DE1496611B1 - TRANSLUCENT CERAMIC GLASS WITH LOW THERMAL EXPANSION COEFFICIENT PROCESS FOR MANUFACTURING AN OBJECT OF YOUR EXISTING USE IN TELESCOPIC MIRRORS AND THERMAL CRYSTALIZABLE GLASS - Google Patents

Description

that the ratio of (CaO + MgO + ZnO + Na ₂ O + B ₂ O ₃ ) to .. Li ₂ O is less than 2.4 and the ratio of SiO ₂ to Al ₂ O _{3 is} not greater than 3.8, that the glass ceramic as the predominant crystalline phase / 3-eucryptite and / or /? - contains spodumene, which as crystals essentially with a diameter of less than ¹ Z ₃ μπα, over the greatest linear crystal expansion, enjoy a large number of ceramics in large numbers and random orientation are distributed in a remaining as a residual in the in-situ crystallization of the glass matrix, and that the transparent crystallized glass-ceramic has a linear thermal expansion coefficient of -10 to +10 · 10- ⁷ / ° C (O to 30O ⁰ C).

2. Transparent glass ceramic according to claim 1, characterized in that the base glass has an SiO ₂ content of 56 to 68 percent by weight.

3. Transparent glass ceramic according to claim 1 or 2, characterized in that with a content of TiO ₂ from 0 to 1.5 percent by weight or content of (TiO ₂ + ZrO) _{2 is} 2 to 3 percent by weight.

4. Transparent glass ceramic according to claim 1 or 2, characterized in that the ratio of SiO ₂ to Al ₂ O _{3 is} not greater than 3.3.

5. A method for producing an at least partially crystalline, non-porous, transparent glass-ceramic article having a thickness of at least 1.25 cm, characterized in that a thermally crystallizable glass melt of a composition according to claim 4 with reference to claim 1 is produced, a glass article of a predetermined size and Shape is formed from the glass melt, the object is subjected to a heat treatment for nucleation at a temperature of 17 ° C below the upper cooling temperature to 140 ⁰ C above the upper cooling temperature of the glass to form a plurality of nuclei, then the _: glass in a temperature range is held, in which the object crystallizes in situ to a transparent crystalline glass ceramic, in which the predominant crystalline phase / S-Eücryptit and / or ^ -SpodumenmitemDiameter under ¹ J ₃ μm, measured over the largest linear crystal expansion, in a random orientation r are distributed as a residual in the in-situ crystallization of the remaining glass matrix, so that the transparent crystallized glass-ceramic has a substantially through the entire thickness of the article uniform linear thermal expansion coefficient of -10 to +10 · IO ^7/0 C (O to 300 ° C).

6. The method according to claim 5, characterized in that the object is heated in such a way, ' that between the temperature of the outer surface and the temperature inside there is a difference of 28 to 55 ° C prevails.

7. The method according to claim 5, characterized in, that the object is first heated to a higher temperature and kept at that temperature becomes, until the temperature inside has increased significantly, the temperature of the outer surface of the object is then lowered until it is again relatively lower than the temperature inside, the temperature differences being in the range of 28 to 55 ° C, and this periodic heating and cooling is repeated continuously until the glass ceramic object originated.

8. Use of the transparent glass ceramic low heat expansion according to the claims 1 to 4 as mirror plates for astronomical telescopes.

9. telescope mirror plate according to claim, characterized in that it consists of a glass ceramic having a linear thermal expansion coefficient in the range from -3 to + 3 x 10- ⁷ / ° C.

10. Telescope mirror plate according to claim 9, characterized in that "that-the crystals in the ceramic glass from which they are made have a largest longitudinal extension of less than ¹ U [Lm, preferably under violin.

11. Thermally crystallizable glass, characterized by a composition according to a of claims 1 to 4.

The invention relates to transparent glass-ceramic with a low coefficient of thermal expansion Process for the production of an object consisting of it, the use of the glass ceramic in Telescopic mirrors as well as a thermally crystallizable glass for the production of the transparent glass ceramic.

It is known that certain glasses which _{contain crystal nucleating agents, such as TiO 2} or ZrO ₂ , can be converted by heat treatment into glass ceramics which, to a considerable extent, have a finely crystalline structure and are characterized by advantageous properties, in particular high strength and low thermal properties Expansion coefficients (German Auslegeschrift 1045 056, USA.-Patent 13117 881).

It has also already been recognized that glass-ceramic masses in which microcrystals of Li-Al-silicate jS-eucryptite in every microcrystal completely

3 4

surrounding glass phase are embedded, mecha- that the ratio of (CaO + MgO + ZnO + Na ₂ O

nisch very hard and firm and a value around zero + B ₂ O ₃ ) to O ₂ O less than 2.4 and the ratio

low expansion coefficient can have (W. from SiO ₂ to Al ₂ O _{3 is} not greater than 3.8 that the

Baum: Glass technical reports, 36, pp. 444 to 453 Glass ceramic as the predominant crystalline phase and 468 to 481). The prak- S ß-eucryptite and / or ß-spodumene that have become known, which as

Table experiments led to the conclusion that crystals with a diameter below ¹ J ₃ μm, about

These properties approximate only achieved the greatest linear crystal expansion measured in

are when a relatively complicated procedure- large numbers and random orientation in an as

ren of heterogeneous devitrification is applied. Remainder of the in-situ crystallization remaining glass

The known glass ceramics are more or less distributed in a matrix, and that the transparent, crystalline opaque and have the peculiarity that the obtained glass ceramic has a linear thermal expansion coefficient of low thermal expansion coefficient of -10 to +10 \ 10 ~ ⁷ / ° C ( O to moderately strong depending on the type of heat treatment, ins- 300 ° C).

