FIRE-RESISTANT CERAMIC PRODUCT

Abstract

The invention relates to a fire-resistant ceramic product.

Claims

1. A refractory ceramic product whose microstructure has the following features: a matrix composed of at least one first material; grains of at least one second material are embedded in the matrix; the grains of the second material have a coating composed of at least one third material on at least part of their surface; the first and second material have a different coefficient of thermal expansion; the third material is stable during use of the product.

2. The product as claimed in claim 1 in the form of a sintered product.

3. The product as claimed in claim 1, wherein the first material is based on one or more of the following oxides or compounds: MgO, Al.sub.2O.sub.3, Fe.sub.2O.sub.3, SiO.sub.2, CaO, Cr.sub.2O.sub.3, ZrO.sub.2, Mn.sub.2O.sub.3, TiO.sub.2 or one or more of the compounds magnesia spinel, hercynite, galaxite or forsterite.

4. The product as claimed in claim 1, wherein the second material is based on one or more of the following oxides or compounds thereof: Al.sub.2O.sub.3, MgO, SiO.sub.2 or ZrO.sub.2.

5. The product as claimed in claim 1, wherein the third material is based on at least one of the following materials: gahnite, magnesia spinel, forsterite, mullite, calcium zirconate or AB.sub.2O.sub.4 (where A=Al.sup.3+, Cr.sup.3+ or Fe.sup.3+ and B=Mg.sup.2+, Zn.sup.2+, Fe.sup.2+, Mn.sup.2+ or Ni.sup.2+).

6. The product as claimed in claim 1, wherein the thickness of the coating is in the range from 5 to 300 m.

7. The product as claimed in claim 1, wherein the first material is in the form of grains sintered to one another.

8. The product as claimed in claim 1, wherein the coefficient of thermal expansion of the second material is at least 10% greater or less than the coefficient of thermal expansion of the first material, based on the coefficient of thermal expansion of the first material.

9. The product as claimed in claim 1, wherein the particle size of the grains of the second material is between the particle size of the smallest grains and the largest grains of the first material.

Description

[0066] FIGS. 1 to 3 show enlarged views of polished sections of the products produced according to the above working examples. Here, FIG. 1 shows a part of a product fired at 1300 C. and FIGS. 2 and 3 show parts of a product fired at 1500 C.

[0067] FIG. 1 shows a part of about 1.270.95 mm. The white bar at the bottom in the middle of the image corresponds to a length of 100 m. The matrix 3 which is formed by the first material in the form of sintered magnesia and appears black in FIG. 1 can be seen. The grains 1 of the second material in the form of alumina, which appear dark gray, are embedded in this matrix 3. The coating 2 in the form of the third material composed of gahnite which is present on the surface of the grains 1 appears as light-gray seam surrounding the grains 1 in FIG. 1. The coating 2 has a thickness in the range from about 10 to 30 m; the average thickness of the coating 2 is about 20 m.

[0068] FIG. 2 depicts a part of the product on the same scale as FIG. 1. Once again, the matrix of sintered magnesia is denoted by the reference numeral 3. The coating 2 composed of gahnite can be seen particularly well on the large grain 1 composed of alumina embedded in the matrix 3. Owing to the higher firing temperatures, the coating 2 composed of gahnite has a greater thickness, namely in the range from about 50 to 150 m; the average thickness of the coating 2 is about 100 m.

[0069] FIG. 3 shows a more highly magnified part of the product as per FIG. 2. The part depicted has a size of about 270200 m. A section of the peripheral region of an alumina grain 1 with the coating 2 of gahnite can be seen. On the side of the coating 2 facing the magnesia matrix 3, the coating 2 comprises not only gahnite but also regions containing proportions of magnesia, and on its side facing the alumina grain 1 the coating 2 has regions containing proportions of alumina. The mass ratio of ZnO to Al.sub.2O.sub.3 in the interior of the coating 2 is thus about 44.4:55.6 and therefore corresponds approximately to the stoichiometric ratio of these oxides in gahnite. In contrast, for example, the mass ratio of ZnO to Al.sub.2O.sub.3 in the region 4 of the coating 2 is about 21:79.