DE2452076A1 - Glass-ceramic having good mechanical workability - based on sodium magnesium aluminosilicate glass contg. fluorophlogopite crystals - Google Patents

Abstract

Glass-ceramic having good mechanical workability contains (in wt. %): SiO2 45-75 (pref. 50-69), Al2O3 10-35 (pref. 15-28), MgO 5-25 (pref. 8-18), F 2-10 (pref. 3-7), Na2O 3-15 (pref. 5-12), and opt. R2O 0-15, R2O being Li2O + K2O or K2O + Na2O. The material is produced by controlled crystallisation resulting in formation of fluorophlogopite crystals (>=20 vol. degrees 6). Apart from good workability, the above glass-ceramic has very good acid and alkali resistance (hydrolytic class 1, lye class 1-2), low thermal expansion (50-75 x 10-7 degrees C-1), high mechanical strength (bending strength 18-20 kg./mm.2), and very good resistance to temp. fluctuations.

Description

Machinable glass-ceramics with excellent properties The invention relates to a glass-ceramic material which is excellent mechanical Machinability, very good chemical resistance, comparatively low thermal Has expansion and high thermal shock resistance, as well as a process for its manufacture.

To date, about 1,000 patents pertaining to its manufacture have been issued of glass ceramics by way of controlled crystallization. Because of your The area of application of the material glass was able to achieve excellent properties can be expanded considerably. But only recently has it succeeded, too to develop machinable glass-ceramics, giving additional application options of glass ceramics creates.

In the DT-OLS 2.133.652 the production of machine was for the first time machinable Pluor-Mica-Glaakeramiken described. The general formula for Fluorine mica is X0.5-1Y2-3Z401oF2, with those labeled 1, Y, and Z. Cations have the following radii: X = 1-1.6 #, Y = 0.6-0.9 #, Z = 0.3-0.5 Q in this The patent specification was based on glasses of the SiO2-R2O3-B2O-MgO-F system, with R203 A1203 and B2O3 and R2O can be Li2O, Na2O, Rb2O or Cs2O.

A machinability of glass-ceramics of the simple system K20-Mg0-Al203-SiO2-F can only be obtained with the addition of considerable amounts of B203 will. To achieve the desired good dielectric properties of the glass ceramics To achieve this, K20 in particular is used to fill the 1 positions in general Pormel related to fluorine mica. The chemical resistance of these materials however, it deteriorates through the use of B2O3 and K20.

Starting with the goal of having a machinable glass-ceramic Developing excellent dielectric properties can be found in DT-OLS 2,224,990 the use of B203 can be dispensed with.

The required high contents of BaO or SrO in the starting glasses however lead to a severe deterioration in the chemical resistance of these Glass ceramics and influence - by increasing the thermal expansion coefficient in addition, the thermal properties are unfavorable.

The object of the present invention is to provide a machinable glass-ceramic with improved chemical resistance, good thermal properties and high mechanical strength.

This object is achieved by the invention of the fluorine mica glass ceramic dissolved, which, based on the oxides, has the following composition in% by weight: 45-75 SiO2, 10-35 Al203 '5-25 MgO, 3-15 R2O and 2 10 P ", the crystalline portion is at least 20% by volume. R20 here means Na20 or, if appropriate, the sums a mixture of Na20 and K20 or of K20 and Li2O.

The invention is based on the surprising finding that Made of glasses of the Ma20-MgO-Al203-SiO2 F system, glass-ceramics with machinability can be produced, although the naturally occurring phlogopites are comparable Crystal phase is not more than 50 vol.% Of the total mass.

The discovery of machinability on which the invention is based of glass-ceramics from glasses of the simple system a20-Mg0-Al203-Si02-F makes it possible to dispense with such components as K20, B203, ~ BaO or SrO, which in the known patents for the precipitation of the mica structure and thus the machinability were absolutely necessary.

The deliberate exclusion of this. Components brings in for the properties the glass-ceramic materials great advantages and allows the object of the invention to realize.

Since the components K208 BaO and also SrO the chemical resistance of the glasses and also of the glass-ceramic materials made from them reduce them, doing without them leads to glass ceramics with high chemical resistance. The chemical resistance is additionally due to the high content of SiO2 and the addition increased by Al203.

Since such large cations as those produced by the incorporation of K20, BaO or SrO come into the glass structure, at the same time the thermal expansion coefficient increase, the exclusion of these components provides advantageous thermal properties achieved and achieved better thermal shock resistance.

