阅读说明：本技术 一种银微纳线的制备方法 (Preparation method of silver micro-nano wire ) 是由 李臻 周剑 黄良辉 吴照坤 于 2021-06-29 设计创作，主要内容包括：本发明提供一种银微纳线的制备方法,本发明采用离心纺丝法、利用离心力克服旋转流体的表面张力,使得射流在离心力、空气阻力和流变力三个力的共同作用下喷出,历经溶剂挥发、纤维拉伸、煅烧,最终制得长度明显增长的银微纳线,不需要拼接,克服了现有技术得到的银纳米线长度短需要拼接的缺陷。(The invention provides a preparation method of silver micro-nano wires, which adopts a centrifugal spinning method and utilizes centrifugal force to overcome the surface tension of rotating fluid, so that jet flow is sprayed out under the combined action of the centrifugal force, air resistance and rheological force, and finally the silver micro-nano wires with obviously increased length are prepared through solvent volatilization, fiber stretching and calcination without splicing, thereby overcoming the defects that the silver nano wires obtained by the prior art are short in length and need to be spliced.)

1. A preparation method of silver micro-nano wires is characterized by comprising the following steps: the method comprises the following steps: and carrying out centrifugal spinning on spinning solution containing silver salt, a reducing agent with a coating effect, a surfactant and an organic solvent to prepare a silver micro-nano wire precursor, and calcining the silver micro-nano wire precursor to prepare the silver micro-nano wire.

2. The method of preparing silver micro-nano wire according to claim 1, characterized in that: the mass ratio of the reducing agent with the coating effect to the silver salt in the spinning solution is (3-8): 15.

3. the method of preparing silver micro-nano wire according to claim 1, characterized in that: the mass fraction of the surfactant in the spinning solution is 0.5-2.0%.

4. The method of preparing silver micro-nano wire according to claim 1, characterized in that: the mass fraction of the organic solvent in the spinning solution is 7.0-14.0%.

5. The method of preparing silver micro-nano wire according to claim 1, characterized in that: the reducing agent with the coating function is any one selected from polyvinylpyrrolidone, polyethylene oxide and polyvinyl alcohol.

6. The method of preparing silver micro-nano wire according to claim 1, characterized in that: the organic solvent is any one selected from acetonitrile, ethanol and acetone.

7. The method of preparing silver micro-nano wire according to claim 1, characterized in that: the inner diameter of a spinning nozzle adopted by centrifugal spinning is 0.06 mm-0.21 mm.

8. The method of preparing silver micro-nano wire according to claim 1, characterized in that: the calcination temperature is 230-350 ℃.

9. A silver micro-nano wire produced by the method for producing a silver micro-nano wire according to any one of claims 1 to 8.

10. The silver micro-nanowire line of claim 9, wherein: the length of the silver micro-nano wire is 5 cm-50 cm.

Technical Field

The invention belongs to the technical field of fiber preparation, and particularly relates to a preparation method of a silver micro-nano wire.

Background

The nanofiber is the most advanced fiber material at present, and is widely applied to tissue engineering scaffolds, drug delivery, high-performance filter materials, artificial blood vessels, biochips, nanosensors, composite materials and other emerging fields due to the characteristics of high porosity, excellent mechanical properties, high specific surface area and the like.

The conventional electrospinning process is the most common method for producing nanofibers. However, the productivity of electrospinning is low, which limits its large-scale application. Other spinning processes, such as melt blowing, phase separation, templated synthesis, and self-assembly processes, are relatively more complex and can only produce nanofibers from a limited class of polymers. For example, melt blowing, although a highly productive process, is widely used in industry to produce fibers having a diameter greater than 1 μm. However, when used to produce nanofibers, meltblowing is limited to a few polymers, such as polypropylene (PP) and Polystyrene (PS). The phase separation method involves multiple steps of gelation, phase separation, solvent exchange and freeze-drying, which is very complicated. To date, only a few polymers, such as polylactic acid (PLA) and Polyglycolide (PGA), can be made into nanofibers by a phase separation process. In the template synthesis method, nanofibers are prepared by filling a polymer in hollow channels of a porous template and then performing a cumbersome template removal process, so that this method cannot produce long-fiber-length nanofibers.

