Preparation method of high-temperature-resistant non-shrinkage insulating boron nitride ceramic for quartz continuous melting furnace

Abstract

The invention discloses a preparation method of high-temperature-resistant non-shrinkage insulating boron nitride ceramic for a quartz continuous melting furnace. The preparation method comprises the following steps: adding hexagonal boron nitride nano powder into a solution containing pure boric acid and guanidine hydrochloride, dispersing, dropwise adding polyacrylamide, freeze-drying, introducing wet nitrogen, and carrying out nitridation reaction at about 700 DEG C to prepare boron nitride powder; carrying out dry pressing on the obtained powder to form a green body, calcining, and crushing to obtain boron nitride particles; and mixing the boron nitride powder and the boron nitride particles, performing dry pressing to form a green body, and sintering to prepare the boron nitride ceramic for the quartz continuous melting furnace. Boron nitride powder and boron nitride particles for forming are self-made powder, the two materials are high in purity and good in matching performance, phase change does not occur in the high-temperature sintering process, and cracks are not prone to being formed; the preparation process is simple, and the prepared boron nitride ceramic structure is good in high-temperature stability and good in thermal creep resistance, and can realize long-acting service in an ultrahigh-temperature quartz continuous melting furnace.

Description

Technical Field

[0001] The invention belongs to the technical field of advanced functional ceramic preparation, and in particular relates to a method for preparing high-temperature resistant, non-shrinkage insulating boron nitride ceramics for a quartz continuous melting furnace. Background Art

[0002] Quartz glass is a special glass material composed of a single component of silicon dioxide (SiO2). It has the characteristics of high purity, high optical performance, high temperature resistance, low thermal expansion coefficient, etc. It is widely used in optical transparent windows, microelectronics processing, corrosion-resistant chemical devices, and high-temperature equipment observation windows. At present, the production and manufacturing of quartz glass is mainly based on the electric melting method, which uses electricity as the power source and uses resistance, arc, high-frequency ions, etc. to heat quartz sand to above 1800℃ to melt and realize the preparation of quartz glass products. However, in continuous melting production, the temperature in the quartz continuous melting furnace cavity is maintained at 2150℃~2250℃ for a long time, which puts forward new requirements for the use of cavity materials.

[0003] At present, the cavity material used in the quartz continuous melting furnace is mainly zirconia refractory material, which has a melting point of up to 2715℃ and can meet the use requirements of various atmospheres. However, since the cavity material not only faces an ultra-high service temperature, but also needs to bear the functions of heating body fixation and insulation as a connecting device, zirconia often has problems such as local cracking, loose structure and deterioration after being used in the continuous melting furnace for a period of time, which seriously affects the continuous production of equipment and the safety of operators. In order to solve the above problems, Chinese patent application CN111848179A discloses a method for preparing high-strength boron nitride ceramics that can be used in ultra-high temperature environments. It improves the strength of traditional boron nitride ceramics while maintaining the high-temperature performance of boron nitride. However, the preparation method of this product is prepared by hot pressing and sintering, which requires a pressure of 20 to 60Mpa in an environment of 1800℃ to 2100℃, which has high requirements for equipment. Chinese scholar Sun Zhiyuan and others found that boron nitride ceramics will decompose in an ultra-high temperature environment of 2000℃, releasing elemental boron and nitrogen. When the furnace environment is vacuum, the nitrogen is continuously pumped out of the furnace cavity, which will aggravate the decomposition of boron nitride; and when the graphite heating body in the furnace is graphite, the elemental boron and graphite will meet to generate boron carbide (B4C), and when the heating body in the furnace is metal tungsten, the elemental boron will corrode the heating body; this will seriously affect the long-term stable operation of the equipment. Summary of the invention

[0004] The purpose of the present invention is to provide a high-temperature resistant, shrinkage-free, insulating boron nitride ceramic material for a quartz continuous melting furnace, so as to solve the problem of decomposition of boron nitride (BN) in an ultra-high temperature environment and realize the preparation of high-strength, shrinkage-free, complex-shaped, insulating BN ceramics.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] The present invention provides a method for preparing high-temperature resistant non-shrinkage insulating boron nitride ceramics for a quartz continuous melting furnace, the method specifically comprising the following steps:

