Aem Lect15

Advanced Electronic Ceramics I (2004)

Starting Point in Tape Casting: Surface

D. J. Shanefield, Organic Additives & Ceramic Processing

Greendensity

Surfaceenergy

Fireddensity

Homogeneousslurry formationusing small amount of organic additive to the active(small)powder


Tape Casting

Ceramic Powder Binder Plasticizer Solvent Dispersent

Ball milling in the jar

Deairing

Tape Casting

Drying

Cutting

Electroding

Lamination

Co-firing

Packaging


Tape Casting

http://www.algonet.se/~keram/pdf/Tape%20Casting.pdf


Tape Casting Machine 1

http://yoojintech.co.kr/frame1.htm

Tape casting machine

Slurry feeder


Tape Casting Machine 2

http://www.glass-ceramics.uni-erlangen.de/Staff/Research/Functceramics/

http://www.nrel.gov/ncpv/pdfs/26122.pdf


Multi-Layer Casting

R.E.Mistler, Am.Ceram.Bull., 52(11), 850-854 (1973)


Control Parameters: Thickness

♦ Thickness of the film1. Casting thickness (t)2. The thickness after drying(td) : 0.5t ~ 0.8t3. 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

Window region RecycleRecycle

Carrier film

Ceramic green sheet


Control Parameters: Casting Velocity

R. E. Mistler and E. R. Twiname, Tape Casting, Theory and Practice


Control Parameters: Drying

♦ Designing the temperature-profile for drying (in order to keep thehomogeneity of the tape after sintering)

1. Thickness of the casting film2. The volatility and content of organic (especially solvent) in the slurry3. The total length of the drying line4. Feeding rate for casting

[Key items]1. Employ the Azeotropic Mixture, : solution that contains the same ratio of chemical constituents after itis distilled (see distillation). The most common example is a solutionof 4.43% water and 95.57% ethyl alcohol.

2. Controlling drying


Binary Azeotropic Mixtures

R. Moreno, Am.Ceram.Soc.Bull., 71(10), 1521 (1992)


Drying

First stage1. 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 vaporto prevent quick drying. Quick drying can promote skin formation or

cracking.

Second stageA. Ceramic green body becomes stiffB. 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


Tape Casting: examples

http://www.umr.edu/~rahaman/Forming.pdf


Solvent


Desirable properties of solvents1. Ability to dissolve other additives2. Low viscosity at high solid loading3. Low tendency to form bubbles during milling4. High evaporation rate5. Safe, including

(a) nonflammability(b) nontoxicity

6. Low cost7. Lack of chemical attack on the ceramic powder


Reported Solvent Systems


1. Methyl ethyl ketone(MEK)2. MEK/95% ethanol3. MEK/anhydrous ethanol4. Xylenes/95% ethanol5. Xylene/anhydrous ethanol6. MEK/toluene7. Toluene8. 1,1,1 trichloroethane(TCE)9. TCE/ anhydrous ethanol10. TCE/MEK/ethanol11. TCE/acetone12. Toluene/95% ethanol13. MEK/95% ethanol/toluene14. MEK/methanol/buthanol


Various Solvents


n↑ in alkane⇒ density, m.p., b.p. ↑ex) methane, ethane - gas

octane - liquid

HCH

H H

n=8

H

C

H

H

H

C

OH

H

C

H

H

CH3

O

C C2H5

Isopropanol

Methyl Ethyl Ketone (MEK)- flammable

Trichloroethylene (TCE)- not flammable- probable carcinogen- slowly being phased out due to environmental problem

C

Cl

C Cl

Cl

C


Various Solvents


Benzene- carcinogen- leukemia, liver cancer- remain in the blood streamafter exposure

CH3 Toluene- less toxic than benzene- human body can metabolizetoluene into carbon dioxideand water

- flammable

CH3 CH3CH3

CH3

CH3

CH3

CH3

CH3

Ortho-Xylene Meta-Xylene Para-Xylene Mixture

- don not remain in the human body for a long time


Physical Properties of Some Usual Solvents

R. Moreno, Am.Ceram.Soc.Bull., 71(10), 1521 (1992)


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


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) glazeone 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


청자상감운학문매병(해강유근영)

국보제68호청자상감운학문매병을그대로재현한작품이다.


Evaporation rate


Solvent

waterEtOHTolueneTCEHeptane

∆Hvap.(cal/g)580204955776

b.p.(oC)10078

1118798

Flash point(oC)

203

- 1

Explosive limit(vol%)

3-191-7

1-7

1) Energy for drying2) 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)


Binder

Binder gives green strength for machining, inspection, and storage.

Desirable properties of binders1. Easy Burn-out2. Strong Green Body(a) Adhesion to Powder(b) Cohesive Strength

3. Solubility in Fluidizing liquid(solubility parameter)4. Low cost



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 AlNsystems requiring reducing or inert atm.


Binder: PVA

- 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

B



Polyvinyl Butyral(PVB)

Binder: PVBH

C

HH

H

C

O

H

C

OH

H

C

H

O

CH H

H

C

H

H

C

O

H

C

O

H

C

H

C

H H

H

C

HH

H

C

O

H

C

OH

H

C

H

C3H7

O

C H

H

C

H

H

C

O

H

C

O

H

C

H

C

H

H

C

H

H

C

H

H

C

H

Polyvinyl Alcohol(PVA)

FormaldehydePolyvinyl Formal

Butyraldehyde

Popular binderin ceramicprocessing

B



Other Binders

Polymethacrylic Acid(PMA)

HCH

CH3

C

C O

OHn

HCH

CH3

C

C O

O-CH3

n

Poly(methylmethacrylate) (PMMA)

HOHCH

HCH

O Hn

Polyethylene Glycol (PEG)

D P BD B

B

Polypropylene

C Cn

C

B



Polymer Characterization: molecular weight by GPC

HOHCH

HCH

O Hn

m.w. (n=1) = 1 x 44 + 18 = 62m.w. (n=2) = 2 x 44 + 18 = 106m.w. (n=n) = 44n + 18

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 = 400.13 x 1500 = 1950.41 x 2500 = 10250.29 x 3500 = 10150.09 x 4500 = 405

total 1.00 2680/1 = 2680 # avg.m.w.

8% below 100013% between 1000 and 200041% between 2000 and 300029% between 3000 and 40009% between 4000 and 5000



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


Advanced Electronic Ceramics I (2004)D. J. Shanefield, Organic Additives & Ceramic Processing

Polymer Characterization: Tg

Glass

RubberV

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)

Below Tg : relatively hard and brittlelike glass

Above Tg: relatively soft and elasticlike rubber

The addition of plasticizer- lower the Tg

- for easy handling

Health & Medicine

Aem Lect15