CN112979312A

CN112979312A - AB2O6Niobate ceramic and preparation method thereof

Info

Publication number: CN112979312A
Application number: CN202110480659.1A
Authority: CN
Inventors: 李柏辉; 冯晶; 陈琳; 罗可人; 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

Abstract

The invention belongs to the technical field of thermal barrier and environmental barrier coating materials, and discloses an AB₂O₆Niobate ceramic and its preparation method, the structural formula of the ceramic is AB₂O₆Wherein A is one or more of Ni, Co, Mg, Ca, Sr, Ba or Zn, and B is Nb; the ceramic is of a single phase structure. The preparation method comprises the steps of firstly, preparing A (OH)₂、ACO₃And niobium oxalate are subjected to thermal decomposition under heat preservation to obtain AO and Nb with high reaction activity₂O₅Powder; then adding AO and Nb₂O₅Grinding and mixing the powder to obtain a nano-sized highly reactive powder mixture; finally, sintering the highly reactive powder mixture by spark plasma sintering to obtain blocky AB₂O₆A type niobate ceramic. The invention solves the manufacturing cost of the existing thermal barrier/environmental barrier coating rare earth tantalate and rare earth niobateHigher problems.

Description

AB2O6Niobate ceramic and preparation method thereof

Technical Field

The present invention belongs to the field of heat barrier and environment barrier coating material technologyField, in particular to an AB₂O₆A niobate ceramic and a preparation method thereof.

Background

In recent years, the aero-engine gradually develops towards the direction of high thrust-weight ratio, high flow ratio and high air inlet temperature, so that the working temperature and pressure required to be born by high-temperature parts and single crystal blades of a combustion chamber are continuously increased; meanwhile, in order to improve the energy utilization efficiency, it is urgently required to improve the power generation efficiency of the gas turbine applied to the large-sized power generation unit, and the improvement of the working temperature is the most direct and effective method. In order to withstand the operating temperatures at which an aircraft engine operates, it is necessary for the materials from which the aircraft engine is made to have high service temperatures. In order to meet the development requirements of the existing aircraft, high-temperature alloy is usually used as a raw material for preparing an aircraft engine, and in order to further improve the use temperature and prolong the service life, a layer of heat-insulating protective ceramic coating is prepared on the surface of a high-temperature alloy material to provide heat-insulating protective effect for the high-temperature alloy material.

Thermal barrier/environmental barrier coating materials used as thermal insulation protective ceramic coatings are required to have the properties of low thermal conductivity, coefficient of thermal expansion matched with a substrate, low modulus, high hardness, high temperature resistance and the like. The most widely used thermal barrier/environmental barrier coating material is yttria-stabilized zirconia (YSZ), but the YSZ material has poor stability at high temperature, and undergoes phase change at 1200 ℃ (a metastable monoclinic phase (M') is converted into a mixture of a tetragonal phase (t) and a cubic phase (c), and a thermal stress is generated due to a large volume difference generated when the tetragonal phase (t) is continuously converted into a monoclinic phase (M) in a cooling process), so that the use temperature of YSZ is lower than 1200 ℃, and the requirement of an aeroengine on the thermal barrier/environmental barrier coating material cannot be met, and therefore, a novel thermal barrier/environmental barrier coating material is required to meet the development requirement of the aeroengine.

In recent years, rare earth tantalates and rare earth niobates (REMO)₄、RE₃MO₇、REM₃O₉(RE-Y, Sc or La-Lu; M-Ta or Nb)) ceramic materials are gradually entering the field of view and therefore have very low thermal conductivity (1.0W/M-K), high coefficient of thermal expansion (11 × 10)^-6

K

^-11200 ℃ C.) and excellent comprehensive mechanical properties are widely researched as thermal barrier/environmental barrier coating materials. However, when rare earth tantalate and rare earth niobate are prepared, the main raw materials include 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 and the rare earth niobate is high.

In order to reduce the cost of the thermal barrier/environmental barrier coating material, the inventor researches the thermal barrier/environmental barrier coating material to form an AB₂O₆A type niobate ceramic.

Disclosure of Invention

The invention aims to provide an AB₂O₆The niobate ceramic and the preparation method thereof solve the problem that the existing thermal barrier/environmental barrier coating rare earth tantalate and rare earth niobate have higher manufacturing cost.

In order to achieve the purpose, the invention provides the following technical scheme, namely an AB₂O₆The structural formula of the niobate ceramic is AB₂O₆Wherein A is one or more of Ni, Co, Mg, Ca, Sr, Ba or Zn, and B is Nb; the ceramic is of a single phase structure.

