Composite ceramic, preparation method thereof, aluminum segregation purification equipment and aluminum segregation purification method

Abstract

The invention relates to composite ceramic, a preparation method thereof, aluminum segregation purification equipment and an aluminum segregation purification method. The preparation raw materials of the composite ceramic comprise silicon nitride, lithium titanate and silicon carbide. The composite ceramic is high in mechanical property, high in thermal conductivity and good in chemical stability and can be used as a crystallization rod in aluminum segregation and purification equipment for segregation, crystallization and purification of aluminum, and the crystallization rod made of the composite ceramic has longer service life compared with a graphite crystallization rod, so that the replacement frequency of the crystallization rod can be reduced, and the production cost is reduced. And the cost of aluminum segregation extraction is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of materials, in particular to a composite ceramic, a preparation method thereof, an aluminum segregation purification device and an aluminum segregation purification method. BACKGROUND

[0002] High-purity graphite products are widely used in the process of three-layer electrolysis and segregation purification of high-purity aluminum due to their good high-temperature resistance, chemical stability, thermal shock resistance and excellent electrical and thermal conductivity. However, graphite materials have poor wear resistance and are prone to wear in the process of segregation purification. The wear of graphite directly affects the stability of the quality of the purified product in the segregation purification process. Moreover, graphite has the disadvantage of poor oxidation resistance in a high-temperature aluminum liquid environment, which gradually reduces the thermal conductivity and mechanical properties of graphite during use, thereby shortening the service life of the crystallization rod made of graphite in the segregation purification device, increasing the replacement frequency and the consumption of the crystallization rod. Moreover, high-purity graphite is expensive, and the cost of graphite materials accounts for about 10% of the cost of segregation purification, thereby greatly increasing the purification cost. SUMMARY

[0003] Therefore, it is necessary to provide a composite ceramic with good mechanical properties, high thermal conductivity, good thermal shock resistance and good chemical stability, and a preparation method thereof, which can be applied to an aluminum segregation purification device.

[0004] In addition, the present application also provides an aluminum segregation purification device and an aluminum segregation purification method.

[0005] The first aspect of the present application provides a composite ceramic, and the preparation raw materials thereof include silicon nitride, lithium titanate and silicon carbide.

[0006] The preparation raw materials of the composite ceramic include silicon nitride, lithium titanate and silicon carbide. The silicon nitride has the characteristics of high thermal conductivity, high-temperature resistance, good thermal shock resistance, good thermal stability and good chemical stability. The further addition of the silicon carbide component in the composite ceramic can further improve the hardness of the composite ceramic. The lithium titanate has a face-centered cubic structure, and through high-temperature sintering, Li4Ti5O 12 The high crystallinity and small particle size of the lithium titanate can cooperate with the silicon nitride and the silicon carbide to further improve the thermal conductivity of the composite ceramic. The composite ceramic obtained by the mutual cooperation of the silicon nitride, the lithium titanate and the silicon carbide has high mechanical properties, high thermal conductivity and good chemical stability.

[0007] In addition, the composite ceramic has high thermal conductivity and mechanical properties, as well as good thermal shock resistance and chemical stability. It can be used as a crystallizing rod in aluminum segregation purification equipment to purify aluminum through segregation crystallization. Compared with graphite crystallizing rods, the crystallizing rod made of composite ceramic has a longer service life, which can reduce the frequency of crystallizing rod replacement and reduce the cost of aluminum segregation purification.

[0008] In some embodiments, the raw materials for preparing the composite ceramic include 4 to 5 parts of silicon nitride, 3 to 4 parts of lithium titanate, and 1 to 2 parts of silicon carbide by mass.

[0009] In some embodiments, the raw materials for preparation further include sintering aids. By mass percentage, the raw materials for preparing the composite ceramic include 40% to 50% silicon nitride, 30% to 40% lithium titanate, 10% to 20% silicon carbide, and 5% to 10% sintering aids.

[0010] In some embodiments, the composite ceramic satisfies at least one of the following conditions:

[0011] (1) The thermal conductivity of the composite ceramic is 80 W / (m·K) ~ 100 W / (m·K).

