NO138594B - PHOTOTROPT GLASS IN SYSTEM P2O5 - SIO2 -AL2O3 - R2O - RO - Google Patents

Description

Various phototropic glasses are previously known. Like-

then phosphate glass with different composition as well as photo-

Trope glass has been known for a long time. Thus, Sakka and MacKenzie [US 3,615,761 or J. Am. Ceram. Soc. 55 (1972), 553]

including silver and halogen-containing phosphate glass with phototropic properties. A description of phototropic phosphate glass with regard to the breadth of composition options is available in DOS 2,234,283

and DOS 2,260,879. In these cases, the silver halide crystal leads

clay that is dispersed in the glass for phototropism. They thus differ, for example, from glass on a silicate and borate basis, which likewise contain silver halide crystals as carriers for the phototropy, as described in, for example, DT 1,421,838 or DT 1,596,847, only with regard to the base glass composition.

Glass of one or more oxides is made up of networks

of main components. The main components are like coordination polyhedra, connected via the vertices, bound to the network. These structural units (main components) are formed, for example, in silicate glass of SiO^-tetrahedra, similar structural units exist in borate and phosphate glass. These structural units are among themselves

different strongly bound in different glasses. The stronger the central cations

in these structural units, ambient oxygen polarizes, however min-

dre is the tensile strength of adjacent structural units (e.g. of the adjacent tetrahedron). The polarization of oxygen through the central cations appears from Dietzel [Z. Electrochem. 4_8

(1942) 9] in the following way:

The greater the field strength of the central cation of such a structural unit, the more strongly the surrounding oxygen shell is now polarized and the smaller the binding force of this structural unit (consisting of the central cation and surrounding oxygen shells) outwards to the adjacent structural units.

As a result, the bond strength between the main components decreases, i.e. the entire glass structure becomes porous if one switches from silicate to borate or even to phosphate glass.

German patent document 1,596,847 describes phototropic glasses whose phototropic properties are determined by sblv halide crystals and possibly small amounts of metallic sblv, which are characterized by the fact that they consist of one or more glass-forming oxides as main components, the bonds between them in the glass are weaker than the bonds in a silicate base glass with SiCX as the glass-forming component.

In particular, DT 1,596,847 describes borate glass which, compared to the known silicate glasses, shows better phototropic properties due to the weaker binding of the main components between them.

From the above generally available explanation, it appears that phosphate glass must also be equally suitable to provide phototropic glass with advantageous properties within the optical identity change under the influence of a stimulating light current.

If, according to what is stated in DT-PS 1,596,847, the main component B2C>3 is replaced with P2G5, the bond between the main components becomes weaker in the glass then formed. From the examples in the specified patent, the following compositions appear which do indeed have phototropic properties, but whose phototropism is of low quality.

As already described in DT-PS 1,596,847, the use of SiCX can contribute to stabilization in small quantities. Thereby, the structure of the glass becomes firmer again. According to DT-PS 1,596,847, it is thus possible, taking into account the above explanation, to provide glass of the kind listed, for example, in Table 3.

Examples 7 to 11 thereby show that also a certain amount

& 2°3 can be invited in such phototropic phosphate glasses.

Phosphate glass is generally known for its particularly poor chemical resistance. This can of course be improved with a high content of A120^, but this in turn entails a weakening of the already poor crystallization strength.

A glass that should. used as spectacle lenses must meet certain requirements with regard to profitability during production, i.e. yield in normal manufacturing aggregates must be combined with sufficient yield and as few recyclings as possible.

Above all, glass can be processed on the glass manufacturing equipment commonly used today, which guarantees a production rate of more than 60 kg/h. For this purpose, it is necessary that this glass at a viscosity between 10^ and 10<4>'^ poise is portioned through shears and then pressed. At this relatively high viscosity for liquid glass, however, many non-silicate glasses already crystallize at such a high crystallization rate that a smooth production becomes impossible. To remedy this disadvantage, one can go back to a viscosity reduction and special production (while the portioning through shearing is no longer possible at low viscosities) or take into account a reduction in yield, by sometimes interrupting production and removing the formed crystal disturbances during production -tion progress in case of short-term temperature restrictions.

