Thermomechanical Behavior of Ceramic Green Bodies During Presintering

A testing methodology, which includes the evaluation of free sintering strain, stress-induced dimensional changes, and weight changes, was developed to determine the critical dimensional changes and thermomechanical response during presintering (i.e., before densification). The effects of organic binder burnout, decomposition of phases, and phase changes on the thermomechanical behavior of a ceramic green body, consisting of methylcellulose as a binder, gibbsite, silica, and alumina, were studied. The compressive stress-strain behavior was found to be nonlinear. The average compressive and tensile strengths of the sample at room temperature were -14.5 and 1.06 MPa, respectively. Both the compressive and tensile strengths decrease by two orders of magnitude with the increasing temperature as a result of binder removal and phase changes. Moreover, the tensile strengths are typically an order of magnitude lower than the ultimate compressive strength. Dynamic measurements, such as constant strain-rate deformation, can be used to further quantify the deformation mechanics during heating. Such data are particularly useful for the modeling of stresses that arise in the early stages of the presintering process, when green bodies have low strength.