CN116217244A - Method for uniformly coating silicon nitride sintering aid by coprecipitation reaction - Google Patents
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- 229910052581 Si3N4 Inorganic materials 0.000 title claims abstract description 172
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 title claims abstract description 172
- 238000005245 sintering Methods 0.000 title claims abstract description 139
- 238000000034 method Methods 0.000 title claims abstract description 68
- 239000011248 coating agent Substances 0.000 title claims abstract description 62
- 238000000576 coating method Methods 0.000 title claims abstract description 62
- 238000000975 co-precipitation Methods 0.000 title claims abstract description 47
- 238000006243 chemical reaction Methods 0.000 title claims abstract description 46
- 239000000843 powder Substances 0.000 claims abstract description 79
- 229910021578 Iron(III) chloride Inorganic materials 0.000 claims abstract description 44
- RBTARNINKXHZNM-UHFFFAOYSA-K iron trichloride Chemical compound Cl[Fe](Cl)Cl RBTARNINKXHZNM-UHFFFAOYSA-K 0.000 claims abstract description 44
- BNGXYYYYKUGPPF-UHFFFAOYSA-M (3-methylphenyl)methyl-triphenylphosphanium;chloride Chemical compound [Cl-].CC1=CC=CC(C[P+](C=2C=CC=CC=2)(C=2C=CC=CC=2)C=2C=CC=CC=2)=C1 BNGXYYYYKUGPPF-UHFFFAOYSA-M 0.000 claims abstract description 43
- NGDQQLAVJWUYSF-UHFFFAOYSA-N 4-methyl-2-phenyl-1,3-thiazole-5-sulfonyl chloride Chemical compound S1C(S(Cl)(=O)=O)=C(C)N=C1C1=CC=CC=C1 NGDQQLAVJWUYSF-UHFFFAOYSA-N 0.000 claims abstract description 43
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 41
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 claims abstract description 34
- 239000004202 carbamide Substances 0.000 claims abstract description 34
- 239000002243 precursor Substances 0.000 claims abstract description 27
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- 239000002210 silicon-based material Substances 0.000 abstract description 5
- 150000002500 ions Chemical class 0.000 abstract description 4
- 238000002156 mixing Methods 0.000 description 17
- WNROFYMDJYEPJX-UHFFFAOYSA-K aluminium hydroxide Chemical compound [OH-].[OH-].[OH-].[Al+3] WNROFYMDJYEPJX-UHFFFAOYSA-K 0.000 description 13
- QVOIJBIQBYRBCF-UHFFFAOYSA-H yttrium(3+);tricarbonate Chemical compound [Y+3].[Y+3].[O-]C([O-])=O.[O-]C([O-])=O.[O-]C([O-])=O QVOIJBIQBYRBCF-UHFFFAOYSA-H 0.000 description 13
- DEXZEPDUSNRVTN-UHFFFAOYSA-K yttrium(3+);trihydroxide Chemical compound [OH-].[OH-].[OH-].[Y+3] DEXZEPDUSNRVTN-UHFFFAOYSA-K 0.000 description 13
- 239000000463 material Substances 0.000 description 12
- 239000002131 composite material Substances 0.000 description 11
- -1 hydroxyl ions Chemical class 0.000 description 11
- 238000009472 formulation Methods 0.000 description 9
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 9
- 238000004448 titration Methods 0.000 description 9
- 229960004887 ferric hydroxide Drugs 0.000 description 8
- IEECXTSVVFWGSE-UHFFFAOYSA-M iron(3+);oxygen(2-);hydroxide Chemical compound [OH-].[O-2].[Fe+3] IEECXTSVVFWGSE-UHFFFAOYSA-M 0.000 description 8
- 239000002245 particle Substances 0.000 description 8
- 238000003917 TEM image Methods 0.000 description 7
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- 238000009210 therapy by ultrasound Methods 0.000 description 5
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 4
- 238000000280 densification Methods 0.000 description 4
- 239000002270 dispersing agent Substances 0.000 description 4
- 230000007062 hydrolysis Effects 0.000 description 4
- 229910001404 rare earth metal oxide Inorganic materials 0.000 description 4
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- 229910052727 yttrium Inorganic materials 0.000 description 3
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 2
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 2
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 2
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- 229920001223 polyethylene glycol Polymers 0.000 description 2
- 239000000377 silicon dioxide Substances 0.000 description 2
- VTLYFUHAOXGGBS-UHFFFAOYSA-N Fe3+ Chemical compound [Fe+3] VTLYFUHAOXGGBS-UHFFFAOYSA-N 0.000 description 1
- BPQQTUXANYXVAA-UHFFFAOYSA-N Orthosilicate Chemical compound [O-][Si]([O-])([O-])[O-] BPQQTUXANYXVAA-UHFFFAOYSA-N 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910021529 ammonia Inorganic materials 0.000 description 1
- 238000005253 cladding Methods 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 239000002612 dispersion medium Substances 0.000 description 1
- 229910001447 ferric ion Inorganic materials 0.000 description 1
- 238000005324 grain boundary diffusion Methods 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 235000014413 iron hydroxide Nutrition 0.000 description 1
- NCNCGGDMXMBVIA-UHFFFAOYSA-L iron(ii) hydroxide Chemical compound [OH-].[OH-].[Fe+2] NCNCGGDMXMBVIA-UHFFFAOYSA-L 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
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- 239000002086 nanomaterial Substances 0.000 description 1
- 238000000634 powder X-ray diffraction Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000012827 research and development Methods 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 235000012239 silicon dioxide Nutrition 0.000 description 1
- 239000007790 solid phase Substances 0.000 description 1
- VWQVUPCCIRVNHF-UHFFFAOYSA-N yttrium atom Chemical compound [Y] VWQVUPCCIRVNHF-UHFFFAOYSA-N 0.000 description 1
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Abstract
The invention relates to the technical field of silicon nitride ceramic materials, in particular to a method for uniformly coating a silicon nitride sintering aid by utilizing a coprecipitation reaction. Aiming at the requirement of sintering silicon nitride on the uniformity of a sintering aid, the uniform coating of the sintering aid is realized through coprecipitation reaction, firstly, aluminum nitrate, yttrium nitrate and ferric chloride are sequentially added into water to form a sintering aid precursor solution; adding urea and silicon nitride powder into the raw material solution to form suspension containing coprecipitation ions; and carrying out water bath heat treatment and drying treatment on the suspension to obtain the silicon nitride formula powder uniformly coated with the sintering aid. The method for uniformly coating the silicon nitride sintering aid has good coating and precipitation effects, can realize nano-scale uniform coating of the sintering aid on the surface of the silicon nitride powder, has simple process and easily controlled pH value, is convenient to popularize, and is suitable for preparing Guan Danhua silicon materials such as high-heat-conductivity silicon nitride, high-density silicon nitride, high-hardness silicon nitride and the like and producing products.
