Epoxy / Graphite Micro-chip Conductive Composite Material

The preparative law and conducting characteristics of epoxy resin/graphite microflake conducting composites were studied in this article. The expanded graphite was fragmentated to the nm-size graphite microflake by ultrasonic waves. Epoxy resin/graphite microflake composites were prepared by dispersing the graphite microflakes as conducting fillers. The technique of dispersing the graphite miroflake was studied. The influence laws of the curing system for the resistivity of composites, and the percolation thresholds were researched. Three conducting characteristics of epoxy resin/graphite microflake composites were researched in detail too.Because the diluent is disadvantageous to obtain the low resistivity and good mechanics of composites, we heated epoxy resin for dispersing the graphite microflakes in the oven, and avoided using diluents. It was found that ethylenediaminc s sulfmyldianiline, cyanoguanidine (sulfocarbamide as promoter) could obtain the lower resistivity of composites than other curing agents after experimenting on 15 kinds of curing agents. After researching the three compound systems in detail, we found the optium curing agent content and the optium curing conditions for obtaining the lowest resistivity of composites. Synthesizing the percolation carves of the three compound systems, we found the graphite microflake content ranged from 2%(or l%)to 5% in the percolation area, and correspondingly the resistivity ranged from 10 12(or 10 11) Ω .cm to 104(or 105) Ω.cm, Which is much lower than common graphites. It was found that the larger aspect ratio was the cause of the much lower graphite microflake content after analysed. The mechanical properties of epoxy resin /graphite microflake composites gradually decreased with the increasing of the graphite content. But the composites still maintained enough mechanical properties for used even the higher graphite content.Three conducting characteristics of epoxy resin/ graphite microflake composites were found and researched in this article. (l)The compositespossess PTC effect. The final current is related to voltage used and the conditions of dissipating heat. The final temperature of composites increases with the increasing of voltage used in PTC effect. The electricity-heat equilibrium law about PTC effect was researched on the basis of experimental results. The formula of electricity-heat equilibrium is UIt =KA(t-t ).(2)The composites possess non-ohmic characteristic. The resistivity gradually decreases with the increasing of voltage used. Non-ohmic formula was founded on the basis of experimental results. (3)Theresistivity of composites will change with electrifying or no electrifying. The resistivity will decrease after electrifying, and will slowly rise again in no electrifying. Reversible dielectric breakdown theoretic model was founded on the basis of experimental results. Reversible dielectric breakdown is an equilibrium relation about conducting parts and nonconducting parts in non-homogeneous composites when current acting on . It is a reversible and slight dielectric breakdown.