Super-high porosity high-entropy rare earth silicate with good high-temperature resistance and preparation method

Abstract

The present application relates to the field of lightweight porous high-temperature thermal insulation materials, and particularly relates to a high-porosity high-entropy rare earth silicate with good high-temperature resistance and a preparation method. a Ho b Yb c Lu d X e )2Si2O7, wherein a, b, c and d are in the range of 10% to 35% in terms of molar percentage, e is in the range of 0% to 35% in terms of molar percentage, a+b+c+d+e=1, and X is Sc, Tm, Er, Dy or Tb; the porosity of the high-entropy rare earth silicate material is in the range of 85% to 96%. The above rare earth oxide and silicon oxide powder are used as raw materials, a ceramic slurry is prepared with water as a dispersion medium, a dispersant is added to uniformly disperse the slurry particles, a foaming agent is then added and rapidly stirred to foam, followed by mold injection and low-temperature freezing, then vacuum drying and demolding. Finally, high-temperature sintering in a muffle furnace is performed to prepare the porous high-entropy rare earth silicate high-temperature thermal insulation material. The present application has simple preparation process, low cost, and is green and environmentally friendly, and has broad application prospects in the field of thermal protection of aerospace.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lightweight porous high-temperature thermal insulation materials, in particular to a super-high-porosity high-entropy rare earth silicate with good high-temperature resistance and a preparation method. BACKGROUND

[0002] With the rapid development of aerospace technology, hypersonic vehicles will produce serious aerodynamic heating when flying at high speed, causing the surface temperature of the vehicle to rise rapidly (> 1500℃). Severe aerodynamic heating will cause thermal stress to the internal structure of the vehicle, reducing the strength of the vehicle and damaging the integrity of the structure. Ceramic fiber rigid insulation tiles are one of the commonly used thermal protection materials, and their application area accounts for 68% of the total thermal protection surface, such as the BRI series and AETB series of the third generation of fiber insulation tiles in the United States, which have the advantages of light weight and good thermal insulation performance; however, their long-term service temperature is generally less than 1300℃, and the shortcoming is poor high-temperature resistance, as shown in Table 1. Although these materials have low density and thermal conductivity, they will undergo severe shrinkage during thermal cycling (i.e., during service). Such high shrinkage will significantly affect the aerodynamic shape of the vehicle, and the thermal protection system will produce large gaps, posing a serious threat to the safety of the vehicle. Therefore, it is of great significance to develop a new type of lightweight high-strength low-thermal-conductivity thermal insulation material with good high-temperature resistance.

[0003] Table 1 Shrinkage change of LI-2200 and AETB after heating in air for 10 min

[0004]

[0005] Rare earth silicates have become the matrix material of new high-temperature thermal insulation materials due to their high melting point, very low thermal conductivity, good machinability and resistance to hot gas corrosion, high chemical and thermal stability, and low linear thermal expansion coefficient. In addition, high-entropy ceramics have four core effects, so they exhibit more excellent comprehensive performance in terms of performance, such as better strength, lower thermal conductivity, and higher melting point. For example, multi-principal-element rare earth silicates have higher melting points (about 100-200℃ higher) and better phase stability than single-principal-element rare earth silicates (L.C. Sun et al. Materials Research Letters. 2020; 8: 424-430.). Therefore, using high-entropy rare earth silicates as the matrix material of new thermal insulation materials is expected to achieve better high-temperature resistance, thereby developing new high-temperature thermal insulation materials with excellent comprehensive performance. SUMMARY

[0006] In order to solve the problems existing in the high-temperature insulation field and the urgent need for new insulation materials, the purpose of the present application is to provide a high-temperature-resistant super-high-porosity high-entropy rare earth silicate and a preparation method, which can obtain a high-entropy rare earth silicate porous ceramic insulation material with super-high porosity, low thermal conductivity and excellent high-temperature resistance.

[0007] The technical scheme of the present application is as follows:

[0008] A high-temperature-resistant super-high-porosity high-entropy rare earth silicate, the high-entropy rare earth silicate is specifically a single-phase (Y a Ho b Yb c Lu d X e )2Si2O7, the value range of a, b, c and d is 10% to 35% in terms of mole percentage, the value range of e is 0% to 35%, and a+b+c+d+e=1, X is Sc, Tm, Er, Dy or Tb, and the porosity range of the high-entropy rare earth silicate material is 85% to 96%.

