Hafnium oxide ceramic, preparation method and application thereof

Abstract

The present invention discloses a hafnium oxide ceramic, its preparation method, and application, belonging to the technical field of hafnium oxide ceramic preparation. The preparation method comprises the following steps: 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; hot pressing the slurry into a blank, cooling it to form a blank, and then subjecting the blank to a gradient temperature pre-sintering process to remove the binder to form a green blank; and subjecting the green blank to a gradient temperature sintering process to form a green blank. The hafnium oxide ceramic prepared using this method does not introduce other impurities, has high purity and density, and is free of defects such as deformation, bending, cracking, and defects.

Description

Technical Field

[0001] The present 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 HfO2 and a theoretical density of 9.68 g / 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. Their advantages lie in their antioxidant, corrosion resistance, and excellent insulation properties, making them irreplaceable by other materials.

[0004] However, the main problems and defects of 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 response to the above-mentioned deficiencies in the prior art, the present invention provides a hafnium oxide ceramic, a preparation method and application thereof. The hafnium oxide ceramic prepared by this method does not introduce other impurities, has high purity and high density, and is free from defects such as deformation, bending, cracking and defects.

[0006] To achieve the above-mentioned 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 dry 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 heating 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, the particle size of the hafnium oxide powder in step (1) 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] Furthermore, the specific procedure of the gradient temperature pre-sintering in step (2) is as follows:

[0015] The room temperature is raised to 150°C, which takes 4-7 hours;

[0016] Heating from 150℃ to 400℃ takes 8-12h;

[0017] Heating from 400℃ to 800℃ takes 4-6h;

[0018] Heating from 800℃ to 1200℃ takes 1-3h;

[0019] 1200℃ holding time: 1-3h.

[0020] Furthermore, the gradient temperature rising sintering process in step (3) is as follows:

[0021] The room temperature is raised to 180°C, which takes 1-3 hours;

[0022] Heating from 180℃ to 450℃ takes 2-4h;

[0023] Heating from 450℃ to 920℃ takes 5-10h;

[0024] Heating from 920℃ to 1470℃ takes 6-12h;

[0025] Heating from 1470℃ to 1750℃ takes 4-6 hours;

[0026] 1750℃ holding time 2-4h;

[0027] Cooling from 1750℃ to 1470℃ takes 1-3h;

[0028] Cooling from 1470℃ to 900℃ takes 3-5h.

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

[0030] The hafnium oxide ceramic is used in the preparation of tungsten-rhenium thermocouple sheaths.

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

[0032] The present invention uses ultrafine hafnium oxide powder as raw material and utilizes hot pressing and room temperature and pressure sintering processes to prepare a variety of complex devices. The product appearance is uniform, without defects, bending, denaturation, cracking and other problems. The purity of the prepared product is ≥99.9%, the volume density is ≥9.4g / cm3, reaching more than 97% of the theoretical density, and the grain size is 2-5μm. The preparation process has the advantages of simple flow and low cost, and no auxiliary sintering agent is used in the entire 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 the particles through different diffusion pathways, causing the necks to gradually grow, the contact interface between the particles to expand, the pores to shrink, and the degree of densification to increase. Isolated pores are distributed at the intersection of the grains. As the sintering temperature increases and the sintering time increases, the grains continue to grow through diffusion and mass transfer, and the pores move along with the grain boundaries until a densified ceramic is obtained. From the perspective of process control, the patent of the present invention considers the following: first, a raw material powder with high surface energy is selected. First, the initial particle size of the original powder is about 1-3 microns. Various lattice defects appear on the surface and inside the powder, making it unstable. Its excess surface energy becomes the driving force of the sintering process. Secondly, the smaller the size, the shorter the migration path of the grains, and the faster the densification rate. Second, a suitable sintering system is used. In the early, middle and final stages of sintering, the setting of the heating rate, firing temperature and holding time allows the grains to obtain sufficient driving force for diffusion and mass transfer (surface diffusion, volume diffusion, etc.) to achieve the purpose of densification. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0036] Figure 3 This is the SEM image of the product in Comparative Example 2. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. That is, the embodiments described are only part of the embodiments of the present invention, rather than all embodiments.

