GB2266677A - A method of leaching ceramic, eg alumina, cores from turbine blade castings - Google Patents
A method of leaching ceramic, eg alumina, cores from turbine blade castings Download PDFInfo
- Publication number
- GB2266677A GB2266677A GB9305293A GB9305293A GB2266677A GB 2266677 A GB2266677 A GB 2266677A GB 9305293 A GB9305293 A GB 9305293A GB 9305293 A GB9305293 A GB 9305293A GB 2266677 A GB2266677 A GB 2266677A
- Authority
- GB
- United Kingdom
- Prior art keywords
- leaching
- liquor
- ceramic material
- pressure
- enclosure
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 238000002386 leaching Methods 0.000 title claims abstract description 55
- 238000000034 method Methods 0.000 title claims abstract description 43
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 title claims abstract description 25
- 239000000919 ceramic Substances 0.000 title description 10
- 238000005266 casting Methods 0.000 title description 7
- 238000009835 boiling Methods 0.000 claims abstract description 25
- RUDFQVOCFDJEEF-UHFFFAOYSA-N yttrium(III) oxide Inorganic materials [O-2].[O-2].[O-2].[Y+3].[Y+3] RUDFQVOCFDJEEF-UHFFFAOYSA-N 0.000 claims abstract description 9
- 238000005495 investment casting Methods 0.000 claims abstract description 7
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims abstract description 4
- 238000013019 agitation Methods 0.000 claims abstract description 4
- 229910017604 nitric acid Inorganic materials 0.000 claims abstract description 4
- 238000011065 in-situ storage Methods 0.000 claims abstract description 3
- 238000007789 sealing Methods 0.000 claims abstract description 3
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 23
- 229910010293 ceramic material Inorganic materials 0.000 claims description 20
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 12
- 239000000377 silicon dioxide Substances 0.000 claims description 9
- 239000002253 acid Substances 0.000 claims description 8
- 229910001854 alkali hydroxide Inorganic materials 0.000 claims description 7
- 150000008044 alkali metal hydroxides Chemical class 0.000 claims description 7
- 230000000694 effects Effects 0.000 claims description 7
- 239000000126 substance Substances 0.000 claims description 5
- WCUXLLCKKVVCTQ-UHFFFAOYSA-M Potassium chloride Chemical compound [Cl-].[K+] WCUXLLCKKVVCTQ-UHFFFAOYSA-M 0.000 claims description 4
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 claims description 4
- 239000003513 alkali Substances 0.000 claims description 4
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 claims description 3
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims description 3
- 150000004820 halides Chemical class 0.000 claims description 3
- 229910052744 lithium Inorganic materials 0.000 claims description 3
- 229910052708 sodium Inorganic materials 0.000 claims description 3
- 239000011734 sodium Substances 0.000 claims description 3
- 239000007864 aqueous solution Substances 0.000 claims description 2
- 229910052792 caesium Inorganic materials 0.000 claims description 2
- TVFDJXOCXUVLDH-UHFFFAOYSA-N caesium atom Chemical compound [Cs] TVFDJXOCXUVLDH-UHFFFAOYSA-N 0.000 claims description 2
- 239000001103 potassium chloride Substances 0.000 claims description 2
- 235000011164 potassium chloride Nutrition 0.000 claims description 2
- 239000011780 sodium chloride Substances 0.000 claims description 2
- ZDCPCNYMFTYBBX-UHFFFAOYSA-N potassium rubidium Chemical compound [K].[Rb] ZDCPCNYMFTYBBX-UHFFFAOYSA-N 0.000 claims 1
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 abstract description 24
- 238000001816 cooling Methods 0.000 abstract description 7
- 239000011162 core material Substances 0.000 description 32
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 10
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 6
- 239000000654 additive Substances 0.000 description 6
- 230000000996 additive effect Effects 0.000 description 6
- 229910045601 alloy Inorganic materials 0.000 description 6
- 239000000956 alloy Substances 0.000 description 6
- 229910052759 nickel Inorganic materials 0.000 description 5
- 239000000203 mixture Substances 0.000 description 4
- 230000002378 acidificating effect Effects 0.000 description 3
- HUCVOHYBFXVBRW-UHFFFAOYSA-M caesium hydroxide Chemical class [OH-].[Cs+] HUCVOHYBFXVBRW-UHFFFAOYSA-M 0.000 description 3
- 239000000498 cooling water Substances 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 229910000601 superalloy Inorganic materials 0.000 description 3
- 229910000838 Al alloy Inorganic materials 0.000 description 2
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 description 2
- 229910000861 Mg alloy Inorganic materials 0.000 description 2
- 239000004411 aluminium Substances 0.000 description 2
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
- 239000003795 chemical substances by application Substances 0.000 description 2
- 238000004891 communication Methods 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 239000012633 leachable Substances 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 229910052701 rubidium Inorganic materials 0.000 description 2