The glass ceramic according to the invention, which essentially depends on the temperature used. This has the consequence that, especially in the case of relatively thick objects which also contain a nucleating agent, according to the Ent- ■ SiO ₂ - Al ₂ O ₃ - Li ₂ O system with relatively glazed different expansion coefficients at narrow limits prescribed composition of the surface and present in the material depth, has the expected very low expansion at the heat treatment coefficient used for devitrification around 0 and, moreover, the evaluation of the temperature inside the object in the full property that it was a range of EntD average lower than an the surface. Glazing or crystallization temperatures gives j. Such local differences in the thermal from which essentially the same coefficient of thermal expansion result, for example, in the coefficient of expansion. This means that the object is deformed in an undesirable manner during the heat treatment during the heat treatment of the objects formed from the base glass or after completion in the event of temperature changes. This appearance of objects with no special consideration is particularly undesirable and annoying, any temperature differences between more outside when one needs glass-ceramic objects precisely because of their low thermal expansion coefficient and more internal areas of the object and yet glass-ceramic objects with good mechanical properties for precision 30 receives, which uses a device over its entire mass, for example in the form of part-uniform, very low expansion coefficients scopes mirrors, in which deformations as far as have, so that they should not be avoided during the heat as possible. ■ treatment, even having warped at later

It is true that the disadvantage described here can be forgiven for temperature changes or under tension

by counteracting the fact that the 35 "serving for devitrification" is set.

Heat treatment proceed slowly. The fact that the glass according to the invention, but this is for reasons of economy ceramics because of the small size of their crystals undesirable, these are transparent, offers obviously very significant

Accordingly, the present invention has advantages, particularly in connection with the

the underlying task of creating a glass ceramic, 40 also described freedom from distortion and tension

in which the achieved coefficient of thermal expansion is very relatively thick objects,

small and of the type of devitrification heat treatment- Overall, the glass ceramic according to the invention have

ment is largely independent. miken advantages over both glasses and

According to the invention, this object is achieved by compared to conventional ceramics, since they as well as

a clear low-heat glass-ceramic 45 glass are clear and non-porous, but one

elongation, which is characterized by the fact that it 'very low and moreover uniform expansion

have a thermal coefficient due to thermal in-situ crystallization and due to their

Mixed crystallizable base glass is formed, the fine crystalline structure is considerably stronger and more durable

essentially contains the following components: are as glasses.

Weight percent ⁵ ° The base glass preferably has an SiO ₂ content

^ ß kj _s 70 ^from 56 to 68 percent by weight. TiO ₂ is preferred "

ο "'* 18 to 27 * ^m B ^ere i ^{cn from} 0 to 1> 5 weight percent used,

² Q ³ '''"3 4kj _s 4 5 where TiO ₂ + ZrO ₂ between 2 and 3 weight percent

θ 'kj _{s make} 3 ^cent . The weight ratio SiO ₂ to

O to 2 -A ^ ⁵⁵ ^ Os ^st preferably not greater than 3.3.

Q | jj _s 4 The volume in the glass ceramic according to the invention

"'Q kis 6 predominantly crystalline substances in terms of quantity

O to 3 are from X-ray diffraction images as / S-eucryptite or

Q kjs 3 'crystals similar to these or ß-spodumene or

QJ ₃ J ₈ ■, 60 crystals similar to these have been determined.

PQ '■■'"Q kj _s 3 In addition to the specified components, in

²⁵ 'of the glass ceramic or its base glass is also low

subject to the following conditions: Amounts of other compatible ingredients present

(SiO ₂ + Al ₈ O ₃ ) .... at least 82, for example fluorine as fluoride, arsenic or

(SiO ₂ ) + Al ₂ O ₃ + B ₂ O ₃ + P ₂ O ₅ ) 86 to 91. 65 antiinone oxides, which are often used as refining agents

(CaO) + MgO + ZnO + Na ₂ O) 2.5 to 6 are used, or other compatible inorganic substances

(SiO ₂ ) + Al ₂ O ₃ + P ₂ O ₅ + Li ₂ O) not over 93 oxides. Usually arsenic is not present in amounts

TiO ₂ + ZrO ₂ , ". 2 to 6 more than 0.3 percent by weight vorhariden, expressed

as Al ₂ O ₃ ; Antimony seldom in amounts above 1 weight - the ceramic glass of which they are made, a largest longitudinal percentage, expressed as Sb ₂ O ₅ . expansion below% (^ m, preferably below Vio ^ ^m J

The present invention also provides for having.

In the manufacture of transparent glass-ceramic

sable glass, which is characterized by the 5, the base glass is brought into the desired shape

wrote compositions according to the invention, and then crystallized by heat treatment. the

In accordance with the described advantageous intrinsic optimal heat treatment, of course, the glass ceramic according to the invention creates the special glass composition, the invention also provides a method for producing the ratio of components, the type and amount of an at least partially crystalline, non-porous nucleating agent as well as the desired Properties of a transparent glass ceramic object in the form of the end product. It is therefore not possible to describe an object with a thickness of at least approximately 1.25 cm, which is characterized in that a glass melt of an additive which can be thermally crystallized according to the invention can be applied to all glasses. Preferably, however, the composition according to claim 4 is produced, with the first stage of the heat treatment being produced in relation to claim 1, a glass-moderately low temperature in the range of maximum object of a predetermined size and shape or high nucleation or crystallite formation rate is formed from the glass melt, the subject is carried out, the "nuclei" being defined as a submicro nucleation ^{temperature of 17 0} C below the scopic precursors of the crystalline body or as an upper cooling temperature to 140 ° C above the upper 2 °, a finely dispersed submicroscopic immiscible cooling temperature of the glass to form a large number of glass phases are. It is difficult to subject the temperature to nucleation, then to directly measure the glass in the temperature range in which the maximum temperature range is maintained at which the nucleation rates occur, or, in other words, to indicate the object in situ to a transparent crystalline Where the optimal Tem glass-ceramic crystallizes, in which the prevailing temperatures for the first heat treatment lie, crystalline phase / S-Eueryptit and / or /? - Spodumene These temperatures are usually included, however, the object a large number of such ranges from 17 ° C below to 140 ° C above the upper crystals in random orientation in one as the rest at the relaxation temperature of the glass,
The glass matrix remaining after the in situ crystallization. The upper KUbI or relaxation temperature can contain essentially all the crystals of 30 which can be determined in accordance with ASTM C 336-54T. For potash ceramics with a diameter below ¹ I ₃ [UOa, over the brierung of the test apparatus one uses fibers of the greatest linear crystal expansion measured, on standard glasses with known upper and lower ways, the transparent crystallized glass ceramic relaxation temperatures, which by the National Bureau a linear Thermal expansion coefficients are described and published by of Standards.
-10 to + 10- ⁷ / ^o C (0 to 300 ° C) and this expansion is usually the same in the manufacture of the transparent expansion coefficient through the entire glass ceramic, the glass for at least 15 minutes, ge-thickness of the object . comfortably at least 1 hour, at one temperature

