CN113716959B - Spherical powder for thermal barrier coating and preparation method thereof - Google Patents
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Abstract
Hair brushDisclosed is a spherical powder for thermal barrier coating and its preparation method, which is prepared by weighing CaWO in proportion 4 、CaMoO 4 、Nb 2 O 5 /Ta 2 O 5 As a raw material; ball-milling and uniformly mixing the raw materials and the molten salt, and then sequentially drying, sieving and calcining; crushing and grinding the calcined raw materials until a powder solution with a preset particle size range is obtained; filter-pressing the powder solution, and simultaneously adding deionized water, a binder and a defoaming agent to obtain spray granulation preform slurry; spray granulation is carried out by utilizing the spray granulation prefabricated body slurry to obtain Ca (W) for the thermal barrier coating x Mo 1‑x )RE 2 O 9 Spherical powder; according to the invention, tungsten and molybdenum are added into the raw materials of the thermal barrier coating, so that the sphericity rate of the powder can be improved, the fluidity of the powder can be increased, and the thermal conductivity of the subsequent thermal barrier coating can be reduced.
Description
Technical Field
The invention belongs to the technical field of ceramic powder preparation, and particularly relates to spherical powder for a thermal barrier coating and a preparation method thereof.
Background
With the development of aviation, aerospace and civil technologies, the requirement on the use temperature of hot-end parts is higher and higher, and the limit condition of high-temperature alloy and single crystal materials is reached. Taking the heated components of a fuel turbine (such as nozzles, blades, combustors) as an example, they are subjected to severe environments such as high temperature oxidation and high temperature gas stream erosion, and are subjected to temperatures as high as 1100 ℃, which exceed the limit temperature (1075 ℃) for high temperature nickel alloys. The thermal barrier coating prepared by combining the advantages of high strength and high toughness of metal and high temperature resistance of ceramic can solve the problems, and has been applied to hot end materials such as steam turbines, diesel generators, jet engines and the like. It can play the role of heat insulation, oxidation resistance and corrosion resistance, and prolong the service life of the hot end component.
Currently used thermal barrier coating materials, TBCs, are 6-8YSZ, which undergo phase transformation and sintering at temperatures above 1200 ℃, with attendant degradation of thermophysical and mechanical properties, reduced strain tolerance and crack generation, high thermal conductivity, etc., ultimately leading to coating failure, poor volume generation, and cracking and spalling of the coating.
Disclosure of Invention
The invention aims to provide spherical powder for a thermal barrier coating and a preparation method thereof, so as to reduce the thermal conductivity of a thermal barrier coating material.
The invention adopts the following technical scheme: a preparation method of spherical powder for a thermal barrier coating comprises the following steps:
weighing CaWO in proportion 4 、CaMoO 4 、Nb 2 O 5 /Ta 2 O 5 As a raw material;
ball-milling and mixing the raw materials and the molten salt uniformly, and then drying, sieving and calcining the mixture in sequence;
crushing and grinding the calcined raw materials until a powder solution with a preset particle size range is obtained;
filter-pressing the powder solution, and adding deionized water, a binder and a defoaming agent to obtain spray granulation preform slurry;
spray granulation is carried out by utilizing the spray granulation prefabricated body slurry to obtain Ca (W) for the thermal barrier coating x Mo 1-x )RE 2 O 9 Spherical powder; wherein RE is Nb or Ta.
Further, caWO 4 、CaMoO 4 And Nb 2 O 5 /Ta 2 O 5 In a molar ratio of x: (1-x): 1; wherein x is more than 0 and less than 1.
Further, the binder is prepared from binder powder PVA and deionized water;
the mass ratio of the powder obtained after filter pressing, deionized water, adhesive powder PVA and defoaming agent is (8-12): (4-5): (1-2): (0.001-0.01).
Further, the spray granulation parameters were:
the air inlet temperature is 250-270 ℃, the air outlet temperature is 120-150 ℃, the frequency of the spray head is 31-50 Hz, and the frequency of the peristaltic pump is 31-40 Hz.
Further, the molten salt is at least one of potassium chloride, sodium chloride and sodium sulfate.
