Reduction of Titanium Oxide to Titanium Alloy by Hydrogen
Hidehiro Sekimoto, Ryosuke Shioi, Tetsuya Uda, Yasuhiro Awakura(Kyoto University, Japan), and Shigeo Sato (Nissan Arc, Ltd.)
The 3rd Workshop on Reactive Metal processingMarch 2-3, 2007
Massachusetts Institute of Technology,Cambridge, MA, USA
2
Outline
• Titanium alloy• Reduction of titanium oxide to Ti-Pt alloy• Reduction of titanium oxide to Ti-Ni alloy• Summary
3
Outline
• Titanium alloy• Reduction of titanium oxide to Ti-Pt alloy• Reduction of titanium oxide to Ti-Ni alloy• Summary
4
Introduction
Ti-Ni alloy; Shape Memory, Superelasticity
Titanium alloys have many unique features and they are used in various situations.
However, titanium alloy is very expensive for its production cost.
It is necessary to develop a new process of titanium alloy.
Photographs; Daido Steel Co., ltd., Wacoal Co.
5
Production process of titanium base alloy
Current production process
New production process
This process is very simple and clean!
This process is very complicated and consumes much energy.
6
Thermodynamics of the new process at 1000°C
② Ti+3M = M3Ti③ TiO2+2H2 +3M = M3Ti +2H2O
In the case of reducing TiO2 to pure titanium
If ΔG°2 is negatively large, it is possible to reduce TiO2 to M3Ti.
ΔG°2 was estimated by the formation enthalpy
and the formation entropy.
It is very difficult to reduce TiO2 to pure titanium by hydrogen.
① TiO2+2H2 = Ti +2H2O 0molkJ563359G 11 >⋅= − ） （.oΔ
When some other metal coexists with TiO2 (In our process) o
2GΔo
3GΔooo
213 GGG ΔΔΔ +=
The Gibbs energy is positively large.
)( ff TΔΔΔ SHG2 −=o
7
1 2 3 4 5 6 7 8 9 10 11 12 13 14
-300-200-100
0100200300
Pt
Ni
2 3 4 5 6
ΔH
f / k
J･m
ol-
1
Pb
AlGaInTl
ZnCdHg
CuAgAu
NiPdPt
Per
iod
CoRhIr
FeRuOs
MnTcRe
CrMoW
VNbTa
TiZrHf
ScYLa
BeMgCaSrBa
LiNaK
RbCs
Group
Pt<Pd<Ir<Rh<Au<Ru<Al, Os<Be, Ni, Tc
Estimate the formation enthalpy of M3Ti （ΔHf）
The order of the formation enthalpy is as follows.
8
Estimate the formation entropy of M3Ti (ΔSf) at 1000°C
The formation entropy of typical M3Ti is as follows
Comparing the value of ΔHf, the value of TΔSf is not so large that it does not affect the order of ΔG°
2.
ΔG°2 can be estimated by the formation enthalpy of M3Ti.
Al3Ti Ni3Ti Pt3Ti
ΔHf / kJ mol-1 -182.310 -152.205 -341.833
−TΔSf / kJ mol-1 27.755 39.615 42.663
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The metals chosen in this study
•Platinum （Pt）; it has the negatively largest value of ΔHf.
•Nickel （Ni）; it has relatively large negative value of ΔHfand the alloy is practical.
10
Outline
• Introduction• Reduction of titanium oxide to Ti-Pt alloy• Reduction of titanium oxide to Ti-Ni alloy• Summary
11
Thermodynamic estimation of the possibility of the process
It is possible to reduce TiO2 to Pt3Ti by hydrogen.
logpO2at Pt/Pt3Ti/TiO2 equilibria > logpO2
at H2/H2O equilibria
12
Experimental 1; Reduction by hydrogen
SamplePrepared by mixing TiO2 (rutile type) powder and Pt powderto the atomic ratio of 1 : 3 by ball milling
Flow rate100 ml min-1
Reduction Temperature1000℃
AnalysisX-ray Diffraction (XRD); identify products
Set-up
13
The results of reduction by hydrogen at 1000 °C
20 40 60 80
TiO2PtPt3Ti
Inte
nsity
/ a.
u.
