The nickel fiber was added into the cement-based composite materials as a shielding medium. Influences of the three different types and amount of dispersants and weight fraction of nickel fiber on the electrical conductivity and electromagnetic shielding effectiveness of the cement matrix composite were discussed. The conductivity of cement based composite materials and the uniformity distribution of shielding medium were characterized by four-point probe meter and scanning electron microscopy, respectively. Electromagnetic interference shielding effectiveness in the frequency range of 1 MHz to 1500 MHz was characterized by coaxial cable method. The results indicated that the improved dispersion of nickel by incorporation of dispersants might yield the enhancement of the electrical properties of nickel fiber-reinforced cement composites. When the dosage of methyl cellulose reaches 0.4 wt.%, the pre-dispersing nickel fiber enhances the electrical conductivity of the cement-based composite materials significantly. With the increase of fiber volume fraction, the shielding effectiveness and trend of frequency change of the corresponding fiber-reinforced concrete were enhanced. When the content of nickel fiber powder was 9.0 vol.%, the conductivity was 2.65×10-3 s·cm-1, and the average shielding effectiveness of the specimen in 1MHz-1500 MHz was about 21.78 dB, with the maximum shielding effectiveness of 24.48 dB and the minimum shielding effectiveness 19.85 dB.
Polymer modified cementitious waterproof coating is an important construction material. In this paper, starting from the classification and choice of waterproof coatings, the importance, advantages and application prospects of the polymer cement waterproof coatings were discussed. The approaches for solving the existing problems and limitations of polymer modified cementitious waterproof coatings were put forward.
The deep cryogenic temperatures encountered in aerospace present significant challenges for the performance of elastic materials in spacecrafts and related apparatus. Reported elastic carbon or ceramic aerogels overcome the low-temperature brittleness in conventional elastic polymers. However, complicated fabrication process and high costs greatly limited their applications. In this work, super-elasticity at deep cryogenic temperature of covalently crosslinked polyimide (PI) aerogels is achieved based on scalable and low-cost directional dimethyl sulfoxide crystals assisted freeze-gelling and freeze-drying strategy. The covalently crosslinked chemical structure, cellular architecture, negative Poisson’s ratio (-0.2), extremely low volume shrinkage (3.1%) and ultralow density (6.1 mg/cm3) endow the PI aerogels with an elastic compressive strain up to 99% even in liquid helium (4K), almost zero loss of resilience after dramatic thermal shocks (∆T = 569 K), and fatigue resistance over 5000 times compressive cycles. This work provides a new pathway for constructing polymer-based materials with super-elasticity at deep cryogenic temperature, demonstrating much promise for extensive applications in ongoing and near-future aerospace exploration.
In order to improve the conductivity of the nickel fiber, polyaniline (PANI) of synthesis by chemical oxidative polymerization was coated. The influences of dopant type and content, reaction time, reaction temperature and stirring rate on the conductivity of the PANI coated nickel fiber were investigated. SEM and NMR were used to characterize morphology of products. The conductive of the PANI coated nickel fiber was tested by four-point probe conductivity tester. The results showed that the PANI coated layer was uniform and stabilized when the p-toluene sulfonic acid (PTS) used as dopant, the PANI coated nickel fiber has the highest conductivity of 5×10-5 s∙cm−1when was coated at parameters of the C (PTS) of 0.1 mol/L, the reaction time of 5 hours, the reaction temperature of 5 °C, as well as the stirring rate of 60 r/min.
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