Further, caWO 4 、CaMoO 4 And Nb 2 O 5 /Ta 2 O 5 The purity of the product is more than 99.9%, and the particle size is 100-800 nm.
Further, the mass ratio of the raw materials to the molten salt is (1-2): (0.1-1).
Further, when ball milling and mixing are carried out, the ball material ratio is (2-5): (1-2), the rotating speed of the ball mill is 300-500 r/min, and the ball milling time is 180-360 min.
Furthermore, the calcining temperature is 900-1500 ℃, and the sintering time is 5-10 h.
The other technical scheme of the invention is as follows: the spherical powder for the thermal barrier coating is prepared by the preparation method.
The invention has the beneficial effects that: according to the invention, tungsten and molybdenum are added into the raw materials of the thermal barrier coating, so that the sphericity rate of the powder can be improved, the fluidity of the powder can be increased, the thermal conductivity of the subsequent thermal barrier coating can be reduced, a filter press is adopted to remove water in the powder solution, the production efficiency can be improved, the time cost can be saved, the preparation process is simple, the production efficiency is higher, the production cost is low, the operation is simple and stable, the control is convenient, and the automatic operation can be easily realized.
Drawings
FIG. 1 shows the W-Mo-Nb/Ta salt Ca (W) prepared in example 1 of the present invention 1/3 Mo 2/3 )Nb 2 O 9 Scanning electron microscope image of spherical powder;
FIG. 2 shows Ca (W) prepared in example 1 of the present invention 1/3 Mo 2/3 )Nb 2 O 9 The thermal conductivity of the material is compared with that of niobate and yttria-stabilized zirconia (YSZ).
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
The invention discloses a preparation method of spherical powder for a thermal barrier coating, which comprises the following steps: weighing CaWO in proportion 4 、CaMoO 4 、Nb 2 O 5 /Ta 2 O 5 As a starting material. In this raw material, caWO 4 、CaMoO 4 And Nb 2 O 5 /Ta 2 O 5 The purity of the product is more than 99.9%, and the particle size is 100-800 nm. In the present invention, caWO in the starting material 4 、CaMoO 4 And Nb 2 O 5 /Ta 2 O 5 In a molar ratio of x: (1-x): 1; wherein x is more than 0 and less than 1. When the ball milling is carried out, chemical reaction takes place, and the specific reaction formula is RE 2 O 5 +xCaWO 4 +(1-x)CaMoO 4 ＝Ca(W x Mo 1-x )RE 2 O 9 。
Then, the raw materials and the fused salt are ball-milled and mixed evenly, and then are dried, sieved and calcined in sequence. The fused salt is preferably potassium chloride, sodium chloride or sodium sulfate, the reaction temperature and the reaction time can be reduced by adding the fused salt, the calcination temperature is reduced from 1700-1800 ℃ to 900-1500 ℃ after the fused salt is added, and the calcination time is reduced from 10-30 h to 2-10 h. The reaction temperature can be effectively reduced, the synthesis efficiency is improved, and the mass ratio of the raw materials to the molten salt is (1-2): (0.1-1). In the step, the drying temperature is 60-80 ℃, the drying time is 15-30 h, and the powder is sieved by a 300-mesh sieve during sieving. When ball milling and mixing are carried out, the ball material ratio is (2-5): (1-2), the rotating speed of the ball mill is 300-500 r/min, and the ball milling time is 180-360 min. The calcining temperature is 900-1500 ℃, and the sintering time is 5-10 h.
Crushing and grinding the calcined raw materials, directly using a crusher, and grinding the crushed powder to 0.01-1 mm. It should be noted that, when a grinding machine is used, the ball-to-feed ratio is (4-5): (1-2), grinding for 180-360 min at the rotating speed of 300-600 r/min, finishing grinding when the particle size range of particles in the slurry obtained by grinding is 500-1000 nm to obtain a powder solution, carrying out filter pressing on the powder solution, and adding deionized water, a binder and a defoaming agent to obtain the spray granulation preform slurry. In the grinding process, the particle size distribution in the slurry is required to be detected at any time, a laser particle sizer can be used for detection, and then deionized water, a binder and a defoaming agent are added into the powder obtained after filter pressing to obtain the spray granulation preform slurry.
