CN102503418B - A kind of low temperature liquid phase sintering La2Zr2O7 ceramics and sintering method - Google Patents

Abstract

A low-temperature liquid-phase sintered La ₂ Zr ₂ O ₇ ceramic, which is composed of 97% to 99.5% of La ₂ Zr ₂ O ₇ and 0.5% to 3% of CuO-TiO ₂ by weight percentage, and its preparation method includes: mixing ingredients Material, pressing and sintering are three steps. The present invention introduces the binary sintering aid CuO-TiO ₂ into La ₂ Zr ₂ O ₇ and obtains La ₂ Zr ₂ O ₇ ceramics by normal pressure sintering; by adjusting the content of CuO-TiO ₂ and controlling the sintering process, the CuO _-TiO2 forms a liquid phase at low temperature, which changes the sintering mechanism of La ₂ Zr ₂ O ₇ from solid phase sintering to liquid phase sintering, thus greatly reducing the sintering temperature and obtaining dense La ₂ Zr ₂ O ₇ ceramic blocks at about 1100 °C body, the prepared ceramic grains are smaller, the mechanical properties are good, and the energy consumption is low. The composition of the invention is reasonable, the preparation process is simple, the sintering temperature is low, and the La ₂ Zr ₂ O ₇ grains prepared by sintering are fine and dense; it can realize the preparation of La ₂ Zr ₂ O ₇ thermal barrier coating or La ₂ Zr ₂ O at low temperature ₇ bulk ceramic materials. Suitable for industrial applications.

Description

A kind of low temperature liquid phase sintering La2Zr2O7 ceramics and sintering method

Technical field:

The invention relates to a low-temperature liquid-phase sintered La ₂ Zr ₂ O ₇ ceramic and a sintering method, specifically referring to adding different contents of binary sintering additive CuO-TiO ₂ to realize low-temperature sintering of La ₂ Zr ₂ O ₇ . The invention belongs to the technical field of preparation of structural ceramic materials.

Background technique:

Thermal barrier coating is a thermal protective coating consisting of a ceramic thermal insulation surface layer and an anti-oxidation bonding primer. Aiming at the problem of poor high temperature thermal stability of the traditional ceramic heat insulation surface material 8YSZ (8wt.%Y ₂ O ₃ -ZrO ₂ ), a series of zirconia stabilized by different stabilizers have been developed. Studies have shown that these materials are compared with 8YSZ , the overall performance has not been significantly improved. In recent years, zirconate ceramics with a pyrochlore structure have become one of the hot spots in the research of thermal barrier coating ceramic thermal insulation surface materials due to their good high temperature thermal stability and thermal insulation performance. Among them, La ₂ Zr ₂ O ₇ has excellent high-temperature thermal stability, does not undergo phase transition in the temperature range from room temperature to 1300 ° C, and has a lower thermal conductivity than 8YSZ, and has become a promising development for temperature A new type of thermal barrier coating ceramic material over 1200 °C.

Thermal barrier coatings are usually prepared by plasma spraying or electron beam physical vapor deposition, but these two methods require large equipment investment and high production costs, and are not suitable for substrates with complex shapes. To this end, a variety of thermal barrier coating preparation methods have been developed, such as slurry spraying, electrophoretic deposition, sol-gel, etc. Among them, the slurry spraying method is not limited by the shape of the metal substrate, and is suitable for various shapes. In addition to the characteristics of simple, cheap and low-cost equipment, it also has the advantages of large film-forming area, uniform film thickness, fast film-forming rate and easy control of film thickness. Therefore, this method has a wide range of applications and is suitable for mass production. , is a very promising thermal barrier coating preparation method developed in recent years. At present, the key factor why the slurry spraying method has not been widely used in the preparation of thermal barrier coatings is that the ceramic material of thermal barrier coatings (8YSZ) has a high melting point, and the sintering temperature above 1400 ° C is required to make the coatings. The layer reaches a certain density to obtain a coating that can be used in practice, and the long-term use temperature of the matrix Ni alloy is about 1100 ° C. Using conventional sintering methods, the metal matrix will be deformed or even melted at high temperatures, and the preparation process is difficult. the

Although La ₂ Zr ₂ O ₇ has a lower melting point than 8YSZ, its sintering temperature is also around 1400°C. The sintering temperature must be lowered to obtain dense La ₂ Zr ₂ O on the Ni alloy substrate by slurry spraying method. ₇ thermal barrier coating. Generally, there are two main methods to reduce the sintering temperature of ceramic materials: one is to reduce the particle size of the powder, and use ultra-fine powder as raw material. However, this method is complicated in process and high in cost. Another method is to add suitable additives, which will generate a liquid phase during sintering to form liquid phase sintering, or the additives will form a replacement solid solution with the ceramic matrix, which will deform the lattice to activate the lattice, form holes or The migration of atoms and the deformation of the crystal lattice play a role in activating sintering, thereby promoting the densification process, so that the material can be sintered and dense at a lower temperature. So far, there have been no literature or patent reports on low-temperature sintering of La ₂ Zr ₂ O ₇ ceramics.

