CS204133B1 - Ceramic material for producing coatable,impervious sintered corpuscles - Google Patents

Abstract

Dense bodies suitable for glazing, consisting mainly of quartz. and glass sintered non-reactively at temps. below 1000 degrees, are improved in that the compsn. comprises (a) 39-64 wt.% of a comminuted quartz-rich material (contg. in wt.%: SiO2>=97, Al2O3=1, Fe2O3=0.4, R2O=0.5, alkaline earth metal carbonates =0.5, and water-soluble salts =0.1); compsn. further comprises (b) 35-60 wt.% of a comminuted glass (contg. in mole%: SiO2 65-77, Al2O3 3.0-5.5, B2o3 0-12, Na2O+K2O 11-16, BaO 1.5-5., MgO and/or CaO and/or SrO 2.5-7.0); and (c) 0.5-4 wt.% of AlF3 or its source. The material has a softening temp. of 700-850 degrees C. The dielectric loss than 35 x 10-4 (at 1 MHz). The thermal expansion coefft. alpha >8 x 10-6 degrees C-1 (50-400 degrees C). The grain size is: 60 wt.% 15 mu; 15 wt.% 2 mu. These materials can be used in electroceramics, as they have mechanical and electrical properties similar to stearite. They can be produced from cheap materials such as low-grade quartz sand and wastes from kaolin processing.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glass and quartz ceramic mass with an additive of 0.5 to 4% by weight of aluminum fluoride for the production of glazable, impermeable sintered bodies having mechanical and electrical properties analogous to steatity by non-reactive sintering at temperatures below 1000 ° C.

It is known that products of electroceramic steatite KER 200 TGL 7838 from magnesium silicates, clay, and fluxing agents such as feldspar or barium carbonate produced by firing at temperatures above 1,350 DEG C. When ^Q that forms a ceramic body which consists of glass and the crystalline phases of protoenstatite. The electrical properties of the body are essentially determined by the chemical composition of the glass phase. If it contains alkali derived from flux, feldspar, the electrical properties of this product of type KER 220, when using barium carbonate flux, on the other hand, are of type KER 221 or KER 225. The high firing temperatures required to produce these materials prove to be most disadvantageous. On the other hand, glass and quartz-based materials are already known which are sintered impermeable even at temperatures below 900 ° C (German patents 114 250; 115 104).

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In doing so goes. porcelain-like products. In any case, they will not achieve the values required by KER 220 TGL 7838.

The KER symbolism used. these are internationally used abbreviations (see Dekker P. in Glas-Email-Keřamo-Technik1972, workbook 4, page 129, and Scholz H: Glas Braunschweig: P. Wieweg and Sohn 1965, p. 51 f, p. 69, p. 180).

KER 200 TGL 7838 stands for KER 220, KER 221, KER 2.25 etc. These are mainly results containing magnesium silicate with a relative dielectric constant of about 6 ·.

According to the strength in kp / cm ^2, they are graded as follows:

KER 220 tensile strength: 450, compressive strength: 8500

KER 221 tensile strength: 450, compressive strength: 9000

KER 225 tensile strength: 500. compressive strength: 9000.

In Table 1, the depicted condition is demonstrated by the measured values.

294133

Table 1

characteristics optimal mass according to German economic pat optimal mass according to German Pat. 114 250 KER 220 TGL 7838 sintering temperature to impermeability in ° C 850 850 falls away sintering time in h at sintering temperature to impermeability 1 2 falls away bending strength (not cast) in MPa 118 159 118 TGA loss factor of 10 ^-4 at 1 MHz nad 25 15 to 25 spec, electr. resistivity φ in Ω. m at 200 ° C average 1.3.10 ⁵ 10 ⁸ to 10 ⁹ at 400 ° C average 4.6.10 ² 10 ⁵ to IO ² at 600 ° C on average 1,4.10 ¹ 10 ³ to 10 ⁴

It is therefore an object of the present invention to provide a ceramic mass that sinters to impermeability at temperatures below 1000 ° C to products that exhibit electrical and mechanical properties analogous to steatite.

In addition, aluminum fluoride, a component according to the invention of special composition, special properties and with a certain range of grain sizes are used in the compositions of the glass and quartz compositions known per se.

