Transcript Slide 1

The Guggenheim Museum
Bilbao, Spain., October 1997
The green metal for the
st
21
George Zheng Chen
1. School of Chemical and Environmental Engineering
University of Nottingham
2. College of Chemistry and Molecular Sciences
Wuhan University
Email: [email protected]
century
Which element is the most abundant/plentiful in the earth’s crust?
Which are the next ten?
Which can be used/considered as engineering materials?
Periodic Table of Elements
11
IVB 22 47.88
Ti
d 4.54 mp
6
8
7
5
12
1670oC
3
9
13
1
2 10
4
(O, Si, Al, Fe, Ca, Na, K, Mg, Ti, P, H, C, Mn）
Source: Los Alamos National Laboratory's Chemistry Division, Periodic Table of the Elements
for School Students. (http://pearl1.lanl.gov/periodic/default.htm)
Titanium is as strong as steel,
but 45% lighter.
Titanium's corrosion resistance, low
weight and high strength make it a
material ideally suited for long life cycle
(LLC) offshore applications.
Pressure vessels/reactor manufactured by
Nanjing Baose Titanium Industry Co. Ltd.
Titanium alloys offer much greater corrosion
resistance in comparison with stainless steels
and other metals for applications such as
chemical reactors,
pressure vessels,
gas/liquid transport pipes and
off-shore constructions,
and hence long service life.
1,300, 000 visitors
in the first year.
The exterior of the Museum is
clad with thin titanium plates
that were supplied by Timet.
The Guggenheim Museum
in Bilbao, Spain.
October 1997
Titanium has many aesthetic qualities.
Titanium Q&A
Q: Is titanium a good material?
A: Yes!
As strong as steel but 45% lighter;
60% heavier than aluminium but twice as strong;
highly corrosion resistant;
some stainless steels may have both
properties but are much heavier.
physiologically inert;
aesthetic qualities; .........
Q: Is titanium expensive?
A: Yes, more expensive than most stainless steel.
Q: Is titanium rare on the earth?
A: No!
The 9th most abundant element in the earth's crust;
The 4th structural metal element,
(O, Si, Al, Fe, Ca, Na, K, Mg, Ti, P, H, C, Mn）
More abundant than carbon (coal)!
Q: Is it difficult to produce titanium?
A: Yes, but shouldn't be.
Unsatisfactory process efficiency
 much higher CO2 emission !!
Ways of Metal Production
6e
chemistry:
Fe2O3 + 3/2 C
~ 700 million tonnes / year
electrochemistry:
cathode:
2 Fe + 3/2 CO2
Al
Al3+ + 3e
carbon anode: O2O2- + C
1/2 O2 + 2e
CO + 2e
+1/2 O2
overall reaction:
Al2O3 +3/2 C
6e
2 Al + 3/2 CO2
~ 45 million tonnes / year
CO2
Achievements and Challenges
Comparison of Major Structural Metals
Materials
World Production
Market Prices
steel
stainless steel
~1,200,000,000 tonnes
$100 ~ 150 / tonne
$1500 ~ 3000 / tonne
aluminium
magnesium
~35,000,000 tonnes
~450,000 tonnes
$1500 ~ 2000 / tonne
$1300 ~ 1500 / tonne
titanium
titanium alloys
~60,000 tonnes
$5000 ~ 8000 / tonne
$25,000 ~ 30,000 / tonne
titania (pigment) ~4,200,000 tonnes
$1100 ~ 1500 / tonne
Extraction Energetics (Thermodynamics)
TiO2 = Ti + O2
2/3 Al2O3 = 4/3 Al + O2
2 MgO = 2 Mg + O2
DGo (1000K) = 762 kJ / mol O2
DGo (1000K) = 937 kJ / mol O2
DGo (1000K) = 986 kJ / mol O2
Extraction
energy
increases
Why Is Titanium Expensive?
Titanium has high affinity with oxygen,
not only reacting with oxygen to form oxides,
but also absorbing oxygen to form solid solution.
Production (extraction & refining)
Fabrication (alloying & fabrication)
Operation
Production
(The Kroll Process,
invented in 1940)
Fabrication
Details
Rutile (96% TiO2) or concentrated
TiO2 from Ilmenite (FeTiO3)
Chlorination to TiCl4
Magnesium reduction
Preliminary arc melting with
master alloy addition
Second melting
Fabrication to end products
(e.g. 2.5 cm thick plate)
Cost
4%
($
(£1,200 / tonne)
9%
25%
12%
(£15,000 / tonne)
($
3%
47%
($
(£30,000 / tonne)
The Kroll Process (1)
Carbo-chlorination (~900oC)
Magnesium reduction
(~900oC, some heat from reaction, slow)
source: D. McQuillan and M. K. McQuillan, Titanium, Butterworths Scientific Publications, London (1961).
The Kroll Process (2)
Distribution of Ti metal after magnesium
reduction (cross section view).
