Aem Lect15

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Aem Lect15

  1. 1. Starting Point in Tape Casting: Surface Homogeneous Fired slurry formation density using small amount of organic additive to the active(small) powder Green Surface density energy D. J. Shanefield, Organic Additives & Ceramic Processing Advanced Electronic Ceramics I (2004) Tape Casting Ceramic Powder Binder Plasticizer Solvent Dispersent Ball milling in the jar Deairing Electroding Tape Casting Lamination Drying Co-firing Cutting Packaging Advanced Electronic Ceramics I (2004)
  2. 2. Tape Casting http://www.algonet.se/~keram/pdf/Tape%20Casting.pdf Advanced Electronic Ceramics I (2004) Tape Casting Machine 1 Tape casting machine Slurry feeder http://yoojintech.co.kr/frame1.htm Advanced Electronic Ceramics I (2004)
  3. 3. Tape Casting Machine 2 http://www.glass-ceramics.uni- http://www.nrel.gov/ncpv/pdfs/26122.pdf erlangen.de/Staff/Research/Functceramics/ Advanced Electronic Ceramics I (2004) Multi-Layer Casting R.E.Mistler, Am.Ceram.Bull., 52(11), 850-854 (1973) Advanced Electronic Ceramics I (2004)
  4. 4. Control Parameters: Thickness ♦ Thickness of the film 1. Casting thickness (t) 2. The thickness after drying(td) : 0.5t ~ 0.8t 3. The thickness after sintering(Ts) : 0.5td ~ 0.7td * The overall thickness variation due to the change in the pool level (constant feed can be employed to achieve constant pool height) * The thickness variation at the edge of the casting Recycle Window region Recycle Ceramic green sheet Carrier film Advanced Electronic Ceramics I (2004) Control Parameters: Casting Velocity R. E. Mistler and E. R. Twiname, Tape Casting, Theory and Practice Advanced Electronic Ceramics I (2004)
  5. 5. Control Parameters: Drying ♦ Designing the temperature-profile for drying (in order to keep the homogeneity of the tape after sintering) 1. Thickness of the casting film 2. The volatility and content of organic (especially solvent) in the slurry 3. The total length of the drying line 4. Feeding rate for casting [Key items] 1. Employ the Azeotropic Mixture, : solution that contains the same ratio of chemical constituents after it is distilled (see distillation). The most common example is a solution of 4.43% water and 95.57% ethyl alcohol. 2. Controlling drying Advanced Electronic Ceramics I (2004) Binary Azeotropic Mixtures R. Moreno, Am.Ceram.Soc.Bull., 71(10), 1521 (1992) Advanced Electronic Ceramics I (2004)
  6. 6. Drying First stage 1. The solvent diffuse through the body to the surface, and then the solvent waits for the right number of calories to diffuse to it via the random motion of warm molecules (fast) 2. It then evaporates (slowest) 3. It swept away by moving air (slow) It is usually useful to nearly saturate the air with solvent vapor to prevent quick drying. Quick drying can promote skin formation or cracking. Second stage A. Ceramic green body becomes stiff B. 1 becomes much slower (it becomes controlling step) - drying rate is dependent upon T and remaining solvent (that affect diffusion rate) the temperature can be greatly increased without damage Advanced Electronic Ceramics I (2004) Tape Casting: examples http://www.umr.edu/~rahaman/Forming.pdf Advanced Electronic Ceramics I (2004)
