DE1421838C - Photochromic glass object - Google Patents

Description

The invention relates to a photochromic glass object made of a silicate glass that contains at least one part of at least 0.005 percent by volume of silver chloride, Contains dispersed silver bromide and / or silver iodide crystals, the silver content of this part is at least 0.2 percent by weight. The optical transparency of these objects changes reversibly with the intensity of the incident actinic radiation.

Considerable effort has already been made to ensure that glasses are permeable to light and / or heat for windows. To reduce walls, ophthalmic lenses and the like. B. tinted, colored or opacified glasses developed, all of which have the disadvantage that their permeability is not variable or is not reversible.

-The desired property of variable permeability show organic developed for this Plastics that can be used as such or as a laminate for glass panes. This However, materials lose their desired properties within a very short time.

It has also developed photosensitive glasses in which the irradiation with ultraviolet light one creates a latent image that is made irreversibly visible by subsequent heat treatment can (see. German Patent 844 648). Such glasses generally contain less silver than the photochromic glasses of the present invention, and they contain the silver in dissolved form and not in the form of dispersed silver chloride. Silver bromide and / or silver iodide crystals. When the photosensitive If glasses are to be made irreversibly opaque, irradiation takes place first with ultraviolet light with subsequent heat treatment, resulting in submicroscopic nuclei form colloidal silver. The light-sensitive glasses 1.8 contain up to 3.0% analytically determined fluorine by cooling and renewed heat treatment Crystallites of alkali fluoride.

It has now been found that photochromic glasses, i.e. H. Glasses that change when exposed to light a Reversible discoloration of wavelengths from 3000 to 5000 Ä, arise when these glasses are in at least one Part of silver chloride, bromide and / or iodide crystals in an amount of at least 0.005 percent by volume and the silver content of this part is at least 0.2 percent by weight. Lower silver content lead to the formation of colloidal silver nuclei with the formation of a light-sensitive glass like it is described in the aforementioned patent, but not for the formation of photochromic glasses. requirement for the phototropic effect is also that the silver chloride, bromide and / or iodide crystals in the Glass or glass part are completely embedded.

F i g. 1 illustrates the reversible change in the transmittance of visible radiation when a photochromic article according to the invention alternately exposed to actinic radiation and withdrawn from it will.

Transparent photochromic glasses are obtained according to the invention when the glass or the "glass part contains up to 0.1 percent by volume of the silver halide crystals mentioned, the diameter of these crystals does not exceed 0.1 μ and the glass or the glass part contains no further crystalline phase, The visible rays of these glasses are reduced when they are exposed to actinic rays in the ultraviolet and blue regions of the spectrum, ie rays with a wavelength between 0.3 and 0.5 microns, and regain their original transmittance for visible rays, however, if they are removed from actinic radiation. The reason for this effect is not known, but it is believed that it is a consequence of the action of actinic radiation on the crystals dispersed in the glass, this radiation being the absorption capacity of the Crystals with respect to visible rays changes reversibly and the crystal e return to their original state after removal of the actinic radiation.

To achieve a recognizable effect, the silver halide crystals must be present in the photochromic part of the glass object in a concentration of at least 0.005 percent by volume. Although neither the maximum concentration nor the size of the silver halide crystals appear to be critical for the photochromic properties, provided that these are completely embedded in the silicate glass in order to prevent permanent changes due to actinic radiation, as mentioned, the concentration of the Silver halide crystals do not exceed 0.1 percent by volume and the diameter of the crystals does not exceed 0.1 μ and the glass does not contain any other crystalline phases, ie be essentially amorphous. Such glasses contain enough crystals to noticeably absorb the visible rays even if they have negligible scattering effects.

The size and concentration of crystals, the translucent glasses the desired sensitivity can usually be seen with optical microscopes. The size and focus however, of crystals in clear glasses must be determined with an electron microscope will. An electron microscope with a resolution of up to 20 Å was used for this. Thereby posed it is found that a sheet of transparent silicate glass with a content of 0.01 percent by volume Silver chloride crystals as determined by petrographic analysis using the electron microscope was found, with the crystals predominantly having a diameter of 50 to 60 Å and in amorphous silica glass were dispersed, has the desired photochromic properties.