10 m
Ti sponge
Vacuum distillation (>1000oC, slow)
source: D. McQuillan and M. K. McQuillan, Titanium, Butterworths Scientific Publications, London (1961). + GZ Chen
The Kroll Process (Summary)
1. Carbo-chlorination (~900oC)
TiO2 (rutile) + 1.5 C + 2Cl2 (g)
= TiCl4 (g) + 0.5 CO2 (g) + CO (g)
C Cl2
2. Magnesium reduction (Metallothermic
reduction)
TiCl4
(~900oC, some heat from reaction, slow)
Mg
TiCl4 (g) + 2 Mg = Ti (sponge) + 2 MgCl2
3. Vacuum distillation (>1000oC, slow)
4. Pneumatic collection
（Ti + MgCl2）
vacuum distillation
5. Electrolytic recycling of by product
(~500oC, molten salt, continuous)
MgCl2 = Mg + Cl2 (g)
Ti
molten salt electrolysis
TiO2 (金红石)
(rutile)
MgCl2
The Kroll Process is a multi-step and batch type pyrometallurgical
process and runs for a couple of weeks to produce a few tonnes of
titanium sponge, even when using a modern reactor (d. & h: ~1.5 & ~8 m).
During his visit in Japan in 1953, Dr.
William J Kroll predicted the
replacement of his invention, the
Kroll Process, by an electrochemical
method in the next 15 years!
(The photo shows Kroll at a vacuum-type highfrequency melting furnace during testing in a
laboratory of KOBE Titanium.)
Source: http://www.kobelco.co.jp/titan/e/history.htm
In later years, Dr. Kroll was quoted many times by saying,
“It might, however, be fair to say, that titanium will be made
competitively by fusion electrolysis within the next 5 to 10
years.” (1959, Extractive Metallurgy Division Lecture, American Institute of Mining,
Metallurgy, and Petroleum Engineers)
Electrolytic Extraction
Conventional concept of electrolysis
Dissolving titanium compounds (e.g. TiCl4 and TiO)
in molten salts
TiCl4 = Ti4+ + 4Cl- or
TiO = Ti2+ + O2Electrowinning titanium from the molten salt solution
(electro-deposition)
Ti4+
+ 4e = Ti or
Ti2+
+ 2e = Ti (cathode)
deposited
Ti
Cl2
Electrolyte +
Ti compound
Advantage: cost = £0.03 (UK) x 6718 = £202 / tonne Ti
energy = nFEW / mM = 6718 kWh/tonne
n: number of electrons transferred (4)
F: Faraday constant (96500 C/mol)
E: voltage of electrolysis (3.0 V)
W: mass of titanium produced (1 t = 106 g)
m: number of joules per kWh (3.6x106 J)
M: molar mass of titanium (47.88 g)
Electrolytic cell for titanium
deposition from a solution of
TiCl2/TiCl3 (0.1~1M) in
0.73 SrCl2 + 0.27 NaCl
(m.p. 565oC, Sr2+ helps
formation of larger crystals).
[M.B. Alpert, F.J. Schultz
and W.F. Sullivan, J.
Electrochem. Soc.,
104(1957)555]
TiCl4 gas
Problems
Redox cycling of the
multi- valent titanium ions
cathode: Ti4+ + e = Ti3+;
Ti3+ + e = Ti2+
anode: Ti2+ = Ti3+ + e;
Ti3+ = Ti4+
Failure of diaphragm
Dendritic deposition
0.73 SrCl2 + 0.27 LiCl (m.p. 565oC)
(Sr2+ helps formation of larger crystals)
Titanium dendrite deposited from a solution
of K2TiF6 in 850-950oC molten NaCl [M. A.
Steinberg, M. E. Sibert, J. Electrochem. Soc., 102
(1955) 641.]
Titanium dendrite deposited from a solution
of TiO in 850-900oC molten CaCl2 [M. E.
Sibert, Q. H. McKenna, M. A. Steinberg, & E.
Wainer, J. Electrochem. Soc., 102 (1955) 252.]
What Can We Do?
Electrolysis of Solid TiO2
before
after
10 m
Cathode:
TiO2 + 4e = Ti + 2O2O2-
3.0 V, 950oC, molten CaCl2
Anode (inert):
Experimentally
2O2- = O2(gas) + 4e confirmed in
Cambridge
Carbon anode:
3O2- + 2C = CO + CO2 + 6e
Electrolysis of an Insulator Oxide:
Separated Electron and Oxygen Transfer at 3PI
3PI: electrolyte-oxide-metal three phase interline (boundary), e.g. (CaCl2 | TiO2 | Ti)
electron
conductor
(Mo wire)
e
O2-
to anode
Oxygen transfer occurs at the oxide
electrolyte interface of the 3PI
metal
metal oxide
particle
(e.g. TiO2)
3PI
electrolyte
(molten CaCl2)
electrolyte
O2-O2-O2-O2-O2-
e e e e e
3PI
3PI3PI
3PI
3PI
3PI
oxide
Electron transfer occurs at the
metal | oxide interface of the 3PI
Consequence:
(1) continuous formation of new 3PI (propagation of 3PI).