The observance of the correct thermal conditions heated in the aforementioned range. Afterward

During crystallization, in a further embodiment it is heated to a higher temperature until the

According to the invention, it is expedient to ensure a linear thermal expansion coefficient of at most 40

that during the crystallization process, the tem- 12 × 10 ^-7 is to the crystallization up to the

to bring the temperature of the outer surface and the temperature in the undesired degree. The maximum tem-

differ by 28 to 55 ° C. The temperature of this last stage of treatment is customary

A particularly even temperature distribution Hch not higher than 195 ° C above the upper relaxation ■

in thick objects at the invention temperature, although higher temperatures,

According to the method can be achieved in particular as long as the glass ceramic

that the object remains transparent to a higher temperature first, and essentially all of the crystals

heated temperature and kept at this temperature therein have a diameter below ^x / ₃ μπι. the

times vary from about 0 at maximum temperature until the temperature inside is considerably increased

has increased the temperature of the outer surface of the 50 (simply heating to a higher temperature and

Object is then lowered until it disappears again, then cooling down) for up to many hours or even

is proportionally lower than the temperature in in-days. Of course, for a given

neren, where the temperature differences in the area given degree of crystallization, the times are reversed

from 28 to 55 ° C, and this periodic earth temperature.

heating and cooling continuously for so long - 55 Although often after the first heat treatment stage is fetched until the glass ceramic object has arisen for nucleation at a second, higher temperature, is turned, it is usually also possible to use the

The described advantageous properties of the overall heat treatment at the relatively low

Glass ceramic according to the invention come to carry out in a further temperature of the first temperature stage

Embodiment of the invention particularly effective 60 or the crystallization at a lower temperature

when using them as mirror plates for astro- - as long as they are no more than 17 ° C below the upper one

nomic telescopes, he * has a particularly advantageous relaxation temperature - to be completed,

The telescope mirror plate according to the invention is thereby naturally required for such a heat treatment

indicates that it consists of a glass ceramic, low temperatures a longer time than when the

which a linear thermal expansion coefficient is increased 65 temperature for final crystallization. the

having coefficients in the range from 3 to + 3 x 10- ⁷ / ° C. total times for heat treatment in this

Such a telescopic mirror plate is preferably an embodiment that can range between% and hour

further characterized in that the crystals are many weeks. These "isothermal" heat

7 8

treatments at low temperature give a CaO 2.5 to 3

Product that has more uniform ZnO - .... 1 to 1.5

thermal expansion coefficients at all points B ₂ O ₃ 3 to 4

of the item. These products are also 4.5 to 5 _{in TiO 2}

generally more opaque and have a smaller 5 (SiO ₂ + Al ₂ O ₃ ) ....... 83 to 85

Crystal size. (SiO ₂ + Al ₂ O ₃ + B ₂ O ₃ ) 86 to 88

It has been found that thermally crystallizable (CaO + ZnO) 3.5 to 4

Glass with a composition according to the invention

a sufficient nucleation time then a glass and a clear ceramic, which for

can be treated at a final temperature that is typical for this range, are given in Example 2.

over a wide range, usually from about 28 to give.

55 ⁰ C or more, can vary without the thermal Another preferred range of these glasses and mixed expansion coefficient of the end product ceramics consists essentially of the following is substantially influenced; the final temperature can be constituents which, in the following percentages by weight, are equal to or even lower than the nucleation temperature, based on the composition of the ger. This statement is particularly important for total glass in the glass mix, which includes: the production of transparent glass ceramic counter- ^ q ™ ^ - g-,

stands of considerable thickness (e.g. 1 to 5 cm or Al O 24 to 26

more), such as telescope mirror plates, where there is Li ² O ³ 3 8 to 4

it is desirable that the thermal expansion coefficient 20 q ^ q " 2 ° 5 to 3

cient of the level is zero or as close as possible to 2jqC \ 1 bis

Is zero. For example, such a plate can have a ώ η ι ο w * ^ c

τ ». 1 . , η r 1 ·. 1 t - "2 ^ S · .- J ₅ ^ DlS J, O

Thickness of at least 2.5 cm and one about six times TiO 15-2

have such a large diameter. ZrO ² 1 * 5 to 2

The invention is explained below on the basis of 25 fSiO ² + Al O ) 84 'to 86

preferred narrower composition _{ranges and (SiO 2} + Al ₂ O ₃ + B ₂ O ₃ ) "!" iΓ! 88 to 89

more closely related to these corresponding exemplary embodiments ("CaO -t-ZnOf 3 5 to 4

wrote. ^} '''

The F i g. 1 to 5 explain in exemplary embodiments a glass and a transparent ceramic which are used for

present dependence of the linear thermal 30 this range are typical, are given in example 4.

Give the expansion coefficient of the finished glass ceramic.