[0007] Step 1: Dry commercial high-purity boric acid and guanidine hydrochloride, then mix the high-purity boric acid and guanidine hydrochloride in a molar ratio of 1:1.1 to 1:1.5, dissolve them in anhydrous ethanol, pass gas through the resulting solution, heat it to 30°C to 45°C, and keep it warm for 2h to 4h;

[0008] Step 2: adding hexagonal boron nitride nanopowder to the solution obtained in step 1 for high-speed dispersion, wherein the amount of hexagonal boron nitride nanopowder added is 1% to 5% of the mass of high-purity boric acid, and dripping polyacrylamide, wherein the amount of polyacrylamide dripped is 1% to 1.5% of the mass of the hexagonal boron nitride nanopowder;

[0009] Step 3: passing liquid nitrogen into the suspension obtained in step 2 to obtain a mixture block, and then freeze-drying to obtain a high-polymer mixture with boron nitride as the core, passing wet nitrogen into the obtained mixture, the volume ratio of nitrogen to water vapor is 95:5 to 98:2, and the nitridation reaction temperature is 600 to 800° C. to obtain boron nitride powder;

[0010] Step 4: washing and drying the boron nitride powder obtained in step 3, dry-pressing part of the obtained powder, calcining the obtained green body at a calcination temperature of 600°C to 650°C for 6h to 8h, and then crushing the obtained sample to obtain boron nitride particles;

[0011] Step 5: mixing the boron nitride particles obtained in step 4 with the boron nitride powder obtained in step 3, and then performing dry pressing to form the obtained green body, and performing isostatic pressing to form a boron nitride green body;

[0012] Step 6: Sinter the obtained boron nitride blank in an inert atmosphere, and after natural cooling, obtain the boron nitride ceramic for quartz continuous melting furnace.

[0013] Preferably, in step 1, the introduced gas is ammonia (NH 3 ).

[0014] Preferably, in step 2, the rotation speed used for the high-speed dispersion is 6000 r / min to 8000 r / min, and the dispersion time is 30 min to 45 min.

[0015] Preferably, in step three, the wet nitrogen is formed by mixing nitrogen and water vapor in a volume ratio of 95:5 to 98:2.

[0016] Preferably, in step 4, the mesh size of the boron nitride particles is 50 to 100 meshes.

[0017] Preferably, in step five, the mass ratio of the boron nitride particles to the boron nitride powder is 3:7 to 4:6, and the mixing is performed by planetary dry grinding, the dry grinding speed is 180 r / min to 220 r / min, and the dry grinding time is 4 h to 8 h to obtain a uniformly mixed powder.

[0018] Preferably, in step five, the isostatic pressing pressure is 200 MPa, and the pressure is maintained for 5 minutes.

[0019] Preferably, in step six, the sintering temperature is 2200° C. to 2400° C., and the insulation time is 4 h to 6 h.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The boron nitride materials used for molding in the present invention are all homemade powders with high material purity and no additional by-products. The two materials have a high degree of matching, and no phase change occurs during high-temperature sintering, and there is no size difference, so cracks are not easily formed.

[0022] 2. The preparation process of the present invention is simple, and the prepared boron nitride ceramic structure has good high-temperature stability and good thermal creep resistance, and can achieve long-term service in an ultra-high temperature quartz continuous melting furnace.

