CS215253B1 - Method of treating the ceramic materials for increasing workability and rigidity by the dry bending - Google Patents

Abstract

The plasticity and/or dry flexural strength of ceramic masses are improved by using as plasticizer a water-soluble or colloidally-soluble microbial polysaccharide (I) of mean mol. wt. >2 x 105, at 0.005-0.5% based on the material to be plasticized. Pref. (I) is Xanthomonas polysaccharide and may be added to one component of the mixt. of raw materials, or to a complete blend either as slurry, partly-dewatered material or as dry substance. Esp. it is added to a ceramic spray-granulate before or during conversion of the granulate to a processable form. Used. esp. for porcelain and earthenware mfr. No undesirable materials are produced from (I) during sintering and starting materials of poor plasticity can now be used.

Description

The invention relates to a process for the processing of ceramic materials to increase their ductility and dry flexural strength, which can be used in particular in conventional formulations for hard porcelain, electrotechnical porcelain and medical porcelain, as well as for porcelain.

For the production of ceramic goods, raw materials, namely kaolins, clays, feldspars and sands, are processed into foundry, ductile or molding materials. Sufficient ductility and dry strength are assumed for the forming of the ductile materials to provide crack-free forming and rapid drying as well as the desired strength for further processing.

Generally, the ductility of ceramic materials is ensured by the use of highly ductile kaolins a) or clays. There is an increasing shortage of these materials and, moreover, very ductile kaolins and / or clays generally contain harmful substances as they do not. A considerable proportion of coloring oxides is obtained in the molding mixture. These ceramics are therefore not applicable to the production of articles with a high degree of whiteness.

Numerous methods have already been proposed to increase ductility, and suitable materials have been added to the raw materials or materials. However, the addition of hydrophobic substances, such as emulsions or possibly dispersible, also in conjunction with hydrophilic soluble components, has the disadvantage that it does not satisfy the requirements for the circulation of the mass since irreversible changes occur during drying.

In addition, emulsions, when used in casting materials, are characterized by certain negative effects due to density differences, or agglomerations may occur, since the stability regions of the emulsion and the casting material are generally not consistent. Although the use of water-soluble substances or colloidal solutes, such as starch, starch derivatives, casein or esters, makes it possible to increase the ductility of the ceramic masses when choosing the appropriate concentration, the amount of these compounds used is so significant that (soda, water glass, tannin derivatives, humic acid derivatives) is not possible due to the thickening of these substances. The sharp reduction of the plasticizer content makes it possible to manufacture the casting compound, but then it is no longer possible to show an improvement in the formability. Thus, for example, for a cold-soluble starch, a significant increase in ductility at a concentration of 1% was used, while the production of a casting composition with the same starch below 0.05% is possible, but an increase in ductility can no longer be demonstrated.

Low-molecular-weight substances, such as plasticizers, have the serious disadvantage of leaving the site of action simultaneously with the filter water, since they are filterable and penetrate into the forming substances, which in turn adversely affect their function.

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Indeed, there is no known method for producing ceramics in which the use of suitable materials would not substantially increase their malleability and at the same content of these materials - if such ceramics could be processed by any conventional means such as continuous molding, injection molding, pressing, dialing and pouring. In addition, it is currently not possible to process kaolins (a) or clays with substances or add such substances at the raw material manufacturer during the treatment process, since the amount used also determines the processing method.

It has been found that it is possible to improve the ductility a) or the dry bending strength of ceramics by the addition of high molecular weight, water-soluble microbial polysaccharides and mixtures thereof, the concentration of which is chosen such that arbitrary conventional molding and processing methods can be selected. With the newly discovered addition, it is furthermore possible to plasticize the raw materials already at the treatment stage with the previously mentioned substances and to market them without adversely affecting the method of further ceramic use. As a result, it is also possible to make generally ceramically processable coarse-grained kaolins with a low content of harmful substances a) or clays, as well as to choose the most favorable raw materials with respect to product properties such as optical properties (whiteness, transparency), mechanical strength and tendency to deformation sintering, regardless of their original processing characteristics.

