CA2152977A1 - Xerogels, a process for their preparation, and their use - Google Patents
Xerogels, a process for their preparation, and their useInfo
- Publication number
- CA2152977A1 CA2152977A1 CA002152977A CA2152977A CA2152977A1 CA 2152977 A1 CA2152977 A1 CA 2152977A1 CA 002152977 A CA002152977 A CA 002152977A CA 2152977 A CA2152977 A CA 2152977A CA 2152977 A1 CA2152977 A1 CA 2152977A1
- Authority
- CA
- Canada
- Prior art keywords
- gel
- water
- employed
- organic solvent
- xerogels
- 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.)
- Abandoned
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/113—Silicon oxides; Hydrates thereof
- C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
- C01B33/14—Colloidal silica, e.g. dispersions, gels, sols
- C01B33/152—Preparation of hydrogels
- C01B33/154—Preparation of hydrogels by acidic treatment of aqueous silicate solutions
- C01B33/1543—Preparation of hydrogels by acidic treatment of aqueous silicate solutions using ion exchangers
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/113—Silicon oxides; Hydrates thereof
- C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
- C01B33/14—Colloidal silica, e.g. dispersions, gels, sols
- C01B33/152—Preparation of hydrogels
- C01B33/154—Preparation of hydrogels by acidic treatment of aqueous silicate solutions
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B30/00—Compositions for artificial stone, not containing binders
Abstract
The invention relates to modified SiO2 gels (xerogels), the preparationthereof and the use thereof as thermal insulators. The xerogels are prepared by acidifying an aqueous waterglass solution, polycondensing the silicic acid produced thereby, by adding a base, to an SiO2 gel, removing the water from the resulting gel by extractive distillation with an organic solvent which forms with water an azeotrope which separates on cooling into two phases, reacting the gel with a silylating agent, and then drying at pressures and temperatures which are below the critical pressure and/or the critical temperature of the organic solvent used for removing the water.
Description
21~2977 HOECHST AKTIENGESELLSCHAFT HOE 94/F 187 Dr.DK/pp Description Xerogels, a process for their preparation, and their use The invention relates to a process for the preparation of modified SiO2 gels, called "xerogels" hereinafter, and to the xerogels prepared in this way themselves and to the use thereof.
Aerogels in the wider sense, i.e. in the sense of "gel with air as dispersion medium", are prepared by drying a suitable gel. The term "aerogel" in this sense includes the aerogels in the narrower sense, xerogels and cryogels. In this connection, a dried gel is designated an aerogel in the narrower sense when the liquid of the gel is removed very substantially at temperatures above the critical temperature and starting from pressures above the critical pressure. On the other hand, if the liquid of the gel is removed under subcritical conditions, for example with formation of a liquid/vapor boundary phase, the resulting gel is then designated a xerogel.
The prepared xerogels are related to the customary SiO2 aerogels but are not identical to them.
SiO2 aerogels are known to have an excellent insulating action. They are prepared, for example, by acid hydrolysis of tetraethyl orthosilicate in ethanol. The hydrolysis results in a gel whose structure is determined by the temperature, the pH and the duration of the gelling process. However, in general, the gel structure collapses on drying the wet gels because the capillary forces arising during the drying are extremely large. The collapse of the gel can be prevented by carrying out the drying above the critical temperature and the critical pressure of the solvent. Since the liquid/gas phase boundary disappears in this region, the capillary forces also do not apply, and the gel does not change during the drying, i.e. there is no shrinkage of the gel during the drying either. Preparation processes based on this drying technique, are disclosed, for example, in EP-A-0 396 076 or W0 92 03378. However, this technique requires, for example when ethanol is used, a temperature above 240C and pressures above 40 bar. Although replacement of ethanol by C02 before the drying lowers the drying temperature to about 40C, the pressure required is then 80 bar.
It has now been found that SiO2 gels can be dried under subcritical conditions when they are reacted before the drying with a silylating agent. The resulting products are designated "xerogels" hereinafter.
