Mg-α-SiAlON / MgO Composite Material, Preparation Method Thereof and Application Thereof

Abstract

The present invention provides a Mg-α-SiAlON / MgO composite material, a preparation method thereof and applications thereof, belonging to the technical field of ceramic materials. A Mg-α-SiAlON / MgO composite material, the raw materials for its preparation include: metallic Al powder, elemental Si powder, AlN, α-Al2O3 and sintered magnesite. The weight fraction of the Al powder is 1 to 10 parts, the weight fraction of the Si powder is 15 to 30 parts, the weight fraction of the AlN powder is 3 to 20 parts, the weight fraction of the α-Al2O3 is 5 to 20 parts, and the weight fraction of the sintered magnesite is 40 to 70 parts. The technical solution of the present invention improves the comprehensive utilization rate of low-grade magnesite while enabling the product to have high strength and high oxidation resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic materials, and particularly to an Mg-α-SiAlON / MgO composite material, a preparation method thereof, and an application thereof. Background Art

[0002] Mineral resources are an important foundation for the economic and social development of our country. In recent years, with the continuous development of mineral resources and the implementation of environmental pollution control measures, the efficient utilization of low-grade mineral resources has gradually received more and more attention. Magnesium-based materials have a wide range of applications in medical treatment, refractory materials, daily use, military industry, aerospace, etc. Magnesite, as the main source of magnesium, has rich reserves in our country. However, with continuous development and utilization, the magnesite resources that can be directly used for commercialization can no longer meet the needs of some regions at present. Since low-grade magnesite cannot be directly used for the synthesis of high-precision materials, improving the utilization rate of low-grade magnesite is a problem that needs to be solved at present. The current development and utilization of low-grade magnesite mainly focus on beneficiation. High-grade magnesite is prepared by thermal beneficiation and flotation to improve the utilization rate of magnesite. However, this method has the disadvantages of high cost and low utilization rate at the same time.

[0003] SiAlON is the general name of a variety of Si-Al-O-N solid solutions, which has excellent physical and chemical properties and biological properties, and is widely used in refractory materials, wear-resistant materials and other aspects. α-SiAlON, as a kind of SiAlON, is a solid solution based on α-Si3N4, generally equiaxed crystals, and has excellent mechanical properties and corrosion resistance.

[0004] Due to the excellent properties of Sialon, a large number of studies have been carried out on it in recent years. The synthesis research of Sialon mainly focuses on how to reduce costs and control the microstructure to improve the properties of materials. Discussing and researching Sialon composite materials can further improve the properties of materials, and finally materials that meet the theoretical design and actual application expectations can be prepared.

[0005] In view of this, the present invention is specifically proposed. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide an Mg-α-SiAlON / MgO composite material aiming at the deficiencies of the prior art, which can improve the comprehensive utilization rate of low-grade magnesite while enabling the product to have high strength and high oxidation resistance.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is:

[0008] A Mg-α-SiAlON / MgO composite material, the raw materials for its preparation include: metallic Al powder, elemental Si powder, AlN, α-Al2O3, and sintered magnesite. The weight parts of the Al powder are 1-10 parts, the weight parts of the Si powder are 15-30 parts, the weight parts of the AlN powder are 3-20 parts, the weight parts of the α-Al2O3 are 5-20 parts, and the weight parts of the sintered magnesite are 40-70 parts.

[0009] Preferably, for the Mg-α-SiAlON / MgO composite material, the raw materials for its preparation further include: a sintering aid; the sintering aid can be selected from one or a combination of two or more of Y2O3, CaO, Li2O, and TiO2.

[0010] Preferably, the weight parts of the sintering aid are 2-8 parts.

[0011] Preferably, for the Mg-α-SiAlON / MgO composite material, the raw materials for its preparation further include: a binder, and the binder is an alcohol solution or an aqueous solution of one or a combination of two or more of polyvinyl alcohol, polyvinyl butyral, polyethylene glycol, and polyvinylpyrrolidone.

[0012] Preferably, the weight parts of the binder are 5-10 parts.

[0013] Preferably, the particle size of the AlN powder is below 200 mesh, the particle size of the Al powder is below 325 mesh, and the particle size of the α-Al2O3 is below 325 mesh.

