阅读说明：本技术 一种热压烧结制备钙钛矿型复合氧化物高熵陶瓷的方法 (Method for preparing perovskite type composite oxide high-entropy ceramic by hot-pressing sintering ) 是由 闫桂炜 陈智慧 任玉荣 邱建华 朱媛媛 于 2019-11-19 设计创作，主要内容包括：本发明属于高熵陶瓷材料领域,具体公开了一种热压烧结制备钙钛矿型复合氧化物高熵陶瓷的方法,该钙钛矿型复合氧化物高熵陶瓷的A位由Sr占据,B位由近等摩尔比的Zr、Sn、Ti、Hf元素以及Nb,Ta,Mn,Tb中的任意一种元素组成。本发明采用热压烧结技术制备Sr(Zr<Sub>0.2</Sub>Sn<Sub>0.2</Sub>Ti<Sub>0.2</Sub>Hf<Sub>0.2</Sub>M<Sub>0.2</Sub>)O<Sub>3</Sub>(M＝Nb、Ta、Mn、Tb)复合氧化物高熵陶瓷材料,所制备的陶瓷材料晶粒为亚微米级,结构致密,制备工艺简单、周期短。(The invention belongs to the field of high-entropy ceramic materials, and particularly discloses a method for preparing perovskite type composite oxide high-entropy ceramic through hot-pressing sintering. The invention adopts the hot-pressing sintering technology to prepare Sr (Zr) 0.2 Sn 0.2 Ti 0.2 Hf 0.2 M 0.2 )O 3 The (M ═ Nb, Ta, Mn and Tb) composite oxide high-entropy ceramic material has submicron-order crystal grains, compact structure, simple preparation process and short period.)

1. A method for preparing perovskite type composite oxide high-entropy ceramic by hot-pressing sintering is characterized by comprising the following specific steps:

(1) according to Sr (Zr) _0.2Sn _0.2Ti _0.2Hf _0.2M _0.2)O ₃Adding strontium carbonate and other metal oxides into a nylon tank respectively, mixing and ball-milling for 12-36 hours on a planetary ball mill by using absolute ethyl alcohol as a ball-milling medium, and drying at the temperature of 120 ℃ at 100-;

(2) pre-burning the raw material precursor, grinding, sieving with a 200-mesh sieve, putting into a high-strength graphite mold, and putting into a hot-pressing furnace;

(3) heating at a constant speed of 20 ℃/min, when the temperature rises to 500 ℃, the loaded external pressure reaches 10-15MPa, controlling the temperature by a sintering furnace program to rise to 1200 ℃ and 1300 ℃, preserving the temperature for 120 minutes, then unloading the pressure, and naturally cooling the sample along with the furnace body;

(4) and (4) putting the cooled ceramic wafer into a tube furnace, and heating and annealing in a flowing air atmosphere to obtain a ceramic sample.

2. The method for preparing perovskite type composite oxide high-entropy ceramic through hot-pressing sintering according to claim 1, wherein the pre-sintering temperature in the step (2) is 1000-1100 ℃, and the pre-sintering time is 2 hours.

3. The method for preparing perovskite type composite oxide high-entropy ceramic by hot-pressing sintering according to claim 1, wherein the external pressure loading and unloading process of the step (3) adopts the following mode: when the temperature is increased to 500 ℃, the loaded pressure reaches the maximum value and starts to maintain pressure, the constant-speed pressure reduction is started when the temperature is maintained at the maximum temperature for 90 minutes, and the external pressure is unloaded to zero after 30 minutes.

4. The method for preparing perovskite type composite oxide high-entropy ceramic through hot-pressing sintering according to claim 1, wherein the annealing temperature in the step (4) is 1000-1100 ℃, and the annealing time is 2 h.

5. A perovskite-type composite oxide high-entropy ceramic prepared according to the method of claim 1, wherein: the high-entropy ceramic is ABO ₃The perovskite structure has five metal atoms occupying B site, namely Zr, Sn, Ti, Nb and metal atom M with nearly equal molar ratio, and the tolerance factor of the five metal ions is between 0.95 and 1.02.

6. The perovskite-type composite oxide high-entropy ceramic according to claim 5, characterized in that: the metal atom M is one of Nb, Ta, Mn and Tb atoms.

Technical Field

The invention belongs to the field of high-entropy ceramic materials, and particularly relates to a method for preparing perovskite type composite oxide high-entropy ceramic through hot-pressing sintering.

Background

The high-entropy ceramic has the characteristics of high thermal conductivity, high melting point, good corrosion resistance, good electrochemical performance and the like, is a novel ceramic material developed on the basis of high-entropy alloy in recent years, and has potential application value in the fields of ultrahigh-temperature materials and new energy materials. Since 1995 the concept of high entropy was first proposed, only a few structures of high entropy oxide ceramics were successfully synthesized.