[0012] (2) The fracture toughness of the composite ceramic is 7 MPa·m. 1 / 2 ~9MPa·m 1 / 2 ;

[0013] (3) The compressive strength of the composite ceramic is 1400 MPa to 1600 MPa;

[0014] (4) The coefficient of friction of the composite ceramic is 0.2~0.4;

[0015] (5) The coefficient of thermal expansion of the composite ceramic is 2.5 × 10⁻⁶. -6 / ℃~3.5×10 -6 / ℃.

[0016] In some embodiments, the composite ceramic is a rod.

[0017] The second aspect of this application provides a method for preparing the composite ceramic described in the first aspect, comprising the following preparation steps:

[0018] The raw materials are mixed and then subjected to molding and sintering processes in sequence.

[0019] A third aspect of this application provides a segregation purification device, comprising: a crystallizing rod, wherein the crystallizing rod is made of the composite ceramic described in the first aspect.

[0020] The fourth aspect of this application provides a method for aluminum segregation purification, comprising the following steps: placing the aluminum liquid to be purified in the segregation purification equipment described in the third aspect, and performing segregation crystallization purification treatment to obtain purified aluminum.

[0021] In some embodiments, when the aluminum liquid to be purified is subjected to segregation crystallization purification treatment, the aluminum crystallization temperature is 655℃~685℃.

[0022] In some embodiments, when the aluminum liquid to be purified is subjected to segregation crystallization purification treatment, the growth rate of the aluminum crystals is 5 cm / h to 6 cm / h. Attached Figure Description

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

[0024] Figure 1 This is a schematic diagram of the longitudinal cross-sectional structure of the crystallizing rod in the segregation purification device provided in one embodiment of this application.

[0025] Figure 2 This is a schematic cross-sectional view of the crystallizing rod in the segregation purification apparatus provided in one embodiment of this application.

[0026] Explanation of reference numerals in the attached figures

[0027] 1. The U-shaped inner cavity in the crystal rod. Detailed Implementation

[0028] To facilitate understanding of the present invention, a more comprehensive description is provided below, along with preferred embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. It should be understood that these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0029] Unless otherwise defined, 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 invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0030] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0031] One embodiment of this application provides a composite ceramic, the raw materials for which include silicon nitride, lithium titanate and silicon carbide.

[0032] The raw materials for preparing the above-mentioned composite ceramics include silicon nitride (Si3N4) and lithium titanate (Li4Ti5O). 12 The composite ceramics contain silicon carbide (SiC) and lithium titanate. Silicon nitride possesses high thermal conductivity, high temperature resistance, good thermal shock resistance, good thermal stability, and good chemical stability. Further addition of silicon carbide to the composite ceramics can further improve their hardness. Lithium titanate, with its face-centered cubic structure, is sintered at high temperatures to form Li₄Ti₅O₅. 12 With high crystallinity and small particle size, it can synergize with silicon nitride and silicon carbide to further improve the thermal conductivity of the composite ceramic. The above-mentioned composite ceramic, through the synergistic effect of silicon nitride, lithium titanate, and silicon carbide, yields a composite ceramic with high mechanical properties, high thermal conductivity, and good chemical stability.

[0033] In addition, the composite ceramic has high thermal conductivity and mechanical properties, as well as good thermal shock resistance and chemical stability. It can be used as a crystallizer in aluminum segregation purification equipment to purify aluminum through segregation crystallization. Compared with graphite crystallizers, the composite ceramic crystallizer has a longer service life, which can reduce the frequency of crystallizer replacement and reduce the cost of aluminum segregation purification.

[0034] In some embodiments, the raw materials for preparing composite ceramics include 40 to 50 parts by mass of silicon nitride, 30 to 40 parts by mass of lithium titanate, and 10 to 20 parts by mass of silicon carbide.

[0035] As an example, the mass fraction of silicon nitride in the raw materials for preparing composite ceramics can be 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50 parts. Furthermore, the mass fraction of silicon nitride in the raw materials for preparing composite ceramics can be a range defined by any two of the above values ​​as endpoints.

[0036] As an example, the mass fraction of lithium titanate in the raw materials for preparing composite ceramics can be 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 parts. Furthermore, the mass fraction of lithium titanate in the raw materials for preparing composite ceramics can be a range defined by any two of the above values ​​as endpoints.

[0037] As an example, the mass fraction of silicon carbide in the raw materials for preparing composite ceramics can be 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 parts. Furthermore, the mass fraction of silicon carbide in the raw materials for preparing composite ceramics can be a range defined by any two of the above values ​​as endpoints.

