ABSTRACT
Lightweight concrete is widely used in the construction industry due to its low density and high strength. In this paper, lightweight concrete was prepared by a simple two-step method. Firstly, the light calcium carbonate reinforced epoxy macrospheres (LCR-EMS) material was obtained by adhering calcium lighter carbonate powder to the expanded polystyrene foam spheres (EPS) material using the "balling method". In the second step, the LCR-EMS was mixed with water, cement, and the hollow glass microspheres (HGMS) material using the "molding method" to obtain lightweight concrete. The combination of macroscopic photographs and microscopic morphology shows that the LCR-EMS material itself is uniformly encapsulated and well bonded to the matrix. Test results show that the density of the lightweight concrete decreases with an increase in the volume fraction of stacked LCR-EMS, the diameter, and the proportion of HGMS in the matrix, but it decreases with a decrease in the number of layers of LCR-EMS. The compressive strength of lightweight concrete exhibits a completely opposite trend. When three layers of LCR-EMS were used as filler material, the density and compressive strength of the concrete were 1.246 g/cm3 and 8.19 MPa, respectively. The density and maximum compressive strength of lightweight concrete were 1.146 g/cm3 and 6.37 Mpa, respectively, when filled with 8-9 mm-2L-90 svol% of LCR-EMS and 40 wt% of HGMS in the matrix. Compared with lightweight concrete filled with 90% EPS, the density increased by 20% while the compressive strength increased by 300%.
ABSTRACT
Modern highly integrated microelectronic devices are unable to dissipate heat over time, which greatly affects the operating efficiency and service life of electronic equipment. Constructing high-thermal-conductivity composites with 3D network structures is a hot research topic. In this article, carbon fiber felt (CFF) was prepared by airflow netting forming technology and needle punching combined with stepped heat treatment. Then, carbon-coated carbon fiber felt (C@CFF) with a three-dimensional network structure was constructed in situ by high-temperature chemical vapor deposition (CVD). Finally, high-temperature treatment was used to improve the degree of crystallinity of C@CFF and further enhance its graphitization. The epoxy (EP) composites were prepared by simple vacuum infiltration-molding curing. The test results showed that the in-plane thermal conductivity (Kâ¥) and through-plane thermal conductivity (Kâ¥) of EP/C@CFF-2300 °C could reach up to 13.08 and 2.78 W/mK, respectively, where the deposited carbon content was 11.76 vol %. The in-plane thermal conductivity enhancement (TCE) of EP/C@CFF-2300 °C was improved by 6440 and 808% compared to those of pure EP and EP/CFF, respectively. The high-temperature treatment greatly provides an improvement in thermal conductivity for the in-plane and the through-plane. Infrared imaging showed excellent thermal management properties of the prepared epoxy composites. EP/C@CFF-2300 °C owned an in-plane AC conductivity of up to 0.035 S/cm at 10 kHz, and Lorentz-Drude-type negative permittivity behaviors were observed at the tested frequency region. The CFF thermally conductive composites prepared by the above method have a broad application prospect in the field of advanced thermal management and electromagnetics.
ABSTRACT
In this work, a great synergistic effect of 2D clay platelets and 1D carbon nanotubes (CNTs) on reinforcing chitosan matrix has been observed for the first time. With incorporation of 3 wt % clay and 0.4 wt % CNTs, the tensile strength and Young's modulus of the nanocomposites are significantly improved by about 171 and 124%, respectively, compared with neat chitosan. This could be understood as due to the formation of much jammed fillers network with 1D CNTs and 2D clay platelets combined together, as indicated by rheological measurement. Our work demonstrates a good example for the preparation of high performance polymer nanocomposites by using nanofillers of different dimension together.
