Preparation method of zigzag nitrogen-doped SiC nanowires growing on carbon fiber cloth

文档序号:764484 发布日期:2021-04-06 浏览:34次 中文

阅读说明:本技术 一种生长在碳纤维布上的锯齿状氮掺杂SiC纳米线的制备方法 (Preparation method of zigzag nitrogen-doped SiC nanowires growing on carbon fiber cloth ) 是由 杨为佑 李笑笑 牛昌明 李侃 李维俊 刘乔 陈善亮 钱桂荣 于 2020-11-03 设计创作,主要内容包括:本发明提供的一种生长在碳纤维布上的锯齿状氮掺杂SiC纳米线的制备方法,包括以下步骤:将生长在碳纤维布上的三棱柱状氮掺杂SiC纳米线置于氢氟酸和硝酸的混合溶液中,加热腐蚀反应,冷却后,水洗、干燥得生长在碳纤维布上的锯齿状氮掺杂SiC纳米线。本发明提供的一种生长在碳纤维布上的锯齿状氮掺杂SiC纳米线的制备方法,实现了锯齿状氮掺杂SiC纳米线的简单制备,增加了电化学活性反应位点,提高比电容和高温服役循环寿命。(The invention provides a preparation method of zigzag nitrogen-doped SiC nanowires growing on carbon fiber cloth, which comprises the following steps: and (3) placing the triangular prism-shaped nitrogen-doped SiC nanowires growing on the carbon fiber cloth in a mixed solution of hydrofluoric acid and nitric acid, heating for corrosion reaction, cooling, washing with water, and drying to obtain the sawtooth-shaped nitrogen-doped SiC nanowires growing on the carbon fiber cloth. The preparation method of the zigzag nitrogen-doped SiC nanowire grown on the carbon fiber cloth realizes simple preparation of the zigzag nitrogen-doped SiC nanowire, increases electrochemical active reaction sites, and improves specific capacitance and high-temperature service cycle life.)

1. A preparation method of zigzag nitrogen-doped SiC nanowires growing on carbon fiber cloth is characterized by comprising the following steps:

and (3) placing the triangular prism-shaped nitrogen-doped SiC nanowires growing on the carbon fiber cloth in a mixed solution of hydrofluoric acid and nitric acid, heating for corrosion reaction, cooling, washing with water, and drying to obtain the sawtooth-shaped nitrogen-doped SiC nanowires growing on the carbon fiber cloth.

2. The method for preparing the zigzag nitrogen-doped SiC nanowires grown on the carbon fiber cloth according to claim 1, wherein the heating corrosion reaction comprises the following steps: reacting for 2-3h at 50-70 ℃.

3. The method for preparing the zigzag nitrogen-doped SiC nanowires grown on the carbon fiber cloth according to claim 2, wherein the heating corrosion reaction is as follows: the reaction was carried out at 60 ℃ for 2.5 h.

4. The method for preparing zigzag nitrogen-doped SiC nanowires grown on carbon fiber cloth according to claim 1, wherein the concentration of hydrofluoric acid is 35-45 wt%, and the concentration of nitric acid is 60-70 wt%.

5. The method for preparing zigzag nitrogen-doped SiC nanowires grown on carbon fiber cloth according to claim 4, wherein the volume ratio of hydrofluoric acid to nitric acid is (2.5-3.5): 1.

6. the method for preparing sawtooth-shaped nitrogen-doped SiC nanowires grown on the carbon fiber cloth according to claim 1, wherein the method for preparing triangular prism-shaped nitrogen-doped SiC nanowires grown on the carbon fiber cloth comprises the following steps:

the preparation method comprises the steps of carrying out thermal crosslinking curing and ball milling on an organic precursor containing Si and C elements to obtain organic precursor powder, mixing the organic precursor powder with nitrogen source powder, placing the mixture at the bottom of a graphite crucible, placing a carbon fiber cloth substrate soaked with a catalyst at the top of the graphite crucible, placing the graphite crucible in an atmosphere sintering furnace, heating to 1400-1500 ℃ at the speed of 46-55 ℃/min under the protection of inert gas, heating to 1550-1650 ℃ at the speed of 3-6 ℃/min, and cooling to room temperature along with the furnace to obtain the triangular-prism-shaped nitrogen-doped SiC nanowire growing on the carbon fiber cloth.