Another preferred range of these glasses and those used in heat treatment

Crystallization temperature. Ceramics essentially consists of the following

The following narrower composition ranges Components that are in the following percentages by weight

the transparent boundaries crystallized in situ according to the invention, based on the mixture of the total glass,

term glass ceramics with low thermal expansion are contained in the glass mixture,

have been found to be particularly useful. At ^ q ^ ₂ to 64

each of these areas results in the sense of FIG. 1 Al O 20 to 22

up to 5 a low coefficient of expansion in a Li ² O * 3 8 to 4

flat area of the curve. 40 CaO 2'5 to 3

A first narrower compositional range is in ^ _n O ' 1 bis

essentially through the following components - q '3 to A

give, the components in percent by weight, _t ? q ³ '1 5 to 2

based on the composition of the total glass ZrO ² 1 * 8 to 2

the glass mix states: 45 ''

in the glass mixture, the following are given: 45

SiO ₂ 63 to 65 (SiO ₂ + Al ₂ O ₃ ) 83 to 85

Al ₂ O ₃ 20 to 22 (SiO ₂ + Al ₂ O ₃ + B ₂ O ₃ ) .87 to 88

Li ₂ O 3.8 to 4 (CaO + ZnO) 4.3 to 5

l 'to 15 ⁵ ° glasses and clear ceramics for this

"3 ^ j _s 4 'range are typical, are in Examples 5 and 6 an-

TH. '. Yy [yyyyvy'. '.'. '.'. '.'. 3.5u _s α given.

(SiO + Al O) 84 to 86 Another preferred range of these glasses and

(SiO + AlO + BO) 88 to 89 ceramics consists essentially of the following

(Cad + ZnO) ^Z. . ³ ............ 3.5 to 4.5 ⁵⁵ components that are in the following weight percentage limits, based on the total glass composition

A typical glass and a clear ceramic composition in the glass mixture are included; from this area is the one further back in example 1

Table I given below. SiO ₂ 66 to 68

Another preferred range of these glasses and 60 Al ₂ O ₃ . 20 to 22

Ceramic consists essentially of the following Li ₂ O ... 3.8 to 4

Components in the following weight percent- CaO 2.5 to 3

limits, based on the composition of the Ge ZnO 1 to 1.5

Velvet glass in the glass mixture, contains: TiO ₂ , 1.5 to 2

65 ZrO ₂ 1.8 to 2.2

SiO ₂ 58 to 60 Na ₂ O up to 1

Al ₂ O ₃ 24 to 26 (SiO ₂ + Al ₂ O ₃ ) 87 to 88

Li ₂ O 4.3 to 4.5 (CaO + ZnO + Na ₂ O) 4 to 5

109586/187

A glass and a clear ceramic which are typical for this area are given in Example 7.

Another preferred range of these glasses and ceramics consists essentially of the following Components in the glass mixture with the following weight percent limits, based on the total Glass mixture, includes:

SiO ₂ ; 63 to 65

Al ₂ O ₃ .... 20 to 22

Li ₂ O 3.6 to 3.8

CaO 2.5 to 3

ZnO 1 to 1.5

B ₂ O ₃ 2.7-3.2

TiO ₂ 1.5 to 2

ZrO ₂ 1.8 to 2.2

Na ₂ O up to 1

(SiO ₂ + Al ₂ O ₃ ) 84 to 86

(SiO ₂ + Al ₂ O ₃ + B ₂ O ₃ ) 87 to 89

(CaO + ZnO + Na ₂ O) 4 to 5

A glass and a transparent ceramic which are typical for this area are given in Example 8.

Another preferred range of these glasses and ceramics consists essentially of the following Ingredients in the following weight percent limits, based on the total glass composition the glass mix, includes:

SiO ₂ 63 to 65

Al ₂ O ₃ 20 to 22

Li ₂ O 3.8-4

CaO 2.5 to 3

ZnO 1 to 1.5

B ₂ O ₃ 3.2 to 3.7

TiO ₂ 1.5 to 2

ZrO ₂ 1.5 to 2

Na ₂ O up to 1

(SiO ₂ + Al ₂ O ₃ ) 84 to 85

(SiO ₂ -I-Al ₂ Oa-IB ₂ O ₃ ) 88 to 89

(CaO + ZnO + Na ₂ O) 4 to 5

A glass and a clear ceramic typical of this area are given in Example 9.

Another preferred range of these glasses and ceramics essentially includes the following Components that are in the glass mix in the following Weight percentage limits, based on the total glass composition of the glass mixture, contain are:

SiO ₂ 64 to 66

Al ₂ O ₃ 20 to 22

Li ₂ O 3.8-4

CaO 2.5 to 3

ZnO, 1 to 1.5

B ₂ O ₃ 3 to 4

ZrO ₂ 1.8 to 2.2

Na ₂ O ............ up to 1

Cr ₂ O ₃ up to 0.3

(SiO ₂ + Al ₂ O ₃ ) 85 to 87

(SiO ₂ + Al ₂ O ₃ + B ₂ O ₃ ) 89 to 90

(CaO + ZnO + Na ₂ O) 4 to 5

A glass and a transparent ceramic, which are typical for this area, are shown in the example specified.

Another preferred range of such glasses and ceramics consists of the following components, those in the following weight percentage limits, based on the total glass composition in the glass mixture, included are:

SiO ₂ 63 to 65

Al ₂ O ₃ 19-20

Li ₂ O 3.8-4

CaO 2.5 to 3

ZnO 1 to 1.5

B ₂ O ₃ 3.2 to 3.7

TiO ₂ 1.5 to 2

ZrO ₂ 1.8 to 2.2

Na ₂ O up to 1

(SiO ₂ + Al ₂ O ₃ ) 83 to 84

(SiO ₂ + Al ₂ O ₃ + B ₂ O ₃ ) 87 to 89

(CaO + ZnO + Na ₂ O) 4 to 5

A glass and a clear ceramic typical of this area are given in Example 11.

