DE1771427A1 - Process for strengthening glass objects - Google Patents

Description

■ ERNST STORM. a "onchen". *. ₂₁

Bank AG. Munich Account No. 77SW LEOPOLDSTR. 20 / IV ^ '· ^Mal '" ^bö PofHcheckkonto: Munich 91707 iConcordiol »ui) S Ch

Telephone 331451

Telegram gnidirifti Iwrpotenf

Applicant: Corning Glass Works

Corning, New York 14830, USA

Process for strengthening glass objects

• The invention "relates to the solidification (hardening) of Glass objects (bodies) by forming a surface layer with internal compressive stresses with the help of a Ion exchange process. In particular, the invention relates the consolidation of sodium aluminum silicate glasses, in which potassium ions have been exchanged for sodium ions,

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heating the glasses in air prior to ion exchange is provided.

! i

j ■

A recent development in the field of glassware was the discovery that alkali silicate glasses can be solidified several times with the help of an ion exchange process. Here, a glass body that contains Id1; hium is also used

ofor sodium ions

an alkali metal ion / tanthene containing compound that has a have larger ionic radius than lithium or sodium ions, at elevated temperature, but below the stress point (strain pOint) of the glass, brought into contact for as long as that the larger ions change into the surface of the glass and replace the smaller ions in it. Since this exchange takes place at temperatures below the

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The expansion point of the glass takes place, can not be viscous Flow occurs which takes the compressive stresses caused by the penetration of the larger ions into the glass structure the smaller ions are generated, reduces · In this way a surface hardening layer is created in the glass body formed, which greatly improves its strength

Done by the method of US Pat. No. 3,218,220 the ion exchange by electrochemical means, while according to the method of British patent specification 917 338 thermal diffusion of the ions is carried out The latter method leads to a further expansion of the industrial glass production led to the production of glasses with previously unattainable strengths made possible. The method according to the invention provides a Improvement of this method · dar · j

You British Patent 966 733 be

lohreibt the unge

Ordinary effect, which the addition of substantial amounts, i.e., over 5 percent, of AIgO, jtö alkali silicate glasses has on the strength, which is accomplished by ion exchange of ions with a larger surohm for ions with a smaller office knife, special examples show the exchange of potassium! on * n for sodium ions in sodium aluminum silicate glasses, and this would result in strength in comparison with other halide glass glasses in which the AlgO ^ content is less than 5 $ . It was

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also observed that to a real evaluation of the glass strength also its measurement after at least one heard moderate abrasion of the surface of the vitreous · Therefore, the original strength clay is recently discovered Glass objects are very high, but usually are of a very short length, generally the common use of the objects eu leads to damage to the surface of the glass, which greatly reduces its original strength Is the mechanical strength of a glass object * generally of little concern unless measured after the surface has been scuffed was subjected to in order to create conditions similar to those found in the use of glass. For comparison Two tests are used with the conditions of use. These are described in British patent specification 966 733 and are explained in the following because they are used to test the mechanical strengths of those produced according to the invention Glasses were used

One test trial uses a specimen, generally A glass tube 10 cm old with a diameter of 0.6 cm is mechanically attached and fast for about 30 seconds in contact with 150 silicon carbide paper while maintaining a weak constant pressure for one rotated uniform contact.

The second type of test for an abrasion specimen, which is called buffing abrasion

(tumble abrasion) is that

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10 identically shaped glass rods in a No. O ball mill device after adding 200 ecm of 30 grit silicon carbide particles rotated at 90-100 revolutions / .15 minutes.

Surface scratches in the first type of test correspond to abrasion in practical use by rubbing against hard materials such as glass objects rubbing against each other. Surface defects »the the second type of test (polishing abrasion) correspond to a combined effect of abrasion and impact. It will believed that this type of test better at abrasion Use of the glass objects corresponds, it was therefore also used in most of the samples according to the invention.

