METHOD FOR MANUFACTURING A BODY MADE OF A POROUS MATERIAL

Abstract

A method for manufacturing a body made of a porous material derived from precursors of the porous material in a sol-gel process, including (i) providing a mold, containing a lower part defining an interior volume for receiving the precursors of the porous material, wherein the lower part comprises a first opening, and surfaces of the lower part facing the interior volume are at least partially provided with a coating made of a material being electrically dissipative and non-sticky to the precursors of the porous material and/or the body, (ii) filling precursors of the porous material into the lower part in a first inert or ventilated region, wherein the precursors include two reactive components and a solvent, (iii) removing the body from the lower part through the first opening after a predetermined time, (iv) disposing the body onto a support, and (v) removing the solvent from the body.

Claims

1. A method for manufacturing a body made of a porous material derived from precursors of the porous material in a sol-gel process, the method comprising: (i) providing a mold, wherein the mold comprises a lower part defining an interior volume for receiving the precursors of the porous material, wherein the interior volume defines a shape of the body, and at least a first opening through which the body is removed from the lower part, wherein surfaces of the lower part facing the interior volume are at least partially provided with a coating made of a material being electrically dissipative and non-sticky to the precursors of the porous material and/or the body, (ii) filling precursors of the porous material into the lower part in a first inert or ventilated region, wherein the precursors comprise two reactive components and a solvent, (iii) removing the body from the lower part through the first opening after a predetermined time in which the body is formed from the precursors of the porous material, (iv) disposing the body onto a support, and (v) removing the solvent from the body.

2. The method according to claim 1, wherein the mold further comprises a cover part configured to close the first opening, a second opening, and a lid configured to close the second opening, wherein the method further comprises closing the first opening by means of the cover part, filling precursors of the porous material into the lower part through the second opening, and closing the second opening by means of the lid.

3. The method according to claim 2, further comprising closing the first opening and/or the second opening in a gas tight manner.

4. The method according to claim 2, further comprising removing the cover part from the lower part in a second inert or ventilated region after a predetermined time in which the body is formed from the precursors of the porous material.

5. The method according to claim 1, wherein the removing the body from the lower part and the disposing the body onto the support comprise disposing the support onto the lower part and turning the lower part together with the support.

6. The method according to claim 5, further comprising fixing the support onto the lower part.

7. The method according to claim 1, wherein the support comprises openings.

8. The method according to claim 1, further comprising buffering the body in a third inert region before removing the solvent from the body.

9. The method according to claim 1, further comprising buffering a plurality of bodies in a third inert region and subsequently simultaneously removing the solvent from the plurality of bodies.

10. The method according to claim 4, further comprising repeating steps (i) to (iv) a predetermined number of times in a subsequent order so as to provide the plurality of bodies.

11. The method according to claim 9, wherein a volume of the third inert region is adapted to a total volume of the plurality of bodies and/or the third inert region is filled or pre-saturated with vapor of the solvent such that a substantial shrinking of the gel is prevented.

12. The method according to claim 9, further comprising sealing the first inert or ventilated region, a second inert or ventilated region and/or the third inert region in a gas tight manner.

13. The method according to claim 1, wherein the first inert or ventilated region and/or a second inert or ventilated region are defined by a chamber.

14. The method according to claim 13, wherein the first inert or ventilated region is a ventilated region and/or the second inert or ventilated region is a ventilated region, wherein the chamber comprises an airlock.

15. The method according to claim 1, wherein removing the solvent from the body is performed by means of an autoclave or oven.

Description

SHORT DESCRIPTION OF THE FIGURES

[0190] Further features and embodiments of the invention will be disclosed in more detail in the subsequent description, particularly in conjunction with the dependent claims. Therein the respective features may be realized in an isolated fashion as well as in any arbitrary feasible combination, as a skilled person will realize. The embodiments are schematically depicted in the figures. Therein, identical reference numbers in these figures refer to identical elements or functionally identical elements.

[0191] In the Figures:

[0192] FIG. 1 shows a perspective view of a mold in an open state useable with the method according to the present invention;

[0193] FIG. 2 shows a perspective view of the mold in a closed state;

[0194] FIG. 3 shows a flow chart of the method according to the present invention; and

[0195] FIG. 4 shows a perspective view of a demolding apparatus for removing a body from the mold.

