Insulating, refractory molded body, especially plate, and process for its manufacture and its usage
An unfired, refractory molded body ( 1 ), especially a plate, especially for thermal insulation of molten metal and/or an ingot solidifying from molten metal, that includes a binding agent matrix ( 2 ) of a set binder and aggregate grains ( 3 ) of biogenic silicic acid, preferably of rice husk ash, which are incorporated into the binding agent matrix ( 2 ), wherein the binding agent matrix ( 2 ) consists of silica gel, as well as a process for its production and its usage.
1. An unfired, refractory molded body comprising a binding agent matrix and an aggregate, the binding agent matrix consisting of silica gel as a binding agent and the aggregate consisting of at least one aggregate material of aggregate grains which grains are incorporated into the binding agent matrix,
wherein with respect to a total dry mass of the aggregate, the aggregate comprises at least 50 wt. % of biogenic silicic acid as rice husk ash, and 0 to <10 wt. % of at least one additional aggregate material of a refractory material, which is not solely composed of SiO 2 , including expanded perlite, expanded vermiculite, expanded clay, inorganic fibers, fly ash, filter dust, or combinations thereof,
wherein the molded body has a softening point, determined with a heating microscope according to DIN EN 51730:2007-09 of 1500 to 1700° C.
2. The molded body according to claim 1 , wherein the aggregate is comprised of at least 80 wt. % of rice husk ash, with respect to the total dry mass of the aggregate.
3. The molded body ( 1 ) according to claim 1 , wherein the molded body has a dry apparent density ρ 0 from 0.3 to 1.5 g/cm 3 according to DIN EN 1094-4:1995-09.
4. The molded body ( 1 ) according to claim 1 , wherein the molded body has a porosity of 60 to 90% according to DIN EN 1094-4:1995-09.
5. The molded body ( 1 ) according to claim 1 , wherein the molded body has a cold compression strength of 0.5 to 15.0 MPa according to DIN EN 993-5:1998-12.
6. The molded body ( 1 ) according to claim 1 , wherein the molded body has a cold bending strength of 0.3 to 7.0 MPa according to DIN EN 993-6:1995-04.
7. The molded body ( 1 ) according to claim 1 , wherein the molded body has a hot bending strength of 0.5 to 5.0 MPa according to DIN EN 993-7:1995-04.
8. The molded body ( 1 ) according to claim 1 , wherein the molded body has a softening point, determined with a heating microscope according to DIN EN 51730:2007-09 of 1650 to 1700° C.
9. The molded body ( 1 ) according to claim 1 , wherein the molded body has the following thermal conductivities according to DIN EN 993-15:2005-07:
Thermal
Conductivity [W/mK]
At 26° C.
0.10 to 0.14 0.12 to 0.16 0.17 to 0.21 0.25 to 0.29
At 307° C.
At 700° C.
At 995° C.
10. The molded body according to claim 1 , wherein the molded body is a plate.
11. The molded body according to claim 1 , wherein the molded body comprises at least one additional aggregate material, consisting of SiO 2 in a form of microsilica and/or pyrogenic silica and/or precipitated silica.
12. The molded body according to claim 2 , wherein the aggregate of the molded body is comprised of at least 90 wt. % of rice husk ash, with respect to the total dry mass of the aggregate.
13. The molded body according to claim 2 , wherein the aggregate of the molded body is comprised 100 wt. % of rice husk ash, with respect to the total dry mass of the aggregate.
14. The molded body according to claim 3 , wherein the molded body has a dry apparent density ρ0 from 0.5 to 1.3 g/cm 3 according to DIN EN 1094-4:1995-09.
15. The molded body according to claim 4 , wherein the molded body has a porosity from 70 to 80% according to DIN EN 1094-4:1995-09.
16. The molded body according to claim 5 , wherein the molded body has a cold compression strength of 1.0 to 10.0 MPa according to DIN EN 993-5:1998-12.
17. The molded body according to claim 6 , wherein the molded body has a cold bending strength of 0.5 to 5.0 MPa according to DIN EN 993-6:1995-04.
18. The molded body according to claim 7 , wherein the molded body has a hot bending strength of 1.0 to 3.0 MPa according to DIN EN 993-7:1995-04.
19. A process for producing a molded body according to claim 1 , characterized by the following steps:
a) Producing a mixture comprising aggregate and silica sol,
b) Filling the mixture into a mold,
c) Compacting of the mixture to form a green body,
d) Demolding the green molded body, and
e) Allowing the molded body to set.
20. The process according to claim 19 , wherein the composition of the mixture is adjusted such that the mixture has a slump—determined in reference to DIN EN ISO 1927-4:2013-03—of 200 to 500 mm.