CERAMIC COMPOSITION FOR COATING METALLIC SURFACES, METHOD AND RESULTING CERAMIC LAYER

Abstract

A ceramic composition for coating metallic surfaces, a method and a resulting ceramic layer, which layer refers to a ceramic composition which, after deposition, is subjected to a thermal treatment to generate a ceramic layer. The resulting ceramic layer displays, among other characteristics, appropriate adhesion to the metallic surface and remains stable at temperatures between 750 C. and 950 C.

Claims

1. A ceramic composition for the coating of metallic surfaces by means of thermal treatment that comprises: a. At least one frit whose percentage by weight is between 40% and 82%, b. At least one refractory compound with a melting point higher than 1600 C., and c. At least one synthetic compound whose composition contains Co or Ni or Cu or Fe or Mo or Mn or Cr, or a mixture of them.

2. The ceramic composition according to claim 1, in which the composition by weight of the at least one frit comprises Si0.sub.2 between 55% and 70% by weight, R.sub.20 between 7% and 20% by weight, RO between 0% and 15% by weight, MOx between 0% and 8% by weight, MO.sub.2 between 0% and 7% by weight, Al.sub.20.sub.3 0.5% and 8% by weight, and B.sub.20.sub.3 between 3% and 10% by weight; where R.sub.20 represents at least one oxide selected from among Li.sub.20, Na.sub.20 and K.sub.20 or a mixture of them, where RO represents at least one oxide selected from among ZnO, MgO, CaO and BaO, or a mixture of them, where MOx represents at least one oxide selected from among CuO, Mn0.sub.2, Fe.sub.20.sub.3, MoO.sub.3, CoO and NiO, or a mixture of them, and where MO.sub.2 represents at least one oxide selected from between Ti0.sub.2 and Ce0.sub.2 or a mixture of them.

3. The ceramic composition according to claim 1 in which the percentage by weight of the mixture of one or more refractory compounds is between 15% and 50%.

4. The ceramic composition according to claim 3, in which the mixture of one or more refractory compounds is selected from among Zr0.sub.2, Cr.sub.20.sub.3, Al.sub.20.sub.3, Si0.sub.2, ZrSi0.sub.4, Mullite, compounds that contain Zr and/or Cr and/or Cu, or a mixture of them.

5. The ceramic composition according to claim 1 in which the percentage by weight of the mixture of one or more synthetic compounds is between 3% and 10%.

6. The ceramic composition according to claim 1, characterised in that its softening point after the thermal treatment is between 850 C. and 960 C.

7. The ceramic composition according to claim 1, characterised in that its coefficient of thermal expansion at 300 C. after the thermal treatment is between 8010.sup.7 C..sup.1 and 10010.sup.7 C..sup.1.

8. The ceramic composition according to claim 1 in which the at least one frit has a softening point higher than 675 C.

9. The method for coating the metallic surface for the formation of the ceramic layer, characterised in that it comprises two stages: Depositing of a ceramic composition according to claim 1 on the metallic surface, and Subjecting said surface to a thermal treatment at a maximum temperature of 980 C. for a maximum time of 10 minutes.

10. The method, according to claim 9, characterised in that the ceramic composition is deposited using the technique of airbrushing, curtain enamelling, ink injection, electrostatic deposition, electrophoretic deposition, silk-screening, dip coating, rotogravure, flexography, pad printing, or brush.

11. The ceramic layer, according to the procedure of claim 9, characterised in that it comprises a softening point of between 850 C. and 960 C.

12. The ceramic layer, according to the procedure in claim 9, characterised in that its coefficient of thermal expansion at 300 C. between 8010.sup.7 C..sup.1 and 10010.sup.7 C..sup.1.

Description

EXAMPLE 1

[0026] First, two frits designated F1 and F2 were melted, varying their oxide compositions were based on the desired thermal properties (softening point, sphere temperature, and fluidity temperature). Specifically, the oxide compositions of both frits comprise Si0.sub.2 between 55% and 70% by weight, R.sub.20 between 7% and 20% by weight, RO between 0% and 15% by weight, MOx between 0% and 8% by weight, MO.sub.2 between 0% and 7% by weight, Al.sub.20.sub.3 0.5% and 8% by weight, and B.sub.20.sub.3 between 3% and 10% by weight; where R.sub.20 represents at least one oxide selected from among Li.sub.20, Na.sub.20 and K.sub.20 OR A mixture of them, where RO represents at least one oxide selected from among ZnO, MgO, CaO and BaO, or a mixture of them, where MOx represents at least one oxide selected from among CuO, Mn0.sub.2, Fe.sub.20.sub.3, Mo0.sub.3, CoO and NiO, or a mixture of them, and where MO.sub.2 represents at least one oxide selected from between Ti0.sub.2 and Ce0.sub.2 or a mixture of them. Table 1 shows the thermal properties of frits F1 and F2.

TABLE-US-00001 TABLE 1 F1 F2 Softening point ( C.) 700 715 sphere T. (C.) 792 876 Fluidity T. ( C.) 828 968

[0027] The two frits are prepared using conventional techniques for melting industrial frit. The different raw materials that were the precursors of the oxides were mixed according to the composition of the frit. The mixture was then melted in an industrial oven at the typical temperatures for this process, using a mixture of gas and oxygen. The molten mixture was quickly cooled in a water bath to form the frit.

[0028] Based on frits F1 and F2, three ceramic compositions designated C1, C2 and C3 were prepared. The three compositions were adapted for correct application using airbrushing. In all cases, 250 g/m2, expressed as grams of solids, were applied to a metallic surface of AISI 316 steel. In all cases, the thermal treatment was at a maximum temperature of 960 C. for 3 minutes. Table 2 shows each one of the compositions, as well as the softening point and coefficient of thermal expansion of the obtained ceramic layer.

