DE10256214A1 - Production of a fibrous body used in the production of a ceramic material as a photovoltaic element comprises digesting a natural material such as wood to form fibrous particles, adding purified carbon black or ground graphite and pressing - Google Patents

Abstract

Production of a fibrous body comprises digesting a natural material such as wood to form fibrous particles, adding 5-50 wt.% purified carbon black or ground graphite and pressing to form a fibrous body.

Description

The invention relates to a method for the production of a fiber body according to the preamble of claim 1 and a ceramic material according to the preamble of claim 6.

Such methods are known. For example, WO 01/81270 by the applicant describes a method according to the preamble of claim 1.

In this known method provided the fiber body after coking with a high carbon (C) substance in dissolved or more melted, i.e. more liquid Impregnate shape. As such a high carbon (C) -containing substance comes in particular Phenolic resin and / or starch in question. By repeated impregnation with heating and cooling cycles the carbon content of the material can be increased. hereby Is it possible, a very even, isotropic To achieve structure of the material and thus a good predictability to ensure its properties. Furthermore, the shrinkage becomes significant during further processing restricted what among other things to save costs through reduced processing volume of the material leads. The porosity can further of the end product can be adjusted very precisely by the carbon content. Finally let yourself the density of the material by appropriate choice of carbon content influence and thus the required properties of the end product to adjust.

Such, possibly multiple Nachimprägnierungen of the material after coking are procedural and extraordinary in terms of energy technology elaborate so that they the manufacturing process significantly expensive. Furthermore, the leads high entry of high carbon (C) substances such as phenolic resin to a significant cost burden due to high material costs, and pollutes the environment.

It is also known from WO 01/81270 coking an impregnation of the fibrous body with highly carbon (C) -containing substances in dissolved or melted, so liquid Form.

A carbon entry by the in principle same impregnation materials, as with the re-impregnation used, shows the pre-impregnation in the case of Manufacture of the fiber body in the wet process only reduced effect: The strongly dissolved in the suspension Carbon (C) -containing substances are dewatered with the water components the suspension washed out together, so that only a limited proportion of these substances in the drained moldings can be enriched. In the case of post-impregnation, on the other hand, if already a porous, pyrolyzed body is present, pressing in such substances as phenolic resin results and / or strength, a pore filling with these substances, and therefore a high level of body retention for these substances. So that can in a post-impregnation step more impregnation material be introduced as in a pre-impregnation step in the wet process.

Also in a dry process for Manufacture of the fiber body is a strong enrichment with impregnating agent in question standing type not possible; because that in liquid Form impregnation agent can only in the dry fiber mass by impregnation of the individual fibers and soaking at best of the fiber material are kept while gaps between the fibers to drain excess impregnating agent by gravity. Consequently is also the amount of the impregnation agent that can be entered and thus of the carbon to be enriched is limited to values that are still significant below the values of a post-impregnation level lie.

Therefore it is according to WO 01/81270 proposed addition of substances with a high carbon content (C) before coking in the course of the production of the fiber body from little benefit in terms of carbon enrichment and thus a reduction in achieving the desired quality required impregnation levels.

In addition, that for the production of ceramic Suitable fiber body z. B. in plate form independently represent tradable product, which from production facilities for ceramic Materials are purchased as semi-finished products. The better the carbon content of the fibrous body as a preliminary product to the relatively high carbon requirements of the subsequent ones Further processing to the ceramic product is set so the subsequent effort at the manufacturer of the ceramic is less Material with the necessary post-impregnation steps following the Coking of the fiber material, and the bigger it is with the preliminary product purchased added value.

The object of the invention is a Method of the preamble of claim 1 or claim 6 to indicate the genus in which a ceramic end product with a desired high Carbon content despite elimination or minimization of re-impregnation is achieved.

Surprisingly, this object is achieved in that, in the course of shaping the fiber body before pressing, elemental carbon in the form of, for example, cleaned carbon black, ground graphite or the like in an amount of 5 to 50% by weight, based on the weight of the dry NEN fiber body is added. The fact that the elemental carbon is introduced as a solid (granules, powder, flour, dust) of a desired particle size means that it can adhere to the fibers of the fiber body that is being formed and is thus protected from excessive suspension by the suspension in the wet process. In the case of a drying process, the solid can fill gaps between fibers and be held there. In any case, the introduction of carbon in elemental form as a solid (instead of being incorporated into a chemical compound in liquid form) is decisive for ensuring that a high proportion of carbon can be successfully introduced into the fiber body during its formation before the pre-pressing and there during of the coking step. The upper limit of 50% by weight results on the one hand from the practicability because introducing a higher carbon content would generally be associated with particular difficulties and, moreover, a higher carbon content in the course of fiber body production, for example under the influence of heat during pressing, leads to problems. In addition, a higher carbon content (even without re-impregnation) is not expedient, not necessary or even undesirable for most applications of the ceramic material.

Carbon black, graphite and other carbon particles are common available as waste and are therefore extraordinary inexpensive. For example, the price of such carbon is included as waste significantly less than 5% of the price of phenolic resin. To this In this way, the method according to the invention is particularly economical.

The use of elemental carbon as an additive in fiber body production, of course, also results because of the particularly high carbon content that the introduced Carbon 1: 1 is available as carbon. In case of a Incorporation in the form of a chemical containing carbon Connection, however, is always only a certain percentage of the total registered aggregate are present as carbon and thus process engineering effective; in the case of phenolic resin, this is around 50% by weight, in the case of strength a share of usually around 40 wt .-% of the total strong carbon (C) -containing substance. In other words, should Achieving an entry of 50 wt .-% carbon, based on the weight of the dry fiber body, a proportion of 100 wt .-% phenolic resin can be introduced, which already is excluded from logic; also much smaller proportions from e.g. 20% by weight cannot be introduced in this way, since an introduction from e.g. Phenolic resin in an amount significantly more than about 10 wt .-% is not technologically practical.

The elementally added carbon can the high carbon (C) containing aggregate of the generic state replace the technology or if this over the carbon entry has no further functionality, also form. He can however also additional to the high carbon (C) containing substance if this, such as phenolic resin as a binder in fiber body production, because of other functionality still needed becomes. Such a process with the addition of elemental carbon is in the claims 3 and 4 and 8 and 9 specified. In the method according to claims 5 and 10, if necessary, only carbon can be used as an additive.

Under elemental carbon in For the purposes of the present application, every form of carbon is to understand that not as a chemical compound with other elements is present.

By the features of claims 2 and 6 will be a particularly affordable one Composition of the ceramic material, as he achieved in particular results in good efficiency when used as a photovoltaic element.

The invention is explained below closer to the drawing explained.

It shows:

1 2 shows a schematic view of a suspension present in a mixing container with a schematic enlargement shown below,

2 2 shows a schematic cross-sectional representation of the fiber body present after the dewatering, with a schematic enlargement shown below, and

3 is a schematic cross-sectional view of the fiber body present after pressing with a schematic enlargement shown below.

How 1 schematically illustrated, cellulose fibers are used in the usual way for pressed fiber boards 2 placed in a water bath and there to form a suspension 1 intimately mixed. Instead of cellulose fibers 2 Fibrous particles such as wood shavings or the like could also be used, but fibrous ingredients in the form of single fibers or thin fiber bundles are preferred for many applications due to their better homogeneity. An organic binder such as phenolic resin is stirred in in an amount of a few percent by weight based on the total weight of the finished dry fiberboard. After curing in the finished plate, the binder serves to produce the character of a hard plate.

After thorough mixing of the ingredients in the suspension 1 takes place in 2 Illustrated drainage, in which most of the water is squeezed out at relatively low pressure. The process water is for reasons of process economy circulated so that the suspension 1 enriched with wood ingredients such as lignin, resins, wood sugar, soluble cellulose components etc. Certain portions of these are flushed out during dewatering, and these portions are contained in the recycled process water fed in to form the following suspension.

The dewatered fiber mat is then according to 3 fed to a press and pressed on a lower molecular sieve with residual water removal under heat and high pressure to the finished plate, whereby the binder cures. The finished plate according to 3 contains the fiber 2 in relatively dense mutual contact, the positions of the fibers in the fiber composite being secured by the hardened binder.

As a rule, a flat fiberboard is produced in this way, even if a three-dimensional shaped body is to be obtained. Instead of pressing the fibers directly 2 For the three-dimensional body, it is often more efficient to first produce a flat plate and then to press it into the desired shape under pressure and in hot water. The application of, for example, 180 ° C hot pressurized water leads to the achievement of such a relative mobility of the fibers despite previous hardening of the binder 2 , which allows forming within certain limits.

The process steps described so far are well known and are customary for producing a plate or a shaped body from cellulose fibers 2 or the like in a wet process. The person skilled in the art completely masters this procedure, also with regard to details which are not explained in more detail above.

The special feature of the invention is that in the suspension 1 additional elemental carbon 3 is added in particle form and mixed in to form a fiber body which is to be further processed by coking (pyrolysis) to form a ceramic material known per se with a high carbon content. A more detailed explanation of the procedural steps in this regard can be dispensed with, since these are well known and by their nature are not changed by the invention. However, the invention leads to the provision of a fiber body as a preliminary product for the ceramic material, which already has such a high carbon content that complex post-impregnations with carbon after the coking can be dispensed with or at least greatly reduced.

Surprisingly, it has been found that elemental carbon, that is to say which is not in a chemical compound with other substances 3 for example in the form of ground graphite or carbon black in the suspension 1 so good on the fibers 2 adheres to the fact that an extremely high proportion of 50% by weight, based on the total weight of the finished dry fiberboard, can be introduced into the finished panel, and is not largely washed out again during dewatering. This is probably due to the good adhesion of the carbon in particle form 3 on the fibers 2 in suspension 1 to have. Of course, it is inevitable that the process water will still wash out a certain part of the carbon particles introduced during dewatering. However, these particles remain in the recycled process water and are therefore returned to the suspension with the process water. In the process circulation there is thus a balance between the components which have been flushed out and which are fed back in with the process water of the next batch, in such a way that the amount of the suspension is always on balance 1 must be added, which should also be included in the finished product. If a wet process without process water circulation should be used, the suspension would have to 1 amount of carbon added 3 be increased by the amount flushed out compared to the amount desired in the finished product; the amount washed out can easily be determined by orientation tests.

