Core-shell corundum aggregate coated with lanthanum hexaaluminate coating as well as preparation method and application of core-shell corundum aggregate

Abstract

The invention belongs to the technical field of refractory casting materials, and particularly relates to core-shell corundum aggregate wrapped with a lanthanum hexaaluminate coating as well as a preparation method and application of the core-shell corundum aggregate. The preparation method of the core-shell corundum aggregate wrapped with the lanthanum hexaaluminate coating comprises the following steps: firstly preparing a precursor solution, then impregnating the corundum aggregate with the precursor solution by a vacuum uniform impregnation method, and finally performing drying and heat treatment on the impregnated corundum aggregate to obtain the core-shell corundum aggregate wrapped with the lanthanum hexaaluminate coating. The preparation method disclosed by the invention is simple and rapid in preparation process and low in cost; the prepared core-shell corundum aggregate is formed by coating the surface of corundum aggregate with a micron-sized lanthanum hexaaluminate coating, the corundum-spinel castable is prepared from the core-shell corundum aggregate, and a lanthanum hexaaluminate interface layer which is not suitable for falling can be introduced to an aggregate / matrix interface, so that the thermal shock resistance of the refractory castable is effectively improved, and the service life of the refractory castable is prolonged. The method has an extremely wide development prospect in the field of aggregate modification of corundum-spinel castable.

Description

Technical Field

[0001] The present invention belongs to the technical field of refractory castables, and particularly relates to core-shell corundum aggregates wrapped with a lanthanum hexaaluminate coating, a preparation method thereof, and an application thereof. Background Art

[0002] Corundum-spinel castables are widely used as ladle lining materials due to their excellent thermal shock resistance and slag erosion resistance. During the service of the ladle, the repeated erosion of molten steel and the thermal stress caused by rapid temperature fluctuations can easily deteriorate the performance of the ladle lining material and ultimately lead to its failure. With the increasing demand for clean steel and the continuous increase in the refining ratio, the service conditions of the ladle lining are becoming increasingly harsh. Therefore, the thermal shock resistance of corundum-spinel castables needs to be further improved.

[0003] Refractory castables are multiphase heterogeneous composites composed of large-particle aggregates, fine powders, and binding phases. Under the action of thermal stress, the propagation behavior of microcracks inside refractory castables mainly falls into three types: propagation inside the matrix, propagation inside the aggregates, and propagation at the aggregate / matrix interface. Currently, the research on the thermal shock resistance of corundum-spinel castables mainly focuses on matrix toughening and aggregate lightweighting. Although these methods can improve the thermal shock resistance to a certain extent, they still cannot meet the higher development requirements for thermal shock resistance in the industry.

[0004] Lanthanum hexaaluminate has been used as a reinforcing phase in ceramic matrix composites due to its high melting point, thermal chemical stability at high temperatures, high thermal expansion coefficient, and hexagonal layered structure. However, there is currently no feasible method for modifying the interface of corundum aggregates with lanthanum hexaaluminate to improve the thermal shock resistance of corundum-spinel castables. Summary of the Invention

[0005] Aiming at the defects and deficiencies in the prior art, one of the objectives of the present invention is to provide a preparation method for core-shell corundum aggregates wrapped with a lanthanum hexaaluminate coating, which can effectively improve the thermal shock resistance of corundum-spinel castables by introducing a layered lanthanum hexaaluminate interface layer at the aggregate / matrix interface of refractory castables.

[0006] Another objective of the present invention is to provide core-shell corundum aggregates wrapped with a lanthanum hexaaluminate coating prepared by the above preparation method, which have excellent thermal shock resistance.

[0007] Another objective of the present invention is to provide an application of the core-shell corundum aggregates wrapped with a lanthanum hexaaluminate coating prepared by the above preparation method.

[0008] To achieve the above objectives, the present invention adopts the following technical solutions:

[0009] A preparation method for core-shell corundum aggregates wrapped with a lanthanum hexaaluminate coating, comprising the following steps:

[0010] (1) uniformly mixing lanthanum nitrate, aluminum nitrate, citric acid, and a surfactant in water to obtain a precursor solution; wherein the molar ratio of lanthanum nitrate, aluminum nitrate, and citric acid is 1:(10-15):(1-5);

[0011] (2) Immersing the corundum aggregate in the precursor solution for vacuum impregnation treatment, and then drying and heat treating the solution to obtain a core-shell corundum aggregate coated with a lanthanum hexaaluminate coating.

