suspension plasma sprayed titanium oxide and hydroxyapatite...

Suspension plasma sprayed titanium oxide and hydroxyapatite coatings

Atelier « Procédé plasma thermique », Limoges, June 3 - 5 2009

R. Jaworski, Lech Pawlowski, C. Pierlot, S. Kozerski, F. Petit

Service of Thermal Spraying at Ecole NationaleSupérieure de Chimie de Lille

avenue Mendeleiev

F-59652 Villeneuve d’Ascq, France

Phone/Fax: (+33) 320 33 61 65

E-mail: [email protected]

Outline

1. Introduction2. Technology of suspension thermal

spraying3. Methods of coatings g

characterizations4. Properties of coatings related to

spray parameters5. Conclusions6. 4RIPT

Titanium oxide : physical properties and phase diagram

TiO2 phases: rutile, anatase, brookite

Titanium oxide : possible application of thick TiO2 coatings

• Rutile and anatase are diélectrics of high resistivity, �=109-1013 �.cm• Magnéli phases are semiconductors of a weak résistivity, for

example TiO1.996 has the resistivity of �=0.464 �.cm • Reduction of TiO2 is associated with a modification of resistivity• Modification of resistivity is useful for:

• Design of sensors of H2• Design of sensors of O2

• Anatase is useful in photocatalysis to degrade organic pollutants• Magnéli phases can be used as conducting pathes in electron

emitters

Hydroxyapatite: phase diagram, phases at spraying, properties

CaO+TTCP

a’-TCP + TTCP

a-TCP+ DCP

a-TCP+ liquid

a’-TCP+ liquid

TTCP +liquid

a’TCP +liquid

HA + a-TCP

HA + TTCP

1360

1570

a’-TCP + TTCP

1200

1300

1400

1500

1600

1700

TP > 3500 K

TP > 1843 K

Form ation of liquid phase by incongruent

m elting(am orphous phase on solidification)

1843 K >TP > 1823 K

Solid state

Solid HA + OA + OHA

60 50

HA + �-TCP

�-TCP+ DCP

70 %CaO

CaO+HA

1000

1100

P

Evaporation of P 2O 5 and

formation of CaO

Solid state transformation of HA

into αααα −−−−ΤΤΤΤCP and TP

Symbol Name Formula Ca/P

TTCP Tetra calcium phosphate

Ca4 P2O9 2

α-TCP Tricalcium phosphate Ca3(PO4)2 1.5

HA Hydroxyapatite Ca10(PO4)6(OH)21.67

Constants for HA ValuesHeat of melting, kJ/mol 15.5Melting point, K 1843Heat of evaporation,kJ/mol

458.24

Boiling point, K 3500Molecular mass, kg 1.668x10-24

Density, kg/m3 3156Thermal expansioncoefficient, 1/K

13.3x10-6

HA for bioactive coatings

The primary application concerns the coating onto prostheses made of bioinert materials as stainless steel, CoCrMo alloy or TiAlV alloy to insert in: • hip, knee, arm, tooth.

About 1 million of knee and hip prostheses are implanted yearly.

Knee

Great market represents that of bioactive coatings. The coatings, made usually of hydroxyapatite, accelerate implantation of prosthesis in the bone.

Principal property: dissolution in the body tested often in vitro in body simulated fluids. The rapidity of dissolution depends on the phase:

ACP>>TTCP>a-TCP>OHAP>�-TCP>>HA

Hip

•ceramics becomes slightly ductile what results from a capacity of sliding of small grains over other.

• Its optical, catalytic and electric properties are also very different than that of ceramics having micro-

Ceramics - ductility

Sliding difficult Sliding easy

Benefits of small nano/submicron crystal grains

or millimeter crystal grains morphology.

•Nanophased metals become stronger, what results from the, well known in metallurgy, Hall-Petch law.

•This improved strength results from the fact that the nanophased metals are nearly dislocation-free.

Sliding difficult Sliding easy

Hardness test

Moving of dislocations:analogy to a carpet on a floor

Dislocations

Easy to pull

Hard to pull

• Possible modification of morphology of individual particles at impact due to the modification of

Fundamental differences of using small powder particles to spray

equilibrium between kinetics energy of particle and surface energy keeping liquid together

• Modification of nucleation condition of liquid particles after impact with a substrate due to the decrease in latent heat of solidification

Motivation for the study

Development of deposition technology for nanometric and submicrometric titanium oxide and hydroxyapatite coatings by plasma spraying in view of:in view of:

•Reduction of thickness of resulting coating and materials saving

•Investigation of microstructure expecting useful modifications in comparison with coarse powders sprayed coatings




spray parameters5. Acknowledgments6. 4RIPT

Technology of TiO2 fine powder suspensions preparation

Two aqueous suspensions were prepared for spraying.

