High-purity high-density gadolinium oxide ceramic and preparation method thereof

Abstract

The invention discloses high-purity and high-density gadolinium oxide ceramic and a preparation method thereof, and belongs to the technical field of inorganic nonmetal hot pressed sintering. The preparation method comprises the following steps: firstly, pouring high-purity gadolinium oxide powder into a graphite mold, tamping and flattening, then transferring the mold into a vacuum hot-pressing furnace, carrying out normal-temperature pre-pressing, heating and pressurizing after pre-pressing, carrying out hot-pressing sintering, cooling after sintering, and annealing to obtain the high-purity and high-density gadolinium oxide ceramic. Through the raw powder hot-pressing limiting sintering technology, the defects and deficiencies of pressureless sintering are overcome, no sintering aid needs to be added, the high-quality gadolinium oxide ceramic with the density exceeding 7.5 g / cm < 3 > and the purity reaching 5N grade can be prepared, and the high-quality gadolinium oxide ceramic has good market competitiveness.

Description

Technical Field

[0001] The invention belongs to the technical field of inorganic non-metal hot pressing and sintering, and specifically relates to a high-purity and high-density gadolinium oxide ceramic and a preparation method thereof. Background Art

[0002] Gadolinium (Gd) element mainly exists in the form of gadolinium oxide (Gd2O3), of which 155 Gd and 157 The content of the two isotopes of Gd exceeds 30%, and it has a large thermal neutron absorption cross section (60900 and 254000 Barn respectively), so it can be widely used in the fields of nuclear physics and nuclear medicine for neutron shielding and neutron capture.

[0003] Gadolinium oxide ceramics are an important rare earth functional material. They are made by high-temperature treatment to form a dense, uniform ceramic body with certain microstructural characteristics from powdered gadolinium oxide raw materials. Gadolinium oxide ceramics have excellent electrical, optical, magnetic and high temperature resistance properties, and are widely used in electronic components, catalyst carriers, nuclear reactor control materials and other fields. The current existing gadolinium oxide ceramic preparation process usually adds sintering aids for pressureless sintering: such as adding additives such as yttrium aluminum garnet, titanium oxide or aluminum oxide, using anhydrous ethanol as a medium, using zirconium oxide balls for ball milling and mixing, drying under a vacuum environment, adding a binder, isostatically pressing at a pressure of 100-180 MPa, and then sintering the resulting molded body at 1400-1650 ℃. However, the sintering aids and binders in this process inevitably lead to a decrease in the purity of the resulting gadolinium oxide ceramic products, and the ability to improve the density of the ceramics is also relatively limited. Based on this, it is of great significance to study and produce a high-purity, high-density gadolinium oxide ceramic. Summary of the invention

[0004] In view of the problems raised by the background technology, the purpose of the present invention is to provide a high-purity and high-density gadolinium oxide ceramic and a preparation method thereof. The process of the present invention adopts the raw powder hot pressing limited sintering technology: no sintering aid is added, high pressure limited sintering is used during sintering to control the density; then annealing and decarbonization are performed to obtain high-purity and high-density gadolinium oxide ceramics.

[0005] The present invention provides a method for preparing high-purity and high-density gadolinium oxide ceramics, comprising the following steps: Step 1: Take high-purity gadolinium oxide powder, pour it into a graphite mold and compact it flat; Step 2: transfer the mold into a vacuum hot pressing furnace for pre-pressing at room temperature; Step 3: After pre-pressing, the temperature is increased and the pressure is increased to perform hot pressing sintering; Step 4: Cooling after sintering and then annealing to obtain high-purity and high-density gadolinium oxide ceramics.

[0006] Preferably, the purity of the high-purity gadolinium oxide powder in step 1 is 5N.

[0007] Preferably, the pressure value used for the normal temperature pre-pressing in step 2 is 10-20 MPa.

[0008] Preferably, the hot pressing sintering temperature in step 3 is 1150-1400°C, and the heating rate is 1-3°C / min.

[0009] Preferably, the hot pressing sintering pressure in step 3 is 60-80 MPa, and the heat preservation and pressure sintering time is 2-5h.

[0010] Preferably, the annealing temperature in step 4 is 1100-1500°C, and the annealing heating rate is 0.5-1.5°C / min.

[0011] Preferably, the annealing treatment time in step 4 is 10-20 h.

[0012] The present invention also provides a high-purity and high-density gadolinium oxide ceramic obtained by the above preparation method, the purity of which is 5N and the density is not less than 7.5 g / cm 3 , the appearance is white.

