CN111995403B - Corrosion-resistant silicon nitride ceramic and preparation method thereof - Google Patents
Corrosion-resistant silicon nitride ceramic and preparation method thereof Download PDFInfo
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- CN111995403B CN111995403B CN202010925516.2A CN202010925516A CN111995403B CN 111995403 B CN111995403 B CN 111995403B CN 202010925516 A CN202010925516 A CN 202010925516A CN 111995403 B CN111995403 B CN 111995403B
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- 229910052581 Si3N4 Inorganic materials 0.000 title claims abstract description 104
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 title claims abstract description 104
- 239000000919 ceramic Substances 0.000 title claims abstract description 97
- 238000005260 corrosion Methods 0.000 title claims abstract description 67
- 230000007797 corrosion Effects 0.000 title claims abstract description 67
- 238000002360 preparation method Methods 0.000 title claims abstract description 19
- 239000000843 powder Substances 0.000 claims abstract description 105
- 238000005245 sintering Methods 0.000 claims abstract description 54
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 37
- 239000011575 calcium Substances 0.000 claims abstract description 37
- 229910052791 calcium Inorganic materials 0.000 claims abstract description 36
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 claims abstract description 35
- WGLPBDUCMAPZCE-UHFFFAOYSA-N Trioxochromium Chemical compound O=[Cr](=O)=O WGLPBDUCMAPZCE-UHFFFAOYSA-N 0.000 claims abstract description 26
- 229910000423 chromium oxide Inorganic materials 0.000 claims abstract description 26
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 claims abstract description 25
- 239000002994 raw material Substances 0.000 claims abstract description 17
- 238000000034 method Methods 0.000 claims abstract description 7
- 239000000377 silicon dioxide Substances 0.000 claims abstract description 7
- 235000012239 silicon dioxide Nutrition 0.000 claims abstract description 5
- 239000002245 particle Substances 0.000 claims description 43
- 239000011812 mixed powder Substances 0.000 claims description 31
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 25
- 239000002002 slurry Substances 0.000 claims description 22
- 238000000227 grinding Methods 0.000 claims description 17
- 239000011230 binding agent Substances 0.000 claims description 16
- 238000003825 pressing Methods 0.000 claims description 16
- 238000009694 cold isostatic pressing Methods 0.000 claims description 15
- 238000002156 mixing Methods 0.000 claims description 14
- 229910052757 nitrogen Inorganic materials 0.000 claims description 14
- 239000002904 solvent Substances 0.000 claims description 13
- 238000001694 spray drying Methods 0.000 claims description 13
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical group CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 12
- 239000003292 glue Substances 0.000 claims description 12
- 239000000463 material Substances 0.000 claims description 11
- 238000003756 stirring Methods 0.000 claims description 11
- 229920002037 poly(vinyl butyral) polymer Polymers 0.000 claims description 9
- 239000000839 emulsion Substances 0.000 claims description 7
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 5
- 238000007599 discharging Methods 0.000 claims description 5
- 239000001301 oxygen Substances 0.000 claims description 5
- 229910052760 oxygen Inorganic materials 0.000 claims description 5
- 239000012299 nitrogen atmosphere Substances 0.000 claims description 4
- 235000019441 ethanol Nutrition 0.000 claims description 2
- 238000004519 manufacturing process Methods 0.000 claims description 2
- 238000005452 bending Methods 0.000 abstract description 8
- 239000013585 weight reducing agent Substances 0.000 abstract description 6
- 230000002378 acidificating effect Effects 0.000 abstract description 4
- 230000000052 comparative effect Effects 0.000 description 12
- 239000012298 atmosphere Substances 0.000 description 9
- 239000007787 solid Substances 0.000 description 9
- 238000012360 testing method Methods 0.000 description 7
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 6
- 239000002253 acid Substances 0.000 description 6
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 6
- 238000000280 densification Methods 0.000 description 6
- SIWVEOZUMHYXCS-UHFFFAOYSA-N oxo(oxoyttriooxy)yttrium Chemical compound O=[Y]O[Y]=O SIWVEOZUMHYXCS-UHFFFAOYSA-N 0.000 description 6
- 238000004321 preservation Methods 0.000 description 6
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 5
- 239000003513 alkali Substances 0.000 description 5
- 238000005469 granulation Methods 0.000 description 5
- 230000003179 granulation Effects 0.000 description 5
- 239000012071 phase Substances 0.000 description 5
- 229910052782 aluminium Inorganic materials 0.000 description 4
- 239000007789 gas Substances 0.000 description 4
- 239000004576 sand Substances 0.000 description 4
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 3
- 238000003801 milling Methods 0.000 description 3
- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 description 3
- 238000005034 decoration Methods 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- 239000007791 liquid phase Substances 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000000465 moulding Methods 0.000 description 2
- 229910010271 silicon carbide Inorganic materials 0.000 description 2
- 230000002194 synthesizing effect Effects 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 1
- 235000015895 biscuits Nutrition 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 229910010293 ceramic material Inorganic materials 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000005272 metallurgy Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910021420 polycrystalline silicon Inorganic materials 0.000 description 1
- 229920005591 polysilicon Polymers 0.000 description 1
- 239000007858 starting material Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000004580 weight loss Effects 0.000 description 1
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Abstract
The invention provides corrosion-resistant silicon nitride ceramic and a preparation method and application thereof, belonging to the technical field of silicon nitride ceramic preparation. The corrosion-resistant silicon nitride ceramic is prepared from the following raw materials in percentage by mass: 75-92% of silicon nitride powder; 2-10% of calcium hexaluminate powder; 3-15% of silicon carbide powder; 0.5-5% of chromium oxide powder; 0.2-3% of silicon dioxide powder. According to the invention, calcium hexaluminate is used as a main sintering aid, chromium oxide and silicon dioxide are used as auxiliary sintering aids, wherein the calcium hexaluminate has excellent corrosion resistance, and can form a high-corrosion-resistance grain boundary phase in a sintering process, so that the corrosion resistance of the silicon nitride ceramic is improved, and the obtained silicon nitride ceramic has a low weight reduction rate and a low bending strength reduction rate in an acidic or alkaline environment.
Description
Technical Field
The invention relates to the technical field of silicon nitride ceramics, in particular to corrosion-resistant silicon nitride ceramics and a preparation method thereof.
Background
The silicon nitride ceramic has excellent comprehensive performance, and can be widely applied to the fields of machinery, metallurgy, chemical industry, electronics, aerospace and the like as an engineering ceramic material. Silicon nitride is a strong covalent bond compound, has a very low self-diffusion coefficient, needs to be added with a certain amount of sintering aid, and realizes densification through liquid phase sintering. After sintering, a liquid phase formed by the sintering aid exists in the silicon nitride ceramic as a grain boundary phase, and has important influence on the performance of the silicon nitride ceramic.
Y 2 O 3 -Al 2 O 3 The system is the most common sintering aid for silicon nitride ceramics, and the silicon nitride ceramics prepared by using the system as the sintering aid have higher bending strength and fracture toughness, but Y 2 O 3 -Al 2 O 3 The grain boundary phase formed in the silicon nitride sintering process has relatively poor corrosion resistance, so that the silicon nitride ceramic prepared by using the silicon nitride ceramic as a sintering aid has a short service life in some environments with strong corrosion.
Disclosure of Invention
In view of the above, the invention provides a corrosion-resistant silicon nitride ceramic, and a preparation method and application thereof. The invention provides a corrosion-resistant silicon nitride ceramic and a method for preparing the same 2 O 3 -Al 2 O 3 Compared with silicon nitride ceramics prepared by using the system as a sintering aid, the silicon nitride ceramics prepared by using the system has higher corrosion resistance.
In order to achieve the purpose of the invention, the invention provides the following technical scheme:
the invention provides corrosion-resistant silicon nitride ceramic, which takes calcium hexaluminate as a main sintering aid and chromium oxide and silicon dioxide as auxiliary sintering aids; the corrosion-resistant silicon nitride ceramic is prepared from the following raw materials in percentage by mass:
preferably, the material is prepared from the following raw materials in percentage by mass:
preferably, the particle size D50 of the silicon nitride powder is less than or equal to 10 μm, and the purity is more than or equal to 98.5%; the particle size D50 of the calcium hexaluminate powder is less than or equal to 40 mu m, and the purity is more than or equal to 99 percent; the grain diameter D50 of the silicon carbide powder is less than or equal to 5 mu m, and the purity is more than or equal to 98 percent; the grain diameter D50 of the chromium oxide powder is less than or equal to 3 mu m, and the purity is more than or equal to 99 percent; the particle size D50 of the silicon dioxide powder is less than or equal to 1 mu m, and the purity is 99.9%.