•Suspension A was formulated with the use of rutile manufactured by Tioxide (R-TC90 ofH Ti id ) b ki di ill d

A

Huntsman Tioxide) by taking distilled water+4wt.% rutile+0.3wt.% dispersant. The dispersant was an aqueous solution of sodium polyacrylate (Hydropalat N, Congis).

•A commercial powder Metco 102 was used for suspension B preparation. The powder was ball-milled in ethanol for 8 hours using zirconia balls. Then, the suspension was prepared in the same, as suspension A, way

3 μm

2 μm

B

TiO2 fine powder characteristics

A

0

5

10

15

Vol

ume

%

- TiO2 (rutile)

coun

ts (a.

u.)

Size distribution XRD

B

0,1 1 10 1000

2

4

6

8

10

12

14

16

18

Vol

ume

[%]

Particle size [μm]

TiO2 Metco 102 3 hours ball-milled 8 hours ball-milled

0,1 1 10

Particle size [μm]

20 30 40 50 60 700

5

10

15

20

25

30

35

40

- TiXO

2X-1 (Magneli-phases)

- TiO2 (rutile)

coun

ts (a.

u.)

2Θ (°)

20 25 30 35 40 45 50 55 60 65 70 75

2θ (degree)

Technology of HA fine powder suspensions preparation

•Commercial powder Tomita (Japan) was used for preparation of suspension HA. The powder was ball-milled using moliNEx system (Netsch, Germany) in ethanol for 8 hours using zirconia balls. The suspension was then formulated with 10 wt. % HA and ��

Two aqueous suspensions were prepared for spraying:

0.3 wt. % tetra-sodium diposphate. �

•Home made HA powder was synthesized using calcium nitrate and diamonium phosphate in ammoniacal solution according to the following equation:

6(NH4)2HPO4 + 10Ca(NO3)2 + 8NH4OH � 6H2O + 20NH4NO3 + Ca10(PO4)6(OH)2Followed by calcination at T = 1000 � C . The powder after calcination was crushedand ball milled. The particles size distribution in ethanol is monomodal and the mean diameter is about 1 μm. The suspension was formulated taking about 20 wt. % of dry powder with distilled water, ethanol or with a mixture of water with 50 wt. % ethanol.

HA fine powder characteristics

5

10

15

20

Initial Tomita HA

8 hours ball-milled

In ethanol0,1 1 10 100

0

Particle size [μm]

Commercial

20 30 40 50 60 70 80

2q (degree)

Ball-milled HA

Initial HAHA

HA

HA

Ca

O

αa

nd

βT

CP

2θ

Inte

nsi

ty

Home made

In ethanol

Types of liquids’ injectors

Nozzles

Torch

Nozzle

Torch

d

D

�

Atomizer pneumatic nozzles including “two-fluids” nozzles (see below)

Types of liquids’ injectors

Torch

Atomizer

D

d� Compressed airInjected liquid

• Aluminum/stainless steel/TiAl6V plates of size 15x15x3mm were used as the substrates;

•They were alumina grit blasted;

•Plasma sprayed using Praxair SG-100 torch on 5-axis ABB IRB-6 industrial robot;

TiO2, HA, composite coatings constant spray parameters

trajectory of one torch pass

•Throughout all the experiments the following parameters were kept constant:

•composition of plasma working gas: Ar + H2;•flow rates of plasma working gas: qAr= 45 slpmand qH2=5 slpm;•linear torch velocity: v=200 - 500 mm/s;•total number of passes reached with some interruptions for cooling down

Parameters are varying often following to design of experiments:

• Electrical power in kW

• Plasma working gases (Ar+H2) composition in slpm

TiO2/HA/composite coatings variable spray parameters

• Spray distance in cm

• Suspension feed rate in ml/min

• Atomizing gaz pressure in bar

• Type of suspension feeder (pressurized, peristaltic pump)

• Atomizer (TiO2, composite), atomizer or nozzle injector (HA).

XRD - TiO2 coatings

•Bruker set up with Cu-K� radiadion, EVA software used to phase analysis, phases from the database JCPDS

AARR

AAAcor II

IC

ρρ

ρ

/8/13

/8

+=

• Anatase content in TiO2 coatings anatase was found following the expression

XRD - HAcoatings

The percentage of the other phases with regard to hydroxyapatite were determined from the reference intensity ratio (RIR), the method described by Prevey.

