CS217958B2 - Colourless transparent glass crystaline substance - Google Patents

Description

FIELD OF THE INVENTION The present invention relates to a colorless transparent vitreous crystalline mass comprising as base crystalline phase beta-modification of quartz and having a basic composition consisting of lithium oxide-alumina-silicon dioxide, further comprising 0.5-6% by weight of silica and optionally up to 500 ppm of iron oxide calculated in the starting strain. The substance according to the invention is characterized in that it additionally contains neodymium oxide in an amount of 0.08 to 0.75% by weight.

The invention relates to a colorless transparent glassy crystalline mass.

It is known that a number of glass compositions can provide a transparent glassy crystalline mass after proper heat treatment. Some such mixtures are described, for example, in the description of the invention in French Patent Nos. 1,221,174 and 1,562,377. These transparent vitreous crystalline masses consist of a mass which retains its vitreous character and which surrounds very small crystals. Depending on the composition of the glass and the heat treatment, these crystals may be mixed with a structure of beta-quartz (or mixed crystals of eucriptide beta, spodumene, zinc spinel, celsian, titanium aluminate, rutile and others).

Certain amounts of titanium dioxide often exist in these translucent glass crystalline masses; this plays an important role in the formation of the crystalline nuclei required to obtain the desired crystalline structures. Titanium dioxide causes difficulties because it causes the amber coloring of the glassy crystalline masses surrounding it, which may adversely affect some applications. For example, in the production of utensils such as pots or kettles, the amber coloration of the material may adversely affect the perception of the color of the food and beverage contained in the container. Such cookware is then difficult to sell as its coloration is further aggravated by the fact that manufacturers tend to use lower quality feedstocks, also containing iron oxides, which, in combination with the titanium dioxide present, tend to produce as much profit as possible. they lead to an increase in the undesirable spring color.

In order to eliminate the amber color of transparent glassy crystalline masses, masses have been proposed in which titanium dioxide has been replaced by another oxide. These include, for example, the glassy crystalline compositions described in the specification. However, even this replacement of titanium dioxide with another oxide, such as zirconium oxide, is not a satisfactory solution, as this leads to a deterioration of the meltability, formability, recrystallization time, thermal dilatation. and diffusion of the light of the mixture produced. Consequently, it would be expedient to use titanium dioxide in the crystalline crystalline masses and to neutralize its color in some way.

It is known in glass technology that the unwanted coloring of the glass resulting from the impurities present can be neutralized by the addition of a colorant which produces a complementary color in the glass.

For example, the yellowish color produced by lead oxide in the lead crystal, contained as an impurity in the glass batch, is neutralized by the addition of the appropriate amounts of nickel oxides and cobalt. As a result, although higher absorption of light by the glass mass occurs, this deterioration of the patriotic glass mass is, on the other hand, counterbalanced by obtaining an almost colorless glass mass.

French Patent No. 1,474,726 describes transparent and non-transparent colored glassy crystalline masses; it is clear from the contents of this patent that the oxides that are used in the manufacture of colored glass for its coloration provide completely unexpected colors when used in glassy crystalline compositions. That is, the oxide known to give a certain coloring to the glass does not necessarily provide that coloring also when the glassy crystalline masses are colored.

This has been verified for transparent glassy crystalline masses consisting of beta-quartz mixed crystals having the following weight composition: silica 60 to 70% alumina 15 to 2 | 5% lithium oxide 3 to 4% titanium dioxide 2 to 6% and whose raw materials contain 500 ppm of iron oxide. Glass prior to recrystallization may lose color by adding one of the following three substances at the following weight concentrations:

Ϊ. by adding 0.0025 to 0.005% of cobalt oxide ·

2. by adding 0.25 to 0.50% of zinc selenite

3. by adding 0,0025% of cobalt oxide and 0,010% of cuprous oxide.

The first and third admixtures provide, after recrystallization, different shades of purple red, which may pass to auburn red, while the second admixture practically does not mask the amber color typically found in titanium dioxide glasses.

None of the prior art treatments of cobalt, chromium, copper, manganese, nickel and vanadium provide, after recrystallization, a coloration capable of masking the amber coloration caused by the presence of titanium dioxide and iron oxide.

Thus, it is desirable to develop a process which makes it possible to neutralize the coloration which the glassy crystalline masses impart to titanium dioxide and iron oxide.