According to the invention, the plasticization of kaolins or clays or ceramics is essentially carried out by adding to the mixture or the individual components water-soluble or colloidal-soluble microbial polysaccharides having an average molecular weight of more than 200,000 and a content of 0.005 to 0, as plasticizers. 5%, based on the material to be plasticized. The water-soluble solutions of the microbial polysaccharides are introduced into suspensions or partially dehydrated suspensions of kaolins a) or clays or ceramic materials by mixing. The plasticized substances can then be suitably further processed, in particular, these basic operations have no effect on the plasticization, namely the dewatering of the suspension on the filter presses, the drying up to a maximum of 120 [deg.] C. as well as the dry grinding and wetting of the plasticized material.

In the case of raw materials or materials which are dewatered by spray drying, it is necessary to add plasticizers after this operation.

If only a portion of the raw material of the forming composition or mass according to the process is plasticized, this portion can be introduced into the entire forming composition as a slurry or as a partially dewatered material or as a dry mass before further processing.

The added amount of the above substances necessary to achieve plasticization is remarkably small and is less than 0.5% by weight. In general, from 0.01 to 0.05% by weight, based on the dry mass of the ceramic, is sufficient. ° / o.

With such a small proportion, no harmful effects occur as a result of the burning of the introduced substances in the sintering and thus of the processed materials. If the raw materials or materials plasticized by the substances are stored in a moist state for a longer period of time, it is expedient to add bactericidal and antifungal additives to prevent biodegradation.

The following examples illustrate the invention in more detail.

He did

0.1% of xanthomonas polysaccharides, based on its dry mass, was added to a slurry containing 45% water of low-plastic, coarse-grained kaolin with low pollutant content. Polysaccharide xanthomonase had a mean molecular weight of 1.2 million Daltons. After three hours of treatment, the plasticized kaolin was sintered. As a measure of plasticization for partially dewatered kaolin, the coefficient was determined from the tensile strength and shear of the material zone. The following results were achieved:

Kaolin v Plasticity value for the same processing consistency Little plastic kaolin '.

a) without addition of 0.047

b) with 0.1% xanthomonas polysaccharides 0.069

Very plastic kaolin Zettlitz la (for comparison) 0,070. Example 2

In the hard porcelain molding composition, very plastic kaolin was replaced by low-plastic kaolin in such a way that the rational analysis in the molding composition did not change, while in the molding composition, the very plastic kaolin was replaced by low-plastic kaolin and non-plastic hard materials.

0.014% of the polysaccharide, xanthomonase, based on dry substance, was used to plasticize the formation composition containing low plastic kaolin. In this process, the entire mixture was doped in suspension prior to compression on filter presses and the mixture was used in the wet state. For the second time, the low-plastic kaolin was doped with 0.1% xanthomonas polysaccharides in the sus. The mixture was then dried and stored for 2 months before being used in the dried state in the manufacture of the molding composition.

The following overview lists the plasticity coefficients for the dialing mass and several characteristics for the casting masses produced from said forming compositions.

Formation mixture 1 2 3 4

Formation mixture with very plastic kaolin Forming mixture with little 0,039 4.2 0.18 2.8 plastic kaolin 0.027 Formation mixture with 0.014% xanthomonase polysaccharides a) Whole formulating mixture 4.2 0.17 2.7 subsidized (b) low-plastic kaolin 0,044 3.2 0.22 separately subsidized It means: 0,042 3.6 0.26 3.2

Column 1 - plasticity coefficients

Column 2 - thickness of the body after 10 minutes in mm,

Column 3 - Apparent Viscosity in Pa. s at a shear rate of 170 s ¹ and a tap density

1.68 Gem ' ³ ,

Column 4 - dry bending strength in MPa

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Claims (4)

CLAIMS 1. A method for processing ceramic materials to increase their ductility and dry bending strength, characterized in that they are incorporated into a mixture. or the individual components add, as plasticizers, water-soluble or colloid-soluble microbial polysaccharides with an average molecular weight of more than 200,000 and a proportion of 0.005 to 0.5%, based on the material to be plasticized. 2. The method according to claim 1, characterized in that as. microbial. carbohydrate is used polysaccharide xanthomonase. 3. Method according to claims 1 and 2, characterized in that the raw material processed by the plasticizer is. they are introduced into the entire formulation mixture as a suspension, as a partially dewatered material, or as. dried substance. 4. A process according to any one of claims 1 to 3, wherein the plasticizer is added to the ceramic. spray granulate before. or during conversion of the granulate into a processing form.