The essence of glass-quartz ceramic mass with the addition of 0.5 to 4% by weight of aluminum fluoride and optionally with the addition of known molding aids for the production of glazing, impermeable, sintered bodies by non-reactive sintering at temperatures below 1000 ° C according to the invention is whereas, in order to achieve mechanical and electrical properties analogous to steatite, the proportion of optionally ground, quartz-rich raw materials is 39 to 64% by weight and the proportion of comminuted glass is 35 to 60% by weight, the quartz-rich raw material consisting of 97 to 100% by weight silica; % composed of alumina, iron oxide, alkali metal oxides, alkaline earth carbonates and water-soluble salts, and the ground glass consists of 65.0 to 77.0 mol%. 3.0 to 5.0 mol. of aluminum oxide, 11.0 to 16.0 mol%. sodium and potassium oxide, 1.5 to 5.0 mol%. 2.5 to 7 mol% of barium oxide; mixtures of magnesium oxide, calcium oxide and strontium oxide and the residue consisting of borate oxide and exhibiting the following physical characteristics:

700-850 ° C

280 to 350 ° C to 35.10 ⁴ to 35. IO ⁶ KTsoft tlMflm tg <5 (at 1 MHz) and (50 .. 400 ° C) and glass fraction from 0,5 μπι up to 15 μΐη 60 to 91% by mass, and from 0,5 μιη up to 1 %, 9 to 15% to 33% by weight;

They mean:

Tso _(t temperature at which the glass exhibits a certain viscosity, tmM temperature at which the specific electrical resistance is just 100 πιΩ. Cm, or more recently 1 ΜΩ m, tgá dielectric loss factor at 20 ° C at the specified frequency of 1 MHz and ( 50 ... 400 ° C) linear thermal expansion coefficient in the temperature range 50 to 400 ° C.

By X-ray diffraction and microscopic examination, it was found that the proportions of the amount of quartz, its grain shape and grain size distribution in the raw material mixture, the overall ceramic composition and the glazing bodies according to the invention agree within a range of common errors. This behavior of the quartz in the mass during firing shows that it is essentially a non-reaction process. Further, in order to achieve impermeable sintering bodies, it is necessary to select the proportion of glass in the overall composition at least as large as to be able to completely fill all the cavities that occur during the coating of the quartz grains. Taking into account the sintering aspect, higher proportions of glass are permissible, but if the proportion of glass in the body is too large, its strength decreases.

Furthermore, it has been found that the sintering temperatures of the molding compositions according to the invention are determined by the ratios of the glassy and crystalline components of the raw material resulting from the overall composition, its particle size distribution and the viscosity and temperature behavior of the glass used. Herein, the viscosity and temperature behavior of the glass is preferably characterized as the softening temperature T _soft . It has been found that the most favorable firing temperatures of the ceramic material according to the invention are between the softening temperature of the glass used and the temperature 100 K higher, with higher firing temperatures corresponding to shorter firing times.

Finally, it has emerged from extensive investigations that, within the overall ceramic composition of the invention, certain physical requirements must be imposed on the glasses to be used in order to provide, in conjunction with a major proportion of quartz, sintered bodies meeting the essential requirements of KER 220 TGL 7838 Thus, matrix glasses should already exhibit comparatively favorable electrical insulating properties, since in the present case substantially non-reactive sintering of the overall composition contributes considerably to the formation of corresponding properties of the sintered body. Further, the average linear thermal coefficient of longitudinal expansion of the glass should be approximately matched to the average linear thermal coefficient of longitudinal expansion of the quartz to avoid critical stresses in the body.

Furthermore, it has been shown that aluminum plastic parts in excess of 2% by weight of the total composition which could be introduced into it by the corresponding quartz raw materials deteriorate the substantial mechanical and electrical properties of the sintered bodies.

The advantages of the invention are that, compared to the conventional production of ceramic products KER 220 TGL, the raw materials, preferably quartz of a wide variety of raw materials, preferably quartz of various kinds, can be made inexpensively and readily available from the conventional ceramic production of KER 220 TGL. basically equally valuable products. It is also particularly advantageous that borax-free glass frits are also useful in the overall composition of the invention.

Finally, another advantage of the composition according to the invention is that it is suitable for hot pressing.

The invention will be further elucidated by means of the following examples, without being limited thereto.

