Separation of Ultra High Purity Alpha Titanium Sponge...

Separation of Ultra High Purity Alpha Titanium Sponge (>98%) from

Titanium dioxide by Direct Reduction

*Jeya Ephraim and Raj Patel

School of Engineering and Informatics, University of Bradford BD7 1DP

[email protected]

Introduction:

The extraction of highly reactive metals is challenging and requires expensive electrolysis

methods. Titanium, a reactive metal, has desirable properties (light weight and strength), but

its usage is limited due to its exorbitant processing cost.

The current industrial production methods reduce titanium tetrachloride with magnesium

(Kroll’s process)1,2 or sodium (Hunter’s process)3 to produce titanium metal. Kyto University

in Japan was focussed on studying the thermodynamic properties of the titanium – oxygen

system at high temperature 4-6, the calciothermic reduction of titanium dioxide (TiO2)7-10, the

deoxidation of titanium by calcium halide flux11-12 and the electrochemical de-oxidation of

titanium13. Several authors attempted to reduce titanium dioxide directly using electrolytic

process in fused CaCl214,15. Oki and Inoue16 converted directly cathodic TiO2 powder into

titanium metal using fused CaCl2 electrolyte and a carbon anode. However they did not

achieve sufficient purity. Despite decades of on-going research, a cheaper production route

has not been found. The FFC process17, 18, electrochemical de-oxidation of metal oxide in

molten salt, is still undergoing refinement for complete removal of oxygen. Several

researchers have attempted electro-deposition of titanium from ionic solutions but have faced

difficulties in eliminating multivalent titanium ions and highly reactive dendrite products 19,20.

Here we report, for the first time, the direct de-oxidation of titanium dioxide with calcium

metal, under suitable conditions, to form solid titanium sponge metal (> 98% pure) without

any oxygen impurity. On analysing the phase diagram of Ca-Ti-O at high temperature, it is

found that there exists a solid titanium phase at around 1173 K and the Gibbs free energy at

that temperature was around -289.8 kJ/mol. The existence of solid phase was further

confirmed from Factsage software21.

Experimental Method:

Having understood the stability of titanium dioxide for reductants, a suitable chamber was

designed for the reduction study. Laboratory grade titanium dioxide (anatase 99.7% –

crystallite size 10 to 15 nm) was mixed with calcium metal homogeneously, at suitable ratios, and

then dried. The dried sample was transferred to a stainless steel crucible, specially designed for this

purpose, and reduced between 1123 and 1223K in a chamber where a partial pressure could be

maintained. The chamber temperature was increased at a rate of 10 K/min from room temperature to

reaction temperature. After reducing it for 5 hours, the sample was cooled to room temperature. It was

then leached for 2 hours with water and subsequently washed in very dilute acid. The sample was

dried and analysed for the titanium content using XRF (Oxford ED2000 XRF), XRD (Bruker D8

diffractometer; wavelength of X-rays 0.154 nm Cu source, Voltage 40kV, filament emission 30 mA),

SEM-EDX (FEI Quanta 400 Environmental SEM with Oxford Instruments Energy Dispersive X-Ray

Microanalysis) and Raman spectroscopy (Renishaw InVia Raman Microscope with 785, 633 and 514

nm excitation).

Results and Discussions

The wet chemical analysis and XRF analysis shows that the purity of titanium sponge obtained was in

the range 98.5 – 99.4%. During the presentation the XRF pattern of the prepared sponge will be

compared with that of standard titanium in detail. Both patterns are almost identical with an

exemption of trace impurities such as iron, aluminium, phosphorous, etc in the prepared sponge which

is expected from the anatase (impurities). None of the prepared samples showed any oxygen

impurities showing > 98% purity. Both Kα and Kβ peaks are significant and the particle size changed

from nano to micron meters (Fig 1a & 1b).

Fig 1a XRF of the prepared sponge Fig 1b. XRF of standard Titanium

On phase characterisation using XRD (Fig 2a & 2b) it was found that homogeneous α-

titanium was produced where all the d values corresponded to the α-titanium phase and its planes

(010) (002) (011) (012) (110) (103) (112) (201) were identified, without the presence of any Magneli

phases as impurity. The titanium sponge produced has crystallite sizes up to 200 µm and the lattice

parameters were found to be a = 2.95 Å and c = 4.688 Å which is in very close agreement with the

literature values of a = 2.9508 Å and c = 4.6855 Å for standard titanium. The diffraction pattern

obtained shows that the sample is pure and crystalline with homogeneous α-titanium. Alpha titanium

has lower strength than β-Ti, which makes the former an ideal raw material for the production of

alloys and compounds. The characteristics of this phase are low to medium strength, good notch

toughness, reasonably good ductility, excellent mechanical properties at cryogenic temperatures and

high corrosion resistance. The crystalline structure of α-titanium is stable from room temperature up

to 1160 K. Above this temperature it is transformed to β-titanium which is harder, stronger and less

ductile at room temperature.

