CN108840683B - Process for preparing zirconium nitride ceramic microspheres and zirconium nitride ceramic microspheres - Google Patents
Process for preparing zirconium nitride ceramic microspheres and zirconium nitride ceramic microspheres Download PDFInfo
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Abstract
The invention discloses a process for preparing zirconium nitride ceramic microspheres and the zirconium nitride ceramic microspheres, wherein the process comprises the following steps: ZrO (NO)3)2·xH2O, hexamethylenetetramine, urea and concentrated HNO3Mixing with carbon black to obtain a glue solution; dispersing the glue solution into hot silicone oil drop by drop, and curing the glue solution in the silicone oil drop by drop to obtain gel microspheres; aging the gel microspheres in hot silicone oil to ensure that the gel microspheres completely react; washing the gel microspheres to remove silicone oil on the surfaces of the microspheres and residual unreacted substances; drying the washed gel microspheres to obtain dried gel microspheres; and (3) performing carbothermal nitridation treatment on the dried gel microspheres and synchronously sintering and densifying to obtain the zirconium nitride ceramic microspheres. The process produces the zirconium nitride ceramic microspheres by combining an internal gel method with a carbothermic nitriding method, and the obtained zirconium nitride ceramic microspheres are pure-phase zirconium nitride and have the advantages of good sphericity, uniform size, complete structure, no crack and good mechanical property.
Description
Technical Field
The invention relates to the technical field of ceramic processes, in particular to a process for preparing zirconium nitride ceramic microspheres and the zirconium nitride ceramic microspheres.
Background
Zirconium nitride (ZrN) has the advantages of high melting point, high hardness, good chemical stability, low neutron capture cross section, high thermal conductivity and the like, and is a nuclear fuel inert matrix material with a good application prospect.
At present, many reports are related to the preparation of zirconium nitride powder and bulk materials, but no patent report is available about the preparation of zirconium nitride ceramic microspheres. The existing preparation process of zirconium nitride powder and blocks can not be directly applied to the preparation of zirconium nitride ceramic microspheres due to the characteristics of the process. In addition, NH is mostly adopted in the existing nitriding process3Or N2-H2The mixed gas is a nitrogen source and undergoes a nitriding reaction, which is dangerous to some extent.
Disclosure of Invention
The present invention is directed to solving, at least to some extent, one of the technical problems in the related art.
Therefore, one object of the present invention is to provide a process for preparing zirconium nitride ceramic microspheres, wherein the zirconium nitride ceramic microspheres obtained by the process have the advantages of good size uniformity, complete microspheres, no cracking phenomenon, good mechanical properties, etc.
Another object of the present invention is to provide zirconium nitride ceramic microspheres.
In order to achieve the above object, an embodiment of an aspect of the present invention provides a process for preparing zirconium nitride ceramic microspheres, comprising the following steps: step S1: ZrO (NO)3)2·xH2O, hexamethylenetetramine, urea and concentrated HNO3Mixing with carbon black to obtain a glue solution; step S2: dropwise dispersing the glue solution into hot silicone oil, and curing the liquid drops in the silicone oil to obtain gel microspheres; step S3: aging the gel microspheres in hot silicone oil to completely react the gel microspheres; step S4: washing the gel microspheres to remove silicone oil on the surfaces of the microspheres and residual unreacted substances; step S5: drying the washed gel microspheres to obtain dried gel microspheres; step S6: and carrying out carbothermal nitridation treatment on the dried gel microspheres and synchronously sintering and densifying to obtain the zirconium nitride ceramic microspheres.
The process for preparing the zirconium nitride ceramic microspheres in the embodiment of the invention adopts an inner gel method to form the microspheres and adopts N2As a nitrogen source, zirconium nitride is obtained through carbothermal nitridation high-temperature treatment, and simultaneously, the microspheres are sintered compactly, so that the obtained zirconium nitride ceramic microspheres have the advantages of good size uniformity, complete microspheres, no cracking phenomenon, good mechanical properties and the like.
In addition, the process for preparing zirconium nitride ceramic microspheres according to the above embodiment of the present invention has the following additional technical features:
further, in an embodiment of the present invention, the step S1 further includes: according to the ZrO (NO)3)2·xH2O-ZrO (NO)3)2Adding water solution, and adding preset concentrated HNO3Obtaining a first solution; preparing a mixed aqueous solution of hexamethylene tetramine and urea, and uniformly dispersing the carbon black in the mixed aqueous solution to obtain a second solution; respectively placing the first solution and the second solution in a cooling tank for cooling; and dropwise adding the cooled second solution into the cooled first solution to obtain the glue solution.
