Fabrication of high density magnesia-aluminum spinel ceramics by low temperature pressureless sintering

Abstract

This invention relates to a method for producing high density magnesia-aluminum spinel ceramics by low temperature pressureless sintering, 2 O 4 The powder is used as a raw material powder, calcium phosphate is added as a sintering aid, the Ca element in the calcium phosphate is controlled so as not to exceed 500 ppm of the total mass of the raw material powder, and pressureless sintering is further performed to produce a high-density magnesia-aluminum spinel ceramic, and the pressureless sintering includes atmospheric sintering or vacuum sintering.

Description

[Technical field]

[0001] The present invention belongs to the ceramics technical field and relates to transparent spinel ceramics and opaque spinel ceramics and their manufacturing methods, in particular to a sintering aid for lowering the pressureless sintering temperature of magnesia-aluminum spinel ceramics, and more particularly to a manufacturing method for high-density magnesia-aluminum spinel ceramics by low-temperature pressureless sintering. [Background technology]

[0002] Spinel ceramics have excellent mechanical properties, corrosion resistance, and high temperature resistance, and are one of the materials that are widely used in the field of traditional fire-resistant materials. In addition to the above excellent properties, transparent spinel ceramics also have excellent optical properties. Transparent spinel ceramics have high transmittance in the ultraviolet to mid-infrared wavelength range, and are widely used in many fields such as transparent armor, infrared fairings, surface acoustic wave filters, smartphone panels, camera protection windows, and high-energy laser emission windows.

[0003] However, to obtain the ideal density, the production of transparent spinel ceramics requires a relatively high sintering temperature, which usually results in a very large energy loss, and the various existing advanced sintering methods have many limitations.In addition, the existing magnesia-aluminum spinel ceramics are prone to the phenomenon of abnormal grain growth during the sintering process, which mainly affects many properties of ceramic materials, including mechanical properties and optical properties.

[0004] For opaque magnesia-aluminum spinel ceramics, the mechanical properties are of primary interest in many applications, so it is very important to suppress the grain growth of magnesia-aluminum spinel ceramics and improve their mechanical properties. For transparent magnesia-aluminum spinel ceramics, both the mechanical properties and optical properties are of primary interest. Therefore, obtaining magnesia-aluminum spinel transparent ceramics with small grain size and excellent optical performance is an important trend in the current development.

[0005] Adding sintering aids to the raw materials of magnesia-aluminum spinel ceramics is a common method to accelerate sintering, reduce the sintering temperature, inhibit grain growth, and improve the mechanical properties, optical performance, and high temperature properties. For several years, the use of CaO, CaCO 3 , LiF, B 2 O 3 , MgF 2 / AlF 3 , TiO 2 , V 2 O 5 , Cr 2 O 3 , Y 2 O 3 , MnO 2 , ZrO 2 , CoCO 3 Many kinds of sintering aids such as CaO, CaCO3, etc. have been developed and have shown certain effects. At the same time, there are some sintering aids that are effective in improving the transmittance of transparent ceramics. However, in general, these sintering aids have more or less some deficiencies, such as no effect on lowering the sintering temperature, or reacting with the raw materials to produce miscellaneous phases (e.g., CaO or CaCO 3 and magnesia-aluminum spinel and CaAl 4 O 7 These include those which require a large addition amount and affect the inherent performance of the ceramic material. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] China Patent Application Publication No. 107721406 Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, developing new sintering aids that can be used to lower the sintering temperature of magnesia-aluminum spinel ceramics, slow down the grain growth, and obtain magnesia-aluminum spinel ceramics with excellent mechanical properties and high-temperature properties is of great value for obtaining magnesia-aluminum spinel transparent ceramics with excellent mechanical properties, high-temperature properties, and optical performance. [Means for solving the problem]

[0008] In response to the above problems, in a first aspect, the present invention provides a method for producing high density magnesia aluminum spinel ceramics by low temperature pressureless sintering, comprising the steps of: 2 O 4 The present invention also includes the steps of: using a powder as a raw material powder, adding calcium phosphate as a sintering aid, controlling the Ca element in the calcium phosphate so as not to exceed 500 ppm of the total mass of the raw material powder, and then carrying out pressureless sintering to produce a high-density magnesia-aluminum spinel ceramics; and preferably, the composition of the calcium phosphate is 10 (PO 4 ) 6 (OH) 2 , Ca 3 (PO 4 ) 2 , Ca 4 O(PO 4 ) 2 , Ca 10-X H 2X (PO 4 ) 6 (OH) 2 , Ca 8 H 2 (PO 4 ) 6.5 H2 O, CaHPO 4 2H 2 O, CaHPO 4 , Ca 2 P 2 O 7 , CaP 2 O 7 2H 2 O, Ca 7 (P 5 O 16 ) 2 , Ca 4 H 2 P 6 O 20 , Ca(H 2 PO 4 ) 2 H 2 O, Ca(PO 3 ) 2 The pressureless sintering includes at least one of the above, and the pressureless sintering is pressureless sintering or vacuum sintering.

