Nathalie Jongen

Synthesis of nickel hydroxide powders by urea decomposition

Abstract Synthesis of nickel hydroxide from aqueous solutions by decomposition of urea was investigated. Spherical agglomerates of nanocrystalline particles were obtained. Precipitated powders show turbostratic α-phase with significant carbonate intercalated into the structure. Addition of dispersant HPMC increases the specific surface area and reduces the median agglomerate size, whereas increase in aging time increases the precipitation yield considerably.

New morphology of calcium oxalate trihydrate precipitated in a segmented flow tubular reactor

Reference LTP-ARTICLE-2000-007doi:10.1023/A:1006771428827View record in Web of Science Record created on 2005-01-12, modified on 2017-05-10

High-quality nickel manganese oxalate powders synthesized in a new segmented flow tubular reactor

Abstract High-quality nickel manganese oxalates have been prepared using an innovative approach for the production of homogeneous powders, the continuous Segmented Flow Tubular Reactor (SFTR). This new reactor is mainly composed of a mixer, a segmenter, a tubular section and a decanter. Mixed Ni–Mn oxalates are synthesized in the SFTR. The powders present controlled morphology, narrow particle size distribution, high purity and desired stoichiometry. Their characteristics are compared to those of powders obtained in a batch reactor. These oxalates are precursors for nickel manganites, used as negative temperature coefficient thermistor (NTC) ceramics.

Calcination and morphological evolution of cubic copper oxalate particles

Reference LTP-ARTICLE-2000-009doi:10.1023/A:1006711724828View record in Web of Science Record created on 2005-01-12, modified on 2017-05-10

Control of morphology and nanostructure of copper and cobalt oxalates: Effect of complexing ions, polymeric additives and molecular weight

Precipitated oxalates are often nanostructured and can be used as precursors for nanostructured oxides for different applications. The modification of the particle shape and nanostructures of both copper and cobalt oxalates has been demonstrated using polymeric additives or complexing counter-ions. In the case of cobalt oxalate the characteristic elongated rod particle shape (axial ratio of 10) can be modified by using polymethymethacrylate (PMMA) to produce particles with lower axial ratios of 2, through cubes all the way to platelets (axial ratio 0.2). The PMMA inhibits the growth of the particles along the [101] direction more and more strongly as the concentration of the polymer increases. The crystallite size from XRD line broadening is not modified by the PMMA indicating that the PMMA does not influence the nucleation and growth but modifies the aggregation kinetics. Copper oxalates precipitated in the presence of different cellulose derived polymers with different molecular weights and functional groups (methyl and propyl) showed sensitivity to both molecular weight and functional group. Higher molecular weights did not influence the copper oxalate particle shape, whereas methyl cellulose gave elongated particles and propyl celluloses gave platelet like particles. Copper oxalate precipitated in the presence of acetate counter ions gave platelets with an axial ratio of 0.15 compared to the cushion-like morphology (axial ratio 0.5). The primary crystallites were more elongated along the [001] direction in the presence of acetate, modifying the proportion of the hydrophobic and hydrophilic surfaces and hence influencing the aggregation kinetics and particle shape. The copper and cobalt oxalate particle formation seems to be dominated by the primary particle aggregation with the different additives interacting specifically with different crystallographic faces of the primary particles. By tuning this interaction particles with different shapes and substructures can be formed.

Nano-composite powders, a new concept for their synthesis

Reference LTP-ARTICLE-2001-005doi:10.1016/S1359-6462(01)00903-4View record in Web of Science Record created on 2005-01-12, modified on 2017-05-10