DIELECTRIC BEHAVIOR AND THERMO-MECHANICAL PERFORMANCE OF BATIO 3 - PDF document

18 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS DIELECTRIC BEHAVIOR AND THERMO-MECHANICAL PERFORMANCE OF BATIO 3 REINFORCED AND CARBON REINGORCED EPOXY COMPOSITES A. C. Patsidis 1,2 , G. C. Psarras 2, K. Kalaitzidou 1 * 1 Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, USA, 2 Department of Materials Science, University of Patras, Patras, Greece * Kyriaki Kalaitzidou (kyriaki.kalaitzidou@me.gatech.edu) Keywords : keywords list (no more than 7) 1 General Introduction supplied by Sigma Aldrich. The carbon fillers used Polymer composites incorporating ferroelectric and are: i) nano-size high structure carbon black (CB) piezoelectric particles, randomly distributed within with mean particle diameter in the range of 40-50 the polymer matrix, are considered as a novel class nm (KETJENBLACK EC-600 JD), provided by of engineering materials. The electrical response of Akzo Novel Polymer Chemicals LLC, ii) vapor these hybrid materials can be suitably adjusted by grown carbon fibers (VGCF) with mean particle controlling the type and the amount of the ceramic diameter less than 150 nm (Pyrograf III, PR-19 PS inclusions. Modern electronic devices require new grade), supplied by Pyrograf Products, Inc., and iii) high dielectric permittivity materials with enhanced exfoliated graphite nanoplatelets (xGnP-1) with mean particle diameter less than 0.1 μm and an dielectric strength [1-3]. These materials are expected to address the engineering demands for average thickness of 10-20 nm supplied by XG suitable dielectric properties and exhibit improved Sciences (East Lansing, MI). mechanical strength and ease processing at a relative 2.2 Fabrication of Composites low cost. Ceramic-polymer composites can be used The dispersion of the BaTiO 3 in the epoxy took in various applications including integrated place in a dissolver device (VMA Getzmann capacitors, acoustic emission sensors, smart skins and leakage current controllers [1-4]. GmbH). The compound was stirred in a vacuum container to avoid air entrapment. During processing In this study, ceramic fillers and carbon materials are the temperature was increased up to 60 o C to used as epoxy reinforcements resulting in composites with enhanced dielectric, electrical, and facilitate the filler wetting by the epoxy. The compound was placed in a sonic bath for 20 min to thermo-mechanical properties. The carbon fillers used are carbon black [CB], vapor grown carbon enhance further the dispersion quality by breaking any remaining agglomerations. The above process fibers [VGCF] and exfoliated graphite nanoplatelets was used to produced a BaTiO 3 -epoxy master-batch [xGnP]. Possible synergy on the composites performance between ceramic and carbon fillers is compound with a content of 20 phr (filler parts per hundred epoxy parts) BaTiO 3 . Dilution down to 5 also investigated by fabricating and characterizing and 10 phr was used to produce composites with composites containing both ceramic and carbon different filler content. Both sizes of BaTiO 3 powder fillers at various ratios. were used. The filler-epoxy solution was purred in to a mold and cured at T=80 o C for 1 hour followed by 2 Experimental post curing at T=100 o C for 4 hours. 2.1 Materials Alternatively, a second fabrication method was used. The polymer used is a low viscosity epoxy resin In order to avoid agglomeration the filler powder with the trade name Araldite LY 564 and curing (ceramic or carbon) was mixed with isopropyl agent Aradur-HY2954 both provided by Huntsman alcohol (IPA) using a sonication probe (misonix Advanced Materials. The ceramic reinforcement is 4000) for 40 minutes at 40% amplitude. The BaTiO 3 powder of two sizes. One with mean particle agglomerate free powder, collected after the removal diameter less than 2 μm and another with mean of IPA through filtration, was mixed at room particle diameter in the range of 30-50 nm both temperature with the proper amount of monomer

DIELECTRIC BEHAVIOR AND THERMO-MECHANICAL PERFORMANCE OF BATIO 3 REINFORCED AND CARBON REINGORCED EPOXY COMPOSITES using sonication. The curing agent was added to the diffraction, the crystalline structure depends also on filler-monomer solution and mixing continued for 10 the particle size. As shown in Figure 1b, the min. The mixture was degassed in a vacuum oven, transition between the two structures is detected for cast in a mold and cured at T=80 o C for 1 hour the micro-sized BaTiO 3 particles only which exhibit followed by post curing at T=100 o C for 4 hours. a tetragonal structure at T=40 o C whereas their structure is cubic at T=170 o C. It is noted that 2.3 Characterization of Composites T c =130 o C. The nano-sized BaTiO 3 exhibits hybrid The electrical characterization of the composites was cubic/tetragonal structure at all temperatures. conducted by means of Broadband Dielectric Spectroscopy (BDS) in the frequency range of 0.1 Hz to 10MHz, using Alpha-N Frequency Response Analyser and a 1200 BDS dielectric cell provided by Novocontrol. Isothermal frequency scans were conducted, for each specimen, from ambient temperature to 160 o C with a step of 10 o C. Novotherm system supplied by Novocontrol was used to control the temperature. Other properties that were examined are crystalline structure of the ceramic powders using X-ray diffraction to detect the transition from the non symmetrical polar to cubic non-polar structure of BaTiO 3 . This was done using D8 Advance (Bruker AXS) with a CuKa (1.54 angstrom) source and 1.6 kW power. The viscoelastic properties, including storage and loss modulus and tan delta, of the composites were determined using a Dynamic Mechanical Analyzer (DMA, Q800, TA Instruments). The specimens were characterized using single-cantilever mode as a function of temperature (30 to 160 o C, heating rate 5 o C/min). A constant force of 100 mN was applied at frequency of 1 Hz. Fig. 1. a) Schematic of the crystalline structure of Finally the composites morphology was investigated BaTiO 3 (cubic on the left and tetragonal on the right) using scanning electron microscopy (SEM, Leo and b) X-ray diffraction spectra of BaTiO 3 as a Supra 35VP) for presence of voids and function of particle size and temperature. agglomerates, and the state of filler dispersion within the polymer matrix. In addition to the transition between the two structures, BaTiO 3 is used as filler because it is a 3 Results and Discussion piezoelectric and ferroelectric material. The ability to utilize these unique properties of BaTiO 3 can lead 3.1 Dielectric Properties to responsive (smart) materials and enable many BaTiO 3 is chosen as the ceramic filler because of its technological applications. unique characteristic to change its crystalline The real part of dielectric permittivity of structure in a controllable and reversible manner. BaTiO 3 /epoxy composites, made by the first The cubic structure (paralectric phase), shown in compounding method, and measured at T=70 o C is Figure 1a (left) is present at high temperatures shown in Figure 2 as a function of frequency, whereas the tetragonal crystalline structure particle size and concentration. The following (ferroelectric phase) is present at lower observations can be made i) all the composites have temperatures. The temperature at which this higher ε΄ values than the epoxy, ii) the micro size transition occurs is the Curie temperature, T c , and composite shows higher values than the nano-size it’s a characteristic of the material. Based on X -ray 2