Nano-composite powders, a new concept for their synthesis (original) (raw)
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ChemInform Abstract: Formation Mechanisms of Uniform Colloid Particles
ChemInform, 2008
The relationship of the shape and structure of uniform colloidal particles to different mechanisms of formation by precipitation in homogeneous solutions is reviewed. Specifically, conditions leading to (a) amorphous spheres, (b) nonspherical crystals of different shapes, and (c) polycrystalline particles of different morphologies including spheres are distinguished. The last case is observed when larger particles are formed by aggregation of nanosized precursors. It is now recognized that the latter process is more common than previously understood. A model explaining the size selection of monodispersed spheres by aggregation is illustrated in the case of silver particles. It was also demonstrated that uniform polycrystalline particles of other shapes are generated by the aggregation process. Challenges faced in the effort to develop at least a semi-quantitative explanation of the shape factor in the latter case are outlined.
Solid particles formation from solutions, an intellectual and industrial meeting point and challenge
2001
In this paper we will attempt to summarize a number of experiences and ideas concerning the problem of the formation of nanometric and micrometric solid particles from solutions. We will present the scope of the problem, some new advanced in techniques to produce and control the formation of solid particles, a description of a number of formation mechanisms of particles from solution, together with an analysis of the influence of the surface energy created in the nucleation process on the aggregation behavior of the nuclei formed. A new heuristic model on the aggregation mechanisms of particles, based on the action of impurities is proposed. Resum En aquest article presentem un recull d'experiències i idees sobre el problema de la formació de partícules sòlides nanomètriques i micromètriques a partir d'una solució. Presentem l'estat de la qüestió, alguns avanços en tècniques de precipitació, una descripció dels mecanismes de formació de partícules a partir d'una solució, amb una anàlisi de la influència de l'energia superficial formada en el curs de la nucleació sobre el procés d'agregació de nuclis. Es presenta un model d'agregació de partícules basat en la influència de les impureses.
Permanent agglomerates in powdered nanoparticles: Formation and future prospects
In pace with the advancement in nanotechnology, different types of nanoparticles, have been largely produced and are now commercially available. Considering both transport and storage efficiencies, these nanoparticles are normally sold in powder form. Unfortunately, one of the major issues associated with nanopowders is that they tend to form hard agglomerates. These hard agglomerates are hardly segregated even external driving force (such as sonication) has been provided. Such kind of agglomerates is undesired as it reduces the surface area-to-volume ratio of the nanoparticles and thus limits their application performance. Formation of hard agglomerates has to do with the drying step, which is also the main step to convert nanosuspensions into dry powders. Thus, the present work aims to provide a comprehensive review of the occurrence and factors that lead to the hard agglomerates formation in nanopowders. In particular, the creation of interparticle necks upon sintering is reviewed. Approaches to avoid hard agglomerate formation, as well as dissolution of the interparticle necks are also considered here. Lastly, prospects of these nanopowders (if formation of hard agglomerates is unavoidable) in the future nano-research are discussed.
New technologies for the precipitation of solid particles with controlled properties
2002
ABSTRACT Precipitation is a decisive unit operation for the production of fine particles with controlled properties. New technologies are developed in order to better control the production process. For example, sliding surface mixing device, vortex reactor or impinging jets may be cited. These reactors are studied in large intervals of operating conditions, showing therefore their possibilities and applications in precipitation. These new technologies are considered as “multifunctional”, because they allow in some ways the separation of the different mechanisms of precipitation (nucleation, growth, agglomeration, ripening). Thus, their contribution may be clearly identified in the control of the precipitation process and, particularly, their advantages in front of standard reactors.RésuméLa précipitation est un procédé décisif pour la production de solides divisés à propriété contrôlée. De nouvelles technologies sont développées, afin d’assurer une meilleure maı̂trise du procédé d’élaboration. A titre d’exemple, on peut citer le réacteur à disque tournant, le réacteur à effet vortex ou encore le dispositif de jets d’impact. Ces réacteurs sont étudiés dans une large gamme de conditions opératoires, montrant ainsi leurs possibilités et applications en précipitation. Ces nouvelles technologies sont considérées comme multi-fonctionnelles, car elles permettent dans une certaine mesure de découpler les différents mécanismes de la précipitation (nucléation, croissance, agglomération, mûrissement). On identifie ainsi clairement leur contribution dans la maı̂trise du procédé de précipitation, et notamment leurs avantages face aux réacteurs agités standards.
Aggregation during precipitation from solution: an experimental investigation using Poiseuille flow
Chemical Engineering Science, 2000
rized by the theory of Derjaguin, Landau, Verwey, and Over-This paper considers aggregation during precipitation from sobeek (DLVO) theory, as presented, for example, by Hielution in a batch system. Unlike the aggregation of colloidal partimenz (1). However, aggregation during precipitation from cles in ionic solutions which has been extensively studied, aggregasupersaturated solutions in which other size enlargement tion during precipitation from supersaturated solutions in which mechanisms such as crystal growth occur is less well underother size enlargement mechanisms occur is less well understood.
Nanostructured particles by controlled precipitation techniques
Catalysis Today, 2007
By controlling the conditions of homogeneous precipitation reactions, it is possible to obtain more and more complex structures from individualized nanoparticles to multi-scale micrometric particles. This is shown in the case of nickel and cobalt hydroxide. Precipitation using the combination of ammonia decomplexation and dodecylsulfate templating leads to nanostructured nickel hydroxide submicronic cylinders and flower-like cobalt hydroxide. After calcination, surfactant is removed and their respective oxides keep the original shapes. NiO nanostructured cylinders exhibit a relatively high specific surface area around 130 m 2 /g and a pore size around 4 nm, consistent with the observed nanostructure. #
Journal of Supercritical Fluids, 2008
Ethanol is a commonly added modifier to supercritical CO 2 for particle formation from aqueous solutions. Four modifiers -methanol, ethanol, 2-propanol and acetone -were studied to determine the extent of the effect of the modifier selection on the particles produced and to determine more precisely the precipitation mechanisms. The strong anti-solvent effect of methanol on the solute was shown by the production of metastable -glycine, phenylalanine anhydrate and lysozyme agglomerated nanoparticles. Ethanol showed such an anti-solvent effect only when use at higher fraction in the supercritical phase, followed by 2-propanol and acetone. 2-Propanol and acetone mainly contributed to the precipitation of the solute by increasing the solubility of the water in the supercritical phase. In such precipitation conditions the more stable ␣-glycine, phenylalanine monohydrate and lysozyme microspheres were produced by the evaporation of the solution into the CO 2 phase.