CZ124892A3 - crystal lead glass with a low extract of lead - Google Patents

Abstract

Lead crystal glass with a low lead extract, suitable for glass and mechanical manufacture of utility glass, especially of luxurious character, with higher refractive index contains 50-60 wt. per cent of silicon (IV) oxide, 24-27 wt. per cent of lead (II) oxide, 0.1-3.5 wt. per cent of aluminium oxide, 0.1-2 wt. per cent of boron oxide, 1.5-7 wt. per cent of calcium oxide, 6.5-11.5 wt. per cent of potassium oxide and 0.5-4.5 wt. per cent of sodium oxide, a content of iron (III) oxide is 0.01-0.02 wt. per cent, sum mole per cent of lead (II) oxide and alkaline oxide is less then 21. Its quality may be modificated at least by one oxide from a group, consisting of zinc oxide, barium oxide and magnesium oxide in amount of 0.1-7 wt. per cent. Next modifiers are individually or in combination - antimony (III) oxide and arsenic (III) oxide in amount of 0.1-0.7 wt. per cent.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to crystal lead glass, in particular intended for the manual and mechanical production of utility glass, with a refractive index greater than 1.545. The glass contains silica, lead, aluminum, boron, calcium, potassium and sodium.

Background

The classification of crystal utility glass according to ČSN 70 001 is as follows:

sodium-potassium crystal, where Σ of potassium and calcium oxide is> 10% by weight, refractive index of these glasses is not required, where sklo of potassium, barium and lead oxide is> 10% by weight, with a refractive index of about 1.51

- special crystal glass, where Σ of potassium, zinc, barium and lead oxide is> 10wt%, with a refractive index of 1,51 to 1,525

- lead crystal where the lead oxide content is> 24% by weight, with a refractive index> 1.545 highly lead crystal, where the lead oxide content is> 30% by weight. and the refractive index is > 1.545.

Crystal - & k - t - sodium - potassium - j - e - Czech - specialty.

The remaining t-types of crystal glasses conform to the EEC directives.

The first two above-mentioned crystal glasses are used for so-called cheap crystal glass products, where the low price is accentuated and the refractive index is around 1.51.

Barium and lead oxide are used only by some manufacturers and in smaller quantities, as reported by A. Smrček in Sklář a keramik 38 (1988), pp. 286-294. The group of special crystal glass already represents more noble products, in which the refractive index, which is to be around 1.52, is achieved, which is achieved by dosing barium, zinc oxide, or in smaller quantities also lead oxide, as stated in the patent, for example. Germany 1987 No. 2839645, according to which such glass contains by weight: silica 65 to 75, aluminum 0.1 to 2, calcium 2 to 12, magnesium 0 to 8, sodium 7 to 15, potassium 0 to 10 , lithium 0 to 3, barium 1 to 6, zinc 0.2 to 3, lead 0 to 10 and titanium 0.2 to 5. The present invention, by its chemical composition, besides the titanium dioxide content, covers most of the crystal glasses produced except lead and glass. high - lead crystal glass containing lead oxide>

% wt.

For luxury products decorated mostly with cut, lead and high-lead crystal is used, for which a refractive index of 2 1,545 is required. Presently, the hygienic safety of the glasses is preferred, especially in terms of lead and barium content in the leachate. Since these special crystal glasses achieve an increase in the refractive index to the required value mainly due to the increased content of barium and lead oxide, this hygienic requirement raises problems especially when using these lead glasses, especially in cups and all beverage sets where prolonged storage of beverages for leaching lead beyond the level currently under discussion.

SUMMARY OF THE INVENTION

These disadvantages will be avoided or substantially reduced by the reduced lead alkali oxide glass according to the present invention, which comprises 50 to 60 wt. % silica, 24 to 27 wt. % lead oxide, 0.1 to 3.5 wt. % alumina, 0.1 to 2 wt. boron oxide,

1.5 to 7 wt. % of calcium oxide, 6.5 to 11.5 wt. % potassium oxide, 0.5 to 4.5 wt. sodium oxide, the total iron content expressed as iron oxide being in the range 0.01 to 0.02. % by weight, with Σ mol. % of lead oxide and alkali oxides is less than 21%.

Preferably, the crystal lead glass further comprises, individually or in combination, 0.1 to 7 wt. zinc, barium and magnesium oxide.

It is preferred that the crystal lead glass further comprises, individually or in combination, 0.1 to 0.7 wt. antimony trioxide and arsenic trioxide.

The advantage of this optimum glass composition is the considerably reduced lead leachability even in acidic solutions, with unchanged grindability, engraving and polishing of the products. Since this glass is largely used to produce utility products, such as beverage kits and household glass, virtually no unwanted lead oxide is transferred to the beverages, due to the reinforcement of the grid of this type of glass.

The optimum content of zinc, barium and magnesium oxide favorably affects the crystallization properties and viscosity of the glass.