Preferably, alpha-Si in the silicon nitride powder 3 N 4 The content of the oxygen is more than or equal to 80 percent, and the oxygen content is less than or equal to 3 percent.
The invention provides a preparation method of the corrosion-resistant silicon nitride ceramic, which comprises the following steps:
(1) mixing silicon nitride powder, calcium hexaluminate powder, silicon carbide powder, chromium oxide powder and silicon dioxide powder with a solvent, and grinding to obtain mixed powder slurry;
(2) adding a binder into the mixed powder slurry, and sequentially stirring, mixing and spray-drying to obtain granulated powder;
(3) sequentially carrying out dry pressing forming and cold isostatic pressing forming on the granulated powder to obtain a ceramic sample block;
(4) and sequentially carrying out glue discharging and air pressure sintering on the ceramic sample block to obtain the silicon nitride ceramic with high corrosion resistance.
Preferably, the solvent is ethanol, the grinding medium is silicon nitride balls, and the ball-to-material ratio is 2-5: 1;
the grinding time is 1-10 h, and the rotating speed is 800-1400 r/min;
the particle size D50 of the mixed powder in the mixed powder slurry is not more than 1 μm.
Preferably, the binder is polyvinyl butyral and/or polyacrylic emulsion, and the mass of the binder is 1-5% of the total mass of the mixed powder.
Preferably, the rotating speed of stirring and mixing is 200-400 r/min, and the time is more than or equal to 3 h; the particle size D50 of the granulated powder is 30-150 μm.
Preferably, the pressure of the dry pressing is 20-50 MPa; and the pressure of the cold isostatic pressing is 120-300 MPa.
Preferably, the temperature of the rubber discharge is 400-600 ℃, and the time is 1-10 h;
the air pressure sintering is carried out in a nitrogen atmosphere, and the pressure of the nitrogen is 0.3-10 MPa; the temperature of the air pressure sintering is 1750-1950 ℃, and the time is 1-6 h.
The invention provides application of the corrosion-resistant silicon nitride ceramic in preparation of thermocouple protection tubes, lift tubes, insulating rings and bearing materials.
The invention provides a corrosion-resistant silicon nitride ceramic which is prepared from the following raw materials in percentage by mass: 75-92% of silicon nitride powder; 3-15% of silicon carbide powder; 2-10% of calcium hexaluminate powder; 0.5-5% of chromium oxide powder; 0.2-3% of silicon dioxide powder. According to the invention, calcium hexaluminate is used as a sintering aid, and a high corrosion resistance grain boundary phase can be formed in the sintering process by utilizing the excellent corrosion resistance of the calcium hexaluminate, so that the corrosion resistance of the silicon nitride ceramic is improved; chromium oxide and silicon dioxide are used as auxiliary sintering aids, so that sintering densification can be promoted; by adding the silicon carbide powder into the ceramic raw material, the silicon carbide has good corrosion resistance, so that the corrosion resistance of the silicon nitride ceramic can be further improved, and the obtained silicon nitride ceramic has low weight reduction rate and bending strength reduction rate in an acidic or alkaline environment. The results of the examples show that the corrosion-resistant silicon nitride ceramic provided by the invention has H of 3mol/L at 80 DEG C 2 SO 4 The solution is kept for 100 hours under the acidic condition, the weight reduction rate is only 0.012-0.015 percent, and the bending strength reduction rate is only 11-14 percent; the composite material is kept for 100 hours at 80 ℃ under the alkaline condition of 6mol/L NaOH solution, the weight reduction rate is only 0.018-0.023%, and the bending strength reduction rate is only 8-11%.
The invention provides a preparation method of the corrosion-resistant silicon nitride ceramic, which is characterized in that raw materials are ground, a binder is added, granulation powder is obtained through spray drying, ceramic sample blocks are obtained through dry pressing and cold isostatic pressing, finally, binder removal and gas pressure sintering are carried out, and the silicon nitride ceramic with high corrosion resistance is obtained.
Drawings
FIG. 1 is a graph showing the comparison of the weight loss rate of silicon nitride ceramics obtained in examples and comparative examples under acid and alkali conditions;
FIG. 2 is a graph showing a comparison of the reduction rate of the flexural strength of the silicon nitride ceramics obtained in examples and comparative examples under acid and alkali conditions.
Detailed Description
The invention provides a corrosion-resistant silicon nitride ceramic which is prepared from the following raw materials in percentage by mass:
unless otherwise specified, the starting materials used in the present invention are commercially available.
