AT9900071

Coating of ceramic powders by chemical vapor depositiontechniques (CVD)

R. Haubner and B. Lux

Insitute of Chemical Technology of Inorganic MaterialsTechnical University of Vienna

New ceramic materials with selected advanced properties can be designed by coating of

ceramic powders prior to sintering. By variation of the core and coating material a large

number of various powders and ceramic materials can be produced. Powders which react with

the binder phase during sintering can be coated with stable materials.

Thermal expansion of the ceramic materials can be adjusted by varying the coating thickness

(ratio core/layer). Electrical and wear resistant properties can be optimized for electrical

contacts. A fluidized bed reactor will be designed which allow the deposition of various

coatings on ceramic powders.

309

O H

for Functional ApplicationJune 5-6, 1997, Vienna / Austria

COATING OF CERAMIC POWDERS BYCHEMICAL VAPOR DEPOSITION

TECHNIQUES (CVD)

R.Haubner, B.LuxInstitute for Chemical Technology of Inorganic Materials

Vienna University of Technology

coating / powder application

TiN / TiC

AI2O3 /TiN /AIN /

c /TiN /

TiB2 - TiN /

Al /TiN /TiO2 /

SiCAI2O3SiC

U,ThFeFe

micamicamica

+ Si3N4 structural ceramic

structural ceramics•I

high thermal conductivity,low thermal expansion

feed- and breed-materialsoxidation resistance

pigment with various colours

T I J W1ENChemliche Technologic

anorganijcher StotTe

1997

CVD coatings on powdersCoating / powder variations described in literature

310

reactors:

fluidized bedfloating-type fluidized bed

rotary powder bed

vibration bed

" | " | J W1ENChemische Tcchnologie

gnorganiicher Sloffe

1997

CVD coatings on powdersVarious reactors for coating of powders described inliterature

Vs = [4 x g x dp x (DP-DG) / (3 X DG X CW)]" '

VS = terminal velocity (velocity of single particle)g = gravitationdp = particle diameterDP = density of particleDG = density of carrier gasCw = resistance coefficient

Cw = 24 / Re + 4 / Re0'5 + 0.4Re = Reynolds number

= V S X 8 4 6 5 s = 1-eVG = superficial velocityE = porositye = solid loading

TU WIENChemische Tecbnologle

anorganlscher Stoffe

97-68

Fluidized bed reactorsEquations to calculate fluidization systems

311

80

(0

g 60

8 40o1c

o

20

. . . .

. . . .

10 J

/

"760 T

. . . .

. . . .

Torr/

orr

4 6 8

particle diameter dp [|~im]

~ y WIENChemische Technologie

anorganischer Stoffe

97-64

Fluidized bed reactorsTerminal velocity for various particle diameters and twogas pressures (diamond powder, hydrogen, 1000K)

% 1.0o

rec

•|iCO U

*" O

0.8

0.6

CO

1 0.2oa</> 0 . 0

•x- \\ \ •

•

: \

\

I N.-..„

-9--9-\

e = loading withpowder at thebeginning ofthe CVDreaction

50 100 150increase of particle size [%]

Y\) WIENCbemische Technologie

anorganiscber StofTe

97-65

Fluidized bed reactorsChanges in gas velocity during particle growth(constant density)

312

0.00 0.05 0.10 0.15

Solid loading e (starting condition)

I U W1ENChemische Technologie

anorganischer Stoffe

97-66

Fluidized bed reactorsComparison of partical growth and solid loading(velocity in reactor is constant)

«: 105

O

f0)

J2

10 50 100 500 1000

particle diameter [pm]

Chemische Technologieuiorganischer Stoffe

97-67

Fluidized bed reactorsComparison of partivie diameter to particle volume andsolid loading

313

reactive gasfor CVD

deposition

gas for Afluidization (I

pump

reactive gasfor CVD

deposition

powderinlet

pomp

gas forfluidization

powderoutlet.

~ J J W1ENChemische Technologie

anorganijcher StofTe

97-69

CVD coating of powdersFluidized bed reactors

external circulationreactive gas

for CVDdeposition

powderinlet

\

"• v

• /

pump

internal circulationreactive gas

for CVDdeposition

I V powderinlet\

powderoutlet

gas for Afluidization U

pump

gas forfluidization

powderoutlet

V1>V2~ I J WIEN

Chcmiichc Technologie•Dorginlicher Sloffe

97-70

CVD coating of powdersFluidized bed reactors with circulation

314

uctiLrii

reactive gasfor CVD

deposition

gas forfluidization

pumpreactive gas

for CVDdeposition

powdecinlet \

pump

gas forfluidization

\ powder1 outlet

f y W1ENCbemiscbe Technologic

anorganischer Stoffe

97-71

CVD coating of powdersStream bed reactors

LU

<

315

Al-donor

Al-x

+

+

Oxygen-donor

0-y -

A12O3

A12O3

+ reactionproducts

• + xy

Example:

TUW 1 "Ch«mltche Technotogle

•norganlschir Slolle

8 4 - 1 4

CVD GROWTH OF C L - A I 2 O 3

Arcarrier gas

CVD growth of CL-A12O3

Al(0- iPr ) 3 decomposition onWC/Co/TiC substrates „ ,

, ,̂

316

as

O(N

HiLA

i CO

1100°C 1200°C 1300°C10 /im

CJ)«irii»ch« TecMologi*•KHguucMi suite

95 - 33

/?-SiC deposition from CH3SiH2SiH2CH3 on WC-CoChanging deposition temperature

X. TANG

317

AH

oE

CO . *

uoQ

LJJX

COCOLJ

Q

<T>

! oo

deposition of diamond

coated with A12O3 fracture

TO"-ltcMTichAOloganliehti Slott

87 - 87

COMPOSITE LAYER: LOW PRESSURE DIAMOND, CORUNDUMThermal CVD; Substrate: WC/Co/TiC

318.R. BICHLER

deposition of diamond

coated with A12 03 fracture

TU»-Ctomiich* Tachncio

87 - 87

COMPOSITE LAYER: LOW PRESSURE DIAMOND, CORUNDUMThermal CVD; Substrate: WC/Co/TiC R. BICHLER

well-facetted non-facetted

TU

88 - 56

cub-BN (WURZITE TYPE)R. HAUBNER

319

Diamond cub-BN

Diamond nucleation Intermediate stage Covered with diamond shell

Chtff»i»ch« T*chAologI«•norganlichar Slotlt

89-44

COMPOSITE POWDERScub-BN core/ diamond shell

pure

cub-BN

10

5 h

10 \m

5 h

CK.j

88

nJtchir Ston*

- 60

Thermal

EpiCVD

taxialLOW-PRESSURE DIAMOND:

growth on non- facet ted320

cub-BN powder

R. HAUBNER

- 100 urn

ChM4tch>T*chft«J»ot«•norganliclMfSLofl*

87 - 197 Thermal CVDDeposition

LOW: growth ontime: 5 h

PRESSUREcub-BN

DIAMOND

R. HAUBNERj

SiC Diamond

Diamond nucleation100 um '—' 10 urn —• 10 um

Intermediate stage Covered with diamond shell

tiamlcche Technologic

89-45COMPOSITE POWDERS

SiC core/ diamond shell

321

LITOS 1988

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