Anticorrosive magnetic nanocolloids protected by precious metals

Abstract

The invention relates to new single- or multi-metallic magnetic colloid particles (for example, Fe, Co, Ni, Fe/Co) having a size of up to 20 nm, the surface of which is protected against corrosion by precious metals, such as Pd, Ag, Pt or Au. The invention also relates to a method for producing such materials. In isolated form or in solution said materials are used among other things as sealing media against dust and gas in magnetic fluid seals (liquid O ring), for lubricating and mounting rotating shafts (magnetic levitation bearing), for the magnetooptic storage of information as well as for the magnetic marking of cells and their separation in biological samples or for the local administration of medicines.

1 . A process for the preparation of precious-metal protected, anticorrosive metal and alloy colloids, characterized in that previously prepared or in situ prepared magnetic nanocolloids are treated with strong reductants in a solvent, and precious metal salts are added to the resulting mixtures.  
     
     
         2 . The process according to  claim 1 , wherein Fe, Co, Ni or Fe/Co colloids are employed as said previously prepared or in situ prepared magnetic nanocolloids.  
     
     
         3 . The process according to  claim 1 , wherein hydrides of elements from main groups 1 to 3 of the Periodic Table or complex hydrides of these elements or of tetraalkylammonium are employed as said strong reductants.  
     
     
         4 . The process according to  claim 1 , wherein reducing organometallic compounds of main groups 1 to 4 of the Periodic Table are employed as said strong reductants.  
     
     
         5 . Magnetic nanocolloids having a particle size of smaller than 20 nm, characterized in that said magnetic particles are provided with a precious-metal coating and are stable towards corrosion for more than 3 hours as seen from their magnetogram and their UV/Vis spectra.  
     
     
         6 . The magnetic nanocolloids according to  claim 5 , wherein Au is employed as said precious metal, and Fe as said magnetic particles, and said nanocolloids are stable towards corrosion for more than 100 hours.  
     
     
         7 . The magnetic nanocolloids according to  claim 5 , wherein Au is employed as said precious metal, and Co as said magnetic particles, and said nanocolloids are stable towards corrosion for more than 20 hours.  
     
     
         8 . Use of the magnetic nanocolloids according to  claims 5  to  7  as a magnetic fluid having a high saturation magnetization and at the same time a low filler content in a magnetic fluid seal.  
     
     
         9 . Use of the magnetic nanocolloids according to  claims 5  to  7  as a magnetic cell label after applying an additional cell-compatible coating.  
     
     
         10 . Use of the magnetic nanocolloids according to  claims 5  to  7  for magnetic cell separation.  
     
     
         11 . Use of the magnetic nanocolloids according to  claims 5  to  7  for magnetooptical storage of information.