DD295618A5 - Process for the preparation of dense quartz ceramic moldings - Google Patents

Abstract

The invention relates to a method for producing dense quartz ceramic moldings and subsequently produced dense shaped bodies of quartz and glass. The invention includes a method of producing dense, high-strength quartz ceramic moldings for electrical insulation technology. According to the invention, the preparation is carried out by a reactive milling process in a medium at p H 10 of a mixture of 30 to 80 parts by mass in% quartz and 70 to 20 parts by mass in% alkali-alkaline-earth aluminoborosilicate glass, the solids-liquid ratio being from 60 to 70:40 to 30, and milling up to particle sizes greater than 95% of the particles below 0.008 mm and a d84 value of particle size distribution below 0.005 mm. During subsequent ceramic technological processing of the slip, a corresponding ceramic mass with a specific surface area of 5 to 10 m 2 / g is obtained by drying. The shaping of the ceramic mass is followed by a reactive sintering process at 1000 to 1500 K. In this case, moldings are obtained with 25 to 64 parts by weight in% quartz and a maximum porosity of 5 *, whose 3-point bending strength is 140 to 180 MPa. The quartz particles are homogeneously distributed in the shards and wetted virtually completely by the glass phase. The properties of the moldings meet the essential requirements placed on KER 220 electroceramic materials. Sintered ceramic; Formkoerper; Electric ceramics; Quartz; Glass; Grinding, alkaline; Sintering process, reactive}

Description

Field of application of the invention

The invention relates to a method for producing dense ceramic shaped bodies starting from a ceramic slurry and a ceramic mass to be obtained therefrom. The invention also relates to a dense ceramic made of quartz and high-strength glass, whose essential properties meet the requirements On materials of type KER 220 is sufficient

Characteristic of the known state of the art

Ceramic slurries and ceramic masses prepared therefrom for the production of materials according to KER 220 on the basis of natural magnesium silicates (soapstone, talc), clay and feldspar or barium carbonate are known / 1 / By a firing process at temperatures above 160OKiSt from these masses a shard available which consists of proto and / or clinostatite as a crystalline fugue phase and less than 25% glass phase Although various additions to the basic offset or the replacement of mass components influence the structure and properties of the material, they do not lead to a fundamental reduction in the firing temperature

DD-PS 120 008, DD-PS 116 815 and DD-PS 119 200 dense materials based on Erdalkalialumoborosilicatglas and the crystalline phases are described corundum or zirconium, which meet the required according to TGL 7838 for the material type KER 220 properties However, their manufacture requires comparatively expensive crystalline components and high-melting glaziers

A ceramic composition consisting of quartz and light-melting alkaline-containing glass and certain fluorides is proposed in DE-PS 2 706 659

It can be made by firing below 1 300K a material that meets the essential requirements of TGL 7838 on the materials of type KER 220 Furthermore, in DD-PS 132 262 a ceramic mass based on quartz and glass from which a material according to KER 220 is obtained if the glass phase recrystallizes to a considerable extent after densification

On the basis of the starting materials quartz and glass, a ceramic composition is also proposed in DD-PS 241 895 from which a material according to KER 220 can be produced by firing if the quartz grain fraction produced by dry grinding and air classification does not contain any quartz particles with a grain size above 0.006 mm The disadvantage of the compositions given in the three last-mentioned patents is that the achievement of the required flexural strength of at least 120 MPa requires the addition of certain fluorides and / or the recrystallization of the glass phase and a certain quartz grain fraction. This is associated with additional technological complexity, ζ Β Measures to prevent fluorine emission, increased demands on the conduct of the firing process and increased expenses for the production of certain narrow quartz grain fractions

Object of the invention

It is an object of the invention to avoid the disadvantages of the known methods

Essence of the invention

The invention has for its object to provide by denser process conditions, a dense ceramic material that meets the essential property requirements of electroceramic materials of the type KER 220 due to its substantial composition and specific Erfmdungsgemaß prepared by a common wet grinding a ceramic slurry The solids content consists of 30 to 80 parts by weight in% of a quartz raw material and from 70 to 20 parts by mass in% of a silicate glass which is preferably stable to cystallisation

The offset components quartz sand and glass are milled together with water in a solids-to-liquid ratio of up to 70 to 40 to 30 and added after completion of grinding or shortly before temporary shaping aids The common wet grinding of the offset components takes place up to a particle size of more than 95% of the particles below 0.008 mm and a d value of the particle size distribution below 0.005 mm Erfmdungsgemaß it comes through the treatment process of the offset components in the aqueous medium to ion exchange reactions on the surface of the silicate glass particles, as a result, a strong alkaline slip having a pH equal to or greater Obtained by ion exchange reactions, alkaline hydrolysis of the offset components and tribochemical reactions during the Zerklemerungsprozesses an increased degradation of the glass network and a decrease in the crystalline quartz content causes in the slurry solution occur there s high alkali and alkaline earth metal ion concentrations and an increased concentration of Si-O assemblies In the subsequent ceramics processing of the ceramic slurry to a corresponding ceramic mass, preferably by spray drying, the dissolved reaction products on the particles of the quartz and glass components are homogeneous secluded

