Hafnium oxide ceramic as well as preparation method and application thereof

Abstract

The invention discloses hafnium oxide ceramic and a preparation method and application thereof, and belongs to the technical field of hafnium oxide ceramic preparation.The preparation method comprises the following steps that hafnium oxide powder with the purity larger than or equal to 99.9% and a binding agent are taken, the binding agent is melted, then the dried hafnium oxide powder and the binding agent are evenly mixed, and slurry is prepared; carrying out hot press molding and cooling on the slurry to prepare a blank, then carrying out gradient heating presintering on the blank, and removing the binder to prepare a biscuit; and carrying out gradient heating sintering treatment on the biscuit to obtain the ceramic. Other impurity components are not introduced into the hafnium oxide ceramic prepared by the method, and the hafnium oxide ceramic has the advantages of high purity, high density and no deformation, bending, cracking defect and other defects.

Description

Technical Field

[0001] The invention belongs to the technical field of hafnium oxide ceramic preparation, and in particular relates to a hafnium oxide ceramic and a preparation method and application thereof. Background Art

[0002] Hafnium oxide is an inorganic compound with the chemical formula HfO 2 , the theoretical density is 9.68g / cm 3 , with a melting point of 2840°C. Hafnium oxide has good electrical insulation properties and can be used to make capacitors, lasers, thermocouple sheaths in high-temperature measurement fields, etc.

[0003] High-purity and high-density hafnium oxide ceramics are currently widely used in the field of ultra-high temperature measurement. They are used as tungsten-rhenium thermocouple wire sheaths in oxidizing atmospheres above 2000°C. They have the advantages of anti-oxidation, corrosion resistance, and excellent insulation properties, and are irreplaceable by other materials.

[0004] However, the main problems and defects of the current high-purity and high-density hafnium oxide ceramics are: low purity, low density, complex existing formulas and processes, and difficulty in controlling quality consistency. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention provides a hafnium oxide ceramic and a preparation method and application thereof. The hafnium oxide ceramic prepared by the method does not introduce other impurities, has high purity and high density, and the product has no defects such as deformation, bending, cracking, etc.

[0006] To achieve the above purpose, the technical solution adopted by the present invention to solve the technical problem is:

[0007] A method for preparing hafnium oxide ceramics comprises the following steps:

[0008] (1) taking hafnium oxide powder with a purity of ≥99.9% and a binder, melting the binder, and then mixing the dried hafnium oxide powder and the binder to form a slurry;

[0009] (2) hot pressing the slurry into a shape, cooling it to obtain a blank, and then pre-sintering the blank by gradient temperature increase to remove the binder to obtain a green blank;

[0010] (3) The green blank is subjected to a gradient temperature rising sintering process to obtain a product.

[0011] Furthermore, in step (1), the particle size of the hafnium oxide powder is 1-3 μm.

[0012] Furthermore, in step (1), the mass ratio of hafnium oxide powder to binder is 75-90:20-25.

[0013] Furthermore, in step (1), the binder is paraffin wax.

[0014] Further, the specific procedure for gradient temperature rise pre-sintering in step (2) is as follows:

[0015] Raise the temperature from room temperature to 150°C, and the required time is 4 - 7 h;

[0016] Raise the temperature from 150°C to 400°C, and the required time is 8 - 12 h;

[0017] Raise the temperature from 400°C to 800°C, and the required time is 4 - 6 h;

[0018] Raise the temperature from 800°C to 1200°C, and the required time is 1 - 3 h;

[0019] Keep the temperature at 1200°C for 1 - 3 h.