He did

Raw materials

1. Hohenbock quartz sand with a silica content exceeding 98% by weight. This quartz sand was dry ground in a laboratory vibrating ball mill to batches of 400 g, so that an average grain size of the milled product of 6.4 μΐη was finally achieved,

2. Glass frit of chemical composition;

S1O2 74.00 mol%

AI2O3 3.30 mol%

B2O3 2.00 mol%

CaO 4,35 mol%

BaO 4,35 mol%

Na 2 O 3.00 mol% / oa

9.00 mol% K2O and physical properties T _g = 559 ° C

M _g = 635 ° C

T _{α (t} = 772 ° C)

T _k ж. _n > = 310 ° C tg δ (at 1 MHz) = 22.3. 10 ~ ⁴ and (50 ... 400 ° C) = 9.04.10-® Ki

They mean:

t _g transformation temperature

Mg dilatometric deformation temperature (softening point) of other variables were explained earlier.

The frit was first pre-ground by a jaw crusher to a grain size below 0.8 millimeters and stripped by iron-abrasion by means of a magnetic separator. 400 g of the pre-ground glass was dry ground in a laboratory, vibratory, ball mill, so that the milled product finally showed an average grain size of 6 μΐη.

3. Aluminum fluoride, pure, of chemical composition corresponding to the summary formula

AlF3,0.45 H2O.

g of raw material 1 was mixed with 40 g of raw material 2 and 1 g of raw material 3, and the resulting mixture was ground dry in an impact disk mill to 75 g batches.

a grain fraction of less than 15 µm = 85% by weight, a grain fraction of less than 2 µm = 33% by weight, and an average grain size of 3.8 µm.

To 100 g of this milled product 12 ml of a 4.75% aqueous polyvinyl alcohol solution was added, mixed hot, preformed and passed through a 0.8 mm sieve.

The necessary test specimen was manufactured from the granulate by dry pressing at pressures of about 60 MPa / cm ² . The densification achieved by compression was between 60 and 63% of the theoretical specific weight.

An ever greater number of test pieces were heated in an electrically heated muffle furnace to 600 ° C and after a 30 to 60 minute delay for

equalizing the temperatures in the furnace, during which the organic substance also burned, the test pieces were heated to a sintering temperature of 2 K at a heating rate. min ^-1 . At this temperature, the test pieces were held for various periods of time (sintering time) and then cooled at a constantly lowering temperature to room temperature.

The sintering conditions and measured properties of the test specimens can be found in Table 2.

Example 1 a d 2

Raw materials:

1. Quartz according to Example 1.

2. Glass frit of chemical composition:

S1O2 75.5 mol%.

Al 2 O 3 3.36 mol%.

CaO 4.43 mol%.

BaO 4.43 mol%.

Na 2 O 3.07 mol%.

K 2 O 9.19 mol%. and physical properties:

mp = 546 ° C

Mp = 643 ° C

T _soft = 783 ° C tl ΜΩ m = 290 ° C tg δ (at 1 MHz) = 18.8.10-Ί aa (50 ... 400 ° C) = 9.15.10-® K ¹ '.

This glass frit was pre-ground as described in Example 1 so that the glass finally showed an average grain size of 10 μΐη.

3. aluminum fluoride as in Example 1.

g of raw material 1 was mixed with 40 g of raw material 2 and 1 g of raw material 3, and the resulting mixture was dry ground in a disk impact mill to batches of 75 g. The milled product thus produced shows the following grain size:

grain size less than 15 μΐη = 77% by weight grain size less than 2 μΐη = 23% by weight and average grain size is 6 μτη.

The impermeable bodies described in Example 1 were prepared from this milled product. Their sintering conditions and measured properties can be seen in Table 2.

Example 3

Raw materials:

1. Weferling glass sand of type C having a silica content of 99% by weight and a grain size of 100 to 400 .mu.m.

2. Dried downstream hydrocyclone from the preparation of sandy-clay saliva (chemical composition):

SIO2 94.9% by weight

Al2O3 3.26 wt.% Loss on ignition 1.21 wt.%

TiOž 0.12% w / w

CaO alkali oxide 0.09% by weight of mineralogical composition:

quartz 91.4 wt.% and kaolinite 8.0 wt.%.

3. Glass frit of chemical composition:

S1O2 Al2O3 B2O3 MgO BaO Na2O

K2O

65.6 mol. %

4.5 mol. %

11.0 mol. %

2.0 mol. %

2.0 mol. %

4.1 mol. %

10.9 mol. % and physical properties:

tg

М _й

Tsofl tl ΜΩ · m tg δ (at 1 MHz) a (50 ... 400 ° C) = 570 ° C = 640 ° C = 750 ° C = 335 ° C = 30.10 ⁴ a = 9,5.10-® К " ⁴ .