Further, in an embodiment of the present invention, wherein ZrO (NO) in the first solution3)2The concentration of the carbon black is 1.6-1.7 mol/L, the concentration of hexamethylene tetramine in the second solution is 3.0-3.2 mol/L, the concentration of urea is 2.6-2.7 mol/L, the carbon black is water-soluble nano-scale particles, wherein the addition amount of the carbon black ensures that the molar ratio of C/Zr is 1.2-1.4, and the ultrasound is carried out for 15 minutes after the addition.
Further, in an embodiment of the present invention, wherein the volume ratio of the first solution to the second solution is 3:2, wherein the first solution contains 8% by volume of concentrated nitric acid; the first solution and the second solution are placed in a cooling tank, the cooling temperature is 4 ℃, and the cooling time is at least 30 minutes; the cooling temperature of the glue solution is 4 ℃, and the cooling time is at least 30 minutes.
Further, in an embodiment of the present invention, the dropwise adding the cooled second solution to the cooled first solution to obtain the glue solution further includes: the second solution was added dropwise to the first solution under magnetic stirring at 500 rpm, and stirring was continued under this condition for 5 minutes after obtaining a mixed solution.
Further, in an embodiment of the present invention, the temperature of the hot silicone oil in step S2 is 85 to 90 ℃, and the aging time of the gel microspheres in step S3 is 30 to 60 minutes.
Further, in an embodiment of the present invention, the washing sequence in step S4 is trichloroethylene washing, ammonia water washing, hydrothermal washing, deionized water washing and propylene glycol methyl ether washing, and each washing time is 20 to 30 minutes, wherein the trichloroethylene is washed 4 to 5 times; the ammonia water concentration is 0.5 mol/L, and the washing is carried out for 8-10 times until the conductivity of the ammonia water waste liquid after the washing is less than 800 mu S/cm; carrying out hydrothermal washing in a reaction kettle at 200 ℃ for 3 hours; washing with deionized water for 8-10 times, wherein each time of washing is 20-30 minutes, until the conductivity of the waste liquid after washing is less than 20 mu S/cm; washing with propylene glycol methyl ether for 4-5 times, and washing for 20-30 minutes each time.
Further, in one embodiment of the present invention, the washed gel microspheres in step S5 are dried at room temperature for 12 hours, and then dried at 60 ℃ for 30-60 minutes.
Further, in an embodiment of the present invention, the step S6 further includes spreading the dried gel microspheres on the bottom of a crucible, covering a graphite plate above the crucible, performing a carbothermal nitridation heat treatment at a temperature rising rate of 0.5 ℃/min below 600 ℃, 1 ℃/min above 600 ℃ and a temperature falling rate of 5 ℃/min, introducing Ar below 800 ℃, a gas flow rate of 100m L/min, and introducing N above 800 ℃2The gas valve is closed when the gas flow is 300m L/min and the temperature is cooled to 300 ℃, and the temperature is respectively kept at 60, 80, 200, 300, 470, 600, 800 and 1000 ℃ for 60-180 minutes and 1500 ℃ for 5 hours in the temperature rising process.
In order to achieve the above purpose, another embodiment of the present invention provides a zirconium nitride ceramic microsphere, which is prepared according to the above process.
The zirconium nitride ceramic microspheres of the embodiment of the invention are pure-phase zirconium nitride, and the microspheres have the advantages of good sphericity, uniform size, complete structure, no crack and good mechanical property.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The above-mentioned additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a process flow diagram for preparing zirconium nitride ceramic microspheres according to one embodiment of the present invention;
FIG. 2 is a schematic illustration of a carbothermic nitridation sintering regime for gel-dried microspheres in accordance with one embodiment of the present invention;
FIG. 3 is a schematic representation of dried gel microspheres (a) and carbothermal nitridation sintered zirconium nitride ceramic microspheres (b) according to one embodiment of the present invention;
FIG. 4 is an X-ray diffraction pattern of carbothermal nitridation sintered zirconium nitride ceramic microspheres according to one embodiment of the present invention.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
The process for preparing zirconium nitride ceramic microspheres and zirconium nitride ceramic microspheres according to embodiments of the present invention will be described below with reference to the accompanying drawings, and first, the process for preparing zirconium nitride ceramic microspheres will be described with reference to the accompanying drawings.
