On the thermal decomposition of [Ni(H2O)6](NO3)2 and its deuterated analogue

Abstract

The methods of TG, DTA and DSC were used to study the thermal decompositions of [Ni(H20)6](NO3)2 and [Ni(D20)6](NO3)2 in an atmospheric air medium. Intermediates were isolated at 145, 230 and 245 ~ and were identified by quantitative analysis and IR spectroscopy. The following phase transitions were observed under the conditions of the experiment: melting of the salts, partial dehydration to the tetrahydrate, formation of basic nickel nitrate hydrate stable within) a narrow temperature interval, and formation of NiO.The enthalpies of the phase transitions were calculated from the DSC data.The DTA and DSC data show that in [Ni(D20)6](NO3)2 the phase conversions take place at somewhat lower temperatures than those for [Ni(H20)6](NO3)zThe experimental decomposition of [Ni(H20)6](NO3)2 has been studied by a number of authors. Some of the data obtained are contradictory, while others are complementary.Publications [1][2][3][4][5][6][7][8][9][10] deal with thermal decomposition in air. According to these authors, the compound melts in its crystal water and undergoes step= wise dehydration, the intermediate hydrates differing in composition, depending on the heating rate. It is pointed out in [5] that all the phase tran= sitions occur in the solid phase a t a low rate of heating of 5-20 deg/min. The pentahydrate was reported in [4]. The tetrahydrate, described in [3,5,8], is unstable and is readily converted into the trihydrate [8] or the dihydrate [3,5]. Some authors [i, 9] report that the hexahydrate is converted into the trihydratr without anu tetrahydrate or dihydrate being observed.

How NO Affects Nickel and Cobalt Nitrates at Low Temperatures To Arrive at Highly Dispersed Silica-Supported Nickel and Cobalt Catalysts

“…While this observation has been reported by Petrov et al as well, no assignment was made and the nature of these bands is uncertain . Likely the nickel hydroxynitrate retained some crystal water, resulting in hydrogen-bonded hydroxyl bands at lower frequencies. − The basic formula for hydroxynitrates is x Ni(NO 3 ) 2 ·y Ni(OH) 2 ·z H 2 O, and several authors reported mono- or dihydrated nickel hydroxynitrates as the predominant species during the decomposition of nickel nitrate hexahydrate. ,, Unfortunately, nickel hydroxynitrate hydrates such as Ni 2 (OH) 2 (NO 3 ) 2 ·2H 2 O are poorly characterized in the literature, making assignment difficult. However, spectra of the isostructural Zn 2 (OH) 2 (NO 3 ) 2 ·2H 2 O phase shows similar features in the lower end of the hydroxyl region, unlike its anhydrous counterpart which shows only a single absorption band .…”

“…[49][50][51] The basic formula for hydroxynitrates is xNi(NO 3 ) 2 3 yNi(OH) 2 3 zH 2 O, and several authors reported mono-or dihydrated nickel hydroxynitrates as the predominant species during the decomposition of nickel nitrate hexahydrate. 35,52,53 Unfortunately, nickel hydroxynitrate hydrates such as Ni 2 (OH) 2 (NO 3 ) 2 3 2H 2 O are poorly characterized in the literature, making assignment difficult. However, spectra of the isostructural Zn 2 (OH) 2 (NO 3 ) 2 3 2H 2 O phase shows similar features in the lower end of the hydroxyl region, unlike its anhydrous counterpart which shows only a single absorption band.…”

How nitric oxide affects the decomposition of supported nickel nitrate to arrive at highly dispersed catalysts

“…9. Firstly, both heat flow curves showed to be endothermic, as expected, and similar to the decomposition of Ni(NO 3 ) 2 ·6H 2 O [54,55]. Secondly, the trace recorded during decomposition in air had a very sharp peak with a maximum at 268 • C, whereas the NO/He trace consisted of a broad peak from 250 to 277 • C. Hence, the DSC results confirmed that NO moderated the decomposition rate of Ni 3 (NO 3 ) 2 (OH) 4 .…”

Characterization of Bulk and Surface Composition of CoxNi1-xOy Mixed Oxides for Electrocatalysis

“…Upon hydrolysis, Ni and Co hexaaquo cations become hydroxylated, polymerize, and form the nuclei of hydrated oxides before completion of nitrogen oxide evolution. Even the thermolysis of the dry crystalline hydrate Ni(NO 3 ) 2 ·6H 2 O forms intermediate aquo- and hydroxynitrate complexes (−[Ni(H 2 O) 4 ](NO 3 ) 2 at 145 °C, −Ni 2 (OH) 2 (NO 3 ) 2 ·2H 2 O at 230 °C, and −Ni 2 (OH) 2 (NO 3 ) 2 ·H 2 O at 245−350 °C) . Therefore, among the products of decomposition of Co and Ni nitrates one can anticipate the presence of partly dehydrated oxides such as MO·H 2 O, M(OH) x , or MOOH, besides MO, in an amount depending on the hydrolytic history (M = metal).…”