- IGLNJRXAVVLDKE-UHFFFAOYSA-N rubidium atom Chemical compound [Rb] IGLNJRXAVVLDKE-UHFFFAOYSA-N 0.000 description 2
- CPRMKOQKXYSDML-UHFFFAOYSA-M rubidium hydroxide Chemical compound [OH-].[Rb+] CPRMKOQKXYSDML-UHFFFAOYSA-M 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 239000002904 solvent Substances 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 description 1
- 229910001069 Ti alloy Inorganic materials 0.000 description 1
- 150000007513 acids Chemical class 0.000 description 1
- 239000011449 brick Substances 0.000 description 1
- 239000008364 bulk solution Substances 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 239000003518 caustics Substances 0.000 description 1
- 239000007795 chemical reaction product Substances 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 150000004679 hydroxides Chemical class 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 239000011777 magnesium Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 239000000206 moulding compound Substances 0.000 description 1
- 239000008188 pellet Substances 0.000 description 1
- 229910052700 potassium Inorganic materials 0.000 description 1
- 239000011591 potassium Substances 0.000 description 1
- 230000000750 progressive effect Effects 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D29/00—Removing castings from moulds, not restricted to casting processes covered by a single main group; Removing cores; Handling ingots
- B22D29/001—Removing cores
- B22D29/002—Removing cores by leaching, washing or dissolving
Abstract
A method of leaching an alumina core 18 from a cooling passage 12 within a turbine blade 10 that has been cast by an investment casting process comprises the steps of, (a) placing the blade together with the alumina core in situ in a sealable vessel 22 containing a concentrated aqueous potassium hydroxide leaching liquor 20 at a temperature immediately below its normal atmospheric boiling point eg 213 DEG C, (b) sealing the vessel, (c) reducing the pressure within the vessel to less than atmospheric pressure so as to induce boiling and agitation of the leaching liquor within the passage in the blade, (d) raising the pressure in the vessel to atmospheric pressure, (e) repeating steps (b)-(d) as necessary, and finally removing spent leaching liquor together with leached alumina core from within the blade. An yttria core may be removed by the method using nitric acid. <IMAGE>
Description
2266677 IMPROVEMENTS IN OR RELATING TO THE LEACHING OF CERAMIC MATERIALS
This invention concerns improvements in or relating to the leaching of ceramic materials. In particular, it relates to the leaching of preformed ceramic cores in an investment casting process.
in high performance gas turbine engines, for instance those used in aircraft, certain components such as engine turbine blades are subject to high temperatures which may be near or even above the melting point of the alloy of which the blades are composed. When the engine is operated at high temperatures the blades are cooled by passing relatively cold air through passages within the blades. Consequently, the blades are able to function successfully in a gas stream which is at a temperature above the melting point of the blade material. The ability of a gas turbine engine to run at high temperatures is one of the most important factors controlling its power output. The ability of components such as blades and vanes to withstand high temperatures is therefore of great importance.
The cooling passages within the blades have to be carefully designed in order to achieve their objective and are frequently of labyrinthine complexity. Such complexity can only conveniently be achieved by investment casting techniques around male cores formed in the shape and configuration of the passages that are to be made.
It will be understood that the term "passage" in the context of the present invention implies any hollow portion within an article that has communication with the outside of the article, and includes cavities that have such communication.
In the investment casting of blades it is necessary to fabricate the cores of a material which can not only withstand and be inert to the molten alloy used to cast the blades, but which can subsequently be easily removed so as to form the required passages. Preformed ceramic cores are usually used for this purpose and, although in the simplest cases the ceramic may be removable by mechanical means after the alloy has solidified, in those cases where the passages are of a complex shape and mechanical removal of the core is not possible, it will be necessary to leach or dissolve the ceramic from within the casting.
Hitherto, most preformed ceramic cores for investment casting have been based on silica compositions. The silica is leached out after casting is complete by means of aqueous alkali hydroxides which do not corrode to any significant extent the alloys and superalloys now used in high performance gas turbine engines.
The requirement that the preformed core should be leachable has hitherto restricted the use of other core materials having high temperature properties superior to those of silica.
