CN1127177A - Ionization radiation chemistry redox preparation method for nm metal powder - Google Patents

Abstract

The invented method uses the proper concentration aqueous solution of metal salt, metal halide or metal complex, and adds the optimized surfactant, oxidizability free-radical remover and/or metal ion complexing agent to regulate the solution to proper pH value, after desoxydation of the solution, it is radiated with proper radiation dose under the ionization radiation field, through separating and washing the product, the nm metal powder is obtained after drying. Said method can prepare the product under normal atmospheric temp and pressure. The operative process is simple and easy, the distribution of size range is narrow, the average particle diameter is less than 100 nm, the particle form is uniform, the pureness and yield are relative high, and it is suitable for batch production.

Description

Ionizing radiation chemical oxidation-reduction preparation method of nano metal micropowder

The present invention relates to a preparation technology of nano metal micropowder, in particular, the nano micropowder of noble metal, more active metal and metal with low melting point.

The commonlyadopted inert gas evaporation method for preparing the nano material needs high vacuum and high temperature conditions, has low yield and is not suitable for mass production. Some scholars studied low concentrations (10)^-4M) radiochemical Effect of aqueous solutions of metallic salts, e.g. Foky Tower (Fujita), et al, by gamma irradiation 10^-4MHAuCl₄Obtaining a colloidal solution of gold having an average particle size of 80nm in an aqueous solution, which is reported in Nature, 196,666(1962) of the United kingdom]The above. Since the metal ultrafine particles generated by the radiochemical reduction are generally dispersed in an aqueous solution in a colloidal state, the metal ultrafine particles need to be reprocessed to obtain metal nano-powder.For more active metals and low-melting point metals, the oxidation-reduction potential has a larger negative value and the chemical activity is higher, so that the metals are easy to oxidize in the preparation process, and are more unstable particularly when the metals are in an atom or atom cluster state, which causes great difficulty in preparing the nano metal micro powder.

The invention develops the ionizing radiation chemical oxidation-reduction method into an effective method for preparing the nano metal micro powder, and successfully solves the problem of large concentration (more than or equal to 10)^-3M) metal salt or metal complex aqueous solution, which is particularly suitable for producing nano-micro-powder of noble metals, more active metals and low-melting point metals.

The preparation of nanometer metal powder is realized by carrying out oxidation-reduction reaction on aqueous solution of metal salt or complex thereof under normal temperature and pressure by ionizing radiation under certain conditions, and the method specifically comprises the following steps:

1. preparing an aqueous solution:

the composition of the aqueous solution comprises:

1) a water-soluble metal salt or metal complex (hereinafter referred to as component A). The metal is any one of Au, Ag, Pt, Pd, Cu, Ni, Co, Sn, Pb and Cd; the salt can be sulfate, nitrate, hydrochloride, acetate, halide, etc. all water soluble salts or their complex; the concentration of metal ions is not less than 1X 10^-3M, typically 1X 10^-3—1M，1×10^-2—1×10^-1Preferably.

2) At least one surfactant or colloidal stabilizer (hereinafter referred to as component B). Is selected from polyvinyl alcohol, sodium dodecyl sulfate, sodium lauryl sulfate, polyvinylpyrrolidone and sodium polyphosphate, and has a concentration of 1 × 10 below 1M^-2—5×10^-2M is preferably.

3) At least one scavenger of oxidative free radicals of water-radiation decomposition products (hereinafter referred to as component C). Can be selected from n-butanol, isopropanol, ethanol, propanol, gelatin, n-octanol, n-pentanol or other alcohols, and the concentration is below 10M, preferably 1-4M.

4) For the aqueous solution of copper, cobalt, nickel, cadmium, tin metal ions, a complexing agent (hereinafter referred to as component D) is added. Such as EDTA, or NH₃H₂O, or an alkali metal hydroxide, and the concentration thereof is 10M or less.

