From amorphous precipitates to sub-micronic crystalline platelets of Co(OH) 2: a kinetic study of the transformation process

• Published in: Powder technology Vol. 128; no. 2; pp. 332 - 337
• Main Authors: Gaunand, A, Lim, W.L
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Lausanne Elsevier B.V 01.12.2002; Elsevier
• Subjects: Chemistry; Cobalt hydroxide; Cross-disciplinary physics: materials science; rheology; Elements and non-metal compounds (oxides, hydroxides, hydrides, sulfides, carbides, ...); Exact sciences and technology; General and physical chemistry; Growth from solutions; Inorganic chemistry and origins of life; Materials science; Methods of crystal growth; physics of crystal growth; Physics; Precipitation and phase transformation; Preparations and properties; Solution properties; Solutions; Sulphate; Cobalt hydroxide; Sulphate; Precipitation and phase transformation; Scanning electron microscopy; Chemical precipitation; Transition metal Compounds; Experimental study; X ray diffraction; Dissolution; Modeling; Kinetic model; Phase transformation; Cobalt Hydroxides; Sodium Hydroxides; Recrystallization; Reaction mechanism; Kinetics; Cobalt Sulfates; Neutralization
• ISSN: 0032-5910; 1873-328X
• DOI: 10.1016/S0032-5910(02)00276-0

α-Cobalt hydroxide is precipitated by soda from its sulphate salt in a double-jet standard stirred reactor, and its transformation into its stable phase β is characterized by recording the pH of the solution. The α precipitate is amorphous, whereas, from XRD patterns, the β precipitate is crystalline; its SEM micrographs display thin hexagonal platelets. Higher sulphate concentration in the reactor increases their size, but reduces the transformation kinetics only when added before the injection of reagents. The transformation is found to be controlled by the dissolution of the α precipitate: the sulphate ions both reduce the dissolution of the micronic agglomerates of α precipitate, as they are probably adsorbed on their internal surface, and lead to wider β platelets, because of their specific adsorption on their two lateral faces.