7. The method for preparing zigzag nitrogen-doped SiC nanowires grown on carbon fiber cloth according to claim 6, wherein the organic precursor is polysilazane and the nitrogen source is one or more of melamine, dicyandiamide, cyanamide and urea.

8. The method for preparing zigzag nitrogen-doped SiC nanowires grown on carbon fiber cloth according to claim 6, wherein the mass ratio of the organic precursor to the nitrogen source is (2-4): 1.

9. the method for preparing the sawtooth-shaped nitrogen-doped SiC nanowires grown on the carbon fiber cloth according to claim 6, wherein the catalyst is one or more of cobalt nitrate, nickel nitrate, ferric nitrate and nickel sulfate.

10. The application of the zigzag nitrogen-doped SiC nanowires grown on the carbon fiber cloth, obtained by the preparation method according to claim 1, in a supercapacitor.

Technical Field

The invention belongs to the technical field of nano material preparation, and relates to a preparation method of zigzag nitrogen-doped SiC nanowires growing on carbon fiber cloth.

Background

SiC, as a third-generation semiconductor material, has excellent physicochemical properties such as a wide band gap, high electron mobility, high thermal conductivity, and good corrosion resistance. The high-stability photoelectric sensor has strong stability under the conditions of high frequency, high temperature, strong radiation and the like, and has unique application prospect in the fields of photoelectric and force-electricity sensors such as luminescence, field effect transistors, force-electricity conversion and the like.

The SiC nanometer material is particularly stable in performance in all aspects, so that the SiC nanometer material is used for a super capacitor and also shows excellent cycling stability. But the conductivity of the SiC nanometer material is poor, so that the increase of the SiC nanometer material in the aspect of electrochemical energy storage capacity is restricted. At present, an additive strategy is mostly adopted in a method for increasing the electrochemical capacity of a SiC nano material as a super capacitor electrode, namely a surface modification method for introducing a foreign substance on the surface of the SiC nano material, such as Zhao (Journal of Power resources, 332, (2016)355-2S4、NiCo2O4/NiO、 NiCo2O4/Ni(OH)2Iso-active material, increaseThe specific surface area of the whole material is increased, and scientific research of the SiC nanowire composite material in the aspect of the super capacitor is promoted.

At present, foreign substances introduced by an 'addition strategy' inevitably contact the surface of the SiC nanowire at an interface, and the cycling stability, especially the high-temperature stability of the SiC nanowire as a supercapacitor electrode is seriously influenced. Therefore, finding an alternative method to increase the electrochemical active reaction sites of the SiC nanometer material and improve the energy storage performance of the super capacitor has very important significance.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a preparation method of the zigzag nitrogen-doped SiC nanowire grown on the carbon fiber cloth, which realizes the simple preparation of the zigzag nitrogen-doped SiC nanowire, increases the electrochemical active reaction sites, and improves the specific capacitance and the high-temperature service cycle life.

One purpose of the invention is realized by the following technical scheme:

a preparation method of zigzag nitrogen-doped SiC nanowires growing on carbon fiber cloth is characterized by comprising the following steps:

and (3) placing the triangular prism-shaped nitrogen-doped SiC nanowires growing on the carbon fiber cloth in a mixed solution of hydrofluoric acid and nitric acid, heating for corrosion reaction, cooling, washing with water, and drying to obtain the sawtooth-shaped nitrogen-doped SiC nanowires growing on the carbon fiber cloth.

The triangular prism-shaped nitrogen-doped SiC nanowire is in a sawtooth shape in a mixed solution of hydrofluoric acid and nitric acid, and the nanowire obtained through corrosion reaction is used for achieving the purpose of increasing the electrochemical reaction sites.

The triangular prism-shaped nitrogen-doped SiC nanowires growing on the carbon fiber cloth are corroded in a mixed solution of hydrofluoric acid and nitric acid, the corrosion temperature and the corrosion time are critical, the corrosion temperature is too low to cause corrosion reaction, and the corrosion reaction is too violent due to too high temperature to cause excessive loss of the SiC nanowires; the corrosion reaction time is too short to achieve the purpose of generating serrated SiC nanowires and increasing the electrochemical reaction sites of the serrated SiC nanowires, and the corrosion reaction time is too long to cause over-reaction and aggravate over-consumption of the SiC nanomaterials. The invention controls the corrosion temperature to be 50-70 ℃ and the corrosion time to be 2-3h, so that the obtained nitrogen-doped SiC nanowire growing on the carbon fiber cloth has an excellent saw-tooth structure, and the obtained nitrogen-doped SiC nanowire has excellent specific capacitance and high-temperature cycle stability when being used as an electrode material of a super capacitor.