According to the invention, the shape of the ceramic mass and the reactive sintering process at temperatures between 1000 and 1500 K results in a dense ceramic material. The quartz used in the process consists of a quartz-rich raw material with at least 97% by mass of quartz, preferably of a glass sand, a quartz sand a residue of the rock treatment, for example, the Koalinaufbereitung or a mixture of the components mentioned

For the targeted materials quartz proportions of 62 to 80 parts by weight in% are preferably used, in particular 66

literature

1 Hecht, A - electroceramics, 2 edition, Springer Verlag, Berlin 1976, S 334

The above-mentioned ratio of solid to liquid in the milling is preferably in the range of 63 to 68 to 37 to

The glass used according to the invention is an alkali-alkaline earth aluminoborosilicate glass and has the following properties

Tg equal to or less than 840K

alpha _3O o 7οοκ equal to or greater than 8 χ 10 " ⁶ K" ¹

Т _х юо equal to or greater than 550K

tan δ is equal to or smaller than 35 × 10 -5 "(tan δ at 1 MHz)

The electrical properties of the glass must ensure that the material according to the invention meets the relevant requirements for materials of the type KER 220 A suitable glass composition range is (in mol%)

SiO ₂ 65 to 77

Al ₂ O ₃ 2 to 6

B ₂ O ₃ 0.1 to 12

Alkaline earth metal oxides 3 to 14, preferably 1 to 58aO

Alkali metal oxides 10 to 16

PbO 0.1 to 2

The use of temporary adjuvants, preferably plasticizers, which can be removed by burning at temperatures below 830 K, is provided. Preferred formers are isostatic pressing with optionally subsequent white machining, dry pressing and hot-spinning. The molded articles are preferably used in aggregates known per se This can be done either in a single-pass continuous-flow furnace with an oven throughput time of 2Ѵg hours or in a laboratory muffle oven with a burning time of 15 minutes at the corresponding maximum temperature

According to the invention, a dense ceramic molded body of quartz and glass is provided, which has a quartz content of 25 to 64 parts by mass in%, a flexural strength of 140 to 180 MPa and a maximum porosity of 5% by volume, and whose thermomechanical and electrical properties are essentially the same as those of Electroceramic type KER 220 according to ICE standard 672-3

The erfmdungsgemaße molding has a glass-quartz pore Gefuge whose Gefuge due to the reactive sintering process contains a comparatively lower quartz content compared to the ceramic mass, due to on and on solution of the very fine quartz particles in the glass melting phase or in the high alkali and The quartz particles are thus practically completely wetted and enclosed by the glass phase. The pores are homogeneously distributed and rounded. The body has the essential mechanical and electrical properties required for the KER 220 electroceramics

As a result of an investigation on the influence of the process of crushing the offset components on the material properties, an unexpectedly high increase in strength was observed when the combined wet milling of the offset components in the strongly alkaline medium having a pH equal to or greater than 10 is performed, the grain size of all the particles in the ceramic mass and thus the quartz particles in the material to 95% less than 0.008 mm, and the Durchgangsskorngröße d ^ the particle size distribution falls below a value of 0.005mm and thus leaves that range, which is claimed in DD-PS 197 245 or is characterized as a preferred range of this Strength increase goes well beyond the extent that was found for a specified in DD-PS 241 896 glass quartz Sintermatenal with comparable particle size distribution of quartz particles It is also surprising that the unexpectedly high bending strength of the glass-quartz sintered material almost the Festi equivalent to those determined on a quartz crystal

The unexpected effect of the increase in strength is due to the improvement in the degree of incorporation of the quartz particles in the matrix material, which is due to the reactive treatment process by increasing the alkali and Erdalkalimetalloxidkonzentration in the grain boundary layer of the particles and due to the associated reactive sintering process at the quartz grain boundary surfaces Only with the invention according to the common wet grinding of the offset components in a strongly alkaline medium which is generally observed in the dry masses of the offset components, slurry preparation and Zerstäubungstrocknung ceramic mass observed insufficient and dependent on offset build-up and sintering temperature quartz binding overcome, so that even ceramic masses with quartz proportions equal 70Ma% can be fired to dense materials At the same time a significant increase in strength is achieved The improvement d The material bond with good quartz inclusion is characterized by a low pore number and size. The number of cracking nuclei and the cracking tendency are thus significantly lower than in the fluorine-free glass-quartz sintered material of the prior art As for the inventive Ausgangsmatenal glassy mass all "K ^{6" 1} and a transformation temperature can in itself stable crystallization silicate glasses having an average linear expansion coefficient of at least 8 χ 10 are below the high-low-quartz conversion