The raw material of the corrosion-resistant silicon nitride ceramic comprises 75-92% of silicon nitride powder by mass percentage, and preferably 80-90%. In the present invention, the particle diameter D50 of the silicon nitride powder is preferably 10 μm or less, more preferably 5 μm or less. In the invention, the purity of the silicon nitride powder is preferably more than or equal to 98.5 percent, and more preferably more than or equal to 99 percent; alpha-Si in the silicon nitride powder 3 N 4 The content of (B) is preferably not less than 80%, more preferably not less than 85%. The present invention enables the formation of a grain boundary phase having high corrosion resistance by using calcium hexaluminate having excellent corrosion resistance as a sintering aid.
The raw material of the corrosion-resistant silicon nitride ceramic comprises, by mass, 2-10% of calcium hexaluminate powder, and preferably 4-8%. In the invention, the purity of the calcium hexaluminate powder is preferably more than or equal to 99 percent, and more preferably more than or equal to 99.5 percent; the particle size D50 of the calcium hexaluminate powder is preferably less than or equal to 40 mu m, and more preferably less than or equal to 20 mu m.
The raw material of the corrosion-resistant silicon nitride ceramic comprises 3-15% of silicon carbide powder by mass percentage, and preferably 5-10%. In the invention, the purity of the silicon carbide powder is preferably equal to or more than 98 percent, and more preferably equal to or more than 98.5 percent; the particle size D50 of the silicon carbide powder is preferably less than or equal to 10 μm, and more preferably less than or equal to 5 μm. In the invention, the silicon carbide powder has excellent corrosion resistance, and the corrosion resistance of the silicon nitride ceramic can be further improved.
The raw material of the corrosion-resistant silicon nitride ceramic comprises, by mass, 0.5-5% of chromium oxide powder, preferably 1-3%. In the invention, the purity of the chromium oxide powder is preferably more than or equal to 99 percent, and more preferably more than or equal to 99.5 percent; the particle size D50 of the chromium oxide powder is preferably less than or equal to 3 mu m, and more preferably less than or equal to 1 mu m. According to the invention, the sintering densification can be promoted by adding the chromium oxide powder.
The raw material of the corrosion-resistant silicon nitride ceramic comprises 0.2-3% of silicon dioxide powder by mass percentage, and preferably 0.5-2%. In the invention, the purity of the silicon dioxide powder is preferably more than or equal to 99.9 percent; the particle size D50 of the silicon dioxide powder is preferably less than or equal to 1 mu m. According to the invention, the sintering densification can be promoted by adding the silicon dioxide powder.
According to the invention, calcium hexaluminate is used as a sintering aid, and a high corrosion resistance grain boundary phase can be formed in the sintering process by utilizing the excellent corrosion resistance of the calcium hexaluminate, so that the corrosion resistance of the silicon nitride ceramic is improved; chromium oxide and silicon dioxide are used as auxiliary sintering aids, so that sintering densification can be promoted; by adding the silicon carbide powder into the ceramic raw material, the silicon carbide has good corrosion resistance, so that the corrosion resistance of the silicon nitride ceramic can be further improved, and the obtained silicon nitride ceramic has low weight reduction rate and bending strength reduction rate in an acidic or alkaline environment.
The invention provides a preparation method of the corrosion-resistant silicon nitride ceramic, which comprises the following steps:
(1) mixing silicon nitride powder, calcium hexaluminate powder, silicon carbide powder, chromium oxide powder and silicon dioxide powder with a solvent, and grinding to obtain mixed powder slurry;
(2) adding a binder into the mixed powder slurry, and sequentially stirring, mixing and spray-drying to obtain granulated powder;
(3) sequentially carrying out dry pressing forming and cold isostatic pressing forming on the granulated powder to obtain a ceramic sample block;
(4) and sequentially carrying out glue discharging and air pressure sintering on the ceramic sample block to obtain the silicon nitride ceramic with high corrosion resistance.
According to the invention, silicon nitride powder, calcium hexaaluminate powder, silicon carbide powder, chromium oxide powder and silicon dioxide powder are mixed with a solvent and ground to obtain mixed powder slurry. In the present invention, the solvent is preferably absolute ethanol. The invention has no special requirements on the mixing mode, and the mixing mode known by the technicians in the field can be used; the present invention preferably uses a sand mill for the grinding. In the invention, the grinding medium is preferably silicon nitride balls, the ball-to-material ratio is preferably 2-5: 1, and more preferably 3-4: 1; the grinding time is preferably 1-10 h, more preferably 3-8 h, and the rotating speed is preferably 800-1400 r/min, more preferably 1000-1200 r/min; the particle size of the mixed powder in the mixed powder slurry is preferably less than or equal to 1 micron, more preferably 0.5-0.8 micron, and the solid content of the mixed powder slurry is preferably 40-50%, more preferably 42-46%.