2. The solution is adjusted to the appropriate pH.

3. And removing oxygen. The solution can be filled with inert gas, nitrogen or hydrogen.

4. The solution is irradiated in an ionizing radiation field at a suitable dose rate for several hours to several tens of hours. In general, the dose rate may be in the range of 0.1 to 10³Selected within the range of Gy/s. The total absorbed dose of radiation is 5 × 10²—1×10⁵Ionizing radiation sources used include accelerated electron beams, α rays, β rays, gamma rays, and X-rays.

5. And separating the product in the solution after irradiation. The separation method comprises standing at room temperature for a long time, precipitating and filtering, or separating by centrifugation, or performing hydrothermal treatment. The separated product is washed several times with distilled water and/or aqueous ammonia until free of impurities. Finally drying at 60-150 ℃ to obtain the metal nano micro powder.

The method for preparing the metal nano micro powder utilizes the radiation chemical oxidation-reduction action of metal ions in an aqueous solution, the basic principle is that water is decomposed by radiation to generate reducing free radicals such as hydrated electrons, H atoms, organic free radicals and the like in the water, and the reducing particles reduce the metal ions into metal atoms step by step:

the metal atoms are gathered into metal atom clusters, then colloidal aggregates are formed, and finally nucleation grows into metal ultrafine particles. Since the radiochemical reduction is carried out stepwise in an aqueous solution and the stabilization effect of the surfactant is exhibited, the resulting ultrafine metal particles have a small particle diameter and a narrow distribution range.

The method can be used for preparing the nano-scale metal micro-powder at normal temperature and normal pressure, the nano-scale metal micro-powder comprises inactive metals of Au, Pt, Pd, Ag and Cu and active metals of Ni, Cd, Sn, Pb and Co, the particle size of the obtained product is smaller, generally between 5 and 40nm, and the maximum particle size is not more than 100 nm. The yield of the product is high; and no matter the metal is an inert metal or an active metal, the metal is stable as common corresponding metal in the air atmosphere.

The concentration of the component A is not suitable to be too small and is lower than 1 multiplied by 10 when the method is adopted to prepare the nano-scale metal micro powder^-3M often does not yield a fine powder but only colloidal metal particles. However, if the concentration of component A is more than 1M, the particle size of the ultrafine metal powder obtained is difficult to ensure. The amount of component B is related to the amount of component A, wherein the amount of A is less than that of B, and the amount of A is larger than that of B. Too little B is insufficient to stabilize the colloidal solution, too much B is disadvantageous for the redox reaction to proceed, and it is also economically disadvantageous. The dosage of the component C is 10-100 times of the dosage of the component A, so as to ensure that oxidative free radicals generated in the water radiation decomposition process are 100 percent eliminated. The amounts of components D and E depend on the nature of the metallic submicron powder to be prepared.

The particle size is determined by the composition, concentration, pH, total radiation dose, dose rate and treatment temperature of the aqueous mixture. Suitable radiation sources, radiation rates and total radiation doses will depend on the composition of the mixture in aqueous solution and its concentration, the irradiation atmosphere and temperature and other factors that may affect product yield and submicron particle size.

The hydrothermal treatment is that the water solution after irradiation is put into an autoclave, heated for 1-10 hours at a constant temperature of 80-200 ℃, cooled and filtered to separate the product.

The solution is adjusted to a proper pH value, namely the pH value of the salt of the relatively active metal or the complex compound thereof is controlled in an alkaline range. For the salt solution of metals such as nickel, cobalt, tin, cadmium, etc., a buffer pair or an alkaline agent such as NH is added₃H₂O/ammonium salt, NH₃H₂O or alkali metal hydroxides to adjustIts pH is brought to the desired value.

The method for preparing the nano metal micro powder has the following advantages:

1) the product metal submicron powder has small particles, generally less than 100 nm.

2) The product metal superfine powder has narrow particle size distribution range and uniform particle size.

3) The particle size and shape of the product metal submicron powder can be controlled by adjusting the preparation conditions, and the metal particles generated under proper conditions have uniform morphology.

4) The reduction process of the metal ions can be carried out at room temperature (generally within the range of-5 to 50 ℃) and normal pressure, so that the oxidation of the metal or the further growth of particles under high temperature conditions and high temperature which are required to be adopted by other methods is avoided.