They are excellent thermal insulators.
The invention relates to a process for the preparation of xerogels, which comprises a) adjusting an aqueous waterglass solution to a pH < 3.0, preferably c 2.2, using an acid ion exchange resin or a mineral acid, b) polycondensing the silicic acid produced thereby, by adding a base, to an SiO2 gel and, if a mineral acid was used in step a), washing the gel with water until free of electrolytes where appropriate, c) removing the water from the gel obtained in step b) by extractive distillation with an organic solvent which forms with water an azeotrope which separates into two phases on cooling, until the water content of the gel is < 5% by weight, d) reacting the gel obtained in step c) with a silylating agent, e) drying the silylated gel obtained in step d) at pressures and temperatures which are below the critical pressure and/or the critical temperature of the organic solvent used in step c).
2l~2~77 An acid ion exchange resin is preferably employed in step a);
particularly suitable for this purpose are those which contain sulfonic acid groups. If mineral acids are employed, hydrochloric acid and sulfuric acid are particularly suitable. In general, sodium and/or potassium waterglass is used as waterglass. The concentration of the waterglass is thereby preferably in the range from 1 to 20 % by weight and most preferably in the range from 5 to 12 % by weight.
The base preferably employed in step b) is NH40H, NaOH, KOH, Al(OH)3 and/or colloidal silicic acid. If a mineral acid was used in step a), the SiO2 gel produced using the base is washed where appropriate with water until free of electrolytes; washing is preferably continued until the draining wash water has the same electrical conductivity as demineralized water.
Before step c), the gel is preferably allowed to age, in general at O to 1 50C, preferably at 80 to 1 30C, and at a pH of 4 to 11, preferably 4 to 9. The time for this is generally from 10 seconds to 48 hours, preferably from 10 seconds to 5 hours.
In step c), the water contained in the gel is removed by extractive distillation with an organic solvent until the water content of the gel does not exceed 5% by weight and is preferably s 2% by weight. The solvent employed must form with water an azeotrope which separates into two liquid phases on cooling, an aqueous phase an a solvent phase. Examples of suitable solvents are toluene, di-n-butyl ether or methyl isobutyl ketone. Toluene is preferably used.
The solvent phase resulting on cooling of the azeotrope can be returned to the process.
Steps a) to c) are generally carried out at a temperature between the freezing point of the solution and the boiling point of the solvent.
21~2977 _~ 4 In step d), the solvent-containing gel is reacted with a silylating agent.
The silylating agents employed are generally silanes of the formulae R14 nSiCln or R14 nSi(OR2)n with n = 1 to 3, where R1 and R2 are, independently of one another, C1-C6-alkyl, cyclohexyl or phenyl.
Silazanes are also suitable. Mono, di- or trimethylchlorosilane, trimethylmethoxysilane or hexamethyl-disilazane is preferably used.
The reaction is generally carried out at 20 to 100C, preferably 30 to 70C, if necessary in a solvent such as toluene, acetone, n-hexane, n-heptane, di-n-butyl ether, i-propanol or methyl isobutyl ketone. The silylation can also be carried out, where appropriate, under pressure, preferably up to 25 bar. Where appropriate, the silylated gel can also be washed before drying.
In step e), the silylated gel is dried at temperatures from -30 to the boiling point of the solvent, preferably from -30 to 200C, particularly preferably from 0 to 1 50C. The pressures used for the drying are preferably from 0.001 to 20 bar, particularly preferably from 0.01 to 5 bar. The drying is generally continued until the gel has a remaining solvent content of less than 0.1% by weight.
To obtain special thermal properties it may be advantageous for the xerogel additionally to contain IR opacifiers (such as, for example, carbon black, titanium dioxide, iron oxides and zirconium dioxide).
These IR opacifiers are preferably added before step b) in such cases.
The process according to the invention is to be illustrated by an example.
