CN110655330A

CN110655330A - Preparation method of phenolic resin ordered mesoporous film based on rapid thermal treatment

Info

Publication number: CN110655330A
Application number: CN201911035325.2A
Authority: CN
Inventors: 赵镍; 黄文超; 齐福刚; 刘应都; 欧阳晓平
Original assignee: Xiangtan University
Current assignee: Xiangtan University
Priority date: 2019-10-29
Filing date: 2019-10-29
Publication date: 2020-01-07
Anticipated expiration: 2039-10-29
Also published as: CN110655330B

Abstract

The invention discloses a preparation method of a phenolic resin ordered mesoporous film based on rapid thermal treatment, which comprises the following steps of a, obtaining a phenolic resin solution and a block copolymer solution; b. mixing the phenolic resin solution obtained in the step a with the block copolymer solution to prepare a phenolic resin precursor solution containing the block copolymer; c. and c, mechanically stirring the phenolic resin precursor solution containing the block copolymer prepared in the step b, coating a film on a hydrophilized substrate, performing aging treatment at the temperature of 140 ℃ for 23-25 hours at 100-.

Description

Preparation method of phenolic resin ordered mesoporous film based on rapid thermal treatment

Technical Field

The invention relates to a film preparation method in the field of materials, in particular to a preparation method of a phenolic resin ordered mesoporous film based on rapid thermal treatment.

Background

The mesoporous material is a porous solid material with the pore size of 2-50 nanometers. Because of the characteristics of larger specific surface area, larger pore volume, better thermal stability, continuous and adjustable pore size, easy modification of the pore surface and the like, the porous material is valued by people in the aspects of chemistry, life science, material science, biology and the like. The mesoporous film does not have the non-directional disadvantage of the traditional powder mesoporous material, so that the mesoporous film has wide application in the aspects of separation membranes, optics, microelectronic components, photoelectric equipment arrangement and the like.

Rapid Thermal Processing (RTP) refers to a Thermal Processing method with a very fast temperature rise rate and a short heat preservation time, and the temperature rise rate can reach 10-100 ℃/second. The rapid heat treatment has the advantages of easily controlled heat source, high temperature rise speed, convenient sample introduction and the like, and an infrared halogen lamp or a resistance rod is adopted for heating. The current and power are high during heating. Can greatly save the heat treatment time and reduce the production cost.

The traditional inorganic material for preparing the mesoporous film has the following defects: difficult processing, no high temperature resistance of homopolymer films, easy softening, overlong preparation period and the like. Therefore, it is very important to select a material that has good properties and is easy to process. The phenolic resin can realize the controllability of molecular weight and can form polymers with narrower molecular weight distribution, so that the preparation of the ordered mesoporous film by adopting the phenolic resin has important significance in both theoretical research and practical application. The conventional methods for preparing the phenolic resin mesoporous film comprise a hard template method, a pulling method and the like, but the methods respectively have the limitations of difficult template agent removal, long heat treatment processing period and the like, and the template agent can be removed in a short time by adopting the method. Meanwhile, the phenolic resin mesoporous film is prepared by adopting rapid thermal treatment, so that the preparation period of the phenolic resin mesoporous film can be greatly shortened, the cost is reduced, the deformation and collapse rate of the mesopores is low, and the utilization efficiency of the mesopores is increased.

Disclosure of Invention

Aiming at the defects of the prior art, the technical problems to be solved by the invention are as follows: how to provide a method for preparing the phenolic resin ordered mesoporous film based on rapid thermal treatment, which has simple process method, short processing time and can more thoroughly remove the template agent.

In order to solve the technical problems, the invention adopts the following technical scheme:

a preparation method of a phenolic resin ordered mesoporous film based on rapid thermal treatment is characterized by comprising the following steps of a, obtaining a phenolic resin solution and a block copolymer solution; b. mixing the phenolic resin solution obtained in the step a with the block copolymer solution to prepare a phenolic resin precursor solution containing the block copolymer; c. and c, mechanically stirring the phenolic resin precursor solution containing the block copolymer prepared in the step b, coating a film on a hydrophilized substrate, performing aging treatment at the temperature of 100-140 ℃ for 23-25 hours (preferably 24 hours), annealing under the atmosphere protection condition, wherein the annealing process comprises multiple times of cyclic rapid heat treatment and temperature reduction heat treatment in turn, heating to 390-410 ℃ for rapid heat treatment, cooling to 240-260 ℃ for temperature reduction heat treatment, cooling to 250 ℃ for temperature reduction heat treatment, the temperature rise and fall rate of the rapid heat treatment is 5-30 ℃/s, and the heat preservation time of each rapid heat treatment is 25-35 seconds (preferably 30 seconds), so as to prepare the phenolic resin ordered mesoporous film.