The perovskite type composite oxide is a compound having the same structure as perovskite, and ABO can be used ₃The A site is alkaline earth element, the cation is in 12 coordination structure and is positioned in a cavity formed by octahedron; the B site is transition metal element, and cation and six oxygen ions form octahedral coordination. The perovskite composite oxide high-entropy material refers to a perovskite structure with B sites occupied by four to five metal ions together in the same molar ratio. The large number of possible permutations of atoms with different B-positions leads to confusion (high entropy).

A document "A new class of high-entry Perovskite oxides, Sicong Jiang, TaoHu, Jian Luo, et al.Scripta Materialia 142(2018) 116-120") reports that ABO is synthesized by a method combining solid-phase sintering and heat treatment ₃A type multi-principal element perovskite structure oxide. But the sintering temperature of the method is high and reaches 1500 ℃; the ceramic prepared by the solid-phase sintering method has large crystal grains and low density.

Disclosure of Invention

The invention aims to provide a hot-pressing sintering method of perovskite type composite oxide high-entropy ceramic, and the prepared high-entropy ceramic is ABO ₃The perovskite structure has five metal atoms occupying the B site, namely Zr, Sn, Ti, Hf and metal atom M with equal molar ratio. The metal atom M includes Nb, Ta, Mn,One of Tb atoms; the tolerance factor for the five metal ions is between 0.95 and 1.02.

The invention relates to a hot-pressing sintering method of perovskite type composite oxide high-entropy ceramic, which comprises the following steps:

(1) according to Sr (Zr) _0.2Sn _0.2Ti _0.2Hf _0.2M _0.2)O ₃Respectively adding strontium carbonate and other metal oxides into a nylon tank according to the stoichiometric ratio of (M ═ Nb, Ta, Mn or Tb), mixing and ball-milling for 12-36 hours on a planetary ball mill by using absolute ethyl alcohol as a ball-milling medium, and drying at the temperature of 100 ℃ and 120 ℃ to obtain a raw material precursor;

(2) presintering the raw material precursor at 1000-1100 ℃ for 2 hours, grinding, sieving with a 200-mesh sieve, placing into a high-strength graphite mold, placing into a hot pressing furnace, vacuumizing to make the vacuum degree in the furnace reach 10 ^-2Pa；

The presintering can enable the raw material components to firstly undergo chemical reaction according to the stoichiometric ratio to generate ceramic powder meeting the high-entropy ceramic ratio.

(3) The program temperature control of the sintering furnace enables the sintering temperature to reach 1200-1300 ℃, the heat preservation time to be 120 minutes, and the heating rate to be 20 ℃/min. When the temperature is increased to 500 ℃, the loaded pressure reaches the maximum value (10-15MPa) and pressure maintaining is started, constant-speed pressure reduction is started when the temperature is kept at the maximum temperature for 90 minutes, the applied pressure is unloaded to zero after 30 minutes, and the sample is naturally cooled along with the furnace body.

(4) And (3) putting the cooled ceramic wafer into a tubular furnace, and carrying out thermal annealing at the temperature of 1000-1100 ℃ for 2 hours in a flowing air atmosphere to obtain a ceramic sample.

Wherein, in the ball milling process in the step (1), in order to prevent the ball milling medium from being overheated, the ball milling is stopped for 10 minutes every 30 minutes;

in the step (2), before the raw material precursor is placed into a graphite mold, a layer of boron nitride powder is coated on the inner surface of the mold;

in the step (3), the pressure loading and unloading process adopts the following mode: when the temperature rises to 500 ℃, the loaded pressure reaches the maximum value and starts to maintain pressure, and the pressure is quickly reduced at the later stage of the heat preservation process at the highest temperature, so that the external pressure is gradually unloaded to zero when the heat preservation process is finished.

The advantage of synchronous pressurization with sintering is that additional sintering driving force is provided by using external pressure, and rapid sintering densification of the high-entropy ceramic at a lower temperature is promoted. In the later sintering period, the diffusion and migration rates of ions are high, and a solid phase skeleton of a sintered body is gradually formed; meanwhile, a large amount of residual thermal stress generated at high temperature is accumulated in the sintered body, and the solid framework is easy to form a large amount of microcracks by continuously loading external pressure, so that brittle fracture occurs. The rapid pressure relief can avoid the generation of microcracks, so that the residual thermal stress can be slowly released from the sintered body under the condition of no external force interference.

