Zirconium oxide-based high-temperature protective coating

Abstract

The invention belongs to the technical field of refractory coatings, and relates to a zirconia-based high-temperature protective coating. The zirconia-based refractory material protective coating comprises the following raw materials in percentage by weight: 50-65% of monoclinic zirconia micro powder, 10-15% of spinel, 5-10% of alumina micro powder, 3-8% of anorthite, 1-3% of titanium dioxide, 5-10% of silica fume and 3-6% of sodium silicate. Sodium silicate plays a role of a binder at 1000 DEG C or below, a certain amount of monoclinic zirconium oxide is dissolved in a high-temperature stage, and sintering growth of monoclinic zirconium oxide and formation of a network skeleton are promoted; the zirconium oxide-based high-temperature protective coating further comprises other additives including a water reducing agent, a thickening agent and a defoaming agent, and water accounting for 10-15% of the total weight of the raw materials needs to be added into the zirconium oxide-based high-temperature protective coating. The coating has excellent high-temperature resistance, can be used for a long time in a working environment of 1550 DEG C or below, and has strong adhesive force with a refractory material and comprehensive protection performance.

Description

Technical Field

[0001] This invention belongs to the field of refractory coating technology, specifically relating to a zirconia-based high-temperature protective coating. Background Technology

[0002] In industrial production, many high-temperature equipment require refractory materials to withstand high-temperature environments, such as kilns and pipelines in metallurgy, chemical industry, and power industry. However, these refractory materials are exposed to high temperatures (>800℃) and corrosive atmospheres (such as sulfides, chlorides, and slag) for extended periods, making their surfaces susceptible to chemical corrosion and structural spalling. Currently, to improve the corrosion resistance of refractory materials, protective coatings are typically applied to their surfaces. However, existing protective coatings have several problems. For example, some coatings lack sufficient high-temperature resistance; traditional inorganic silicate coatings, for instance, are limited to temperatures below 1300℃ and are prone to decomposition and corrosion at higher temperatures, thus losing their protective function. Other coatings... Poor adhesion to refractory materials, or a mismatch in the coefficient of thermal expansion with the refractory matrix (such as magnesium-aluminum-silica molded products and castables), can easily lead to detachment under temperature changes or mechanical vibration, failing to provide effective protection. Furthermore, some protective coatings offer limited protection with narrow temperature windows, making them ill-suited for more complex high-temperature corrosive environments. Therefore, existing high-temperature protective coatings generally have short service lives when facing highly corrosive environments exceeding 1300℃, failing to meet the long-term needs of industrial production. Thus, developing a high-temperature protective coating for refractory materials with excellent high-temperature resistance, strong adhesion, and good protective effects is of significant practical importance.

[0003] Zirconia plasma spray coatings (stabilized zirconia powder) are coatings formed through plasma spraying, an indispensable protective coating solution in modern high-temperature technology fields, especially in gas turbines and aero engines. Zirconia-based coatings are resistant to high temperatures (>1300℃). Zirconia plasma spray coatings refer to powder materials with zirconia as the main component, which are deposited on the substrate surface through plasma spraying to form a high-performance coating. Currently, their preparation cost is high, making them unsuitable for traditional refractory materials. Therefore, the biggest problem facing zirconia-based coatings is how to achieve adhesion (construction process) and densification sintering on refractory substrates. To address this, zirconia-based high-temperature coatings for refractory materials need to introduce other phases. However, when using traditional silicate phases to stabilize zirconia, at operating temperatures, the silicate phase easily causes the zirconia stabilizer to desolvate, leading to zirconia instability. When zirconia undergoes monoclinic phase formation at around 1200℃... m -ZrO2) and tetragonal phase ( t The transformation of ZrO2, accompanied by a 3-5% volume change, can also cause the coating to crack and fail during thermal cycling. Summary of the Invention

[0004] The purpose of this invention is to provide a zirconia-based high-temperature protective coating that is suitable for working environments exceeding 1300°C, is resistant to peeling, and has low preparation cost and simple application.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A zirconia-based high-temperature protective coating, comprising the following raw materials and weight percentages: monoclinic zirconia micro powder 50-65%, spinel 10-15%, alumina micro powder 5-10%, anorthite 3-8%, titanium dioxide 1-3%, silica fume 5-10%, and sodium silicate 3-6%. Sodium silicate acts as a binder below 1000℃ and, together with anorthite, silica fume, and alumina micro powder, can melt at high temperatures to form a glassy coating, filling the pores in the coating, improving its density and sealing properties, enhancing its protective effect, and providing high-temperature protection. A certain amount of monoclinic zirconium oxide is dissolved in the warm stage to promote the sintering growth of monoclinic zirconium oxide and the formation of the network skeleton; the zirconium oxide-based high-temperature protective coating also includes other additives: water reducing agent is Sima Chemical T85, with an addition amount of 0.01-0.03% of the total weight of raw materials; thickener is magnesium aluminum silicate, with an addition amount of 0.5-1.5% of the total weight of raw materials; defoamer is DF-677, with an addition amount of 0.05-0.15% of the total weight of raw materials; the zirconium oxide-based high-temperature protective coating also requires the addition of 10-15% water of the total weight of raw materials.

