DE102012017822B3 - Use of a mixture of konjac flour and welan gum as a binder for ceramic and powder metallurgy shaping - Google Patents

Abstract

The invention relates to the use of a mixture of konjac flour and welan gum as a binder for ceramic and powder metallurgy shaping. The inorganic grain used in the molding may consist of oxide, non-oxide ceramics, carbon or metallic grains. The particle sizes of the inorganic grains used are in the range from 50 nm to 10 mm. The binder used in the invention is particularly suitable for conventional slip casting, for Druckschlickerguss, for the casting of vibrating masses and self-flowing masses, as a binder in viscous masses in the extrusion, as a binder for the production of thin-walled products by means of film casting and paper technology, and also as a binder in the production of granules in the press molding. The object of the invention is to develop an environmentally friendly binder for ceramic and powder metallurgical shaping, which leads to a higher green strength of the moldings and during demolding to high-quality surfaces. According to the invention the object is achieved in that a mixture of konjak flour and welan gum is used as a binder for the ceramic and powder metallurgy shaping.

Description

The invention relates to the use of a mixture of konjac flour and welan gum as a binder for ceramic and powder metallurgy shaping. The inorganic grain used in the molding may consist of oxide, non-oxide ceramics, carbon or metallic grains. The particle sizes of the inorganic grains used are in the range from 50 nm to 10 mm. The binder used in the invention is particularly suitable for conventional slip casting, for Druckschlickerguss, for the casting of vibrating masses and self-flowing masses, as a binder in viscous masses in the extrusion, as a binder for the production of thin-walled products by means of film casting and paper technology, and also as a binder in the production of granules in the press molding.

In the ceramic and powder metallurgical shaping demolding flawless ceramic and metallic body is difficult. In order to ensure sufficient dimensional stability, the use of suitable binders is necessary.

The use of binders in the pressure slip casting is kaolin-free, technical ceramics particularly important. In Druckschlickergussverfahren a ceramic, metalloceramic or metallic slip by means of pressure up to 40 bar in a porous plastic mold, consisting of polymethyl methacrylate, promoted and dehydrated. After a casting time of a few minutes, stable shards can be demolded. This manufacturing process is especially established in sanitary / silicate ceramics. In contrast to slip casting in plaster molds, the casting time could be shortened considerably with the help of the pressure slip casting process. A longer service life of the plastic molds in contrast to gypsum is another advantage of this method. The use of kaolin in the silicate industry brings significant advantages for the pressure slip casting process. On the one hand, water is stored in the kaolin matrix, so that a stable body can be removed from the mold after only a short time, that is to say at a still higher water content. On the other hand, the platelet-like structure of kaolin closes the open porosity of the mold so that the water can continue to flow away, but prevents penetration of the fine-grained particles into the mold. The sticking of the ceramic cullet to the mold can thus be avoided. These kaolin benefits must be achieved with kaolin-free slips by selecting suitable binders [1].

In addition to the Druckschlickergussverfahren the use of binders in the production of ceramic, metalloceramic or metallic papers is necessary. Travitzky et al. represent the production of ceramics using paper technology [2]. In this case, a connection between the cellulose used and the ceramic and / or metallic particles must be achieved. Since the surface charges of both raw materials are negative, an additive with a positive surface charge is necessary as a mediator. The additives used today are mostly toxic, so replacement with environmentally friendly additives is necessary.

Welan Gum is an anionic polysaccharide produced by fermentation using Alcaligenes bacteria. The welan gum molecule consists of repeating tetrasaccharide units with L-rhamnose or L-mannose as the side chain. shows the schematic representation of a welan gum molecule [3].

Welan Gum is especially used as an additive in the cement industry. The patent US 5 004 506 A [4] highlights a variety of property improvements in cement mixtures by Welan Gum. For example, improved control of water loss, improvement in processability, and prevention of separation between water and cement. An improvement in the homogeneity of concrete preparations is disclosed in the patent AT 406 048 B [5]. Another application of Welan Gum is the production of ceramic filters. It serves as a spacer between the framework particles and leads to a targeted adjustment of the pore size of the membranes, such as the patent DE 600 321 98 T2 [6] clarifies.

