A method for preparing corrosion-resistant and ablation-resistant calcium tantalate ceramic

Abstract

The invention discloses a method for preparing a corrosion-resistant and ablation-resistant calcium tantalate ceramic, wherein the chemical formula of the calcium tantalate ceramic is CaTa2O6 or Ca2Ta2O7; the calcium tantalate ceramic is prepared by the following steps: step S1: dissolving an inorganic salt containing calcium ions in water and a tantalum oxalate solution to prepare a mixed solution A; step S2: preparing a mixture containing NH4 + The solution containing NH4 + A high molecular surfactant and carbonic acid are added to the solution to prepare a mixed precipitant solution B, step S3: the mixed solution A is heated and maintained at a predetermined temperature, and then the precipitant solution B is added dropwise to the mixed solution A, and is continuously stirred to form a uniform mixed solution C, step S4: (NH4)2CO3 solution is added dropwise to the mixed solution C to maintain the pH value at a predetermined value, and then the suspension is obtained after standing, step S5: the suspension is filtered and washed to obtain the desired precursor, step S6: the precursor is ground and sieved, and then calcined to obtain calcium tantalate ceramic powder; the calcium tantalate ceramic prepared by the present invention has a strong ability to resist CMAS corrosion.

Description

Technical Field

[0001] The invention belongs to the field of high-temperature thermal protection and environmental barrier coatings, and in particular relates to a method for preparing corrosion-resistant and ablation-resistant calcium tantalate ceramics. Background Art

[0002] In recent years, SiC fiber reinforced SiC ceramic matrix composites (SiC f / SiC CMCs) have been used in hot end parts of turbine engines and can be used in related high temperature applications. f / SiC and other CMC (C f / SiC、C f / C and SiC f / C) include light weight, high melting point and strength, and good oxidation resistance. f After long-term operation at high temperatures, SiC CMCs are oxidized in the atmosphere to generate SiO2, which is then corroded by steam, leading to component failure.

[0003] To protect SiC f / SiC CMC is protected from damage under operating conditions such as high temperature atmosphere and steam by depositing an environmental barrier coating (EBC) on its surface. The main function of EBC is to separate oxygen and steam from SiC f / SiC CMC isolation and extend its life. In addition, EBC is used to mitigate silicate deposits (CaO-MgO-AlO 1.5 -SiO2, i.e. CMAS). Therefore, EBC must have a high melting point, good steam resistance and CMAS resistance, and its thermal expansion coefficient (TEC) should be similar to that of CMC. Existing environmental barrier coating materials are rare earth silicates, which are easily reacted with CMAS in the atmosphere and thus fail. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing corrosion-resistant and ablation-resistant calcium tantalate ceramics to solve the problem that the existing environmental barrier coating materials are easily reacted with CMAS in the atmosphere and thus fail.

[0005] The present invention adopts the following technical scheme: a method for preparing corrosion-resistant and ablation-resistant calcium tantalate ceramics, the chemical formula of which is CaTa2O6 or Ca2Ta2O7;

[0006] It is prepared by the following steps:

[0007] Step S1: dissolving an inorganic salt containing calcium ions in water and a tantalum oxalate solution to prepare a mixed solution A.

[0008] Step S2: Prepare NH4 + The solution containing NH4+ Add high molecular surfactant and carbonic acid to the solution to prepare mixed precipitant solution B.

[0009] Step S3: heating the mixed solution A and maintaining it at a predetermined temperature, then adding the precipitant solution B dropwise into the mixed solution A, and continuously stirring to form a uniform mixed solution C.

[0010] Step S4: Add (NH4)2CO3 solution dropwise to the mixed solution C so that the pH value is maintained at a predetermined value, and then stand to obtain a suspension.

[0011] Step S5: Filter and wash the suspension to obtain the desired precursor.

[0012] Step S6: Grind and sieve the precursor, and then calcine to obtain calcium tantalate ceramic powder.

[0013] Further, in step S1, the inorganic salt is Ca(OH)2.

[0014] Further, in step S2, a NH4 + The raw material used for the solution is (NH4)2CO3 or NH3·H2O.

[0015] Further, in step S4, the predetermined pH value is 9-10.

[0016] Further, in step S4, the standing time is 15-35 hours.

[0017] Furthermore, in step S6, the calcination conditions are: 1500-1700° C., and calcination time is 24-60 hours.

[0018] Further, in step S3, the predetermined temperature is 40-50°C, and the NH4 + The molar ratio of tantalum oxalate is 5 to 8:1.

[0019] Further, in step S2, the NH4 + With CO3 - The molar ratio is 1:(6~8).

[0020] Further, in step S2, the molecular surfactant is polyoxyethylene styrene, acrylamide or polyoxyethylene acrylate.

[0021] Further, in step S3, the stirring speed is 100-150 rad / min;

[0022] In step S5, during washing, deionized water is first used for washing and then anhydrous ethanol is used for washing.

[0023] In step S6, the mesh size of the sieving is 400 meshes.