[0038] Therefore, the detailed description of the embodiments of the present invention provided below is not intended to limit the scope of the invention as claimed, but is merely intended to represent 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 work are within the scope of protection of the present invention.

[0039] It should be noted that relational terms such as "first" and "second" are used only 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 "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or apparatus comprising the element.

[0040] The features and performance of the present invention are further described in detail below with reference to the embodiments and drawings.

[0041] Example 1

[0042] A hafnium oxide ceramic, the preparation method of which comprises the following steps:

[0043] (1) preparing a slurry by mixing dry hafnium oxide powder with a purity of ≥99.9% and a particle size of 2 μm with paraffin wax, wherein the mass ratio of hafnium oxide powder to binder is 75:25, melting the paraffin wax at 70°C to form a liquid, and then mixing the dry hafnium oxide powder and the paraffin wax to form a slurry;

[0044] (2) The slurry is hot-pressed at a pressure of 0.6 MPa, a barrel temperature of 90°C, and a nozzle temperature of 90°C; cooled, demolded, and a blank is obtained; the blank is then pre-sintered at a gradient temperature to remove the binder and obtain a green blank. The specific procedure is as follows:

[0045] The room temperature is raised to 150°C, which takes 4 hours;

[0046] The temperature rises from 150℃ to 400℃, which takes 8 hours;

[0047] The temperature rises from 400℃ to 800℃, which takes 4 hours;

[0048] The temperature is raised from 800℃ to 1200℃, which takes 1 hour;

[0049] 1200℃ holding time 1h;

[0050] (3) The green billet is subjected to a gradient temperature sintering process. The specific procedure is as follows:

[0051] The room temperature is raised to 180°C, which takes 1 hour;

[0052] Heating from 180℃ to 450℃ takes 2h;

[0053] Heating from 450℃ to 920℃ takes 5h;

[0054] Heating from 920℃ to 1470℃ takes 6h;

[0055] 1470℃ to 1750℃, the required time is 4h;

[0056] 1750℃ holding time 2h;

[0057] Cooling from 1750℃ to 1470℃ takes 1 hour;

[0058] It takes 3 hours to cool from 1470℃ to 900℃.

[0059] Example 2

[0060] A hafnium oxide ceramic, the preparation method of which comprises the following steps:

[0061] (1) preparing a slurry by mixing dry hafnium oxide powder with a purity of ≥99.9% and a particle size of 3 μm with paraffin wax, wherein the mass ratio of hafnium oxide powder to binder is 90:10, melting the paraffin wax at 70°C to form a liquid, and then uniformly mixing the dry hafnium oxide powder and the paraffin wax to form a slurry;

[0062] (2) The slurry is hot-pressed at a pressure of 0.6 MPa, a barrel temperature of 90°C, and a nozzle temperature of 90°C; cooled, demolded, and a blank is obtained; the blank is then pre-sintered at a gradient temperature to remove the binder and obtain a green blank. The specific procedure is as follows:

[0063] The room temperature is raised to 150°C, which takes 7 hours;

[0064] The temperature rises from 150℃ to 400℃, which takes 12 hours;

[0065] The temperature rises from 400℃ to 800℃, which takes 6 hours;

[0066] The temperature is raised from 800℃ to 1200℃, which takes 3 hours;

[0067] 1200℃ holding time 3h;

[0068] (3) The green billet is subjected to a gradient temperature sintering process. The specific procedure is as follows:

[0069] The room temperature is raised to 180°C, which takes 3 hours;

[0070] The temperature is raised from 180℃ to 450℃, which takes 4 hours;

[0071] Heating from 450℃ to 920℃ takes 10h;

[0072] Heating from 920℃ to 1470℃ takes 12h;

[0073] The temperature is raised from 1470℃ to 1750℃, which takes 6 hours.