[0020] Further, the procedure for gradient temperature rise sintering treatment in step (3) is as follows:

[0021] Raise the temperature from room temperature to 180°C, and the required time is 1 - 3 h;

[0022] Raise the temperature from 180°C to 450°C, and the required time is 2 - 4 h;

[0023] Raise the temperature from 450°C to 920°C, and the required time is 5 - 10 h;

[0024] Raise the temperature from 920°C to 1470°C, and the required time is 6 - 12 h;

[0025] Raise the temperature from 1470°C to 1750°C, and the required time is 4 - 6 h;

[0026] Keep the temperature at 1750°C for 2 - 4 h;

[0027] Lower the temperature from 1750°C to 1470°C, and the required time is 1 - 3 h;

[0028] Lower the temperature from 1470°C to 900°C, and the required time is 3 - 5 h.

[0029] A hafnium oxide ceramic is prepared by the above method.

[0030] The application of the above hafnium oxide ceramic in the preparation of a tungsten-rhenium thermocouple protective wire sleeve.

[0031] The beneficial effects produced by the present invention are:

[0032] In the present invention, ultrafine hafnium oxide powder is used as the raw material, and a variety of complex devices are prepared by means of hot pressing and sintering processes at normal temperature and pressure. The appearance of the products is uniform, without defects such as bending, deformation, and cracking. The purity of the prepared products is ≥99.9%, the bulk density is ≥9.4 g / cm3, reaching more than 97% of the theoretical density, and the grain size is 2 - 5 μm. The preparation process has the advantages of simple process flow and low cost, and no auxiliary sintering agent is used during the whole process, further reducing the introduction of impurities.

[0033] During sintering, the ceramic green body particles are in point contact. At high temperatures, substances fill the necks and pores between particles through different diffusion paths, causing the necks to gradually grow, the contact interfaces between particles to expand, the pores to shrink, and the densification degree to increase. Isolated pores are distributed at the grain intersection positions. With the increase of sintering temperature and the prolongation of sintering time, the grains continue to grow through diffusion mass transfer, and the pores move along with the grain boundaries until a dense ceramic is obtained. From the perspective of process control, this invention patent has two aspects. One is to select raw material powders with relatively high surface energy. Firstly, the initial particle size of the original powder is about 1 - 3 microns. There are various lattice defects on the surface and inside of the powder, which are in an unstable state, and its excess surface energy becomes the driving force for the sintering process. Secondly, the smaller size makes the migration path of the grains shorter, and the densification rate is faster. The other is a suitable sintering system. In the initial, middle, and final stages of sintering, the settings of the heating rate, firing temperature, and holding time enable the grains to obtain sufficient driving forces for diffusion mass transfer (such as surface diffusion, volume diffusion, etc.) to achieve the purpose of densification. Description of the Drawings

[0034] Figure 1 SEM image of the product in Example 3;

[0035] Figure 2 SEM image of the product in Comparative Example 1;

[0036] Figure 3 SEM image of the product in Comparative Example 2. Detailed Description of the Invention

[0037] In order to make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the following further details the present invention in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0038] Therefore, the following detailed description of the provided embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0039] It should be noted that relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising one..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the element.

[0040] The features and performance of the present invention will be further described in detail below in conjunction with embodiments and drawings.

[0041] Example 1

[0042] A hafnium oxide ceramic, the preparation method thereof comprising the following steps:

[0043] (1) Take dry hafnium oxide powder with a purity ≥ 99.9% and a particle size of 2 μm and paraffin. The mass ratio of hafnium oxide powder to binder is 75:25. Melt the paraffin into a liquid at 70 °C, and then mix the dry hafnium oxide powder with the paraffin to make a slurry.

[0044] (2) Hot press the slurry into a shape. The specific pressure is 0.6 MPa, the temperature of the charging cylinder is 90 °C, and the temperature of the injection port is 90 °C; cool and demold to obtain a blank, and then perform gradient temperature rise pre-sintering on the blank to remove the binder to obtain a green body. The specific procedure is as follows:

[0045] Raise the temperature from room temperature to 150 °C, and the required time is 4 h;

[0046] Raise the temperature from 150 °C to 400 °C, and the required time is 8 h;

[0047] Raise the temperature from 400 °C to 800 °C, and the required time is 4 h;