The current methods for preparing silver nanowires can be classified into physical methods and chemical methods according to the process principle. The chemical methods mainly include a template method, a polyol method (alcohol thermal method), and an electrochemical deposition method. At present, the silver nanowires are most commonly prepared by using a polyol method, namely, using polyol as a solvent and a reducing agent, using a metal compound as a precursor, and heating and synthesizing AgNWs (silver nanowires) under the action of the reducing agent and a stabilizing agent. The silver nanowire prepared by the alcohol heating method has the length of less than 100 mu m, the diameter of less than 100nm and the maximum length-diameter ratio of about 2000. The polyol process used to produce AgNWs inevitably produces nanoparticles as a by-product, which is a not trivial challenge for producing high purity AgNWs. In the template synthesis method, nanofibers are prepared by filling a polymer in hollow channels of a porous template and then performing a cumbersome template removal process, so that this method cannot produce long-fiber-length nanofibers.

Physical methods for producing metal nanowires have been developed to date by techniques such as electrospinning, melt spinning, and wet spinning. Electrospinning methods have been widely used to produce ultrafine fibers of polymers, ceramics, metals and carbon. However, the production efficiency is not high and the energy consumption is very high by using electrostatic spinning, so that the method is not suitable for large-scale production. Melt spinning and conventional wet spinning can efficiently obtain polymer wires at high speed, however, the diameter of the fiber is usually more than 10 μm.

Disclosure of Invention

The present invention is directed to solving at least one of the problems of the prior art described above. To this end, the first aspect of the present invention provides a method for manufacturing a silver micro-nano wire, which can manufacture a silver micro-nano wire having a significantly increased length. The silver micro-nano wire refers to a silver micron and/or a nano wire.

In a second aspect of the invention, a silver nanowire is provided.

According to a first aspect of the present invention, there is provided a method for preparing a silver micro-nano wire, comprising the steps of: and carrying out centrifugal spinning on spinning solution containing silver salt, a reducing agent with a coating effect, a surfactant and an organic solvent to prepare a silver micro-nano wire precursor, and calcining the silver micro-nano wire precursor to prepare the silver micro-nano wire.

In the invention, centrifugal spinning overcomes the surface tension of rotating fluid by using centrifugal force, so that jet flow is sprayed out under the combined action of the centrifugal force, air resistance and rheological force, and finally silver micro-nano wires with obviously increased length are prepared through solvent volatilization, fiber stretching and calcination without splicing, thereby overcoming the defect that the silver nano wires obtained by the prior art are short in length and need to be spliced.

In some embodiments of the invention, the mass ratio of the reducing agent with a coating effect to the silver salt in the spinning solution is (3-8): 15; more preferably (4-6): 15. the spinning performance of the silver micro-nano wire is better when the content of the reducing agent with the coating function in the spinning solution is higher, but when the content of the reducing agent with the coating function is too high, excessive carbon elements are remained after sintering, and the purity of the silver micro-nano wire is influenced.

In some preferred embodiments of the present invention, the mass fraction of the surfactant in the spinning solution is 0.5% to 2.0%; more preferably, the mass fraction of the organic solvent in the spinning solution is 7.0% to 14.0%.

In some more preferred embodiments of the present invention, the silver salt is any one selected from the group consisting of silver nitrate, silver chloride, and silver sulfate.

In some more preferred embodiments of the present invention, the reducing agent having a coating effect is any one selected from polyvinylpyrrolidone (PVP), polyethylene oxide (PEO), and polyvinyl alcohol (PVA). The reducing agent molecular chain with the coating function contains lone pair electrons, and can form a complex (AgNWs) with anions, so that the reducing agent has the function of carrying silver salt to prepare a nanofiber precursor material, and can perform redox reaction under certain conditions so as to reduce silver ions on the complex to obtain a silver simple substance; secondly, the reducing agent with the coating function has strong adhesive force to the side surface of the AgNWs complex, and the adhesive force to the silver terminal surface is obviously smaller, so that the reducing agent with the coating function can limit the transverse growth of the AgNWs complex and promote the longitudinal growth of the AgNWs complex. The silver salt-containing spinning solution has spinnability due to the coating effect of the reducing agent for coating on silver salt, so that the spinning solution can be prepared into a product by a centrifugal spinning mode.

In some more preferred embodiments of the present invention, the surfactant is any one selected from Sodium Dodecyl Sulfate (SDS) and lignin.

In some more preferred embodiments of the present invention, the organic solvent is any one selected from acetonitrile, ethanol, acetone; further preferred is acetonitrile. In particular, the acetonitrile has better surface tension and volatility, so that the acetonitrile is selected as the organic solvent, and the spinnability of the spinning solution can be improved.

