CN113387709B - Compact lanthanum tantalum oxynitride ceramic and preparation method thereof - Google Patents
Compact lanthanum tantalum oxynitride ceramic and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a compact lanthanum tantalum oxynitride ceramic and a preparation method thereof, wherein the compact lanthanum tantalum oxynitride ceramic comprises lanthanum tantalum oxynitride ceramic powder and ethanol which are uniformly mixed, dried after ball milling and sieved to obtain pre-sintered powder; and (2) performing discharge plasma sintering on the pre-sintered powder under the conditions of pressurization and protective atmosphere or pressurization and vacuum, wherein the sintering temperature is 1450-1550 ℃, naturally cooling to obtain a ceramic primary sintered body, performing secondary sintering on the ceramic primary sintered body under the conditions of ammonia atmosphere and no mechanical pressure, and cooling to obtain the dense lanthanum-tantalum oxynitride ceramic. The preparation method of the invention has short time, and the prepared compact lanthanum tantalum oxynitride ceramic has high density, high purity and wide application prospect.
Description
Technical Field
The invention relates to the technical field of preparation of high-performance ceramic materials, in particular to a compact lanthanum-tantalum oxynitride ceramic and a preparation method thereof.
Background
With the continuous development of material science, people have an increasing demand for novel perovskite functional materials having functional characteristics such as dielectric/electronic, magnetic, photocatalytic and energy conversion applications. As a novel perovskite material, the perovskite lanthanum tantalum oxynitride has wide application prospects in the directions of nontoxic dyes, dielectrics, giant magnetoresistance materials, photocatalytic hydrogen production and the like.
Although rare earth perovskite oxynitride has excellent multifunctionality and potential application prospects in multiple fields, an important problem encountered in practical research and application is that a well-sintered compact material is difficult to obtain, the processes of ceramic densification and grain growth are caused, the main influencing factors are sintering temperature, heating rate and holding time, and pressure in the process of pressure sintering also influences the densification of the ceramic. Common sintering modes of perovskite oxynitride include hot-pressing sintering, hot isostatic pressing sintering and pressureless sintering. Zhang et al uses SrCO3Or La2O3SrTaO is used as sintering aid2N and 5 wt.% of a sintering aid are mixed and then cold isostatic pressed at a pressure of 150MPa, thenThen sintering at 1400 ℃ for 3h and annealing in ammonia gas at 1000 ℃ for 12h to obtain ceramic wafer samples with relative density higher than 90%. However, the method has long preparation time and the effect is not optimal. Therefore, it is highly desirable to develop a method for sintering a lanthanum tantalum oxynitride ceramic with high density and high purity in a short time.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a compact lanthanum tantalum oxynitride ceramic with high density, high purity and short preparation period and a preparation method thereof.
In order to solve the technical problems, the invention adopts the following technical scheme:
a preparation method of the compact lanthanum tantalum oxynitride ceramic comprises the following steps:
s1, uniformly mixing lanthanum-tantalum oxynitride ceramic powder with ethanol, performing ball milling, drying and sieving to obtain pre-sintered powder;
s2, performing spark plasma sintering on the pre-sintered powder obtained in the step S1 under the conditions of pressurization and protective atmosphere or pressurization and vacuum, wherein the pressurization is the pressure of 130 MPa-150 MPa, the sintering temperature of the spark plasma sintering is 1450-1550 ℃, the heating rate is 400 ℃/min-500 ℃/min, the sintering temperature is kept for 0-10 min, and then the ceramic primary sintered body is obtained through natural cooling;
and S3, carrying out secondary sintering on the ceramic initial sintered body obtained in the step S2 under the conditions of ammonia gas atmosphere and no mechanical pressure, wherein the sintering temperature is 1460-1800 ℃, the sintering temperature is required to be higher than that in the step S2, the heating rate is 20-40 ℃/min, the sintering heat preservation time is 10-120 min, and then cooling to obtain the dense lanthanum tantalum oxynitride ceramic.
In the preparation method of the dense lanthanum tantalum oxynitride ceramic, in step S2, the sintering temperature is preferably maintained for 0-5 min.
In the above method for preparing the dense lanthanum tantalum oxynitride ceramic, preferably, in step S3, the sintering is performed for 50min to 60 min.