[0023] 3. The present invention realizes the nitridation reaction of high-purity boric acid and guanidine hydrochloride in a low temperature environment of about 700°C. Compared with the existing nitridation reaction, the reaction process of the present invention is faster. The reaction occurs based on the induction effect of ultra-high activity boron nitride powder, which amplifies the redox reaction between boric acid and boron nitride. Due to the presence of water vapor in wet nitrogen, water and boron generate boron hydroxide, and with the help of the auxiliary agent guanidine hydrochloride, boron nitride powder is generated under nitrogen conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 a is the surface of the continuous melting furnace after use for 1000 h in Example 1, and b is the fresh surface of the sample in Example 1. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0026] Example 1

[0027] Step 1: Use a blast drying oven to dry commercial high-purity boric acid and guanidine hydrochloride at a drying temperature of 55°C, then mix the high-purity boric acid and guanidine hydrochloride at a molar ratio of 1:1.5, use anhydrous ethanol as a solvent, dissolve the resulting solution in NH3 gas, heat to 45°C, and keep warm for 2 hours;

[0028] Step 2: adding hexagonal boron nitride nanopowder to the solution obtained in step 1, the amount of hexagonal boron nitride nanopowder added is 1% of the mass of high-purity boric acid, using a high-speed disperser to disperse the hexagonal boron nitride nanopowder, the speed of the high-speed disperser is 6000r / min, the dispersion time is 45min, and polyacrylamide is dripped into it, and the amount of polyacrylamide dripped into it is 1.5% of the mass of the hexagonal boron nitride nanopowder;

[0029] Step 3: passing liquid nitrogen into the suspension obtained in step 2 to obtain a mixture block, and then freeze-drying to obtain a high-polymer mixture with boron nitride as the core, passing wet nitrogen into the obtained mixture, the volume ratio of nitrogen to water vapor is 98:2, and the nitridation reaction temperature is 800° C. to obtain boron nitride powder;

[0030] Step 4: The boron nitride powder obtained in step 3 is washed with deionized water for 3 times, and then dried, and a portion of the obtained powder is dry-pressed into a mold, and then the obtained green body is calcined at a calcination temperature of 650° C. for 6 hours, and then the obtained sample is crushed to obtain boron nitride particles with a mesh size of 50 mesh;

[0031] Step 5: The boron nitride particles obtained in step 4 are mixed with the boron nitride powder in a mass ratio of 3:7, and the mixing is performed by planetary dry grinding, the dry grinding speed is 220r / min, and the dry grinding time is 8h to obtain a uniformly mixed powder; then dry pressing is performed, and the obtained green body is isostatically pressed at an isostatic pressing pressure of 200MPa and maintained for 5min to obtain a boron nitride green body;

[0032] Step 6: Sinter the obtained boron nitride green body at a sintering temperature of 2200°C for 6 hours in a nitrogen atmosphere. After natural cooling, boron nitride ceramics for quartz continuous melting furnace can be obtained.

[0033] Example 2

[0034] Step 1: Use a forced air drying oven to dry commercial high-purity boric acid and guanidine hydrochloride at a drying temperature of 55°C, then mix the high-purity boric acid and guanidine hydrochloride at a molar ratio of 1:1.1, use anhydrous ethanol as a solvent, pass NH3 gas into the resulting solution, heat it to 30°C, and keep it warm for 4 hours;

[0035] Step 2: adding hexagonal boron nitride nanopowder to the solution obtained in step 1, the amount of hexagonal boron nitride nanopowder added is 5% of the mass of high-purity boric acid, using a high-speed disperser to disperse the hexagonal boron nitride nanopowder, the speed of the high-speed disperser is 8000r / min, the dispersion time is 30min, and polyacrylamide is dripped into it, and the amount of polyacrylamide dripped into it is 1% of the mass of the hexagonal boron nitride nanopowder;

[0036] Step 3: passing liquid nitrogen into the suspension obtained in step 2 to obtain a mixture block, and then freeze-drying to obtain a high-polymer mixture with boron nitride as the core, passing wet nitrogen into the obtained mixture, the volume ratio of nitrogen to water vapor is 95:5, and the nitridation reaction temperature is 600° C. to obtain boron nitride powder;

[0037] Step 4: The boron nitride powder obtained in step 3 is washed with deionized water for 3 times, and then dried, a part of the obtained powder is dry-pressed, and then the obtained green body is calcined at a calcination temperature of 600°C for 8 hours, and then the obtained sample is crushed to obtain boron nitride particles with a mesh size of 70 meshes;

[0038] Step 5: The boron nitride particles obtained in step 4 are mixed with the boron nitride powder in a mass ratio of 4:6, and the mixing is performed by planetary dry grinding, the dry grinding speed is 220r / min, and the dry grinding time is 4h to obtain a uniformly mixed powder; then dry pressing is performed, and the obtained green body is isostatically pressed at an isostatic pressing pressure of 200MPa and the pressure is maintained for 5min to obtain a boron nitride green body;

[0039] Step 6: Sinter the obtained boron nitride blank at a sintering temperature of 2300°C for 4 hours in a nitrogen atmosphere. After natural cooling, boron nitride ceramics for quartz continuous melting furnace can be obtained.