[0038] In some embodiments, the raw materials may further include sintering aids.

[0039] In some embodiments, the raw materials for preparing composite ceramics include, by mass percentage, 40% to 50% silicon nitride, 30% to 40% lithium titanate, 10% to 20% silicon carbide, and 5% to 10% sintering aids.

[0040] In some embodiments, the sintering aid is selected from at least one of Al2O3, LaB6, and MgO.

[0041] In some embodiments, the thermal conductivity of the composite ceramic is 80 W / (m·K) to 100 W / (m·K). As an example, the thermal conductivity of the composite ceramic can be 80 W / (m·K), 81 W / (m·K), 82 W / (m·K), 83 W / (m·K), 84 W / (m·K), 85 W / (m·K), 86 W / (m·K), 87 W / (m·K), 88 W / (m·K), 89 W / (m·K), 90 W / (m·K), 92 W / (m·K), or 100 W / (m·K). Further, the thermal conductivity of the composite ceramic can be a range of values ​​defined by any two of the above points as endpoints.

[0042] In some embodiments, the fracture toughness of the composite ceramic is 7 MPa·m. 1 / 2 ~9MPa·m 1 / 2 As an example, the fracture toughness of composite ceramics can reach 7 MPa·m. 1 / 2 7.5 MPa·m 1 / 2 8MPa·m 1 / 2 8.5 MPa·m 1 / 2 or 9MPa·m 1 / 2 Furthermore, the fracture toughness of the composite ceramic can be a range of values ​​formed by any two of the above point values ​​as endpoints.

[0043] In some embodiments, the compressive strength of the composite ceramic is 1400 MPa to 1600 MPa. As an example, the compressive strength of the composite ceramic can be 1400 MPa, 1450 MPa, 1500 MPa, 1550 MPa, or 1600 MPa. Further, the compressive strength of the composite ceramic can be a range of values ​​defined by any two of the above points as endpoints.

[0044] In some embodiments, the coefficient of friction of the composite ceramic is 0.2 to 0.4.

[0045] In some embodiments, the coefficient of thermal expansion of the composite ceramic is 2.5 × 10⁻⁶. -6 / ℃~3.5×10 -6 / ℃.

[0046] In some embodiments, the composite ceramic is a profile. The profile can be a sheet, rod, spherical particle, or other special shape. Preferably, the composite ceramic is a rod.

[0047] In some embodiments, the composite ceramic rod has an internal cavity. Further, the cavity may be U-shaped.

[0048] One embodiment of this application provides a method for preparing the above-mentioned composite ceramic, comprising the following preparation steps:

[0049] The raw materials are mixed and then subjected to molding and sintering processes in sequence.

[0050] In some embodiments, the above-described molding process is an isostatic pressing method.

[0051] In some embodiments, the molding pressure during the molding process is 150 MPa to 200 MPa. Controlling the molding pressure helps to ensure the density and uniformity of the ceramic structure.

[0052] In some embodiments, the sintering process is isostatic pressing.

[0053] In some embodiments, the sintering temperature is 1500℃ to 2000℃. As an example, the sintering temperature can be 1500℃, 1550℃, 1600℃, 1650℃, 1700℃, 1750℃, 1800℃, 1850℃, 1900℃, 1950℃, or 2000℃. Further, the sintering temperature can be a range defined by any two of the above points as endpoints. Controlling the sintering temperature is beneficial for improving the strength and density of the ceramic.

[0054] In some embodiments, the pressure during sintering is 150 MPa to 200 MPa. For example, the pressure during sintering can be 150 MPa, 155 MPa, 160 MPa, 165 MPa, 170 MPa, 175 MPa, 180 MPa, 185 MPa, 190 MPa, 195 MPa, or 200 MPa. Further, the pressure during sintering can be a range defined by any two of the above points as endpoints. Controlling the pressure during sintering is beneficial for improving the toughness and wear resistance of ceramics.

[0055] In some embodiments, the heat holding and pressure holding time during sintering is 4h to 8h.

[0056] One embodiment of this application provides a segregation purification device, including a crystallizing rod made of composite ceramic. As an example, when using the above-mentioned segregation purification device to purify molten aluminum through segregation crystallization, the crystallizing rod needs to continuously move up and down in the molten aluminum during the crystallization process. During this movement, the crystallizing rod comes into contact with the molten aluminum. The crystallizing rod has high thermal conductivity, which can transfer heat from the molten aluminum, reducing the heat of the molten aluminum in contact with the crystallizing rod, thereby causing crystallization and achieving the effect of purifying the molten aluminum through segregation crystallization.