• For comparison a method recommended by the French norm was used

Microstructure investigations tools

•SEM (Uni Lille, Uni Wroclaw)

•Electron microprobe analyses were made with the use of CAMECA SX100 set up and the profiles of Ca and P were made with TAP and PET crystals. Th fil d ith t f 1 (ENSCL)The profiles were made with a step of 1 μm (ENSCL)

•Micro-Raman spectroscopic investigations The spot of the Raman analysis was equal approximately to 1 �m (Uni Lille).

•XPS analysis was made using VG ESCALAB model 220 XL set up. The spectrometer was equipped with Mg K� source of energy 1253.6 eV (Uni Lille).

•TEM study a Hitachi H8100 microscope at 200 kV was used (Uni Chemnitz)

Electron emission home made set up (Uni Wroclaw)

ballastresistor

vacuum chamber

high voltagesupply

VA

1:10

00 p

robe

sample

anode

neonlamp

vacuum chamber

Mechanical properties by scratch test

Lc

Pyramid of diamondScratch hardness following to ASTM G171-03 norm

•The scratch test was realized with a icroCombiTester of CSM Instrumentsequipped with a Rockwell diamond indenter of having a tip radius of 0.2 mm at Belgium Ceramic Research Centrum in Mons

Lc

Coating

Substrate

2

8

d

LHS cL

⋅

⋅=

π

d




spray parameters5. Acknowledgments6. 4RIPT

TiO2 particles morphologies after impact

Big particles at impact : flower Fine TiO2 particles at impact : pancake

20 �m

5 �m5 �m

SEM (secondary electrons) investigations: optimization of spray parameters of TiO2

Torch

Parameters optimizedP – arc powerVr – torch linear velocityn – number of cyclesD, d – distances

P = 30 kW, V = 500mm/s n = 30, D^d = 18^14 mm

d

DAtomizer

P = 35 kW, V = 500mm/s n = 30, D^d = 18^14 mm

P = 35 kW, V = 100mm/s n = 20, D^d = 18^14 mm

P = 40 kW, V = 125mm/s n = 10, D^d = 18^11 mm

P = 40 kW, V = 125mm/s n = 10, D^d = 15^11 mm

10 μm10 μm

SEM and TEM sections of TiO2

Porous structure

Fig. 23

Columnar grain growth

Regression analysis of influence of spray parameters on phases content for TiO2

Variable Spray process parameter Low level

Central point

High level

Xi=-1 Xi=0 Xi=+1

X1 Suspension feed rate, 20 30 40

Variables

ml/min

X2 Spray distance, cm 8 10 12

X3 Power input to plasma, kW 38 39 40

AARR

AAAcor II

IC

ρρ

ρ

/8/13

/8

+=

Response Y1: intensity of anatase peaks 21 3.25.12 XY +=

Anatase content depends mainly on spray distance

Distribution of phases in TiO2 coatings

10 μm

24000

26000

28000

30000

32000

R+A

R+A(b)

MicroRaman microscopy

0 200 400 600 800 1000 12000

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

22000

24000

Y A

xis

Titl

e

X Axis Title

R

R

R+A R+A

A

(c)

(a)

XPS investigations: qualitative chemical analysis of TiO2

Element Orbit %atom

O(O Ti) 1s 34.44

Element Orbit %atom.

Initial fine powder Coating

O(O-Ti) 1s 34.44

O(O-Al, OH) 1s 13.64

O(O²) 1s 4.92

Ti 2p 15.3

C 1s 12.2

Al 2p 10.2

Na 1s 7.1

Si 2p 2.3

O(O-Ti) 1s 21.81

O(O-Al, OH) 1s 28.54

O(O²) 1s 3.74

Ti 2p 5.71

C 1s 23.38

Al 2p 16.82

Conclusion: processing (suspension preparation/spraying) introduces Na and Si impurities

A few passes of HA suspension plasma sprayed over substrate (nozzle injector)

Big rests of liquid droplet Fine sintered particles

Zoom

Deduction of suspensions droplets behavior in plasma jet

Evaporation of liquid Sintering of some fine solids

Melting offine solidsand

Evaporationfrom melt

ImpactAerodynamic breadown

agglomerates

XRD investigations of HA coatings : phases analysis (atomizer injector)

Variable Spray processparameter

Low levelXi=-1

Central pointXi=0

High levelXi=+1

X1 Power input to plasma, kW

35 37.5 40

X2 Atomizing gas 0.4 0.5 0.6

Regression analysis of influence of spray parameters on phases content for HA (atomizer injector)

2 g gpressure, bar

X3 Spray distance, cm

8 10 12

X4 Suspension flow rate, mL/min

20 30 40

Statistical analysis shows that only

β-TCP depends on spray parameters

Y=59.5+13X1-13 X1 X4 X1=1 and X4=-1 results in more β-TCP

Response Y: intensity of phases of HA decomposition

peaks :TTCP, α,β-TCP, CaO

SEM (B.S.E.) and electron microprobe analysis of HA coatings (nozzle injector)