The above-mentioned drawbacks have no colorless transparent vitreous crystalline mass, comprising as the crystalline base phase a beta-modification of quartz and having a basic composition consisting of a lithium oxide-alumina-silica system, further comprising 0.5 to 6% by weight of titanium dioxide. And optionally up to 500 ppm of ferric oxide, calculated in the starting strain, which additionally comprises 0.03 to 0.75% by weight of non-hydrous oxide.

The colorless transparent glassy crystalline mass according to the invention preferably contains 3 to 4 wt. lithium oxide, 15 to 25% by weight of alumina and 60 to 70% by weight of silica, calculated on the starting strain.

The exact amount of neodymium oxide to be added varies within the above limits according to the reduction in the glassy crystalline mass and, in particular, the titanium dioxide and iron oxide contents. In this case, it is necessary to carry out tests with varying amounts of added neodymium oxide for each mixture separately, for example as described in the rest of the description. Too small amounts of neodymium oxide lead to a yellow color in the glassy crystalline masses, while too much amount of this oxide leads to blue-violet colored glassy crystalline masses.

An advantage of the process according to the invention is that it effectively achieves the elimination of the amber coloration of the glassy crystalline masses caused by the presence of titanium dioxide and optionally iron oxide.

The invention is further elucidated by the following figures and specific examples, all of which in the examples represent weight concentration.

Fig. 1 is a graph depicting the light transmittance (%) curves of the base glass wavelength for admixture of glassy crystalline matter (curve 1j, with cobalt oxide (curve 2) and neodymium oxide (curve 3); base thickness); the glass was 4 mm.

Giant. 2 shows a similar graph as in FIG. 1, but after recrystallization of the base glass.

Example 1

A. Glass having the following composition by weight was used:

silicon dioxide 6 · 0% aluminum oxide 24 ·% lithium oxide 3.5% titanium dioxide 6% iron oxide 0.0% phosphorus pentoxide 4 ° / o.

The glass was melted at 1603 ° C for 24 hours in a 1 liter quartz crucible (the quartz crucible was used to avoid affecting the coloration that the rhodioplatin crucible could possibly cause). The color of this glass is characterized by the light transmittance curve No. 1 in Figure 1; it can be described as very pale yellow. A sample of this glass was converted to a transparent glassy crystalline mass containing a significant amount (up to 90%) of mixed quartz-type crystals by heat treatment at 870 ° C for 2 hours. in Figure 2, this color can be referred to as amber.

B. Base glass of the same composition was melted with an addition of 0.004% cobalt oxide. The colors before and after crystallization are characterized by curves No. 2 in Figures 1 and 2. The sample appears to be colorless before recrystallization and purple after recrystallization. Comparison of Fig. 1 from Fig. 1 and Fig. 2 shows that saline color modification occurred during recrystallization. Although the light transmittance around 0.65 micron is maintained, it decreases by about 10% around the 0.50 micron wavelength, which explains the color development.

C. The base glass of the same composition was melted with an admixture of 0.3% neodymium oxide. The colors before and after recrystallization are characterized by curves No. 3 in Fig. 1 and Fig. 2. The eye appears colorless before and after recrystallization. Comparison of curves No. 3 in Fig. 1 and Fig. 2 shows that in recrystallization, in contrast to the previous case, there was little modification of the absorption band of neodymium oxide. This glassy crystalline mass has a coefficient of expansion less than 15.10 ~ 7 to ^-1 .

The nature of the phenomenon used in the present invention to decolorize a glassy crystalline mass containing titanium dioxide has not been sufficiently elucidated. Without limiting the invention to any theory, two hypotheses are proposed.

The first hypothesis attributes the stability of the light absorption of rare earth oxides to the stability of their moceinities and their coordination number in the glass, unlike other color-producing oxides, which ‘easily change their valence and coordination number depending on ambient conditions.

The second hypothesis attributes the stability of light absorption of rare earth oxides to the ionic radii of metal ions. Indeed, other metals used in the past for coloring or clearing glasses have ionic radii of less than 0.9. ^_1 1O ° m, which theoretically allows them to substitute in mixed crystals of type quartz · lithium; it can be accepted that this association with this crystal modifies their electron structure and thus their absorption. In contrast, the ion radius of neodymium is 1.04. . 10 ~ ю m, which forces him to remain in a glassy state where he retains the same characteristics as in glasses.

Example 2

This example illustrates how to experimentally determine the amount of neodymium oxide to be added in a glassy crystalline mass mixture to obtain a colorless glassy crystalline mass.

The procedure is similar to Example 1; In the case of a series of glassy crystalline compositions of the glass compositions A, B, C and D shown in Table 1 containing different amounts of iron oxide and neodymium oxide, the same table shows the colors before and after recrystallization.