Fig. 2a XRD of the titanium sponge (all peaks Fig 2b XRD of TiO2 (anatse) used for the Corresponds to alpha titanium phase reduction

The SEM micrograph for the prepared sponge, prior to leaching with water, shows the presence of

titanium nodules (bright areas) and calcium oxide (grey areas). The EDX analysis confirms the

presence of calcium and oxygen along with titanium (Fig 3a & 3b). After leaching the reduced sample

with water, followed by drying, the morphology studies (SEM) showed a honey-comb structure and

the corresponding EDX analysis confirmed the presence of high purity titanium (98.62%) and traces

of phosphorus (Fig 4a & 4b).

Fig 3a SEM of reduced TiO2 with calcium Fig 3b Corresponding EDX

Titanium

Operations: Import

Titanium - File: Titanium.raw - Type: 2Th/Th locked - Start: 20.000 ° - End: 90.000 ° - Step: 0.020 ° - Step time: 0.5 s - Temp.: 25 °C (Room) - Time Started: 11 s - 2-Theta: 20.000 ° - Theta: 10.000 ° - Chi: 0.00 ° - Phi: 0.

Lin

(C

oun

ts)

0

100

200

300

400

2-Theta - Scale

20 30 40 50 60 70 80 9

d=2.

5603

3

d=2.

3767

1

d=1.

7435

5

d=1.

4811

8

d=1.

3499

3

d=1.

2582

1

d=1.

2393

4

d=1.

1300

2

d=2.

2549

6

Titanium oxide

Operations: Smooth 0.150 | Fourier 20.000 x 1 | Fourier 20.000 x 1 | Import

Titanium oxide - File: Titanium oxide.raw - Type: 2Th/Th locked - Start: 20.000 ° - End: 90.000 ° - Step: 0.020 ° - Step time: 0.5 s - Temp.: 25 °C (Room) - Time Started: 12 s - 2-Theta: 20.000 ° - Theta: 10.000 ° - Chi: 0.0

Lin

(C

oun

ts)

0

10

20

30

40

50

60

70

80

90

100

110

120

130

2-Theta - Scale

20 30 40 50 60 70 80 9

d=3.

5072

4

d=2.

3782

2

d=1.

8932

7

d=1.

6804

4

d=1.

4813

0

d=1.

3413

8

d=1.

2626

4

Fig 4a SEM of the titanium sponge obtained Fig 4b Corresponding EDX after reduction and leaching The Raman spectroscopy for Ti sponge did not show any scattering peak which indicates that the

sponge obtained is in the pure form. Theoretically, in metals the surface molecules are Raman inactive

because the incident light is completely reflected with no polarisation of the crystal lattice i.e lack of

vibration, stretching or bending of the bonds. On the other hand, the spectra for TiO2 is Raman active

due to the presence of O-Ti-O bonds which are susceptible to movement (Fig 5a & 5b).

Fig 5a Raman Spectroscopy of TiO2 used for reduction Fig 5b Raman Spectroscopy of Ti sponge Obtained after reduction

Conclusion: The presentation will includes the results and interpretations obtained using

quantitative analysis, XRF, XRD, particle size analysis, SEM – EDX and Raman

Spectroscopy. The process is simple and rapid compared to conventional routes and should

result in massive reduction of production costs. The energy required for producing a kilogram

of titanium is calculated to be 3500 kJ. This approach should also be applicable for producing

a wide range of other reactive metals.

SEM of titanium sponge produced after reducing titanium dioxide with calcium and the corresponding EDX

References:

1. Direct reduction processes for the production of titanium metal, National Materials Advisory Board (NRC), NMAB – 304 (1974), 80

2. Foundation Nicolas Lanners, ed., William J. Kroll: A Luxembourg Scientist, (Luxembourg, 1998), 64

3. Fathi Habashi, ed., Handbook of Extractive Metallurgy vol II, (Wiley – VCH, 1977) 1129 – 1180

4. S. Miyazaki, T. Oishi, and K. Ono, Proc. 5th Intern. Conf. on Titanium (Deutsche Gesellschaftfuer Metallkunde E.V. Oberursei, Germany: 1984), pp. 2657–2663.

5. K. Ono and M. Miyazaki, J. Jpn. Inst. Metals, 49 (10), (1985), pp. 870–875. 6. T.H. Okabe et al., Materials Trans. Jpn. Inst. Metals,32 (5) (1991), pp. 485–488. 7. K. Ono, Molten Salts, 31 (3) (1988), pp. 222–240. 8. R.O. Suzuki et al., Proc. 6th World Conference on Titanium 1988, vol. II (Cannes,

France: Socièté Française de Métallurgie, 1988), pp. 701–706. 9. K. Ono et al., Tetsu-to-Hagané, 76 (4) (1990), pp. 568–575. 10. K. Ono and R.O. Suzuki, Proc. Emerging Technology for Metals Production, ed.

