| Electronic and informational industries have continuously provided the impetus for the development of easy processable materials with high dielectric constant. Ceramic-polymer composite, which combines processability and flexibility of polymer, is a promising material in electrical engineering and electronic industry fields, such as dielectric materials in capacitors with all kinds of shapes. The trend of miniaturization and multi-functionality of electron components requires that dielectric materials have dielectric constant as high as possible. Therefore, it is of great researchable significant for improving the dielectric constant of the ceramic-polymer composites.We choose dicyandiamide and 2-ethyl-4-methyl imidazole as curing agent and analyze its optimal curing process. The results show that the curing agent, with 6% amount of epoxy weight, is a mesothermal latent curing agent, and curing temperature is about 120℃(1h). The curing products have good heat resisting property and the heat resisting temperature even can reach about 280℃. It is very important to some applications of needing higher temperature. In this work, BaTiO3/epoxy composites with mass fraction between 0.3 and 0.7 were prepared. The results show that dielectric constant and dielectric loss of composites not only depend on ceramic contents but the dispersion of BaTiO3 particles. Dielectric constant values present nonlinear growth with increasing ceramic mass fraction, but will reach the highest value at 60wt.% and decrease with more than 60wt.% BaTiO3. In epoxy resin matrix, the dipole-dipole interaction among ceramic particles has a significant effect on dielectric properties of composite materials. From the SEM analysis, we can see that distribution density of surface and cross-section of composites increase gradually with increasing ceramic mass fraction. BaTiO3 particles are enwrapped well by polymer matrix and also can be distributed evenly throughout all of finite continuous polymer matrix. In view of frequency, Dielectric constant values of composite materials are quite stable in the frequency range from 20 KHz to 150KHz. Dielectric loss will increase with the frequency increasing, but the increasing trend is not obvious and the variation range is from 0.036 to 0.039.From the XRD analysis of composites, we can reach the conclusion, from its diffraction peaks having no change in comparison with diffraction peak of pure BaTiO3 particles, that crystal textures of BaTiO3 particles in the composite maintain stability during the preparation process. However, the diffraction peaks of epoxy in the composite, in comparison with pure epoxy, have distinct change. In XRD spectra of pure epoxy, the diffraction peak at 2θ=18.2°, looking like the shape of steamed bread, shows that polymer macromolecule in epoxy resin gather and form a ordered structure. As for epoxy resin of composites, the diffraction peak appears at 2θ=17.6°and intensity of the peak drops rapidly. According to Braggs formula, we know that interplanar crystal spacing of epoxy increase because the addition of BaTiO3 particles has destroyed ordered molecular structure of epoxy resin and reduced array density of epoxy molecular chain.Moreover, with the addition or more increase of BaTiO3, curing temperature and pyrolysis temperature have increased. Epoxy polymer macromolecule permeates through BaTiO3 particles and is in a restricted state. The free volume of epoxy resin reduces and, with increase of BaTiO3 particles content, the segment motion will be more difficult when they are heated. In a word, the thermo-stability of composite materials will be increased from the energy analysis.The main conclusions with innovative significance acquired from the present work are as follows:(1) Among pretreated BaTiO3 powder, the particles, which have size range from 38nm to 2.672μm, are of a wider distribution. The research results show that the powder can be dispersed in the matrix without any surface dispersants.(2) We choose dicyandiamide and 2-ethyl-4-methyl imidazole as curing agent. According to the mass ratio of 5 to 1 between dicyandiamide and 2-ethyl-4-methyl imidazole, the curing system belongs to a mesothermal latent curing agent. The results show that curing products have good heat resisting property.In general speaking, the results in this work have a great help for the application of novel high dielectric constant ceramic/polymer composites.
|
PDF Full Text Request