FIG. 1 is a flow chart of a process for preparing zirconium nitride ceramic microspheres according to one embodiment of the present invention.
As shown in fig. 1, the process comprises the following steps:
step S1: ZrO (NO)3)2·xH2O, hexamethylenetetramine, urea and concentrated HNO3Mixing with carbon black to obtain the glue solution.
Further, in an embodiment of the present invention, the step S1 further includes: using ZrO (NO)3)2·xH2O-ZrO (NO)3)2Adding water solution, and adding preset concentrated HNO3Obtaining a first solution; preparing a mixed aqueous solution of hexamethylenetetramine and urea, and uniformly dispersing carbon black in the mixed aqueous solution to obtain a second solution; respectively will be respectively provided withPlacing the first solution and the second solution in a cooling tank for cooling; and dropwise adding the cooled second solution into the cooled first solution to obtain a glue solution.
It is understood that the glue solution is prepared by the following steps:
(1-1) with ZrO (NO)3)2·xH2Preparing ZrO (NO) by using O as raw material3)2And adding trace amount of concentrated HNO3(first solution);
(1-2) preparing a mixed aqueous solution of hexamethylenetetramine and urea, and uniformly dispersing carbon black in the mixed aqueous solution (second solution);
(1-3) respectively placing the first solution and the second solution obtained in the steps (1-1) and (1-2) into a cooling tank for cooling for later use;
and (1-4) dropwise adding the cooled second solution into the first solution to obtain a glue solution, and continuously storing the glue solution in a cooling tank.
Further, in one embodiment of the present invention, ZrO (NO) in the first solution3)2The concentration of the carbon black is 1.6-1.7 mol/L, the concentration of hexamethylene tetramine in the second solution is 3.0-3.2 mol/L, the concentration of urea is 2.6-2.7 mol/L, and the carbon black is water-soluble nano-scale particles, wherein the adding amount of the carbon black ensures that the molar ratio of C/Zr is 1.2-1.4, and the carbon black is added for 15 minutes by ultrasonic treatment.
Further, in one embodiment of the present invention, the volume ratio of the first solution to the second solution is 3:2, wherein the first solution contains 8% by volume of concentrated nitric acid; placing the first solution and the second solution in a cooling tank to cool at 4 ℃ for at least 30 minutes; the cooling temperature of the glue solution is also 4 ℃, and the cooling time is at least 30 minutes.
Further, in an embodiment of the present invention, the step of dropwise adding the cooled second solution to the cooled first solution to obtain a glue solution further includes: the second solution was added dropwise to the first solution under magnetic stirring at 500 revolutions per minute, and stirring was continued under these conditions for 5 minutes after the mixed solution was obtained.
It is understood that, in the preparation of the glue solution, the second solution is dropwise added into the first solution under the condition of magnetic stirring at 500 rpm, and the mixed solution is obtained and then stirred under the condition for 5 minutes.
Step S2: and (4) dropwise dispersing the glue solution into hot silicone oil, and curing the glue solution in the silicone oil to obtain the gel microspheres.
Further, in one embodiment of the present invention, the temperature of the hot silicone oil in step S2 is in the range of 85-90 ℃.
Step S3: and aging the gel microspheres in hot silicone oil to ensure that the gel microspheres react completely.
Further, in one embodiment of the present invention, the gel microspheres are aged for 30 to 60 minutes in step S3.
Step S4: and washing the gel microspheres to remove silicone oil and unreacted substances on the surfaces of the microspheres.
Further, in an embodiment of the present invention, the washing sequence in step S4 is trichloroethylene washing, ammonia water washing, hydrothermal washing, deionized water washing and propylene glycol methyl ether washing, and each washing time is 20 to 30 minutes, wherein the trichloroethylene is washed 4 to 5 times; the ammonia water concentration is 0.5 mol/L, and the washing is carried out for 8-10 times until the conductivity of the ammonia water waste liquid after the washing is less than 800 mu S/cm; carrying out hydrothermal washing in a reaction kettle at 200 ℃ for 3 hours; washing with deionized water for 8-10 times, wherein each time of washing is 20-30 minutes, until the conductivity of the waste liquid after washing is less than 20 mu S/cm; washing with propylene glycol methyl ether for 4-5 times, and washing for 20-30 minutes each time.