In some more preferred embodiments of the present invention, the centrifugal spinning uses a spinneret with an inner diameter of 0.06mm to 0.21 mm; more preferably 0.13mm to 0.18 mm. The diameter of the silver micro nano wire tends to decrease as the inner diameter of the spinneret decreases, and the surface of the silver micro nano wire becomes smooth as the inner diameter of the spinneret decreases, but the inner diameter of the spinneret is too thin and is blocked in the process of preparing the silver micro nano wire, resulting in interruption of spinning.

In some more preferred embodiments of the present invention, the calcination temperature is 230 ℃ to 350 ℃, and more preferably 230 ℃ to 300 ℃. The higher the temperature, the more favorable the growth and development of grains in the silver micro-nano wire, thereby reducing the resistance, but the higher the temperature, the more AgO the generated influences the conductivity, and the higher the calcination temperature, the more easily the silver micro-nano wire is broken by the action of the decomposition gas.

According to a second aspect of the invention, the silver micro-nano wire prepared by the silver micro-nano wire preparation method is provided.

In some embodiments of the invention, the silver micro-nano wires have a diameter of 80nm to 1.6 μm.

In some preferred embodiments of the present invention, the length of the silver micro-nano wire is 5cm to 50cm, and the length of the silver micro-nano wire prepared by the present invention is significantly increased without splicing.

The invention has the beneficial effects that:

the silver micro-nano wire with obviously increased length and without splicing can be obtained by the spinning solution containing silver salt through a centrifugal spinning method, the preparation method is simple, high voltage and electric field are not required to be applied like an electrostatic spinning method, the operability is strong, the preparation speed is high (up to 60g/h), and the preparation method is suitable for large-scale industrial production; compared with a melt-blowing method, the technical scheme of the invention has less limitation on raw materials and low production cost; compared with a phase separation method, the technical scheme of the invention has the advantages of wide raw material selection range, no involvement of medicines with high cost and higher safety; compared with a template synthesis method, the technical scheme of the invention can synthesize the silver micro-nano wire which does not need splicing and has obviously increased length.

According to the invention, the silver micro-nano wire is prepared by adopting a centrifugal spinning method, nano particle impurities are not generated in the preparation process, the prepared silver micro-nano wire has high purity, and an additional purification process is not required.

Drawings

The invention is further described with reference to the following figures and examples, in which:

fig. 1 is a schematic view of a process for preparing a silver nanowire according to an embodiment of the present invention.

Fig. 2 is an SEM image of silver precursor before sintering in example 2 of the present invention, wherein a-c are PVP: AgNO₃4:15, obtaining a topography of the silver precursor, wherein the magnification is 200X, 1000X and 10000X respectively; d-f is PVP: AgNO₃5:15, the magnification ratios of the morphology graph of the silver precursor are respectively 200X, 1000X and,10000X; g-i is PVP: AgNO₃6:15, the magnification of the obtained silver precursor is respectively 200X, 1000X and 10000X.

FIG. 3 shows PVP: AgNO₃4:15, and obtaining a diameter distribution diagram of the silver precursor.

Fig. 4 shows PVP: AgNO₃5:15, and obtaining a diameter distribution diagram of the silver precursor.

FIG. 5 shows PVP: AgNO₃6:15, and obtaining a diameter distribution diagram of the silver precursor.

Fig. 6 is an SEM image of sintered silver micro-nano wires in example 2 of the present invention, where a-c are PVP: AgNO₃4:15, obtaining a topography of the silver micro-nano line, wherein the magnification is respectively 200X, 2000X and 5000X; d-f is PVP: AgNO₃5:15, obtaining a topography of the silver micro-nano line, wherein the magnification is respectively 200X, 2000X and 5000X; g-i is PVP: AgNO₃6:15 and the magnification ratios of the obtained morphology graphs of the silver micro-nano lines are respectively 200X, 2000X and 5000X.

Fig. 7 shows PVP: AgNO₃4:15, obtaining a diameter distribution diagram of the silver micro-nano wires.

Fig. 8 shows PVP: AgNO₃5:15, obtaining a diameter distribution diagram of the silver micro-nano wires.

Fig. 9 shows PVP: AgNO₃6:15, obtaining a diameter distribution diagram of the silver micro-nano wires.

