CN112209725B - Pretreatment method for sintering silicon nitride ceramic, silicon nitride ceramic and preparation method thereof - Google Patents
Pretreatment method for sintering silicon nitride ceramic, silicon nitride ceramic and preparation method thereof Download PDFInfo
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- 229910052581 Si3N4 Inorganic materials 0.000 title claims abstract description 178
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 title claims abstract description 176
- 239000000919 ceramic Substances 0.000 title claims abstract description 89
- 238000005245 sintering Methods 0.000 title claims abstract description 82
- 238000002203 pretreatment Methods 0.000 title claims abstract description 28
- 238000002360 preparation method Methods 0.000 title claims abstract description 20
- 239000000843 powder Substances 0.000 claims abstract description 117
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 38
- 239000011214 refractory ceramic Substances 0.000 claims abstract description 8
- 238000003892 spreading Methods 0.000 claims abstract description 6
- PQXKHYXIUOZZFA-UHFFFAOYSA-M lithium fluoride Chemical compound [Li+].[F-] PQXKHYXIUOZZFA-UHFFFAOYSA-M 0.000 claims description 22
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 claims description 16
- 239000002245 particle Substances 0.000 claims description 15
- 229910001404 rare earth metal oxide Inorganic materials 0.000 claims description 13
- 239000000395 magnesium oxide Substances 0.000 claims description 11
- 238000000034 method Methods 0.000 claims description 11
- 239000000377 silicon dioxide Substances 0.000 claims description 10
- AXZKOIWUVFPNLO-UHFFFAOYSA-N magnesium;oxygen(2-) Chemical compound [O-2].[Mg+2] AXZKOIWUVFPNLO-UHFFFAOYSA-N 0.000 claims description 6
- 238000004519 manufacturing process Methods 0.000 claims description 6
- 239000002994 raw material Substances 0.000 claims description 4
- 229910021193 La 2 O 3 Inorganic materials 0.000 claims description 2
- 229910017493 Nd 2 O 3 Inorganic materials 0.000 claims description 2
- 230000003647 oxidation Effects 0.000 abstract description 11
- 238000007254 oxidation reaction Methods 0.000 abstract description 11
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 30
- 230000000052 comparative effect Effects 0.000 description 11
- 238000002156 mixing Methods 0.000 description 9
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 8
- 239000002612 dispersion medium Substances 0.000 description 6
- 238000000498 ball milling Methods 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- 238000009694 cold isostatic pressing Methods 0.000 description 4
- 238000001035 drying Methods 0.000 description 4
- 238000007873 sieving Methods 0.000 description 4
- 239000012752 auxiliary agent Substances 0.000 description 3
- 230000009286 beneficial effect Effects 0.000 description 3
- 238000005056 compaction Methods 0.000 description 3
- 238000000280 densification Methods 0.000 description 3
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 description 3
- 238000003825 pressing Methods 0.000 description 3
- 238000001272 pressureless sintering Methods 0.000 description 3
- 235000012239 silicon dioxide Nutrition 0.000 description 3
- 229910004298 SiO 2 Inorganic materials 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 239000007791 liquid phase Substances 0.000 description 2
- 239000011777 magnesium Substances 0.000 description 2
- 238000000465 moulding Methods 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 238000004321 preservation Methods 0.000 description 2
- 230000001681 protective effect Effects 0.000 description 2
- 238000001228 spectrum Methods 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- 229910004283 SiO 4 Inorganic materials 0.000 description 1
- 238000002441 X-ray diffraction Methods 0.000 description 1
- ORUCDOXAKFCOJF-UHFFFAOYSA-N [O-2].[Mg+2].[Li+] Chemical compound [O-2].[Mg+2].[Li+] ORUCDOXAKFCOJF-UHFFFAOYSA-N 0.000 description 1
- 238000005054 agglomeration Methods 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 235000019441 ethanol Nutrition 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 238000001746 injection moulding Methods 0.000 description 1
- 238000002955 isolation Methods 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 238000012856 packing Methods 0.000 description 1
- 239000012071 phase Substances 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 238000004064 recycling Methods 0.000 description 1
- 238000007493 shaping process Methods 0.000 description 1
- 230000035939 shock Effects 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
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Abstract
The invention belongs to the technical field of silicon nitride ceramics, and particularly relates to a pretreatment method for sintering silicon nitride ceramics, and also relates to silicon nitride ceramics and a preparation method thereof. The pretreatment method for sintering the silicon nitride ceramics comprises the following steps: embedding a silicon nitride blank into silicon nitride powder in a sintering container, covering a cover plate on the surface of the silicon nitride powder, and spreading silicon dioxide powder on the cover plate; the cover plate is an inert refractory ceramic plate. The pretreatment method effectively avoids the oxidation of the silicon nitride ceramics in the air atmosphere sintering, can effectively reduce the oxidation of the silicon nitride buried powder, and realizes the sintering of the silicon nitride ceramics in the air atmosphere; the silicon nitride buried powder and the silicon dioxide powder are easy to separate, can be repeatedly reused, and can greatly reduce the buried powder consumption and the cost.
