CN1005710B - Glass ceramics with special thermal expansion properties - Google Patents

Abstract

Glass-ceramics with original glass containing h-quartz solid solution crystals and having a maximum value of 1X 15 relative length change^－５And has a coefficient of linear thermal expansion of less than 0.1X 10^－６(ii)/K is composed of (by weight%) 50-65 SiO₂，１８－２７Ａｌ₂Ｏ₃，０－１０Ｐ₂Ｏ₅，０－１Ｂ₂Ｏ₃，２．５－４Ｌｉ₂Ｏ，０－２Ｎａ₂Ｏ，０－２Ｋ₂Ｏ，０－０．５ＭｇＯ，１－５ＺｎＯ，０－４Ｃａ０．１－５ＢａＯ，０－５ＴｉＯ₂，０－３ＺｒＯ₂And 0-1.5 As₂Ｏ₃The components are as follows.

Description

Glass ceramic with special thermal expansion performance

The invention relates to the composition of a starting glass for the production of a glass ceramic which can be converted into a transparent glass ceramic containing crystals in the solid state of h-quartz by controlled crystallization and which can satisfy the following three conditions:

1. The difference between the maximum value of the relative length variation (Delta1/1) and its minimum value is less than or equal to 1X 10 ^-5, i.e. between a temperature range of-50 ℃ and +100 DEG C

The absolute value (delta 1/1) is the maximum- ([ delta 1/1) and the minimum absolute value is less than or equal to 1 multiplied by 10 ^-5;

2. The absolute value of the linear thermal expansion coefficient alpha 0/50 DEG should be less than or equal to 0.1X10 ^-6/K in the temperature range of 0 ℃ and 50 ℃, and the optimum upper limit value is 0.066X10 ^-6/K;

3. In the temperature range that allows use, the reversible adjustment of the length after cooling at different speeds should be less than or equal to 0.1 x 10 ^-5, as expressed by the relative change in length at 20 ℃, with an optimum upper limit of 0.14 x 10 ^-5.

In the literature, transparent glass ceramics have been disclosed which have a low expansion coefficient and which contain h-quartz solid-solution crystals in their crystalline phase. Glass ceramics with optical special effects have also been developed for some time, in particular for reflector telescope support materials. For such glass ceramics, it is of paramount importance that the thermal expansion is low over the temperature range from-50 ℃ to +100 ℃.

The above materials have been described, for example, in the Reed patent Specification 1496611 in which the expansion properties are characterized by a linear thermal expansion coefficient (α0/300) in the temperature range from 0 ℃ to 300 ℃ and the numerical range α0/300, i.e., -3≤α0/300≤3X10 ^-7/K, is also given. In some examples it is also stated that the value of α0/300 is less than |1.0|×10 ^-7/K.

The melting conditions of the readily processable glass are described in the schde patent specification 1902432 and can be converted to a glass-ceramic state by controlled crystallization to produce a transparent glass-ceramic having a low coefficient of linear expansion. A composition was thus successfully obtained for which the linear expansion coefficient alpha-30/70 in the temperature range of-30 ℃ to +70 ℃ could be adjusted to 0.+ -. 0.15X10 ^-6/K by ceramming over a wide range of 750 ℃ T≤870 ℃ and 4 hours t≤100 hours. The latter condition is important because it also ensures that the same alpha value can be obtained for large casting blocks. For large casting blocks, even if heated at a slow rate, a uniform temperature distribution must be obtained under certain conditions.

The characteristics of glass ceramics, as indicated in the mentioned patent specification, in optical applications have often not been able to meet the technical requirements of modern length constancy. Instead of a single value of the linear thermal expansion coefficient over a range of temperatures, the three conditions mentioned above, which characterize the length and shape constancy, are now employed.

When commercially available glass ceramics such as CERVIT and ZERODUR were tested, it was found that neither glass could meet the aforementioned conditions at the same time.