Example 1 1 of a sodium waterglass solution (with a content of 6% by weight SiO2 and an Na20:SiO2 ratio of 2:3) was passed through a column (diameter 50 mm, length 300 mm) which was packed with 0.5 1 of an 21~2977 acid ion exchange resin (styrene/divinylbenzene copolymer with sulfonic acid groups, commercially available under the name ~Duolite C20). The solution flowing out had a pH of 1.5. The solution was then adjusted to a pH of 5.6 with 1 molar NH40H solution. The resulting gel was then aged at 50C for 24 hours and subsequently the water was extracted using 3 1 of toluene in an extraction vessel with water separator at about 100C. The extraction was stopped when the calculated amount of water (about 920 ml) had separated out. The toluene-containing gel was then silylated with trimethylchlorosilane (TMCS) at 50C for 12 hours (0.05 9 of TMCS
per gram of toluene-containing gel). The gel was dried in a drier flushed with N2 under atmospheric pressure (6 hours at 40C then 2 hours at 50C and 12 hours at 150C) .
The transparent xerogel obtained in this way had a density of 0.12 g/cm3. The BET specific surface area was 920 m2/g. The ,1 value was 0.016 W/mK.
The thermal conductivity was measured by a hot wire method (see, for example, 0. Nielsson, G. Ruschenpohler, J. Grol3, J. Fricke, High-Temperatures-High-Pressures, Vol. 21, 267-274 (1989)).
Aerogels in the wider sense, i.e. in the sense of "gel with air as dispersion medium", are prepared by drying a suitable gel. The term "aerogel" in this sense includes the aerogels in the narrower sense, xerogels and cryogels. In this connection, a dried gel is designated an aerogel in the narrower sense when the liquid of the gel is removed very substantially at temperatures above the critical temperature and starting from pressures above the critical pressure. On the other hand, if the liquid of the gel is removed under subcritical conditions, for example with formation of a liquid/vapor boundary phase, the resulting gel is then designated a xerogel.
The prepared xerogels are related to the customary SiO2 aerogels but are not identical to them.
SiO2 aerogels are known to have an excellent insulating action. They are prepared, for example, by acid hydrolysis of tetraethyl orthosilicate in ethanol. The hydrolysis results in a gel whose structure is determined by the temperature, the pH and the duration of the gelling process. However, in general, the gel structure collapses on drying the wet gels because the capillary forces arising during the drying are extremely large. The collapse of the gel can be prevented by carrying out the drying above the critical temperature and the critical pressure of the solvent. Since the liquid/gas phase boundary disappears in this region, the capillary forces also do not apply, and the gel does not change during the drying, i.e. there is no shrinkage of the gel during the drying either. Preparation processes based on this drying technique, are disclosed, for example, in EP-A-0 396 076 or W0 92 03378. However, this technique requires, for example when ethanol is used, a temperature above 240C and pressures above 40 bar. Although replacement of ethanol by C02 before the drying lowers the drying temperature to about 40C, the pressure required is then 80 bar.
It has now been found that SiO2 gels can be dried under subcritical conditions when they are reacted before the drying with a silylating agent. The resulting products are designated "xerogels" hereinafter.
They are excellent thermal insulators.
The invention relates to a process for the preparation of xerogels, which comprises a) adjusting an aqueous waterglass solution to a pH < 3.0, preferably c 2.2, using an acid ion exchange resin or a mineral acid, b) polycondensing the silicic acid produced thereby, by adding a base, to an SiO2 gel and, if a mineral acid was used in step a), washing the gel with water until free of electrolytes where appropriate, c) removing the water from the gel obtained in step b) by extractive distillation with an organic solvent which forms with water an azeotrope which separates into two phases on cooling, until the water content of the gel is < 5% by weight, d) reacting the gel obtained in step c) with a silylating agent, e) drying the silylated gel obtained in step d) at pressures and temperatures which are below the critical pressure and/or the critical temperature of the organic solvent used in step c).