Description
Technical Field
The invention belongs to the technical field of silicon nitride ceramics, and particularly relates to a pretreatment method for sintering silicon nitride ceramics, and also relates to silicon nitride ceramics and a preparation method thereof.
Background
The silicon nitride ceramic has excellent room temperature and high temperature strength, high hardness and fracture toughness, preferable thermal shock resistance and oxidation resistance, excellent chemical stability, high heat conductivity and good wave-transmitting performance, so that the silicon nitride ceramic has wide application in various fields such as high and low temperature mechanical parts, special cutters, engine materials, aerospace wave-transmitting materials, electronic industry heat-conducting substrates and the like.
Since silicon nitride is a strongly covalent bond material, sintering densification is very difficult, and thus it is generally necessary to add a sintering aid, high sintering temperature, and sintering in a protective atmosphere to prevent oxidation and decomposition of silicon nitride when silicon nitride is sintered to form silicon nitride ceramics. For example, a silicon nitride ceramic and a preparation method thereof are disclosed in the chinese patent application publication No. CN105016738A, wherein metal oxide (such as magnesium oxide) and rare earth oxide are used as sintering aids, and high-temperature sintering is performed in nitrogen or in a mixed gas of hydrogen and nitrogen. Because the sintering in the protective atmosphere requires expensive high-temperature atmosphere equipment, the production cost is increased, so that the price of the silicon nitride ceramic product is higher, and the application range of the silicon nitride ceramic product is limited.
If the preparation can be carried out by using common non-vacuum sintering equipment in air atmosphere, the preparation cost is greatly reduced, and the preparation of a large-sized member with low cost is hopeful to be realized. The Chinese patent application publication No. CN110590377A discloses an air-buried powder pressureless sintering method, namely, putting a formed silicon nitride green body into a crucible embedded with silicon nitride powder, and then pressureless sintering under air atmosphere. The single silicon nitride powder is adopted as the buried powder, the silicon nitride buried powder is seriously oxidized in the sintering process to cause poor reusability, and the prepared silicon nitride ceramic has poor performance due to certain oxidation.
Disclosure of Invention
The invention aims to provide a pretreatment method for sintering silicon nitride ceramics, which aims to solve the problems of silicon nitride buried powder and silicon nitride ceramic oxidation.
The invention also aims to provide a preparation method of the silicon nitride ceramic, and the silicon nitride ceramic prepared by the method has high densification degree and low cost.
The invention also aims to provide the silicon nitride ceramic prepared by the preparation method of the silicon nitride ceramic.
In order to achieve the above purpose, the invention adopts the following technical scheme:
a pretreatment method for sintering silicon nitride ceramics comprises the following steps: embedding a silicon nitride blank into silicon nitride powder in a sintering container, covering a cover plate on the surface of the silicon nitride powder, and spreading silicon dioxide powder on the cover plate; the cover plate is an inert refractory ceramic plate.
