Fig xA Thermal treatment employed for
Composition of the mixtures (wt% of raw materials and vol% of ceramic and starch fractions).Ref.Raw materialsVolume fractionClay (wt%)Sodium feldspar (wt%)Fedspatic sand (wt%)StarchCeramic (vol%)Starch (vol%)Typewt%C0404020––100.000.00C1343417S11576.4623.54C2343417S21576.4823.52C3343417S31576.4523.55C4343417S41576.4523.55C5343417S51576.2523.75C6343417S61574.6525.35C7343417S71574.6525.35Full-size tableTable optionsView in workspaceDownload as CSV
The eight mixtures were moistened up to CCG 2046 water content of 5.5 kg H2O/100 kg dry solid. Cylindrical test specimens of 50 mm diameter and 3–4 mm thickness were formed by uniaxial dry pressing at 300 kg cm−2 and dried in an oven at 110 °C for not less than 24 h. The bulk density of the green samples, and later of the sintered ones, was measured by mercury displacement.
The green specimens were sintered in two steps (Fig. 1). Initially, the starch was oxidized in a amensalism muffle furnace with a slow treatment characterized by a maximum temperature of 500 °C and a soaking time of 1 h (K60L, Nannetti Spa., Italy). Finally, the specimens were sintered in a fast electric kiln (Pirometrol S.A., Spain). This last thermal step was designed to balance the porosity and mechanical strength in the sintered membranes, and was characterized by a soaking time of 1 h at 1100 °C.