Naslov
Crystal Growth of Lanthanum Fluoride using the Constant Composition Method

Autori
Stubičar, Nada

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Book of Abstracts 14th ECIS 2000 Conference, ISBN: 960-7839-02-1. / Koutsoukos, Petros G. ; Kontoyannis Christos G. - Patras : ICE/HT -FORTH Hellas(Inst.Chem.Eng.and High Temp.), 2000, 194-194

Skup
14th European Colloid and Interface Society Conference

Mjesto i datum
Patras, Grčka; Río, Grčka, 17.09.2000. - 22.09.2000

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
Computation of equilibrium ionic species in solns; Constant composition method; Dynamic light scattering;Influence of pH on the kinetics of growth; Kinetics of crystal growth; Lanthanum fluoride.

Sažetak
The constant composition method, in this particular case the pF-stat method, is very favorable to study the kinetics of growth of the micrometer and submicrometer size particles as well, going on in the processes far from equilibrium. Hence, it was used in this work to study LaF3 system at 25 oC : i) at stoichiometric ratio of the activities of lattice ions 1/3 and pH = 5 over a range of supersaturating, as well as ii) very far from this ratio and at pH˘ s in the range 4 – 6. The pF-stat rate of growth of the seeds, from the supersaturated solutions at pH = 5 and activity ratio 1/3, was determined to be of the fourth order. Large hexagonal crystals of LaF3 were characterized by XRD method and by polarizing microscopy. At a pH ~ 4 that is with large excess of La(NO3)3 in a supersaturated solution, monodisperse, rather stable, colloidal systems have been formed showing the dendrite morphology and the rate was found to be of the first order. The size and the PSD of these submicrometer particles were determined by DLS method. At a pH ~ 6 the glassy precipitate was formed from the supersaturated solution being deficient in La-ions, which are fully hydrolyzed, so that much less soluble La(OH)3 prevail and the growth rate was independent of supersaturating. The XRD diffractograms of amorphous phase was recorded for these systems, with scarce denoted peaks of the started, ordered phase afterwards. These systems are anisotropic fibbers and ribbon-like morphologies, with growing crystals inside them. The supersaturating was calculated using Mineql+ program by taking into account all main relevant complexes and their equilibrium constants checked experimentally and taken from the literature, until calculated and measured pH values of the titration curves agreed fairly well.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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