Thus, according to the invention, machine-workable glass ceramics can be used are produced, which are additionally characterized by excellent chemical, thermal and mechanical properties and thus all known glass ceramics exceed in their possible range of application, the partial substitution of Na20 through K20 improves machinability in some cases, although at the same time the chemical resistance and also the thermal properties thereby worsen. Depending on the intended use of the glass ceramics If necessary, a mixture of Na20 and K20 or of K20 and Li2O also turns out as cheap.

The starting glass can also be up to a few percent, but not overall contain more than 9% by weight of the compatible oxides: Fe203, FeO, NiO, Eins, ZrO2, ZnO, CaO, BeO or CoO. These additives can be used to adapt the starting glass to the respective melting conditions or to vary the chemical and physical Properties of the starting glass or the glass-ceramic product are important be. However, it must be taken into account that in some cases, e.g. with a higher iron oxide content, the machinability deteriorates or the addition of such Components such as CaO the chemical resistance of the glass and the glass ceramics reduced.

The present invention thus relates to a machinable one Glass ceramic, consisting of up to 50% by volume of the total mass of one of the natural ones Phlogopiten comparable crystal phase, which at the same time a very high chemical Resistance, comparatively low thermal expansion and high resistance to temperature changes owns.

In other patents, such as in DT-OLS 1.421.942 in some cases the compositions of the starting glasses selected in this invention touched. In these inventions, however, it occurs during an annealing treatment of the glasses without exception to a precipitation of cordierite, mullite or tridymite as crystal phases. Phlogopites are never obtained and, in contrast to the present invention, can the mentioned excellent properties of the glass-ceramic materials in none Way to be achieved.

According to the method of the invention, the molten glasses of the Na20-MgO-Al203-SiO2-S system when cooling below the transformation temperature shaped into a body.

Subsequently, the vitreous are one necessary for the excretion of the Amount of phlogopite crystals subjected to targeted tempering treatment.

To do this, the glasses are kept at one temperature for a sufficiently long time kept between 600 - 11000C. A phlogopite crystal phase separates from, which is 20-50% by volume of the total mass of the starting glass.

For the production of the glass-ceramic material, one turns out to be Two-stage tempering program as favorable, with the glass in the first tempering step is annealed for a certain time in the region of the maximum nucleation temperature. on the crystallization nuclei brought to the separation in this way wake up during the subsequent Anneal the phlogopite crystals near the temperature of maximum crystal growth on.

For reasons of economy, it is advantageous to use the temperature as precisely as possible to anneal the maximum nucleation or that of the maximum crystal growth.

It is therefore necessary to determine these temperatures.

This was done with the help of DTA, radiographic methods or through Density measurements or a combination of one of these methods with an annealing treatment in the gradient oven.

The maximum nucleation temperature determined in this way was around 70 - 900C above the Tg point determined by dilatometry.

For the glasses examined according to the invention, this corresponds to a temperature range from 600 - 750 ° C.

The temperatures of the maximum determined with the help of the DTA examinations Crystal growths are in the range of 800-110,000.

It is therefore beneficial to bring the glasses to a temperature of 600 - 750 ° C to heat and hold at this temperature until nucleation in the is essentially complete and then to heat the glasses to 800 - 110,000 and to keep them at this temperature until the crystallization has ended. In general, nucleation must be maintained at the first temperature level of 2-5 hours and for crystal growth a hold of 1-3 hours on @ the second Tempered mare necessary.

In some cases, one-step annealing on a Temperature in the range of 700-1040 ° C achieved satisfactory results.

Table I. contains exemplary embodiments of the glasses that are produced according to the Annealing treatment according to the invention, glass ceramics with excellent properties (given in weight R) The following are used as raw materials for the batch: double-ground Quartzite or sand aluminum oxide or basic aluminum oxide magnesium carbonate Magnesium fluoride or aluminum fluoride.

To minimize the fluorine evaporation during the melting process as possible, it makes sense to do as possible anhydrous batch raw materials to use. In this way, over 50% of the amount of fluorine used is in the Glass built in.

Table 1.