[0048] Raise the temperature from 800 °C to 1200 °C, and the required time is 1 h;

[0049] Keep the temperature at 1200 °C for 1 h;

[0050] (3) Gradient temperature rise sintering treatment is carried out on the green body, and the specific procedure is as follows:

[0051] The temperature is raised from room temperature to 180 °C, and the required time is 1 h;

[0052] The temperature is raised from 180 °C to 450 °C, and the required time is 2 h;

[0053] The temperature is raised from 450 °C to 920 °C, and the required time is 5 h;

[0054] The temperature is raised from 920 °C to 1470 °C, and the required time is 6 h;

[0055] The temperature is raised from 1470 °C to 1750 °C, and the required time is 4 h;

[0056] The holding time at 1750 °C is 2 h;

[0057] The temperature is lowered from 1750 °C to 1470 °C, and the required time is 1 h;

[0058] The temperature is lowered from 1470 °C to 900 °C, and the required time is 3 h.

[0059] Example 2

[0060] A hafnium oxide ceramic, and its preparation method includes the following steps:

[0061] (1) Take dry hafnium oxide powder with a purity ≥ 99.9% and a particle size of 3 μm and paraffin. The mass ratio of hafnium oxide powder to binder is 90:10. Melt the paraffin into a liquid at 70 °C, and then mix the dry hafnium oxide powder with the paraffin to make a slurry;

[0062] (2) Hot press the slurry into shape, with a specific pressure of 0.6 MPa, the temperature of the material holding cylinder is 90 °C, and the temperature of the injection port is 90 °C; Cool down and demold to obtain a blank, and then perform gradient temperature rise pre-sintering on the blank to remove the binder to obtain a green body. The specific procedure is as follows:

[0063] The temperature is raised from room temperature to 150 °C, and the required time is 7 h;

[0064] The temperature is raised from 150 °C to 400 °C, and the required time is 12 h;

[0065] The temperature is raised from 400 °C to 800 °C, and the required time is 6 h;

[0066] The temperature is raised from 800 °C to 1200 °C, and the required time is 3 h;

[0067] The holding time at 1200 °C is 3 h;

[0068] (3) Gradient temperature rise sintering treatment is carried out on the green body, and the specific procedure is as follows:

[0069] Heat the room temperature to 180°C, and the required time is 3 h;

[0070] Heat from 180°C to 450°C, and the required time is 4 h;

[0071] Heat from 450°C to 920°C, and the required time is 10 h;

[0072] Heat from 920°C to 1470°C, and the required time is 12 h;

[0073] Heat from 1470°C to 1750°C, and the required time is 6 h;

[0074] Keep the temperature at 1750°C for 4 h;

[0075] Cool from 1750°C to 1470°C, and the required time is 3 h;

[0076] Cool from 1470°C to 900°C, and the required time is 5 h.

[0077] Example 3

[0078] A hafnium oxide ceramic, and its preparation method comprises the following steps:

[0079] (1) Take dry hafnium oxide powder with a purity ≥ 99.9% and a particle size of 1 μm and paraffin. The mass ratio of hafnium oxide powder to binder is 85:15. Melt the paraffin into a liquid at 70°C, and then mix the dry hafnium oxide powder with the paraffin to make a slurry;

[0080] (2) Hot press the slurry into shape. The specific pressure is 0.6 MPa, the temperature of the material cylinder is 90°C, and the temperature of the injection port is 90°C; Cool and demold to obtain a blank, and then perform gradient temperature rise pre-sintering on the blank to remove the binder to obtain a green body. The specific procedure is as follows:

[0081] Heat the room temperature to 150°C, and the required time is 6 h;

[0082] Heat from 150°C to 400°C, and the required time is 10 h;

[0083] Heat from 400°C to 800°C, and the required time is 5 h;

[0084] Heat from 800°C to 1200°C, and the required time is 2 h;

[0085] Keep the temperature at 1200°C for 2 h;

