CN114716228A - Ultrahigh temperature resistant low-heat-conductivity magnesium-aluminum-chromium multi-phosphate composite material and preparation method thereof - Google Patents

Abstract

The invention discloses a magnesium-aluminum-chromium polyphosphate composite material with ultra-high temperature resistance and low thermal conductivity and a preparation method thereof. The composite material is composed of magnesium oxide dispersed in a polyphosphate matrix, wherein the polyphosphate matrix is composed of phosphates including magnesium phosphate, aluminum phosphate and chromium phosphate; the composite material cleverly utilizes magnesium aluminum chromate phosphate It is designed in combination with the respective advantages of high-melting magnesium oxide oxide, and the synergistic effect of the two is used to obtain a magnesium-aluminum-chromium polyphosphate composite material with high temperature resistance over 2400 ° C and excellent thermal insulation properties. The method has the advantages of simple process and low cost of raw materials, and is favorable for large-scale industrial production.

Description

A kind of magnesium-aluminum-chromium polyphosphate composite material with ultra-high temperature resistance and low thermal conductivity and preparation method thereof

technical field

The invention relates to a thermal protection material, in particular to a magnesium-aluminum-chromium polyphosphate composite material with ultra-high temperature resistance and low thermal conductivity, and a preparation method thereof, belonging to the technical field of aerospace thermal protection material preparation.

Background technique

With the development of aerospace technology, the exploration of aerospace science has gradually spread to the wider solar system, which poses a challenge to the thermal protection system of the spacecraft. Insulation material is one of the key components in the thermal protection system, and it is an important guarantee for the normal operation of the electronic control system inside the spacecraft. Insulating materials prevent heat flow from being transferred to the interior of the aircraft through many complex chemical and physical reactions that melt or sublime in extreme environments. Insulation materials have played a vital role in thermal protection systems for the past half century. Ceramic-based thermal insulation materials are widely used in thermal insulation due to their high temperature resistance, high strength and low thermal conductivity. The two most representative categories are ceramic-based thermal insulation tiles and ceramic-based aerogel thermal insulation materials. However, these two materials have two common disadvantages: first, the preparation process is complicated, and both require heat treatment; second, the high temperature resistance is limited, and the highest is only 1500 °C. The limited thermal stability greatly limits its application in ultra-high temperature environments (above 2000 °C). Therefore, it is urgent to develop a new type of thermal insulation material with simple preparation process and high temperature resistance above 2000 °C.

Phosphate is a class of chemically bonded ceramic materials based on alkaline metal oxides and phosphoric acid or phosphate solution through acid-base reaction to achieve low temperature curing, with excellent thermal insulation properties, high temperature resistance and environmental protection properties. For example, Chinese patent (publication number CN106634626B) discloses a preparation method of phenolic resin modified high temperature resistant alcohol-soluble phosphate adhesive, which obtains a high temperature resistant and low-cost phosphate composite material, but because the resin itself The characteristic low melting point makes the phosphate composite material do not have the ability to withstand ultra-high temperature. Chinese Patent (Publication No. CN110105904A) discloses a sizing method of 1500 ℃ high temperature adhesive, which uses chemical methods to improve phosphate to obtain a phosphate composite material that can withstand 1500 ℃, but its composition is complex, forming There are many uncontrollable factors in the process, and it still cannot adapt to the working environment above 2000 °C. In order to obtain a phosphate composite material with better high temperature resistance, the applicant has done a lot of research in the early days. The prepared aluminum lanthanide phosphate composite material can withstand short-time ablation under oxyacetylene flame at 2000 °C, but the sample will be ablated after ablation. Cracks will affect engineering applications, and at the same time, it does not have the function of heat insulation. Therefore, simultaneously improving the high temperature resistance and thermal insulation performance of phosphate has become one of the important research directions of many researchers in the industry.

SUMMARY OF THE INVENTION

In view of the deficiencies in the prior art, the first object of the present invention is to provide a magnesium-aluminum-chromium polyphosphate composite material with ultra-high temperature resistance and low thermal conductivity, which cleverly utilizes magnesium-aluminum-chromium phosphate and high-melting point oxidation The respective advantages of magnesium oxides are combined and designed, and the synergistic effect of the two is used to obtain a magnesium-aluminum-chromium polyphosphate composite material with a high temperature resistance of over 2400 ° C and excellent thermal insulation properties; the magnesium-aluminum-chromium polyphosphate The composite material breaks the technical bottleneck that the existing thermal insulation materials cannot have excellent ultra-high temperature and thermal insulation properties at the same time, making it suitable for ultra-high temperature environments of 2400 ℃ and above, especially after 60s ablation of polyphosphate composite materials It still shows a state of ablation resistance close to zero line ablation rate and excellent thermal insulation performance with a maximum backside temperature of only 129 °C.