From S.F.Jacobs, M.A.Norton, J.W.Berthold III, pages 1973;AIP Conf.Proc.No.17,280 to 293 and J.W.Berthold III, S.F.Jacobs: appl.Opt.15 (1976), pages 2344 to 2347, it is stated that CERVIT does not satisfy condition 1. From the paper S.J.Bennett, J.Phys.E.Vol.10 (1977), pages 525 to 530, it is known that ZERODUR cannot meet condition 3.

The object of the present invention is therefore to provide a composition of the glass ceramic and a ceramming condition of the original glass, so that three requirements on the expansion properties can be met. In addition to the above requirements, there is a further requirement that the temperature corresponding to a viscosity of 10 ⁺⁴ dPas (hereinafter referred to as the V _A value) should be below 1300 ℃ in order to give good processing properties to the raw glass.

First, it is necessary to further explain a method for determining a relative change value of the length at room temperature after cooling at different rates. It has been found that the cooling rate in the temperature range 150 to 350 ℃ has an effect on adjusting the length of the rod at room temperature for different test materials. Thus, to determine the relative length difference at room temperature for different cooling rates, a rod length of about 100mm and a diameter of about 5mm was compared with a rod length cooled from 350 ℃ to 20 ℃ by air quenching at a rate of 6 ℃ per hour.

The new glass consists of the following components, SiO₂,B₂O₃,Al₂O₃,P₂O₅,Li₂O,Na₂O,K₂O,MgO,CaO,BaO,ZnO,ZrO₂,TiO₂,As₂O₃ and Sb ₂O₃. Wherein P ₂O₅,TiO₂ and ZrO ₂ are essentially the core former which initiates and promotes the crystallization process. As ₂O₃ and/or Sb ₂O₃ are used for purifying the melt. The other components, by means of their respective mixing ratios, determine the phase of the crystals that condense during the ceramming process and thus the properties of the glass ceramic produced.

It has been unexpectedly found that the problem of insufficient length at room temperature for reversible regulation after cooling at different rates in the above temperature range is directly related to the MgO content, the smaller the MgO content, the less the change in relative length at room temperature at different cooling rates. It is therefore clear that the composition of the glass-ceramic raw glass which can meet the above requirements preferably contains no or very little MgO.

A further task of the invention is to find a composition range in which the relative length variation Δ1/1 (hereinafter referred to as Δ1/1 curve) has a nearly linear dependence and α0/50 is nearly zero, over the temperature range from-50 ℃ to 100 ℃. It has been found that most components can only be varied within small limits, i.e. within a few 1/10 wt.%, if α0/50 is kept close to zero, and that such small variations hardly affect the curvature of the Δ1/1 curve. The coupling exchange between the components SiO ₂,Al₂O₃ and P ₂O₅ is an exception, and if the percentage of SiO ₂+Al₂O₃+P₂O₅ is a defined value, several weight percent exchanges can be performed between the three components without a drastic change in α0/50. Small changes in α0/50 can be compensated for by other components. It can then be seen that the curvature of the Δ1/1 curve can be systematically varied by means of a large variation in the percentages of the components SiO ₂,Al₂O₃ and P ₂O₅. If a composition of the nearly linear Δ1/1 curve has been found, then all other compositions of the nearly linear Δ1/1 curve can be approximately determined by substituting ±1 wt% SiO ₂ >, ±1/3 wt% Al ₂O₃, and ±2/3 wt% P ₂O₅.

The composition range of the invention is as follows:

Weight percent

SiO₂ 50.0-65.0

Al₂O₃ 18.0-27.0

B₂O₃ 0-1.0

P₂O₅ 0-10.0

Li₂O 2.5-4.0

Na₂O 0-2.0

K₂O 0-2.0

MgO 0-0.5

ZnO 1.0-5.0

CaO 0-4.0

BaO 1.0-5.0

TiO₂ 0-5.0

ZrO₂ 0-3.0

As₂O₃ 0-1.5

In the present invention, sb ₂O₃ functions As compared to As ₂O₃.

The following examples further illustrate the invention, in order to compare the characteristics of glass ceramics, using a ceramming procedure of heating to 730 ℃ at 4 ℃ per minute, holding at 730 ℃ for 1 hour, further heating to 850 ℃ at 4 ℃ per minute, holding at 850 ℃ for 1.5 hours, stopping the electric furnace heating and cooling to room temperature.

