Materials Science Forum, Vol.416-4, 512-518, 2003
Gelcasting ceramic foams with alternative gelling agents
Gelcasting is a near net shape forming process based on the in situ polymerization of water-soluble monomers previously added to a ceramic suspension. The association of this process to the aeration of a suspension containing foaming agents led to the development of a new class of ceramic foams with porosity levels of up to 90%. The structure of these foams is characterized by nearly spherical pores and highly dense struts, which results in unprecedented properties, such as high permeability, low thermal conductivity, high specific surface area and high mechanical strength. The main drawback of this process is the inhibition of the polymerization in the presence of oxygen, which requires the atmosphere control. Moreover, the monomers used in this process are generally toxic. This work investigates two harmless alternative gelling agents that do not require atmosphere control to set foamed suspensions. The first route consists of the crosslinking of a previously dissolved polyvinyl-alcohol with the addition of an organotitanate. The other approach assessed the use of gelatin as a setting agent. This polymer gels the suspension due to changes in the structure of polypeptidic chains caused by the reduction of temperature. Gelatin-based systems presented higher storage modulus (G') than those obtained with crosslinked polyvinyl-alcohol chains. This feature prevented the formation of cracks during drying of gelatin-based samples, as occurred with PVAl-based systems. The results points out gelatin as a promising gelling agent to produce ceramic foams without the disadvantages of monomeric systems, such as the toxicity and the necessity of atmosphere control.