The addition of antimony trioxide and arsenic oxide facilitates enamel fining.

Conventional means and technological processes are used to clarify and decolourize these glasses.

DETAILED DESCRIPTION OF THE INVENTION

The invention is illustrated by the following examples.

Example # Glass components 1 content v % by weight 3 silica 56.89 57.29 57.09 lead oxide 24.2 24.2 24.2 zinc oxide 0.0 1,25 0.5 calcium oxide 5.0 5.0 4,5 magnesium oxide 0.0 0.0 0.5 barium oxide 0.0 0.25 0.0 boron trioxide 0.9 0.5 0.5 potassium oxide 9.3 7.8 8.8 sodium oxide 2,0 2,0 2,0 aluminum oxide 1.5 1.5 1.5 antimony trioxide 0.0 0.0 0.4 arsenic trioxide 0.2 0.2 0.0 iron content expressed iron oxide content 0.01 0.01 0.01

Σ oxides 100.00 100.00 100.00 t · -: ·· / [° C]

1496

1522

1544

^t iogETA = 3 [° C] 1216 1244 1250 ^t lc _? ETA = 13 [° C] 527 552 530 ^ liquidus [° C] 856 1025 989 refractive index at 589.3 nm 1,563 1,564 1.563 abrasion [wt. min ' ¹ ] 0.375 0.380 0.381

hydrol. resistance

[ml 0.01 mol. HCl] 0.12 0.10 0.11 leachate Pb [mg / 1] solution of 4% acetic acid. 0,033 0,029 0,032

In the above embodiments corresponds to _t: approximately the melting temperature of glass processing temperature of glass = 13 ^ 1οσΕΤΑ upper cooling temperature. The abrasion is expressed by the loss of glass sample in pm.min ^-1 on a 120 µm diamond disk at a load of 1.71 g.mm -1.

Lead leach in 4% acetic acid after 24 hours for conventional lead glasses with 24% lead oxide by weight ranges from 0.25 to 0.40 mg / ^l . In the glasses according to the invention, the lead leachate values are about one order of magnitude lower, while the melting and processing temperatures are comparable.

All liquidus temperatures are lower than the respective processing temperatures corresponding to the glass viscosity temperature log ETA = 3, so that the tendency to undesired crystallization is suppressed in these glass melts.

For lead crystal, the refractive index is about 1.545, for the glasses according to the invention it is substantially higher, for example, 1,563, which has a very favorable effect on the optical properties of said glasses, especially in products decorated with grinding and engraving.

Mean coefficient of linear thermal expansion of glass and in the range 20 to 300 ^c C is comparable to the values of most of the manufactured lead glass having 24% lead hmot.oxidu.

The abrasion for lead crystal is 0.350 pm.min 'according to the chosen method and is higher in the exemplary embodiments 1 to 3, which will have a positive effect on the processing speed of these glasses by grinding and engraving.

Conventional arsenic trioxide and / or antimony trioxide based oxidizing fines in combination with potassium or sodium nitrate can be used to clarify said types of enamel.

Conventional colorants added to the batch may be used to decolorize these glasses, for example, nickel oxide, cobalt oxide, selenium compounds, rare earth oxides, manganese compounds, and combinations thereof.

Industrial applicability

The lead crystal glass according to the invention is intended for both manual and machine production of utility glass with a higher refractive index. It is particularly suitable for decorating with grinding, engraving and other decoration techniques for luxury products. This glass is hygienically harmless with respect to the content of pollutants in the leachate and by its brilliance it outperforms products made up to now, unpaved lead crystal.

This type of glass is intended for the production of glass items used in households and in the hospitality industry, eg cups, castings, decanters, bowls, as well as containers of various shapes and sizes used to decorate eg vases, bowls, etc.

Claims (3)

1. Low lead leachate crystal glass suitable, in particular, for the manual and mechanical production of utility glass having a refractive index exceeding 1,545, containing silica, lead, aluminum, boron, calcium, potassium and sodium, characterized in that it contains 50 to 50 60 wt. % silica, 24 to 27 wt. % lead oxide, 0.1 to 3.5 wt. % alumina, 0.1 to 2 wt. % boron oxide, 1.5 to 7 wt. calcium oxide, 6.5 to 11.5 wt. % of potassium oxide and 0.5 to 4.5 wt. sodium oxide, the content of ferric oxide being in the range 0,01 to 0,02% by weight, with Σ mol% of lead oxide and alkali oxides being less than 21%. 2. Low lead lead crystal glass according to »Dro4u 1, characterized in that it contains, individually or in combination, 0.1 to 7 wt. of zinc, barium and magnesium oxide. 3. Lead-free crystal lead glass with low lead leachate 1 to 2, characterized in that it contains, individually or in combination, 0.1 to 0.7 wt. antimony trioxide and arsenic trioxide.