DE1596759C - Process for reducing the damage to glass surfaces during treatment in a molten alkali salt bath, in particular for the purpose of surface strengthening - Google Patents

Description

1 2

The invention relates to a method for degrading this material obviously not subject to any Settlement of damage to glass surfaces when reacting with the main salt component of the bath Treatment in a molten alkali salt bath, which remains effective for a long time. It will be in is characterized in that the bath 2 to 5 Ge of a molten salt is easily kept in suspension and weight percent diatomaceous earth can be added .. 5 can be added in amounts up to about 5 weight percent

Molten salt baths can be turned on in treating before viscosity becomes an issue. Glassware for various purposes, such as surface such quantities generally correspond to the pre-coloring, Heat treatment and chemical strengthening, ■ underlying purpose. "- -..

to be used. In the latter case, glass is replaced by diatomaceous earth - is a naturally occurring /

Ion exchange solidifies, and an alkali salt melt io finely divided material, which mainly consists of silica as a source, for ion exchange. The acid present exists, but usually up to a few at a time The invention is particularly focused on the solution which contains "percent alumina and soda. For the." Such chemical strengthening in practice can be the purpose of the material in its normal. targeted problems. paint dry form without further treatment

In a typical process of consolidation 15 are applied. An object made of a material can be mixed with a granulated salt by ion exchange before the salt is melted to form the alkali oxide-aluminum oxide-silica glass or, after the salt has melted, mainly from the nitrate of a larger alkali, is stirred into a molten bath are treated, metallions existing molten salt bath. The 'Usually, the amount of added Diato treatment with the bath for a period of up to 20 meenerde least 2 weight percent of the Schmelzzu 6 to 8 hours at a temperature of 350 to, bath to a sufficiently improved chemical Be-60O ⁰ C, Depending on the physical properties of the resistance of the treated glass surface to V) Glass, continued. , works. Larger additives up to about 5 weight J

Experience has shown that the surface percentages are required and can be required for some glasses

After such treatment, the glass object is used in other cases as a precaution can be severely damaged. In severe cases erupt. Additions of this magnitude remain norfährf dj.e surface dissolves or is chemically attacked for some time in a molten salt suspension, what is dated by an etched or matt one. However, stirring or mixing devices can be used Appearance shows. In other cases, the appearance will be used to ensure an even disper-.der Surface, not changed, but a yellowing occurs in the entire bathroom over a period of Reduction in chemical resistance, which can be guaranteed in a few days. Additions of more than in a typical acid resistance test by about 5 percent by weight tend to form a Film formation shows. In any case, such a salt bath mixture can be used for proper handling Surface damage the subsequent use of the glass in the bath is too viscous. Disturb the glass considerably. It is therefore the main addition of diatomaceous earth for chloride and sulphate purposes of the present invention, these undesirable baths that work at temperatures above 600 ° C, avoid circumstances. · May offer some advantages. However, "the

Investigations have shown that an alkali salt, the main advantages of using nitrate bath, in particular a nitrate, usually working at elevated temperatures at temperatures below 600 ⁰ C a slight decomposition to form the corresponding 40th A nitrate bath is usually used in the type of alkali oxide in the salt bath. In chemical solidification, relative to the assumption that the glass surface reacts with a large monovalent ion for smaller monovalent such alkaline material, a multi-ion would be exchanged . That kind of exchange! The number of acidic materials examined as additives must react below the glass transition range with such an alkali oxide and it must act so that the voltage thus induced is to be neutralized. ^l not by flow or rearrangement within the

The sulphates and chlorides of transition metals, glass is removed again. The invention is as follows Zinc and aluminum were, in some cases, quite half in the further especially with regard to glasses effective. However, such materials are hygroscopic, * and salt baths of the type described in a and it is difficult to use them in such chemical strengthening. Maintain molten salt in a dry state. The effectiveness of diatomaceous earth as a means of

• also tend to either volatilize or under-regulate attack on the glass surface by a chemical reaction with smoke formation, the kind of etching was carried out on test pipe pieces when they are added to the bath. As a result, its use with a diameter of 6.35 mm made of Li ₂ O — Na ₂ O— is undesirable and can also be used as healthy 55 Al ₃ O ₃ —SiO ₂ -GIaS. "Composition especially for a solidification

Various oxide materials such as sand, aluminum by exchanging sodium for lithium ions Umoxide, and boron oxide, were also determined as possible inside the glass. With this kind of Additives studied: However, when such materials are chemically strengthened, a shaped glass is generally difficult to keep in suspension and are subject to an electrically heated sodium nitrate bath for the main purpose, the surface vulnerability for a period of usually not more than Keeping glass to a minimum is surprisingly ineffective. immersed for four hours.

It has now been found that a naturally occurring bath was used for the present purpose of the experiment.

