An environmentally friendly chromium-containing spinel infrared radiation coating and its preparation method

Abstract

This invention relates to an environmentally friendly chromium-containing spinel infrared radiation coating and its preparation method. The technical solution is as follows: the environmentally friendly chromium-containing spinel infrared radiation coating consists of a transition layer and a working layer. Fine aluminum-chromium solid solution powder, fine zirconium oxide powder, and silica sol are used as raw materials for the transition layer. Fine titanium-iron co-doped magnesium-chromium spinel powder, fine aluminum-chromium solid solution powder, borosilicate glass powder, silica micropowder, and aluminum dihydrogen phosphate solution are used as raw materials for the working layer. The two raw materials are separately mixed with deionized water and ball-milled to obtain transition layer slurry and working layer slurry, respectively. The transition layer slurry and working layer slurry are sequentially coated onto the surface of alumina-silicon refractory bricks and dried to obtain the environmentally friendly chromium-containing spinel infrared radiation coating. The environmentally friendly chromium-containing spinel infrared radiation coating prepared by this method is suitable for high-temperature environments above 1400℃, can firmly bond with the substrate, can stably exert radiation, and the hexavalent chromium meets emission standards.

Description

Technical Field

[0001] This invention belongs to the field of infrared radiation coating technology. In particular, it relates to an environmentally friendly chromium-containing spinel infrared radiation coating and its preparation method. Background Technology

[0002] Currently, industrial kilns used in high-temperature industries both domestically and internationally consume enormous amounts of energy, accounting for over 60% of total industrial energy consumption. In high-temperature environments exceeding 800℃, heat transfer is primarily radiative, and the higher the temperature, the greater the proportion of radiative heat transfer. Furthermore, the energy of radiation gradually shifts towards the 0.8–2.5 μm near-infrared band. During operation, industrial kilns operate at temperatures exceeding 1000℃ for extended periods, with an average thermal efficiency of less than 40%. To address this issue, coating the surface of traditional furnace lining refractory materials with high-emissivity infrared radiation coatings has become a consensus. Spinel-based materials, due to their stability in oxidizing atmospheres and the presence of numerous interstitial structures, provide favorable conditions for ion doping, leading to materials with even higher emissivity, and have thus become a research hotspot.

[0003] Zhang et al. (Xinyang Zhang, Zhaofeng Chen, Cao Wu et al., Solvothermal synthesis of spinel ZnFe2O4 nanoparticles with enhanced infrared radiation property[J]. Chemical Physics Letters, 2019, 732: 136647.) prepared nano-zinc-iron spinel particles using a solvothermal synthesis method. They found that as the synthesis temperature increased from 700℃ to 1100℃, the emissivity of the zinc-iron spinel increased from 0.81 to 0.97. However, when the synthesis temperature reached 1200℃, the specific surface area of ​​the sample decreased due to grain growth, resulting in a decrease in its infrared emissivity. Therefore, it is difficult to use iron-containing spinel directly for the preparation of infrared radiation coatings in industrial kilns with operating temperatures exceeding 1200℃ for extended periods. Furthermore, industrial kilns using aluminosilicate refractories such as corundum-mullite bricks as furnace lining materials typically operate at temperatures exceeding 1400℃. These kilns have even higher temperatures and greater energy consumption, and this technology cannot adequately meet the energy-saving requirements of these high-temperature kilns.

[0004] The patented technology, "A High-Temperature Infrared Radiation Coating and Its Preparation Method and Application" (CN 107573731 A), uses cerium-doped nickel-chromium spinel as an emissive to prepare a coating with an infrared emissivity greater than 0.85 on the surface of refractory fiber materials. Although the coating has excellent stability and anti-radiation attenuation performance, and its emissivity can still reach 0.86 after 30 days of service in a high-temperature furnace at 1500℃, the surface of conventional aluminosilicate refractory bricks is not as rough as refractory fiber materials. Applying this coating to the surface of conventional aluminosilicate refractory bricks poses a risk of cracking and peeling.

[0005] The preparation of copper chromium black coating and its infrared radiation properties were studied. Copper chromium black (CuCr2O4) powder was synthesized by sol-gel method, and an infrared radiation coating was prepared on Q235 alloy steel by spraying. Although the coating has good radiation performance, good thermal shock resistance and significant heating energy saving effect in the 3-5μm band, it cannot exist stably at high temperature when directly coated on the surface of aluminosilicate refractory bricks. It is easy to react with the substrate, which will cause the infrared radiation performance of the coating to decay and reduce the service life of the coating.

[0006] The patented technology, "A High-Temperature, High-Emissivity Infrared Radiation Coating and Its Preparation and Application Methods" (CN 113214685 A), uses CuO-doped magnesium chromium spinel powder and silicide expanded graphite as main raw materials. It prepares an infrared radiation coating on the surface of an industrial kiln wall using brushing or spraying methods. This coating exhibits high emissivity in the 1–5 μm wavelength band and can be used long-term in industrial kilns above 1000°C and without air isolation. However, the silicide expanded graphite used in the coating is a non-oxide; it will oxidize at higher temperatures, leading to a decrease in the coating's radiation performance. Furthermore, measured Cr(VI) content in the CuO-doped magnesium chromium spinel powder was found to be 182 ppm, exceeding the national emission standard, posing a risk of Cr(VI) pollution. Summary of the Invention

[0007] The present invention aims to overcome the defects of the prior art and provides a method for preparing an environmentally friendly chromium-containing spinel infrared radiation coating that is low in cost and simple in process. The environmentally friendly chromium-containing spinel infrared radiation coating prepared by this method is suitable for high-temperature environments above 1400℃, can be firmly bonded to the substrate, can stably exert radiation effect, and the hexavalent chromium meets the emission standards.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: the environmentally friendly chromium-containing spinel infrared radiation coating is composed of a transition layer and a working layer.