When determining the mechanical strength of the abraded glass, measurements of the modulus of rupture were carried out on the samples in the usual manner. Such measurements gave the " ¹ x abrasion resistance of the glass and correspond to the practical strength of the glass.

What was inventive in the process of British patent specification 966 733 lay in the discovery that by the presence of substantial amounts of AlgO », i.e. at least 5 percent by weight, high abrasion resistance can be obtained in glasses. After undergoing the after alkali aluminum obtained by the British process

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Silicate glasses of the two test samples, the glasses still showed strengths several times higher than those of annealed Glasses of the same composition lay. Comparisons

. were placed between the aluminum silicate glasses and glasses that contained little or no AIoO, and especially the commercially available sodium lime glasses. These comparisons showed that while alkali silicate glasses with little or no AIpO, initially by ion exchange * Could be brought to high mechanical strength, the surface abrasion after the tests described above greatly reduced the strength obtained so that the advantage over tempered glass was minimal. Therefore, this improvement in the thermal diffusion technology of the exchange of large ions for small ions pach the process of British Patent 966 733 allows commercial exploitation of the increased strength.

Although abrasion resistance on ion-exchanged alkali aluminum silicate glasses were obtained that are several times larger than with tempered glasses and many times over were three to four times larger than the thermally tempered glasses shown, means were sought to to improve these strengths even further.

In accordance with the invention, such improvements of up to 50-6 in strength are possible in a particular range of sodium aluminum glasses by having that one specified Heat treatment from the ion exchange process

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subject. The invention therefore relates to the heating of glass objects of a certain composition in air or another inert atmosphere at temperatures of about 25 ⁰ C below the transformation range to temperatures within the transformation range of the glass and then an ion exchange of potassium ions for sodium ions at temperatures below the Strain point of the glass.

To carry out the process according to the invention, glass-forming starting material, which essentially consists in percent by weight on an oxide basis - of about 50-659 * SiO ₂ , IO-2596 Al ₂ O, and 10-209 * Va ₂ O, is placed in open crucibles at 150-160 ° ⁰ O melted for about 16 hours. In most cases, the sole melts are stirred for better homogenization. Tubes about 0.6 cm in diameter were drawn out of each crucible and many times

0.6 cm thick strips rolled out « ^;

The glass bodies were then placed in an electrically heated furnace and the temperature was increased to a little below or within the deformation area of the individual glass II . The deformation range of a glass is the temperature range within which a liquid melt presumably becomes an amorphous solid. This Berti oh jj lies between the Dthnungspunlrk (strain point) and dta Temperungapunkt (annealing point) a «« <Uft * t ·· The expansion points of the invention-aüen β1 * · # Γ lie

= ■ *

between about 550 ° and 600 ⁰ G, the annealing points between about 600 ° and 65O ⁰ O. The glass bodies were slightly lower than in the furnace at temperatures or held for at least 4 hours over the forming area of the individual lenses. Significantly longer times can be widely used with advantage is sowiit intended as a consolidation improvement, 3 ^e but improve retention times longer than 24 hours is not much strength compared to shorter holding times, they are therefore not rational. A residence time of about 24 hours is therefore practically the maximum, although longer times can be used without danger. As has been found, for the highest strengths the heat treatment should be carried out at temperatures of about 5 35 ⁰ O above the expansion point of the glass. The heat treatment was carried out in the preceding oven air, but it can also be carried out in any other inert atmosphere.

After the air-hot treatment, the vitreous were immersed in a bath of molten KNO. at an elevated temperature, but submerged below the strain point of the glass. It was found that the highest strengths were obtained when the ion exchange at about 50 to 150 ⁰ C below dec Dehnungsχ: unl-: tes took place. The glass bodies were then removed from the salt bath, washed with water and then rubbed using one of the methods described above to determine the brucii module.