The photochromic articles according to the invention are preferably manufactured in such a way that the constituents of the desired crystalline phase are incorporated into the glass mass and the crystals Fails "in situ" in the glass. You can add the desired silver halide to the glassware, melt the glassware, bring it into the desired shape and cool it in the usual way.

In order to produce the required minimum amount of crystalline phase in the finished glass, it must

The silver concentration should be at least 0.2 percent by weight based on a customary analysis (e.g. gravimetric or spectrophotometric) and the halogen concentration (chlorine, bromine, iodine and their mixtures) is sufficient for a stoichiometric reaction with the minimum amount of silver. For the stoichiometric conversion with 0.2'V ₁ , silver, about 0.077 "chlorine or 0.15" / "bromine or 0.24" / "iodine are required if the halogens are used individually

will. If, however, mixtures are used, it is only necessary that the molar amounts of these halogens total at least about 0.0019 moles. Although the maximum amounts of silver and / or the listed halogens do not appear to be critical, glasses with an analyzed Silver concentration greater than 0.7% translucent or opal. Glasses with a silver content of more than 1.5 ",, show no more favorable photochromic properties. A silver content of more than 1.5% silver is therefore superfluous. The total amount of halogens listed should be practical Reasons to be limited to about 2.0 weight percent. With a transparent, photochromic. Silver halide crystals containing glass, the analytically determined silver concentration of the glass may be 0.7 percent by weight and the total concentration of halogens analyzed does not exceed 0.4 percent by weight. It is known that halides tend to volatilize during the melting process. the the resulting losses can amount to 30 to 60% of the amount added to the glassware, depending according to melting temperature and time, according to the melting device used and the halide concentration in the melt. Silver loss can also occur during melting, probably due to the volatilization of silver halide, but the amount lost in this way is only about 15 to 30% of the added amount. However, the losses occurring under the conditions used in each case can be readily recognized compensate by adjusting the glassware accordingly, because the wide range of permissible quantities of the essential components makes it possible to obtain the desired values despite the use of rough approximations Obtain item.

Although the silver halide crystals are used to achieve an object with the desired properties must be completely embedded in the glass mass, these crystals can thereby be obtained be that, as stated above, the appropriate ingredients are added to the glassware or that one Introduces silver ions into a glass article that contains halide ions and alkali metal oxides, but is free of silver. This can be achieved by applying a finely divided silver or a silver compound containing material on the surface of such a glass object and heating the Glass object, as it is common in silver plating, whereby at least in the surface of the glass the alkali metal ions are exchanged for silver ions, which then with the halide ions to the desired silver halide crystals are able to react.

The silver halide crystals responsible for the phototropic effect can when the Molten glass are precipitated. It is, however, also possible that the cooling is carried out so rapidly that no crystallites of the desired silver halide or only an insufficient number of these crystallites precipitated to produce a noticeable photochromic effect in the glass. This deficiency can be caused by it be remedied that the glass is at a temperature above its stress temperature sufficient heated for a long time so that the silver cations and the halide anions within the glass closer can arrange to each other and so a second amorphous, consisting of submicroscopic droplets Phase arises that contains molten silver halide in an amount of at least 0.005 percent by volume of the glass contains. This silver halide crystallizes on cooling below its melting point. Preferably the object should not have to achieve the additional precipitation of the silver halide a temperature above its softening point, as such a treatment is too strong deformation of the molded glass object

ίο would cause.

The heat treatment should enable the silver cations and halide anions to reassemble to form a separate phase in the glass mass. It is clear that this reorganization is so The faster it goes, the higher the temperature, because the viscosity of the glass increases with the temperature decreases so that the resistance to the movement for rearrangement is decreased. One A satisfactory heat treatment usually consists of leaving the glass object in place for about 16 hours heated to its tension temperature or about 15 minutes to its softening temperature. There other reactions can occur during the heat treatment, e.g. B. an agglomeration or a Growth of the silver halide droplets and / or the precipitation of other crystalline phases must be the Heat treatment in the higher temperature range can be shorter in order to prevent this undesirable occurrence To prevent side effects.

The appropriate heat treatment can easily be determined by taking about five samples a certain composition in the form of a tube about 6 mm in diameter and more sufficient Length in a zoned oven at an even temperature between voltage and Maintains softening temperature of the composition and the samples after various times, e.g. B. takes out of the oven after 1, 2, 4, 8 and 16 hours. An examination of the photochromic properties of the Glass allows the determination of the appropriate heat treatment for the most beneficial, photochromic Properties.

