Composites dielectric characteristics

The composition of an optoelectronic memory card (eg. Laser Card of Drexler Technology Corp.) (162) is outlined in Figure 21 (163). Primary elements are polycarbonate foils with thicknesses of 250 to 400 )Tm, respectively, that are employed because of their high operating temperature and their good mechanical, optical, and dielectric characteristics. The OMC can be used as a ROM or a WORM media. Both possibiUties of information deposition can be used separately or in combination. 

Chapter 10 deals with composite films synthesized by the physical vapor deposition method. These films consist of dielectric matrix containing metal or semiconductor (M/SC) nanoparticles. The film structure is considered and discussed in relation to the mechanism of their formation. Some models of nucleation and growth of M/SC nanoparticles in dielectric matrix are presented. The properties of films including dark and photo-induced conductivity, conductometric sensor properties, dielectric characteristics, and catalytic activity as well as their dependence on film structure are discussed. There is special focus on the physical and chemical effects caused by the interaction of M/SC nanoparticles with the environment and charge transfer between nanoparticles in the matrix. 

Physical and chemical properties of PVD-produced composite films with M/SC nanoparticles including dark- and photo-induced conductivity, conductometric sensoring properties, dielectric characteristics, and catalytic activity. 

Research on the dielectric characteristics of coating films was performed using a teraohmmeter. Five samples of different coating compositions were examined on a metal substrate. Samples were prepared on the basis of two types of water dispersion rubbers, CSM-200 and CSM-400. The test samples were placed in a drying oven. The electrical resistance of the samples was measured via thermocouple wires that were connected to the teraohmmeter. The results of tests are shown on Figures 5.3 and 5.4. 

The measurements of the dielectric characteristics of composites were carried out at a frequency of lO Hz using an alternating current bridge P-5058. The specimens prepared had a disc-like shape with a diameter equal to the diameter of the electrode (15-18 mm). The thickness of the specimen was about 1 mm. The temperature dependencies of the dielectric permeability (e) and of the tangent of the dielectric losses (tan 8) were found at the heating rate 3-4 K/min. 

Jacob M, Varughese KT, Thomas S et al (2006) Dielectric characteristics of sisal-oil pahn hybrid bio-fiber reinforced natural rubber bio-composites. Society of Plastics Engineers, pp 671-680... 

The conductivity of metallopolymeric nanocomposites is substantially affected by the dispersity of an inorganic component. Different nanocomposites are characterized by different relationships between the conductivity and the metal content. The percolation threshold of composites containing layered polypyromellitimide films filled by inserted silver particles is attained at a filler content >9 wt%. When nanosize silver particles (10-15 nm), were prepared by thermolysis of a solution of silver acetate in poly(pyromellitamide acid), they became uniformly distributed over a film. This composite does not exibit conducting properties at the same filler content. The dielectric characteristics of films (o = 10 - 10 Sm ) are retained at a high... 

Figure 10-6 (a) is a cross sectional photograph of the BaTi03 composition of AD film formed on a resin substrate. A dense structure packed with ceramic particles of several dozen nm can be observed. The dielectric characteristics ( 100 kHz) that can currently be obtained are dielectric constant 400, tan 8 2% or so (dielectric constant of bulk BaTiO. around 3,000). Figure 10-6 (b) is the microstructure of the microwave dielectric structure of Ba(Zni/3Ta2/3)03-Al203 AD film. This exhibits a microstructure of alumina particles distributed uniformly in a BZT matrix. The Q value (1/tan 8) of the film is 500 (Q value of bulk Ba(Zni/3Ta2/3)03 around 5,000). 

Figure 8.6 Dielectric characteristics of sisal-oil palm hybrid fiber-reinforced natural rubber composites [50]. with permission from Springer Science + Business Media.

Barium carbonate also reacts with titania to form barium titanate [12047-27-7] BaTiO, a ferroelectric material with a very high dielectric constant (see Ferroelectrics). Barium titanate is best manufactured as a single-phase composition by a soHd-state sintering technique. The asymmetrical perovskite stmcture of the titanate develops a potential difference when compressed in specific crystallographic directions, and vice versa. This material is most widely used for its strong piezoelectric characteristics in transducers for ultrasonic technical appHcations such as the emulsification of Hquids, mixing of powders and paints, and homogenization of milk, or in sonar devices (see Piezoelectrics Ultrasonics). 

Barium titanate is usually produced by the soHd-state reaction of barium carbonate and titanium dioxide. Dielectric and pie2oelectric properties of BaTiO can be affected by stoichiometry, micro stmcture, and additive ions that can enter into soHd solution. In the perovskite lattice, substitutions of Pb ", Sr ", Ca ", and Cd " can be made for part of the barium ions, maintaining the ferroelectric characteristics. Similarly, the TP" ion can partially be replaced with Sn +, Zr +, Ce +, and Th +. The possibihties for forming solution alloys in all these stmctures offer a range of compositions, which present a... 

Biphenyl, terphenyl, and their alkyl or hydrogenated derivatives generally serve markets where price and performance, rather than composition, is the customer s primary concern. Performance standards for heat-transfer appHcations are usually set by the fluid suppHer. The biphenyl—diphenyl oxide eutectic (26.5% biphenyl, 73.5% DPO) represents a special case. This composition has become a widely recogni2ed standard vapor-phase heat-transfer medium. It is sold throughout the world under various trademarks. In the United States, Dow (Dowtherm A) and Monsanto (Therminol VP-1) are the primary suppHers. Alkylated biphenyls and partially hydrogenated terphenyls serving the dielectric and carbonless copy paper dye solvent markets likewise are sold primarily on the basis of price and performance characteristics jointly agreed on by producer and user. 

In the broad range of ceramic materials that are used for electrical and electronic apphcations, each category of material exhibits unique property characteristics which directiy reflect composition, processing, and microstmcture. Detailed treatment is given primarily to those property characteristics relating to insulation behavior and electrical conduction processes. Further details concerning the more specialized electrical behavior in ceramic materials, eg, polarization, dielectric, ferroelectric, piezoelectric, electrooptic, and magnetic phenomena, are covered in References 1—9. 

In addition to the amount of filler content, the shape, size and size distribution, surface wettability, interface bonding, and compatibility with the matrix resin of the filler can all influence electrical conductivity, mechanical properties, and other performance characteristics of the composite plates. As mentioned previously, to achieve higher electrical conductivity, the conductive graphite or carbon fillers must form an interconnected or percolated network in the dielectrical matrix like that in GrafTech plates. The interface bonding and compatibility between... 

One interesting application of the dielectric properties of the resins in these composite systems is that it provides an opportunity to monitor the cure characteristics of... 

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