This study presents the results of the morphological dependence of alumina granules obtained by spray freeze drying (SFD) with twin‐fluid atomization. It is shown that the introduction of 1‐, 2‐ and 4‐wt.% polyvinyl alcohol (PVA) as a binder in an alumina suspension leads to the formation of irregular granules. Depending on atomization conditions, spherical, “tadpole‐like,” granule‐satellite and granule aggregates may form during SFD. Increasing the flight time of droplets before the fixing of their shape when they come in contact with liquid nitrogen effectively contributes to the spheroidization of alumina granules. Compacting PVA‐free SFD granules leads to the formation of diagonal flaws in a green‐body structure. Adding PVA prevents the abovementioned defects by increasing the strength of alumina granules. Increasing the amount of PVA leads to an increase in “tadpole‐like” granule content and, consequently, a decrease in a green‐body density.
The paper presents the results of a study of the synthesis of a highly dispersed silicon carbide powder by combining exo-and endothermic reactions (synthesis from elements and carbothermic reduction) using carbon nanofibers as carbon material. The reaction products were studied by the X-ray phase and elemental analyses as well as by scanning electron microscopy using the local energy-dispersive X-ray microanalysis. The specific surface of the samples was determined by the BET method. A sedimentation analysis was performed. The thermo-oxidative stability was studied by synchronous thermogravimetry (TG) and differential scanning calorimetry (DSC). The material obtained under optimal conditions is represented by one phase -high-temperature modification silicon carbide. An average size of aggregated particles is 6.3…7.2 μm. The specific surface area of the samples is up to 8 m 2 /g. The content of impurities is insignificant (no more than 4 % by weight). Optimal conditions for the synthesis of silicon carbide with the use of NFC(s) as a reducing agent and carbidizer are the following: the mass ratio of reagents according to SiC carbide stoichiometry, the mass ratio of charges of 1:1, and the process in argon at 1800 °C.
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