Description
Technical Field
The invention relates to the technical field of silicon nitride ceramic materials, in particular to a method for uniformly coating a silicon nitride sintering aid by utilizing a coprecipitation reaction.
Background
Silicon nitride is an important ceramic material, has higher strength and hardness, good oxidation resistance (the temperature for starting oxidation in air is 1300-1400 ℃), good hot corrosion resistance and stability, can resist most of acid corrosion, and has wide application in industries of metallurgy, machinery, chemical industry, aerospace, electronic information, semiconductors and the like. However, the silicon nitride material itself has high bond energy, the structure is not easily broken, and the grain boundary diffusion coefficient is low, so that the sintering driving force is small, and densification is difficult to realize under the condition of solid phase sintering. Metal oxides and rare earth oxides are generally added as sintering aids to form a low melting glass phase to promote dissolution and diffusion, and finally densification is achieved. At the same time, the microstructure of the ceramic material also plays an important role in its macroscopic properties. Factors of the microstructure include grain size, grain size distribution, grain morphology, grain boundary composition, grain boundary feature distribution, and the like. The addition of the sintering aid promotes the sintering of the silicon nitride ceramic, and meanwhile, the sintering aid can be used as a grain boundary phase to remain at the grain boundary position of the silicon nitride, so that the grain boundary morphology of the silicon nitride is affected, and the component uniformity and even the material performance are affected. It can be said that the microstructure of the silicon nitride ceramic is affected by the sintering aid system and the sintering preparation process, and how to reasonably select and design the sintering aid for sintering the silicon nitride ceramic, and by reasonably preparing the sintering aid and the sintering system, obtaining the product with high density, high uniformity and high performance is the key point of the research and development of the silicon nitride at present.
The conventional ceramic material preparation process generally comprises: the preparation method comprises four basic steps of formula powder preparation, powder mixing, material forming and material sintering. The preparation of the formula powder has great influence on the sintering characteristic and microstructure uniformity of the ceramic material, and the densification and microstructure uniformity of the ceramic material can be influenced in the powder mixing process. For the silicon nitride ceramic material, if the preparation of the formula powder is started, the precipitation cladding method is utilized to realize the uniform mixing of the silicon nitride raw material powder and the sintering auxiliary agent at the nanometer and micrometer level, so that the agglomeration state of the powder can be better controlled, the mixing uniformity of the sintering auxiliary agent is improved, the sintering process of the powder is further promoted, and the uniformity of the prepared ceramic microstructure and the stability of the material performance are improved.
At present, three main methods for realizing the mixing of the micron-scale and nano-scale sintering aids in the silicon nitride formula powder are as follows: (1) Mixing silicon nitride raw material powder with a micron-sized and nano-sized sintering aid by using a mechanical mixing method; (2) Mixing the silicon nitride raw material powder with the micron-sized and nano-sized sintering auxiliary agent by using a method of adding a dispersing agent; (3) A precipitation method is adopted to add a nano-scale sintering aid into the silicon nitride.
In the prior art methods (1) and (2), because the silicon nitride raw material powder and the sintering aid powder particles generally have volume and even density differences, the mixing uniformity has a certain degree of defects. For example: zheng Guangming, zhao Jun, zhouhui, etc., sialon-Si 3 N 4 Design and preparation of gradient nano composite ceramic cutting tool material [ J ]]Silicate journal, 2011, 39 (5): 783-788; zheng Guangming, zhao Jun, zhouhui and the like will be nano Si 3 N 4 And nano Al 2 O 3 Respectively mixing the powder with liquid phase dispersion medium (anhydrous ethanol), and nanometer Si 3 N 4 Adding relative nanometer Si into suspension 3 N 4 0.5% by mass of polyethylene glycol with molecular weight of 4000, which is used for preparing nano Al 2 O 3 Adding relative nanometer Al into the solution 2 O 3 Polyethylene glycol with a relative molecular mass of 4000 and a mass of 1.5% is respectively prepared into suspensions with a total mass fraction of 0.2% of nano materials, and the pH value of each suspension is adjusted to 9.5-10 so as to promote uniform mixing of the suspensions. One disadvantage of this method is that the dispersing effect of the dispersant must be used to achieve uniform dispersion, so as to avoid agglomeration of the nano-sized particles in the solution. Moreover, the dispersant which can be used is limited to the characteristics of the added sintering aid, and the requirements of a complex sintering aid system are difficult to meet.
