WO2008122251A1

WO2008122251A1 - A method of preparation of suspensions of micrometer crystals of silver

Info

Publication number: WO2008122251A1
Application number: PCT/CZ2007/000064
Authority: WO
Inventors: Tomas Base; Jan Subrt
Original assignee: Institute Of Inorganic Chemistry Ascr, V.V.I.
Priority date: 2007-04-06
Filing date: 2007-06-28
Publication date: 2008-10-16
Also published as: CZ2007246A3

Abstract

The suspensions of micrometer crystals of silver are prepared according to this invention by mixing a silver salt, advantageously silver nitrate (AgNO3), a reduction agent from a group of species containing -OH or -CHO functional groups, advantageously compounds based on diols or polyols, and a surface active component of polymer character with nitrogen and oxygen atoms in its molecule, advantageously polyvinylpyrrolidone, so that the concentration of the silver salt in the mixture is bigger than 0.1 μmol/l, advantageously in the range from 0.5 mol/l to 2 mol/l, the reaction mixture is heated to 20 - 350 °C, advantageously to 160 - 190 °C, for 1 min to 12 hours, advantageously for 2 hours. After cooling the mixture, the silver crystals are washed by decantation with an excess of a solvent, advantageously with ethanol. As reducing agents are optimally used 1,2-ethanediol or 1,3-propanediol or 2,3-butanediol or 1,5-pentanediol or 1,6-hexanediolor diethyleneglycol or triethylenglycol or glycerol.

Description

A method of preparation of suspensions of micrometer crystals of silver

Technical fields

This invention deals with a method of preparation of suspensions of micrometer crystals of silver.

Background art

Crystals of metallic elements attract significant interest because of their applicability in a number of industrial areas. To selected metals such as, for instance, gold and silver is dedicated a great deal of specialized literature, [e.g. N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, Pergamon Press Ltd. 1^st ed. 1984, Oxford, England] There are numerous ways of preparation of colloidal particles described in the literature and most of these ways are based on the reduction of precious metal salts. However the described methods lead nearly exclusively to colloidal solutions with small crystalline particles with dimensions of up to hundreds of nanometers [F. Kim, S. Connor, H. Song, T. Kuykendall, P. Yang, Angew. Chem. Int. Ed. 2004, 43, 3673; C. S. Ah, Y. J. Yun, H. J. Park, W.-J. Kim, D. H. Ha, W. S. Yun, Chem. Mater. 2005, 17, 5558]. Silver colloidal solutions possess a yellowish-brown colour and, from all the possible ways of preparation is described a particular method that is referred to as 'polyol'. In association with this method there are discussed, for example, silver nano-wires [B. Wiley, Y. Sun, Y. Xia, Langmuir 2005, 21, 8077] or silver nano-cubes [Y. Sun, Y. Xia, Science 2002, 298, 2176] in the literature.

The preparation of suspensions of micrometer gold crystals using a similar method was for the first time presented by us at a conference in France [T. Base, Z. Bastl, M. Slouf, N. Murafa, J. Subrt. J. Plesek, M. G. S. Londesborough, O. Kfϊz 24^th European Conference on Surface Science (ECOSS-24), September 4-8 2006, Paris, France, contribution SAM-We 1-163]. It is using the same method that is claimed herein for the preparation of suspensions of micrometer silver crystals, for which this method has never been described or presented.