[0040] Example 3

[0041] Step 1: Use a forced air drying oven to dry commercial high-purity boric acid and guanidine hydrochloride at a drying temperature of 55°C, then mix high-purity boric acid and guanidine hydrochloride at a molar ratio of 1:1.3, use anhydrous ethanol as a solvent, pass NH3 gas into the resulting solution, heat it to 40°C, and keep it warm for 3 hours;

[0042] Step 2: adding hexagonal boron nitride nanopowder to the solution obtained in step 1, the amount of hexagonal boron nitride nanopowder added is 2.5% of the mass of high-purity boric acid, using a high-speed disperser to disperse the hexagonal boron nitride nanopowder, the speed of the high-speed disperser is 7000r / min, the dispersion time is 30min, and polyacrylamide is dripped into it, and the amount of polyacrylamide dripped into it is 1.5% of the mass of the hexagonal boron nitride nanopowder;

[0043] Step 3: Liquid nitrogen is introduced into the suspension obtained in step 2 to obtain a mixture block, and then freeze-dried to obtain a high-polymer mixture with boron nitride as the core, and wet nitrogen is introduced into the obtained mixture, with a nitrogen to water vapor volume ratio of 97:3 and a nitridation reaction temperature of 700° C. to obtain boron nitride powder;

[0044] Step 4: The boron nitride powder obtained in step 3 is washed with deionized water for 3 times, and then dried, a part of the obtained powder is dry-pressed, and then the obtained green body is calcined at a calcination temperature of 625°C for 7 hours, and then the obtained sample is crushed to obtain boron nitride particles with a mesh size of 100 mesh;

[0045] Step 5: The boron nitride particles obtained in step 4 are mixed with the boron nitride powder in a mass ratio of 3.5:6.5, and the mixing is performed by planetary dry grinding, the dry grinding speed is 200r / min, and the dry grinding time is 6h to obtain a uniformly mixed powder; then dry pressing is performed, and the obtained green body is isostatically pressed, the isostatic pressing pressure is 200MPa, and the pressure is maintained for 5min to obtain a boron nitride green body;

[0046] Step 6: Sinter the obtained boron nitride blank at a sintering temperature of 2400°C for 4 hours in a nitrogen atmosphere. After natural cooling, boron nitride ceramics for quartz continuous melting furnace can be obtained.

[0047] Comparative Example 1

[0048] Step 1: Use a forced air drying oven to dry commercial high-purity boric acid and guanidine hydrochloride at a drying temperature of 55°C, then mix high-purity boric acid and guanidine hydrochloride at a molar ratio of 1:1.3, use anhydrous ethanol as a solvent, pass NH3 gas into the resulting solution, heat it to 40°C, and keep it warm for 3 hours;

[0049] Step 2: adding hexagonal boron nitride nanopowder to the solution obtained in step 1, the amount of hexagonal boron nitride nanopowder added is 2.5% of the mass of high-purity boric acid, using a high-speed disperser to disperse the hexagonal boron nitride nanopowder, the speed of the high-speed disperser is 7000r / min, the dispersion time is 30min, and polyacrylamide is dripped into it, and the amount of polyacrylamide dripped into it is 1.5% of the mass of the hexagonal boron nitride nanopowder;

[0050] Step 3: Liquid nitrogen is introduced into the suspension obtained in step 2 to obtain a mixture block, and then freeze-dried to obtain a high-polymer mixture with boron nitride as the core, and wet nitrogen is introduced into the obtained mixture, with a nitrogen to water vapor volume ratio of 97:3 and a nitridation reaction temperature of 700° C. to obtain boron nitride powder;