In the prior art method (3), the silicon nitride raw material powder is mixed with the micron-level and nano-level sintering auxiliary agents by a precipitation method, so that the preparation method is high in efficiency and good in mixing effect. For example: li Guo by reacting Y (NO 3 ) 3 ·6H 2 O and AlCl 3 ·6H 2 O is added toMixing the ionized water, adding ammonia water to regulate the pH value of the solution to 10, and then stirring, drying and calcining sequentially to obtain Al 2 O 3 -Y 2 O 3 And (5) uniformly coating the nano-scale sintering auxiliary agent. The method has the following defects: 1. the precipitation process is titrated by ammonia water, so that the uniformity of the titration rate is difficult to control; 2. the pH of the suspension is unstable and difficult to control; 3. the mixed raw material precursor obtained by ammonia titration is coated by dot coating, and uniform coating is difficult to realize on the surface of silicon nitride powder.
Disclosure of Invention
The invention aims to provide a method for uniformly coating a sintering aid by utilizing a coprecipitation reaction, which has good coating effect, simple process and convenient popularization, and is suitable for preparing Guan Danhua silicon materials such as high-heat-conductivity silicon nitride, high-density silicon nitride, high-hardness silicon nitride and the like and producing products.
The technical scheme of the invention is as follows:
a method for uniformly coating a silicon nitride sintering aid by utilizing a coprecipitation reaction comprises the following steps:
(1) Sequentially adding aluminum nitrate, yttrium nitrate and ferric chloride into water according to a target molar ratio to form a sintering aid precursor solution, wherein the aluminum nitrate, the yttrium nitrate and the ferric chloride are mixed according to a target molar ratio of 5: (0.5-5): (0.01-0.5);
(2) Adding urea into the precursor solution obtained in the step (1) to further obtain a mixed solution containing all ionic components required by the coprecipitation reaction;
(3) Adding silicon nitride powder into the mixed solution obtained in the step (2) to form a suspension with uniformly dispersed silicon nitride powder and sintering aid precursors, wherein the molar ratio of silicon nitride to a mixture of aluminum nitrate, yttrium nitrate and ferric chloride is 28:0.3 to 6;
(4) Controlling the decomposition reaction of urea in the suspension obtained in the step (3) by utilizing water bath heat treatment, and further controlling the precipitation of solid precipitates to obtain a solid-liquid separated mixture;
(5) And (3) performing centrifugal treatment, drying and calcination treatment on the mixture obtained in the step (4) to obtain the silicon nitride powder uniformly coated with the sintering aid.
In the method for uniformly coating the silicon nitride sintering aid by utilizing the coprecipitation reaction, in the precursor solution in the step (1), the molar ratio of aluminum nitrate, yttrium nitrate and ferric chloride is adjusted according to the specific requirements of production conditions and product performance on the sintering aid, and preferably, the molar ratio of aluminum nitrate, yttrium nitrate and ferric chloride is 5:2.5:0.01.
in the method for uniformly coating the silicon nitride sintering aid by utilizing the coprecipitation reaction, water bath stirring treatment is carried out according to the requirement in the preparation process of the precursor solution.
In the method for uniformly coating the silicon nitride sintering aid by utilizing the coprecipitation reaction, when urea is added into the precursor solution in the step (2), the molar ratio of the urea to the mixture of aluminum nitrate, yttrium nitrate and ferric chloride is not less than 5:1.
in the method for uniformly coating the silicon nitride sintering aid by utilizing the coprecipitation reaction, preferably, the molar ratio of urea to the mixture of aluminum nitrate, yttrium nitrate and ferric chloride is 20:1.
in the method for uniformly coating the silicon nitride sintering aid by utilizing the coprecipitation reaction, in the step (3), when silicon nitride powder is added into the mixed solution, ultrasonic auxiliary treatment and/or water bath stirring auxiliary treatment are/is needed; and the molar ratio of the silicon nitride to the mixture of aluminum nitrate, yttrium nitrate and ferric chloride is adjusted according to the specific requirements of production conditions and product performance on the sintering aid, preferably, the molar ratio of the silicon nitride to the mixture is 28:5.56.
in the method for uniformly coating the silicon nitride sintering aid by utilizing the coprecipitation reaction, in the step (4), the suspension is subjected to heat treatment by water bath reaction, the heat treatment temperature is 22-95 ℃, and the heat preservation time is 1-10 h.
In the method for uniformly coating the silicon nitride sintering aid by utilizing the coprecipitation reaction, the temperature of heat treatment is preferably 80 ℃, and the heat preservation time is preferably 3 hours.