Another preferred range of these glasses and ceramics essentially includes the following Components in the following weight percent limits, based on the total glass composition in the glass mix:

SiO ₂ 63 to 65

Al ₂ O ₃ .20 to 22

Li ₂ O 3.8-4

CaO + MgO 2.5 to 3

B ₂ O ₃ 3.2 to 3.7

TiO ₂ 1.3 to 2

ZrO ₂ 1 to 1.7

P ₂ O ₅ 1.3 to 2

Na ₂ O. up to 1

(SiO ₂ + Al ₂ O ₃ ). 84 to 86

(SiO ₂ + Al ₂ O ₃ + B ₂ O ₃ + P ₂ O ₅ ) .. 89 to 91 (CaO + MgO + Na ₂ O) 3 to 3.5

Glasses and clear ceramics typical of this area are in Examples 12 and specified.

Another preferred range of these glasses and ceramics consists essentially of the following Components. The components have the following weight percentage limits in the glass mixture on the entire glass mixture:

SiO ₂ 63 to 65

Al ₂ O ₃ 20 to 22

Li ₂ O 4.3 to 4.5

CaO 2.5 to 3

ZnO 1 to 1.5

B ₂ O ₃ 3.2 to 3.7

TiO ₂ 1.5 to 2

ZrO ₂ 1.8 to 2.2

Na ₂ O, up to 1

(SiO ₂ -I-Al ₂ O ₃ ) 83 to 85

(SiO ₂ + Al ₂ O ₃ + B ₂ O ₃ ) 87 to 88

(CaO + ZnO + Na ₂ O) 4 to 5

A glass and a clear ceramic that is used for this range is typical are given in Example 14.

The mixtures of crystallizable glasses of Examples 1 to 14 including Table I were melted and shaped at glass melting temperatures. Then the molded glasses were nucleated for 4 hours at a temperature corresponding to ^{a viscosity of about IQ 11} · ^{7 poise.}

11th 12th

■ sets. Each nucleated glass was ■ then in most cases a final temperature for 1 hour exposed in the range of 760 to 982 ° C. Then, the coefficient of thermal expansion of each transparent molded one was crystallized Body measured.

There were curves of thermal expansion versus heat treatment for each Composition set up. Several of these curves are shown in FIG. 1 of the drawing.

In Fig. 1 the curves show the expansion coefficients for various final temperatures at which the converted glasses were held for 1 hour. Only in example 3 was tempering for 2 hours. The foregoing nucleation temperatures and times for the curves of the examples and 5 were 2 and 4 hours in the range of ⁰ to 705 C. For the curve 5 A, the glass of Example 5 was long initially at a temperature of 7O5 ° C hours of Subjected to nucleation and then completed for 16 hours at the indicated temperatures.

Table I. example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7

Components
(Weight percent)

SiO ₂

Al ₂ O ₃

Li ₂ O

CaO, ...

ZnO

B ₂ O ₃

TiO ₂

ZrO ₂

MgO

CoO

NOK

Na ₂ O

K ₂ O

As ₂ O ₃

P ₂ O ₅

Fe ₂ O ₃

Cr ₂ O ₃

Expansion coefficient (0 to 30O ⁰ C) -IO ⁷

Temperature range ⁰ C nucleation temperature, ⁰ C (hours)

64

20.9 3.9 2.7 1.3. 3.4 3.8

58.8

24.9

4.4

2.7

3.4 4.8

60.3
24.9
3.9
2.7
1.3
3.4
1.8
1.6

l ± 0.5 816 to

718 (4)

-1.0 ± 0.5 788 to

691 (4)

-8 771

691 (2) -1.5 ± 1.0
to 860

(4)

63.3
20.7
3.9
2.8
1.4
3.5
1.8
2

0.5
0.1

O ± 0.5
up to 810

704 (4)

63.8

20.2

3.6

2.8

1.1 3.4 1.8 2.2

0.05

0.4

0.6

0.1

1.5 ± 0.5 to

(4)

66.7

20.8

3.9

2.7 1.3

1.8 2

0.05

0.4

0.4

-l ± 0.5 829 to

746 (4)

Example 8 Example 9 example Example 11 Example 12 example example

Components
(Weight percent)

SiO ₂

Al ₂ O ₃

Li ₂ O

CaO

ZnO

B ₂ O ₃

TiO ₂

ZrO ₂

MgO

CoO

NOK

Na ₂ O

K ₂ O

As ₂ O ₃ -

P ₂ O ₅

Fe ₂ O ₃

Cr ₂ O ₃

Expansion coefficient (0 to 300 ° C) 10- '

Temperature range ⁰ C nucleation temperature, ⁰ C (hours) ...

64.1 20.9 3.7 2.7 1.3 2.9 1.8 2

0.5 0.1

5.0 ± 1.5 771 to

718 (4)

63.8 20.9 3.9 2.6 1.3 3.5 1.7 1.7

0.5 0.1 0.02

-3 ± 0.5 768 to

704 (4)

9 ± 0.5 927 to

746 (4) 64.1
19.4
3.9
2.8 =
1.3
3.5
1.8
2

0.8
0.4

9.5 ± 0.5
to 981

(44)

64.1

20.8

3.9

3.4
1.8
1.4
2.7

0.4

1.5

7.5 ± 0.5
to 916

732 (4)

64.1

20.8

3.9

2.7

3.4 1.5 1.4

0.4 1.8

5 ± 0.5 to

732 (4)

63.2 20.8 4.4 2.7 1.3 3.4 1.8 2

0.4

-4.2 ± 0.5 893 to

677 (4)

While all of the ceramic glasses of Examples 1 to 14 showed good transparency, Example 13 is outside the composition range given above for low expansion ceramic glasses.