2θ / degree (Cu-Kα)
(b) After reduction at 1000 oC
(a) Before reduction
X-ray diffraction pattern
TiO2 is reduced to Pt3Ti by hydrogen!
The XRD peaks of TiO2 disappeared and that of Pt3Ti appeared at this temperature.
14
Outline
• Introduction• Reduction of titanium oxide to Ti-Pt alloy• Reduction of titanium oxide to Ti-Ni alloy• Summary
15
Thermodynamic estimation of the possibility of the process
It is difficult to reduce TiO2 to Ni3Ti by hydrogen.
logpO2at Ni/Ni3Ti/Ti2O3 equilibria < logpO2
at H2/H2O equilibria
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Enhance reduction ability of hydrogen
The hydrogen plasma has higher reduction abilitythan the hydrogen molecule.
700 800 900 1000 1100 1200 1300 1400-60
-40
-20
973 1073 1173 1273 1373 1473 1573 1673
H/H2O, p
H2O=10-2
Ni/Ni3Ti/Ti
2O
3
Huet, et. al.
H2/H
2O, p
H2O=10-4
H2/H
2O, p
H2O=10-2
Temperature / K
log(p O
2 / at
m)
Temperature / oC
Possibility of hydrogen plasma reductionHydrogen plasma consists of mainly monatomic hydrogen,and partially proton, electron, and so on.
17
Experimental 2; Reduction by hydrogen plasma
SamplePrepared by mixing TiO2 (rutile type) powder and Ni powderto the atomic ratio of 1 : 3, and then, forming to pellet.
Hydrogen plasmaGenerated by RF plasma equipment
Sample temperature800 °C
Treatment timePressure[Pa]
H2 flow rate[ml min-1] [min]
Microwave power[W]
100 100 3601500
AnalysisGrazing Incidence X-ray Analysis;identify products on the surface of samples
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The results of reduction by hydrogen plasma at 800 °C
20 30 40 50 60
(b) After reduction at 800℃
(a) Before reduction NiTiO2Ti2O3
Inte
nsity
/ a.
u.
2θ / degree (Cu-Kα)
(a) Before
(b) After
The color of the surfacechanged to black.
TiO2 on the surface was reduced to Ti2O3but Ni3Ti was not obtained by hydrogen plasma at 800 °C.
Grazing incidence X-ray analysisPhotograph
The peaks of Ti2O3 appeared,but the peaks of Ni3Ti did not appear.
1 cm
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Estimate the oxygen potential of hydrogen plasma
700 800 900 1000 1100 1200 1300 1400-60
-40
-20
973 1073 1173 1273 1373 1473 1573 1673
pH2
=1
H/H2O, pH2O=10-2
This work (Hydrogen plasma)Ni/Ni3Ti/Ti2O3
Huet, et. al.
H2/H2O, pH2O=10-4
H2/H2O, pH2O=10-2
Temperature / K
log(p O
2 / at
m)
Temperature / ℃
The oxygen potential of hydrogen plasma takes almost the same potential value required for Ni3Ti.
20
700 800 900 1000 1100 1200 1300 1400-60
-40
-20
973 1073 1173 1273 1373 1473 1573 1673
pH2
=1
H/H2O, pH2O=10-2
This work (Hydrogen plasma)Ni/Ni3Ti/Ti2O3
Huet, et. al.
H2/H2O, pH2O=10-4
H2/H2O, pH2O=10-2
Temperature / Klo
g(p O
2 / at
m)
Temperature / ℃
As next work…
Raise reduction temperature
Optimize plasma condition
21
Outline
• Introduction• Reduction of titanium oxide to Ti-Pt alloy• Reduction of titanium oxide to Ti-Ni alloy• Summary
22
Summary
1. TiO2 coexisting with Pt was reduced to Pt3Ti by hydrogen at 1000 °C.
2. Ti-Ni alloy was not formed by hydrogen plasma reduction.
3. TiO2 was reduced to Ti2O3 by hydrogen plasma at 800 °C.
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End
Thank you for your attention !