Konjac flour is obtained from the tuber of the arum family and is rich in glucomannans. The main chain of the polysaccharide consists of D-glucose and D-mannose in a ratio of 1: 1.6. Konjac flour is characterized by a high water absorption capacity [7]. Konjac flour is used as a thickener in the food industry. In the patent EP 2 005 845 A1 [8] describes the effect of konjac flour as a thickener for preparing a base dispersion which is used, for example, for making lemonade.

Blends of welan gum and konjac flour are made according to US 2007/0275347 A1 [9] proposed as a thickening agent for an oral composition. The object of the invention is to develop an environmentally friendly binder for ceramic and powder metallurgical shaping, which leads to a higher green strength of the moldings and during demolding to high-quality surfaces.

According to the invention the object is achieved in that a mixture of konjak flour and welan gum is used as a binder for the ceramic and powder metallurgy shaping. The binder contains 20 to 80% konjac flour and 80 to 20% mahan gum. Particularly suitable are binders with a content of 55 to 75% by mass Konjakmehl and 25 to 45% by mass Welan gum. The binder is used by adding the binder powder mixture to the suspensions in proportions of up to 5% by mass based on the solids content of the suspension. However, it may also be expedient to suspend welan gum and Konjakmehl in water and then add this solution, the ceramic and / or powder metallurgical raw materials with stirring. Furthermore, it is possible to mix the binder dry with the ceramic and / or powder metallurgical raw materials and then to use this mixture for suspension production. Both Konjakmehl and Welan gum absorb water in their structure and can thus ensure the necessary stability for demolding, even at elevated water contents in the green body. The binder according to the invention leads to a lower water requirement in the preparation of the suspensions. A reduction of the water content from 14% to 10% by mass is possible. This results in fewer problems (no drying cracks) during drying. Furthermore, higher green strengths can be achieved and, finally, the new binder has no harmful environmental impact. Since konjac flour and welan gum are polysaccharides, they are non-toxic or environmentally harmful.

Using the example of pressure slip casting technology and paper technology, the advantages of the new binder are demonstrated in the following examples: Example 1: Offset table raw material Grain size in mm Share in% Calcined clay 0.0-3.0 85 reactive alumina 0.0 to 0.003 15 Welan gum 0.11 ¹ konjac flour 0.22 ^{1 1} addition amount based on solids content

To prepare a ceramic slip for pressure slip casting, a mixture of welan gum and konjak flour was weighed in a ratio of 1: 2. The total share was 0.33% by mass. This binder mixture was stirred with the aid of a rotor-stator homogenizer (Heidolph DIAX 600) into the required water (total water content: 10% by mass) and homogenized for 5 min. This mixture was subsequently homogenized with 90% by mass of Al ₂ O ₃ in a mixer from Eirich for 15 min. The slip was then dewatered by pressure slip casting for 15 minutes and a stable and faultless shard could be demolded. Example 2 Offset table raw material Grain size in mm Share in% Calcined clay 0.0-3.0 75 reactive alumina 0.0 to 0.003 15 steel powder d ₅₀ = 20 μm 10 Welan gum 0.11 ¹ konjac flour 0.22 ^{1 1} addition amount based on solids content

The preparation of the material according to the invention is carried out analogously to Example 1. The slip for the pressure slip casting according to the invention contains both ceramic and metallic raw materials. Example 3 Offset table raw material Grain size in mm Share in% Calcined clay 0.0-3.0 85 reactive alumina 0.0 to 0.003 15 konjac flour 0.33 ^{1 1} addition amount based on solids content

The preparation of the material according to the invention is carried out analogously to Example 1. In this case, only Konjakmehl was used as a binder. The resulting slurry was then dewatered by pressure slip casting. The casting time was extended to 30 minutes and the shards were not stable at the corners and could not be demoulded correctly. Example 4 Offset table raw material Grain size in mm Share in% Calcined clay 0.0-3.0 85 reactive alumina 0.0 to 0.003 15 Welan gum 0.33 ^{1 1} addition amount based on solids content