Step S5: and drying the washed gel microspheres to obtain dried gel microspheres.
Further, in one embodiment of the present invention, the gel microspheres washed in step S5 are dried at room temperature for about 12 hours, and then dried at 60 ℃ for 30-60 minutes.
The washed and dried gel microspheres are shown in fig. 3 (a).
Step S6: and (3) performing carbothermal nitridation treatment on the dried gel microspheres and synchronously sintering and densifying to obtain the zirconium nitride ceramic microspheres.
Wherein, the carbothermal nitridation sintering system of the gel dried microspheres is shown in fig. 2, the carbothermal nitridation sintered zirconium nitride ceramic microspheres are shown in fig. 3(b), and the X-ray diffraction pattern of the carbothermal nitridation sintered zirconium nitride ceramic microspheres is shown in fig. 4, which indicates that the phase is single-phase zirconium nitride.
Further, in an embodiment of the present invention, the step S6 further includes spreading the dried gel microspheres on the bottom of a graphite crucible, and covering a graphite plate above the crucible to create a strong reducing atmosphere, wherein during the carbothermal nitridation heat treatment, the temperature rising rate is 0.5 ℃/min below 600 ℃, 1 ℃/min above 600 ℃, and the temperature lowering rate is 5 ℃/min, Ar is introduced below 800 ℃, the gas flow rate is 100m L/min, and N is introduced above 800 ℃2The gas valve is closed when the gas flow is 300m L/min and the temperature is cooled to 300 ℃, and the temperature is respectively kept at 60, 80, 200, 300, 470, 600, 800 and 1000 ℃ for 60-180 minutes and 1500 ℃ for 5 hours in the temperature rising process.
It should be noted that, in order to obtain zirconium nitride ceramic microspheres with good size uniformity, good sphericity and no cracking, the technological parameters and conditions of each link need to be strictly controlled, (1) carbon source is necessary reducing agent for carbothermal nitridation reaction, and carbon black with nano-scale particle size is used as carbon source to be added into glue solution to ensure good dispersibility of carbon black in the glue solution; (2) a large amount of organic matters are remained in the microspheres after internal gelation, the organic matter residues need to be removed through washing, and particularly, the hydrothermal washing time and temperature need to be strictly controlled to prevent the microspheres from cracking; (3) the heating rate and the cooling rate of the carbothermal nitridation process are strictly controlled to prevent the microspheres from cracking; (4) heat preservation is carried out at a proper temperature point in the heat treatment process, so that the residual organic matters are fully released, and the microspheres are prevented from cracking; (5) through a reasonable sintering system, the nitridation rate and the sintering rate are coordinately controlled, and the zirconium oxide is prevented from being sintered before the zirconium nitride is formed; (6) creates stronger reducing atmosphere and ensures the full progress of the nitridation reaction so as to obtain pure-phase zirconium nitride.
The process for preparing zirconium nitride ceramic microspheres is further illustrated by the specific examples below.
The embodiment of the invention adopts an inner gel method to form microspheres, adopts carbothermal nitridation high-temperature treatment to obtain zirconium nitride products, and simultaneously leads the microspheres to be sintered compactly, and has the following specific technical process:
(1) preparing a mixture containing 1.6 to 1.7 mol/L ZrO (NO)3)2And an aqueous solution containing 3.0 to 3.2 mol/l of hexamethylenetetramine and 2.6 to 2.7 mol/l of urea. Selecting carbon black with nano-scale particle size, adding the carbon black into a solution containing hexamethylenetetramine and urea, and performing ultrasonic treatment for 15-20 minutes to fully disperse the carbon black. And cooling the prepared two solutions at 4 ℃ for 30-60 minutes for later use. Then ZrO (NO)3)2Adding trace amount of concentrated nitric acid into the solution, and dropwise adding a mixed solution containing carbon black, hexamethylenetetramine and urea into ZrO (NO)3)2The solution was stirred while being dropped. And then stirring for 5-10 minutes to fully mix the solution to obtain a glue solution for later use. The adding amount of the carbon black is required to ensure that the molar ratio of C/Zr is between 1.2 and 1.4;