All glasses ifblce DT-OS 2,234,283 were post-melted taking this into account and were tested with regard to their crystal lysis ionic properties. After 60 melts had been made, it turned out that these compositions do not meet the qualification for technical production.

As a qualification for the applicability of any glass as a spectacle lens, the following generally recognized specifications apply: 1) the refractive index n^ between 1.5225 and 1.5235

b) no crystallization between 10^ and 10<4>'^ poisé

c) sufficient chemical resistance (characterized by the hydrolytic resistance according to DIN 12,111 and the weld test resistance) d) sufficient chemical hardenability in standard baths for normal spectacle crown lenses (this requirement is normally made when the holding strength bending is..."

legally prescribed for all spectacle lenses).

The object of the present invention is an improved

phototropic spectacle glass which consists of one or more glass-forming oxides as main components, the bond between them in the glass is weaker than the bond in a silicate base glass with SiO2 as the main glass-forming component and likewise weaker than in a borate base glass;: with B,0 as the main glass-forming component. . -

A further object of the invention is. an improved phototropic lens having a refractive index nd between 1.5225 and -1.5235.

A further object of the invention is an improved photo-troped spectacle lens which, in the viscosity range between 10 and 10 poise, shows no or as little crystallization as possible. chemical resistance sufficient for use as a scope glass and exhibiting a linear coefficient of thermal expansion...; between 20 and 300°C on ICI to 104 x 10"?/°C. -

Another object of the invention is an improved phototrope.

glasses whose holding strength can be improved by ion exchange below the transformation temperature in a medium containing potassium ions, whereby smaller alkali ions diffuse out of the glass.

This goal is achieved according to the invention by replacing B2°3 in the phototropic glass according to DT-PS 1,596,847 with P2°5 and that the phototropic properties in glass according to the invention are induced by the formation of sblv- and halogen-rich, non-crystalline precipitation phases in this glass:.

According to the invention, the content of <p>2^5 is between 30.4

and 33.9% by weight.

Furthermore, according to the invention, the proportion of A1„0_ is increased from 14% by weight to approx. 23% by weight, whereby the optimum range is between 22.5 and 25.7% by weight.

The known phototropic, sblv and halogen-containing glasses only show good phototropy if they contain B,,03. B^O^-free phototropic glass of the conventional type, on the other hand, exhibits no or only deficient phototropy. In Table 4, upfort glasses with and without ^ 2^ 3 saint their phototropic properties. To improve clarity, this table is given in parts by weight.

Table 4 shows that exclusion of the component ^ 2°3 reduces the phototropy. Efforts have therefore been made to incorporate a minimum amount of B,,03 into the glass, so that the separation of the solvohalide crystals (microcrystals of the type described in DT-PS 1,421,838 or DT-PS 1,596,847) proceeds favorably and is not disturbed by other phase separations.

It has now been shown, quite surprisingly, that glass with phototropic properties can also be obtained in the complete absence of B2O3

which are at least equivalent to those for glasses in which the phototropy is formed by solid halide crystals (DT-PS 1,421,838, DT-PS 1,596,847 and DT-OS 2,234,283). The glass according to the invention can even exhibit phototropy which is superior to the phototropy of the known glasses with regard to blackening depth and regeneration speed.

It has turned out to be even more surprising that the phototropy of the glass according to the invention is not transmitted by solvide crystals but by solvide-rich, non-crystalline precipitation phases.

In order to achieve particularly suitable separation conditions for the non-crystalline silver- and halogen-rich separation phases, an upper limit of P2O5 ^4% by weight must be maintained.

To avoid crystallization of the silver- and halogen-rich precipitation phases, the haloenides must also be subjected to a special selection. Fluorine should not be used as a halpgenide, it already seems in small concentrations to promote the crystallization of the excretory phases.