[0013] Pressureless sintering is also called normal pressure sintering. The sintering process is carried out without an external driving force. The sintering driving force mainly comes from the change in the surface free energy of the ceramic powder, that is, the reduction of the total surface area of ​​the powder and the decrease in the interface energy. However, for compounds with strong covalent bonds, due to their small self-diffusion coefficient, it is impossible to obtain dense products by solid phase sintering alone. It is necessary to adopt the method of adding sintering aids to reduce the grain boundary energy of the solid phase diffusion process and promote the densification of the material, which will inevitably lead to a decrease in purity. Based on this, the present invention adopts a sintering method of hot pressing limited sintering: first, the gadolinium oxide powder is placed in the mold cavity, and the powder is heated to the sintering temperature while being pressurized. Since the driving force is supplemented by the external pressure, densification can be achieved in a relatively short time, and a microstructure with fine and uniform grains is obtained, which helps to improve the mechanical properties of the material, reduce the sintering time, and reduce the sintering temperature. There is no need to use covalent bond ceramic sintering aids, which improves the high-temperature mechanical properties of the material while ensuring the purity of the product.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The hot pressing sintering process of the present invention does not require the addition of any additives, thus avoiding the introduction of other element impurities; the prepared gadolinium oxide ceramic has a high density (≥7.5 g / cm 3 ), compared with the density of the finished gadolinium oxide ceramics prepared by existing pressureless sintering (≈6.0 g / cm 3 ) is significantly improved; at the same time, the purity reaches 5N level, which has good market competitiveness. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the embodiments. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0016] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0017] The purity of the gadolinium oxide powder used in the experiment of the present invention is 99.999%, and its component detection report is shown in Table 1.

[0018] Table 1 Gadolinium oxide raw material composition test report

[0019] Example 1 A method for preparing high-purity and high-density gadolinium oxide ceramics, comprising the following steps: 1. Take 5N grade gadolinium oxide powder, pour it into the graphite mold, tamp and flatten it. Then transfer it to a vacuum hot press furnace and pre-press it at room temperature under a pressure of 15 MPa. After the pre-pressing is completed, heat it to 1300 °C at a rate of 2 °C / min, and sinter it under vacuum and a pressure of 65 MPa for 4 hours.

[0020] 2. After hot pressing and sintering, the product is cooled to room temperature in the furnace, and then the ceramic product is placed in a high-temperature box furnace, heated to 1200°C at a rate of 1°C / min, and kept at this temperature for 12 hours for annealing and decarbonization. After annealing, the product is cooled in the furnace to obtain gadolinium oxide ceramics.

[0021] Example 2 A method for preparing high-purity and high-density gadolinium oxide ceramics, comprising the following steps: 1. Take 5N grade gadolinium oxide powder, pour it into the graphite mold, and compact it. Then transfer it to a vacuum hot press furnace and pre-press it at room temperature under a pressure of 15 MPa. After the pre-pressing is completed, heat it to 1400 °C at a rate of 3 °C / min, and sinter it under vacuum and a pressure of 60 MPa for 2 h.

[0022] 2. After hot pressing and sintering, the product is cooled to room temperature in the furnace, and then the ceramic product is placed in a high-temperature box furnace, heated to 1200°C at a rate of 1°C / min, and kept at this temperature for 12 hours for annealing and decarbonization. After annealing, the product is cooled in the furnace to obtain gadolinium oxide ceramics.

[0023] Example 3 A method for preparing high-purity and high-density gadolinium oxide ceramics, comprising the following steps: 1. Take 5N grade gadolinium oxide powder, pour it into the graphite mold, tamp and flatten it. Then transfer it to a vacuum hot press furnace and pre-press it at room temperature under a pressure of 15 MPa. After the pre-pressing is completed, heat it to 1150 °C at a rate of 1 °C / min, and sinter it under vacuum and a pressure of 80 MPa for 5 hours.

[0024] 2. After hot pressing and sintering, the product is cooled to room temperature in the furnace, and then the ceramic product is placed in a high-temperature box furnace, heated to 1200°C at a rate of 1°C / min, and kept at this temperature for 12 hours for annealing and decarbonization. After annealing, the product is cooled in the furnace to obtain gadolinium oxide ceramics.

[0025] Example 4 A method for preparing high-purity and high-density gadolinium oxide ceramics, comprising the following steps: 1. Take 5N grade gadolinium oxide powder, pour it into the graphite mold, tamp and flatten it. Then transfer it to a vacuum hot press furnace and pre-press it at room temperature under a pressure of 15 MPa. After the pre-pressing is completed, heat it to 1300 °C at a rate of 2 °C / min, and sinter it under vacuum and a pressure of 65 MPa for 3 h.

[0026] 2. After hot pressing and sintering, the product is cooled to room temperature in the furnace, and then the ceramic product is placed in a high-temperature box furnace, heated to 1100 °C at a rate of 1.5 °C / min, and kept at this temperature for 15 h for annealing and decarbonization. After annealing, the product is cooled in the furnace to obtain gadolinium oxide ceramics.

[0027] Comparative Example 1 The step parameters are as in Example 1, except that the temperature of hot pressing sintering in step 1 is changed to 1100°C.

[0028] Comparative Example 2 The step parameters are as in Example 1, except that the pressure of hot pressing sintering in step 1 is changed to 35 MPa.

[0029] Comparative Example 3 The step parameters of Example 1 are referred to, except that the heating rate of hot pressing sintering in step 1 is changed to 5°C / min, and the heat preservation and pressure holding time is changed to 1 h.

[0030] Comparative Example 4 The step parameters are as in Example 1, except that the annealing temperature in step 2 is changed to 800°C.

[0031] Comparative Example 5 The step parameters are as in Example 1, except that in step 2, the temperature is raised to 1200° C. at a rate of 3° C. / min and kept at that temperature for 6 h.

[0032] The gadolinium oxide ceramic samples prepared in the above embodiments and comparative examples were tested, and the results are shown in Table 2.

[0033] Table 2 Test results of gadolinium oxide ceramic samples

[0034] The gadolinium oxide ceramic prepared in Example 1 was tested for composition, and the test report is as follows: Table 3 Test report of finished gadolinium oxide ceramic components

[0035] From the above, it can be seen that the sintering process of the present invention can maintain the purity of the gadolinium oxide raw material, and will not introduce impurities due to the sintering process, which effectively improves the purity of the obtained gadolinium oxide ceramic product; at the same time, the present invention can also greatly improve the density of the prepared ceramic product, which is significantly improved compared with the density of the ceramic obtained by conventional pressureless sintering. The present invention uses hot pressing limited sintering, and strictly controls the parameters such as the heating rate, sintering temperature, and hot pressing time during the sintering process to prepare a gadolinium oxide ceramic product with a density greater than 7.5 g / cm 3 , high-density and high-purity gadolinium oxide ceramics with a purity of up to 5N.

[0036] The embodiments described above only express several preferred embodiments of the present invention, and the descriptions thereof are relatively specific and detailed, but are not intended to limit the present invention. It should be noted that for those skilled in the art, the present invention may also have various changes and modifications, and any modifications, equivalent substitutions, improvements, etc. made within the concept and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing high-purity and high-density gadolinium oxide ceramics, characterized in that: The steps include: Step 1: Take high-purity gadolinium oxide powder, pour it into a graphite mold and compact it flat; Step 2: transfer the mold into a vacuum hot pressing furnace for pre-pressing at room temperature; Step 3: After pre-pressing, the temperature is increased and the pressure is increased to perform hot pressing sintering; Step 4: Cooling after sintering and then annealing to obtain high-purity and high-density gadolinium oxide ceramics.

2. The method for preparing a high-purity and high-density gadolinium oxide ceramic according to claim 1, characterized in that: The purity of the high-purity gadolinium oxide powder in step 1 is 5N.

3. The method for preparing a high-purity and high-density gadolinium oxide ceramic according to claim 1, characterized in that: The pressure value used in the normal temperature pre-pressing in step 2 is 10-20 MPa.

4. The method for preparing a high-purity and high-density gadolinium oxide ceramic according to claim 1, characterized in that: In step 3, the temperature of the hot pressing sintering is 1150-1400°C, and the heating rate is 1-3°C / min.

5. The method for preparing a high-purity and high-density gadolinium oxide ceramic according to claim 1, characterized in that: The pressure value of the hot pressing sintering in step 3 is 60-80 MPa, and the heat preservation and pressure holding sintering time is 2-5 h.

6. The method for preparing a high-purity and high-density gadolinium oxide ceramic according to claim 1, characterized in that: The annealing temperature in step 4 is 1100-1500° C., and the annealing heating rate is 0.5-1.5° C. / min.

7. The method for preparing a high-purity and high-density gadolinium oxide ceramic according to claim 1, characterized in that: The annealing treatment time in step 4 is 10-20 h.

8. The high-purity and high-density gadolinium oxide ceramic obtained by the preparation method according to any one of claims 1 to 7.

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