[0009] The preparation method of the environmentally friendly chromium-containing spinel infrared radiation coating is as follows: First, the environmentally friendly chromium-containing spinel infrared radiation transition layer slurry is coated onto the surface of an aluminosilicate refractory brick to obtain a transition layer; then, the environmentally friendly chromium-containing spinel infrared radiation working layer slurry is coated onto the surface of the transition layer to obtain a working layer; then, the transition layer and working layer coated on the surface of the aluminosilicate refractory brick are dried at 70-100℃, and the thickness of the dried coating is 200-400μm, thus obtaining the environmentally friendly chromium-containing spinel infrared radiation coating.

[0010] The preparation method of the environmentally friendly chromium-containing spinel infrared radiation transition layer slurry is as follows: using 50-80 wt% aluminum-chromium solid solution fine powder, 10-34 wt% zirconium oxide fine powder and 4-22 wt% silica sol as transition layer raw materials, and adding 40-70 wt% deionized water to the transition layer raw materials, ball milling in a planetary ball mill for 0.5-2 hours, with a ball-to-material ratio of 2-4:1, the resulting slurry is the environmentally friendly chromium-containing spinel infrared radiation transition layer slurry.

[0011] The preparation method of the environmentally friendly chromium-containing spinel infrared radiation working layer slurry is as follows: using 40-70 wt% titanium-iron co-doped magnesium-chromium spinel fine powder, 16-22 wt% aluminum-chromium solid solution fine powder, 1-4 wt% borosilicate glass powder, 2-5 wt% silicon micro powder and 5-35 wt% aluminum dihydrogen phosphate solution as working layer raw materials, and adding 20-50 wt% deionized water to the working layer raw materials, ball milling in a planetary ball mill for 0.5-2 hours, with a ball-to-material ratio of 2-4:1, the resulting slurry is the environmentally friendly chromium-containing spinel infrared radiation working layer slurry.

[0012] The preparation method of the titanium-iron co-doped magnesium-chromium spinel fine powder is as follows: First, magnesium oxide, chromium trioxide, titanium dioxide and iron oxide are used as raw materials for the spinel fine powder, and they are placed in a planetary ball mill and ball-milled for 1-4 hours with a ball-to-material ratio of 2-4:1; then, the slurry obtained from ball milling is dried, pressed into a billet under 10-25 MPa, kept at 1250-1550℃ for 2.5-4 hours, cooled in the furnace, crushed, and sieved to obtain titanium-iron co-doped magnesium-chromium spinel fine powder; the particle size of the titanium-iron co-doped magnesium-chromium spinel fine powder is less than 45 μm.

[0013] In the raw materials of the spinel fine powder: the sum of the amounts of chromium trioxide, titanium dioxide, and iron oxide to the amount of magnesium oxide is 1:1 to 1.5; the sum of the amounts of chromium trioxide, titanium dioxide, and iron oxide is 2 to 5:1; and the sum of the amounts of titanium dioxide and iron oxide is 2 to 3:1. The purity of magnesium oxide, chromium trioxide, titanium dioxide, and iron oxide is ≥99%, and the particle size is less than 10 μm.

[0014] The aluminum-chromium solid solution fine powder used in the environmentally friendly chromium-containing spinel infrared radiation transition layer slurry is the same as that used in the environmentally friendly chromium-containing spinel infrared radiation working layer slurry; the molar ratio of Cr2O3 to Al2O3 in the aluminum-chromium solid solution fine powder is less than 1:10; and the average particle size of the aluminum-chromium solid solution fine powder is less than 74 μm.

[0015] The zirconia fine powder is calcium-stabilized zirconia, with a ZrO2 content ≥90wt% and an average particle size of less than 45μm.

[0016] The silica sol has a SiO2 content ≥ 25 wt% and a pH less than 4.

[0017] The silicon micropowder has a SiO2 content of ≥95wt% and an average particle size of less than 5μm.

[0018] The boron-containing glass powder has a B2O3 content of ≥8wt% and an average particle size of less than 45μm.

[0019] The aluminum dihydrogen phosphate solution has an Al(H2PO4)3 content ≥30wt% and a pH less than 2.

[0020] The aluminosilicate refractory bricks are mullite bricks or corundum-mullite bricks.

[0021] By adopting the above technical solution, the present invention has the following advantages compared with the prior art:

[0022] The environmentally friendly chromium-containing spinel infrared radiation coating of this invention consists of a transition layer and a working layer. The transition layer uses fine aluminum-chromium solid solution powder, fine zirconium oxide powder, and silica sol as raw materials, while the working layer uses fine titanium-iron co-doped magnesium-chromium spinel powder, fine aluminum-chromium solid solution powder, borosilicate glass powder, silica micropowder, and aluminum dihydrogen phosphate solution as raw materials. The two raw materials are respectively mixed with deionized water and ball-milled to obtain transition layer slurry and working layer slurry. The transition layer slurry and working layer slurry are sequentially coated onto the surface of alumina-silica refractory bricks and dried to obtain the environmentally friendly chromium-containing spinel infrared radiation coating, which is low in cost and simple in process.

[0023] The titanium-iron co-doped magnesium-chromium spinel used in this invention employs TiO2 and Fe2O3 as dopants. On the one hand, Ti... 4+ radius and Cr 3+ The radii are very close, Ti 4+ Able to replace Cr 3+ Infiltrating the octahedral voids of spinel, Ti causes defects such as lattice distortion, disrupts the symmetry of the internal crystal structure, and enhances lattice vibration absorption; simultaneously, Ti is also a variable-valence element. 4+ During high-temperature solid-state sintering, some electrons are gained and the material transforms into Ti. 3+This process prevents the formation of oxygen vacancies in the spinel's lattice oxygen, increasing the electron transport rate and enhancing free carrier absorption. On the other hand, TiO2 doping introduces impurity levels at the top of the valence band and the bottom of the conduction band, increasing the electron transition probability and enhancing free electron impurity level absorption. The enhanced absorption by lattice vibrations, free carriers, and impurity levels all improve the material's infrared radiation performance, thus giving TiO2-doped magnesium chromium spinel its high emissivity. A portion of the added Fe2O3 participates in the spinel synthesis reaction. 3+ Able to replace Cr 3+ Occupying the octahedral voids of spinel makes the structure of magnesium chromium spinel more complex, generating more lattice distortion and defects, which is beneficial to improving emissivity. Another portion of Fe2O3 reacts at high temperatures to form Fe3O4, which is itself a high-emissivity material, contributing to the overall emissivity improvement of the spinel. Therefore, the doping of TiO2 and Fe2O3 significantly improves the infrared radiation performance of magnesium chromium spinel and the environmentally friendly chromium-containing spinel infrared radiation coating made from it in the 0.8–2.5 μm wavelength range.

