Conductive composite particles useful as conductive filler for sealant compsns., etc. - have electrically conductive core and conductive refractory material conductively welded together with intermediate noble metal

摘要

Composite particles comprise, in combination, (I) an electrically conductive core material with a surface oxide layer; (II) an electrically conductive refractory material and (III), situated between the (I) and (II), a noble metal or noble metal alloy, whereby the (I) and (II) are conductively bonded together. The core is esp. of a metal or metal alloy, such as Al, Sn, Zn, Ni or Mg. The refractory material is esp. WC, NbB, NbB2, TiN, VSi2, MoB, TiB2, ZrB2, B4C, ZrN, CoSi2 or MoSi2. Pref. the particles are made up of 10-97.5% core material, 88-0.5 wt.% refractory material and 2-8 wt.% noble metal or noble metal alloy. Pref. the core material has an average particle size of 0.5-200 micron and the oxide layer is e.g. 2-10,000 Angstroms thick. The refractory material is pref. in the form of particles with a particle size of ca. 0.005-20 micron and esp. in a size range of from ca. twice the thickness of the oxide layer to one-tenth of the size of the core particles. Each of the refractory particles pref. penetrates through the oxide layer into the core particle and extends outwards beyond the oxide layer to form a conductive path through the oxide layer. The noble metal or noble metal alloy is pref. present as discrete formations on the surface of the oxide-carrying core particles. A specifically claimed particle compsn. comprises an Al core, Ag as noble metal and WC as refractory material. Pref. the particles have a powder resistance of 300 milliohm cm or less. USE/ADVANTAGE - The particles are esp. useful as conductive filler in suitable binder or matrix materials in the prodn. of electrically conductive compsn. such as sealants, gaskets, adhesives, plastics, coatings, etc., and used in the fabrication of electromagnetic interference (EMI) screens, antistatic devices for dissipation of electrostatic charges and corrosion protection materials. The new conductive filler particles overcome problems of galvanic corrosion which can occur when conductive metallic filler particles in a plastics matrix come into contact with metal casings in the appts. The particles also overcome problems of formation of insulating oxide coatings forming on metal filler particles e.g. of Al and which prevent the conduction of electricity; the conductive refractory component of the composite particles now penetrates through the oxide film on the surface of the core particles to overcome this drawback, so that a core material can be chosen which is compatible with the housing.