METHOD FOR PRODUCING A CERAMIC ABSORBER, CERAMIC ABSORBER, AND USE OF SAME

Abstract

A ceramic absorber for damping, in particular absorbing, vibrations, in particular combustion vibrations, preferably in gas turbines, which has a foam structure. For the ceramic absorber, the sound absorption capacity is set in a defined way and the efficiency is improved. The foam structure is based on a ceramic powder which contains either a component from the class of silicates or a component from the class of oxides, or a combination of a component from the class of silicates and a component from the class of oxides, and the foam structure has a homogeneous pore distribution.

Claims

1.-22. (canceled)

23. A process for producing a ceramic absorber, comprising: providing a ceramic powder, producing a slip and wherein the slip is foamed to generate a foam and a homogeneous pore distribution in the foam structure is generated, wherein the ceramic powder is provided using a combination of at least one component from the class of the silicates and at least one component from the class of the oxides, wherein the ceramic powder is provided with a proportion of the component or components from the class of the silicates within a range from fifty percent by weight to sixty percent by weight and, wherein, correspondingly, a proportion of the component or components from the class of the oxides within a range from forty percent by weight to fifty percent by weight.

24. The process as claimed in claim 23, wherein the silicates and/or the oxides have different particle sizes when more than one component is used, where the mass ratio of a component having coarser particles to a component having finer particles is sixty to eighty percent by mass to, correspondingly, forty to twenty percent by mass, especially a mass ratio of seventy percent by mass to thirty percent by mass, or a mass ratio of fifty to seventy percent by mass to, correspondingly, fifty to thirty percent by mass, especially a mass ratio of sixty percent by mass to forty percent by mass.

25. The process as claimed in claim 23, wherein mullite is used from the class of the silicates and/or alumina from the class of the oxides.

26. The process as claimed in claim 23, wherein the slip is produced by adding the ceramic powder, dispersant and foam former to a dispersion medium.

27. The process as claimed in claim 23, wherein the slip comprising the ceramic powder comprising a component from the class of the silicates or a combination of a component from the class of the silicates and at least one component from the class of the oxides is produced based on silica sol, or wherein the slip comprising the ceramic powder comprising components, especially exclusively from the class of the oxides, is produced based on water.

28. The process as claimed in claim 23, wherein the dispersant used is an organic and/or alkali-free medium, and/or based on carboxylic acid.

29. The process as claimed in claim 23, wherein the foam former used is an anion-active surfactant, and/or based on fatty alcohol sulfate.

30. The process as claimed in claim 23, wherein the slip is foamed by means of a stirrer.

31. The process as claimed in claim 23, wherein binder, especially alumina, is added to the ceramic powder produced that comprises at least one, preferably two or more, components, exclusively from the class of the oxides.

32. The process as claimed in claim 23, wherein the foam, for shaping and/or for solidification, is introduced into a nonabsorptive mold, and/or a mold with a smooth surface.

33. The process as claimed in claim 23, wherein the foam is sintered, wherein the sintering is effected at a temperature in a range from 1500° C. to 1750° C., preferably 1600° C. to 1750° C., more preferably at a temperature of 1700° C., and/or over a period of time within a range from sixty minutes to one hundred and eighty minutes, preferably ninety minutes to one hundred and fifty minutes, more preferably over a period of time of one hundred and twenty minutes.

34. A ceramic absorber for damping or absorption of vibrations and/or combustion vibrations, comprising: a foam structure based on a ceramic powder, having a combination of a component from the class of the silicates and a component from the class of the oxides, wherein the foam structure has a homogeneous pore distribution; wherein the proportion of the component from the class of the silicates is within a range from fifty percent by weight to sixty percent by weight, and wherein the proportion of the component from the class of the oxides is correspondingly within a range from forty percent by weight to fifty percent by weight.

35. The ceramic absorber as claimed in claim 34, wherein the silicate is mullite and/or the oxide is alumina.

36. The ceramic absorber as claimed in claim 34, wherein the foam structure is an open-pore structure, especially on all outer surfaces, preferably with a porosity within a range from sixty percent to ninety percent and/or an area porosity of seventy percent to eighty percent.