[0012] Furthermore, in step (1), the surfactant is one or more of sodium lauryl sulfonate, sodium lauryl sulfate, polyvinyl alcohol, and polyethylene glycol, more preferably sodium lauryl sulfate. Further preferably, the amount of the surfactant in the precursor solution is 0.01 wt% to 0.1 wt%, more preferably 0.05 wt%.

[0013] Furthermore, in step (1), the concentration of lanthanum nitrate added to the precursor solution is 0.02 to 0.1 mol / L, more preferably 0.06 mol / L. After lanthanum nitrate is added, La 3+ By regulating La 3+ The concentration can achieve the regulation of the morphology and thickness of the lanthanum hexaaluminate coating.

[0014] Furthermore, in step (1), the specific process of uniformly mixing lanthanum nitrate, aluminum nitrate, citric acid, and a surfactant in water is as follows: uniformly mixing citric acid in water to obtain a citric acid solution; then adding lanthanum nitrate, aluminum nitrate, and a surfactant to the citric acid aqueous solution, ultrasonically shaking and mixing for 20 to 60 minutes, and then stirring and mixing at a temperature of 50 to 80° C. for 40 to 100 minutes.

[0015] Furthermore, in step (2), the corundum aggregate is a plate-shaped corundum aggregate; and the particle size of the plate-shaped corundum aggregate is 1 to 5 mm.

[0016] Furthermore, in step (2), the process conditions of the vacuum impregnation treatment are: vacuum degree of -0.05 to -0.098 MPa, and impregnation time of 0.8 to 2.0 h. More preferably, the impregnation time is 1 h.

[0017] Furthermore, in step (2), the drying temperature is 80-120°C, the heat treatment temperature is 1500-1700°C, and the heat treatment time is 2-4 hours. More preferably, the heat treatment temperature is 1600°C, and the heat treatment time is 3 hours.

[0018] A core-shell corundum aggregate coated with a lanthanum hexaaluminate coating prepared by the above preparation method. In the core-shell corundum aggregate coated with a lanthanum hexaaluminate coating, the thickness of the lanthanum hexaaluminate coating is 6-12 μm; the lanthanum hexaaluminate coating is mainly composed of hexagonal layered lanthanum hexaaluminate; the grain size of the hexagonal layered lanthanum hexaaluminate is 2-4 μm.

[0019] Application of a core-shell corundum aggregate coated with a lanthanum hexaaluminate coating prepared by the above preparation method, as an aggregate in the preparation of refractory castables; the refractory castable is a corundum-spinel castable.

[0020] Furthermore, the composition materials of the corundum-spinel castable include: core-shell corundum aggregate coated with a lanthanum hexaaluminate coating, activated alumina, magnesite, silica fume, Secar71 cement; the addition amount of the core-shell corundum aggregate coated with a lanthanum hexaaluminate coating is 75wt% - 86wt%.

[0021] The technical solution of the present invention has the following advantages and beneficial effects:

[0022] (1) The preparation method of the core-shell corundum aggregate coated with a lanthanum hexaaluminate coating provided by the present invention first prepares a precursor solution, then impregnates the prepared precursor solution into the corundum aggregate by vacuum uniform impregnation method, and finally dries and heat-treats the impregnated corundum aggregate to obtain a core-shell corundum aggregate coated with a lanthanum hexaaluminate coating.

[0023] The above preparation method of the present invention combines precursor impregnation and heat treatment. The preparation process is simple, fast and low-cost, which is convenient for industrial production; and the prepared core-shell corundum aggregate coated with a lanthanum hexaaluminate coating is coated with a micron-level lanthanum hexaaluminate (LHA) coating on the surface of tabular corundum aggregate. The corundum-spinel castable prepared with this core-shell corundum aggregate can introduce an LHA interface layer that is not easy to fall off at the aggregate / matrix interface, thereby effectively improving the mechanical strength and thermal shock resistance of the refractory castable.

[0024] (2) The core-shell corundum aggregate coated with a lanthanum hexaaluminate coating provided by the present invention has a hexagonal layered lanthanum hexaaluminate coating diffusely distributed on the surface of the corundum aggregate, forming a core-shell structure, and the morphology and thickness of the coating can be adjusted according to the La 3+ concentration in the precursor impregnation solution. Moreover, the core-shell corundum aggregate provided by the present invention, after being used as an aggregate for the preparation of corundum-spinel castables, can form a hexagonal layered LHA interface layer between the aggregate / matrix interface of the corundum-spinel castable, and the bonding strength is high and not easy to fall off, thereby effectively improving the mechanical properties and thermal shock resistance of the castable.

