Novel V‐shaped negative temperature coefficient of conductivity thermistors and electromagnetic interference shielding effectiveness from butyl rubber–loaded boron carbide ceramic composites

Abstract

ABSTRACT:The presentation of a new conductive composite with good effective applications like negative and positive temperature coefficient of conductivity thermistors (i.e., V-shaped thermistors) and electromagnetic interference shielding effectiveness (EMI) was the aim of this study. The effect of boron carbide (B 4 C) contents on the vulcanization characteristics and network structure of butyl rubber (IIR) composites were analyzed in detail. The prediction of the type of crosslinks based on the affine and phantom network theory was also analyzed. The influence of the volume fraction of B 4 C on the dc conductivity and thermoelectric power was investigated. The electrical and dielectric properties of IIR composites were investigated. The results suggest that the conduction occurs by a tunneling mechanism and behaves as a p-type semiconductor. Isothermal resistance at different temperatures, as a function of B 4 C content, was displayed. The current-voltage characteristics showed properties of switches, which were explained by coulombic repulsive force. For practical applications, as self-electrical heating the temperature-time cycles were investigated under certain applied power. It was found that increasing the B 4 C content increases the thermal stability of the composite. However, the theoretical modeling of the current-voltage characteristic is very useful for planning groups in industrial applications of conducting polymer composites. Furthermore, the endurance test under applied power indicates that the proposed composites could be useful as temperature sensors with good reliability. Specific heat as a function of B 4 C contents was evaluated by experimental and various energy balance models. Furthermore, the temperature dependency of thermal conductivity and thermal diffusivity were investigated. Finally, the standing wave ratio, reflection coefficient, return loss, and attenuation of IIR/B 4 C composites were studied in the 1-to 4-GHz frequency range. The resulting values of electromagnetic interference shielding effectiveness were compared with theoretical models.

The interrelation among network structures, molecular transport of solvent, and creep behaviors of TiB2 ceramic containing butyl rubber composites

“…Butyl rubber (IIR) was manufactured by Transport and Engineering (rubber manufacturing) (TRENCO, Alexandria, Egypt) and had density 0.94 g/cm 3 . Zinc oxide (ZnO), stearic acid, sulfur, tetramethyl thiuram disulfide (TMTD), and phenyl-␤-naphthylamine (P␤N) were of chemically pure grade.…”

“…The microstructure was observed with a scanning electron microscope (SEM) and it was performed in a JEOL operated at 30 kV on surface samples without conducting coating. For mechanical measurements, the dumbbell-shape samples were prepared from the vulcanized rubber sheets with a different content of TiB 2 with dimensions 105 ϫ 205 ϫ 20 mm 3 . Tensile strength (TS), Young's modules (YM), and elongation at break (EB) were determined using a tensile testing machine (ASTM D412).…”

“…This is thought to be due to an increase in the high local stresses concentrations that occur from progressive rupture of individual chain segment within the rubber matrix and/or radial stresses at the TiB 2 butyl rubber interface. [1][2][3] The steady-state creep rate ͑ st ͒ increases with increasing applied stress () while it decreases with increasing TiB 2 content. The noticeable dependence of strain rate on the applied stress is simply associated with the onset of significant plastic flow, and on a molecular level it is anticipated that it may be associated with interaction sliding and chain segmental motion.…”

“…The interaction of polymeric materials with solvents is a serious problem from both the scientific and the practical view point. 3,4 The high degree of swelling is a common problem to all the bulk rubber composites. Two factors deteriorating the degree of swelling have been pointed out.…”

Effect of Activated Carbons on the Dielectric and Microwave Properties of Natural Rubber Based Composites

“…The inherent charge transport characteristics and the factors that limit the charge carrier mobility differ significantly between the various carbonaceous nanostructures reflecting, on the one hand, the electronic dimensionality of the structures, and, on the other hand, the achievable dimensions of the respective π-systems 8 . Carbon black and graphite remained the favorite absorbing candidates until the discovery of CNTs in the 1990s, which have been exploited to a wide range of potential industrial applications, including microwave absorbers [9][10][11][12][13][14][15][16] . Since the beginning of this millennium, other forms of carbonaceousbased absorbers with good absorption characteristics have appeared.…”