One such core material is alumina, which possesses desired properties in that it is refractory and chemically inert to molten nickel-based alloys. Alumina is suitable for superalloys and is soluble in aqueous alkali hydroxides, but with slow rates of leaching when compared with silica.
Yet another attractive core material is yttria which is inert to a wide range of casting alloys, including alloys of titanium, aluminium and magnesium. However, the very inertness of alumina and yttria renders these core materials significantly more difficult to remove from labyrinthine passages than core materials based on silica.
Methods of making alumina core bodies which are sufficiently leachable so that they are able to provide a usable leaching time have been disclosed in the prior art.
A first such prior art method uses an alumina core material that has a high porosity but a smooth surface. The prior art suggests that over 50% porosity is required even to approach the conventional leaching times encountered with silica cores. This method is inherently expensive and is not extensively used.
A second prior art method proposes increasing the porosity of the alumina core material by adding carbon as a burn-off additive to the moulding compound in the manufacture of cores, in much the same manner that porous ceramic bricks are made.
We believe that about 50% porosity is the practical limit for easy alumina core manufacture using an additive that can be burned off, and not the higher porosities envisaged by the first prior art method.
When alumina is used as a core material it is necessary in the prior art leaching methods to increase the leaching reaction rate by increasing the activity of the caustic alkali leaching liquor. This is done by using an autoclave. This technique is also used for the removal of silica cores.
There are three commonly used systems for silica core removal, viz:
(1) a 20-40% aqueous sodium hydroxide solution boiling at about 1200C (at normal atmospheric pressure ie 1014 millibar); (2) a low pressure autoclave operating at about 80psi (5.6kg/CM2), at a temperature up to 1600C, with intermittent release of the pressure to boil the solution (i.e. to agitate the liquor); (3) a high pressure autoclave operating in the range 1000psi (70kg/Cm2) at about 250C to 1500psi (105kg/CM2) at 3500C.
We have found that alumina cores with 45-50% porosity are not effectively leached by a silica core removal cycle as typified in methods (1) and (2) above, but that method (3) will remove alumina cores, albeit at a significantly slower rate than for silica. It will be appreciated that method (3) also has the disadvantage that a high pressure autoclave is a significant capital expense and is expensive to operate.
It is an object of the present invention to provide a method of leaching ceramic cores, especially those made of alumina, silica or yttria, that avoids the use of a high pressure autoclave and the expense inherent therein.
According to the present invention there is provided a method of leaching a ceramic material from a passage within an article, the method comprising the steps of, (a) placing the article together with the ceramic material in situ therein in a sealable enclosure, in which there is provided a leaching liquor at a temperature immediately below its normal atmospheric boiling point, (b) sealing the enclosure, (c) for a first period of time, maintaining the liquor in a quiescent state in contact with the ceramic material, (d) reducing the pressure within the enclosure to less than atmospheric pressure so as to induce boiling and agitation of the leaching within said passage within the article for a second period of time, thereby to enhance leaching of the ceramic material within the passage, (e) raising the pressure within the enclosure to atmospheric pressure, and returning the liquor to a quiescent state, (f) removing spent leaching liquor together with leached ceramic material from within the article.
The enclosure may also have access to the external atmosphere via a water cooled condenser.
The method preferably includes repeating steps (c)-(e) at least once before step (f) is carried out.
Preferably, in step (d) the pressure within the enclosure is reduced below atmospheric pressure by no more than 0.45bar, and typically 0.2 bar.
Preferably, when the ceramic material is based on silica or alumina, the leaching liquor has as its active component an aqueous solution of one or more alkali hydroxide having the formula MOH, where M is selected from the group consisting of lithium, sodium, potassium, rubidium and cesium. The molar ratio of MOH:H 2 0 is preferably 1.8:1.
Preferably, when the ceramic material is yttria, the leaching liquor has an acid as its active component. The acid may be nitric acid.
The leaching liquor may contain a further component adapted to raise the boiling point of the liquor without otherwise increasing the concentration of the active component.
The further component may be inert, or it may be adapted to enhance the leaching activity of the active component.
The ceramic material may be a prefabricated structure, and may be a core for an investment casting.
The invention will now be described by way of example only with reference to the accompanying diagrammatic Figure 1 which shows a section through an apparatus for carrying out the invention, together with a longitudinal section through a turbine blade provided with a cooling passage.
Referring to Figure 1 there is shown in longitudinal section an aero engine turbine blade 10 provided with a internal cooling passage 12 having exits 14, 16 at the root of the blade. For the sake of simplicity the blade and the cooling passage are shown stylised; in practice the cooling passage is likely to be of far more complex configuration.