��

��

��

1 2

1.4

1.6

1.8

2

2.2

Ca/

P

HA

TTCP

TCP

Profile 1Two zones microstructure

��

��

1

1.2

0 10 20 30 40 50 60 70

Length of profle, μm

1

1.2

1.4

1.6

1.8

2

2.2

0 20 40 60

Profile 2TTCP

HA

TCP

Initial fine powder

Sample Peak %atom Ca/P ratio

Initial HAp powder

O 1s 54.6 1.38

Sample Peak %atom Ca/P ratio

D1

O 1s 50.9

Ca 2p 19 7 1 33

XPS investigations: qualitative chemical analysis of HA (atomizer injector)

Coating

Ca 2p 22.0

P 2p 15.9

C 1s 7.5

8h ball-milled HAp

O 1s 52.1

Ca 2p 20.9 1.37

P 2p 15.2

C 1s 11.8

Ca 2p 19.7 1.33

P 2p 14.8

C 1s 12.5

Na 2p 2.1

D2

O 1s 52.9

Ca 2p 20.5 1.35

P 2p 15.2

C 1s 9.2

Na 2p 2.2

Conclusion : processing (suspension preparation/spraying) introduces Na impurities

SEM/EMPA investigations: chemical gradient coatings Ti/TiO2/HA

EMPA (wavelength dispersion spectroscopy)

Ti P Ca

SEM (secondary electrons)

Electron emission from TiO2 coatings (atomizer injector)

UAC = 1200 V UAC = 2000 V

UAC =3000 V UAC = 4000 V

Mechansm of electron emission from TiO2 coatings

Model of emissi

Conducting path(Magnéli phases)

Equipotentials

weakly conducting medium (rutile and anatase)

rutile anatase Magneli phases

Possible application of suspension sprayed TiO2 coatings : electron emitters

kr

h

EE

~

0

β

β ⋅=vacuum

insulator ��

�

�

��

�

�=

EB

EAJ

2

32

expφ

φ

Forbes model of electron emissions

SPS coating ~ 2-10 �m

Conducting grains and substrates

Electric field is amplified on surface irregularities (left), surface inclusions (middle) or below surface inclusions

(right).

SPS coating

APS coating

Substrate

~ 50 �m 2 10 �m

��

��

��

Variable, Spray process parameter Low level Central point High level

Xi=-1 Xi=0 Xi=+1

X1 Pressure in atomizer of suspension, bar 0.4 0.5 0.6

X2 Suspension feed rate, ml/min 20 30 40

Regression analysis of influence of spray parameters on breakdown voltage, Y1, and loss factor, Y2, of HA coatings (atomizer injector)

2 p

X3 Spray distance, cm 8 10 12

X4 Power input to plasma, kW 35 37.5 40

Breakdown voltage

431 1.526.75412 XXY +−=

Loss factor

41412 2.0262.0258.0411.0 XXXXY +−−=

on

dep

th, μ

m

co

effi

cien

t

mal

forc

e, N

fri

ctio

n, N Critical load, N

Mechanical properties thin of suspension sprayed TiO2 coating by scratch test

Pen

etra

tio

Fri

ctio

n

No

rm

Fo

rce

of

Load, N

Scratch length, mm

Regression analysis of influence of spray parameters on critical load, Y1, of TiO2 coating (atomizer injector)

Variable Spray process parameter Low level Central point High level

X 1 X 0 X 1Xi=-1 Xi=0 Xi=+1X1 Suspension feed rate, ml/min 20 30 40X2 Spray distance, cm 8 10 12X3 Power input to plasma, kW 38 39 40

Y1=12.5-1.5 X2

Scratch test results of suspension plasma sprayed HA coating (nozzle injector)

•Lc=10.5 1.2 N for coating on Al substrate 2.5

3

Pa

• Lc=12.3 0.6 N for the Ti substrate

0

0.5

1

1.5

2

0 2 4 6 8 10

Scra

tch

hard

ness

, GP

Applied load, N

Ti Al

• Suspension plasma sprayed TiO2 coatings:

� Crystallization partly as anatase useful feature for photocatalysis

� Possible application as electron emitters

Conclusions

� Possible application as electron emitters

• Suspension plasma sprayed HA coatings:

� Similar crystalization phases to coarse powder sprayed coatings

� Two zones microstructure to be further tested

• Development of adhesion test method for intermediate thickness suspension thermal sprayed coatings (normalization)




spray parameters5. Conclusions6. Bibliography ENSCL7. Acknowledgments8. 4RIPT

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suspension plasma sprayed titanium oxide and hydroxyapatite...

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