  7. 7. Solvent Desirable properties of solvents 1. Ability to dissolve other additives 2. Low viscosity at high solid loading 3. Low tendency to form bubbles during milling 4. High evaporation rate 5. Safe, including (a) nonflammability (b) nontoxicity 6. Low cost 7. Lack of chemical attack on the ceramic powder D. J. Shanefield, Organic Additives & Ceramic Processing Advanced Electronic Ceramics I (2004) Reported Solvent Systems 1. Methyl ethyl ketone(MEK) 2. MEK/95% ethanol 3. MEK/anhydrous ethanol 4. Xylenes/95% ethanol 5. Xylene/anhydrous ethanol 6. MEK/toluene 7. Toluene 8. 1,1,1 trichloroethane(TCE) 9. TCE/ anhydrous ethanol 10. TCE/MEK/ethanol 11. TCE/acetone 12. Toluene/95% ethanol 13. MEK/95% ethanol/toluene 14. MEK/methanol/buthanol R. E. Mistler and E. R. Twiname, Tape Casting, Theory and Practice Advanced Electronic Ceramics I (2004)
  8. 8. Various Solvents H H H n↑ in alkane H ⇒ density, m.p., b.p. ↑ C C C H H H C H ex) methane, ethane - gas H H OH H Isopropanol n=8 octane - liquid Trichloroethylene (TCE) Cl Cl - not flammable C C C Cl - probable carcinogen - slowly being phased out due to environmental problem Methyl Ethyl Ketone (MEK) O - flammable CH3 C C2H5 D. J. Shanefield, Organic Additives & Ceramic Processing Advanced Electronic Ceramics I (2004) Various Solvents CH3 Toluene Benzene - less toxic than benzene - carcinogen - human body can metabolize - leukemia, liver cancer toluene into carbon dioxide - remain in the blood stream and water after exposure - flammable CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 Ortho-Xylene Meta-Xylene Para-Xylene Mixture - don not remain in the human body for a long time D. J. Shanefield, Organic Additives & Ceramic Processing Advanced Electronic Ceramics I (2004)
  9. 9. Physical Properties of Some Usual Solvents R. Moreno, Am.Ceram.Soc.Bull., 71(10), 1521 (1992) Advanced Electronic Ceramics I (2004) Solvent: H-bond m.w. of H2O ≅ m.w. of liquefied CH4 viscosity of H2O > viscosity of liquefied CH4 ⇒ H-bonding H-bonding between ceramic (covered with OH group adsorbed from air) and water molecule ⇒ tends to raise the viscosity of slip In order to achieve low porosity in the fired state ⇒ solid loading as high as possible ⇒ minimize the shrinkage during drying and firing to full density ⇒ minimize the warpage and cracking H-bonding is major cause for high viscosity ⇒ non-aqueous solvent such as toluene are used D. J. Shanefield, Organic Additives & Ceramic Processing Advanced Electronic Ceramics I (2004)
  10. 10. Solvent: H-bond m.w. of H2O ≅ m.w. of liquefied CH4 viscosity of H2O > viscosity of liquefied CH4 surface tension of H2O > surface tension of liquefied CH4 ⇒ high surface tension stabilize bubbles ⇒ bubble can be a serious problem in water system (ex.1) glaze one stable bubble can ruin the appearance of the fired ceramics (ex.2) single bubble of the same diameter as the thickness of the fired sheet can result problem D. J. Shanefield, Organic Additives & Ceramic Processing Advanced Electronic Ceramics I (2004) 청자상감운학문매병 (해강 유근영) 국보 제68호 청자상감운학문매병을 그대로 재현한 작품이다. Advanced Electronic Ceramics I (2004)
  11. 11. Evaporation rate ∆Hvap. Solvent b.p. Flash Explosive (cal/g) (oC) point(oC) limit(vol%) water 580 100 EtOH 204 78 20 3-19 Toluene 95 111 3 1-7 TCE 57 87 Heptane 76 98 -1 1-7 1) Energy for drying 2) The length of drying line (30 m line for full drying in Toluene system. Then, how long will it be for the water system?) TCE + EtOH → non-flammable (chloro carbon such as PCB, DDT, CFC) D. J. Shanefield, Organic Additives & Ceramic Processing Advanced Electronic Ceramics I (2004) Binder Binder gives green strength for machining, inspection, and storage. Desirable properties of binders 1. Easy Burn-out 2. Strong Green Body (a) Adhesion to Powder (b) Cohesive Strength 3. Solubility in Fluidizing liquid(solubility parameter) 4. Low cost D. J. Shanefield, Organic Additives & Ceramic Processing Advanced Electronic Ceramics I (2004)
  12. 12. Reported Binder Systems - Vinyl polymer burns at elevated temperature and requires oxygen - Should be fired at oxidizing atmosphere - Acrylic polymers dissemble and evaporate - Removal of binder in reducing or neutral atmosphere is possible - Proper for SiC and AlN systems requiring reducing or inert atm. R. E. Mistler and E. R. Twiname, Tape Casting, Theory and Practice Advanced Electronic Ceramics I (2004) Binder: PVA B - reaction can continue until all of the starting materials is used up - large molecule tends to be brittle solid - for desired(proper) molecule size, small amount of terminator is added - water ↑ ⇒ molecular weight↓ - there is a variation in chain length (in molecular weight) - average molecular weight is usually used D. J. Shanefield, Organic Additives & Ceramic Processing Advanced Electronic Ceramics I (2004)
  13. 13. Binder: PVB Polyvinyl Alcohol(PVA) HHHH H H HH Popular binder C C CC C C CC in ceramic H O HO H O HO processing H H O C C H H Polyvinyl Formal HH Formaldehyde H H HH H H HH C C CC C C CC B H O HO H O HO H H CHH H O CC C H C3H7 C H HH H Butyraldehyde Polyvinyl Butyral(PVB) D. J. Shanefield, Organic Additives & Ceramic Processing Advanced Electronic Ceramics I (2004) Other Binders DPB H CH3 DB H H CC HO C CO H H C On H H n OH Polymethacrylic Acid(PMA) Polyethylene Glycol (PEG) H CH3 B B CC C C H C On n C O-CH3 Poly(methylmethacrylate) (PMMA) Polypropylene D. J. Shanefield, Organic Additives & Ceramic Processing Advanced Electronic Ceramics I (2004)
  14. 14. Polymer Characterization: molecular weight by GPC m.w. (n=1) = 1 x 44 + 18 = 62 HH m.w. (n=2) = 2 x 44 + 18 = 106 HO C C O H m.w. (n=n) = 44n + 18 HH n GPC (Gel Permeation Chromatography) - a solution of the polymer diffuses through the inert gel - the smaller molecule (with low m.w.) diffuses fastest - get the m.w. distribution relative amount median m.w. 0.08 x 500 = 40 8% below 1000 0.13 x 1500 = 195 13% between 1000 and 2000 0.41 x 2500 = 1025 41% between 2000 and 3000 0.29 x 3500 = 1015 29% between 3000 and 4000 0.09 x 4500 = 405 9% between 4000 and 5000 total 1.00 2680/1 = 2680 # avg.m.w. D. J. Shanefield, Organic Additives & Ceramic Processing Advanced Electronic Ceramics I (2004) Polymer Characterization: m.w. by other methods Light scattering - larger molecule scatter more ultraviolet light than the smaller one - large ones actually scatter much more than the smaller one - yields weight average molecular weight - Because the larger molecules count much more than the smaller one, usually weight avg.m.w. > number avg.m.w. by GPC Other methods - viscosity - osmosis - sedimentation - ultracentrifuge D. J. Shanefield, Organic Additives & Ceramic Processing Advanced Electronic Ceramics I (2004)
  15. 15. Polymer Characterization: Tg Below Tg : relatively hard and brittle like glass Above Tg: relatively soft and elastic like rubber V The addition of plasticizer Rubber - lower the Tg - for easy handling Glass Tg Temperature TMA(Thermomehcanical analysis) : The height of polymer molecule is measured with a mechanical prove resting on its top surface during heating (similar with the dilatometery) D. J. Shanefield, Organic Additives & Ceramic Processing Advanced Electronic Ceramics I (2004)

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