According to FIG. 1, the composition of Example 5 has an almost flat area in the curve, so that the coefficient of thermal expansion in the temperature range from 760 to 815 ^° C. is 0 ± 1 · 10- 'per ^° C. As can be seen from the curve of Example 3 (FIG. 1), there is a steep increase in the coefficient which is directly proportional to an increase in the final temperature. Under the nucleation conditions given above, Example 3 does not show an expansion curve with a flat mairdmum. At 771 ° C final temperature for 2 hours α about -8 · 10- ⁷ / ° while Q was at a final temperature of 760 ° C for 2 hours α was about 44th Essentially everything was still made of glass. The other examples in Table I (with a 1 hour final temperature) show fairly flat curves which correspond in appearance to those of Example 5 (see Figs. 2 to 5).

Table IA shows further examples of glasses according to this aspect of the invention which, as described in FIG Table IB indicated were heat treated. They gave clear crystalline products with the specified coefficient of thermal expansion. The use of these compositions allows one Temperature difference between different parts of a thermally crystallized body is considerable Thickness without any damage to the uniformity of the low coefficient of expansion throughout the body.

Table IA

Components (percent by weight)

SiO ₂

Al ₂ O ₃

Li ₂ O

CaO

ZnO

TiO ₂

ZrO ₂

P ₂ O ₅

Na ₂ O

K ₂ O

Sb ₂ O ₃

67.2 20.7 3.9 2.4 1.3 1.8 1.5

0.7 0.2 0.3

67.1 20.6 3.9

Table IB

66.9
20.6
3.8
2.8
1.1
1.8
1.9

0.7

67.3
20.4
3.8
2.5
1.2
1.5
1.5
1
0.5

0.1

69

19.2 3.6 2.7 0.9 1.9 2.2

0.4

67.3 20.7 3.9 2.5 1.6 1.4 1.4

0.7 0.2 0.3

Glass no J ^J - 1 K • L. First heat treatment stage hours Second heat treatment stage hours Expansion coefficient ^H I Temperature ° C 16 Temperature ⁰ C 1 «• 10 ⁷ / ° C (0 to 300 ⁰ Q ¹ { 1350 16 1450 1 -0.5 f 1350 16 1550 1 -2.2 1350 16 1525 1 -3.1 1350 2 1600 1 -3.8 1375 2 1550 1 -1.7 1375 2 1600 1 -0.6 1375 64 1650 4th -2.8 1250 16 1500 4th -4.3 1300 120 1600 4th -3.4 1250 960 1500 -4.5 1375 486 no -4.5 1375 264 no -4.6 Μ "J 1375 16 no 1 -3.8 M < 1375 16 1550 1 -0.4 1375 16 1600 1 -0.4 1375 1000 1650 -0.7 1375 1000 no -0.5 1425 64 no 1 0.2 1300 64 1600 1 -1.5 1300 1500 -2.9

Even with very long heat treatments at a relatively low temperature, very uniform expansion coefficients can be obtained in thick bodies, even with a glass after Example 3 showing no flat area in its curve (Fig. 1). However, such long heating times are very expensive and justified only at relatively high sales prices for the pieces. Warmth-

15 16

Treatments of this type result in very small crystals, as required, and the mirror can move faster and high transparency and the tendency to be made from the plate even lighter than before, slightly lower coefficient of thermal expansion- It is important that the mirror is transparent so that th. For example, he gave the glass of Example 8 after being precisely placed in a telescope (upper relaxation temperature 636 ° C) the following Er- 5 can be checked visually to ensure that results, whereby individual samples with the specified he is free of physical stresses. The through times and temperatures were heated isothermally: visible glass ceramic mirrors contain a multitude

_Λ interlocking crystals, but these are

^{α '10} crystals so small that the surface can be ground and polished 718 ° C 16 hours 5.3 663 ⁰ C 240 hours 26 ₁₀ without the structures with

718 ° C 32 hours 3.9 663 ⁰ C 256 hours 7.7 larger crystals observed scarring

718 ⁰ C 64 hours 663 ° C 3.1 480 hours 4.8 occurs.

718 ⁰ C 120 hours 2.6 As already mentioned, the present compilations

718 ° C 240 hours 3.6 settings can be used to make transparent

15 glass ceramic objects of considerable size

In Table IB other examples of long term thickness are to be made because of the effects of the

isothermal heat treatments indicated. F i g. 1 to 5 visible flat sections of the

A glass ceramic telescope mirror of the contraction characteristics, which each of the composition of Example 6 has by casting a glass body cylindrical at the low end or crystallization temperature with a diameter of 20 and in a wide temperature range.
of 15 cm and a thickness of about 3.75 cm and it has also been found that by changing the subsequent heat treatment according to the following of the nucleation and crystallization conditions, scheme: the glass object is exposed to heating, the curves speed of 2, 8 ° C / min. to 704 ^° C; Hold for 6 hours at downward in the graph and after 704 ° C; Heating can be shifted left at a speed of 25. For example, 2.8 ° C / min. to 788 ° C; hold at 788 ° C for 1 hour; Fi g. 1, Example 5, a flat curve with a slow cooling to room temperature. elongation of 0 ± 0.5 in a final temperature range

The article thus obtained had shown a thermal 760-843 ⁰ C. The glass according to example 5

see expansion coefficients of 1.4 · 10 ~ ⁷ (0 to was 4 hours of a temperature for nucleation

300 ° C). It was then ground and polished in such a way as to have been exposed to temperatures of 704 ° C. If the same

that a parabolic curve formed on its surface - base glass for 16 hours at 704 ° C and then

det was. Then, to form a reflection 16 hours at the specified end temperature,

If a thin aluminum layer is heated in the usual way, one obtains in a lower end temperature

applied to the prepared surface. temperature range a lower thermal output

Since a telescope is exposed to variable temperatures 35 coefficients of expansion, as in example 5A of the

is e.g. B. about -20 to +30 ⁰ C in the earth's atmosphere F i g. 1 is shown.

or significantly larger temperature differences with different nucleation times and temperatures