The second object of the present invention is to provide a method for preparing a magnesium-aluminum-chromium polyphosphate composite material with ultra-high temperature resistance and low thermal conductivity, which is simple in process, low in cost of raw materials, and conducive to large-scale industrial production.

In order to achieve the above technical purpose, the present invention provides a magnesium-aluminum-chromium polyphosphate composite material with ultra-high temperature resistance and low thermal conductivity, which is composed of magnesium oxide dispersed in a polyphosphate matrix; the polyphosphate matrix is composed of phosphoric acid. Phosphate composition including magnesium, aluminum phosphate and chromium phosphate.

The ultra-high temperature resistant and low thermal conductivity magnesium-aluminum-chromium polyphosphate composite material provided by the invention takes magnesium oxide and magnesium-aluminum-chromium polyphosphate as the main phase, and magnesium oxide, as one of the oxides with the highest melting point, has high strength, high melting point, chemical High activity characteristics; magnesium aluminum chromium polyphosphate has the characteristics of low temperature forming, low thermal conductivity and high strength. The inventors found that magnesium oxide and polyphosphate have excellent chemical compatibility and thermal matching, and can penetrate and closely combine with each other at low temperature to form a polyphosphate phase as a matrix, and the magnesium oxide phase is dispersed in a starburst shape. Polyphosphate composite material distributed therein. When the ultra-high temperature heat flow acts, the heat accumulates on the surface of the composite material, the temperature rises rapidly, and the polyphosphate phase gradually decomposes, which will lead to two phenomena at the same time: one is that the oxides left on the surface and the magnesium oxide form a high melting point in situ The magnesia-chromium spinel ceramic phase consolidates the ultra-high temperature resistance of the composite material; the other is that there will be a temperature gradient from the surface to the interior of the composite material, which will cause the phosphate in different positions to decompose to varying degrees, thus spontaneously forming a large number of microscopic particles. The pores hinder the transfer of heat, so that the entire composite material exhibits excellent ultra-high temperature resistance and low thermal conductivity.

As a preferred solution, the molar ratio of aluminum phosphate, chromium phosphate and magnesium phosphate in the polybasic phosphate matrix is 1:1-1.2:0.1-0.7. More preferably, the molar ratio of aluminum phosphate, chromium phosphate and magnesium phosphate is 1:1:0.1-0.7; most preferably, it is 1:1:0.1-0.3. When the molar ratio of aluminum phosphate, chromium phosphate, and magnesium phosphate in the polyphosphate matrix is within the above range, the magnesium-aluminum-chromium polyphosphate composite material has the most excellent ablation resistance and thermal insulation performance.

As a preferred solution, the magnesium oxide accounts for 30-80% of the total mass of the magnesium oxide and the polybasic phosphate matrix. Further preferably, the magnesium oxide accounts for 50-80% of the total mass of the magnesium oxide and the polybasic phosphate matrix; most preferably, it is 50-70%, and the magnesium oxide particles are dispersed in the polybasic phosphate matrix in a star-like shape after the reaction with the phosphate.

As a preferred solution, the particle size of the magnesium oxide is 300-800 nm. By controlling the particle size of magnesium oxide within the above range, the reaction between magnesium oxide and polyphosphate can form a magnesium-aluminum-chromium polyphosphate composite material with high strength, and the magnesium-aluminum-chromium polyphosphate composite material can also be It has excellent ablation performance and thermal insulation performance. If the particle size is too small, the ablation performance will be affected, and if the particle size is too large, the strength will be affected.

The invention also provides a preparation method of a magnesium-aluminum-chromium polyphosphate composite material with ultra-high temperature resistance and low thermal conductivity, which comprises the following steps:

1) uniformly mixing aluminum phosphate solution and chromium phosphate solution to obtain aluminum-chromium phosphate solution;

2) diluting the aluminum-chromium phosphate solution with water to obtain a dilute solution of aluminum-chromium phosphate;

3) After the aluminum-chromium phosphate dilute solution and the magnesium oxide powder are evenly mixed, solidify and form, and then the product is obtained.

As a preferred solution, in step 1), in the mixing process, the mixing ratio of the aluminum phosphate solution and the chromium phosphate solution is measured with the molar ratio of aluminum phosphate and chromium phosphate as 1:1 to 1.2, and the controlled mixing temperature is 85 to 95 ° C, The viscosity of the obtained aluminum-chromium phosphate solution is 7-16 Pa·s. The preferred concentration of the aluminum phosphate solution is 0.2-0.3 mol/L; the preferred concentration of the chromium phosphate solution is 0.2-0.35 mol/L. The preferred molar ratio of aluminum phosphate and chromium phosphate is 1:1.1-1.15. A preferable temperature is 90-95 degreeC. The mixing method can adopt the conventional stirring method, and the stirring time is 0.5-2h.

