Green mechanical evaluation of mullite porous compacts prepared by pre-gelling starch consolidation

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 549; pp. 30 - 37
• Main Authors: Talou, M.H., Martinez, A.G. Tomba, Camerucci, M.A.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 15-07-2012; Elsevier
• Subjects: Condensed matter: structure, mechanical and thermal properties; Deformation and plasticity (including yield, ductility, and superplasticity); Exact sciences and technology; Green porous microstructures; Mechanical and acoustical properties of condensed matter; Mechanical properties; Mechanical properties of solids; Mullite; Physics; Starch direct consolidation; Mechanical properties; Mullite; Starch direct consolidation; Green porous microstructures; Scanning electron microscopy; Elastic modulus; Densification; Ruptures; Compressive testing; Porous materials; Displacement(deformation); Stress-strain relations; Yield strength; Porosity; Rupture strength
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2012.03.111

► Mullite green porous disks were prepared with cassava, corn and potato starches. ► Mechanical behavior of unburnt and burnt disks was evaluated in diametral compression. ► Mechanical results were analyzed in relation to starches, gels, and microstructures. ► The machinability of the mullite compacts was also discussed. ► Cassava- and corn-disks have better mechanical properties and are able to be machined.
The mechanical behavior of green porous mullite disks (volume porosity>55%) prepared by the thermogelation of mullite aqueous suspensions with different native starches (i.e. potato, cassava and corn starches) was studied. One set of disks was prepared by thermal consolidation (70–80°C, 2h) of aqueous mullite suspensions (40vol.%) containing 10vol.% of starch pre-gelled at 55–60°C and dried at 40°C for 24h. Another set of specimens was prepared by additional firing at 650°C for 2h to burn-out the starches. Both sets of disks were characterized by density measurements (Archimedes method), apparent porosity calculus, and microstructural analysis by SEM. Mechanical parameters such as fracture strength, apparent elastic modulus, fracture and final deformations and yield stress were determined from apparent stress–strain relations derived from load-displacement curves obtained by diametral compression testing. Moreover, typical crack patterns were evaluated and fractographic analysis was carried out by SEM. Mechanical results were analyzed in relation to the behavior of the starches in aqueous suspension and the properties of the developed gels, together with the respective microstructures before and after the burn-out process. Mechanical data were also considered taking into account the possibility of machining the green compacts formed by pre-gelling starch consolidation.