Polytypic transformations during the thermal decomposition of cobalt hydroxide and cobalt hydroxynitrate

Abstract

a b s t r a c tThe isothermal decomposition of cobalt hydroxide and cobalt hydroxynitrate at different intervals of temperature leads to the formation of Co 3 O 4 . The phase evolution during the decomposition process was monitored using powder X-ray diffraction. The transformation of cobalt hydroxide to cobalt oxide occurs via three phase mixture while cobalt hydroxynitrate to cobalt oxide occurs through a two phase mixture. The nature of the sample and its preparation method controls the decomposition mechanism. The comparison of topotactical relationship between the precursors to the decomposed product has been reported in relation to polytypism.

Preparation–Morphology–Performance Relationships in Cobalt Aerogels as Supercapacitors

“…The well-established thermogravimetric profiles for cobalt basic salts, Co(OH) 2 , Co 2 (OH) 3 Cl, , and Co 2 (OH) 3 (NO 3 ) , support the general assignment of these sol–gel materials as possessing the formula Co(OH) 2– n X n (X = Cl, NO 3 ). Specimens 3 , 4 , 5 , and 6 , which are derived from Co(NO 3 ) 2 , all undergo a single, sharp mass loss between 220 and 230 °C corresponding to dehydroxylation of either Co(OH) 3 (NO 3 ) or Co(OH) 2 .…”

“…Specimens 4, 5, and 6 were all prepared from Co(NO 3 ) 2 in methanol and display identical broad PXRD patterns and thermograms. In contrast, the PXRD pattern of specimen 3, which is prepared from Co(NO 3 ) 2 in ethanol more closely resembles the Co 2 (OH) 3 (NO 3 ) phase 19 and displays a slightly lower thermal decomposition onset. These observations suggest higher retention of the nitrate anion in this structure, which likely arises from the reduced polarity of the ethanol relative to the methanol, which in turn results in poorer solvation of the anionic nitrate in solution.…”

Highly Active Cobalt Oxide Catalysts Prepared by SACOP for the Preferential Oxidation of CO in Excess Hydrogen

“…This is ascribed to the partial calcination of Co(OH) 2 at 200 °C. It is known that bulk Co(OH) 2 is converted to Co 3 O 4 in two steps:16 first it is transformed to CoOOH at temperatures below 200 °C; then the CoOOH is converted to Co 3 O 4 in the temperature range of 200–300 °C. It can therefore be assumed that the CoOOH formed by the partial calcination of bulk Co(OH) 2 has a lower surface area than the Co 3 O 4 phase formed after complete calcination.…”

Synthesis and spectroscopic identification of nickel and cobalt layered hydroxides and hydroxynitrates

“…These bands were also present in the data published for these phases prepared by Ramesh and suggest these are mixed-anion materials with both nitrate and isocyanate incorporated into the structure. This compositional discrepancy may have caused the previous confusion where samples prepared by Ramesh using this method had both Co 2 (OH) 3 (NO 3 ) 64 and Co 3 (OH) 4 (NO 3 ) 2 compositions assigned in different publications. 36,64,65 The exact formulae of the nickel and cobalt hydroxysalt materials prepared by the solid-state urea flux method cannot be determined with certainty from the TGA data alone.…”