Fig. 10 is an X-ray diffraction pattern obtained from silver micro-nanowires obtained by sintering of three different PVP contents in example 2.

FIG. 11 is an SEM topography of a silver precursor before sintering for centrifugal spinning of spinnerets with different diameters in example 3, wherein a-c are topography of the silver precursor obtained from a 30G spinneret, and magnifications are 200X, 1000X and 10000X respectively; d-f is a morphology graph of a silver precursor obtained by a 32G spinning head, and the magnification is 200X, 1000X and 10000X respectively; g-i is a morphology graph of a silver precursor obtained by a 34G spinning head, and the magnification is 200X, 1000X and 10000X respectively.

Fig. 12 is a diameter distribution diagram of a silver precursor obtained from a 30G spinneret in example 3 of the present invention.

Fig. 13 is a diameter distribution diagram of a silver precursor obtained from a 32G spinneret in example 3 of the present invention.

Fig. 14 is a diameter distribution diagram of a silver precursor obtained from a 34G spinneret in example 3 of the present invention.

FIG. 15 is an SEM topography of sintered silver micro-nano wires obtained by centrifugal spinning of spinnerets with different diameters in example 3 of the invention, wherein a-c are topography of silver micro-nano wires obtained by 30G spinnerets, and magnifications are 200X, 1000X and 10000X respectively; d-f is a topography of the silver micro-nano wire obtained by a 32G spinning head, and the magnification is respectively 200X, 1000X and 10000X; g-i is a morphology graph of the silver micro-nano line obtained by a 34G spinning head, and the magnification is respectively 200X, 1000X and 10000X.

Fig. 16 is a diameter distribution diagram of silver micro-nano wires obtained by a 30G spinneret in example 3 of the present invention.

Fig. 17 is a distribution diagram of the diameter of a silver micro-nano wire obtained by a 32G spinneret in example 3 of the present invention.

Fig. 18 is a diameter distribution diagram of silver micro-nano wires obtained by a 34G spinneret in example 3 of the present invention.

Fig. 19 is SEM images of silver micro-nano wires obtained at different sintering temperatures in example 4 of the present invention, wherein a-c are topography images of silver micro-nano wires obtained at a sintering temperature of 250 ℃, and the magnifications are 200X, 1000X, and 5000X, respectively; d-f is a morphology graph of the silver micro-nano line obtained at the sintering temperature of 280 ℃, and the magnification is respectively 200X, 1000X and 5000X; g-i is a morphology graph of the silver micro-nano line obtained at the sintering temperature of 300 ℃, and the magnification is 200X, 1000X and 5000X respectively; j-l is a morphology graph of the silver micro-nano line obtained at the sintering temperature of 350 ℃, and the magnification is 200X, 1000X and 5000X respectively.

FIG. 20 shows the X-ray diffraction patterns of silver micro-nano wires obtained at different sintering temperatures in example 4 of the present invention.

Detailed Description

The concept and technical effects of the present invention will be clearly and completely described below in conjunction with the embodiments to fully understand the objects, features and effects of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and those skilled in the art can obtain other embodiments without inventive effort based on the embodiments of the present invention, and all embodiments are within the protection scope of the present invention.

Fig. 1 shows a schematic flow chart of the preparation of silver micro-nano wire according to the embodiment of the invention.

Example 1

The embodiment prepares the silver micro-nano wire, and the specific process is as follows:

s1: adding 5mL of acetonitrile to 1.0g of polyvinylpyrrolidone (PVP), dissolving under stirring with a magnetic stirrer, and allowing the solution to stand at room temperature for about 2h to obtain solution A; mixing and stirring 3g of silver nitrate, 0.1g of Sodium Dodecyl Sulfate (SDS) and 1mL of deionized water at room temperature for 4 hours to obtain a solution B; fully mixing the solution A and the solution B to obtain spinning solution;

s2: extruding the spinning solution into a liquid storage module of a centrifugal spinning machine, setting the rotating speed of a spinning head at 6000rpm, setting the collecting distance at 30cm, spinning at 6000rpm and 30G, and starting a motor to spin for centrifugal spinning to obtain a silver micro-nano wire precursor;

s3: calcining the silver micro-nano wire precursor at 250 ℃ for 2h, and naturally cooling to obtain the silver micro-nano wire.