The blade 10, as illustrated, has been cast in, and subsequently removed from, an alumina faced mould (not shown); but the cooling passage 12 still retains within it an alumina core structure 18 left over from the casting process. In practical terms, if the core shape has any degree of complexity the core will effectively be impossible to remove mechanically and will only be removeable by chemical methods.
The blade 10 is shown immersed in a leaching liquor 20 comprising a composition consisting nominally of 85% by weight of potassium hydroxide and 15% by weight of water (ie a molar ratio of KOH:H 2 0 of about 1.8:1), and contained in a nickel vessel or enclosure 22. The vessel 22 is provided with heating coils 24, a thermocouple 42, and a water cooled condenser 25 with inlet and outlet pipes to allow the flow of cooling water 38 40. The vessel 22 is also provided with a removeable cover 26 to allow access in operation.
The exit end of the condenser 25 is provided with a switchable tap 30 allowing the enclosure 22 to be either open to ambient atmospheric pressure 34 through the condenser, or linked to a vacuum reservoir 28 via the tap. The vacuum reservoir is maintained under vacuum by a conventional water trap and vacuum pump unit 32. By operating the tap 30, the enclosure 22 can either be at atmospheric pressure or at a sub- atmospheric pressure depending on the position of the tap.
In an example, the leaching liquor 20 as specified above was prepared and the enclosure 22 filled with the liquor to a suitable level. Suitable cast blades 10 were placed in a nickel basket, immersed in the liquor 20, and the lid 26 of the vessel sealed down. The liquor 20 was then heated by means of the heating coils 24, the tap 30 being set so that the vessel and its contents were at atmospheric pressure, until the liquor boiled. At the same time as the liquor was being heated the condenser cooling water was turned on to prevent loss of water. The precise boiling point of the liquor was determined by means of the immersed thermocouple 42.
Since alkali hydroxides have a tendency to absorb moisture if supplied in the flake or pellet form it was necessary to adjust the natural boiling point of the liquor either by boiling off some water from the liquor, by stopping the flow of cooling water through the condenser for a short period, or carefully adding more water to the liquor to obtain the desired temperature. Even with an accurately set up chemical composition minor adjustment may be required due to slight variations in atmospheric pressure that may occur. The boiling point aimed for was 225 0 C which was have found to be sufficient to leach alumina cores.
The temperature of the liquor was then allowed to fall to 213 0 C, 12 0 below the set boiling point. The liquor at this temperature started to dissolve the alumina ceramic material at the open ends of the core passages 14,16. This was allowed to continue for 10 minutes. A small reduction in pressure was then applied to the system by changing the switch 30 to the position 36 connecting the vacuum reservoir with the enclosure through the condenser, thereby reducing the pressure to about 0. 75 bar.
The reduction in pressure caused the liquor to boil, as could be viewed through a sight gloss in the vessel (not shown). This boiling condition was allowed to continue for 16 seconds when the switch 30 was returned to atmospheric pressure, thus creating a further quiescent condition in the liquor.
The procedure of reducing the pressure within the vessel 22 so as to induce boiling of the leaching liquor 20 within the vessel, and maintaining the concentration and predetermined natural boiling point by preventing any moisture fro escaping using a condenser, and returning the system back to atmospheric pressure, was then repeated throughout the leaching cycle until the alumina core 18 was completely removed.
We have found that the above exemplified leaching liquor composition of 85:15 potassium hydroxide:water (boiling point 225C) is highly active in dissolving alumina. An even higher concentration of the leaching liquor, for example, 90:10 potassium hydroxide:water with a boiling point in excess of 2250C, may also be used, but the chemical activity of such a concentration is so high that it may not be suitable for use with some superalloys and may in fact even corrode stainless steel. We have chosen nickel as the material for the vessel 22 because nickel is resistant to the effects of such high concentrations of potassium hydroxide in the long term.
An alternative alkaline leaching agent to potassium hydroxide may be one or more hydroxides selected from the group consisting of sodium, lithium, rubidium and cesium hydroxides. We have found that a suitable concentration of the alkaline leaching agent to give satisfactory performance when leaching alumina is a molar ratio of hydroxide to water of about 1.8:1. This is equivalent to the following percentage weights of alkaline hydroxide in the aqueous leaching liquor:
KOH 85 NaOH 80 RbOH 91 CsOH 93.75 LiOH 70.5 The high temperature of reaction of the leaching liquor with the alumina before boiling occurs may also be achieved by adding an additive to the leaching liquor. This has the advantage of reducing the amount of alkali hydroxide required whilst raising the boiling point. The additive is preferably chemically inert, and may be an alkali halide such as sodium chloride or potassium chloride. However, circumstances may be envisaged wherein the additive may not be inert and may be chosen to enhance the chemical activity of the leaching liquor. A non-inert additive may for example be another alkali hydroxide.