5) The product purity is higher.

6) The preparation process is simple and the cost is low.

7) High yield and easy batch production.

The present invention will be described in more detail with reference toexamples.

Example 1 preparation of silver nanopowder

To 0.05M AgNO₃Adding a certain amount of C into the aqueous solution₁₂H₂₅NaSO₄Making the concentration of the mixture to be 0.1M, and adding a certain amount of (CH)₃)₂CHOH was adjusted to a concentration of 6.0M. Introducing high-purity N into the solution₂0.8 hour. The prepared solution is⁶⁰1.0X 10 in Co gamma-radiation field²Gy/min for 5 hours. Hydrothermal treatment at 105 ℃ for 2 hours, collecting the product, washing the product with ammonia water three times, and then washing the product with distilled water three times. And (5) placing the mixture in a drying oven, and drying the mixture for 2 hours at the temperature of 80 ℃ to obtain the nano Ag powder. Transmission Electron Microscope (TEM) and X-ray powder diffraction (XRD) analysis show that the average grain diameter of the product Ag powder is less than 15nm, and the Ag particles are spherical. The yield of the product Ag powder can reach more than 95%, and the radiochemical yield G value (atom/100 eV) of Ag can reach more than 10.

EXAMPLE 2 preparation of Nano-copper powder

Preparing a solution containing 0.01M CuSO₄、0.01M EDTA、0.1M C₁₂H₂₅NaSO₄、3.0M(CH₃)₂Introducing high-purity N into aqueous solution of CHOH₂For 1 hour. The prepared solution is⁶⁰3.6X 10 in Co gamma-radiation field⁴Gy absorbed dose irradiation, hydrothermal treatment at 110 deg.c for 2 hr to collect product, washing with ammonia water and distilled water three times each, and drying to obtain nanometer material^CuAnd (3) pulverizing. TEM and XRD analysis showed that the product^CuThe powder is composed of spherical particles, the average particle size is less than 20nm,and the yield of the copper powder can reach more than 70%.

EXAMPLE 3 preparation of Nano platinum powder

The formulation contains 0.001M H₂PtCl₆、0.001M C₁₂H₂₅NaSO₄、2.0M(CH₃)₂Introducing high-purity N into aqueous solution of CHOH₂Oxygen was removed in 0.5 hour. In that⁶⁰1.8X 10 in Co gamma radiation field³Gy inhalationAnd (5) receiving dose irradiation. Standing, precipitating and collecting a product, washing the product with distilled water twice, and drying to obtain the nano Pt powder. TEM analysis showed that the product Pt powder consisted of spherical particles with an average particle size of less than 5 nm.

EXAMPLE 4 preparation of Nano Nickel powder

Preparing the alloy containing 0.05M Ni (CH)₃COO)₂、0.4M NH₃H₂O or NH₃H₂O/ammonium salt buffer couple, 0.01M C₁₂H₂₅NaSO₄、2.0M(CH₃)₂And introducing high-purity Ar into the CHOH aqueous solution for 1 hour. The prepared solution is⁶⁰6.0X 10 in Co gamma-radiation field⁴Gy absorbed dose irradiation. Standing, precipitating and collecting a product, washing the product twice with ammonia water, washing the product three times with distilled water, and drying to obtain the nano Ni powder. XRD analysis shows that the product consists of a metal Ni single phase with a face-centered cubic structure; TEM showed that the average particle size was less than 10 nm. The optimal yield of the Ni powder can reach more than 90 percent. The thermal analysis result shows that the Ni powder can stably exist in the air atmosphere below 220 ℃.

EXAMPLE 5 preparation of Nano cadmium powder

Preparing a solution containing 0.01M CdSO₄、0.01M C₁₂H₂₅NaSO₄、1.0MNH₃H₂O/(NH₄)₂SO₄Buffer Pair, 6.0M (CH)₃)₂Aqueous solution of CHOH. Introducing high-purity H into the solution₂For 1 hour. Then placing the solution in⁶⁰2.9X 10 in Co gamma-radiation field⁴Gy absorbed dose irradiation, and the product was collected by centrifugation. Washing the product with distilled water for three times, and drying to obtain the nano Cd powder. The product is composed of spherical metal Cd particles, the average particle size is less than 30nm, and the yield of Cd powder can reach 30%.

