Refractory filter
A refractory filter suitable for filtering molten metal, such as steel, and a method and powdered composition for producing the filter. The filter comprises refractory material, the refractory material comprising: 60-90 wt % alumina; 8-30 wt % zirconia; and 3-20 wt % magnesia. The powdered composition comprises: 60-90 wt % alumina; 8-30 wt % zirconia; and 3-20 wt % magnesia, wherein the powdered composition comprises less than 12.5 wt % reactive alumina, calcined alumina or a mixture thereof, and wherein the remainder of the alumina is tabular alumina. The method comprises: providing a powdered composition in accordance with the invention; forming a filter precursor from the powdered composition and a liquid component; and firing the filter precursor to form a refractory filter.
1. A powdered composition for making a refractory filter comprising 60-90 wt % alumina; 8-30 wt % zirconia; and 3-20 wt % magnesia, wherein the powdered composition comprises less than 12.5 wt % reactive alumina, calcined alumina or a mixture thereof, the remainder of the alumina being tabular alumina, and wherein the zirconia has a D50 particle size of less than 3 μm.
2. The powdered composition of claim 1 , wherein the powdered composition comprises from 0 to 10 wt % reactive alumina, calcined alumina or a mixture thereof.
3. The powdered composition of claim 1 , wherein the powdered composition comprises at least 60 wt % tabular alumina.
4. The powdered composition of claim 1 , wherein the tabular alumina has a D50 particle size of less than 500 μm.
5. The powdered composition of claim 1 , wherein the tabular alumina comprises a mixture of finer grade tabular alumina having a D50 particle size of 20 to 50 μm and coarser grade tabular alumina having a D50 particle size of 100 to 500 μm.
6. The powdered composition of claim 5 , wherein the ratio of finer grade tabular alumina to coarser grade tabular alumina is from 40:60 to 60:40.
7. The powdered composition of claim 1 , wherein the reactive alumina, when present, has a D50 particle size of less than 10 μm.
8. The powdered composition of claim 1 , wherein the magnesia has a D50 particle size of less than 30 μm.
9. The powdered composition of claim 1 , wherein the zirconia has a D50 particle size of less than 1 μm.
10. The powdered composition of claim 1 , wherein the powdered composition comprises less than 1 wt % silica.
11. The powdered composition of claim 10 , wherein the powdered composition is substantially free of silica.
12. The powdered component of claim 1 , wherein the magnesia is at least partially replaced by ceria.
13. The powder composition of claim 1 , further comprising up to 5 wt % titania.
14. A refractory filter for filtering molten steel, comprising refractory material, said refractory material formed from the powdered composition of claim 1 .
15. The refractory filter of claim 14 , wherein the refractory material is substantially silica-free.
16. The refractory filter of claim 14 , wherein the refractory filter has a compressive strength of at least 4 MPa.
17. The refractory filter of claim 14 , wherein the refractory filter has at least one first surface forming a side face of the filter and two opposed second surfaces forming the through-flow faces of the filter, the second surfaces having an area of no greater than 500 cm 2 .
18. The refractory filter of claim 14 , wherein the filter is framed.
19. The refractory filter of claim 14 , wherein the refractory filter is either a foam filter, a cellular filter, or a pressed filter.
20. The refractory filter of claim 14 , wherein the refractory material further comprises up to 5 wt % titania.
21. The refractory filter of claim 14 , wherein the refractory material is made using less than 12.5 wt % reactive or calcined alumina.
22. Use of a powdered composition according to claim 1 to form a refractory filter.
23. A method for the production of a refractory filter, comprising:
providing a powdered composition according to claim 1 ;
forming a filter precursor from the powdered composition and a liquid component; and
firing the filter precursor to form a refractory filter.
24. The method of claim 23 , wherein the filter precursor is dried prior to firing.
25. The method of claim 23 , wherein forming the filter precursor comprises 3D printing.
26. The method of claim 23 , wherein forming the filter precursor comprises:
combining the powdered composition and the liquid component to form a slurry, and
impregnating a reticulated foam substrate with the slurry to form the filter precursor.
27. The method of claim 26 , wherein the reticulated foam substrate is impregnated with the slurry by spraying, roller impregnation, dipping, centrifuging, or any combination thereof.
28. The method of claim 23 , wherein the filter precursor is fired at a temperature of greater than 1500° C.
29. The method of claim 23 , wherein the filter precursor is fired for at least 30 minutes.
30. The method of claim 23 , wherein the filter precursor is fired in an oxidizing atmosphere.