Thus, compared with the prior art, the method comprises the steps of mixing phenolic resin with block copolymer to form phenolic resin precursor solution containing the block copolymer, coating a film on a hydrophilized substrate to form a mesoporous structure, stabilizing the mesoporous structure through multiple cycles of 'rapid heat treatment-cooling-rapid heat treatment' and removing the template agent block copolymer Pluronic P123, thereby obtaining the mesoporous structure only containing the phenolic resin.

High molecular weight polymer having a glass transition temperature (T)_g) The glass state is formed, the polymer is hard and brittle in the glass state, the tensile rate of the high molecular chain of the glass state is very low, and the polymer can be broken to a very small extent; when the temperature is higher than the glass transition temperature, the high molecular polymer is gradually softened and enters a high elastic state; raising the temperature above the polymerWhen the melting point of the polymer is higher than the melting point of the polymer, the high molecular polymer is melted and generates viscous flow; when the temperature is further raised, the decomposition point of the high molecular weight polymer is exceeded, and the high molecular weight polymer is decomposed.

The method controls the temperature to be higher than the decomposition temperature of the pluronic P123 (the decomposition temperature range of the pluronic P123 is approximately 150-242 ℃) and higher than the glass transition temperature of the phenolic resin (the glass transition temperature of the phenolic resin is a range value and is in a range of 116-242 ℃) through multiple cycles of 'rapid heat treatment-cooling-rapid heat treatment', and the temperature is lower than the carbonization temperature of the phenolic resin (the carbonization degree of the phenolic resin is smaller below 400 ℃); because the heat preservation time is short, the mesoporous film carbon skeleton is not decomposed, and through repeated circulation, the Pluronic P123 is thoroughly decomposed, the deformation of the mesoporous film carbon skeleton is reduced, and the excessive carbonization of the phenolic resin is avoided.

The rapid heat treatment has a high heating rate (the heating rate can reach 10-100 ℃/second), can save a large amount of processing time compared with the traditional heating process (1 ℃/minute), saves time cost and economic cost; because the phenolic resin can generate viscous flow when the duration time is too long at a higher temperature (about 400 ℃), the heat treatment heat preservation time is controlled to be about 30 seconds, and the decomposition process of the template agent pluronic P123 is always carried out through repeated circulation of heating and cooling of multiple times of heat treatment, and the viscous flow of the phenolic resin is blocked, so that the template agent pluronic P123 can be removed, the order degree of mesopores can be ensured, and the collapse degree of the mesopores in the removal process of the template agent can be controlled.

Compared with the prior art, the method has the advantages of simple process, short processing time, low cost and good template agent removing effect. The test result shows that: the phenolic resin mesoporous film prepared by the method is of a hexagonal stacking ordered structure.

Preferably, the temperature is raised to 400 ℃ for rapid heat treatment, and the temperature is lowered to 250 ℃ for temperature-lowering heat treatment.

Therefore, the temperature selection of the rapid heat treatment and the cooling heat treatment is more reasonable, and the quality of the prepared phenolic resin ordered mesoporous film is better.

As optimization, the phenolic resin solution is prepared in the step a by adopting the following steps; s1, mixing phenol and a sodium hydroxide solution at the temperature of 45-50 ℃, stirring and melting, and dropwise adding a formaldehyde solution at the temperature of 45-50 ℃ to obtain a phenolic aldehyde mixed solution; s2, stirring the phenolic aldehyde mixed solution obtained in the step S1 at the temperature of 50-60 ℃ for 1 hour, cooling to room temperature, and adjusting the pH of the solution to be neutral to obtain a neutral phenolic aldehyde mixed solution; and S3, performing rotary evaporation on the neutral phenolic mixed solution obtained in the step S2 to remove water, and then dissolving to obtain a phenolic resin solution.