As a specific embodiment, the binder is made of binder powder PVA and deionized water. Specifically, the adhesive powder PVA and deionized water are heated to 80-90 ℃ by a glue melting machine, and the adhesive powder PVA is obtained after heat preservation for 60-120 min, wherein the mass ratio of the deionized water to the adhesive powder PVA is (9-12): (1-2). The antifoaming agent may be selected to be n-octanol. The mass ratio of the powder obtained after filter pressing, deionized water, adhesive powder PVA and defoaming agent is (8-12): (4-5): (1-2): (0.001-0.01).
Spray granulation is carried out by utilizing the spray granulation prefabricated body slurry to obtain Ca (W) for the thermal barrier coating x Mo 1-x )RE 2 O 9 Spherical powder; wherein RE is Nb or Ta. Specifically, before spray granulation, a winch needs to be used for stirring the preform slurry in advance, specifically, five minutes can be used in advance, and the preform slurry is continuously stirred in the spray granulation process until the spray granulation is finished. After spray granulation is finished, the prepared powder is placed in an oven to be dried and then is sieved to obtain a product, the drying temperature is 60-100 ℃, the drying time is 5-24 hours, 180-mesh and 400-mesh sieving is performed successively during sieving, then the particle size of the powder is tested by using a laser particle sizer, the flowability is tested by using a Hall flow meter, the morphology of the powder particles is observed by using a scanning electron microscope, and the sphericity ratio is calculated.
In the process of spray granulation, the shape and the size of crystal grains can be adjusted by changing the water-material ratio, the proportion of slurry and glue, the frequency of a spray head and the feeding rate, so that spherical powder with different particle sizes and shapes can be obtained, the spherical spraying powder with the optimal grading can be obtained, and the thermal conductivity of the coating can be reduced. In the invention, the spray granulation parameters are as follows:
the air inlet temperature is 250-270 ℃, the air outlet temperature is 120-150 ℃, the frequency of the spray head is 31-50 Hz, and the frequency of the peristaltic pump is 31-40 Hz. The peristaltic pump frequency was used to reflect the feed rate.
According to the invention, tungsten and molybdenum are added into the raw materials of the thermal barrier coating, so that the sphericity rate of the powder can be improved, the fluidity of the powder can be increased, the thermal conductivity of the subsequent thermal barrier coating can be reduced, the preparation process is simple, the production efficiency is higher, the production cost is low, the operation is simple and stable, the control is convenient, and the automatic operation is easy to realize.
The invention is doped with W containing hexavalent elements 6+ And Mo 6+ The compound optimizes the comprehensive performance of the rare earth tantalate, can cause the distortion of a crystal structure through a doping effect, increases the defects of the crystal structure, including the increase of oxygen vacancies and grain boundary concentration, and reduces the thermal conductivity of the coating. And centrifugal spray granulation is adopted to prepare spherical powder for serving as a thermal barrier coating material. Heretofore CaWO 4 Because of having stable physicochemical properties, the rare earth element is widely applied to luminescent materials for X-ray intensifying screens, X-ray neutralization X-ray luminescent materials, and is activated by taking the rare earth element as an activator, when the rare earth element is doped into CaWO 4 After lattice formation, it has some special luminescent phenomena, caWO 4 The material for preparing the thermal barrier coating belongs to the first case, and the CaWTa prepared 2 O 9 Compared with low-valence ion rare earth tantalate and the currently used 7-8YSZ, the material has lower thermal conductivity and thermal diffusion coefficient, no phase change at high temperature and good phase stability, and the target product is expected to be a novel high-temperature-resistant, oxidation-resistant and wear-resistant ceramic material.