[0024] In addition, Ti 4+ The valence state is higher than that of Cr 3+ It belongs to high-valence ion substitution. In order to maintain the balance of valence, Cr 3+ It is difficult to further increase the price of Cr. 6+ The transformation, and the fact that both TiO2 and Fe2O3 are acidic oxides, can also inhibit the formation of Cr(VI), further reducing the Cr(VI) content in chromium-containing spinel. Using titanium-iron co-doped magnesium-chromium spinel as a radiation functional raw material reduces the Cr(VI) content in the coating from the source. The transition layer and working layer of this invention use silica sol and aluminum dihydrogen phosphate solution as binders, respectively. Both are acidic and can also inhibit the formation of Cr(VI) in the coating to a certain extent, reducing Cr(VI) emissions from the coating. More importantly, this invention adds a certain amount of aluminum-chromium solid solution fine powder to both the transition layer and the working layer. Aluminum-chromium solid solution is an infinite solid solution, so even if Cr(VI) is generated in the coating, it can be dissolved into the aluminum-chromium solid solution, further inhibiting Cr(VI) emissions from the environmentally friendly chromium-containing spinel infrared radiation coating.

[0025] Meanwhile, the silica sol and aluminum dihydrogen phosphate solution can cure at room temperature, giving the coating high strength after drying. Secondly, aluminum dihydrogen phosphate gradually decomposes above 1000℃, and the resulting Al2O3 reacts with SiO2 in the silica sol at the interface between the working layer and the transition layer, thus strengthening the bond between them. The boron-containing glass powder and silica micropowder used in this invention ensure good adhesion of the infrared radiation coating at low and medium temperatures. When the infrared radiation coating is heated to 600℃, these two raw materials gradually form a liquid phase, effectively improving the bonding strength between the infrared radiation coating and the transition layer, preventing defects such as cracks in the infrared radiation coating. The appropriate formation of the liquid phase at high temperatures also ensures good thermal shock stability of the environmentally friendly chromium-containing spinel infrared radiation coating, ensuring its service life at high temperatures.

[0026] This invention utilizes fine aluminum-chromium solid solution powder in both the transition layer and the working layer. The coefficient of thermal expansion of aluminum-chromium solid solution is similar to that of corundum-mullite, exhibiting high compatibility. This ensures a strong bond between the transition layer and the substrate and working layer, guaranteeing the coating's adhesion strength. Furthermore, the aluminum-chromium solid solution in the transition layer prevents penetration from the working layer into the substrate, avoiding reactions between the chromium-containing spinel and the substrate. This ensures excellent radiation attenuation resistance and helps extend the service life of the prepared environmentally friendly chromium-containing spinel infrared radiation coating under high-temperature conditions.

[0027] This invention uses titanium-iron co-doped magnesium-chromium spinel fine powder as the main infrared radiation raw material. The doping with TiO2 and Fe2O3 not only significantly improves the infrared radiation performance but also greatly reduces the Cr(VI) content, providing a useful reference for the application of chromium-containing spinel in infrared radiation coatings. A transition layer mainly composed of aluminum-chromium solid solution is set between the working layer of the coating and the aluminosilicate refractory substrate. This helps improve the interfacial bonding strength and reduce cracking at the interface between the working layer and the substrate, preventing the working layer of the infrared radiation coating from reacting with the aluminosilicate refractory substrate most commonly used in kilns, thereby effectively suppressing the attenuation of emissivity. Furthermore, the components of both the transition layer and the working layer have multiple functions, and there are mutual influences between the components. The transition layer and the working layer, as a whole, ensure that the environmentally friendly chromium-containing spinel infrared radiation coating can firmly bond to the substrate and stably exert its radiation effect in high-temperature service environments.

[0028] The environmentally friendly chromium-containing spinel infrared radiation coating prepared by this invention can be firmly bonded to aluminum-silicon refractory materials. The average emissivity of the environmentally friendly chromium-containing spinel infrared radiation coating in the 0.8-2.5 μm band was tested using a high-temperature infrared emissivity testing device and found to be 0.82-0.93. The Cr(VI) content of the environmentally friendly chromium-containing spinel infrared radiation coating was tested using spectrophotometry and found to be 2-14 ppm. After the prepared environmentally friendly chromium-containing spinel high emissivity infrared radiation coating was placed in a kiln at 1400℃ for 3 months, its emissivity was measured to be 0.79-0.89, and no peeling, cracking or flaking occurred.

[0029] Therefore, the present invention has low cost and simple process. The environmentally friendly chromium-containing spinel infrared radiation coating prepared is suitable for high temperature environments above 1400℃, can be firmly bonded to the substrate, can stably exert radiation effect, and the hexavalent chromium meets the emission standards. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments, but this is not intended to limit the scope of protection thereof.

[0031] An environmentally friendly chromium-containing spinel infrared radiation coating and its preparation method. The preparation method described in this specific embodiment is as follows:

[0032] First, the environmentally friendly chromium-containing spinel infrared radiation transition layer slurry is coated onto the surface of an aluminosilicate refractory brick to obtain a transition layer; then, the environmentally friendly chromium-containing spinel infrared radiation working layer slurry is coated onto the surface of the transition layer to obtain a working layer; then, the transition layer and working layer coated on the surface of the aluminosilicate refractory brick are dried at 70-100℃, and the thickness of the dried coating is 200-400μm, thus obtaining the environmentally friendly chromium-containing spinel infrared radiation coating.