2l~2~77 An acid ion exchange resin is preferably employed in step a);
particularly suitable for this purpose are those which contain sulfonic acid groups. If mineral acids are employed, hydrochloric acid and sulfuric acid are particularly suitable. In general, sodium and/or potassium waterglass is used as waterglass. The concentration of the waterglass is thereby preferably in the range from 1 to 20 % by weight and most preferably in the range from 5 to 12 % by weight.
The base preferably employed in step b) is NH40H, NaOH, KOH, Al(OH)3 and/or colloidal silicic acid. If a mineral acid was used in step a), the SiO2 gel produced using the base is washed where appropriate with water until free of electrolytes; washing is preferably continued until the draining wash water has the same electrical conductivity as demineralized water.
Before step c), the gel is preferably allowed to age, in general at O to 1 50C, preferably at 80 to 1 30C, and at a pH of 4 to 11, preferably 4 to 9. The time for this is generally from 10 seconds to 48 hours, preferably from 10 seconds to 5 hours.
In step c), the water contained in the gel is removed by extractive distillation with an organic solvent until the water content of the gel does not exceed 5% by weight and is preferably s 2% by weight. The solvent employed must form with water an azeotrope which separates into two liquid phases on cooling, an aqueous phase an a solvent phase. Examples of suitable solvents are toluene, di-n-butyl ether or methyl isobutyl ketone. Toluene is preferably used.
The solvent phase resulting on cooling of the azeotrope can be returned to the process.
Steps a) to c) are generally carried out at a temperature between the freezing point of the solution and the boiling point of the solvent.
21~2977 _~ 4 In step d), the solvent-containing gel is reacted with a silylating agent.
The silylating agents employed are generally silanes of the formulae R14 nSiCln or R14 nSi(OR2)n with n = 1 to 3, where R1 and R2 are, independently of one another, C1-C6-alkyl, cyclohexyl or phenyl.
Silazanes are also suitable. Mono, di- or trimethylchlorosilane, trimethylmethoxysilane or hexamethyl-disilazane is preferably used.
The reaction is generally carried out at 20 to 100C, preferably 30 to 70C, if necessary in a solvent such as toluene, acetone, n-hexane, n-heptane, di-n-butyl ether, i-propanol or methyl isobutyl ketone. The silylation can also be carried out, where appropriate, under pressure, preferably up to 25 bar. Where appropriate, the silylated gel can also be washed before drying.
In step e), the silylated gel is dried at temperatures from -30 to the boiling point of the solvent, preferably from -30 to 200C, particularly preferably from 0 to 1 50C. The pressures used for the drying are preferably from 0.001 to 20 bar, particularly preferably from 0.01 to 5 bar. The drying is generally continued until the gel has a remaining solvent content of less than 0.1% by weight.
To obtain special thermal properties it may be advantageous for the xerogel additionally to contain IR opacifiers (such as, for example, carbon black, titanium dioxide, iron oxides and zirconium dioxide).
These IR opacifiers are preferably added before step b) in such cases.
The process according to the invention is to be illustrated by an example.
Example 1 1 of a sodium waterglass solution (with a content of 6% by weight SiO2 and an Na20:SiO2 ratio of 2:3) was passed through a column (diameter 50 mm, length 300 mm) which was packed with 0.5 1 of an 21~2977 acid ion exchange resin (styrene/divinylbenzene copolymer with sulfonic acid groups, commercially available under the name ~Duolite C20). The solution flowing out had a pH of 1.5. The solution was then adjusted to a pH of 5.6 with 1 molar NH40H solution. The resulting gel was then aged at 50C for 24 hours and subsequently the water was extracted using 3 1 of toluene in an extraction vessel with water separator at about 100C. The extraction was stopped when the calculated amount of water (about 920 ml) had separated out. The toluene-containing gel was then silylated with trimethylchlorosilane (TMCS) at 50C for 12 hours (0.05 9 of TMCS
per gram of toluene-containing gel). The gel was dried in a drier flushed with N2 under atmospheric pressure (6 hours at 40C then 2 hours at 50C and 12 hours at 150C) .