DETAILED DESCRIPTION

[0196] As used in the following, the terms have, comprise or include or any arbitrary grammatical variations thereof are used in a non-exclusive way. Thus, these terms may both refer to a situation in which, besides the feature introduced by these terms, no further features are present in the entity described in this context and to a situation in which one or more further features are present. As an example, the expressions A has B, A comprises B and A includes B may both refer to a situation in which, besides B, no other element is present in A (i.e. a situation in which A solely and exclusively consists of B) and to a situation in which, besides B, one or more further elements are present in entity A, such as element C, elements C and D or even further elements.

[0197] Further, it shall be noted that the terms at least one, one or more or similar expressions indicating that a feature or element may be present once or more than once typically will be used only once when introducing the respective feature or element. In the following, in most cases, when referring to the respective feature or element, the expressions at least one or one or more will not be repeated, non-withstanding the fact that the respective feature or element may be present once or more than once.

[0198] Further, as used in the following, the terms particularly, more particularly, specifically, more specifically or similar terms are used in conjunction with additional/alternative features, without restricting alternative possibilities. Thus, features introduced by these terms are additional/alternative features and are not intended to restrict the scope of the claims in any way. The invention may, as the skilled person will recognize, be performed by using alternative features. Similarly, features introduced by in an embodiment of the invention or similar expressions are intended to be additional/alternative features, without any restriction regarding alternative embodiments of the invention, without any restrictions regarding the scope of the invention and without any restriction regarding the possibility of combining the features introduced in such way with other additional/alternative or non-additional/alternative features of the invention.

[0199] Further, it shall be noted that the terms first, second and third are used to exclusively facilitate to differ between the respective constructional members or elements and shall not be construed to define a certain order or importance.

[0200] The term mold as used herein refers to a hollowed-out block or container that is configured to be filled with a liquid or pliable material provided by precursors of a sol gel provided by precursors of a sol gel. Particularly, the sol-gel process is carried out within the mold. During the sol-gel process the precursors form a sol which subsequently starts to gel. Thus, the liquid hardens or sets inside the mold, adopting its shape defined by the interior volume thereof. The mold is basically used to carry out the sol-gel process. However, it is to be noted that the solvent may be removed from the thus formed gel with the gel remaining within the mold or with the gel removed from the mold. In the present invention, the mold may consist of more than one part, wherein the interior volume is defined by a lower part.

[0201] The term sol gel process as used herein refers to a method for producing solid materials from small molecules. In the present case, the method is used for the fabrication of porous materials such as aerogels, xerogels and/or kryogels. The process involves conversion of monomers as precursors into a colloidal solution, the so-called sol, that subsequently reacts to an integrated network, the so-called gel, of either discrete particles or network polymers. In this chemical procedure, the sol gradually evolves towards the formation of a gel-like diphasic system containing both a liquid phase and solid phase whose morphologies range from discrete particles to continuous polymer networks. This gel-like diphasic system is called gel. Particularly, the gel encapsulates or surrounds the solvent within pores which are connected to one another, i.e. the pores form an interpenetrating network. Removal of the remaining liquid phase, i.e. the solvent, requires a drying process, which is typically accompanied by a certain amount of shrinkage and densification. The rate at which the solvent can be removed is ultimately determined by the distribution of porosity in the gel. The ultimate microstructure of the final component will clearly be strongly influenced by changes imposed upon the structural template during this phase of processing.

[0202] The term body as used herein refers to a solid object formed by an identifiable collection of matter, which may be constrained by an identifiable boundary, and may move or may be moved as a unit by translation or rotation, in 3-dimensional space.

[0203] The term porous as used herein refers to material characteristics of having pores. As the solvent may be removed from the gel either with the gel being or remaining within the mold or after the gel is removed from the mold, the term porous covers both pores being filled with a liquid, particularly, the solvent, or a gas such as air. The pores may be connected to one another so as to form a type of network.

[0204] The term coating as used herein refers to a covering that is applied to the inner surfaces of the lower part of the mold. Particularly, the coating may be applied at least to those areas of the lower part intended to come into contact with the precursors of the porous material and the body made thereof. Needless to say, the coating may be applied to the total inner surfaces of the lower part defining the interior volume.

[0205] The term electrically dissipative as used herein refers to material characteristics, wherein electric charges are allowed to flow to ground but more slowly in a more controlled manner if compared to electrically conductive materials.

[0206] The term non-sticky as uses herein refers to characteristics wherein one part does not adhere to another part. Thus, both parts are in loose contact to one another. According to the present invention, the coating does not stick to the gel formed or resulting from the precursors filled into the mold. In case the solvent used with the sol gel process is removed with the gel being within the mold, the coating is configured not to stick to the thus formed body in order to allow the body being removed from the mold.

[0207] The terms width and length of the shape of the body as used herein refer to dimensions perpendicular to a height or thickness of the shape of the body.