Example 6 preparation of Nano tin powder

Preparing a solution containing 0.01M SnCl₂、0.5M NaOH、2.0M(CH₃)₂Aqueous solution of CHOH. In this example, NaOH was added to dissolve Sn in the solution²⁺Ion with HSnO₂ ^-The form exists and keeps the solution alkaline. Introducing high-purity N₂For 1 hour. Placing the above solution in⁶⁰In Co gamma-radiation field, at 2.5X 10⁴Gy absorbed dose irradiation. Standing, precipitating and collecting a product, washing the product with distilled water for four times, and drying to obtain the nano Sn powder. TEM and XRD analysis show that the product is single-phase tetragonal metal Sn, which is composed of spherical particles with the average particle size of less than 30 nm. The yield of Sn powder can reach more than 40%. Thermal analysis shows that the product Sn powder can exist stably in an air atmosphere below about 200 ℃.Some of the nanosized metal powders prepared by the radiochemical process of the present invention and their properties are listed in the table below.

Example (b)	Product of	Yield of	Average particle diameter (nm)	Differential thermal analysis
					Conversion% G value	XRD method by TEM method	Tm o(℃) Toxi o(℃)
		1	Ag	＞95 9.6				15 13	944(952)
2	Cu				＞70	20 16	(1083) 160
		3	Pt					5 5	(1773.5)
4	Ni				＞90 4.4	10 8	(1455) 220
		5	Cd	～30				15 20	(320.8)
6	Sn				～40	30	220(231.89)
		It is composed of It is composed of a base, a cover and a cover	Pb					45	(327)
Pd					10	(1549.4)
			Au				10	(1063)
Co					22	(1495)

Note: 1.T_m ^o(DEG C) initial melting temperature;

2.T_oxi ^o(DEG C) initial oxidation temperature;

3. the data in brackets () are the melting points of the corresponding common polycrystalline metals.

Claims (8)

1. A process for preparing the nm-class metal powder features that the powder with a concentration greater than or equal to 10^-3M, at least one surfactant (component B), at least one oxidizing free radical scavenger (component C) and a metal ion complexing agent (component D) are added to the aqueous solution of the metal salt or the halide or the complex thereof (component A) of M, the solution is adjusted to a proper pH value, after oxygen removal treatment, the solution is placed in an ionizing radiation field at a rate of 0.1-10³Gy/s irradiation dose rate, total absorbed dose of irradiation 5X 10²－－1×10⁵Gy, finally separating, washing and drying.

2. The method of claim 1, wherein said ionizing radiation source is α rays, β rays, gamma rays, X-rays, or accelerated electrons.

3. A method according to claim 1, characterized in that the metal elements in component a comprise gold, silver, copper, platinum, palladium, cobalt, nickel, cadmium, tin, lead.

4. A process according to claim 1, characterized in that the surfactant (component B) is selected from polyvinyl alcohol, sodium lauryl sulfate, polyvinyl pyrrolidone, sodium polyphosphates, preferably in a concentration of less than 1M.

5. A process according to claim 1, characterized in that the oxidizing radical scavenger (component C) is selected from n-butanol, isopropanol, ethanol, propanol, gelatin, n-octanol and n-pentanol or other alcohols, suitably in a concentration of 10M or less.

6. A method according to claim 1, characterized in that the complexing agent (component D) is selected from ammonia, EDTA or alkali metal hydroxides, and is used in concentrations below 10M.

7. The method according to claim 1, characterized in that said suitable pH means that the pH of the aqueous solution of the salt of the more active metal or its complex is controlled in the alkaline range.

8. A method according to claim 1, characterized in that the method for separating the nano-sized metal particles from the irradiated aqueous solution is hydrothermal treatment, or static precipitation, or centrifugal separation.