37. The ceramic absorber as claimed in claim 36, wherein the pores take the form of spherical pores and/or matrix pores, wherein the spherical pores preferably have a diameter within a range from sixty micrometers to six hundred micrometers, especially within a range from sixty micrometers to three hundred micrometers, and/or the matrix pores preferably have a pore size of less than thirty micrometers, especially less than ten micrometers.

38. The ceramic absorber as claimed in claim 37, wherein the spherical pores have pore windows, wherein the diameter of the pore windows is preferably within a range from forty micrometers to sixty micrometers, especially fifty micrometers.

39. The ceramic absorber as claimed in claim 34, wherein a density within a range from 0.55 g/cm.sup.3 to 0.70 g/cm.sup.3.

40. The ceramic absorber as claimed in claim 34, wherein a sound-absorbing action within a frequency range from twenty hertz to twenty kilohertz.

41. The ceramic absorber as claimed in claim 34, wherein a flow resistance within a range from 10 kPa/m.sup.2 to 3000 kPa/m.sup.2, preferably within a range from 50 kPa/m.sup.2 to 100 kPa/m.sup.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The process for producing a ceramic absorber is elucidated hereinafter with reference to the FIGURE. The FIGURE shows:

[0038] FIG. 1 a flow diagram of the progression of a process for producing a ceramic absorber.

DETAILED DESCRIPTION OF INVENTION

[0039] FIG. 1 shows a flow diagram of the progression of a process for producing a ceramic absorber. Process step S10 indicates the start of the process, process step S17 the end of the process.

[0040] In process step S11, a ceramic powder is provided. More particularly, the ratio of various components in the ceramic powder relative to one another is adjusted if the ceramic powder consists of more than one component.

[0041] There follows a description by way of example of the progression of the process for production of a ceramic absorber in which the ceramic powder consists of a material combination:

[0042] For production of a ceramic powder consisting of a material combination of silicate and oxide, in process step S11, one component from the class of the silicates and two components from the class of the oxides are combined. In the working example, the silicate used is mullite. More particularly, the fused mullite Alodur WFM (white fused mullite) from the manufacturer Treibacher is used, which has particle sizes of forty micrometers. From the class of the oxides, alumina is used. More particularly, both components are from the class of oxides of alumina. The aluminas used here are coarse-grain alumina and fine-grain alumina. The coarse-grain alumina used is the alumina Tabular Alumina T60, Li from the manufacturer Almatis, with particle sizes of less than forty-five micrometers. The fine-grain alumina used is the alumina CT-3000 SG from the manufacturer Alcoa, with particle sizes within a range from 0.5 micrometer to 0.8 micrometer and spherical particles. The ratio of alumina having coarser particles to alumina having finer particles is sixty percent by mass to forty percent by mass. The proportion of mullite and alumina in the working example is fifty percent by weight in each case. A different ratio of mullite to alumina may be provided. The ceramic powder may have a proportion of mullite within a range from fifty percent by weight to sixty percent by weight and a proportion of alumina within a range from forty percent by weight to fifty percent by weight.

[0043] In process step S12, a slip is produced. The dispersion medium used is silica sol. Silica sol is an aqueous colloidal suspension of silicon dioxide. In the working example, silica sol having thirty percent silicon dioxide and having a primary colloid size of eight nanometers is used. The ceramic powder and a dispersant are added to the silica sol. The dispersion is effected by means of addition of the dispersant. The dispersant used in the working example is the dispersant Dolapix CE 64, from Zschimmer & Schwartz.

[0044] In process step S13, the slip is foamed. A homogeneous pore distribution is generated in the foam structure. For this purpose, a foam former is first added to the slip. The foam former used in the working example is the foaming agent W53 from the manufacturer Zschimmer & Schwartz. After the foam former has been added, the slip is foamed with a stirrer. The foaming to different volumes enables generation of foams of different density. The foam density generated is within a range from 0.4 g/cm.sup.3 to 1.5 g/cm.sup.3. Owing to the very good foam stability, a homogeneous foam is formed.

