REFRACTORY ARTICLE RESISTANT TO NON-FERROUS METAL AND PRODUCTION PROCESS THEREOF

Abstract

A refractory article used at high temperature contains a silica, calcium silicate or mullite matrix with at least a surface having an open porosity filled at least partially with a sulfate, phosphate, or carbonate salt or a mixture of sulfate, phosphate or carbonate salts. The refractory article is resistant to the corrosion and build-up of non-ferrous metals and their alloys.

Claims

1-14. (canceled)

15. Refractory article for use at high temperature having a silica, calcium silicate or mullite matrix with at least a surface having an open porosity wherein a sulfate, phosphate, carbonate salt or a mixture of thereof is present in the open porosity of at least a portion of at least a surface of the article and has a thermal decomposition temperature higher than 500 C. and wherein the solubility of the salt in water at 20 C. is higher than 100 g/l.

16. Refractory article according to claim 15 wherein the thermal decomposition temperature of the salt is higher than 900 C.

17. Refractory article according to claim 15 wherein the salt cation is neither sodium nor potassium.

18. Refractory article according to claim 15 wherein the salt cation is selected from the group consisting of magnesium and zinc.

19. Refractory article according to claim 15 wherein the silica is fused silica.

20. Refractory article according to claim 15 wherein the salt is present in a quantity of 0.001 to 0.1 g/cm.sup.2.

21. Refractory article according to claim 15 wherein the salt is selected from the group consisting of magnesium sulfate and zinc sulfate.

22. Refractory article according to claim 15 wherein the refractory article is an article selected from the group consisting of a roll and a riser tube.

23. Refractory article according to claim 15 wherein a top coating is present on the surface of the refractory article.

24. Refractory article according to claim 23 wherein the top coating comprises at least 90 wt. % of Si.sub.3N.sub.4.

25. Process for the manufacture of a refractory article according to claim 15, comprising the steps of: a) applying an aqueous solution of 10-30 wt % of a material selected from the group consisting of sulfate, phosphate, carbonate salt and a mixture of thereof on the refractory article, b) drying the refractory article.

26. Process according to claim 11 wherein the first and second steps a) and b) are repeated.

27. Process according to claim 11 wherein the salt cation is selected form the group consisting of magnesium and zinc.

28. Process according to claim 11 further comprising a third step c) of applying a further coating.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0031] FIG. 1 schematically illustrates the chain of phenomena;

[0032] FIG. 2a, 2b illustrate trials with example 1; and

[0033] FIG. 3a, 3b illustrate trials with example 2

DETAILED DESCRIPTION OF THE INVENTION

[0034] In order to better describe the invention, it will now be illustrated by means of examples that are not intended to limit the scope of the present patent application.

EXAMPLE 1

[0035] An aqueous solution of 23 wt. % MgSO.sub.4 is prepared. 1.79 g of this solution is painted on an internal surface of 37 cm.sup.2 in a fused silica crucible (6). The quantity of the salt is around to 0.011 g/cm.sup.2. The crucible was then filled with aluminum alloy powder (90 wt. % Al/10 wt. % Si) and heated at 1000 C. for 100 hours. The trial was also performed with a crucible without any protection. After cooling down of the crucible, the crucible and the solidified alloy (4) are cut in a transverse direction.

[0036] FIG. 2a (comparative example) clearly shows the infiltration of the alloy in the reference cup and the presence of Al.sub.2O.sub.3 (5). With the protection of MgSO.sub.4, the corrosion is clearly limited: FIG. 2b shows the integrity of the silica crucible (6).

EXAMPLE 2

[0037] A similar trial was carried out with a solution of ZnSO.sub.4.

[0038] FIG. 3a (comparative example) clearly shows the infiltration of the alloy in the reference cup leading to the presence of Al.sub.2O.sub.3 (5). With the protection of ZnSO.sub.4 (FIG. 3b), the corrosion is clearly limited.

[0039] It is to be noted that the protection occurs in this case because the alloy was in contact with the matrix infiltrated with ZnSO.sub.4 during heating up. When reaching a temperature of 600 C., a layer of alumina is created at the interface between the metal melt and the crucible resulting in a protection at higher temperature. If the alloy is only put into contact with the refractory article after reaching temperatures above 700-750 C., this effect is lost due to thermal decomposition of ZnSO.sub.4 before reaction with the alloy melt.

EXAMPLE 3

[0040] An aqueous solution of 23 wt. % MgSO.sub.4 is prepared. 97 g of this solution is applied by painting using a wet cloth on the external surface of silica rolls, two layers were painted on the surface with a drying time of about 5 min between the two layers. The rolls are then dried at 90 C. for at least 2 hours. The quantity of the salt is 0.0026 g/cm.sup.2 of MgSO.sub.4 on those rolls. These rolls were also tested in a furnace for the transportation of coated conveyed metal sheet at 930 C. for 6 months without corrosion or build-up having been reported.