[0208] The term opening area as used herein refers to the area of an opening defined by the boundary of the opening.

[0209] The term sealing as used herein refers to a device that helps join two parts together by preventing leakage, containing pressure, or excluding contamination.

[0210] The term gas tight as used herein refers to characteristics of a material to be impermeable to gases. Needless to say, the impermeability is not feasible to a complete or absolute extension but the impermeability is to be understood in the sense of an extension as far as technically feasible.

[0211] FIG. 1 shows a perspective view of a mold 10 for manufacturing a body made of a porous material derived from precursors of the porous material in a sol-gel process carried out within the mold 10 according to the present invention. The mold 10 is shown in an open state. The mold 10 comprises a lower part 12. The lower part 12 is made of metal. The lower part 12 defines an interior volume 14 for receiving the precursors of the porous material. The interior volume 14 defines the shape of the body to be manufactured. Particularly, the lower part 12 comprises a bottom 16 and side walls 18 extending from the bottom 16. The interior volume 14 is defined by the bottom 16 and the side walls 18. The mold 10 further comprises at least a first opening 20 through which the body is removable from the lower part 12. In the present example, the lower part 12 comprises the first opening 20. Particularly, an upper rim 22 of the side walls 18 opposite to the bottom 16 defines the first opening 20.

[0212] Surfaces 24 of the lower part 12 facing the interior volume 14 are at least partially provided with a coating 26 made of a material being electrically dissipative and non-sticky to a gel formed from the precursors of the porous material and/or the body. More particularly, the surfaces 24 of the lower part 12 comprise the coating 26 at least at areas intended for coming into contact with the gel formed from the precursors of the porous material. With other words, the coating 26 does not need to cover the complete surfaces 24 of the lower part which face the interior volume 14 but may only cover those portions or areas which are intended to come into contact with the precursors of the porous material. The material of the coating 26 comprises an electrical resistivity of not more than 10.sup.8 m such as 10.sup.6 m. The material of the coating 26 is noncorroding. The material of the coating 26 comprises a shore hardness in a range of D60 to D80 such as D70. The coating 26 comprises a thickness in a range of 20 m to 70 m such as 50 m. The coating 26 is a reusable coating. Particularly, the coating 26 is reusable for at least 50 and preferably at least 100 cycles of the sol gel process. The coating preferably comprises at least one halogen-containing polymer and at least one inorganic filler. More preferably, the halogen-containing polymer is a fluorinated polymer such as for example polytetrafluoroethylene, a perfluoro alkoxy polymer or a fluorinated ethylene propylene polymer. The coating preferably comprises at least one inorganic filler and at least one polymer selected from the group consisting of polytetrafluoroethylene, perfluoro alkoxy polymers and fluorinated ethylene propylene polymers. Particularly preferred are fluorinated ethylene propylene polymers such as perfluoro ethylene propylene. In the present embodiment, the coating 26 is made of a fluorinated polymer with conductive additive and anti-scratch additive. Such a material is commercially available under the name Rhenolease MK IIIG clear SiC/leitf. (hereinafter called Rhenolease) from the company Rhenotherm Kunststoffbeschichtungs GmbH, 47906 Kempen, Germany.

[0213] Basically, the interior volume 14 may define any shape for the body such as round, oval, elliptical, polygonal, polygonal with rounded edges. In the present example, the interior volume 14 defines a cuboid shape for the body. The shape has a length 28 in a range of 10 cm to 100 cm such as 60 cm and a width 30 in a range of 10 cm to 100 cm such as 40 cm. A height 32 of the shape is variable and may be adjusted by means of the filling level of the precursors within the lower part 12.

[0214] The mold 10 further comprises a cover part 34 configured to close the first opening 20, a second opening 36, and a lid 38 configured to close the second opening 36. In the present example, the cover part 34 comprises the second opening 36. The first opening 20 comprises a first opening area and the second opening 36 comprises a second opening area. The second opening area is smaller than the first opening area. The mold 10 further comprises at least a first sealing 40 configured to be arranged between the lower part 12 and the cover part 34. The first sealing 40 is configured to provide a gas tight closing of the first opening 20 by means of the cover part 34. Optionally, the mold 10 may further comprises a second sealing (not shown in detail) configured to be arranged between the lid 38 and the cover part 34 and configured to provide a gas tight closing of the second opening 36 by means of the lid 38.