[0014] The present invention also provides a preparation method of a Mg-α-SiAlON / MgO composite material, and the steps are as follows:

[0015] 1) Weigh metallic Al powder, elemental Si powder, AlN, α-Al2O3, sintered magnesite, and the sintering aid according to the ratio, add an ethanol solution, and mix uniformly by ultrasonic assistance to obtain a slurry;

[0016] 2) Place the mixed slurry in a vacuum drying oven to dry, add the binder, and obtain a ceramic green body after molding by pressing and drying;

[0017] 3) Place the above green body in a nitrogen atmosphere for sintering, and the sintered green body is cooled with the furnace to obtain a composite ceramic.

[0018] Preferably, the process parameters of the ultrasonic wave include: the ultrasonic frequency is 20-30 KHz, and the ultrasonic time is 15-60 min.

[0019] Preferably, the process parameters of the molding by pressing include: the pressure is 50-300 MPa.

[0020] Preferably, the process parameters for sintering include: heating up to 600 - 800 °C at a rate of 5 - 10 °C / min in a nitrogen furnace and holding for 2 - 4 h; then heating up to 1000 - 1200 °C at a rate of 3 - 5 °C / min and holding for 1 - 3 h; finally heating up to 1300 - 1600 °C at a rate of 1 - 3 °C / min and holding for 4 - 6 h.

[0021] The Mg-α-SiAlON / MgO composite material of the present invention can be applied to the preparation of magnesia crucibles.

[0022] α-sialon is a solid solution based on α-Si3N4, and its chemical formula can generally be expressed as: M x Si 12-m-n Al m+n O n N 16-n (where the values of the solid solution parameters m and n represent that m + n Si-N bonds in the α-sialon solid solution are replaced by m Al-N bonds and n Al-O bonds), when Al 3+ replaces Si 4+ the electrical neutrality is maintained by the entry of additional metal ions M (M can be Li, Mg, Ca, Y, and rare earth cations except La, Ce, Pr, Eu) into the lattice interstitial sites of α-sialon. In this study, Mg-α-SiAlON is formed and then reacts with the excess MgO to form the Mg-α-SiAlON / MgO composite material.

[0023] The components of the raw materials are closely related to the microstructure of the sintered body. Different raw material components will cause great differences in the microstructure of the sintered body. Based on this concept, the microstructure of the material can be regulated by designing the raw material components. It is found that the higher the Al and O contents (the larger the m and n values) in the raw material components, the more long rod-shaped α-sialon grains contained in the prepared α-sialon ceramic. However, when the Al and O contents exceed a certain value, some β-sialon grains or AlN polymorphic phases will be generated, and single-phase α-sialon grains cannot be obtained.

[0024] Si3N4 is the main raw material for preparing sialon ceramics. The Si-N in Si3N4 is bonded by very strong covalent bonds, and its sintering diffusion coefficient is relatively low, making it difficult to sinter pure Si3N4 densely. Therefore, sintering aids need to be added during the preparation of sialon ceramics to provide a liquid phase to promote its sintering densification.

[0025] The sintering process has a great influence on the microstructure of materials. Generally, it is believed that the higher the sintering temperature, the longer the holding time, and the faster the heating rate, the more long rod-shaped α-sialon grains contained in the prepared α-sialon ceramics. The growth of α-sialon grains follows the Ostwald Ripening mechanism (Lennon Ná raigh, Gloster A. A large-scale statistical study of the coarsening rate in models of Ostwald-Ripening[J]. 2019.). The higher the sintering temperature and the longer the holding time, the corresponding increase in the amount of liquid phase during sintering, the decrease in the viscosity of the liquid phase, which can promote the anisotropic growth of grains and more easily form long rod-shaped α-sialon grains. The faster the heating rate, the fewer the number of α-sialon nuclei at low temperatures, and at the same time, it can reduce the probability of other reactions occurring, avoiding consuming more liquid phase at low temperatures, so as to ensure that there is enough liquid phase at high temperatures to promote grain growth and increase the number of long rod-shaped α-sialon grains. However, simply increasing the heating rate does not necessarily result in a microstructure with long rod-shaped α-sialon grains. For different sintering aid systems, the influence of the heating rate on the microstructure will be very different.