Preferably, in step S1, the ball milling pot used in the ball milling is made of polyurethane, alumina or zirconia, the ball milling beads used in the ball milling are made of polyurethane, alumina or zirconia, the ball milling time is 3h to 8h, the drying temperature is 50 ℃ to 150 ℃, the drying time is 5h to 20h, and the mesh number of the screen is 1000 meshes to 10000 meshes.
In the preparation method of the dense lanthanum tantalum oxynitride ceramic, preferably, in step S1, the ball milling time is 4h to 6h, the drying temperature is 80 ℃ to 120 ℃, the drying time is 5h to 8h, and the mesh number of the sieve is 3000 meshes to 7000 meshes.
In the above method for preparing the dense lanthanum tantalum oxynitride ceramic, preferably, in step S3, the cooling rate of the temperature reduction cooling is 1 ℃/min to 200 ℃/min.
In the above method for preparing the dense lanthanum tantalum oxynitride ceramic, in step S3, the cooling rate of the temperature reduction cooling is preferably 20 ℃/min to 80 ℃/min.
In the above method for preparing the dense lanthanum tantalum oxynitride ceramic, preferably, in step S2, the protective atmosphere is one or more of nitrogen, helium and argon.
As a general technical concept, the invention also provides a dense lanthanum tantalum oxynitride ceramic prepared by the preparation method.
In the present invention, the preparation process of the raw material lanthanum tantalum oxynitride ceramic powder adopted in step S1 is as follows:
(1) dissolving 5.0g of lanthanum oxide powder, 6.8g of tantalum pentoxide powder and 12.2g of urea in 50mL of absolute ethyl alcohol to obtain mixed slurry;
(2) fully drying the mixed slurry to obtain mixed precursor powder;
(3) and placing the mixed precursor powder in a crucible, and calcining at 1150 ℃ under the argon protective atmosphere to obtain the lanthanum-tantalum oxynitride ceramic powder.
Compared with the prior art, the invention has the advantages that:
the invention adopts urea method to synthesize oxynitride ceramic powder in one step, and adopts two steps of spark plasma pressure sintering and pressureless sintering to realize rapid densification of the material, compared with the current mainstream gas-solid amination and pressureless sintering method, the method has the advantages of short time consumption and high nitridation efficiency, and is expected to obtain ceramic with higher purity and density (more than 99 TD). The invention adopts a pressurizing and discharging plasma sintering method for preliminary densification in the first step, can improve the density of the product, simultaneously keeps the highest proportion of the open porosity of the material to the total porosity through temperature, pressure and heat preservation time, is convenient for the entry of ammonia gas during secondary sintering, and adopts a conventional sintering furnace for secondary sintering in the ammonia gas atmosphere in the second step, thereby not only restoring the stoichiometric ratio of oxynitride decomposed in the discharging plasma sintering, but also eliminating most of the residual porosity, and further improving the density and the purity of the product.
The method adopts the spark plasma sintering method for primary densification, greatly shortens the time, reduces the sintering temperature compared with the traditional sintering method, and simultaneously inhibits the decomposition of oxynitride from the aspects of thermodynamics and kinetics.
Drawings
FIG. 1 is an optical picture of a dense lanthanum tantalum oxynitride ceramic prepared in example 1 of the present invention.
FIG. 2 is an XRD spectrum of the dense lanthanum tantalum oxynitride ceramic obtained in example 1 of the present invention.
FIG. 3 is an SEM image of a dense lanthanum tantalum oxynitride ceramic obtained in example 1 of the present invention.
Detailed Description
The invention is further described below with reference to the drawings and specific preferred embodiments of the description, without thereby limiting the scope of protection of the invention. The starting materials and equipment used in the following examples are commercially available.
Example 1:
the preparation method of the dense lanthanum tantalum oxynitride ceramic comprises the following steps:
s1, mixing 5g of lanthanum tantalum oxynitride ceramic powder with 20mL of absolute ethyl alcohol uniformly, ball-milling for 4h in a polyurethane ball-milling tank by using polyurethane ball-milling beads, drying for 8h at 100 ℃, and then sieving by a 5000-mesh sieve to obtain pre-sintered powder.
S2, putting 4g of pre-sintered powder into a graphite die with phi 12mm, and performing initial sintering in spark plasma sintering equipment, wherein the process conditions are as follows: the mechanical pressure is 140MPa, the atmosphere is nitrogen, the heating rate is 400 ℃/min, the sintering temperature is 1500 ℃, the heat preservation time is 1min, and the ceramic primary sintered body is obtained after natural cooling.