[0057] Understandably, the segregation purification equipment also includes a crystallization chamber, in which the molten aluminum to be purified is placed. Furthermore, the crystallizing rod can move up and down relative to the crystallization chamber, thereby allowing the crystallizing rod to move up and down within the molten aluminum.

[0058] In some embodiments, see Figure 1 and Figure 2 The crystallizing rod has a U-shaped inner cavity 1 inside. The cooling medium is input through one port of the U-shaped inner cavity and output through the other port. This allows the cooling medium to cool the crystallizing rod and keep its temperature within a low range, thereby further controlling the crystallization effect of the aluminum liquid.

[0059] In some embodiments, the segregation purification apparatus further includes a cooling medium storage device, which is connected to the U-shaped inner cavity of the crystallizing rod to allow the cooling medium to be introduced.

[0060] One embodiment of this application provides a method for purifying aluminum segregation, comprising the following steps:

[0061] The molten aluminum to be purified is placed in a segregation purification device for segregation crystallization purification to obtain purified aluminum. The segregation purification device contains a crystallizing rod that moves up and down in the high-temperature molten aluminum. The crystallizing rod has high thermal conductivity, and during its movement, it transfers heat from the molten aluminum, lowering the temperature of the molten aluminum in contact with the rod. This causes crystallization to occur on the surface of the crystallizing rod, while impurities fail to crystallize, resulting in high-purity aluminum crystals and achieving aluminum segregation crystallization purification.

[0062] In some embodiments, when performing segregation crystallization purification treatment on the molten aluminum, the aluminum crystallization temperature is 655°C to 685°C. The aluminum crystallization temperature can be controlled by controlling the temperature of the molten aluminum in the segregation purification equipment. As an example, the aluminum crystallization temperature can be 655°C, 660°C, 665°C, 670°C, 675°C, 680°C, or 685°C. Further, the aluminum crystallization temperature can be a range of values ​​defined by any two of the above points as endpoints.

[0063] In some embodiments, when performing segregation crystallization purification on the molten aluminum, the temperature of the molten aluminum in the segregation purification equipment can be allowed to fluctuate within a preset range of ±3°C. This crystallization temperature gradient ensures that the temperature difference between the molten aluminum and the crystallizing rod is always controlled within the molten aluminum crystallization temperature range. A suitable temperature difference makes the grain gradient of the crystals more obvious. By controlling the size of the crystals through the temperature difference, and relying on the periodic up-and-down reciprocating movement of the crystallizing rod, precise control of the crystallization rate can be achieved.

[0064] In some embodiments, during the segregation crystallization purification treatment of the molten aluminum, the growth rate of the aluminum crystals is 5 cm / h to 6 cm / h. The growth rate of the aluminum crystals is controlled by adjusting the moving speed of the crystallization rod and the crystallization temperature. Controlling the growth rate of the aluminum crystals is beneficial for controlling the segregation behavior of impurity elements, thereby ensuring the purity of the purified material.

[0065] In some embodiments, the method for aluminum segregation purification further includes the step of first melting the aluminum ingot to be purified to form molten aluminum.

[0066] In some embodiments, the melting temperature of the aluminum ingot to be purified is 720°C to 760°C.

[0067] In some embodiments, the purity of aluminum in the aluminum ingot to be purified is Al99.70%~Al99.90%.

[0068] In some embodiments, the aluminum segregation purification method further includes first homogenizing the molten aluminum, and then placing the molten aluminum in a segregation purification device. The homogenization process described above employs conventional aluminum homogenization methods. By homogenizing the molten aluminum, the levels of V, Ti, Cr, and Mn in the molten aluminum can be reduced beforehand.

[0069] In some embodiments, the purity of the purified aluminum obtained by the above method is Al99.99%~Al99.996%.

[0070] In some embodiments, the mass content of purified aluminum (Fe) is 0.0005% to 0.002%.

[0071] In some embodiments, the mass content of Si element in the purified aluminum is 0.0008%~0.003%.

[0072] In some embodiments, the mass content of Ti in the purified aluminum is 0.0001% to 0.0005%.

