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Aem Lect16
Aem Lect16
Aem Lect16
Aem Lect16
Aem Lect16
Aem Lect16
Aem Lect16
Aem Lect16
Aem Lect16
Aem Lect16
Aem Lect16
Aem Lect16
Aem Lect16
Aem Lect16
Aem Lect16
Aem Lect16
Aem Lect16
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Aem Lect16

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  • 1. Plasticizer - structurally expands the binder - improves the distribution of the binder in the slurry (binder solvent) - causes flexibility (by lowering glass transition point, Tg) of green tape In order to reduce Tg 1. Use of less rigid side groups PEG addition 2. Reduction of the # of polar group to PVA 3. Lowered molecular weight 4. Lowered intermolecular contact R. Moreno, Am.Ceram.Soc.Bull., 71(11), 1647 (1992) Advanced Electronic Ceramics I (2004) Plasticizer plasticizer 1. Low molecular weight - decrease Tg 2. Significant decrease in green strength Strength of alumina green sheet as a function of plasticizer, DBP R. Moreno, Am.Ceram.Soc.Bull., 71(11), 1647 (1992) Advanced Electronic Ceramics I (2004)
  • 2. Plasticizer Plasticizer concentration low plasticizer concentration porosity decrease due to the increase inflexibility too high plasticizer concentration increasing interparticle distance decreasing the green density R. Moreno, Am.Ceram.Soc.Bull., 71(11), 1647 (1992) Advanced Electronic Ceramics I (2004) R. E. Mistler and E. R. Twiname, Tape Casting, Theory and Practice Advanced Electronic Ceramics I (2004)
  • 3. No plasticizer Type II plasticizer -Lubricant -Easy to release of σ σ green tape from carrier film ε ε Type I & Type II Type I plasticizer - lower Tg σ σ - binder solvent ε ε R. E. Mistler and E. R. Twiname, Tape Casting, Theory and Practice Advanced Electronic Ceramics I (2004) Various Plasticizers DPB P H H H HH HO C C O H C C C H H HH n OH OH OH Polyethylene Glycol (PEG) Glycerin Plasticizer m.p.(oC) b.p .(oC) Water 0 100 Ethylene glycol -16 197 Diethylene glycol -8 245 Tetraethylene glycol -7 288 Poly(ethylene glycol) -10 >330 Glycerine 18 290 Dimethyl phthalate 1 284 Dibutyl phthalate 1 340 Octyl phthalate Benzyl butyl phthalate Diethyloxalate D. J. Shanefield, Organic Additives & Ceramic Processing R. Moreno, Am.Ceram.Soc.Bull., 71(11), 1647 (1992) Advanced Electronic Ceramics I (2004)
  • 4. Common binder(binder + plasticizer) choice Application Binders System Advantages Tape Casting Polyvinyl Butyral Nonaqueous Strong Methacrylate Solution Nonaqueous Easy burnout (in MEK) Methacrylate Emulsion Aqueous Easy burnout Ammonium Polyacrylate Aqueous High Solids Screen Printing Alginates Aqueous Inexpensive Gums Aqueous Inexpensive Ethyl Cellulose Nonaqueous Pseudoplastic Polyvinyl Butyral Nonaqueous Easy Burnout D. J. Shanefield, Organic Additives & Ceramic Processing Advanced Electronic Ceramics I (2004) When large amount of plasticizer is added evaporation of plasticizer Binder Burnout 1 leaves many pores for the air, CO2, and solvent vapor. Without the powder, the dotted line shows the same starting weight of binder alone dropping more rapidly TGA of the binder plus the ceramic powder. Non-evaporating binder being fired in N2 Mostly binder + small amount of plasticizer Plasticizer(liquid) can evaporate at lower T mostly plasticizer, residual solvent, small amount of binder D. J. Shanefield, Organic Additives & Ceramic Processing Advanced Electronic Ceramics I (2004)