Or, the synthetic raw materials of silicon nitride powder and calcium hexaluminate, silicon carbide powder, chromium oxide powder and silicon dioxide powder are mixed and ground to obtain mixed powder slurry. In the invention, the raw materials for synthesizing the calcium hexaluminate powder comprise an aluminum source and a calcium source, wherein the aluminum source is Al 2 O 3 And/or Al (OH) 3 The calcium source is CaO and/or CaCO 3 And/or Ca (OH) 2 . In the invention, the atomic ratio of Ca and Al in the raw materials for synthesizing the calcium hexaluminate powder is preferably 1: 12.
After the mixed powder slurry is obtained, the invention adds the binder into the mixed powder slurry, and then the granulation powder is obtained by stirring, mixing and spray drying in turn. In the invention, the binder is preferably polyvinyl butyral and/or polyacrylic emulsion, and the solid content of the polyacrylic emulsion is preferably 30-60%, and more preferably 40-50%. In the present invention, the mass of the binder is preferably 1 to 5%, more preferably 2 to 4% of the total mass of the mixed powder. In the invention, the stirring and mixing speed is preferably 200-400 r/min, more preferably 300r/min, and the time is preferably not less than 3h, more preferably 3-5 h. In the invention, the drying mode is preferably spray drying, and the spray drying is preferably nitrogen protection pressure type spray drying or centrifugal type spray drying; the invention has no special requirement on the drying time, and the constant weight of the dried solid is ensured. In the present invention, the particle diameter D50 of the granulated powder is preferably 30 to 150 μm, and more preferably 50 to 120 μm.
After the granulated powder is obtained, the invention carries out dry pressing forming and cold isostatic pressing forming on the granulated powder in sequence to obtain a ceramic sample block. The invention preferably uses a dry press machine to carry out the dry pressing molding on the granulated powder; the pressure of the dry pressing molding is preferably 20-50 MPa, and more preferably 30-40 MPa; the invention does not require any particular time for dry pressing, and dry pressing times known to those skilled in the art can be used. The cold isostatic pressing is preferably carried out by using a cold isostatic press, and the pressure of the cold isostatic pressing is preferably 120-300 MPa, more preferably 150-250 MPa; the invention does not require any particular time for the cold isostatic pressing, and cold isostatic pressing times known to those skilled in the art can be used.
After a ceramic sample block biscuit is obtained, the ceramic sample block is sequentially subjected to glue removal and air pressure sintering to obtain the silicon nitride ceramic with high corrosion resistance. In the present invention, the degumming is preferably performed under a flowing air atmosphere, a flowing inert gas atmosphere or a vacuum condition, and more preferably under a flowing air atmosphere. In the invention, the temperature of the rubber discharge is preferably 400-600 ℃, and more preferably 450-550 ℃; the time is preferably 1 to 10 hours, and more preferably 4 to 8 hours. According to the invention, the binder in the ceramic sample block can be removed through the glue discharging.
In the invention, the air pressure sintering is preferably carried out in a nitrogen atmosphere, and the pressure of the nitrogen is preferably 0.3-10 MPa, and more preferably 2-6 MPa; the temperature of the air pressure sintering is preferably 1750-1950 ℃, and more preferably 1800-1900 ℃; the air pressure sintering time is preferably 1-6 h, and more preferably 2-5 h. The invention can realize the densification of the silicon nitride ceramic by the gas pressure sintering.
The invention provides application of the corrosion-resistant silicon nitride ceramic in preparation of thermocouple protection tubes, riser tubes, insulating rings and bearing materials. The corrosion-resistant silicon nitride ceramic has longer service life when used for manufacturing thermocouple protection tubes and liquid lifting tubes in the aluminum casting industry, insulating rings in the polysilicon industry and bearing materials working in a corrosive environment.
The corrosion-resistant silicon nitride ceramics provided by the present invention, and the preparation method and application thereof are described in detail below with reference to examples, but they should not be construed as limiting the scope of the present invention.