[0215] FIG. 2 shows a perspective view of the mold 10 in a closed state. Particularly, the cover part 34 is arranged on the lower part 12 such that the first opening 20 is closed. The cover part 34 is removably mounted to the lower part 12. For example, the cover part 34 may be connected to the lower part 12 by means of a snap-fit connection, screws, hooks or the like. Further, the lid 38 closes the second opening 36.

[0216] The mold 10 may be used as follows. The cover part 34 is disposed onto the lower part 12 with the first opening 20 being closed. The precursors of the porous material, which are solved in a solvent, are filled into the lower part 12 up to a predetermined amount through the second opening 36. Subsequently, the second opening 36 is closed by the lid 38. Thereby, any solvent vapor is prevented from leaking or releasing from the mold 10. Then, the sol-gel reaction takes place wherein the precursors first form a sol with the solvent and subsequently form a gel. After gelling, the gel is hardened for a predetermined time such as at least 2 hours and preferably at least 8 hours. The hardening causes a kind of ageing of the gel which is necessary for the sol-gel reaction to proceed far enough such that the gel can be removed from the mold. If the sol-gel reaction was not to proceed far enough, the gel might not be sufficiently mechanically stable for handling, particularly for drying, or unreacted material could leak out of the gel during drying or could cause other problems such as negative impact on performance, e.g. fire behavior, unwanted emissions. After hardening, the cover part 34 is removed from the lower part 12. Thereby, the first opening 20 is exposed again. Then, the solvent is removed from the gel. The solvent may be removed by drying the gel in an oven or the like. It is to be noted that the solvent may be removed while the gel is in the lower part 12 or the gel may be removed from the lower part 12 before the gel is dried. After the solvent is removed from the gel, the body is formed. If the gel has been dried within the lower part 12, the body may subsequently be removed from the mold 10 and lower part 12, respectively. Due to the specific coating 26, neither the gel formed from the precursors within the lower part 12 nor the body sticks to the mold 10. If it is intended to remove the solvent with the gel being removed from the lower part 12 of the mold 10, the material of the coating may be selected such that it merely does not stick to the formed gel.

[0217] The mold 10 may be modified as follows. The lower part 12 may be made of a polymer. The coating 26 may completely cover the surfaces 24 facing the interior volume 14 or may even cover the complete lower part 12. The mold 12 may be used without the cover part 34 if an excessive release of any solvent vapor is otherwise prevented. The second opening 36 may be provided at the lower part 12. The shape of the body may be any shape such as square, rounded or the like. The mold 10 may comprise more parts than the lower part 12 and the cover part 34 such as an intermediate part arrangeable between the lower part 12 and the cover part 34.

[0218] FIG. 3 shows a flow chart of a method for manufacturing a body made of a porous material derived from precursors of the porous material in a sol-gel process according to the present invention. The mold 10 is provided. The cover part 34 is disposed onto the lower part 12 with the first opening 20 being closed. Particularly, the first opening 20 is closed in a gas tight manner by means of the cover part 34 and the first sealing 40. The precursors of the porous material are prepared. In the present example, a first reactive component CA and a solvent S are supplied to a first receiving tank 42. Further, a second reactive component CB and the solvent S are supplied to a second receiving tank 44. A predetermined amount of the first reactive component and solvent is supplied to a mixing device 46 from the first receiving tank 42. In the present example, the predetermined amount is defined as a volumetric dosing by means of a first volumetric dosing device 48. A predetermined amount of the second reactive component and solvent is supplied to the mixing device 46 from the second receiving tank 44. In the present example, the predetermined amount is defined as a volumetric dosing by means of a second volumetric dosing device 50. Optionally, a closed loop operation may be provided with the first receiving tank 42 and the mixing device 46 and/or with the second receiving tank 46 and the mixing device 46.

[0219] The precursors of the porous material are filled into the lower part 12 up to a predetermined amount through the second opening 36. In the present example, the filling process is carried out by means of the mixing device 46. Particularly, the precursors are mixed by means of the mixing device 46 before being filled into the lower part 12. The precursors are filled into the lower part 12 in a first inert or ventilated region 52. For example, the filling is carried out in a carbon dioxide atmosphere or in a device similar to a laboratory hood. The first inert or ventilated region 52 may be defined by a chamber. The first inert or ventilated region 52 may be sealed in a gas tight manner. Subsequently, the second opening 36 is closed by the lid 38. Particularly, the second opening 36 is closed in a gas tight manner. Thereby, any solvent vapor is prevented from leaking from the mold 10. Then, the sol gel reaction from the two reactive components of the precursors takes place wherein the precursors gel. After gelling, the gel is hardened or aged for a predetermined time such as at least 3 hours and preferably at least 8 hours in order to complete the gelation reaction and to exclude a negative impact on the further handling of the gel body such as in case the gel body is not sufficiently hard. In the present example, the hardening or ageing process is carried out by means of a hardening device 54. In the hardening device 54, a plurality of molds 10 including the gel may be buffered. After hardening, the body is formed and the cover part 34 may be removed from the lower part 12. Thereby, the first opening 20 is exposed again and the body may be removed from the mold 10 and lower part 12, respectively, as indicated by arrow 56. That is, the body is removed from the lower part 12 through the first opening 20 after a predetermined time in which the body is formed from the precursors of the porous material. Due to the specific coating 26, the body does not stick to the mold 10. Further, the solvent is recycled or re-extracted by means of a re-extraction device 58. Hereinafter, the further handling for removing of the body from the lower part 12 and subsequent method steps will be described in further detail.

