KR20100100208A - Preparation method of silver powders - Google Patents

Abstract

PURPOSE: A preparation method for silver powder is provided to obtain silver powder at the room temperature because of low reduction temperature and to reduce the reduction time without using complexing agent or surfactant. CONSTITUTION: A preparation method for silver powder comprises steps of: dissolving silver nitrate in ethyl alcohol to obtain a mixed solution, adding NaOH in the mixed solution to create sodium ethoxide and automatically obtaining Ag powder precipitate through the reaction, and completing Ag powder through filtering, washing, and drying.

Description

Preparation method of silver powder

The present invention relates to a method for producing silver powder using sodium ethoxide as a reducing agent of silver nitrate by adding sodium hydroxide to a mixed solution of silver nitrate dissolved in ethyl alcohol.

The silver powder is classified into chemical reduction and physical (mechanical) methods. The physical methods are known as gas phase (flame) decomposition by aerosol injection and pulverization of bulk silver ingots. Due to constraints, chemical reduction is widely used due to relatively fast reduction rate and efficient recovery of silver particles. The chemical reduction method is briefly introduced below.

Republic of Korea Patent Publication No. 10-2005-40226 is prepared by dissolving a silver lump in an aqueous solution of nitric acid to prepare an aqueous solution of silver nitrate and adding ammonium hydroxide to form a silver-ammonium complex ion, and then reduced formaldehyde by adding a surfactant, pH control It is known to produce silver particles. Korean Patent No. 368055 discloses a method of preparing spherical silver powder by mixing aqueous solution at room temperature after preparing an aqueous solution in which hydroquinone is dissolved by adjusting a pH 11 by adding ammonia water to an aqueous solution of silver nitrate. Known. Korean Patent Laid-Open Publication No. 10-2005-116544 discloses a method of preparing silver plate-shaped particles by mixing a solution of silver nitrate with a solution of hydroquinone and potassium sulfite (or ammonium sulfite) dissolved in distilled water and adding ammonia water. . Korean Patent No. 10-449369 discloses a step of adding ammonium hydroxide to ethylene glycol; Dissolving silver nitrate and polyvinylpyrrolidone (PVP) in a solution in which ethylene glycol and ammonium hydroxide are mixed; A method for producing a plate-like silver powder is described through three steps of adding hydrogen peroxide and chloroplatinic acid (H ₂ PtCl ₆ ) to ethylene glycol. Korean Unexamined Patent Publication No. 10-12141 is immersed in a concentrated nitric acid and dissolved by maintaining the temperature at 70 ℃ to 80 ℃, and then prepared by adding an aqueous sodium chloride solution and adjusted to pH 4 by adding an aqueous hydrochloric acid solution. Then, the method of recovering silver powder is described when rotating the stirrer which iron piece adhered to this solution.

In addition, in order to obtain silver particles, a method of recovering a 4 nm size silver powder using trisodium citrate as a complexing agent and NaBH ₄ as a reducing agent is known. In addition, a technique is known in which silver nanowires and silver nanorod particles are prepared from cetyltrimethylammonium bromide (CTAB) as a surfactant and ascorbic acid as a reducing agent (Chem.Commum., 617 (2001)). In addition, Sinha et al. Used glycerol as a solvent and a reducing agent, and heated the silver salt solution to 175 ° C. to prepare 1.5 μm to 11 μm silver particles (Bull. Mater. Sci., 28 (3), 213). (2005)). Sondi et al. Produced silver particles with an average particle diameter of 14.7 nm to 26.3 nm using silver nitrate (5 wt%), ascorbic acid (4.4 wt%) and Daxad 19 (naphthalene sulfonate formaldehyde condensate, MW 8000, 10 wt%). In this method, the silver particles have a reduction time ranging from 1 minute to 7 minutes (Journal of Colloid and Interface Science, 260, 75 (2003)). Wang et al prepared silver wire (100 nm × 500 nm) using silver chloride as silver salt and glucose as reducing agent at a reduction time of 18 hours and a reaction temperature of 180 ° C. (Chem. Eur. J., 11, 160 (2005). ).

The above-described chemical reduction method is mainly a method for producing silver powder by wet reduction. Conventional silver powder manufacturing conditions are 50 ℃ ~ 175 ℃, conditions other than room temperature, low silver concentration (<5% by weight) and long reduction time (18 Time ~ 24 hours). Therefore, the existing production method of the silver powder has a problem of low productivity, the demand for a new silver powder production method is increasing.

