CN113200746A

CN113200746A - Method for preparing infrared transparent ceramic through pressureless rapid sintering

Info

Publication number: CN113200746A
Application number: CN202110483166.3A
Authority: CN
Inventors: 范金太; 沈宗云; 钱凯臣; 张龙; 冯涛; 姜本学; 冯明辉; 张露露; 范翔龙; 陈柏键
Original assignee: Shanghai Institute of Optics and Fine Mechanics of CAS
Current assignee: Shanghai Institute of Optics and Fine Mechanics of CAS
Priority date: 2021-04-30
Filing date: 2021-04-30
Publication date: 2021-08-03

Abstract

A method for preparing infrared transparent ceramics by pressureless fast sintering comprises the steps of firstly pressing and forming nano powder into ceramic biscuit, putting the biscuit into a muffle furnace for presintering to eliminate internal stress, then putting the biscuit into a discharge plasma sintering furnace, starting discharge plasma fast sintering without applying external pressure, cooling and taking out after sintering, and annealing a sample to obtain infrared transparent ceramics with compact nano crystal grains, wherein the density of the obtained ceramic sample is higher than 95%, the size of the crystal grains is smaller than 250nm, and the infrared transparent ceramics have better optical performance and mechanical performance.

Description

Method for preparing infrared transparent ceramic through pressureless rapid sintering

Technical Field

The invention relates to a process for preparing transparent ceramic through pressureless rapid sintering, and belongs to the field of preparation of transparent ceramic materials.

Background

Mature ceramic forming and sintering technologies have been in history for thousands of years, and pottery and porcelain prepared by different sintering process technologies meet different requirements of people in production and life. In recent years, the high-performance ceramic with the densified fine grains prepared by adopting different sintering process technologies has better optical, mechanical, thermal, electrical and magnetic properties, meets more practical application requirements such as environmental protection, security protection, military industry, national defense and the like, and is pursued by related scientific researchers all the time. According to the Hall-Petch relationship, the smaller the grain size of the ceramic, the higher the hardness and strength. In the nanocrystalline ceramics, the smaller the crystal grain size and the higher the relative density, the smaller the loss such as optical scattering and absorption, and the closer the transmittance is to the theoretical transmittance, the wider the transmission band is.

By Y₂O₃Preparing Y from-MgO composite nano powder₂O₃The volume ratio of two phases of MgO is close to 1:1, the two phases are uniformly distributed, the mid-infrared transmittance can reach 84%, the theoretical transmittance is close, the room-temperature bending strength is over 400MPa, and the high-temperature (600 ℃) bending strength is over 350 MPa. The infrared emissivity at the high temperature of 300 ℃ is lower than 0.02, which is superior to the prior infrared transparent ceramics, such as sapphire, spinel, zirconia and the like. The material can realize high near-infrared transmittance and visible translucency under the conditions of extremely fine grain size and high density, and becomes a hope and an important candidate for future hypersonic aircraft infrared window materials.

At present, there are many sintering techniques for making densified fine grain ceramics, such as hot press sintering(HP), conventional post-sinter assisted Hot Isostatic Pressing (HIP), and the like, can produce dense ceramics. But Y prepared by these sintering processes₂O₃MgO nano complex phase ceramic products have problems, such as uneven density of large-size samples prepared by hot-pressing sintering and poor overall performance; the grain size of the samples sintered by conventional post-sintering assisted hot isostatic pressing is relatively large (>300nm), the average transmittance is low, the bending strength is greatly reduced, and the optimization is difficult; the sample prepared by adopting the hot-pressing sintering process is sintered, and carbon-containing groups remained in the sample are difficult to completely remove due to carbon diffusion pollution of the graphite mold at high temperature, so that the thermal, optical, mechanical and other properties of the product can be influenced, the high-temperature properties such as thermal shock resistance and the like of the sample are unfavorable, and the Y is finally influenced₂O₃-comprehensive properties of the MgO nano complex phase ceramic product.

