A glass-ceramic coating for a metal surface and its preparation method

Abstract

This invention discloses a glass-ceramic coating for a metal surface and its preparation method. The glass is a ferrophosphate glass with the following composition: P2O5 37.2-41.2 wt%, Al2O3 16.3-18.3 wt%, Fe2O3 0.5-3 wt%, Na2O 16.7-22.5 wt%, SiO2 0.5-7 wt%, B2O3 1.6-4.9 wt%, SrO 2-5.5 wt%, BaO 4.5-9.4 wt%, La2O3 0.5-1.5 wt%, Nd2O3 0.5-1.8 wt%, ZrO2 1-2.5 wt%, and Nb2O5 0.5-1.5 wt%. The glass powder and zirconia ceramic powder are mixed in a ratio of 3.5:6.5 to 4.5:5.5 and then sprayed onto the surface of a metal substrate. After heat treatment and annealing, the porosity of the glass-ceramic coating is significantly reduced.

Description

Technical Field

[0001] This invention relates to a glass-ceramic coating preparation process, specifically a glass-ceramic coating for improving the corrosion resistance of metal surfaces and its preparation method. Background Technology

[0002] To control global warming, the increasing proportion of low-carbon energy in the global energy structure is an inevitable trend. To this end, countries worldwide are continuously advancing the development of nuclear power technology, and more nuclear power plants have achieved commercial operation while improving their safety. At the same time, the amount of radioactive waste generated by nuclear power plants is also increasing. To address the problem of radioactive waste disposal, researchers have developed a method for vitrification. To date, vitrification is recognized worldwide as the best solution for treating high-level radioactive waste and is the only high-level radioactive waste disposal method internationally to have achieved engineering application. Since the engineering application of radioactive waste vitrification, the process has successively evolved from a one-step tank process, to a two-step process using a rotary kiln and induction heating metal furnace, to a Joule-heated ceramic furnace, and a cold crucible induction heating process. Currently, the third-generation Joule-heated ceramic furnace vitrification technology, represented by the US, Germany, Japan, and Russia, and the fourth-generation cold crucible vitrification technology, represented by France and Russia, are widely used in engineering.

[0003] Compared to the third-generation Joule-heated ceramic furnace vitrification technology, the fourth-generation cold crucible vitrification technology has the advantages of longer furnace service life, simpler decommissioning, higher melting temperature, higher waste oxide mass containment rate and higher precious metal content in the vitrified body. It is more suitable for processing radioactive waste generated by new reactor types and spent fuel reprocessing technologies with higher burnup.

[0004] In cold crucible glass solidification technology, both the crucible body and key components within the furnace are made of metallic materials (stainless steel or nickel-based alloys). During use, water cooling creates a solidified glass shell below the molten glass, protecting it from corrosion by the high-temperature molten glass. However, the portion above the molten glass level, lacking this protective shell, is easily corroded by the combined effects of volatiles, nitrogen oxides, and water vapor generated during glass melting, thus reducing the service life of the crucible body and key components.

[0005] To improve the service life of the crucible body and key internal components, the French Atomic Energy Commission patent (US8753722B2) discloses a method for coating cold crucible segments with a glass-ceramic mixture. This method uses plasma spraying to coat a stainless steel substrate with a glass-ceramic mixture, where the glass and ceramic components are in proportions of 50-70% and 30-50%, respectively. The glass transition temperature is below 650°C, and the heat treatment temperature is between 650-850°C. The ceramic used is alumina, mullite, or rutile alumina. However, this patent fails to improve the compatibility between the glass-ceramic coating and the substrate's expansion coefficients by adjusting the glass's expansion coefficient according to the substrate's expansion coefficient. Secondly, because the heat treatment temperature exceeds 650°C, excessively high temperatures can cause workpiece deformation, affecting assembly. Thirdly, the high heat treatment temperature increases the risk of oxidation of the substrate material, reducing the adhesion of the glass-ceramic coating. Fourthly, the patent uses alumina as the ceramic material, which is prone to crystal transformation during heat treatment, leading to increased porosity and reduced adhesion. Fifth, the patent does not specify the chemical stability of the glass in the glass-ceramic coating. If the glass has poor chemical stability, the coating will be corroded and peel off.