Further preferably, the heating corrosion reaction is: the reaction was carried out at 60 ℃ for 2.5 h. The sawtoothed nitrogen-doped SiC nanowires grown on the carbon fiber cloth prepared by the method have better specific capacitance and high-temperature cycle stability when used as an electrode material after being heated and corroded for 2.5h at the temperature of 60 ℃.

Preferably, the concentration of hydrofluoric acid is 35 to 45 wt% and the concentration of nitric acid is 60 to 70 wt%.

Preferably, the volume ratio of the hydrofluoric acid to the nitric acid is (2.5-3.5): 1.

by controlling the concentration and volume ratio of hydrofluoric acid and nitric acid, the corrosion effect is better, and a more excellent saw-toothed structure is obtained.

Preferably, the preparation method of the triangular-prism-shaped nitrogen-doped SiC nanowire grown on the carbon fiber cloth comprises the following steps:

the preparation method comprises the steps of carrying out thermal crosslinking curing and ball milling on an organic precursor containing Si and C elements to obtain organic precursor powder, mixing the organic precursor powder with nitrogen source powder, placing the mixture at the bottom of a graphite crucible, placing a carbon fiber cloth substrate soaked with a catalyst at the top of the graphite crucible, placing the graphite crucible in an atmosphere sintering furnace, heating to 1400-1500 ℃ at the speed of 46-55 ℃/min under the protection of inert gas, heating to 1550-1650 ℃ at the speed of 3-6 ℃/min, and cooling to room temperature along with the furnace to obtain the triangular-prism-shaped nitrogen-doped SiC nanowire growing on the carbon fiber cloth. The prepared nitrogen-doped SiC nanowire is triangular prism-shaped, the surface is rough, and a large number of obvious defects exist at the edge.

Preferably, the organic precursor is polysilazane, the organic precursor is thermally crosslinked and cured at the temperature of 240-280 ℃ for 20-40min under the protection of inert atmosphere, the cured solid is filled into a nylon resin ball milling tank, and ball milling and crushing are carried out to obtain the organic precursor powder. The nitrogen source is one or more of melamine, dicyandiamide, cyanamide and urea.

Preferably, the mass ratio of the organic precursor to the nitrogen source is (2-4): 1.

preferably, the catalyst is one or more of cobalt nitrate, nickel nitrate, ferric nitrate and nickel sulfate. And (3) soaking the carbon fiber cloth substrate in a catalyst solution (the molar concentration of the catalyst solution is 0.05mol/L) for 10-30min to obtain the carbon fiber cloth substrate soaked with the catalyst.

Placing the graphite crucible in an atmosphere sintering furnace for graphite resistance heating, and vacuumizing the atmosphere furnace to 10 DEG first-4And Pa, filling inert gas (the inert gas is preferably one of argon, helium and nitrogen, the purity is 99.99%) until the pressure is atmospheric pressure, then keeping the pressure constant, heating to 1500 ℃ at the speed of 46-55 ℃/min, then heating to 1650 ℃ at the speed of 3-6 ℃/min, and cooling to room temperature along with the furnace to obtain the triangular-prism-shaped nitrogen-doped SiC nanowire growing on the carbon fiber cloth.

The other purpose of the invention is realized by the following technical scheme:

the application of the zigzag nitrogen-doped SiC nanowires grown on the carbon fiber cloth and obtained by the preparation method in the super capacitor takes the zigzag nitrogen-doped SiC nanowires grown on the carbon fiber cloth as the positive electrode and the negative electrode of the super capacitor.