As a preferred solution, in step 2), in the dilution process, the mass ratio of the aluminum-chromium phosphate solution to water is 1 to 5:1, the control dilution temperature is 85 to 95°C, and the viscosity of the obtained aluminum-chromium phosphate dilute solution is 3～6Pa·s. By properly diluting the aluminum-chromium phosphate solution, the main purpose is the following two aspects. On the one hand, in order to slow down the coagulation and curing speed, if the concentration of the phosphate solution is too high, it will react violently with alkali metal oxides and affect the final performance; on the other hand, In order to make the system reach a suitable pH value, a large amount of metal cations and phosphate anions will be released during this process. The mass ratio of the aluminum-chromium phosphate solution to water is preferably 1 to 3:1. A preferable temperature is 85-95 degreeC. During the dilution process, a conventional stirring method is adopted, and the stirring time is 0.5-2h.

As a preferred solution, the magnesium oxide powder is subjected to the following high temperature pretreatment: heat preservation at 1300-1600° C. for 3-5 hours. The main purpose of high temperature heat treatment of magnesium oxide is to appropriately reduce its activity. Magnesium oxide without high temperature treatment has too high activity, and the reaction with phosphate is too violent, which will cause the material to solidify rapidly, and the solidification rate is too fast to achieve the expected effect. After high temperature treatment, the surface of magnesium oxide crystals is sufficient, the specific surface area is reduced, the defects are reduced, and the activity is also reduced. A preferable temperature is 1300-1500 degreeC.

As a preferred solution, in step 3), the aluminum-chromium phosphate dilute solution and the magnesium oxide powder are mixed with high-speed stirring, and the stirring speed is 2000-4000 r/min, and the time is 15-30 min. The molar ratio of aluminum chromate phosphate to magnesium oxide is preferably 1:1-3; more preferably 1:1-2. The purity of the preferred magnesium oxide powder is greater than 99.9%, and the particle size is nanoscale. The mixing process uses a common paddle mixer. The stirring rotation speed is preferably 2500 to 4000 r/min. The temperature for high-speed stirring and mixing is 10 to 30°C, preferably room temperature.

As a preferred solution, the curing conditions are: static curing at normal temperature and pressure for 0.5-3 hours; more preferably, 0.5-1.5 hours.

The preparation method of a magnesium-aluminum-chromium polyphosphate composite material with ultra-high temperature resistance and low thermal conductivity provided by the invention comprises the following specific steps:

1) stirring and mixing the aluminum phosphate solution and the chromium phosphate solution in a constant temperature water bath to obtain a mixed phosphate solution, the concentration of the aluminum phosphate solution is 0.2-0.3 mol/L, and the concentration of the chromium phosphate solution is 0.2-0.35 mol/L; the mixing In the phosphate solution, in molar ratio, aluminum phosphate:chromium phosphate=1:1～1.2, the stirring temperature is 85～95℃, the stirring time is 0.5～2h, the viscosity of the phosphate solution after stirring and mixing 7～16pa·s;

2) the mixed solution obtained in the above-mentioned steps is mixed with deionized water to obtain the diluted aluminum-chromic phosphate solution; in the diluted aluminum-chromic phosphate, by mass ratio, the aluminum-chromic phosphate solution: deionized water=1 ～5:1, the stirring and mixing temperature is 85～95℃, the stirring time is 0.5～2h, and the viscosity of the diluted aluminum-chromium phosphate solution is 3～6pa·s;

3) The diluted aluminum-chromium phosphate solution and the magnesium oxide powder are uniformly stirred and mixed according to the molar ratio of the aluminum-chromium phosphate to the magnesium oxide, and the stirring time is 10-30 minutes to obtain magnesium-aluminum-chromium polyphosphoric acid. For salt composite material, the polyphosphate composite material after stirring is placed in a mold, and it is solidified under normal temperature and pressure for 0.5-1.5 hours to obtain a block product.

The design principle and effect advantages of the magnesium-aluminum-chromium polyphosphate composite material with ultra-high temperature resistance and low thermal conductivity of the present invention:

The invention takes the idea that high melting point oxide and phosphate react at high temperature to form high melting point spinel phase as the starting point, and prepares magnesium-aluminum-chromium polyphosphate composite material by designing specific components, which has high strength, ultra-high temperature resistance, Features such as low thermal conductivity.

The magnesium-aluminum-chromium polyphosphate composite material provided by the invention is composed of a polyphosphate matrix such as magnesium phosphate, aluminum phosphate and chromium phosphate, and magnesium oxide dispersed in the polyphosphate matrix. When the aluminum-chromium phosphate solution reacts with magnesium oxide, the PO ₄ ^3- ions in the solution will react with magnesium oxide to form magnesium phosphate, which makes the magnesium phosphate formed on the surface of magnesium oxide interspersed with the aluminum-chromium phosphate in the solution. At this time, magnesium oxide is fixed in the network structure, and the chemical bonding generated in the combination reaction is combined to form a high-strength polyphosphate composite material that can be cured and formed at low temperature.