(2) cooling the glue solution containing the carbon black obtained in the step (1) at 4 ℃ for 30-60 minutes to ensure the stability of the glue solution;
(3) dropwise dispersing the glue solution obtained in the step (2) into silicone oil at 85-90 ℃ to form gel microspheres;
(4) placing the gel microspheres obtained in the step (3) in hot silicone oil for aging for 30-60 minutes;
(5) taking out the gel microspheres and washing. Firstly, washing with trichloroethylene for 4-5 times, wherein each time of washing is 20-30 minutes; then washing with 0.5 mol/L ammonia water for 8-10 times, and washing for 20-30 minutes each time until the conductivity of the ammonia water waste liquid after washing is less than 800 mu S/cm; then placing the gel microspheres in a polytetrafluoroethylene reaction kettle, and carrying out hydrothermal treatment for 3 hours at the temperature of 200 ℃ to decompose a large amount of organic matters in the microspheres; taking out the gel microspheres after hydrothermal washing, washing with deionized water for 8-10 times, and washing for 20-30 minutes each time until the conductivity of the waste liquid after washing is less than 20 mu S/cm; finally, washing with propylene glycol methyl ether to remove water for 4-5 times, wherein each washing time is 20-30 minutes;
(6) drying the gel microspheres obtained after washing in the step (5) at room temperature for 30-60 minutes, and then drying in a drying oven at 60 ℃ for 12 hours;
(7) and (4) placing the gel dried microspheres obtained in the step (6) into a square graphite crucible, and placing the crucible into a heating furnace for carbothermal nitridation sintering. The microspheres are spread at the bottom of the crucible, and the graphite plate is covered above the crucible to ensure that the microspheres are in a strong reducing atmosphere at a high temperature and ensure N2Carrying out circulation participation reaction, respectively keeping the temperature at 60, 80, 200, 300 and 470 ℃ for a period of time in the temperature rising process to slowly and fully release the adsorbed water, the crystal water and the residual organic matters, respectively keeping the temperature at 600, 800 and 1000 ℃ for a period of time to slowly and fully carry out the zirconium oxide crystallization, keeping the temperature at 1500 ℃ for 5 hours to fully carry out the carbothermal nitridation reaction, besides, the heating rate is 0.5 ℃/minute below 600 ℃ and 1 ℃/minute above 600 ℃ to prevent the microspheres from generating cracks, introducing Ar below 800 ℃, the gas flow is 100m L/min, aiming at bringing out the water vapor and the decomposition products of the residual organic matters, and introducing N instead of introducing above 800 ℃2Gas flow 300m L/min, for N2As nitrogen source, carbothermal nitridation reaction is carried out to obtain zirconium nitride product. Cooling at 5 deg.C/min to 600 deg.C, and introducing N2And cooling to 300 deg.c to avoid oxidation of product microsphere caused by contact with air at relatively high temperature.
In summary, the embodiment of the present invention provides a complete process for preparing zirconium nitride ceramic microspheres, and the complete zirconium nitride ceramic microspheres without cracking are prepared by adopting a process of combining inner gel and carbothermal nitridation. The process can realize near-net shape, and avoid dust pollution and dangerous gas NH3And H2The introduction of the method is suitable for preparing the zirconium nitride ceramic microspheres with the diameter of 500-1000 microns, and the obtained zirconium nitride ceramic microspheres have good sphericity and size uniformity, are complete and have no cracking, and have good mechanical properties.
According to the process for preparing the zirconium nitride ceramic microspheres provided by the embodiment of the invention, in the process of preparing the glue solution, the carbon black with the nano-scale particle size is uniformly dispersed in the glue solution, and the gel is obtained after the processes of gelling, aging, washing and dryingMicrospheres; followed by the use of N2The obtained zirconium nitride ceramic microspheres are pure-phase zirconium nitride, and have good sphericity, uniform size, complete structure, no crack and good mechanical property.