Accordingly, the present inventors have studied the steps necessary for producing a conventional silver powder and a method for preparing the silver powder which can avoid the addition of a reducing agent and a surfactant recognized as a compound, a long reduction time, and a high reduction temperature. By using sodium ethoxide (CH ₃ ONa) produced by the mixture of ethyl alcohol and sodium hydroxide as a reducing agent, a method of preparing a large amount of silver powder was completed. That is, an object of the present invention is to provide a method for producing a new silver powder with improved productivity.

Silver powder manufacturing method of the present invention for achieving the above object is a first step of preparing a mixed solution by dissolving silver nitrate in ethyl alcohol; A second step of preparing a silver powder precipitate by autoreduction by sodium ethoxide generated by adding sodium hydroxide to the mixed solution; And a third step of preparing the silver powder by filtration, washing with water and drying the silver powder precipitate.

Unlike the conventional silver powder manufacturing method, the silver powder manufacturing method of the present invention does not use a complexing agent and a surfactant, and can reduce the reduction time, which was previously 18 hours to 24 hours, to several minutes. In addition, unlike the existing manufacturing method that requires a high reduction temperature of 150 ℃ or more, the present invention has a low reduction temperature (10 ℃ ~ 35 ℃) not only can be manufactured at room temperature, but also has a high yield of silver powder productivity Very high.

Referring to the present invention described above in more detail as follows.

The present invention relates to a silver powder manufacturing method, the first step of preparing a mixed solution by dissolving silver nitrate in ethyl alcohol; A second step of preparing a silver powder precipitate by autoreduction by sodium ethoxide generated by adding sodium hydroxide to the mixed solution; And a third step of preparing the silver powder by filtration, washing with water and drying the silver powder precipitate.

Each of the above steps is performed at a room temperature of 10 to 35 ℃, it is characterized by the high temperature reduction (150 ℃ or more) and long reduction time (within 18 hours to 24 hours) required in the prior art is not required.

Referring to the first step, the solubility of silver nitrate in ethyl alcohol at 25 ° C. is about 7.61 g for 100 g of ethyl alcohol. Therefore, it is preferable that the weight ratio of the ethyl alcohol and the silver nitrate is 1: 0.02 to 0.2, more preferably 1: 0.05 to 0.15.

In addition, the most important point in the present invention is the moisture content contained in the ethyl alcohol, if the moisture is contained in more than 0.05% by weight relative to the total weight of ethyl alcohol, the silver powder is not produced and the silver oxide is produced because the ethyl For alcohol, it is preferable to use anhydrous ethyl alcohol without water content or ethyl alcohol containing water at least less than 0.05% by weight.

Referring to the second step, the sodium hydroxide is added to produce sodium ethoxide, and when the sodium hydroxide is added to the mixed solution, the automatic reduction reaction proceeds rapidly. The amount of sodium hydroxide added is determined by the solubility of sodium hydroxide in ethyl alcohol. The solubility of sodium hydroxide is about 11.65 g with respect to 100 g of ethyl alcohol, so the weight ratio of ethyl alcohol and sodium hydroxide is about 1: 0.02 to 20, More preferably, it is 1: 0.05-5. Here, if the weight ratio of the ethyl alcohol and sodium hydroxide is less than 1: 0.02, a problem may occur that the reduction reaction does not proceed, and if the ratio exceeds 1: 20, the pH of the mixed solution is too high, so the range is It is good to keep.

In addition, the sodium ethoxide produced by the reaction of the ethyl alcohol and sodium hydroxide (sodium ethoxide) is a chemical species having a high electron donating ability (chemical species), the production of sodium ethoxide used as a reducing agent in the present invention is shown in Scheme 1 (DW Williams, RWBost, Reaction Products of Ethyl Alcohol and Sodium Hydroxide, Journal of Chemical Physics, 4, 251-253 (1936)).

CH ₃ CH ₂ OH (ℓ) + NaOH (s) → CH ₃ CH ₂ ONa (s) + H ₂ O (ℓ)

Scheme 1 has an equilibrium Gibbs free energy of -3.62 kJ / mole at 25 ° C and an equilibrium entropy of -22.57 J / mole. The equilibrium constant is 4.3 at 25 ° C, and the equilibrium constant is 3.85 at 50 ° C. Thus, about 80% of the sodium hydroxide described in Scheme 1 is converted to sodium ethoxide. The production of sodium ethoxide is confirmed by the presence of water or the content of NaOH in the reaction mixture, with 4.7 μm (4650 nm) peak in the UV spectrum identified as the absorption band of water. NaOH concentration is determined by titration with HCl and phenolphthalein (indicator). When all NaOH has disappeared in the reaction, it is not detected by titration with HCl.

