CN111410439A - Chemical tempering method based on glass stress relaxation and tempered glass - Google Patents
Chemical tempering method based on glass stress relaxation and tempered glass Download PDFInfo
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- CN111410439A CN111410439A CN202010212591.4A CN202010212591A CN111410439A CN 111410439 A CN111410439 A CN 111410439A CN 202010212591 A CN202010212591 A CN 202010212591A CN 111410439 A CN111410439 A CN 111410439A
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C21/00—Treatment of glass, not in the form of fibres or filaments, by diffusing ions or metals in the surface
- C03C21/001—Treatment of glass, not in the form of fibres or filaments, by diffusing ions or metals in the surface in liquid phase, e.g. molten salts, solutions
- C03C21/002—Treatment of glass, not in the form of fibres or filaments, by diffusing ions or metals in the surface in liquid phase, e.g. molten salts, solutions to perform ion-exchange between alkali ions
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Abstract
The invention relates to a chemical toughening method based on glass stress relaxation and toughened glass thereof. The method generates proper stress relaxation through the first step of high-temperature chemical tempering under the condition of determining the relaxation starting temperature and time of the glass, then improves the surface compressive stress and the bending strength of the glass through the second step of low-temperature chemical tempering, and simultaneously has larger stress layer depth and higher Vickers hardness, thereby obviously improving the overall mechanical property of the tempered glass.
Description
Technical Field
The invention relates to the field of preparation of chemically toughened glass, in particular to a chemically toughening method based on glass stress relaxation and toughened glass.
Background
In recent years, smart electronic products such as portable communication, video, wearable, traffic display and the like are being developed toward thinning and light weight. Chemical tempering (or chemical strengthening, or ion exchange) is one of the important methods for improving the mechanical properties of the ultrathin glass. The main principle of chemical tempering is that the ion species and distribution in network gaps in a certain depth on the surface of the glass are different from those in the glass, so that the 'squeezing effect' is generated in the treatment process, the pressure stress is formed on the surface, and the mechanical property of the glass is improved.
In the chemical toughening process of glass, the toughening process (toughening temperature, toughening time, formula of molten salt for toughening and the like) has a decisive influence on the mechanical property of the toughened glass. Therefore, there is still a need to further explore ways to improve the mechanical properties of chemically tempered glass.
Disclosure of Invention
The invention provides a chemical toughening method based on glass stress relaxation and toughened glass thereof for solving the technical problems.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a chemical toughening method based on glass stress relaxation comprises the following steps:
placing an unreinforced glass sheet into pure nitrate A, carrying out chemical toughening under different temperature and time conditions, simultaneously measuring the glass surface compressive stress under different temperature and time conditions, and determining the temperature T1 and the time T1 required by the highest compressive stress CS1 of the glass surface;
putting the same glass sheet which is not toughened into molten salt B, and carrying out first-step chemical toughening at a temperature of T2, wherein the toughening time is T2, the compressive stress of the glass surface is CS2, T2 is more than or equal to T1, T2 is more than or equal to T1, and CS2/CS1 is more than or equal to 0.14 and less than or equal to 0.35;
the glass is put into molten salt C, and is subjected to secondary chemical toughening at the temperature of T3, the toughening time is T3, and the compressive stress of the glass surface is CS3, wherein T2-80 is more than or equal to T3 and less than or equal to T2-40, T3 is more than or equal to 0.5T2, and CS3/CS1 is more than or equal to 0.94.
In the above scheme, pure nitrate A includes sodium nitrate when the content of L i in the glass is higher than that of Na and higher than that of K, and potassium nitrate when the content of Na in the glass is higher than L i and higher than that of K.
In the scheme, when the surface pressure stress of the glass under different temperature and time conditions is measured, the temperature interval does not exceed 10 ℃, and the time interval does not exceed 1 h.
In the above scheme, the molten salt B includes a mixed molten salt of lithium nitrate and sodium nitrate, pure sodium nitrate, or a mixed molten salt of sodium nitrate and potassium nitrate.