[0073] In some embodiments, the mass content of Mn in the purified aluminum is 0.0005% to 0.001%.

[0074] In some embodiments, the mass content of Cr in the purified aluminum is 0.0001% to 0.0005%.

[0075] In some embodiments, the mass content of V in the purified aluminum is 0.0002% to 0.001%.

[0076] To make the objectives, technical solutions, and advantages of this invention clearer and more concise, the invention is described using the following specific embodiments, but the invention is by no means limited to these embodiments. The embodiments described below are merely preferred embodiments of the invention and can be used to describe the invention, but should not be construed as limiting the scope of the invention. It should be noted that any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the protection scope of this invention.

[0077] To better illustrate the present invention, the following embodiments are provided for further explanation. The specific embodiments are as follows.

[0078] Example 1: Preparation of composite ceramics:

[0079] Example 1-1

[0080] The raw material formula of the composite ceramic in this embodiment is as follows: by mass percentage, it includes 40% silicon nitride powder, 36% lithium titanate powder, 17% silicon carbide powder and 7% Al2O3.

[0081] Weigh the raw materials according to the above formula, mix them evenly, place them in a powder hydraulic press, and press them at 150 MPa to obtain a billet. Place the billet in a hot isostatic pressing furnace, introduce nitrogen gas, and turn on the circulating cooling water to press and sinter the billet. The temperature of the hot isostatic pressing furnace is set to 1850℃, the working pressure is 180 MPa, and the holding time is 4 hours. Then stop heating and let the furnace body cool naturally to room temperature to obtain composite ceramics.

[0082] Examples 1-2

[0083] The raw material formula of the composite ceramic in this embodiment is as follows: by mass percentage, it includes 50% silicon nitride powder, 30% lithium titanate powder, 13% silicon carbide powder, and 7% MgO.

[0084] Weigh the raw materials according to the above formula, mix them evenly, place them in a powder hydraulic press, and press them at 150 MPa to obtain a billet. Place the billet in a hot isostatic pressing furnace, introduce nitrogen gas, and turn on the circulating cooling water to press and sinter the billet. The temperature of the hot isostatic pressing furnace is set to 1900℃, the working pressure is 190 MPa, and the holding time is 4 hours. Then stop heating and allow the furnace to cool naturally to room temperature to obtain composite ceramics.

[0085] Examples 1-3

[0086] The raw material formula of the composite ceramic in this embodiment is as follows: by mass percentage, it includes 45% silicon nitride powder, 35% lithium titanate powder, 15% silicon carbide powder, and 5% LaB6.

[0087] Weigh the raw materials according to the above formula, mix them evenly, place them in a powder hydraulic press, and press them at 150 MPa to obtain a billet. Place the billet in a hot isostatic pressing furnace, introduce nitrogen gas, and turn on the circulating cooling water to press and sinter the billet. The temperature of the hot isostatic pressing furnace is set to 2000℃, the working pressure is 195 MPa, and the holding time is 4 hours. Then stop heating and allow the furnace to cool naturally to room temperature to obtain composite ceramics.

[0088] Performance testing:

[0089] The thermal conductivity, fracture toughness, and compressive strength of the composite ceramics prepared in Examples 1-1 to 1-3 were measured according to the methods specified in GB / T 22588-2008 and GB / T 23806-2009. The performance test data of the composite ceramics in Examples 1-1 to 1-3 are shown in Table 1.

[0090] The friction coefficients of the composite ceramics prepared in Examples 1-1 to 1-3 were measured according to the method specified in GB / T 4100-2015.

[0091] The coefficients of thermal expansion of the composite ceramics prepared in Examples 1-1 to 1-3 were measured according to the method specified in GB / T 16535.

[0092] The oxidation resistance of the composite ceramics prepared in Examples 1-1 to 1-3 was determined using the high-temperature oxidation weight loss method. The high-temperature oxidation weight loss method involves placing the sample at 800℃ for 24 hours, recording the mass of the sample before and after oxidation, and calculating the high-temperature oxidation weight loss rate: high-temperature oxidation weight loss rate = (weight before oxidation - weight after oxidation) / weight before oxidation × 100%.

[0093] Table 1

[0094]

[0095] Note: The graphite in Table 1 is commercially available, and the procurement standard is YB / T 2818-2005.