AB provided by the technical scheme₂O₆The niobate ceramic does not need to use rare earth elements as main raw materials, so that the cost of the ceramic material is low; meanwhile, the ceramic has low content of internal defects (cracks and pores), so that the ceramic has low thermal conductivity at high temperature and can be used as a thermal barrier/environmental barrier coating.

The average grain size of the ceramic is less than 200nm, and the heat conductivity is reduced by scattering phonons through smaller nanocrystals, so that the heat insulation and protection performance of the material is improved.

The density of the ceramic is more than 97 percent, the purity is more than 98 percent, and the Vickers hardness can be effectively increased, so that the generation of cracks in the material is reduced, the damage caused by residual thermal stress is reduced, and the service life of the ceramic is longer.

The invention also provides another basic scheme, namely an AB₂O₆The preparation method of the type niobate ceramic comprises the following steps:

in the first step of the method,

a (OH)₂、ACO₃And niobium oxalate are respectively subjected to thermal decomposition under heat preservation to obtain AO and Nb with high reaction activity₂O₅Powder;

in the second step, the first step is that,

reacting AO with Nb₂O₅Grinding and mixing the powder to obtain a nano-sized highly reactive powder mixture;

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

sintering the highly reactive powder mixture by spark plasma sintering to obtain a blocky AB₂O₆A type niobate ceramic.

The beneficial effects of the technical scheme are as follows:

1. the blocky AB prepared by the technical scheme₂O₆The average grain size of the niobate ceramic is less than 200nm, and fine and uniform nanocrystals can effectively scatter phonons and reduce the thermal conductivity of the material, so that the heat insulation protection capability is improved, and the niobate ceramic can be used as a thermal barrier coating; the purity of the ceramic is more than 98 percent, the density is more than 97 percent, namely, the content of cracks and air holes in the ceramic is very little, so that the thermal conductivity of the ceramic is lower at high temperature, the heat transfer is reduced, and the thermodynamic property of the ceramic is improved; meanwhile, the high density can effectively increase the Vickers hardness, reduce the damage caused by residual thermal stress and prolong the service life;

2. in the technical scheme, the raw materials are subjected to thermal insulation and thermal decomposition before sintering, so that the powder has high reactivity, sintering can be completed at a lower temperature in a shorter time, and AB is formed₂O₆The niobate ceramic has the functions of high efficiency and energy saving; moreover, because the sintering temperature is low, the problems of high porosity in the block and poor thermo-mechanical property of the material caused by over-sintering and over-growth of crystal grains can be avoided;

3. in the technical scheme, the powder is sintered in a spark plasma sintering mode, and pulse current and pressure are applied to a pressed compact, so that the powder particles can be plastically deformed, and the densification speed is accelerated; the applied pulse current can generate direct current pulse voltage among the particle powder, so that a discharge effect occurs among adjacent particles, and self-heating is generated by discharge among the particles, so that the temperature required by sintering can be further reduced; meanwhile, discharge plasma is generated in gaps due to the discharge effect, impact of high-energy particles on particles and evaporation of substances can be caused, the purification and activation effects are achieved, the sintering activity of the particles is improved due to the purification of the surfaces of the metal particles, the free energy of diffusion is reduced, and therefore the sintering efficiency is improved;

when the pulse current is large enough, the insulating layer of the particles can be punctured, the discharge effect is severe, the self-heating effect of the particles is obvious, the temperature is increased, the electric field intensity is high and covers the whole powder, local high temperature can occur, the evaporation melting phenomenon occurs on the surfaces of the particles, evaporation substances can be deposited near the contact points of the particles to form sintering necks, and under the action of the pulse current and the applied pressure, crystal grains are subjected to bulk diffusion and grain boundary diffusion, so that the densification speed is accelerated.

Further, in the first step, the heat preservation temperature during thermal decomposition is 950-.

Has the advantages that: by setting the holding temperature and time during thermal decomposition, the raw materials can be sufficiently thermally decomposed to form highly reactive powder.

Further, in the second step, the rotation speed for polishing is 2200-2500rpm, and the polishing time is 15-20 h.

Has the advantages that: by setting the rotation speed and the grinding time at the time of grinding, it can be ensured that the powder is ground to a nano size.

Further, in the second step, alcohol with the concentration of more than 99.9 percent is added during grinding, and the mass ratio of the powder to the alcohol is 1: 5-20.

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

Further, in the second step, after grinding is finished, heat preservation treatment is carried out on the powder, the heat preservation temperature is 50-75 ℃, and the heat preservation time is 8-10 hours.

Has the advantages that: after grinding, the powder is kept warm, so that the alcohol in the powder can be fully volatilized, and the drying of the powder is completed.

Further, in the third step, the BN spraying treatment is firstly carried out in the mould for sintering, and then the high reactivity powder mixture is put into the mould for sintering.

