Validation of the swelling formalism via evaluation of bending moments from literature: Comparison of theoretical predictions and measurements

The volume of silica expands by the hydroxyl generation when silica surfaces react with water. These volume strains are proportional to the mass concentration of the hydroxyl. They were measured by Wiederhorn et al. by evaluating the curvature of disks undergoing this reaction on only one side. The obtained bending moments were found to be proportional to square-root of heat-treatment time.
In the present considerations we pay particular attention to global bending moments caused by swelling, which, in contrast to local swelling stresses, do not require assumptions about the type of stress distribution.
It can be stated that
• The bending moments from disk curvature and hydroxyl measurements via the IR-evaluation procedure by Libowitzky and Rossman are in excellent agreement.
• Predictions of moments M based on diffusivities and surface water concentrations by Helmich and Rauch also show good agreement with correlation coefficients R$^2$>0.95. Consequently, we can sufficiently write: M$_{predict}$ = M$_{measured}$.