(2) electrolytic conversion of insulator oxide to metal.
Dr Chen and the philosopher's stone
Sep 21st 2000
From The Economist print edition
TITANIUM ought to be a gift to engineers. It is light, strong and heat resistant. But gifts are supposed to be free, and titanium is expensive. That is
not because it is particularly rare (titanium dioxide is the basis of white paint) but because it is hard to extract as a pure metal. If George Chen of
Cambridge University and his colleagues are correct, however, that extraction could soon become a lot easier and cheaper.
There are two ways to get metal out of an oxide ore. One is to react the ore with a substance that has a greater affinity for oxygen than the metal in
question, a process known as chemical reduction. The other is to break it up with electricity, a process known as electrolysis. Iron is made
industrially by the first process. Aluminium is made by the second. At the moment, titanium is made by the first, but unlike purifying iron, from
which the oxygen is removed cheaply by reaction with carbon in the form of coke, purifying titanium is a two-stage operation. First, the ore is
heated with carbon and chlorine to produce titanium tetrachloride. Second, the titanium tetrachloride is reduced with either sodium or magnesium.
The result was that the electrode turned from oxide to metal
in a way that would have pleased a medieval alchemist. And
In standard electrolysis, the compound to be broken up is dissolved in a fluid called an electrolyte. Remember those chemistry lessons spent
sticking electrodes
into copper
sulphate solution?
the electrolyte up,
was water.
For thesort
electrolysis
dioxide,that
the preferred
if the
process
canIn thatbecase,scaled
the
ofof titanium
riches
electrolyte is molten calcium chloride. Past attempts, however, have relied on dissolving the tetrachloride (or sometimes the dioxide) into the
molten calcium chloride. These have failed because of the way that titanium atoms behave when they are in such a solution.
alchemists dreamed of might be available.
These reducing agents are more expensive than coke. They require batch processes rather than continuous ones. And titanium tetrachloride is a
volatile, corrosive liquid that is difficult to handle. Metallurgists have thus been searching for years for a way to coax titanium out of its ore by
electrolysis. Dr Chen, who has published his results in this week’s Nature, believes he has found one.
Dr Chen’s calculations showed, however, that it should be possible to reduce titanium dioxide electrically without having to dissolve it. Instead,
one of the electrodes dipped into the calcium chloride is made of solid titanium dioxide. Other chemists have avoided doing this because they
reckoned that solid dioxide is an insulator and therefore could not be electrolysed. But Dr Chen’s observation suggested this electrolysis could
happen because the dioxide becomes a conductor once a tiny amount of oxygen is removed from it.
The result was that the electrode turned from oxide to metal in a way that would have pleased a medieval alchemist. And if the process can be
scaled up, the sort of riches that alchemists dreamed of might be available. For not only titanium could be produced this way. Other expensive
metals, such as vanadium and chromium, could also become cheaper. And by compounding the electrodes out of mixed oxides it may be possible
to create useful alloys in one go, rather than purifying their ingredients separately.
current / A
2.0
Typical
relations
current-time
oxygen insoluble in
metal, e.g. Cr
oxide of multivalent
metal, e.g. Ti, Nb
1.5
1.0
0.5
oxygen soluble
in metal, e.g. Zr
60
120
time / min
180
240
300
360
420
molten CaCl2
metal oxide powder porous cathode
(single or mixed) preforms (pellets)
pellets of
metal oxide
molten salt electrolysis
FFC Cambridge Process
metal powder
powder
metallurgy
metallised pellets
washing in water crushing/milling
conventional
metallurgy
This past March the U.S. Defense
Advanced Research Projects
Agency (DARPA) tapped three
materials research groups to
address this persistent problem.
Agency managers awarded
separate contracts totaling $5
million to Titanium Metals
Corporation (TIMET) and two
others to fund parallel efforts to
develop potentially low-cost
production routes for titanium and
its alloys.
TIMET predicts many titanium uses in family cars.
Source: http://aftermarket.theautochannel.com/articles/2001/01/11/012676.html
The Volkswagen Lupo FSI is being
marketed as the lowest fuel
consumption gasoline car in the world,
achieving 94 miles per gallon.
The Volkswagen Lupo springs,
produced from TIMET’s patented
TIMETAL LCB alloy, contributed to the
180 lb. overall weight reduction
achieved by the FSI model versus the
standard model Lupo.
Similar in strength to steel at half the
weight, titanium is also about twice as
flexible as steel--resulting in spring
designs that are 60 to 70 percent
lighter and offer up to a 40 percent
height reduction compared to
corresponding steel springs, according
to the company.
60 million units per year
150 kg titanium per unit
9 million tonne titanium per year
$4000 per tonne titanium
Market: $36 billion per year
Titanium & Cars
Energy saving
Miles per gallon
Car weight reduction
Vehicle weight / lb
Less emission
Uncompromised safety
Encourage the use of hydrogen storage and fuel cell systems.
A dream of tomorrow
Titanium alloys
Hydrogen fuel cells/Li-ion batteries
Supercapacitors
Zero emission titanium electric cars