In the scheme, when the content of L i in the glass is higher than that of Na and higher than that of K, the molten salt B comprises a mixed molten salt of lithium nitrate and sodium nitrate or a pure sodium nitrate salt, and when the content of Na in the glass is higher than L i and higher than that of K, the molten salt B comprises a mixed molten salt of sodium nitrate and potassium nitrate or a pure potassium nitrate salt.
In the scheme, the nitrate with smaller cation radius accounts for more than 10% but less than 50% of the mixed molten salt by weight.
In the above scheme, the molten salt C includes pure sodium nitrate, a mixed molten salt of sodium nitrate and potassium nitrate, or pure potassium nitrate.
In the above scheme, when the molten salt B comprises a mixed molten salt of lithium nitrate and sodium nitrate, the molten salt C comprises pure sodium nitrate, a mixed molten salt of sodium nitrate and potassium nitrate, or a pure potassium nitrate molten salt; when the molten salt B comprises pure sodium nitrate, the molten salt C comprises a mixed molten salt of sodium nitrate and potassium nitrate or a pure potassium nitrate molten salt; when the molten salt B includes a mixed molten salt of sodium nitrate and potassium nitrate, the molten salt C includes pure potassium nitrate.
In the scheme, the glass is aluminosilicate glass, and the molar percentage of alumina in the glass is not less than 10%.
The toughened glass is prepared by the chemical toughening method.
In the scheme, chemical toughening catalysts can be added into the molten salt according to needs.
The principle of the invention is as follows: the invention utilizes the structural relaxation of the glass to improve the mechanical property of the chemically toughened glass based on the structural relaxation of the glass in the chemical toughening process and the stress relaxation phenomenon caused by the structural relaxation. The structural relaxation of the glass is closely related to the composition and structure, the thermal history of the glass, the thickness of the glass sheet, etc., and the subsequent heat treatment conditions of the glass, etc. For glass produced by the float or overflow process, the structural relaxation of the glass is incomplete during annealing due to the short annealing time. In the chemical toughening process, the structural relaxation of the glass is closely related to the composition of molten salt and the toughening temperature and time. Under the condition of chemical tempering temperature, the ion exchange can form compressive stress in the ion exchange layer, further promote the relaxation of the glass structure and further cause the reduction of the compressive stress on the surface of the glass. Besides the reduction of the surface compressive stress of the glass, the relaxation of the glass structure is beneficial to the reduction of the central tensile stress of the glass, and the structure of the glass after the relaxation is also beneficial to obtaining higher surface compressive stress through subsequent ion exchange. The temperature T1 and the time T1 at which the surface stress relaxation of the glass starts are determined by step 1 in the present invention, and the obtained surface compressive stress of the glass is CS 1. According to the result, the original piece of glass which is not chemically toughened is subjected to first-step chemical toughening, the temperature T2 is not less than T1, the time T2 is not less than T1, and the surface compressive stress CS2 of the glass is under the condition; by optimizing T2 and T2, the surface compressive stress of the glass is relaxed and satisfies 0.14 ≦ CS2/CS1 ≦ 0.35. Under the condition, the ion exchange depth of the glass is larger due to higher temperature and longer time of chemical toughening, and meanwhile, the central tensile stress of the glass is smaller due to relaxation of the surface compressive stress of the glass; when the surface compressive stress of the glass relaxes, the glass structure also relaxes correspondingly, thereby creating conditions for obtaining higher surface compressive stress after the next chemical tempering. Carrying out second-step chemical toughening on the glass subjected to the first-step chemical toughening, wherein the temperature is T3, the time is T3, T2-80 is not less than T3 is not less than T2-40, and T3 is not more than 0.5T2, namely, the surface compressive stress of the glass is recovered to a greater extent and is even further improved through short-time chemical toughening under the low-temperature condition; through the steps, the surface compressive stress CS3 of the glass meets CS3/CS1 being more than or equal to 0.94. Meanwhile, the depth of the larger ion exchange layer formed in the first step of chemical toughening can not be obviously changed in the subsequent second step of exchange, namely the depth of the larger stress layer can be kept, and correspondingly, the central tensile stress of the glass can also be kept at a lower level; after the first step of chemical toughening, the glass structure relaxes, and after the second step of chemical toughening at a lower temperature for a shorter time, the surface hardness of the glass is greatly improved.
Therefore, the chemical toughening scheme and the chemical toughening process have the beneficial effects that the toughened glass can simultaneously have higher surface compressive stress, stress layer depth, surface hardness and bending strength.
Detailed Description
The present invention will be further illustrated by the following examples, but the present invention is not limited to the following examples, and the examples should not be construed as limiting the present invention.
In order to clarify the effect of the present invention, the present invention uses a domestic aluminosilicate glass in which the content of alumina is 13.0 mol%, the content of sodium oxide of the glass is higher than that of potassium oxide, and no lithium oxide is contained; the glass transition point was 627 ℃ and the thickness of the glass sheet was 0.7 mm. It will be appreciated that the invention is not limited to this glass and that aluminosilicate glasses of other compositions may also be used.
In the following cases, the surface compressive stress and the depth of the ion exchange layer of the tempered glass were measured using a surface stress meter, the bending strength of the tempered glass was measured using a universal tester (conditions for measuring the bending strength: 20mm in the upper span, 40mm in the lower span, and 5mm/min in the pressing speed of the indenter), and the Vickers hardness of the tempered glass was measured using a microhardness meter (conditions for measuring the Vickers hardness: 0.2kgf in load, 10s in loading time).
The specific embodiment of the glass is as follows:
1) putting glass into molten salt A, wherein the glass does not contain L i, the Na content in the glass is higher than the K content, the molten salt A is pure potassium nitrate molten salt, chemically toughening is carried out under different temperature and time conditions, and the surface pressure stress of the glass under different temperature and time conditions is measured at the same time, so that the highest pressure stress CS1 of the surface of the glass is 980MPa, the corresponding temperature T1 is 400 ℃, the time T1 is 4h2。
2) Placing the same glass original sheet which is not subjected to chemical tempering as the step 1) into molten salt B, and performing first-step chemical tempering at the temperature T2 for time T2, wherein the mixed molten salt of sodium nitrate and potassium nitrate is selected as a tempering medium because the glass does not contain L i, and the Na content in the glass is higher than the K content, the temperature T2 is 470 ℃, the tempering time T2 is 6 hours, 8 hours or 10 hours, the sodium nitrate content in the mixed molten salt is 10%, 20%, 30%, 40% or 50%, 10% and 50% are used as comparative examples, and 20%, 30% and 40% are used as examples, and the results are shown in Table 1.
3) And (3) putting the glass subjected to the first-step chemical strengthening into molten salt C, and performing second-step chemical toughening for T3 under the condition of a temperature T3. Since the molten salt B is a mixed molten salt of sodium nitrate and potassium nitrate, the molten salt C is preferably pure potassium nitrate. The temperature T3 used was 390 ℃, 410 ℃ or 420 ℃ and the time T3 used was 2 h. The results are shown in Table 2.
Table 1: first-step performance test result of chemically tempered glass
Table 2: second step chemical tempering glass performance test result
As shown in the results of Table 1, the compressive stress on the surface of the glass after the first step of chemical tempering is low, wherein the compressive stress CS2 on the surface of the glass is not 0.14 in comparative examples 1 to 6<CS2/CS1<Within the range of 0.35. In all cases in Table 1, the glass had a surface compressive stress well below 980MPa, a flexural strength below 822MPa and a Vickers hardness below 632kgf/mm2。
As shown in the results of Table 2, the surface compressive stress, bending strength and Vickers hardness of the glass can be restored to higher levels after the second step of chemical tempering. In comparative examples 1 to 3, Vickers hardness was higher than 632kgf/mm although glass could obtain a larger stress layer depth2However, the glass surface compressive stress is lower than 920MPa, and the bending strength is lower than 800 MPa. In comparative examples 4 to 6, the depth of stress layer of glass was low due to the high sodium nitrate content (50%) in the molten salt (<55 μm, see table 1), and the surface compressive stress is relaxed excessively, resulting in lower bending strength than the examples. In examples 1 to 8, the compressive stress on the surface of the glass was 980MPa or more (except for examples 3 and 4), the bending strength was 870MPa or more (in which examples 1 to 5 and 7 were 900MPa or more), and the Vickers hardness was restored to 600kgf/mm2Above, the glass also has larger stress layer depth (more than or equal to 55 μm, see table 1).