The transparent xerogel obtained in this way had a density of 0.12 g/cm3. The BET specific surface area was 920 m2/g. The ,1 value was 0.016 W/mK.
The thermal conductivity was measured by a hot wire method (see, for example, 0. Nielsson, G. Ruschenpohler, J. Grol3, J. Fricke, High-Temperatures-High-Pressures, Vol. 21, 267-274 (1989)).
Claims (10)
1. A process for the preparation of xerogels, which comprises a) adjusting an aqueous waterglass solution to a pH 8.0, using an acid ion exchange resin or a mineral acid, b) polycondensing the silicic acid produced thereby, by adding a base, to an SiO2 gel and, if a mineral acid was used in step a), washing the gel with water until free of electrolytes where appropriate, c) removing the water from the gel obtained in step b) by extractive distillation with an organic solvent which forms with water an azeotrope which separates into two phases on cooling, until the water content of the gel is 5% by weight, d) reacting the gel obtained in step c) with a silylating agent, e) drying the silylated gel obtained in step d) at pressures and temperatures which are below the critical pressure and/or the critical temperature of the organic solvent used in step c).
2. The process as claimed in claim 1, wherein an acid ion exchange resin is employed in step a).
3. The process as claimed in claim 1 or 2, wherein NH4OH, NaOH, KOH, Al(OH)3 and/or colloidal silicic acid is employed as base in step b).
4. The process as claimed in at least one of claims 1 to 3, wherein the SiO2 gel obtained in step b) is allowed to age at 0 to 150°C
and at a pH of 4 to 11 for a period of from 10 seconds to 48 hours before the water is removed in step c).
and at a pH of 4 to 11 for a period of from 10 seconds to 48 hours before the water is removed in step c).
5. The process as claimed in at least one of claims 1 to 4, wherein toluene, di-n-butyl ether or methyl isobutyl ketone is employed as organic solvent in step c).
6. The process as claimed in at least one of claims 1 to 5, wherein mono-, di- or trimethylchlorosilane, trimethylmethoxysilane or hexamethyldisilazane is employed as silylating agent in step d).
7. The process as claimed in any of claims 1 to 6, wherein the silylated gel is dried at -30 to 200°C in step e).
8. The process as claimed in any of claims 1 to 7, wherein the silylated gel is dried under 0.001 to 20 bar in step e).
9. A xerogel obtainable by the process as claimed in any of claims 1 to 8.
10. The use of the xerogel as claimed in claim 9 as thermal insulator.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP4422912.7 | 1994-06-30 | ||
| DE4422912A DE4422912A1 (en) | 1994-06-30 | 1994-06-30 | Xerogels, processes for their manufacture and their use |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2152977A1 true CA2152977A1 (en) | 1995-12-31 |
Family
ID=6521904
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002152977A Abandoned CA2152977A1 (en) | 1994-06-30 | 1995-06-29 | Xerogels, a process for their preparation, and their use |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US5647962A (en) |
| EP (1) | EP0690023B1 (en) |
| JP (1) | JP3808115B2 (en) |
| CN (1) | CN1048696C (en) |
| CA (1) | CA2152977A1 (en) |
| DE (2) | DE4422912A1 (en) |
| ES (1) | ES2134377T3 (en) |