  • 5. Binder Burnout 2 1. Typical temperature schedule for binder burnout - halted at 500oV for ~ 1h and then rise to the sintering temperature 2. Single binder with narrow range of m.w. - binder burnout occurs at the small range of temperature - abrupt burnout might cause crack 3. For the gradual binder burnout (desirable) - employs wide range of molecular weight - employs the mixture of different molecular species D. J. Shanefield, Organic Additives & Ceramic Processing Advanced Electronic Ceramics I (2004) Binder Burnout 3 Problems in binder burnout 1. Green ceramic body is so large that both the oxygen diffusion inward to the binder and the outdiffusion of combustion products are slow - burnout in pressurized air for the thick body(diffusion is slow) - addition of ~100ppm of transition metal (Mn, Pd) to catalyze oxidation - use of self-oxidizing binder (cellulose nitrate) that is soluble in ethyl acetate or methanol (restriction in the choice of solvent) 2. Binder can not burn without oxygen when the non-oxidizing atmosphere is required for protecting the ceramic or its metallization. - use of wet hydrogen(water vapor oxidize the binder) - electrical conductor (Mo or W ) on the insulating alumina D. J. Shanefield, Organic Additives & Ceramic Processing Advanced Electronic Ceramics I (2004)
  • 6. Binder Burnout: TMA study (TMA) Thermo Mechanical Analysis Height monitoring using (LVDT) Linear Voltage Differential Transformer H.T.Kim et al., Am. Ceram. Soc. Bull., 80(10), 34 (2001) Advanced Electronic Ceramics I (2004) Binder Burnout: TMA study Various stage of Binder Removal can be resolved using TMA analysis H.T.Kim et al., Am. Ceram. Soc. Bull., 80(10), 34 (2001) Advanced Electronic Ceramics I (2004)
  • 7. Binder Burnout: Design of Belt Furnace Design factor 1. Belt speed 2. Flow rate of purging gas T.C.K.Yang et al., Am. Ceram. Soc. Bull., 80(10), 43 (2001) Advanced Electronic Ceramics I (2004) Dispersent Surfactant (SURFace ACTive AgeNT) The role 1. To separate the primary particles so the binder coat them individually (Trapped air in the interstitial space trouble in deairing and sintering) 2. To increase solids loading in the powder suspension in order ro maintain moderate viscosities after binder addition (Many 2ndary particles result in the loose packing in the green tape.) 3. To decrease the amount of solvent in the powder suspension in order to save money on solvent or in order to dry the slip faster and with less shrinkage 4. To burn out clearly prior to sintering in order not to contaminate final part R. E. Mistler and E. R. Twiname, Tape Casting, Theory and Practice Advanced Electronic Ceramics I (2004)
  • 8. Dispersent Measures 1. Sedimentation height (the lower, the more effective dispersion) - difficult to analyze the very fine powder 2. Minimum viscosity - used in scientific studies of dispersent (precise determination of optimum dispersent amount) - powerful in tape casting technique - can not ordinarily be used with the high solids loadings because the slips are nearly solids except right near the point of minimum viscosity. 3. Maximum solid loading at maximum usable viscosity - at the constant dispersent amount, measure the viscosity increment as increasing solid loading - helpful to know the best dispersent conc. - used in engineering field. D. J. Shanefield, Organic Additives & Ceramic Processing Advanced Electronic Ceramics I (2004) Dispersent H CH3 DB CC DB H C On O ONa C OH O Polymethacrylic Acid(PMA) D C=C C=C - C - C - C - C -n C=O + C=O C=O C=O Sodium Alginate (water soluble) OH OH OH OH acrylic Acid Polyacrylic Acid D. J. Shanefield, Organic Additives & Ceramic Processing Advanced Electronic Ceramics I (2004)
  • 9. Dispersent D C3H4(OH) 3 + 3C17H33COOH → C3H5(C17H33COO) 3 + 3H2O Glycerin Oleic Acid Glyceryl Triolate(Olein) Naturally occurring liquid (vegetable, fishes) - Polyunsaturated (contains several double bond) Cf. saturated fat (glyceryl tri stearate found in red meat) → sodium stearate soap - Stimulate the production of cholesterol → solid soap - heart disease 1. Olein heating with NaOH → Reverse reaction (glycerin + oleic acid) 2. NaOH + oleic acid → sodium oleate (soap) [saponification reaction] Manufactured by heating vegetable oil with alkali (liquid soap.) D. J. Shanefield, Organic Additives & Ceramic Processing Advanced Electronic Ceramics I (2004) Most of dispersents for organic solvent contain various fatty acid and esters Advanced Electronic Ceramics I (2004)Twiname, Tape Casting, Theory and Practice R. E. Mistler and E. R.
