In-vitro dissolution rate of mineral fibres at pH 4.5 and 7.4 - A new mathematical tool to evaluate the dependency on composition

Abstract

Useful mathematical models for the compositional dependency of the dissolution rate in flow-through measurements are presented. The rate of dissolution Kdis(Si) was determined for 81 different compositions at pH 4.5 and 7.4, respectively. A high degree of correlation to composition was found at both pH regimes. In this work, the commonly used regression equation: Kdis= K0 exp(S) or In Kdis = In K0 + S has been replaced by: Kdis = K∞ exp(S)/(exp(S)+l) , where S = ∑CiXi is a linear combination ("index") of oxide contents. K0 and K∞ are constants, the latter is a limiting dissolution rate for S → ∞. At the other extreme S → -∞ is tends to zero. This feature of the new regression equation improves the correlation for the data sets applied and allows it to cover wider ranges of compositions. The coefficients in ∑CiXi are clearly different in the two regimes (pH 4.5 and 7.4). The most important difference is between the coefficients of alumina. At pH 4.5, it is highly positive, and at pH 7.4, it is highly negative.