A closer look at some natural materials from animal and plant sources and the phenomenon driving their use in day to day applications resulted in investigation of their potential in processing of ceramic foams. Ceramic foams were made using aqueous ceramic slurries based on chicken egg white, soap nut fruit extract and sucrose. Egg white and soap nut extract were utilised for their natural foaming ability and binding of ceramic particles. Ceramic foams were produced by foaming the aqueous ceramic slurries by mechanical agitation followed by casting. The egg white based foams were set by coagulation achieved through sprinkling of acid, however use of acid was not successful with foams made from slurries with low and high ceramic loadings. Sucrose was utilised for its moisture retention ability and it not only simplified the egg white based process but also helped to achieve foams with exceptional characteristics including porosity exceeding 95%. Sucrose containing egg white based ceramic foams could be set by heating soon after casting. The soap nut based foams were processed in a similar way and were set simply by drying. Soap nut based foams exhibited a much higher number of interconnections per cell. Foams with a range of porosity and microstructural features could be produced from egg white and soap nut based slurries by using different combinations of ceramic loading and binder content in the premix or by varying the foaming time and slurry to container volume ratio.

Ceramic foams with porosity exceeding 90% were prepared by direct foaming and casting of aqueous suspensions containing cetyl trimethyl ammonium bromide (CTAB) as a foaming agent. Foaming of the suspensions, particularly with lower viscosity, was initially non-homogeneous but the foam appeared to homogenize with milling time. Addition of sucrose to ceramic suspensions resulted in lowering of the suspension viscosity, stabilized the foams by reducing drainage of the suspension, and minimized coalescence of bubbles leading to lower cell sizes in sintered foams. Ceramic foams prepared from sucrose based suspensions were strengthened to such an extent that foams with porosity above 90% could be machined in the green state. J ournal

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Gelcasting is a promising technique for shape forming of bulk dense or porous ceramic, metal structures. The process offers a number of advantages over processes such as slip casting, injection molding in forming complex ceramic shapes. It is shown here that the optimization of slurry rheology, choice of mold material, mold design and the drying conditions have a significant role in the overall success of the process. In this process, components of simple or complex shapes can be produced to near net shape by direct casting. If required complex shapes can also be produced by machining the green gelcast bodies. The process of gelcasting also has a lot of potential in forming highly porous ceramic shapes.

The effect of sucrose addition on rheology of alumina slurries, dispersed with a polyacrylate dispersant (Darvan 821 A), was studied for different alumina loading. Smaller amount of sucrose addition (10 wt%) had a more significant influence on rheological behavior of the slurries than the incremental addition to 30 wt% sucrose. Addition of sucrose resulted in a decrease in the apparent yield stress, viscosity, thixotropy, and increase in non‐Newtonian index as compared with the slurries containing just the polyacrylate, indicating weakening of the inter‐particle network. Weakening of the inter‐particle network arose from the enhanced steric hindrance because of the presence of sucrose molecules in association with the polyacrylate molecules adsorbed on alumina particle surfaces. This association is because of intermolecular hydrogen bond formation between free hydroxyl (−OH) groups of sucrose and carboxylate ions of polyacrylate molecules. Use of sucrose resulted in cast green bodies with higher strength.