Table I shows the composition determined on the basis of a chemical analysis (percent by weight) of glasses listed, which become phototropic through appropriate heat treatment:

Table I.

1 2 3 4th SiO,
Na ₁ O
⁵⁵ AUO ₃
. B ₂ O _3. ·
Ag
Br 60.1
10.0
9.5
20.0
0.40
0.17
0.1
0.84 60.3
10.0
9.5
20.0
0.24
0.26
0.80 59.9
10.0
9.5
20.0
0.58
0.31
0.94 59.8
10.0
9.5
20.0
0.70
0.09
0.16
0.85 ⁶⁰ cl Q .:

In accordance with conventional practice, the halide content of these glasses, including fluorine, is in percent by weight expressed as an excess over the gesanita glass composition in which all components with the exception of halogens, about 100%

do. Although, as is well known, at least a considerable one Some, if not all of the silver in the glass is in the form of ions, probably bound to oxygen and / or the halogens, it is expressed in the above table, as usual, as silver.

It is also believed that the phototropic properties obtained in accordance with the present invention are enhanced by the inclusion of a small amount of metallic or atomic silver in the silver halide crystals. Although it has not hitherto been possible to detect the presence of silver in this form by any known technique or device, the fact that controlling the silver-halide ratio or the amount ¹ S of the so-called cryogenic reducing agent in the glass mass leaves within a range , which tends to reduce a smaller proportion of the silver content to metallic silver, improves the desired properties of silver halide crystals in the lower range described, ie compositions containing between 0.005 and 0.1 percent by volume, strongly suspect that metallic silver is the reason for the improvement in the photochromic properties . ^2S

In particular, it has been found that. If the total weight of the listed halogens determined by chemical analysis lies between that for the stoichiometric conversion with 0.2 weight percent silver and the weight percent silver calculated as free silver, the photochromic properties are improved, probably because the equilibrium dissociation of the silver halide to metallic silver and nascent halogen sufficient to generate a catalytic amount of ato- - ¹ ? maren silver in the silver halide crystals. A similar result is obtained even if the total amount of halogens is substantially greater than the amount of silver, provided that a cryogenic reducing agent is present in the specified amount in the glass, namely 0.002 to 0.10 "" Tin oxide, calculated as SnO: 0.002 to 0.02 "" Iron oxide, calculated as FcO: 0.01 to 0.1 "," Copper oxide, calculated as Cu ₂ O: 0.04 to 0.4 ", arsenic oxide. calculated as As ₂ O ,. and 0.1 to 1.0 "" antimony oxide. calculated as Sb ₂ O ,.

It is known that the polyvalent cations of these oxides have the ability to act as a reducing agent in glasses at the softening temperatures of conventional glasses. Although these oxides can be converted to their highest oxidation state at the beginning of the melting process, it is believed that at least some of these oxides are converted to a low oxidation state at the melting temperature. This reduced form - ^s - ^{s of} the oxides presumably reduces a very small but important part of the silver halide to metallic silver. Each of the reducing agents listed are effective within the stated ranges, but amounts smaller than the stated amounts do not appear to bring about the desired improvement in the phototropic properties, while larger amounts convert such a large proportion of the silver halide into the metallic state that the silver halide crystals become precipitated. the supply ⁶ - to give ^s composition photochromic properties affected and / or the glass is black and cloudy. Copper oxide is particularly advantageous because it is effective in small amounts that do not undesirably discolor the glass and also compensates for the yellowish discoloration of the glass caused by the silver content.

It has also been found that a particularly inexpensive transparent phototropic glass can be obtained in a base glass composition which contains 40 to 76 percent by weight SiO ₂ . 4 to 26 percent by weight AKO ,. 4 to 26 percent by weight B, O, and as alkali metal oxides 2 to 8% Li ₂ O, 4 to "15% Na, O, 6 to 20", "K ₂ O. 8 to 25", "Rb ₂ O and or 10 to 3Ö "" contains Cs ₂ O, the total amount of these basic constituents together with the silver halide crystals making up at least 85 "" of the total glass composition, if the glassware is melted for this purpose in a non-reducing atmosphere at a temperature between 1400 and 1500 C for 4 to 8 hours, Brings the melt into the desired shape in a known manner, for example by drawing, pressing, rolling, blowing and the like and achieves the desired crystallization of the silver halide crystals during the shaping and cooling or by subsequent heat treatment.

