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Aem Lect13
- 1. Forming : Nomenclature 1. Pressure Fabrication Conventional pressing Isostatic pressing 2. Plastic Forming Extrusion Jiggering Plastic forming 3. Slip Casting Conventional slip casting Pressure casting Tape casting From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press Advanced Electronic Ceramics I (2004) Ceramic Shaping Methods Shapes Viscosity Fluidization Solidification Compaction Process Yes Dry Mostly- Very None Plastic Flow Pressing uniform high of Binder cross section No Injection Almost High Melted Cooling molding any binder Extrusion Uniform High Water Plastic Flow No cross section Roll Thin High Water Plastic Flow Yes Compaction Sheets No Tape Thin Medium Organic Evaporation Casting Sheets or water Pressure Various Medium Water Wicking and/or No Casting Plastic Flow Slip Various Low Water Wicking No Casting From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press Advanced Electronic Ceramics I (2004)
- 2. Schematic of Shaping 1 From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press Advanced Electronic Ceramics I (2004) Schematic of Shaping 2 porous polymer Slip casting of wet slip From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press Advanced Electronic Ceramics I (2004)
- 3. Viscosity: the door to the Rheology y A F F dv =η A dy v=0 Velocity gradient x (Shear rate) z Shear Stress Advanced Electronic Ceramics I (2004) Pseudoplastic : Shear thinning The shear rate increases abruptly above certain stress level viscosity - called as “shear thinning” stress - useful in paint industry Pseudoplastic : Thin film spread well along the vertical wall Apparent while painting (thinned state) viscosity : do not drip or streak Shear rate during the drying period - Useful for screen printing of Another example? thick film ink (many thick film (mustard, catsup, salad dressing) pastes wrongly described as thixotropic) From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press Advanced Electronic Ceramics I (2004)
- 4. Plastic : Bingham ♦Desirable pattern for many ceramic Yield processes Point ♦material flow(shear) while being stress molded at the high force(stress) ♦do not flow(shear) at the waiting Plastic before firing(only gravity plays the (Bingham) role of the force) Shear rate From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press Advanced Electronic Ceramics I (2004) Linear : Newtonian ♦ desirable for the slip casting ♦ the slurry for the slip casting should easily fill the mold (like water) and stress prevent the trapping of air bubbles ♦ help prevent sudden slumping caused by thixotropy during handling Linear and transport of the cast piece (Newtonian) ♦ good for uniform casting rate Shear rate Advanced Electronic Ceramics I (2004)
- 5. Dilatant : Shear thicknening ♦ materials becomes too stiff to flow smoothly at high shear rate - called as ‘shear thickening’ ♦can crack or even explode a die or mold stress during extrusion ♦occurs at very high solid loading Dilatant - horizontal shear of closely packed (Shear thickening) spheres requires the top layer to ride up over the bottom one (dilating the Shear rate volume) - lowering of solid loading, use of dispersent can avoid or reduce the dilatancy From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press Advanced Electronic Ceramics I (2004) Yield Dilatant ♦ shear thinning at low shear rate and shear thickening at stress high shear rate ♦ sometimes observed in clay Yield slip Dilatant Shear rate From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press Advanced Electronic Ceramics I (2004)