The invention uses silicon nitride powder as buried powder, and then a cover plate and silicon dioxide powder are arranged on the surface of the silicon nitride buried powder. When sintering is carried out in the air atmosphere, the upper silicon dioxide powder is contacted with air first, so that the effect of isolating air can be achieved; and then the cover plate further isolates air from downward contact with the silicon nitride powder, and separates the silicon dioxide powder from the silicon nitride buried powder, thereby being beneficial to recycling of the follow-up silicon dioxide and silicon nitride powder. The pretreatment method effectively avoids the oxidation of the silicon nitride ceramics in the air atmosphere during sintering, can effectively reduce the oxidation of the silicon nitride buried powder, and realizes the sintering of the silicon nitride ceramics in the air atmosphere; the silicon nitride buried powder and the silicon dioxide are easy to separate, and can be repeatedly reused, so that the buried powder consumption can be greatly reduced, and the cost is reduced.
The particle sizes of the silicon nitride powder and the silicon dioxide powder are controlled to realize close packing of the silicon nitride powder and the silicon dioxide powder, so that the pores are reduced, and the air isolation effect is further optimized. Preferably, the particle size of the silicon nitride powder is 0.3-2 μm. Further preferably, the particle size of the silicon nitride powder is 0.3 to 1 μm. Preferably, the particle size of the silica powder is 10 to 100. Mu.m. Further preferably, the particle size of the silica powder is 20 to 74. Mu.m.
The silicon nitride blank body is completely embedded in the silicon nitride powder, and the embedding thickness of the silicon nitride powder around is preferably more than 2cm, namely the distance between the position of the silicon nitride blank body in the silicon nitride powder and the upper, lower, left and right outer edges of the silicon nitride powder is more than 2cm.
In the pretreatment method of the invention, the cover plate is an inert refractory ceramic plate, and the specific material is only required to bear the sintering temperature of the silicon nitride ceramic and not react with silicon nitride and silicon dioxide. The size of the cover plate is adjusted according to the size of the sintering container, so long as the silicon nitride powder can be completely covered. Preferably, the cover plate used is a silicon nitride plate. The thickness of the silicon nitride plate is 0.5-2 cm, and the relative density is more than 70%.
In order to avoid excessive air entering the sintering vessel, it is preferable to cover the opening of the sintering vessel with a cover body after laying the silica powder. The sintering vessel used is a vessel commonly used such as a crucible.
In the pretreatment method of the present invention, the laying height of the silica powder is greater than 5cm and lower than the opening of the sintering vessel. The flat height of the silica should be as close as possible to the open part of the sintering vessel but not so great as to affect the complete coverage of the open part of the sintering vessel by the cover.
The pretreatment method is suitable for sintering all silicon nitride blanks in air atmosphere, and the sintering temperature and the sintering mode (pressureless sintering or pressure sintering) can be selected according to actual needs during sintering.
The invention also provides a method for preparing silicon nitride ceramics by adopting the pretreatment method, which adopts the following technical scheme:
a preparation method of silicon nitride ceramics comprises the following steps:
(a) Preparing a silicon nitride ceramic blank;
(b) Pretreatment: embedding a silicon nitride blank into silicon nitride powder in a sintering container, covering a cover plate on the surface of the silicon nitride powder, and spreading silicon dioxide powder on the cover plate; the cover plate is an inert refractory ceramic plate;
(c) And covering the opening of the sintering container with a cover to form a sintering system, and then placing the sintering system in an air atmosphere for sintering.
In the preparation method of the silicon nitride ceramic, the pretreatment method of the invention is adopted to sinter under the air atmosphere, so that the oxidation of a silicon nitride blank is effectively avoided, the density of the silicon nitride ceramic is improved, and the production cost is reduced.
