Conductive composites particulate

R. Pal, New models for thermal conductivity of particulate composites. Journal of Reinforced Plastics and Composites 26 (2007) 643-651. 

High thermal conductivity in these materials provides an additional benefit to these lightweight, high specific stiffness composites. A number of factors can influence the thermal conductivity of particulate based composites such as the conductivity of the individual constituents, the size and volume of particles present, and the interfacial thermal barrier between two materials. Models for predicting the thermal conductivity of materials have been developed and are provided in the literature such as the Hasselman-Johnson model of the form... 

C.-W Nan, R. Birringer, D. R. Clarke, and H. Gleiter. Effective thermal conductivity of particulate composites with interfacial thermal resistance. Journal of Applied Physics, 81 (1997), 6692-6699. 

Grunlan JC, Gerberich WW, Francis LF (2001) Lowtaing the percolation threshold of conductive composites using particulate polymer microstnicture. J Appl Polym Sci 80 692 Kim D, Kim Y, Choi K, Giunlan JC, Yu C (2010) Improved thermoelectric behavior of nanotube-fiUed polymer composites with poly(3,4-ethylenedioxythiophene) poly(styrene-sulfonate). ACS Nano 4 513... 

Fig. 9. Thermal conductivity of particulate and UD-fiber epoxy resin composites (60 vol %) in fiber direction vs temperature. For pol5nmide/ceramic powder, d O-l At -...

By the term particulate composites we are referring to composites reinforced with particles having dimensions of the same order of magnitude. Particulate composites are produced from a polymeric matrix, into which a suitable metal powder has been dispersed, and exhibit highly improved mechanical properties, better electrical and thermal conductivity than either phase, lower thermal expansivity, and improved dimensional stability and behaviour at elevated temperatures. 

The dynamic viscoelasticity of particulate gels of silicone gel and lightly doped poly-p-phenylene (PPP) particles has been studied under ac excitation [55]. The influence of the dielectric constant of the PPP particles has been investigated in detail. It is well known that the dielectric constant varies with the frequency of the applied field, the content of doping, or the measured temperature. In Fig. 11 is displayed the relationship between an increase in shear modulus induced by ac excitation of 0.4kV/mm and the dielectric constant of PPP particles, which was varied by changing the frequency of the applied field. AG increases with s2 and then reaches a constant value. Although the composite gel of PPP particles has dc conductivity, the viscoelastic behavior of the gel in an electric field is qualitatively explained by the model in Sect. 4.2.1, in which the effect of dc conductivity is neglected. 

Steinfeld et al. [133] demonstrated the technical feasibility of solar decomposition of methane using a reactor with a fluidized bed of catalyst particulates. Experimentation was conducted at the Paul Scherrer Institute (PSI, Switzerland) solar furnace delivering up to 15 kW with a peak concentration ratio of 3500 sun. A quartz reactor (diameter 2 cm) with a fluidized bed of Ni (90%)/Al2O3 catalyst and alumina grains was positioned in the focus of the solar furnace. The direct irradiation of the catalyst provided effective heat transfer to the reaction zone. The temperature was maintained below 577°C to prevent rapid deactivation of the catalyst. The outlet gas composition corresponded to 40% conversion of methane to H2 in a single pass. Concentrated solar radiation was used as a source of high-temperature process heat for the production of hydrogen and filamentous... 

In order to obtain quantitative data on particulate air quality in the Owens Valley, a study sponsored by the California Air Resources Board was conducted by the Air Quality Group at UCD. The primary objective was to determine the impact of the dry lake bed on the average particulate concentration and on the dust storm particulate concentrations in the valley. In order to accomplish this, it was necessary to determine the elemental composition of the dry lake bed and to determine the average weekly and dust storm concentration of aerosols. 

The storage and feed equipment, when delivered on site, is assembled by our own mechanical department. It is checked out and tests are conducted over a 4 - 6 week period to optimize the additive type and composition and demonstrate the most effective means of reducing particulate emissions. A technical services engineer monitors performance as part of the steady state operation. 

Numerous studies have been conducted on the nature of the dissolved and particulate organic matter in natural waters. In general, these studies have shown that the composition of the bulk of the organic matter is undefined. Many of the laboratory studies on the nature of the dissolved organic matter in natural waters are of limited value owing to possible alteration of the compounds by the concentration and analytical methods used. The selectivity of the methods used to concentrate the solute to analytically detectable levels presents another problem in many analytical procedures used to study trace compounds in natural waters. Concentration procedures such as freezing, flocculation, sorption columns, and solvent extraction, have been shown to be selective for certain types of compounds (32, 34, 38). Extreme care must be exercised to insure... 

Prior to toxicity testing, an appropriate volume of each composite sample is vacuum-filtered (0.45 p membrane) to remove suspended material which would otherwise interfere with the conduct of some of the bioassays employed. In removing particulates from effluent samples, it is important to note that the PEEP scale only evaluates their soluble toxicity. This issue is further discussed in Section 6.3. 

Fig. 8.17 AC conductivity versus frequency for a variety of carbon-black composites O crosslinked EBA with 8.3% acetylene black (AC), thermoplastic EBA with 11.3% AC, + thermoplastic EB with 14.5% AC, EBA particulate composite with 9.1% AC, EBA particulate composite with 10.7% AC, O blended PE with 9.2% AC, blended PE with 11.1% AC, A EPDM with 15.2% furnace black (FB), EPDM with 21.1% FB and EPDM with 26.3% FB (all percentages are by volume). Reproduced with permission of the Institute of Physics from Jager et al. (2001).

Additional studies have been conducted using intratracheal instillation exposures to aggregates of ultrafine and fine carbon black, as well as to TiOi particles in rats. The results have demonstrated a significantly enhanced lung inflammatory potency of the ultrafine particles when compared to fine-sized particulates of similar composition. However, when the instilled doses were expressed in terms of particle surface area, the responses of the ultrafine and fine TiOi particles fell on the same dose-response curve. This is because a given mass of ultrafine particles has a much greater surface area (and particle number)... 

Closed-form expressions from composite theory are also useful in correlating and predicting the transport properties (dielectric constant, electrical conductivity, magnetic susceptibility, thermal conductivity, gas diffusivity and gas permeability) of multiphase materials. The models lor these properties often utilize mathematical treatments [54,55] which are similar to those used for the thermoelastic properties, once the appropriate mathematical analogies [56,57] are made. Such analogies and the resulting composite models have been pursued quite extensively for both particulate-reinforced and fiber-reinforced composites where the filler phase consists of discrete entities dispersed within a continuous polymeric matrix. 

Sorting of X rays by energy is termed energy dispersive spectroscopy (EDS) and can be accomplished by adding a detector and its attendant electronics and computer to aTEM (or STEM) column. This device, with its X-ray detector immersed in the objective lens, can provide elemental analysis of particulate or ultrathin specimens (Fig. 1) (23-27). Elements from sodium to einsteinium can be detected using a standard EDS system. In addition, qualitative data on elemental concentration can be produced, and compositional mapping of elemental location can be conducted. 

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