S3, placing the ceramic primary sintered body obtained in the step S2 into a tube furnace, and carrying out secondary sintering under the conditions of no mechanical pressure and ammonia atmosphere, wherein the sintering process conditions are as follows: the heating rate is 20 ℃/min, the sintering temperature is 1550 ℃, the heat preservation time is 60min, and the cooling rate is 30 ℃/min. And cooling to obtain the compact lanthanum tantalum oxynitride ceramic.
In this embodiment, the preparation process of the lanthanum tantalum oxynitride ceramic powder is as follows:
(1) dissolving 5.0g of lanthanum oxide powder, 6.8g of tantalum pentoxide powder and 12.2g of urea in 50mL of absolute ethyl alcohol to obtain mixed slurry;
(2) fully drying the mixed slurry to obtain mixed precursor powder;
(3) and placing the mixed precursor powder in a crucible, and calcining at 1150 ℃ under the argon protective atmosphere to obtain the lanthanum-tantalum oxynitride ceramic powder.
The upper and lower surfaces of the dense lanthanum tantalum oxynitride ceramic wafer prepared in the embodiment were polished, and the optical picture thereof is shown in fig. 1, the color thereof is dark brown, which is similar to the oxynitride ceramic powder, and the phase composition and the microstructure thereof are respectively shown in fig. 2 and fig. 3. As is clear from FIGS. 2 and 3, LaTaO prepared in this example2The N oxynitride ceramic is almost pure phase and its microstructure is dense. The test shows that the density of the obtained ceramic chip is 94.53% (the density is volume density/theoretical density, LaTaO)2The theoretical density of N is 9.007g/cm3) The closed cell ratio was 3.54%.
Comparative example 1:
a method of making a lanthanum tantalum oxynitride ceramic substantially the same as example 1, except that:
in step S2, instead of using spark plasma sintering equipment for primary sintering, a conventional pressureless sintering furnace is used, the temperature rise rate is 10 ℃/min, the sintering temperature is 1500 ℃, and the heat preservation time is 1 min.
LaTaO prepared in this comparative example2The density of the N oxynitride ceramic plate is 48.57%, and the closed porosity is 32.18%. The comparative product has obviously lower relative density and purity than the product of the example 1, and the closed porosity is high. The ceramic primary sintered body is low in density, high in porosity and large in pore size due to the adoption of the traditional pressureless primary sintering mode, so that the ceramic primary sintered body is difficult to densify during secondary sintering, and the decomposition of oxynitride is accelerated dynamically due to the slow temperature rise rate of the traditional primary sintering.
Comparative example 2:
the preparation method of the lanthanum tantalum oxynitride ceramic is different from the preparation method of the lanthanum tantalum oxynitride ceramic in the following steps of: and step S3 is omitted, namely, directly carrying out discharge plasma sintering on the oxynitride, wherein the mechanical pressure is 140MPa, the atmosphere is nitrogen, the heating rate is 400 ℃/min, the sintering temperature is 1500 ℃, the heat preservation time is 1min, and naturally cooling to obtain the ceramic sintered body.
LaTaO prepared in this comparative example2The relative density of the N oxynitride ceramic sheet was 90.37%, and the closed porosity was 7.21%. This comparative example product was less pure than example 1 because the spark plasma sintering process using high pressure, rapid temperature rise and elevated sintering temperature, while rapidly densifying the oxynitride to some extent, the product decomposed severely and could not be restored to stoichiometric ratios because its decomposition temperature was below the sintering temperature.
Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Those skilled in the art can make numerous possible variations and modifications to the present invention, or modify equivalent embodiments to equivalent variations, without departing from the scope of the invention, using the teachings disclosed above. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical spirit of the present invention should fall within the protection scope of the technical scheme of the present invention, unless the technical spirit of the present invention departs from the content of the technical scheme of the present invention.
