Hydrothermal reaction kinetics. The decomposition of nickel(II) hydroxide

Abstract

The fractional extent α of decomposition of ripened Ni(OH)2 into green NiO in alkaline hydrothermal conditions under nitrogen is given by the rate law α1/3 = kc[OH−]t, where kc = 2.4 × 10−5 kg mol−1 s−1 at 561 K. The Arrhenius activation energy is 220 + 25 kJ mol−1. The reaction is accelerated moderately by O2 (giving black NiO1+δ) and strongly by added NiO. A reaction mechanism involving dissolution of Ni(OH)2 as Ni(OH)3− (aq) and rate-determining, surface-controlled reprecipitation of this as NiO is proposed.

Isothermal decomposition kinetics of nickel (II) hydroxide powder

“…This activation is slightly higher (although perhaps not significantly) than most of the reported activation energies listed in Section 1 for isothermal decomposition. Perhaps more significantly, this study deduced that the nickel hydroxide decomposition obeyed first-order kinetics, not a contracting area/volume mechanism as other isothermal kinetic studies reported [19,21]. Sample size could certainly affect the observed mechanism.…”

“…El-Salaam and Hassan [19] used a much larger sample size (500 mg) than our study (10 mg), so differing observed mechanisms would not be unexpected. However, Swaddle and Wong [21] used similar sized sample mass as this study, and still reported a contracting area/volume reaction model. The study by Swaddle and Wong did not appear to consider a great number of possible reaction mechanisms, nor did it perform any visual analysis or further study in an attempt to identify a mechanism, so perhaps a first-order decay fit their data equally well, but was not considered.…”

“…They observed that product water retention became significant at higher conversions values, thus making kinetic fitting difficult. Swaddle and Wong [21] used two types of nickel hydroxide in their isothermal kinetic studies: unripened (less crystalline, more attached water) and ripened (highly crystalline, less attached water). The authors found that both contracting area and volume mechanisms fit the data equally well (in part due to the authors essentially needing to use the incubation time as a fit parameter).…”

Hydrothermal Decomposition of Cobalt Hydroxide in Saturated Water Vapor

“…Ziemniak et al and Basavalingu et al, studied stability and thermodynamics of the CoO–H 2 O system under hydrothermal conditions and reported the P–T stability curve for the system. Swaddle et al studied hydrothermal decomposition of Ni­(OH) 2 in alkaline hydrothermal conditions under nitrogen, where NiO was the final product. Hazell et al studied hydrothermal decomposition and reported the kinetics to be much slower than that for vacuum, but quantitative kinetic data could not be obtained.…”

Experimental investigation of trace element dissolution in formation water in the presence of supercritical CO2 fluid for a potential geological storage site of CO2 in Taiwan

“…For Se, its concentration in the formation water increased by 11,800% (Table 3a). Adsorption of Se species onto the Fe, Mn, and Al-oxyhydroxides surfaces played an important role in Se concentrations in formation water (Swaddle and Wong, 1978). The extractable Fe and Mn extents in sandstone after reaction decreased, suggesting the contents of Fe and Mn-oxyhydroxides in sandstone decreased, resulting in the dissolution of the adsorbed selenium species into formation water (Table 3a).…”