The polybasic phosphate composite material provided by the invention can be solidified and formed at normal pressure and normal temperature, and can be directly used without further heat treatment, high temperature sintering and other processes, and can achieve the effects of energy saving, environmental protection and the like. In addition, the preparation process provided by the present invention is simple, the cost of raw materials is low, the equipment requirements are low, and the cycle of the whole preparation process is short.

More importantly, the magnesium-aluminum-chromium polyphosphate composite material provided by the present invention has excellent comprehensive properties. As far as high temperature resistance is concerned, the linear ablation rate of the sample under the ultra-high temperature oxyacetylene flame at 2400° C. is almost zero. , a high-temperature phase mainly composed of magnesia-chromium spinel and magnesium oxide is formed on the ablation surface, which breaks through the existing heat-resistant temperature of phosphate materials and surpasses the ablation resistance of some ultra-high temperature ceramic matrix composite materials. performance, and there is no cracking phenomenon caused by thermal mismatch after ablation, indicating that the polybasic phosphate composite material provided by the present invention has excellent high temperature resistance; After ablation for 60s, the backside temperature is only 129°C, which shows excellent ultra-high temperature thermal insulation performance, which breaks through the limit of 1400°C maximum high temperature resistance of existing advanced thermal insulation materials. This is because when the ultra-high temperature heat flow acts, heat accumulates on the surface of the composite material, the temperature rises rapidly, and the polyphosphate phase gradually decomposes, which will lead to two phenomena at the same time: one is the in-situ oxide and magnesium oxide left on the surface The high melting point magnesia-chromium spinel ceramic phase is formed to consolidate the ultra-high temperature resistance of the composite material; the other is that there will be a temperature gradient from the surface to the interior of the composite material, which will cause the phosphates in different positions to decompose to different degrees, thus forming spontaneously. A large number of micropores hinder the transfer of heat.

The most important innovation of the aluminum-chromium-magnesium polyphosphate composite material provided by the present invention is that a large amount of water vapor will be generated on the back of the sample during the ablation process of the polyphosphate composite material, and water is an excellent heat sink material. , which can greatly reduce the temperature of the back, which is not available in all anti-ablation materials and thermal insulation materials.

Compared with the prior art, the advantages and positive effects of the present invention are reflected in:

1) The cost of raw materials is low, and composite materials with excellent thermal stability can be obtained from raw materials with lower melting points. The preparation process is simple and feasible, the preparation cycle is short, the cost is low, and the equipment requirements are not high;

2) The prepared sample has excellent high temperature resistance and ablation resistance. It remains intact after 60s after ablation in an oxyacetylene flame environment at 2400 °C, and the linear ablation rate is only 100%, which is the best in the existing reports. Phosphate composite;

3) The thermal insulation performance of the prepared sample is excellent, and the backside temperature is only 129°C after 60s ablation in an oxyacetylene flame environment at 2400°C.

Description of drawings

1 is an image of the microstructure of the aluminum-chromium-magnesium polyphosphate composite prepared in Example 1 after curing at room temperature. FIG. 2 is the TG-DSC curve of the aluminum-chromium-magnesium-based polyphosphate composite prepared in Example 1 from room temperature to 1400°C.

3 is an image of the microstructure of the aluminum-chromium-magnesium-based polyphosphate composite prepared in Example 1 after being treated at 1700° C. for 5 hours.

4 is an image of the microstructure of the aluminum-chromium-magnesium polyphosphate composite prepared in Example 2 after curing at room temperature.

5 is the TG-DSC curve of the aluminum-chromium-magnesium-based polyphosphate composite prepared in Example 2 from room temperature to 1400°C.

6 is an image of the microstructure of the aluminum-chromium-magnesium-based polyphosphate composite prepared in Example 2 after being treated at 1700° C. for 5 hours.

FIG. 7 is the XRD pattern of the aluminum-chromium-magnesium-based phosphate composite material prepared in Example 2 after high-temperature heat treatment experiments at different temperatures.

8 is a graph showing the temperature change of the surface and the back of the aluminum-chromium-magnesium-based phosphate heat insulating material prepared in Example 2 during ablation at 2400°C.

FIG. 9 is a macroscopic physical view of the central area of the surface of the aluminum-chromium-magnesium-based phosphate heat insulating material prepared in Example 2 after ablation at 2400° C. for 60s.

FIG. 10 is a profile curve diagram of the central area of the surface of the aluminum-chromium-magnesium-based phosphate heat insulating material prepared in Example 2 after ablation at 2400° C. for 60s.

Detailed ways

The content of the present invention will be further described below in detail through examples, and the scope of protection of the claims of the present application includes but is not limited to this.

The chemical reagents involved in the following examples are all commercially available conventional commercial reagents unless otherwise specified.

