CS253080B1 - Ground ceramic mixture - Google Patents

Abstract

The solution concerns the composition of the ground mixture for the production of sintered quartz porcelain. This is a special case of a ceramic mixture containing significant amounts of finely ground quartz, the high-temperature modification of which during sintering is stabilized by the presence of an active flux (rocks of the syenite group with foids) or by the addition of alumina or by the addition of a radical flux component (Ti, Ca, Mg, Ba, AI). All components can complement each other.

Description

The invention relates to a ground ceramic mixture for the production of sintered quartz porcelain, preferably electrical, processed by plastic forming, casting, pressing and isostatic pressing technology with firing temperatures of 1,050 °C to 1,300 °C.

The ground ceramic mixture contains significant amounts of finely ground quartz, the high-temperature modification of which is stabilized during sintering by the presence of an active alkaline flux component or by the addition of an alumina component or by the addition of a radical flux component. The above components may be complementary.

For ground quartz porcelain mixtures with a higher content of fine quartz grains, for normal firing at temperatures higher than 1,300 °C, feldspar flux is still mostly used. During sintering, the feldspar flux partially dissolves the quartz, forming a heterogeneously distributed high-silica melt, from which secondary cristobalite can crystallize upon cooling after reaching the maximum firing temperature. This principle is used in Japanese mullitocristobalite porcelain, where the cristobalite content is maintained at a constant level by high technological discipline throughout the production process. Failure to maintain a constant cristobalite content in the fired shard has very adverse consequences on the quality of the shard-glaze bond and leads to defects and even destruction of the products. If mullitocristobalite porcelain is produced under optimal conditions, it has excellent mechanical strength and a highly ductile fracture. Its resistance to sudden temperature changes is somewhat lower, due to the modification transformation of (-β cristobalite.

In European and Czechoslovak conditions, mullite-cristobalite porcelain was prepared in the laboratory using silica schists, bulla and quartzites, or other raw materials containing fine-grained quartz with a grain size of less than 30 μm. However, in production conditions, preference was given to corundum porcelain due to its lower technological complexity. Some manufacturers, especially in both German states, produce porcelain with a high quartz content (over 30% in the original mixture), while suppressing the formation of cristobalite by selecting a suitable quartz raw material that has a higher resistance to dissolution in the feldspar melt and it is also necessary to use forced cooling (subcooling) immediately after firing to prevent the possibility of cristobalite crystallization from the melt.

For common firing temperatures in the vicinity and above 1,300 °C, it is not possible to use sinter or similar materials as a flux for quartz porcelain. Due to the very low viscosity of its melt at these temperatures and its high reactivity and aggressiveness towards quartz, it converts it almost quantitatively into a homogeneous melt, from which secondary mullite crystallizes after cooling. Since the closed porosity of the fired shard increases significantly at the same time, the expected positive effect of the originally increased quartz content on the resulting mechanical strength is lost.

The disadvantage of the prior art is that at relatively high firing temperatures, usually above 1,300 °C, the cristobalization of finely ground mixtures for the production of quartz porcelain is difficult to control during firing, or it is relatively difficult to eliminate this cristobalization. The existing technology is therefore significantly dependent on the human factor in controlling the grinding and firing operation, while the investment requirements are not negligible.

The disadvantages of the current state of the art are solved by a ground ceramic mixture for the production of sintered quartz porcelain fired at 1,050 to 1,300 °C containing 7 to 55% by weight of quartz component, up to 40% by weight of feldspar flux component, up to 55% by weight of clay component, up to 30% by weight of kaolin clay component, characterized in that it further contains 0.1 to 20% by weight of active alkaline flux component or 0.1 to 10% by weight of alumina component or 0.1 to 10% by weight of radical flux component or a combination thereof.

The active alkaline flux component is formed by rocks of the syenite group with fiody, preferably phonolite.

The alumina component is formed by alumina, preferably alumina in alpha modification, or possibly hydrated alumina.

The radical flux component contains compounds of titanium, or calcium, or magnesium, or barium, or aluminum, or a combination thereof, the desired content being possible to achieve in the form of accompanying impurities of the basic components of the mixture.

The advantage of the invention is that the required sintering temperature of quartz porcelain is significantly reduced. In addition to direct energy savings, secondary savings are achieved on furnace units and firing aids both in terms of reduced acquisition costs and their service life. In the actual sintering of quartz porcelain, stabilization of the high-temperature modification of quartz is achieved and, consequently, the expansion ratios between the fired shard and the glaze are also stabilized (without the risk of cristobalation of the shard), which contributes to reducing the dispersion of the results of the monitored properties of sintered products manufactured from the ground ceramic mixture according to the invention. In all possible weight ratios of the individual components of the ground ceramic mixture according to the invention, zero water absorption of the shard is ensured, unlike utility ceramics.