[0026] In this regard, Zenotchkine et al. (Zenotchkine M, Shuba R, Chen I. Effect of heatingschedule on the microstructure and fracture Toughness of α -SiAlON-cause andsolution [J]. Journal of the American Ceramic Society, 2010,85(7): 1882-1884.) selected Y2O3, Nd2O3, and Yb2O3 as sintering aids respectively to study the influence of different heating rates on the microstructure and properties of α-sialon. Using Nd2O3 as the sintering aid, the heating rate has little influence on the microstructure of α-sialon. For heating rates of 5°C / min and 25°C / min, dense α-sialon with long rod-shaped grains can be obtained; while using Yb2O3 as the sintering aid, only when the heating rate is 15°C / min can α-sialon with long rod-shaped grains be obtained; when using Y2O3 as the sintering aid, it is found that the increase in the heating rate is not conducive to the formation of rod-shaped grain α-sialon.

[0027] In addition, the method of preparing composite materials by introducing a second phase is considered a new attempt in modern material preparation, and some unexpected effects can be obtained. Early literature also reported the preparation of α-sialon / SiC composite ceramic materials by introducing the second phase SiC into α-sialon ceramics. It was found that the introduction of SiC could improve the hardness of the ceramics, but it would seriously reduce the grain size and aspect ratio of the α phase, thereby reducing the fracture toughness of the material and failing to achieve the toughening effect.

[0028] Like other nitride ceramics, α-sialon also faces the problem of high-temperature oxidation in an oxygen-containing environment at high temperatures, which will limit its application in actual engineering fields. To improve the high-temperature oxidation resistance of α-sialon ceramics and reveal the high-temperature oxidation mechanism of α-sialon, although relevant researchers have done a lot of research work, the oxidation mechanism of α-sialon ceramics still needs to be further explored and studied.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] The present invention uses metallic Al powder, elemental Si powder, AlN, α-Al2O3 and low-grade sintered magnesite as base materials, and at the same time adds specific sintering aids. By exploring appropriate ratios and reacting and sintering under high-temperature and nitrogen conditions, a Mg-α-SiAlON / MgO composite ceramic with high strength and good oxidation resistance is obtained.

[0031] The phases of the Mg-α-SiAlON / MgO composite ceramic prepared by the present invention mainly include MgO, Mg-α-SiAlON, forsterite, magnesium aluminate spinel and a small amount of Si3N4. The high-temperature sintering adopts a multi-stage heating process, and the temperature is controlled at 400-600 °C to remove excess organic matter. At a temperature of 1300-1600 °C, Si3N4 and Al2O3, AlN and MgO are mutually dissolved to form a Mg-α-SiAlON / MgO composite ceramic. The characteristics of instantaneous liquid-phase sintering of Mg-α-SiAlON can purify the grain boundaries, reduce the presence of low-melting-point phases, improve the performance of the composite phase material, and make the product have the characteristics of high compressive strength, low porosity and strong oxidation resistance.

[0032] The present invention enables the raw materials to be transformed into high-performance Mg-α-SiAlON / MgO composite ceramics at high temperatures through component and reaction design, realizes the improvement of the comprehensive performance of the materials, and obtains composite refractory materials with expected service performance. After testing, the compressive strength of the Mg-α-SiAlON / MgO composite ceramic of the present invention can reach 1 GPa; after oxidation at 1400 °C for 20 h, the oxidation weight gain is less than 7%; when the bulk density is less than 3 g / cm 3 , the apparent porosity is less than 11%.

[0033] Moreover, the composite material prepared by the present invention can also improve the utilization rate of low-grade sintered magnesite, reduce the cost and energy consumption in the production process, and is conducive to popularization and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0035] Figure 1 : XRD spectrum of the Mg-α-SiAlON / MgO composite material of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] To better understand the present invention, the following will further clearly elaborate on the content of the present invention in combination with embodiments. However, the protected content of the present invention is not limited to the following embodiments. In the following description, a large number of specific details are given to provide a more thorough understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be implemented without one or more of these details.