| NO (1) | NO952618L (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5888425A (en) * | 1995-01-27 | 1999-03-30 | Hoechst Aktiengesellschaft | Process for the preparation of modified aerogels, and their use |
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| CN108976803B (en) * | 2018-07-12 | 2021-07-09 | 杨帮燕 | Organic fireproof blocking material |
| WO2021204815A1 (en) | 2020-04-06 | 2021-10-14 | Empa Eidgenössische Materialprüfungs- Und Forschungsanstalt | Silica aerogels |
| EP3896035A1 (en) | 2020-04-15 | 2021-10-20 | EMPA Eidgenössische Materialprüfungs- und Forschungsanstalt | Silica aerogels and silica aerogel blankets |
Family Cites Families (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB682574A (en) * | 1950-05-04 | 1952-11-12 | Dow Corning Ltd | Improvements in or relating to silica compositions |
| US3801705A (en) * | 1968-10-11 | 1974-04-02 | Nat Petro Chem | Preparation of silica gels |
| JPS4938899A (en) * | 1972-08-19 | 1974-04-11 | ||
| US3846537A (en) * | 1972-08-21 | 1974-11-05 | Monsanto Co | Process of preparing silica xerogels |
| DE2455535A1 (en) * | 1974-11-23 | 1976-05-26 | Basf Ag | PROCESS FOR PREPARING OLEFINE POLYMERIZES |
| US4190457A (en) * | 1978-06-09 | 1980-02-26 | Phillips Petroleum Co. | Preparation of inorganic xerogels |
| CS208879B1 (en) * | 1979-07-09 | 1981-10-30 | Ivan Novak | Preparation method of silicic acid xerogel with high volumen of pores |
| US4649037A (en) * | 1985-03-29 | 1987-03-10 | Allied Corporation | Spray-dried inorganic oxides from non-aqueous gels or solutions |
| JPS62207712A (en) * | 1986-03-05 | 1987-09-12 | Fuji Debuison Kagaku Kk | Hydrous silica gel for stabilizing beer |
| DE3914850A1 (en) * | 1989-05-05 | 1990-11-08 | Basf Ag | THERMAL INSULATING MATERIAL BASED ON PIGMENT-BASED SILICONE ACULATE ARRAY |
| WO1992003378A1 (en) | 1990-08-23 | 1992-03-05 | United States Department Of Energy | A METHOD FOR PRODUCING METAL OXIDE AEROGELS HAVING DENSITIES LESS THAN 0.02 g/cm?3¿ |
-
1994
- 1994-06-30 DE DE4422912A patent/DE4422912A1/en not_active Withdrawn
-
1995
- 1995-06-19 EP EP95109422A patent/EP0690023B1/en not_active Expired - Lifetime
- 1995-06-19 DE DE59505881T patent/DE59505881D1/en not_active Expired - Lifetime
- 1995-06-19 ES ES95109422T patent/ES2134377T3/en not_active Expired - Lifetime
- 1995-06-28 CN CN95108111A patent/CN1048696C/en not_active Expired - Lifetime
- 1995-06-28 US US08/495,931 patent/US5647962A/en not_active Expired - Lifetime
- 1995-06-29 CA CA002152977A patent/CA2152977A1/en not_active Abandoned
- 1995-06-29 NO NO952618A patent/NO952618L/en not_active Application Discontinuation
- 1995-06-30 JP JP16595995A patent/JP3808115B2/en not_active Expired - Lifetime
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5888425A (en) * | 1995-01-27 | 1999-03-30 | Hoechst Aktiengesellschaft | Process for the preparation of modified aerogels, and their use |
Also Published As
| Publication number | Publication date |
|---|---|
| EP0690023A3 (en) | 1996-04-10 |
| CN1124229A (en) | 1996-06-12 |
| DE4422912A1 (en) | 1996-01-11 |
| CN1048696C (en) | 2000-01-26 |
| EP0690023B1 (en) | 1999-05-12 |
| DE59505881D1 (en) | 1999-06-17 |
| NO952618L (en) | 1996-01-02 |
| JP3808115B2 (en) | 2006-08-09 |
| NO952618D0 (en) | 1995-06-29 |
| ES2134377T3 (en) | 1999-10-01 |
| US5647962A (en) | 1997-07-15 |
| EP0690023A2 (en) | 1996-01-03 |
| JPH0859224A (en) | 1996-03-05 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued |