of the coarse alumina particles is 20.3 μm, and the D50 of the first portion of fine alumina particles and the second portion of fine alumina particles are both 0.88 μm.

[0011] Preferably, in step S1, under stirring conditions, the zirconium oxychloride solution is added first within 10 minutes, and then the urea solution is added within 10 minutes. After the addition is completed, the temperature is increased to 95°C at 2°C / min and kept at that temperature for 6 hours.

[0012] Preferably, in step S2, the wet coated powder is dried to 120°C with a drying loss rate of 7.5% under conditions of 60°C and gauge pressure of -0.08MPa. The wet coated powder is then transferred to a mechanical fusion device with a 25°C circulating water jacket. The first portion of fine alumina particles is added within 2 minutes under conditions of a rotor linear velocity of 4m / s. The rotor linear velocity is then increased to 14m / s and mechanically fused for 6 minutes, so that the net mechanical specific energy is 0.13kWh / kg.

[0013] Preferably, in step S3, the powder obtained by mechanical fusion is pre-dried at 110°C for 2 hours, then heated to 700°C at 3°C / min and kept warm in air for 2 hours.

[0014] Preferably, the calcined powder obtained in step S3 is sieved through a sieve with a pore size of 150 μm before proceeding to step S4; in step S4, the powder is mixed in a V-shaped mixer at 20 r / min for 15 min.

[0015] Furthermore, the present invention also provides the application of the ceramic composite powder in the preparation of organosilicon-based ceramicized refractory composite materials.

[0016] The “fixed-state fine particles” refer to the fine particles that, after mechanical fusion and calcination, remain with the coarse particles having a zirconium oxide shell on their surface under specified deagglomeration conditions; the “free-state second-part fine particles” refer to the fine particles added after calcination that have not undergone the mechanical fusion and calcination fixation treatment of the precursor shell.

[0017] Beneficial effects (1) By adding a first part of fine alumina particles to a zirconium hydroxide precursor shell with controlled water content and mechanically fusing it with a defined net mechanical specific energy, the first part of fine particles can establish a relatively stable bond with the surface of coarse particles before the precursor shell is transformed; then the shell transformation and fine particle fixation are completed in the same calcination process, without the need for an additional organic adhesive layer or a second coating, which helps to reduce the influence of additional materials on the calcination process.

[0018] (2) The dry weight of the first part of fine alumina is controlled to be 20% to 30% of the total dry weight of fine alumina. The remaining second part of fine particles is added after calcination, so that the fine particles fixed by the shell and the free fine particles coexist. The fine particles fixed by the shell help maintain the discrete contact points retained with the coarse particles, while the free fine particles continue to play the role of filling the interparticle gaps, thus taking into account both the maintenance of the coarse and fine particle size relationship and the gap-filling ability.

[0019] (3) The drying state of the precursor shell is limited by the drying weight loss rate at 120℃, and the mechanical action intensity is limited by the net mechanical specific energy. This can reduce the insufficient adhesion of fine particles caused by excessive drying of the precursor shell or insufficient mechanical action, and can also inhibit continuous agglomeration caused by mismatch of water content or energy input. This joint control helps to maintain a suitable particle size distribution of the powder after deagglomeration and avoid obtaining apparent large particle size in the form of continuous agglomeration.

[0020] (4) When the ceramic composite powder is used in hydroxyl-terminated polydimethylsiloxane ceramic refractory composite material, the coarse particles form a load-bearing skeleton, the fixed fine particles provide discrete contact points, and the free fine particles fill gaps together, which is conducive to the escape of pyrolysis gas and the continuous formation of ceramic layer after ignition, thereby reducing the possibility of blistering and through crack formation. Attached Figure Description

[0021] Figure 1 The volumetric particle size distribution curves of ceramic composite powders from Examples 1, 1, 2, 5, and 7 after deagglomeration are shown. Detailed Implementation

[0022] Raw material description: The coarse alumina particles used are Sumitomo Chemical Co., Ltd. AA-18, with the crystal form α-Al2O3, a purity of not less than 99.99%, a D50 of 20.3 μm, and a particle morphology of near-spherical polyhedra.

[0023] The fine-particle alumina used is Sumitomo Chemical Co., Ltd. AA-07, with crystal form α-Al2O3, purity not less than 99.99%, and D50 of 0.88μm.

[0024] The hydroxyl-terminated polydimethylsiloxane used was Dow Chemical's XIAMETER OHX-4060 Polymer, with 100% active material content and a kinematic viscosity of 20,000 cSt at 25°C. All other reagents were conventional industrial products or analytical grade reagents.