Contents of the invention

The purpose of the present _invention is to overcome the deficiencies of the prior art and provide a low-temperature liquid-phase _{sintered La2Zr2O7} ceramics with reasonable components, simple sintering process, easy operation, low sintering temperature, fine grains of sintered products, and compactness. Sintered side.

A low-temperature liquid-phase sintered _La2Zr2O7 ceramic of the present _invention is _composed of the following components by weight percentage:

La ₂ Zr ₂ O ₇ 97%～99.5%,

CuO-TiO ₂ 0.5%-3%, wherein: the mass ratio of CuO to TiO ₂ is 5:1.

In the low-temperature liquid phase sintered La ₂ Zr ₂ O ₇ ceramics of the present invention, the particle size of the La ₂ Zr ₂ O ₇ powder is ≤1 μm, and the purity is >99.5%; the CuO-TiO ₂ powder is analytically pure.

A kind of sintering method of low temperature liquid phase _{sintering La2Zr2O7} ceramics of the present _invention , comprises the following steps:

The first step: ingredients and mixing

Weigh 97% to 99.5% of La ₂ Zr ₂ O ₇ and 0.5% to 3% of CuO-TiO ₂ powder by weight percentage and mix them for wet ball milling; dry the slurry obtained after ball milling at 80°C for 20 hours, Pass through a 100-mesh standard sieve after drying to obtain mixed powder; wherein, CuO and _TiO The mass ratio is 5: 1;

The second step: pressing

Add 1% to 3% polyvinyl alcohol as a binder in the mixed powder, mix it evenly and press it at 35Mpa, then raise the temperature to 300°C to 400°C at a heating rate of 3 to 8°C, and keep it warm for 0.5 to 1.5°C h, remove the added binder; obtain compact;

The third step: sintering

The compact is raised to 1100-1400°C at a heating rate of 3-8°C/min, held at a temperature of 3-5 hours for normal pressure sintering, and then cooled in a furnace to obtain a La ₂ Zr ₂ O ₇ ceramic material.

In the present invention, the wet ball milling is carried out in a zirconia ball milling tank on a planetary ball mill, the ball-to-material ratio: (4-6): 1, the balls: zirconia balls, the ball milling medium: absolute ethanol, and the milling time is 12 ~24h. the

In the present invention, the atmospheric pressure sintering is carried out in a high temperature atmospheric pressure oxidation furnace. the

The method proposed by the present invention can be used to prepare La ₂ Zr ₂ O ₇ thermal barrier coatings or La ₂ Zr ₂ O ₇ bulk ceramic materials at low temperature (1100° C.).

Advantage and beneficial effect that the present invention has with respect to prior art:

(1) In the present invention, by adding CuO-TiO ₂ composite powder as a sintering aid, the sintering and densification of La ₂ Zr ₂ O ₇ ceramics can be completed at a lower sintering temperature (1100°C), air atmosphere and normal pressure conditions process. Therefore, the method of the present invention can make the preparation of La ₂ Zr ₂ O ₇ thermal barrier coating adopt the process of slurry spraying-low temperature sintering, avoid the use of high-cost plasma spraying or electron beam physical vapor deposition process, and can greatly reduce the La _{2 Production} costs of _Zr2O7 thermal barrier coatings.

(2) In the method of the present invention, by adding sintering aid CuO-TiO ₂ to La ₂ Zr ₂ O ₇ , a liquid phase will appear during the sintering process, thereby greatly reducing the sintering temperature, and the prepared La ₂ Zr ₂ O ₇ material has a High density, uniform distribution of fine grains, good mechanical properties, and reduced energy consumption. When the mass ratio of CuO to _TiO2 is 5:1, there is a low eutectic point at 919 ° C, and a liquid phase will appear during the sintering process, which will accelerate the diffusion rate of lanthanum zirconate and promote its densification, but the temperature is too high When it is low, the solid-phase diffusion between lanthanum zirconate particles is still very slow, and densification cannot be achieved. The experimental results show that when the sintering temperature reaches 1100°C, dense La ₂ Zr ₂ O ₇ blocks can be obtained, which is more than 300°C lower than the sintering temperature without adding sintering aids.

(3) The equipment and process route used in the present invention are simple, with good stability and reproducibility, which is beneficial to industrial production and further promotes the application of La ₂ Zr ₂ O ₇ materials.