[0033] The preparation method of the environmentally friendly chromium-containing spinel infrared radiation transition layer slurry is as follows: using 50-80 wt% aluminum-chromium solid solution fine powder, 10-34 wt% zirconium oxide fine powder and 4-22 wt% silica sol as transition layer raw materials, and adding 40-70 wt% deionized water to the transition layer raw materials, ball milling in a planetary ball mill for 0.5-2 hours, with a ball-to-material ratio of 2-4:1, the resulting slurry is the environmentally friendly chromium-containing spinel infrared radiation transition layer slurry.

[0034] The preparation method of the environmentally friendly chromium-containing spinel infrared radiation working layer slurry is as follows: using 40-70 wt% titanium-iron co-doped magnesium-chromium spinel fine powder, 16-22 wt% aluminum-chromium solid solution fine powder, 1-4 wt% borosilicate glass powder, 2-5 wt% silicon micro powder and 5-35 wt% aluminum dihydrogen phosphate solution as working layer raw materials, and adding 20-50 wt% deionized water to the working layer raw materials, ball milling in a planetary ball mill for 0.5-2 hours, with a ball-to-material ratio of 2-4:1, the resulting slurry is the environmentally friendly chromium-containing spinel infrared radiation working layer slurry.

[0035] The preparation method of the titanium-iron co-doped magnesium-chromium spinel fine powder is as follows: First, magnesium oxide, chromium trioxide, titanium dioxide and iron oxide are used as raw materials for the spinel fine powder. They are placed in a planetary ball mill and ball-milled for 1 to 4 hours with a ball-to-material ratio of 2 to 4:1. Then, the slurry obtained from ball milling is dried, pressed into a billet under a pressure of 10 to 25 MPa, kept at 1250 to 1550℃ for 2.5 to 4 hours, cooled in the furnace, crushed, and sieved to obtain titanium-iron co-doped magnesium-chromium spinel fine powder.

[0036] In the raw materials of the spinel fine powder, the sum of the amounts of chromium trioxide, titanium dioxide, and iron oxide to the amount of magnesium oxide is 1:1 to 1.5, the sum of the amounts of chromium trioxide, titanium dioxide, and iron oxide is 2 to 5:1, and the sum of the amounts of titanium dioxide and iron oxide is 2 to 3:1.

[0037] The aluminosilicate refractory bricks are mullite bricks or corundum-mullite bricks.

[0038] In this specific implementation:

[0039] The environmentally friendly chromium-containing spinel infrared radiation coating consists of a transition layer and a working layer.

[0040] The fine powder of titanium-iron co-doped magnesium-chromium spinel has a particle size of less than 45 μm.

[0041] The purity of the magnesium oxide, chromium trioxide, titanium dioxide, and iron oxide is ≥99%, and the particle size is less than 10μm.

[0042] The aluminum-chromium solid solution fine powder used in the environmentally friendly chromium-containing spinel infrared radiation transition layer slurry is the same as that used in the environmentally friendly chromium-containing spinel infrared radiation working layer slurry; the molar ratio of Cr2O3 to Al2O3 in the aluminum-chromium solid solution fine powder is less than 1:10; and the average particle size of the aluminum-chromium solid solution fine powder is less than 74 μm.

[0043] The zirconia fine powder is calcium-stabilized zirconia, with a ZrO2 content ≥90wt% and an average particle size of less than 45μm.

[0044] The silica sol has a SiO2 content ≥ 25 wt% and a pH less than 4.

[0045] The silicon micropowder has a SiO2 content of ≥95wt% and an average particle size of less than 5μm.

[0046] The boron-containing glass powder has a B2O3 content of ≥8wt% and an average particle size of less than 45μm.

[0047] The aluminum dihydrogen phosphate solution has an Al(H2PO4)3 content ≥30wt% and a pH less than 2.

[0048] The details will not be repeated in the examples.

[0049] Example 1

[0050] An environmentally friendly chromium-containing spinel infrared radiation coating and its preparation method. The preparation method described in this embodiment is as follows:

[0051] First, the environmentally friendly chromium-containing spinel infrared radiation transition layer slurry is coated onto the surface of an aluminosilicate refractory brick to obtain a transition layer; then, the environmentally friendly chromium-containing spinel infrared radiation working layer slurry is coated onto the surface of the transition layer to obtain a working layer; then, the transition layer and working layer coated on the surface of the aluminosilicate refractory brick are dried at 70°C, and the thickness of the dried coating is 200μm, thus obtaining the environmentally friendly chromium-containing spinel infrared radiation coating.

[0052] The preparation method of the environmentally friendly chromium-containing spinel infrared radiation transition layer slurry is as follows: 50 wt% aluminum chromium solid solution fine powder, 34 wt% zirconium oxide fine powder and 16 wt% silica sol are used as transition layer raw materials, and 40 wt% of deionized water is added to the transition layer raw materials. The mixture is ball-milled in a planetary ball mill for 0.5 h with a ball-to-material ratio of 2:1. The resulting slurry is the environmentally friendly chromium-containing spinel infrared radiation transition layer slurry.

[0053] The preparation method of the environmentally friendly chromium-containing spinel infrared radiation working layer slurry is as follows: using 40wt% titanium-iron co-doped magnesium-chromium spinel fine powder, 16wt% aluminum-chromium solid solution fine powder, 4wt% borosilicate glass powder, 5wt% silicon micro powder and 35wt% aluminum dihydrogen phosphate solution as working layer raw materials, and adding 20wt% deionized water to the working layer raw materials, ball milling in a planetary ball mill for 0.5h, with a ball-to-material ratio of 2:1, the resulting slurry is the environmentally friendly chromium-containing spinel infrared radiation working layer slurry.

[0054] The preparation method of the titanium-iron co-doped magnesium-chromium spinel fine powder is as follows: first, magnesium oxide, chromium trioxide, titanium dioxide and iron oxide are used as raw materials for the spinel fine powder, and they are placed in a planetary ball mill and ball-milled for 1 hour with a ball-to-material ratio of 2:1; then, the slurry obtained from ball milling is dried, pressed into a billet under 10 MPa, kept at 1250℃ for 2.5 hours, cooled in the furnace, crushed, and sieved to obtain titanium-iron co-doped magnesium-chromium spinel fine powder.