This adhesion between the carbon particles and the fibers can be further improved if necessary by adding a flocculant. Such flocculants, also known as precipitants or retention aids, are known in cellulose fiber processing (for example paper manufacture) and are used to better integrate long fibers, fine fibers and fillers to improve the yield and the drainage behavior. It has been shown that the change in the electrical charge distribution in the suspension caused by such flocculants further supports the adhesion of carbon particles 3 on the fibers 2 , probably due to electrostatic forces. The carbon particles 3 are also in large quantities on the fibers 2 held.

example

Ash wood is shredded at a grinding distance of 0.1 mm and thermally digested. Fibers result 2 relatively large length with a maximum of the frequency distribution of the fiber length over 12 mm.

The fibers 2 are added to the suspension in an amount of 75% by weight, based on the total weight of the finished dry fiberboard. 3% by weight phenolic resin, based on the total weight of the finished dry fiberboard, is stirred in as a binder. Finally, graphite powder is stirred in in an amount of 22% by weight, based on the total weight of the finished dry fiberboard, and the mixing process is continued until completely homogeneous mixing is achieved.

Then ent is carried out in a conventional manner watered and pressed in order to obtain a finished fiberboard with a proportion of 22% by weight of elemental carbon (in addition to the carbon in the phenolic resin and in the cellulose). This plate, possibly after being formed into a three-dimensional fiber body, is then used, possibly at a different location, as a preliminary product for the production of a ceramic material and subjected to coking (pyrolysis) with the exclusion of air and infiltrated with molten silicon and, if necessary, a final shaping subjected. All of these process steps are well known and therefore require no further explanation.

The one according to the present example manufactured molded body made of ceramic material is particularly suitable for the formation of a Photovoltaic element.

Claims (10)

Process for the production of a fiber body for the production of a ceramic material, in which a charrable, renewable natural raw material such as wood is broken down to form fibrous or fibrous particles, in which the particles are then pressed to form a fiber body, and in which the particles are pressed before being pressed a high-carbon (C) -containing substance such as an organic binder is added, characterized in that as or in addition to the high-carbon (C) -containing material (s) before the injection of elemental carbon in the form of, for example, purified soot, ground graphite or the like is added in an amount of 5 to 50% by weight based on the total weight of the dry fiber body thus formed. A method according to claim 1, characterized in that the elemental carbon for the production of a ceramic material, especially for use as a photovoltaic element, in an amount of 8 to 40% by weight, preferably 15 to 30% by weight, more preferably 20 to 25% by weight and in particular of about 22% by weight, based on the weight of the finished product fiber body is added. A method according to claim 1 or 2, characterized in that that the Particles to form the fiber body in a usual Wet technique in an aqueous Suspension preferably with water-soluble organic binder and suspended the elemental carbon and to form the fiber body after drainage pressed become. A method according to claim 3, characterized in that the suspension ( 1 ) a flocculant is added. A method according to claim 1 or 2, characterized in that that the Fibers to form the fiber body from digested fiber components in a usual Filed dry process to form a nonwoven and preferably needled, and the elemental carbon on the so formed if necessary, needled fiber fleece is added and incorporated into it becomes. A process for producing a ceramic material with the following process steps: (1) a carbonizable substance broken down into fibrous or fibrous particles in the form of a renewable natural raw material such as wood is shaped and pressed into a fibrous body and coked under non-oxidizing conditions; (2) the after level ( 1 ) formed fiber body is infiltrated with silicon above the melting point of silicon and cooled to room temperature; (3) the according to level ( 2 ) obtained body is then optionally subjected to a usual mechanical post-processing for final shaping; with the shredded material in step ( 1 ) before the pressing, a high carbon (C) -containing substance such as an organic binder is added, characterized in that as or in addition to the high carbon (C) -containing material (s) at step ( 1 ) before the injection of elemental carbon in the form of, for example, cleaned carbon black, ground graphite or the like, in an amount of 5 to 50% by weight, based on the weight of the dry fiber body before coking, is added. A method according to claim 6, characterized in that the elementary carbon for the production of a ceramic material, especially for use as a photovoltaic element, in an amount of 8 to 40 % By weight, preferably 15 to 30% by weight, more preferably 20 to 25% by weight and in particular by 22% by weight, based on the weight of the dry fibrous body before coking is added. A method according to claim 6 or 7, characterized in that that the Particles to form the fiber body in a usual Wet technique in an aqueous Suspension preferably with water-soluble organic binder and suspended the elemental carbon and to form the fiber body after drainage pressed become. A method according to claim 8, characterized in that the suspension ( 1 ) a flocculant is added. A method according to claim 6 or 7, characterized in that the fibers for forming the fiber body from disintegrated fiber components are deposited in a conventional drying process to form a nonwoven and preferably needled are, and the elementary carbon is applied to the possibly formed needled nonwoven fabric and incorporated into it.