[0006] The monoclinic zirconia micro powder has a particle size of <5μm; the spinel is one of magnesium iron spinel, iron aluminum spinel, or manganese iron spinel, with a particle size of <10μm; the silica fume is zirconium-containing silica fume with a zirconium oxide content >8wt% and a particle size of <1μm; the titanium dioxide has a particle size of <5μm; the alumina micro powder has a particle size of <5μm; and the sodium silicate is fine sodium silicate powder with a particle size of <1mm.

[0007] The zirconia-based high-temperature protective coating contains zirconia, which possesses high hardness, high wear resistance, and good high-temperature resistance, enhancing the coating's mechanical properties and corrosion resistance. It acts as a framework at both medium and high temperatures. The spinel in the coating provides skeletal support at medium and low temperatures. Sodium silicate acts as a binder below 1000℃ and, together with anorthite, silica fume, and alumina powder, can melt at high temperatures to form a glassy coating, filling the pores in the coating, improving its density and sealing properties, enhancing its protective effect, and dissolving a certain amount of monoclinic zirconia at high temperatures, promoting the sintering growth of the monoclinic zirconia. The coating contains a large network framework; the titanium dioxide in the coating has good hiding power and whiteness, which can improve the decorative properties and weather resistance of the coating, and at the same time enhance the shielding effect of the coating to prevent the penetration of corrosive media; the dispersant in the coating helps the raw materials to be evenly dispersed in the coating, prevents particle agglomeration, and ensures the stability and consistency of the coating; the defoamer in the coating can eliminate the bubbles generated in the coating during preparation and construction, and avoid the bubbles from having an adverse effect on the performance and appearance of the coating; the thickener in the coating is an inorganic material and is not affected by the pH value of the coating. Its function is to ensure that the coating has good suspension and construction performance.

[0008] The method for preparing the zirconia-based high-temperature protective coating is as follows: monoclinic zirconia, spinel, alumina, anorthite, titanium dioxide, silica fume, water-reducing agent, and water are wet-mixed in a ball mill for 4-8 hours according to the proportions in the table. Then, sodium silicate is added and wet-mixed in the ball mill for another 4-8 hours. Finally, a thickener and defoamer are added and wet-mixed for 2-4 hours to adjust the viscosity of the coating, thereby obtaining the zirconia-based high-temperature protective coating. The coating can be applied to the surface of refractory materials by spraying or brushing and allowed to dry naturally.

[0009] This invention proposes a zirconia-based high-temperature protective coating. The components work synergistically. Sodium silicate acts as a film-forming substance at low temperatures, creating a continuous coating framework. Inorganic fillers such as zirconia, spinel, alumina, silica fume, titanium dioxide, and anorthite are uniformly dispersed within it. The coating cures at room temperature, resulting in excellent adhesion and stability. At medium temperatures, the silicate phase undergoes physicochemical changes to form a high-viscosity glass phase, further filling the coating pores and increasing its density, thus preventing the intrusion of corrosive media. As the temperature continues to rise, the amount of glass phase increases, and the viscosity decreases. At this point, some of the monoclinic zirconia dissolves into the glass phase, while some undergoes a crystal transformation. Because the glass phase in the coating is in a molten state, it can mitigate oxidation. The volume shrinkage effect during zirconium crystal transformation leads to precipitation as the concentration of zirconium oxide in the glass phase of the coating increases further with higher temperatures. This precipitation occurs as zirconium oxide adheres to the periphery of zirconium oxide particles and grows, resulting in liquid-phase sintering of the coating. The microstructure of the coating is shown in the attached figure, revealing a dense structure that forms a zirconium oxide-based network framework, exhibiting high refractory properties. Simultaneously, the coating can adhere to the refractory material surface and, together with the refractory material, withstand repeated heating and cooling processes. During cooling, zirconium oxide transforms from a tetragonal phase to a monoclinic phase. At this transformation temperature, the glass phase in the zirconium oxide framework network remains in a certain molten state, exhibiting toughness and mitigating the system expansion effect after the crystal transformation. Therefore, the coating remains resistant to peeling and cracking.

