Method for producing metal particles, metal particles produced thereby, and the use thereof
Inventors
Kijlstra, Johan • Weuta, Peter H. • Storch, Dirk • Duff, Daniel • Hoheisel, Werner
Assignees
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Publication Number
US-8133932-B2
Publication Date
2012-03-13
Expiration Date
Abstract
Process for producing metal particle sols having a metal particle content of ≧1 g/l, comprising the steps of a) reacting a metal salt solution with a solution containing hydroxide ionsb) reacting the solution obtained from step a) with a reducing agent, wherein at least one of the solutions in step a) comprises a dispersing assistant, metal particles produced by the process and the use thereof.
Core Innovation
The disclosed invention relates to a process for producing silver metal particle sols having a metal particle content of at least 1 g/l. The process includes reacting a silver metal salt solution with a solution containing hydroxide ions to form silver metal oxides or hydrates, silver metal hydroxides or hydrates, mixed silver metal oxide hydroxides or hydrates, or any combination thereof.
The solution obtained from the precipitation step is then reacted with a reducing agent to form the silver metal particle sols. At least one of the solutions used in the hydroxide/oxide-forming step comprises a dispersing assistant. The precipitation step and the reducing step are performed continuously in a microreactor.
The continuous microreactor implementation combined with the dispersing assistant is used to obtain high metal particle content sols without post-concentration, while maintaining colloidal stability. The produced sols are reported to exhibit narrow particle size distributions using UV/Vis plasmon peak ratios, and reduced agglomeration/redisperibility effects indicated by UV/Vis ratios. The particle size distribution and pH stability are described as adjustable within a specified pH stability window.
Claims Coverage
The provided claim set contains one independent claim, which defines a continuous microreactor process for producing silver metal particle sols with a specified minimum metal particle content. Dependent claims further refine dispersing assistant selection, concentration constraints, hydroxide-source bases, reducing agent selection, and a particle size d50 range.
Continuous precipitation-reduction in microreactor for silver metal particle sols
A process for producing silver metal particle sols having a metal particle content of at least 1 g/l by reacting a silver metal salt solution with a solution containing hydroxide ions to form silver metal oxides or hydrates, silver metal hydroxides or hydrates, mixed silver metal oxide hydroxides or hydrates, or any combination thereof, and then reacting the obtained solution with a reducing agent, wherein at least one of the solutions comprises a dispersing assistant and both steps are performed continuously in a microreactor.
Dispersing assistant present in the precipitation step
The process of claim 1 is carried out such that at least one of the solutions in step a) comprises a dispersing assistant.
Dispersing assistant selected from enumerated classes
The process of claim 1 uses a dispersing assistant chosen from a specified set of surfactant and polymer classes.
Dispersing assistant concentration constraint
The process of claim 1 is performed such that a solution containing the dispersing assistant is present at a concentration of at least 0.1 g/l and up to 100 g/l.
Hydroxide ions solution from enumerated base sources
The process of claim 1 is performed such that a solution containing hydroxide ions is obtained by reacting selected bases including LiOH, NaOH, KOH, Mg(OH)2, Ca(OH)2, aliphatic amines, aromatic amines, alkali metal amides, and alkoxides.
Reducing agent selected from enumerated reducing agents
The process of claim 1 uses a reducing agent chosen from an enumerated group including polyalcohols, acids, reducing compounds, and their salts, including ascorbic acid and sodium borohydride among the listed options.
Produced metal particles with d50 particle size range
Metal particles are characterized by a particle size d50 in the range of at least 0.01 µm up to 0.5 µm.
Across the independent claim and its dependents, the core coverage centers on continuously performing both precipitation from a silver salt and hydroxide ions and reduction with a reducing agent in a microreactor, with a dispersing assistant included in at least one precipitation reactant solution. The claim set further narrows dispersing assistant chemistry and concentration, constrains hydroxide-source bases, enumerates reducing agent options, and specifies a d50 particle size range for the produced metal particles.
Stated Advantages
High solids (metal particle content of at least 1 g/l) without post-concentration.
Narrow particle size distributions as indicated by UV/Vis plasmon peak ratios.
High colloidal stability maintained upon concentration.
Reduced agglomeration/redisperibility indicated by UV/Vis ratios.
Adjustability of particle size distribution.
pH stability within a described pH stability window.
Documented Applications
Catalysts.
Coatings.
Conductive layers and transparent conductive layers.
Electronics.
Antimicrobial materials.
Ink formulations, including inkjet or screen printing.
Polymer composites.
Biolabels.
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