Silica, boron oxide, is used to achieve the best results. Alumina and the alkali metal oxides are preferably kept within the prescribed ranges, since a glass with a lower silica content tends to precipitate undesired crystalline phases simultaneously with or before the desired silver halide precipitation, whereby an undesirably opaque glass is obtained, while others soap a glass that is more than 76 "" SiO ₂ or less than the specified amount of alkali metal oxide contains, is difficult to melt at the conventional melting temperatures and a glass which contains more than 24 "',, B ₂ O, or more than the specified amount of alkali metal oxide, undesirable chemical attacks or Exposed to the elements. The use of at least 4 "" B ₂ O ensures that the silver halide crystals precipitate at temperatures between the stress and softening temperature of the glass within a reasonable time. The use of aluminum oxide in the specified amounts ensures that the glass does not occur simultaneously with or before the desired Halide formation, undesirable glassy or crystalline phases arise.

In addition to the listed components of the preferred base glass compound, other components such as fluorine, divalent metal oxides and P ₂ O ₅ . to be available. For example, fluorine in the form of fluorides can be added to the glassware to increase the meltability of the glass, although it is not possible. Precipitate silver fluoride crystals in a glass phase. However, the amount of fluorine should not be so great that other crystalline fluorides are precipitated in the glass, especially when divalent metal oxides such as calcium oxide and barium oxide are contained in the glass composition.

Although the divalent metal oxides such as MgO, CaO. BaO. SrO. ZnO and PbO. little influence on have the photochromic properties of the preferred glasses, their quantities should be limited, about the formation of other crystalline phases which cause an undesirable opaque nature of the glass would prevent. For this reason, no more than 4 "" MgO. 6 "" CaO. 7 "" SrO. S "" BaO. X "" ZnO or M) ",, PbO before-

be available and the total amount of these ingredients composition is in percent by weight, calculated from

make up no more than 15 percent by weight of the total glass composition.

Glazers of this preferred type which are given photochromic properties by heat treatment are listed in Table II. The moreover glass set, indicated, with the silver as metallic Silver and the halides expressed as a percentage excess over the total composition in which the total components, with the exception of the halogens, make up 100%.

SiO ₂

AI ₂ O., .... B ₂ O ₃ ... Na, O ....

Ag

CuO ....

F.

Br

Look

SiO ₂

Al ₂ O., ... B ₂ O., ... Na ₂ O ... Ag ...,. CuO ...

egg

Br

Look

12th

61.5

10.7

16.6

10.7 0.44 0.016 2.5

translucent white

62.8 62.8 7.0 1Ό.0 22.9 20.9 6.9 5.9 0.38 0.38 0.016 0.016 2.5 2.5 1.7 1.6 clear through
shining
(translucent '
White

13th

68.7 10.0 12.9 10.0

0.38

0.016

2.5

1.7

clear

Table II

"

62.8

4.0 19.9 12.9

0.38

0.016

2.5

1.7

clear

7th 8th 62.8 62.7 10.0 6.0 15.9 19.9 10.9 10.9 0.38 0.38 0.016 0.016 2.5 2.5 1.7 U clear clear

15th

62.8
5.0

24.9
6.9
0.38
0.016
2.5 ■
1.7

clear

60.4 9.5 19.0 10.0 1.08 - 0.02 2.5 1.9

cloudy white (opal)

62.7 9.9

19.9 7.0 0.45 0.016 2.5 0.3

clear

K) 11th 60.7 61.5 9.6 10.7 19.2 16.6 10.1 ■ 10.7 0.36 0.44 0.05 0.016 2.5 2.5 1.7 - 0.8 clear clear

17th

60.8 9.6

19.3

10.1 0.22 0.01 2.5 1.7

clear

18th

60.7

9.6 19.3 10.1

0.29

0.002

2.5

1.7

clear

SiO ₂ Al ₂ O ....., ... B ₂ O.,. '.. Na ₁ O ...

Ag

CuO ... Sb ₂ O., ..

F.