The magnesium oxide used in the following examples is 99.9% pure, the particle size is nanoscale, and the particle size distribution range is between 300 and 800 nm. Magnesium oxide powder was pretreated at high temperature as follows: 4h at 1400°C.

Example 1

The 0.3mol/L aluminum phosphate solution and the 0.3mol/L chromium phosphate solution were heated and stirred in a constant temperature water bath at 90°C for 1 hour according to the volume ratio of 1:1, and the mixture was uniform. ·s of mixed phosphate solution. Then, deionized water was added to the mixed phosphate solution according to the mass ratio of 3:1, the temperature was maintained at 90 °C, and the aluminum-chromium phosphate solution with a viscosity of about 5 Pa·s was obtained after fully stirring for 1 h for dilution. Finally, MgO was weighed and mixed into the aluminum-chromium phosphate solution. Magnesium oxide was measured at 40% of the total mass of the composite material, and was continuously stirred at a rate of 3000 r/min for 20 minutes at room temperature until the color was light yellow, and then poured into the prepared In the mold, the aluminum-chromium-magnesium-based polyphosphate composite material was obtained after standing for 1 hour at normal temperature and pressure.

The long-term thermal stability test was carried out on the aluminum-chromium-magnesium-based polyphosphate composite material prepared in Example 1.

Long-term high temperature resistance testing of aluminum-chromium-magnesium polyphosphate composite materials, the process parameters are as follows:

1) Temperature: 1500℃; Time: 5h; Atmosphere: Air; Cooling method: cooling with the furnace.

2) Temperature: 1700℃; Time: 5h; Atmosphere: Air; Cooling method: cooling with the furnace.

It can be seen from FIG. 1 that FIG. 1 is an image of the microstructure of the aluminum-chromium-magnesium polyphosphate composite material prepared in Example 1 of the present invention after curing at room temperature. It can be seen from FIG. 1 that the microstructure of the aluminum-chromium-magnesium polyphosphate composite material prepared in Example 1 of the present invention after curing at room temperature is mainly composed of amorphous phosphate phase and crystalline magnesium oxide.

Figure 2 is the TG-DSC curve of the aluminum-chromium-magnesium-based polyphosphate composite material prepared in Example 1 of the present invention from room temperature to 1400°C. It can be seen from Figure 2 that the aluminum-chromium-magnesium-based polyphosphate-based composite material will have an endothermic peak that removes free water at around 200 °C, and the TG curve tends to be flat as the temperature increases. This shows that the aluminum-chromium-magnesium polyphosphate composite material is relatively stable in this temperature range.

Figure 3 is an image of the microstructure of the aluminum-chromium-magnesium polyphosphate composite after being treated at 1700 °C for 5 h. It can be seen from Figure 3 that the aluminum-chromium-magnesium-based polyphosphate composite material prepared in Example 1 of the present invention has a dense surface and no cracks after long-term heat treatment at 1700 °C, which shows that the aluminum-chromium-magnesium polyphosphate composite material can withstand at least 1700 °C. ℃ high temperature.

Example 2

The 0.3mol/L aluminum phosphate solution and the 0.3mol/L chromium phosphate solution were heated and stirred in a constant temperature water bath at 90°C for 1 hour according to the volume ratio of 1:1, and the mixture was uniform. ·s of mixed phosphate solution. Then, deionized water was added to the mixed phosphate solution at a mass ratio of 3:1, the temperature was maintained at 90 °C, and the solution was fully stirred for 1 h. After dilution, an aluminum-chromium phosphate solution with a viscosity of about 5 Pa·s was obtained. Finally, MgO was weighed and mixed into the aluminum-chromium phosphate solution. Magnesium oxide was measured at 50% of the total mass of the composite material, and was continuously stirred at a rate of 3000 r/min for 20 minutes at room temperature until the color was light yellow, and then poured into the prepared In the mold, the aluminum-chromium-magnesium-based polyphosphate composite material was obtained after standing for 1 hour at normal temperature and pressure.

The long-term thermal stability test was carried out on the aluminum-chromium-magnesium-based polyphosphate composite material prepared in Example 2.

Long-term high temperature resistance testing of aluminum-chromium-magnesium polyphosphate composite materials, the process parameters are as follows:

1) Temperature: 1500℃; Time: 5h; Atmosphere: Air; Cooling method: cooling with the furnace.

2) Temperature: 1700℃; Time: 5h; Atmosphere: Air; Cooling method: cooling with the furnace.

Fig. 4 shows that Fig. 4 is an image of the microstructure of the aluminum-chromium-magnesium polyphosphate composite prepared in Example 2 of the present invention after curing at room temperature. It can be seen from FIG. 4 that the microstructure of the aluminum-chromium-magnesium polyphosphate composite material prepared in Example 2 of the present invention after solidification at room temperature is mainly composed of amorphous phosphate phase and crystalline magnesium oxide.