[0009] In a second aspect, the present invention further provides a method for producing high density magnesia aluminum spinel ceramics by low temperature pressureless sintering, comprising the steps of: 2 O 3 The present invention also includes the steps of: using a powder as a raw material powder, adding calcium phosphate as a sintering aid, controlling the Ca element in the calcium phosphate so as not to exceed 500 ppm of the total mass of the raw material powder, and then carrying out pressureless sintering to produce a high-density magnesia-aluminum spinel ceramics; and preferably, the composition of the calcium phosphate is 10 (PO 4 ) 6 (OH) 2 , Ca 3 (PO 4 ) 2 , Ca 4 O(PO 4 ) 2 , Ca 10-X H 2X (PO 4 ) 6 (OH) 2 , Ca 8 H 2 (PO 4 ) 6.5 H 2O, CaHPO 4 2H 2 O, CaHPO 4 , Ca 2 P 2 O 7 , CaP 2 O 7 2H 2 O, Ca 7 (P 5 O 16 ) 2 , Ca 4 H 2 P 6 O 20 , Ca(H 2 PO 4 ) 2 H 2 O, Ca(PO 3 ) 2 The pressureless sintering includes at least one of the above, and the pressureless sintering is pressureless sintering or vacuum sintering.

[0010] Preferably, the pressureless sintering temperature is lowered by 40 to 200°C compared to the densification temperature of pressureless sintering when calcium phosphate is not added. Compared to when no sintering aid is added, a pressureless sintering temperature can be lowered at which the same sintering effect can be obtained with the other steps being exactly the same. Specifically, the pressureless sintering temperature at which the open porosity of the magnesia-aluminum spinel ceramics does not exceed 1% is lowered by 40 to 220°C, preferably 70 to 220°C, and most preferably 100 to 220°C. CaO or CaCO 3 In comparison with the case where a sintering agent is added, the pressureless sintering temperature can be lowered while obtaining the same sintering effect with the other steps being exactly the same. Specifically, the pressureless sintering temperature at which the open porosity of the magnesia-aluminum spinel ceramic does not exceed 1% is lowered by 20 to 220°C, preferably by 40 to 220°C.

[0011] Preferably, the pressureless sintering temperature is 1360-1460° C., and the pressureless sintering time does not exceed 20 hours.

[0012] Preferably, before the pressureless sintering, the raw material powder is molded to prepare a green body, and the molding method is dry molding or / and wet molding.

[0013] Preferably, the MgO powder and Al 2 O 3 The molar ratio to the powder is 1:(0.98-2.2).

[0014] In a third aspect, the present invention provides a magnesia-aluminum spinel ceramic produced by the above-mentioned method for producing high density magnesia-aluminum spinel ceramic by low temperature pressureless sintering, wherein the magnesia-aluminum spinel has a density of 90% or more and an open porosity of not more than 1%.

[0015] In a fourth aspect, the present invention provides a method for producing a magnesia-aluminum spinel transparent ceramic, the method comprising sintering the magnesia-aluminum spinel ceramic produced as described above by hot isostatic pressing to obtain the magnesia-aluminum spinel transparent ceramic.

[0016] Preferably, the sintering temperature of the hot isostatic press is 1350-1800° C., the sintering pressure of the hot isostatic press is 50-200 MPa, and the sintering time of the hot isostatic press does not exceed 20 hours.

[0017] No. 5 In another aspect, the present invention provides a magnesia-aluminum spinel transparent ceramic produced by the above-mentioned production method. Effect of the Invention

[0018] In the present invention, the obtained magnesia-aluminum spinel transparent ceramic has no visible defects and has a transmittance of greater than 70%, preferably greater than 80%, more preferably greater than 85%, when measured in a wavelength range of 200 nm to 2500 nm, when the ceramic has a thickness of ≧3 mm. [Brief description of the drawings]

[0019] [Figure 1] The microstructure (SEM) and element distribution map (EDS) of a pre-sintered magnesia-aluminum spinel ceramic body (pressureless sintering temperature: 1360°C) containing 450 ppm of sintering additive. [Diagram 2] These are X-ray diffraction spectra (XRD) of pre-sintered magnesia-aluminum spinel ceramics (pressureless sintering temperature: 1400°C) with Ca addition in the sintering aid of 0 ppm, 350 ppm, and 15,000 ppm, respectively. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The present invention will be further described in conjunction with the following embodiments. The following embodiments are provided to illustrate the present invention, but are not intended to limit the present invention.