Cl

Look

19th

20th

74.5 62.7 60.5 10.0 9.9 9.6 4.0 19.8 19.1 10.9 6.9 10.0 0.38 0.60 0.72 0.016 0.063 0.05 0.10 2.5 2.5 2.5 0.3 0.8 1.8 clear yellow yellow- cloudy cloudy

21 22nd

60.3

9.5

19.1

10.0

1.08

2.5.

0.7
pinkish

60.3 9.5 19.0 10.0 1.08 0.08

2.5 1.9 cloudy yellow

24

60.3

9.5

19.1

10.0

1.08

2.5 2.4 cloudy white

60.2. 19.1 10.0 1.22

2.5 2.0 cloudy white

SiO ₂ . . AM) ₁ .

26th

60.6 9.6

27

42.9

25.7

2S

59.1 9.2 29

59.1
13.3

30th

59.2 ¹ U

31

59.2 9.4

32

59.3 9.4

109 613/13

9 26th 27 continuation 28 29 30th 10 31 32 19.1
10.0
0.72
2.5.
1.8
pink
cloudy 20.0
10.9
0.51
0.016
1.45
0.4
clear 20.1
IU
0.50
0.008
1.4
0.4
clear 16.0
11.1
0.50
• 0.007
1.45
0.4
clear 20.0
10.9
0.50
0.016
1.45
0.39
clear 16.0
14.9
0.50
0.015
1.45
0.6
clear 20.0
10.9
0.41
0.016
1.45 Β, Ο,. . . ".. 0.6
clear Na ₂ O Ag CuO F. Cl Br Look ..

SiO ₂ .... AI ₂ O ₃ ... B ₂ O ₃ ... Na ₂ O ... CaÖ ... ZnO ... BaO ....

Ag

CuO ..., F

Cl

Look

35

36

59.1 58.1 59.1 9.3 9.2 9.2 17.0 20.6 17.0 8.0 11.2 8.0 6.1 _ - 6.2 0.50 0.86 0.50 0.015 0.02 0.015 1.45 1.69 1.45 0.4 0.49 0.4 dar ,, clear clear

37

SiO ₂ .

Al ₂ O ₃

Na ₂ O

K ₂ O.

Cs ₂ O

B ₂ O ₃

CuO.

Ag

Cl ...

57.1 9.7

11.3

21.4 0.016 0.50 1.0 1.45

36.2 9.1

27.1 27.1 0.016 0.50 0.87 1.37

40

59.8 9.9 9.9

19.9 0.016 0.50

1.40 0.59

The glass compositions listed in Table II can be prepared by melting in conventional Way manufactured glass sets, are manufactured, whereby one sees the volatilization of a substantial Include some of the halide components (30 to 50%) and possibly up to 30% of the silver

55 must. Examples of glass sets, as used for the production of glasses according to Table II in _1/2 kg batches in a crucible which was kept at 1450 ° C. for 6 hours, are summarized in Table III:

Table III

sand

Alumina hydrate

Boric acid

borax

NaNO ₃

5 I! 28 30th 34 35 285 276 562 548 289 275 49 75 150 150 75 75 135 91 33 92 92 586 586 293 2 () () 42 40 23 24 12th 12th

37

275 75 33

200 12

continuation

5 11th 28 30th 34 35 13th 7th 7 · 3.5 4th 25th 25th 26th 26th 13th 13th 25th - .... - ■ - 0.08 0.08 0.08 - .._ - - 25th - - .._ - - 5 ■ - - 35 - .._ - - 70 70 25th 35 - 16 8th 8th - - - - 9 - - - - - - 30th

37

NaCl

Na ₂ SiF ,,

AgCl mixture ").

CuO

Na ₂ CO ₃

NaBr

AgNOj mixture ' ¹ )
AgNO ₃ mixture ')
CuO mixture '') ..

CaCo ₃

CaCO ₃

ZnO

4th
13th

35
8th

38.4

") AgCl mixture: 10 percent by weight AgCl, 90 percent by weight sand. *) AgNOj mixture: 10 percent by weight AgNO ₃ , 90 percent by weight sand.") AgN O ₃ mixture: 12 percent by weight AgNO ₃ , 88 percent by weight sand. Ό CuO- Mixture: 1 percent by weight CuO, 99 percent by weight sand.