[0086] (3) Perform gradient temperature rise sintering treatment on the green body. The specific procedure is as follows:

[0087] Heat the room temperature to 180°C, and the required time is 2 h;

[0088] Heat from 180°C to 450°C, and the required time is 3 h;

[0089] Heat up from 450 °C to 920 °C, the required time is 8 h;

[0090] Heat up from 920 °C to 1470 °C, the required time is 9 h;

[0091] Heat up from 1470 °C to 1750 °C, the required time is 5 h;

[0092] Keep the temperature at 1750 °C for 3 h;

[0093] Cool down from 1750 °C to 1470 °C, the required time is 2 h;

[0094] Cool down from 1470 °C to 900 °C, the required time is 4 h.

[0095] Comparative Example 1

[0096] A hafnium oxide ceramic, and its preparation method includes the following steps:

[0097] (1) Take dry hafnium oxide powder with a purity ≥ 99.9% and a particle size of 2 μm and paraffin. The mass ratio of hafnium oxide powder to binder is 85:15. Melt the paraffin into a liquid at 70 °C, and then mix the dry hafnium oxide powder with the paraffin to make a slurry;

[0098] (2) Hot press the slurry into a shape. The specific pressure is 0.6 MPa, the temperature of the material holding cylinder is 90 °C, and the temperature of the injection port is 90 °C; Cool down and demold to obtain a blank, and then perform gradient temperature rise pre-sintering on the blank to remove the binder to obtain a green body. The specific procedure is as follows:

[0099] Heat up from room temperature to 150 °C, the required time is 6 h;

[0100] Heat up from 150 °C to 400 °C, the required time is 10 h;

[0101] Heat up from 400 °C to 800 °C, the required time is 5 h;

[0102] Heat up from 800 °C to 1200 °C, the required time is 2 h;

[0103] Keep the temperature at 1200 °C for 2 h;

[0104] (3) Perform gradient temperature rise sintering treatment on the green body. The specific procedure is as follows:

[0105] Heat up from room temperature to 180 °C, the required time is 1 h;

[0106] Heat up from 180 °C to 920 °C, the required time is 5 h;

[0107] Heat up from 920 °C to 1700 °C, the required time is 6 h;

[0108] Keep the temperature at 1700°C for 3 hours;

[0109] Cool from 1700°C to 900°C, which takes 3 hours.

[0110] Comparative Example 2

[0111] A hafnium oxide ceramic, and its preparation method includes the following steps:

[0112] (1) Take dry hafnium oxide powder with a purity ≥ 99.9% and a particle size of 2 μm and paraffin. The mass ratio of hafnium oxide powder to binder is 85:15. Melt the paraffin into a liquid at 70°C, and then mix the dry hafnium oxide powder with the paraffin to make a slurry;

[0113] (2) Hot-press the slurry into shape. The specific pressure is 0.6 MPa, the temperature of the material cylinder is 90°C, and the temperature of the injection port is 90°C; Cool and demold to obtain a blank, and then perform gradient temperature rise pre-sintering on the blank to remove the binder to obtain a green body. The specific procedure is as follows:

[0114] Raise the temperature from room temperature to 150°C, which takes 4 hours;

[0115] Raise the temperature from 150°C to 400°C, which takes 6 hours;

[0116] Raise the temperature from 400°C to 800°C, which takes 3 hours;

[0117] Raise the temperature from 800°C to 1200°C, which takes 1 hour;

[0118] Raise the temperature from 1200°C to 1400°C, which takes 2 hours;

[0119] Keep the temperature at 1400°C for 2 hours;

[0120] (3) Perform gradient temperature rise sintering treatment on the green body. The specific procedure is as follows:

[0121] Raise the temperature from room temperature to 180°C, which takes 2 hours;

[0122] Raise the temperature from 180°C to 450°C, which takes 3 hours;

[0123] Raise the temperature from 450°C to 920°C, which takes 8 hours;

[0124] Raise the temperature from 920°C to 1470°C, which takes 9 hours;

[0125] Raise the temperature from 1470°C to 1750°C, which takes 5 hours;

[0126] Keep the temperature at 1750°C for 3 hours;

[0127] Cooling from 1750°C to 1470°C takes 2 hours;

[0128] Cooling from 1470°C to 900°C takes 4 hours.