[0021] In the present disclosure, in the manufacturing process of magnesia-aluminum spinel ceramics, calcium element of 500 ppm or less (e.g., 25 ppm, 50 ppm, 75 ppm, 100 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm, 350 ppm, 400 ppm, 450 ppm, 500 ppm, etc.) is introduced as a sintering aid to realize densification of the magnesia-aluminum spinel ceramics during low-temperature sintering. Among them, the calcium element exists in the form of calcium phosphate, and the composition of the calcium phosphate is Ca 10 (PO 4 ) 6 (OH) 2 or Ca 3 (PO 4 ) 2 Contains Ca 4 O(PO 4 ) 2 , Ca 10-X H 2X (PO 4 ) 6 (OH) 2 , Ca 8 H 2 (PO 4 )6.5 H 2 O, CaHPO 4 2H 2 O, CaHPO 4 , Ca 2 P 2 O 7 , CaP 2 O 7 2H 2 O,Ca 7 (P 5 O 16 ) 2 , Ca 4 H 2 P 6 O 20 , Ca(H 2 PO 4 ) 2 H 2 O,Ca(PO 3 ) 2 The calcium phosphate may have other Ca / P ratios, including

[0022] According to the present invention, the magnesia-aluminum spinel ceramics may be manufactured by using the magnesia-aluminum spinel powder already formed into a phase as the raw material, or by using magnesium oxide and aluminum oxide powder as the raw material through reactive sintering, and the above-mentioned changes in the manufacturing method do not affect the implementation of the present invention. The adjustment of the particle size of the raw material powder used for the magnesia-aluminum spinel before sintering does not affect the implementation of the present invention.

[0023] According to the present invention, the magnesia-aluminum spinel ceramics can be manufactured by dry molding such as direct dry pressing and cold isostatic pressing, and wet molding such as injection molding, casting, tape casting, pressure-assisted injection molding, and pressure filtration molding, without affecting the implementation of the present invention. The subsequent process involves a discharge process, in which the discharge temperature can be 300-800°C and the discharge time can be 0-10 hours.

[0024] According to the present invention, adjustments to the molding steps in the dry molding and cold isostatic pressing processes, such as treatment of raw material powder including calcination, granulation, washing, etc., and adjustment of molding pressure, do not affect the implementation of the present invention.

[0025] According to the present invention, adjustments to the molding step in the wet molding process, such as the type and content of dispersant, adjustment of slurry solid content, and adjustment of curing temperature and time, do not affect the implementation of the present invention.

[0026] According to the present invention, in the method for producing the spinel ceramics, elemental calcium may be introduced in the preparation of the ceramic slurry or formulation.

[0027] According to the present invention, in the method for producing the spinel ceramics, the reduction in the sintering temperature includes reducing the pressureless sintering temperature by 220°C or less. At the same time, the sintering temperature of the subsequent hot isostatic pressing is also reduced. In the present invention, the relative density of the magnesia-aluminum spinel ceramics is made higher than 90% and the open porosity does not exceed 1% by adjusting the content of Ca element in the sintering aid and the temperature of the pressureless sintering.

[0028] According to the present invention, the obtained magnesia-aluminum spinel ceramic has a relative density higher than 90% and an open porosity not exceeding 1%.

[0029] Furthermore, the magnesia-aluminum spinel ceramics were sintered by hot isostatic pressing to obtain transparent magnesia-aluminum spinel ceramics.

[0030] The obtained magnesia-aluminum spinel transparent ceramics have a transmittance higher than 70% when measured within the wavelength range of 300 nm to 2500 nm when the thickness is ≥ 3 mm.

[0031] The present invention will be described in more detail through the following examples. Similarly, the following examples are provided to further explain the present invention and do not limit the scope of the present invention. Non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention are both within the scope of the present invention. Specific process variables in the following examples are merely examples within the applicable range, that is, those skilled in the art can select within an appropriate range based on the description of the present invention, and are not limited to the specific numerical values ​​in the following examples.

[0032] Example 1 (25 ppm, 44 vol%, wet molding) Magnesia-aluminum spinel powder, deionized water, sintering aid, and dispersant were mixed uniformly in a ball mill for 2 hours to obtain a magnesia-aluminum spinel ceramic slurry. In this slurry, the volumetric percentage of the magnesia-aluminum spinel powder was 44 vol%, the volumetric percentage of the deionized water was 56 vol%, the mass ratio of the Ca element in the sintering aid (relative to the magnesia-aluminum spinel powder) was 0.0025 wt%, and the mass ratio of the dispersant was 1.8 wt%. The particle size of the magnesia-aluminum spinel powder was 250 nm, and the molecular weight of the dispersant was 350. The sintering aid was Ca 3 (PO 4 ) 2 and the particle size was 300 nm.

[0033] The obtained magnesia-aluminum spinel slurry was subjected to pressure-assisted injection molding to obtain a magnesia-aluminum spinel ceramic body.

[0034] The magnesia-aluminum spinel ceramic body was dried and discharged at 300°C for 20 hours.

[0035] The magnesia-aluminum spinel ceramic bodies after the discharging process were pre-sintered (i.e., pressureless sintering) in a muffle furnace (air atmosphere, normal pressure; the following Examples and Comparative Examples are the same as Example 1) at pre-sintering temperatures of 1420°C, 1400°C, 1460°C, and 1480°C, respectively, to obtain pre-sintered ceramic bodies of opaque spinel ceramic with relative densities of 91.6%, 93.1%, 94.5%, and 95.6%, respectively, and open porosities of 7.0%, 1.8%, 0.32%, and 0.10%, respectively.

