CN112979311A

CN112979311A - Nanocrystalline A4B2O9 type tantalate ceramic prepared by ultralow temperature sintering and method thereof

Info

Publication number: CN112979311A
Application number: CN202110480391.1A
Authority: CN
Inventors: 冯晶; 陈琳; 罗可人; 李柏辉; 王建坤; 张陆洋; 张鹤瀛
Original assignee: Kunming University of Science and Technology
Current assignee: Kunming University of Science and Technology
Priority date: 2021-04-30
Filing date: 2021-04-30
Publication date: 2021-06-18
Anticipated expiration: 2041-04-30
Also published as: CN112979311B

Abstract

The invention belongs to the technical field of thermal barrier coating materials, and discloses a nanocrystalline A4B2O9 type tantalate ceramic prepared by ultralow temperature sintering and a preparation method thereof, wherein the structural formula of the ceramic is A₄B₂O₉Wherein A is one or more of Ni, Co, Mg, Ca, Sr, Ba or Zn, and B is Ta; the preparation method of the ceramic comprises the following steps of A (OH)₂、ACO₃And the tantalum oxalate is respectively subjected to thermal decomposition for 1-2h at the temperature of 350-₂O₅Powder; then adding AO and Ta₂O₅Grinding the powder to obtain a nano-scale highly reactive powder mixture; and finally, performing discharge plasma sintering on the highly reactive powder mixture to prepare blocky A4B2O9 type tantalate ceramic. The invention solves the problems in the prior artThe cost of the thermal barrier coating and the environmental barrier coating material is high.

Description

Nanocrystalline A4B2O9 type tantalate ceramic prepared by ultralow temperature sintering and method thereof

Technical Field

The invention belongs to the technical field of thermal barrier coating materials, and particularly relates to nanocrystalline A4B2O9 type tantalate ceramic prepared by ultralow temperature sintering and a method thereof.

Background

In recent years, the rapid development of thermal barrier coatings and environmental barrier coating materials has led to the development and application of oxide ceramics of different types of crystal structures. Wherein the rare earth tantalate (RETaO)₄、RE₃TaO₇And Reta₃O₉) Due to excellent thermo-mechanical properties (low thermal conductivity, high coefficient of thermal expansion, high fracture toughness, low modulus, high temperature stability, corrosion resistance, etc.), they are continuously studied and applied. However, the main raw material of the rare earth tantalate is rare earth elements, and the rare earth elements are protected as strategic resources in China, so that the exploitation amount of the rare earth elements is small, and the price of the rare earth elements is very high, so that the manufacturing cost of the rare earth tantalate is high.

In order to reduce the cost of thermal barrier coatings and materials for environmental barrier coatings, the inventors have studied the materials of thermal barrier coatings and materials for environmental barrier coatings to form tantalate ceramics of type A4B2O 9.

Disclosure of Invention

The invention aims to provide nanocrystalline A4B2O9 type tantalate ceramic prepared by ultralow temperature sintering and a method thereof, so as to solve the problem that the existing thermal barrier coating and environmental barrier coating materials are high in manufacturing cost.

In order to realize the purpose, the invention provides the following technical scheme that the nanocrystalline A4B2O9 type tantalate ceramic prepared by ultralow temperature sintering has a structural formula A₄B₂O₉Wherein A is one or more of Ni, Co, Mg, Ca, Sr, Ba or Zn, and B is Ta.

The A4B2O9 type tantalate ceramic provided by the technical scheme has the characteristics of high compactness, high purity and nanocrystalline, and the hardness, fracture toughness and modulus of the ceramic material are very high, so that the thermophysical properties of the ceramic material can be regulated and controlled, and the A4B2O9 type tantalate ceramic can be used as a thermal barrier coating and an environmental barrier coating; moreover, the A4B2O9 type tantalate ceramics do not contain rare earth elements, so the manufacturing cost is relatively low.

The invention also provides another basic scheme, and the method for preparing the nanocrystalline A4B2O9 type tantalate ceramic by ultralow temperature sintering comprises the following steps:

in the first step of the method,

a (OH)₂、ACO₃And the tantalum oxalate is respectively subjected to thermal decomposition at the temperature of 350-900 ℃ for 1-2h to obtain AO and Ta with high reaction activity₂O₅Powder;

in the second step, the first step is that,

reacting AO with Ta₂O₅Grinding the powder to obtain a nano-scale highly reactive powder mixture;

step three, performing a first step of cleaning the substrate,

and (3) performing spark plasma sintering on the highly reactive powder mixture to prepare blocky A4B2O9 type tantalate ceramic.

The beneficial effects of the technical scheme are as follows:

1. the blocky A4B2O9 type tantalate ceramic prepared by the technical scheme has the purity of more than 99 percent, the compactness of more than 98 percent and the average grain size of less than 300nm, and because the A4B2O9 type tantalate ceramic has fine and uniform nano crystals, phonons can be effectively scattered, the thermal conductivity of the material is reduced, and the heat insulation protection capability of the material is improved; the hardness, the fracture toughness and the modulus of the A4B2O9 type tantalate ceramic prepared by the method can be improved by high compactness, high purity and nanocrystalline, so that the A4B2O9 type tantalate ceramic has better thermophysical properties;

2. according to the technical scheme, the raw materials are subjected to thermal decomposition to form powder with high reactivity, so that the temperature required by the reaction between oxides during sintering can be reduced, the time can be shortened, the energy can be saved, and the efficiency can be improved; in addition, the problems of overburning and excessive growth of crystal grains generated by a common sintering method can be avoided, and the problems of high porosity and poor material thermo-mechanical property in the generated ceramic block are further avoided.

Further, in the second step, alcohol with the concentration of 99.99% is added during grinding, and the mass ratio of the powder to the alcohol is 1: 6-10.

Has the advantages that: can keep the powder moist, conveniently grind.

Further, in the second step, the rotation speed of the polishing is 2200-3000rpm, and the polishing time is 12-20 h.

Has the advantages that: by controlling the rotating speed and the grinding time, the nano-scale powder meeting the requirement can be obtained.

Further, in the second step, after grinding, taking out the powder, and preserving heat for 6-10h at 65-80 ℃.

Has the advantages that: and (3) carrying out heat preservation treatment on the powder after grinding to realize volatilization of alcohol mixed in the powder, and drying the powder.

Further, in the third step, the sintering temperature is 620-700 ℃, the heat preservation time is 6-10min, and the heat preservation pressure is 100-300 MPa.

Has the advantages that: sintering the powder into blocky A4B2O9 type tantalate ceramics can be realized by controlling the sintering temperature, the heat preservation time and the heat preservation pressure; meanwhile, the sintering temperature is low, the phenomena of overburning and excessive growth of crystal grains can be prevented, the formation and the maintenance of nano crystals are facilitated, and the energy consumption is low; and the time cost is also lower.

And further, in the third step, before sintering, spraying BN on the die.

Has the advantages that: and BN is sprayed before sintering, so that carbon in a sintering die can be prevented from permeating into the powder, and the high purity of the prepared blocky A4B2O9 type tantalate ceramic can be ensured. Meanwhile, the annealing and decarbonization process after sintering is avoided, and pores and cracks are introduced into the block body during annealing and decarbonization, so that the density of the material is reduced, and the technical scheme can ensure that the prepared blocky A4B2O9 type tantalate ceramic has high density.

Further, sintering the high-reactivity powder mixture obtained in the step two at 700 ℃ for 1-5h, cooling, and preparing the A in a spray granulation mode₄B₂O₉And (3) forming tantalate spherical powder.

Has the advantages that: because the powder has high reactivity, the energy required by sintering is lower, the sintering can be completed at lower temperature, and the energy consumption is reduced; at the same time, the agglomeration phenomenon among the powder can be inhibited, so that the prepared A₄B₂O₉The type tantalate spherical powder can be used as an atmospheric plasma spraying raw material for preparing a coating without grinding and sieving.