[0025] Measurement method: Weight loss at 120℃: Take 1.00g of wet-coated powder and dry it at 120℃. Weigh it every 30 minutes until the mass difference between two adjacent weighings is no more than 1mg. The percentage of the mass difference before and after drying to the mass before drying is taken as the weight loss at 120℃.

[0026] Net mechanical energy: Record the change of load power of the mechanical fusion equipment over time, subtract the no-load power at the same speed, integrate the power difference over the mechanical fusion time, and then divide by the dry basis mass of all input materials. The result is expressed in kWh / kg.

[0027] Depolymerization particle size retention test: 0.50 g of ceramic composite powder was added to 50.0 g of anhydrous ethanol and placed in a 100 mL glass beaker with an inner diameter of 45 mm. The mixture was stirred at 300 r / min for 2 min at 25 ± 1 °C. A 20 kHz probe-type ultrasonic processor and a 6 mm diameter titanium alloy probe were used, with the probe tip positioned 10 mm below the liquid surface and 15 mm from the bottom of the beaker. Ultrasonic energy of 600 J was input with a pulse mode of 2 s operation followed by a 1 s interval and an effective power of 20 W. During the treatment, a constant temperature water bath was used to keep the dispersion temperature below 26 °C. A laser particle size analyzer calibrated with particle size standard material and with background corrected by anhydrous ethanol was used to collect the volumetric discrete particle size distribution within 2 min after the ultrasonic treatment.

[0028] Test of the refractory ceramic layer of silicone composite material: Three 50mm × 50mm specimens were cut from a 3.0mm thick cured board. The back of the specimen was placed on a fire-resistant insulation board, and the front was radiantly heated from one side, raising the hot surface temperature from 25℃ to 950℃ at a rate of 10℃ / min and holding for 20min. Before the test, the hot surface temperature was verified using a calibrated thermocouple, and the maximum blister height was measured using a side view image with a scale. After cooling to 25℃, the complete ceramic layer area was segmented using a top view image with a scale, and the continuous ceramic layer area ratio was calculated. The number of cracks penetrating the specimen thickness and with a length of not less than 5mm was recorded. The maximum blister height and continuous ceramic layer area ratio were taken as the arithmetic mean of the three specimens, and the number of cracks was taken as the median.

[0029] Example 1: 1980 g of deionized water and 206.6 g of coarse alumina particles were added to a 5 L reactor equipped with an 80 mm diameter four-bladed swashplate and a reflux condenser, and stirred at 600 rpm for 20 min. 35.0 g of zirconium oxychloride octahydrate and 65.2 g of urea were dissolved in 330 g of deionized water. Under stirring at 600 rpm, the zirconium oxychloride solution was added first over 10 min, followed by the urea solution over another 10 min. After the addition was complete, the temperature was increased to 95 °C at a rate of 2 °C / min, and the stirring speed was adjusted to 500 rpm. Timing was started from when the system reached 95 °C, and the mixture was held at this temperature for 6 h to obtain the precursor slurry.

[0030] The precursor slurry was cooled to 25°C and vacuum filtered. The filter cake was washed four times with deionized water, using 1000g of deionized water each time, to obtain wet coated powder. The wet coated powder was dried at 60°C and a gauge pressure of -0.08MPa until the weight loss at 120°C reached 7.5%.

[0031] After the drying weight loss rate is reached, the wet coated powder is transferred into a mechanical fusion device with a 25°C circulating water jacket within 30 minutes. Under the condition that the rotor linear speed is 4 m / s, 23.5 g of fine alumina particles are uniformly added within 2 minutes. After the feeding is completed, the rotor linear speed is increased to 14 m / s, and mechanical fusion is carried out for 6 minutes to make the net mechanical specific energy 0.13 kWh / kg.

[0032] The mechanically fused powder was dried at 110℃ for 2 hours, then heated to 700℃ at a rate of 3℃ / min, held in air for 2 hours, and cooled to 25℃ in the furnace to allow the powder to pass through a 150μm sieve. 221.4g of calcined powder was mixed with 64.3g of fine alumina particles in a V-mixer at 20r / min for 15 minutes to obtain the ceramic composite powder. Material balance analysis showed that the fixed-state fine particles accounted for approximately 25% of the total fine particles.