[0036] The pre-sintered ceramics were subjected to hot isostatic pressing at 1450℃ with a pressure of 180MPa and a heat retention time of 3 hours to obtain transparent magnesia-aluminum spinel ceramics. Measurements showed that the transmittance in the 300-2000nm wavelength range was higher than 80% (3mm thickness).

[0037] Example 2 (450 ppm, 44 vol%, wet molding) Magnesia-aluminum spinel powder, deionized water, sintering aid, and dispersant were mixed uniformly in a ball mill for 2 hours to obtain a magnesia-aluminum spinel ceramic slurry. The volume ratio of the magnesia-aluminum spinel powder was 44 vol%, the volume ratio of deionized water was 56 vol%, the mass ratio of Ca element in the sintering aid (relative to the magnesia-aluminum spinel powder) was 0.045 wt%, and the mass ratio of the dispersant was 1.8 wt%. The particle size of the magnesia-aluminum spinel powder was 250 nm, and the molecular weight of the dispersant was 350. The sintering aid was Ca 3 (PO 4 ) 2 and the particle size was 300 nm.

[0038] The obtained magnesia-aluminum spinel slurry was subjected to pressure-assisted injection molding to obtain a magnesia-aluminum spinel ceramic body.

[0039] The magnesia-aluminum spinel ceramic body was dried and then subjected to the discharging process, the temperature of which was 800℃.

[0040] The magnesia-aluminum spinel ceramic bodies after the discharging process were pre-sintered in a muffle furnace at pre-sintering temperatures of 1360°C, 1380°C, 1400°C, 1420°C, 1400°C, 1460°C, and 1480°C, respectively, to obtain pre-sintered ceramic bodies of opaque spinel ceramic with relative densities of 90.7%, 92.3%, 93.4%, 94.2%, 95.0%, 95.0%, and 95.4%, respectively, and open porosities of 1.9%, 0.6%, 0.5%, 0.5%, 0.13%, 0.5%, and 0.4%, respectively.

[0041] The pre-sintered ceramic body was subjected to hot isostatic pressing at 1450℃ with a pressure of 180MPa and a heat retention time of 3 hours to obtain transparent magnesia-aluminum spinel ceramics. Measurements showed that the transmittance of the obtained transparent magnesia-aluminum spinel ceramics in the wavelength range of 200 to 2000 nm was higher than 80%.

[0042] In order to verify the extremely low doping amount of the sintering aid in the present invention, the ceramic pre-sintered body pressurelessly sintered at 1360°C in this example was analyzed using a scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS), and the analysis results are shown in Figure 1. The microstructure photograph taken by SEM showed that no second phase material was generated during the sintering process. The energy spectrum results showed that the doped sintering aid of the present invention was below the detection limit of the EDS energy spectrum, and only three elements, Mg, Al, and O, were detectable, indicating that no new material was generated during the sintering process.

[0043] Example 3 (350 ppm, 44 vol%, wet molding) Magnesia-aluminum spinel powder, deionized water, sintering aid, and dispersant were mixed uniformly in a ball mill for 2 hours to obtain magnesia-aluminum spinel ceramic slurry. The volume ratio of the magnesia-aluminum spinel powder was 44 vol%, the volume ratio of deionized water was 56 vol%, the mass ratio of Ca element of the sintering aid (relative to the magnesia-aluminum spinel powder) was 0.035 wt%, and the mass ratio of the dispersant was 1.8 wt%. The particle size of the magnesia-aluminum spinel powder was 250 nm, and the molecular weight of the dispersant was 350. The sintering aid was Ca 3 (PO 4 ) 2 and the particle size was 300 nm.

[0044] The obtained magnesia-aluminum spinel slurry was subjected to pressure-assisted injection molding to obtain a magnesia-aluminum spinel ceramic body.

[0045] The magnesia-aluminum spinel ceramic body was dried and then subjected to the discharging process, the temperature of which was 800℃.

[0046] The magnesia-aluminum spinel ceramic bodies after the discharging process were pre-sintered in a muffle furnace at pre-sintering temperatures of 1360°C, 1380°C, 1400°C, 1420°C, 1400°C, 1460°C, and 1480°C, respectively, to obtain pre-sintered ceramic bodies of opaque spinel ceramic with relative densities of 91.7%, 93.3%, 94.3%, 95.1%, 95.9%, 96.0%, and 96.2%, respectively, and open porosities of 0.5%, 0.5%, 0.6%, 0.4%, 0.3%, 0.6%, and 0.4%, respectively.

[0047] The pre-sintered ceramic body was subjected to hot isostatic pressing at 1350℃ with a pressure of 180MPa and a heat retention time of 6 hours to obtain transparent magnesia-aluminum spinel ceramics. Measurements showed that the transmittance of the obtained transparent magnesia-aluminum spinel ceramics in the wavelength range of 200 to 2000 nm was higher than 80%.