It has also been shown that for a profitable production it is necessary to have a relatively high viscosity for phosphate glass in the range between 10 1 and 10 5 poise, but that at a content of SiO2 between 12.1 and 13.9% by weight it is also necessary to keep the content of MgO as low as possible, preferably at 0% by weight, whereby the crystallization of the base glass is significantly affected

(this base glass crystallization must be kept separate from crystallization of the silver halide crystals or the silver halide-rich, non-crystalline secretions as carriers of the phototropy).

The crystallization ratio is further affected by other components. Thus, it has been shown that the concentration of Ti02 ^k'ce b<zSr exceeds • 0.6% by weight, and that, on the other hand, Zr02 should be present at least in a concentration above 1% by weight, even if beg-. ge components are known as fine formers for inducing crystallization. For optical reasons, the upper limit for Zr02 is 2.6% by weight, as otherwise the refractive value of the glass would exceed the set values of 1.5225 to 1.5235. The same applies to an upper limit for La^O^ at 2.0% by weight. Both components exhibit a further importance for the formation of a sufficient chemical resistance of glass. In addition, ZrO2 should be included in glass in a minimum amount of 1.0% by weight, and I^O^ in a minimum amount of 0.05% by weight, as these components likewise have an influence on the secretion of the non-crystalline silver halide-rich excretion phases.

The content of alkali oxides and alkaline earth oxides not only affects the precipitation kinetics in the non-crystalline silver halide-rich precipitation phases, but also the other glass properties. It has been shown that the sum of the alkali oxides should preferably lie between 6.2 and 14.2% by weight, which is particularly important for the possibility of increasing the holding strength of the glass chemically by ion exchange below 10 14 '5poise in a medium containing potassium ions, f .ex. in a KON^ melt, whereby smaller alkali ions diffuse out from the glass. It has thereby been shown that, contrary to expectations, Li20 should be included in the lowest possible concentration, preferably not at all in the output glass for ion exchange, even though Li20 in the hitherto known phototropic glasses plays an important role for crystallization of the silver halide crystals.

In addition to the phase separation process, alkaline earth and alkali oxides also strongly influence the linear thermal expansion coefficient. It has been shown that a content of at least 8% by weight, but at most 11.8% by weight, is particularly advantageous.

BaO and CaO can be used with good results, CaO however not exceeding 5.0% by weight, as the secretion of the silver halogen-rich, non-crystalline secretions is otherwise disturbed. Small amounts of SrO have a stabilizing effect. Lead oxide (PbO) is particularly advantageous at a content of between 0.4 and 2.5% by weight and can be used for correction of the refractive value like TiO2"

The content of Ag20 and halogens in the mixture calculated according to the synthesis depends on the melting method and the other mixture composition. In the glass, it is desirable to have approx. 0.1 - 0.5 wt% Ag2O and 0.2 - 1.0 wt% halogens. (The indication for A<?2° and halogens is calculated from the analytically determined content of silver and halogen ions in which they are present in the glass. A proportion of metallic silver is unlikely, but possible. The silver ions and halogen ions do not have to be present in stoichiometric relative to each other, as other components are also included in the non-crystalline, silver halogen-rich secretions).

The most advantageous content of silver oxide and halogens in the entire synthesis, taking into account evaporation loss during melting, is between 0.05 and 1.0% by weight Ag20, and for the halogens, chlorine and bromine together between 0.15 and 6% by weight. The distribution of bromine and chlorine can thereby be varied. Copper oxide (CuO) can be added for sensitization in amounts between 0 <p>g 0.1% by weight.

The invention thus relates to a phototropic glass in the system P20^ - Si02 - Al203 - R20 - RO, which is characterized by the fact that, in order to prevent the formation of crystallization of the glass mass and to achieve non-crystalline, silver- and halogen-containing secretions, it consists of the following composition in % by weight:

The composition examples given in the subsequent table 5 show, including falling compositions, the limits of the invention. The properties indicated in Tables 6 and 7 show how severely limited the composition range according to the invention is.