[0025] Therefore, the present invention adopts a modification strategy of vacuum impregnation combined with heat treatment, which can provide a feasible strategy for improving the thermal shock resistance of corundum-spinel castables, and at the same time has extremely broad development prospects in the field of aggregate modification of corundum-spinel castables. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 XRD patterns of the surface coatings of the core-shell corundum aggregates coated with lanthanum hexaaluminate coatings in Examples 1 to 4 of the present invention;

[0027] Figure 2 SEM images of the surface and cross-section of the core-shell corundum aggregate coated with lanthanum hexaaluminate coating in Example 1 of the present invention;

[0028] Figure 3 SEM images of the surface and cross-section of the core-shell corundum aggregate coated with lanthanum hexaaluminate coating in Example 2 of the present invention;

[0029] Figure 4 SEM images of the surface and cross-section of the core-shell corundum aggregate coated with lanthanum hexaaluminate coating in Example 3 of the present invention;

[0030] Figure 5 SEM images of the surface and cross-section of the core-shell corundum aggregate coated with lanthanum hexaaluminate coating in Example 4 of the present invention;

[0031] Figure 6 Results of the thermal shock resistance of the corundum-spinel castables prepared from the core-shell corundum aggregates coated with lanthanum hexaaluminate coatings in Examples 1 to 4 of the present invention;

[0032] Figure 7 SEM image of the corundum-spinel castable prepared from the core-shell corundum aggregate coated with lanthanum hexaaluminate coating in Example 3 of the present invention;

[0033] Figure 8 SEM image of the corundum-spinel castable prepared from the core-shell corundum aggregate coated with lanthanum hexaaluminate coating in Example 3 of the present invention after thermal shock testing. DETAILED DESCRIPTION OF THE INVENTION

[0034] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. The test methods used in the following embodiments are all conventional methods unless otherwise specified; the raw materials used, etc. are all commonly used in the art, publicly available or commercially available items unless otherwise specified.

[0035] The following embodiments of the present invention provide a preparation method of core-shell corundum aggregate coated with lanthanum hexaaluminate coating, comprising the following steps:

[0036] (1) Mix lanthanum nitrate, aluminum nitrate, citric acid, and surfactant evenly in water to obtain a precursor solution; wherein, the molar ratio of lanthanum nitrate, aluminum nitrate, and citric acid is 1∶(10-15)∶(1-5);

[0037] (2) Immerse the corundum aggregate in the precursor solution for vacuum impregnation treatment, and then perform drying and heat treatment to obtain the core-shell corundum aggregate coated with lanthanum hexaaluminate coating.

[0038] Further, in step (1), the surfactant is one or more of sodium dodecyl sulfonate, sodium dodecyl sulfate, polyvinyl alcohol, and polyethylene glycol, and more preferably sodium dodecyl sulfate.

[0039] The present invention does not specifically limit the specific ratios of the various raw materials in the precursor solution. In the embodiments of the present invention, those skilled in the art can prepare the core-shell corundum aggregate coated with lanthanum hexaaluminate coating of the present invention by formulating within the ratio range of the various raw materials in the precursor solution, and achieve the technical effects of the present invention through the vacuum impregnation method.

[0040] Further, in step (1), in the precursor solution, the dosage of the surfactant is 0.01wt% - 0.1wt%, and more preferably 0.05wt%.

[0041] Further, in step (1), in the precursor solution, the added concentration of lanthanum nitrate is 0.02 - 0.1mol / L, and more preferably 0.06mol / L. After adding lanthanum nitrate, La 3+ . is formed in the solution. By regulating the concentration of La 3+ , the morphology and thickness of the LHA coating can be regulated.

[0042] Further, in step (1), the specific process of mixing lanthanum nitrate, aluminum nitrate, citric acid, and surfactant evenly in water is: mix citric acid evenly in water to obtain a citric acid solution; then add lanthanum nitrate, aluminum nitrate, and surfactant to the citric acid aqueous solution, ultrasonically oscillate and mix for 20 - 60min, and then stir and mix at a temperature of 50 - 80°C for 40 - 100min.

[0043] Further, in step (2), the corundum aggregate is plate-shaped corundum aggregate; the particle size of the plate-shaped corundum aggregate is 1 - 5mm.

[0044] Further, in step (2), the process conditions of the vacuum impregnation treatment are: the vacuum degree is -0.05 - -0.098MPa, and the impregnation time is 0.8 - 2.0h.

[0045] To improve the impregnation effect and ensure that most of the solution wraps the corundum aggregate, further preferably, the specific process of the vacuum impregnation treatment is as follows: First, immerse the corundum aggregate in the precursor solution and stir for 4 - 8 min, then pour out the impregnated solution; repeat the above operations of immersion, stirring, and pouring out 3 - 5 times, and finally add the precursor solution again and keep the impregnation under vacuum conditions for 0.8 - 2.0 h.

[0046] Further, in step (2), the drying temperature is 80 - 120 °C; the heat treatment temperature is 1500 - 1700 °C, and the heat treatment time is 2 - 4 h. Further preferably, the heat treatment temperature is 1600 °C and the heat treatment time is 3 h.

[0047] Further preferably, when the heat treatment temperature is 1600 °C, the concentration of lanthanum nitrate in the precursor solution is 0.06 mol / L; the surfactant is sodium dodecyl sulfate and the dosage is 0.05 wt%, at this time, the number of LHA crystals on the surface of the prepared corundum aggregate is the largest, the growth is the best, and the layered crystal structure is the best, the continuity of the LHA coating is the best, the average thickness of the coating is 12 μm, and the effect of the thermal shock resistance is the best.

[0048] Example 1

[0049] The core - shell corundum aggregate wrapped with lanthanum hexaaluminate coating in this example is prepared by the following steps:

[0050] Step 1: Add citric acid to water and stir in a water bath at 40 °C for 20 min to obtain an aqueous citric acid solution; then add lanthanum nitrate, aluminum nitrate, and surfactant (sodium dodecyl sulfonate) to the aqueous citric acid solution in sequence, ultrasonically vibrate for 30 min, and then stir in a water bath at 60 °C for 1 h to obtain a precursor solution. Among them, the molar ratio of lanthanum nitrate, aluminum nitrate, and citric acid is 1:10:1. In the precursor solution, the dosage of lanthanum nitrate, that is, the concentration of La 3+ is 0.02 mol / L, and the content of sodium dodecyl sulfonate is 0.01 wt%.

[0051] Step 2: Put the plate - shaped corundum aggregate into a special vessel (vacuum impregnation chamber), then slowly add the precursor solution obtained in step 1 to immerse the plate - shaped corundum aggregate, and keep stirring for 5 min, then pour out the impregnated solution, add a new precursor solution again, repeat the above operations of immersion, stirring, and pouring out (the total number of operations of immersion, stirring, and pouring out is 4 times), finally add the precursor solution again, keep the impregnation under a vacuum degree of - 0.098 MPa for 1 h, then dry at 110 °C for 24 h, and finally heat - treat at 1500 °C for 3 h to obtain the core - shell corundum aggregate wrapped with lanthanum hexaaluminate coating in Example 1 (the sample number of this example is L2).

[0052] This embodiment also provides a refractory castable, which is a corundum-spinel castable; the constituent materials of the corundum-spinel castable include: the core-shell corundum aggregate (content 82.5 wt.%) coated with lanthanum hexaaluminate in Example 1, activated alumina (content 6.5 wt.%), magnesite (content 8 wt.%), silica fume (content 1 wt.%), and Secar71 cement (content 2 wt.%).

[0053] Example 2

[0054] The core-shell corundum aggregate coated with lanthanum hexaaluminate in this example is prepared in basically the same way as in Example 1, and the difference between the two is that: in Step 1, the molar ratio of lanthanum nitrate, aluminum nitrate, and citric acid is adjusted to 1:12:2. In the precursor solution, the concentration of La 3+ is adjusted to 0.04 mol / L; the surfactant is adjusted to polyethylene glycol, and the content of polyethylene glycol is 0.03 wt%. In Step 2, the heat treatment temperature is adjusted to 1550 °C, and the other conditions are the same as in Example 1, thereby preparing the core-shell corundum aggregate coated with lanthanum hexaaluminate in Example 2 (the sample number of this example is L4).

[0055] This embodiment also provides a refractory castable, which is a corundum-spinel castable; the constituent materials of the corundum-spinel castable include: the core-shell corundum aggregate (content 82.5 wt.%) coated with lanthanum hexaaluminate in Example 2, activated alumina (content 6.5 wt.%), magnesite (content 8 wt.%), silica fume (content 1 wt.%), and Secar71 cement (content 2 wt.%).

[0056] Example 3

[0057] The core-shell corundum aggregate coated with lanthanum hexaaluminate in this example is prepared in basically the same way as in Example 1, and the difference between the two is that: in Step 1, the molar ratio of lanthanum nitrate, aluminum nitrate, and citric acid is adjusted to 1:14:3. In the precursor solution, the concentration of La 3+ is adjusted to 0.06 mol / L; the surfactant is adjusted to sodium dodecyl sulfate, and the content of sodium dodecyl sulfate is 0.05 wt%. In Step 2, the heat treatment temperature is adjusted to 1600 °C, and the other conditions are the same as in Example 1, thereby preparing the core-shell corundum aggregate coated with lanthanum hexaaluminate in Example 3 (the sample number of this example is L6).

[0058] This embodiment also provides a refractory castable, which is a corundum-spinel castable; the composition materials of the corundum-spinel castable include: the core-shell corundum aggregate (content 82.5 wt.%) coated with lanthanum hexaaluminate in Example 3, activated alumina (content 6.5 wt.%), magnesite (content 8 wt.%), silica fume (content 1 wt.%), and Secar71 cement (content 2 wt.%).

[0059] Example 4

[0060] The core-shell corundum aggregate coated with lanthanum hexaaluminate in this example has a preparation method basically the same as that in Example 1, and the difference between the two is that: in Step 1, the molar ratio of lanthanum nitrate, aluminum nitrate, and citric acid is adjusted to 1∶15∶5. In the precursor solution, the concentration of La 3+ is adjusted to 0.1 mol / L; the surfactant is adjusted to sodium dodecyl sulfonate, and the content of sodium dodecyl sulfonate is 0.1 wt%. In Step 2, the heat treatment temperature is adjusted to 1700 °C, and the other conditions are the same as those in Example 1, thus preparing the core-shell corundum aggregate coated with lanthanum hexaaluminate in Example 4 (the sample number of this example is L10).

[0061] This embodiment also provides a refractory castable, which is a corundum-spinel castable; the composition materials of the corundum-spinel castable include: the core-shell corundum aggregate (content 82.5 wt.%) coated with lanthanum hexaaluminate in Example 4, activated alumina (content 6.5 wt.%), magnesite (content 8 wt.%), silica fume (content 1 wt.%), and Secar71 cement (content 2 wt.%).

[0062] After testing, the core-shell corundum aggregate coated with lanthanum hexaaluminate prepared in Examples 1 to 4 of the present invention has a weight gain of 0.1 wt% to 0.5 wt% compared with the corundum aggregate raw material without coating (specifically, the weight gains of Examples 1 to 4 are 0.16 wt%, 0.24 wt%, 0.38 wt%, and 0.49 wt% in sequence). Therefore, in the following comparative examples of the present invention, lanthanum hexaaluminate powder of the same mass (0.1 wt% to 0.5 wt%) is directly mixed to prepare a corundum-spinel castable, and its influence on the thermal shock resistance of the corundum-spinel castable is explored.

[0063] Comparative Example 1

[0064] In this comparative example, commercially available lanthanum hexaaluminate powder is directly added to the corundum-spinel castable at a content of 0.1 wt% for mixing, and its influence on the thermal shock resistance of the corundum-spinel castable is investigated.

[0065] Comparative Example 2

[0066] In this comparative example, commercially available lanthanum hexaaluminate powder was directly added to the corundum-spinel castable at a content of 0.3 wt% for mixing, and its effect on the thermal shock resistance of the corundum-spinel castable was investigated.

[0067] Comparative Example 3

[0068] In this comparative example, commercially available lanthanum hexaaluminate powder was directly added to the corundum-spinel castable at a content of 0.5 wt% for mixing, and its effect on the thermal shock resistance of the corundum-spinel castable was investigated.

[0069] Test Example 1. X-ray Diffraction Analysis

[0070] The surface coatings of the core-shell corundum aggregates (corresponding samples were L2, L4, L6, and L10) coated with lanthanum hexaaluminate coatings prepared in Examples 1 to 4 were analyzed by X-ray diffraction analysis technology, and the obtained XRD patterns are as Figure 1 shown. Among them, Figure 1 in the figure, the abscissa "2θ" is the diffraction angle, and the ordinate "Intensity" is the diffraction intensity.

[0071] It can be seen from Figure 1 that lanthanum hexaaluminate was formed on the surfaces of the core-shell corundum aggregates prepared in Examples 1 to 4, and the remaining phase was only α-Al2O3. As the heat treatment temperature increased, α-Al2O3 continuously decreased, and the content of lanthanum hexaaluminate increased with the increase of the La 3+ concentration and the molar ratio of lanthanum nitrate to aluminum nitrate.

[0072] Test Example 2. Scanning Electron Microscopy Analysis

[0073] The surfaces and cross-sections of the core-shell corundum aggregates (corresponding samples were L2, L4, L6, and L10) coated with lanthanum hexaaluminate coatings prepared in Examples 1 to 4 were analyzed by scanning electron microscopy, and the obtained SEM images are successively as Figures 2 to 5 shown.

[0074] Figure 2 The SEM images of the surface and cross-section of the core-shell corundum aggregate coated with lanthanum hexaaluminate coating prepared in Example 1 are shown. It can be seen that hexagonal layered lanthanum hexaaluminate (LHA) was formed in an aggregated state and was diffusely distributed on the surface of the corundum aggregate. The LHA grain size was 2 - 4 μm, and the average thickness of the LHA coating was 6 μm. The coating was discontinuously distributed on the surface of the corundum aggregate.

[0075] Figure 3SEM images of the surface and cross-section of the core-shell corundum aggregate coated with lanthanum hexaaluminate prepared in Example 2. It can be seen that the hexagonal layered LHA is formed in an aggregated state and is diffusely distributed on the surface of the corundum aggregate. The grain size of LHA is 2-4 μm, the average thickness of the LHA coating is 10 μm, and the coating is discontinuously distributed on the surface of the corundum aggregate.

[0076] Figure 4 SEM images of the surface and cross-section of the core-shell corundum aggregate coated with lanthanum hexaaluminate prepared in Example 3. It can be seen that the hexagonal layered LHA is formed in an aggregated state and is diffusely distributed on the surface of the corundum aggregate. The grain size of LHA is 2-4 μm. In Example 3, when the La 3+ concentration is 0.06 mol / L, the average thickness of the LHA coating is 12 μm. With the increase in the dosage of the surfactant, the wetting angle of the precursor solution decreases, making the LHA coating more continuously distributed on the surface of the corundum aggregate.

[0077] Figure 5 SEM images of the surface and cross-section of the core-shell corundum aggregate coated with lanthanum hexaaluminate prepared in Example 4. It can be seen that the hexagonal layered LHA is formed in an aggregated state and is diffusely distributed on the surface of the corundum aggregate. The grain size of LHA is 2-4 μm. When the heat treatment temperature increases, the LHA crystals grow excessively, and its layered structure is no longer obvious. And with the addition of a high content of sodium dodecyl sulfonate, the precursor solution wets the corundum aggregate more, resulting in a decrease in the thickness of the LHA coating, with an average thickness of 10 μm.

[0078] Based on the above results, it can be known that the layered morphology of the LHA coating in the core-shell corundum aggregate prepared in Example 3 is the best, the continuity of the coating is the best, and the coating property is relatively strong.

[0079] Test Example III: Analysis of the Thermal Shock Resistance of Corundum-Spinel Castables

[0080] The present invention also provides the application of the above core-shell corundum aggregate coated with lanthanum hexaaluminate in the preparation of corundum-spinel castables. Specifically, the core-shell corundum aggregates coated with lanthanum hexaaluminate prepared in Examples 1-4 are used to replace the original untreated tabular corundum aggregates in the preparation of corundum-spinel refractory castables, and the original untreated tabular corundum aggregates are used as a control group for the preparation of corundum-spinel refractory castables. All examples and the control group use the same specification of corundum aggregate raw materials, and the examples are the preparation of core-shell corundum aggregates coated with lanthanum hexaaluminate. Among them, the formula of the corundum-spinel castable prepared with corundum aggregate is shown in Table 1.

[0081] Table 1. Formula of Corundum-Spinel Castable

[0082]

[0083] Weigh the raw materials (tabular corundum aggregate, activated alumina, magnesite, silica fume, Secar71 cement, water reducer) according to the ratio in Table 1, dry mix them in a mixer for 2 min, then add water and wet mix for 4 min, pour them into a mold of 40 mm×40 mm×160 mm and vibrate for 2 min to form; then cure at room temperature for 24 h and demold. The obtained castable is cured at room temperature for 24 h, dried at 100 °C for 24 h, and then heat-insulated at 1500 °C in air for 3 h to obtain the corundum-spinel castable. The corundum-spinel refractory castable samples prepared in the control group and Examples 1-4 are named S0, S2, S4, S6 and S10 respectively.

[0084] The thermal shock resistance of the prepared corundum-spinel refractory castable was tested by the water quenching method. The test was carried out according to GB / T30873-2014 "Test method for thermal shock resistance of refractories". The thermal shock resistance of the corundum-spinel castable was evaluated by the residual strength retention rate before and after the thermal shock test. The results are as Figure 6 shown.

[0085] It can be Figure 6 seen that the blank sample (S0) in the control group has the worst thermal shock resistance, and its residual strength retention rate after the thermal shock test is 10.5%. The corundum-spinel refractory castable samples (S2, S4, S6 and S10) prepared with the core-shell corundum aggregate coated with lanthanum hexaaluminate coating in Examples 1-4 of the present invention have significantly improved thermal shock resistance. Among them, the S6 sample corresponding to Example 3 has the best growth and development of the lamellar LHA crystals on the surface of the corundum aggregate, and the LHA coating has the best continuity, and a continuous LHA interface layer that is not easy to fall off is formed at the corundum-spinel castable aggregate / matrix interface. Therefore, the thermal shock resistance of this sample is the best, and the residual strength retention rate has increased from 10.5% of the S0 sample to 16.3%, and the improvement effect is the most significant. Followed by the S4 (13.8%), S2 (1%) 3.1%), S10 (11.5%) samples.

[0086] Furthermore, the formula of the corundum-spinel castable in Table 1 was used for batching (the tabular corundum aggregate used was the original untreated tabular corundum aggregate), and then lanthanum hexaaluminate powder was added to the corundum-spinel castable at addition amounts of 0.1 wt%, 0.3 wt% and 0.5 wt% respectively for mixing to prepare the corundum-spinel refractory castable samples of Comparative Examples 1-3, and the same method as above was used for the thermal shock experiment to compare with the samples prepared in the examples of the present invention.

[0087] The test results show that the residual strength retention rates of the corundum-spinel refractory castable samples prepared in Comparative Examples 1, 2, and 3 are 11.2%, 12.1%, and 12.8% respectively, all of which are higher than that of the S0 sample, but lower than those of the corundum-spinel refractory castable samples S2, S4, and S6 of the present invention.

[0088] Therefore, compared with directly adding lanthanum hexaaluminate powder, the improvement effect of the thermal shock resistance of the corundum-spinel castable prepared by adding the core-shell corundum aggregate coated with a lanthanum hexaaluminate coating in the present invention is more obvious. It is thus confirmed that introducing the LHA interface layer at the aggregate / matrix interface of the corundum-spinel castable in the present invention has a better improvement effect on the thermal shock resistance than the scheme of directly adding lanthanum hexaaluminate powder.

[0089] Furthermore, a SU6600 type field emission electron microscope was used to analyze and characterize the distribution of the coating of the corundum-spinel castable prepared with the core-shell corundum aggregate coated with a lanthanum hexaaluminate coating in Example 3 inside the corundum-spinel castable and the microstructure of the sample after the thermal shock experiment. The results are respectively as Figure 7 and Figure 8 shown.

[0090] It can be seen from Figure 7 that the LHA coating coated on the surface of the corundum aggregate did not fall off during the preparation of the corundum-spinel castable, and a LHA interface layer with a certain thickness and high continuity was formed at the aggregate / matrix interface.

[0091] It can be seen from Figure 8 that when the crack propagated to the LHA interface layer after the thermal shock experiment, the crack deflected and branched from a single crack into two cracks that continuously expanded along the edge of the aggregate, which consumed more elastic strain energy and reduced the number of transgranular cracks, thereby effectively improving the thermal shock resistance of the corundum-spinel castable ( Figure 8 a~ Figure 8 f).

[0092] In summary, for the core-shell corundum aggregate coated with a lanthanum hexaaluminate coating prepared in the present invention, the cluster-like layered LHA is diffusely distributed on the surface of the corundum aggregate. When the concentration of La 3+ in the precursor solution increases, the thickness of the LHA coating on the surface of the corundum aggregate first increases and then decreases with the increase of the heat treatment temperature, and the thickness range of the LHA coating is 6-12 μm. Adding the prepared core-shell corundum aggregate coated with a lanthanum hexaaluminate coating to the corundum-spinel castable can form a LHA interface layer that is not easy to fall off at the aggregate / matrix interface, thereby effectively improving the mechanical properties and thermal shock resistance of the castable, and having extremely broad development prospects in the field of aggregate preparation of refractory castables.

[0093] Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of core-shell corundum aggregate wrapped with lanthanum hexaaluminate coating, characterized in that, It includes the following steps: (1) Mix lanthanum nitrate, aluminum nitrate, citric acid, and surfactant evenly in water to obtain a precursor solution; wherein, the molar ratio of lanthanum nitrate, aluminum nitrate, and citric acid is 1∶(10 - 15)∶(1 - 5); (2) Immerse the corundum aggregate in the precursor solution for vacuum impregnation treatment, and then perform drying and heat treatment to obtain a core-shell corundum aggregate coated with lanthanum hexaaluminate coating.

2. The preparation method of the core-shell corundum aggregate wrapped with a lanthanum hexaaluminate coating according to claim 1, characterized in that, In step (1), the surfactant is one or more of sodium dodecyl sulfonate, sodium dodecyl sulfate, polyvinyl alcohol, and polyethylene glycol; in the precursor solution, the dosage of the surfactant is 0.01wt% - 0.1wt%.

3. The preparation method of the core-shell corundum aggregate wrapped with a lanthanum hexaaluminate coating according to claim 1, characterized in that, In step (1), in the precursor solution, the addition concentration of lanthanum nitrate is 0.02 - 0.1mol / L.

4. The preparation method of the core-shell corundum aggregate wrapped with a lanthanum hexaaluminate coating according to claim 1, characterized in that, In step (1), the specific process of mixing lanthanum nitrate, aluminum nitrate, citric acid, and surfactant evenly in water is: mix citric acid evenly in water to obtain a citric acid solution; then add lanthanum nitrate, aluminum nitrate, and surfactant to the citric acid aqueous solution, ultrasonically oscillate and mix for 20 - 60min, and then stir and mix at a temperature of 50 - 80°C for 40 - 100min.

5. The preparation method of the core-shell corundum aggregate wrapped with a lanthanum hexaaluminate coating according to any one of claims 1 to 4, characterized in that, In step (2), the corundum aggregate is a tabular corundum aggregate; the particle size of the tabular corundum aggregate is 1 - 5mm.

6. The preparation method of the core-shell corundum aggregate wrapped with a lanthanum hexaaluminate coating according to any one of claims 1 to 4, characterized in that, In step (2), the process conditions of the vacuum impregnation treatment are: the vacuum degree is -0.05 - -0.098MPa, and the impregnation time is 0.8 - 2.0h.

7. The preparation method of the core-shell corundum aggregate wrapped with a lanthanum hexaaluminate coating according to any one of claims 1 to 4, characterized in that, In step (2), the drying temperature is 80 - 120°C; the heat treatment temperature is 1500 - 1700°C, and the heat treatment time is 2 - 4h.

8. A core-shell corundum aggregate coated with a lanthanum hexaaluminate coating prepared by the preparation method according to any one of claims 1 to 7, characterized in that, In the core-shell corundum aggregate coated with lanthanum hexaaluminate coating, the thickness of the lanthanum hexaaluminate coating is 6 - 12μm; the lanthanum hexaaluminate coating is mainly composed of hexagonal layered lanthanum hexaaluminate; the grain size of the hexagonal layered lanthanum hexaaluminate is 2 - 4μm.

9. Use of a core-shell corundum aggregate coated with a lanthanum hexaaluminate coating prepared by the preparation method according to any one of claims 1 to 7, characterized in that, Application as an aggregate in the preparation of refractory castables; the refractory castable is a corundum-spinel castable.

10. Use of the core-shell corundum aggregate coated with lanthanum hexaaluminate according to claim 9, characterized in that, The composition materials of the corundum-spinel castable include: core-shell corundum aggregate coated with lanthanum hexaaluminate coating, activated alumina, magnesite, silica fume, Secar71 cement; the addition amount of the core-shell corundum aggregate coated with lanthanum hexaaluminate coating is 75wt% - 86wt%.

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