[0048] Example 4 (100 ppm, 44 vol%, wet molding) The manufacturing process of the opaque spinel ceramics in this Example 6 was the same as that in Example 1, except that the sintering aid Ca 3 (PO 4 ) 2 The only difference is that the mass ratio of Ca (to the magnesia-aluminum spinel powder) in was 0.01 wt%. The pre-sintering temperatures were set at 1400°C, 1420°C, 1400°C, 1460, and 1480°C, respectively, and the pre-sintered ceramic bodies of opaque spinel ceramics with relative densities of 92.0%, 95.0%, 96.9%, 97.8%, and 98.2%, respectively, and open porosities of 6.3%, 0.8%, 0.4%, 0.1%, and 0.2%, respectively, were obtained.

[0049] Example 5 (50 ppm, 44 vol%, wet molding) The manufacturing process of the opaque spinel ceramics in this Example 9 was the same as that in Example 1, except that the sintering aid Ca 3 (PO 4 ) 2 The only difference is that the mass ratio of Ca (to the magnesia-aluminum spinel powder) in was 0.005 wt%. The pre-sintering temperatures were set at 1400°C, 1420°C, 1400°C, 1460°C, and 1480°C, respectively, and the pre-sintered ceramic bodies of opaque spinel ceramics with relative densities of 91.8%, 93.6%, 94.2%, 98.1%, and 98.6%, respectively, and open porosities of 7.0%, 3.1%, 0.5%, 0.2%, and 0.2%, respectively, were obtained.

[0050] Example 6 (350 ppm, 44 vol%, wet molding) Magnesia-aluminum spinel powder, deionized water, sintering aid, and dispersant were mixed uniformly in a ball mill for 2 hours to obtain a magnesia-aluminum spinel ceramic slurry. In this slurry, the volume ratio of the magnesia-aluminum spinel powder was 44 vol%, the volume ratio of the deionized water was 56 vol%, the mass ratio of the Ca element in the sintering aid (relative to the magnesia-aluminum spinel powder) was 0.035 wt%, and the mass ratio of the dispersant was 1.8 wt%. The particle size of the magnesia-aluminum spinel powder was 250 nm, and the molecular weight of the dispersant was 350. The sintering aid was Ca 10 (PO 4 ) 6 (OH) 2 and the particle size was 300 nm.

[0051] The obtained magnesia-aluminum spinel slurry was subjected to pressure-assisted injection molding to obtain a magnesia-aluminum spinel ceramic body.

[0052] The magnesia-aluminum spinel ceramic body was dried and then subjected to the discharging process, the temperature of which was 800℃.

[0053] The magnesia-aluminum spinel ceramic bodies after the discharging process were pre-sintered in a muffle furnace at pre-sintering temperatures of 1360°C, 1380°C, 1400°C, 1420°C, 1400°C, 1460°C, and 1480°C, respectively, to obtain pre-sintered ceramic bodies of opaque spinel ceramic with relative densities of 91.3%, 93.5%, 94.1%, 95.4%, 95.6%, 96.1%, and 96.3%, respectively, and open porosities of 0.3%, 0.1%, 0.3%, 0.6%, 0.2%, 0.3%, and 0.4%, respectively.

[0054] Example 7 (350 ppm, dry molding) Magnesia-aluminum spinel powder, absolute ethanol, and sintering aid were mixed uniformly in a ball mill for 2 hours to obtain magnesia-aluminum spinel ceramic slurry. In this slurry, the volume ratio of magnesia-aluminum spinel powder was 10 vol%, the volume ratio of absolute ethanol was 90 vol%, and the mass ratio of Ca element of the sintering aid (relative to the magnesia-aluminum spinel powder) was 0.035 wt%. The particle diameter of the magnesia-aluminum spinel powder was 250 nm. The sintering aid was Ca 3 (PO 4 ) 2 and the particle size was 300 nm.

[0055] The resulting magnesia-aluminum spinel slurry was dried and sieved to obtain a uniformly mixed powder raw material. It was then molded by a combination of dry pressing and cold isostatic pressing at a pressure of 200 MPa to obtain a magnesia-aluminum spinel ceramic body.

[0056] The magnesia-aluminum spinel ceramic body was subjected to the discharging process, and the temperature of the discharging process was 800℃.

[0057] The magnesia-aluminum spinel ceramic bodies after the discharging process were pre-sintered in a muffle furnace at pre-sintering temperatures of 1360°C, 1380°C, 1400°C, 1420°C, 1400°C, 1460°C, and 1480°C, respectively, to obtain pre-sintered ceramic bodies of opaque spinel ceramic with relative densities of 95.8%, 97.0%, 97.5%, 98.1%, 98.4%, 98.4%, and 98.7%, respectively, and open porosities of 0.3%, 0.3%, 0.5%, 0.3%, 0.3%, 0.4%, and 0.25%, respectively.

[0058] The pre-sintered ceramic body was subjected to hot isostatic pressing at 1350℃ with a pressure of 180MPa and a heat retention time of 6 hours to obtain transparent magnesia-aluminum spinel ceramics. Measurements showed that the transmittance of the obtained transparent magnesia-aluminum spinel ceramics in the wavelength range of 200 to 2000 nm was higher than 80%.