1 2 3 4 5 6 7 8 SiO2 62.5 60.2 58.4 60.0 59.9 60.1 50.1 70.0 Al203 20> 5 20.0 18.4 19.2 18.1 19.0 30.0 10.2 MgO 7.4 10.0 13.0 8.1 7.0 7.8 8.2 8.1 Na2O 5.T 6.0 6.3 8.9 11.3 7.0 8.0 7.9 F 3.9 3.8 3.9 3.8 3.7 6.1 3.7 3.8 The batch ingredients were homogenized in a ball mill, melted in a glass furnace at 1500-1550 ° C and processed into rods, blocks or discs.

The melted glasses are clear (glasses # 1-5 and # 7) or also cloudy due to segregation (glass no. 6 and 8).

Then the glasses were subjected to a differentiated tempering treatment, the heating rate up to the respective stopping point was 3 ° C / minute, however, it can also be larger. After the crystallization was complete, the samples were cooled with the cooling speed of the furnace.

The properties of glass-ceramics, especially the mechanical ones Machinability depends very much on the selected tempering program. This is shown in the table II, in which some tempering programs are listed, which glasses No. 1 to No. 5 have been subjected.

Table II.

Tempering program crystal phase Comments 22 h 670 ° 0 sodium - fluoro very good machinability 4 h 8600C phlogopite 1. h 70006 sodium - fluoro very good machinability 2 h 9600C Phlogopit 22 h 9600C sodium - fluoro good mechanical phlogopite workability 21 h 870 0 hardly evaluable 2 h 1050 ° C X-ray reflections brittle 1 h 700 ° C 2 h 1170 ° C Glassy-brittle tion Some of the most important Properties of the glass-ceramics according to the invention, produced by suitable tempering treatment of the glasses from Table 1. are in Table III. listed.

Table III.

Property Experimental values for glass ceramics made from glasses no. 1 - 8 .1 2 3 4 5 6. 7 8 linear thermal expansion 60 64 70 73 75 62 58 50 coefficient (in 10-7 / ° C) hydrolytic class 1 1 1 1 1 1 1 - 2 1 alkali class 1 - 2 2 2 2 2 1 - 2 2 1 Acid resistance - 8.3 11.8 12.4 - 15.7 - 4.4 (etching in mg / dm) excellent- frieze- good very mechanical designation- di- friedizeich- good workability net net net low good The specified hydrolytic Class was determined according to TGL - 14 809 and the caustic class according to TGL - 14 802. The values for the acid resistance were determined according to TGL regulation 14 801.

The chemical resistance of the materials produced according to the invention thus fully corresponds to the task at hand.

Likewise, the corresponding parameters for the thermal and mechanical properties achieved.

The linear thermal expansion coefficient of the glass ceramics is between 50 and 70 x 10 7 / ° C.

In addition, the fine crystalline glass ceramics show both a relatively high flexural strength (18-20 kp / mm2) as well as great resistance to temperature changes.

It is beneficial for achieving these properties mentioned that the To allow crystallization processes to run in such a way that an average Can form crystal size of 2 jum.

Claims (5)

Claims 1. Machinable glass-ceramics with high chemical Resistance (very good acid resistance, hydrolytic class 1, alkali class 1-2), low thermal expansion (α = 50 - 75 x 10-7), high mechanical Strength (bending strength 18-20 kp / mm2) and very good thermal shock resistance, characterized in that in a glass the composition is in weight percent on an oxide basis 45 - 75 SiO2 10 - 35 Al2O3 5 - 25 MgO 2 - 10 P 3 - 15 Na20 and possibly 0 - 15 R20, where R20 can be the sum of Li20 + K20 or K20 and Na20 controlled crystallization a solid solution of fluorophlogopite crystals with a Total volume of at least 20% is created. 2. Glass ceramic according to claim 1, characterized in that the starting glass consists of 50 - 69 SiO2 15 - 28 Al203 8 - 18 MgO 3 - 7 F 5 - 12 Na20. 3. A method for producing a glass ceramic according to the claims 1 and 2, characterized in that the melted and shaped into an object Glass for producing the fluorophlogopite glass-ceramic for a sufficiently long time within the Temperature range of 600 - 11 oo ° a is tempered. 4. A method for producing a glass ceramic according to claim 3, characterized in that characterized in that the glass is at a temperature in the range of from 3 to 30 hours 700-104000 is held. 5. A method for producing a glass ceramic according to claim 3, characterized in that characterized in that the glass is initially at a temperature between 2 - 5 hours 600 - 7500C and then 1 - 4 hours at a temperature of 800 - 110,000 is exposed.