[0033] 100g of hydroxyl-terminated polydimethylsiloxane and 130g of the obtained ceramic composite powder were placed in a planetary mixer and mixed at 300r / min for 5min, then at 600r / min for 8min. Subsequently, the mixture was degassed and mixed at 300r / min for 5min under a gauge pressure of -0.09MPa. 4.0g of methyltriethoxysilane and 0.20g of dibutyltin dilaurate were added and mixed at 200r / min for 2min. Within 5min of the end of mixing, the material was injected into a flat mold with a 3.0mm thick limiting sheet. The mixture was cured at 25℃ and 50% relative humidity for 24h, then cured at 80℃ for 4h, and cooled to 25℃ to obtain an organosilicon-based ceramic refractory composite material.

[0034] Example 2: Based on the raw material ratios of Example 1, the dry basis masses of coarse alumina, zirconium oxide, and all fine alumina in the final ceramic composite powder were 187.9 g, 12.2 g, and 85.7 g, respectively. The reaction feed consisted of 187.9 g of coarse alumina, 1800 g of deionized water, 31.8 g of zirconium oxychloride octahydrate, 59.3 g of urea, and 300 g of deionized water for dissolving zirconium oxychloride and urea, respectively; the remaining deposition, filtration, and washing conditions were the same as in Example 1.

[0035] The wet-coated powder was dried to 120°C with a weight loss of 6.0%. Before calcination, 17.1 g of fine alumina particles were added and mechanically fused to a net mechanical energy of 0.10 kWh / kg. After calcination at 700°C for 2 hours, 68.6 g of fine alumina particles were added, ensuring that the fixed fine particles accounted for 20% of all fine particles. The mixing, degassing, curing, and post-curing conditions of the resulting powder with organosilicon were the same as in Example 1.

[0036] Example 3: The powder was prepared according to the dry-based composition and reaction feed method of Example 2. The wet-coated powder was dried to 120°C with a weight loss of 9.0%. Before calcination, 25.7 g of fine alumina particles were added and mechanically fused to a net mechanical energy of 0.16 kWh / kg. After calcination at 700°C for 2 h, 60.0 g of fine alumina particles were added to make the fixed fine particles account for 30% of the total fine particles. The mixing, degassing, curing, and post-curing conditions of the resulting powder with organosilicon were the same as in Example 1.

[0037] Comparative Example 1: 187.9g of coarse alumina, 12.2g of zirconia powder and 85.7g of fine alumina were mixed in a V-shaped mixer at 20r / min for 15min without a zirconia precursor shell or mechanical fusion before calcination; the sample preparation conditions of the resulting powder and organosilicon were the same as in Example 1.

[0038] Comparative Example 2: A zirconium hydroxide precursor shell was formed on the surface of coarse alumina particles according to the feeding method of Example 2, but fine alumina particles were not added before calcination; after calcination at 700°C, 85.7g of fine alumina particles were added at once and mixed, and the sample preparation conditions of the resulting powder and organosilicon were the same as those in Example 1.

[0039] Comparative Example 3: The wet-coated powder prepared according to Example 1 had a weight loss of 7.5% when dried at 120°C. Before calcination, fine alumina particles, the same as in Example 1, were added, but only mixed at a low energy level of 0.03 kWh / kg net mechanical energy. The remaining calcination, addition of fine particles, and organosilicon sample preparation conditions were the same as in Example 1.

[0040] Comparative Example 4: The weight loss rate at 120°C in Example 1 was adjusted to 4.5%, and the net mechanical energy was maintained at 0.13 kWh / kg. All other conditions were the same as in Example 1.

[0041] Comparative Example 5: The weight loss rate at 120°C in Example 1 was adjusted to 11.0%, the net mechanical energy was maintained at 0.13 kWh / kg, and the other conditions were the same as in Example 1.

[0042] Comparative Example 6: The net mechanical energy of Example 1 was adjusted to 0.06 kWh / kg, the weight loss rate at 120°C was maintained at 7.5%, and the other conditions were the same as in Example 1.

[0043] Comparative Example 7: The net mechanical energy of Example 1 was adjusted to 0.22 kWh / kg, the weight loss rate during drying at 120°C was maintained at 7.5%, and the other conditions were the same as in Example 1.

[0044] Results and Analysis: Particle size retention results after deagglomeration: The results obtained by the deagglomeration particle size retention test are shown in Table 1, and the representative volumetric particle size distribution curves are shown in Table 2. Figure 1 .