For devices operating in space, it is important that temperatures for different compositions in

the reflection mirror as low as possible, in front of the area specified above, results in different

preferably at 0 expansion coefficient 40 borrowed positions of the flat part of the curve, which is a low one

so that the picture is not distorted. Almost all expansion of the clear crystallized ceramic

these mirrors are usually made from molten mic in a fairly wide final temperature range

Quartz has a coefficient of thermal expansion, and it is difficult to maintain these temperatures

th of 5.5 · 10 - '/ ⁰ C (0 to 300 ° C), whereby and times are to be defined differently than by the specification,

the costs because of the required production time 45 that they must be sufficient to reach a final temperature

are very high, or made of Pyrex glass with a range of 28 to 55 ⁰ C or more a flat

to generate expansion coefficients of about 25 · 10- ⁷ / ° C for Ob- part of the curve, in which the thermal expansion

Servatory telescopes and about 33 · ^{10- '/ 0} C for a partial expansion coefficient about ± 10 · 10- ⁷ / ° C, preferably

scopes for amateur astronomers. In contrast, the wise is ± 3 · 10 - '/ ⁰ C.

enormous economic advantage of the invention. 50 Da large clear glass ceramic objects moderate cheap telescopic plates with low thermal with a thickness of, for example, 12.5 cm or more shear expansion obviously. Also in the case of a nucleation treatment during a time use of the telescope mirror must be subjected to considerable lead time, which is sufficient to parts available, since neither the setting of a temperature divides the temperature in the object evenly Waiting for natural equilibrium with the environment to bring the nucleation point is the amount needs to be blurred or distorted of the nucleating agent as noted above due to temperature fluctuations and borders. Larger amounts of the nucleating agent caused by changes in the mirror geometry - can cause undesired crystallization, trie occur. before a large item has time to cool down

The mirror plates according to the invention have the optimal nucleation temperature at 6 °. The additional advantage that they are compared to the standing crystals could then be so large that quartz and Pyrex glass plates relatively quickly the object is no longer transparent.
can be sanded, polished and shaped. The areas of application in which the formed glass objects or glass ceramic objects during the manufacture of a telescopic reflection mirror have to be kept in temperature ranges for a longer time during grinding, polishing, etc. the geometry. Thus, cooling occurs, it has been found that the amount of pauses is not or only to a considerably lower extent from TiO ₂ + ZrO ₂ to a maximum value of about 3 times.

weight percent and the amount of TiO _{2 is} limited to about 1.5% of the glass compositions specified here. _{The TiO 2} content is usually 1 to 1.5 percent by weight. One area of application in which such a low nucleating agent content is required is, for example, the manufacture of very large objects, such as telescopic mirror plates. These plates require a very long relaxation time in which the glass must not crystallize prematurely. The crystallizable glass mixtures according to the invention, as shown in examples in Tables I and IA, can of course also be subjected to a heat treatment which leads to the formation of opaque white or colored ceramics. Various heat treatments of typical glasses that have been crystallized into opaque ceramics are given in the following tables. The base glass compositions of the examples in Table II correspond to those given in Table I.

Table II

Opaque glass ceramic Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Heat treatment, ° C (hours) ..
Color of the opaque glass
ceramic. 732 (1)
982 (2V ₂ )
White
10.1 677 (2)
788 (2)
1038 (1)
White
1300 677 (2)
760 (2)
982 (1)
White
12th
1400 649 (2)
760 (2)
982 (1)
White 704 (2)
816 (1)
982 (1)
blue 704 (2)
899 (2)
1038 (1)
White α (O to 300 ⁰ C) -IO- ⁷
Tensile modulus

Here are a few more examples relating to the manufacture of telescope mirror plates,

Example A.

First of all, the following glass offset was melted: Component weight in kg

Zircon sand 8.85

Petalite 238.0

Al ₂ O ₃ 22.4

Boric acid 18.8

High-grade limestone 14.35

ZnO 3.68

Li ₂ CO ₃ , 1.63

TiO ₂ 5.30

NiO, 1.17

CO ₃ O ₄ 0.156

As ₂ O ₃ 0.732

Saltpetre 0.732

The molten glass then became a cylindrical body with a diameter of 15 cm and cast to a thickness of 3.75 cm. The glass body had the following theoretical composition in Weight percent:

Ingredient weight percent

SiO ₂ 64.0

Al ₂ O ₃ 20.9

CaO 2.7

ZnO 1.3

Li ₂ O ₃ 3.9

B ₂ O ₃ 3.4

TiO ₂ 1.8

ZrO ₂ 2.0

As ₂ O ₃ 0.25

NaNO ₃ . 0.25

NiO 0.4

CoO 0.05

The thermally crystallizable glass body was at a rate of 0.8 ° C / min. heated to 704 ⁰ C and held at this temperature for 6 hours. The temperature was then increased at a rate of 2.8 ° C / min. increased to 788 ° C. The body was kept at this temperature for 1 hour and then slowly cooled to room temperature.

The transparent glass-ceramic body had a thermal expansion coefficient of 1.4 x 10 ~ ^7/0 C (0 to 300 ⁰ C). The mean crystal size, measured over the largest linear expansion of the crystal, was 0.1 μm. The glass ceramic body was ground, polished and "shaped", ie a parabolic curvature was formed on the surface. A thin aluminum layer was applied in the usual way to the surface produced in this way, and a reflective surface was produced in this way.

For example, "B

A molten crystallizable glass of the composition of Example A, but without NiO and CoO, was poured into a graphite crucible having a diameter of 42.5 cm and a height of 7.5 cm. The glass body was allowed to cool and solidify so that it could be removed from the crucible. It was then placed in an oven previously heated to 621 ° C. The temperature of the oven was increased to 649 ° C. The glass body, which was essentially the size of the crucible, was kept at this temperature for 1 hour. Then the glass body was at a rate of 2.8 ° C / min. heated to 704 ⁰ C and held at this temperature for 16 hours. Then the temperature was raised at a rate of 2.8 ° C / min. increased to 76o C ^0. The body was kept at this temperature for 8 hours and then slowly cooled to room temperature at the oven speed, that is, the oven with the contained body was switched off until the room temperature was reached. The transparent glass-ceramic body had a thermal expansion coefficient of 2.0 x 10- ⁷ / ° C (0 to 300 ⁰ C). After grinding, polishing, designing and coating the outer surface with a reflective layer, an excellent optical reflective mirror for a telescope was created.