[0220] FIG. 4 shows a perspective view of a demolding apparatus 60 for removing a body from the mold 10. The mold 10 is transported in the closed state to an input 62 of the demolding apparatus 60. For example, the closed mold 10 is transported on a carriage or the like. The input 62 is located adjacent a second inert or ventilated region 64. The second inert or ventilated region 64 may be defined by a chamber. The second inert or ventilated region 64 may be sealed in a gas tight manner. A door (not shown in detail) similar to the door of a laboratory hood between the input 62 and the second inert or ventilated region 64 is opened and the closed mold 10 is disposed within the second inert or ventilated region 64. The cover part 34 is removed from the lower part 12 in the second inert or ventilated region 64 after a predetermined time in which the body is formed from the precursors of the porous material. Further, the door is closed. The body is disposed onto a support 66. For this purpose, the support 66 is disposed and fixed onto the lower part 12. For example, the support 66 is pneumatically fixed onto the lower part 12. Further, the lower part 12 together with the support 66 are turned, preferably at 180 such that lower part 12 is arranged onto the support 66. The turning may be carried out by means of a lever (not shown in detail). Due to gravity, the body moves out of the lower part 12 and onto the support 66. The lever is moved into its initial position such that the empty lower part 12 may be removed from the second inert or ventilated region 64 when the door is opened. The support 66 comprises openings (not shown in detail).

[0221] The chamber defining the second inert or ventilated region 64 comprises an airlock 68 by means of which the second inert or ventilated region 64 is connected to a third inert region 70 before the solvent is removed from the body. The third inert region 70 is defined by a chamber. The third inert region 70 includes an atmosphere of carbon dioxide, nitrogen, argon or the like. The body is transported from the second inert or ventilated region 64 to the third inert region 70 through the airlock 68. For this purpose, the airlock 68 comprises a first door (not shown in detail) allowing a communication of the airlock 68 with the second inert or ventilated region 64 and a second door (not shown in detail) allowing a communication of the airlock 68 with the third inert region 70. First, the first door is opened while the second door is closed. Then the body is transported into the airlock 68. The body is transported into the airlock 68 by means of a first conveyor such as a chain conveyor. Subsequently, the first door is closed while the second door is still closed. Then, the airlock 68 is rendered inert. Subsequently, the second door is opened while the first door remains closed. Then, the body is transported from the airlock 68 into the third inert region 70 by means of a second conveyor such as a chain conveyor. It is to be noted that this transport through the airlock 68 is carried out rather fast in a time of not more than 30 seconds in order to avoid an excessive loss of the solvent from the body.

[0222] The body is buffered in the third inert region 70. The third inert region 70 is sealed in a gas tight manner so as to avoid any leakage of solvent therefrom. It is to be noted that the method steps described before may be repeated a predetermined number of times in a subsequent order so as to provide a plurality of bodies, which are buffered in the third inert region 70. As mentioned above, the support 66 comprises openings. Thus, a diffusion of the solvent from the body is possible on all sides thereof. Needless to say, the support 66 is stable so as to avoid any deformation of the support and the body disposed thereon. Preferably, a volume of the third inert region 70 is adapted to a total volume of the plurality of bodies which means that only a small amount of the solvent may evaporate from the body up to a degree of saturation in the atmosphere of the third inert region 70 such that a substantial shrinking of the gel is prevented. In addition or alternatively, the third inert region 70 is already filled or even pre-saturated with vapor of the solvent such that the degree of saturation is already achieved or is achieved rather fast. The third inert region 70 may be provided with positive pressure in order to prevent oxygen to enter the third inert region 70.