Description of the figures/tables

FIG. 1 is a comparison of the XRD diffractogram of example 1 of the present invention with a standard card;

FIG. 2 shows Ca provided in example 1 of the present invention₄Ta₂O₉A surface micro-topography of the bulk ceramic;

FIG. 3 shows Ca provided in example 8 of the present invention₂Mg₂Ta₂O₉Schematic of thermal conductivity as a function of temperature.

Detailed Description

The following is further detailed by way of specific embodiments:

a nanocrystalline A4B2O9 type tantalate ceramic prepared by ultralow temperature sintering has a structural formula of A₄B₂O₉Wherein A is one or more of Ni, Co, Mg, Ca, Sr, Ba or Zn, and B is Ta. The purity of the ceramic is more than 99%, the density is more than 98%, and the average grain size is less than 300 nm.

Example 1:

a nanocrystalline A4B2O9 type tantalate ceramic prepared by ultralow temperature sintering has a structural formula of Ca₄Ta₂O₉The preparation method comprises the following steps:

in the first step of the method,

reacting Ca (OH)₂、CaCO₃Respectively preserving the oxalic acid at the temperature of 350-900 ℃ for 1-2h, and thermally decomposing the raw materials in the heat preservation process to obtain CaO and Ta with high reaction activity₂O₅And (3) powder. In the embodiment, the heat preservation temperature is preferably 900 ℃, and the heat preservation time is preferably 1 h.

In the second step, the first step is that,

according to Ca₄Ta₂O₉The structural formula of (A) is to weigh CaO and Ta with high reactivity₂O₅Powdering and mixing highly reactive CaO and Ta₂O₅Putting the powder into a high-energy ball mill, putting 99.99% alcohol into the high-energy ball mill at a weight ratio of 1:6-10, and adding CaO and Ta at a rotation speed of 2200-₂O₅Grinding the powder for 12-20h, taking out the powder, and preserving heat at 65-80 ℃ for 6-10h to obtain a nanoscale high-reactivity powder mixture. In the embodiment, the weight ratio of the powder to the alcohol is 1:8, the rotation speed during grinding is preferably 2200rpm, and the grinding time is preferably 16 h; after grinding, the temperature for heat preservation is preferably 75 ℃, and the time for heat preservation is preferably 6 hours.

Step three, performing a first step of cleaning the substrate,

spraying BN treatment on the graphite mold for sintering, and putting the nano-scale highly reactive powder mixture formed in the step two into the graphite mold for sintering at the sintering temperature of 620-300 MPa, the heat preservation time of 6-10min and the heat preservation pressure of 100-300MPa to obtain the blocky Ca-containing material₄Ta₂O₉A ceramic. In this embodiment, the sintering temperature is preferably 620 ℃, the heat preservation time is preferably 10min, and the heat preservation pressure is preferably 150 MPa.

Example 2:

example 2 is different from example 1 in that the structure of the A4B2O9 type tantalate ceramic in this example is Ni₄Ta₂O₉The preparation process is identical to example 1.

Example 3:

example 3 is different from example 1 in that the structure of the A4B2O9 type tantalate ceramic in this example is Co₄Ta₂O₉The preparation process is identical to example 1.

Example 4:

example 4 is different from example 1 in that the A4B2O9 type tantalate ceramic in this example has the structural formula of Mg₄Ta₂O₉The preparation process is identical to example 1.

Example 5:

example 5 differs from example 1 in that the A4B2O9 type tantalate ceramic in this example has the structural formula Sr₄Ta₂O₉The preparation process is identical to example 1.

Example 6:

example 6 is different from example 1 in that the structural formula of the A4B2O9 type tantalate ceramic in this example is Ba₄Ta₂O₉The preparation process is identical to example 1.

Example 7:

example 7 is different from example 1 in that the A4B2O9 type tantalate ceramic in this example has a structural formula of Zn₄Ta₂O₉The preparation process is identical to example 1.