[0051] Step 4: The boron nitride powder obtained in step 3 is washed with deionized water for 3 times, and then dried, a portion of the obtained powder is dry-pressed, and then the obtained green body is calcined at a calcination temperature of 625°C for 7 hours, and then the obtained sample is crushed to obtain boron nitride particles with a mesh size of 50 to 100 meshes;

[0052] Step 5: dry-pressing the boron nitride particles obtained in step 4, and isostatically pressing the obtained green body, wherein the isostatic pressing pressure is 200 MPa and the pressure is maintained for 5 minutes to obtain a boron nitride green body;

[0053] Step 6: Sinter the obtained boron nitride blank at a sintering temperature of 2400°C for 4 hours in a nitrogen atmosphere. After natural cooling, boron nitride ceramics for quartz continuous melting furnace can be obtained.

[0054] Comparative Example 2

[0055] Step 1: Use a forced air drying oven to dry commercial high-purity boric acid and guanidine hydrochloride at a drying temperature of 55°C, then mix high-purity boric acid and guanidine hydrochloride at a molar ratio of 1:1.3, use anhydrous ethanol as a solvent, pass NH3 gas into the resulting solution, heat it to 40°C, and keep it warm for 3 hours;

[0056] Step 2: adding hexagonal boron nitride nanopowder to the solution obtained in step 1, the amount of hexagonal boron nitride nanopowder added is 2.5% of the mass of high-purity boric acid, using a high-speed disperser to disperse the hexagonal boron nitride nanopowder, the speed of the high-speed disperser is 7000r / min, the dispersion time is 30min, and polyacrylamide is dripped into it, and the amount of polyacrylamide dripped into it is 1.5% of the mass of the hexagonal boron nitride nanopowder;

[0057] Step 3: Liquid nitrogen is introduced into the suspension obtained in step 2 to obtain a mixture block, and then freeze-dried to obtain a high-polymer mixture with boron nitride as the core, and wet nitrogen is introduced into the obtained mixture, with a nitrogen to water vapor volume ratio of 97:3 and a nitridation reaction temperature of 700° C. to obtain boron nitride powder;

[0058] Step 4: dry-press the boron nitride powder obtained in step 3, and isostatically press the obtained green body at a pressure of 200 MPa and hold the pressure for 5 minutes to obtain a boron nitride green body;

[0059] Step 5: Sinter the obtained boron nitride green body at a sintering temperature of 2400°C for 4 hours in a nitrogen atmosphere. After natural cooling, boron nitride ceramics for quartz continuous melting furnace can be obtained.

[0060] Table 1 Mechanical properties and shrinkage of Examples 1 to 3

[0061]

[0062] from Figure 1 It can be seen from a that the surface ratio of the continuous melting furnace in Example 1 after 1000h use is Figure 1 b The fresh surface structure of the sample is more uniform and compact, indicating that the grain size of the sample has been further developed and no significant cracks are observed.

[0063] Hexagonal boron nitride nanopowder is added to a solution containing pure boric acid and guanidine hydrochloride, dispersed, and then dripped into polyacrylamide, freeze-dried, and then wet nitrogen is introduced to react with nitridation at 600-800°C to obtain boron nitride powder; the obtained powder is dry-pressed into a green body and then calcined, and then crushed to obtain boron nitride particles; the boron nitride powder and the boron nitride particles are mixed, dry-pressed into a green body, and then sintered to obtain a high-temperature resistant, non-shrinkage insulating boron nitride ceramic for a quartz continuous melting furnace, which has good fracture toughness, up to 1.41Mpa.m 1 / 2 The bending strength increases from 37Mpa to about 103Mpa. No phase change occurs during high-temperature sintering, and cracks are not easily formed. It can also be seen from Table 1 that the shrinkage index of the continuous melting furnace in Examples 1 to 3 is very small after 1000h and 2000h, and there is almost no difference, indicating that the high-temperature resistant non-shrinkage insulating boron nitride ceramic structure for the quartz continuous melting furnace prepared by the present invention has good high-temperature stability and good thermal creep resistance, solves the problem of boron nitride decomposition in ultra-high temperature environment, realizes the preparation of high-strength, non-shrinkage, insulating BN ceramics, and can achieve long-term service in ultra-high temperature quartz continuous melting furnaces.