Example 1:
the embodiment specifically comprises the following steps:
weighing 2658.2g of niobium pentoxide, 959.6g of calcium tungstate, 1333.5g of calcium molybdate and Na fused salt 2 SO 4 500g and 2Kg of absolute ethyl alcohol are put into a ball milling tank together to be mixed, sealed and then put into a planetary ball mill to be ball milled for 360min (the rotating speed is 500r/min, the weight of zirconia balls is 16 Kg) so as to be uniformly mixed, and then the ball milled solution is dried for 24 hours at 80 ℃ and then sieved by a 300-mesh sieve, and is presintered for 10 hours at 1500 ℃.
Crushing the grown and hardened particles by using a crusher, weighing 10Kg of zirconia balls and 2Kg of mixed powder, placing 5Kg of deionized water into a ball mill, ball-milling to 800nm (ball-milling time is 360min, and the rotating speed of the ball mill is 600 r/min), and removing water in the powder solution by using a filter press. Weighing 12Kg of deionized water and 2Kg of PVA powder, placing the materials in a glue melting machine, heating to 90 ℃, and keeping the temperature for 120min to obtain a binder colloid; weighing 2.65Kg of powder obtained after filter pressing and deionized water according to the proportion shown in Table 1, meanwhile weighing 160g of binder and 9ml of defoaming agent, stirring the slurry for 15 minutes, and granulating the slurry by using spray drying equipment to prepare spherical powder, wherein the air inlet temperature of a spray granulator is 250 ℃, the air outlet temperature is 150 ℃, and the frequency of a spray head is 50Hz; drying the prepared ball powder at 80 ℃ for 8h to obtain tantalate ball powder for thermal spraying, and testing the particle size of the powder by a laser particle sizer, wherein the particle size ranges from 20 micrometers to 100 micrometers and is in normal distribution.
Ca (W) calcined in this example 1/3 Mo 2/3 )Nb 2 O 9 Degree of sphericity>99 percent of the powder has good fluidity, and the particle size range of the SEM image shown in figure 1 is 20-50 mu m, which is smaller than the particle size measured by a laser particle sizer, because the taken picture is an enlarged image of a part of particles and cannot represent the range of all the particle sizes, and the particle sizes can be observed to be more uniform in the SEM image. The raw materials of calcium tungstate and calcium molybdate are used for preparing thermal barrier coating materials. As shown in FIG. 2, ca (W) was prepared 1/3 Mo 2/3 )Nb 2 O 9 Compared with low-valence ion niobium/tantalate and currently used 7-8YSZ, the material has lower thermal conductivity, no phase change at high temperature and good phase stability.
In addition, in this example, in order to test the influence of the powder obtained after filter pressing and deionized water on the product of the process, the experiment was repeated with different ratios of raw material to deionized water changed, as shown in table 1, it can be seen that the ratio of raw material to deionized water was 6: at 4, ca (W) 1/3 Mo 2/3 )Nb 2 O 9 Degree of sphericity>99% good flowability (29 s/50g,50g spherical powder run out of the funnel, taking 29 s).
TABLE 1
Example 2:
the embodiment specifically comprises the following steps:
weighing 4418.2g of tantalum pentoxide, 959.6g of calcium tungstate, 1333.5g of calcium molybdate and Na fused salt 2 SO 4 3356g, 2Kg of absolute ethyl alcohol, wherein the ratio of raw materials to molten salt is 2:1 and weighing. Placing the mixture into a ball milling tank, mixing, sealing, placing on a planetary ball mill, ball milling for 300min (the rotating speed is 500r/min, and the weight of zirconia balls is 18 Kg) to uniformly mix, drying the ball-milled solution at 80 ℃ for 24 hours, sieving with a 300-mesh sieve, and presintering at 900 ℃ for 10 hours.
Crushing the grown and hardened particles by using a crusher, weighing 14Kg of zirconia balls and 3Kg of mixed powder, and placing 4Kg of deionized water into a ball mill for ball milling to 1000nm (the ball milling time is 360min, and the rotating speed of the ball mill is 600 r/min); the water in the powder solution was then removed using a filter press.
Weighing 12Kg of PVA powder and 5Kg of deionized water, placing in a glue melting machine, heating to 80 ℃, and keeping the temperature for 100min to obtain the binder colloid.
