Obtenção e caracterização de metafosfatos de aluminio : um novo pigmento branco

AUTOR(ES)
DATA DE PUBLICAÇÃO

1991

RESUMO

Titanium dioxide is widle used as a white pigment, because it is a powerful light backscatterer due to its high refractive index. It may be predicted, following Mie s theory, that hollow particles of any refractive index may also be good scatterers. The subject of this thesis is the preparation and characterization of aluminum metaphosphates and the evaluation of the products of of their thermal treatment, as light scatterers. Non-stoichiometric aluminum metaphosphates of diferent chemical compositions were prepared by mixture of aluminum nitrate, ammonium hydroxide and (vitreous) sodium metaphosphate aqueous solutions. These preparations followed a 2 factorial plan, in which the variables were the molar concentrations of reagents, in two levels. The characterization of aluminum metaphosphates and of the products of their thermal treatment was done by elemental analysis, infrared spectra, X-ray difraction, thermocondutivity measurements, transmission and scanning eletron microscopy, optical microscopy and ultramicroscopy. The properties of these preciptates are closely related to their chemical compositions. High-phosphate powder soften at lower temperatures and expand under heating, allowing the preparation of clossed cell particles and monolyths. Aluminum-rich powders undergo sintering at higher temperatures and do not expand, under heating. The detection of softening temperatures of the solids was conviniently done by thermocondutimetric analysis. PVA films were obtained, either containing TiO2 or partly replacing TiO2 with aluminum metaphosphate hollow particles. The reflectances of these films were determined and they shaw that the hollow particles can replace at least 60% of TiO2 as pigment, without impairing the opacity of films.

ASSUNTO(S)

fosfatos luz - espalhamento

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