- 6. Thixotropic ♦ hyteresis ♦ viscosity reduces with time stress Yield Dilatant Shear rate From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press Advanced Electronic Ceramics I (2004) The viscosity ranges for the ceramic-forming processes Approximate Viscosity's in Ceramic Processing Shear rate Process Viscosity 1/sec. Centipoise 1000 Injection Molding and Extrusion 100,000 400 to 1000 Screen Printing of Decorative Ink 40,000 700 to 1000 Doctor Blade Tape Casting 7,000 7 Slip Casting into Porous Molds 700 1000 cp (centipoise) = 1 Pa•sec = 1N/m2 From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press Advanced Electronic Ceramics I (2004)
- 7. Preparation of a Homogeneous Slurry Inorganic Content Design of Slurry Ceramic Powder 1. Viscosity 2. Stress-Shear + - method of shaping 3. Homogeneity Organic Contents (Solubility Parameter) 1. Binder 4. Drying Parameter 2. Plasticizer 5. Organic Content 3. Solvent (Solid Loading) 4. Dispersent From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press Advanced Electronic Ceramics I (2004) Heat of vaporization & solubility Cohesive energy density (c) Reflect van der Waals forces holding the molecules ∆H - RT of the liquid together c= Vm Amount of energy c: cohesive energy (cal/cm3) required to separate the ∆H : Heat of vaporization (cal/mol) liquid into gas R : gas constant (1.987 cal/degree•mole) T : temperature (degree) Vm : molar volume (cm3/mol) For a solution to occur, the solvent molecules must overcome this intermolecular stickiness in the solute and find their way between and around the solute molecules. This is accomplished best when the attractions between the molecules of both components are similar. http://sul-server-2.stanford.edu/byauth/burke/solpar/ Advanced Electronic Ceramics I (2004)
- 8. Hildebrand Solubility Parameter In 1936, Joel H. Jildebrand proposed the following solubility parameter ∆H - RT 1/2 δ = c 1/2 = Vm Unit δ /cal1/2cm-3/2 = 0.48888 x δ /MPa1/2 δ /MPa1/2 = 2.0455 x δ /cal1/2cm-3/2 (cal/cm3)1/2=(4.184x106J/m3)1/2 =(4.184MPa)1/2=2.0455MPa1/2 Advanced Electronic Ceramics I (2004) Hildebrand Solubility Parameter for solvents http://sul-server-2.stanford.edu/byauth/burke/solpar/ Advanced Electronic Ceramics I (2004)
- 9. Hildebrand Solubility Parameter: Plasticizer δ Plasticizer TCP 9.1 DMP 8.4 DBP 8.4 DOP 8.3 BBP 8.8 Citroflex 4 7.4 Citroflex A-4 7.5 DBM 8.15 DOA 8.15 TOP 7.9 Advanced Electronic Ceramics I (2004) Solubility Parameter of Mixture Hydrogen Bonding γ ratio wt% vol% SP Index n-Heptane 4 57.15 60.51 7.4 2.2 isopropylalcohol 2 28.56 27.02 11.5 8.9 n-butylacetate 1 14.29 12.47 8.5 5.4 SP= 0.6051x7.4 + 0.2702x11.5 + 0.1247x8.5 = 8.64 γ= 0.6051x2.2 + 0.2702x8.9 + 0.1247x5.4 = 4.4 Binder A Binder B 10 10 γ γ Soluble Soluble 1 1 δ δ 5 17 5 17 Advanced Electronic Ceramics I (2004)
- 10. The properties for the casting slip 1. Low viscosity 2. High specific gravity (shorten casting time, increase green density, and lower drying shrinkage) 3. Deflocculated slip 4. Good casting rate 5. Easy mold release 6. Good drainage 7. Adequate green strength 8. Low drying shrinkage 9. Newtonian flow Advanced Electronic Ceramics I (2004) slip casting ♦ Porous mold absorb the water from the slip. After the body becomes dry enough to have self-supporting strength, the mold halves are separated for removal. (ex.) slip casting of clay in plaster of Paris molds - plaster of Paris is calcium sulfate - some divalent calcium ions from the mold dissolve the in the slip, slightly collapsing the double layer - the slip then agglomerates to some degree, causing the deposited clay body becomes more porous - Water can easily diffuse through the highly porous first-deposited clay, allowing more clay to also deposit quickly and build up to a practical thickness From D. J. Shanefield, “Organic Additives and Ceramic Processing,” Kluwer Academic Press Advanced Electronic Ceramics I (2004)
- 11. slip casting http://www.algonet.se/~keram/pdf/Slip%20Casting.pdf Advanced Electronic Ceramics I (2004) slip casting U. P. Schönholzer et al., Am.Ceram. Soc. Bull., 79(12), 45 (2000) Advanced Electronic Ceramics I (2004)