As can be seen from the attached table, the vitreous crystalline masses may be present in the base glass. 3% titanium dioxide, 'discolored by adding 0.20% neodymium oxide if it contains 140 ppm of ferric oxide (Test No 3) and by adding 0.35% neodymium oxide if it contains 380 ppm of ferric oxide' (as can be deduced) by interpolation between test # 8 and # 9).

Glassy crystalline compositions having a base glass composition B of 1.8% titanium dioxide may be discolored by adding 0.15% neodymium oxide if they contain 100 ppm of iron oxide (Test No. 14) and by adding 0.25% neodymium oxide if they contain 350 ppm of iron oxide (Test No 19). Glassy crystalline masses having the composition of the basic glass C-a. 6% titanium dioxide and having a relatively high phosphorus pentoxide content can be decolorized by adding -as 0.40% neodymium oxide if they contain 160 ppm iron oxide (as can be deduced by interpolation between Test Nos. 22 and 23).

Glass masses having a base glass composition D with 4% titanium dioxide and containing relatively much phosphorus pentoxide may be discolored by addition. · 0.25% neodymium oxide, if they contain 16Ό ppm of iron oxide (Test No 25), and the addition of 0.32% neo · dsmlttho, if they contain 440 ppm of iron oxide (as can be deduced by interpolation between experiments No. 27 and No. 28).

As can be seen from the results, the amount of neodymium oxide to be added to the base glass mixture to obtain a colorless transparent glassy crystalline mass, containing titanium dioxide (present as an impurity in the glassy crystalline raw materials) and composition of the glass glassy crystalline mass. Thus, it is practically impossible to predict the amount of neodymium oxide to be added to the glassy crystalline mass in order to obtain a colorless form of the glassy crystalline mass. In general, therefore, it is necessary to prepare a series of mixtures with increasing amounts of neodymium oxide in order to determine the appropriate amount of neodymium oxide required for the desired decolorization.

The discolouring effect can also be achieved with glassy crystalline compositions of a different composition from that described in the examples; therefore, the invention is not limited to a given composition. The invention is generally applicable to all mixtures of transparent glassy crystalline compositions which contain titanium dioxide or other dyes such as iron oxide.

Base glass composition (%) Content Exam number Color FezO3 (ppm) Nd2O3 (%) before recrystallization after recrystallization AND: SiOz 6 <9.4 1410 0 1 yellow yellow AI2O3 18.7 140 0.1 2 pale yellow yellow Li2O3 3.5 140 0.2 3 colorless colorless MgO 1,8 140 0.3 4 pale violet pale violet to Pinky faintly pinkish BaO -. 140 1 5 pale violet bledefialcvá ZnO 0.8 380 0 6 yellow dark yellow T1O2 3 380 0.2 7 yellow yellow ZrO2 2 380 0.3 8 very pale yellow very pale yellow P2O3 - 380 0.4 9 whitish to very colorless to very pale pink • Copper pink As? O3 B: SiO2 0.8 380 1 10 pale purple pale purple 62 100 ALIGN! 0 11 light yellow yellow AI2O3 21.3 100 ALIGN! 0 05 12 Bright yellow yellow LižO 2.7 100 ALIGN! 0.1 13 very bright yellow very bright yellow MgO 1 100 ALIGN! 0.15 14 colorless colorless BaO 1.3 100 ALIGN! 0.30 15 Dec pale purple pale purple CaO 0.5 ZnO 6 350 0 16 yellow fairly dark yellow T1O2 1,8 350 0.1 17 Bright yellow yellow ZrO2 2 350 0.2 18 very bright yellow Bright yellow P2O5 0.7 350 0.25 19 Dec colorless colorless AS2O3 0.7 350 0.40 20 May pale purple pale purple

Basic composition Contents Test Glass color (° / o] ГегОз εο ^ε ΡΝ number before recrystallization after recrystallization (ppm) (%)

Claims (2)

CLAIMS 1. A colorless transparent vitreous crystalline mass comprising a quartz beta modification as a basic crystalline phase and having a basic composition consisting of 1'-lithium-alumina-silica-system, the composition further comprising 0.5 to 6% by weight. % of silicon dioxide and optionally up to 500 ppm of iron oxide calculated in the starting strain, characterized in that it additionally contains neodymium oxide in an amount of 0.03 to 0.75% by weight. 2. A colorless transparent vitreous crystalline mass according to claim 1, characterized in that it contains 3 to 4% by weight, lithium oxide, 15 to 25% by weight, alumina and 60 to 70% by weight, silica.