The principles exemplified above whereby there is provided active concentration of liquor to maintain a high temperature and creating a boil condition to agitate the liquor can also be applied to other ceramics and solvents. For instance, the invention contemplates the acid leaching of a ceramic core material which reacts with acid. One such core material is pure yttria which has desirable high temperature properties and can be used for the casting of reactive metals such as aluminium or magnesium alloys, to which yttria is very inert. Yttria may be leached by acids such as nitric acid.
The choice of a leaching liquor, whether alkaline or acidic, should be made on the twin aims of higher leaching rate and minimum corrosion of the casting. In the case of an acidic leaching liquor it is preferable to choose an acid of relatively low volatility to maintain proper control of the solvent throughout the process.
It should be noted that one of the reaction products of both alkaline and acidic leaching liquors during the leaching process is water. This implies that deep within partially cleared core passages, just where agitation is needed to remove partially spent liquor, the reaction face liquor will be slightly diluted compared to the external bulk of the liquor, and this is progressive as the reaction proceeds. Due to depleted liquor, the reaction will slow down, particularly within deep passages, and the boiling point of the liquor here will be less than the bulk boiling point. By operating a few degrees below the bulk boiling point we can obtain a quiescent condition where a slight system pressure reduction will drive the spent leaching liquor out without excessive boiling of the bulk solution. This has the effect of being able to optimise the time that liquor will be in contact with the exposed core material. By choice of temperature of operation, and reduction in pressure, bulk liquor boil can be avoided if so desired. The pressure may for instance be reduced by anything between 0.2 and 0.45 bar, if required.
The method of the invention, using alkaline hydroxide leaching liquor, may also be used to remove silica cores.
Claims (17)
- A method of leaching a ceramic material from a passage within an article, the method comprising the steps of, (a) placing the article together with the ceramic material in situ therein in a sealable enclosure, in which there is provided a leaching liquor at a temperature immediately below its normal atmospheric boiling point, (b) sealing the enclosure, (c) for a first period of time, maintaining the liquor in a quiescent state in contact with the ceramic material, (d) reducing the pressure within the enclosure to less than atmospheric pressure so as to induce boiling and agitation of the leaching within said passage within the article for a second period of time, thereby to enhance leaching of the ceramic material within the passage, (e) raising the pressure within the enclosure to atmospheric pressure, and returning the liquor to a quiescent state, (f) removing spent leaching liquor together with leached ceramic material from within the article.
- 2 A method as claimed in claim 1 wherein in step (d) the pressure within the enclosure is reduced below atmospheric by no more than 0.45 bar.
- 3 A method as claimed in claim 2 wherein the pressure is reduced below atmospheric by about 0.25 bar.
- 4 A method as claimed in any preceding claim wherein, when the ceramic material is based on alumina or silica, the leaching liquor has as its active component in aqueous solution an alkali hydroxide having the formula MOH, where M is selected from the group consisting of lithium, sodium, potassium rubidium and cesium.
- A method as claimed in claim 4 wherein the molar ratio of MOH:H 2 0 is 1. 8:1.
- 6 A method as claimed in any one of claims 1 to 3 wherein, when the ceramic material is yttria, the leaching liquor has an acid as its active component.
- 7 A method as claimed in claim 6 wherein the acid is nitric acid.
- 8 A method as claimed in any preceding claim wherein the leaching liquor contains a further component adapted to raise the boiling point of the liquor without otherwise increasing the concentration of the active component.
- 9 A method as claimed in claim 8 wherein the further component is an inert substance.
- A method as claimed in claim 8 or 9 wherein the further component is adapted to enhance the leaching activity of the active component.
- 11 A method as claimed in claim 9 or 10 wherein the further component is an alkali halide.
- 12 A method as claimed in claim 11 wherein the alkali halide is selected from the group consisting of sodium chloride and potassium chloride.
- 13 A method as claimed in any preceding claim including repeating steps (c)-(e) at least once before step (f) is carried out.
- 14 A method as claimed in any preceding claim wherein the ceramic material is a prefabricated structure.