Disclosure of the invention

The subject of the invention described below is a method of preparation of suspensions of micrometer crystals of silver that leads to formation of silver crystals with dimensions ranging from one to tens of micrometers. The crystals of these dimensions have shapes of polyhedra or thin wires or rods (Fig. 1). Silver crystals are prepared according to this invention by mixing a silver salt, advantageously silver nitrate (AgNO₃), a reducing agent from a group of species containing -OH or -CHO functional groups, advantageously compounds based on diols or polyols, and a surface active component of polymer character with nitrogen and oxygen atoms in its molecule, advantageously polyvinylpyrrolidone, so that the concentration of the silver salt in the mixture is bigger than 0.1 μmol/1, advantageously in the range from 0.5 mol/1 to 2 mol/1, the reaction mixture is heated to 20 - 350 ⁰C, advantageously between 160 - 190 °C, for 1 min to 12 hours, advantageously for 2 hours. After cooling the mixture the silver crystals are washed by decantation with an excess of a solvent, advantageously with ethanol. Using very low concentrations of silver salts in the starting mixture leads to formation of yellow or yellowish brown colloidal solutions containing silver crystals of nanometer dimensions. The most important factor which leads to formation of the desired suspensions of micrometer silver crystals is the concentration of the starting silver salt. The concentration of silver salts together with the amount of polymeric additive and the type of reduction agent all influence the shapes of the resulting crystals. On the contrary to colloidal particles of silver, which form yellow solutions, the suspensions of silver crystals can be simply washed by decanting with a suitable solvent (e.g. ethanol). Colloidal particles described in the literature have sizes in nanometer dimensions (10^"9m) and the prepared silver crystals have dimensions ranging from one to tens of micrometers (10^" m) . Metal crystals prepared according to this method can be used for example in electronics for the preparation of components of electric circuits or directly as components of electric circuits. An especially important possibility for the use of these crystals is the area of powder metallurgy where suspensions of Ag crystals can be used as a very fine silver powder for sintering. Another possible area of use is the restoration, preparation of conductive silver pastes, glues and others.

Description of figures

Fig. 1 shows silver crystals with shapes of polyhedra or thin wires or rods.

Examples of preparation:

Example 1

5 g of polyvinylpyrrolidone was dissolved with stirring and heating in 15 ml of 1,3- propanediol. To this pure solution was added 5 g AgNO₃ and another 15 ml 1,3- propanediol. This mixture was heated for 2 hours on an oil bath pre-heated to 185 ⁰C. During heating a cloudy mixture containing silver crystals formed in the flask. The crystals can be described as a mixture of polyhedra, wires and rods. The length of the crystals is ranges from one to tens of micrometers. These crystals can be easily washed by decanting with an excess of suitable solvent (for example with ethanol). The resulting mixture has the appearance of very fine silver dust laying at the bottom of the flask and overlayered with pure ethanol. A stirring of the mixture gives a suspension of Ag crystals in the solution.

Example 2

15 g OfAgNO₃, 5 g of polyvinylpyrrolidone and 50 ml of 1,2-ethanediol were mixed together. The mixture was heated to 175 ⁰C and both solid materials, polyvinylpyrrolidone and AgNO₃, started to dissolve. A mixture of grey colour appeared during stirring and heating. The total time of the reaction was 1 hour. After cooling to room temperature the mixture was diluted with an excess of ethanol (500 ml) and left for one week. There was a layer of Ag crystals of silvery appearance at the bottom. Afterwards the mixture was washed by decanting with ethanol to remove the soluble starting components that remain in the maternal solution. The resulting product had the appearance of very fine silver powder suspended in ethanol.

Industrial applicability

Crystals of silver prepared according to this invention can be used in electronics, powder metallurgy, or in restoration.

Claims

C L A I M S

1. A method of preparation of suspensions of micrometer crystals of silver characterized in that mixed together are a silver salt, advantageously silver nitrate (AgNO₃), a reduction agent from a group of species containing -OH or -CHO functional groups, advantageously compounds based on diols or polyols, and a surface active component of polymer character with nitrogen and oxygen atoms in its molecule, advantageously polyvinylpyrrolidone, so that the concentration of the silver salt in the mixture is bigger than 0.1 μmol/1, advantageously in the range from 0.5 mol/1 to 2 mol/1, the reaction mixture is heated to 20 - 350 °C, advantageously to 160 - 190 ⁰C, for 1 min to 12 hours, advantageously for 2 hours. After cooling the mixture, the silver crystals are washed by decantation with an excess of a solvent, advantageously with ethanol.

2. A method of preparation of suspensions of micrometer crystals of silver according to the point one characterized in that as reducing agents are advantageously used 1,2-ethanediol or 1,3-propanediol or 2,3- butanediol or 1,5-pentanediol or 1,6-hexanediol or diethyleneglycol or triethyleneglycol or glycerol.