To illustrate halide volatilization, some were compared with those described above Glass etching, melted glasses are chemically analyzed. The results are shown in Table IV.

Table IV

SiO ₂ .

32

60.7

9.5

19.5

10.0

0.33

0.0089

0.86

0.26

34

59.6 9.5

19.6

10.2 1.0 0.38 0.011 0.87 0.27

As can be seen from a comparison of the analysis values with the values calculated from the glassware, there are only significant deviations in the amounts of silver and halide.

The compositions shown in Table II illustrate a variety of ingredients and proportions form appropriate glass base materials for the silver halide crystallites. They also show that glasses that are chemically analyzed and expressed as free silver have 0.2 to 0.7 percent by weight Contain silver and a total of up to 0.4 percent by weight of the desired three halogens Glass that is essentially transparent, while larger amounts of silver up to 1.5 percent by weight due to an increased size and number of precipitated silver halide crystallites lead through translucent glasses.

That means glasses, which by melting a corresponding glass set, shapes the melt small pieces and about 1 hour of heat treatment at 450 to 550 ° C are obtained show a different permeability, as illustrated by the description of the appearance of the glass bodies produced.

The glasses have the desired photochromic properties either at the end of the above Molding process or after being brought to a temperature between the stress and the softening temperature of the glass were heated. For example, a glass body of the composition according to Example 10 is phototropic after molding, while a glass body of the composition according to Example 30 j after molding for a sufficiently long time a temperature between the stress and the softening temperature must be heated to the To enable the formation of silver chloride particles in the glass. This is preferably achieved in that the body is heated to a temperature of 575 ° C as quickly as possible without damaging it, keep it at this temperature for 4 hours and then cool it.

The desired property of the glasses according to the invention, to become under the action of ultraviolet Reversible discoloration of rays and thus changing the permeability of visible light is on Hand of the measured values for the permeability of the glass according to Example 10 illustrated. The permeability was measured before and after exposing the glass to the above-described ultraviolet rays for 2 minutes, and further for 10 minutes after irradiation. Figure 1, which plots permeability versus time, shows that in ten results obtained from such cycles of irradiation and non-irradiation.

Claims (7)

Patent claims: 1. Photochromic glass object, thereby characterized in that it consists of a silicate glass, which in at least one part at least 0.005 percent by volume of silver chloride, silver bromide and / or silver iodide crystals dispersed and the silver content of this part is at least 0.2 percent by weight. 2. Phototropic glass article according to claim 1, characterized in that the silver halide crystals present in an amount of 0.005 to 0.1 percent by volume, their diameter not exceeding is about 0.1 μ and the object is transparent. 3. Photochromic glass article according to claim 1 or 2, characterized in that the total amount of halogen is not more than 0.4 percent by weight and the total amount of silver is not more than 0.7 percent by weight.
- 4. Photochromic glass object according to claim 1 to 3, characterized in that the glass, determined analytically, 40 to 76 percent by weight SiO ₂ , 4 to 26 percent by weight Al ₂ O ₃ , 4 to 26 percent by weight B ₂ O ₃ and 2 to 8 as alkali metal oxides Weight percent Li ₂ O, 4 to 15 weight percent Na ₂ O, 6 to 20 weight percent K ₂ O, 8 to 25 weight percent Rb ₂ O and / or 10 to 30 weight percent Cs ₂ O, the total amount of these basic ingredients together with the silver and the halogen constitutes at least 85 percent by weight of the total glass composition. 5. Phototropic glass object according to claim 1 to 4, characterized in that the silver halide crystals contain at least traces of metallic silver. 6. Photochromic glass article according to claim 5, characterized in that the silver halide crystals containing part of the glass with the halogen unreacted, excess silver contains / 7. Photochromic glass object according to claim 5, characterized in that the part of the glass containing the silver halide crystals, calculated as SnO, 0.002 to 0.10 percent by weight tin oxide, calculated as FeO, 0.002 to 0.02 percent by weight iron oxide, calculated as CuO, 0 0.1 to 0.1 percent by weight of copper oxide, calculated as As ₂ O ₃ , 0.04 to 0.4 percent by weight of arsenic _{oxide and / or, calculated as Sb 2} O ₃ , 0.1 to 1.0 percent by weight of antimony oxide. 1 sheet of drawings