[0055] In the raw materials of the spinel fine powder, the sum of the amounts of chromium trioxide, titanium dioxide, and iron oxide to the amount of magnesium oxide is 1:1, the sum of the amounts of chromium trioxide, titanium dioxide, and iron oxide is 2:1, and the sum of the amounts of titanium dioxide and iron oxide is 2:1.

[0056] The aluminosilicate refractory bricks are corundum-mullite bricks.

[0057] The environmentally friendly chromium-containing spinel infrared radiation coating prepared in this embodiment can be firmly bonded to aluminum-silicon refractory materials. The average emissivity of the environmentally friendly chromium-containing spinel infrared radiation coating in the 0.8-2.5 μm band was 0.82, as tested using a high-temperature infrared emissivity testing device. The Cr(VI) content of the environmentally friendly chromium-containing spinel infrared radiation coating was 14 ppm, as tested using spectrophotometry. After the prepared environmentally friendly chromium-containing spinel infrared radiation coating was placed in a kiln at 1400℃ for 3 months, its emissivity was measured to be 0.79, and no peeling, cracking, or flaking occurred.

[0058] Example 2

[0059] An environmentally friendly chromium-containing spinel infrared radiation coating and its preparation method. The preparation method described in this embodiment is as follows:

[0060] First, the environmentally friendly chromium-containing spinel infrared radiation transition layer slurry is coated onto the surface of an aluminosilicate refractory brick to obtain a transition layer; then, the environmentally friendly chromium-containing spinel infrared radiation working layer slurry is coated onto the surface of the transition layer to obtain a working layer; then, the transition layer and working layer coated on the surface of the aluminosilicate refractory brick are dried at 80°C, and the thickness of the dried coating is 260μm, thus obtaining the environmentally friendly chromium-containing spinel infrared radiation coating.

[0061] The preparation method of the environmentally friendly chromium-containing spinel infrared radiation transition layer slurry is as follows: using 60wt% aluminum chromium solid solution fine powder, 18wt% zirconium oxide fine powder and 22wt% silica sol as transition layer raw materials, and adding 50wt% deionized water to the transition layer raw materials, ball milling in a planetary ball mill for 1 hour, with a ball-to-material ratio of 3:1, the resulting slurry is the environmentally friendly chromium-containing spinel infrared radiation transition layer slurry.

[0062] The preparation method of the environmentally friendly chromium-containing spinel infrared radiation working layer slurry is as follows: using 50wt% titanium-iron co-doped magnesium-chromium spinel fine powder, 18wt% aluminum-chromium solid solution fine powder, 3wt% borosilicate glass powder, 4wt% silicon micro powder and 25wt% aluminum dihydrogen phosphate solution as working layer raw materials, and adding 30wt% deionized water to the working layer raw materials, ball milling in a planetary ball mill for 1 hour, with a ball-to-material ratio of 3:1, the resulting slurry is the environmentally friendly chromium-containing spinel infrared radiation working layer slurry.

[0063] The preparation method of the titanium-iron co-doped magnesium-chromium spinel fine powder is as follows: first, magnesium oxide, chromium trioxide, titanium dioxide and iron oxide are used as raw materials for the spinel fine powder, and they are placed in a planetary ball mill and ball-milled for 2 hours with a ball-to-material ratio of 3:1; then, the slurry obtained from ball milling is dried, pressed into a billet under 15 MPa, kept at 1350℃ for 3 hours, cooled in the furnace, crushed, and sieved to obtain titanium-iron co-doped magnesium-chromium spinel fine powder.

[0064] In the raw materials of the spinel fine powder: the sum of the amounts of chromium trioxide, titanium dioxide and iron oxide to the amount of magnesium oxide is 1:1.2, the sum of the amounts of chromium trioxide to the amounts of titanium dioxide and iron oxide is 4:1, and the sum of the amounts of titanium dioxide to the amounts of iron oxide is 2.5:1.

[0065] The aluminosilicate refractory bricks mentioned are mullite bricks.

[0066] The environmentally friendly chromium-containing spinel infrared radiation coating prepared in this embodiment can be firmly bonded to aluminum-silicon refractory materials. The average emissivity of the environmentally friendly chromium-containing spinel infrared radiation coating in the 0.8-2.5 μm band was 0.85, as tested using a high-temperature infrared emissivity testing device. The Cr(VI) content of the environmentally friendly chromium-containing spinel infrared radiation coating was 9 ppm, as tested using spectrophotometry. After the prepared environmentally friendly chromium-containing spinel high emissivity infrared radiation coating was placed in a kiln at 1400℃ for 3 months, its emissivity was measured to be 0.81, and no peeling, cracking, or flaking occurred.

[0067] Example 3

[0068] An environmentally friendly chromium-containing spinel infrared radiation coating and its preparation method. The preparation method described in this embodiment is as follows:

[0069] First, the environmentally friendly chromium-containing spinel infrared radiation transition layer slurry is coated onto the surface of an aluminosilicate refractory brick to obtain a transition layer; then, the environmentally friendly chromium-containing spinel infrared radiation working layer slurry is coated onto the surface of the transition layer to obtain a working layer; then, the transition layer and working layer coated on the surface of the aluminosilicate refractory brick are dried at 90°C, and the thickness of the dried coating is 330 μm, thus obtaining the environmentally friendly chromium-containing spinel infrared radiation coating.

[0070] The preparation method of the environmentally friendly chromium-containing spinel infrared radiation transition layer slurry is as follows: 70 wt% aluminum chromium solid solution fine powder, 26 wt% zirconium oxide fine powder and 4 wt% silica sol are used as transition layer raw materials, and 60 wt% of the transition layer raw materials are added with deionized water. The mixture is ball-milled in a planetary ball mill for 1.5 h with a ball-to-material ratio of 3:1. The resulting slurry is the environmentally friendly chromium-containing spinel infrared radiation transition layer slurry.

