The effect of nanoparticle aggregation on the thermal conductivity of nanocomposites or nanofluids is typically nonnegligible. A universal model（Maxwell model） including nanoparticle aggregation is modified in order...The effect of nanoparticle aggregation on the thermal conductivity of nanocomposites or nanofluids is typically nonnegligible. A universal model（Maxwell model） including nanoparticle aggregation is modified in order to predict the thermal conductivity of nanocomposites more accurately. The predicted thermal conductivities of silica and titania nanoparticle powders are compared first with that measured by a hot-wire method and then with those in previous experimental works.The results show that there is good agreement between our model and experiments, and that nanoparticle aggregation in a nanocomposite enhances the thermal conductivity greatly and should not be ignored. Because it considers the effect of aggregation, our model is expected to yield precise predictions of the thermal conductivity of composites.展开更多
Refractory materials are subjected to mechanical and chemical loads during application,which respectively lead to fracture and corrosion. The understanding of the mechanical fracture and the microstructural modificati...Refractory materials are subjected to mechanical and chemical loads during application,which respectively lead to fracture and corrosion. The understanding of the mechanical fracture and the microstructural modification after progressive thermal shocks is necessary for the suitable design of high performance refractory materials.The fracture process zone can be divided into two areas,where different toughening mechanisms are likely to take place： the crack tip and the following process region called wake region. In this study,the emphasis is laid on the microstructural mechanisms occurring in the wake region of the crack and the crack tip. Therefore,functional aggregates,namely fused eutectic aggregates of Al2O3- ZrO 2- SiO 2and Al2O3- ZrO 2,and andalusite,are added to a model high alumina castable formulation based on tabular alumina. The discrepancy in thermal behavior between aggregates and matrix as well as phase transformation such as mullite formation favor further the nucleation of microcracks that reduce the stress field at the level of the crack tip. Two different grain fractions of tabular alumina（ 0. 2- 0. 6 mm or2. 24- 3. 00 mm） are substituted by these functional aggregates. After sintering at 1 500 ℃ for 6 h,the samplesare quenched up to 10 times in air without pressure from950 ℃ to room temperature. The resulting elastic properties are examined after each thermal shock cycle,as well as the residual bending strength after 0,1,3,5,7and 10 thermal shocks. These results are correlated with Scanning Electron Microscopy analyses after the different thermal shock cycles.展开更多
基金Project supported by the Fundamental Research Funds for the Central Universities of China(Grant No.2015XKMS062)
文摘The effect of nanoparticle aggregation on the thermal conductivity of nanocomposites or nanofluids is typically nonnegligible. A universal model（Maxwell model） including nanoparticle aggregation is modified in order to predict the thermal conductivity of nanocomposites more accurately. The predicted thermal conductivities of silica and titania nanoparticle powders are compared first with that measured by a hot-wire method and then with those in previous experimental works.The results show that there is good agreement between our model and experiments, and that nanoparticle aggregation in a nanocomposite enhances the thermal conductivity greatly and should not be ignored. Because it considers the effect of aggregation, our model is expected to yield precise predictions of the thermal conductivity of composites.
基金the Federation for International Refractory Research and Education ( FIRE) for having supported this academic research study and for having promoted these student exchangesthe German Research Foundation (DFG) +1 种基金supported in the framework of the priority program 1418 "Refractory - Initiative to Reduce Emissions"ALTEO,KERl NEOS,DAMREC,REFEL and BASF for supporting this work with raw materials
文摘Refractory materials are subjected to mechanical and chemical loads during application,which respectively lead to fracture and corrosion. The understanding of the mechanical fracture and the microstructural modification after progressive thermal shocks is necessary for the suitable design of high performance refractory materials.The fracture process zone can be divided into two areas,where different toughening mechanisms are likely to take place： the crack tip and the following process region called wake region. In this study,the emphasis is laid on the microstructural mechanisms occurring in the wake region of the crack and the crack tip. Therefore,functional aggregates,namely fused eutectic aggregates of Al2O3- ZrO 2- SiO 2and Al2O3- ZrO 2,and andalusite,are added to a model high alumina castable formulation based on tabular alumina. The discrepancy in thermal behavior between aggregates and matrix as well as phase transformation such as mullite formation favor further the nucleation of microcracks that reduce the stress field at the level of the crack tip. Two different grain fractions of tabular alumina（ 0. 2- 0. 6 mm or2. 24- 3. 00 mm） are substituted by these functional aggregates. After sintering at 1 500 ℃ for 6 h,the samplesare quenched up to 10 times in air without pressure from950 ℃ to room temperature. The resulting elastic properties are examined after each thermal shock cycle,as well as the residual bending strength after 0,1,3,5,7and 10 thermal shocks. These results are correlated with Scanning Electron Microscopy analyses after the different thermal shock cycles.