  • 10. Menhaden Fish Oil Primarily (not entirely) “Steric hindrance” deflocculant Phosphate ester - function both as ionic repulsion and Steric hindrance deflocculant R. E. Mistler and E. R. Twiname, Tape Casting, Theory and Practice Advanced Electronic Ceramics I (2004) 1000e2Na 1/2 κ= ΣZi2Mi Dispersent εkT Aqueous : high ε, high ionic concentration - electrostatic stabilization Nonaqueous: low ε, low ionic concentration -Steric stabilization 1. Unsaturation (double bond) 2. m.w.~1000 - high m.w. - long molecule cause bridging & tangling 3. Ester linkage D. J. Shanefield, Organic Additives & Ceramic Processing Advanced Electronic Ceramics I (2004)
  • 11. Steric Hindrance ♦ Steric: comes from Greek word that means ‘solid’, and refers to size and shape being the important factors. ♦ definition : mechanical prevention of two particles approaching each other ♦ Uniform coating of non-polar organic compound ♦ Two reasons for not sticking 1. Non-polar materials have much less van der Waals attraction than the higher polar oxide surface 2. Coatings are weak and will break easily even if they do adhere D. J. Shanefield, Organic Additives & Ceramic Processing Advanced Electronic Ceramics I (2004) Dispersent W.R.Cannon et.al, Advances in Ceramics, Vol.26, p525 (1989) Advanced Electronic Ceramics I (2004)
  • 12. Two-stage milling 1st stage (ceramic powder + part of solvent + dispersant) - low-viscosity-slurry preparation - breaking down agglomerates - uniformly distribute a dispersant on the surface of ceramic powder 2nd stage ( + binder + plasticizer + part of solvent) - homogeneous mixing of binder and plasticizer Advanced Electronic Ceramics I (2004) Vacuum deairing Purpose - remove bubbles inside the slurry - agitation + vacuum deairing (635 - 710 mmHg) - till the moderate viscosity(1000 - 5000 mPa·sec) Advanced Electronic Ceramics I (2004)
  • 13. Tape casting Thickness of film depends on 1. Slurry viscosity 2. Casting carrier speed 3. Doctor-blade gap setting 4. Reservoir depth behind the doctor blade In the most cases, (The thickness of dried green tape) = 1/2 x (The blade gap setting) Casting speed : 5 -100 cm / min Polymeric carrier film : Mylar, Teflon, cellulose triacetate, Aclar, silicon-coated Mylar, polyethylene Advanced Electronic Ceramics I (2004) Tape casting: Problem shooting 1 Problem Solution Tape sticks excessively to 1. More release agent (dispersant of liquid, and.or carrier film plasticizer), or use 2.Silicon surface-treated carrier film Tape releases from carrier film 1. Less of above, or too soon and curls up 2. Add some more-powerful solvent (such as methylene chloride), to attack carrier film slightly Tape is too week to handle 1. More plasticizer, up to the point of almost filling the once it is released from pores between ceramic powder particles carrier film 2. Shorter milling time after adding binder Tape is hard but brittle More plasticizer, up to the point of 2.5 times the binder weight (which would make the tape too sticky) 1. Higher solid loading in slip (might require up to 4 gm Cracks during drying of dispersant per 100 gm of ceramic powder), or 2. More binder and plasticizer, up to the point of preventing high fired density 3. More release agent (dispersant or plasticizer) 4. Slower drying (lower temp. and/or air flow, or more highly saturated solvent vapor in the air) D. J. Shanefield, Organic Additives & Ceramic Processing Advanced Electronic Ceramics I (2004)
  • 14. Tape casting: Problem shooting 2 Problem Solution Cracks during firing 1. High green density (a. better dispersant, or more dispersant, or more milling before adding binder, or b. less total organics) 2. Slower firing heat-up (if cracked pieces do not match up) 3. Slower firing cool down Warpage during firing 1. Try the same 3 things above 2. Use optimized weight of porous pre-fired ceramic plates Fired density too low 1, More milling before adding binder, or 2. More milling after adding binder, or 3. Less total binder and plasticizer D. J. Shanefield, Organic Additives & Ceramic Processing Advanced Electronic Ceramics I (2004) Automatic stacking and Printing machine The machine is designed for stacking ( soft pressing ) the ceramic green sheets on the carrier palettes and for screen printing of electrodes in MLC production, based on highly refined “print on stack technology”. - Uses both carrier and freestanding tapes - Print on stack yields superior stacking at high layer counts - Perfect carrier film removal (optional) ensures high quality products - Sheets of tape are cut automatically from the roll and pressed onto the stack. - Screen printer is specially designed for precise printing of electrodes. - It enables very accurate alignment of electrodes and uniform printing conditions for printing all the layers of stacks. http://www.keko-equipment.com/ Advanced Electronic Ceramics I (2004)
  • 15. Heating Press for Lamination of green tape http://www.tester.co.jp/sa03.html Advanced Electronic Ceramics I (2004) Shrinkage matching in co-firing of two different layers 1. Shrinkage matching during the sintering 2. Shrinkage matching after sintering ~ the matching of ∆L/L during and after the sintering in order to avoid the cracking 3. The matching of thermal expansion coefficient to improve the resistance against cyclic thermal shock - particle size and distribution of powder and organic content should be controlled Cracking during sintering Cracking after sintering Good adhesion shrinkage T T T Advanced Electronic Ceramics I (2004)
  • 16. Shrinkage matching: Example, wide range air-to-fuel ratio sensor Advanced Electronic Ceramics I (2004) Shrinkage matching: Example, wide range air-to-fuel ratio sensor Matching sintering temperature Matching thermal expansion by controlling particle size and between alumina and YSZ by adding flux S.Iwanaga et al., from Hitach Co. Ltd Advanced Electronic Ceramics I (2004)
  • 17. Shrinkage matching: Example, wide range air-to-fuel ratio sensor Matching shrinkage by controlling the content of organic binder S.Iwanaga et al., from Hitach Co. Ltd Advanced Electronic Ceramics I (2004)

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