SU1057864A1 - Glass surface quality evaluation method - Google Patents

Abstract

1. METHOD FOR ESTIMATING THE QUALITY OF THE GLASS SURFACE By processing samples in a molten salt of lithium or a mixture of it with melts of other salts, postgraduate hydrofluoric acid, and determining the number of microcracks per unit of area, p l and h and y and , in order to increase accuracy and reliability, before processing the samples in the molten salt in the marginal zone of the samples not less than 10 mm wide, compressive stresses of more than 150 MPa are applied to the treatment in the molten alkali salt, metal, whose radius is larger than the alkali radius glass ion, at a temperature 50–200 ° C below the softening temperature of the glass for the time required to exchange ions to a depth of at least 5 µm. 2. The method according to claim 1, for those who for industrial. Sheet glass, a compressive zone for S 9 strands is created in the interval 400500 0 for 0.5-2 hours.

Description

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This invention relates to a method for evaluating the quality of a glass surface and can be used in the glass industry.

A known method for the detection of microcracks, the essence of which is reduced to the replacement of ions of a larger radius from glass (for example, sodium) with ions of a smaller radius from a salt melt (for example, lithium). Due to the ion exchange reaction, the surface layer of glass tends to shrink (the ratio of the lithium ion radius to the sodium ion radius is 0.63), and since the inner layers prevent this, a two-dimensional field of tensile stresses forms on the surface, which leads to the opening of griffiths cracks cl.

Using this method to detect surface microcracks in its traditional form by immersing a glass sample in a eutectic mixture NYO3 / KYO3 (or NaNOj / distorts the actual picture of the distribution of surface microcracks due to the influence of edge defects, which, in turn, depend on method of processing edge glass.

Closest to the present invention is a method for assessing the quality of a glass surface by processing. samples in the molten salt of lithium or a mixture of it with melts of other salts, subsequent etching in hydrofluoric acid and determining the number of microcracks per unit area 2.

The disadvantages of the method include applying a lithium salt solution with a brush, swab or rubber stamp, which does not ensure uniform distribution of lithium ions on the glass surface / hence, the developed cracks, and the use of dilute lithium salt solutions does not allow the ion exchange reaction to be sufficient surface microcracks degree, which can lead to erroneous conclusions about the quality of the surface of the glass.

The purpose of the invention is to increase accuracy and reliability.

The goal is achieved in that according to the method of assessing the quality of the glass surface by processing samples in a molten lithium salt or a mixture of it with melts of other salts, subsequent etching in hydrofluoric acid and determining the number of microcracks per unit area, before processing samples in a molten salt in the edge zone of the samples a width of at least 10 mm create compressive stresses of more than 150 MPa by treatment in the molten salt of an alkali metal, the radius of the ion

which is larger than the radius of the alkaline glass ion, at a temperature 50–200 ° C lower than the temperature once f rIfc, nor the glass for the time i: eo6 required to exchange ions to a depth of at least 5 µm.

In addition, for industrial sheet glass, a zone of compressive stresses is created in the range of 400,500 ° C for 0.5-2 hours.

The choice of parameters for the pre-treatment of glass is determined by the following conditions.

1.When treating Na-containing glass in molten lithium salts, tensile stresses are formed, not exceeding 140 MPa. Therefore, to block the propagation of cracks from tensile stresses resulting from the exchange of ions, it is first necessary to create compressive stresses

(for example, ion exchange) exceeding 140 MPa. The upper limit of compressive stresses is not limited; it is determined by the type of exchanging ions.

2. When ions are exchanged, a fissured layer with a depth of 2-3 microns is formed in the surface layer of the glass. Therefore, the lower limit of the depth of the previously created compressive stresses is determined by this value. The upper limit of the depth of the compressed layer, as well as for surface compressive stress, is not limited.

3. The selection of the temperature-time interval is determined by the achievement of the required hardening parameters (surface compressive stresses, more than 150 MPa and the depth of the compressed layer of more than 5 microns) in a minimum time.