Compared with the prior art, the invention has the following beneficial effects:

1. according to the invention, the preparation of the triangular prism-shaped nitrogen-doped SiC nanowire is realized through an organic precursor pyrolysis method, and then the triangular prism-shaped nitrogen-doped SiC nanowire is corroded in a mixed solution of hydrofluoric acid and nitric acid, so that a zigzag nitrogen-doped SiC nanowire material is finally obtained;

2. the process for preparing the zigzag nitrogen-doped SiC nanowire material is simple and controllable, and has good repeatability;

3. the zigzag nitrogen-doped SiC nanowire material prepared by the method is used as a supercapacitor electrode material, so that the number of reactive active sites of the electrode material is increased, the specific capacitance of the supercapacitor is improved, and the high-temperature cycle life of the supercapacitor is prolonged;

4. according to the invention, the corrosion temperature is controlled to be 60 ℃, the corrosion time is 2.5h, the prepared carbon fiber cloth with the sawtooth-shaped nitrogen-doped SiC nanowires is unique in structure, and the super capacitor constructed by the carbon fiber cloth has better specific capacitance and high-temperature capacitance retention rate.

Drawings

FIG. 1(a-d) is a Scanning Electron Microscope (SEM) image of a triangular prism-shaped nitrogen-doped SiC nanowire prepared in example 1;

fig. 2(a) is a Transmission Electron Microscope (TEM) view of a triangular-prism-shaped nitrogen-doped SiC nanowire prepared in example 1; fig. 2(b) is a high-resolution transmission electron microscope (HRTEM) view of the triangular-prism-shaped nitrogen-doped SiC nanowire prepared in example 1;

fig. 3 is an energy dispersive X-ray spectroscopy (EDS) plot of a triangular prism-shaped nitrogen-doped SiC nanowire prepared in example 1;

fig. 4 (a1, a2) is an SEM image of the nitrogen-doped SiC nanowire prepared in example 2 after etching for 2 h; fig. 4 (b1, b2) is an SEM image of the nitrogen-doped SiC nanowire prepared in example 1 after 2.5h etching; fig. 4 (c1, c2) is a SEM image of the nitrogen-doped SiC nanowire prepared in example 3 after 3h etching;

fig. 5 (a) is a TEM image of nitrogen-doped SiC nanowires prepared in example 1 after etching for 2.5 h; fig. 5 (b) is a High Resolution Transmission Electron Microscope (HRTEM) image of nitrogen-doped SiC nanowires prepared in example 1 after 2.5h etching;

fig. 6 is an X-ray diffraction spectrum (XRD) pattern of the triangular-prism-shaped nitrogen-doped SiC nanowire prepared in example 1 and the nitrogen-doped SiC nanowire after 2.5h of etching;

FIG. 7 is a graph of specific capacitance versus erosion time for a supercapacitor constructed from zigzag nitrogen-doped SiC nanowires;

FIG. 8 is a graph of the current density of 2mA/cm at various temperatures for a supercapacitor constructed from example 12Lower electrode stability curve.

Detailed Description

The technical solution of the present invention will be further described and explained with reference to the following embodiments and the accompanying drawings. The raw materials used in the examples of the present invention are those commonly used in the art, and the methods used in the examples are those conventional in the art, unless otherwise specified.

Example 1

The zigzag nitrogen-doped SiC nanowire grown on the carbon fiber cloth in the embodiment is prepared by the following steps:

selecting polysilazane as an organic precursor, preserving heat for 25min at 250 ℃ under the protection of Ar atmosphere for thermal crosslinking curing, filling the cured solid into a nylon resin ball milling tank, and carrying out ball milling and crushing to obtain powder. 300mg of polysilazane powder and 100mg of melamine powder were weighed, mixed uniformly and placed at the bottom of a graphite crucible. Cutting 7 x 7cm of carbon fiber cloth2Soaking in 0.05mol/L cobalt nitrate solution for 20min, taking out, naturally drying, placing carbon fiber cloth soaked with cobalt nitrate as substrate on top of graphite crucible, placing the graphite crucible in graphite resistance heating atmosphere sintering furnace, and vacuumizing the atmosphere furnace to 10 deg.C- 4Pa, filling Ar gas (the purity is 99.99 percent) until the pressure is one atmosphere, keeping the pressure constant, heating to 1500 ℃ at the speed of 54 ℃/min, then heating to 1600 ℃ at the speed of 5 ℃/min, and finally cooling to room temperature along with a furnace to obtain the triangular-prism-shaped nitrogen-doped SiC nanowire growing on the carbon fiber cloth;

placing the prepared triangular-prism-shaped nitrogen-doped SiC nanowires growing on the carbon fiber cloth in a mixed solution of hydrofluoric acid and nitric acid, wherein the concentrations of the hydrofluoric acid and the nitric acid are 40 wt% and 65 wt%, respectively, and the volume ratio of the hydrofluoric acid to the nitric acid in the mixed acid solution is 3: 1. And then heating and corroding for 2.5h at the temperature of 60 ℃, stopping heating, cooling, washing with deionized water, and drying in an air-blast drying oven to obtain the zigzag nitrogen-doped SiC nanowires growing on the carbon fiber cloth.