[0006] Chinese patent application (CN 107056074A) discloses a glass powder for modifying plasma-sprayed ceramic coatings. Its composition is silicate, with a SiO2 content of 55-59%. The excessively high silica content results in a very high softening temperature for the glass, making it unsuitable for reducing the coating porosity through a secondary heat treatment after spraying. During the spraying process, although the glass melts, its temperature drops rapidly upon reaching the substrate, causing the glass to solidify and fail to fully fill the coating pores.

[0007] The paper "Temperature profiles and thermal stress analysis of plasmasprayed glass-composite coatings" (ZHANG T, et al., boletín de las cofradías desevilla, 2000.) proposes that the stress of glass-ceramic coatings can be reduced by selecting glasses with low transition temperatures and high coefficients of thermal expansion. However, it does not propose how to develop glasses with low transition temperatures and high coefficients of thermal expansion, nor does it explain how to reduce the porosity of glass-ceramic coatings.

[0008] Document "Abrasive wear resistance of plasma-sprayed glass-compositecoatings" (

[0009] GAWNE D, et al., Journal of Thermal Spray Technology, 2001, 10(4): 599-603. reported a glass-ceramic coating on a stainless steel substrate. The coating material has a softening temperature of 430℃ and a coefficient of thermal expansion of 14.5×10⁻⁶. -6 A mixture of glass and alumina of / K, applied by plasma spraying, showed improved hardness, abrasion resistance, and scratch resistance. However, the literature did not propose how to improve corrosion resistance by reducing the porosity of the coating.

[0010] The paper "Glass-alumina composite coatings by plasma spraying. Part I: Microstructural and mechanical characterization" (BOLELLI G, et al., Surface and Coatings Technology, 2006, 201(1): 458-73.) proposes a method for spraying glass-alumina onto ceramics, analyzes the effect of heat treatment on the porosity of coatings with different compositions, and points out that excessively high heat treatment temperature will cause the alumina in the coating to undergo a crystal transformation, leading to an increase in porosity. Summary of the Invention

[0011] The technical problem to be solved by this invention is to provide a glass-ceramic coating for improving the corrosion resistance of stainless steel and nickel-based alloys, so as to protect the stainless steel or nickel-based alloy substrate material from corrosion by corrosive gases or liquids. The glass-ceramic coating needs to meet the following requirements: 1) Matching coefficients of thermal expansion; the coefficients of thermal expansion of commonly used stainless steel and nickel-based alloys are between 13-16.5 × 10⁻⁶. -6To match the coefficient of thermal expansion of these commonly used metals, the coefficient of thermal expansion of the glass in the glass-ceramic coating needs to be adjusted through the glass composition; 2) Glass is a brittle material and is easily detached upon impact. To enhance the toughness of the coating, appropriate ceramics need to be introduced into the glass to strengthen its toughness; 3) The ceramics in the glass-ceramic coating usually have good corrosion resistance, so the corrosion resistance of the glass-ceramic coating depends on the corrosion resistance of the glass composition; 4) The protective effect of the glass-ceramic coating on the substrate material is also affected by the porosity of the coating. High porosity allows corrosive gases and liquids to corrode the substrate material through the pores. Therefore, to improve the protective effect of the glass-ceramic coating on the substrate metal material, the porosity of the coating must be reduced to prevent corrosive gases from penetrating the pores and corroding the metal substrate material during use. Based on the above requirements for glass-ceramic coatings, this invention uses chemically stable ferrophosphate glass and selects zirconia ceramic as the toughening material. The coefficient of thermal expansion of the ferrophosphate glass is adjusted to match the coefficient of thermal expansion of the coating with that of the substrate material. The porosity of the glass-ceramic coating is addressed through a heat treatment process after coating application. To avoid oxidation and deformation of the substrate material due to excessively high temperatures during heat treatment, the softening temperature of the glass material should not exceed 500℃.

[0012] The technical solution adopted in this invention is as follows:

[0013] A glass-ceramic coating for a metal surface and its preparation method are disclosed. The method involves mixing glass powder and ceramic powder in a specific ratio, then spraying the mixture onto a metal surface using plasma spraying, followed by heat treatment annealing to form a dense glass-ceramic coating. The mass ratio of the glass-ceramic mixture is 3.5:6.5 to 4.5:5.5 (glass / ceramic).