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Tests in the laboratory and in practice have shown that the compacted layer produced by the exchange of Sodium ions versus potassium ions obtained should be at least 5 microns deep in order to be practical To get abrasion resistance. Furthermore, this strength usually increases up to a maximum value increasing treatment time or temperature for ion r exchange. This factor shows a complex relationship between layer thickness after ion exchange, depth of weakening defects in the glass surface and mechanical strength. In general, it was determined that the ions from Treatment should take place for at least 2 hours, longer periods being applicable and often advantageous are. However, it should be noted that the ion exchange should not be carried out for so long that the replacement of sodium ions is carried out by potassium ions through the entire thickness of the vitreous humor.

Table I contains various glass compositions in percent by weight on an oxide basis - of the starting material - / which have been treated according to the invention. The material can consist of oxides or other compounds which n ^ ch the melting into the desired oxidic compositions in the appropriate proportions are. Although the melts according to Table I have a fairly low viscosity, a common

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Fining agents such as As ₂ O can be added. Generally about 0.5-1 percent by weight is added. However, this addition has not been included in the table because the amount remaining in the glass after melting is too small to have any noticeable effect on the basic properties of the glass.

61 * .9 » Tabel I. i
57.0 BATH 1
61.5 6th
58.6 1
51 * -10- .6 SiO ₂ 17th 8th
63- .0 2
62.5 2
62.2 10.0 18.0 19.7 25th 0, .0 Al ₂ O ₅ 12th 16, .8th 17.0 17.0 16.0 11.7 12.5 16, * .0 Na ₂ O 3 12, .6 13.0 12.5 4.0 3.7 4.1 7th .0 κ ₂ ο 3 3. .7 3.6 3.6 - 2.7 2.7 Ii
62. MgO 0 1, .2 3.7 4.5 - 0.4 0.4 16. .4 OaO 0 0. .8th 0.2 0.2 - 2.0 2.0 11. m TiO ₂ 2. ■ a - - 13.0 - - 4th W. ZrO ₂ 4M "8th - - IL
58.9 Ii
58.6 η
60.1 2. Ϊ
.7 SiO ₂ .5 1
62.45 IP.
53.6 15.4 17.5 22.0 0. , 5 Al ₂ O ₃ .5 18.0 25.0 18.8 11.8 12.0 2. ,8th Ha ₂ O , 4 12.5 15.0 3.3 3.6 2.5 - 0 κ ₂ ο 5 4.05 5.0 3.4 0.8 - 6th MgO 3 2.65 - 0.2 3.8 0.4 4th OaO 0 0.35 0.4 - 3.9 1.0 0 TiO ₂ 2.0 1.0 - - 2.0 B ₂ Q ₃ - - ORIGINAL 109851 / 0367

It has been found that the amounts of Al ₂ O and Ha ₂ O used are critical in order to obtain the desired increased mechanical strength and that the addition of various compatible metal oxides is severely limited and should not exceed 20% by weight of the total amount. The addition should preferably be less than 10 percent by weight of the total amount. Such metal oxides are K ₂ O, alkaline earth metal oxides ZrO ₂ , PbO, P ₂ O ₅ , TiO ₂ and B ₂ O on the strength of the glass and should not be in excess of £ 1.

Table II shows various heat and salt bath treatments from Example 1 according to Table I, as well as abrasion values (HOR) according to the polishing abrasion method (tumble abraeioi). The expansion point of this glass is 581 ⁰ O, the tempering point 631 ° 0. In every j

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Trap a ¹ bath of molten I) TO was used, although other potassium salts and their mixtures * that melt in the required temperature range can be used. Table II also gives a comparison of the moisture values obtained according to the invention with values "dl" obtained without prior treatment. * Each MOR value represents an average value of measurements on 6 samples with an error limit τοη + 3000 pel

of ■ ■ I ·

(211 kg / cm *). ) / ■■ ,.