It should be noted that example 54 is the only example within the scope of the invention, while all the other examples are comparative examples, which serve to show how narrow and critical the composition according to the invention is.

The phototropic properties of the following base glass composition according to the invention were examined:

Different amounts of silver and halogen components were added to this base glass in different melts, introduced as silver nitrate and coke salt respectively potassium bromide, and sometimes the sensitizing amount of CuO was also introduced as oxide varied. After blending, the components were introduced together into a crucible at 1435°C and were there melted and purified. The melt was then cooled to 1200°C, poured into s 1 needle molds and cooled at 22°C/hour to room temperature. Samples of each glass with dimensions 40 x 40 x 5 mm were then prepared, and these samples were heated at 50°C/10 min to 615°C, and held at this temperature for 115 minutes and then cooled at 190°C/hour to 300°C. The continued cooling to room temperature took place at 50°C/hour. On these samples, the relative content of Ag, Cl and Br was determined by X-ray fluorescence analysis, furthermore, the refractive value, the phototropy and the degree of crystallization of the secretions were measured, which constitute the carriers of the phototropy, as well as their size. Table 8 shows the results. An addition of only 0.10% by weight F, for example, already resulted in crystallization of the carriers of the phototropy.

The refractive index n^ was determined with the commercially available Abbe refractometer. The viscosity was measured depending on the temperature with a rotary viscometer. The chemical resistance is characterized by the titrometrically determined values for the release of alkali according to DIN 12 111. Ion exchange was assessed by producing a thinly ground sample of ion-exchanged glass, whereby the grinding is arranged perpendicular to the glass surface. The thickness of the ion exchange layer and the compressive stress prevailing therein were determined by voltage optical measurements with polarized light. The crystallization resistance of a glass was carried out by a 60-minute tempering in a temperature gradient furnace. Thereby, the glass is protected against surface evaporation. Microscopically, after tempering, the upper glass transition limit (=Liquidus temperature), the lower devitrification limit, the crystallisation maximum (KG max ) and the growth rate of the 3 required crystals are then determined. The thermal expansion and transformation temperature were determined dilatometrically.

The darkening ratio and regeneration in phototropic glass are measured as monochromatic transmission saturation at 545 nm as a function of time. The stimulation takes place with unfiltered xenon light with an intensity of 2 cal cm -2 c min -1. Unless otherwise stated, the temperature during the measurement is 20°C, and the thickness of the measured glass is 2 mm.

The electromicroscopic examinations are carried out on samples that have been made thin with the ion beam etching method. Compared to other methods, this method has the particular advantage that the preparation does not come into contact with liquids or solutions during the thinning process or, in connection with this, and that thus there is no contamination of the preparation during the flotation and circulation, because the preparation is already fixed during the thinning process on the electron microscope's object holder and enclosed with this without further post-processing in the electron microscope. By avoiding liquids and solutions, hydration of the preparation is also avoided. Thus, the structures visible in or on the preparation through radiation can be unambiguously attributed to the preparation itself. If, in contrast, methods are used in which the preparation comes into contact with liquids, crystalline reaction products are often obtained which can be fed back into reactions between the glass surface and the liquid. From the preparations diluted with ib, the presence and distribution of substances with different mass absorption can be deduced by irradiation with electrons of contrast. From the electron diffraction and fine-range electron diffraction recordings, one can also obtain references to the crystal structure in the matrix and leaching areas of the examined phototropic glasses.

More recent studies with regard to the chemical hardenability occurred, for example, on compositions 22, 25 and composition 54 according to the invention. The following Table 9 shows the results with regard to the duration of the ion exchange and the temperature used thereby. This thing happened in a KN03 salt melt bath.

Claims (1)

Phototropic glass in the system P2°5 -S-;-io A-*"203 - R2° ~R<-)' characterized in that to prevent formation of crystallization of the glass mass within the viscosity range lO^-lO^ pois and to obtain non-crystalline silver and halogen-containing precipitates consist of the following composition in % by weight: