Post on 25-May-2015
Advanced Electronic Ceramics I (2004)
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
R. Moreno, Am.Ceram.Soc.Bull., 71(11), 1647 (1992)
PEG additionto PVA
In order to reduce Tg
1. Use of less rigid side groups2. Reduction of the # of polar group3. Lowered molecular weight4. Lowered intermolecular contact
Advanced Electronic Ceramics I (2004)
Plasticizer
plasticizer1. Low molecular weight
- decrease Tg
2. Significant decrease in green strength
Strength of alumina green sheetas a function of plasticizer, DBP
R. Moreno, Am.Ceram.Soc.Bull., 71(11), 1647 (1992)
Advanced Electronic Ceramics I (2004)
Plasticizer
R. Moreno, Am.Ceram.Soc.Bull., 71(11), 1647 (1992)
Plasticizer concentration
low plasticizer concentrationporosity decrease due to the increaseinflexibility
too high plasticizer concentrationincreasing interparticle distancedecreasing the green density
Advanced Electronic Ceramics I (2004)R. E. Mistler and E. R. Twiname, Tape Casting, Theory and Practice
Advanced Electronic Ceramics I (2004)R. E. Mistler and E. R. Twiname, Tape Casting, Theory and Practice
σ
ε
σ
ε
σ
ε
σ
ε
No plasticizer Type II plasticizer
Type I plasticizerType I & Type II
- lower Tg
- binder solvent
-Lubricant-Easy to release of green tapefrom carrier film
Advanced Electronic Ceramics I (2004)D. J. Shanefield, Organic Additives & Ceramic Processing
H
C
OH
H
H
C
OH
H
C
OH
H
Glycerin
P
HOHCH
HCH
O Hn
Polyethylene Glycol (PEG)
D P B
Various Plasticizers
Plasticizer m.p.(oC) b.p .(oC)Water 0 100Ethylene glycol -16 197Diethylene glycol - 8 245Tetraethylene glycol - 7 288Poly(ethylene glycol) -10 >330Glycerine 18 290Dimethyl phthalate 1 284Dibutyl phthalate 1 340Octyl phthalateBenzyl butyl phthalateDiethyloxalate
R. Moreno, Am.Ceram.Soc.Bull., 71(11), 1647 (1992)
Advanced Electronic Ceramics I (2004)
Common binder(binder + plasticizer) choice
Application
Tape Casting
Screen Printing
Binders
Polyvinyl ButyralMethacrylate Solution(in MEK)Methacrylate EmulsionAmmonium Polyacrylate
AlginatesGumsEthyl CellulosePolyvinyl Butyral
System
NonaqueousNonaqueous
AqueousAqueous
AqueousAqueousNonaqueousNonaqueous
Advantages
StrongEasy burnout
Easy burnoutHigh Solids
InexpensiveInexpensivePseudoplasticEasy Burnout
D. J. Shanefield, Organic Additives & Ceramic Processing
Advanced Electronic Ceramics I (2004)
Binder Burnout 1
D. J. Shanefield, Organic Additives & Ceramic Processing
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 plasticizerPlasticizer(liquid) can evaporate at lower Tmostly plasticizer, residual solvent, small amount of binder
When large amount of plasticizer is added evaporation of plasticizer leaves many pores for the air, CO2, and solvent vapor.
Advanced Electronic Ceramics I (2004)
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
D. J. Shanefield, Organic Additives & Ceramic Processing
Problems in binder burnout1. 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
Advanced Electronic Ceramics I (2004)
Binder Burnout: TMA study
H.T.Kim et al., Am. Ceram. Soc. Bull., 80(10), 34 (2001)
(TMA)ThermoMechanicalAnalysis
Heightmonitoringusing(LVDT)LinearVoltageDifferentialTransformer
Advanced Electronic Ceramics I (2004)
Binder Burnout: TMA study
H.T.Kim et al., Am. Ceram. Soc. Bull., 80(10), 34 (2001)
Various stage of Binder Removalcan be resolved using TMAanalysis
Advanced Electronic Ceramics I (2004)
Binder Burnout: Design of Belt Furnace
T.C.K.Yang et al., Am. Ceram. Soc. Bull., 80(10), 43 (2001)
Design factor1. Belt speed2. Flow rate of purging gas
Advanced Electronic Ceramics I (2004)
Dispersent
Surfactant (SURFace ACTive AgeNT)
The role1. 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 romaintain 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)
Dispersent
D. J. Shanefield, Organic Additives & Ceramic Processing
Measures1. 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 ofoptimum 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.
Advanced Electronic Ceramics I (2004)
Dispersent
D. J. Shanefield, Organic Additives & Ceramic Processing
Polymethacrylic Acid(PMA)
HCH
CH3
C
C O
OHn
D B
C=C
C=O
OH
C=C
C=O
OH
+
- C - C - C - C -
C=O
OH
C=O
OH
n
acrylic Acid Polyacrylic Acid
D
D
OC
O ONa
Sodium Alginate(water soluble)
B
Advanced Electronic Ceramics I (2004)
Dispersent
D. J. Shanefield, Organic Additives & Ceramic Processing
C3H4(OH) 3 + 3C17H33COOH → C3H5(C17H33COO) 3 + 3H2OGlycerin Oleic Acid Glyceryl Triolate(Olein)
D
Naturally occurring liquid (vegetable, fishes)- Polyunsaturated (contains several double bond)
Cf. saturated fat (glyceryl tri stearate found in red meat)- Stimulate the production of cholesterol - 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.)
→ sodium stearate soap→ solid soap
Advanced Electronic Ceramics I (2004)R. E. Mistler and E. R. Twiname, Tape Casting, Theory and Practice
Most of dispersents for organic solvent contain various fatty acid and esters
Advanced Electronic Ceramics I (2004)
R. E. Mistler and E. R. Twiname, Tape Casting, Theory and Practice
Menhaden Fish OilPrimarily(not entirely)“Steric hindrance”deflocculant
Phosphate ester- function both asionic repulsion andSteric hindrancedeflocculant
Advanced Electronic Ceramics I (2004)
Dispersent
D. J. Shanefield, Organic Additives & Ceramic Processing
1. Unsaturation(double bond)
2. m.w.~1000- high m.w.- long moleculecause bridging &tangling
3. Ester linkage
Aqueous : high ε, high ionic concentration - electrostatic stabilizationNonaqueous: low ε, low ionic concentration -Steric stabilization
1000e2Na 1/2
κ = ΣZi2MiεkT
Advanced Electronic Ceramics I (2004)
Steric Hindrance
D. J. Shanefield, Organic Additives & Ceramic Processing
♦ 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 sticking1. 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
Advanced Electronic Ceramics I (2004)
Dispersent
W.R.Cannon et.al, Advances in Ceramics, Vol.26, p525 (1989)
Advanced Electronic Ceramics I (2004)
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)
Tape casting
Thickness of film depends on1. Slurry viscosity2. Casting carrier speed3. Doctor-blade gap setting4. 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
D. J. Shanefield, Organic Additives & Ceramic Processing
ProblemTape sticks excessively to
carrier film
Tape releases from carrier film too soon and curls up
Tape is too week to handle once it is released from carrier film
Tape is hard but brittle
Cracks during drying
Solution1. More release agent (dispersant of liquid, and.or
plasticizer), or use2.Silicon surface-treated carrier film1. Less of above, or2. Add some more-powerful solvent (such as
methylene chloride), to attack carrier film slightly1. More plasticizer, up to the point of almost filling the
pores between ceramic powder particles2. Shorter milling time after adding binderMore 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
of dispersant per 100 gm of ceramic powder), or2. More binder and plasticizer, up to the point of
preventing high fired density3. More release agent (dispersant or plasticizer)4. Slower drying (lower temp. and/or air flow, or more
highly saturated solvent vapor in the air)
Advanced Electronic Ceramics I (2004)
Tape casting: Problem shooting 2
D. J. Shanefield, Organic Additives & Ceramic Processing
ProblemCracks during firing
Warpage during firing
Fired density too low
Solution1. High green density(a. better dispersant, or more dispersant, or more
milling before adding binder, orb. less total organics)
2. Slower firing heat-up (if cracked pieces do not match up)3. Slower firing cool down1. Try the same 3 things above2. Use optimized weight of porous pre-fired
ceramic plates1, More milling before adding binder, or2. More milling after adding binder, or3. Less total binder and plasticizer
Advanced Electronic Ceramics I (2004)
- 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.
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”.
http://www.keko-equipment.com/
Automatic stacking andPrinting machine
Advanced Electronic Ceramics I (2004)
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 layers1. Shrinkage matching during the sintering
T TT
shrinkage
Cracking during sintering Cracking after sintering Good adhesion
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
Advanced Electronic Ceramics I (2004)
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 thermal expansionbetween alumina and YSZ
Matching sintering temperatureby controlling particle size andby adding flux
S.Iwanaga et al., from Hitach Co. Ltd
Advanced Electronic Ceramics I (2004)
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