Qianjin Mao

Characteristics of Self-Healing Microcapsules for Cementitious Composites

Urea formaldehyde/epoxy resin microcapsules were prepared by an in situ polymerization method and the effect of emulsifier on the syntheses process of the microcapsules was discussed. The surface morphology of the microcapsules was observed by optical microscopy and scanning electron microscopy (SEM). Chemical structure was characterized by Fourier transform infrared spectroscopy (FTIR). Thermal stability was obtained using simultaneous thermal analysis (STA). The microcapsules were composed of urea-formaldehyde resin shell and epoxy resin core. Emulsifier played an important role in the polymerization process when the core material was packed by pre-polymer, so the effects of different emulsifiers (OP-10, SDS and SDBS) were discussed respectively. Results showed that the particle size of the microcapsules was uniform when SDBS as an emulsifier. Microcapsules showed good thermal stability below 240 °C and the initial decomposition temperature of the microcapsules was 265 °C. The core materials released after microcapsules rupturing, which could be proven by the images of SEM. When implanted in cementitious composites, complete shape of microcapsules and good interface between microcapsules and cement specimen substrate could also be observed.

The Influence of Volume Changes in Portland and Calcium Sulfoaluminate Binary Cement

The long-term volume changes of Portland-Calcium sulfoaluminate cement systems has been studied for samples cured under different conditions. Three curing conditions were chosen in this study and the composite cement systems showed different results with different CSA dosages. Progressively higher amount of CSA was added to the composite cement system and it was found that there was a critical dosage of CSA leading to unstable expansion and failure of the samples by curing under water. But in drying condition, the systems showed shrinkage and the degree of volume changes were similar than expansion by curing under water. By selecting the composition of CSA-PC systems and curing conditions, the volume stability of composite cement could be controlled.

Effect of Conductivity and Radiation on Heat Dissipation Performance of Coating

Aiming at the problem of heat dissipation of electronic devices in low temperature environment, the effect of thermal conductivity and emissivity of coating on its heat dissipation performance was studied by theoretical calculations and experiments in this study. The results show that the heat dissipation performance of organic coating with emissivity of 0.7–0.95 is improved as its thermal conductivity increasing. And temperature difference between inside and surface of object is inversely proportional to thermal conductivity. That is, when thermal conductivity exceeds a certain value, it will no longer affect heat dissipation performance of coating. In addition, emissivity of coating directly affects its cooling performance, and the proper matching interaction between thermal conductivity and emissivity of coating can enhance heat dissipation effects. In the case of non-forced convection cooling, the thermal conductivity of the organic coating is preferably 2–10 W/m·K.