Lihong Liu et al [ Lihong Liu, Koji Morita, Tohru S.Suzuki, Byung-Nam Kim. evolution of microstructure, mechanical, and optical properties of Y in Japan, 2020₂O₃-MgO nanocomposites fabricated by high pressure spark plasma sintering[J].Journal of the European Ceramic Society,2020,40(13):4547–4555.]Reports that high-quality Y of high-density nanocrystalline grains is prepared by adopting high-voltage auxiliary discharge plasma sintering technology₂O₃-MgO complex phase infrared transparent ceramics. However, the research also has some defects, carbon pollution which is difficult to completely eliminate exists in samples prepared by the high-voltage assisted spark plasma sintering technology, the requirements on equipment and used molds are high, and high-performance samples with large sizes and complex shapes are difficult to prepare. Therefore, exploring the sintering preparation technology for efficiently preparing high-quality large-size compact nanocrystalline ceramic products is a difficult problem to be solved in industrialization and low-cost production, and the pressure-free auxiliary discharge plasma rapid sintering technology provided by the method of the invention just effectively solves the problems, and has great significance for low-cost large-scale production and industrialization.

Disclosure of Invention

The invention aims to provide a method for preparing infrared transparent ceramics by pressureless rapid sintering,overcomes the defects of the existing ceramic sintering preparation process in the aspects of simultaneously realizing densification, grain refinement and high-quality large-size preparation. The method comprises the steps of placing a ceramic biscuit which is formed by pressing nanometer powder in a muffle furnace for presintering to eliminate internal stress, then placing the biscuit in a discharge plasma sintering furnace, starting discharge plasma rapid sintering without applying external pressure, cooling and taking out after sintering, and annealing a sample to prepare the fine-grain densified infrared transparent ceramic and the product thereof. Y prepared by the method₂O₃High density of MgO nano complex phase ceramic sample (2)>95%) fine grain size<200nm) in a spark plasma sintering furnace, reaches the sintering temperature at a very fast temperature rise rate, shortens the temperature rise time, maintains the sintering activity of the ceramic biscuit, inhibits the abnormal growth of the grain diameter of powder grains in the slow temperature rise stage of the conventional sintering, solves the problem of the reduction of the sintering activity of the powder in the longer temperature rise process, and the ceramic biscuit is fast and compact in the high-temperature sintering stage, and can simultaneously realize the densification of an exhaust hole and the maintenance of fine grains in a short time. The biscuit is placed in a muffle furnace for pre-sintering in advance, which is beneficial to eliminating the internal stress of the sample in the forming process and reducing the moisture absorbed by the sample from the environment in the preparation process. The method needs short sintering time and does not need to apply external pressure for assistance; the sintering process is simple, the experimental period is short, the production cost is low, and the method is suitable for preparing samples with any shapes and is convenient for industrial production.

The technical scheme of the invention is as follows:

and placing the ceramic biscuit which is formed by pressing the nano powder in a muffle furnace for presintering to eliminate internal stress, then placing the biscuit in a discharge plasma sintering furnace, performing discharge plasma rapid sintering without applying external pressure, cooling and taking out after sintering, and annealing the sample to obtain the fine-grain densified infrared transparent ceramic and the product thereof.

The preparation method comprises the following specific steps:

step 1.1), weighing a proper amount of nano powder, performing dry pressing by using a mould to form a blank, and performing cold isostatic pressing treatment to obtain a ceramic biscuit;

step 1.2) putting the ceramic biscuit in the step 1.1) into a muffle furnace for pre-sintering, eliminating the internal stress of a sample, and cooling along with the furnace after pre-sintering and taking out for later use;

step 1.3) putting the ceramic biscuit obtained in the step 1.2) into a discharge plasma sintering furnace, carrying out non-pressure discharge plasma rapid sintering without applying external pressure, and cooling and taking out after sintering;

step 1.4) annealing the sample obtained in step 1.3) to obtain a compact nano-crystalline ceramic sample.