- A method as claimed in claim 14 wherein the prefabricated structure is a core for an investment casting.
- 16 A method as claimed in any preceding claim wherein the enclosure is provided with access to the external atmosphere via a water cooled condenser.
- 17 A method of leaching a ceramic material from a passage within an article substantially as hereinbefore described with reference to the accompanying drawing and example.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9305293A GB2266677B (en) | 1992-05-08 | 1993-03-15 | Improvements in or relating to the leaching of ceramic materials |
| US08/053,263 US5332023A (en) | 1992-05-08 | 1993-04-28 | Leaching of ceramic materials |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB929210008A GB9210008D0 (en) | 1992-05-08 | 1992-05-08 | Improvements in or relating to the leaching of ceramic materials |
| GB9305293A GB2266677B (en) | 1992-05-08 | 1993-03-15 | Improvements in or relating to the leaching of ceramic materials |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9305293D0 GB9305293D0 (en) | 1993-05-05 |
| GB2266677A true GB2266677A (en) | 1993-11-10 |
| GB2266677B GB2266677B (en) | 1995-02-01 |
Family
ID=26300853
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9305293A Expired - Lifetime GB2266677B (en) | 1992-05-08 | 1993-03-15 | Improvements in or relating to the leaching of ceramic materials |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US5332023A (en) |
| GB (1) | GB2266677B (en) |
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| EP0747151A1 (en) * | 1995-06-07 | 1996-12-11 | Howmet Corporation | Method and apparatus for removing cores from castings |
| US6132520A (en) * | 1998-07-30 | 2000-10-17 | Howmet Research Corporation | Removal of thermal barrier coatings |
| EP1782899A3 (en) * | 2005-10-27 | 2007-11-21 | United Technologies Corporation | Method for casting core removal |
| EP2471615A1 (en) * | 2010-12-30 | 2012-07-04 | Rolls-Royce Corporation | System, method and apparatus for leaching cast components |
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| US5814161A (en) * | 1992-11-30 | 1998-09-29 | Massachusetts Institute Of Technology | Ceramic mold finishing techniques for removing powder |
| US5779809A (en) * | 1995-12-26 | 1998-07-14 | General Electric Company | Method of dissolving or leaching ceramic cores in airfoils |
| JP3297305B2 (en) * | 1996-06-13 | 2002-07-02 | 三菱重工業株式会社 | Method for removing clogged dust from honeycomb catalyst |
| US6194026B1 (en) * | 1998-10-19 | 2001-02-27 | Howmet Research Corporation | Superalloy component with abrasive grit-free coating |
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| US3698467A (en) * | 1971-01-04 | 1972-10-17 | United Aircraft Corp | Method of removing silaceous cores from nickel and cobalt superalloy castings |
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Cited By (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0744233A2 (en) * | 1995-05-22 | 1996-11-27 | Howmet Corporation | Removal of ceramic shell mold material from castings |
| EP0744233A3 (en) * | 1995-05-22 | 1997-02-26 | Howmet Corp | Removal of ceramic shell mold material from castings |
| US5678583A (en) * | 1995-05-22 | 1997-10-21 | Howmet Research Corporation | Removal of ceramic shell mold material from castings |
| US5913354A (en) * | 1995-05-22 | 1999-06-22 | Howmet Research Corporation | Removal of ceramic shell mold material from castings |
| EP0747151A1 (en) * | 1995-06-07 | 1996-12-11 | Howmet Corporation | Method and apparatus for removing cores from castings |
| US5915452A (en) * | 1995-06-07 | 1999-06-29 | Howmet Research Corporation | Apparatus for removing cores from castings |
| US6241000B1 (en) | 1995-06-07 | 2001-06-05 | Howmet Research Corporation | Method for removing cores from castings |
| US6132520A (en) * | 1998-07-30 | 2000-10-17 | Howmet Research Corporation | Removal of thermal barrier coatings |
| EP1782899A3 (en) * | 2005-10-27 | 2007-11-21 | United Technologies Corporation | Method for casting core removal |
| EP2471615A1 (en) * | 2010-12-30 | 2012-07-04 | Rolls-Royce Corporation | System, method and apparatus for leaching cast components |
| US8828214B2 (en) | 2010-12-30 | 2014-09-09 | Rolls-Royce Corporation | System, method, and apparatus for leaching cast components |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2266677B (en) | 1995-02-01 |
| US5332023A (en) | 1994-07-26 |
| GB9305293D0 (en) | 1993-05-05 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PE20 | Patent expired after termination of 20 years |
Expiry date: 20130314 |