Preferably, the silicon nitride ceramic body is prepared from the following raw materials in percentage by mass: 80-90% of silicon nitride, 5-9% of magnesium oxide, 1-3% of lithium fluoride and 4-8% of rare earth oxide. Adopts a magnesium oxide-lithium fluoride-rare earth oxide ternary auxiliary agent system, the addition of the lithium fluoride can greatly reduce the liquid phase generation temperature to about 1100 ℃,lithium fluoride is volatilized and removed at high temperature, the liquid phase generated by magnesium oxide and rare earth oxide is continuously kept in the sintering densification process, and meanwhile, the addition of the rare earth oxide is beneficial to beta-Si 3 N 4 The anisotropic growth of the crystal grains is beneficial to the improvement of mechanical properties. The ternary auxiliary agent system is adopted, so that the sintering temperature is effectively reduced, and the higher relative density is also facilitated to be obtained.
Further preferably, the silicon nitride blank is prepared from the following raw materials in percentage by mass: 86-90% of silicon nitride, 5-7% of magnesium oxide, 1-2% of lithium fluoride and 4-5% of rare earth oxide.
The rare earth oxide is a rare earth oxide auxiliary agent commonly used in the prior art. Preferably, the rare earth oxide is Y 2 O 3 、Yb 2 O 3 、Sm 2 O 3 、Sc 2 O 3 、La 2 O 3 、CeO 2 、Nd 2 O 3 One of them. Further preferably, the rare earth oxide is Y 2 O 3 Or Yb 2 O 3 。
Preferably, the silicon nitride body is prepared by the following method: mixing silicon nitride, magnesium oxide, lithium fluoride and rare earth oxide, and then forming to obtain a silicon nitride blank. Preferably, the mixing is wet mixing. Further preferably, the mixing is ball milled in an ethanol dispersion medium. Wherein the molding mode is cold isostatic pressing, gel injection molding or casting molding. Preferably, the shaping is by cold isostatic pressing.
Preferably, the sintering temperature is 1500-1650 ℃ and the sintering time is 2-15 h.
In the pretreatment process, the grain size of the silicon nitride powder is 0.3-2 mu m. The particle size of the silicon dioxide powder is 10-100 mu m. The embedding thickness of the silicon nitride powder around the silicon nitride ceramic body is more than 2cm. The laying height of the silicon dioxide powder is more than 5cm and is lower than the opening part of the sintering container. The cover plate is a silicon nitride cover plate.
The invention also provides the silicon nitride ceramic prepared by the preparation method of the silicon nitride ceramic. The silicon nitride ceramic has high compactness and good performance.
Drawings
FIG. 1 is a schematic diagram of the architecture formed after pretreatment in example 1 of the present invention;
FIG. 2 is an XRD pattern of the silicon nitride ceramic obtained in example 4 of the present invention;
FIG. 3 is a photograph showing the inside of a crucible after sintering in example 4 of the present invention;
FIG. 4 is a photograph of the inside of the crucible after sintering in comparative example 1;
FIG. 5 is a photograph of the inside of the crucible after sintering in comparative example 2;
reference numerals: 1-an alumina crucible; 2-silicon nitride green body; 3-Si 3 N 4 Burying powder; a 4-silicon nitride plate; 5-SiO 2 Powder; 6-alumina crucible cover.
Detailed Description
The invention is further described below with reference to specific embodiments and the accompanying drawings.
1. Examples of pretreatment methods for sintering silicon nitride ceramics
Example 1
The pretreatment method for sintering the silicon nitride ceramic of the embodiment, the structure of the finally formed system is shown in fig. 1, and the method comprises the following steps: a silicon nitride green body 2 having a diameter of 30mm by 5mm was placed in an alumina crucible 1 (diameter 100mm by 120 mm) and Si was embedded 3 N 4 Embedding powder 3 (particle size of 0.3 μm) to make silicon nitride blank 2 in Si 3 N 4 The distance between the embedded position in the embedded powder 3 and the upper, lower, left and right outer edges is larger than 2cm (Si) 3 N 4 The height of buried powder 3 is about 5 cm), and then at Si 3 N 4 The buried powder 3 covers a silicon nitride plate 4 (the relative density is 87%) with a thickness of 0.5cm, and then SiO is spread on the silicon nitride plate 2 Powder 5 (particle size 20 μm), siO 2 The thickness of the powder 5 was 6cm, and then an alumina crucible cover 6 was attached to the alumina crucible, and the alumina crucible cover 6 was allowed to completely cover the upper opening of the alumina crucible 1.