FIG. 1 shows a plot of Δ1/1, i.e., the change in Δ1/1 versus temperature for three glass-ceramics of different compositions.

In Table 1, for better illustration of the invention, the compositions of 12 glass-ceramic raw glasses are listed.

In Table 2, several properties of the glasses of importance to the present invention are listed, together with the corresponding glass-ceramic products.

The column listing the V _A values shows that most compositions have a V _A value below 1300 ℃, whereby the desired objective, i.e. finding an easy to process glass-ceramic raw glass, can be achieved. The V _A value of example 4 is 1235 ℃, which is well below 1300 ℃, and this glass also melts well and is further processed.

The four previous examples all met the condition of SiO ₂+Al₂O₃+P₂O₅ =84.5 wt%. These examples illustrate that, by coupling substitution between the above three components, the condition of | (Δ1/1) maximum- (. DELTA.1/1) minimum |≤1X10 ^-5 can be satisfied despite a large variation in the percentages of the components. Furthermore, it is shown by these examples that the variation of the α0/50 value can be compensated by small variations in other components, in particular Li ₂ O, znO, caO and BaO.

Examples 2,5 and 6 show that the curvature of the Δ1/1 curve can be influenced by exchanging P ₂O₅ with Al ₂O₃ when the content of SiO ₂ is constant. Because exchanging P ₂O₅ with Al ₂O₃ changes the α0/50 value, this value is adjusted to be close to zero by means of the other components. To illustrate this, three example Δ1/1 curves are shown in FIG. 1.

From examples 2,7,8 and 9 it can be shown that for a certain combination of SiO ₂+Al₂O₃+P₂O₅ contents of 85.5 and 86.5% by weight, it is also possible to find compositions, the glass ceramics associated therewith meeting the requirements of three conditions concerning expansion. Furthermore, it can be seen from these examples how the glass composition should be changed if the SiO ₂+Al₂O₃+P₂O₅ composition content is to be made to be less than 84.5 or greater than 86.5.

Finally, comparative examples 10 to 12 can illustrate the case where the relative length difference is affected by the variation of the MgO content according to the cooling rate at room temperature. And it can be seen that the value continuously increases as the MgO content increases.

TABLE 1

TABLE 2

Claims (1)

1. Glass-ceramic containing crystals in the solid state of h-quartz, wherein

A. The change in relative length is expressed in terms of the difference between the maximum and minimum values of Δ1/1, | (Δ1/1) max- (. DELTA.1/1) min, which is equal to or less than 1X 10 ^-5 when the temperature ranges from-50 ℃ to 100 ℃,

B. The absolute value of the coefficient of linear thermal expansion is 0.1X10 ^-6/K or less at a temperature in the range of 0 ℃ to 50 ℃, and

C. I ₁ after cooling with Rate 1-i.e. i ₂/l₁ after cooling with Rate 2

Δ1=l ₁-l₂/l₁, a value of 0.1X10: 10 ^-5 (expressed as relative change in length at 20 ℃),

Where l is the length, rate 1 is the cooling rate from 350 ℃ to 20 ℃ at 5 ℃ per hour, and rate 2 is the rate at which it is cooled by air from 350 ℃ to 20 ℃,

Meanwhile, their original glasses have the following composition:

Weight percent

SiO₂ 50.0-65.0

Al₂O₃ 18.0-27.0

B₂O₃ 0-1.0

P₂O₅ 0-10.0

Li₂O 2.5-4.0

Na₂O 0-2.0

K₂O 0-2.0

MgO 0-0.5

ZnO 1.0-5.0

CaO 0-4.0

BaO 1.0-5.0

TiO₂ 0-5.0

ZrO₂ 0-3.0

As₂O₃ 0-1.5

Wherein the sum of the contents of SiO ₂+Al₂O₃+P₂O₅ is in the range of 84.5-86.5%.

And according to the difference in relative lengths shown at 20 ℃.