Thus, the prepared phenolic resin solution has better performance.

In step S1, the sodium hydroxide solution is preferably 25% by mass and the formaldehyde solution is preferably 37% by mass.

In step S3, the solvent of the phenolic resin solution is absolute ethyl alcohol. Thus, the ethanol is a good solvent for the phenolic resin, can well dissolve the phenolic resin, and can make sodium chloride (NaCl) generated by the neutralization of hydrochloric acid and sodium hydroxide precipitate; the absolute ethanol as a solvent is easily removed during the subsequent spin coating and heat treatment.

Preferably, the block copolymer solution is prepared by dissolving the block copolymer Pluronic P123 in the step a.

Preferably, the solvent of the block copolymer solution is absolute ethyl alcohol. Thus, ethanol is a good solvent for the polypropylene oxide block of the block copolymer pluronic P123 and a poor solvent for the polyethylene oxide block, so that the block copolymer can be microphase separated; and the absolute ethyl alcohol as a solvent is easily removed during the subsequent spin coating and heat treatment processes.

For optimization, the number average molecular weight of the block copolymer pluronic P123 is 5800; the mass fraction of the block copolymer solution is in the range of 4.5 to 5%.

In the step c, the glass substrate is firstly immersed into a mixed solution of concentrated sulfuric acid and aqueous hydrogen peroxide solution with the volume ratio of 7:3, then the mixed solution is heated to 60-100 ℃ and is kept for 30-60 minutes, and the hydrophilized substrate with the surface hydrophilization treatment is obtained. Therefore, game residues and dust on the surface of the substrate can be washed away, and the substrate is cleaner; meanwhile, the phenolic resin is easier to spin-coat on the substrate.

Preferably, spin coating is used to coat the hydrophilized substrate with a film in step c. Thus, the coating on the hydrophilized substrate by adopting the spin coating method can ensure that the thickness of the coating is more uniform, and the quality of the phenolic resin ordered mesoporous film is improved.

As optimization, the times of repeatedly heating and cooling are 5-50 times.

Thus, the carbon skeleton of the mesoporous film is partially decomposed due to short heat preservation time; through repeated circulation, the decomposition of the pluronic P123 is thorough, and the deformation of the mesoporous film carbon skeleton is reduced. The times of repeated heating and cooling and the time of each heat preservation are more reasonable, and the growth of the preparation time is shortened; the template agent P123 is removed, the order degree of mesopores can be ensured, and the collapse degree of the mesopores in the template agent removing process can be controlled.

Preferably, the protective gas used for atmosphere protection is argon.

Thus, the argon is used as the protective gas for atmosphere protection, so that the high polymer material can be prevented from being burnt at high temperature and carbonized under the environment containing oxygen; compared with the adoption of various mixed shielding gases and the like, the argon gas adopted has the advantages of economy, safety and good protection effect.

Drawings

In order to make the object, technical scheme and beneficial effect of the invention more clear, the invention provides the following drawings for explanation:

FIG. 1 is a small-angle X-ray diffraction one-dimensional diagram of a mesoporous phenolic resin film prepared in example 1 of the present invention.

FIG. 2 is a grazing incidence small-angle X-ray scattering two-dimensional diagram of the mesoporous phenolic resin film prepared in example 1 of the present invention.

Fig. 3 is a small-angle X-ray diffraction one-dimensional diagram of the phenolic resin mesoporous thin film prepared in example 2 of the present invention.

FIG. 4 is a grazing incidence small-angle X-ray scattering two-dimensional graph of the mesoporous phenolic resin film prepared in example 2 of the present invention.

FIG. 5 is a grazing incidence small-angle X-ray scattering two-dimensional graph of the mesoporous phenolic resin film prepared in example 3 of the present invention.

FIG. 6 is a grazing incidence small-angle X-ray scattering two-dimensional graph of the mesoporous phenolic resin film prepared in example 4 of the present invention.

FIG. 7 is a solid nuclear magnetic resonance spectrum of the mesoporous phenolic resin film prepared by the present invention.

FIG. 8 is a solid NMR spectrum of a mesoporous phenolic resin film prepared by a conventional process in accordance with the present invention.

Fig. 9 shows that the phenolic resin mesoporous film sample prepared in example 4 of the present invention is in two cases: 1. only aging; 2. and comparing the test results of small-angle X-ray diffraction after aging, performing circulating annealing for 25 times.