[0037] In all the examples shown and discussed here, any specific value should be interpreted as merely exemplary, rather than as a limitation. Therefore, other examples of the exemplary embodiments may have different values.

[0038] Unless otherwise specified, all raw materials are commercially available products, and unless otherwise specified, they do not contain other components not explicitly mentioned except for inevitable impurities.

[0039] In some specific embodiments of the present invention, the mass percentage composition of the chemical components in the sintered magnesite is: MgO≥88%, SiO2≤4%, CaO≤5%, and the ignition loss≤0.5%. This sintered magnesite is prepared from low-grade magnesite ore and belongs to ordinary magnesite in terms of composition. Compared with high-purity magnesite (MgO≥96%, SiO2≤1.5%, ignition loss≤0.3%), the cost is more controllable. At the same time, the ceramic obtained by the raw material formulation and preparation method of the present invention has a low apparent porosity, is lightweight, has high strength, and has good oxidation resistance, and is expected to be used for preparing magnesia crucibles.

[0040] Example 1

[0041] A preparation method of Mg-α-SiAlON / MgO composite material comprises the following steps: Weigh metal Al powder, elemental Si powder, AlN, α-Al2O3, sintered magnesia and sintering aid according to the ratio, add ethanol solution and mix evenly by ultrasonic assistance to obtain a slurry; Place the mixed slurry in a vacuum drying oven to dry, add a binder, and obtain a ceramic green body after molding by pressing and drying; Place the above green body in a nitrogen atmosphere for sintering, and the sintered green body is cooled with the furnace to obtain the composite ceramic.

[0042] Among them: The weight parts of metal Al powder, elemental Si powder, AlN, α-Al2O3, sintered magnesia, sintering aid, and binder are in turn: 1 part, 17 parts, 3 parts, 7 parts, 70 parts, 2 parts, 5 parts;

[0043] The sintering aid is Y2O3;

[0044] The binder is an ethanol solution of 5wt% polyvinyl butyral;

[0045] The process parameters of ultrasonic include: The ultrasonic frequency is 20KHz, and the ultrasonic time is 15min.

[0046] The process parameters of molding by pressing include: The pressure is 100MPa.

[0047] The process parameters of sintering include: Heating to 600°C at a rate of 5°C / min in a nitrogen furnace and holding for 3h; Then heating to 1000°C at a rate of 3°C / min and holding for 3h, and finally heating to 1300°C at a rate of 1°C / min and holding for 6h.

[0048] Example 2

[0049] A preparation method of Mg-α-SiAlON / MgO composite material comprises the following steps: Weigh metal Al powder, elemental Si powder, AlN, α-Al2O3, sintered magnesia and sintering aid according to the ratio, add ethanol solution and mix evenly by ultrasonic assistance to obtain a slurry; Place the mixed slurry in a vacuum drying oven to dry, add a binder, and obtain a ceramic green body after molding by pressing and drying; Place the above green body in a nitrogen atmosphere for sintering, and the sintered green body is cooled with the furnace to obtain the composite ceramic.

[0050] Among them: The weight parts of metal Al powder, elemental Si powder, AlN, α-Al2O3, sintered magnesia, sintering aid, and binder are in turn: 6 parts, 30 parts, 7 parts, 7 parts, 46 parts, 4 parts, 8 parts;

[0051] The sintering aid is CaO;

[0052] The binder is an ethanol solution of 8wt% polyvinyl butyral;

[0053] The process parameters of ultrasonic treatment include: the ultrasonic frequency is 25KHz, and the ultrasonic time is 30min.

[0054] The process parameters of compression molding include: the pressure is 200MPa.

[0055] The process parameters of sintering include: heating up to 700℃ at a rate of 8℃ / min in a nitrogen furnace and holding for 2h; then heating up to 1100℃ at a rate of 4℃ / min and holding for 2h, and finally heating up to 1450℃ at a rate of 2℃ / min and holding for 5h.

[0056] Example 3

[0057] A preparation method of Mg-α-SiAlON / MgO composite material comprises the following steps: weighing metal Al powder, elemental Si powder, AlN, α-Al2O3, sintered magnesia and sintering aid according to the ratio, adding ethanol solution and mixing evenly by ultrasonic assistance to obtain a slurry; drying the mixed slurry in a vacuum drying oven, adding a binder, and obtaining a ceramic green body after compression molding and drying; sintering the above green body in a nitrogen atmosphere, and cooling the sintered green body with the furnace to obtain the composite ceramic.

