A variant of FFC Cambridge process (Fray, 1998) for direct
production of Titanium is presented. The declared intention is to
replace Kroll process (Kroll, 1940).
The method consists in reduction of Ti oxide through an
electro-deoxidation and electro-reduction process, with molten Calcium
chloride as electrolyte.
The cathode is a pressed-sintered disc, consisting in Ti dioxide
The established method is based on the following physical and
--CaO solubility in Calcium chloride is very high (about 20%
moles), making possible the electrolysis process and cathode deposited
Calcium reduces the metal oxide that constitutes the cathode (Fray et
--decomposition voltage of CaO is less than that of Ca[Cl.sub.2],
hereby only CaO electrolysis determines oxygen liberation in anode
(eventually with C[O.sub.2] and CO forming), avoiding gaseous Chlorine
liberation. Concomitantly, by Oxygen consuming during electrolysis,
through dissolved CaO re-establishment (Ca solubility in Ca[Cl.sub.2] is
about 4% mol), the chemical composition of the electrolyte maintains
quasi-constant, with a favorably influence on the electrochemical
--high affinity of Ca for Oxygen allows the advanced reduction of
the Oxygen content in cathode, towards level of ppm, enabling high
quality alloys obtaining.
The procedure bases are the flowing electrochemical processes,
expressed as characteristic reactions (Chen et al., 2000; Chen &
Fray, 2000; J.F Suzuki et al., 2003, Suzuki, 2005):
--deoxidation of Ti[O.sub.2] through contained Oxygen ionization as
a result of applied voltage on the electrodes.
1/2[O.sub.2] + [2.sub.e.sup.-] = [O.sup.2-] (1)
2Ca[Cl.sub.2] + [O.sup.2-] = 2CaO + 2[Cl.sup.-] (2)
[Me.sub.x][O.sub.y] + [2.sup.e-] = xM + y[O.sup.2-] (3)
--calciothermic reduction of the oxides through the action of
deposited Ca on cathode, as a result of the dissolved CaO electrolysis
in Ca[Cl.sub.2] electrolyte.
[FIGURE 1 OMITTED]
CaO = [Ca.sup.2+] + [O.sup.2-] (4)
2[O.sup.2-] [right arrow] [O.sub.2] (gas) + 2[e.sup.-] (5)
[O.sub.2] + C = C[O.sub.2] (or CO) (6)
yCa + [Me.sub.x][O.sub.y] = xMe + yCaO (7)
2. EXPERIMENTAL PROCESS EVOLUTION
The experimental installation for electro-reduction process (fig.
1) consists mainly in a crucible (Silicon and Aluminum oxy-nitride) that
contains the electrolyte (Calcium and Sodium chloride), having an anode
(super dense graphite) and a cathode (pressed/sintered disc of Titanium
dioxide to be reduced). All of them are included in a heating furnace to
assure the necessary thermal conditions.
The electrochemical process develops in two stages (fig. 2). In the
first stage the electric potential is 2.6 V (less than CaO decomposition
voltage); during this stage current intensity constantly decayed (fig.
2). In the second stage the voltage was increased to 3 V (less than
Ca[Cl.sub.2] decomposition voltage, to avoid gaseous Chlorine
appearance), with an initial current intensity of about 3.7 A. The time
current intensity decay was more abrupt in the second stage (fig. 2).
Entire process develops at 850[degrees]C. The main process parameters
are listed in Table 1.
[FIGURE 2 OMITTED]
After electrolyte removal and disc extraction from cathode holder,
disc was washed in a slightly acid solution (pH = 2+4) and physical,
chemical and structural analyzed. Dimensional measurements of discs
before the electrochemical reduction process are presented in Table 2.
Chemical analysis on samples assayed from plane surfaces of discs,
in depth towards 1 mm, (Table 3), demonstrates the success of this
direct obtaining method; the Titanium content can be raised further, by
raising the cathode discs porosity.
SEM and EDAX analysis of the sintered cathode after electrolysis
was performed to reveal the structural aspects (fig. 3) and to determine
phase composition on the analyzed surface (fig. 4) for the sample C. It
is also obvious the advanced reduction of Titanium oxide to metallic
In the first stage of the electrochemical process, the current
intensity decay can be explained through the corresponding decay of
dissolved Oxygen in melted electrolyte by its discharging at anode. The
same phenomenon, in the second stage of the electrochemical process, can
be explained through the raise of the ions quantity in the melted
electrolyte, as a result of dissolved CaO decomposition.
