Alumina ceramic and mehtod for its manufacture
A ceramic material made of alumina and titanium oxide, which is practically free from additives, achieves a high quality factor Q by annealing the material after sintering. Qualities of up to 17,900 at a measuring frequency of 10 GHz can be achieved.
1 - 14 . (canceled)
15 . A method of manufacturing alumina ceramic, comprising the steps of: sintering a mixture containing alumina powder and titaniferous oxide powder into a ceramic body; and annealing the ceramic body at an annealing temperature below 1,280° C.
16 . The method of claim 15 , and selecting the titaniferous oxide powder from one of titanium oxide, an earth alkali titanate, and a mixture of titanium oxide and at least one earth alkali titanate.
17 . The method of claim 15 , and selecting the titaniferous oxide powder from pure titanium dioxide.
18 . The method of claim 15 , wherein the sintering is performed at a temperature between 1,300° C. and 1,500° C., preferably between 1,350° C. and 1,450° C.
19 . The method of claim 15 , wherein the annealing is performed at the annealing temperature between 1,000° C. and 1,200° C., preferably between 1,075° C. and 1,125° C.
20 . The method of claim 15 , wherein the annealing is performed for a duration of at least one hour, preferably less than five hours.
21 . The method of claim 15 , wherein the annealing is performed until an aluminum titanate content of less than 2% is achieved.
22 . The method of claim 15 , wherein at least 99.9% of a mineral fraction of the mixture is formed of Al 2 O 3 and TiO 2 .
23 . The method of claim 22 , wherein the mineral fraction contains between 89 and 93 mol % of Al 2 O 3 and between 7 and 11 mol % TiO 2 .
24 . An alumina-based ceramic material comprising: an alumina content between 89 and 93 mol %; a content of titaniferous oxide between 7 and 11 mol %; and a total content of alumina and titaniferous oxide of at least 99.95 mol % and a Qf-factor of at least 100,000.
25 . The ceramic material of claim 24 , wherein the titaniferous oxide is selected from a group including titanium dioxide, an earth alkali titanate, and a mixture of titanium dioxide and at least one earth alkali titanate.
26 . The ceramic material of claim 24 , wherein the titaniferous oxide is pure titanium dioxide.
27 . The ceramic material of claim 26 , wherein a maximum 2 mol %, preferably a maximum 1 mol %, of the alumina and the titanium dioxide is present in the form of aluminium titanate.
28 . The ceramic material of claim 24 , comprising a relative dielectric constant between 10.5 and 12.0, preferably between 10.9 and 11.6, and a temperature coefficient of relative permittivity between −60 ppm and +40 ppm.