[0074] 1750℃ holding time 4h;

[0075] Cooling from 1750℃ to 1470℃ takes 3h;

[0076] The temperature is cooled from 1470℃ to 900℃, which takes 5 hours.

[0077] Example 3

[0078] A hafnium oxide ceramic, the preparation method of which comprises the following steps:

[0079] (1) preparing a slurry by mixing dry hafnium oxide powder with a purity of ≥99.9% and a particle size of 1 μm with paraffin wax, wherein the mass ratio of hafnium oxide powder to binder is 85:15, melting the paraffin wax at 70°C to form a liquid, and then mixing the dry hafnium oxide powder and the paraffin wax to form a slurry;

[0080] (2) The slurry is hot-pressed at a pressure of 0.6 MPa, a barrel temperature of 90°C, and a nozzle temperature of 90°C; cooled, demolded, and a blank is obtained; the blank is then pre-sintered at a gradient temperature to remove the binder and obtain a green blank. The specific procedure is as follows:

[0081] The room temperature is raised to 150°C, which takes 6 hours;

[0082] The temperature is raised from 150℃ to 400℃, which takes 10 hours;

[0083] The temperature is raised from 400℃ to 800℃, which takes 5 hours;

[0084] The temperature is raised from 800℃ to 1200℃, which takes 2h;

[0085] 1200℃ holding time 2h;

[0086] (3) The green billet is subjected to a gradient temperature sintering process. The specific procedure is as follows:

[0087] The room temperature is raised to 180°C, which takes 2 hours;

[0088] Heating from 180℃ to 450℃ takes 3h;

[0089] Heating from 450℃ to 920℃ takes 8h;

[0090] Heating from 920℃ to 1470℃ takes 9h;

[0091] Heating from 1470℃ to 1750℃ takes 5h;

[0092] 1750℃ holding time 3h;

[0093] Cooling from 1750℃ to 1470℃ takes 2h;

[0094] The temperature is cooled from 1470℃ to 900℃, which takes 4 hours.

[0095] Comparative Example 1

[0096] A hafnium oxide ceramic, the preparation method of which comprises the following steps:

[0097] (1) preparing a slurry by mixing dry hafnium oxide powder with a purity of ≥99.9% and a particle size of 2 μm with paraffin wax, wherein the mass ratio of hafnium oxide powder to binder is 85:15, melting the paraffin wax at 70°C to form a liquid, and then uniformly mixing the dry hafnium oxide powder and the paraffin wax to form a slurry;

[0098] (2) The slurry is hot-pressed at a pressure of 0.6 MPa, a barrel temperature of 90°C, and a nozzle temperature of 90°C; cooled, demolded, and a blank is obtained; the blank is then pre-sintered at a gradient temperature to remove the binder and obtain a green blank. The specific procedure is as follows:

[0099] The room temperature is raised to 150°C, which takes 6 hours;

[0100] The temperature is raised from 150℃ to 400℃, which takes 10 hours;

[0101] The temperature is raised from 400℃ to 800℃, which takes 5 hours;

[0102] The temperature is raised from 800℃ to 1200℃, which takes 2h;

[0103] 1200℃ holding time 2h;

[0104] (3) The green billet is subjected to a gradient temperature sintering process. The specific procedure is as follows:

[0105] The room temperature is raised to 180°C, which takes 1 hour;

[0106] Heating from 180℃ to 920℃ takes 5h;

[0107] The temperature rises from 920℃ to 1700℃, which takes 6 hours;

[0108] 1700℃ holding time 3h;

[0109] It takes 3 hours to cool from 1700℃ to 900℃.