The pressureless rapid sintering process for producing infrared transparent ceramics according to claim, wherein:

the nano powder in the step 1.1) is Y₂O₃Nano powder and Al₂O₃Nano powder, ZrO₂Nanopowder or Y₂O₃-MgO composite nanopowder with a powder grain size of 5-100 nm.

The pressure in the dry pressing of the step 1.1) is 3-15 MPa.

The cold isostatic pressing pressure in the step 1.1) is 100-250MPa, and the pressure maintaining time is 2-20 min.

The muffle furnace presintering temperature rising rate in the step 1.2) is 0.5-10 ℃/min, the presintering temperature is 800-1200 ℃, the presintering time is 20-300min, and the internal stress of the sample is eliminated.

The pressureless discharge plasma rapid sintering in the step 1.3) does not apply external pressure to the ceramic biscuit, and the discharge plasma rapid sintering is directly carried out.

The pressureless discharge plasma rapid sintering in the step 1.3) has the temperature rise rate of 15-300 ℃/min, the sintering temperature of 1250-.

The annealing treatment in the step 1.4) has the annealing temperature of 800-1100 ℃ and the annealing time of 10-30 hours.

The relative compactness of the nano-crystalline ceramic sample in the step 1.4) is between 95% and 100%.

The nano-crystalline grain ceramic sample in the step 1.4) has the grain size of 30-250 nm.

Compared with the prior art, the invention has the technical effects that:

the compact fine-grain nano complex-phase ceramic sample obtained by the method has higher relative density (> 95%) and fine grain size (<250nm), and is superior to a sample prepared by auxiliary hot isostatic pressing sintering after conventional sintering. The method is characterized in that a sample subjected to presintering treatment reaches the sintering temperature at a very fast temperature rise rate, the temperature rise time is greatly shortened, the sintering activity of a ceramic biscuit is maintained, abnormal growth of the grain size of powder grains in a slow temperature rise stage of conventional sintering is inhibited, the problem of reduction of the sintering activity of powder in a longer temperature rise process is solved, the ceramic biscuit is fast and compact in a high-temperature sintering stage, air holes can be removed and fine grains can be maintained in a short time, and the prepared sample has good optical performance and mechanical performance. And the method with lower cost can be easily used for preparing other oxides or oxide composite ceramic materials.

The method has short sintering time and does not need additional pressure assistance; the sintering process is simple, the experimental period is short, the production cost is low, and the method is suitable for preparing samples with any shapes and is convenient for industrial production. The pressureless discharge plasma rapid sintering technology provided by the method effectively solves a plurality of problems in the process of preparing high-quality large-size compact nanocrystalline ceramic products with high efficiency, and has great significance for low-cost large-scale production and industrialization.

Drawings

FIG. 1 shows the dense nanocrystal particle Y prepared in example 1₂O₃Infrared transmittance curve of the MgO complex phase infrared transparent ceramic, wherein (a) is near infrared transmittance curve and (b) is intermediate infrared transmittance curve.

FIG. 2 shows the compact nanocrystal particle Y obtained in example 1₂O₃SEM topography of the MgO complex phase infrared transparent ceramic.

FIG. 3 shows the compact nanocrystal particle Y obtained in example 2₂O₃Infrared transmittance curve of the MgO complex phase infrared transparent ceramic, wherein (a) is near infrared transmittance curve and (b) is intermediate infrared transmittance curve.

FIG. 4 shows the compact nanocrystal particle Y obtained in example 2₂O₃SEM topography of the MgO complex phase infrared transparent ceramic.

FIG. 5 shows the compact nanocrystal particle Y obtained in example 3₂O₃Infrared transmittance curve of the MgO complex phase infrared transparent ceramic, wherein (a) is near infrared transmittance curve and (b) is intermediate infrared transmittance curve.

FIG. 6 shows the compact nanocrystal particle Y obtained in example 3₂O₃SEM topography of the MgO complex phase infrared transparent ceramic.