[0009] The high-temperature-resistant super-high-porosity high-entropy rare earth silicate, preferably, the value range of a is 20% to 30%, the value range of b is 20% to 30%, the value range of c is 15% to 30%, the value range of d is 15% to 30%, and the value range of e is 0% to 15%.

[0010] A preparation method of a high-temperature-resistant super-high-porosity high-entropy rare earth silicate, the specific steps are as follows:

[0011] (1) mixing: uniformly ball-milling Y2O3 powder, Ho2O3 powder, Yb2O3 powder, Lu2O3 powder, X2O3 powder and SiO2 powder to form a mixed powder;

[0012] (2) preparing slurry: adding deionized water 20 to 45 parts, dispersant 0.5 to 5 parts, YSZ fiber 0 to 35 parts, and mixed powder 10 to 50 parts as raw materials in sequence according to mass fraction, stirring for 1 to 5 hours to form a slurry with uniformly dispersed particles;

[0013] (3) foaming-gel casting: placing the above slurry in a water bath at 35 to 75 DEG C, then adding foaming agent 1 to 10 parts according to mass fraction, quickly stirring to foam, then adding gelatin 1 to 10 parts and surfactant 1 to 5 parts, stirring and casting;

[0014] (4) freeze-drying: placing the ceramic foam body and mold after casting into a freezer at-25 to-70 DEG C for low-temperature freezing, then drying in a vacuum environment, and then demolding the body;

[0015] (5) high-temperature sintering: high-temperature reaction sintering is carried out at 1400-1600 DEG C in air for 1-5 hours, and high-entropy (Y a Ho b Yb c Lu d X e )2Si2O7 porous ceramics with super-high porosity, low thermal conductivity and excellent high-temperature resistance are prepared.

[0016] The preparation method of the super-high porosity high-entropy rare earth silicate with good high-temperature resistance, in step (1), the ball milling method is wet planetary ball milling, and the wet planetary ball milling process parameters are as follows: the rotation speed is 100-500 r / min, and the ball milling time is 6-48 h.

[0017] The preparation method of the super-high porosity high-entropy rare earth silicate with good high-temperature resistance, in step (2), the dispersing agent is poly-methyl-acrylic acid ammonium, citric acid or ammonium citrate.

[0018] The preparation method of the super-high porosity high-entropy rare earth silicate with good high-temperature resistance, in step (2), the YSZ fiber is preferably 1-20 parts.

[0019] The preparation method of the super-high porosity high-entropy rare earth silicate with good high-temperature resistance, in step (3), the foaming agent is ammonium lauryl sulfate or sodium lauryl sulfate, the gelling agent is starch, gelatin or agar, and the surface active agent is glycerol or polyethylene glycol, and the stirring speed of the rapid stirring mixer ranges from 500 to 5000 rpm.

[0020] The preparation method of the super-high porosity high-entropy rare earth silicate with good high-temperature resistance, in step (4), the low-temperature freezing time is 1-24 hours, and the vacuum drying time is 10-48 hours.

[0021] The preparation method of the super-high porosity high-entropy rare earth silicate with good high-temperature resistance, the compressive strength of the prepared high-entropy rare earth silicate porous ceramic is 0.3-10 MPa, the thermal conductivity is 0.05-0.35 W / (m*K), and the heat treatment line shrinkage is less than 1.5%.

[0022] The design idea of the present application is:

[0023] In order to solve the problem of high shrinkage of thermal protection materials at high temperature in the current thermal insulation field, the present application adopts a foaming-precipitation-cold drying process, which has the advantages of direct foaming method, gel injection molding method and cold drying method, and can easily prepare low-density, low-thermal-conductivity, super-high-porosity (85%-96%), high-temperature-resistant and complex-shaped porous ceramics. Using multi-principal-element rare earth silicate as raw material, the high-entropy effect is used to improve the melting point, phase stability and high-temperature resistance of the material, reduce the thermal conductivity and improve the mechanical properties.

[0024] The advantages and beneficial effects of the present application are as follows:

[0025] 1. The present application prepares ultra-light high-entropy rare earth silicate porous ceramic thermal insulation materials by foaming-injection gelling-freeze drying method, the porosity of which is as high as 85-96%, the compressive strength reaches 0.3-10 MPa, the thermal conductivity reaches 0.05-0.35 W / (m·K), and the heat treatment linear shrinkage is less than 1.5%.

[0026] 2. The present application is easy to operate, has a simple process flow, is green and environmentally friendly, and is easy to realize industrialization.

[0027] 3. The ultra-high porosity high-entropy rare earth silicate porous ceramic prepared by the present application is expected to become a high-temperature thermal insulation material (~1500℃) with excellent performance, and has a broad application prospect in the field of aerospace thermal protection. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 Scanning electron microscope (SEM) photos of high-entropy (Y 0.2 Ho 0.1 Yb 0.3 Lu 0.3 Dy 0.1 )2Si2O7 porous ceramics.

[0029] Figure 2 X-ray tomography photos of YSZ fiber reinforced high-entropy (Y 0.3 Ho 0.2 Yb 0.1 Lu 0.35 Sc 0.05 )2Si2O7 porous ceramics.

[0030] Figure 3 X-ray diffraction spectra of YSZ fiber reinforced high-entropy (Y 0.25 Ho 0.25 Yb 0.25 Lu 0.25 )2Si2O7 porous ceramics. DETAILED DESCRIPTION

[0031] In the specific implementation process, the present application takes rare earth oxide and silicon oxide powder as raw materials, adjusts the adding amount of YSZ fiber, YSZ acts as a reinforcing phase, improves the mechanical strength of the super-high porosity porous ceramic through fiber bridging or fiber pulling-out mechanism, and optimizes the thermal performance to reduce the thermal conductivity of the material, configures slurry with water as a dispersion medium, stirs the slurry for 1-5 hours, adds a dispersing agent (poly-methyl-acrylic-ammonium, citric acid or ammonium citrate), then heats the above slurry to 35-75 DEG C, sequentially adds a foaming agent (ammonium lauryl sulfate or sodium lauryl sulfate), a gelling agent (starch, gelatin or agar) and a surfactant (glycerol or polyethylene glycol) under rapid stirring, and then performs mold injection and freezing, followed by vacuum drying, green body demolding. Finally, high-temperature sintering is performed at 1400-1600 DEG C to prepare high-entropy rare earth silicate porous ceramic, so as to obtain a heat insulation material with high porosity, low thermal conductivity and excellent high-temperature resistance, the preparation process is simple, convenient to operate, low in cost, and has wide industrial production prospect.

[0032] The present application is further described in detail below with reference to the drawings and examples.

[0033] Example 1

[0034] In this embodiment, 35g of deionized water is first weighed, and 0.5g of citric acid and 25g of mixed powder with a molar ratio of Y2O3:Ho2O3:Yb2O3:Lu2O3:Dy2O3:SiO2 being 2:1:3:3:1:20 are sequentially added under constant stirring to mix and stir for 1 hour to form a uniformly dispersed slurry; then the above slurry is placed in a water bath at 35 DEG C, 10g of ammonium lauryl sulfate is added, and foaming is performed under rapid stirring (stirring machine speed is 1500rpm) for 10 minutes, followed by adding 10g of gelatin and 5g of polyethylene glycol, and then the slurry is stirred and injected into a mold;

[0035] The green body after mold injection and the mold are placed in a freezing box at-25 DEG C for low-temperature freezing for 24 hours, then dried for 20 hours in a vacuum environment, and then the green body is demolded; finally, high-temperature reaction sintering is performed at 1600 DEG C in air for 1 hour to prepare high-entropy (Y 0.2 Ho 0.1 Yb 0.3 Lu 0.3 Dy 0.1 )2Si2O7 porous heat insulation ceramic with super-high porosity and low thermal conductivity.

[0036] In this embodiment, high-entropy (Y 0.2 Ho 0.1 Yb 0.3 Lu 0.3 Dy 0.1The porosity of the porous ceramic of Y2Si2O7 is 95%, the compressive strength is 0.36 MPa, and the thermal conductivity is 0.07 W / (m·K). As shown in FIG. 2, it can be seen from the SEM photos of the micro-morphology of the porous ceramic sample that the macropore size distribution of the sample is 50-300 μm, and the micropore size is 0.1-5 μm. After 3 high-temperature thermal cycles of 1550°C for 2h, the shrinkage of the high-entropy rare earth silicate porous ceramic in the plane direction is 0.25%, and the shrinkage in the thickness direction is 0.37%. Figure 1