[0014] The glass powder has the following composition: P2O5 37.2-41.2wt%, Al2O3 16.3-18.3wt%, Fe2O3 0.5-3wt%, Na2O 16.7-22.5wt%, SiO2 0.5-7wt%, B2O3 1.6-4.9wt%, SrO 2-5.5wt%, BaO 4.5-9.4wt%, La2O3 0.5-1.5wt%, Nd2O3 0.5-1.8wt%, ZrO2 1-2.5wt%, Nb2O5 0.5-1.5wt%. The ceramic powder is zirconia ceramic powder.

[0015] The glass powder described above has a glass transition temperature (Tg) of 410-450℃, a glass softening temperature of 448-497℃, and a glass expansion coefficient of 13.3-16.5×10⁻⁶. -6 / K, Total weight loss in glass immersion experiments: 2.17-4.42 g / m 2 .

[0016] The method for preparing the glass powder includes the following steps:

[0017] 1) Weigh out the high-purity raw materials according to the above glass composition;

[0018] 2) After the raw materials are thoroughly mixed, they are placed in a platinum crucible, and then the platinum crucible is placed in a silicon carbide rod electric furnace for melting; the melting temperature is 1000-1100℃, and after the raw materials are completely melted, the temperature is raised to 1200℃ for homogenization and clarification.

[0019] 3) Reduce the furnace temperature to 900-950℃ and pour the molten glass onto a steel mold preheated to 200-300℃;

[0020] 4) Take a portion of the glass and anneal it in a muffle furnace that has been preheated to near the glass transition temperature Tg for chemical stability immersion test and expansion coefficient test, and let the rest of the glass cool down to room temperature naturally.

[0021] 5) Glass that has cooled naturally to room temperature is ground into glass powder in a tungsten carbide grinding tank and used as a raw material for plasma spraying.

[0022] The method for preparing the glass-ceramic coating includes the following steps:

[0023] 1) The glass powder and the zirconia ceramic powder are thoroughly mixed in a ratio of 3.5:6.5-4.5:5.5 and then sprayed onto the metal surface;

[0024] 2) Place the sample with the glass-ceramic coating on the surface into the vacuum furnace, turn on the vacuum pump, and evacuate the pressure inside the furnace to -100kPa;

[0025] 3) Open the argon valve and fill the vacuum furnace with argon gas as a protective gas, maintaining the furnace pressure at 2-5 kPa;

[0026] 4) Heat treatment to 550-630℃ and hold for 2-5 hours;

[0027] 5) Cool to 410-450℃ and anneal for 2-3 hours;

[0028] 6) Allow it to cool naturally to room temperature to form a dense glass-ceramic coating on the metal surface.

[0029] The porosity of the glass-ceramic coating is 2.9-4.1%.

[0030] The beneficial effects of this invention are:

[0031] 1) The coefficient of thermal expansion of glass can be adjusted according to the substrate material to enhance the adhesion of the glass-ceramic coating;

[0032] 2) The glass phase in the glass-ceramic coating is ferrophosphate glass, which has excellent chemical stability, ensuring the corrosion resistance of the glass-ceramic coating.

[0033] 3) Glass has a low softening temperature, which results in a very low heat treatment temperature, reducing the risk of deformation and oxidation of the substrate material during heat treatment;

[0034] 4) Zirconia is selected as the ceramic material for glass-ceramic coating. It will not undergo crystal transformation at the heat treatment temperature of this invention, which would lead to changes in the volume of the ceramic phase and increase the porosity of the glass-ceramic coating. Attached Figure Description

[0035] Figure 1 These are SEM images of the glass-ceramic coating before and after heat treatment annealing, among which... Figure 1 (a) Shown before heat treatment annealing Figure 1 (b) Displayed after heat treatment annealing;

[0036] Figure 2 These are three-dimensional X-CT images of the glass-ceramic coating before and after heat treatment annealing, in which... Figure 2 (a) Shown before heat treatment annealing Figure 2 (b) Shown after heat treatment annealing. Detailed Implementation

[0037] The present invention will be further described below with reference to embodiments and accompanying drawings, but this should not be construed as limiting the scope of protection of the present invention.

[0038] The glass composition percentages provided in the examples are: P2O5 37.2-41.2wt%, Al2O3 16.3-18.3wt%, Fe2O3 0.5-3wt%, Na2O 16.7-22.5wt%, SiO2 0.5-7wt%, B2O3 1.6-4.9wt%, SrO 2-5.5wt%, BaO 4.5-9.4wt%, La2O3 0.5-1.5wt%, Nd2O3 0.5-1.8wt%, ZrO2 1-2.5wt%, and Nb2O5 0.5-1.5wt%.