5 is the TG-DSC curve of the aluminum-chromium-magnesium-based polyphosphate composite material prepared in Example 2 of the present invention from room temperature to 1400°C. It can be seen from Figure 5 that the aluminum-chromium-magnesium-based polyphosphate-based composite material will have an endothermic peak that removes free water at around 200 °C, and the TG curve tends to be flat as the temperature increases. This shows that the aluminum-chromium-magnesium polyphosphate composite material is relatively stable in this temperature range.

Figure 6 is an image of the microstructure of the aluminum-chromium-magnesium-based polyphosphate composite after being treated at 1700 °C for 5 h. It can be seen from Figure 6 that the aluminum-chromium-magnesium-based polyphosphate composite material prepared in Example 2 of the present invention has a dense surface and no cracks after long-term heat treatment at 1700 °C, which shows that the aluminum-chromium-magnesium polyphosphate composite material can withstand at least 1700 °C. ℃ high temperature.

The aluminum-chromium-magnesium-based phosphate composite material prepared in Example 2 of the present invention was subjected to high-temperature heat treatment at different temperatures. FIG. 7 is an XRD pattern of the aluminum-chromium-magnesium-based phosphate composite material prepared in Example 2 of the present invention subjected to high-temperature heat treatment experiments at different temperatures. It can be seen from Figure 7 that with the increase of temperature, the crystalline ceramic phase in the aluminum-chromium-magnesium phosphate composite gradually increases, and only magnesia-chromium spinel and magnesium oxide phases exist at 1700 °C, which implies that at ultra-high temperature Ambient composites rely on these two phases to resist high temperatures.

The aluminum-chromium-magnesium-based phosphate composite material prepared in Example 2 of the present invention was subjected to oxyacetylene flame ablation and thermal insulation experiments at 2400°C. 8 is a graph showing the temperature change of the surface and the back of the aluminum-chromium-magnesium-based phosphate heat insulating material prepared in Example 2 of the present invention during ablation at 2400°C. It can be seen from the figure that when the surface temperature is as high as 2400°C, the temperature of the back of the sample after ablation for 60s is only 129°C, indicating that the phosphate heat insulating material prepared by the present invention has excellent ultra-high temperature heat insulating properties.

9 is a macroscopic physical view of the central area of the surface of the aluminum-chromium-magnesium-based phosphate heat insulating material prepared in Example 2 of the present invention after ablation at 2400° C. for 60s. It can be seen from the figure that the surface of the sample is complete, there is no obvious ablation pit, and the color of the ablation surface is green, which is due to the formation of a large number of high-melting magnesium chromate phases.

FIG. 10 is a profile curve diagram of the central area of the surface of the aluminum-chromium-magnesium-based phosphate heat insulating material prepared in Example 2 of the present invention after ablation at 2400° C. for 60s. It can be seen from the figure that the depth of the ablation pit in the central area is only in the order of microns, which shows that the thermal insulation material prepared by the present invention has excellent ablation resistance.

Example 3

The 0.3mol/L aluminum phosphate solution and the 0.3mol/L chromium phosphate solution were heated and stirred in a constant temperature water bath at 90°C for 1 hour according to the volume ratio of 1:1, and the mixture was uniform. ·s of mixed phosphate solution. Then, deionized water was added to the mixed phosphate solution according to a mass ratio of 2:1, the temperature was maintained at 95 °C, and the mixture was fully stirred for 1 h. After dilution, an aluminum-chromium phosphate solution with a viscosity of about 3 Pa·s was obtained. Finally, MgO was weighed and mixed into the aluminum-chromium phosphate solution. Magnesium oxide was measured at 50% of the total mass of the composite material, and was continuously stirred at a rate of 3000 r/min for 20 minutes at room temperature until the color was light yellow, and then poured into the prepared In the mold, the aluminum-chromium-magnesium-based polyphosphate composite material was obtained after standing for 1 hour at normal temperature and pressure.

The long-term thermal stability test was carried out on the aluminum-chromium-magnesium polyphosphate composite material prepared in Example 3. The thermal weight loss after holding for 5h at 1700℃ for a long time is only 6.3%. There is no obvious ablation pit on the surface after ablation by oxyacetylene flame at 2400℃ for 60s.

Example 4

The 0.6mol/L aluminum phosphate solution and the 0.6mol/L chromium phosphate solution were heated and stirred in a constant temperature water bath at 85°C for 1 hour according to the volume ratio of 1:1, and the mixture was uniform. ·s of mixed phosphate solution. Then, deionized water was added to the mixed phosphate solution according to a mass ratio of 3:1, the temperature was maintained at 85 °C, and the mixture was fully stirred for 1 h. After dilution, an aluminum-chromium phosphate solution with a viscosity of about 5.3 Pa·s was obtained. Finally, MgO was weighed and mixed into the aluminum-chromium phosphate solution. Magnesium oxide was measured at 50% of the total mass of the composite material, and was continuously stirred at a rate of 3000 r/min for 20 minutes at room temperature until the color was light yellow, and then poured into the prepared In the mold, the aluminum-chromium-magnesium-based polyphosphate composite material was obtained after standing for 1 hour at normal temperature and pressure.

