Studies of the Hydrous Niobium(V) Oxide Ion Exchanger. V. Effect of Heat Treatment on the Sodium Isotopic Exchange Rates between Hydrous Niobium(V) Oxide in Na+ Form and Aqueous Solutions

Abstract

The effect of a heat treatment was studied on the sodium isotopic exchange rate between the hydrous niobium(V) oxide in the Na+ form and aqueous solutions. The rate was controlled by the particle diffusion of sodium ions and increased with the heat-treatment temperature. The increase in the rate for the exchanger heat-treated at 200 °C was due to a decrease in the effective particle radius brought about by cracks which developed in the particles. A further increase in the rate at temperatures higher than 200 °C could be explained in terms of an increase in the Na+-diffusion coefficient, which was produced by an increase in the pore size responsinble for the movement of sodium ions.

Estudo da adsorção de surfactante catiônico na matriz inorgânica fosfato de nióbio hidratado

“…Esse estudo é importante, porque o grau de hidratação corresponde aos sítios ativos de troca iônica que, conseqüentemente, podem influenciar na sua capacidade de troca iônica. 5,34,35 A curva TG do fosfato de nióbio hidratado (Figura 3) apresenta perda de massa ocorrendo em duas etapas distintas no intervalo temperatura entre 25 e 550 ºC. Na primeira etapa, entre 25 e 170 ºC, houve perda de massa devido à eliminação das moléculas de água mais fracamente ligadas, enquanto que na segunda etapa, entre 170 e 550 ºC, houve eliminação das moléculas de água mais fortemente ligadas à estrutura da matriz.…”

Kinetic aspects and swelling changes of magnesium and cerium titano-antimonates in aqueous and mixed solvents

“…Accordingly, effects of the solvents with different concentrations (25% and 50% of methanol and ethanol) on the particle radius of MgTiSb and CeTiSb were studied assuming constant D i values for Cs + ions. The effective particle radius (r 0 ) can be calculated assuming the equation [31] …”