Fig. 10 is a comparison of the small-angle X-ray diffraction test result of the phenolic resin mesoporous film sample prepared in example 4 of the present invention after being cyclically annealed for 25 times and the small-angle X-ray diffraction test result of the phenolic resin mesoporous film sample prepared in the conventional process.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

Reference will now be made in detail to the preferred embodiments of the present invention

The implementation case is as follows:

example 1

A preparation method of a phenolic resin ordered mesoporous film based on rapid thermal treatment comprises the following steps of a, obtaining a phenolic resin solution and a block copolymer solution; b. mixing the phenolic resin solution obtained in the step a with the block copolymer solution to prepare a phenolic resin precursor solution containing the block copolymer; c. c, mechanically stirring the phenolic resin precursor solution containing the block copolymer prepared in the step b for 10 minutes, coating a film on a hydrophilized substrate, performing aging treatment at 120 ℃ for 24 hours, and annealing under the atmosphere protection condition, wherein the annealing process is to perform rapid heat treatment and cooling heat treatment in turn for multiple cycles; and preparing the phenolic resin ordered mesoporous film.

Wherein, the phenolic resin solution is prepared by the following steps in the step a;

s1, mixing phenol and a sodium hydroxide solution (the mass fraction is 25%) at the temperature of 45 ℃, stirring and melting, and then dropwise adding a formaldehyde solution at the temperature of 50 ℃, wherein the mass fraction of the formaldehyde solution is 37%, so as to obtain a phenolic aldehyde mixed solution;

s2, stirring the phenolic aldehyde mixed solution obtained in the step S1 at the temperature of 60 ℃ for 1 hour, cooling to room temperature, and adjusting the pH of the solution to be neutral to obtain a neutral phenolic aldehyde mixed solution;

and S3, performing rotary evaporation on the neutral phenolic aldehyde mixed solution obtained in the step S2 to remove water, and dissolving the neutral phenolic aldehyde mixed solution in absolute ethyl alcohol to obtain a phenolic resin solution.

Wherein, 1g of the block copolymer Pluronic P123 is dissolved in 19g of absolute ethanol in step a. A block copolymer solution with a mass fraction of 5% was obtained. Wherein the number average molecular weight of the block copolymer Plannik P123 is 5800; the mass fraction of the block copolymer solution obtained is in the range of 4.5 to 5%.

Wherein the preparation process of the hydrophilized substrate in the step c comprises the following steps: the glass substrate is immersed into a mixed solution of concentrated sulfuric acid (with the mass fraction of 98%) and aqueous hydrogen peroxide (with the mass fraction of 30%) in a volume ratio of 7:3, and then the liquid is heated to 80 ℃ and kept for 40 minutes, so that the glass substrate with the surface subjected to hydrophilization treatment is obtained.

Wherein, in the step c, a spin coating method is adopted to coat a film on the hydrophilized substrate. Specifically, in the spin coating, the spin coating apparatus spin-coats the hydrophilized glass substrate at a rotation speed of 3000 rpm for 60 seconds.

Wherein, during annealing in the step c, the temperature is increased to 400 ℃ at the heating rate of 15 ℃/second, the temperature is preserved for 30 seconds for the first time, and the temperature is reduced to 250 ℃; then, 10 times of repeated heating and cooling treatments are carried out between the temperature ranges of 250 ℃ and 400 ℃, wherein the heating rate is 15 ℃/second and the heat preservation time is 30 seconds.

The sample treated in example 1 is subjected to a small angle X-ray diffraction test and a grazing incidence small angle X-ray scattering test, as shown in fig. 1, a (100) peak appears near a 2 theta angle of about 1.3 degrees, the peak is very sharp, and the size of a mesoporous pore channel is approximately 6.1 nm calculated by a bragg equation 2dsin theta = lambda (wherein d is a interplanar distance, theta is a diffraction angle, and lambda is an incident X-ray wavelength); as shown in fig. 2, a two-dimensional hexagonal lattice of spots appears in the figure.

Example 2

Example 2 is similar to example 1, except that there is a difference in the parameters during annealing in step c, specifically, in example 2, the temperature rise rate for the first temperature rise is 25 ℃/sec, and then the temperature rise and decrease processes are repeated 15 times, and the temperature rise rate for each time is 25 ℃/sec. The remaining steps and parameters were the same as in example 1.