[0096] Example 2: Analysis of the chemical stability and thermal shock resistance of ceramics

[0097] Commercially available alumina ceramics (product model: 96 ceramic), silicon carbide ceramics, silicon nitride ceramics, and composite ceramics prepared in Example 1-1 were subjected to immersion tests to verify the chemical stability and thermal shock resistance of the ceramic materials.

[0098] Example 2-1

[0099] The specific method for verifying chemical stability is as follows:

[0100] Four alumina crucibles were taken and labeled 1#, 2#, 3#, and 4#, respectively. High-purity aluminum with a purity of 5N was placed in each crucible. Then, all the crucibles were placed side-by-side in a muffle furnace, and the furnace temperature was set to 850°C to melt the 5N high-purity aluminum in the crucibles, obtaining molten 5N aluminum. Alumina ceramics were then immersed in the molten 5N aluminum in crucible 1#, silicon carbide ceramics in crucible 2#, and silicon nitride ceramics in crucible 3#. The composite ceramics prepared in Example 1-1 were immersed in the molten 5N aluminum in crucible 4#, with the immersion temperature of the aluminum in each crucible controlled at 750°C.

[0101] Samples of 5N high-purity aluminum liquid were taken from each alumina crucible after soaking for 4 h, 8 h, 12 h, and 24 h, respectively, and the contents of Fe, Si, V, Cr, Na, and Ca in the 5N high-purity aluminum liquid were determined. The elemental contents of the 5N high-purity aluminum liquid are shown in Table 2.

[0102] Table 2

[0103]

[0104] Note: The elemental changes in Table 1 refer to the changes in the content of each element in the 5N high-purity aluminum liquid before and after the ceramic material is immersed in the 5N high-purity aluminum liquid for 24 hours; the elemental content when the immersion time is 0 indicates the content of the relevant elements in the 5N high-purity aluminum liquid when the ceramic is not immersed.

[0105] Example 2-2

[0106] The method for verifying thermal shock resistance stability is as follows:

[0107] Test method for thermal shock resistance of alumina ceramics: Take three alumina crucibles; place 5N high-purity aluminum in each alumina crucible; then place all the alumina crucibles together in a muffle furnace, set the temperature of the muffle furnace to 850℃, so that the 5N high-purity aluminum is melted in the alumina crucibles to obtain 5N high-purity aluminum liquid. Then take three tubular alumina ceramic samples, put them into the three alumina crucibles respectively, and immerse them in 5N high-purity aluminum liquid, controlling the immersion temperature of the aluminum liquid at 750℃. Then, take out the ceramic tubes every two hours, air-cool them to room temperature, and observe whether there is any breakage; if there is no breakage, continue to put them into the alumina crucibles for immersion; until the ceramic tubes break, the test ends, and record the number of times the ceramic tubes in each alumina crucible are removed without breakage.

[0108] The thermal shock resistance test methods for silicon carbide ceramics, silicon nitride ceramics, and the composite ceramics prepared in Example 1 are the same as those for alumina ceramics, and the dimensions and thickness of each sample are the same as those of the tubular alumina ceramics.

[0109] The number of times each ceramic item did not break after soaking is shown in Table 3.

[0110] Table 3

[0111]

[0112] As shown in Tables 2 and 3, alumina ceramics exhibit good chemical stability, but in terms of thermal shock resistance, they fractured after an average of 3.67 cycles of alternating hot and cold treatment. Silicon carbide ceramics showed good thermal shock resistance, fractured after an average of 13.67 cycles of alternating hot and cold treatment; however, in the chemical stability verification test, the Si element content in the 5N high-purity aluminum liquid immersed in silicon carbide ceramics increased by 8.4 ppm, indicating that silicon carbide ceramics can contaminate the purified aluminum liquid. Silicon nitride ceramics fractured after an average of 13.33 cycles of alternating hot and cold treatment, and the changes in impurity elements in the 5N high-purity aluminum liquid immersed in silicon nitride ceramics were smaller than those in the 5N high-purity aluminum liquids immersed in alumina and silicon carbide ceramics, indicating that silicon nitride ceramics have better chemical stability and thermal shock resistance than alumina and silicon carbide ceramics. However, the composite ceramics prepared in Example 1-1 only fractured after an average of 18.33 cycles of thermal shock, indicating that the composite ceramics prepared in Example 1-1 have better thermal shock resistance. This may be because, in addition to the main component silicon nitride, the silicon carbide in the composite ceramics increases the ceramic's hardness. Furthermore, the addition of lithium titanate, which has a face-centered cubic structure, and high-temperature sintering, results in a small particle size distribution, high crystallinity, and good product uniformity, thus improving the ceramic's thermal conductivity. The thermal conductivity of the new composite ceramic can reach 90 W / (m·K), while its fracture toughness is higher than that of single silicon nitride ceramics, reaching 7 MPa·m. 1 / 2Therefore, the new ceramic has the best thermal shock resistance and chemical stability comparable to other ceramics. The new composite ceramic can meet the requirements of the high-purity aluminum segregation purification process.