[0039] To ensure the compatibility of glass-ceramic coatings with metals of varying coefficients of thermal expansion, glass with different coefficients of thermal expansion is selected based on the coefficient of thermal expansion of the metal. Since the coefficient of thermal expansion of glass is determined by its composition, glass with different compositions is chosen to prepare glass-ceramic coatings for metals with different coefficients of thermal expansion.

[0040] Table 1: Glass Formulations and Basic Measurement Parameters of Six Embodiments of the Invention

[0041]

[0042] The method for preparing ferric phosphate glass powder of the present invention includes the following steps:

[0043] 1) Weigh out the high-purity raw materials according to the above glass composition;

[0044] 2) After the raw materials are thoroughly mixed, they are placed in a platinum crucible, and then the platinum crucible is placed in a silicon carbide rod electric furnace for melting; the melting temperature is 1000-1100℃, and after the raw materials are completely melted, the temperature is raised to 1200℃ for homogenization and clarification.

[0045] 3) Remove the molten glass from the furnace when the temperature drops to 900-950℃, and pour the molten glass onto a steel mold preheated to 200-300℃;

[0046] 4) Take a portion of the glass and anneal it in a muffle furnace that has been preheated to near the glass transition temperature Tg for chemical stability testing and expansion coefficient testing. Let the rest of the glass cool down to room temperature naturally.

[0047] 5) Glass that has cooled naturally to room temperature is ground in a tungsten carbide grinding tank, and the glass powder is used as a raw material for plasma spraying.

[0048] To measure the chemical stability of the glass itself, the annealed glass sample was processed into a size of 1cm × 1cm × 0.5cm (surface area 4cm²). 2 The sample was polished on all six sides. It was then placed in a PTFE container filled with deionized water and immersed in a constant temperature water bath at 90°C for 28 days. Subsequently, the elemental composition of the leachate was analyzed using ICP-OES. The experimental results are expressed as total weight loss per unit surface area (g / m²). 2 )express.

[0049] Total weight loss per unit surface area (NL) j :

[0050]

[0051] Where: m j S represents the total weight loss of sample j after immersion, in grams (g). j The surface area of ​​sample j is expressed in meters (m²). 2 .

[0052] To measure the coefficient of thermal expansion of glass, the annealed glass is processed into... The round bar with both ends finely ground was used to measure the coefficient of thermal expansion of the glass sample using a dilatometer.

[0053] To test the adhesion of the coating, the metal material was processed into... A round bar with a coating sprayed on one end and an M16 internal thread tapped on the other end is used for testing the adhesion of glass-ceramic coatings.

[0054] The glass powder produced by the above process using the above glass composition has a glass transition temperature (Tg) of 410-450℃ and a coefficient of thermal expansion of 13.3-16.5×10⁻⁶. -6The glass has a coefficient of thermal expansion that matches that of commonly used stainless steel and nickel-based alloys, making it suitable for glass-ceramic coating on stainless steel and nickel-based alloy surfaces. The total weight loss of the glass after immersion in deionized water at 90°C for 28 days is 2.17-4.42 g / m², indicating excellent chemical stability and the ability to function as a coating under harsh conditions without corrosion. The glass softening temperature is between 448-497°C, facilitating heat treatment of the glass-ceramic coating at relatively low temperatures. After heat treatment, the glass fills the internal pores of the coating, reducing its porosity. Because the heat treatment temperature is relatively low, the substrate material will not oxidize due to excessively high temperatures, reducing the coating's adhesion and minimizing the risk of workpiece deformation at high temperatures affecting subsequent assembly.

[0055] The coefficient of thermal expansion of 316 stainless steel is 16.5 × 10⁻⁶. -6 / K, the matching glass composition is glass #1 and #2 in Table 1 above, with a composition range of P2O5 37.2-38.2wt%, Al2O3 17.2-18.1wt%, Fe2O3 1-2wt%, Na2O 21.5-22.5wt%, SiO2 0.5-1wt%, B2O3 3-3.4wt%, SrO 4-5.5wt%, BaO 8-8.5wt%, La2O3 1-1.2wt%, Nd2O3 1-1.2wt%, ZrO2 1-1.5wt%, Nb2O5 0.5-1wt%.