19 20

B ice T he 1 C ° ^ ^{επ to} S ^e S ^just was, the glass-ceramic body as a predominant containing crystals formed in situ

By mixing and heating the following lithium-containing crystalline phases for 4 days, namely after

Glass offset to a temperature of 1593 ° C, X-ray diffraction was either / S-eucryptite or

a glass melt formed: 5 / S-eucryptite-like crystals or / S-spodumene or

Component weight in kg / 7-spodumene-like crystals or both together.

The ceramic glass contains many such crystals in

Zircon sand 6, oil of random orientation in ceramics and in the

^p e ^tan t · · ι-'L glass matrix dispersed. Almost all crystals in ceramics

Alumina 13.96 _{10 have dunes by measuring} e _r jan among V _3, preferential

_High-grade limestone 11.05 _{wise under} ^ μΓη In every case, the diameter is

ZpO - '° ⁴ below about 0.1 μm, the diameter being the longest

. r ,. ² ^ - - linear crystal expansion is to be measured.

Z ¹ Wr _n r, 'Vt Optically reflective mirrors made from mirror plates

LiNO ₃ Ü, D_ ₁₅ ^ ₆₁ , have the compositions given above

Sodium Monthly 0.56 has _{a large number of ideal} properties. You are full

The glass produced had the following theoretical come homogeneous and amorphous body, i.e. h., they

Composition in percent by weight: show no variable expansion rate

, -γ α speed and no bubbles. You don't have any thermal

Λ 2o'9 ^ao prehistory, that is, they are in their dimensions

³ _Ί 'η constant, and the optical shape remains constant.

7 * 3 You are easily »able to create« and can use the

29 desired shape can be brought. You generate

pQ ^ high contrast in the captured image.

~ Q ² 2'n ²⁵ mirrors up to about 90 cm in diameter can be used as

² · * undivided bodies are produced. Bigger mirrors

ρ q2

Cu Q 0 * 2 ^{sm <} ^ 8 ^ew oholich "ribbed" and are

-VT _a Q ³ nc melt large hexagonal and triangular parts

² 'manufactured. The ratio of the diameter to the

The molten glass was circular in a 30 th thickness is about 6: 1 for undivided mirrors up to Graphite crucible with a diameter of 42.5 cm by 90 cm diameter and about 8: 1 for ribbed mirrors and poured to a height of 7.5 cm. The vitreous body with a larger diameter.

was left to cool and solidify until the mirror surface was coated with a

it can be safely removed from the crucible and placed in an oven reflective layer, such as aluminum, after previously heated to 621 ° C 35 by any known method,
had been. The vitreous was 3 ^x / ₂ hours at In this description the expressions / S-Eu-

kept this temperature. Then the furnace cryptite crystal and / J-eucryptite-like crystals in temperature at a rate of 2.8 ° C / min. have been used alternately. Often it is increased below to 774 ° C. This temperature was maintained / S-eucryptite a crystal form with 1 mole of lithium oxide, 6IIV2 hours. The furnace was then sealed and the body in the furnace until it stood. In this specification, both outputs are cooled to room temperature. The throughput pressures generated to designate crystalline body with cautious crystallized glass-ceramic had a linear / J-eucryptite structure, the thermal expansion coefficient by X-ray diffraction of 0.0 x 10 ^-7 / is displayed in use. The peaks can easily be ° C (0 to 300 ⁰ C). Being pushed through grinding, polishing, shaping, depending on whether a defined _{amount of SiO 2} and coating with a reflective layer is added, which is not exactly 2 mol, the result is an excellent optical mirror and can be either more or less. Similar reflector for an astronomical telescope. The expressions / S-spodumene-

The transparency of the mirror is important so that crystals and / 5-spodumene-like crystals can be used optically and as a generic term for crystalline bodies for freedom from physical tensions after they have been attached in a telescope, which means that the crystal structure of / 3-spodumene can be used. Even if the mirror contains many under- with 4 moles of SiO ₂ to 1 mole of aluminum oxide and 1 mole of interlocked crystals, they are still lithium oxide, whereby the peaks are somewhat small enough that they can be pushed on during grinding and polishing, if the crystal structure more surface no scarring, which contains the sequence 55 or less than 4 mol SiO ₂ . In the claims of large crystals there is no "tearing out" from which the expressions / 5-eucryptite and / 3-spodumene in the surface occurs during the dissection work. As used in this general meaning.

1 sheet of drawings

Claims (1)

I 496 patent claims: 1. Transparent glass ceramic with low thermal expansion, characterized in that that they are formed by thermal in-situ crystallization of a thermally crystallizable base glass which essentially contains the following components: Weight percent SiQ ₂ .... 56th to 70th Al ₂ O ₃ 18 to 27 Li ₂ O 3.4 to 4.5 CaO O to 3 ZnO O to 2 B ₂ O ₃ ..... O to 4 TiO _2,. O to 6 ZrO ₂ O to 3 MgO ...... O to 3 Na ₂ OO to 1 P ₂ O ₅ O to 3 with the following conditions: (SiO ₂ + Al ₃ O ₃ ) at least 82 (SiO ₂ + Al ₂ O ₃ + B ₂ O ₃ + P ₂ O ₅ ) 86 to 91 ^a 5 (CaO + MgO + ZnO + Na ₂ O) 2.5 to 6
(SiO ₂ + Al ₂ O ₃ + P ₂ O ₅ + Li ₂ O) not over 93 (TiO ₂ + ZrO ₂ ) ... 2 to 6