Chemical reduction of hematite by sodium borohydride
Well-crystallized hematite was suspended in water and treated at room-temperature (RT) with sodium borohydride. The product of the reaction is a highly magnetic black powder, which is stable at RT. The NaBH4 treatment converts about half of the hematite to an amorphous Fe–B alloy and to a small fraction of sub-micron sized, amorphous metallic-Fe nodules. Heating at 400°C of this composite has resulted in the crystallization and/or oxidation of more than half of the amorphous Fe–B phase to α-Fe and Fe3O4 and B2O3, respectively. After treatment at 800°C, the metallic Fe and the amorphous Fe–B have completely vanished, and the resulting product consists of hematite and FeBO3 embedded in the matrix of α-Fe2O3.
Reduction of oxides by sodium borohydride solutions: A ‘chimie douce’ preparation of oxide bronzes
Abstract This work describes the use of sodium borohydride at room temperature as a reducing agent in aqueous medium in order to prepare oxide bronzes in which a cation is inserted. Two possibilities are offered depending on pH: a topotactic reaction leading to a final compound isostructural with the starting oxide, or a non-topotactic reaction leading to a bronze which may differ significantly from the parent phase. They are illustrated by two examples, respectively: the preparation of a hexagonal potassium tungsten bronze from a metastable hexagonal WO 3 (conservation of the tunnel structure), and that of the lamellar vanadyl vanadate (NH 4 ) 2 V 3 O 8 from the stable form of V 2 O 5 .
Effects of Equipment Dimensions on Liquid Mixing Time of Bubble Column with Draft Tube
The liquid mixing time of a bubble column with a draft tube is experimentally studied. The diameter and height of the column, the diameter and length of the draft tube, and the mode of sparging gas were changed and the liquid mixing time was measured.The lengths of bottom and top clearances have significant effects on the liquid mixing time. The liquid mixing time increases with increasing column aspect ratio of height to diameter. The liquid mixing time of the bubble column with a draft tube is longer than that of a standard bubble column when the column aspect ratio is relatively high. The liquid mixing time has a minimum when the diameter ratio of draft tube to column is 0.5 to 0.6. These effects of equipment dimensions are expressed by an equation. In the experiment using different solutions, the liquid mixing time becomes shorter with increasing liquid surface tension, or with increasing liquid viscosity.