[0058] Among them: the weight parts of metal Al powder, elemental Si powder, AlN, α-Al2O3, sintered magnesia, sintering aid, and binder are in turn: 6 parts, 18 parts, 13 parts, 15 parts, 40 parts, 8 parts, 10 parts;

[0059] The sintering aid is TiO2;

[0060] The binder is an ethanol solution of 10wt% polyvinyl butyral;

[0061] The process parameters of ultrasonic treatment include: the ultrasonic frequency is 30KHz, and the ultrasonic time is 60min.

[0062] The process parameters of compression molding include: the pressure is 300MPa.

[0063] The process parameters of sintering include: heating up to 800℃ at a rate of 10℃ / min in a nitrogen furnace and holding for 4h; then heating up to 1200℃ at a rate of 5℃ / min and holding for 3h, and finally heating up to 1600℃ at a rate of 3℃ / min and holding for 6h.

[0064] Example 4

[0065] A preparation method of Mg-α-SiAlON / MgO composite material comprises the following steps: weighing metallic Al powder, elemental Si powder, AlN, α-Al2O3, sintered magnesite and sintering aid according to the ratio, adding ethanol solution and mixing uniformly by ultrasonic assistance to obtain a slurry; drying the mixed slurry in a vacuum drying oven, adding a binder, and obtaining a ceramic green body after molding by pressing and drying; sintering the above green body in a nitrogen atmosphere, and cooling the sintered green body with the furnace to obtain the composite ceramic.

[0066] Among them: the weight parts of metallic Al powder, elemental Si powder, AlN, α-Al2O3, sintered magnesite, sintering aid, and binder are in turn: 10 parts, 15 parts, 5 parts, 5 parts, 60 parts, 5 parts, 7 parts;

[0067] The sintering aid is CaO;

[0068] The binder is an aqueous solution of 10wt% polyethylene glycol;

[0069] The process parameters of ultrasonic include: the ultrasonic frequency is 23KHz, and the ultrasonic time is 45min.

[0070] The process parameters of molding by pressing include: the pressure is 150MPa.

[0071] The process parameters of sintering include: heating to 650°C at a rate of 6°C / min in a nitrogen furnace and holding for 2.5h; then heating to 1070°C at a rate of 3.5°C / min and holding for 1.5h, and finally heating to 1400°C at a rate of 1.5°C / min and holding for 4.5h.

[0072] Example 5

[0073] A preparation method of Mg-α-SiAlON / MgO composite material comprises the following steps: weighing metallic Al powder, elemental Si powder, AlN, α-Al2O3, sintered magnesite and sintering aid according to the ratio, adding ethanol solution and mixing uniformly by ultrasonic assistance to obtain a slurry; drying the mixed slurry in a vacuum drying oven, adding a binder, and obtaining a ceramic green body after molding by pressing and drying; sintering the above green body in a nitrogen atmosphere, and cooling the sintered green body with the furnace to obtain the composite ceramic.

[0074] Among them: the weight parts of metallic Al powder, elemental Si powder, AlN, α-Al2O3, sintered magnesite, sintering aid, and binder are in turn: 2 parts, 15 parts, 20 parts, 10 parts, 50 parts, 3 parts, 6 parts;

[0075] The sintering aid is Li2O;

[0076] The binder is an aqueous solution of 5wt% polyvinyl alcohol;

[0077] The process parameters of ultrasonic treatment include: the ultrasonic frequency is 28 KHz, and the ultrasonic time is 30 min.

[0078] The process parameters of molding by pressing include: the pressure is 200 MPa.

[0079] The process parameters of sintering include: heating up to 730 °C at a rate of 8 °C / min in a nitrogen furnace and holding for 3 h; then heating up to 1130 °C at a rate of 4 °C / min and holding for 2 h, and finally heating up to 1550 °C at a rate of 2.3 °C / min and holding for 5 h.