Has the advantages that: BN is sprayed in the sintering die, so that carbon can be effectively prevented from permeating into the sample, and the prepared AB can be ensured₂O₆The purity of the type niobate ceramic is high. Meanwhile, the annealing and carbon removal process for improving the purity of the prepared ceramic can be avoided, the energy consumption can be saved, and the preparation time can be shortened. In addition, in the annealing and carbon removal process, pores and cracks are introduced into the ceramic block, thereby reducing the compactness of the material. Therefore, the technical scheme can ensure the prepared blocky AB₂O₆The niobate ceramic has high purity and density.

Further, in the third step, the sintering temperature is 850-1000 ℃, the heat preservation time is 8-10min, and the pressure maintaining pressure is 70-90 MPa.

Has the advantages that: the sintering temperature can complete the sintering of the powder and form block-shaped AB₂O₆Type niobate ceramics; the powder after grinding has high reactivity, so that the sintering of the powder can be completed at a lower temperature, and the low-temperature sintering can avoid the phenomena of overburning and excessive growth of crystal grains, so that the formation and the maintenance of nano crystals are facilitated, and the problems of high porosity in a block and poor thermo-mechanical properties of the material cannot occur.

Drawings

FIG. 1 is a schematic representation of CaNb prepared in example 1 of the present invention₂O₆SEM image of the ceramic block;

FIG. 2 shows CaNb prepared in example 1 of the present invention₂O₆XRD pattern of ceramic block;

FIG. 3 shows CaNb prepared in example 1 of the present invention₂O₆A plot of thermal conductivity of the ceramic mass as a function of temperature;

FIG. 4 is a CaNb prepared in example 1 of the present invention₂O₆Graph of the coefficient of thermal expansion of a ceramic block as a function of temperature.

Detailed Description

The following is further detailed by way of specific embodiments:

AB₂O₆The structural formula of the niobate ceramic is AB₂O₆Wherein A is one or more of Ni, Co, Mg, Ca, Sr, Ba or Zn, and B is Nb; the ceramic is of a single phase structure. The purity of the ceramic is more than 98%, the density is more than 97%, and the average grain size is less than 200 nm.

Example 1:

AB₂O₆The structural formula of the niobate ceramic is CaNb₂O₆The preparation method comprises the following steps:

in the first step of the method,

mixing CaCO₃And niobium oxalate are respectively insulated for 1-1.5h at the temperature of 950-₂O₅And (3) powder. In the embodiment, the heat preservation temperature is preferably 1000 ℃, and the heat preservation time is preferably 1h

In the second step, the first step is that,

CaO, Nb₂O₅And putting the alcohol with the concentration of more than 99.9 percent into a high-energy ball mill for grinding, wherein the weight ratio of the powder to the alcohol is 1:5-20, the rotation speed during grinding is 2200-. After the milling is completed, the powder is taken out and kept at a temperature of 50-75 ℃ for 8-10h to form a nano-sized highly reactive powder mixture. In the embodiment, the weight ratio of the powder to the alcohol is preferably 1:10, the rotation speed during grinding is preferably 2500rpm, the grinding time is preferably 20h, the heat preservation temperature is preferably 75 ℃, and the heat preservation time is preferably 10 h.

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

firstly, carrying out BN spraying treatment on a graphite mold, then placing a highly reactive powder mixture in the graphite mold, and sintering by using a spark plasma sintering mode, wherein the sintering temperature is 850-1000 ℃, the heat preservation time is 8-10min, and the pressure maintaining pressure is 70-90Mpa, so that the blocky CaNb is obtained₂O₆A ceramic. In the embodiment, the sintering temperature is preferably 850 ℃, the holding time is preferably 8min, and the holding pressure is preferably 90Mpa。

Example 2-example 7 differs from example 1 only in the elements at a, with example 2 being NiNb₂O₆Ceramic, CoNb in example 3₂O₆Ceramic, example 4 MgNb₂O₆Ceramic, example 5 is SrNb₂O₆Ceramic, BaNb in example 6₂O₆Ceramic, example 7 is ZnNb₂O₆A ceramic.

Experiment:

the AB of example 1 to example 7 was selected₂O₆Type niobate ceramics, the following experiment was performed:

SEM characterization

Scanning Electron microscopy was used for the AB prepared in examples 1-7₂O₆The type niobate ceramic blocks were examined, wherein the SEM spectrum of example 1 is shown in fig. 1. As can be seen from FIG. 1, CaNb₂O₆The grain size of the ceramic is uniform, the grain size is between 15 and 30nm, the grain boundary is clear, and no second phase exists in or among the grains, so that the grain size is consistent with the XRD result; and no obvious air holes and cracks exist on the surface, and the density is as high as 97.7%.