In addition, the embodiment of the invention also provides the zirconium nitride ceramic microspheres prepared by the process for preparing the zirconium nitride ceramic microspheres. The zirconium nitride ceramic microspheres are pure-phase zirconium nitride, and have the advantages of good sphericity, uniform size, complete structure, no crack and good mechanical property.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (7)
1. A process for preparing zirconium nitride ceramic microspheres, comprising the steps of:
step S1: ZrO (NO)3)2·xH2O, hexamethylene tetrakisAmine, urea, concentrated HNO3And carbon black to obtain a glue solution, wherein the step S1 further comprises: using ZrO (NO)3)2·xH2O-ZrO (NO)3)2Adding water solution, and adding preset concentrated HNO3Obtaining a first solution; preparing a mixed aqueous solution of hexamethylene tetramine and urea, and uniformly dispersing the carbon black in the mixed aqueous solution to obtain a second solution; respectively placing the first solution and the second solution in a cooling tank for cooling; dropwise adding the cooled second solution into the cooled first solution to obtain a glue solution; wherein ZrO (NO) in the first solution3)2The concentration of the carbon black is 1.6-1.7 mol/l, the concentration of hexamethylenetetramine in the second solution is 3.0-3.2 mol/l, the concentration of urea is 2.6-2.7 mol/l, the carbon black is water-soluble nano-particles, ultrasonic treatment is carried out for 15 minutes after the carbon black is added, and the molar ratio of C atoms and Zr atoms introduced by the carbon black is required to be ensured to be 1.2-1.4 in the raw material proportion;
step S2: dropwise dispersing the glue solution into hot silicone oil, and curing the glue solution in the silicone oil to obtain gel microspheres;
step S3: aging the gel microspheres in the hot silicone oil to completely react the gel microspheres;
step S4: washing the aged gel microspheres to remove silicone oil on the surfaces of the microspheres and residual unreacted substances;
step S5: drying the washed gel microspheres to obtain dried gel microspheres;
step S6, performing carbothermic nitridation treatment and synchronous sintering densification on the dried gel microspheres to obtain zirconium nitride ceramic microspheres, wherein the step S6 further comprises the steps of spreading the dried gel microspheres at the bottom of a crucible and covering a graphite plate above the crucible, wherein during carbothermic nitridation treatment, the heating rate is 0.5 ℃/min below 600 ℃, 1 ℃/min above 600 ℃, the cooling rate is 5 ℃/min, Ar is introduced below 800 ℃, the gas flow is 100m L/min, and N is introduced above 800 DEG, and the temperature is controlled to be within the range of 100 DEG, and the temperature of the ceramic microspheres is controlled to be within the range of zero DEG C2The gas flow is 300m L/min, the gas valve is closed until the temperature is cooled to 300 ℃, and the temperature rising processRespectively preserving heat at 60, 80, 200, 300, 470, 600, 800 and 1000 ℃ for 60-180 minutes, and preserving heat at 1500 ℃ for 5 hours.
2. The process for preparing zirconium nitride ceramic microspheres according to claim 1, wherein,
the volume ratio of the first solution to the second solution is 3:2, wherein the first solution contains concentrated nitric acid with volume fraction of 8%;
the first solution and the second solution are placed in a cooling tank, the cooling temperature is 4 ℃, and the cooling time is at least 30 minutes;
the cooling temperature of the glue solution is also 4 ℃, and the cooling time is at least 30 minutes.
3. The process for preparing zirconium nitride ceramic microspheres according to claim 1, wherein the cooled second solution is added dropwise to the cooled first solution to obtain a glue solution, further comprising:
the second solution was added dropwise to the first solution under magnetic stirring at 500 revolutions per minute, and stirring was continued under these conditions for 5 minutes after the mixed solution was obtained.
4. The process for preparing zirconium nitride ceramic microspheres according to claim 1, wherein the temperature of the hot silicone oil in step S2 is 85-90 ℃, and the aging time of the gel microspheres in step S3 is 30-60 minutes.
5. The process for preparing zirconium nitride ceramic microspheres according to claim 1, wherein the washing in step S4 is trichloroethylene washing, ammonia water washing, hydrothermal washing, deionized water washing and propylene glycol methyl ether washing, each washing time is 20-30 minutes, wherein the trichloroethylene washing is 4-5 times; the ammonia water concentration is 0.5 mol/L, and the washing is carried out for 8-10 times until the conductivity of the ammonia water waste liquid after the washing is less than 800 mu S/cm; carrying out hydrothermal washing in a reaction kettle at 200 ℃ for 3 hours; washing with deionized water for 8-10 times, wherein each time of washing is 20-30 minutes, until the conductivity of the waste liquid after washing is less than 20 mu S/cm; washing with propylene glycol methyl ether for 4-5 times, and washing for 20-30 minutes each time.
6. The process for preparing zirconium nitride ceramic microspheres according to claim 1, wherein the gel microspheres washed in the step S5 are dried at room temperature for 12 hours, and then dried at 60 ℃ for 30-60 minutes.
7. Zirconium nitride ceramic microspheres, characterized in that they are prepared according to the process of any one of claims 1-6.
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