DE10348798A1 - Carbide and oxide ceramics and process for their preparation - Google Patents

Abstract

The invention relates to a carbide and oxide ceramic in a certain, previously imaged in a paper structure form. According to the invention, an inner skeleton consists of a metal carbide, such as silicon carbide (SiC), and an outer layer of oxide ceramics. The invention further relates to a method for producing such a ceramic.

Description

The The invention relates to a carbide and oxide ceramic after The preamble of claim 1 and a method for the production such a ceramic.

For a variety of applications such as thermal insulation structures, kiln furniture, pore burner substrates as well as fire protection structures, porous ceramics are needed. One other application for porous Ceramics is in the range of catalyst supports.

1 shows a ceramic body according to the prior art. A method is already known in which corrugated cardboard bodies or other paper structures are immersed in a slurry of metallic or ceramic powders, whereby an outer coating takes place. (Sieber T. Fey, D. Schwarze, M. Weidner and M. Kress, "Production of Porous Ceramics from Paper Structures", in Das Keramiker Jahrbuch 2002, Ed .: H. Reh, Göller Verlag, Baden-Baden / Germany Pages 47-54 (2003).) The correspondingly dipped papers are subsequently subjected to pyrolysis in inert gas at 1400 ° C. and to a subsequent tempering treatment in the air at 1400 ° C. This process procedure already produces high-temperature-resistant, relatively low-weight cellular ceramics . In the 1 Such a corrugated cardboard structure is shown, denoted here by 10 the core of paper fibers and 12 the metal powder coating surrounding this core. Disadvantage of the previously known method is that on the one hand, the coating to be made is relatively expensive. Furthermore, no coating with the reactive substances is possible inside the paper structure. In addition, a coating is only possible for bodies that are submersible. This excludes any type of hollow bodies into which the slurry can not penetrate. Furthermore, in a coating of finest structures, such as a fine wave in the corrugated board, a uniform coating of the surface by immersion in the slurry is no longer guaranteed.

task The invention is a carbide and oxide ceramic and to admit a process for their preparation to the hand, with the preferably any body, which were previously imaged in a paper structure can be.

According to the invention this Task by a carbide and oxide ceramic with the features of claim 1.

Therefore are carbide and oxide ceramics in a particular, previously provided in a paper structure, provided an inner skeleton of a metal carbide such as silicon carbide (SiC), and an outer layer made of oxide ceramic.

Prefers The carbide and oxide ceramics can also be in the form of a previously imaged paper structure may be formed as a composite ceramic.

• – Cellulosefasern und Metallpulver werden gemischt und zu einem Papier verarbeitet,
• – das hergestellte Papier wird über eine Pyrolyse bei Temperaturen zwischen 800°C und 1400°C in inerter Atmosphäre karbonisiert,
• – das karbonisierte Celluloseskelett wird mit dem vorhandenen Metall zu Metallcarbid reagiert,
• – die restlichen Füllmaterialien werden an der Luft bei Temperaturen zwischen 800°C und 1400°C oxidiert.

According to the invention, the method for producing such a carbide and oxide ceramic comprises the following steps:

• Cellulose fibers and metal powders are mixed and made into a paper
• The paper produced is carbonized by pyrolysis at temperatures between 800 ° C and 1400 ° C in an inert atmosphere,
• The carbonated cellulose skeleton is reacted with the metal present to form metal carbide,
• - The remaining filler materials are oxidized in air at temperatures between 800 ° C and 1400 ° C.

The The aforementioned process brings the reactive fillers already in papermaking one. Here papers are achieved with high filler content, wherein a homogeneous distribution of the metal powder is achieved.

The use of filled papers, in which a high proportion of metal powders (for example Si, Al) is introduced as filler already in papermaking, substantial advantages can be achieved in the implementation in ceramic components. On the one hand eliminates the one or more infiltration of the paper structure with a slurry, which leads to a reduction in manufacturing costs. On the other hand, the Ho significantly improves the homogeneity of the distribution of the filler powder in the cellulose paper structure, resulting in a more homogeneous and improved property of the reacted ceramic. As an improved property, in particular an improved mechanical strength can be determined.

Finally, too closed-porous Paper structures, for example, covered with a layer of paper cellular structures.

The filled paper is further processed into hollow bodies and converted into ceramic by an annealing treatment. The reacted ceramic thus consists of an inner metal carbide skeleton, z. B. in SiC reacted cellulose fibers, and an outer layer of oxide ceramic by the oxidation of the fillers (eg., Al ₂ O ₃ , SiO _2, etc.).

Special Advantages of the invention are in accordance with the claim 3 subsequent under claims achieved. So can advantageous for achieving a high filler content of 75% by weight or more based on the dry matter of cellulose fibers and metal powders existing mixture of organic binders added become.

When For example, organic binder may be starch, preferably in a proportion of 3% by weight to 6% by weight. alternative can according to a Another advantageous embodiment of the invention as organic Binder a synthetic binder such as latex, Here, preferably to a proportion of up to 5 wt.%, Are used.

In addition, flocculation and retention agents are used.

The starting paper more preferably has a basis weight of 80 to 350 g / m ² .

Preferably The prepared base paper is a molding step before the pyrolysis step subjected, for example, a corrugation or corrugated board production.

Further Details and features of the invention will become apparent from a in the drawing illustrated embodiment. Show it:

1 : a cellular ceramic in corrugated form according to the prior art,

2 FIG. 2 is a schematic drawing of a metal powder filler web of the present invention and FIG

3 FIG. 3 is a schematic drawing of the ceramic-reacted paper structure of the present invention. FIG.

In the 2 is shown schematically a paper web with metal powder filler, here pulp or paper fibers 14 with metal powder 16 mixed as homogeneously as possible. In accordance with the process of the invention, the reactive fillers are already incorporated in papermaking. Of particular importance is to achieve a high filler content and to achieve a homogeneous distribution of the metal powder. Examples of recipes for papermaking with such high filler contents result from the following formulations.

Option A:

Execution:

Experiments A: Preparation of sheets with 80-100 g / m ²

A 3% pulp suspension was prepared from sulfate pulp fibers. This 3% suspension was diluted to 0.3% with tap water. 13.33 g of small particle size silica powder were weighed into a watch glass. The silicon powder was used in 1800 g of tap water with stirring. 18 ml of CaCl ₂ solution were used to achieve at least a water hardness of 35 ° dH. Subsequently, 3.81 ml of latex (5%) were diluted to 30 ml with distilled water and used for the solution. The mixture was stirred for at least 15 minutes to form flakes. 317 g of pulp suspension were weighed in and stirred vigorously. 0.635 ml of 1% fixer solution was added to the fibers. After 2 minutes of mixing, 3.175 ml of retention aid (0.1%) was added. After the addition of retention aid, the fibers were agglomerated. After 5 minutes, the fibers were separated again. After a further 5 minutes reaction time, 310 g of the silicon-latex mixture was added. The mixture was stirred for 30 seconds before being transferred to the foliar former. From the mixture, a leaf was prepared and dried.

Experiment B: Preparation of sheets at 200 g / m ²

A 3% pulp suspension of sulfate pulp fibers was prepared and diluted to 0.3% with tap water. 13.33 g of small particle size silicon powder were weighed in a watch glass. The silicon was added to 1800 g of tap water with stirring. 18 ml of CaCl ₂ solution were used to achieve a minimum water hardness of 35 ° dH. 3.81 ml of latex (5%) was diluted to 30 ml with distilled water and added to the solution. The mixture was stirred for at least 15 minutes to form flocculates. 634 g of pulp suspension were weighed in and stirred vigorously. Twice 0.635 ml of 1% fixer solution was added to the fibers. After 2 minutes of mixing time, 3.175 ml of retention aid (0.1%) was added twice. After addition of the retention agent, the fibers were agglomerated. After 5 minutes, the fibers were separated again. After 5 minutes reaction time, 620 g of the silicon-latex mixture was added. The mixture was then stirred for 30 seconds before being transferred to the foliar former. A sheet was prepared and dried.

The leaves from experiment A had a leaf weight of 100 g / m ² . The filler retention is slightly higher than 60% of the added silicon, assuming that 100% of the fibers remain on the sheet.

The leaves according to trial B have a very good retention, namely about 80%. The strength is extremely high here. It has reached a full opacity here. The formation has no visible gap. The surface is smooth.

Variant B:

According to one second variant can 30% by weight of fibers with 35% by weight of silicon powder, 35% by weight of aluminum Powder, 4.5% by weight starch based on 100% filling and pulp, 1.5 wt% polyaluminum chloride and 3 wt% fixer (a polymer based on vinylamine and N-vinyl-formamide) become.

The papers produced according to the variants A and B are then subjected to a molding process, so that they, for example, a in 3 have shown corrugated structure. These preformed structures are then carbonized in a pyrolysis step at temperatures between 800 and 1400 ° C. in an inert atmosphere, and then the carbonated cellulose skeleton is reacted with the Si present to form SiC. In the following, the remaining fillers are oxidized in air at temperatures between 800 and 1400 ° C.

As a result, thin-walled, hollow-walled structures in any conceivable spatial form, which can be derived from the paper preform, for example, a corrugated cardboard structure, as in 3 shown prepared.

Claims (10)

Carbide and oxide ceramics in a specific, previously depicted in a paper structure by an inner skeleton of a metal carbide, such as Silicon carbide (SiC), and an outer layer made of oxide ceramics. Carbide and oxide ceramic according to claim 1, characterized in that they are in the form of a previously depicted Paper structure is formed as a composite ceramic. Process for producing a carbide and oxide ceramic according to claim 1 or 2, characterized by following steps: - Cellulose fibers and metal powders are mixed and made into a paper, - the produced Paper is over pyrolysis at temperatures between 800 ° C and 1400 ° C in an inert atmosphere, - the carbonized Celluloskeletal is present with the existing in the molten metal Metal reacts to metal carbide, - the remaining filling materials are oxidized in air at temperatures between 800 ° C and 1400 ° C. Method according to claim 3, characterized that to achieve a high filler content of 75 wt.% based on the dry matter of cellulose fibers and metal powders existing mixture of organic binders are added. Method according to claim 4, characterized in that that as organic binder starch, preferably to a Proportion of 3 wt.% To 6 wt.% Is used. Method according to claim 4, characterized in that in that as organic binder a synthetic binder, such as latex, preferably in an amount of up to 5% by weight, is used. Method according to one of claims 4 to 6, characterized that in addition Flocculants and retention agents are used. Method according to one of claims 4 to 7, characterized in that the starting paper has a basis weight of 80 to 350 g / m ² . Method according to one of claims 4 to 8, characterized that before the pyrolysis step, the prepared base paper a forming step is subjected, for example, a corrugation or corrugated board production. A method according to claim 3, characterized in that the reaction to the metal carbide is preferred takes place at about 1200 ° C.