DD241896A1 - CERAMIC MASS AND A CERAMIC MATERIAL MADE FROM HERB - Google Patents

Abstract

The subject of the invention is a ceramic mass based on glass and quartz and a dense ceramic material made of it with a bending strength of more than 120 MPa. The invention aims to provide a ceramic mass of inexpensive starting materials, from which below 1 300 K and avoiding the disadvantages of the prior art, a material with a bending strength of more than 120 MPa can be produced. The object of the invention is to find a ceramic mass based on relatively low melting glass, readily available quartz and temporary auxiliaries, from which a dense material can be produced by sintering below 1 300 K without addition of fluoride and without crystallization of the glass phase, which has a flexural strength of over 120 MPa. According to the invention, after the auxiliary substances have burned out, the ceramic composition consists of 40 to 60% by weight of a quartz powder of a certain grain size and of up to 100% by weight of a crystallization-stable silicate glass powder having a certain half-value grain size and specific physical properties.

Description

Field of application of the invention

The invention relates to a ceramic composition based on glass and quartz and to a material to be produced from it by sintering at a temperature below 1300 K with a flexural strength of more than 120 MPa.

Characteristic of the known technical solutions

The conventional ceramic compositions consist of clay minerals, fluxes, in particular feldspars, and fillers, which are preferably quartz. The materials produced therefrom have high flexural strengths only if they achieve a dense structure in the firing process. Depending on the substantial and granulometric offset buildup, the sealing firing temperatures are in the range above 1500K. It has already been proposed to replace the Feldspar by prefabricated frits to reduce the sealing temperature. An underrun of 1 300 K with simultaneous dimensional stability of the body to be burned is not achieved thereby.

A reduction of the sealing firing temperature below T / 300K has been achieved by using ceramic masses consisting of a crystalline component and a prefabricated glass frit. In the DD-PS 120.008, DD-PS 116.815 and DD-PS 119.200 such on the basis of Erdalkaliumosilicatglas and corundum or zirconium produced Massen.ausden from which receives dense sintered body with a bending strength of more than 120MPa during firing. To exceed the mentioned.? =

Strength limit, however, comparatively expensive crystalline components and refractory glasses are required. It has also been proposed masses based on glass and the relatively cheap and readily available raw material quartz, whose sealing firing temperature is also below 1300K. However, the solutions present hitherto have various shortcomings: With the mass described in DD-PS 115.104, only sintered bodies can be produced whose flexural strength reaches a maximum of 100 MPa and, when using quartz raw materials with increased clay mineral content (silt), a maximum of 120 MPa.

In DD-PS 133.430 a method for the wet processing of plastic materials is described, which refers in particular to the production of glass-quartz offsets with low sintering temperature. However, the description does not indicate how materials with flexural strength values above 120 MPa would be produced. Although the compositions described in the specifications DD-PS 132.262 and DE-PS 2.706.659 can be fired into dense sintered bodies having a flexural strength of more than 120 MPa; The prerequisite for the high strength, however, is that the glass phase is crystallized after compression to a considerable extent or that the mass of certain fluorides are added. Both are with an additional technological effort, eg. B. increased demands on the leadership of the combustion process and / or measures to prevent fluorine emission and higher raw material costs.

Object of the invention

The object of the invention is to provide a ceramic mass of inexpensive starting materials from which a material with a bending strength of more than 120 MPa can be produced at a temperature below 1300 K and while avoiding the disadvantages mentioned in the prior art.

-2- Explanation of the nature of the invention

It is an object of the invention to find a ceramic composition based on relatively low-melting glass, cheap and readily available quartz and temporary auxiliaries, from the

- without addition of inorganic fluorides

- Without crystallization of the glass phase

by a substantially non-reactive sintering process at a temperature below 1300 K, a dense material can be produced, which has a flexural strength of more than 120 MPa due to its substantial composition and a specific microstructure.

According to the invention, the ceramic mass after burnout of the excipients from 40 to 60Ma .-% of a quartz powder and each up to 100% to complementary mass fraction of a crystallization-stable silicate glass powder, wherein the grain size of the quartz powder for more than 99.9% of the particles below 0.010 mm lie and the particle size distribution preferably has a d ^ value below 0.005mm. According to the invention, the silicate glass powder has a half-grain size d ₅₀ is equal to or less than 0.005 mm and has a T _g equal to or less than 840 K and a value _α 3Ο ο ... 7οοκ equal to or greater than 8 x 10 ^"6 K ^'6. The quartz powder preferably consists of a quartz-rich raw material with at least 97% by mass of quartz, in particular of a glass sand, a quartz sand, a residue of the rock preparation, for example kaolin treatment, or a mixture of the raw materials mentioned. It can also be produced therefrom by comminution in a manner known per se