P.R. Talor (Warrendale, PA: TMS, 2001), pp. 79–88. 11. T.H. Okabe et al., Proc. of Inter. Conf. of Titanium Products and Applications,

Titanium 1990 (Titanium Development Association, 1991), pp. 822–829. 12. T.H. Okabe et al., Tetsu-to-Hagané, 77 (1) (1991), pp. 93–99. 13. T.H. Okabe, T. Oishi, and K. Ono, J. Alloys Comp., 184 (1992), pp. 43–56. 14. T.H. Okabe et al., Metall. Trans. B, 24B, (1993), pp. 449–455. 15. 12. M. Nakamura et al., Proc. Intern. Symp. Molten Salt Chemistry and

Technology (1993), pp. 529–540. 16. T. Oki and H. Inoue, Mem. Fac. Eng., Nagoya Univ., 19 (1) (1967), pp. 164–166. 17. G.Z. Chen, D.J. Fray, and T.W. Farthing, Nature, 407, (21 Sept. 2000), pp. 361–

364. 18. 15. D.J. Fray, JOM, 53 (10) (2001), pp. 26–31. 19. Froes, F. H. Titanium and other light metals: let's do something about cost. JOM (1998),

50, 15. 20. Hartman, A. D., Gerdemann, S. J. & Hansen, J. S. Producing lower-cost titanium for

automotive applications. JOM (1998) 50, 16–19. 21. http://www.crct.polymtl.ca/factsage/fs_reaction.php

Jeya Ephraim DrMay 19-21, 2014 • Hilton Sorrento Palace, Sorrento, Italy

Separation of Ultra-high Purity Alpha Phase Titanium Sponge (>98%) from Titanium dioxide (anatase) by Direct

Reduction


ObjectiveTo produce ultra pure high grade titanium sponge without any oxygen impurity


OutlineIntroductionState of artExisting technologiesBradford ProcessResults and discussion (wet chemical, XRF, XRD, SEM‐EDX and Raman spectroscopy)Energy comparisonScale upConclusion


Introduction Titanium (Ti) is a transition metal, a lightweight, silver-gray material atomic number of 22 and an atomic weight of 47.90. It has a density of 4510 kg/m 3 , which is somewhere between the densities of

aluminium and stainless steel. It has a melting point of roughly 3,032°F (1,667°C) and a boiling point of

5,948°F (3,287 C). It behaves chemically similar to zirconium and silicon. It has excellent

corrosion resistance and a high strength to weight ratio.

• Ti is extracted from rutile, ilmenite and anatase. These ores are abundantly available in India, Australia, Canada, USA, South Africa





The current process is Kroll process

Metal


LIMITATIONS

Titanium is obtained along with partially reduced chlorides of Ti (TiCl2 and TiCl3). The removal of these chlorides complicates matters and increases the cost of titanium productionThe whole batch requires 2 weeks for completion.

Michal Eshed, Alexander Irzh and Aharon Gedanken, Inorg. Chem., 48, 2009, 7066 – 7069


Market use of Ti is 40% aerospace (aero-engines, aircrafts), 50% industrial (power, chemical pulp and paper, desalination) and 10% emerging sectors (land based military equipment, architectural, sporting goods)

Titanium alloys have outstanding combination of properties including high strength, density 40% less than steel, withstand elevated temperature capability up to 600º C and four times corrosion resistance better than steel.

Current production of titanium is 60000 tonnes/annum compared to 25 million tonnes of aluminium.

Price reduction would lead to much more rapid increase in usage, with long term potential similar to that of stainless steel


Why the cost of production is high?First-Row Transition-Metal-Oxygen Bond Strengths (kcal/mol)

Metal Do(M+-O)Sc 159 ± 7Ti 161 ± 5V 131 ± 5Cr 85.3 ± 1.3Mn 57 ± 3Fe 69 ± 3Co 64 ± 3Ni 45 ± 3


Emerging TechnologiesName/organisation Process

FFC/ Cambridge

Armstrong internationalMER Corp.