Weighing 2.4Kg of filter-pressed powder and 1.2Kg of deionized water, weighing the addition proportion of the binder according to the table 2 (in the embodiment, other steps and conditions are unchanged, the proportion of the binder is independently adjusted to obtain products with different properties, shown in the table 2), stirring the slurry for 10 minutes by 12ml of defoaming agent, carrying out suction filtration for 5-8 times, and granulating the slurry by using spray drying equipment to prepare spherical powder, wherein the air inlet temperature of a spray granulator is 270 ℃, the air outlet temperature is 150 ℃, and the frequency of a spray head is 40Hz; the particle size of the powder is measured by a laser particle sizer, and the particle size ranges from 40 mu m to 90 mu m. Flowability was measured using a hall rheometer and the ratio of slurry to binder was adjusted to obtain products of different properties as shown in table 2.
TABLE 2
The other technical scheme of the invention is as follows: the spherical powder for the thermal barrier coating is prepared by the preparation method. The tungsten-molybdenum-niobium/tantalate Ca (WxMo 1-x) RE2O9 (RE = Nb, ta) spherical powder prepared by the method has relatively low thermal conductivity, high sphericity rate, good fluidity and uniform particle size, is expected to be used as a novel ultrahigh-temperature thermal barrier ceramic coating material, and the spherical powder prepared by a centrifugal spray granulation method has uniform particles, good fluidity, high conversion and production efficiency, low production cost, simple and stable operation, convenient control and easy realization of automatic operation.
Claims (7)
1. A preparation method of spherical powder for a thermal barrier coating is characterized by comprising the following steps:
weighing CaWO in proportion 4 、CaMoO 4 、Nb 2 O 5 /Ta 2 O 5 As a raw material;
ball-milling and uniformly mixing the raw materials and the molten salt, and then sequentially drying, sieving and calcining; the mass ratio of the raw materials to the molten salt is (1~2): (0.1 to 1);
crushing and grinding the calcined raw materials until a powder solution with a preset particle size range is obtained;
filter-pressing the powder solution, and then adding deionized water, a binder and a defoaming agent to obtain spray granulation preform slurry;
spray granulation is carried out by utilizing the spray granulation preform slurry to obtain Ca (W) for the thermal barrier coating x Mo 1-x )RE 2 O 9 Spherical powder; wherein RE is Nb or Ta;
the CaWO 4 、CaMoO 4 And Nb 2 O 5 /Ta 2 O 5 In a molar ratio of x: (1-x): 1; wherein x is more than 0 and less than 1;
the binder is prepared from binder powder PVA and deionized water;
the mass ratio of the powder obtained after filter pressing, deionized water, adhesive powder PVA and defoaming agent is (6-12): (4-5): (1-2): (0.001-0.01).
2. The method of claim 1, wherein the spray granulation parameters are:
the air inlet temperature is 250-270 ℃, the air outlet temperature is 120-150 ℃, the frequency of the spray head is 31-50 Hz, and the frequency of the peristaltic pump is 31-40 Hz.
3. The method of any one of claims 1 or 2, wherein the molten salt is at least one of potassium chloride, sodium chloride, and sodium sulfate.
4. The method of claim 3, wherein the CaWO is a spherical powder 4 、CaMoO 4 And Nb 2 O 5 /Ta 2 O 5 The purity of the nano-particles is more than 99.9%, and the particle sizes are 100 to 800nm.
5. The method for preparing spherical powder for thermal barrier coating according to claim 1, wherein the ratio of the ball to the material is (2-5): (1-2), the rotating speed of the ball mill is 300-500 r/min, and the ball milling time is 180-360 min.
6. The method for preparing spherical powder for thermal barrier coating of claim 5, wherein the calcination temperature is 900-1500 ℃ and the calcination time is 5-10 h.
7. Spherical powder for thermal barrier coating, characterized in that it is prepared by the method of any one of claims 1 to 6.
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| CN202110913823.3A CN113716959B (en) | 2021-08-10 | 2021-08-10 | Spherical powder for thermal barrier coating and preparation method thereof |
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| CN202110913823.3A CN113716959B (en) | 2021-08-10 | 2021-08-10 | Spherical powder for thermal barrier coating and preparation method thereof |
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