The long-term thermal stability test was carried out on the aluminum-chromium-magnesium-based polyphosphate composite material prepared in Example 4. The thermal weight loss after holding for 5h at 1700℃ for a long time is only 6.8%. There is no obvious ablation pit on the surface after ablation by oxyacetylene flame at 2400℃ for 60s.

Example 5

The 0.3mol/L aluminum phosphate solution and the 0.3mol/L chromium phosphate solution were heated and stirred in a constant temperature water bath at 90°C for 1 hour according to the volume ratio of 1:1, and the mixture was uniform. ·s of mixed phosphate solution. Then, deionized water was added to the mixed phosphate solution according to a mass ratio of 3:1, the temperature was maintained at 90 °C, and the mixture was fully stirred for 2 h. After dilution, an aluminum-chromium phosphate solution with a viscosity of about 3 Pa·s was obtained. Finally, MgO was weighed and mixed into the aluminum-chromium phosphate solution. Magnesium oxide was measured at 50% of the total mass of the composite material, and was continuously stirred at a rate of 3000 r/min for 20 minutes at room temperature until the color was light yellow, and then poured into the prepared In the mold, the aluminum-chromium-magnesium polyphosphate composite material was obtained after standing for 3 hours at normal temperature and pressure.

The long-term thermal stability test was carried out on the aluminum-chromium-magnesium-based polyphosphate composite material prepared in Example 5. Almost no thermal weight loss occurred at 1700°C for a long time for 5h. There is no obvious ablation pit on the surface after ablation by oxyacetylene flame at 2400℃ for 60s.

Comparative Example 1

The 0.3mol/L aluminum phosphate solution and the 0.3mol/L chromium phosphate solution were heated and stirred in a constant temperature water bath at 90°C for 1 hour according to the volume ratio of 1:1, and the mixture was uniform. ·s of mixed phosphate solution. Then, deionized water was added to the mixed phosphate solution according to the mass ratio of 3:1, the temperature was maintained at 90 °C, and the aluminum-chromium phosphate solution with a viscosity of about 5 Pa·s was obtained after fully stirring for 1 h for dilution. Finally, the magnesium phosphate was weighed and mixed into the aluminum-chromium phosphate solution. The magnesium phosphate was measured at 50% of the total mass of the composite material, and was continuously stirred at a rate of 3000 r/min at room temperature for 20 minutes until the color was light yellow, and then poured into the prepared In the mold, the aluminum-chromium-magnesium polyphosphate composite material was obtained after standing for 1 h at normal temperature and pressure.

The detection and analysis of the sample found that after replacing magnesium oxide with ready-made magnesium phosphate, the thermal stability of the sample at high temperature was greatly reduced, and the thermal weight loss at 1400 ° C was close to 40%. The number of alkali reactions is reduced, so that the structure of the sample is looser than that of the example, and the strength is very low, which can be destroyed by hand. Therefore, Comparative Example 1 shows that the polyphosphate composite material system formed by directly adding magnesium phosphate cannot achieve the purpose of ultra-high temperature resistance and heat insulation.

Comparative Example 2

The 0.3mol/L aluminum phosphate solution was heated and stirred in a constant temperature water bath at 90 °C for 1 h, then deionized water was added to the aluminum phosphate solution in a mass ratio of 3:1, the temperature was maintained at 90 °C, and the temperature was fully stirred for 1 h to dilute . Finally, MgO was weighed and mixed into the aluminum phosphate solution. Magnesium oxide was measured at 50% of the total mass of the composite material. After stirring continuously for 20 minutes at a rate of 3000 r/min in a constant temperature water bath, poured into the prepared mold. The aluminum-chromium-magnesium polyphosphate composite material was obtained after pressing and standing for 1 hour.

The sample detection and analysis found that the high temperature resistance of the material at medium temperature was not much different from that of Example 2, but the ablation resistance at ultra-high temperature was not as good as that of Example 2. This is due to the decomposition and evaporation of aluminum phosphate at high temperature, and the stability of the formed magnesia-aluminum spinel is not as good as that of magnesia-chromium spinel, which will bring about a huge difference in performance. Therefore, it is difficult for mere dibasic phosphate composites to achieve thermal stability at ultra-high temperatures.