[0037] Example 2

[0038] In this embodiment, 20 g of deionized water is weighed out, and 5 g of poly (ammonium methacrylate), 4 g of YSZ fiber and 24 g of mixed powder of Y2O3: Ho2O3: Yb2O3: Lu2O3: Sc2O3: SiO2 in a molar ratio of 6:4:2:7:1:40 are sequentially added under constant stirring, mixed and stirred for 2 hours to form a uniformly dispersed slurry; then the above slurry is placed in a water bath at 50°C, 1 g of sodium dodecyl sulfate is added, and rapid stirring (stirring speed of 3000 rpm) is carried out for foaming for 30 minutes, followed by adding 5 g of starch and 3 g of glycerol, and then pouring into a mold after stirring;

[0039] The green body and the mold after pouring are placed in a freezer at -40°C for low-temperature freezing for 12 hours, and then dried in a vacuum environment for 36 hours, after which the green body is demolded; finally, high-temperature reaction sintering is carried out at 1400°C in air for 5 hours to prepare a fiber-reinforced high-entropy (Y 0.3 Ho 0.2 Yb 0.1 Lu 0.35 Sc 0.05 )2Si2O7 porous ceramic with ultrahigh porosity and low thermal conductivity.

[0040] In this embodiment, the YSZ fiber-reinforced high-entropy (Y 0.3 Ho 0.2 Yb 0.1 Lu 0.35 Sc 0.05 )2Si2O7 porous ceramic has a porosity of 89%, a compressive strength of 3.96 MPa, and a thermal conductivity of 0.15 W / (m·K). As shown in FIG. 4, it can be seen from the XRT photos of the X-ray tomography of the YSZ fiber-reinforced porous ceramic that the fibers are uniformly distributed in the sample. Figure 2

[0041] After 3 high-temperature thermal cycles of 1550°C for 2h, the shrinkage of the YSZ fiber-reinforced high-entropy rare earth silicate porous ceramic in the plane direction is 0.71%, and the shrinkage in the thickness direction is 1.16%. ​​

[0042] Example 3

[0043] In this embodiment, 45g of deionized water was first weighed, and 3g of ammonium citrate, 6g of YSZ fiber, and 40g of mixed powder with a molar ratio of Y2O3:Ho2O3:Yb2O3:Lu2O3:SiO2 of 1:1:1:1:8 were added sequentially while stirring continuously. The mixture was stirred for 3 hours to form a uniformly dispersed slurry. Then, the slurry was placed in a 70°C water bath, and 5g of sodium dodecyl sulfate was added. The mixture was stirred rapidly (stirring speed of 500 rpm) for 50 minutes to foam. Then, 1g of agar and 1g of glycerol were added, stirred, and then poured into a mold.

[0044] The preform and mold were placed in a -50°C freezer for 2 hours after injection molding, followed by vacuum drying for 10 hours. The preform was then demolded. Finally, it was sintered in air at 1550°C for 2 hours to produce YSZ fiber-reinforced high-entropy (YSZ) fiber-reinforced high-entropy (YSZ) fiber-reinforced high-entropy (YSZ) fiber with ultra-high porosity and low thermal conductivity. 0.25 Ho 0.25 Yb 0.25 Lu 0.25 )2Si2O7 porous ceramic.

[0045] In this embodiment, YSZ fiber reinforced high entropy (Y 0.25 Ho 0.25 Yb 0.25 Lu 0.25 The porous ceramic Si₂O₇ has a porosity of 92%, a compressive strength of 1.56 MPa, and a thermal conductivity of 0.10 W / (m·K). Figure 3 As shown in the XRD pattern, the phase composition of YSZ fiber-reinforced high-entropy rare-earth silicate porous ceramic and undoped fiber ceramic shows that after the addition of YSZ fibers, the YSZ fibers and (Y 0.25 Ho 0.25 Yb 0.25 Lu 0.25 The two phases of the 2Si2O7 matrix can coexist stably. After three high-temperature thermal cycles of 1550℃ for 2 hours, the planar shrinkage rate of the YSZ fiber-reinforced high-entropy rare-earth silicate porous ceramic is 0.59%, and the thickness shrinkage rate is 0.91%.

[0046] The results of the examples show that the present invention, using a foaming-injection-freeze-drying process, produces a high-entropy rare-earth silicate porous ceramic thermal insulation material with ultra-high porosity and low thermal conductivity. It also exhibits excellent high-temperature resistance; after heat treatment at 1550℃ for several hours, the linear shrinkage rate is less than 1.5%, significantly lower than the heat treatment shrinkage rate of the benchmark American rigid thermal insulation tile (by an order of magnitude). Furthermore, the preparation process of this invention is simple, low-cost, environmentally friendly, suitable for large-scale production, and has broad application prospects.

