Nanoparticulas de polifosfato de aluminio

AUTOR(ES)
DATA DE PUBLICAÇÃO

1998

RESUMO

M polyphosphates colloidal systems are versatile sources of new materials. In recent years we have demonstrated the formation of sols, gels, foams and hollow particles, by using these salts. They are formed by precipitation in aqueous media; this phase separation yields different products, depending on the actual conditions used. Particles of noncrystalline aluminum polyphosphate (AIPP) of many different compositions (3P/AI0.4) are prepared from aqueous solutions of aluminum sulphate, sodium polyphosphate and ammonium hydroxide within a broad concentration range. The admixture of dilute aqueous solutions of the parent reagents, under strong stirring and at a room temperature yields stable aqueous dispersions of AIPP nanoparticles within 3P/AI2 molar ratios. After centrifugation, the supernatants of these dispersions have an effective particle diameter ranging from 120 to 200 nm. However, the analysis of the autocorrelation function assuming a multimodal particle size distribution reveals the presence of a population of particles as small as 10 nm. In the presence of an excess of phosphate (P/AI4.5), the number of nanoparticles obtained is reduced while in the presence of an excess of aluminum the effective particle diameter is increased. The transmission electron micrographs of the particles show large regions with isolated nanoparticles and also aggregates, formed during sample drying probably by capillary adhesion and coalescence among particles. The diameters of isolated nanoparticles are in 2 -16 nm range. All the features of the metal polyphosphates colloids are understood following this model: the strongly hydrated polyvalent ions associate in solution, forming polyionic network domains, with a high degree of hydration. The network domains separate as a new phase when a critical size is reached, but the interfacial tension with the parent liquid is strongly dependent on the chemical composition. Very low interfacial tensions allow the formation of nanoparticles, depending on the extent of the networks and thus on the ionic concentration .

ASSUNTO(S)

nanoparticulas microscopia eletronica coloides

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