2. Density detection

The ceramic blocks provided in examples 1 to 7 were examined by archimedes' drainage method, and the results are shown in table 1.

As can be seen from the SEM representation and the compactness detection result, the AB prepared by the invention₂O₆The micro-cracks in the niobate ceramic block are few, the content of air holes is low, and the density of the ceramic block is high.

Characterization by XRD

Using an X-ray diffractometer, AB obtained in examples 1 to 7 was measured₂O₆The type niobate ceramic blocks were tested, wherein the XRD pattern of example 1 is shown in fig. 2. According to the results shown in FIG. 1, CaNb₂O₆The diffraction peaks of the ceramics correspond to the standard PDF #71-2406 one by one, which shows that no second phase diffraction peak exists. As can be seen from FIG. 1, CaNb₂O₆The crystal structure of the ceramic being in an orthorhombic phase, whichWhere a ≠ b ≠ c, α ═ β ═ γ ═ 90 °, theoretical density is 4.749g/cm³。

4. Thermal conductivity detection

The ceramic blocks obtained in examples 1 to 7 were polished into round sheets of 6X 1mm in diameter and the thermal conductivity thereof was measured by a laser thermal conductivity meter, and the thermal conductivity of each of the ceramic blocks of examples 1 to 7 at 900 ℃ was as shown in Table 1, and CaNb was measured at room temperature to 900 ℃ in the range of CaNb₂O₆The 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 400 ℃. When the temperature is 900 ℃, CaNb₂O₆The thermal conductivity of the niobate ceramic block is reduced to 1.63W.m^-1.K^-1Thus, the material has excellent heat insulation capability in high-temperature environment.

At room temperature to 1200 deg.C, CaNb₂O₆The thermal expansion coefficient curve of the ceramic block is shown in FIG. 4, and CaNb is increased with the temperature₂O₆The thermal expansion coefficient of the ceramic block rises sharply, and after the temperature rises to over 300 ℃, the thermal expansion coefficient rises slowly. At a temperature of 1200 deg.C, CaNb₂O₆The thermal expansion coefficient of the niobate ceramic block reaches 8.5W.m^-1.K^-1。

TABLE 1

In conclusion, the AB prepared by the invention₂O₆The niobate ceramic has high density of more than 97 percent, good high-temperature thermal stability and low thermal conductivity at high temperature, can be used as a novel high-temperature ceramic material, has low price compared with rare earth niobate and rare earth niobate, and has similar excellent mechanical property and thermal property.

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. AB₂O₆The type niobate ceramic is characterized in that: the structural formula of the ceramic is AB₂O₆Wherein A is one or more of Ni, Co, Mg, Ca, Sr, Ba or Zn, and B is Nb; the ceramic is of a single phase structure.

2. An AB as claimed in claim 1₂O₆The preparation method of the type niobate ceramic is characterized by comprising the following steps:

in the first step of the method,

in the second step, the first step is that,

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

3. An AB as claimed in claim 2₂O₆The preparation method of the type niobate ceramic is characterized by comprising the following steps: in the first step, the heat preservation temperature during thermal decomposition is 950-.

4. An AB as claimed in claim 3₂O₆The preparation method of the type niobate ceramic is characterized by comprising the following steps: in the second step, the rotation speed for polishing is 2200-2500rpm, and the polishing time is 15-20 h.

5. An AB as claimed in claim 4₂O₆The preparation method of the type niobate ceramic is characterized by comprising the following steps: in the second step, during grinding, theAdding alcohol with concentration of more than 99.9%, wherein the mass ratio of the powder to the alcohol is 1: 5-20.

6. An AB as claimed in claim 5₂O₆The preparation method of the type niobate ceramic is characterized by comprising the following steps: and in the second step, after grinding is finished, carrying out heat preservation treatment on the powder, wherein the heat preservation temperature is 50-75 ℃, and the heat preservation time is 8-10 h.

7. An AB as claimed in claim 6₂O₆The preparation method of the type niobate ceramic is characterized by comprising the following steps: and in the third step, the BN spraying treatment is firstly carried out in the mould for sintering, and then the high-reactivity powder mixture is put into the mould for sintering.

8. An AB as claimed in claim 7₂O₆The preparation method of the type niobate ceramic is characterized by comprising the following steps: in the third step, the sintering temperature is 850-.

9. An AB as claimed in claim 2₂O₆The preparation method of the type niobate ceramic is characterized by comprising the following steps: sintering the highly reactive powder mixture obtained in the second step at 1000 ℃ for 300min to obtain blocky AB with higher density₂O₆A type niobate ceramic.