Method for preparing frit with high thermal stability from glass waste

Abstract

The invention discloses a method for preparing a high-thermal-stability frit from glass waste, and relates to the technical field of ceramic frits, and the method comprises the following steps: reducing and sintering preparation raw materials to obtain the high-thermal-stability frit; the composite material is prepared from the following raw materials in parts by mass: 40-60 parts of waste glass powder, 10-20 parts of boron tail powder, 2-8 parts of a fixing agent and 1-5 parts of a phosphate mineralizer, the fixing agent is at least one of zirconium oxide, lanthanum oxide and tin oxide; and the phosphate mineralizer is aluminophosphate or magnesium pyrophosphate. The reduction sintering process comprises the following steps: firstly, raising the temperature to 750-850 DEG C in a reducing atmosphere, and keeping the temperature for 20-30 minutes; the temperature is increased to 1100-1250 DEG C, melting is conducted for 25-50 min, and finally the molten mass is quenched. The main raw materials are all glass wastes, the cost of the raw materials is low, and the prepared ceramic frit is high in thermal stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of ceramic frit, and specifically relates to a method for preparing a frit with high thermal stability by using glass waste. Background Art

[0002] Preparing ceramic frit by using waste glass can effectively reduce the exploitation of natural mineral resources, and thus realize the recycling of resources, which is of great significance to environmental protection and sustainable economic development. However, the current treatment methods of waste glass are mostly limited to simple decontamination treatment and high-temperature melting and reprocessing, and there is little research on the resource utilization of high-boron and high-halogen glass.

[0003] In the existing technology, the patent document CN118270980A provides a method for preparing a thermally stable frit by using waste glass. The core of this method lies in accurately adjusting the sintering performance of glass powder by adding feldspar and boric acid as fluxes to ensure that the frit can obtain ideal melting performance during the sintering process. In addition, this solution further improves the thermal stability of the frit by carefully adjusting the type and proportion of titanium dioxide, making its performance more excellent in a high-temperature environment. Nevertheless, this solution still has the problem of high cost during the preparation process.

[0004] In addition, the existing process usually volatilizes halogens in the form of elemental substances or acid gases at high temperature, which not only corrodes equipment but also pollutes the environment. Halogens themselves can be used as functional components. If they are completely volatilized, additional additives need to be added to compensate, increasing costs. Summary of the Invention

[0005] In order to overcome the above technical problems, the present invention provides a method for preparing a frit with high thermal stability by using glass waste. The main raw materials of the present invention are all glass waste, with low raw material costs and high thermal stability of the prepared ceramic frit.

[0006] The present invention solves the above technical problems through the following technical solutions.

[0007] A method for preparing a frit with high thermal stability by using glass waste, comprising the following steps: obtaining a frit with high thermal stability after reducing and sintering the preparation raw materials; By mass, the preparation raw materials include: 40 - 60 parts of waste glass powder, 10 - 20 parts of boron tail powder, 2 - 8 parts of fixing agent, and 1 - 5 parts of phosphate mineralizer; The boron tail powder includes the following chemical components by mass: 40 - 45% B2O3, 14 - 18% K2O, 18 - 23% Na2O, 6 - 9% Cl element, and 6 - 9% F element; the contents of F and Cl in the boron tail powder are both in the form of elemental contents; The process of reduction sintering: First, heat it to 600 - 750 °C in a reducing atmosphere and hold for 20 - 30 min; then heat it to 900 - 1050 °C for melting for 25 - 50 min, and finally quench the melt.

[0008] According to some preferred embodiments of the present invention, the preparation raw materials include 40 - 55 parts of waste glass powder, 10 - 15 parts of boron tail powder, 3 - 7 parts of fixative, and 2 - 5 parts of phosphate mineralizer.

[0009] In the present invention, the waste glass powder includes the following chemical components by mass percentage: 69 - 75% SiO2, 2 - 7% Al2O3, B2O3 ≥ 5%, 4 - 12% alkali metal oxides, and 1 - 6% alkaline earth metal oxides; Among them, the alkaline earth metal oxides include at least one of CaO, MgO, BaO, and ZnO; the alkali metal oxides include at least one of K2O and Na2O.

[0010] Preferably, the waste glass powder includes 70 - 75% SiO2, 2 - 7% Al2O3, 5 - 11% B2O3, 5 - 9% NaO, 1 - 4% K2O, 1 - 3% BaO, 0 - 1.5% CaO, 0 - 1.5% MgO, and 0 - 1.5% ZnO.

[0011] In the present invention, the particle size of the waste glass powder is 300 - 500 mesh.

[0012] According to some preferred embodiments of the present invention, the boron tail powder includes the following chemical components by mass: 42 - 44% B2O3, 15.5 - 17% K2O, 19 - 22% Na2O, 6.5 - 8% Cl element, and 6.5 - 8% F element.

[0013] For example, the boron tail powder includes the following chemical components by mass percentage: 43.03% B2O3, 16.19% K2O, 20.07% Na2O, 7.22% Cl element, 7.72% F element, 2.96% SiO2, 0.41% Ti2O, and 0.38% BaO.

[0014] In the present invention, the particle size of the boron tail powder is 300 - 500 mesh.

[0015] In the present invention, the fixative is at least one of zirconia, lanthanum oxide, and tin oxide. Among them, the fixative can form a stable M - O - Cl / F bond with the halogen ions in the boron tail powder, and can inhibit halogen volatilization even in a high - temperature sintering environment above 1000 °C. Due to its strong bonding ability, the halogen forms chemical bonds with its molecules to enhance thermal stability.

[0016] In the present invention, the D50 of the fixing agent is 20 to 50 μm, preferably 30 to 40 μm.

[0017] In the present invention, the phosphate mineralizer is aluminum phosphate (AlPO4) or magnesium pyrophosphate (Mg2P2O7). Among them, the P2O5 decomposed from aluminum phosphate at high temperature can form [PO4] 3- -[BO3] 3- mixed network to enhance the stability of the glass phase. Compared with aluminum phosphate, magnesium pyrophosphate has higher activity in releasing P2O5 and is more likely to form a glass phase with B2O3. However, it should be noted that excessive addition of the phosphate mineralizer may cause opacification. In addition, [PO4] 3- is easily reacted with free halogens to form thermally stable chlorophosphates and fluorapatite analogs, reducing high-temperature volatilization.

[0018] According to some preferred embodiments of the present invention, the process of the reduction sintering is as follows: first, heat up to 600 - 650 °C in a reducing atmosphere and keep it warm for 25 - 30 min; then heat up to 900 - 1000 °C and melt for 40 - 50 min, and finally quench the melt.

[0019] In the present invention, the volume ratio of CO:N2 in the reducing atmosphere is 1:3 - 6, preferably 1:4 - 5.

[0020] In the present invention, the heating rate is 5 - 8 °C / min.

[0021] In the present invention, after the heat preservation is completed, nitrogen is introduced and then heated up to make the melting process carried out in a nitrogen atmosphere.

[0022] In the present invention, the halogen retention rate of the high thermal stability frit: the Cl element ≥ 70%, preferably 70 - 75%.

[0023] In the present invention, the halogen retention rate of the high thermal stability frit: the F element ≥ 69%, preferably 69 - 77%.

[0024] The halogen retention rate in the present invention is a key index to measure the fixing efficiency of fluorine and chlorine, and its calculation is obtained according to the mass percentage of halogen content in the raw materials and products.

[0025] In the present invention, the high thermal stability frit is quenched from 350 °C to 0 °C, and the number of thermal shock resistance tests is repeated ≥ 30 times.

[0026] On the basis of conforming to the common knowledge in the art, the above preferred conditions can be combined arbitrarily to obtain various preferred examples of the present invention.

[0027] Compared with the prior art, the beneficial effects of the present invention are: 1. The present invention uses waste glass powder and boron tail powder as the main raw materials, without the need to additionally add high-purity quartz sand or flux, thus significantly reducing the raw material cost. During the preparation process, chlorine and fluorine in the boron tail powder are directly converted into stable compounds through the synergistic effect of a fixing agent and a phosphate mineralizer, which can significantly improve the high-temperature resistance and thermal shock resistance of the frit. Moreover, this process realizes the resource utilization of halogens and effectively avoids environmental pollution.

[0028] 2. The present invention adopts a two-stage sintering process of reduction-melting. In the reduction heat preservation stage of the low-temperature section, it promotes the formation of a low-temperature eutectic phase between Na2O / K2O and B2O3; at the same time, it avoids the corrosion of equipment and solves the problem of halogen element pollution in the recycling process of high-halogen glass waste.

[0029] 3. The high-temperature stability frit prepared by the present invention has excellent thermal shock resistance, and the number of thermal shock resistance is ≥ 30 times, and can reach 32 - 36 times in some preferred embodiments. Brief Description of the Drawings

[0030] Figure 1 It is a flow chart of the present invention for preparing a high-temperature stability frit using waste glass materials. Detailed Embodiments

[0031] To facilitate the understanding of the present invention, the following will describe the present invention more comprehensively and meticulously in combination with preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0032] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0033] The "range" disclosed by the present invention is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The range defined in this way can include or exclude the end values, and any combination is possible, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In the present invention, unless otherwise stated, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where both a and b are real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" are fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0034] If there is no special instruction, all embodiments and optional embodiments of the present invention can be combined with each other to form a new technical solution.

[0035] If there is no special instruction, all technical features and optional technical features of the present invention can be combined with each other to form a new technical solution.

[0036] If there is no special instruction, all steps of the present invention can be carried out in sequence or randomly, preferably in sequence. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out in sequence, or can also include steps (b) and (a) carried out in sequence. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0037] If there is no special instruction, the "including" and "comprising" mentioned in the present invention mean open-ended, and can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or can also mean only including or comprising the listed components.

[0038] Unless otherwise specified, in the present invention, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or present) and B is false (or absent); A is false (or absent) while B is true (or present); or both A and B are true (or present).

[0039] The raw material information used in the following examples is as follows: The waste glass powder and boron tail powder are derived from medical waste glass; The waste glass powder is prepared from waste glass, that is, waste glass is decontaminated, crushed, cleaned, dried and ground to obtain it; the waste glass mainly refers to waste injection bottles; Chemical composition of the waste glass powder: 70.3% SiO2, 6.2% Al2O3, 8.3% B2O3, 7.9% NaO, 1.6% K2O, 2.3% BaO, 1.1% CaO, 0.67% MgO, 0.56% ZnO and the balance impurities; The boron tail powder is derived from culture dishes, micromanipulation dishes and their lids; Chemical composition of the boron tail powder: 43.03% B2O3, 16.19% K2O, 20.07% Na2O, 7.22% Cl element, 7.72% F element, 2.96% SiO2, 0.41% Ti2O, 0.38% BaO and the balance impurities.

[0040] The various components in the raw materials of the present invention are measured by chemical analysis methods, and the test methods refer to the conventional standards in the art, such as GB / T 16537-2010, GB / T 4734-2022, GB / T 3050-2000 and GB / T 14506.12-2010, etc.

[0041] The following process converts the above glass waste into a high thermal stability frit, and this process is shown in Figure 1 .

[0042] Example 1 The method for preparing a high thermal stability frit using glass waste in this example is as follows: The raw materials for preparation are 50 parts of waste glass powder, 15 parts of boron tail powder, 6 parts of a fixing agent (zirconia, D50 = 32 μm) and 4 parts of a phosphate mineralizer (aluminum phosphate); After ball-milling the above-prepared raw materials, they are heated to 600 °C in a reducing atmosphere with a CO:N2 volume ratio of 1:5 and held for 25 min; then heated to 950 °C and melted for 45 min, and finally the melt is quenched in water. The heating rate of this process is 5 °C / min.

[0043] Halogen retention rate: 74.2% Cl, 72.8% F.

[0044] Example 2 The method for preparing the frit with high thermal stability using waste glass in this example is as follows: The preparation raw materials are 55 parts of waste glass powder, 10 parts of boron tail powder, 4.5 parts of fixing agent (2.4 parts of lanthanum oxide and 2.1 parts of zirconium oxide, D50 of the fixing agent = 40 μm), and 5 parts of phosphate mineralizer (aluminum phosphate); After ball-milling the above-mentioned preparation raw materials, heat them to 600 °C in a reducing atmosphere with a CO:N2 volume ratio of 1:5 and hold for 25 min; then heat to 950 °C and melt for 45 min, and finally quench the melt in water. The heating rate of this process is 5 °C / min.

[0045] Halogen retention rate: 71.5% Cl, 73.7% F.

[0046] Example 3 The method for preparing the frit with high thermal stability using waste glass in this example is as follows: The preparation raw materials are 50 parts of waste glass powder, 15 parts of boron tail powder, 7 parts of fixing agent (3 parts of lanthanum oxide and 4 parts of tin oxide, D50 of the fixing agent = 37 μm), and 3.5 parts of phosphate mineralizer (aluminum phosphate); After ball-milling the above-mentioned preparation raw materials, heat them to 600 °C in a reducing atmosphere with a CO:N2 volume ratio of 1:5 and hold for 25 min; introduce nitrogen, then heat to 950 °C and melt for 45 min, and finally quench the melt in water. The heating rate of this process is 5 °C / min.

[0047] Halogen retention rate: 72.1% Cl, 76.7% F.

[0048] Example 4 The method for preparing the frit with high thermal stability using waste glass in this example is as follows: The preparation raw materials are 44 parts of waste glass powder, 12 parts of boron tail powder, 6 parts of fixing agent (zirconium oxide, D50 = 32 μm), and 3 parts of phosphate mineralizer (magnesium pyrophosphate); After ball-milling the above-mentioned preparation raw materials, heat them to 600 °C in a reducing atmosphere with a CO:N2 volume ratio of 1:5 and hold for 25 min; introduce nitrogen, then heat to 950 °C and melt for 45 min, and finally quench the melt in water. The heating rate of this process is 5 °C / min.

[0049] Halogen retention rate: 73.7% Cl, 70.0% F.

[0050] Example 5 The method for preparing the frit with high thermal stability using waste glass in this example is as follows: The preparation raw materials are 50 parts of waste glass powder, 15 parts of boron tail powder, 6 parts of a fixing agent (zirconia, D50 = 32 μm), and 4 parts of a phosphate mineralizer (aluminum phosphate); After ball-milling the above-mentioned preparation raw materials, heat them to 650 °C in a reducing atmosphere with a volume ratio of CO:N2 of 1:3 and hold for 30 min; introduce nitrogen, then heat to 900 °C and melt for 50 min, and finally quench the melt in water. The heating rate of this process is 8 °C / min.

[0051] Halogen retention rate: 70.6% Cl, 69.2% F.

[0052] Example 6 The method for preparing a frit with high thermal stability using glass waste in this example is as follows: The preparation raw materials are 50 parts of waste glass powder, 15 parts of boron tail powder, 6 parts of a fixing agent (zirconia, D50 = 32 μm), and 4 parts of a phosphate mineralizer (aluminum phosphate); After ball-milling the above-mentioned preparation raw materials, heat them to 600 °C in a reducing atmosphere with a volume ratio of CO:N2 of 1:5 and hold for 30 min; introduce nitrogen, then heat to 1100 °C and melt for 20 min, and finally quench the melt in water. The heating rate of this process is 10 °C / min.

[0053] Halogen retention rate: 67.2% Cl, 63.7% F.

[0054] Comparative Example 1 The method for preparing a frit with high thermal stability using glass waste in this comparative example is as follows: The preparation raw materials are 54 parts of waste glass powder, 13 parts of boron tail powder, and 4.8 parts of a phosphate mineralizer (aluminum phosphate); After ball-milling the above-mentioned preparation raw materials, heat them to 600 °C in a reducing atmosphere with a volume ratio of CO:N2 of 1:4 and hold for 30 min; introduce nitrogen, then heat to 950 °C and melt for 40 min, and finally quench the melt in water. The heating rate of this process is 5 °C / min.

[0055] Without the fixing agent, the halogens almost completely volatilize; in addition, compared with the toughening effect brought by ZrO2 in Example 1, the strength of the frit prepared by the method of this comparative example is poor.

[0056] Halogen retention rate: 7.2% Cl, 1.6% F.

[0057] Comparative Example 2 The method for preparing a frit with high thermal stability using glass waste in this comparative example is as follows: The preparation raw materials are 50 parts of waste glass powder, 13 parts of boron tail powder, and 7 parts of a fixing agent (zirconia, D50 = 32 μm); After ball-milling the above-mentioned preparation raw materials, heat them up to 600 °C in a reducing atmosphere with a volume ratio of CO:N2 of 1:5 and hold for 25 min; introduce nitrogen, then heat up to 950 °C and melt for 40 min, and finally quench the melt in water. The heating rate of this process is 5 °C / min.

[0058] In this comparative example, the [BO3] unit cannot form a mixed network with [PO4], and a stable glass phase cannot be obtained. The frit finally prepared is prone to thermal shock cracking.

[0059] Halogen retention rate: 12.3% Cl, 5.8% F.

[0060] Comparative Example 3 The difference between this comparative example and Example 1 lies in: The method for preparing a frit with high thermal stability using glass waste in this comparative example is as follows: The preparation raw materials are 52 parts of waste glass powder, 11.7 parts of boron tail powder, 15 parts of a fixing agent (zirconia, D50 = 32 μm), and 7 parts of a phosphate mineralizer (aluminum phosphate); After ball-milling the above-mentioned preparation raw materials, heat them up to 600 °C in a reducing atmosphere with a volume ratio of CO:N2 of 1:5 and hold for 20 min; introduce nitrogen, then heat up to 950 °C and melt for 40 min, and finally quench the melt in water. The heating rate of this process is 5 °C / min.

[0061] In this comparative example, too much zirconia is added, the melt viscosity is high, which hinders the flow of the glass phase; the frit prepared has many pores and the thermal shock resistance decreases. In addition, too much aluminum phosphate added will lead to an excess of P2O5, forming a phosphorus-rich phase with B2O3, and this phase is incompatible with the silicate glass phase, resulting in phase separation.

[0062] Halogen retention rate: 62.6% Cl, 58.9% F.

[0063] Comparative Example 4 The difference between this comparative example and Example 1 lies in: The method for preparing a frit with high thermal stability using glass waste in this comparative example is as follows: The preparation raw materials are 50 parts of waste glass powder, 13.6 parts of boron tail powder, 5.2 parts of a fixing agent (zirconia, D50 = 32 μm), and 3.8 parts of a phosphate mineralizer (aluminum phosphate); After ball-milling the above-mentioned preparation raw materials, heat them up to 600 °C and hold for 20 min; then heat up to 950 °C and melt for 40 min, and finally quench the melt in water. The heating rate of this process is 5 °C / min.

[0064] During the preparation process of this embodiment, no reducing gas was introduced, and the oxidation atmosphere existing in the system caused the halogen to react to generate the corresponding acid and volatilize; moreover, a large amount of alkali metal oxide was lost, and the melt fluidity was poor.

[0065] Halogen retention rate: 19.8% Cl, 4.5% F.

[0066] Test example The high thermal stability frit prepared in the above-mentioned examples and comparative examples was subjected to a thermal shock resistance test. The test method was to take 10 high thermal stability frits in each example or comparative example as specimens, and place the 10 specimens in a high temperature furnace at 350 °C for 10 minutes and then quickly put them into ice water for rapid cooling, repeating the cycle until the surface of the specimen cracked. The following Table 1 shows the average value of the results of the 10 specimens.

[0067] 。

[0068] Unless otherwise specified, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchase or can be prepared by existing methods. The specific embodiments described above further elaborate on the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing frit with high thermal stability using glass waste, characterized in that, It includes the following steps: The preparation raw materials are reduced and sintered to obtain a high heat stability frit. By mass, the preparation raw materials include: 40 - 60 parts of waste glass powder, 10 - 20 parts of boron tailing powder, 2 - 8 parts of fixing agent, and 1 - 5 parts of phosphate mineralizer. The boron tailing powder includes the following chemical components by mass: 40 - 45% B2O3, 14 - 18% K2O, 18 - 23% Na2O, 6 - 9% Cl element, and 6 - 9% F element. The process of reduction sintering: First, heat up to 600 - 750 °C in a reducing atmosphere and keep it warm for 20 - 30 min; then heat up to 900 - 1050 °C and melt for 25 - 50 min, and finally quench the melt.

2. The method for preparing frit with high thermal stability using glass waste as claimed in claim 1, wherein, By mass, the preparation raw materials include: 40 - 55 parts of waste glass powder, 10 - 15 parts of boron tailing powder, 3 - 7 parts of fixing agent, and 2 - 5 parts of phosphate mineralizer.

3. The method for preparing frit with high thermal stability using glass waste as claimed in claim 2, wherein, The waste glass powder includes the following chemical components by mass percentage: 69 - 75% SiO2, 2 - 7% Al2O3, B2O3 ≥ 5%, 4 - 12% alkali metal oxide, and 1 - 6% alkaline earth metal oxide.

4. The method for preparing frit with high thermal stability using glass waste as claimed in claim 2, wherein The boron tailing powder includes the following chemical components by mass: 42 - 44% B2O3, 15.5 - 17% K2O, 19 - 22% Na2O, 6.5 - 8% Cl element, and 6.5 - 8% F element.

5. The method for preparing frit with high thermal stability by using glass waste according to claim 1, characterized in that, The fixing agent is at least one of zirconia, lanthanum oxide, and tin oxide.

6. The method for preparing frit with high thermal stability using glass waste as claimed in claim 1, wherein, The phosphate mineralizer is aluminum phosphate or magnesium pyrophosphate.

7. The method for preparing frit with high thermal stability using glass waste as claimed in claim 1, wherein The process of reduction sintering: First, heat up to 600 - 650 °C in a reducing atmosphere and keep it warm for 25 - 30 min; then heat up to 900 - 1000 °C and melt for 40 - 50 min, and finally quench the melt.

8. The method for preparing frit with high thermal stability using glass waste as claimed in claim 7, wherein Meet at least one of the following conditions ① - ③: ① In the reducing atmosphere, the volume ratio of CO:N2 is 1:3 - 6, preferably the volume ratio of CO:N2 is 1:4 - 5; ② The heating rate is 5 - 8 °C / min; ③ After the heat preservation, introduce nitrogen and then heat up to make the melting process carried out in a nitrogen atmosphere.

9. The method for preparing frit with high thermal stability using glass waste as claimed in claim 1, wherein Meet at least one of the following conditions ① - ②: ① The halogen retention rate of the high heat stability frit: Cl element ≥ 70%; ② The halogen retention rate of the high heat stability frit: F element ≥ 69%.

10. The method for preparing frit with high thermal stability using glass waste according to any one of claims 1 to 9, characterized in that, The number of thermal shock resistances of the high heat stability frit ≥ 30 times.

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