In summary, the composition of the present invention is reasonable, the sintering process is simple, the operation is convenient, the sintering temperature is low, and the La ₂ Zr ₂ O ₇ grains prepared by sintering are fine and dense; La ₂ Zr ₂ can be prepared at low temperature (1100°C). O ₇ thermal barrier coating or La ₂ Zr ₂ O ₇ bulk ceramic material. Suitable for industrial applications.

Description of drawings:

Accompanying drawing 1 is the SEM photo of the La ₂ Zr ₂ O ₇ ceramic block prepared in Example 1 of the present invention.

Accompanying drawing 2 is the SEM picture of the La ₂ Zr ₂ O ₇ ceramic block prepared in the comparative example of the present invention.

It can be seen from the SEM photos of accompanying drawings 1 and 2 that when sintered at 1100°C, the La ₂ Zr ₂ O ₇ ceramics prepared by the method of the present invention have higher density, fine grains, and almost no pores. The structure of ₂ Zr ₂ O ₇ ceramic sintered blocks is loose, and the shape of the particles basically does not change, but only bonded.

Detailed ways

The method for testing and analyzing the structure and performance of the La ₂ Zr ₂ O ₇ ceramic material prepared in the embodiment of the present invention is as follows:

1. Determine the density of ceramic block materials by Archimedes drainage method;

2. Use a Sirion 200 field emission scanning electron microscope (Scanning Electron Microscope, SEM) to observe the microstructure and morphology of the samples. the

3. Use an electronic universal testing machine to test the flexural strength of the sample. The hardness of the samples was tested using a Vickers microhardness tester. the

Example 1:

Weigh raw materials La ₂ Zr ₂ O ₇ and CuO-16.7wt% TiO ₂ according to the ratio of La ₂ Zr ₂ O ₇ +0.5wt% (CuO-16.7wt%TiO ₂ ): Weigh 49.75g of La ₂ Zr ₂ O ₇ , CuO 0.2083g, TiO ₂ 0.0417g. Put the powder in a zirconia ball mill jar, add absolute ethanol as a ball milling medium according to 1.5 times the total weight of the mixture, add zirconia balls at a ball-to-material ratio of 4:1, and ball mill on a planetary ball mill for 12 hours to obtain a slurry. The mixed slurry was dried at 80°C for 20 hours, and passed through a 100-mesh standard sieve to obtain a mixture; 1wt.% polyvinyl alcohol was added to the mixture as a binder, and then pressed into small discs at 35MPa, and the small The wafer was heated to 300°C at a rate of 5°C/min in a high-temperature atmospheric pressure oxidation furnace, and kept at a temperature of 0.5h for degumming treatment. After degumming, the sample was sintered without pressure at a heating rate of 5°C/min to 1100°C for 5 hours. After cooling in the furnace, a dense La ₂ Zr ₂ O ₇ ceramic block was obtained. The SEM photo of the prepared La ₂ Zr ₂ O ₇ ceramic block is shown in Figure 1, and the density, hardness and bending strength of the ceramic block were measured. Under these conditions, the density of the sample is 96.34%, its hardness is 1790.96Hv, and the bending strength is 354.23MPa.

Example 2:

Weigh raw materials La ₂ Zr ₂ O ₇ and CuO-16.7wt% TiO ₂ according to the ratio of La ₂ Zr ₂ O ₇ +1.5wt% (CuO-16.7wt%TiO ₂ ): Weigh 49.25g of La ₂ Zr ₂ O ₇ , CuO 0.625g, TiO ₂ 0.125g. Put the powder in a zirconia ball mill jar, add absolute ethanol as a ball milling medium according to 1.5 times the total weight of the mixture, add zirconia balls at a ball-to-material ratio of 5:1, and ball mill on a planetary ball mill for 18 hours to obtain a slurry. The mixed slurry was dried at 80°C for 20 hours, and passed through a 100-mesh standard sieve to obtain a mixture; 2wt.% polyvinyl alcohol was added to the mixture as a binder, and then pressed into small discs at 35MPa, and the small The wafer was heated to 350°C at a rate of 3°C/min in a high-temperature atmospheric pressure oxidation furnace, and held for 1 hour to perform degumming treatment. After degumming, the sample was heated up to 1250°C at a rate of 3°C/min for pressureless sintering for 4 hours. After cooling in the furnace, a dense La ₂ Zr ₂ O ₇ ceramic block was obtained. Density, hardness and flexural strength of the ceramic block were measured. Under these conditions, the density of the sample is 97.13%, the hardness is 1524.25Hv, and the bending strength is 286.52MPa.

Example 3:

Weigh raw materials La ₂ Zr ₂ O ₇ and CuO-16.7wt% TiO ₂ according to the ratio of La ₂ Zr ₂ O ₇ +3.0wt% (CuO-16.7wt%TiO ₂ ): Weigh 48.5g of La ₂ Zr ₂ O ₇ , CuO 0.1.25g, TiO ₂ 0.25g. Put the powder in a zirconia ball mill jar, add absolute ethanol as a ball milling medium according to 1.5 times the total weight of the mixture, add zirconia balls at a ball-to-material ratio of 6:1, and ball mill on a planetary ball mill for 24 hours to obtain a slurry. The mixed slurry was dried at 80°C for 20 hours, and the mixture was obtained after passing through a 100-mesh standard sieve; 3wt.% polyvinyl alcohol was added to the mixture as a binder, and then pressed into small discs at 35MPa, and the small The wafer was heated to 400°C at a rate of 8°C/min in a high-temperature atmospheric pressure oxidation furnace, and kept for 1.5h for degumming treatment. After degumming, the sample was sintered without pressure at a heating rate of 8°C/min to 1400°C for 5 hours. After cooling in the furnace, a dense La ₂ Zr ₂ O ₇ ceramic block was obtained. Density, hardness and flexural strength of the ceramic block were measured. Under these conditions, the density of the sample is 98.66%, the hardness is 1859.25Hv, and the bending strength is 362.03MPa.

Comparative example;

Weigh 50g of 8YSZ powder, place the powder in a zirconia ball mill jar, add absolute ethanol as a ball mill medium by 1.5 times the total weight of the mixture, and ball mill it on a planetary ball mill for 12 hours to obtain a slurry. Dry at 80°C for 20 hours, and pass through a 100-mesh standard sieve to obtain a mixture; add 1wt.% polyvinyl alcohol as a binder in the mixture, and then press it into small discs at 35MPa, and put the small discs under high temperature and normal pressure In the oxidation furnace, the temperature was raised to 300°C at a rate of 5°C/min, and kept at a temperature of 0.5h for degumming treatment. After degumming, the sample was sintered without pressure at a heating rate of 5°C/min to 1100°C for 5 hours. After cooling in the furnace, a dense La ₂ Zr ₂ O ₇ ceramic block was obtained. The SEM photo of the prepared La ₂ Zr ₂ O ₇ ceramic block is shown in Figure 2, and the density, hardness and bending strength of the ceramic block are measured. Density, hardness and flexural strength of the ceramic block were measured. Under these conditions, the density of the sample is 62.51%, the hardness is 138.18Hv, and the bending strength is 45.32MPa.

It can be seen from the above experimental examples that after adding sintering aids, the sintering temperature is reduced, the density of the sample is greatly improved, and the mechanical properties are also improved. the

Claims (4)

1. a low-temp liquid-phase sintering La ₂zr ₂o ₇pottery, by weight percentage, is comprised of following component:

La ₂Zr ₂O ₇97%～99.5%，

CuO-TiO ₂0.5%～3%, wherein: CuO and TiO ₂mass ratio be 5:1;

Described low-temp liquid-phase sintering La ₂zr ₂o ₇the sintering method of pottery, comprises the steps:

The first step: batching, batch mixing

Percentage composition takes 97%～99.5% La by weight ₂zr ₂o ₇with 0.5%～3% CuO-TiO ₂wet ball-milling is carried out in powder mixing; By the slip obtaining after ball milling dry 20h at 80 ℃, after drying, cross 100 mesh standard sieves, obtain mixed powder; Wherein, CuO and TiO ₂mass ratio be 5:1;

Second step: die mould

In mixed powder, add 1%～3% polyvinyl alcohol as binding agent, after mixing, under 35Mpa after compression moulding, with the temperature rise rate of 3～8 ℃/min, be warming up to 300 ℃～400 ℃, insulation 0.5～1.5h, sloughs the binding agent of interpolation; Obtain pressed compact;

The 3rd step: sintering

Pressed compact is warming up to 1100 ℃～1400 ℃ with the temperature rise rate of 3～8 ℃/min, and insulation 3～5h carries out normal pressure-sintered, obtains La after furnace cooling ₂zr ₂o ₇stupalith.

2. a kind of low-temp liquid-phase sintering La according to claim 1 ₂zr ₂o ₇pottery, is characterized in that: described La ₂zr ₂o ₇the granularity of powder is≤1 μ m, purity >99.5%; Described CuO-TiO ₂powder is analytical pure.

3. a kind of low-temp liquid-phase sintering La according to claim 1 ₂zr ₂o ₇pottery, is characterized in that: in the zirconia ball grinding jar of described wet ball-milling on planetary ball mill, carry out ratio of grinding media to material: (4～6): 1, and abrading-ball: zirconium oxide balls, ball-milling medium: dehydrated alcohol, Ball-milling Time 12～24h.

4. a kind of low-temp liquid-phase sintering La according to claim 1 ₂zr ₂o ₇pottery, is characterized in that: described normal pressure-sinteredly carry out in high-temperature pressure oxidized still.

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