[0056] The coefficient of thermal expansion of 310S stainless steel is 16.0 × 10⁻⁶. -6 / K, the matching glass composition is glass #3 and #4 in Table 1 above, with a composition range of P2O5 39.2-40.1wt%, Al2O3 17.3-18.3wt%, Fe2O3 0.5-3wt%, Na2O 18.8-19.8wt%, SiO2 2-2.6wt%, B2O3 1.6-2.8wt%, SrO 3-4wt%, BaO 8.4-9.4wt%, La2O3 1-1.5wt%, Nd2O3 0.5-1wt%, ZrO2 1.2-1.5wt%, Nb2O5 1-1.5wt%.

[0057] The coefficient of thermal expansion of Inconel 690 alloy is 13.3 × 10⁻⁶. -6 / K, the matching glass composition is glass #5 and #6 in Table 1 above, with a composition range of P2O5 40.7-41.2wt%, Al2O3 16.3-17.3wt%, Fe2O3 1.5-2.5wt%, Na2O 16.7-18.2wt%, SiO2 5-7wt%, B2O3 2.9-4.9wt%, SrO 2-2.5wt%, BaO 4.5-6.5wt%, La2O3 0.5-0.8wt%, Nd2O3 0.7-1.8wt%, ZrO2 1.8-2.5wt%, Nb2O5 0.9-1.3wt%.

[0058] The following description, based on six embodiments of the present invention, details the heat treatment process, annealing process, and basic parameters measured after spraying glass powder and zirconium oxide powder in different proportions onto stainless steel 316, stainless steel 310S, and Inconel 690 alloy.

[0059] Table 2: Heat treatment process, annealing process, and basic measured parameters of glass-ceramic coatings after spraying different proportions of glass powder and zirconium oxide powder onto stainless steel 316, stainless steel 310S, and Inconel 690 alloys in six embodiments of the present invention.

[0060]

[0061]

[0062]

[0063] The method for preparing the glass-ceramic coating includes the following steps:

[0064] 1) The glass powder and the zirconia ceramic powder are thoroughly mixed in a ratio of 3.5:6.5 to 4.5:5.5 and then sprayed onto the metal surface;

[0065] 2) Place the sample with the glass-ceramic coating on the surface into the vacuum furnace, turn on the vacuum pump, and evacuate the pressure inside the furnace to -100kPa;

[0066] 3) Open the argon valve and fill the vacuum furnace with argon gas as a protective gas, maintaining the furnace pressure at 2-5 kPa;

[0067] 4) Heat treatment to 550-630℃ and hold for 2-5 hours;

[0068] 5) Cool to 410-450℃ and anneal for 2-3 hours;

[0069] 6) Allow it to cool naturally to room temperature to form a dense glass-ceramic coating on the metal surface.

[0070] The data in Table 2 show that glasses with different coefficients of thermal expansion were matched with stainless steel 316, stainless steel 310S, and Inconel 690 alloy, respectively. When glass powder and zirconia ceramic powder were mixed in a ratio of 3.5:6.5 to 4.5:5.5 as the glass-ceramic coating components, the coating was sprayed and then heat-treated under vacuum at 550-630℃ for 2-5 hours. After high-temperature heat treatment, it was annealed at 410-450℃ for 2-3 hours. The adhesion strength of the glass-ceramic coating obtained according to this heat treatment and annealing process was 22.3-27.9 MPa, which is not significantly different from the adhesion strength of 21.5-26.8 MPa before heat treatment and annealing. This indicates that the adhesion strength of the coating did not decrease due to substrate oxidation during heat treatment and annealing. The adhesion strength data shows that the glass-ceramic coating is firmly bonded to the substrate material after heat treatment and annealing, with no risk of detachment. The porosity decreased from 12.5-14.5% before heat treatment annealing to 2.9-4.1% after heat treatment annealing, indicating that the use of zirconia ceramic powder will not cause a phase transformation at the heat treatment annealing temperature of this invention, which would lead to an increase in porosity. Furthermore, heat treatment annealing significantly reduced the porosity of the glass-ceramic coating, thereby enhancing the glass-ceramic coating's resistance to liquid and gas corrosion.