Example 2
The pretreatment method for sintering the silicon nitride ceramic in the embodiment specifically comprises the following steps: diameter 60mm by heightThe 5mm silicon nitride blank is placed in an alumina crucible (diameter 180 mm. Times.220 mm high) and embedded with Si 3 N 4 Embedding powder (particle size of 0.8 μm) to make silicon nitride blank in Si 3 N 4 The distance between the embedded position in the embedded powder and the upper, lower, left and right outer edges is larger than 5cm (Si) 3 N 4 About 11cm high for buried powder) and then at Si 3 N 4 Covering a silicon nitride plate 4 (the relative density is more than 80%) with 1cm thick by buried powder, and then laying SiO on the silicon nitride plate 2 Powder (particle size 50 μm), siO 2 The powder had a thickness of 10cm, and then an alumina crucible cover was attached to the alumina crucible, and the alumina crucible cover was allowed to completely cover the upper port of the alumina crucible.
Example 3
The pretreatment method for sintering the silicon nitride ceramic in the embodiment specifically comprises the following steps: a silicon nitride blank having a diameter of 100mm by 10mm was placed in an alumina crucible (diameter 300mm by 350 mm) and Si was embedded 3 N 4 Embedding powder (particle size of 1 μm) to make silicon nitride blank in Si 3 N 4 The distance between the embedded position in the embedded powder and the upper, lower, left and right outer edges is larger than 8cm (Si) 3 N 4 About 18cm in height) of buried powder, then at Si 3 N 4 Covering a silicon nitride plate (the relative density is more than 80%) with the thickness of 2cm by using buried powder, and then paving SiO on the silicon nitride plate 2 Powder (particle size 74 μm), siO 2 The powder had a thickness of 14cm, and then an alumina crucible cover was applied over the alumina crucible, with the alumina crucible cover completely covering the upper port of the alumina crucible.
2. Examples of methods for preparing silicon nitride ceramics
Example 4
The preparation method of the silicon nitride ceramic in the embodiment comprises the following steps:
(1) 90g of Si 3 N 4 Powder, 5g MgO powder, 1g LiF powder and 4g Y 2 O 3 Powder is weighed, absolute ethyl alcohol is used as a dispersion medium for ball milling and mixing, sintered powder is obtained after drying and sieving, and 10g of sintered powder is subjected to cold isostatic pressing to prepare a silicon nitride ceramic wafer green body with the diameter of 30 mm;
(2) The pretreatment method in example 1 was used to pretreat a silicon nitride ceramic wafer, and then the silicon nitride wafer green body, si 3 N 4 And (3) placing a sintering system formed by the powder, the silicon nitride plate, the silicon dioxide powder and the aluminum oxide crucible into an electric furnace, and sintering at the temperature of 1650 ℃ for 2 hours to obtain the silicon nitride ceramic.
Example 5
The preparation method of the silicon nitride ceramic in the embodiment comprises the following steps:
(1) 88g of Si 3 N 4 Powder, 6g MgO powder, 2g LiF powder and 4g Yb 2 O 3 Powder is weighed, absolute ethyl alcohol is used as a dispersion medium for ball milling and mixing, sintered powder is obtained after drying and sieving, 45g of sintered powder is subjected to cold isostatic pressing to prepare a silicon nitride ceramic wafer green body with the diameter of 60 mm;
(2) The pretreatment method in example 2 was used to pretreat a silicon nitride ceramic wafer, and then the silicon nitride wafer green body, si 3 N 4 And (3) placing a sintering system formed by the powder, the silicon nitride plate, the silicon dioxide powder and the aluminum oxide crucible into an electric furnace, and sintering at 1600 ℃ for 8 hours to obtain the silicon nitride ceramic.