[0024] The beneficial effects of the present invention are as follows: the calcium tantalate ceramics prepared by the present invention have strong resistance to CMAS corrosion, the calcium tantalate ceramic powder prepared by the present invention can obtain nano-scale ceramic powder with good dispersibility without the need for ball milling and mixing, and the entire preparation process has a low safety factor, simple operation, low cost and low energy consumption. The present invention utilizes a chemical coprecipitation method to achieve uniform reaction at the molecular scale, and the high molecular surfactant added in the preparation process can avoid agglomeration in the precipitation reaction process, thereby maintaining the integrity of the crystal form. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the XRD pattern of the CaTa2O6 ceramic prepared in Example 5 of the present invention;

[0026] Figure 2 This is a physical picture of the CaTa2O6 ceramic block prepared in Example 5 of the present invention after long-term calcination;

[0027] Figure 3 A schematic diagram of the CMAS corrosion resistance of the calcium tantalate ceramic prepared in the present invention;

[0028] Figure 4 The thickness variation trend during the sintering process of Examples 1 to 5 and Comparative Examples 1 to 3 of the present invention;

[0029] Figure 5 The diameter variation trend during the sintering process of Examples 1 to 5 and Comparative Examples 1 to 3 of the present invention;

[0030] Figure 6 It is a hardness comparison chart of Examples 1 to 5 and Comparative Examples 1 to 3 in the present invention. DETAILED DESCRIPTION

[0031] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] The present invention discloses a method for preparing corrosion-resistant and ablation-resistant calcium tantalate ceramics. Figure 1 As shown, its chemical formula is CaTa2O6 or Ca2Ta2O7; it is prepared by the following steps:

[0033] Step S1: dissolving an inorganic salt containing calcium ions in water and a tantalum oxalate solution to prepare a mixed solution A.

[0034] Step S2: Prepare NH4 + The solution containing NH4 + Add high molecular surfactant and carbonic acid to the solution to prepare mixed precipitant solution B.

[0035] Step S3: heating the mixed solution A and maintaining it at a predetermined temperature, then adding the precipitant solution B dropwise into the mixed solution A, and continuously stirring to form a uniform mixed solution C.

[0036] Step S4: Add (NH4)2CO3 solution dropwise to the mixed solution C so that the pH value is maintained at a predetermined value, and then stand to obtain a suspension.

[0037] Step S5: Filter and wash the suspension to obtain the desired precursor.

[0038] Step S6: Grind and sieve the precursor, and then calcine to obtain calcium tantalate ceramic powder.

[0039] In step S1, the inorganic salt is Ca(OH)2, and in step S2, a NH4 + The raw materials used in the solution are (NH4)2CO3 or NH3·H2O, NH4 + With CO3 - The molar ratio is 1:(6-8), and the molecular surfactant is polyoxyethylene styrene, acrylamide or polyoxyethylene acrylate.

[0040] In step S3, the predetermined temperature is 40-50°C, the stirring speed is 100-150 rad / min, and the NH + 4 and tantalum oxalate in a molar ratio of 5 to 8:1.

[0041] In step S4, the predetermined pH value is 9-10, and the standing time is 15-35 hours.

[0042] In step S5, during washing, deionized water is used for washing first and then anhydrous ethanol is used for washing.

[0043] In step S6, the calcination conditions are: 1500-1700° C., calcination time is 24-60 hours, and the mesh size of the sieve is 400 mesh.

[0044] Example 1

[0045] Step S1: dissolving Ca(OH)2 in water to form a solution and then mixing it with tantalum oxalate solution to form a mixed solution A.

[0046] Step S2: Use (NH4)2CO3 to prepare a 2 mol / L NH4 + The solution containing NH4 + Add polymer surfactant acrylamide and carbonic acid to the solution to make mixed precipitant solution B. NH4 + With CO3 - The molar ratio of NH + 4 and tantalum oxalate in a molar ratio of 5:1.

[0047] Step S3: heating the mixed solution A and maintaining it at 40-50° C., then adding the precipitant solution B dropwise into the mixed solution A, and stirring continuously at a stirring speed of 100-150 rad / min to form a uniform mixed solution C.

[0048] Step S4: Add (NH4)2CO3 solution dropwise to the mixed solution C to maintain the pH value at 9-10, and then stand for 15 hours to obtain a suspension.

[0049] Step S5: Filter and wash the suspension to obtain the desired precursor. When washing, first use deionized water and then use anhydrous ethanol to wash at least 5 times.

[0050] Step S6: After grinding and screening the precursor, calcining is performed to obtain calcium tantalate ceramic powder. The calcination condition is 1600° C. for 24 hours to obtain CaTa2O6 ceramic powder.

[0051] Example 2

[0052] The other steps of Example 2 are the same as those of Example 1. The difference from Example 1 is that the standing time in step S4 is adjusted to 25 hours, and the calcination conditions in step 6 are adjusted to calcination at 1600° C. for 30 hours.

[0053] Example 3

[0054] The other steps of Example 3 are the same as those of Example 1. The difference from Example 1 is that the standing time in step S4 is adjusted to 30 hours, and the calcination conditions in step 6 are adjusted to calcination at 1600° C. for 40 hours.