[0010] This invention offers the following advantages: It exhibits excellent high-temperature resistance, allowing for long-term use in environments below 1550℃ without significant peeling or flow. It demonstrates strong adhesion to refractory materials, maintaining good adhesion even after thermal cycling tests and resisting detachment. It provides comprehensive protection, effectively resisting erosion from various corrosive media such as acidic gases, molten metal, and slag, significantly extending the service life of refractory materials. The manufacturing process is simple and cost-effective, making it suitable for large-scale industrial production and application. Attached Figure Description

[0011] Figure 1 The image shows the microstructure of this coating after heat treatment at 1550℃. The white part represents zirconium oxide, and the dark part represents the amorphous phase. Detailed Implementation

[0012] The present invention will be described in detail with reference to the accompanying drawings and specific embodiments: Example 1:

[0013] A method for preparing a zirconia-based high-temperature protective coating: According to the proportions in the table below, monoclinic zirconia, magnesium iron spinel, alumina, calcium feldspar, titanium dioxide, silica fume, and a certain amount of water-reducing agent (0.01% of the raw material mass in the table) and water (10% of the raw material mass in the table) are wet-mixed in a ball mill for 4 hours. Then, sodium silicate is added and wet-mixed in the ball mill for 5 hours. Finally, a thickener (0.5% of the raw material mass in the table) and an antifoamer (0.05% of the raw material mass in the table) are added and wet-mixed for 2 hours. The viscosity of the coating is then adjusted to obtain the zirconia-based high-temperature protective coating. The above coating can be applied to the surface of refractory materials by spraying or brushing, and then dried in a ventilated environment.

[0014] Example 2:

[0015] A method for preparing a zirconia-based high-temperature protective coating: According to the proportions in the table below, monoclinic zirconia, iron-aluminum spinel, alumina, calcium feldspar, titanium dioxide, silica fume, and a certain amount of water-reducing agent (0.03% of the raw material mass in the table) and water (15% of the raw material mass in the table) are wet-mixed in a ball mill for 8 hours. Then, sodium silicate is added and wet-mixed in the ball mill for another 8 hours. Finally, a thickener (1.5% of the raw material mass in the table) and an defoamer (0.15% of the raw material mass in the table) are added and wet-mixed for 4 hours. The viscosity of the coating is then adjusted to obtain the zirconia-based high-temperature protective coating. The above coating can be applied to the surface of refractory materials by spraying and dried after ventilation.

[0016] Example 3:

[0017] A method for preparing a zirconia-based high-temperature protective coating: According to the proportions in the table below, monoclinic zirconia, manganese iron spinel, alumina, calcium feldspar, titanium dioxide, silica fume, and a certain amount of water-reducing agent (0.02% of the raw material mass in the table) and water (13% of the raw material mass in the table) are wet-mixed in a ball mill for 6 hours. Then, sodium silicate is added and wet-mixed in the ball mill for 4 hours. Finally, a thickener (1.0% of the raw material mass in the table) and an antifoamer (0.10% of the raw material mass in the table) are added and wet-mixed for 3 hours. The viscosity of the coating is then adjusted to obtain the zirconia-based high-temperature protective coating. The above coating can be applied to the surface of refractory materials by brushing and allowed to dry in a ventilated environment.

[0018]

Claims

1. A zirconia-based high-temperature protective coating, characterized in that: The raw material composition and weight percentage of the zirconia-based refractory protective coating are as follows: monoclinic zirconia micro powder 50-65%, spinel 10-15%, alumina micro powder 5-10%, anorthite 3-8%, titanium dioxide 1-3%, silica fume 5-10%, and sodium silicate 3-6%. Sodium silicate acts as a binder below 1000℃ and, together with anorthite, silica fume, and alumina micro powder, can melt at high temperatures to form a glassy coating, filling the pores in the coating, improving its density and sealing properties, enhancing its protective effect, and dissolving at high temperatures. A certain amount of monoclinic zirconia promotes the sintering growth of monoclinic zirconia and the formation of the network skeleton; the zirconia-based high-temperature protective coating also includes other additives: water reducing agent is Sima Chemical T85, added at 0.01-0.03% of the total weight of raw materials; thickener is magnesium aluminum silicate, added at 0.5-1.5% of the total weight of raw materials; defoamer is DF-677, added at 0.05-0.15% of the total weight of raw materials; the zirconia-based high-temperature protective coating also requires the addition of 10-15% water of the total weight of raw materials.

2. The zirconia-based high-temperature protective coating as described in claim 1, characterized in that: The monoclinic zirconia micro powder has a particle size of <5μm; the spinel is one of magnesium iron spinel, iron aluminum spinel, or manganese iron spinel, with a particle size of <10μm; the silica fume is zirconium-containing silica fume with a zirconium oxide content >8wt% and a particle size of <1μm; the titanium dioxide has a particle size of <5μm; the alumina micro powder has a particle size of <5μm; and the sodium silicate is fine sodium silicate powder with a particle size of <1mm.

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