Pore architectures and oil absorption behavior of porous mullite beads fabricated via dripping-ice templating

Porous mullite beads with a good spherical shape and a uniform size distribution of about 1.2 mm were fabricated by ice-templating in combination with dripping methods. These internal pore structures exhibited a radially oriented laminar channel from the center of the sphere to the surface. With the decreasing of freeze temperature to −196°C, the thickness of pore walls and the width of pore decreased. The mullite grain morphology in the pore wall was also influenced by the frozen temperature. High aspect ratio mullite grain was formed in the pore wall of beads frozen at −25°C, while low aspect ratio mullite whiskers constituted the pore wall of beads frozen at −196°C. In addition, the obtained porous mullite beads exhibited a good oil adsorption performance under capillary force for kerosene, edible oil, and motor oil with adsorption values of 3.37, 4.07, and 4.04 g/g, respectively.     

用冰模板法制备羟基磷灰石多孔陶瓷

使用水基羟基磷灰石(HA,Ca5(PO4)3OH)浆料,用冰模板法制备定向层状多孔HA陶瓷,研究了浆料中HA陶瓷颗粒含量和冷端温度的影响.结果表明:随着浆料中HA陶瓷颗粒含量的提高,浆料的粘度值增大,层状多孔结构的层厚度相应增加,孔道层间距减小甚至消失,多孔材料的抗压强度从1.4 MPa提高到5.7 MPa,孔隙率从7...     

The effect of gelation on statically and dynamically freeze-cast structures

Freeze-casting is a technique used to produce structures with anisotropic porosity in the form of well-defined microchannels throughout a sample. Here, this technique is used on the magnetocaloric ceramic La_0.66Ca_0.26Sr_0.07 Mn_1.05O₃. We show that a dynamic freezing profile, where the temperature is decreased continuously at −10 K/min, results in homogeneous, lamellar channels with widths of ∼15 µm, while static freezing, where the temperature is kept constant at 177 K, results in channels of increasing size away from the initial ice crystal nucleation site. The effect of gelation before freeze-casting is also investigated. Gelation inhibits ice crystal growth, which significantly changes the morphology by making channel cross sections less elongated, while additionally introducing more dendrites and ceramic bridges in the structure. The latter significantly dominates the flow path through the gelated structures, affecting the calculated tortuosity, which increases to τ ≈ 4 when compared to non-gelated samples where calculated tortuosities are in the range of ∼1.3 to ∼3. Finally, we present a systematic and automatic approach for evaluating channel and wall sizes and calculating tortuosities. This is based on analysis of images obtained by scanning electron microscopy using a continuous particle size distribution method and the TauFactor application in MATLAB^®.     

Ice-Templated,Large-Area Silver Nanowire Pattern for Flexible Transparent Electrode

Flexible transparent electrodes are critically important for the emerging flexible and stretchable electronic and optoelectronic devices. To this end, transparent polymer films coated with silver nanowires (AgNWs) have been intensively studied in the past decade. However, it remains a grand challenge to achieve both high conductivity and transmittance in large-area films, mainly due to the poor alignment of AgNWs and their high junction resistance. Here, the successful attempt to realize large-area AgNW patterns on various substrates by a 2D ice-templating approach is reported. With a relatively low dosage of AgNWs (4 µg·cm⁻²), the resulted flexible electrode simultaneously achieves high optical transmittance (≈91%) and low sheet resistance (20 Ω·sq⁻¹). In addition, the electrode exhibits excellent durability during cyclic bending (≈10 000 times) and stretching (50% strain). The potential applications of the flexible transparent electrode in both touch screen and electronic skin sensor, which can monitor the sliding pressure and direction in real-time, are demonstrated. More importantly, it is believed that the study represents a facile and low-cost approach to assemble various nanomaterials into large-area functional patterns for advanced flexible devices.     

Micromechanical modeling of compressive behavior in freeze-casted ceramic

In this study, a novel computational micromechanical framework is proposed to predict the effective mechanical properties of the ice-templated ceramics under off-axis compressive loading. The mechanical behavior is simulated by a computational micromechanical model and validated against experimental results. Smeared cracking approach was used to describe failure in ice-templated alumina. The representative volume element (RVE) was developed based on the honeycomb analogy of lamellar walls considering the morphology of the material. The periodic boundary conditions were applied in RVE to simulate bulk behavior of the material. The compression testing was conducted on the ice-templated alumina samples to obtain the effective compressive moduli and strength with different loading angles. Digital image correlation method was used to measure strain field during the experiment and quantify the effective misalignment angle corresponding to porous material. The effective stiffness and strength obtained from RVE analysis compared well with experimental results. The proposed micro-mechanical RVE model allows for determining the properties of the ice-templated porous ceramic for various off-axis angles.     

基于冰模板法构筑孔道结构的合成策略及研究进展

冰模板法也称为定向冷冻法或冷冻铸造法，具有微观结构可调控性强、原料适用范围广、可制备大尺寸材料等优势，被广泛应用于定向调控陶瓷、聚合物、金属和碳材料等材料的制备领域。探讨冰模板法控制功能纳米材料组装成分级多孔复合材料的影响机制，解析冰模板法与其他材料的加工工艺的相互作用关系，对改善材料性能和开发新材料具有重要意义。该文阐述了冰模板法制备多尺度复杂仿生结构材料的基本原理、合成策略以及孔隙调控作用，并以冰晶成核和生长为重点，总结了冰模板法对孔道结构进行调控的措施。此外，还介绍了冰模板法辅助构造孔几何形状（0D、1D、2D和3D宏观结构），以及组装成块状物体（微球、纤维、薄膜和整体）。最后分析了复合材料的微观结构和宏观形貌的相关性，总结了不同冷冻过程对孔道结构的影响机制，并展望了该领域未来的发展方向。