[0059] Example 8 (300 ppm, reactive sintering) MgO powder, Al 2 O 3 Powder (MgO and Al 2 O 3 The molar ratio of MgO powder, absolute ethanol, and sintering aid were mixed uniformly in a ball mill for 2 hours to obtain a magnesia-aluminum spinel ceramic slurry. In this slurry, the volume ratio of the magnesia-aluminum spinel powder was 10 vol%, the volume ratio of absolute ethanol was 90 vol%, and the mass ratio of Ca element in the sintering aid (relative to the magnesia-aluminum spinel powder) was 0.03 wt%. 2 O 3 The particle size of the powders was 250 nm. The sintering aid was Ca. 3 (PO 4 ) 2 and the particle size was 300 nm.

[0060] The obtained magnesia-aluminum spinel slurry was molded by dry pressing and cold isostatic pressing at a pressure of 200 MPa to obtain a magnesia-aluminum spinel ceramic body.

[0061] The magnesia-aluminum spinel ceramic body was subjected to the discharging process, and the temperature of the discharging process was 800℃.

[0062] The magnesia-aluminum spinel ceramic bodies after the discharging process were pre-sintered in a muffle furnace at pre-sintering temperatures of 1360°C, 1380°C, 1400°C, 1410°C, 1430°C, and 1450°C, respectively, to obtain pre-sintered ceramic bodies of opaque spinel ceramic with relative densities of 90.7%, 96.1%, 97.5%, 97.5%, 98.2%, and 99.3%, respectively, and open porosities of 9.8%, 0.02%, 0.1%, 0.1%, 0.02%, and 0.07%, respectively.

[0063] The pre-sintered ceramics were subjected to hot isostatic pressing at 1450℃ with a pressure of 180MPa and a heat retention time of 6 hours to obtain transparent magnesia-aluminum spinel ceramics. Measurements showed that the transmittance of the obtained transparent magnesia-aluminum spinel ceramics in the wavelength range of 200 to 2000 nm was higher than 85%.

[0064] Example 9 (500 ppm, 44 vol%, wet molding) Magnesia-aluminum spinel powder, deionized water, sintering aid, and dispersant were mixed uniformly in a ball mill for 2 hours to obtain a magnesia-aluminum spinel ceramic slurry. In this slurry, the volume ratio of the magnesia-aluminum spinel powder was 44 vol%, the volume ratio of the deionized water was 56 vol%, the mass ratio of the Ca element in the sintering aid (relative to the magnesia-aluminum spinel powder) was 0.050 wt%, and the mass ratio of the dispersant was 1.8 wt%. The particle size of the magnesia-aluminum spinel powder was 250 nm, and the molecular weight of the dispersant was 350. The sintering aid was Ca 3 (PO 4 ) 2 and the particle size was 300 nm.

[0065] The obtained magnesia-aluminum spinel slurry was subjected to pressure-assisted injection molding to obtain a magnesia-aluminum spinel ceramic body.

[0066] The magnesia-aluminum spinel ceramic body was dried and then subjected to the discharging process, the temperature of which was 800℃.

[0067] The magnesia-aluminum spinel ceramic bodies after the discharge process were pre-sintered in a muffle furnace at pre-sintering temperatures of 1360℃, 1380℃, 1400℃, 1420℃, 1400℃, 1460℃, 1480℃, and 1500℃, respectively, to obtain opaque spinel ceramic pre-sintered bodies with relative densities of 89.1%, 90.9%, 92.2%, 91.2%, 91.3%, 93.1%, 93.7%, and 93.9%, respectively, and open porosities of 8.3%, 2.8%, 2.7%, 2.8%, 2.95%, 0.5%, 0.7%, and 0.4%, respectively. The ceramic pre-sintered bodies were subjected to hot isostatic pressing at 1550℃ under a pressure of 180MPa and a heat retention time of 3 hours to obtain transparent magnesia-aluminum spinel ceramics. Measurements showed that the transmittance of the obtained transparent magnesia-aluminum spinel ceramics in the wavelength range of 200-2000 nm was lower than 65%.

[0068] Comparative Example 1 (0 ppm, dry molding) Magnesia-aluminum spinel powder and absolute ethanol were mixed uniformly in a ball mill for 2 hours to obtain a magnesia-aluminum spinel ceramic slurry. The slurry contained 10 vol% of magnesia-aluminum spinel powder, 90 vol% of absolute ethanol, and no sintering aid. The particle size of the magnesia-aluminum spinel powder was 250 nm.

[0069] The resulting magnesia-aluminum spinel slurry was dried and sieved to obtain a uniformly mixed powder raw material. It was then molded by a combination of dry pressing and cold isostatic pressing at a pressure of 200 MPa to obtain a magnesia-aluminum spinel ceramic body.

[0070] The magnesia-aluminum spinel ceramic body was subjected to the discharging process, and the temperature of the discharging process was 800℃.