In the method for uniformly coating the silicon nitride sintering aid by utilizing the coprecipitation reaction, in the step (5), the centrifugal treatment mode is that alcohol centrifugation is carried out after water washing and centrifugation; the drying treatment mode is drying, and the drying temperature is 40-100 ℃; the calcination is carried out in air, vacuum or inert atmosphere, and the calcination temperature is 500-1400 ℃.
In the method for uniformly coating the silicon nitride sintering aid by utilizing the coprecipitation reaction, preferably, the water washing centrifugation and the alcohol centrifugation are respectively carried out for more than two times, the drying temperature is 60 ℃, and the calcining temperature is 1150 ℃.
The design idea of the invention is as follows:
in order to realize the preparation and research of Guan Danhua silicon materials such as high-heat-conductivity silicon nitride, high-density silicon nitride, high-hardness silicon nitride and the like, a low-melting-point glass phase is formed by adding metal oxide and rare earth oxide as sintering aids so as to promote dissolution and diffusion, and finally, the purpose of densification of the material is achieved. In order to avoid non-uniformization of the microstructure of the material due to the addition of the sintering aid and further to cause deterioration of the material performance, the problem that the silicon nitride raw material powder and the sintering aid are difficult to uniformly mix must be solved. Conventional mechanical mixing methods or dispersant addition methods cannot overcome the non-uniform mixing problems of complex sintering aid systems due to density differences or particle agglomeration. The invention adopts a coprecipitation reaction to realize a method for uniformly coating a sintering aid. Firstly, uniformly mixing by adopting water-soluble rare earth oxide sintering aid precursors such as aluminum nitrate, yttrium nitrate and the like in a solution mixing mode, and then realizing nano-grade Al in a coprecipitation precipitation mode 2 O 3 And Y 2 O 3 Coating the uniform layer of the sintering aid on the irregular surface of the silicon nitride powder; second, the rate of the coprecipitation reaction is controlled by controlling the hydrolysis reaction of urea. The hydrolysis reaction of urea is controlled by controlling the temperature and time of the hydrolysis of urea after the urea is uniformly dissolved in the mixed solution. When the temperature and time of urea hydrolysis are fixed, the generation speed of hydroxyl ions generated by urea hydrolysis is fixed, the hydroxyl ions are dispersed more uniformly, the concentration is controllable, and then the pH value control of the solution can be realized. Therefore, the limitation that the uniformity of the initial concentration of the titration is difficult to control in the titration process is avoided, the process is simple, and the pH value is controlled more accurately; third, fe ions are introduced into the sintering aid by adding ferric chlorideThe sintering temperature is lowered, and the generation of beta-phase silicon nitride is promoted. The method for realizing uniform coating of the sintering aid by utilizing the coprecipitation reaction has the advantages of easy control of pH value, good coating precipitation effect and capability of realizing nano-scale uniform coating of the sintering aid on the surface of the silicon nitride powder.
The invention has the advantages and beneficial effects that:
1. the method for uniformly coating the silicon nitride sintering aid by utilizing the coprecipitation reaction aims at realizing nanoscale Y 2 O 3 、Al 2 O 3 And Fe (Fe) x O y The sintering aid as main component is coated on the surface of silicon nitride powder in homogeneous layer, water soluble aluminum nitrate, yttrium nitrate and ferric chloride are used as yttrium source, aluminum source and iron source, and aluminum nitrate, yttrium nitrate and ferric chloride are added into water in target molar ratio to prepare solution, and the subsequent coprecipitation reaction and heat treatment process are combined to obtain the composite material containing Y 2 O 3 And Al 2 O 3 The nano-scale sintering aid coated silicon nitride formula powder is beneficial to ensuring uniform coating of the target sintering aid.
2. The method for uniformly coating the silicon nitride sintering aid by utilizing the coprecipitation reaction aims at commonly used Y 2 O 3 And Al 2 O 3 The sintering temperature of the sintering aid is high, and the sintering aid component containing Fe ions is further added, so that the sintering temperature can be effectively reduced in the subsequent sintering process, the generation rate of beta-phase silicon nitride is promoted, and the preparation and production requirements of high-density, high-uniformity and high-performance silicon nitride materials can be better met.
3. According to the method for uniformly coating the silicon nitride sintering aid by utilizing the coprecipitation reaction, urea is added into a raw material solution formed by aluminum nitrate, yttrium nitrate and ferric chloride water to form a mixed solution, silicon nitride is added into the mixed solution to form a mixture, when the mixture is subjected to heat treatment, the urea absorbs heat to generate hydrolysis reaction, hydroxide ions are generated, and compared with a titration method, the hydroxide ions are more uniformly dispersed, the uniformity of the titration rate is not required to be controlled, the process is simple, the pH value is easy to control, and the popularization is convenient.
4. According to the method for uniformly coating the silicon nitride sintering aid by utilizing the coprecipitation reaction, hydroxyl ions and carbonate ions generated by urea hydrolysis are uniformly dispersed in the mixed solution, and the irregular surface of each particle of the silicon nitride powder can be fully contacted with the liquid phase mixed solution. During solid-liquid separation, aluminum hydroxide, yttrium hydroxide and ferric hydroxide generated by hydroxyl ions, aluminum ions, yttrium ions and ferric ions and yttrium carbonate generated by carbonate ions and yttrium ions take silicon nitride powder particles as a matrix and are coated on irregular surfaces of the silicon nitride particles, so that the nano-scale sintering aid coated on the silicon nitride surface is a uniform layer.