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Table II

example
Nt- . Heat treatment 24 hours Ion exchange £ Pool abrasion
(MOR - T) Si) -1 Hl «
1 565 ⁰ C - 24 hours 50O ⁰ C - 24 hours 87,000 1 57O ⁰ C - 48 hours 50O ⁰ C τ 24 hours 90,000 1 57O ⁰ C - ^v 1 H. 50O ⁰ C - 24 hours 88,000 1 58O ⁰ C - 2 iätd. 50O ⁰ C - 24 hours 73,000 1 580 ⁰ C - 4 hours 50O ⁰ C - 24 hours 73,000 1 580 ⁰ C - 8 hours 50O ⁰ C - 24 hours 85,000 1 580 ⁰ C- 24 hours 50O ⁰ C - 24 hours 84,000 1 580 ⁰ C - 1 H. 50O ⁰ C - 24 hours 88,000 1 59O ⁰ C - 2 hours. 50O ⁰ C - 24 hours 74,000 1 59O ⁰ C - 4 hours 50O ⁰ C - 24 hours 74,000 1 590 ⁰ C - 8 hours 50O ⁰ C - 24 hours 84,000 1 59O ⁰ C - 24 hours 50O ⁰ C - 24 hours 89,000 1 59O ⁰ C - 50O ⁰ C - 24 hours 90,000 1 No 1 H. 50O ⁰ C - 24 hours 68,000 1 600 ⁰ C - 2 hours. 50O ⁰ C - 24 hours 75,000 1 600 ⁰ C - 4 hours 50O ⁰ C - 24 hours 75,000 1 600 ⁰ C - 8 hours 50O ⁰ C - 24 hours 85,000 1 600 ⁰ C - 16 hours 50O ⁰ C - 24 hours 88,000 1 600 ⁰ C - 24 hours 50O ⁰ C - 24 hours 89,000 1 600 ⁰ C - 48 hours 50O ⁰ C - 24 hours 93,000 1 600 ⁰ C - 50O ⁰ C - 48 hours 95,000 1 No 24 hours 525 ⁰ C - 16 hours 64,000 1 600 ⁰ C - 525 ⁰ C - 16 hours 87,000 1 No . 24 ötd. 550 ⁰ C - 6 hours 61,000 1 600 ⁰ C - 109851 550 ⁰ C - 6 hours 80,000 / 0367 3AD ORIGINAL

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Table II (continued)

example
No. Heat treatment Ion exchange Hours. Polishing abrasion
(MOR-psi) 1 No 55O ⁰ C-16 Hours· 64,000 1 600 ⁰ C - 24 hours 55O ⁰ C-16 Ötd. 86,000 1 No 450 ⁰ C-48 Hours. 64,000 1 580 ⁰ C - 24 hours 450 ⁰ C-48 Hours. 85,000 1 610 ⁰ C - 1 hour 50O ⁰ C-24 Hours. 75,000 1 610 ⁰ C - 2 hours 50O ⁰ C-24 Hours. 76,000 1 61O ⁰ C - 4 hours, 50O ⁰ C-24 Hours. 87,000 1 61O ⁰ C - 8 hours 50O ⁰ C-24 Hours. 88,000 1 61O ⁰ C - 24 hours 50O ⁰ C-24 90,000

Table III clearly shows the improving effect of the previous one Heat treatment for mechanical strength clay Example 1, which has a preferred glass composition according to the invention, based on practical conditions such as melting and formability, as well as the ability to achieve high mechanical strengths. The preferred treatment time for solidification in air is about 24 hours. Such treatment generally results in abrasion resistance of about 90,000 psi (+ 3000 psi). If that Glass is rubbed with silicon carbide paper instead of the polishing abrasion method, results in modulus of rupture of about 110,000 pels compared to about 72,000 pels for samples, which have not previously been heat-treated in air *

Table III shows the effect of the heat treatment on improving the strength of the other examples Table I. In each case the jars were on for 24 hours

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immersed at 50O ⁰ O in a bath of molten KNO. * to perform the exchange of potassium ions for sodium ions