 Preferably, the silicate glass powder has the following chemical composition (in mol%)

SiO ₂ 65 to 77

Al ₂ O ₃ 2 to 6

B ₂ O ₃ 0 to 12

Alkaline earth metal oxides 3 to 14

Alkali metal oxides 10 to 16

PbO. 0bis2

other ingredients such as ZnO, FeO, MnO 0 to 2

According to the invention obtained by treatment of the ceramic mass, shaping and firing at a temperature below 1300K a dense ceramic material with a glass-quartz-pore structure whose structure contains quartz particles, of which more than 99.9%, a particle size smaller than 0.010mm wherein the grain size distribution of the quartz in the material substantially corresponds to that of the ceramic mass, the quartz particles are substantially completely enclosed by the glass phase and encapsulated, the pores are predominantly dispersed in the glass phase and rounded, and the body has a flexural strength of at least 120 MPa.

As a result of an investigation into the influence of the grain size distribution of quartz used in the mass, an unexpectedly high increase in strength was observed when the grain size of all quartz particles in the ceramic mass and thus also in the material a value of 0.010 mm and the passage grain size d _S 4 of the particle size distribution a value of 0.005mm falls below. This increase in strength goes far beyond the level which, as is known, can be expected with a gradual reduction in the average particle size of the disperse phase and was found on the examined glass-quartz sintered material in a particle size range above the stated limit values. It is also surprising that the unexpectedly high increase in strength occurs precisely when the ratio of average quartz and mean glass grain size reaches or falls below the value 1 and thus leaves the range claimed in DD-PS 115.104.132.262 and 114.250, respectively is marked as a preferred area.

Microstructural and acoustic emission studies indicate the following phenomena that could be responsible for the unexpected effect:

With a gradual reduction of the mean diameter of the disperse phase particles, the diameter value critical for spontaneous microcracking is approached or undercut. In this case, the probability of spontaneous and age-related microcracking decreases until finally an almost micro-crack-free structure of particularly high strength and fracture toughness is present (Storch et al., Cfi / Ber. Dt. Keram. Ges. 61 [1984] 7,335 ff). In this view known to those skilled in the art, however, a size which also influences the strength, the degree of incorporation of the quartz particles into the matrix material, remains unconsidered. It is always assumed that the degree of integration is already sufficiently high and thus there is practically no possibility of an additional increase in strength due to a further increase in the degree of integration. For the fluoride-free glass-quartz sintered material, however, a generally insufficient and dependent on the composition of the composition and sintering temperature quartz inclusion is characteristic. Only with the quartz grain size distribution according to the invention is this disadvantage overcome, and at the same time the strength increase significantly exceeding the particle size effect discussed above is achieved. The improvement in the quartz inclusion can thus be taken as the cause of this additional increase in strength.

About the importance of the ratio of quartz and glass grain size can currently be guessed only. However, it is clear that when the ratio value dQd _G decreases, the sintering temperature required to reach the compression maximum increases and thus the conditions for the wetting of the quartz particles by the matrix glass improve.

The structure of the material with almost complete quartz inclusion is characterized by a low pore number and size as well as by pores dispersed in the glass and rounded. The number of cracking nuclei and their tendency to crack are thus significantly lower than in the fluoride-free glass-quartz sintered material of the prior art. As a glassy starting material for the present invention can serve all the mass itself crystallization-stable silicate having an average linear expansion coefficient of at least 8 × 10 ^"6 K" ¹ and a transformation temperature below the quartz transition high-low. Crystallization-stable in the sense mentioned are glasses from the following composition range (in mol .-%):

SiO ₂ 65 to 77 Al ₂ O ₃ 2 to 6 B ₂ O ₃ Obis 12

Alkaline earth metal oxides 3 to

Alkali metal oxides 10 to

PbO O to

other ingredients

like ZnO, FeO, MnO O to

The grain size distribution of the glass is to be chosen so that the highest possible green density and a uniform distribution of quartz particles in the glass matrix of the sintered body is achieved. A glass powder whose half-value grain size d _{60 is} less than 0.005 mm is advantageous.

The preparation of the ceramic composition according to the invention is carried out in a conventional manner from quartz powder having a particle size below 0.010 mm and the pre-shredded glass according to conventional non-plastic mass ceramic techniques.

The use of temporary adjuvants, preferably for plasticization, which can be removed by burnout at temperatures below 830K, is provided. Advantageously, a Mischmahlung the offset. Preferred variants of the shaping are isostatic pressing with subsequent white machining, dry pressing and hot spraying. The moldings are tightly reduced in known units at a temperature below 1300 K.

embodiments

The invention will be explained in more detail by the following embodiments, wherein it is not limited to these examples.

