Coating of Ceramic Powders by Chemical Vapor Deposition Techniques (CVD)

AT9900071 Coating of ceramic powders by chemical vapor deposition techniques (CVD)

R. Haubner and B. Lux

Insitute of Chemical Technology of Inorganic Materials Technical 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 OH for Functional Application June 5-6, 1997, Vienna / Austria

COATING OF CERAMIC POWDERS BY CHEMICAL VAPOR DEPOSITION TECHNIQUES (CVD)

R.Haubner, B.Lux Institute for Chemical Technology of Inorganic Materials Vienna University of Technology

coating / powder application

TiN / TiC + Si3N4 structural ceramic

AI2O3 / SiC structural ceramics TiN / AI2O3 •I AIN / SiC high thermal conductivity, low thermal expansion

c / U,Th feed- and breed-materials TiN / Fe oxidation resistance TiB2 - TiN / Fe

Al / mica pigment with various colours TiN / mica TiO2 / mica

TIJ W1EN Chemliche Technologic CVD coatings on powders anorganijcher StotTe Coating / powder variations described in literature 1997 310 reactors:

fluidized bed floating-type fluidized bed

rotary powder bed

vibration bed

"|"|J W1EN CVD coatings on powders Chemische Tcchnologie gnorganiicher Sloffe Various reactors for coating of powders described in 1997 literature

Vs = [4 x g x dp x (DP-DG) / (3 X DG X CW)]" ' VS = terminal velocity (velocity of single particle) g = gravitation dp = particle diameter DP = density of particle DG = density of carrier gas Cw = resistance coefficient Cw = 24 / Re + 4 / Re0'5 + 0.4 Re = Reynolds number

= VSX8465 s = 1-e VG = superficial velocity E = porosity e = solid loading

TU WIEN Chemische Tecbnologle Fluidized bed reactors anorganlscher Stoffe Equations to calculate fluidization systems 97-68 311 80 ...... J (0 10 Torr/ g 60

8 40 / o 1 c 20 o "760 Torr

...... 4 6 8 particle diameter dp [|~im]

~y WIEN Chemische Technologie Fluidized bed reactors anorganischer Stoffe Terminal velocity for various particle diameters and two 97-64 gas pressures (diamond powder, hydrogen, 1000K)

% 1.0 • o e = loading with powder at the 0.8 beginning of re the CVD c reaction : \ 0.6

•|i \ .-..„ CO U *" O •x- \ I N-9--9- CO \ \ • \ 1 0.2 ao 0.0 50 100 150 increase of particle size [%]

Y\) WIEN Cbemische Technologie Fluidized bed reactors anorganiscber StofTe Changes in gas velocity during particle growth 97-65 (constant density) 312 0.00 0.05 0.10 0.15 Solid loading e (starting condition)

I U W1EN Chemische Technologie Fluidized bed reactors anorganischer Stoffe Comparison of partical growth and solid loading 97-66 (velocity in reactor is constant)

«: 105

O f 0)

10 50 100 500 1000 particle diameter [pm]

Chemische Technologie Fluidized bed reactors uiorganischer Stoffe Comparison of partivie diameter to particle volume and 97-67 solid loading 313 reactive gas reactive gas for CVD for CVD pomp deposition pump deposition

powder inlet

powder outlet. gas for A gas for fluidization (I fluidization

~JJ W1EN Chemische Technologie CVD coating of powders anorganijcher StofTe 97-69 Fluidized bed reactors

external circulation internal circulation reactive gas reactive gas for CVD for CVD pump deposition deposition pump

"• v

powder I V powder inlet • / inlet\

powder outlet

powder gas for A gas for outlet fluidization U fluidization V1>V2 ~IJ WIEN Chcmiichc Technologie CVD coating of powders •Dorginlicher Sloffe 97-70 Fluidized bed reactors with circulation 314 uctiLrii reactive gas reactive gas for CVD pump for CVD deposition deposition pump

powdec inlet \

\ powder gas for gas for 1 outlet fluidization fluidization

fy W1EN Cbemiscbe Technologic CVD coating of powders anorganischer Stoffe 97-71 Stream bed reactors

LU <

315 Al-donor + Oxygen-donor + reaction A12O3 products

Al-x + 0-y - A12O3 • + xy

Example:

TUW1" Ch«mltche Technotogle CVD GROWTH OF CL-AI2O3 •norganlschir Slolle 84-14

carrier gas Ar

CVD growth of CL-A12O3

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

, ,^

316 as

O (N

LA i CO

1100°C 1200°C 1300°C 10 /im

CJ)«irii»ch« TecMologi* /?-SiC deposition from CH SiH SiH CH on WC-Co •KHguucMi suite 3 2 2 3 95 - 33 Changing deposition temperature X. TANG 317 CO .*

u Q o LJJ X o E

CO CO LJ

AH ! oo

deposition of diamond

coated with A12O3 fracture TO"- ltcMTichAOlo COMPOSITE LAYER: LOW PRESSURE DIAMOND, CORUNDUM ganliehti Slott 87 - 87 Thermal CVD; Substrate: WC/Co/TiC R. BICHLER 318. deposition of diamond

coated with A12 03 fracture TU»- COMPOSITE LAYER: LOW PRESSURE DIAMOND, CORUNDUM Ctomiich* Tachncio

87 - 87 Thermal CVD; Substrate: WC/Co/TiC R. BICHLER

well-facetted non-facetted

TU cub-BN (WURZITE TYPE) 88 - 56 R. HAUBNER

319 Diamond cub-BN

Diamond nucleation Intermediate stage Covered with diamond shell

Chtff»i»ch« T*chAologI« COMPOSITE POWDERS •norganlichar Slotlt 89-44 cub-BN core/ diamond shell

pure 5 h cub-BN

5 h

10 \m

CK.j nJtchir Ston* LOW-PRESSURE DIAMOND: 88 - 60 Epi taxial growth on non-facetted cub-BN powder Thermal CVD 320 R. HAUBNER - 100 urn

ChM4tch>T*chft«J»ot« •norganliclMfSLofl* LOW PRESSURE DIAMOND 87 - 197 Thermal CVD : growth on cub-BN Deposition time: 5 h R. HAUBNERj

SiC Diamond

100 um '—' 10 urn —• 10 um Diamond nucleation Intermediate stage Covered with diamond shell

tiamlcche Technologic COMPOSITE POWDERS 89-45 LITOS 1988 SiC core/ diamond shell NEXT PAGE(S) left BLANK 321