Example 1
(1) Silicon nitride powder (alpha-Si) with the total mass of powder being 87% 3 N 4 91% of calcium hexaluminate powder (the purity is 99.5%, the particle size D50 is 20 μm), 5.5% of silicon carbide powder (the purity is 98.5%, the particle size D50 is 5 μm), 2% of chromium oxide powder (the purity is 99.5%, the particle size D50 is 1 μm), 0.5% of silicon dioxide powder (the purity is 99.9%, the particle size D50 is 0.5 μm) are put into a sand mill to be milled for 2 hours at the rotating speed of 1000r/min, the milling solvent is absolute ethyl alcohol, the milling medium is silicon nitride balls, the ball-to-material ratio is 3:1, mixed powder slurry with the solid content of 45% is obtained after milling, and the particle size D50 of the mixed powder is 0.8 μm;
(2) adding polyvinyl butyral (PVB) accounting for 1 percent of the mass of the mixed powder and polyacrylic emulsion accounting for 1.5 percent of the solid content and accounting for 50 percent into the slurry, stirring for 4 hours, and carrying out nitrogen protection pressure type spray drying to obtain granulation powder with the particle size D50 of 100 microns;
(3) dry pressing the granulated powder at 30MPa, and carrying out cold isostatic pressing at 200MPa to obtain a ceramic sample block;
(4) carrying out glue removal on the formed ceramic sample block in a flowing air atmosphere, wherein the glue removal temperature is 450 ℃, and the heat preservation time is 5 hours;
(5) and sintering the ceramic sample block subjected to rubber removal in a pneumatic sintering mode, wherein the sintering temperature is 1850 ℃, the heat preservation time is 5 hours, the atmosphere in the furnace is nitrogen, and the nitrogen pressure is 5MPa, so as to obtain the corrosion-resistant silicon nitride ceramic.
Comparative example 1
Comparative example 1 is different from example 1 in that 5% of calcium hexaluminate powder, 2% of chromium oxide powder and 0.5% of silica powder were replaced with 3.75% of alumina powder and 3.75% of yttrium oxide powder, and 5.5% of silicon carbide powder was replaced with the same weight of silicon nitride powder, wherein the purity of the alumina powder was 99.9%, the particle diameter D50 was 1 μm, the purity of the yttrium oxide powder was 99.9%, and the particle diameter D50 was 1.5 μm. The rest operation conditions are the same, and the silicon nitride ceramics are obtained.
Example 2
(1) Silicon nitride powder (alpha-Si) with the total mass of powder being 87% 3 N 4 91% of silicon carbide powder (with the purity of 98.5% and the particle size of D50 of 5 μm), 5% of calcium hexaluminate powder (with the purity of 99.5% and the particle size of D50 of 20 μm), 1% of chromium oxide powder (with the purity of 99.5% and the particle size of D50 of 1 μm), 1% of silicon dioxide powder (with the purity of 99.9% and the particle size of D50 of 0.5 μm) are put into a sand mill and ground for 2 hours at the rotating speed of 1000r/min, the ground solvent is absolute ethyl alcohol, the grinding medium is silicon nitride balls, the ball-to-material ratio is 3:1, mixed powder slurry with the solid content of 45% is obtained after grinding, and the particle size of the mixed powder D50 is 0.8 μm;
(2) adding PVB (polyvinyl butyral) with the mass of 1% of the mixed powder and polyacrylic emulsion with the solid content of 1.5% of 50% into the slurry, stirring for 4 hours, and carrying out pressure type spray drying under the protection of nitrogen to obtain granulation powder with the particle size D50 of 100 mu m;
(3) dry pressing the granulated powder under 30MPa, and carrying out cold isostatic pressing under 150MPa to obtain a ceramic sample block;
(4) carrying out glue removal on the formed ceramic sample block in a flowing air atmosphere, wherein the glue removal temperature is 500 ℃, and the heat preservation time is 2 hours;
(5) and sintering the ceramic sample block subjected to rubber removal in a gas pressure sintering mode, wherein the sintering temperature is 1900 ℃, the heat preservation time is 2 hours, the atmosphere in the furnace is nitrogen, and the nitrogen pressure is 2MPa, so that the corrosion-resistant silicon nitride ceramic is obtained.