Starting materials:

1. Silicate glass of chemical composition in mol.%:

SiO ₂ 75 CaO 3.7

Al ₂ O ₃ 3.1 BaO 4.6

B ₂ O ₃ 1.9 Na ₂ O 3.2

Fe ₂ O ₃ 0.1 K ₂ O 8.5

as well as with the following physical properties

T ₉ = 840K

* ρ = 2.61 g / cm ³

31 kg of said glass are ground in a 100-l ball mill with 79 kg flint stones as grinding media with the addition of 0.25% ethanol (based on the dry matter) for 168 hours. The milled product has the grain transmission values djä4 = 0.0084 mm d ₅₀ = 0.0029 mm di6 = 0.0007 mm

and a specific surface area of 3.6m ² / g. The SiO ₂ milling abrasion is 2.5Ma .-%. 2. Quartz sand Weferlingen grade B 16kg of the quartz sand are milled in a 40-l ball mill with a grinding media filling of 30 kg flint stones with the addition of 0.25% ethanol for 96 hours. From the ground product by air classification a fraction with the grain size passage values ds4 = 0.0039 mm d ₆₀ = 0.0027 mm d ₁₆ = 0.0016 mm

and a specific surface of 3.5m ² / g separated. The fraction contains no quartz particles with a particle size above 0.006 mm.

Mass preparation and test specimen production:

200 g portions of the separated quartz grain fraction and the glass powder with the glass-quartz volume ratios 60/40, 45/55 and 40/60 are premixed for about one hour in a turbulator and then with the addition of 0.05 η acetic acid ( Solid-liquid mass ratio 1: 1) by intensive stirring in a slip whose pH is kept by 8. A special polyvinyl alcohol (PVA, 2g PVA per 100g offset) serves as setting and pressing aid. The spray granules prepared from the slurry are pressed dry uniaxially with a pressure of 100 MPa to test specimens. The burning out of the auxiliaries (up to approx. 770K) concludes the sintering process at 1145Kan. The burning time is 15min. Structure and properties:

The test specimens obtained show the disclosed structure with the components glass phase, quartz and pores. The closed porosity reaches values of up to 7% by volume. The mean flexural strength is 135 MPa.

Comparative Example:

Starting materials, mass preparation and test specimen production:

The starting materials described in the exemplary embodiments and the conditions of the mass preparation and test specimen production are maintained. By way of derogation, the ground quartz sand having the grain size passage values ds4 = 0.0160 mm d ₅₀ = 0.0065 mm d ₁₆ = 0.0018 mm

and a specific surface of 3m ² / g without prior classification by means of air classification for mass preparation

 Structure and properties:

Due to the coarse grain content of the quartz, the microstructure has on average larger pores than the materials described in the exemplary embodiments. In particular, the larger quartz particles are partially incomplete enveloped by the matrix glass or surrounded by intrinsic stress-induced ring cracks. The flexural strength is on average only 106 MPa and with a probability of error of less than 0.1% below the flexural strength of the materials described in the embodiments.

Claims (4)

Invention claim: 1. Ceramic mass based on glass, quartz and temporary auxiliaries, preferably plasticizers, characterized in that, after burning out the excipients from 40 to 60 wt .-% of a quartz powder whose grain size for more than 99.9% of the particles below 0.010 mm and whose d _S 4 value of the particle size distribution is preferably less than 0.005 mm, and each of up to 100% by mass of a crystallization-stable silicate glass powder having a half grain size d ₆₀ equal to or smaller than 0.005 mm and the physical properties T ₉ equal to or less than 840 K C1300 ... 700K equal to or greater than 8 10 " ⁶ K" ¹ consists. , .. - - 2. Ceramic composition according to item 1, characterized in that the quartz powder according to item 1 from a quartz-rich raw material with at least 97 wt .-% quartz, preferably from a glass sand, a quartz sand, a residue of the rock processing, for example, the kaolin treatment, or a mixture consists of said components or is prepared by crushing it in a conventional manner. 3. Ceramic composition according to item 1 or 2, characterized in that the silicate glass according to item 1 has the following chemical composition in mol .-%: SiO ₂ 65 to 77 alkaline earth metal oxides 3-14 AI2O3 2 to 6 alkali metal oxides 10-16 B ₂ O ₃ 0 to 12 PbO 0 to 2 other ingredients such. ZnO, FeO, MnO 0 to 2 A dense ceramic material having a glass-quartz-pore structure prepared by substantially non-reactive sintering at a temperature below 1300 K from the ceramic composition of item 3, characterized in that the structure of the body contains quartz particles whose grain size increases more than 99.9% is less than 0.010mm, where - The grain size distribution of the quartz in the material substantially equal to the ceramic mass; - The quartz particles are almost completely wetted by the glass phase and enclosed; - The pores are predominantly dispersed in the glass phase and rounded; - The body has a bending strength of at least 120MPa.