As part of a better understanding of drying liquids within porous materials, measurements from 293 to 343 K of deionized water surface tension in air as a function of relative humidity are exposed. Experimental work w...As part of a better understanding of drying liquids within porous materials, measurements from 293 to 343 K of deionized water surface tension in air as a function of relative humidity are exposed. Experimental work was carried out using the pendant drop method coupled with image analysis within an adapted instrumented climatic chamber. Results show that surface tension linearly decreases when relative humidity increases. Although the effect of humidity is less compared to that of the temperature and even less compared to a surfactant impact, it must not be neglected and values have to be mentioned when dealing with water evaporation. Modifying surface tension also affects the pendant drop shape. The drying kinetics of the pendant drop volume and its outer shell are connected to this change of shape. Steam in the air can be assimilated to a wetting agent, hence a surfactant, and can be used in an environmental-friendly way to ease the drying stage. Indeed, the challenge is to limit the risk of cracking and damaging pieces during this crucial step in material processing.展开更多
The evaporation of sessile water droplets on hydrophobic surfaces is a topic which led to numerous investigations. However, how does the liquid behave when the evaporation occurs between two of these particular substr...The evaporation of sessile water droplets on hydrophobic surfaces is a topic which led to numerous investigations. However, how does the liquid behave when the evaporation occurs between two of these particular substrates? The drying stage is governed by capillary phenomena which takes place in a confined space. In the field of material shaping, it is also possible that some regions of a green body exhibit hydrophobic properties. As part of a better understanding of the local mechanisms during drying, liquid bridges have been reproduced in an ideal case. Drying kinetics and parameters measurements from 303 to 343 K (relative humidity of 55%) of deionized water liquid bridges between two plates of hydrophobic substrates are presented. Experimental work was carried out using a specific device to create liquid bridges, coupled with image analysis within an adapted instrumented climatic chamber. While the volume and the exchange surface of liquid bridges decrease regularly throughout the process, contact angles constantly diminish and more significantly at the end. This is different from the evaporation between two hydrophilic plates. From these measurements, the change of curvature of the liquid bridges during evaporation is highlighted.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
In this paper, a glass powder from waste containers was mixed (10 - 40 wt.%) with a kaolinitic sandy clay from Cameroon to elaborate net-shape ceramics, fired at 1100°C. The sintering behavior was from dilatometr...In this paper, a glass powder from waste containers was mixed (10 - 40 wt.%) with a kaolinitic sandy clay from Cameroon to elaborate net-shape ceramics, fired at 1100°C. The sintering behavior was from dilatometry and thermo gravimetric analyses together with the characterization of porosity and flexural strength. The increase of glass to kaolinite ratio reduces the sintering shrinkage leading to a none-densification sintering when 40 wt.% of glass is added in the mixture. The volume variation during the whole firing process is from the individual volume variations during the quartz transformation, the structural reorganization of kaolinite and during sintering. Quartz size and relative quantity have a significant role on the first processes since it leads to either cohesive or un-cohesive behavior. But the glass quantity strongly controls the second and the third thermal processes because glass additions change the recrystallization processes, leading to the formation of dense clay-glass agglomerates distributed within the three dimensional quartz network.展开更多
文摘As part of a better understanding of drying liquids within porous materials, measurements from 293 to 343 K of deionized water surface tension in air as a function of relative humidity are exposed. Experimental work was carried out using the pendant drop method coupled with image analysis within an adapted instrumented climatic chamber. Results show that surface tension linearly decreases when relative humidity increases. Although the effect of humidity is less compared to that of the temperature and even less compared to a surfactant impact, it must not be neglected and values have to be mentioned when dealing with water evaporation. Modifying surface tension also affects the pendant drop shape. The drying kinetics of the pendant drop volume and its outer shell are connected to this change of shape. Steam in the air can be assimilated to a wetting agent, hence a surfactant, and can be used in an environmental-friendly way to ease the drying stage. Indeed, the challenge is to limit the risk of cracking and damaging pieces during this crucial step in material processing.
文摘The evaporation of sessile water droplets on hydrophobic surfaces is a topic which led to numerous investigations. However, how does the liquid behave when the evaporation occurs between two of these particular substrates? The drying stage is governed by capillary phenomena which takes place in a confined space. In the field of material shaping, it is also possible that some regions of a green body exhibit hydrophobic properties. As part of a better understanding of the local mechanisms during drying, liquid bridges have been reproduced in an ideal case. Drying kinetics and parameters measurements from 303 to 343 K (relative humidity of 55%) of deionized water liquid bridges between two plates of hydrophobic substrates are presented. Experimental work was carried out using a specific device to create liquid bridges, coupled with image analysis within an adapted instrumented climatic chamber. While the volume and the exchange surface of liquid bridges decrease regularly throughout the process, contact angles constantly diminish and more significantly at the end. This is different from the evaporation between two hydrophilic plates. From these measurements, the change of curvature of the liquid bridges during evaporation is highlighted.
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.
文摘In this paper, a glass powder from waste containers was mixed (10 - 40 wt.%) with a kaolinitic sandy clay from Cameroon to elaborate net-shape ceramics, fired at 1100°C. The sintering behavior was from dilatometry and thermo gravimetric analyses together with the characterization of porosity and flexural strength. The increase of glass to kaolinite ratio reduces the sintering shrinkage leading to a none-densification sintering when 40 wt.% of glass is added in the mixture. The volume variation during the whole firing process is from the individual volume variations during the quartz transformation, the structural reorganization of kaolinite and during sintering. Quartz size and relative quantity have a significant role on the first processes since it leads to either cohesive or un-cohesive behavior. But the glass quantity strongly controls the second and the third thermal processes because glass additions change the recrystallization processes, leading to the formation of dense clay-glass agglomerates distributed within the three dimensional quartz network.