The samples treated in example 2 were subjected to a small angle X-ray diffraction test and a grazing incidence small angle X-ray scattering test. As shown in fig. 3, a (100) peak appears near an angle 2 θ of about 1.3 °, the peak is sharp, and the size of the mesoporous channel is approximately 6.3 nm as calculated by bragg equation 2dsin θ = λ (where d is the interplanar spacing, θ is the diffraction angle, and λ is the incident X-ray wavelength); as shown in fig. 4, a two-dimensional hexagonal lattice of spots appears in the figure.

Example 3

This example 3 is similar to example 1 except that the mass of the absolute ethanol in step a is 20g and the mass fraction of the resulting block copolymer solution is 4.76%;

in the step b, the aging treatment temperature is 140 ℃;

and c, distinguishing parameters during annealing in the step c, wherein the heating rate of the first heating is 25 ℃/s, and then, the heating and cooling treatment is repeated for 20 times, and the heating rate of each time is 25 ℃/s. The remaining steps and parameters were the same as in example 1.

And carrying out small-angle X-ray diffraction test and grazing incidence small-angle X-ray scattering test on the processed sample. As shown in fig. 5, spots of a two-dimensional hexagonal lattice appear in the figure.

Example 4

This example 4 is similar to example 1 except that the mass of the absolute ethanol in step a is 20g and the mass fraction of the resulting block copolymer solution is 4.76%;

in the step b, the aging treatment temperature is 100 ℃;

and c, distinguishing parameters during annealing in the step c, wherein the heating rate of the first heating is 5 ℃/s, and then repeating heating and cooling treatment for 25 times, wherein the heating rate of each time is 5 ℃/s. The remaining steps and parameters were the same as in example 1.

And (4) carrying out grazing incidence small-angle X-ray scattering test on the processed sample. As shown in fig. 6, spots of a two-dimensional hexagonal lattice appear in the figure.

FIG. 7 shows solid NMR of mesoporous phenolic resin film prepared by the present invention¹³C spectrum, FIG. 8 shows the solid NMR spectrum of the same time heat treatment by the conventional process (no cycle, heat treatment temperature rise rate of 1 ℃/min)¹³C, comparing the spectrogram. The higher and prominent peak at a chemical shift of about 75ppm shown in FIG. 8 represents the templating agent block copolymer Planian P123; while it can be observed in fig. 7 that the peak at 75ppm has disappeared. The invention has the effect of removing all template agent Pluronic P123 in a short time.

Fig. 9 shows the results of small angle X-ray diffraction measurements of the sample of example 4 of the present invention at 1, only aging, 2, and 25 cycles of post-aging annealing, respectively, when only aging is performed at 120 ℃, the (100) peak of the sample appears at about 1.0 ° and approximately 8.8 nm in mesoporous channel size is obtained by bragg equation 2dsin θ = λ calculation, and after 25 cycles of rapid thermal treatment, the curve shifts to the right and the (100) peak of the sample appears at about 1.4 °, approximately 6.4 nm in mesoporous channel size is obtained by bragg equation 2dsin θ = λ calculation, and the mesoporous channel shrinks, since shrinkage = (size after shrinkage/size before shrinkage) X100%, the shrinkage of the mesoporous sample size is approximately 27.3%, much lower than that of the mesoporous (about 45% 8550%) under the current other process treatments, and the Full Width at Half maximum (Half maximum) of the (Half-Width (Half-dtf Å) of the (Half-Width) peak of the (Half-Width) of the peak of the (Half-Width) of the annealed 25 th process after aging.

Fig. 10 is a comparison of small-angle X-ray diffraction test results of a phenolic resin mesoporous thin film sample prepared by a conventional process (without cycle, with a heat treatment temperature rise rate of 1 ℃/min) and a phenolic resin mesoporous thin film sample prepared by the present invention in example 4 after 25 cycles of annealing, wherein the (100) peak of the sample prepared by the conventional process appears at about 2.1 °, the size of the mesoporous channel can be approximately 4.3 nm calculated by bragg equation 2dsin θ = λ, while the (100) peak of the sample prepared by the present invention in example 4 appears at about 1.0 °, the size of the mesoporous channel can be approximately 8.8 nm calculated by bragg equation 2dsin θ = λ, which shows that the size of the mesoporous channel of the sample prepared by the conventional process is much smaller than that of the mesoporous channel of the sample prepared by the present invention in example 4, and the full width at half maximum of the sample prepared by the conventional process is 0.265 angstroms (Å), which shows that the ordered thin film sample prepared by the conventional process has a smaller full width at half maximum than that of the full width of the sample prepared by the ordered thin film prepared by the conventional process in example 4.