[FIGURE 3 OMITTED]
[FIGURE 4 OMITTED]
The experimental data demonstrate the possibility to obtain high
purity Ti through an electrochemical process of deoxidation--reduction
of Titanium oxide as follows:
--deoxidation of metal oxide through Oxygen ionization, developed
at voltages about 2.0 / 2.5 V,
--calciothermic reduction of the oxide through the action of Ca
deposited at the cathode as a result of electrolysis of the dissolved
CaO into electrolyte, at voltages of 2.7 / 3.0V.
Through successive deoxidation processes, starting from Oxygen
ionization from oxide, followed by its reduction with Calcium originated
from the electrolysis of dissolved CaO in the electrolyte, the duration
of alloy obtaining is reduced to about 4 hours, comparing with minimum
15 hours necessary to obtain the alloy only by deoxidation (Chen et al.,
Oxygen and Calcium diffusion into electrolyte bath and sintered
oxides, respectively, can be accelerated by decreasing height of
sintered cathode and increasing cathode porosity. These precautions can
improve the reduction process kinetics, with its duration decreasing.
In contrast to classical technologies for Titanium (Kroll, 1940),
this experimental process presents spectacular advantages: drastic
adjustment of ample operations number, of process duration, and of
production costs through decrease of energetic and raw materials
This new technology is ecological (the electrochemical process
develops at voltages lower than 3.2V, corresponding to Ca[Cl.sub.2]
decomposition potential), without insult emission (Chlorine and
chlorinated compounds, dust, etc).
Our method is based on cathode porosity control. This is the major
difference from other authors' experiments: the use of porous
sintered oxide cathode allows improving Titanium purity, process
duration minimizing and a better process parameters control.
This procedure can be used other refractory metals and alloys
direct obtaining. We already produced Ti6Al4V, following a similar
procedure starting form Ti, Al, and V oxides.
Chen, G.Z., Fray, J.F., (2000), Novel Direct Electrochemical
Reduction of Solid Metal Oxides to Metal using Molten Calcium Chloride
as the Electrolyte, Euchem 2000 Proceeding, Denmark, pp 157-161
Chen, G.Z., Fray, D.J., Farthing, T.W., (2000), Direct
electrochemical Reduction of Titanium Dioxide to Titanium in Molten
Calcium Chloride, Nature, vol. 407, pp. 361-364
Fray, D.J., Farthing, T.W., Chen, G.Z., (1998), Removal of Oxygen
from Metal Oxides and Solid Solutions by Electrolysis in a Fused Salt,
UK Patent, PCT/GB 99/01781, Inter. Pub. No. WO 9964638
Kroll, W.J., (1940), The Production of Ductile Titanium, Trans. Am.
Electrochemical Society, vol. 78, pp. 35-47
Suzuki, R., (2005), Calciothermic Reduction of TiO.sub.2 and in
situ Electrolysis of CaO in Molten CaCl.sub.2, Journal of Physics and
Chemistry of Solids, volume 66, pp. 461-465
Suzuki, R., Teranuma, K., Ono, K., (2003), Calciothermic Reduction
of Titanium Oxide and in-situ Electrolysis in Molten Ca[Cl.sub.2],
Metallurgical and Materials Transactions B, volume 34 B, pp. 277-285
Tab. 1. Process parameters for samples A, B, and C.
Sample Stage Potential, Current A-C, Duration,
V intensity, A mm min
A I 2.6 3.20 / 0.20 20 160
II 3.0 3.75 / 0.30 200
B I 2.6 3.30 / 0.25 15 160
II 3.0 3.80 / 0.35 190
C I 2.6 3.45 / 0.25 10 160
II 3.0 3.95 / 0.35 180
sintered Surface, g/ Porosity,
Ti[O.sub.2]) [cm.sub.2] [cm.sub.3] %
A 6.25 2.33 44.20
B 6.25 2.34 44.05
C 6.20 2.38 42.85
Tab. 3. Chemical composition of cathodes after
calciothermic reduction process.
Sample Chemical composition, % weight
Ti O Ca Cl Fe
A 95,00 0,70 1,49 2,61 0,20
B 95,30 0,75 1,23 2,46 0,26
C 94,43 0,74 1,56 2,98 0,29