SRI internationalIdaho Titanium TechnologiesGinatta

OS processMIR ChemCSIR, South AfricaQubec Fe& Ti (Rio Tinto)EMR/MSEPerform reductionVartechIdaho research foundation

Electrolytic reduction of partially sintered TiO2 electrode in molten CaCl2

Liquid Na reduction of TiCl4 vapourAnode reduction of TiO2 and transport through mixed halide electrolyte and deposition on cathodeFluidised bed reduction of Ti halideH2 reduction of TiCl4 plasma

Electrolytic reduction of TiCl4 vapour dissolved in molten electrolyteCalciothermic reduction of CaCl2

I2 reduction of TiO2 in shaking reactorH2 reduction of TiCl4

Electrolytic reduction of Ti slagElectrolytic cell between TiO2 & liquid Ca alloy reduces TiO2

Reduction of TiO2 by CaGaseous reduction of TiCl4 vapourMechanochemical reduction of liquid TiCl4


Bradford Process


An isothermal section of the phase diagram for the system Ca-Ti-O at 1200 K


TiO2 + 2Ca → Ti + 2CaO -289.8 kJ/molFactsage thermodynamic software also shows the presence of solid Ti at high temperature


ExperimentAbout 12 gms of TiO2 anatase (99.7% – crystallite size 10 to 15 nm) was mixed with 24 gms of calcium metal under suitable conditions. The contents are loaded in a reducing chamber exclusively designed for the experiment. Reduction was carried out for 5 hrs at 900º C under pressure. The reduced contents are leached with 0.05 M HCl for two hrs. Washed and dried.


Wet chemical analysis

Constituents Sample 1 Sample 2 Sample3 Sample4

Titanium 98.78 96.96 98.46 99.1

Calcium 0.7 2.0 1.44 0.88

Aluminium 0.50

Patent GB 1218675.5, Oct 2012


a) XRF patternof titaniumspongeobtainedafterreduction

b) XRF pattern of standard titanium


XRD patterns of TiO2 used for the reduction and the titanium sponge produced.a XRD pattern of TiO2showing all the d-values corresponding to anatase phase and its atomic orbital planes. The d values for alpha titanium phase and the corresponding planes are seen in b. Lattice parameters are a= 2.95 and c=4.688 (literature values are a=2.9508 and c= 4.6855)


Strong peaks at 25° and 48° confirming the anatase phase and its corresponding planes (101), (103), (004), (112), (200), (105), (211), (118), (116) and (220) were identified

(JCPDS No 88-1175 and 84-1286).

All the planes ((010), (002), (011), (012), (110), (103), (112) and (201)) corresponding to the α-titanium phase were identified

(JCPDS No 44-1294).


SEM of anatase and corresponding EDX (10 – 12 nm)


The reduced titanium is indicated by the bright regions whilst the grey area is calcium oxide. b shows the corresponding EDX which shows the peaks for titanium, calcium and oxygen.


Titanium sponge obtained after leaching with 0.05M HCl.


Grain growth from nano size TiO2 particles to micron level Ti metal. a Titanium metal sponge after reduction, at 40X magnification, shows the transformation from nano level TiO2 particles to micron level Ti metal. The maximum grain growth is of the order of 200 microns as seen in b.


Raman spectroscopy for titanium dioxide and the prepared titanium sponge.a) Raman spectrum for titanium dioxide showing the characteristic peaks for anatase. The Raman spectrumof the titanium sponge produced after leaching (b) does not show any significantpeaks, which indicates a metallic structure.


Titanium sponge obtained after reduction was 6.89 gms about 98.6% yield


Energy Comparison

Kroll process – 335000 kJ/kg (Processing time – 2 weeks)FFC process – 125000 kJ/kg (12 – 16 hrs)Bradford process – 3500 kJ/kg (5 hrs)


Scale Up

About 100 g of anatase (TiO2) was mixed with 200g of calcium metal in a cylindrical metal crucible and reduced under vacuum at 900o C for 5 hrs followed by leaching with dil. HCl. The purity of titanium sponge obtained was found to be 98.72%, Ca 0.45% and Fe 0.3%


SEM micrograph and corresponding EDX spectrum of reduced Tio2 obtained after 5 hours of reduction according to the scaled‐up method of the invention


SEM micrograph and corresponding EDX spectrum of titanium sponge obtained after leaching reduced Tio2obtained from the scaled‐up method of the invention

PCT/GB, 2013/052719


Future work

Scale up to around 1 – 5 kg level scale at the University level (spin-out) – communicating with the industries for partnershipDeveloping electrolysis process to recover calciumProduce other metals from their oxides namely zirconium, tantalum, hafnium, niobium, etc


ConclusionAlthough the demand of titanium metal is huge namely in aerospace, implants, desalination, automotives, etc its usage is limited due to the high cost associated with the extraction process

The current processes available produces large quantities of effluents that damage the environment.

Bradford process is quick and does not produce any effluents as it uses a direct reduction of titanium dioxide with calcium metal.

The report obtained from wet chemical analysis shows that more than 98% titanium sponge is produced.

CaO can be sold as a by-product or recovered through electrolysis.

XRD reveals the presence of homogeneous alpha titanium phase SEM – EDX also confirms the high purity titanium sponge without any oxygen impurity


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