[0071] The magnesia-aluminum spinel ceramic bodies after the discharging process were pre-sintered in a muffle furnace at pre-sintering temperatures of 1360°C, 1380°C, 1400°C, 1420°C, 1400°C, 1460°C, and 1480°C, respectively, to obtain pre-sintered ceramic bodies of opaque spinel ceramic with relative densities of 77.8%, 81.1%, 83.5%, 86.4%, 88.5%, 91.3%, and 94.0%, respectively, and open porosities of 21.4%, 18.0%, 15.4%, 12.7%, 6.5%, 1.3%, and 0.2%, respectively.

[0072] The pre-sintered ceramics were subjected to hot isostatic pressing at 1350℃ under a pressure of 180MPa and a heat retention time of 6 hours to obtain transparent magnesia-aluminum spinel ceramics.

[0073] Comparative Example 2 (0 ppm, reactive sintering) MgO powder, Al 2 O 3 Powder (MgO and Al 2 O 3 The molar ratio of MgO powder, Al powder, and absolute ethanol were mixed uniformly in a ball mill for 2 hours to obtain a magnesia-aluminum spinel ceramic slurry. In this slurry, the volume ratio of the magnesia-aluminum spinel powder was 10 vol% and the volume ratio of absolute ethanol was 90 vol%. 2 O 3 The particle size of both powders was 250 nm.

[0074] The obtained magnesia-aluminum spinel slurry was molded by dry pressing and cold isostatic pressing (cold isostatic pressure: 200 MPa) to obtain a magnesia-aluminum spinel ceramic body.

[0075] The magnesia-aluminum spinel ceramic body was subjected to the discharging process, and the temperature of the discharging process was 800℃.

[0076] The magnesia-aluminum spinel ceramic bodies after the discharging process were pre-sintered in a muffle furnace, and the pre-sintering temperatures were set at 1550°C, 1590°C, 1600°C, and 1620°C, respectively, to obtain pre-sintered opaque spinel ceramic bodies with relative densities of 87.8%, 93.1%, 93.9%, and 97.8%, respectively, and open porosities of 10.6%, 0.5%, 0.04%, and 0.09%, respectively.

[0077] Comparative example 3 (0ppm, 44vol%, wet molding) Magnesia-aluminum spinel powder, deionized water, and dispersant were mixed uniformly in a ball mill for 2 hours to obtain a magnesia-aluminum spinel ceramic slurry. In this slurry, the volume ratio of magnesia-aluminum spinel powder was 44 vol%, the volume ratio of deionized water was 56 vol%, no sintering aid was added, and the mass ratio of dispersant was 1.8 wt%. The particle size of the magnesia-aluminum spinel powder was 250 nm, and the molecular weight of the dispersant was 350.

[0078] The obtained magnesia-aluminum spinel slurry was subjected to pressure-assisted injection molding to obtain a magnesia-aluminum spinel ceramic body.

[0079] The magnesia-aluminum spinel ceramic body was dried and then subjected to the discharging process, the temperature of which was 800℃.

[0080] The magnesia-aluminum spinel ceramic bodies after the discharging process were pre-sintered in a muffle furnace at pre-sintering temperatures of 1360°C, 1380°C, 1400°C, 1420°C, 1400°C, 1460°C, 1480°C, and 1500°C, respectively, to obtain pre-sintered ceramic bodies of opaque spinel ceramic with relative densities of 82.7%, 84.6%, 86.4%, 87.9%, 90.5%, 92.1%, 93.0%, and 94.2%, respectively, and open porosities of 17.1%, 14.4%, 12.7%, 10.9%, 8.7%, 1.5%, 1.6%, and 0.1%, respectively.

[0081] The pre-sintered ceramics were subjected to hot isostatic pressing at 1650℃ with a pressure of 180MPa and a heat retention time of 3 hours to obtain transparent magnesia-aluminum spinel ceramics. Measurements showed that the transmittance in the 200-2000nm wavelength range was higher than 80%.

[0082] Comparative Example 4 The manufacturing process of the opaque spinel ceramics in Comparative Example 4 was the same as that in Example 6, except that the amount of Ca added to the sintering aid CaO was 0.010 wt%. The pre-sintering temperatures were set at 1360°C, 1380°C, 1400°C, 1420°C, 1400°C, 1460°C, 1480°C, and 1500°C, respectively, and pre-sintered ceramic bodies of opaque spinel ceramics were obtained with relative densities of 82.3%, 84.2%, 85.9%, 87.8%, 89.1%, 91.2%, 92.4%, and 93.2%, respectively, and open porosities of 17.4%, 15.3%, 13.4%, 11.8%, 9.9%, 7.5%, 2.1%, and 0.3%, respectively.

[0083] Comparative Example 5 The manufacturing process of the opaque spinel ceramics in Comparative Example 5 was the same as that in Example 6, with the only difference being that the amount of Ca element added in the sintering aid CaO was 0.050 wt%. The pre-sintering temperatures were set at 1360°C, 1380°C, 1400°C, 1420°C, 1440°C, 1460°C, 1480°C, and 1500°C, respectively, and pre-sintered ceramic bodies of opaque spinel ceramics were obtained with relative densities of 81.7%, 83.7%, 85.3%, 87.1%, 88.6%, 90.5%, 93.0%, and 93.6%, respectively, and open porosities of 17.8%, 15.9%, 13.9%, 12.2%, 10.2%, 8.1%, 0.6%, and 0.4%, respectively.

