Nature inspired novel processing routes for ceramic foams

Abstract

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.

Microstructural, mechanical and thermal characterization of alumina gel-cast foams manufactured with the use of agarose as gelling agent

“…Many alternative gelling systems for the gel-casting of foams based on low-toxicity monomers were demonstrated by Ortega et al [5] and a low toxic epoxy resin system was demonstrated by Mao et al [6]. Gel-casting techniques utilizing environmentally friendly biopolymers as gelformers in manufacturing of ceramic foams were intensively studied: different biopolymers such as gelatin [6], proteins (ovalbumine and bovine serum albumin) [7][8][9][10], sucrose [11], agar [12], starch [13], and wheat particles [14] have recently been applied as non-toxic components for the fabrication of gel-cast ceramic foams.…”

Processing Routes to Macroporous Ceramics: A Review

“…194,200 In the last years, several alternative methods that apply environmental-friendly setting agents from the food industry have been developed to circumvent the shortcomings of the original gelcasting technique. The temperature or pH-induced gelation of gelatine, 194 ovalbumin, 164,196,195 and bovine serum albumin, 192 for instance, have been successfully used for setting the foam wet structure. A similar approach relying on the temperature-induced gelling of polysaccharides such as sucrose, 193 agar, 199 and carrageenan gum 195 has been recently applied as non-toxic processing route for the fabrication of porous ceramics.…”

“…176 The well-established polymer technology used for the production of thermoplastic polystyrene foams was also recently applied by Williams and Evans 175 to fabricate ceramic foams with up to 84% porosity, as illustrated in Table IV. Foam consolidation has not been restricted only to polymeric setting systems, but has been imparted also by inorganic materials exhibiting sol-gel phase transitions in liquid medium. This approach was used by Fujiu et al 162 to prepare silica foams using Freon for gas incorporation during the condensation Gelcast setting Free radical polymerization 68,158,[187][188][189][190][191] Cross-linking of polyvinyl alcohol with organotitanates and epoxy with ethylene imine 194,200 Temperature-induced setting of polysaccharides: sucrose, 193 carrageenan gum, 195 agar 199 Thermal expansion 192,193 or mechanical frothing 68,158,165,[187][188][189][190]194,195 / agitation 164,196 in the presence of surfactants/proteins Al 2 O 3 , 68,160,164,187,188,[191][192][193][194][195]197,198 Temperature or pH-induced setting of proteins: gelatine, …”

Silicon nitride foams with uniform pore structure prepared by using protein foaming method with a planetary ball-milling foaming route

“…During the thermal consolidation of foamed slurry, bubbles with thinner lamellas are easier to rupture because the volume of air in the bubbles expands with the temperature. The rupture of bubbles finally leads to the formation of windows on the walls [21,24]. In this research, the significantly increase in the count of windows is attributed to the decreasing thickness of lamella when the rotating speed ascends from 400 to 500 r/min.…”

“…The presently use foaming route of protein foaming method in preparing ceramic foam is generally via tumbling [14,[19][20][21][22] or stirring [23][24][25][26] at a relative low speed. This kind of foaming route is generally time-consuming because it usually takes several hours to finish the foaming procedure.…”