Table III

Example of heat treatment Tempering no. Point

Expansion and polishing mark MOR (pai)

2 No 24 hours 637 ⁰ C 584 ⁰ G 72,200 2 600 ⁰ C - 93,300 3 No 24 hours 627 ⁰ C 575 ⁰ C 69,900 3 600 ⁰ C - 88,400 4th No 24 hours 645 ⁰ G 596 ⁰ G 71,200 4th 600 ⁰ C - 91,700 VJl No 24 hours 645 ⁰ C 593 ⁰ C 71,000 VJI 600 ⁰ C - 97,000 6th No 24 hours 643 ⁰ C 593 ⁰ C 77,000 6th 600 ⁰ C - 98,800 7th No
* 24 hours 604 ⁰ C 558 ⁰ C 56,000 7th 50Q ⁰ C - 24 hours 73,000 7th 6QO ⁰ C- 83, QOG 8th No 24 hours 619 ⁰ C 572 ⁰ C 57,000 8th 600 ⁰ C - 77,000 9 No 24 hours 625 ° G 574 ⁰ C 74,000 9 600 ⁰ C - 86,000 10 No 24 hours 652 ⁰ C 606 ⁰ C 68,000 10 600 ⁰ C - 100,000 11 No 8 hours 628 ⁰ C 576 ⁰ O 70,000 11 59O ⁰ C - 93,000

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Table III (continued)

Example of heat treatment Temperunga- l> ohna- polishing abrasion

1fr No - θ Hours. Point Point MOH (Dai) 12th 59O ⁰ O 640 ⁰ O 59O ⁰ O 75,000 12th No - 24th Hours. 85,000 13th 575 ⁰ O 611 ⁰ O 555? 0 52 | 000 13th No - 24th Hours, 72,000 14th 600 ° 0 635 ⁰ O 585 ⁰ O 70,500 14th 93,000

The breaking modulus values given in Table III (average of 6 measurements each) clearly show the remarkable enhancement of the mechanical strengths of glasses by the heat treatment according to the invention before the ion exchange. The size of the ion-exchanged surface layer varies between 2 and 4%. Example 7 states that the heat treatment should take place at a temperature of about 25 ° below the deformation zone of the glass to within the deformation area in order to achieve the greatest increase in liquidity, although, as appropriate, some improvement in performance is achieved when the Hitie ^{treatment is carried out at about 50 0} O below the UaXoraunebereiohee.

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Claims (3)

Ρ «. ERNST STURM t Monks 23, d *. May 21, 196Ö MtadHM »17V t «M« t »14« ' lsarpet «tf Applicant company Corning Glass Works, Oorning. Hew York U830 »USA 3Pat gntamspray marriage (y. Process of strengthening sodium aluminum silicate glasses by exchanging the sodium ions in a surface area of the glass for potassium ions by bringing the glass surface into contact with a compound containing potassium ions at an elevated temperature below the strain point of the glass to form a compressed surface layer (compression layer), characterized in that the glass body is formed from a sodium aluminum silicate glass which essentially contains about 10-2OJi Na ₂ O, 10-25 # AIgO, and 50-65 # SiOg in percent by weight on an oxide basis, that the glass body is at a temperature from about 25 ⁰ O below the transformation range of the glass to within the Umformungsbereiohes is heated for at least 4 hours, and that then a surface of the glass body with a compound containing potassium ions at a temperature between about 50-150 ⁰ O below the expansion point d the glass lies in contact with it until a compacted layer is formed in the glass surface to a depth of at least 5 microns » -2- BATH 109861/0367 177U27 / ft 2. The method according to claim 1, characterized in that the glass body to a temperature between 5 and 35 C. is heated above the expansion point for at least 4 hours. 3. The method according to claim 1, characterized in that the glass body with a potassium ion containing Connection is brought into contact for at least 2 hours. 109851/0367 BATH ORIGINAL