In summary, the method for uniformly coating the silicon nitride sintering aid by utilizing the coprecipitation reaction has good coating and precipitation effects, can realize nano-scale uniform coating of the sintering aid on the surface of the silicon nitride powder, has simple process and easily controlled pH value, is convenient to popularize, and is suitable for preparing Guan Danhua silicon materials such as high-heat-conductivity silicon nitride, high-density silicon nitride, high-hardness silicon nitride and the like and producing products.
Drawings
FIG. 1 is an X-ray diffraction pattern (XRD pattern) of a silicon nitride sintered body obtained by calcining a silicon nitride formulation powder uniformly coated with a sintering aid obtained in example 2 of the present invention.
FIG. 2 is an X-ray diffraction pattern (XRD pattern) of a silicon nitride sintered body obtained by calcining a silicon nitride formulation powder uniformly coated with a sintering aid obtained in example 3 of the present invention.
FIG. 3 is a Scanning Electron Micrograph (SEM) of a silicon nitride formulation powder uniformly coated with a sintering aid on a 200nm scale prepared in accordance with example 3 of the present invention.
FIG. 4 is a Scanning Electron Micrograph (SEM) of a powder of a silicon nitride formulation uniformly coated with a sintering aid on a 100nm scale prepared in example 3 of the present invention.
FIG. 5 is a Transmission Electron Micrograph (TEM) of a silicon nitride formulation powder uniformly coated with a sintering aid at a 500nm scale prepared in example 5 of the present invention.
FIG. 6 is a Transmission Electron Micrograph (TEM) of a silicon nitride formulation powder uniformly coated with a sintering aid on a 50nm scale prepared in example 5 of the present invention.
Detailed Description
The invention will be better explained for understanding by referring to the following detailed description of the embodiments in conjunction with the accompanying drawings.
In a specific implementation process, the method for realizing uniform coating of the sintering aid through the coprecipitation reaction aims at the requirement of the sintering silicon nitride on the uniformity of the sintering aid, and comprises the following specific processes: firstly, sequentially adding aluminum nitrate, yttrium nitrate and ferric chloride into water according to a target molar ratio to form a sintering aid precursor solution; adding urea and silicon nitride powder into the raw material solution to form suspension containing coprecipitation ions; and carrying out water bath heat treatment and drying treatment on the suspension to obtain the silicon nitride formula powder uniformly coated with the sintering aid.
On one hand, the method adopts water-soluble rare earth oxide sintering aid precursors such as aluminum nitrate, yttrium nitrate and the like, so as to ensure the uniform mixing of the sintering aids; on the other hand, the hydrolysis reaction of urea is utilized, after the urea is uniformly dissolved in the mixed solution, the hydrolysis reaction of the urea is controlled by heating, so that the generation speed of hydroxyl ions is controlled, the concentration of the hydroxyl ions is controllable, and the dispersion is more uniform. Compared with titration, the titration method does not need to control the uniformity of the titration rate, and has simple process and easy control of pH value.
The invention is described in further detail below by means of the figures and examples.
Example 1
In this embodiment, the method for uniformly coating the silicon nitride sintering aid by using the coprecipitation reaction comprises the following specific steps:
(1) Adding 5mol of aluminum nitrate, 2.5mol of yttrium nitrate and 0.5mol of ferric chloride into 500ml of deionized water to form a sintering aid precursor solution;
(2) After the aluminum nitrate, the yttrium nitrate and the ferric chloride are completely dissolved, urea is mixed with the aluminum nitrate, the yttrium nitrate and the ferric chloride according to the molar ratio of 20:1, adding the mixture into a raw material solution to form a mixed solution;
(3) Silicon nitride powder (granularity of 200 meshes) is prepared according to the mole ratio of silicon nitride to a mixture of aluminum nitrate, yttrium nitrate and ferric chloride of 28: adding the mixture solution in a proportion of 0.37, performing ultrasonic treatment for 0.5h and water bath stirring treatment for 0.5h, and circulating for three times to form a suspension with uniformly dispersed silicon nitride powder and sintering aid precursors;
(4) Carrying out water bath heat treatment on the obtained suspension, controlling the decomposition reaction of urea and the precipitation of solid precipitate, wherein the heat treatment temperature is 95 ℃, and the heat preservation time is 4 hours;
(5) Cooling the mixture treated in the step (4) to room temperature;
(6) Centrifuging the mixture treated in the step (5), wherein the centrifuging mode is to perform three times of water washing and centrifuging and then perform three times of alcohol centrifuging to obtain a solid precipitate;
(7) Drying the solid precipitate obtained in the step (6) at 80 ℃ to obtain a solid dried substance;
(8) Calcining the solid dried material in air atmosphere at 1150 deg.c to obtain calcined silicon nitride powder with granularity of 200 mesh.
In this embodiment, the solid dry product obtained in the step (7) is a silicon nitride composite powder obtained by coating aluminum hydroxide, yttrium hydroxide, ferric hydroxide and yttrium carbonate with silicon nitride; wherein, the thickness of the aluminum hydroxide, the yttrium hydroxide, the ferric hydroxide and the yttrium carbonate coated on the silicon nitride is 37-66 nm. The silicon nitride sintered body prepared in the step (8) is silicon nitride formula powder uniformly coated by the sintering aid.
Example 2
In this embodiment, the method for uniformly coating the silicon nitride sintering aid by using the coprecipitation reaction comprises the following specific steps:
(1) 5mol of aluminum nitrate, 2.7mol of yttrium nitrate and 0.06mol of ferric chloride are added into 500ml of deionized water to form a sintering aid precursor solution;
(2) After the aluminum nitrate, the yttrium nitrate and the ferric chloride are completely dissolved, urea is mixed with the aluminum nitrate, the yttrium nitrate and the ferric chloride according to the molar ratio of 20:1, adding the mixture into a raw material solution to form a mixed solution;
(3) Silicon nitride powder (particle size 400 mesh) was mixed with aluminum nitrate, yttrium nitrate and ferric chloride in a molar ratio of 28: adding 0.37 into the mixed solution, performing ultrasonic treatment for 0.5h and water bath stirring treatment for 0.5h, and circulating for three times to form a suspension with uniformly dispersed silicon nitride powder and sintering aid precursors;
(4) Carrying out water bath heat treatment on the obtained suspension, controlling the decomposition reaction of urea and the precipitation of solid precipitate, wherein the heat treatment temperature is 95 ℃, and the heat preservation time is 4 hours;
(5) Cooling the mixture treated in the step 4 to room temperature;
(6) Centrifuging the mixture treated in the step 5, wherein the centrifuging mode is to perform three times of water washing and centrifuging and then perform three times of alcohol centrifuging to obtain a solid precipitate;
(7) Drying the solid precipitate obtained in the step 6 at 80 ℃ to obtain a solid dried substance;
(8) Calcining the solid dried material in air atmosphere at 950 ℃ to obtain silicon nitride formula powder (granularity is 400 meshes).
In the embodiment, the solid dry product obtained in the step 7 is silicon nitride composite powder obtained by coating aluminum hydroxide, yttrium hydroxide, ferric hydroxide and yttrium carbonate with silicon nitride; wherein, the thickness of the aluminum hydroxide, the yttrium hydroxide, the ferric hydroxide and the yttrium carbonate coated on the silicon nitride is 37-66 nm. The silicon nitride sintered body prepared in the step 8 is silicon nitride formula powder which is uniformly coated with the sintering aid.
As shown in FIG. 1, the silicon nitride composite powder prepared in step 7 of this example is calcined in step 8 to obtain a silicon nitride formula powder X-ray diffraction pattern (XRD pattern), and as can be seen from FIG. 1, the prepared silicon nitride formula powder contains Y 4 Al 2 O 9 Silicon dioxide and silicon nitride. Wherein Y is 4 Al 2 O 9 And silica is a new sintering aid.
Example 3
In this embodiment, the method for uniformly coating the silicon nitride sintering aid by using the coprecipitation reaction comprises the following specific steps:
(1) Adding 5mol of aluminum nitrate, 3mol of yttrium nitrate and 0.07mol of ferric chloride into 500ml of deionized water to form a sintering aid precursor solution;
(2) After the aluminum nitrate, the yttrium nitrate and the ferric chloride are completely dissolved, urea is mixed with the aluminum nitrate, the yttrium nitrate and the ferric chloride according to the molar ratio of 20:1, adding the mixture into a raw material solution to form a mixed solution;
(3) Silicon nitride powder (particle size 400 mesh) was mixed with aluminum nitrate, yttrium nitrate and ferric chloride in a molar ratio of 28: adding 0.37 into the mixed solution, performing ultrasonic treatment for 0.5h and water bath stirring treatment for 0.5h, and circulating for three times to form a suspension with uniformly dispersed silicon nitride powder and sintering aid precursors;
(4) Carrying out water bath heat treatment on the obtained suspension, controlling the decomposition reaction of urea and the precipitation of solid precipitate, wherein the heat treatment temperature is 95 ℃, and the heat preservation time is 3 hours;
(5) Cooling the mixture treated in the step (4) to room temperature;
(6) Centrifuging the mixture treated in the step (5), wherein the centrifuging mode is to perform three times of water washing and centrifuging and then perform three times of alcohol centrifuging to obtain a solid precipitate;
(7) Drying the solid precipitate obtained in the step (6) at 80 ℃ to obtain a solid dried substance;
(8) Calcining the solid dry matter in an inert atmosphere at 650 ℃ to obtain the silicon nitride formula powder (with granularity of 400 meshes) coated by the sintering aid.
In this embodiment, the solid dry product obtained in the step (7) is a silicon nitride composite powder obtained by coating aluminum hydroxide, yttrium hydroxide, ferric hydroxide and yttrium carbonate with silicon nitride; wherein, the thickness of the aluminum hydroxide, the yttrium hydroxide, the ferric hydroxide and the yttrium carbonate coated on the silicon nitride is 37-66 nm. The silicon nitride sintered body prepared in the step (8) is a product obtained by calcining the silicon nitride composite powder.
As shown in fig. 2, the X-ray diffraction pattern (XRD pattern) of the silicon nitride formulation powder obtained by calcining the silicon nitride composite powder prepared in step (7) in this example in step (8), as can be seen from fig. 2, the silicon nitride formulation powder prepared in step (8) contains only silicon nitride and no impurity phase.