Example 2

In this example, a silver micron nano wire is prepared according to the method of example 1, the difference is only that the mass ratio of PVP to silver nitrate in the spinning solution is different, and the specific process is as follows: preparing three bottles of spinning solutions with different PVP contents, firstly controlling other parameters to be unchanged: 5mL of acetonitrile, 3g of AgNO3, 0.1g of SDS and 1mL of deionized water were added to three bottles, respectively, 0.8g, 1.0g and 1.2g of PVP, to obtain three spinning solutions having PVP and silver nitrate in the mass ratios of (4:15), (5:15) and (6: 15). Three silver nanowire wires with different PVP contents were prepared according to the preparation method of example 1.

Example 3

This example prepared silver micron nano wire according to the method of example 1, except that the spinning head specifications (inside diameter) for centrifugal spinning were different, and the specific process was as follows: preparing a spinning solution with the mass ratio of PVP to silver nitrate being 5:15 by using 1.0g of PVP, 5mL of acetonitrile, 3g of silver nitrate, 0.1g of SDS and 1mL of deionized water, setting the rotating speed of a spinning head to be 6000rpm, collecting the spinning solution at the distance of 30cm, and spinning by using three needles in sequence: and carrying out centrifugal spinning on 27G, 30G and 32G, respectively collecting samples obtained by the three times of spinning, calcining at 250 ℃ for 2h, and naturally cooling to obtain the silver micro-nano wire.

Example 4

In this pair of embodiments, silver nanowires were prepared according to the method of example 1, with the only difference that the calcination temperature was different, and the specific process was: preparing spinning solution with the mass ratio of PVP to silver nitrate being 5:15 by using 1.0g of PVP, 5mL of acetonitrile, 3g of silver nitrate, 0.1g of SDS and 1mL of deionized water. Setting the rotating speed of a spinning head at 6000rpm, the collecting distance at 30cm and the size of a needle at 30G, carrying out centrifugal spinning, respectively collecting four samples after the spinning is finished, and sintering at different temperatures, wherein the sintering heat preservation temperatures are respectively 250 ℃, 280 ℃, 300 ℃ and 350 ℃.

Test examples

Surface topography and diameter analysis: drying the sample before heat treatment for 24h, shearing small pieces, spraying gold, and observing under SEM; the heat treated sample was directly placed under SEM for observation and image taking because of conductivity, and the surface morphology was analyzed from the image. And then, importing the shot Image into Image analysis software Image-J for analysis, selecting 100 fibers from the Image, measuring and recording the diameters of the fibers, and importing the data into Origin to generate a diameter distribution graph.

And (3) component analysis: after the sample before heat treatment is dried in vacuum for 24 hours, cutting small blocks for XRD test; and directly carrying out XRD test on the sample after heat treatment, and comparing the obtained data with a standard PDF card to determine the components in the fiber.

Fig. 2 to 5 are SEM images and diameter distribution diagrams of the silver precursor before sintering in example 2, and it can be easily seen that the diameter distribution of the silver precursor obtained by centrifugal spinning has a certain dispersibility, i.e., has a multi-scale structure, under a Scanning Electron Microscope (SEM) image of 200X. The diameter distribution graph shows that the average diameter value of the obtained silver precursor is between 3 and 5 mu m, and the median, the maximum value, the minimum value and the standard deviation of the diameters of the silver micro-nano wires are slightly different; the spinning solutions with different PVP contents in example 2 can be spun to obtain fibers, but the spinning continuity is greatly different. PVP: AgNO3 ═ 4:15, the fiber length was found to be short and the diameter of the fiber was found to be non-uniform from the collected fibers. PVP: AgNO3 ═ 6:15, the fiber length was found to be longer and the diameter of the fiber was found to be more uniform from the collected fibers. This indicates that as the dope solute concentration increases, the average length of the resulting fiber increases, so that the co-drawing effect of air resistance-spinneret drawing received by the fiber increases, and the diameter of the fiber becomes smaller.

Fig. 6 to 9 are SEM diameter distribution diagrams of silver micro-nano wires after sintering in example 2. As can be seen from the diameter distribution diagram, the average diameter of the obtained silver wires is between 3 and 4 μm, the median, the maximum, the minimum and the standard deviation of the diameters of the silver micro-nano wires are slightly different, and the diameters of the sintered fibers are reduced totally because PVP and SDS are decomposed due to high temperature. Consistent with the silver precursor before sintering, it was also observed that the average diameter of the prepared silver wires of the three different formulations decreased with increasing PVP content.

