Nanoscale corundum powders, sintered compacts produced from these powders and method for producing the same
View Patent ↗Nanoscale corundum powders are obtained by first producing an Al 2 O 3 precursor by adding seed crystals to an aqueous solution of an aluminium compound and adding a base and then converting the Al 2 O 3 precursor into corundum by calcination at a high temperature. Before the calcination, the salts that are present in addition to the Al 2 O 3 precursor are separated off. The resulting product is calcined at temperatures of 700 to 975° C. and any fines that may be present are removed. The resulting corundum powders can be sintered at temperatures of ≦1200° C. to produce compacts or components of multiple layer systems.
1. A process for preparing a nanosize α-alumina powder, comprising:
preparing an Al 2 O 3 precursor by mixing an aqueous solution of an aluminum compound with seed crystals and adding a base;
separating any salts present from the Al 2 O 3 precursor; and
calcining the Al 2 O 3 precursor into nanosize α-alumina powder at a temperature of from 700° C. to 975° C.
2. The process of claim 1 wherein the aluminum compound is selected from the group consisting of aluminum(III) nitrate, aluminum(III) chloride, aluminum(III) acetate, and aluminum(III) ethoxide.
3. The process of claim 1 wherein the seed crystals are corundum or diaspore.
4. The process of claim 1 wherein the base is a base that can be removed by heating.
5. The process of claim 4 wherein the base is ammonia.
6. The process of claim 1 wherein the Al 2 O 3 precursor is precipitated at a temperature of from 50° C. to 100° C.
7. The process of claim 1 wherein any salts present are separated from the Al 2 O 3 precursor by dialysis, thermal decomposition, or both dialysis and thermal decomposition.
8. The process of claim 1 wherein the Al 2 O 3 precursor is calcined at a temperature of from 800° C. to 900° C.
9. The process of claim 1 further comprising:
removing from the nanosize α-alumina powder any fines present having a particle size of less than 40 nm.
10. The process of claim 9 wherein any fines present are removed by dispersion of the nanosize α-alumina powder and subsequent centrifugation.
11. The process of claim 1 further comprising:
mixing the nanosize α-alumina powder with at least one processing aid to give a shapeable composition.
12. The process of claim 11 further comprising
shaping the composition; and
sintering the composition.
13. The process of claim 12 wherein the composition is sintered at a temperature of less than or equal to 1200° C.
14. The process of claim 1 wherein the nanosize α-alumina powder has an α-Al 2 O 3 content of at least 80% by weight and a density of at least 3.90 g/cm 3 .
15. The process of claim 12 wherein the shaping comprises shaping a layer of a multilayer system.
16. The process of claim 15 wherein the sintering comprises sintering the multilayer system in a single cofiring step.