As shown in fig. 3 and 4, as can be seen from fig. 3 and 4, a plush-shaped sintering aid (aluminum hydroxide, yttrium hydroxide, iron hydroxide and yttrium carbonate) is formed on the surface of silicon nitride in the Scanning Electron Microscope (SEM) photograph of the silicon nitride composite powder prepared in the step (7) of the present embodiment.
Example 4
In this embodiment, the method for uniformly coating the silicon nitride sintering aid by using the coprecipitation reaction comprises the following specific steps:
(1) Adding 5mol of aluminum nitrate, 3mol of yttrium nitrate and 0.08mol of ferric chloride into 500ml of deionized water to form a sintering aid precursor solution;
(2) After the aluminum nitrate, the yttrium nitrate and the ferric chloride are completely dissolved, urea is mixed with the aluminum nitrate, the yttrium nitrate and the ferric chloride according to the molar ratio of 20:1, adding the mixture into a raw material solution to form a mixed solution;
(3) Silicon nitride powder (granularity 600 meshes) is prepared according to the mole ratio of silicon nitride to a mixture of aluminum nitrate, yttrium nitrate and ferric chloride of 28: adding 0.37 into the mixed solution, performing ultrasonic treatment for 0.5h and water bath stirring treatment for 0.5h, and circulating for three times to form a suspension with uniformly dispersed silicon nitride powder and sintering aid precursors;
(4) Carrying out water bath heat treatment on the obtained suspension, controlling the decomposition reaction of urea and the precipitation of solid precipitate, wherein the heat treatment temperature is 95 ℃, and the heat preservation time is 3 hours;
(5) Cooling the mixture treated in the step (4) to room temperature;
(6) Centrifuging the mixture treated in the step (5), wherein the centrifuging mode is to perform three times of water washing and centrifuging and then perform three times of alcohol centrifuging to obtain a solid precipitate;
(7) Drying the solid precipitate obtained in the step (6) at 80 ℃ to obtain a solid dried substance;
(8) And calcining the solid dried product under the vacuum condition, wherein the calcining temperature is 850 ℃, and obtaining the silicon nitride formula powder (with the granularity of 600 meshes) coated by the sintering aid.
In the embodiment, the solid dry product obtained in the step (7) is silicon nitride composite powder obtained by coating aluminum hydroxide, yttrium hydroxide, ferric chloride and yttrium carbonate with silicon nitride; wherein, the thickness of the aluminum hydroxide, the yttrium hydroxide, the ferric chloride and the yttrium carbonate coated on the silicon nitride is 37-66 nm. And (3) preparing the silicon nitride formula powder coated by the sintering aid.
Example 5
In this embodiment, the method for uniformly coating the silicon nitride sintering aid by using the coprecipitation reaction comprises the following specific steps:
(1) Adding 5mol of aluminum nitrate, 3mol of yttrium nitrate and 0.09mol of ferric chloride into 500ml of deionized water to form a sintering aid precursor solution;
(2) After the aluminum nitrate, the yttrium nitrate and the ferric chloride are completely dissolved, urea is mixed with the aluminum nitrate, the yttrium nitrate and the ferric chloride according to the molar ratio of 20:1, adding the mixture into a raw material solution to form a mixed solution;
(3) Silicon nitride powder (granularity 600 meshes) is prepared according to the mole ratio of silicon nitride to a mixture of aluminum nitrate, yttrium nitrate and ferric chloride of 28: adding 0.37 into the mixed solution, performing ultrasonic treatment for 0.5h and water bath stirring treatment for 0.5h, and circulating for three times to form a suspension with uniformly dispersed silicon nitride powder and sintering aid precursors;
(4) Carrying out water bath heat treatment on the obtained suspension, controlling the decomposition reaction of urea and the precipitation of solid precipitate, wherein the heat treatment temperature is 95 ℃, and the heat preservation time is 4 hours;
(5) Cooling the mixture treated in the step (4) to room temperature;
(6) Centrifuging the mixture treated in the step (5), wherein the centrifuging mode is to perform three times of water washing and centrifuging and then perform three times of alcohol centrifuging to obtain a solid precipitate;
(7) Drying the solid precipitate obtained in the step (6) at 80 ℃ to obtain a solid dried substance;
(8) Calcining the solid dry matter at 650 ℃ under inert gas to obtain silicon nitride formula powder (with granularity of 600 meshes).
In the embodiment, the solid dry product obtained in the step (7) is silicon nitride composite powder obtained by coating aluminum hydroxide, yttrium hydroxide, ferric chloride and yttrium carbonate with silicon nitride; wherein, the thickness of the aluminum hydroxide, the yttrium hydroxide, the ferric hydroxide and the yttrium carbonate coated on the silicon nitride is 37-66 nm. The silicon nitride formula powder prepared in the step (8) is a product obtained by calcining the silicon nitride composite powder.
As shown in FIG. 5, a Transmission Electron Microscope (TEM) photograph of the silicon nitride formulation powder prepared in the step (8) of this example shows that a plush-shaped sintering aid (aluminum hydroxide, yttrium hydroxide and yttrium carbonate) is formed on the surface of the silicon nitride powder as shown in FIG. 5.
As shown in FIG. 6, a Transmission Electron Microscope (TEM) image obtained by observing the point 1 in FIG. 5 at a high magnification shows that the surface of the silicon nitride powder has a layer of sintering aid with a thickness of 37-66 nm as seen in FIG. 6.
