suspension plasma sprayed titanium oxide and hydroxyapatite...
TRANSCRIPT
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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]
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Outline
1. Introduction2. Technology of suspension thermal
spraying3. Methods of coatings g
characterizations4. Properties of coatings related to
spray parameters5. Conclusions6. 4RIPT
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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
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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
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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
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•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
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• 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
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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
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1. Introduction2. Technology of suspension thermal
spraying3. Methods of coatings g
characterizations4. Properties of coatings related to
spray parameters5. Acknowledgments6. 4RIPT
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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
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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)
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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.
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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
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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
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• 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
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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).
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1. Introduction2. Technology of suspension thermal
spraying3. Methods of coatings g
characterizations4. Properties of coatings related to
spray parameters5. Conclusions6. 4RIPT
-
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
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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
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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)
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Electron emission home made set up (Uni Wroclaw)
ballastresistor
vacuum chamber
high voltagesupply
VA
1:10
00 p
robe
sample
anode
neonlamp
vacuum chamber
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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
-
1. Introduction2. Technology of suspension thermal
spraying3. Methods of coatings g
characterizations4. Properties of coatings related to
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
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10 μm10 μm
SEM and TEM sections of TiO2
Porous structure
Fig. 23
Columnar grain growth
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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)
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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
-
1. Introduction2. Technology of suspension thermal
spraying3. Methods of coatings g
characterizations4. Properties of coatings related to
spray parameters5. Conclusions6. 4RIPT
-
• 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)
-
1. Introduction2. Technology of suspension thermal
spraying3. Methods of coatings g
characterizations4. Properties of coatings related to
spray parameters5. Conclusions6. 4RIPT
-
1. Introduction2. Technology of suspension thermal
spraying3. Methods of coatings g
characterizations4. Properties of coatings related to
spray parameters5. Conclusions6. Bibliography ENSCL7. Acknowledgments8. 4RIPT
-
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