[0045] In process step S14, the foam is shaped. For this purpose, the freshly foamed foam is poured into a nonabsorptive mold. More particularly, the nonabsorptive mold has a smooth inner wall. The fresh casting formed in this way remains in the mold until it has sufficient strength for demolding by virtue of self-consolidation.

[0046] In process step S15, the foam is solidified by means of self-consolidation. The self-consolidation is effected through agglomeration or through precipitation of the sol, on account of a drop in the pH resulting from the hydration of alumina particles. In this way, the moist ceramic foam solidifies of its own accord. Subsequently, the consolidated foam is dried stepwise.

[0047] In process step S16, the foam is sintered. In the working example, the sintering is effected at a temperature of 1700° C. and over a period of time of 2 hours. Sintering at a different temperature and/or over a different period of time may be envisaged. Shrinkage occurs in the course of sintering. The adjustment of the foam densities determines the porosity of the ceramic foam after sintering since the volume of air introduced and the porosity of the sintered ceramic correlate with one another. After the sintering, the ceramic body has a density within a range from 0.55 g/cm.sup.3 to 0.70 g/cm.sup.3.

[0048] There follows a description, likewise by way of example, of the progression of the process for producing a ceramic absorber, in which the ceramic powder consists either of silicate or of oxide:

[0049] For production of a ceramic powder consisting exclusively of silicate, the ceramic powder used in step S11 is mullite. More particularly, fused mullite Alodur WFM (white fused mullite) from the manufacturer Treibacher is used, which has particle sizes of forty micrometers. The further process steps S12 to S16 correspond to the process steps described above.

[0050] For production of a ceramic powder consisting exclusively of oxide, in process step S11, two components from the class of the oxides are combined. The oxide used in the working example is alumina. More particularly, both components from the class of the oxides are alumina. Both course-grain alumina and fine-grain alumina are used. The course-grain alumina used is the alumina Tabular Alumina T60, Li from the manufacturer Almatis, with particle sizes of less than forty-five micrometers. The fine-grain alumina used is the alumina CT-3000 SG from the manufacturer Alcoa, with particle sizes within a range from 0.5 micrometer to 0.8 micrometer and spherical particles. The ratio of alumina having coarser particles to alumina having finer particles is seventy percent by mass to thirty percent by mass.

[0051] In process step S12, a slip is produced based on water. The slip contains the ceramic powder consisting exclusively of oxide and a dispersant. The dispersion is effected by means of addition of the dispersant. The dispersant used in the working example is the dispersant Dolapix CE 64, from the manufacturer Zschimmer & Schwartz. Prior to the foaming of the slip that follows in process step S13, a binder for the subsequent consolidation is additionally supplied to the suspension.

[0052] In process step S13, the slip is foamed. A homogeneous pore distribution in the foam structure is generated. For this purpose, a foam former is first added to the slip. The foam former used in the working example is the foaming agent W53, from the manufacturer Zschimmer & Schwartz. Subsequently, the slip is foamed to completion with a stirrer. The foaming to different volumes enables generation of foams of different density. The foam density generated is within a range from 0.75 g/cm.sup.3 to 0.9 g/cm.sup.3.

[0053] In process step S14, the foam is shaped. For this purpose, the freshly foamed foam is poured into nonabsorptive molds. More particularly, the nonabsorptive molds have a smooth inner wall. The fresh casting formed in this way remains in the mold until it has sufficient strength for demolding by virtue of consolidation.

[0054] In process step S15, the foam is solidified by means of consolidation. The consolidation is effected by means of hydration of the binder added in process step S12. In this way, the moist ceramic foam solidifies of its own accord. Subsequently, the consolidated foam is dried stepwise.

[0055] In process step S16, the foam is sintered. In the working example, the sintering is effected at a temperature of 1700° C. and over a period of time of two hours. Sintering at a different temperature and/or over a different period of time may be envisaged. Shrinkage occurs in the course of sintering. The adjustment of the foam densities determines the porosity of the ceramic foam after sintering since the volume of air introduced and the porosity of the sintered ceramic correlate with one another. After the sintering, the ceramic body has a density within a range from 0.55 g/cm.sup.3 to 0.70 g/cm.sup.3.