A preferred quartz content for the molded article according to the invention is between 40 and 55 parts by weight in%. The porosity is preferably 1 to 5% by volume. The shaped article contains about 4 to 10 parts by weight of corundum as a result of grinding ball abrasion. The surface is generally matt or matt glossy

embodiments

The invention will be explained in more detail by exemplary embodiments

Examples 1 to 6

30 to 80% by weight in% quartz sand Weferlingen grade B are mixed with 70 to 20 parts by weight in% of pre-shredded silicate glass of the chemical composition in mass fractions in%

SiO ₂ 62 CaO 4.2 Al ₂ O ₃ 6.5 BaO 9.0 B ₂ O ₃ 2.8 Na ₂ O 3.0 Fe ₂ O ₃ 0.1 K ₂ O 11.6

as well as with the following physical properties

alpha ₃ oo 7οοκ equal to 8.9 x 10 ^"6 K" ¹ Tg equal to 819K density equal to 2.6 g / cm ³

in a 40-l drum mill with sintered corundum balls as grinding media and a grinding medium grinding medium grinding ratio of 5 0.5 1 20 to 80 hours preferably 48 or 65 hours wet-ground The aqueous suspension has a pH of 10 or 11, their solids content points Grain size throughput values that are smaller than

d ₉₅ = 0.0075 mm

do4 = 0.0049 mm

d5o = 0.0024mm

d ₁₆ = 0.0007 mm

and the specific surface area of the ceramic mass is equal to or greater than 6.5 m ² / g. By adding an aqueous adjuvant solution consisting of 0.5 to 1 parts by weight in% of a polyvinyl alcohol and 0.5 to 2 parts by mass in% of a specific polyethylene glycol, the suspension becomes processed by short-term intensive homogenization in the drum mill to a still-standing slip

Table 1 shows the conditions of the reactive preparation process of the offset components and the powder characteristics of the solids content for Examples 1 to 6. The granules prepared from the ceramic slurry were pressed around the mold to form extrudates at a pressure of 20 to 100 MPa. This was followed by the sintering process both in a single-channel push-through furnace at firing temperatures of 1 000 to 1 280K, firing times of 10 minutes at maximum temperature and a furnace throughput time of 2V2 hours as well as in the laboratory muffle furnace at a firing temperature of 1 000 to 1450 K with a heating rate of 2K / min and a holding time of 15 Minutes at maximum temperature The densely fired shaped bodies show as a result of the reactive treatment and sintering process with a phase inventory of preferably 25 to 55 mass fractions in% quartz, 4 to 8.5 mass fractions in% corundum and the remainder glass the disclosed Gefuge Die geschlossen e Porosity is low and reaches values of 1 to 5 volume percentages. The characteristic properties for a dense quartz ceramic that meets the property requirements for the KER 220 electroceramics are summarized in Table 2 using Examples 1 to 6

Table 1

Conditions of joint wet grinding of the offset components and powder characteristics of the ceramic masses

example 1 Example 2 Example 3 Example 4 drum mill Examples Sintered corundum KER7100 25-30mm 68 h 65 h Example 6 Quartz (Ma -%) 30 40 50 60 40-l-Hartporzellangefaß 70 11 11 80 GlasfMa-%) 70 60 50 40 30 20 solid Liquid- 5 0.5 1 relationship 65 35 65 35 65 35 65 35 65 35 48 h 65 35 grinding unit 11 Mahlgefaß grinding media grinding media grinding media regrind Verhaltms grinding time 49 h 48 h 66 h PH value 11 11 10-11 passage values (μπι)

Table 1 (continued)

example 1 Example 2 Example 3 Example 4 Example 5 Example 6

Spec. Surface

(m ² / g)

Density (g / cm ³ )

6.8 4.2 1.8 1.8 6.5

2.69

7.5 4.6 1.8 0.6 6.7

2.69

7.4 4.7 1.8 0.6 6.9

2.71

2.70

5.8 2.8 1.5 0.4 8.8

2.72

6.0 3.6 1.4 0.4 10.0

2.71

Table 2 Characteristic properties of dense quartz ceramics symbol Einheiter Example 1 Example 2 Example 3 BeispieU Example 5 Example 6 properties K min 990 15 1040 10 1100 15 1190 15 1270 15 1490 15 Burning temperature holding time pr g / cm ³ 2.61 2.61 2.60 2.56 2.52 2.45 density - - - - - - Open porosity Rt MPa 150 164 174 161 175 167 Bending strength unglazed e GPa 80 81 80 83 81 79 modulus of elasticity 10 ^"6 K" ¹ 11.5 12.2 12.4 13.3 12.9 12.0 Mean coefficient of linear expansion alpha ₆ obis5oo'c UX K 150 Thermal shock resistance Ed kV / mm 92 108 114 153 142 129 Dielectric strength ε, 6.4 6.2 5.9 5.7 5.5 5.4 Permittivity number 0.1 MHz