[0223] After buffering the body or the plurality of bodies, the body or the plurality of bodies are transported to an autoclave or oven 72. The third inert region 70 may have an airlock 68 communicating with the third inert region 70 and the oven 72. This transport may be carried out on a carriage having mounts for mounting the supports 66. The solvent is removed from the body or the plurality of bodies is performed by means of the autoclave or oven 72. Preferably, autoclave or oven 72 is supplied with a plurality of bodies and the solvent of the plurality of bodies is removed simultaneously. After removing the solvent from the body or the plurality of bodies, the body or the plurality of bodies are finalized, removed from the autoclave or oven 72 and ready to be used. As the bodies do not stick to the coating 26 of the lower part, the coating 26 may be reused for at least 50 cycles of the sol gel process.

[0224] The mold 10 may be modified as follows. The lower part 12 may be made of a polymer. The coating 26 may completely cover the surfaces 14 facing the interior volume 14 or may even cover the complete lower part 12. The mold 12 may be used without the cover part 34 if used within an inert atmosphere. The second opening 36 may be provided at the lower part 12. The shape of the body may be any shape such as square, rounded or the like. The mold 10 may comprise more parts than the lower part 12 and the cover part 34 such as an intermediate part arrangeable between the lower part 12 and the cover part 34. The support 66 may also be provided with the coating 26.

EXAMPLES

[0225] The mold 10 and more particularly the material of the coating 26 are specified in further detail as follows.

[0226] The following components were prepared:

[0227] Component 1: To methylethylketone (MEK) were added 3-4% MDEA, 1,5-2,5% potassium sorbate solution (20% in methylene glycol), 1,8-3,5% n-butanol.

[0228] Component 2: To MEK were added 15-20% polymeric MDI.

[0229] Components 1 and 2 were combined at room temperature and directly poured into a mold to form a gel slab. The mold was covered to prevent evaporation of the solvent from the gel. After 1 h, the cover was removed and the mold was inverted to demold the gel slab.

[0230] With these materials, a solvent vapor emission from the resulting gel has been detected as 65 g/(minm.sup.2). The solvent vapor emission rate was detected by weighing the gel periodically and determining the weight loss due to the vapor emission. A maximum solvent loss before quality impact due to pore damage is given as 10 wt % based on empiric considerations. The mold comprised a geometry so as to produce cuboid gel slabs each having length of 0.6 m, a width of 0.42 m and a thickness of 20 mm. Each slab comprises 3.5 kg solvent. The demolding time, i.e. the time necessary to remove the body from the mold, was given as 1 min per gel slab. According to hazardous materials regulations in Germany, the lower explosion limit (LEL) of MEK is defined as 45 g/m.sup.3 and the upper explosion limit (UEL) of MEK is defined as 378 g/m.sup.3. The maximum safe working concentration MAK (German MAKMaximale Arbeitsplatz-Konzentration=threshold limit value) for MEK is defined as 600 mg/m.sup.3. In the followings examples concerning inert regions or areas, the inertization was made with N.sub.2 having a saturation concentration of MEK of 301 g/m.sup.3 at a pressure of 10.sup.5 Pa and a temperature of 20 C. Concerning the following examples, 100 open molds were considered with 100 gel slabs, wherein 0.25 m.sup.2 (=0.6 m length0.42 m width) surface area of the gel slab faces the room. Thus, a solvent evaporation was defined as 100 slabs0.25 m.sup.2/slab65 g/(minm.sup.2)=1625 g/min MEK corresponding to an evaporation from 1 gel slab of 16.3 g/min MEK. For the following examples, 100 gel slabs were buffered e.g. during demolding until all slabs have been demolded.

Example 1

[0231] A non-ventilated room or area of 555 m.sup.3 for 100 slabs was analyzed. An open mold was used. The explosion hazard with the above-identified solvent can be calculated as 45 g/m.sup.3125 m.sup.3=5625 g. Thus, the LEL in the room or area is reached in 5625 g/1625 g/min=3.5 min. Accordingly, the explosion hazard is relevant in example 1. The health hazard with the above-identified solvent can be calculated as 600 mg/m.sup.3125 m.sup.3=75 g solvent in total. This threshold is met in 75 g/1625 g/min=0.05 min. Thus, the MAK for the above-identified solvent is reached in significantly less than 1 min. Accordingly, the health hazard is relevant. The quality impact can be calculated as 10 wt %3.5 kg solvent=350 g MEK loss tolerated per gel slab. The evaporation rate is 0.25 m.sup.265 g/(minm.sup.2)=16.3 g/min MEK. The time to quality loss is 350 g/16.3 g/min=21 min. Accordingly, there is not enough time for buffering and demolding which has to be carried out in 100 min for all 100 slabs. Accordingly, a negative impact on quality is relevant. Further, an environmental impact and waste air treatment based on a MEK emission of 1625 g/min is relevant.

