Fig. 1 Annually published papers on freeze casting of porous ceramics from Jan. 2001 to Sep. 2013 based on Web of ISI

Fig. 2 The four processing steps of freeze-casting: slurry preparation, solidification, sublimation and sintering[19]

Fig. 3 Schematic diagram of a typical cooling setup for freeze casting[21]

Fig. 4 Schematic diagram of the basic principle during freezing[18]

Fig. 5 Schematic diagram of the particle-solidification front interactions[27]

Fig. 6 Weight loss of green body during sublimation of the camphene (30vol% solid loading)[29]

Fig. 7 Ice crystal structure (a), anisotropy of ice crystal growth (b) and resulting porous structure (c)[19]

Fig. 8 Typical cross-section SEM images of porous alumina obtained by water-based freeze casting[21] (a) Ice growth direction perpendicular to the page; (b) Ice growth direction from bottom to top

Fig. 9 Dentritic structure during solidification of camphene]43] (a) and typical SEM images of porous alumina obtained by camphene-based freeze casting (b)[20]

Fig. 10 Cross-sectional SEM images of the Al2O3-ZrO2 composite ceramics obtained from slurries with different initial solids loading[23] (a) 40wt%; (b) 50wt%; (c) 60wt%; (d) 70wt%; (e) 80wt%. Solidification direction is perpendicular to the page

Fig. 11 SEM images of the porous alumina ceramics sintered at 1400℃ for 5 h with initial solid loadings of 20vol%(a), 15vol%(b), 10vol%(c), and 5vol% (d), showing porous structures at low magnification[44]

Fig. 12 Porosity vs solids loading forwater- (a) and camphene- (b) based freeze-cast porous ceramics

Fig. 13 Pattern formation and particle segregation during freeze casting of ceramic slurries (a) and the wavelength of the <br/>structure is defined. (b) Variation of structure wavelength vs ice front velocity[21]

Fig. 14 SEM images of porous TiO2 with cross-section parallel and perpendicular to the ice growth direction[52] (a) 3wt% PVA, parallel; (b) 3wt% PVA, perpendicular; (c) 6wt% PVA, parallel; (d) 6wt% PVA, perpendicular

Fig. 15 SEM images of porous alumina ceramics, which are prepared by using (a) 20vol% slurry without glycerol, (b) 20vol% slurry with glycerol, (c) 30vol% slurry without glycerol and (d) 30vol% slurry with glycerol[55] The direction of fracture parallels to the ice front

Fig. 16 Influence of sintering temperature (2 h at dwell temperature) on compressive strength (a) and total porosity(b)[58]

Fig. 17 Comparison of compressive strength of porous hydroxyapatite obtained by different techniques according to literature data

Fig. 18 Compressive strength versus porosity for water-based (a) and camphene-based (b) freeze-cast porous ceramics

Fig. 19 Measured or estimated pore channels size of freeze- cast ceramics[68]

Fig. 20 Graded porosity with three distinct regions[29]

Fig. 21 Typical freeze-tape-casting apparatus[68]

 Fig. 22 Schematic illustration of double-side cooling apparatus[73]

Fig. 23 Compressive strengths of freeze cast and freeze gelcast samples versus solids loading (a) and porosities of the sintered samples versus solids loading (b)[24]