TABLE-US-00002 TABLE 2 Component Designation C1 C2 C3 Frit F1 100 28 25 Frit F2 42 45 Refractory compound Mullite 10 15 Refractory compound Al2O.sub.3 20 10 Synthetic compound M0O.sub.3 5 Softening point ceramic layer ( C.) 705 824 940 Coefficient of thermal expansion at 300 C. 96 89 90 (10.sup.7 C..sup.1)

[0029] Table 3 shows the results of the tests. The ceramic layers obtained from compositions C1 and C2 did not pass some of the tests, while the composition obtained with composition C3 passed all of the tests.

TABLE-US-00003 TABLE 3 Test C1 C2 C3 Resistance to citric acid AA AA AA Resistance to sulphuric acid AA AA AA Resistance to boiling sulphuric acid (g/m.sup.2) <1.6 <1.6 <1.6 Resistance to boiling hydrochloric acid <1.6 <1.6 <1.6 (g/m.sup.2) Resistance to molten salts 1 3 5 Adhesion to the metallic substrate Class 1 Class 3 Class 1 Thermal resistance at 700 C. No No Yes Stain resistance 1 4 5

EXAMPLE 2

[0030] Two frits designated F3 and F4 were melted, varying their oxide compositions were based on the desired thermal properties (softening point, sphere temperature, and fluidity temperature). Specifically, the oxide compositions of both frits comprise Si0.sub.2 between 55% and 70% by weight, R.sub.20 between 7% and 20% by weight, RO between 0% and 15% by weight, MOx between 0% and 8% by weight, MO.sub.2 between 0% and 7% by weight, Al.sub.20.sub.3 0.5% and 8% by weight, and B.sub.20.sub.3 between 3% and 10% by weight; where R.sub.20 represents at least one oxide selected from among Li.sub.20, Na.sub.20 and K.sub.20 or a mixture of them, where RO represents at least one oxide selected from among ZnO, MgO, CaO and BaO, or a mixture of them, where MOx represents at least one oxide selected from among CuO, Mn0.sub.2, Fe.sub.20.sub.3, Mo0.sub.3, CoO and NiO, or a mixture of them, and where MO.sub.2 represents at least one oxide selected from between Ti0.sub.2 and Ce0.sub.2 or a mixture of them. Table 4 shows the thermal properties of frits F3 and F4.

TABLE-US-00004 TABLE 4 F3 F4 Softening point ( C.) 829 755 sphere T. ( C.) 930 844 Fluidity T. ( C.) 1029 860

[0031] A composition designated C4 was prepared. Composition C4 was adapted for correct application by dip coating, and 250 g/m2, expressed as grams of solids, were applied to a metallic surface of AISI 310 steel. The application was subjected to a thermal treatment at a maximum temperature of 940 C. for 3 minutes. Table 5 shows composition C4, as well as the softening point and coefficient of thermal expansion of the obtained ceramic layer.

TABLE-US-00005 TABLE 5 Component Designation C4 Frit F3 48 Frit F4 30 Refractory compound SiO.sub.2 7 Refractory compound Cr.sub.2Zr0.sub.5 8 Synthetic compound (FeCr)(CoNi).sub.20.sub.4 7 Softening point ceramic layer ( C.) 940 Coefficient of thermal expansion 94 at 300 C. (10.sup.7 C..sup.1)

[0032] Table 6 shows that the ceramic layer obtained from composition C4 passed all of the tests.

TABLE-US-00006 TABLE 6 Test C4 Resistance to citric acid AA Resistance to sulphuric acid AA Resistance to boiling sulphuric acid (g/m.sup.2) <1.6 Resistance to boiling hydrochloric acid (g/m.sup.2) <1.6 Resistance to molten salts 5 Adhesion to the metallic substrate Class 1 Thermal resistance at 700 C. Yes Stain resistance 5

EXAMPLE 3

[0033] Three compositions designated compositions C5, C6 and C7 were prepared and adapted for correct application using Electrophoretic Deposition. In all cases, 200 g/m2, expressed as grams of solids, were applied to a metallic surface of AISI 310 steel. In all three cases, thermal treatment at a maximum temperature of 955 C. was applied for 3 minutes. Table 7 shows each one of the compositions, as well as the softening point and coefficient of thermal expansion of the ceramic layer obtained in each case.

TABLE-US-00007 TABLE 7 Component Designation C5 C6 C7 Frit F1 26 25 Frit F2 38 37 Frit F3 75 Refractory compound Cr.sub.20.sub.3 18 15 Refractory compound Zr0.sub.2 12 Refractory compound Cr.sub.2Zr0.sub.5 28 Synthetic compound (CuCrMn).sub.20 6 10 10 Softening point ceramic layer ( C.) 880 900 875 Coefficient of thermal expansion 89 90 93 at 300 C. (10.sup.7 C..sup.1)

[0034] Table 8 shows that the ceramic layers obtained from compositions C5, C6, and C7 passed all of the tests.

TABLE-US-00008 TABLE 8 Test C5 C6 C7 Resistance to citric acid AA AA AA Resistance to sulphuric acid AA AA AA Resistance to boiling sulphuric acid (g/m.sup.2) <1.6 <1.6 <1.6 Resistance to boiling hydrochloric <1.6 <1.6 <1.6 acid (g/m.sup.2) Resistance to molten salts 5 5 5 Adhesion to the metallic substrate Class 1 Class 1 Class 1 Thermal resistance at 700 C. Yes Yes Yes Stain resistance 5 5 5