Fig. 10 represents X-ray diffraction patterns (XRD) obtained by sintering silver micro-nano lines with three different PVP contents in example 2, and the patterns after diffraction are all subjected to normalization treatment. According to the standard diffraction card for the comparative Ag, the Ag simple substance appeared in all three samples. Some peaks were observed in the spectrum, and the presence of silver oxide was confirmed by referring to AgO standard PDF card.

According to the obtained XRD pattern, the grain sizes of the silver wires obtained by three different formulas are calculated by utilizing the Sherle formula, and the obtained grain sizes are shown in the table 1.

The formula of XileK is the Scherrer constant, D is the average thickness of the crystal grain vertical to the crystal face direction, B is the half-height width or the integral width of the diffraction peak of the measured sample, theta is the Bragg angle, gamma is the X-ray wavelength, and

TABLE 1

Sample (I)	Grain size
		PVP：AgNO3＝4：15	22.9nm
PVP：AgNO3＝5：15	25.2nm
		PVP：AgNO3＝6：15	17.3nm

As can be seen from table 1, when PVP: AgNO₃Is 5:15, the grain size reaches 25.2nm, and the grain size is the largest. The grain size of the other samples also approached this value, and the PVP content does not greatly affect the silver grain size in the present invention.

Fig. 11 to 14 are an SEM topography and a diameter distribution of a silver precursor before sintering for centrifugal spinning with different diameter spinnerets in example 3, and it can be seen from fig. 11 to 14 that average diameters of silver micro-nano wires made with needles of different sizes are different, especially that the silver micro-nano wires made with 30G needles and 32G needles and 34G needles have a larger difference, and the median, maximum, minimum and standard deviation of the diameters of the silver micro-nano wires are slightly different. Fig. 15-18 are SEM topography and diameter distribution plots, respectively, for sintered silver micro-nano wires centrifugally spun at different needle diameters in example 3. The diameter distribution diagram shows that the average diameters of the silver precursor and the silver micro-nano wires tend to become smaller along with the diameter reduction of the needle, and the average diameter of the silver precursor and the silver micro-nano wires is thinner after the same sample is sintered than before the same sample is sintered, so that the diameters of most silver micro-nano wires prepared by a 30G needle are distributed in a range of 1-5 mu m, the diameter of 32G is in a range of 0.4-3.5 mu m, and the diameter of 34G is in a range of 0.3-1.2 mu m; the median, the maximum, the minimum and the standard deviation of the diameters of the silver micro-nano wires are slightly different. From the SEM images, it can be seen that the silver precursor before sintering has good homogeneity, and it can be seen that the finer the needle used, the less pronounced the bead structure and the smoother the surface. The 30G and 32G needles can be used for continuous spinning, but when the 34G needle is used, the needle is easily blocked due to the thin needle, so that the spinning is interrupted.

FIG. 19 is SEM topographies of silver micro-nano wires obtained at different sintering temperatures in example 4. It can be seen from the figure that the obtained silver wire is partially broken after the temperature is more than 250 c. In the 5000X picture, it can be seen that there are distinct grains on the surface of the fiber and as the temperature increases the grains develop, growing gradually with a tendency to interconnect.

FIG. 20 shows the X-ray diffraction patterns of silver obtained by sintering at different temperatures in example 4, and the data were normalized. It can be seen that the silver simple substance is obtained at four different temperatures, and the higher the temperature is, the stronger the strength of each crystal face of the silver is, which indicates that the development is more complete. However, the strength of AgO increases rapidly with increasing temperature, and AgO decreases the conductivity of the silver wire, indicating that too high a sintering temperature cannot be used.

The grain size of silver was calculated at different temperatures according to the scherrer equation, and the results are shown in table 2.

TABLE 2

Calcination temperature	Grain size/nm
		250℃	25.2
280℃	39.5
		300℃	65.9
350℃	55.0

As can be seen from table 2, the grain size increased from 25.2nm to 65.9nm from 250 c to 300 c, but the grain size of the silver began to decrease after heating to 350 c. The increased grain size is beneficial for enhancing conductivity because the larger the grain size and the smaller the grain boundary area, the less resistance the electrons encounter through the grain boundary and the lower the resistivity.

The embodiments of the present invention have been described in detail, but the present invention is not limited to the embodiments, and various changes can be made without departing from the gist of the present invention within the knowledge of those skilled in the art. Furthermore, the embodiments of the present invention and the features of the embodiments may be combined with each other without conflict.