Example 2

Example 2 is different from example 1 in that example 2 is the same as example 1 except that the trigonal prism-shaped nitrogen-doped SiC nanowires grown on the carbon fiber cloth were etched at a temperature of 60 ℃ for 2h in a mixed solution of hydrofluoric acid and nitric acid.

Example 3

Example 3 is different from example 1 in that example 3 is the same as example 1 except that the trigonal prism-shaped nitrogen-doped SiC nanowires grown on the carbon fiber cloth were etched at a temperature of 60 ℃ for 3 hours in a mixed solution of hydrofluoric acid and nitric acid.

Example 4

Example 4 is different from example 1 in that example 4 places the nitrogen-doped SiC nanowire having a triangular prism shape grown on the carbon fiber cloth in a mixed solution of hydrofluoric acid and nitric acid, and etches at a temperature of 60 ℃ for 3.5h, otherwise the same as example 1.

Example 5

Example 5 is different from example 1 in that example 5 is the same as example 1 except that trigonal prism-shaped nitrogen-doped SiC nanowires grown on carbon fiber cloth were etched at a temperature of 60 ℃ for 1.5 hours in a mixed solution of hydrofluoric acid and nitric acid.

Fig. 1(a-d) is a scanning electron microscope image of the triangular prism-shaped nitrogen-doped SiC nanowire prepared in example 1, the nanowire grows in a large area and is arranged in a nanowire array, the nanowire is triangular prism-shaped, the surface is rough, and a large number of obvious defects exist at the edge. Fig. 2(a) is a Transmission Electron Microscope (TEM) image of the triangular-prism-shaped nitrogen-doped SiC nanowire prepared in example 1, showing that the prepared triangular-prism-shaped nitrogen-doped SiC nanowire has a diameter of about 700 nm; fig. 2(b) is a high-resolution transmission electron microscope (HRTEM) image of the triangular-prism-shaped nitrogen-doped SiC nanowire prepared in example 1, showing that the prepared triangular-prism-shaped nitrogen-doped SiC nanowire has an adjacent lattice spacing of 0.25nm, which is grown in the direction of [111] (see fig. 2 (a)); fig. 2(b) is a bottom left insert of an electron diffraction (SAED) diagram of a selected region of the triangular-prism-shaped nitrogen-doped SiC nanowire prepared in example 1, which shows that the prepared triangular-prism-shaped nitrogen-doped SiC nanowire has a single crystal structure. Fig. 3 is an energy dispersive X-ray spectroscopy (EDS) diagram of the nitrogen-doped SiC nanowire having a triangular prism shape prepared in example 1, and a partial enlarged view is shown in the upper right corner, and the result shows that nitrogen is successfully doped into the SiC nanowire and the atomic ratio is about 3.07%.

Fig. 4 is an SEM image of the nitrogen-doped SiC nanowire after etching in examples 1-3, wherein (a1, a2) in fig. 4 is an SEM image of the nitrogen-doped SiC nanowire after etching for 2h prepared in example 2, and the image shows that a large number of cusps are generated after the triangular prism-shaped nitrogen-doped SiC nanowire is etched. Fig. 4 (b1, b2) is an SEM image of the nitrogen-doped SiC nanowire prepared in example 1 after 2.5h etching, and the image shows that the triangular prism-shaped nitrogen-doped SiC nanowire is etched to generate a large number of tooth-shaped sharp corners, and the etching depth is deepened with the increase of time to form the tooth-shaped nitrogen-doped SiC nanowire. Fig. 4 (c1, c2) is SEM image of nitrogen-doped SiC nanowires prepared in example 3 after etching for 3h, and the image shows that the density of the nanowires is seriously decreased and excessive etching occurs with time.