Example 6
The preparation method of the silicon nitride ceramic in the embodiment comprises the following steps:
(1) 86g of Si 3 N 4 Powder, 7g MgO powder, 2g LiF powder and 5g Yb 2 O 3 Powder is weighed, absolute ethyl alcohol is used as a dispersion medium for ball milling and mixing, the powder is dried and sieved to obtain sintered powder, 125g of sintered powder is subjected to mould pressing, combining and isostatic compaction to prepare a silicon nitride ceramic wafer green body with the diameter of 100 mm;
(2) The pretreatment method in example 3 was used to pretreat a silicon nitride ceramic wafer, and then the silicon nitride wafer green body, si 3 N 4 And placing a sintering system formed by the powder, the silicon nitride plate, the silicon dioxide powder and the aluminum oxide crucible into an electric furnace, and sintering at the temperature of 1650 ℃ for 12 hours to obtain the silicon nitride ceramic.
3. Examples of silicon nitride ceramics
Example 7
The silicon nitride ceramics of this example were produced by the production method of example 4.
Example 8
The silicon nitride ceramics of this example were produced by the production method of example 5.
Example 9
The silicon nitride ceramics of this example were produced by the production method of example 4.
4. Comparative example
Comparative example 1
The preparation method of the silicon nitride ceramic of the comparative example comprises the following steps: 90g of Si 3 N 4 Powder, 5g MgO powder, 1g LiF powder and 4g Y 2 O 3 Powder is weighed, absolute ethyl alcohol is used as a dispersion medium for ball milling and mixing, sintered powder is obtained after drying and sieving, and 10g of sintered powder is subjected to mould pressing, combining and isostatic compaction to prepare a silicon nitride ceramic wafer green body with the diameter of 30 mm; then placing the silicon nitride wafer green body into an alumina crucible and embedding Si 3 N 4 In the powder, the green compact of the silicon nitride ceramic wafer is formed on Si 3 N 4 The distance between the embedded position in the powder and Si 3 N 4 The outer edges of the powder are larger than 2cm, and then an alumina crucible cover is added on the alumina crucible, and the alumina crucible cover completely covers the upper opening of the alumina crucible. And (3) placing the whole alumina crucible into an electric furnace for sintering under air, wherein the sintering temperature is 1650 ℃, and the heat preservation time is 2 hours.
Comparative example 2
The preparation method of the silicon nitride ceramic of the comparative example comprises the following steps: 90g of Si 3 N 4 Powder, 5g MgO powder, 1g LiF powder and 4g Y 2 O 3 Powder is weighed, absolute ethyl alcohol is used as a dispersion medium for ball milling and mixing, sintered powder is obtained after drying and sieving, and 10g of sintered powder is subjected to mould pressing, combining and isostatic compaction to prepare a silicon nitride ceramic wafer green body with the diameter of 30 mm; then placing the silicon nitride wafer green body into an alumina crucible and embedding Si 3 N 4 In the powder, the green compact of the silicon nitride ceramic wafer is formed on Si 3 N 4 Embedding location in powderUpper, lower, left and right Si 3 N 4 The outer edges of the powder are all larger than 2cm, and then Si 3 N 4 Covering a silicon nitride plate with the thickness of 0.5cm on the buried powder, and then spreading Al on the silicon nitride plate 2 O 3 Powder (particle size of 2 μm), al 2 O 3 The powder had a thickness of 6cm, and then an alumina crucible cover was attached to the alumina crucible, and the alumina crucible cover was allowed to completely cover the upper port of the alumina crucible. And (3) placing the whole alumina crucible into an electric furnace for sintering under air, wherein the sintering temperature is 1650 ℃, and the heat preservation time is 2 hours.
5. Test examples
Test example 1
XRD tests were carried out on the silicon nitride ceramics obtained in examples 4 to 6, and the obtained spectra were substantially the same. Taking the silicon nitride ceramic prepared in example 4 as an example, the XRD spectrum of the silicon nitride ceramic is shown in FIG. 2, and the main constituent phase of the silicon nitride ceramic is alpha-Si 3 N 4 ,β-Si 3 N 4 And Mg (magnesium) 2 SiO 4 Without Si 2 N 2 O and SiO 2 Is detected.