SEM photograph of example 3 and TEM photograph of example 5 show that a uniform layer of sintering aid is coated on the surface of silicon nitride, and the coating effect of the sintering aid coated on the surface of silicon nitride is good. Comparison of examples 1, 2 and 3, 4 and 5 shows that calcination in air does not give the preferred Y 3 Al 5 O 12 And Fe (Fe) 2 O 3 Y can be obtained only by sintering in vacuum at a suitable sintering temperature 3 Al 5 O 12 And Fe (Fe) 2 O 3 . Example 5 demonstrates that the sintering aid thickness is in the range of 37-66 nm, that the sintering aid thickness is moderate, and that the coating effect on the silicon nitride surface is good.
In conclusion, the method for uniformly coating the silicon nitride sintering aid by utilizing the coprecipitation reaction has good coating and precipitation effects, can realize nano-scale uniform coating of the sintering aid on the surface of the silicon nitride powder, has simple process and easily controlled pH value, is convenient to popularize, and is suitable for preparing Guan Danhua silicon materials such as high-heat-conductivity silicon nitride, high-density silicon nitride, high-hardness silicon nitride and the like and producing products.
The foregoing is merely exemplary of the present invention, and those skilled in the art should not be considered as limiting the invention, since modifications may be made in the specific embodiments and application scope of the invention in light of the teachings of the present invention.
Claims (10)
1. A method for uniformly coating a silicon nitride sintering aid by utilizing a coprecipitation reaction is characterized in that the preparation process comprises the following steps:
(1) Sequentially adding aluminum nitrate, yttrium nitrate and ferric chloride into water according to a target molar ratio to form a sintering aid precursor solution, wherein the aluminum nitrate, the yttrium nitrate and the ferric chloride are mixed according to a target molar ratio of 5: (0.5-5): (0.01-0.5);
(2) Adding urea into the precursor solution obtained in the step (1) to further obtain a mixed solution containing all ionic components required by the coprecipitation reaction;
(3) Adding silicon nitride powder into the mixed solution obtained in the step (2) to form a suspension with uniformly dispersed silicon nitride powder and sintering aid precursors, wherein the molar ratio of silicon nitride to a mixture of aluminum nitrate, yttrium nitrate and ferric chloride is 28:0.3 to 6;
(4) Controlling the decomposition reaction of urea in the suspension obtained in the step (3) by utilizing water bath heat treatment, and further controlling the precipitation of solid precipitates to obtain a solid-liquid separated mixture;
(5) And (3) performing centrifugal treatment, drying and calcination treatment on the mixture obtained in the step (4) to obtain the silicon nitride powder uniformly coated with the sintering aid.
2. The method for uniformly coating a silicon nitride sintering aid by using a coprecipitation reaction according to claim 1, wherein in the precursor solution of step (1), the molar ratio of aluminum nitrate, yttrium nitrate and ferric chloride is adjusted according to the specific requirements of production conditions and product properties on the sintering aid, and preferably, the molar ratio of aluminum nitrate, yttrium nitrate and ferric chloride is 5:2.5:0.01.
3. the method for uniformly coating a silicon nitride sintering aid by using a coprecipitation reaction according to claim 2, wherein a water bath stirring treatment is performed as needed in the preparation of the precursor solution.
4. The method for uniformly coating a silicon nitride sintering aid by a coprecipitation reaction according to claim 1, wherein when urea is added to the precursor solution in step (2), a molar ratio of urea to a mixture of aluminum nitrate, yttrium nitrate and ferric chloride is not less than 5:1.
5. the method for uniformly coating a silicon nitride sintering aid by coprecipitation reaction according to claim 4, wherein the molar ratio of urea to the mixture of aluminum nitrate, yttrium nitrate and ferric chloride is preferably 20:1.
6. the method for uniformly coating a silicon nitride sintering aid by using a coprecipitation reaction according to claim 1, wherein in the step (3), when silicon nitride powder is added into the mixed solution, ultrasonic auxiliary treatment and/or water bath stirring auxiliary treatment are/is required; and the molar ratio of the silicon nitride to the mixture of aluminum nitrate, yttrium nitrate and ferric chloride is adjusted according to the specific requirements of production conditions and product performance on the sintering aid, preferably, the molar ratio of the silicon nitride to the mixture is 28:5.56.
7. the method for uniformly coating a silicon nitride sintering aid by using a coprecipitation reaction according to claim 1, wherein in the step (4), the suspension is heat-treated by a water bath reaction at a temperature of 22-95 ℃ for a heat-preservation time of 1-10 hours.
8. The method for uniformly coating a silicon nitride sintering aid by coprecipitation reaction according to claim 7, wherein the temperature of the heat treatment is preferably 80 ℃ and the holding time is 3 hours.
9. The method for uniformly coating a silicon nitride sintering aid by utilizing a coprecipitation reaction according to claim 1, wherein in the step (5), the centrifugal treatment mode is that alcohol centrifugation is performed after water washing and centrifugation; the drying treatment mode is drying, and the drying temperature is 40-100 ℃; the calcination is carried out in air, vacuum or inert atmosphere, and the calcination temperature is 500-1400 ℃.
10. The method for uniformly coating a silicon nitride sintering aid by coprecipitation reaction according to claim 9, wherein the water-washing centrifugation and alcohol centrifugation are preferably performed twice or more, respectively, and the drying temperature is 60 ℃ and the calcining temperature is 1150 ℃.
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