Anti-Corrosion Ceramic Coating for Boilers

EXAMPLE 1

• • Step 1, deionized water that was 1.75 times the loose packing volume of all raw materials for a bottom coating layer was provided.
  • Step 2, the deionized water was added to 25 g of sodium silicate, and they were stirred to be uniform, obtaining a mixture I.
  • Step 3, 2 g of lanthanum oxide, 2 g of niobium pentoxide, 15 g of aluminum oxide, 9 g of bismuth oxide, 2 g of boron oxide, 2 g of zinc oxide, 2 g of silicon oxide, 7 g of titanium dioxide, and 3 g of titanium nitride, each of which had a particle size of 1-10 μm respectively, were mixed and ball milled in a high-energy ball mill for 4-6 h, obtaining a further refined powder mixture II.
  • Step 4, 12 g of graphite fluoride with a thickness of 1-10 μm and a particle size of 1-30 μm, and 4 g of nano silicon carbide whisker with a length of 10-60 μm were added to the powder mixture II obtained in step 3, and they were stirred in a mixer for 0.5-1 h at a stirring rate of 50-150 rpm, obtaining a mixture III.
  • Step 5, the mixture I obtained in step 2 was added to the mixture III obtained in step 4, and they were stirred in a mixer for 0.5-1 h at a stirring rate of 50-150 rpm, obtaining a bottom coating.
  • Step 6, deionized water that was 1.75 times the loose packing volume of all raw materials for a surface coating layer was provided.
  • Step 7, the deionized water was added to 25 g of the sodium silicate, and they were stirred to be uniform, obtaining a mixture IV.
  • Step 8, 2 g of lanthanum oxide, 2 g of niobium pentoxide, 7 g of chromium oxide, 7 g of aluminum oxide, 9 g of bismuth oxide, 2 g of boron oxide, 2 g of zinc oxide, 2 g of silicon oxide, 3 g of titanium nitride, 7 g of silicon carbide, 4 g of nano silicon carbide whisker, and 4 g of cobalt green, each of which had a particle size of 1-10 μm respectively, were mixed and ball milled in a high-energy ball mill for 4-6 h, obtaining a further refined powder mixture V.
  • Step 9, 12 g of graphite fluoride with a thickness of 1-10 μm and a particle size of 1-30 μm, and 4 g of nano silicon carbide whisker with a length of 10-60 μm were added to the powder mixture V obtained in step 8, and they were stirred in a mixer for 0.5-1 h at a stirring rate of 50-150 rpm, obtaining a mixture VI.
  • Step 10, the mixture IV obtained in step 7 was added to the mixture VI obtained in step 9, and they were stirred in a mixer for 0.5-1 h at a stirring rate of 50-150 rpm, obtaining a surface coating.
  • Step 11, the environment was inspected, and a temperature of 25° C. and a relative humidity of 60% were maintained in the construction environment, and the temperature of a substrate was ensured to be at least 3° C. higher than the dew point temperature.
  • Step 12, a surface of the substrate was pretreated by using a sandblasting technology until a cleanliness of Sa3.0 level and a roughness of 25-75 μm were reached.
  • Step 13, the coating was stirred again at 50-150 rpm for 0.5-1 h before spraying. The bottom coating was sprayed onto the surface of the substrate by using an air atomization spray gun, and dried. The thickness of the bottom coating layer was measured, and controlled to be 50-100 μm. When the thickness of the bottom coating layer was qualified, the surface coating was sprayed onto the bottom coating layer, and dried. The overall thickness of the ceramic coating was measured, and controlled to be 200-300 μm. When the overall thickness was qualified, the substrate sample with the two-layer-compounded coating was heated to 400° C. and maintained at the temperature for 30 min, obtaining the anti-corrosion and anti-coking ceramic coating with easy state identification.

The cross-sectional structure of the ceramic coating obtained in Example 1 is shown in FIG. 1. As can be seen from FIG. 1, the bottom coating layer is well combined with the substrate; the bottom coating layer is well combined with the surface coating layer with no obvious gap; the internal structure of the ceramic coating is dense with no visible pores. In the present disclosure, the powder of raw materials is refined by using a high-energy ball mill, such that a micro-nano-scale rough structure with low surface energy is formed on the surface of the prepared ceramic coating, as shown in FIG. 2. Table 1 shows test results of key use parameters such as bonding strength and thermal shock performance of the ceramic coating. The results show that the ceramic coating exhibits a bonding strength of about 38 MPa, and could withstand at least 80-time thermal shock test, indicating that the ceramic coating exhibits excellent reliability in use. FIGS. 3A-3B shows an operating state of a water wall in a combustion region of a boiler of a power station in Hami, China before renovation by using the ceramic coating according to the present disclosure. As shown in FIGS. 3A-3B, the surface of the water wall is seriously coked and there is high-temperature corrosion (FIG. 3A shows the coking situation, and FIG. 3B shows the surface corrosion after coke cleaning). FIG. 4 shows a state of the water wall in this area after operation of 14,000 h, the water wall being renovated by using the ceramic coating according to the present disclosure. As shown in FIG. 4, there is no coking and slagging on the surface of the water wall, and the high-temperature corrosion is completely alleviated.

FIG. 5 shows an inspection situation of a water wall of a boiler of a power station in Changji, China after operation of 8,000 h, the water wall being renovated by using the ceramic coating according to the present disclosure. As shown in FIG. 5, the current operating state of the ceramic coating can be directly judged by visual inspection (a green area represents that the current surface coating layer is in good condition; a white area represents a loss of the surface coating layer, and a further surface coating needs to be re-sprayed onto the white bottom coating layer).

The foregoing description is only preferred implementations of the present disclosure. It should be noted that a person of ordinary skill in the art can also make several improvements and modifications without departing from the principle of the present disclosure. These improvements and modifications should also fall within the scope of the present disclosure.