Finally, it is noted that the above-mentioned preferred embodiments illustrate rather than limit the invention, and that, although the invention has been described in detail with reference to the above-mentioned preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the invention as defined by the appended claims.

Claims

1. A preparation method of a phenolic resin ordered mesoporous film based on rapid thermal treatment is characterized by comprising the following steps of a, obtaining a phenolic resin solution and a block copolymer solution; b. mixing the phenolic resin solution obtained in the step a with the block copolymer solution to prepare a phenolic resin precursor solution containing the block copolymer; c. and c, mechanically stirring the phenolic resin precursor solution containing the block copolymer prepared in the step b, coating a film on a hydrophilized substrate, performing aging treatment at the temperature of 140 ℃ for 23-25 hours at 100-.

2. The method for preparing the ordered mesoporous phenolic resin film based on rapid thermal treatment according to claim 1, wherein the method comprises the following steps: step a, preparing a phenolic resin solution by adopting the following steps;

s1, mixing phenol and a sodium hydroxide solution at the temperature of 45-50 ℃, stirring and melting, and dropwise adding a formaldehyde solution at the temperature of 45-50 ℃ to obtain a phenolic aldehyde mixed solution;

s2, stirring the phenolic aldehyde mixed solution obtained in the step S1 at the temperature of 50-60 ℃ for 1 hour, cooling to room temperature, and adjusting the pH of the solution to be neutral to obtain a neutral phenolic aldehyde mixed solution;

and S3, performing rotary evaporation on the neutral phenolic mixed solution obtained in the step S2 to remove water, and then dissolving to obtain a phenolic resin solution.

3. The method for preparing the ordered mesoporous phenolic resin film based on rapid thermal treatment according to claim 2, wherein the method comprises the following steps: in step S1, the sodium hydroxide solution accounts for 25% by mass, and the formaldehyde solution accounts for 37% by mass.

4. The method for preparing the ordered mesoporous phenolic resin film based on rapid thermal treatment according to claim 2, wherein the method comprises the following steps: in step S3, the solvent of the phenolic resin solution is absolute ethyl alcohol.

5. The method for preparing the ordered mesoporous phenolic resin film based on rapid thermal treatment according to claim 1, wherein the method comprises the following steps: in the step a, the block copolymer Pluronic P123 is dissolved to prepare a block copolymer solution.

6. The method for preparing the ordered mesoporous phenolic resin film based on rapid thermal treatment according to claim 5, wherein the method comprises the following steps: the solvent of the block copolymer solution is absolute ethyl alcohol.

7. The method for preparing the ordered mesoporous phenolic resin film based on rapid thermal treatment according to claim 5, wherein the method comprises the following steps: the number average molecular weight of the block copolymer Pluronic P123 is 5800; the mass fraction of the block copolymer solution is in the range of 4.5 to 5%.

8. The method for preparing the ordered mesoporous phenolic resin film based on rapid thermal treatment according to claim 1, wherein the method comprises the following steps: in the step c, the glass substrate is firstly immersed into a mixed solution of concentrated sulfuric acid and aqueous hydrogen peroxide solution with the volume ratio of 7:3, then the mixed solution is heated to 60-100 ℃ and is kept for 30-60 minutes, and the hydrophilization substrate with the surface hydrophilization treatment is obtained.

9. The method for preparing the ordered mesoporous phenolic resin film based on rapid thermal treatment according to claim 1, wherein the method comprises the following steps: in step c, the hydrophilized substrate is coated with a film by spin coating.

10. The method for preparing the ordered mesoporous phenolic resin film based on rapid thermal treatment according to claim 1, wherein the method comprises the following steps: during annealing in the step c, the times of repeatedly heating and cooling are 5-50 times;

the shielding gas used for atmosphere protection was argon.