The preparation of the material according to the invention is carried out analogously to Example 1. Only Welan gum was used as a binder. The slip obtained showed too high a viscosity for the pressure slip casting. In order to ensure sufficient flowability, the water content had to be increased to 14% by mass. The slurry was then dewatered by pressure slip casting. The casting time was extended to 45 minutes due to the higher water content. Example 5 Offset table raw material Type Manufacturer charge in% ZrO ₂ Mg-PSZ S & G 1.3 μm 94.02 cellulose 5.98 Σ 100.00 additives Catiofast® 0,20 ¹ DADMAC 0,10 ¹ Welan Gum: Konjac flour = 1: 2 1,00 ^{2 1} addition amount based on cellulose fiber
^{2 added} amount based on ceramic and / or metallic raw material

The cellulose is processed with distilled water in a compulsory mixer for 10 min to a fiber suspension (A). In this fiber suspension, the Catiofast is added first and after a mixing time of 2 minutes the CADMAC. The fiber suspension is stirred for a further 5 minutes and allowed to rest in succession for 5 minutes to allow fiber-fiber flakes to form. Following this, the fiber-fiber flakes are re-separated by moderate agitation to homogenize the suspension. The ceramic suspension (B) is prepared in a further mixing vessel. For this, the additive mixture consisting of welan gum and Konjakmehl is dissolved in distilled water and added to the ceramic raw material. Suspension B is stirred for about 20 minutes to form flakes here as well. In the next step, the suspension B is added to the fiber suspension A. This mixture is stirred for 40 s and then transferred to a preceramic paper with the aid of a foliar-forming agent. After drying, the preceramic paper is pressed at a pressure of 50-200 MPa, subsequently debinded and sintered. Example 6 Offset table raw material Type Manufacturer charge in% stole 1.4301 TLS 0751 / 3M 11,95 ZrO ₂ Mg-PSZ S & G 1.3 μm 82.07 cellulose 5.98 Σ 100.00 additives Catiofast® 0.20 DADMAC 0.10 Welan Gum: Konjac Flour: 1: 2 1.00

The preparation of the material according to the invention is carried out analogously to Example 5. The suspension B according to the invention contains both ceramic and metallic raw materials.

Literature:

• [1] Technical Ceramics, Wolfgang Kollenberger, Vulkan Verlag 2004, p. 382-394
• Travitzky, N .; Windsheimer, H .; Fey, T .; Greil, P .: Preceramic Paper-Derived Ceramics, J. Am. Ceram. Soc .: 91 [11] P. 3477-3492 (2008)
• [3] Product data sheet of the company Colltec
• [4] Allen, F., Best, G., Lindroth, Th .: "Welan Gum in Cement Compositions", United States Patent US 5,004,506 , 1991
• [5] Cement Intellectual Property Ltd .: "Process for the preparation of a liquid additive based on water-soluble welan gum", patent AT 406 048 B , 2000
• Takahashi, T., Isomura, M., Murasato, M .: "Process for the preparation of filters with ceramic porous film as a release film", Patent DE 600 321 98 T2 , 2007
• [7] Chao Wang, Mei Xu, Wen-ping Lv, Pei Qiu, Yuan-yuan Gong, Dong-sheng: Study on Rheological Behavior of Konjac Glucomannan, 2012 International Conference on Medical Physics and Biomedical Engineering, Volume 33, 2012, Pages 25-30
• [8] Bonerz, D., Fuesser, H., Wydra, M., Krug, H., Euler Horn, E .: "Disperser base material", patent EP 2 005 845 A1 , 2008
• [9] Gruber, P .: "Pumping System for an oral coposition", patent US 2007/0275347 A1

Claims (3)

Use of a mixture of konjac flour and welan gum as a binder for ceramic and powder metallurgy shaping. Use of a mixture of konjac flour and welan gum as a binder for the ceramic and powder metallurgy shaping according to claim 1, characterized in that the mixture consists of 20 to 80% by mass Konjakmehl and 80 to 20% by mass Welan gum. Use of a mixture of konjac flour and welan gum as a binder for the ceramic and powder metallurgy shaping according to claim 1 and 2, characterized in that the mixture consists of 55 to 75% by mass Konjakmehl and 25 to 45% by weight Welan gum.

Images