[0071] The preparation method of the environmentally friendly chromium-containing spinel infrared radiation working layer slurry is as follows: using 60wt% titanium-iron co-doped magnesium-chromium spinel fine powder, 20wt% aluminum-chromium solid solution fine powder, 2wt% borosilicate glass powder, 3wt% silicon micro powder and 15wt% aluminum dihydrogen phosphate solution as working layer raw materials, and adding 40wt% deionized water to the working layer raw materials, ball milling in a planetary ball mill for 1.5h, with a ball-to-material ratio of 3:1, the resulting slurry is the environmentally friendly chromium-containing spinel infrared radiation working layer slurry.

[0072] The preparation method of the titanium-iron co-doped magnesium-chromium spinel fine powder is as follows: first, magnesium oxide, chromium trioxide, titanium dioxide and iron oxide are used as raw materials for the spinel fine powder, and they are placed in a planetary ball mill and ball-milled for 3 hours with a ball-to-material ratio of 3:1; then, the slurry obtained from ball milling is dried, pressed into a billet under 20 MPa, kept at 1450℃ for 3.5 hours, cooled in the furnace, crushed, and sieved to obtain titanium-iron co-doped magnesium-chromium spinel fine powder.

[0073] In the raw materials of the spinel fine powder: the sum of the amounts of chromium trioxide, titanium dioxide and iron oxide to the amount of magnesium oxide is 1:1.3, the sum of the amounts of chromium trioxide to the amounts of titanium dioxide and iron oxide is 3:1, and the sum of the amounts of titanium dioxide to the amounts of iron oxide is 2.5:1.

[0074] The aluminosilicate refractory bricks are corundum-mullite bricks.

[0075] The environmentally friendly chromium-containing spinel infrared radiation coating prepared in this embodiment can be firmly bonded to aluminum-silicon refractory materials. The average emissivity of the environmentally friendly chromium-containing spinel infrared radiation coating in the 0.8-2.5 μm band was 0.90, as tested using a high-temperature infrared emissivity testing device. The Cr(VI) content of the environmentally friendly chromium-containing spinel infrared radiation coating was 6 ppm, as tested using spectrophotometry. After the prepared environmentally friendly chromium-containing spinel high emissivity infrared radiation coating was placed in a kiln at 1400℃ for 3 months, its emissivity was measured to be 0.86, and no peeling, cracking, or flaking occurred.

[0076] Example 4

[0077] An environmentally friendly chromium-containing spinel infrared radiation coating and its preparation method. The preparation method described in this embodiment is as follows:

[0078] First, the environmentally friendly chromium-containing spinel infrared radiation transition layer slurry is coated onto the surface of an aluminosilicate refractory brick to obtain a transition layer; then, the environmentally friendly chromium-containing spinel infrared radiation working layer slurry is coated onto the surface of the transition layer to obtain a working layer; then, the transition layer and working layer coated on the surface of the aluminosilicate refractory brick are dried at 100°C, and the thickness of the dried coating is 400 μm, thus obtaining the environmentally friendly chromium-containing spinel infrared radiation coating.

[0079] The preparation method of the environmentally friendly chromium-containing spinel infrared radiation transition layer slurry is as follows: using 80wt% aluminum-chromium solid solution fine powder, 10wt% zirconium oxide fine powder and 10wt% silica sol as transition layer raw materials, and adding 70wt% deionized water to the transition layer raw materials, ball milling in a planetary ball mill for 2 hours, with a ball-to-material ratio of 4:1, the resulting slurry is the environmentally friendly chromium-containing spinel infrared radiation transition layer slurry.

[0080] The preparation method of the environmentally friendly chromium-containing spinel infrared radiation working layer slurry is as follows: 70 wt% titanium-iron co-doped magnesium-chromium spinel fine powder, 22 wt% aluminum-chromium solid solution fine powder, 1 wt% borosilicate glass powder, 2 wt% silicon micro powder and 5 wt% aluminum dihydrogen phosphate solution are used as working layer raw materials, and 50 wt% of the working layer raw materials are added with deionized water. The mixture is ball-milled in a planetary ball mill for 2 hours with a ball-to-material ratio of 4:1. The resulting slurry is the environmentally friendly chromium-containing spinel infrared radiation working layer slurry.

[0081] The preparation method of the titanium-iron co-doped magnesium-chromium spinel fine powder is as follows: first, magnesium oxide, chromium trioxide, titanium dioxide and iron oxide are used as raw materials for the spinel fine powder, and they are placed in a planetary ball mill and ball-milled for 4 hours with a ball-to-material ratio of 4:1; then, the slurry obtained from ball milling is dried, pressed into a billet under 25 MPa, kept at 1550℃ for 4 hours, cooled in the furnace, crushed, and sieved to obtain titanium-iron co-doped magnesium-chromium spinel fine powder.

[0082] In the raw materials of the spinel fine powder: the sum of the amounts of chromium trioxide, titanium dioxide and iron oxide to the amount of magnesium oxide is 1:1.5, the sum of the amounts of chromium trioxide to the amounts of titanium dioxide and iron oxide is 5:1, and the sum of the amounts of titanium dioxide to the amounts of iron oxide is 3:1.

[0083] The aluminosilicate refractory bricks mentioned are mullite bricks.

[0084] The environmentally friendly chromium-containing spinel infrared radiation coating prepared in this embodiment can be firmly bonded to aluminum-silicon refractory materials. The average emissivity of the environmentally friendly chromium-containing spinel infrared radiation coating in the 0.8-2.5 μm band was 0.93, as tested using a high-temperature infrared emissivity testing device. The Cr(VI) content of the environmentally friendly chromium-containing spinel infrared radiation coating was 2 ppm, as tested using spectrophotometry. After the prepared environmentally friendly chromium-containing spinel high emissivity infrared radiation coating was placed in a kiln at 1400℃ for 3 months, its emissivity was measured to be 0.89, and no peeling, cracking, or flaking occurred.