Claims (9)
1. The preparation method of the compact lanthanum tantalum oxynitride ceramic is characterized by comprising the following steps of:
s1, uniformly mixing lanthanum-tantalum oxynitride ceramic powder with ethanol, performing ball milling, drying and sieving to obtain pre-sintered powder;
s2, performing spark plasma sintering on the pre-sintered powder obtained in the step S1 under the conditions of pressurization and protective atmosphere or pressurization and vacuum, wherein the pressurization is the pressure of 130 MPa-150 MPa, the sintering temperature of the spark plasma sintering is 1450-1550 ℃, the heating rate is 400 ℃/min-500 ℃/min, the sintering temperature is kept for 0-10 min, and then the ceramic primary sintered body is obtained through natural cooling;
and S3, carrying out secondary sintering on the ceramic initial sintered body obtained in the step S2 under the conditions of ammonia gas atmosphere and no mechanical pressure, wherein the sintering temperature is 1460-1800 ℃, the sintering temperature is required to be higher than that in the step S2, the heating rate is 20-40 ℃/min, the sintering heat preservation time is 10-120 min, and then cooling to obtain the dense lanthanum tantalum oxynitride ceramic.
2. The method for preparing the dense lanthanum tantalum oxynitride ceramic according to claim 1, wherein in step S2, the sintering temperature is kept for 0-5 min.
3. The method for preparing the dense lanthanum tantalum oxynitride ceramic of claim 1, wherein in step S3, the sintering is carried out for 50-60 min.
4. The method for preparing the dense lanthanum tantalum oxynitride ceramic according to any one of claims 1 to 3, wherein in step S1, the ball milling pot material used for ball milling is polyurethane, alumina or zirconia, the ball milling bead material used for ball milling is polyurethane, alumina or zirconia, the ball milling time is 3h to 8h, the drying temperature is 50 ℃ to 150 ℃, the drying time is 5h to 20h, and the mesh number of the screen is 1000 meshes to 10000 meshes.
5. The method of claim 4, wherein in step S1, the ball milling time is 4-6 h, the drying temperature is 80-120 ℃, the drying time is 5-8 h, and the mesh number is 3000-7000.
6. The method of preparing a dense lanthanum tantalum oxynitride ceramic according to claim 1, wherein in step S3, the cooling rate of the temperature-decreasing cooling is 1 ℃/min to 200 ℃/min.
7. The method of manufacturing a dense lanthanum tantalum oxynitride ceramic according to claim 6, wherein in step S3, the cooling rate of the temperature-decreasing cooling is 20 ℃/min to 80 ℃/min.
8. The method for preparing the dense lanthanum tantalum oxynitride ceramic according to any one of claims 1 to 3, wherein in step S2, the protective atmosphere is one or more of nitrogen, helium and argon.
9. A dense lanthanum tantalum oxynitride ceramic prepared by the preparation method of any one of claims 1 to 8.
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DE4317421A1 (en) * | 1993-05-26 | 1994-12-01 | Cerdec Ag | Oxonitrides of the formula LnTaON¶2¶ with increased color brilliance, process for their preparation and their use |
JP2004230306A (en) * | 2003-01-31 | 2004-08-19 | Japan Science & Technology Agency | Method for improving activity of photocatalyst consisting of visible light responsive metal nitride and metal oxynitride |
JP2007175659A (en) * | 2005-12-28 | 2007-07-12 | Niigata Univ | Tantalic oxynitride photocatalyst and its manufacturing method |
CN106637287A (en) * | 2016-10-17 | 2017-05-10 | 南京大学 | Method for preparing tantalic acid lanthanum oxynitride efficient photoelectrode |
CN110156474A (en) * | 2019-05-30 | 2019-08-23 | 中国人民解放军国防科技大学 | Porous tantalum-based oxynitride ceramic and preparation method thereof |
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DE4317421A1 (en) * | 1993-05-26 | 1994-12-01 | Cerdec Ag | Oxonitrides of the formula LnTaON¶2¶ with increased color brilliance, process for their preparation and their use |
JP2004230306A (en) * | 2003-01-31 | 2004-08-19 | Japan Science & Technology Agency | Method for improving activity of photocatalyst consisting of visible light responsive metal nitride and metal oxynitride |
JP2007175659A (en) * | 2005-12-28 | 2007-07-12 | Niigata Univ | Tantalic oxynitride photocatalyst and its manufacturing method |
CN106637287A (en) * | 2016-10-17 | 2017-05-10 | 南京大学 | Method for preparing tantalic acid lanthanum oxynitride efficient photoelectrode |
CN110156474A (en) * | 2019-05-30 | 2019-08-23 | 中国人民解放军国防科技大学 | Porous tantalum-based oxynitride ceramic and preparation method thereof |
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