[0080] Example 6

[0081] A preparation method of Mg-α-SiAlON / MgO composite material comprises the following steps: weighing metallic Al powder, elemental Si powder, AlN, α-Al2O3, sintered magnesite and sintering aid according to the ratio, adding ethanol solution and mixing uniformly by ultrasonic assistance to obtain a slurry; placing the mixed slurry in a vacuum drying oven to dry, adding a binder, and obtaining a ceramic green body after molding by pressing and drying; placing the above green body in a nitrogen atmosphere for sintering, and cooling the sintered green body with the furnace to obtain the composite ceramic.

[0082] Among them: the weight parts of metallic Al powder, elemental Si powder, AlN, α-Al2O3, sintered magnesite, sintering aid, and binder are in turn: 3 parts, 20 parts, 10 parts, 20 parts, 44 parts, 3 parts, 5 parts;

[0083] The sintering aid is CaO;

[0084] The binder is an aqueous solution of 5 wt% polyethylene glycol;

[0085] The process parameters of ultrasonic treatment include: the ultrasonic frequency is 25 KHz, and the ultrasonic time is 20 min.

[0086] The process parameters of molding by pressing include: the pressure is 100 MPa.

[0087] The process parameters of sintering include: heating up to 720 °C at a rate of 7 °C / min in a nitrogen furnace and holding for 4 h; then heating up to 1200 °C at a rate of 5 °C / min and holding for 2 h, and finally heating up to 1450 °C at a rate of 2 °C / min and holding for 5 h.

[0088] Comparative Example 1

[0089] The difference between this comparative example and Example 6 is that: the sintered magnesite is omitted.

[0090] Comparative Example 2

[0091] The difference between this comparative example and Example 6 is that: the sintered magnesite is replaced with the following composition: MgO ≥ 87%, SiO2 ≤ 7%, CaO ≤ 2%, loss on ignition ≤ 0.5%.

[0092] Comparative Example 3

[0093] The difference between this comparative example and Example 6 is as follows: The sintering process parameters were adjusted as follows: In a nitrogen furnace, the temperature was raised to 800 °C at a rate of 20 °C / min and held for 5 h; then the temperature was raised to 1700 °C at a rate of 10 °C / min and held for 4 h.

[0094] Comparative Example 4

[0095] The difference between this comparative example and Example 6 is as follows: The sintering process parameters were adjusted as follows: In a nitrogen furnace, the temperature was raised to 500 °C at a rate of 3 °C / min and held for 5 h; then the temperature was raised to 1100 °C at a rate of 10 °C / min and held for 4 h; finally, the temperature was raised to 1700 °C at a rate of 5 °C / min and held for 5 h.

[0096] Next, the content of the evaluation test will be described. For the evaluation test, the following evaluation items were implemented.

[0097] 1. Phase characterization: X-ray diffraction was used for characterization.

[0098] Figure 1 This is the XRD pattern of the Mg-α-SiAlON / MgO composite material prepared by the present invention. It can be seen from the figure that the phases of the composite material mainly include MgO, Mg-SiAlON, forsterite and spinel, and in addition, a small amount of Si3N4 is contained.

[0099] Next, the following performance tests were carried out on the Mg-α-SiAlON / MgO composite materials prepared in Examples 1-6 and Comparative Examples 1-4.

[0100] 2. Determination of apparent porosity and bulk density: Determined by the hydrostatic weighing method, and the results are shown in Table 1.

[0101] 3. Determination of compressive strength: Determined by a microcomputer-controlled pressure testing machine, and the results are shown in Table 1.

[0102] 4. Determination of oxidation resistance: An oxidation test was carried out in a box furnace, the medium in the furnace was air, the temperature was raised to 1400 °C and kept constant for 20 hours. The oxidation resistance is expressed by the oxidation weight gain rate, and the formula is as follows: △m%=(m - m0) / m0×100%, where m0 is the mass of the sample before oxidation (g); m is the mass of the sample after oxidation (g), and the results are shown in Table 1.

[0103] Table 1 Test results of apparent porosity, bulk density, compressive strength and oxidation resistance

[0104] 。

[0105] From the above results, it can be seen that the compressive strength of the Mg-α-SiAlON / MgO composite ceramic of the present invention can reach 1 GPa; after oxidation at 1400 °C for 20 h, the oxidation weight gain is less than 7%; when the bulk density is less than 3 g / cm 3 , the apparent porosity is less than 11%.

