Separation membrane and its preparation method and application

Abstract

This application belongs to the field of membrane separation technology, specifically to a separation membrane, its preparation method, and its application. The separation membrane described herein comprises a carbon cloth containing pores; and a metal-organic framework disposed on or within the carbon cloth. The separation membrane exhibits high water flux and separation efficiency in oil-water separation, and possesses advantages such as high water permeability, high retention capacity, and long-term performance stability.

Description

Technical Field

[0001] The present application belongs to the field of membrane separation technology, and specifically relates to a separation membrane and its preparation method and application. Background Art

[0002] With the accelerating pace of urbanization and industrialization, oily wastewater pollution has a particularly serious impact on the natural environment and human health. Solving the problem of oil-water separation is a major challenge. Membrane separation technology has shown many significant advantages in oil-water separation applications. It has the advantages of low energy consumption, high separation efficiency, and simple operation. It provides a reliable, efficient, and sustainable solution for oil-water separation. However, the problem of membrane fouling still needs to be solved.

[0003] Therefore, it is crucial to develop oil-water separation membranes with both high flux and high separation efficiency. Summary of the Invention

[0004] In view of the above problems, the present application provides a separation membrane and its preparation method and application, wherein the separation membrane has high water flux and separation efficiency in oil-water separation, and has the advantages of high permeability, high retention performance and long-term performance stability.

[0005] In a first aspect, the present application provides a separation membrane, the separation membrane comprising a carbon cloth, the carbon cloth comprising pores;

[0006] A metal organic framework disposed on the surface or inside of the carbon cloth;

[0007] The metal organic framework includes MOF-303.

[0008] Metal-organic frameworks (MOFs) are three-dimensional materials composed of metal ions or ion clusters chemically linked to organic ligands. MOFs possess exceptionally high porosity, large surface area, highly tunable pore size, well-defined molecular adsorption sites, and a regular geometric shape. They can be used to modify substrates such as stainless steel mesh, fiber cloth, and filter membranes, and are therefore suitable for treating oily wastewater. However, their lack of chemical stability makes the application of MOF membranes in oil-water separation a challenge.

[0009] In the technical solution of the embodiment of the present application, carbon cloth and metal-organic framework are used in combination. Among them, carbon cloth, as a typical carbon-based material, has excellent liquid permeability due to its porous structure characteristics. Its excellent mechanical properties enable it to be flexibly folded and bent during use without destroying its structure. It also has the corrosion resistance common to carbon-based materials. These characteristics greatly improve its recycling efficiency. These advantages make it an ideal substrate material for oil-water separation membranes; the metal-organic framework exhibits significant characteristics such as high specific surface area, high porosity, structural diversity and high adjustability. Its pore size and pore morphology can be precisely controlled by adjusting the length of the organic ligands and their functional groups during the synthesis process. In addition, it also exhibits excellent chemical stability and thermal stability. These characteristics further broaden its potential in oil-containing wastewater treatment. Therefore, the obtained separation membrane has high water flux and separation efficiency in oil-water separation, and has the advantages of high permeability, high retention performance and long-term performance stability.

[0010] In the technical solution of the embodiments of this application, MOF-303 is selected as the metal-organic framework. Compared with other MOF materials, MOF-303 exhibits extremely high water stability and excellent water absorption properties due to its three-dimensional framework composed of hydrophilic one-dimensional diamond-like channels, which helps form an anti-fouling hydration layer. In addition, MOF-303 is prepared using low-cost metal and ligand resources and follows a simple and environmentally friendly process, which is more in line with the green concept. Therefore, MOF-303 was selected.

[0011] In some embodiments, the area of ​​the carbon cloth is 9 cm 2 The mass of the metal organic framework is 0.01-0.05 g, for example, 0.02 g, 0.03 g, 0.04 g, etc.

[0012] In the technical solution of the embodiment of the present application, the area of ​​the carbon cloth is 9 cm 2 The reason for this is that the above technical solution shows the loading amount of the metal-organic framework on the carbon cloth per unit area. Setting it within the above range strikes a balance between porosity, loading amount, and interface bonding. Too much metal-organic framework will lead to pore blockage, reduced permeability, and deterioration of mechanical strength. Too little metal-organic framework will lead to insufficient hydrophilicity and pore size control, resulting in low separation efficiency.

[0013] In the present application, MOF-303 is an aluminum-based metal organic framework material, the coordination metal is aluminum, and the organic ligand is 3,5-pyrazoledicarboxylic acid.

[0014] In the technical solution of the implementation mode of the present application, aluminum is selected as the coordinating metal. Compared with other metals, when combined with carbon cloth, it has the advantages of high stability and water resistance, environmental friendliness and low cost, and easy formation of a rigid skeleton and surface hydroxyl groups. Therefore, aluminum is selected as the coordinating metal.

[0015] The organic ligand is 3,5-pyrazoledicarboxylic acid. Compared with other organic ligands, when combined with carbon cloth, its advantage is that the dicarboxylic acid group provides strong coordination sites and improves hydrophilicity. The pyrazole ring enhances the stability of the MOF framework while its hydrophobic part can synergistically regulate the surface energy to achieve "hydrophilic-oleophobic" selectivity. Therefore, 3,5-pyrazoledicarboxylic acid was selected as the organic ligand.

[0016] In some embodiments, the porosity of the separation membrane is 60%-80%, for example, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, etc.

[0017] In a second aspect, the present application provides a method for preparing a separation membrane, the method comprising the following steps:

[0018] The carbon cloth is subjected to acid treatment, and then a metal organic framework is in situ grown on the surface of the carbon cloth to obtain the separation membrane;

[0019] The metal organic framework includes MOF-303.

[0020] In the technical solution of this embodiment, the carbon cloth is first acid-treated to create more adsorption sites, facilitating the in-situ growth of a metal-organic framework on its surface. Compared to other treatments, acid treatment offers advantages in cleaning the surface and removing impurities; introducing oxygen-containing functional groups; regulating surface roughness and pore structure; and enhancing the uniformity of material growth. Therefore, the preparation method described herein produces a membrane capable of effective oil-water separation in a simple manner.

[0021] In some embodiments, the acid used in the acid treatment includes any one of hydrochloric acid, nitric acid, or sulfuric acid, or a combination of at least two thereof.

[0022] In some embodiments, the acid treatment temperature is 5-45°C, optionally room temperature, such as 5°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, etc.; and / or;

[0023] The acid treatment time is 15-20 h, for example, 16 h, 17 h, 18 h, 19 h, etc.

[0024] In some embodiments, the acid treatment includes washing with acetone, anhydrous ethanol, or deionized water; and / or;

[0025] The acid treatment further includes soaking in an alcohol solvent.

[0026] As an example, the alcohol solvent includes ethanol and / or methanol.

[0027] In some embodiments, the in situ growth comprises immersing the carbon arrangement in a metal organic framework precursor solution and then performing a heating treatment to complete the in situ growth;

[0028] The metal organic framework precursor solution comprises a metal salt, an organic ligand, a base and a solvent.

[0029] As an example, the raw materials for preparing the MOF-303 include metal salts (such as aluminum chloride hexahydrate) and organic ligands (such as 3,5-pyrazoledicarboxylic acid monohydrate).

[0030] As an example, the mass ratio of the metal salt to the organic ligand is 1:(0.1-10), wherein 0.1-10 can be 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, etc.

[0031] As an example, the preparation raw materials further include alkali, for example, the alkali may include any one of sodium hydroxide, potassium hydroxide or ammonia water, or a combination of at least two of them.

[0032] As an example, the mass ratio of the metal salt to the base is 1:(0.1-5), wherein 0.1-5 can be 0.5, 1, 2, 3, 4, etc.

[0033] As an example, the preparation raw material further includes a solvent, for example, the solvent may include water.

[0034] In some embodiments, the soaking time is 5-15 min, such as 6 min, 8 min, 10 min, 12 min, 14 min, etc.; and / or;

[0035] The temperature of the heating treatment is 80-120°C, such as 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, etc.; and / or;

[0036] The heating treatment time is 5-15 h, for example, 6 h, 8 h, 10 h, 12 h, 14 h, etc.

[0037] In the technical solutions of the embodiments of this application, the heating temperature is within the above range. The reason is that: high temperatures can compromise the membrane's permeability, mechanical strength, and oleophobicity, potentially leading to MOF structural collapse; low temperatures can lead to low MOF crystallinity, insufficient loading, an imbalance in hydrophilicity and oleophobicity, and low separation efficiency.

[0038] The heating treatment time is within the above range. The reason is that: combining temperature with process optimization achieves efficient MOF-303 loading and high-performance separation membrane preparation; longer heating times can lead to excessive MOF growth, pore blockage, and structural damage, sacrificing separation efficiency and mechanical strength; shorter heating times can lead to incomplete MOF crystallization, insufficient loading, an imbalance in hydrophilic-oleophobic properties, and low separation efficiency.

[0039] In some embodiments, the preparation method comprises the following steps:

[0040] (1) Preparation of metal organic framework precursor solution: 3,5-pyrazoledicarboxylic acid monohydrate, aluminum chloride hexahydrate and sodium hydroxide were dissolved in water and ultrasonically homogenized to obtain a uniformly mixed metal organic framework precursor solution.

[0041] (2) Treating the carbon cloth: ultrasonically clean the carbon cloth in acetone, anhydrous ethanol, and deionized water, and then soak it in an acid (e.g., hydrochloric acid, etc., with a concentration of 2-4 M) at 5-45°C (e.g., room temperature) for 15-20 h (e.g., 18 h, etc.) to complete the acid treatment; then soak the carbon cloth in an alcohol solvent.

[0042] (3) Preparation of separation membrane: The carbon obtained in step (2) is placed in the metal organic framework precursor solution obtained in step (1), soaked for 5-15 minutes, and then reacted at 80-120°C for 5-15 hours. After the reaction is completed and cooled to room temperature, it is washed and dried to obtain the separation membrane.

[0043] In a third aspect, the present application provides a separation membrane described in the first aspect, or a separation membrane obtained by the preparation method described in the second aspect, and its use in oil-water separation.

[0044] Compared with the prior art, this application has at least the following advantages:

[0045] (1) The separation membrane described in the present application has excellent oil-water separation performance and long-term stability; specifically, the separation membrane has significant hydrophilicity and underwater oleophobicity, high pure water flux, high separation efficiency for different oil-water mixtures, excellent stability, and can remain stable after multiple cycles of filtration, that is, it has the advantages of high water permeability, high retention performance and long-term performance stability.

[0046] (2) The preparation method described in this application has the advantages of being simple to operate and can be mass-produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference numerals are used throughout the drawings to denote the same components. In the drawings:

[0048] Figure 1 Schematic diagram of the preparation method of some embodiments of the present application;

[0049] Among them, 1-raw materials of metal organic framework precursor solution; 2-carbon cloth; 3-metal organic framework precursor solution; 4-separation membrane;

[0050] Figure 2 This is a scanning electron microscope image of the carbon cloth of Comparative Example 1 at a scale of 5 μm;

[0051] Figure 3 This is a scanning electron microscope image of the carbon cloth of Comparative Example 1 at a scale of 2 μm;

[0052] Figure 4 This is a scanning electron microscope image of the carbon cloth of Comparative Example 1 at a scale of 1 μm;

[0053] Figure 5 is a scanning electron microscope image of the separation membrane of Example 1 at a scale of 5 μm;

[0054] Figure 6 is a scanning electron microscope image of the separation membrane of Example 1 at a scale of 2 μm;

[0055] Figure 7 is a scanning electron microscope image of the separation membrane of Example 1 at a scale of 1 μm;

[0056] Figure 8 Element mapping diagram of the separation membrane of Example 1, element is C;

[0057] Figure 9 Element mapping diagram of the separation membrane of Example 1, element is O;

[0058] Figure 10 Element mapping diagram of the separation membrane of Example 1, element is Al;

[0059] Figure 11 This is a comparison diagram of the water contact angles of the carbon cloth of Comparative Example 1 and the separation membrane of Example 1;

[0060] Figure 12 This is a comparison of the underwater oil contact angles of the carbon cloth of Comparative Example 1 and the separation membrane of Example 1;

[0061] Figure 13Graph showing the flux and rejection of the separation membrane of Example 1 for different oil / water mixtures (n-hexane, n-heptane, petroleum ether, gasoline, and edible oil);

[0062] Figure 14 This is a graph showing the stability of the separation membrane of Example 1 after 50 cycles of n-hexane / water mixture. DETAILED DESCRIPTION

[0063] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0064] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0065] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0066] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0067] The "ranges" disclosed herein are defined in terms of lower and upper limits, where a given range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges defined in this manner can be inclusive or exclusive of the end values ​​and can be combined arbitrarily, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise indicated, the numerical range "ab" is a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "2-10" indicates that all real numbers between "2-10" are listed herein, and "2-10" is merely an abbreviation for the combination of these values. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0068] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists, A and B exist at the same time, and B exists. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0069] The composite membrane and its preparation method in this application will be further described below with reference to specific examples. Unless otherwise specified, the materials and reagents used in the following examples can be commercially available products without limitation.

[0070] Example 1

[0071] This embodiment provides a separation membrane having a porosity of 70%. The separation membrane specifically comprises a carbon cloth having holes.

[0072] A metal organic framework (MOF-303) is arranged on the surface or inside of the carbon cloth.

[0073] The area of ​​the carbon cloth is 9 cm 2 The mass of the metal-organic framework is 0.02 g.

[0074] The separation membrane is obtained by the following preparation method, the flow diagram of the preparation method is as follows Figure 1 As shown, the specific steps include:

[0075] (1) Preparation of metal organic framework precursor solution: The raw material 1 of the metal organic framework precursor solution was added to a 50 mL beaker, specifically, 0.22 g of 3,5-pyrazoledicarboxylic acid monohydrate, 0.30 g of aluminum chloride hexahydrate and 0.100 g of sodium hydroxide were added in sequence, the solid mixture was dissolved in 45.0 g of deionized water, and ultrasonically homogenized, specifically, at room temperature, the solution was placed on a magnetic stirrer at a speed of 100 rpm and stirred continuously for 30 min to obtain a uniformly mixed metal organic framework precursor solution 3.

[0076] (2) Treatment of carbon cloth: Carbon cloth 2 (purchased from Taiwan Carbon Energy Technology Co., Ltd., brand W0S1011) was cut into 3 cm × 3 cm square cloths, and then placed in acetone, anhydrous ethanol and deionized water for ultrasonic cleaning in sequence. The ultrasonic conditions were 20 ° C for 30 min; then, it was soaked in 3 M hydrochloric acid at room temperature for 18 h to complete the acid treatment; and the carbon cloth was then soaked in anhydrous ethanol for 10 min.

[0077] (3) Preparation of separation membrane: The carbon cloth obtained in step (2) was placed in the metal organic framework precursor solution obtained in step (1) and soaked for 10 min. The mixture was then transferred to a polytetrafluoroethylene-lined reactor and reacted continuously for 12 h in a forced air drying oven set at 100°C. After the reaction was completed and cooled to room temperature, the carbon cloth covering the product was removed and washed three times with ultrapure water and anhydrous ethanol respectively to remove loose powder on the membrane surface and residues in the membrane channels. The mixture was dried overnight at 60°C in a forced air drying oven to obtain the separation membrane 4.

[0078] Comparative Example 1

[0079] This comparative example provides a carbon cloth without in-situ growth of a metal organic framework.

[0080] Performance Testing

[0081] (1) Morphology and elemental characteristics

[0082] Taking the separation membrane of Example 1 and the carbon cloth of Comparative Example 1 as examples, the morphology was observed using a scanning electron microscope. The results showed that: Figure 2 、 Figure 3 and Figure 4 In the figure, the carbon cloth of Comparative Example 1 is observed under different scales. Its surface is smooth and has evenly distributed root-like fibers. Figure 5 、 Figure 6 and Figure 7 In the figure, the separation membrane of Example 1 is observed under different scales. Its surface is rough. After further magnification, it can be clearly seen that compared with the smoother original carbon cloth membrane, a large number of MOF-303 crystal particles with a rectangular structure are evenly distributed on its surface, and the successful coverage of MOF-303 particles greatly improves the roughness of the separation membrane.

[0083] Taking the separation membrane of Example 1 as an example, the elemental mapping (EDX) diagram is as follows: Figure 8 、 Figure 9 and Figure 10 As shown in the figure, the C, O and Al elements in the separation membrane are evenly distributed on the carbon cloth, indicating that MOF-303 is successfully grown in situ on the carbon cloth and is evenly distributed.

[0084] (2) Hydrophilicity

[0085] Taking the carbon cloth of Comparative Example 1 and the separation membrane of Example 1 as examples, the hydrophilicity of the separation membranes was investigated by conducting water contact angle (WCA) and underwater oil contact angle (UOCA) tests. The specific testing methods are as follows: For water contact angle measurement, the membrane was placed horizontally on a sample table, and ultrapure water droplets were dropped onto the dry sample surface. The droplet morphology was captured using a high-speed camera to read the water contact angle. For underwater oil contact angle measurement, the membrane was fixed horizontally on the bottom of the water, and dichloromethane droplets were injected using a syringe. The droplet morphology was captured using a high-speed camera to read the underwater oil contact angle.

[0086] like Figure 11 As shown, a comparison image of the water contact angles of the carbon cloth of Comparative Example 1 and the separation membrane of Example 1 is shown. When a water drop contacts the surface of the carbon cloth, it is bounced back, indicating that the carbon cloth has superhydrophobic properties; and when a water drop contacts the surface of the separation membrane, it is instantly absorbed, indicating that the separation membrane of the present application has superhydrophilic properties.

[0087] like Figure 12 As shown, a comparison image of the underwater oil contact angles of the carbon cloth of Comparative Example 1 and the separation membrane of Example 1 is shown. When the oil droplet contacts the surface of the carbon cloth, it is quickly absorbed, indicating that the carbon cloth has the property of underwater oleophilicity; and when the oil droplet contacts the surface of the separation membrane, it is adsorbed on it and exhibits an underwater oil contact angle of 155°, indicating that the separation membrane of the present application has the property of underwater super oleophobicity.

[0088] In summary, the separation membrane of the present application has potential value in the field of oil-water separation.

[0089] (3) Separation performance

[0090] The separation membrane was tested for oil-water mixture separation. The specific test process was as follows: a customized effective filtration area of ​​1.78 cm 2 A gravity-driven filtration process was performed using a filtration device. Oil Red O was used to stain different oils red, and methylene blue was used to stain deionized water blue. Equal volumes of the two solutions were weighed and mixed to create simulated oil-water mixtures. The separation performance of the membrane was measured by pouring the oil-water mixture directly onto the membrane surface.

[0091] Taking Example 1 as an example, according to Figure 13The test results shown in the figure show that the water flux of the separation membrane has been greatly improved due to the successful growth of MOF-303. Specifically, the separation efficiency of the separation membrane for five different oil-water mixtures, including n-hexane, n-heptane, petroleum ether, gasoline, and cooking oil, exceeded 99%, and the maximum flux reached 2.66×10 5 L·m -2 ·h -1 The water flux of edible oil decreased slightly due to its high viscosity. The above results show that the separation membrane has high efficiency in oil-water separation for various oil-water mixtures.

[0092] (4) Stability

[0093] The stability of the separation membrane was tested. The specific test process was to use manual circulating filtration to perform the test, following the previously described method for testing membrane separation performance.

[0094] Taking Example 1 as an example, a n-hexane / water-oil-water mixture circulation test was performed on it. Figure 14 The test results shown in the figure show that the carbon cloth MOF composite membrane still maintains high flux and separation efficiency after 50 cycles. This feature demonstrates that the carbon cloth MOF composite membrane has important potential for practical applications in oily wastewater treatment.

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. Application of a separation membrane in oil-water separation, characterized in that: The separation membrane includes carbon cloth, and the carbon cloth includes pores; A metal organic framework disposed on the surface or inside of the carbon cloth; The metal organic framework includes MOF-303.

2. The use according to claim 1, characterized in that The area of ​​the carbon cloth is 9 cm 2 The mass of the metal organic framework is 0.01-0.05 g.

3. The use according to claim 1, characterized in that The porosity of the separation membrane is 60%-80%.

4. The use according to claim 1, characterized in that The method for preparing the separation membrane comprises the following steps: The carbon cloth is subjected to acid treatment, and then a metal organic framework is in situ grown on the surface of the carbon cloth to obtain the separation membrane; The metal organic framework includes MOF-303.

5. The use according to claim 4, characterized in that The acid used in the acid treatment includes any one of hydrochloric acid, nitric acid or sulfuric acid, or a combination of at least two of them.

6. The use according to claim 4, characterized in that The temperature of the acid treatment is 5-45°C; and / or; The acid treatment time is 15-20 h.

7. The use according to claim 4, characterized in that The acid treatment includes cleaning with acetone, anhydrous ethanol and deionized water; The acid treatment further includes soaking in an alcohol solvent.

8. The use according to claim 4, characterized in that The in-situ growth includes immersing the carbon arrangement in a metal organic framework precursor solution and then performing a heating treatment to complete the in-situ growth; The metal organic framework precursor solution comprises a metal salt, an organic ligand, a base and a solvent.

9. The use according to claim 8, characterized in that The soaking time is 5-15 min; and / or; The temperature of the heating treatment is 80-120°C; and / or; The heating treatment time is 5-15 h.

Images