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Freeze-casting porous PTFE foam via constant temperature cold source
Journal of Porous Materials ( IF 2.6 ) Pub Date : 2021-06-05 , DOI: 10.1007/s10934-021-01090-4
Xiaoming Guo , Yongyi Yao , Puxin Zhu , Mi Zhou , Tao Zhou

Porous PTFE foam with unique microstructure fabricated by freeze-casting may provide many potential applications in various fields. In this report, freeze-casting was applied to manufacture porous PTFE foam. The microstructure of the green bodies affected by the freezing temperature, PVA concentration and PTFE concentration was investigated. SEM, the actual temperature change curve, Low-temperature DSC and viscosity were characterized to investigate the microstructure forming process. The green bodies formed in freeze-casting were found bimodal in pore distribution. The underlying mechanism was further discussed by Oswald ripening which may be caused by long crystallization time. Cavities were also formed on the pore walls of the green bodies. That may be caused by PVA gelation during the growth of ice crystals. The orientated pore can be observed in the green bodies clearly. However, the pore orientations become less regular as the number of loaded particles being reduced. The explanation for this is that longer crystallization time may also lead to parts of crystallization occurring far from the original generated ice-front. Undergoing sintering process, the microstructure of the sintered sample had an incredible transformation from green body. Louvered shape of the pore wall with worm-like pore arms appeared, and pore shapes were transformed from oval to polygon. We present the schematic of the microstructure evolution of PTFE foam also.



中文翻译:

恒温冷源冻铸多孔聚四氟乙烯泡沫

通过冷冻铸造制造的具有独特微观结构的多孔聚四氟乙烯泡沫可以在各个领域提供许多潜在的应用。在这份报告中,冷冻铸造被用于制造多孔聚四氟乙烯泡沫。研究了冷冻温度、PVA 浓度和 PTFE 浓度对生坯微观结构的影响。通过扫描电镜、实际温度变化曲线、低温DSC和粘度表征来研究微观结构的形成过程。发现在冷冻铸造中形成的生坯在孔隙分布中是双峰的。Oswald熟化进一步讨论了潜在的机制,这可能是由于结晶时间长造成的。在生坯的孔壁上也形成了空腔。这可能是由于冰晶生长过程中 PVA 凝胶化造成的。在生坯中可以清楚地观察到定向孔。然而,随着负载颗粒数量的减少,孔隙方向变得不那么规则。对此的解释是,较长的结晶时间也可能导致部分结晶发生在远离原始生成冰前的地方。经过烧结过程,烧结样品的微观结构发生了令人难以置信的生坯转变。孔壁出现百叶状的蠕虫状孔臂,孔形由椭圆形变为多边形。我们还展示了 PTFE 泡沫的微观结构演变示意图。对此的解释是,较长的结晶时间也可能导致部分结晶发生在远离原始生成冰前的地方。经过烧结过程,烧结样品的微观结构发生了令人难以置信的生坯转变。孔壁出现百叶状的蠕虫状孔臂,孔形由椭圆形变为多边形。我们还展示了 PTFE 泡沫的微观结构演变示意图。对此的解释是,较长的结晶时间也可能导致部分结晶发生在远离原始生成冰前的地方。经过烧结过程,烧结样品的微观结构发生了令人难以置信的生坯转变。孔壁出现百叶状的蠕虫状孔臂,孔形由椭圆形变为多边形。我们还展示了 PTFE 泡沫的微观结构演变示意图。

更新日期:2021-06-07
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