Crystallization of CaAl₄O₇and CaAl₁₂O₁₉powders

Abstract

Calcium is always present in alumina systems as an unintentional (or intentional) dopant, and yet the fundamental effect of its incorporation into the aluminas is not well understood, and is further complicated by the presence of Si. The synthesis of powders of two calcium aluminate phases (CaAl 4 O 7 , which is also known as CaO Á 2Al 2 O 3 or CA 2 , and CaAl 12 O 19 , which is also known as CaO Á 6Al 2 O 3 or CA 6 ) has been investigated using lowtemperature chemical-processing techniques. The crystallization of these powders from the amorphous precursor has been examined using various characterization techniques. The precursors for the powders were prepared by mixing stoichiometric proportions of the nitrate salts into a 5 wt% aqueous solution of poly(vinyl alcohol). Conversion of the amorphous precursors to crystalline powders and the subsequent phase transitions were monitored using differential thermal analysis (DTA), thermogravimetric analysis (TGA) and powder X-ray diffractometry (XRD). While powders with CA 2 stoichiometry crystallized directly at 883 C, amorphous powders with CA 6 stoichiometry first crystallized into an intermediate structure without partitioning and then transformed into CA 6 at 1175 C. Fully and partially crystallized powders were analyzed using transmission electron microscopy and electron energy-loss spectroscopy (EELS). Measured near-edge structures (Al-L 2,3 , Ca-L 2,3 and O-K) are presented for the CA 2 , -Al 2 O 3 and CA 6 phases. The intermediate phase, identified as -Al 2 O 3 , was found to accommodate a significant concentration of Ca.

Discovery of Oxygen Carriers by Mining a First-Principle Database

“…Only CaCr 2 O 4 has been shown to form spontaneously during solid fuel combustion, however. Even so, experiments indicate that CaAl 4 O 7 and CaCrO 4 are also stable up to relatively high temperatures. , Unfortunately, there seems to be no information available regarding Ca 3 Al 4 O 9 . The Na-based candidate is, nevertheless, more interesting because Na 2 CrO 4 is catalytic while NaAlO 2 has been shown to enhance the performance of an Fe-based OC …”

“…Only CaCr 2 O 4 has been shown to form spontaneously during solid fuel combustion,107 however. Even so, experiments indicate that CaAl 4 O 7 and CaCrO 4 are also stable up to relatively high temperatures 108,109. Unfortunately, there seems to be no information available regarding Ca 3 Al 4 O 9 .…”

Effect of Eu3+ Concentration on the BaAl2O4/CaAl4O7: x% Eu3+ (0 ≤ x ≤ 5.5) Mixed‐Phase Nanophosphors Synthesized Using Citrate Sol‐Gel Method

“…is is because CaAl 4 O 7 crystallizes directly at 883°C [27]. e product from the furnace was then crushed in an agate mortar with a pestle for powder synthesis.…”

Bio‐oil upgrading via ketonization of carboxylic acids on Na promoted Ca/AlOx catalysts

“…The formation of amorphous calcium aluminates upon calcination at 800°C has been reported in earlier works. [24,32] In terms of their XRD patterns, these amorphous compounds are attributed to calcium aluminates, for example, Ca 2 Al 2 O 5 and Ca 12 Al 14 O 33 .…”