Kinetics of Urea Decomposition in the Presence of Transition Metal Ions: Ni²⁺

Abstract

The literature on kinetics of the urea decomposition reaction was reviewed for the 333-373 K range of temperature. Possible reactions in the pH range of 5-9 were identified. Kinetic simulations indicated significant accumulation of the cyanate intermediate in the pH-time-temperature range that was studied. The effects of Ni 21 hydrolysis and complexation with the urea decomposition products were incorporated into the simulations. The kinetic simulation of the rate of Ni 21 removal from the solutions was compared against the experimental data. The experimental results indicated an agglomerative growth mechanism for the precipitation process. Chemical analyses showed that the composition of the precipitate varies with digestion time, in agreement with the predictions of the kinetic simulation.

The Electrochemical Properties of Nanocrystalline Gd0.1Ce0.9O1.95Infiltrated Solid Oxide Co-Electrolysis Cells

“…However, the precipitation of solid phases from urea solutions is a rather complex phenomenon; small variations of precipitation parameters such as the initial cation concentration, aging time and temperature produce dramatic changes in the chemical stoichiometry, crystal structure, size distribution and particle morphology of the precipitated solids. [23][24][25][26] Therefore, before the GDC10 infiltration, an additional experiment was carried out to optimize the urea precipitation method.…”

“…The cell was dipped into the 0.015 M solutions with 30 urea/cation molar ratio which infiltrated the electrode by capillary action. After different time intervals, cells were removed from the solution and dried at room temperature (25 • C). Then, the infiltrated cells were fired with fuel electrode side putting in the reduced condition (5% H 2 balanced by N 2 ) at 600…”

Monodisperse Calcium Carbonate Microtablets Forming at 70°C in Prerefrigerated CaCl2–Gelatin–Urea Solutions

“…Readers interested in learning more about the decomposition kinetics of urea in aqueous solutions containing metal ions are hereby referred to the detailed works of Willard and Tang 45 and Mavis and Akinc, 46 which also gave the stepwise decomposition reactions written in full. The aging temperature was deliberately maintained low at 701C in this study (in contrast to the use of the more common temperature of 901C 46 ) to avoid the instantaneous and rapid decomposition of urea, and to provide a much slower supply of HCO 3 À ions to the Ca-gelatin solutions.…”

“…The aging temperature was deliberately maintained low at 701C in this study (in contrast to the use of the more common temperature of 901C 46 ) to avoid the instantaneous and rapid decomposition of urea, and to provide a much slower supply of HCO 3 À ions to the Ca-gelatin solutions.…”

Homogeneous precipitation of nickel hydroxide powders

“…Nonetheless, the agglomerative growth of primary crystallites will be elaborated in comparing the model predictions to the experimental data. Ni++ + HgO = Ni(OH)+ + H+ (12) Ni++ + 2HgO = Ni(OH)2(aq) + 2H+ (13) Ni++ + 3HgO = Ni(OH)g-+ 3H+ (14) 2NÎ++ + HgO = NÎ2(OH)3+ + H+ (15) 4NÎ++ + 4HgO = Ni^(OH)^ + 4H+ (16)…”