[0055] Example 4

[0056] The other steps of Example 4 are the same as those of Example 1. The difference from Example 1 is that the standing time in step S4 is adjusted to 30 hours, and the calcination conditions in step 6 are adjusted to calcination at 1600° C. for 50 hours.

[0057] Example 5

[0058] The other steps of Example 5 are the same as those of Example 1. The difference from Example 1 is that the standing time in step S4 is adjusted to 35 hours, and the calcination conditions in step 6 are adjusted to calcination at 1650° C. for 60 hours.

[0059] Comparative Example 1

[0060] The other steps of Comparative Example 1 are the same as those of Example 1. The difference from Example 1 is that in step S1, Ca(OH)2 is dissolved in water to form a solution, which is then mixed with niobium oxalate solution to form a mixed solution A, and CaNb2O6 ceramics are prepared.

[0061] The obtained CaNb2O6 ceramic block was found to have low density and poor corrosion resistance during testing. It was easy to react with Mg, Al, and Si in CMAS. After high-temperature sintering at temperatures exceeding 1550°C, the block showed obvious deformation or even melted.

[0062] Comparative Example 2

[0063] The other steps of Comparative Example 2 are the same as those of Example 1, except that in step S2, NH4 + With CO3 - The molar ratio of NH + 4 and tantalum oxalate in a molar ratio of 8:1, the standing time in step S4 is adjusted to 25 h, and the calcination conditions in step 6 are adjusted to calcination at 1600° C. for 40 h to prepare Ca2Ta2O7 ceramics.

[0064] The corrosion resistance of the prepared Ca2Ta2O7 ceramic is slightly lower than that of CaTa2O6, but it is still relatively excellent compared with other tantalate / niobate ceramics.

[0065] The ceramics prepared in Examples 1-5 and Comparative Examples 1-2 were tested, and the results were as follows:

[0066] Table 1 is a comparison of some test results in Examples 1 to 5 and Comparative Examples 1 to 2

[0067]

[0068] Note: The block thickness before sintering is 1.10-1.12 mm and the diameter is 15 mm.

[0069] From the test results in Table 1, it can be seen that the factors affecting the density, purity and corrosion resistance of calcium tantalate ceramics are mainly related to the standing time, calcination temperature and calcination time in the preparation method, but the influence of these three factors is different. Experiments have shown that the influence degree is calcination time>standing time>calcination temperature.

[0070] The slight changes in diameter and thickness in Table 1 indicate that calcium tantalate ceramics have extremely strong ablation resistance, such as Figure 3 As shown in the figure, when CaTa2O6 is corroded by CMAS in a high temperature environment, the Ca 2+ ,Mg 2+ , Al 3+ , Si 4+ ions do not react with CaTa2O6 because the Ca 2+It is saturated and cannot react, and in the process of CMAS corrosion, CaTa2O6 undergoes a transformation from cubic phase to orthorhombic phase, which is very likely to enhance the CMAS corrosion resistance of CaTa2O6. In summary, CaTa2O6 has extremely strong CMAS corrosion resistance in high temperature environment.

[0071] The invention simulates the protective effect of the prepared calcium tantalate ceramic in the CMAS environment in the atmosphere and at the normal working temperature in the experiment. The results show that the calcium tantalate ceramic has extremely strong resistance to CMAS corrosion, and its block is calcined for a long time at 1650°C without obvious changes in the appearance and volume of the material.

[0072] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing corrosion-resistant and ablation-resistant calcium tantalate ceramics, characterized in that: Its chemical formula is CaTa2O6; It is prepared by the following steps: Step S1: Dissolve Ca(OH)2 in water to form a solution and mix it with tantalum oxalate solution to form a mixed solution A. Step S2: Prepare (NH4)2CO3 with a molar concentration of 2 mol / L containing NH4 + The solution containing NH4 + Add polymer surfactant acrylamide and carbonic acid to the solution to make mixed precipitant solution B. NH4 + With CO3 2- The molar ratio is 1:6, NH4 + The molar ratio of tantalum oxalate is 5:1; Step S3: heating the mixed solution A and maintaining it at 40-50° C., then adding the precipitant solution B dropwise into the mixed solution A, and continuously stirring at a stirring speed of 100-150 rad / min to form a uniform mixed solution C; Step S4: adding (NH4)2CO3 solution dropwise to the mixed solution C so that the pH value is maintained at 9-10, and then standing for 35 hours to obtain a suspension; Step S5: filtering and washing the suspension to obtain the desired precursor, wherein the precursor is first washed with deionized water and then washed with anhydrous ethanol for at least 5 times; Step S6: grinding and sieving the precursor, and then calcining to obtain calcium tantalate ceramic powder, the calcination condition is 1650 ° C calcination for 60 hours, to obtain CaTa2O6 ceramic powder; The density of the CaTa2O6 ceramic powder obtained through the above steps is 99.2%, the purity is 99.5% and the hardness is 10.1GPa.

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