[0129] Test Example

[0130] Taking the hafnium oxide materials prepared in Example 3 and Comparative Examples 1-2 as examples, the bulk density and purity of the materials were measured respectively, and the materials were scanned by electron microscopy. The specific results are shown in Table 1 and Figures 1-3 ;

[0131] Table 1: Measurement results

[0132] Case <![CDATA[Bulk density (g / cm 3 )]]> Product purity (%) Example 3 9.4 99.9 Comparative Example 1 9.1 99.9 Comparative Example 2 9.0 99.9

[0133] It can be seen from the data in the above table that the bulk density of the hafnium oxide product prepared by the method in Example 3 is as high as 9.4 g / cm 3 , which is significantly higher than the bulk density of the products in Comparative Examples 1-2.

[0134] Figure 1 Figure is the SEM image of the product in Example 3. The results show that the hafnium oxide grains are of uniform size, and the particle size ranges from 2 to 5 μm.

[0135] Figure 2 Figure is the SEM image of the product in Comparative Example 1. The results show that the hafnium oxide grains are of uneven size, and abnormally large grains are formed.

[0136] Figure 3 Figure is the SEM image of the product in Comparative Example 2. The results show that the hafnium oxide grains are of uneven size, and there are pores and agglomeration phenomena.

Claims

1. A method for preparing hafnium oxide ceramics, characterized in that: The following steps are involved: (1) taking hafnium oxide powder with a purity of ≥99.9% and a binder, melting the binder, and then mixing the dried hafnium oxide powder and the binder to form a slurry; (2) hot pressing the slurry into a shape, cooling it to obtain a blank, and then pre-sintering the blank by gradient temperature increase to remove the binder to obtain a green blank; (3) The green blank is subjected to a gradient temperature rising sintering process to obtain a product.

2. The method for preparing hafnium oxide ceramics according to claim 1, characterized in that: The particle size of the hafnium oxide powder in step (1) is 1-3 μm.

3. The method for preparing hafnium oxide ceramics according to claim 1, characterized in that: In step (1), the mass ratio of hafnium oxide powder to binder is 75-90:20-25.

4. The method for preparing hafnium oxide ceramics according to claim 1, characterized in that: In step (1), the binder is paraffin.

5. The method for preparing the hafnium oxide ceramic according to any one of claims 1 to 4, characterized in that: The specific procedure of the gradient temperature pre-sintering in step (2) is as follows: The room temperature is raised to 150°C, which takes 4-7 hours; The temperature rises from 150℃ to 400℃, and the time required is 8-12h; The temperature rises from 400℃ to 800℃, and the time required is 4-6h; The temperature rises from 800℃ to 1200℃, and the time required is 1-3h; 1200℃ holding time: 1-3h.

6. The method for preparing hafnium oxide ceramics according to claim 5, characterized in that: The gradient temperature rise sintering process in step (3) is as follows: The room temperature is raised to 180°C, which takes 1-3 hours; Heating from 180℃ to 450℃, the time required is 2-4h; Heating from 450℃ to 920℃ takes 5-10h; The temperature rises from 920℃ to 1470℃, and the time required is 6-12h; 1470℃ to 1750℃, the required time is 4-6h; 1750℃ holding time 2-4h; Cooling from 1750℃ to 1470℃ takes 1-3h; Cooling from 1470℃ to 900℃ takes 3-5h.

7. A hafnium oxide ceramic, characterized in that: The method according to any one of claims 1 to 6 is adopted to prepare the present invention.

8. Use of the hafnium oxide ceramic according to claim 7 in the preparation of tungsten-rhenium thermocouple sheathing.

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