Example 2

[0232] A closed mold was used representing a non-ventilated room or area of 0.60.420.05 m.sup.3=0.0126 m.sup.3 for 1 slab. The explosion hazard with the above-identified solvent can be calculated for the LEL as 45 g/m.sup.30.0126 m.sup.3=0.57 g solvent in total. The LEL is met in 0.57 g/16.3 g/min=0.035 min. Thus, the LEL in the mold is reached in approximately 2 s. The explosion hazard with the above-identified solvent can be calculated for the UEL as 378 g/m.sup.30.0126 m.sup.3=4.8 g solvent in total. The UEL is met in 4.8 g/16.3 g/min=0.294 min. So a non-explosive atmosphere is reached very fast. The UEL in the mold is reached in approximately 18 s. Nevertheless, in this respect, it has to be noted that if the closed mold is constructed according to explosion-protection standards, no explosion hazard is given as there is no ignition source in a closed mold. With a closed mold, there is no health hazard. The quality impact can be calculated as 10 wt %3.5 kg solvent=350 g MEK loss tolerated per gel slab. The amount of MEK until saturation is calculated as 301 g/m.sup.3 (saturation concentration of MEK)0.0126 m.sup.3=approximately 4 g. Thus, there is no quality impact. Further, with a closed mold, there is no environmental impact.

Example 3

[0233] A ventilated room or area of 555 m.sup.3 for 100 slabs was analyzed with a 20 times air exchange per hour. An open mold was used.

[0234] The respective calculations are identified in table 1 given below. In table 1, the first column from the left gives the time. The second column from the left gives the emission of the solvent per slab. The third column from the left gives the emission of the solvent of all 100 slabs. The fourth column from the left gives the amount of solvent in the room before air exchange. The fifth column from the left gives the concentration of solvent in the room before air exchange. The sixth column from the left gives the ventilation rate per hour. The seventh column from the left gives the ventilation rate per minute. The eighth column from the left gives the volume exchange per minute. The ninth column from the left gives the concentration of solvent in the room after air exchange. The tenth column from the left gives the amount of solvent in the room after air exchange.

TABLE-US-00001 TABLE 1 m (room, before) Volume c (room, after) m (room, after) Emission before air exchange c (room, before) exchange afterair exchange air exchange slab m (emission) [g] before air exchange Venti- Venti- [/min] [g/m3] [g] Time [g/min] all slabs m (after) + [g/m3] lation lation Venti- (1 Vol. exch.)*c c (room, [min] R*A [g/min] m (emission) m (room, before)/V [m3/h] [m3/min] lation/V (room, before) after)*V 0 0 1 16.25 1625 1625 13.0 2500 41.7 0.33 8.7 1083 2 16.25 1625 2708 21.7 2500 41.7 0.33 14.4 1806 3 16.25 1625 3431 27.4 2500 41.7 0.33 18.3 2287 4 16.25 1625 3912 31.3 2500 41.7 0.33 20.9 2608 5 16.25 1625 4233 33.9 2500 41.7 0.33 22.6 2822 6 16.25 1625 4447 35.6 2500 41.7 0.33 23.7 2965 7 16.25 1625 4590 36.7 2500 41.7 0.33 24.5 3060 8 16.25 1625 4685 37.5 2500 41.7 0.33 25.0 3123 9 16.25 1625 4748 38.0 2500 41.7 0.33 25.3 3165 10 16.25 1625 4790 38.3 2500 41.7 0.33 25.5 3194 11 16.25 1625 4819 38.5 2500 41.7 0.33 25.7 3212 12 16.25 1625 4837 38.7 2500 41.7 0.33 25.8 3225 13 16.25 1625 4850 38.8 2500 41.7 0.33 25.9 3233 14 16.25 1625 4858 38.9 2500 41.7 0.33 25.9 3239 15 16.25 1625 4864 38.9 2500 41.7 0.33 25.9 3243 16 16.25 1625 4868 38.9 2500 41.7 0.33 26.0 3245 17 16.25 1625 4870 39.0 2500 41.7 0.33 26.0 3247 18 16.25 1625 4872 39.0 2500 41.7 0.33 26.0 3248 19 16.25 1625 4873 39.0 2500 41.7 0.33 26.0 3249 20 16.25 1625 4874 39.0 2500 41.7 0.33 26.0 3249