Detailed Description

Following by adopting Y₂O₃The present invention will be further described with reference to the following examples and drawings, which are only used for illustrating the present invention and should not be construed as limiting the scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

Example 1

By Y₂O₃-MgO composite nanopowder, weighing 10g of the powder

Pressurizing the mould to 3MPa, dry-pressing to obtain a blank, and carrying out cold isostatic pressing treatment on the blank under the pressure of 100MPa for 20min for later use; putting the ceramic biscuit into a muffle furnace, heating to 800 ℃ at the heating rate of 0.5 ℃/min, preserving heat for 20min, eliminating the internal stress of a sample, cooling along with the furnace, and taking out for later use; placing the ceramic biscuit into a discharge plasma sintering furnace, performing discharge plasma rapid sintering without applying external pressure, wherein the heating rate is 15 ℃/min, the sintering temperature is 1250 ℃, the heat preservation sintering time is 100min, taking out a ceramic sample along with furnace cooling after sintering, performing annealing treatment on the obtained sample, the annealing temperature is 800 ℃, the annealing time is 30h, and obtaining a compact nano-crystalline grain ceramic sample after annealing treatment; then carrying out double-sided high-precision mirror polishing to obtain Y with the thickness of 3.0mm₂O₃-MgO nano complex phase ceramic product.

FIG. 1 shows the compact nanocrystal particle Y obtained in example 1₂O₃-infrared transmittance curve of the MgO complex phase ceramic, wherein (a) is near infrared transmittance curve and (b) is middle infrared transmittance curve.

FIG. 2 shows the compact nanocrystal particle Y obtained in example 1₂O₃-SEM topography of MgO complex phase ceramic; as can be seen, the average grain size is less than 250 nm.

Example 2

By Y₂O₃-MgO composite nanopowder, 100g of which was weighed

The mould is pressed to 15MPa and dry-pressed to be a blank body, and the blank body is subjected to cold isostatic pressing treatment with the pressure of 250MPa and the pressure maintaining time of 10min for later use; putting the ceramic biscuit into a muffle furnace, heating to 1200 ℃ at a heating rate of 3 ℃/min, preserving heat for 60min, removing internal stress of a sample, cooling along with the furnace, and taking out for later use; placing the ceramic biscuit into a discharge plasma sintering furnace, performing discharge plasma rapid sintering without applying external pressure, wherein the heating rate is 100 ℃/min, the sintering temperature is 1350 ℃, the heat preservation sintering time is 30min, taking out a ceramic sample along with furnace cooling after sintering, performing annealing treatment on the obtained sample, the annealing temperature is 1000 ℃, the annealing time is 20h, and obtaining a compact nano-crystalline grain ceramic sample after annealing treatment; then carrying out double-sided high-precision mirror polishing to obtain Y with the thickness of 3.0mm₂O₃-MgO nano complex phase ceramic product.

FIG. 3 shows the compact nanocrystal particle Y obtained in example 2₂O₃-infrared transmittance curve of the MgO complex phase ceramic, wherein (a) is near infrared transmittance curve and (b) is middle infrared transmittance curve.

FIG. 4 shows the compact nanocrystal particle Y obtained in example 2₂O₃-SEM topography of MgO complex phase ceramic; as can be seen, the average grain size is less than 250 nm.

Example 3

By Y₂O₃-MgO composite nanopowder, 5g of which was weighed

Pressurizing the mould to 3MPa, dry-pressing to obtain a blank, and carrying out cold isostatic pressing treatment on the blank under the pressure of 200MPa for 2min for later use; putting the ceramic biscuit into a muffle furnace, heating to 1000 ℃ at the heating rate of 10 ℃/min, preserving heat for 300min, eliminating the internal stress of a sample, cooling along with the furnace, and taking out for later use; placing the ceramic biscuit into a discharge plasma sintering furnace, performing discharge plasma rapid sintering without applying external pressure, wherein the heating rate is 300 ℃/min, the sintering temperature is 1500 ℃, the heat preservation sintering time is 3min, taking out a ceramic sample along with furnace cooling after sintering, performing annealing treatment on the obtained sample, the annealing temperature is 1100 ℃, the annealing time is 10h, and obtaining a compact nano-crystalline grain ceramic sample after annealing treatment; then carrying out double-sided high-precision mirror polishing to obtain Y with the thickness of 3.0mm₂O₃-MgO nano complex phase ceramic product.

FIG. 5 shows the compact nanocrystal particle Y obtained in example 3₂O₃-infrared transmittance curve of the MgO complex phase ceramic, wherein (a) is near infrared transmittance curve and (b) is middle infrared transmittance curve.

FIG. 6 shows the compact nanocrystal particle Y obtained in example 3₂O₃-SEM topography of MgO nanocomposite ceramic; as can be seen, the average grain size is within 250 nm.

In conclusion, the densified fine-grain nano complex-phase infrared transparent ceramic sample obtained by the method has higher relative density and grain size less than 250nm, is superior to a sample prepared by auxiliary hot isostatic pressing sintering after conventional sintering, avoids abnormal growth of grain size in the temperature rise process of conventional sintering, keeps high-activity sintering of ceramic biscuit, is easy to realize grain refinement and pore-removing densification, and has better optical property and mechanical property. The method has short sintering time, and does not need additional pressure to assist sintering; the sintering process is simple, the required sintering equipment is simple, the experimental period is short, the production cost is low, and the method is suitable for preparing samples in any shapes and is convenient for industrial production. And the method with lower cost can be easily used for preparing other oxides or oxide composite ceramic materials.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not intended to limit the present invention in any way, so that any person skilled in the art can make modifications or changes in the technical content disclosed above. However, any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present invention are still within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing infrared transparent ceramics by pressureless rapid sintering is characterized in that ceramic biscuit which is formed by pressing nanometer powder is placed in a muffle furnace for presintering to eliminate internal stress, then the biscuit is placed in a discharge plasma sintering furnace for discharge plasma rapid sintering without applying external pressure, after sintering, the biscuit is cooled and taken out, and a sample is annealed to obtain an infrared transparent ceramic product with the grain size of 30-250nm and the relative density of 95-100%.

2. The pressureless rapid sintering method for preparing infrared transparent ceramics according to claim 1 is characterized by comprising the following specific steps:

step 1.2) placing the ceramic biscuit obtained in the step 1.1) into a muffle furnace for pre-sintering, eliminating the internal stress of a sample, and cooling along with the furnace after pre-sintering and taking out for later use;

step 1.4) annealing the sample obtained in the step 1.3) to obtain a compact nano-crystalline ceramic sample.

3. The pressureless rapid sintering method for preparing infrared transparent ceramics according to claim 1 or 2, wherein the nano powder in the step 1.1) is Y₂O₃Nano powder and Al₂O₃Nano powder, ZrO₂Nanopowder or Y₂O₃-MgO composite nanopowder, the nanopowder having a grain size of 5-100 nm.

4. The pressureless rapid sintering method for preparing infrared transparent ceramics according to claim 2, wherein the pressure in the dry pressing of step 1.1) is 3-15 MPa.

5. The pressureless rapid sintering method for preparing infrared transparent ceramics according to claim 2, wherein the cold isostatic pressing pressure in step 1.1) is 100-250MPa, and the pressure holding time is 2-20 min.

6. The pressureless rapid sintering method for preparing infrared transparent ceramics according to claim 2, wherein the muffle furnace presintering temperature rise rate in step 1.2) is 0.5-10 ℃/min, the presintering temperature is 800-1200 ℃, and the presintering time is 20-300 min.

7. The method for preparing infrared transparent ceramics through pressureless rapid sintering as claimed in claim 2, wherein the pressureless discharge plasma rapid sintering in step 1.3) is performed at a temperature rise rate of 15-300 ℃/min, a sintering temperature of 1250-.