Example 8:

example 8 is different from example 1 in that the structure of the A4B2O9 type tantalate ceramic in this example is Ca₂Mg₂Ta₂O₉(ii) a The preparation method is different from the embodiment 1 in that the heat preservation temperature of the thermal decomposition in the step one is 545 ℃ and the heat preservation time is 2 hours; in the second step, the rotation speed during grinding is 2800rpm, the grinding time is 20h, the heat preservation temperature after grinding is 80 ℃, and the heat preservation time is 8 h; the sintering temperature in the third step is 650 ℃, the heat preservation time is 8min, and the heat preservation pressure is 200 Mpa.

Example 9:

example 9 differs from example 8 in that the structure of the A4B2O9 type tantalate ceramic in this example is CaMgZnBaTa₂O₉(ii) a The preparation method is different from the embodiment 1 in that the heat preservation temperature of the thermal decomposition in the step one is 350 ℃, and the heat preservation time is 1 h; in the second step, the rotation speed during grinding is 3000rpm, the grinding time is 12 hours, the heat preservation temperature after grinding is 65 ℃, and the heat preservation time is 10 hours; in the third step, the sintering temperature is 680 ℃, the heat preservation time is 6min, and the heat preservation pressure is 230 Mpa.

Example 10:

example 10 differs from example 9 in that in this example, the third step is a stepPutting the nano-scale highly reactive powder mixture into a high-temperature sintering furnace, sintering at 700 ℃ for 1-5h, taking out the sintered powder, cooling, and preparing the CaMgZnBaTa by using a spray granulation method₂O₉The ceramic powder prepared is spherical, can be used as an air plasma spraying raw material for preparing a coating, and the sintering time is preferably 1h in the embodiment. The purity of the powder can be obtained by XRD test, and the result is consistent with that of figure 1.

Experiment:

the nanocrystalline A4B2O9 type tantalate ceramics provided in examples 1-9 were selected for the following experiments:

characterization by XRD

The tantalate ceramic blocks type A4B2O9 obtained in examples 1 to 9 were examined using an X-ray diffractometer, wherein the XRD pattern of example 1 is shown in fig. 1. According to the results shown in FIG. 1, Ca₄Ta₂O₉The diffraction peaks of the ceramics correspond to the standard PDF #31-0308 one by one.

SEM characterization

The A4B2O9 type tantalate ceramic blocks prepared in examples 1-9 were examined by scanning electron microscopy, wherein the surface micro-topography of example 1 is shown in FIG. 2. As can be seen from FIG. 2, Ca₄Ta₂O₉The grain size of the ceramic is uniform, the grain size is less than 300nm, the grain boundary is clear, no obvious air holes and cracks exist on the surface, and the density is as high as 99.5%.

3. Thermal conductivity detection

The ceramic blocks obtained in examples 1 to 9 were polished into round sheets having a diameter of 6X 1mm, and the thermal conductivity thereof was measured by a laser thermal conductivity meter, wherein the thermal conductivity of each of the ceramic blocks of examples 1 to 9 at 900 ℃ is shown in Table 1, and the Ca provided in example 8 at room temperature to 900 ℃ is measured₂Mg₂Ta₂O₉The thermal conductivity curve of the ceramic block is shown in fig. 3. As can be seen from fig. 3, the thermal conductivity of the ceramic block decreases sharply with increasing temperature, and decreases slowly after 600 ℃. At a temperature of 900 ℃ Ca₂Mg₂Ta₂O₉Thermal conductivity of ceramic blocksReduced to 1.4W.m^-1.K^-1Thus, the material has excellent heat insulation capability in high-temperature environment.

4. Density detection

The ceramic blocks provided in examples 1-9 were tested using archimedes' drainage.

The results of the experiments on the tantalate ceramics type A4B2O9 provided in examples 1 to 9 are shown in table 1.