[0113] Example 3

[0114] Application examples of high-purity aluminum segregation purification:

[0115] 1) The composite ceramic prepared in Example 1-1 is processed into a crystallization stopper rod for use in a segregation purification crystallization device, and the interior of the crystallization rod has the following characteristics: Figure 1 The U-shaped inner cavity shown is connected to the cooling device. The cooling medium, air, is input from one port of the U-shaped inner cavity and output from the other port.

[0116] 2) Add primary aluminum ingots with Al content of 99.85% to 99.90% to the melting and mixing furnace according to the required proportions for melting and heating. After melting, homogenization treatment is carried out to obtain molten aluminum. The content of Fe, Si, Zn, Ti, Mn, Cr, V and Ga elements in the molten aluminum is shown in Table 4.

[0117] 3) The homogenized molten aluminum is transported via a chute to the segregation purification and crystallization equipment in step 1). The equipment is started, and the crystallization rod moves up and down in the molten aluminum to perform segregation purification. The process conditions for segregation purification include: controlling the crystallization temperature of aluminum at 663℃ (i.e., controlling the preset temperature of the molten aluminum at 663℃), and allowing the temperature of the molten aluminum to fluctuate within ±3℃ of the preset value; controlling the crystal growth rate at 5cm / hour, and controlling the aluminum crystal particles to be less than 2mm; when the mass of the crystallized crystals reaches 55% of the mass of the molten aluminum, the segregation furnace crystallization purification is completed, and the crystallization rod stops moving up and down.

[0118] 4) After the crystallizing rod stops moving up and down, the crystal continues to grow. When the growth cycle of the segregated crystal reaches the maximum value of segregation purification, solid-liquid separation and pouring are carried out: the crucible is lifted out using a special lifting tool, and the aluminum liquid containing impurity elements in the upper part of the crucible is poured out using an aluminum liquid pourer; after pouring, it is left to stand at room temperature for 25 minutes.

[0119] 5) Sawing of the crystallized material: After the crystal has completely solidified, a hole is drilled in the center and the material is lifted out of the crucible using a special lifting device. It is then sawn to a fixed size using an automatic sawing machine. The high-purity part after sawing can be used for casting high-purity aluminum ingots, and the tailings can be used for the production of cast aluminum alloys.

[0120] The content of elements such as Fe, Si, Zn, and Ga in the high-purity aluminum crystals after sawing was analyzed, as well as the actual yield of the high-purity aluminum crystals. The specific results are shown in Table 5.

[0121] Example 4

[0122] The preparation method in this embodiment is basically the same as that in Example 3, except that the crystal growth rate is controlled at 6 cm / hour when the aluminum liquid is purified by segregation crystallization in this embodiment. Other process conditions are the same as in Example 3.

[0123] Comparative Example 1

[0124] 1) This embodiment uses a traditional segregation purification and crystallization equipment with graphene as the crystallizing rod.

[0125] 2) Add primary aluminum ingots with Al content of 99.85% to 99.90% to the melting and mixing furnace according to the required proportions for melting and heating. After melting, homogenization treatment is carried out to obtain molten aluminum. The content of Fe, Si, Zn, Ti, Mn, Cr, V and Ga elements in the molten aluminum is shown in Table 3.

[0126] 3) The homogenized aluminum liquid is transported via a chute to the segregation purification and crystallization equipment in step 1). The equipment is started, and the crystallization rod moves up and down in the aluminum liquid for segregation purification. The process conditions for segregation purification include: controlling the aluminum crystallization temperature at 665℃ (i.e., controlling the aluminum liquid temperature to a preset value of 665℃), with the aluminum liquid temperature allowed to fluctuate within ±4℃ of the preset value; controlling the crystal growth rate at 6cm / hour, with aluminum crystal particles controlled to be below 2mm; when the crystal mass reaches 60% of the aluminum liquid mass, the segregation furnace crystallization purification is completed, and the crystallization rod stops moving up and down.