Comparative example 2
Comparative example 2 differs from example 2 in that 5% of calcium hexaaluminate powder, 1% of chromium oxide powder and 1% of silicon dioxide powder were replaced with 3.5% of alumina powder and 3.5% of yttrium oxide powder, and 6% of silicon carbide powder was replaced with silicon nitride powder of the same weight, wherein the purity of the alumina powder was 99.9%, the particle diameter D50 was 1 μm, the purity of the yttrium oxide powder was 99.9%, the particle diameter D50 was 1.5 μm, and the remaining operating conditions were the same, to obtain silicon nitride ceramic.
Example 3
(1) Silicon nitride powder (alpha-Si) with the total mass of the powder being 82 percent 3 N 4 The mixture is prepared by putting 91% of calcium hexaluminate powder (the purity is 99.5%, the particle size is 20 μm) with the oxygen content of 2%, 5 μm of particle size D50), 6% of calcium hexaluminate powder (the purity is 99.5%, the particle size is 20 μm), 8% of silicon carbide powder (the purity is 98.5%, the particle size is 5 μm), 2% of chromium oxide powder (the purity is 99.5%, the particle size is 1 μm) and 2% of silicon dioxide powder (the purity is 99.9%, the particle size is 0.5 μm) into a sand mill, grinding for 2h at the rotating speed of 1000r/min, wherein the grinding solvent is absolute ethyl alcohol, the grinding medium is silicon nitride balls, the ball-to-material ratio is 3:1, mixed powder slurry with the solid content of 45% is obtained after grinding, and the particle size of the mixed powder D50 is 0.8 μm;
(2) adding PVB (polyvinyl butyral) with the mass of 1% of the mixed powder and polyacrylic emulsion with the solid content of 1.5% of 50% into the slurry, stirring for 4 hours, and carrying out pressure type spray drying under the protection of nitrogen to obtain granulation powder with the particle size D50 of 100 mu m;
(3) dry pressing the granulated powder at 30MPa, and carrying out cold isostatic pressing at 150MPa to obtain a ceramic sample block;
(4) carrying out glue removal on the formed ceramic sample block in a flowing air atmosphere, wherein the glue removal temperature is 550 ℃, and the heat preservation time is 2 hours;
(5) and sintering the ceramic sample block subjected to binder removal in a gas pressure sintering mode, wherein the sintering temperature is 1800 ℃, the heat preservation time is 5 hours, the atmosphere in the furnace is nitrogen, and the nitrogen pressure is 8MPa, so that the corrosion-resistant silicon nitride ceramic is obtained.
Comparative example 3
Comparative example 3 differs from example 3 in that silicon nitride ceramics were obtained by replacing 6% of calcium hexaluminate powder, 2% of chromium oxide powder and 2% of silica powder with 5% of alumina powder and 5% of yttrium oxide powder, and 8% of silicon carbide powder with the same weight of silicon nitride powder, wherein the purity of alumina powder was 99.9%, the particle size D50 was 1 μm, the purity of yttrium oxide powder was 99.9%, the particle size D50 was 1.5 μm, and the remaining operating conditions were the same.
Performance testing
The silicon nitride ceramics obtained in examples 1 to 3 and comparative examples 1 to 3 were processed into test strips of 40X 3X 4mm in accordance with the requirements of standard GBT6569-2006, and the change of the bending strength and weight of the test strips before and after corrosion was measured and used as the evaluation standard of the acid and alkali corrosion resistance of the test strips. Preparation of corrosive solution and test of acid and alkali resistance reference is made to the method in the standard JCT2138-2012, wherein the acid solution is 3mol/L H 2 SO 4 The solution is 6mol/L NaOH solution. The results of the corrosion resistance test are shown in Table 1, in which a comparison of the weight reduction rate under acid and alkali conditions of the silicon nitride ceramics obtained in examples 1 to 3 and comparative examples 1 to 3 is shown in FIG. 1, and a comparison of the bending strength reduction rate is shown in FIG. 2.