[0045] Table 1. Particle size retention results after deagglomeration Results of the ceramic layer after firing of organosilicon composite material: The results of the organosilicon composite material after being subjected to single-sided firing at 950℃ are shown in Table 2.

[0046] Table 2 Results of ceramic layer after firing of organosilicon composite material Discussion of Results: Depend on Figure 1As shown in Table 1, in Example 1, the volume fraction of particles larger than 10 μm was 73.01%, and the D50 was 19.28 μm. Its particle size distribution curve exhibited a relatively concentrated coarse-grained main peak while still retaining a certain proportion of fine-grained components. In Comparative Example 1, without a zirconia precursor shell and without pre-calcination mechanical fusion, the volume fraction of particles larger than 10 μm and the D50 were 65.76% and 16.60 μm, respectively. In Comparative Example 2, although a zirconia shell was formed, all fine alumina particles were added after calcination, with corresponding values ​​of 64.88% and 17.12 μm, respectively. These results indicate that simply using dry mixing, or forming only a zirconia shell without mechanically fusing some fine alumina particles before calcination, is detrimental to the stable retention of fine particles along with coarse particles during subsequent deagglomeration.

[0047] The D50 of Comparative Example 5 was 20.78 μm, and that of Comparative Example 7 was 26.01 μm, both higher than that of Example 1. However, their particle size distribution curves showed more obvious intermediate particle size peaks or broadened main peaks shifting towards larger particle sizes. Considering that Comparative Example 5 used a drying weight loss rate of 11.0% at 120℃ and Comparative Example 7 used a net mechanical energy of 0.22 kWh / kg, it can be concluded that the increased particle size is mainly related to the continuous agglomeration caused by the high moisture content of the wet-coated powder or excessive mechanical action, rather than the appropriate fixation of fine particles on the surface of coarse particles. Therefore, an increase in D50 or the volume fraction of particles larger than 10 μm does not necessarily indicate that the ceramic composite powder has a more favorable particle bonding state.

[0048] Table 2 shows that the maximum bubble height after firing in Example 1 was 2.10 mm, the continuous ceramic layer area ratio was 95.20%, and no through cracks were observed. Compared with Comparative Example 1, the maximum bubble height decreased by 5.20 mm, the continuous ceramic layer area ratio increased by 25.40 percentage points, and the number of through cracks decreased from 5 to 0. The maximum bubble heights in Examples 2 and 3 were 3.20 mm and 2.60 mm, respectively, and the continuous ceramic layer area ratios were 90.40% and 92.80%, respectively. This indicates that under the conditions of the three sets of drying weight loss rates, net mechanical energy, and fixed fine particle ratios, a refractory ceramic layer with good continuity can be formed.

[0049] Comparative Example 4 had a maximum bubble height of 2.90 mm, lower than the 3.20 mm of Example 2, but its continuous ceramic layer area ratio was only 89.70%, and it produced three through cracks. This may be because the lower moisture content of the wet coating powder reduced gas release during firing, but simultaneously weakened the bond between the fine particles and the precursor shell before calcination. Comparative Example 3 had one through crack, fewer than Example 2, but its maximum bubble height was 4.10 mm, and its continuous ceramic layer area ratio was only 85.60%. Therefore, there is no simple one-way correspondence between fewer through cracks, lower bubble height, and higher ceramic layer area ratio; the integrity of the ceramic layer after firing should be comprehensively evaluated.

[0050] The net mechanical specific energy of Comparative Example 3 and Comparative Example 6 were 0.03 kWh / kg and 0.06 kWh / kg, respectively. With the increase in net mechanical specific energy, the maximum bubble height of Comparative Example 6 decreased from 4.10 mm to 3.80 mm, and the continuous ceramic layer area ratio increased from 85.60% to 87.20%, indicating that appropriately increasing mechanical action is beneficial for improving the retention state of fine particles before calcination; however, its performance was still lower than that of Example 1, which had a net mechanical specific energy of 0.13 kWh / kg. When the net mechanical specific energy was further increased to 0.22 kWh / kg, although Comparative Example 7 had a larger D50 and a higher large particle size volume fraction, its maximum bubble height increased to 6.90 mm, the continuous ceramic layer area ratio decreased to 75.60%, and four through cracks were generated.