[0127] 4) After the crystallizing rod stops moving up and down, the crystal continues to grow. When the growth cycle of the segregated crystal reaches the maximum value of segregation purification, solid-liquid separation and pouring are carried out: the crucible is lifted out using a special lifting tool, and the aluminum liquid containing impurity elements in the upper part of the crucible is poured out using an aluminum liquid pourer; after pouring, it is left to stand at room temperature for 20 minutes.

[0128] 5) Sawing of the crystallized material: After the crystal has completely solidified, a hole is drilled in the center and the material is lifted out of the crucible using a special lifting device. It is then sawn to a fixed size using an automatic sawing machine. The high-purity part after sawing can be used for casting high-purity aluminum ingots, and the tailings can be used for the production of cast aluminum alloys.

[0129] The content of elements such as Fe, Si, Zn, and Ga in the high-purity aluminum crystals after sawing was analyzed, as well as the actual yield of the high-purity aluminum crystals. The specific results are shown in Table 4.

[0130] Crystallizer rod life test method:

[0131] The upper part of the crystallizing rod is fixed and moves up and down periodically. Each production cycle lasts 12-24 hours until the ceramic rod breaks. The service life is calculated based on the time it has been in use.

[0132] Table 4

[0133]

[0134] Note: The purification yield in the table = (total feed amount - total amount of separated liquid - total amount of sawn unqualified material) / total feed amount × 100%.

[0135] As can be seen from Table 4, the effect of the composite ceramic crystallizer prepared in Example 1-1 on purifying aluminum liquid is comparable to that of the graphite crystallizer. However, the service life of the crystallizer prepared in Example 1-1 reaches 24.2 months, which is 6.4 months longer than that of the graphite stopper.

[0136] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0137] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims, and the specification can be used to interpret the content of the claims.

Claims

1. A composite ceramic, characterized by, The preparation raw materials of the composite ceramic include silicon nitride, lithium titanate and silicon carbide.

2. The composite ceramic of claim 1, wherein, The preparation raw materials of the composite ceramic include 40-50 parts of silicon nitride, 30-40 parts of lithium titanate and 10-20 parts of silicon carbide by mass fraction.

3. The composite ceramic of claim 2, wherein, The preparation raw materials further include a sintering aid, and the preparation raw materials of the composite ceramic include 40%-50% of silicon nitride, 30%-40% of lithium titanate, 10%-20% of silicon carbide and 5%-10% of the sintering aid by mass percentage.

4. The composite ceramic according to any one of claims 1 to 3, wherein The composite ceramic satisfies at least one of the following conditions: (1) the thermal conductivity of the composite ceramic is 80-100 W / (m·K); (2) the composite ceramic has a fracture toughness of 7 MPa-m 1 / 2 9 MPa-m 1 / 2 ; (3) the compressive strength of the composite ceramic is 1400-1600 MPa; (4) the friction coefficient of the composite ceramic is 0.2-0.4; (5) the composite ceramic has a coefficient of thermal expansion of 2.5 x 10 -6 / °C to 3.5 x 10 -6 / °C.

5. The composite ceramic according to any one of claims 1 to 3, wherein The composite ceramic is a rod material.

6. The method of producing a composite ceramic according to any one of claims 1 to 5, wherein The preparation steps include: The preparation raw materials are mixed, and then sequentially subjected to a forming treatment and a sintering treatment.

7. A segregation purification apparatus characterized by comprising: The preparation steps include: The crystalline rod is made of the composite ceramic according to any one of claims 1-5.

8. A method of purification by aluminum segregation, characterized by, The preparation steps include: The aluminum liquid to be purified is placed in the segregation purification equipment according to claim 7, and subjected to a segregation crystallization purification treatment to obtain purified aluminum.

9. The method of claim 8, wherein, When the aluminum liquid to be purified is subjected to the segregation crystallization purification treatment, the aluminum crystallization temperature is 655-685℃.

10. The method of claim 8, wherein, When the aluminum liquid to be purified is subjected to the segregation crystallization purification treatment, the growth speed of the aluminum crystalline crystal is 5-6 cm / h.

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