Dielectric loss factor at 20 ⁰ C

0.1 MHz tan δ 10 ~ ³

1MHztan510 " ³

10MHztan610 " ³

2.1 2.3

2.4 2.3 2.4

3.0 3.0 3.1

5.2 5.0 4.8

specific 2O ⁰ C p _v sq cm 1.4-1O ¹⁶ 1,3 Ю ' ⁶ 1.7 · 10 ¹³ 1,6 -10 ¹⁵ 5.9-10 ' ⁴ 7.8 · 10 ¹⁴ resistance 100 ° Cpv Ω cm 6,9 -10 ¹³ 1,4 -10 ¹⁴ 6.8 x 10 ' ³ 1,1 -ΙΟ ¹³ 7.0 · 10 " 4.5-10 " (DC 200 ⁰ C Pv oCM 2.4 to 10 '° 3.6 x 10 '° 3.1 · 10 ¹⁰ 7,3-10 ⁹ 3.2 · ΙΟ ⁹ 8,2-10 ' at given 300 ° C Pv Пет 4.1 · 10 ' 4.3 · 10 ' 3.8 10 ^s 1.2-10 ' 4.3 · 10 ' 2,0 10 ' Temperature)

Claims (12)

1. A process for preparing dense quartz ceramic molded body made of quartz and a crystallization-stable alkali-alkaline earth aluminoborosilicate glass, characterized in that the offset components quartz and glass are used with a quartz content of 30 to 80 parts by mass in% or 70 to 20 parts by mass in% glass, milled together with water in a solid-liquid ratio of from 60 to 70 to 40 to 30 while maintaining the slurry's strongly alkaline pH of equal to or greater than 10; milling the offset components to a particle size greater than 95% of the particles below 0.008mm and a d ₈₄ value of particle size distribution below 0.005mm; after completion of the grinding process, an addition of temporary shaping aids and their homogenization in the grinding unit takes place; after the drying of the ceramic slip, the corresponding ceramic mass is formed by pressing and the burning of the shaped bodies is carried out in a reactive sintering process in the temperature range from 1 000 to 1 500K. 2. The method according to claim 1, characterized in that the quartz between 62 and 80% by weight is used, preferably between 66 and 80 parts by weight in%. 3. The method according to claim 1, characterized in that the ratio of solid to liquid 63 to 68 to 37 to 32. 4. The method according to claim 1, characterized in that a quartz-rich raw material with at least 97 parts by mass in% quartz, preferably glass sand, a residue of the rock treatment or a mixture of these is used as quartz. 5. The method according to claim 1, characterized in that the glass has the following properties: Tg equal to or less than 840K alpha ₃ oo ... 7ooK equal to or larger than 8 x 10 ^"6 K" ¹ T _× equals or exceeds 550K tan delta is equal to or smaller than 35 x 10 ^-4 (at 1 MHz) 6. The method according to claim 1 or 5, characterized in that the glass has the following chemical composition (in mol%) SiO ₂ 65-77 alkaline earth metal oxides 3-14 Al ₂ O ₃ 2-6 Alkali metal oxides 10-16 B ₂ O ₃ 0.1-12 PbO 0.1-2 and optionally further constituents, such as ZnO, FeO, Mn 0-2%. 7. The method according to claim 1, characterized in that the corresponding ceramic material contains a quartz content of 25 to 64 and a Mahlkugelabrieb originating Korundanteil of vorzugsweie 4 to 12 parts by mass in% and has a specific surface area in the range of 5 to 10m ² / g. 8. The method according to claim 1, characterized in that the sintering process takes place in rapid firing. 9. A dense ceramic body made of quartz and glass, characterized in that it has a quartz content of between 35 and 55 parts by mass in%, wherein the quartz particles are homogeneously distributed in the body and wetted and enclosed almost completely by the glass phase; has a maximum porosity of 5 vol .-%, wherein the pores are homogeneous and rounded, has a flexural strength of 140 to 180 MPa and in its electrical properties substantially meets the requirements of the electroceramic materials of the type KER 220 according to ICE standard. 10. Shaped body according to claim 9, characterized in that the porosity is between 1 and 5 vol .-%. 11. Shaped body according to claim 9, characterized in that it contains corundum in a proportion of 4 to 8 parts by weight in%. 12. Shaped body according to claim 9 to 11, characterized in that it has a matt or matt gloss self-glaze and has a smooth surface.