The frit was previously ground by a jaw crusher to a grain size of less than 0.8 mm and stripped of iron abrasion.

4. Aluminum fluoride as in Example 1.

The blend consisting of 33 g of raw material 1, 27 g of raw material 2, 40 g of raw material 3 and 1 g of raw material 4 was dry ground in a laboratory vibratory ball mill to batches of 400 g.

grain size less than 15 μπι = 91% by weight grain size less than 2 μm = 33% by weight average grain size 3.6 μιη.

Further processing of the mixture into test specimens was carried out as in Example 1. The sintering conditions and measured properties can be seen from Table 2.

Example 4

Raw materials:

Quartz sand as in Example 1.

2. Glass frit as in Example 1.

3. Aluminum fluoride as in Example 1.

g of raw material 1 was mixed with 60 g of raw material 2 and 1.5 g of raw material 3, and the resulting mixture was milled under suction in a disk impact mill into batches of 75 g each.

grain size less than 15 µm = 67 weight% grain size less than 2 µm ~ 21 weight% average grain size is 8.6 μκη.

Further processing of the mixture into test bodies was carried out as in Example 1. The sintering conditions and properties of the test bodies can be seen from Table 2.

Table 2

Properties of impermeable sintered test specimens

characteristics example 1 example 2 example 3 example 4 sintering temperature in ° C 800 3 to 6 830 750 sintering time in h 3 850 1 to 3 1 to 6 linear shrinkage by burning based on raw molding in% 12.2 11.3 12.0 12.4 volume% in theoretical weight about 93 about 95 about 96 about 97 bending strength in MPa 141 146 128 126 number of measured values 19 Dec 15 Dec 6 16 standard deviation in MPa 19.5 7.6 10.8 9.1 (50 ... 400 ° C) at 10-6 _K -1 13.1 13.2 13.3 12.0 dielectric loss factor tg δ (at 1 MHz) in IO ⁴ 9.8 10.5 13 9.2 specific electrical resistivity p, v Ω. m at 200 ° C at 10 « 9.0 2.8 2,0 3.0 at 400 ° C in ΙΟ® 1.7 1.6 1.1 1.5 at 500 ° C in ΙΟ * ⁴ 2.4 1,2 0.9 1.1 maximum threshold temperature test specimens in ° C 570 570 570 570

I will invent the subject

Claims (2)

Glass and quartz ceramic mass with an additive of 0,5 to 4% by weight of aluminum fluoride and optionally with the addition of known molding aids for the production of pourable, impermeable sintered bodies by non-reactive sintering at temperatures below 1000 ° C, characterized in that and electrical properties analogous to steatites, the proportion optionally ground to a quartz-rich raw material is 39 to 64% by weight and the proportion of comminuted glass is 35 to 60% by weight, the quartz-rich raw material consisting of 97 to 100 wt.% SiO ₂ and a residue consisting of Al 2 O 3, FeaCh, alkali oxides, alkaline earth carbonates and water-soluble salts, and the ground glass consists of 65.0 to 77.0 mol%; S1O2 3.0 to 5.0 mol. Al2O3 11.0 to 16.0 mol%. At ₂ O and K2O 1.5 to 5.0% by mol. BaO 2.5 to 7.0 mol. , MgO / CaO / SrO and a residue consisting of 22O3 and exhibiting the following physical properties T _S is 700 to 850 ° C tl MQ. m 280 to 350 ° C tg δ (at 1 MHz) 10 to 35. 10> or (50 ... 400 ° C) 8 to 10.10 ° - K <and a grain fraction of 0,5 μπι up to 15 μΐη 60 to 91% by mass, and from 0,5 μ-rn up to 1,9 μνα 15 to 33% by weight, meaning: T _SORT temperature at which the glass has a certain viscosity, thickness ΜΩπί temperature at which the specific electrical resistance is just 100 ΜΩ. cm, or more recently 1 inch. m, tgS dielectric loss factor at 20 ° C, at the specified frequency of 1 MHz, «(50 ... 400 ^Q C) linear thermal expansion coefficient at temperature interval 50-400 ° C.