[0110] Comparative Example 2

[0111] A hafnium oxide ceramic, the preparation method of which comprises the following steps:

[0112] (1) preparing a slurry by mixing dry hafnium oxide powder with a purity of ≥99.9% and a particle size of 2 μm with paraffin wax, wherein the mass ratio of hafnium oxide powder to binder is 85:15, melting the paraffin wax at 70°C to form a liquid, and then uniformly mixing the dry hafnium oxide powder and the paraffin wax to form a slurry;

[0113] (2) The slurry is hot-pressed at a pressure of 0.6 MPa, a barrel temperature of 90°C, and a nozzle temperature of 90°C; cooled, demolded, and a blank is obtained; the blank is then pre-sintered at a gradient temperature to remove the binder and obtain a green blank. The specific procedure is as follows:

[0114] The room temperature is raised to 150°C, which takes 4 hours;

[0115] The temperature rises from 150℃ to 400℃, which takes 6 hours;

[0116] The temperature is raised from 400℃ to 800℃, which takes 3h;

[0117] The temperature is raised from 800℃ to 1200℃, which takes 1 hour;

[0118] The temperature is raised from 1200℃ to 1400℃, which takes 2 hours;

[0119] 1400℃ holding time 2h;

[0120] (3) The green billet is subjected to a gradient temperature sintering process. The specific procedure is as follows:

[0121] The room temperature is raised to 180°C, which takes 2 hours;

[0122] Heating from 180℃ to 450℃ takes 3h;

[0123] Heating from 450℃ to 920℃ takes 8h;

[0124] Heating from 920℃ to 1470℃ takes 9h;

[0125] Heating from 1470℃ to 1750℃ takes 5h;

[0126] 1750℃ holding time 3h;

[0127] Cooling from 1750℃ to 1470℃ takes 2h;

[0128] The temperature is cooled from 1470℃ to 900℃, which 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, and the materials were scanned by electron microscope. The specific results are shown in Tables 1 and Figure 1-3 ;

[0131] Table 1: Measurement results

[0132] Case <![CDATA[Apparent 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] The data in the table above show that the volume 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 product volume density in Comparative Example 1-2.

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

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

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

Claims

1. A method for preparing hafnium oxide ceramics, characterized in that: The following steps are involved: (1) Take hafnium oxide powder with a purity of ≥99.9% and a binder, melt the binder, and then mix the dry hafnium oxide powder and the binder to form a slurry. The particle size of the hafnium oxide powder is 1-3 μm; (2) The slurry is hot-pressed and cooled to obtain a blank, which is then subjected to gradient temperature pre-sintering to remove the binder and obtain a green blank. The specific procedure for gradient temperature pre-sintering is as follows: The room temperature is raised to 150°C, which takes 4-7 hours; Heating from 150℃ to 400℃ takes 8-12h; Heating from 400℃ to 800℃ takes 4-6h; Heating from 800℃ to 1200℃ takes 1-3h; 1200℃ holding time 1-3h; (3) The green blank is subjected to a gradient temperature rise sintering process to obtain a green blank; the gradient temperature rise sintering process procedure is as follows: The room temperature is raised to 180°C, which takes 1-3 hours; Heating from 180℃ to 450℃ takes 2-4h; Heating from 450℃ to 920℃ takes 5-10h; Heating from 920℃ to 1470℃ takes 6-12h; Heating from 1470℃ to 1750℃ takes 4-6 hours; 1750℃ holding time 2-4h; Cooling from 1750℃ to 1470℃ takes 1-3h; Cooling from 1470℃ to 900℃ takes 3-5h.

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

3. The method for preparing hafnium oxide ceramics according to claim 1, wherein: In step (1), the binder is paraffin wax.

4. A hafnium oxide ceramic, characterized in that: The method according to any one of claims 1 to 3 is adopted to prepare the present invention.

5. Use of the hafnium oxide ceramic according to claim 4 in the preparation of tungsten-rhenium thermocouple sheathing.

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