Fig. 5 (a) is a TEM image of the nitrogen-doped SiC nanowire prepared in example 1 after 2.5h etching, and (b) is a high-resolution transmission electron microscope (HRTEM) image of the SiC nanowire prepared in example 1 after 2.5h etching, which shows that the nitrogen-doped SiC nanowire after etching is dentate, and the sharp corner portion of the sawtooth is integral with the nanowire body and no interface exists.

Fig. 6 is an X-ray diffraction (XRD) pattern of the triangular-prism-shaped nitrogen-doped SiC nanowire prepared in example 1 and the saw-tooth-shaped nitrogen-doped SiC nanowire prepared in example 1, which shows that the phase composition of the nanowires is not changed by the etching process, and the nanowires remain 3C-SiC and have high crystallinity.

The serrated nitrogen-doped SiC nanowires grown on the carbon fiber cloth prepared in examples 1 to 5 and the triangular prism-shaped nitrogen-doped SiC nanowires grown on the carbon fiber cloth prepared in example 1 were cut into 2 pieces of the same size (1.5X 1.5 cm)2) The square small piece is used as a working electrode, 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide salt is used as electrolyte, cellulose paper is used as a diaphragm, a super capacitor is constructed, and the electrochemical performance of the super capacitor is tested under the room temperature condition.

FIG. 7 is a graph of specific capacitance versus erosion time for a supercapacitor constructed from serrated nitrogen-doped SiC nanowires, the non-eroded triangular prism of nitrogen-doped SiC nanowires at 2mA/cm2The specific capacitance is 1.8mF/cm under the current density2The specific capacitance increased and then decreased with increasing etch time, and example 1 gave a specific capacitance of 7.1mF/cm2Greater than 5.5 and 6.4mF/cm for examples 2 and 32Is much larger than the implementation5.1 and 4.7mF/cm for examples 4-52It is shown that the etching time of 2.5h used in example 2 is the optimum time choice.

FIG. 8 is a graph of the current density of 2mA/cm at various temperatures for a supercapacitor constructed from example 12Lower electrode stability curves at 0 ℃ and 150 ℃ with a current density of 2mA/cm2The capacity retention after 10000 times of the treatment was 86% and 80%, respectively. As shown in Table 1 below, the supercapacitor constructed from example 2 had a current density of 2mA/cm at 0 ℃ and 150 ℃ C2The capacity retention after 10000 times of the treatment was 85% and 75%, respectively. The supercapacitor constructed from example 3 had a current density of 2mA/cm at 0 ℃ and 150 ℃2The capacity retention after 10000 times is 85% and 76%, respectively. The supercapacitor constructed from example 4 had a current density of 2mA/cm at 0 ℃ and 150 ℃2In this case, the capacity retention ratio after 10000 times was 83% and 69%, respectively. The supercapacitor constructed from example 5 had a current density of 2mA/cm at 0 ℃ and 150 ℃2The capacity retention ratio after 10000 times of the treatment was 84% and 71%, respectively. The super capacitor constructed by the un-corroded triangular prism-shaped nitrogen-doped SiC nanowire has the current density of 2mA/cm at the temperature of 0 ℃ and 150 DEG C2The capacity retention after 10000 times of the treatment was 82% and 62%, respectively.

TABLE 1 Capacity Retention for 10000 cycles of supercapacitors constructed in examples 1-6

When the temperature of the super capacitor constructed by the nitrogen-doped SiC nanowire which is not corroded is increased from 0 ℃ to 150 ℃, the capacitance retention rate is reduced by 20%, and poor high-temperature cycle stability is shown. The supercapacitor constructed from example 2 showed only 6% decrease in capacitance retention when the temperature was increased from 0 ℃ to 150 ℃, showing very reliable high-temperature electrochemical stability. However, in the super capacitor (example 4) constructed by the nitrogen-doped SiC nanowire which is excessively corroded, the high-temperature capacitance retention rate is greatly reduced due to the damaged SiC nanowire structure.

The experiment shows that the supercapacitor constructed by the zigzag nitrogen-doped SiC nanowire obtained by corroding for 2.5 hours has more excellent specific capacitance and high-temperature capacitance retention rate, and shows very excellent high-temperature electrochemical stability at 150 ℃.

The specific embodiments described herein are merely illustrative of the spirit of the invention and do not limit the scope of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.

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