Influence of Al‐Containing Interfacial Coatings on Carbon‐Fiber/Bakelite Composite Thermal and Electrical Properties

Abstract

Carbon-fiber polymer-matrix composites are state-of-theart, low-density, high-strength, and high-modulus structural materials. Besides their traditional applications, new fields have emerged, in which, in addition to their good mechanical properties, the electrical and thermal conductivity of these composites are also exploited. New applications include bipolar plates in polymer electrolyte membrane (PEM) fuel cells, [1] thermal management, [2][3][4] and electronic packaging. [5,6] The material properties of these composites, such as thermal and electrical conductivity, thermal expansion, and viscoelastic mechanical properties, can be influenced greatly by the filler-matrix interface. [7] For example, better contact between the phases reduces the thermal contact resistance, thereby enhancing the overall thermal conductivity. In highperformance microelectronics thermal-management applications, the thermal conductivity should be as high as possible (e.g., for heat-sink materials). Good adhesion between the matrix and the filler can result with lower thermal expansion of the composite, assuming that the filler has a lower thermal expansion than the matrix. [8] In microelectronic materials, low coefficients of thermal expansion are desired: they should match those of common ceramics and silicon.By introducing interfacial coatings on the filler particles it is possible to improve the contact properties to the composite matrix. [9] In the scope of this work, the influence of interfacial Al-containing, thin, metallic and ceramic coatings on composite material properties was investigated. Prior to polymer casting, short carbon fibers were coated using fluidized-bed processes. As targeted interfacial coatings, AlN and Al were chosen, since they are both excellent thermal conductors. ExperimentalA detailed description of the atmospheric-pressure, microwave-plasma fluidized-bed experimental setup has been published elsewhere [10]. Al-containing coatings on carbon particles were deposited by means of two different processes: a chemical vapor deposition (CVD)-based one and a physical vapor deposition (PVD)-based one. By the CVD process, AlN coatings with Al and Al 4 C 3 impurities were deposited from trimethylaluminum (TMA) (Al(CH 3 ) 3 ) in nitrogen plasma [11][12][13]. By the PVD process, AlN coatings were deposited in nitrogen plasma, and Al coatings were deposited in argon/hydrogen plasma [14].As carbon-fiber filler, pitch-based, highly graphitized, short carbon fibers (ThermalGraph DKD, Cytec, USA; density r ¼ 2200 kg m S3 , bulk density r B % 400 kg m S3 , average diameter d ¼ 10 mm, average filament length l ¼ 200 mm) were utilized.As polymer matrix, commercially available Bakelite 1 resin and hardener were used (Rü hl AG & Co., Germany). Low-viscosity resin, EPR L 20, was mixed with hardener, EPH 161, in a weight ratio of 4:1, as prescribed by the manufacturer. They were stirred for about 5 min in a glass beaker with a PTFE-coated magnetic stirrer. The composites were cast in two ways; depending on the filler volume-f...

Single and hybrid mineral fillers (talc/silica and talc/calcium carbonate)‐filled polypropylene composites: Effects of filler loading and ratios

“…It was observed that 40 CC had the lowest value of CTE (6.93 ppm/°C) than 40 T and 40 SI (9.52 and 10.02 ppm/°C). Previous work stated that thermal expansion indirectly indicated poor adhesion existing between filler and matrix. High thermal expansion indicated poor adhesion.…”