Mending material, diatomaceous earth, in the solution of fresh sodium nitrate with a 2 weight pro body Problem is surprisingly effective; H. the 65 percent addition of sodium oxide provided. It was the same corrosive attack and loss of chemical loading of the condition presumably in such a bath resistance to solidification or any other salt condition, in which a nitrate bath treatment during use reduced to a minimum. Decomposition takes place. That so deliberately polluted

Claims (3)

3 4 The bath was then ^{heated to 450 °} C., and a batch of glass test tubes was immersed in the bath for a period of four hours, particularly in the case of optical or ophthalmic ones. After removal from elements, limited so_can a lens from one of the baths, the test pieces had an apparently glass with excellent acid resistance, matted surface, which showed a medium-strong etching as demonstrated by the acid test described above. A further batch of pipe samples was then obtained, a film obtained when it was immersed in the bath after four hours, after the temperature had been increased to 550 ^° C. by means of an ion exchange process. When this "molten salt bath was examined. The addition of these substances was excluded ^ showed a more matted atomic earth to molten salt baths is also effective in appearance a heavier etching of the glass surface. Io in eliminating this adverse effect." Then a 2 percent by weight addition of the chemical resistance was made by ver-diatomaceous earth by showing a search for the amount of the material speaking on small glass plates into the molten pool of Na ₂ O — Al ₂ O ₃ —SiO ₂ Glasses were run, stirred in. The bath was maintained at 550 ⁰ C, and ■ were in particular for the production of solidified parts of pipe samples periodically in an optical 15 and flat glass elements were determined. Immersed for a period of 8 days. When hardening soda-containing glasses this one Samples taken out and cleaned _were saw art it is customary to dip the glass objects in a potassium man little or nothing of an etching or molten nitrate bath in order to exchange a surface attack on the glass. This showed that potassium versus sodium ions within the surface, the addition of diatomaceous earth, brought about the earlier surface layer of the object. The observed etching or the chemical reactions in the glass objects can be switched off for .16 hours if had. 450 ⁰ C for a low temperature treatment or As a comparison, small test baths of 5 hours at 525 ° C for a higher temperature sodium nitrate with a 2 weight percent additional treatment were immersed in the bath,
of sodium oxide for deliberate contamination 25 In an experiment, two potassium nitrate salt baths and a 2 percent by weight addition of powder baths were heated to a temperature of 525 ° C. A bath of prtem sand or powdered boron oxide for experimental purposes was provided with a 5 percent by weight addition of purposes . The baths were provided overall diatomaceous earth at 550 ⁰ C, while the other bathroom stop, and glass test tubes were stayed for four STUN without such an addition. Introduced a batch of trials. In each case, the pipe top plates were then heavily etched in surface for three quarters of an hour, indicating that the acidic oxide was immersed, removed and added to the alkaline etch control to clean a lot of each bath. The experimental panels were then 10 minutes less effective than diatomaceous earth. immersed in a 10% hydrochloric acid solution at 25 ° C. In a further comparative test comparison were There was at no game film formation observed examined baths of 30 g of sodium nitrate with a 35 A further batch of glass test pieces of content of 2 percent by weight Na ₂ O with diatomaceous was then for 5 hours at the same temperature, ie earth or a synthetic SiO ₂ preparation immersed in each salt bath at 525 ° C. These pieces of silicon chloride by vapor phase conversion were then taken out, cleaned and recovered, subjected to acid tests in amounts of 2 each. A film formation weight percent and 5 weight percent offset. In 4 ° was observed on the pieces that had been treated with the pure each test bath for 4 hours in a bath nitrate bath, while at the temperature of 550 ⁰ C a glass tube made of one piece, which in the diatomaceous earth containing bath Li ₂ O - Na ₂ O - Al ₂ O ₃ - SiO ₂ -GIaS dipped- Wäh- dipped, no film formation observed, which was observed in the test baths with the addition of diet. atomic earth treated according to the invention glass tubes 45 In order to further investigate the effectiveness of this material to only a very slight veil and thus almost no veil, three proportions of potassium nitrate salt from etching were shown, which were taken from a large industrially used bath in the test baths, with the addition of the synthetic SiO ₂ - Preparation treated. that had been in operation for several weeks. Each glass tube created a somewhat thicker veil and portion was large enough to make a small salt bath and thus a somewhat stronger etching. In addition, 5 ° had to be produced, into which glass test pieces, as above with the synthetic SiO ₂ preparation - apart from '' was written, could be immersed. A salt bath its cumbersome preparation - also difficult to work in without an additive, while a second one with a salt bath to handle. . 2 weight percent additive, and the third with one The chemical resistance of a glass surface with the addition of 5 percent by weight of diatomaceous earth is usually determined by an acid test, which was shown. A batch of Na ₃ O - Al ₂ O ₃ - SiO ₂ -in a glass test piece in a 10 ° / ₀ aqueous glass samples was Dannin each bath for 16 hours solution of HCl for 10 minutes at 25 ° C received at 450 ⁰ C Treated after such a treatment is immersed. The formation of a visible film or each lot was taken out, cleaned and subjected to cloudiness on the glass surface during the hydrochloric acid test described above. Immersion is a qualitative indication of inadequate film formation. Chemical resistance observed for many optical items in the bath without the addition of diatomaceous earth was considered. Likewise, the lack of such a film suffices, while the pieces in the formation to indicate a suitable chemical resistance to the two other salt bath samples no film formation of the surface. "was established. Experience has shown that even if a 65 _ Salt bath treatment, no visible etching or ■ advisory claims. gripping the glass surface, although a 1st method to reduce the damage Such loss of acid resistance can occur when treating glass surfaces in one I 596 7.59 .5. 6th Alkali salt bath, thus marked and 2 for the solidification of glass objects, because indicates that the bath 2 to 5 weight marked by. that a molten salt bath percent diatomaceous earth can be added. is used whose alkali ion is greater than that of 2. The method according to claim 1, characterized. Glass surface, and that the bath · at one draws that the diatomaceous earth is kept an alkali 5 temperature below that, ' nitrate bath is added. \ "". . in which the induced by the ion exchange . 3. Application of the method according to claim 1 "voltage is removed again.,