Claims

1. A high-temperature resistant, ultra-high porosity, high-entropy rare-earth silicate, characterized in that, High-entropy rare-earth silicates are specifically single-phase (Y) a Ho b Yb c Lu d X e In the high-entropy rare earth silicate material 2Si2O7, the values ​​of a, b, c, and d range from 10% to 35% by molar percentage, and the value of e ranges from 0% to 35%, and a+b+c+d+e=1, where X is Sc, Tm, Er, Dy, or Tb. The porosity range of the high-entropy rare earth silicate material is 85% to 96%, the compressive strength of the high-entropy rare earth silicate porous ceramic is 0.3 to 10 MPa, the thermal conductivity is 0.05 to 0.35 W / (m·K), and the heat treatment linear shrinkage is <1.5%.

2. The high-temperature resistant, ultra-high porosity, high-entropy rare-earth silicate according to claim 1, characterized in that, Preferably, the value of a ranges from 20% to 30%, the value of b ranges from 20% to 30%, the value of c ranges from 15% to 30%, the value of d ranges from 15% to 30%, and the value of e ranges from 0% to 15%.

3. A method for preparing a high-temperature resistant, ultra-high porosity, high-entropy rare-earth silicate according to any one of claims 1 to 2, characterized in that, The specific steps are as follows: (1) Mixing: Ball mill and mix Y2O3 powder, Ho2O3 powder, Yb2O3 powder, Lu2O3 powder, X2O3 powder and SiO2 powder evenly to form a mixed powder; (2) Preparation of slurry: According to the mass fraction, add 20-45 parts of deionized water, 0.5-5 parts of dispersant, 0-35 parts of YSZ fiber and 10-50 parts of mixed powder as raw materials, stir for 1-5 hours to form a slurry with uniform particle dispersion; (3) Foaming-gel casting: Place the above slurry in a water bath at 35-75°C, then add 1-10 parts of foaming agent by mass, stir quickly to foam, then add 1-10 parts of gelling agent and 1-5 parts of surfactant, stir and cast into mold; (4) Freeze-drying: After injection molding, the ceramic foam blank and the mold are placed in a freezer at -25 to -70°C for low-temperature freezing, then dried in a vacuum environment, and then the blank is demolded; (5) High-temperature sintering: High-entropy (Y) material with ultra-high porosity, low thermal conductivity and excellent high-temperature resistance is prepared by high-temperature reaction sintering at 1400-1600℃ in air for 1-5 hours. a Ho b Yb c Lu d X e )2Si2O7 porous ceramic.

4. The method for preparing ultra-high porosity high-entropy rare earth silicates with good high-temperature resistance according to claim 3, characterized in that, In step (1), the ball milling mixing method is wet planetary ball milling. The wet planetary ball milling process parameters are: rotation speed of 100 to 500 rpm and ball milling time of 6 to 48 hours.

5. The method for preparing ultra-high porosity high-entropy rare earth silicates with good high-temperature resistance according to claim 3, characterized in that, In step (2), the dispersant is ammonium polymethacrylate, citric acid or ammonium citrate.

6. The method for preparing ultra-high porosity high-entropy rare earth silicates with good high-temperature resistance according to claim 3, characterized in that, In step (2), the YSZ fiber is preferably 1 to 20 parts.

7. The method for preparing ultra-high porosity high-entropy rare earth silicates with good high-temperature resistance according to claim 3, characterized in that, In step (3), the foaming agent is ammonium dodecyl sulfate or sodium dodecyl sulfate, the gelling agent is starch, gelatin or agar, the surfactant is glycerol or polyethylene glycol, and the speed range of the mixer for rapid stirring is 500 to 5000 rpm.

8. The method for preparing ultra-high porosity high-entropy rare earth silicates with good high-temperature resistance according to claim 3, characterized in that, In step (4), the low-temperature freezing time is 1 to 24 hours, and the vacuum drying time is 10 to 48 hours.

9. The method for preparing ultra-high porosity high-entropy rare earth silicates with good high-temperature resistance according to claim 3, characterized in that, The prepared high-entropy rare-earth silicate porous ceramics have a compressive strength of 0.3–10 MPa, a thermal conductivity of 0.05–0.35 W / (m·K), and a heat treatment linear shrinkage of <1.5%.

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