Test example 2
The silicon nitride ceramics prepared in examples 4 to 6 and comparative example 1 were tested for relative density and hardness by measuring the density of the sintered silicon nitride ceramics prepared by the archimedes' drainage method and dividing by the theoretical density calculated from the raw materials to obtain the relative density of the sintered material; the sintered silicon nitride ceramic was tested for hardness using a vickers hardness tester with a load of 1kgf and a dwell time of 15 seconds. The test results are shown in Table 1.
TABLE 1 silicon nitride ceramic Properties
Test example 3
Examples 4 to 6And the morphology of the inside of the crucible after sintering of comparative examples 1-2 was observed, wherein the upper layer silica powder buried in the crucible in examples 4-6 was free from a large amount of shrinkage and agglomeration, and the upper layer SiO was well covered (as shown in FIG. 3) 2 Buried powder and underlying Si 3 N 4 The buried powder can be completely and respectively taken out after sintering, and the lower layer Si 3 N 4 The buried powder is not oxidized in a large amount, and the two buried powders can be reused; whereas in comparative example 1, the silicon nitride buried powder in the crucible was largely oxidized, agglomerated and bubbled (as shown in FIG. 4); the upper alumina buried powder in comparative example 2 showed sintering shrinkage and could not completely cover the lower buried powder (as shown in fig. 5).
The results of test examples 1 to 3 further show that the pretreatment method of the invention effectively avoids oxidation of the silicon nitride ceramics in air atmosphere sintering and can also effectively reduce oxidation of the silicon nitride buried powder.
Claims (10)
1. A pretreatment method for sintering silicon nitride ceramics, which is characterized by comprising the following steps: embedding a silicon nitride blank into silicon nitride powder in a sintering container, covering a cover plate on the surface of the silicon nitride powder, and spreading silicon dioxide powder on the cover plate; the cover plate is an inert refractory ceramic plate; the inert refractory ceramic plate is a silicon nitride cover plate.
2. The pretreatment method for sintering a silicon nitride ceramic according to claim 1, wherein the particle size of the silicon nitride powder is 0.3 to 2 μm.
3. The pretreatment method for sintering a silicon nitride ceramic according to claim 1, wherein the particle size of the silica powder is 10 to 100 μm.
4. The pretreatment method for sintering of silicon nitride ceramics according to claim 1, wherein the embedding thickness of silicon nitride powder around the silicon nitride blank is more than 2cm.
5. The pretreatment method for sintering a silicon nitride ceramic according to claim 1, wherein a cover is provided at an opening of the sintering vessel after the silicon dioxide powder is spread.
6. The pretreatment method for sintering a silicon nitride ceramic according to any one of claims 1 to 4, wherein the flat height of the silicon dioxide powder is greater than 5cm and lower than the opening of the sintering vessel.
7. The preparation method of the silicon nitride ceramic is characterized by comprising the following steps of:
(a) Preparing a silicon nitride ceramic blank;
(b) Pretreatment: embedding a silicon nitride blank into silicon nitride powder in a sintering container, covering a cover plate on the surface of the silicon nitride powder, and spreading silicon dioxide powder on the cover plate; the cover plate is an inert refractory ceramic plate;
(c) Covering the opening of the sintering container with a cover to form a sintering system, and then placing the sintering system in an air atmosphere for sintering;
the inert refractory ceramic plate is a silicon nitride cover plate.
8. The preparation method of the silicon nitride ceramic according to claim 7, wherein the silicon nitride ceramic body is prepared from the following raw materials in percentage by mass: 80-90% of silicon nitride, 5-9% of magnesium oxide, 1-3% of lithium fluoride and 4-8% of rare earth oxide.
9. The method for producing silicon nitride ceramics according to claim 8, wherein the rare earth oxide is Y 2 O 3 、Yb 2 O 3 、Sm 2 O 3 、Sc 2 O 3 、La 2 O 3 、CeO 2 、Nd 2 O 3 One of them.
10. The method for preparing silicon nitride ceramics according to any one of claims 7 to 9, characterized in that the sintering temperature is 1500 to 1650 ℃ and the time is 2 to 15 hours.
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