[0235] As can be taken from table 1, particularly the ninth column from the left, the LEL of 45 g/m.sup.3 is not reached as an approximation of the concentration of the solvent in the room of maximum 26 g/m.sup.3 occurs. Thus, there is no explosion hazard. As with example 1, the MAK is reached in significantly less than 1 min. Thus, the health hazard is relevant. Accordingly, the health hazard is relevant. The quality impact can be calculated as 10 wt %3.5 kg solvent=350 g MEK loss tolerated per gel slab. The evaporation rate is 0.25 m.sup.265 g/(minm.sup.2)=16.3 g/min MEK. The time to quality loss is 350 g/16.3 g/min=21 min. Accordingly, there is not enough time for buffering and demolding which has to be carried out in 100 min for all 100 slabs. Accordingly, a negative impact on quality is relevant. Further, an environmental impact and waste air treatment based on a MEK emission of 1625 g/min is relevant.

Example 4

[0236] An inert room or area of 555 m.sup.3 for 100 slabs was analyzed. In an inert atmosphere, there is no explosion hazard. Further, in an inert atmosphere, there is no health hazard as human beings are not exposed to this atmosphere. The quality impact can be calculated as 10 wt %3.5 kg solvent=350 g MEK loss tolerated per gel slab. The amount of MEK until saturation is 301 g/m.sup.3125 m.sup.3=37.5 kg. The MEK loss distributed across all gel slabs is 37.5 kg/100 slabs=375 g/slab which is higher than the 350 g limit. Thus, the negative impact on quality is partially relevant. As there is no MEK emission outside of the inert room or area, there is no environmental impact.

Example 5

[0237] An inert room or area with a reduced volume of 333 m.sup.3 for 100 slabs was analyzed. In an inert atmosphere, there is no explosion hazard. Further, in an inert atmosphere, there is no health hazard as human beings are not exposed to this atmosphere. The quality impact can be calculated as 10 wt %3.5 kg solvent=350 g MEK loss tolerated per gel slab. The amount of MEK until saturation is 301 g/m.sup.327 m.sup.3=8.1 kg. The MEK loss distributed across all gel slabs is 8.1 kg/100 slabs=81 g/slab which is significantly lower than the 350 g limit. Thus, there is no negative impact on quality. As there is no MEK emission outside of the inert room or area, there is no environmental impact.

Example 6

[0238] An inert room or area of 555 m.sup.3 with pre-saturated atmosphere for 100 slabs was analyzed. In a pre-saturated inert atmosphere, there is no explosion hazard. Further, in a pre-saturated inert atmosphere, there is no health hazard as human beings are not exposed to this atmosphere. Still further, in a pre-saturated inert atmosphere, there no evaporation from slabs such that there is no impact on quality. As there is no MEK emission outside of the inert room or area, there is no environmental impact.

[0239] Table 2 gives a summary of the results for buffering during demolding according to the above examples 1 to 6. The respective examples 1 to 6 are indicated in the second to seventh columns from the left in this order and the respective analyzed aspects of explosion hazard, health hazard, quality impact and environmental hazard are given in the second to fifth lines from the top in this order.

TABLE-US-00002 TABLE 2 Exam- Exam- Exam- Exam- Exam- Exam- ple 1 ple 2 ple 3 ple 4 ple 5 ple 6 Explosion Yes No No No No No hazard Health hazard Yes No Yes No No No Quality impact Yes No Yes Yes No No Environmental (Yes)* (No)* (Yes)* (No)* (No)* (No)* hazard* *Can be mitigated by off-gas treatment

[0240] Table 3 gives an overview of variations for the process steps of the disclosed method. In table 3, the respective process steps, filling buffering 1, demolding, buffering 2 and drying are indicated in the second to sixth columns in this order. Buffering 1 indicates a step of buffering carried out between filling of the precursors into the mold or lower part thereof, respectively, and demolding. Further, buffering 2 indicates a step of buffering between demolding and drying. The respective examples 1 to 6 are given in the second to seventh lines from the top in this order. The index x indicates the feasibility of a respective method step.

TABLE-US-00003 TABLE 3 Filling Buffering 1 Demolding Buffering 2 Drying Example 1 Example 2 x Example 3 x (x)* Example 4 x x (x)* Example 5 x** x** x** x** x** Example 6 x x x x x *Possible if residence time per slab is low enough to prevent explosion, health hazard and quality impact due to premature solvent evaporation **Possible if solvent evaporation per slab does not exceed maximum for negative impact on quality

[0241] From table 3, it can be taken which of the disclosed method steps are feasible under which circumstances or conditions.

CITED LITERATURE

[0242] WO 00/24799