[0085] This specific implementation method has the following advantages compared with the prior art:

[0086] The environmentally friendly chromium-containing spinel infrared radiation coating described in this specific embodiment consists of a transition layer and a working layer. The transition layer uses fine aluminum-chromium solid solution powder, fine zirconium oxide powder, and silica sol as raw materials, while the working layer uses fine titanium-iron co-doped magnesium-chromium spinel powder, fine aluminum-chromium solid solution powder, borosilicate glass powder, silica micropowder, and aluminum dihydrogen phosphate solution as raw materials. The two raw materials are respectively mixed with deionized water and ball-milled to obtain transition layer slurry and working layer slurry. The transition layer slurry and working layer slurry are sequentially coated onto the surface of aluminum-silicon refractory bricks and dried to obtain the environmentally friendly chromium-containing spinel infrared radiation coating, which is low in cost and simple in process.

[0087] In this specific embodiment, the titanium-iron co-doped magnesium-chromium spinel uses TiO2 and Fe2O3 as dopants. On the one hand, Ti 4+ radius and Cr 3+ The radii are very close, Ti 4+ Able to replace Cr 3+ Infiltrating the octahedral voids of spinel, Ti causes defects such as lattice distortion, disrupts the symmetry of the internal crystal structure, and enhances lattice vibration absorption; simultaneously, Ti is also a variable-valence element. 4+ During high-temperature solid-state sintering, some electrons are gained and the material transforms into Ti. 3+ This process prevents the formation of oxygen vacancies in the spinel's lattice oxygen, increasing the electron transport rate and enhancing free carrier absorption. On the other hand, TiO2 doping introduces impurity levels at the top of the valence band and the bottom of the conduction band, increasing the electron transition probability and enhancing free electron impurity level absorption. The enhanced absorption by lattice vibrations, free carriers, and impurity levels all improve the material's infrared radiation performance, thus giving TiO2-doped magnesium chromium spinel its high emissivity. A portion of the added Fe2O3 participates in the spinel synthesis reaction. 3+ Able to replace Cr 3+Occupying the octahedral voids of spinel makes the structure of magnesium chromium spinel more complex, generating more lattice distortion and defects, which is beneficial to improving emissivity. Another portion of Fe2O3 reacts at high temperatures to form Fe3O4, which is itself a high-emissivity material, contributing to the overall emissivity improvement of the spinel. Therefore, the doping of TiO2 and Fe2O3 significantly improves the infrared radiation performance of magnesium chromium spinel and the environmentally friendly chromium-containing spinel infrared radiation coating made from it in the 0.8–2.5 μm wavelength range.

[0088] In addition, Ti 4+ The valence state is higher than that of Cr 3+ It belongs to high-valence ion substitution. In order to maintain the balance of valence, Cr 3+ It is difficult to obtain Cr in a higher price state. 6+ The transformation, and the fact that both TiO2 and Fe2O3 are acidic oxides, can also inhibit the formation of Cr(VI), further reducing the Cr(VI) content in chromium-containing spinel. Using titanium-iron co-doped magnesium-chromium spinel as a radiation functional raw material reduces the Cr(VI) content in the coating from the source. In this specific embodiment, the transition layer and working layer use silica sol and aluminum dihydrogen phosphate solution as binders, respectively. Both are acidic and can also inhibit the formation of Cr(VI) in the coating to a certain extent, reducing Cr(VI) emissions from the coating. More importantly, this specific embodiment adds a certain amount of aluminum-chromium solid solution fine powder to both the transition layer and the working layer. Aluminum-chromium solid solution is an infinite solid solution, so even if Cr(VI) is generated in the coating, it can be dissolved into the aluminum-chromium solid solution, further inhibiting Cr(VI) emissions from the environmentally friendly chromium-containing spinel infrared radiation coating.

[0089] Meanwhile, the silica sol and aluminum dihydrogen phosphate solution can cure at room temperature, giving the coating high strength after drying. Secondly, aluminum dihydrogen phosphate gradually decomposes above 1000℃, and the resulting Al2O3 reacts with SiO2 in the silica sol at the interface between the working layer and the transition layer, thus strengthening the bond between them. The boron-containing glass powder and silica micropowder used in this specific embodiment ensure good adhesion of the infrared radiation coating at low and medium temperatures. When the infrared radiation coating is heated to 600℃, these two materials gradually form a liquid phase, effectively improving the bonding strength between the infrared radiation coating and the transition layer, preventing defects such as cracks in the infrared radiation coating. The appropriate formation of the liquid phase at high temperatures also ensures good thermal shock stability of the environmentally friendly chromium-containing spinel infrared radiation coating, ensuring its service life at high temperatures.

[0090] In this specific embodiment, fine aluminum-chromium solid solution powder is used in both the transition layer and the working layer. The coefficient of thermal expansion of aluminum-chromium solid solution is similar to that of corundum-mullite, and the two have high compatibility, ensuring a strong bond between the transition layer and the substrate and the working layer, thus guaranteeing the bonding strength of the coating. Furthermore, the aluminum-chromium solid solution in the transition layer prevents penetration from the working layer into the substrate, avoiding reactions between the chromium-containing spinel and the substrate. This ensures excellent anti-radiation attenuation performance and helps extend the service life of the prepared environmentally friendly chromium-containing spinel infrared radiation coating under high-temperature conditions.

[0091] This specific embodiment uses titanium-iron co-doped magnesium-chromium spinel fine powder as the main infrared radiation raw material. The doping with TiO2 and Fe2O3 not only significantly improves the infrared radiation performance but also greatly reduces the Cr(VI) content, providing a useful reference for the application of chromium-containing spinel in infrared radiation coatings. A transition layer mainly composed of aluminum-chromium solid solution is set between the working layer of the coating and the aluminosilicate refractory substrate. This helps improve the interfacial bonding strength and reduce cracking at the interface between the working layer and the substrate, preventing the working layer of the infrared radiation coating from reacting with the aluminosilicate refractory substrate most commonly used in kilns, thereby effectively suppressing the attenuation of emissivity. Furthermore, the components of both the transition layer and the working layer have multiple functions, and there are mutual influences between the components. The transition layer and the working layer, as a whole, ensure that the environmentally friendly chromium-containing spinel infrared radiation coating can firmly bond to the substrate and stably exert its radiation effect in high-temperature service environments.