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

the invention prepares perovskite type composite oxide high-entropy ceramic Sr (Zr) by utilizing a hot-pressing sintering method _0.2Sn _0.2Ti _0.2Hf _0.2M _0.2)O ₃(M-Nb, Ta, Mn, Tb). By regulating the types and the proportion of five metal ions at the B site, the perovskite type composite oxide high-entropy structure with the tolerance factor between 0.95 and 1.02 is obtained. The method has the advantages of rapid sintering process and large sintering driving force, and the high-entropy ceramic product with high density, small crystal grains and good mechanical property can be obtained at the sintering temperature which is lower than 200-300 ℃ of the conventional solid-phase sintering method.

Drawings

FIG. 1 is a schematic view showing the pressure loading and unloading manner in comparative example 1, wherein t _pFor dwell time, T _mAt the maximum sintering temperature, t _TIs T _mTime of heat preservation, P _kThe pressure applied at the highest temperature;

FIG. 2 is a schematic view showing the pressure loading and unloading manner in comparative example 2, wherein t _pFor dwell time, T _mAt the maximum sintering temperature, t _TIs T _mTime of heat preservation, P _kThe pressure applied at the highest temperature;

FIG. 3 is a schematic view showing the pressure loading and unloading manner in example 1, wherein t _pFor dwell time, T _mAt the maximum sintering temperature, t _TIs T _mTime of heat preservation, P _kThe pressure applied at the highest temperature;

FIG. 4 is a schematic view of the surface of the ceramic body obtained in comparative example 1;

FIG. 5 is a schematic view of the surface of the ceramic body obtained in comparative example 2;

FIG. 6 is a schematic view of the surface of the ceramic body obtained in example 1;

FIG. 7 is a physical representation of a sample ceramic body obtained in comparative example 2;

FIG. 8 is a pictorial representation of a sample of the ceramic body obtained in example 1;

fig. 9 is an SEM image of the ceramic sample obtained in example 1.

Detailed Description

The present invention will be described in further detail with reference to examples, but the scope of the present invention is not limited to these examples.

Comparative example 1

According to Sr (Zr) _0.2Sn _0.2Ti _0.2Hf _0.2Nb _0.2)O ₃Respectively weighing strontium carbonate and other metal oxides according to the stoichiometric ratio of 40g in total, and adding the strontium carbonate and other metal oxides into a nylon tank; mixing and ball-milling the mixture for 36 hours on a planetary ball mill by taking absolute ethyl alcohol as a ball-milling medium, and stopping milling for 10 minutes every 30 minutes; drying at 100 ℃ to obtain a raw material precursor; presintering the raw material precursor at 1000 deg.C for 2 hr, grinding, sieving with 200 mesh sieve, placing into high-strength graphite mold, placing into hot-pressing furnace, vacuumizing to make vacuum degree in furnace reach 10 ^-2Pa; heating from room temperature at a rate of 20 ℃/min, and when the furnace temperature is increased to 500 ℃, loading pressure reaches 15 MPa; the sintering temperature is 1250 ℃, and the heat preservation time is 120 minutes; when the sample is cooled to 500 ℃ along with the furnace, the pressure is unloaded; the sample is placed into a tube furnace after being naturally cooled, and is thermally annealed for 2 hours at 1050 ℃ in a flowing air atmosphere to obtain a high-entropy ceramic sample, and the surface of the sample is crushed, as shown in figure 4.

Comparative example 2

According to Sr (Zr) _0.2Sn _0.2Ti _0.2Hf _0.2Nb _0.2)O ₃According to total amount 4Weighing strontium carbonate and other metal oxides in a stoichiometric ratio of 0g respectively, and adding the strontium carbonate and other metal oxides into a nylon tank; mixing and ball-milling the mixture for 36 hours on a planetary ball mill by taking absolute ethyl alcohol as a ball-milling medium, and stopping milling for 10 minutes every 30 minutes; drying at 100 ℃ to obtain a raw material precursor; presintering the raw material precursor at 1000 deg.C for 2 hr, grinding, sieving with 200 mesh sieve, placing into high-strength graphite mold, placing into hot-pressing furnace, vacuumizing to make vacuum degree in furnace reach 10 ^-2Pa; heating from room temperature at a speed of 20 ℃/min, loading the pressure to 15MPa when the temperature is raised to 1250 ℃, keeping for 120 minutes, and synchronizing the temperature reduction process and the pressure unloading process; and naturally cooling the sample along with the furnace body, then placing the sample into a tubular furnace, and carrying out thermal annealing at 1050 ℃ for 2 hours in a flowing air atmosphere to obtain the high-entropy ceramic sample. The sample underwent partial fragmentation as shown in figures 5 and 7. Fig. 5 is a schematic diagram of a sample, and fig. 7 is a pictorial view of a prepared sample.