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The massive increase in telecommunications infrastructure and devices has recently exacerbated the necessity of developing advanced electromagnetic interference (EMI) shielding solutions. Porous structures based on conductive polymer composites (CPCs) are currently promoted as feasible options for this task. In this scenario, the chemical foaming process shows suitability for easily fabricating CPC foams with closed cells and variable porosity. Nonetheless, the process and the products have not yet been fully explored in the literature for EMI shielding purposes. Hence, this work proposes the fabrication of foams made of polylactic acid with 10wf% carbon fiber (CF-PLA) via chemical foaming. After the process assessment, the morphological and dielectric characterizations of the samples were discussed in the function of the process parameters. The results show that chemical blowing agent (CBA) weight fraction % and temperature were key in obtaining target structural and dielectric requirements enabling EMI shielding. Numerical analyses on CF-PLA foams, modeled according to morphological outcomes, were performed via the integral finite difference time domain (IFDTD) method. The obtained Scattering Parameters and shielding effectiveness (SE), between 0.5 and 12 GHz, highlighted that when foam relative density and air pore density are simultaneously high, the shielding is mainly accomplished through absorption (SE $_{\mathrm {A}} =20$ dB) while reflection is minimized (SE $_{\mathrm {R}} =2$ dB). Scattering Parameters and SE were also measured in the X-band showing good agreement with the numerical findings; indeed, CF-PLA foams with higher relative density and air cell density exhibited a reduction of SER (3dB) and a SEA with maxima up to 30dB.

The evolution and control of the temperature field during the chemical foaming of epoxy resin are of paramount importance because the foam structure results from the competition of resin crosslinking and foaming, both of which are highly dependent on temperature distributions. Herein, the epoxy foams, consisting of diglycidyl ether of bisphenol A, glycidyl amine‐type epoxy resin, and 4,4′‐diamino diphenyl sulfone hardener, are prepared using azodicarbonamide and 4,4′‐oxydibenzenesulfonyl hydrazide as a chemical foaming agent (CFA). Kinetic models for heat release and CFA decomposition are established using the auto‐catalytic and n‐th order models, respectively. By integrating the transient flow of resin during the foaming process, numerical simulations of the temperature field evolution within the self‐expanding geometry are conducted to investigate the effects of foaming temperature, heat transfer coefficient, and mold diameter on spatial temperature distributions. A comparison of the kinetic parameters of epoxy curing and CFA decomposition at various foaming temperatures (433, 443, and 453 K) reveals that the acceleration of the curing rate is consistent with that of the decomposition rate as the foaming temperature increases, then the foam structure remains largely unchanged across different foaming temperatures. However, local overheating is unavoidable for the foams at 443 and 453 K. This study offers a method for optimizing the processing parameters in preparing epoxy foams. Highlights: Auto‐catalytic model for predicting heat released rate is well established.The decomposition kinetics of the chemical foaming agent is described by n‐th model.Nonisothermal simulation is implemented to study the self‐expanded process of epoxy foam.The foam structure is predicted by comparing the kinetic between the curing and expansion processes. [ABSTRACT FROM AUTHOR]

Many researchers have studied the miniaturization of the hemisphere resonator gyroscope for decades. The hemisphere resonator (HSR), as the core component, has a size that has been reduced to the submillimeter level. We developed a method of batch production of micro-hemisphere shell resonators based on a glass-blowing process to obtain larger hemisphere shells with a higher ratio of height to diameter (H/D), we introduced the chemical foaming process (CFP) and acquired an optimized hemisphere shell; the contrasted and improved H/D of the hemisphere shell are 0.61 and 0.80, respectively. Finally, we increased the volume of glass shell resonator by 51.48 times while decreasing the four-node wineglass resonant frequencies from 7.24 MHz to 0.98 MHz. The larger HSR with greater surface area is helpful for setting larger surrounding drive and sense capacitive electrodes, thereby enhancing the sensitivity of HSR to the rotation. This CFP method not only provides more convenience to control the shape of a hemisphere shell but also reduces non-negligible cost in the fabrication process. In addition, this method may inspire some other research fields, e.g., microfluidics, chemical analysis, and wafer level package (WLP). [ABSTRACT FROM AUTHOR]

Many researchers have studied the miniaturization of the hemisphere resonator gyroscope for decades. The hemisphere resonator (HSR), as the core component, has a size that has been reduced to the submillimeter level. We developed a method of batch production of micro-hemisphere shell resonators based on a glass-blowing process to obtain larger hemisphere shells with a higher ratio of height to diameter (H/D), we introduced the chemical foaming process (CFP) and acquired an optimized hemisphere shell; the contrasted and improved H/D of the hemisphere shell are 0.61 and 0.80, respectively. Finally, we increased the volume of glass shell resonator by 51.48 times while decreasing the four-node wineglass resonant frequencies from 7.24 MHz to 0.98 MHz. The larger HSR with greater surface area is helpful for setting larger surrounding drive and sense capacitive electrodes, thereby enhancing the sensitivity of HSR to the rotation. This CFP method not only provides more convenience to control the shape of a hemisphere shell but also reduces non-negligible cost in the fabrication process. In addition, this method may inspire some other research fields, e.g., microfluidics, chemical analysis, and wafer level package (WLP).

Magnesium phosphate cement based porous materials (MPCPM) were prepared by means of a chemical foaming process using zinc powders as foaming agent. The influence of the zinc content, W/S ratio and particle size of ammonium dihydrogen phosphate (ADP) on the viscosity, temperature evolution, compressive strength, flexural strength and thermal conductivity of the MPCPM was investigated. The results indicate that with higher content of zinc powder and W/S ratio, a longer hardening time of slurry, higher viscosity values, lower hydration temperature, less mechanical strength and lower thermal conductivity of the MPCPM can be obtained. The effects of the particle size of ADP on the properties of MPCPM are analogous to those of the content of zinc powder and W/S. Strong linear relationships can be found between the dry density or porosity and the compressive strength or thermal conductivity of prepared porous materials. The results also show that the MPCPM has good potential to be used for fireproofing doors and high temperature furnace insulation lining due to its light weight, high strength, and thermal and acoustic insulation. [ABSTRACT FROM AUTHOR]