[0092] The environmentally friendly chromium-containing spinel infrared radiation coating prepared in this specific embodiment can be firmly bonded to aluminum-silicon refractory materials. The average emissivity of the environmentally friendly chromium-containing spinel infrared radiation coating in the 0.8-2.5 μm band was tested using a high-temperature infrared emissivity testing device and found to be 0.82-0.93. The Cr(VI) content of the environmentally friendly chromium-containing spinel infrared radiation coating was tested using spectrophotometry and found to be 2-14 ppm. After the prepared environmentally friendly chromium-containing spinel high emissivity infrared radiation coating was placed in a kiln at 1400℃ for 3 months, its emissivity was measured to be 0.79-0.89, and no peeling, cracking or flaking occurred.

[0093] Therefore, this specific embodiment is low in cost and simple in process. The environmentally friendly chromium-containing spinel infrared radiation coating prepared is suitable for high-temperature environments above 1400℃, can be firmly bonded to the substrate, can stably exert radiation effect, and the hexavalent chromium meets emission standards.

Claims

1. A method for preparing an environmentally friendly chromium-containing spinel infrared radiation coating, characterized in that, The environmentally friendly chromium-containing spinel infrared radiation coating consists of a transition layer and a working layer. The preparation method of the environmentally friendly chromium-containing spinel infrared radiation coating is as follows: First, the environmentally friendly chromium-containing spinel infrared radiation transition layer slurry is coated on the surface of aluminum-silicon refractory bricks to obtain the transition layer; Then, an environmentally friendly chromium-containing spinel infrared radiation working layer slurry is applied to the surface of the transition layer to obtain the working layer; the transition layer and working layer coated on the surface of the aluminosilicate refractory brick are then dried at 70~100℃, and the thickness of the dried coating is 200~400μm, thus obtaining the environmentally friendly chromium-containing spinel infrared radiation coating. The aluminosilicate refractory bricks are mullite bricks or corundum-mullite bricks. The preparation method of the environmentally friendly chromium-containing spinel infrared radiation transition layer slurry is as follows: using 50-80 wt% aluminum-chromium solid solution fine powder, 10-34 wt% zirconium oxide fine powder and 4-22 wt% silica sol as transition layer raw materials, and adding 40-70 wt% deionized water to the transition layer raw materials, ball milling in a planetary ball mill for 0.5-2 hours, with a ball-to-material ratio of 2-4:1, the resulting slurry is the environmentally friendly chromium-containing spinel infrared radiation transition layer slurry; The preparation method of the environmentally friendly chromium-containing spinel infrared radiation working layer slurry is as follows: using 40-70 wt% titanium-iron co-doped magnesium-chromium spinel fine powder, 16-22 wt% aluminum-chromium solid solution fine powder, 1-4 wt% borosilicate glass powder, 2-5 wt% silicon micro powder and 5-35 wt% aluminum dihydrogen phosphate solution as working layer raw materials, and adding 20-50 wt% deionized water to the working layer raw materials, ball milling in a planetary ball mill for 0.5-2 hours, with a ball-to-material ratio of 2-4:1, the resulting slurry is the environmentally friendly chromium-containing spinel infrared radiation working layer slurry; The preparation method of the titanium-iron co-doped magnesium-chromium spinel fine powder is as follows: First, magnesium oxide, chromium trioxide, titanium dioxide, and iron oxide are used as raw materials for the spinel fine powder, and they are placed in a planetary ball mill and ball-milled for 1-4 hours with a ball-to-material ratio of 2-4:1; then, the slurry obtained from ball milling is dried, pressed into a billet under 10-25 MPa, held at 1250-1550℃ for 2.5-4 hours, cooled in the furnace, crushed, and sieved to obtain titanium-iron co-doped magnesium-chromium spinel fine powder; the particle size of the titanium-iron co-doped magnesium-chromium spinel fine powder is less than 45 μm; In the raw materials of the spinel fine powder: the sum of the amounts of chromium trioxide, titanium dioxide, and iron oxide to the amount of magnesium oxide is 1:1 to 1.5; the sum of the amounts of chromium trioxide, titanium dioxide, and iron oxide is 2 to 5:1; and the sum of the amounts of titanium dioxide and iron oxide is 2 to 3:

1. The purity of magnesium oxide, chromium trioxide, titanium dioxide, and iron oxide is ≥99%, and the particle size is less than 10 μm.

2. The method for preparing the environmentally friendly chromium-containing spinel infrared radiation coating according to claim 1, characterized in that... The aluminum-chromium solid solution fine powder used in the environmentally friendly chromium-containing spinel infrared radiation transition layer slurry is the same as that used in the environmentally friendly chromium-containing spinel infrared radiation working layer slurry; the molar ratio of Cr2O3 to Al2O3 in the aluminum-chromium solid solution fine powder is less than 1:10; and the average particle size of the aluminum-chromium solid solution fine powder is less than 74 μm.

3. The method for preparing the environmentally friendly chromium-containing spinel infrared radiation coating according to claim 1, characterized in that... The zirconia fine powder is calcium-stabilized zirconia, with a ZrO2 content ≥90wt% and an average particle size of less than 45μm.

4. The method for preparing the environmentally friendly chromium-containing spinel infrared radiation coating according to claim 1, characterized in that... The silica sol has a SiO2 content ≥ 25 wt% and a pH less than 4.

5. The method for preparing the environmentally friendly chromium-containing spinel infrared radiation coating according to claim 1, characterized in that... The silicon micropowder has a SiO2 content of ≥95wt% and an average particle size of less than 5μm.

6. The method for preparing the environmentally friendly chromium-containing spinel infrared radiation coating according to claim 1, characterized in that... The boron-containing glass powder has a B2O3 content of ≥8wt% and an average particle size of less than 45μm.

7. The method for preparing the environmentally friendly chromium-containing spinel infrared radiation coating according to claim 1, characterized in that... The aluminum dihydrogen phosphate solution has an Al(H2PO4)3 content ≥30wt% and a pH value less than 2.

8. An environmentally friendly chromium-containing spinel infrared radiation coating, characterized in that... The environmentally friendly chromium-containing spinel infrared radiation coating is prepared by the method described in any one of claims 1 to 7.