TABLE 1 Corrosion resistance test results of silicon nitride ceramics obtained in examples 1 to 3 and comparative examples 1 to 3
As can be seen from the above examples and comparative examples, the corrosion-resistant silicon nitride ceramics according to the present invention and the corrosion-resistant silicon nitride ceramics according to the present invention 2 O 3 -Al 2 O 3 Compared with silicon nitride ceramics prepared by using the system as a sintering aid, the silicon nitride ceramics prepared by using the system has higher corrosion resistance.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (8)
1. The corrosion-resistant silicon nitride ceramic is characterized in that calcium hexaluminate is used as a main sintering aid, and chromium oxide and silicon dioxide are used as auxiliary sintering aids; the corrosion-resistant silicon nitride ceramic is prepared from the following raw materials in percentage by mass:
75-92% of silicon nitride powder;
2-10% of calcium hexaluminate powder;
3-15% of silicon carbide powder;
0.5-5% of chromium oxide powder;
0.2-3% of silicon dioxide powder;
alpha-Si in the silicon nitride powder 3 N 4 The content of the oxygen is more than or equal to 80 percent, and the oxygen content is less than or equal to 3 percent;
the preparation method of the corrosion-resistant silicon nitride ceramic comprises the following steps:
(1) mixing silicon nitride powder, calcium hexaluminate powder, silicon carbide powder, chromium oxide powder and silicon dioxide powder with a solvent, and grinding to obtain mixed powder slurry; the solvent is absolute ethyl alcohol;
(2) adding a binder into the mixed powder slurry, and sequentially stirring, mixing and spray-drying to obtain granulated powder;
(3) sequentially carrying out dry pressing forming and cold isostatic pressing forming on the granulated powder to obtain a ceramic sample block; the pressure of the dry pressing is 20-50 MPa;
(4) sequentially carrying out glue discharging and air pressure sintering on the ceramic sample block to obtain silicon nitride ceramic with high corrosion resistance;
the air pressure sintering is carried out in a nitrogen atmosphere, and the pressure of the nitrogen is 0.3-10 MPa; the temperature of the air pressure sintering is 1850-1950 ℃, and the time is 1-6 h; calcium hexaluminate forms a grain boundary phase with high corrosion resistance during sintering.
2. The corrosion-resistant silicon nitride ceramic according to claim 1, wherein the particle size D50 of the silicon nitride powder is not more than 10 μm, and the purity is not less than 98.5%; the particle size D50 of the calcium hexaluminate powder is less than or equal to 40 mu m, and the purity is more than or equal to 99 percent; the grain diameter D50 of the silicon carbide powder is less than or equal to 5 mu m, and the purity is more than or equal to 98 percent; the grain size D50 of the chromium oxide powder is less than or equal to 3 mu m, and the purity is more than or equal to 99 percent; the particle size D50 of the silicon dioxide powder is not more than 1 μm, and the purity is 99.9%.
3. A method for preparing a corrosion-resistant silicon nitride ceramic according to claim 1 or 2, comprising the steps of:
(1) mixing silicon nitride powder, calcium hexaluminate powder, silicon carbide powder, chromium oxide powder and silicon dioxide powder with a solvent, and grinding to obtain mixed powder slurry; the solvent is absolute ethyl alcohol;
(2) adding a binder into the mixed powder slurry, and sequentially stirring, mixing and spray-drying to obtain granulated powder;
(3) sequentially carrying out dry pressing forming and cold isostatic pressing forming on the granulated powder to obtain a ceramic sample block; the pressure of the dry pressing is 20-50 MPa;
(4) sequentially carrying out glue discharging and air pressure sintering on the ceramic sample block to obtain silicon nitride ceramic with high corrosion resistance;
the air pressure sintering is carried out in a nitrogen atmosphere, and the pressure of the nitrogen is 0.3-10 MPa; the temperature of the air pressure sintering is 1850-1950 ℃, and the time is 1-6 h.
4. The preparation method according to claim 3, wherein the solvent is ethanol, the grinding medium is silicon nitride balls, and the ball-to-material ratio is 2-5: 1;
the grinding time is 1-10 h, and the rotating speed is 800-1400 r/min;
the particle size D50 of the mixed powder in the mixed powder slurry is not more than 1 μm.
5. The preparation method according to claim 3, wherein the binder is polyvinyl butyral and/or polyacrylic emulsion, and the mass of the binder is 1-5% of the total mass of the mixed powder;
the rotating speed of stirring and mixing is 200-400 r/min, and the time is more than or equal to 3 h; the particle size D50 of the granulated powder is 30-150 μm.
6. The production method according to claim 3, wherein the pressure of the cold isostatic pressing is 120 to 300 MPa.
7. The preparation method according to claim 3, wherein the temperature of the binder removal is 400-600 ℃ and the time is 1-10 h.
8. Use of the corrosion-resistant silicon nitride ceramic according to claim 1 or 2 or the corrosion-resistant silicon nitride ceramic prepared by the preparation method according to any one of claims 3 to 7 in the preparation of thermocouple protection tubes, riser tubes, insulating rings and bearing materials.
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