Comparative Example 3

The 0.3mol/L aluminum phosphate solution and the 0.3mol/L chromium phosphate solution were heated and stirred in a constant temperature water bath at 90°C for 1 hour according to the volume ratio of 1:1, and the mixture was uniform. ·s of mixed phosphate solution. Then, deionized water was added to the mixed phosphate solution according to a mass ratio of 3:1, fully stirred for 1 h, and diluted to obtain an aluminum-chromium phosphate solution with a viscosity of about 5 Pa·s. Finally, MgO was weighed and mixed into the aluminum-chromium phosphate solution. Magnesium oxide was measured at 5% of the total mass of the composite material, and was continuously stirred at a rate of 3000 r/min for 20 min at room temperature until the color was light yellow, and then poured into the prepared In the mold, the aluminum-chromium-magnesium-based polyphosphate composite material was obtained after standing for 1 hour at normal temperature and pressure.

The detection and analysis of the sample found that the microstructure of the material was similar to that of the embodiment, but the content of the dispersed star-shaped magnesium oxide phase in Comparative Example 3 was less than that in the embodiment. Since the melting point of magnesium oxide is close to 3000 °C, theoretically speaking, only adding a small amount of magnesium oxide can only promote the curing. Similar to Comparative Example 2, it is difficult for the sample to form a stable phase that resists high temperature in an ultra-high temperature environment. , therefore, it is difficult to achieve the expected effect set by our invention.

Claims (10)

1. The magnesium-aluminum-chromium multi-element phosphate composite material with ultrahigh temperature resistance and low heat conductivity is characterized in that: is formed by dispersing and distributing magnesium oxide in a multi-phosphate matrix; the polyphosphate matrix is comprised of phosphates including magnesium phosphate, aluminum phosphate, and chromium phosphate.

2. The magnesium-aluminum-chromium multi-phosphate composite material with ultrahigh temperature resistance and low thermal conductivity as claimed in claim 1, is characterized in that: the molar ratio of the aluminum phosphate to the chromium phosphate to the magnesium phosphate in the multi-phosphate matrix is 1: 1-1.2: 0.1-0.7.

3. The magnesium-aluminum-chromium multi-phosphate composite material with ultrahigh temperature resistance and low thermal conductivity as claimed in claim 1, is characterized in that: the magnesium oxide accounts for 30-80% of the total mass of the magnesium oxide and the multi-element phosphate matrix.

4. The magnesium-aluminum-chromium multi-phosphate composite material with ultrahigh temperature resistance and low thermal conductivity according to claim 1 or 3, characterized in that: the particle size of the magnesium oxide is 300-800 nm.

5. The preparation method of the magnesium-aluminum-chromium multi-phosphate composite material with ultrahigh temperature resistance and low heat conductivity as claimed in any one of claims 1 to 4 is characterized by comprising the following steps: the method comprises the following steps:

1) uniformly mixing an aluminum phosphate solution and a chromium phosphate solution to obtain an aluminum chromium phosphate solution;

2) diluting the aluminum chromium phosphate solution with water to obtain an aluminum chromium phosphate dilute solution;

3) and (3) uniformly mixing the aluminum-chromium phosphate dilute solution and the magnesium oxide powder, and curing and forming to obtain the aluminum-chromium phosphate magnesium powder.

6. The preparation method of the magnesium-aluminum-chromium multi-phosphate composite material with ultrahigh temperature resistance and low heat conductivity according to claim 5, characterized by comprising the following steps:

in the step 1), the mixing ratio of the aluminum phosphate solution and the chromium phosphate solution in the mixing process is measured by the molar ratio of aluminum phosphate to chromium phosphate being 1: 1-1.2, the mixing temperature is controlled to be 85-95 ℃, and the viscosity of the obtained aluminum-chromium phosphate solution is 7-16 Pa.s.

7. The preparation method of the magnesium-aluminum-chromium multi-phosphate composite material with ultrahigh temperature resistance and low heat conductivity according to claim 5, characterized by comprising the following steps:

in the step 2), the mass ratio of the aluminum chromium phosphate solution to water in the dilution process is 1-5: 1, the dilution temperature is controlled to be 85-95 ℃, and the viscosity of the obtained aluminum chromium phosphate dilute solution is 3-6 Pa.s.

8. The preparation method of the magnesium-aluminum-chromium multi-phosphate composite material with ultrahigh temperature resistance and low heat conductivity according to claim 5, characterized by comprising the following steps: the magnesium oxide powder is subjected to the following high-temperature pretreatment: preserving the heat for 3-5 h at 1300-1600 ℃.

9. The preparation method of the magnesium-aluminum-chromium multi-phosphate composite material with ultrahigh temperature resistance and low heat conductivity according to claim 5, characterized by comprising the following steps: in the step 3), the aluminum-chromium phosphate dilute solution and the magnesium oxide powder are stirred and mixed at a high speed, wherein the stirring speed is 2000-4000 r/min, and the stirring time is 15-30 min.

10. The preparation method of the magnesium-aluminum-chromium multi-phosphate composite material with ultrahigh temperature resistance and low heat conductivity according to claim 5, characterized by comprising the following steps: the curing conditions are as follows: standing and curing for 0.5-3 h at normal temperature and normal pressure.

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