[0106] In Comparative Example 1, the use of sintered magnesia was omitted, and the apparent porosity, bulk density, compressive strength and oxidation resistance of the product all changed to varying degrees. Since the sintered magnesia was omitted, a composite phase material could not be formed, and the chemical composition of the product also changed accordingly, uncontrollably affecting the comprehensive performance of the product.

[0107] In Comparative Example 2, sintered magnesia with different physical and chemical indexes was replaced, and the apparent porosity, bulk density, compressive strength and oxidation resistance of the product all changed to varying degrees. Further reducing the purity of the sintered magnesia changed the contents of components such as MgO, SiO2 and CaO in it, which had a significant impact on the structure and sintering strength of the composite material.

[0108] In Comparative Example 3 and Comparative Example 4, different sintering processes were selected, and the apparent porosity, compressive strength and oxidation resistance of the product all changed significantly, indicating that the sintering process has an important impact on the above characteristics of the composite phase material.

[0109] In summary, through the cooperation of raw materials, ratios and processing techniques, the Mg-α-SiAlON / MgO composite ceramic of the present invention endows the product with more remarkable light weight, high strength and oxidation resistance, and is expected to be used for preparing magnesia crucibles.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Any other modifications or equivalent replacements made by those of ordinary skill in the art to the technical solutions of the present invention shall be covered within the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solutions of the present invention.

Claims

1. A preparation method of Mg-α-SiAlON / MgO composite material, characterized in that: The steps are as follows: 1) Weigh metal Al powder, elemental Si powder, AlN, α-Al2O3, sintered magnesite and sintering aids according to the ratio, add ethanol solution and mix evenly by ultrasonic assistance to obtain a slurry; 2) Place the mixed slurry in a vacuum drying oven to dry, add a binder, and obtain a ceramic green body after molding by pressing and drying; 3) Sinter the above green body in a nitrogen atmosphere. In a nitrogen furnace, heat it up to 600-800 °C at a rate of 5-10 °C / min, hold for 2-4 h, then heat it up to 1000-1200 °C at a rate of 3-5 °C / min, hold for 1-3 h, and finally heat it up to 1300-1600 °C at a rate of 1-3 °C / min, hold for 4-6 h. The sintered green body is cooled with the furnace to obtain a composite ceramic; The weight parts of the Al powder are 1-10 parts, the weight parts of the Si powder are 15-30 parts, the weight parts of the AlN powder are 3-20 parts, the weight parts of the α-Al2O3 are 5-20 parts, the weight parts of the sintered magnesite are 40-70 parts, the weight parts of the sintering aids are 2-8 parts, and the weight parts of the binder are 5-10 parts; The sintered magnesite is prepared from low-grade magnesite ore, and the mass percentage composition of the chemical components in the sintered magnesite is: MgO≥88%, SiO2≤4%, CaO≤5%, and ignition loss≤0.5%.

2. The preparation method of a Mg-α-SiAlON / MgO composite material according to claim 1, characterized in that: The sintering aids can be selected from one or a combination of two or more of Y2O3, CaO, Li2O and TiO2.

3. The preparation method of a Mg-α-SiAlON / MgO composite material according to claim 2, characterized in that: The binder is an alcohol solution or an aqueous solution of one or a combination of two or more of polyvinyl alcohol, polyvinyl butyral, polyethylene glycol and polyvinyl pyrrolidone.

4. The preparation method of a Mg-α-SiAlON / MgO composite material according to claim 3, characterized in that: The particle size of the AlN powder is below 200 mesh, the particle size of the Al powder is below 325 mesh, and the particle size of the α-Al2O3 is below 325 mesh.

5. The preparation method of a Mg-α-SiAlON / MgO composite material according to claim 4, wherein: The process parameters of the ultrasonic wave include: the ultrasonic frequency is 20-30 KHz, and the ultrasonic time is 15-60 min.

6. The preparation method of a Mg-α-SiAlON / MgO composite material according to claim 5, characterized in that: The process parameters of the molding by pressing include: the pressure is 50-300 MPa.

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