In the third step, the silver powder precipitate produced in the second step may be filtered and washed with a general method used in the art, and then dried to obtain silver powder in high yield.

The present invention described above will be described in more detail based on the following examples, but the scope of the present invention is not limited to the following examples.

Example 1

1.089 g of silver nitrate powder was dissolved in 10.55 g of ethyl alcohol (water content of less than 0.01% by weight) at 25 ° C to prepare a transparent mixed solution. Sodium hydroxide 1.08 g was added to the mixed solution to produce sodium ethoxide as a reducing agent, thereby producing a white silver powder precipitate through an automatic reduction reaction. Thereafter, the silver powder precipitate was filtered, washed with water and dried to prepare 0.62 g of silver powder (yield 89.7%, reduction time: 9 minutes 30 seconds). When the phenolphthalein solution dissolved in 95% ethyl alcohol was added dropwise to the recovered filter liquor, the silver powder did not appear light pink, indicating that the reaction between ethyl alcohol and sodium hydroxide was completed and converted to sodium ethoxide. Figure 1 shows the X-ray diffraction diagram of the particles recovered during the automatic reduction reaction, Figure 2 is an X-ray diffraction diagram of the silver powder obtained when the final reduction.

Example 2

In the same manner as in Example 1, 0.6 g of silver powder (yield 91%, reduction time: 9 minutes 8 seconds) was prepared using 3 g of the sodium hydroxide. When the phenolphthalein solution dissolved in 95% ethyl alcohol was added dropwise to the recovered mother liquor, the silver powder did not appear light pink, indicating that the reaction between ethyl alcohol and sodium hydroxide was completed.

Example 3

In the same manner as in Example 1, 0.3 g of silver nitrate was added thereto, and 0.165 g of silver powder (yield 87%, reduction time: 8 minutes 42 seconds) was prepared. When the phenolphthalein solution dissolved in 95% ethyl alcohol was added dropwise to the recovered mother liquor, the silver powder did not appear light pink, indicating that the reaction between ethyl alcohol and sodium hydroxide was completed.

Comparative Example 1

At 25 ° C., 1 g of silver nitrate powder was dissolved in 12.08 g of ethyl alcohol (20 wt% of water) to prepare a transparent mixed solution. When 1.47 g of sodium hydroxide was added to the mixed solution, a black precipitate was obtained. Figure 3 is an X-ray diffraction diagram of the particles obtained in Comparative Example 1, the analysis results, the produced particles were identified as silver oxide (AgO), through which it can be seen that the yield of the silver powder is lowered.

Comparative Example 2

Same as Example 1, but 0.2 g of sodium hydroxide was added. Although 24 hours had elapsed, the reduction reaction of silver ions was not visually confirmed.

The silver powder thus prepared has excellent compatibility with polyethylene, polypropylene, polyvinyl chloride, polystyrene, acrylonitrile butadiene styrene (ABS), poly methyl meta acrylate (PMMA), polycarbonate, polyester, and the like. It can be used in plastic molded articles, fibers, paints, and inks having the properties of UV resistance, UV protection, photosensitivity, antistatic properties, electromagnetic shielding and deodorization. It is also expected to be used as a major component of surface enhancer Raman scattering enhancers, additives in ink active portions, or conductive adhesives in various electrical products.

Figure 1 shows the X-ray diffraction curve of the particles recovered in the auto-reduction reaction during the silver powder manufacturing process performed in Example 1.

Figure 2 shows the X-ray diffraction curve of the silver powder prepared in Example 1.

Figure 3 shows the X-ray diffraction curve of the particles prepared in Comparative Example 1 according to the present invention.

Claims (5)

A first step of preparing a mixed solution by dissolving silver nitrate in ethyl alcohol; A second step of preparing a silver powder precipitate by autoreduction by sodium ethoxide generated by adding sodium hydroxide to the mixed solution; And Filtering, washing, and drying the silver powder precipitate to prepare a silver powder; Method for producing a silver powder comprising a. 2. The method of claim 1, wherein the ethyl alcohol is anhydrous ethyl alcohol or ethyl alcohol having a water content of less than 0.05% by weight. The method of claim 1, wherein the weight ratio of the ethyl alcohol and the silver nitrate is 1: 0.02 to 0.2. The method of claim 1, wherein the weight ratio of ethyl alcohol and sodium hydroxide is about 1: 0.02 to 20. The method of claim 1, wherein the first to third steps are performed at 10 ° C. to 35 ° C. temperature.

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