By comparing the above cases, it can be found that the chemical tempering method based on glass stress relaxation of the present invention can significantly improve the surface compressive stress, the depth of stress layer and the bending strength of tempered glass, while substantially maintaining or improving the vickers hardness of the glass.
The above-mentioned embodiments only show a few embodiments of the present invention, and the present invention is described in more detail, but the present invention is not limited to the above-mentioned embodiments. The present invention can be modified and improved by those skilled in the art without departing from the spirit of the present invention, and these are within the scope of the present invention.
Claims (10)
1. A chemical toughening method based on glass stress relaxation is characterized by comprising the following steps:
placing an unreinforced glass sheet into pure nitrate A, carrying out chemical toughening under different temperature and time conditions, simultaneously measuring the glass surface compressive stress under different temperature and time conditions, and determining the temperature T1 and the time T1 required by the highest compressive stress CS1 of the glass surface;
putting the same glass sheet which is not toughened into molten salt B, and carrying out first-step chemical toughening at a temperature of T2, wherein the toughening time is T2, the compressive stress of the glass surface is CS2, T2 is more than or equal to T1, T2 is more than or equal to T1, and CS2/CS1 is more than or equal to 0.14 and less than or equal to 0.35;
the glass is put into molten salt C, and is subjected to secondary chemical toughening at the temperature of T3, the toughening time is T3, and the compressive stress of the glass surface is CS3, wherein T2-80 is more than or equal to T3 and less than or equal to T2-40, T3 is more than or equal to 0.5T2, and CS3/CS1 is more than or equal to 0.94.
2. The glass stress relaxation-based chemical tempering method according to claim 1, wherein the pure nitrate a comprises sodium nitrate when the content of L i in the glass is higher than the content of Na and higher than the content of K, and comprises potassium nitrate when the content of Na in the glass is higher than L i and higher than the content of K.
3. The method for chemically tempering glass based on stress relaxation according to claim 1, wherein a temperature interval is not more than 10 degrees celsius and a time interval is not more than 1 hour when a compressive stress of a surface of the glass under different temperature and time conditions is measured.
4. The glass stress relaxation-based chemical tempering method according to claim 1, wherein the molten salt B comprises a mixed molten salt of lithium nitrate and sodium nitrate, pure sodium nitrate, or a mixed molten salt of sodium nitrate and potassium nitrate.
5. The glass stress relaxation-based chemical tempering method according to claim 1, wherein the molten salt B comprises a mixed molten salt of lithium nitrate and sodium nitrate or a pure sodium nitrate salt when the content of L i in the glass is higher than the content of Na and higher than the content of K, and comprises a mixed molten salt of sodium nitrate and potassium nitrate or a pure potassium nitrate salt when the content of Na in the glass is higher than L i and higher than the content of K.
6. The glass stress relaxation-based chemical tempering method according to claim 4 or 5, wherein the nitrate with smaller cation radius in the mixed molten salt is more than 10% but less than 50% by weight of the mixed molten salt.
7. The glass stress relaxation-based chemical tempering method according to claim 1, wherein the molten salt C comprises pure sodium nitrate, a mixed molten salt of sodium nitrate and potassium nitrate, or pure potassium nitrate.
8. The glass stress relaxation-based chemical tempering method according to claim 4, wherein when the molten salt B comprises a mixed molten salt of lithium nitrate and sodium nitrate, the molten salt C comprises a pure sodium nitrate, a mixed molten salt of sodium nitrate and potassium nitrate, or a pure potassium nitrate molten salt; when the molten salt B comprises pure sodium nitrate, the molten salt C comprises a mixed molten salt of sodium nitrate and potassium nitrate or a pure potassium nitrate molten salt; when the molten salt B includes a mixed molten salt of sodium nitrate and potassium nitrate, the molten salt C includes pure potassium nitrate.
9. The method of glass stress relaxation-based chemical tempering according to claim 1, wherein said glass is an aluminosilicate glass and wherein said glass has a mole percent alumina content not less than 10%.
10. The tempered glass produced by the chemical tempering method according to any one of claims 1 to 9.
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