[0064] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A method for preparing high temperature resistant non-shrinkage insulating boron nitride ceramics for quartz continuous melting furnace, characterized in that: The method specifically comprises the following steps: Step 1: Dry commercial high-purity boric acid and guanidine hydrochloride, then mix the high-purity boric acid and guanidine hydrochloride in a molar ratio of 1:1.1 to 1:1.5, dissolve them in anhydrous ethanol, pass gas through the resulting solution, heat it to 30°C to 45°C, and keep it warm for 2h to 4h; Step 2: adding hexagonal boron nitride nanopowder to the solution obtained in step 1 for high-speed dispersion, wherein the amount of hexagonal boron nitride nanopowder added is 1% to 5% of the mass of high-purity boric acid, and dripping polyacrylamide, wherein the amount of polyacrylamide dripped is 1% to 1.5% of the mass of the hexagonal boron nitride nanopowder; Step 3: passing liquid nitrogen into the suspension obtained in step 2 to obtain a mixture block, and then freeze-drying to obtain a high-polymer mixture with boron nitride as the core, passing wet nitrogen into the obtained mixture, and the nitridation reaction temperature is 600-800° C. to obtain boron nitride powder; Step 4: washing and drying the boron nitride powder obtained in step 3, and then dry-pressing the obtained powder, and then calcining the obtained green body at a calcination temperature of 600°C to 650°C for 6h to 8h, and then crushing the obtained sample to obtain boron nitride particles; Step 5: mixing the boron nitride particles obtained in step 4 with the boron nitride powder obtained in step 3, and then performing dry pressing to form the obtained green body, and performing isostatic pressing to form a boron nitride green body; Step 6: Sinter the boron nitride blank obtained in step 5 under an inert atmosphere, and obtain the boron nitride ceramic for quartz continuous melting furnace after natural cooling.

2. The method for preparing a high temperature resistant non-shrinkage insulating boron nitride ceramic for a quartz continuous melting furnace according to claim 1, characterized in that: In step 1, the gas introduced is ammonia.

3. The method for preparing a high temperature resistant non-shrinkage insulating boron nitride ceramic for a quartz continuous melting furnace according to claim 1, characterized in that: In step 2, the rotation speed used for the high-speed dispersion is 6000r / min to 8000r / min, and the dispersion time is 30min to 45min.

4. The method for preparing a high temperature resistant non-shrinkage insulating boron nitride ceramic for a quartz continuous melting furnace according to claim 1, characterized in that: In step 3, the wet nitrogen is prepared by mixing nitrogen and water vapor in a volume ratio of 95:5 to 98:

2.

5. The method for preparing a high temperature resistant non-shrinkage insulating boron nitride ceramic for a quartz continuous melting furnace according to claim 1, characterized in that: In step 4, the mesh size of the boron nitride particles is 50 to 100 meshes.

6. The method for preparing a high temperature resistant non-shrinkage insulating boron nitride ceramic for a quartz continuous melting furnace according to claim 1, characterized in that: In step 5, the mass ratio of the boron nitride particles to the boron nitride powder is 3:7 to 4:6, and the mixing is performed by planetary dry grinding at a dry grinding speed of 180 r / min to 220 r / min for 4 h to 8 h to obtain a uniformly mixed powder.

7. The method for preparing a high temperature resistant non-shrinkage insulating boron nitride ceramic for a quartz continuous melting furnace according to claim 1, characterized in that: In step 5, the isostatic pressing pressure is 200 MPa, and the pressure is maintained for 5 minutes.

8. The method for preparing a high temperature resistant non-shrinkage insulating boron nitride ceramic for a quartz continuous melting furnace according to claim 1, characterized in that: In step six, the sintering temperature is 2200° C. to 2400° C., and the insulation time is 4 h to 6 h.

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