Understanding and Preventing Structural Changes during Drying of Gels

Co-Precipitation Synthesis of Y2w3o12 and Al2w3o12 Submicronic Powders and Their Application in Polymer Matrix Composites

“…In this technique an aqueous suspension of particles is frozen and subsequently, ice is allowed to sublime under vacuum. Water undergoes some volume expansion when freezing, which can separate adjacent particles when water transforms into ice (see Figure 2.12) [42,45]. Moreover, high-energy liquid/vapor interfaces are replaced by low energy solid/vapor interfaces.…”

“…Thus, agglomeration of adjacent particles induced by capillary forces can be mitigated in theory. However, capillary problems could appear when residual water remains in particle pores as a result of incomplete freezing or when temperature increases too early at the end of the drying process [45]. The freeze-drying is usually carried out at -10 °C and absolute pressures of 2 mmHg (0.013 bar) [46].…”

“…This leads to quick drying without the necessity of heating the atmosphere [46]. Actually, the most evident effect of microwave drying is the considerable reduction in drying time, from more than 20 h for the alternative drying methods (conventional oven drying and freeze drying) to solely a few minutes [45].…”