It is known that a temperature range of 370-520 s is used to achieve the hardening effect. The minimum temperature significantly slows down the formation of surface compressive stresses / a. The maximum leads to their relaxation. The ion exchange time is determined by the specific temperature of the ion exchange treatment and the glass composition.

4. The width of the marginal zone of glass with compressive stresses is determined mainly by the methods of processing the edge of the glass and the size of the sample. Studies have shown that reliable blocking of the distribution of edge defects is provided by the width of the stress zone equal to

10 mm, and its upper limit is limited by the specimen diffusors.

To preliminarily create compressive stresses in the edge zone of the glass, any alkali metal salts or mixtures thereof can be used, with an ion radius of at least

one alkali metal must be greater than the radius of the alkaline ion glass.

The method is carried out as follows.

Diamond is cut out of a sheet of thermally polished glass of 25 samples with a size of GS 60 3 mm. Randomly divide the samples into five batches of five pieces each.

The composition of thermally polished glass, Bec.ltSiO 71.2; 1.36 Fe2Oz 0.12, CaO 7.76, MdO 4.0, 15.14; 803 038. Around the perimeter of four batches of samples create a zone of compressive stresses by successively immersing and holding each side in a potassium nitrate melt for 1 hour. This treatment provides for the creation of surface compressive stresses of 300 MPa and a depth of compressed layer of 8 microns

The width of the zone of the compressed layer of samples of each batch, respectively, is 5.10.15 and 20 mm. After treatment in KNO, the samples are cooled to room temperature, washed with running water and dried in air at 150 ° C for 2 hours. Then all five batches of samples are simultaneously treated in the melt of a mixture consisting of 30 mol.%: LiNOj and 70 mol. .% NaNOj

at for 5 min. After cooling, the remaining molten salt is removed. by washing in running water, then the samples are etched in a 0.5% solution of hydrofluoric acid for 5 seconds, rinsed with water and wiped dry. Next, the samples are examined on a microscope MIN-8, then from the surface of each sample at regular intervals, 6 photographs. The results of microscopic analysis to determine the quality of the surface of the glass are shown in the table. .

Table continuation

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5 From the tables is visible. that the number of surface microcracks remains constant after the creation in the marginal zone of a compressed layer more than 10 mm wide. Consequently, a 10 mm wide compressed layer zone creates a secure blockage for the propagation of edge cracks on the glass surface. Depending on the purpose of the glass parts, the quality of their surface is controlled by various methods. Thus, for glasses used in products of structural optics, a set of optical parameters is controlled, for example, double beam refraction, tapered optical homogeneity, etc., using

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18 9 14 14 16 18 10 special instrumentation design. For glasses with the smallest requirements, for example, for industrial sheet glass, the surface quality is determined visually, and only visible flaws in the glass, blisters, and solid inclusions are controlled. The use of the invention for assessing the quality of the glass surface as compared with the basic object extends the application limits of the method, allows a wide class of glasses to be compared with different content of peelages, improves the accuracy and reliability of surface microcrack detection, which is a numerical measure of the surface quality of the glass under study.

Claims (2)

1. METHOD FOR ESTIMATING GLASS SURFACE QUALITY by treating samples in a molten lithium salt or a mixture thereof with melts of other salts, subsequent etching in hydrofluoric acid and determining the number of microcracks per unit area, rtl that, in order to increase the accuracy and reliability, before processing the samples in the molten salt in the edge zone of the samples with a width of at least 10 mm, create compressive stresses of more than 150 MPa by treatment in a melt with an alkali salt, a metal whose ion radius is greater than the radius of the alkaline glass ion, at a temperature of 50-200 ° C below the softening temperature of the glass for the time required for the exchange of ions to a depth of less than 5 microns. 2. The method of claim 1, wherein with the I that for industrial glass .listovogo zone pose compressive stresses in the range of 400 500 ^e C. for 0.5-2 hours. Сл>