Stabilization of high-temperature modification of quartz is achieved in three possible ways or combinations thereof.

1. The addition of an active alkaline flux, preferably feldspar, significantly reduces the sintering temperature of the porcelain mixture. At temperatures below 1,250 °C, the feldspar melt has a significantly higher viscosity than at normal firing temperatures above 1,300 °C, it is no longer so aggressive towards quartz grains and only converts the peripheral parts of the quartz grains into the melt. Due to the increased content of alkalis and alumina in comparison with the feldspar melt, the feldspar melt blocks the possibility of forming a high-silica melt in the vicinity of the quartz grains and thus the possibility of crystallization of secondary cristobalite.

2. The alumina component again acts against the formation of a high-silica melt around the quartz grains. In mixtures containing feldspar fluxes, alumina, together with the edge parts of the quartz grains, is dissolved in the feldspar melt, thereby shifting the Al^O^ : SiC^ ratio in the resulting melt towards Al^O^. When cooling from such a melt, mullite crystallizes preferentially, while the crystallization of secondary cristobalite is suppressed.

3. Radical flux additives, in addition to their effects on quartz grains, or possibly on A^O^ grains, increase the Al^O^ concentration in the melt by dissolving clay and thus again block the crystallization of secondary cristobalite in the vicinity of the melted quartz grains and support the formation of secondary mullite. They are usually used to supplement the effect of the active flux component or the alumina component.

The invention will be explained by the following examples.

Example 1

From a mixture with the composition % wt. quartz component consisting of sand T 25 % wt. feldspar flux component consisting of feldspar Ž 65KNa % wt. clay component consisting of kaolin Sedlec Ia (15%), clay JHD II (15%) and tumerite (5%) % wt. active alkaline flux consisting of phonolite Železnice, after grinding to a final residue of 1.2 % wt. on mesh 0063, test specimens were prepared by drawing under vacuum on a laboratory belt press. During firing, the sintering interval of this mass was determined between 1,180 and 1,250 °C (determined by the absorbency of the dye). After firing at 1,200 °C, the mean coefficient of linear thermal expansion was determined in the temperature ranges:

horse

20-100 °C 5.85 . . 10' ⁶ (deg 20-200 °C 5.86 . . ίο' ⁶ 20-300 °C 6.21 . , 10- ⁶ 20-400 °C 6.70 . , 10' ⁶

(X 20-500 °c 7.26 . 10- ⁶ d 20-600 °c 8.30. 10- ⁶ λ' 20-700 °c 7.55 . 10- ⁶ A' 20-800 °c 7.13 . 10- ⁶ At the same time, it was detected mechanical bending strength on samples 0 10 mm. and that from oxidation fire to 1,200 °C 68.1 i MPa unglazed and 94.2 MPa glazed samples. From reduction firing

at 1200 °C then 71.3 MPa for unglazed samples and 92.1 MPa for glazed samples. The fired shard of material was perfectly sintered with zero water absorption.

The results of the dilatation measurements show that the significant dilatation effect of quartz was retained for the value of 20-600 °C, the effect of cristobalite at 200 °C was not recorded.

Example 2

The mass with the composition % wt. quartz component formed by sand T 25 % wt. feldspar component formed by feldspar Ž 65KNa % wt. clay component formed by kaolin Krásný Dvůr (16%), clay JHD II (15%), and clay BD (5%) % wt. active alkaline flux component formed by phonolite Železnice % wt. alumina component formed by mineralized alumina AlFg % wt. radical flux component formed by dolomite (compound of magnesium and calcium) was, after grinding to a final residue of 0.5 % wt. on a 0063 mesh, processed by drawing under vacuum into test specimens. During firing, the sintering interval of this mass was found to be 1,170 °C-1,120 °C (determined by the absorbency of the dye). After reduction firing at 1,220 °C, the mean coefficient of linear thermal expansion was found in the temperature ranges:

4 20-100°C 5.46 . . ΙΟ' ⁶ 20-200 °C 5.30 . . ΙΟ' ⁶ 20-300 °C 5.61 . , ΙΟ' ⁶ 20-400 °C 6.06 . . ΙΟ' ⁶ for 20-500 °C 6.50 . . 10 ^_6 dÚ 20-600 °c 7.37 . . ΙΟ' ⁶ about? 20-700 °c 6.82 , . ΙΟ' ⁶ d? 20-800 °c 6.31 . . ΙΟ' ⁶