[0084] Verification example (15000ppm, 44vol%, wet molding) The manufacturing process of the opaque spinel ceramic in this verification example was the same as that of Example 1, except that the sintering aid Ca 3 (PO 4 ) 2The difference is that the mass ratio of Ca element in was 1.5 wt%. The pre-sintering temperature was set at 1400°C, and pre-sintered ceramic bodies, which were opaque spinel ceramics, were obtained.

[0085] In order to verify whether the reaction between the sintering aid and the magnesia-aluminum spinel in the present invention forms an impurity phase, the ceramic pre-sintered body obtained by sintering in this verification example was detected by X-ray diffraction (XRD). The amount of sintering aid doped was set to 15,000 ppm, with the purpose of making the content of the doped material higher than the detection limit of XRD and allowing the reaction that may occur between the sintering aid and the magnesia-aluminum spinel to proceed sufficiently. As shown in Figure 2, the XRD spectrum shows that the ceramic pre-sintered body contains magnesia-aluminum spinel and Ca. 3 (PO 4 ) 2 Therefore, it can be concluded that no reaction occurs between the sintering aid and the magnesia-aluminum spinel, and no new second phase material is generated during the sintering process.

Claims

1. MgAl 2 O 4 The powder is used as a raw material powder, calcium phosphate is added as a sintering aid, the Ca element in the calcium phosphate is controlled so as not to exceed 500 ppm of the total mass of the raw material powder, and pressureless sintering is performed to produce a high density magnesia-aluminum spinel ceramic, the pressureless sintering including atmospheric sintering or vacuum sintering, The composition of the calcium phosphate is as follows: Ca10(PO4)6(OH)2, Ca3(PO4)2, Ca4O(PO4)2, Ca10-XH2X(PO4)6(OH)2, Ca8H2(PO4)6.5H2O, CaHPO4.2H2O, CaHPO4, Ca2P2O7, CaP2O7.2H2O, Ca7(P5O16)2, Ca4H2P6O20, Ca(H2PO4)2.H2O, Ca(PO3)2 At least one of The pressureless sintering temperature is 1360-1460° C., and the pressureless sintering time does not exceed 20 hours.

2. A method for producing high density magnesia-aluminum spinel ceramics by pressureless sintering as described in claim 1, wherein prior to pressureless sintering, raw material powder is molded to prepare a base material, and the molding method is dry molding or wet molding.

3. A method for producing high density magnesia-aluminum spinel ceramics by pressureless sintering as described in claim 1 or 2, further comprising sintering the obtained high density magnesia-aluminum spinel ceramics by hot isostatic pressing to obtain magnesia-aluminum spinel transparent ceramics.

4. A method for producing high density magnesia-aluminum spinel ceramics by pressureless sintering as described in claim 3, wherein the sintering temperature of the hot isostatic press is 1350 to 1800°C, the sintering pressure of the hot isostatic press is 50 to 200 MPa, and the sintering time of the hot isostatic press does not exceed 20 hours.

5. MgO powder and Al 2 O 3 The powder is used as a raw material powder, calcium phosphate is added as a sintering aid, the Ca element in the calcium phosphate is controlled so as not to exceed 500 ppm of the total mass of the raw material powder, and pressureless sintering is further performed to manufacture a high density magnesia-aluminum spinel ceramic, the pressureless sintering including atmospheric sintering or vacuum sintering, The composition of the calcium phosphate is as follows: Ca10(PO4)6(OH)2, Ca3(PO4)2, Ca4O(PO4)2, Ca10-XH2X(PO4)6(OH)2, Ca8H2(PO4)6.5H2O, CaHPO4.2H2O, CaHPO4, Ca2P2O7, CaP2O7.2H2O, Ca7(P5O16)2, Ca4H2P6O20, Ca(H2PO4)2.H2O, Ca(PO3)2 At least one of The pressureless sintering temperature is 1360-1460° C., and the pressureless sintering time does not exceed 20 hours.

6. The MgO powder and Al 2 O 3 The method for producing high density magnesia-aluminum spinel ceramics by pressureless sintering according to claim 5, wherein the molar ratio of the powders is 1:(0.98-2.2).

7. 6. The method for producing high density magnesia-aluminum spinel ceramics by pressureless sintering according to claim 5, wherein the raw material powder is molded to prepare a green body before pressureless sintering, and the molding method is dry molding or wet molding.

8. A method for producing high density magnesia-aluminum spinel ceramics by pressureless sintering as described in claim 5 or 7, further comprising sintering the obtained high density magnesia-aluminum spinel ceramics by hot isostatic pressing to obtain magnesia-aluminum spinel transparent ceramics.

9. The sintering temperature of the hot isostatic press is 1350 to 1800°C; The sintering pressure of the hot isostatic press is 50 to 200 MPa; The method of claim 8, wherein the hot isostatic pressing sintering time does not exceed 20 hours.

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