Claims

1. A ceramic composite powder, characterized in that, The ceramic composite powder comprises coarse alumina particles, a zirconium oxide shell on the surface of the coarse alumina particles, a first portion of fine alumina particles fixed by the zirconium oxide shell, and a second portion of free fine alumina particles coexisting with the coarse alumina particles having the zirconium oxide shell on their surface. The ceramic composite powder is prepared by a method comprising the following steps: forming a zirconium hydroxide precursor shell on the surface of the coarse alumina particles; drying the resulting wet-coated powder to 120°C with a drying loss of 6.0%~9.0%; and adding the first portion of fine alumina particles within 30 minutes after reaching the 120°C drying loss. Alumina is mechanically fused, with the net mechanical energy of the fusion being 0.10~0.16 kWh / kg based on the total dry weight of the materials used in the fusion. The mixture is then calcined in air at 650~750℃ for 1~3 hours to convert the zirconium hydroxide precursor shell into the zirconium oxide shell and fix the first portion of fine alumina particles. After calcination, the second portion of fine alumina particles is added. The dry weight of the first portion of fine alumina particles accounts for 20%~30% of the total dry weight of both the first and second portions of fine alumina particles.

2. The ceramic composite powder according to claim 1, characterized in that, The coarse alumina particles, the first portion of fine alumina particles, and the second portion of fine alumina particles are all α-Al2O3 with a purity of not less than 99.99%. The D50 of the coarse alumina particles is 20.3 μm, and the D50 of the first portion of fine alumina particles and the second portion of fine alumina particles is 0.88 μm.

3. The ceramic composite powder according to claim 1, characterized in that, No organic binder is used in the preparation of the ceramic composite powder, and the second part of fine alumina particles is not coated after calcination.

4. A method for preparing the ceramic composite powder according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Disperse coarse alumina particles in water, add zirconium oxychloride solution and urea solution in sequence, react at 90~98℃ for 4~8h to form a zirconium hydroxide precursor shell on the surface of the coarse alumina particles, filter and wash the reaction slurry to obtain wet coated powder. S2. Dry the wet coated powder at 50~70℃ under negative pressure until the weight loss of the wet coated powder at 120℃ is 6.0%~9.0%. Within 30 minutes after reaching the weight loss at 120℃, add the first part of fine alumina particles and perform mechanical fusion. The net mechanical energy of the mechanical fusion is based on the total dry weight of the materials added in this mechanical fusion, and is 0.10~0.16kWh / kg. S3. The powder obtained by mechanical fusion is pre-dried at 100~120℃, and then heated to 650~750℃ at 2~5℃ / min, and kept in air for 1~3h to convert the zirconium hydroxide precursor shell into a zirconium oxide shell and fix the first part of fine alumina particles. S4. Add the second part of fine alumina to the calcined powder obtained in step S3 and mix. The dry weight of the first part of fine alumina accounts for 20% to 30% of the total dry weight of the first part of fine alumina and the second part of fine alumina.

5. The preparation method according to claim 4, characterized in that, The coarse alumina particles, the first portion of fine alumina particles, and the second portion of fine alumina particles are all α-Al2O3 with a purity of not less than 99.99%. The D50 of the coarse alumina particles is 20.3 μm, and the D50 of the first portion of fine alumina particles and the second portion of fine alumina particles is 0.88 μm.

6. The preparation method according to claim 4, characterized in that, In step S1, under stirring conditions, the zirconium oxychloride solution is added first within 10 minutes, and then the urea solution is added within 10 minutes. After the addition is completed, the temperature is increased to 95°C at 2°C / min and kept at that temperature for 6 hours.

7. The preparation method according to claim 4, characterized in that, In step S2, the wet coated powder is dried to 120°C with a drying loss rate of 7.5% under conditions of 60°C and gauge pressure of -0.08MPa. The wet coated powder is then transferred to a mechanical fusion device with a 25°C circulating water jacket. The first portion of fine alumina particles is added within 2 minutes under conditions of a rotor linear velocity of 4m / s. The rotor linear velocity is then increased to 14m / s and mechanically fused for 6 minutes, so that the net mechanical specific energy is 0.13kWh / kg.

8. The preparation method according to claim 4, characterized in that, In step S3, the powder obtained by mechanical fusion is pre-dried at 110°C for 2 hours, then heated to 700°C at 3°C / min and kept in air for 2 hours.

9. The preparation method according to claim 4, characterized in that, The calcined powder obtained in step S3 is sieved through a sieve with a pore size of 150 μm and then proceeded to step S4; in step S4, it is mixed in a V-shaped mixer at 20 r / min for 15 min.

10. The application of the ceramic composite powder according to any one of claims 1 to 3 in the preparation of organosilicon-based ceramicized refractory composite materials.

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