[0071] Figure 1 (a) and (b) are SEM images of the glass-ceramic coating before and after heat treatment. As can be seen from the images, before heat treatment annealing, the coating surface has a large number of pores (such as...). Figure 1 (a)), while the coating surface after heat treatment annealing (e.g. Figure 1 (b) The pores are filled with a glass phase, and the glass-ceramic coating is smooth and flat, making it difficult for corrosive gases or liquids to penetrate the glass-ceramic coating and corrode the substrate material.

[0072] Figure 2 (a) and (b) are three-dimensional X-CT images of the glass-ceramic coating before and after heat treatment. As can be seen from the images, before heat treatment annealing, the entire coating is relatively loose, exhibiting a high porosity (e.g., ...). Figure 2 (a)) After heat treatment annealing, the entire coating is relatively dense, and the porosity is significantly reduced (e.g. Figure 2 (b)) enhances the corrosion resistance of the glass-ceramic coating.

Claims

1. A glass-ceramic coating for a metal surface, characterized in that, Glass powder and ceramic powder are mixed in a mass percentage ratio of 3.5:6.5 to 4.5:5.5 and then sprayed onto a metal surface. Subsequently, a dense glass-ceramic coating is formed through heat treatment and annealing. The glass powder has the following composition by mass percentage: P2O5 37.2-41.2wt%, Al2O3 16.3-18.3wt%, Fe2O3 0.5-3wt%, Na2O 16.7-22.5wt%, SiO2 0.5-7wt%, B2O3 1.6-4.9wt%, SrO 2-5.5wt%, BaO 4.5-9.4wt%, La2O3 0.5-1.5wt%, Nd2O3 0.5-1.8wt%, ZrO2 1-2.5wt%, Nb2O5 0.5-1.5wt%. The ceramic powder mentioned is zirconia ceramic powder; The heat treatment is carried out at 550-630℃ for 2-5 hours. Annealing is performed at 410-450℃ for 2-3 hours.

2. The glass-ceramic coating on a metal surface as described in claim 1, characterized in that, The glass powder has a glass transition temperature (Tg) of 410-450℃, a glass softening temperature of 448-497℃, and a glass expansion coefficient of 13.3-16.5×10⁻⁶. -6 / K, the total weight loss in the glass powder immersion experiment was 2.17-4.42 g / m 2 .

3. The glass-ceramic coating on a metal surface as described in claim 1, characterized in that, The metal is stainless steel or a nickel-based alloy.

4. The glass-ceramic coating on a metal surface as described in claim 3, characterized in that, The glass powder has the following composition by mass percentage: P2O5 37.2-38.2wt%, Al2O3 17.2-18.1wt%, Fe2O3 1-2wt%, Na2O 21.5-22.5wt%, SiO2 0.5-1wt%, B2O3 3-3.4wt%, SrO 4-5.5wt%, BaO 8-8.5wt%, La2O3 1-1.2wt%, Nd2O3 1-1.2wt%, ZrO2 1-1.5wt%, Nb2O5 0.5-1wt%; the metal is stainless steel 316.

5. The glass-ceramic coating on a metal surface as described in claim 3, characterized in that, The glass powder has the following composition by mass percentage: P2O5 39.2-40.1wt%, Al2O3 17.3-18.3wt%, Fe2O3 0.5-3wt%, Na2O 18.8-19.8wt%, SiO2 2-2.6wt%, B2O3 1.6-2.8wt%, SrO 3-4wt%, BaO 8.4-9.4wt%, La2O3 1-1.5wt%, Nd2O3 0.5-1wt%, ZrO2 1.2-1.5wt%, Nb2O5 1-1.5wt%; the metal is stainless steel 310S.

6. The glass-ceramic coating on a metal surface as described in claim 3, characterized in that, The glass powder has the following composition by mass percentage: P2O5 40.7-41.2wt%, Al2O3 16.3-17.3wt%, Fe2O3 1.5-2.5wt%, Na2O 16.7-18.2wt%, SiO2 5-7wt%, B2O3 2.9-4.9wt%, SrO 2-2.5wt%, BaO 4.5-6.5wt%, La2O3 0.5-0.8wt%, Nd2O3 0.7-1.8wt%, ZrO2 1.8-2.5wt%, Nb2O5 0.9-1.3wt%; the metal is Inconel 690 alloy.

7. A glass-ceramic coating for a metal surface as described in any one of claims 1-6, characterized in that, The porosity of the glass-ceramic coating is 2.9-4.1%.

Images