A perfectly sintered shard had the following parameters:

mechanical bending strength (unglazed samples) 70.3 MPa mechanical bending strength (glazed samples) 91.3 MPa electrical breakdown strength 30.9 kV . mm ¹ dielectric constant 192 . ' 10 ^-4 surface resistivity 6.16 . ίο ¹² Π. specific internal resistance at 25 °c 2.9 . 10 ^x 10 m specific gravity 2,517 0 g/ ^cm2 volumetric weight 2,411 g/ ^cm3 closed porosity 4.21 %

The dilatation measurements showed that no effect of the modification transformation of cristobalite was recorded at 200 °C.

Example 3

Mass with composition % wt. quartz component formed by sand T 25 i

% wt. feldspar component consisting of feldspar Ž 65 KNa % wt. clay component consisting of Premier kaolin (20%), Sedlec Ia kaolin (25%) and BD clay (5%) % wt. radical flux component consisting of Chinese talc (Mg compound - 3% wt. of total content) and barium carbonate (Ba compound - 2% wt. of total content) was ground to a final residue of 1.6% on a 0063 mesh.

After processing into granules with the addition of MK oil-water separator, the mass was flow-pressed into low-voltage insulation products (fuse cases, sockets, etc.), white glazed and fired at 1,220 °C. The white dense shard met the requirements of ČSN 34 6301 (STE SEV 3567-82) group 100, subgroup 111.

Example 4

Material composition % wt. quartz component formed by sand T 25 % wt. clay component formed by kaolin Krásný Dvůr (22%), clay JHD II (16%) and clay BD (3.5%) % wt. feldspar component formed by feldspar Ž 65 KNa i wt. alkaline active flux component formed by phonolite Želenice

1.5% by weight of the radical flux component consisting of rutile (titanium dioxide)

2.5% by weight of the alumina component consisting of alumina mineralized with aluminum fluoride was, after grinding to a final residue of 1.8% by weight on 0063 mesh, processed by vacuum drawing into test specimens. During firing, a sintering interval of 1,160 °C-1,250 °C was found. In the optimum, during reduction-guided firing at 1,220 °C, the fired shard of material showed the following parameters:

mechanical bending strength mechanical bending strength of glazed shard electrical breakdown strength dielectric constant £ _r tg (Γ specific surface resistivity specific internal resistivity

74.9 MPa 93.2 MPa 32 kV . mm ⁴

7.5

184 . 10~ ⁴

4.84 . 10 2.31 . 10 ¹¹ m.

At the same time, the following coefficients of linear thermal expansion were determined in the temperature ranges:

20-100 °C 4.68 . . 10- ⁶ 20-200 °C 4.85 . . 10' ⁶ 20-300 °c 5.14 . . 10- ⁶ 20-400 °c 5.51 , . 10- ⁶ 20-500 °c 5.84 , . 10- ⁶ 20-600 °c 6.50 . . 10- ⁶ 20-700 °c 6.04 . . 10- ⁶ 20-800 °c 6.00 . . 10~ ⁶

jf 20-100 °C 4.68 . 10 ^b (deg ^-1 ) %

A ď Λ d) which again demonstrated the elimination of cristobalite formation in the shard. The dense shard with zero water absorption due to the coloring effect of titanium dioxide is colored dark gray-blue.

Claims (4)

SUBJECT OF THE INVENTION A ground ceramic composition for the production of sintered quartz porcelain fired at 1050 to 1300 ° C containing 7 to 55% by weight of the silica component, up to 40% by weight of the feldspar component, up to 55% by weight of the clay, up to 30% by weight calcined further comprising 0.1 to 20% by weight of the active alkaline flux component or 0.1 to 10% by weight of the alumina component or 0.1 to 10% by weight of the radical flux component or a combination thereof. 2. The ground ceramic composition according to claim 1, wherein the active alkaline flux component is composed of rocks of the group of foen syenites, preferably phonolite. 3. The ground ceramic composition according to claim 1, wherein the alumina component is formed by alumina, preferably alumina in alpha modification, optionally hydrated alumina. 4. The ground ceramic composition of claim 1, wherein the radical flux component comprises titanium or calcium or magnesium or barium or aluminum compounds or a combination thereof, the desired content being obtained by way of the impurities of the constituent components of the composition.