TABLE 1

	Structural formula (I)	Young's modulus	Hardness of	Thermal conductivity	Compactness degree
						Example 1	Ca₄Ta₂O₉	186	9.2	2.1-5.2	99.5
Example 2	Ni₄Ta₂O₉	163	7.6	1.5-4.3	99.0
						Example 3	Co₄Ta₂O₉	201	10.9	2.3-6.0	99.7
Example 4	Mg₄Ta₂O₉	144	7.1	1.2-3.9	99.6
						Example 5	Sr₄Ta₂O₉	169	8.0	1.8-4.6	99.0
Example 6	Ba₄Ta₂O₉	210	12.5	2.5-3.9	99.1
						Example 7	Zn₄Ta₂O₉	152	6.6	2.0-4.3	99.3
Example 8	Ca₂Mg₂Ta₂O₉	162	8.3	1.4-4.2	99.8
						Example 9	CaMgZnBaTa₂O₉	180	10.6	1.3-3.7	99.1

In conclusion, the A4B2O9 type tantalate ceramic provided by the invention has the purity of more than 99%, the compactness of more than 98%, the average grain size of less than 300nm, and low thermal conductivity at high temperature, and can be used as a thermal barrier coating material and an environmental barrier coating material. Compared with the existing rare earth tantalate thermal barrier coating material, the rare earth tantalate thermal barrier coating material does not use rare earth elements in raw materials, has low preparation cost and is more suitable for use and research.

It will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention, and these changes and modifications should not be construed as affecting the performance of the invention and its practical application.

Claims

1. a nanocrystalline _A4B2O9 type tantalate ceramic prepared by ultra-low temperature sintering is characterized in that: the structural formula of this ceramic is _A4B2O9 , wherein _A is in Ni, Co, Mg, Ca, Sr, Ba or Zn One or more of , B is Ta.

2. the method for preparing nanocrystalline A4B2O9 type tantalate ceramics by a kind of ultra-low temperature sintering according to claim 1, is characterized in that, comprises the following steps:

step one,

A(OH) ₂ , ACO ₃ , and tantalum oxalate were thermally decomposed at 350-900° C. for 1-2 hours to obtain highly reactive AO and Ta ₂ O ₅ powders;

Step two,

The AO and Ta ₂ O ₅ powders are ground to obtain a nano-scale highly reactive powder mixture;

Step three,

The highly reactive powder mixture is subjected to spark plasma sintering to prepare bulk A4B2O9 type tantalate ceramics.

3. the method for preparing nanocrystalline A4B2O9 type tantalate ceramics by a kind of ultra-low temperature sintering according to claim 2, is characterized in that: in step 2, when grinding, adding concentration is 99.99% alcohol, the mass ratio of powder and alcohol 1:6-10.

4. A method for preparing nanocrystalline A4B2O9 type tantalate ceramics by ultra-low temperature sintering according to claim 2, characterized in that: in step 2, the grinding speed is 2200-3000rpm, and the grinding time is 12-20h.

5. A method for preparing nanocrystalline A4B2O9 type tantalate ceramics by ultra-low temperature sintering according to claim 2, characterized in that: in step 2, after grinding, the powder is taken out and kept at 65-80 ℃ for 6- 10h.

6. the method for preparing nanocrystalline A4B2O9 type tantalate ceramics by ultra-low temperature sintering according to claim 2, is characterized in that: in step 3, sintering temperature is 620-700 ℃, holding time is 6-10min, holding pressure is 100-300Mpa.

7. The method for preparing nanocrystalline A4B2O9 type tantalate ceramics by ultra-low temperature sintering according to claim 2, wherein in step 3, before sintering, spray BN treatment on the mold.

8. A method for preparing nanocrystalline A4B2O9 type tantalate ceramics by ultra-low temperature sintering according to claim 2, characterized in that: the highly reactive powder mixture in step 2 is sintered at 700 DEG C for 1-5h, and After cooling, A ₄ B ₂ O ₉ type tantalate spherical powder is prepared by spray granulation.