High Temperature Materials and Processes, Vol. 8, No. 1, 1988, 39-46

Ultra Fine Powder from Alloy Resources via Alkoxide. (Resources Chain and Primary Innovation) by Nobuaki Sato and Michio Nanjo

Research Institute of Mineral Dressing and Metallurgy, (SENKEN) Tohoku University, Sendai 980, Japan

CONTENTS Page ABSTRACT 40 1. INTRODUCTION 40 2. FERRONIOBIUM PRODUCTION 40 3. CHLORINATION OF FERRONIOBIUM AND CHLORIDE SEPARATION 41 4. Nb-Ti SUPERCONDUCTOR SCRAP AS Nb SECONDARY RESOURCES 42 5. SYNTHESIS AND SEPARATION OF ALKOXIDES 43 6. PRODUCTION OF ULTRA-FINE POWDER VIA ALKOXIDE 45 7. PROPERTIES OF UFP Nb205 45 8. CONCLUDING REMARKS 46

ISSN 0334-1704 ©1988 by Freund Publishing House Ltd.

39 Vol. 8, No. 1, 1988 Ultra Fine Powder from Alloy Resources via Alkoxide

ABSTRACT The urgent problem is to develop ore processing (first grade purification) to a high level (composition An attempt has been made to combine resource control, super purification) by developing super-refin- chains and primary innovation in high technology ing processes which facilitate process expansion, from fields. Alloy materials from urban mines are discussed alloys to new material applications in high-tech fields. as a new type of rare metal resource. Recovering nio- In this paper, we try to develop a new material, i.e. bium from ferroniobium and Nb-Ti superconducting ultrafine oxide powder (function development) from alloy via chloride methods has been studied. The ferroniobium or Nb-Ti scrap via chlorine metallurgy, production process of alkoxides from alloy resources alkoxide synthesis and purification (organic), and dis- has been investigated. Ultra fine NbiOs powder was cuss the resources and metallurgy for future research. produced by hydrolysis of alkoxides and some proper- ties of the powder are evaluated. 2. FERRONIOBIUM PRODUCTION

1. INTRODUCTION In pyrometallurgy of ores, impurities are usually As rare metals such as Nb, Ta, Zr support the separated between the slag and metal phases. In iron advanced progress of high technology industries, their making, AI2O3, S1O2, MgO are present in slagoff and development for both resource and application has Cr, Co, Cu, Ni, Nb are concentrated in the metal phase become strategic in recent years /1-4/. It is now well /6/. This process corresponds exactly to solvent known that the recent trend of ore-producing coun- extraction from the iron melt to extract valuable tries such as Brazil is to export primary products metals. When applying high temperature solvent instead of raw materials /5/. For example, in Brazil, extraction to rare metal ore processing, i.e. mixing with the biggest niobium resources in the world, concentrate and Al powder, separation of metals they are exporting ferroniobium instead of pyrochlore between slag and melt iron by thermic reduction, this because of the uranium and thorium deposits con- ferroalloy shows a relatively low melting temperature tained in pyrochlore. In the chromium industry, a compared with high temperature refractory metals. similar trend is observed, i.e. ferrochromium exports Ferroniobium is produced from pyrochlore by instead of chromite. In Japan, very new types of high alumino-thermic reduction as shown in Fig. 1. This grade raw material such as ferroalloy can be stocked, ferroniobium contains 60% Nb, 40%Fe, 3% Al and a thus decreasing the need for finance and metallurgy. very small amount of impurities such as Ta, Mn, Ti, Si, Furthermore, secondary resources from production Sn. and waste are also important, and recycling of these resources is imperative.

On the other hand, as compared with the supporting Igniter role in the traditional steel-making; industry, develop- ment of new materials such as the Nb-Ti superconduc- tors, Josephson elements, ceramic catalysts, in which niobium predominates, is now in fashion. In the field Al powder of new material synthesis, ultra-fine oxide powder is Fe?Oi obtained by hydrolysis of chlorides and oxidation in + Thermit Ti.Zr.U.Th^.l Slag phase reduction the vapor phase, but now the "alkoxide process" has Pyrochlore Ferroniobium Metal phase the advantages of homogeneous mixing, monodisper- concentrate (~60%Nb) sion, ultra-fine powder production, easy handling, etc. Also, raw materials for advanced ceramics production Before reaction After reaction are reverting to alkoxides, so that alkoxides have become the "key material" for ceramic production. As

Japan has poor resource deposits, we have to develop Fig. 1: Production of ferroniobium from pyrochlore concentrate. higher level technology, with continuous primary innovations assisting rapid progress in underdeve- loped countries, and a new resource strategy aiming for additional values.

40 Ν. Sato and Μ. Nanjo High Temperature Materials and Processes

3. CHLORINATION OF FERRONIOBIUM AND CHLORIDE Ar gas over FNb powder, dry CI2 gas flowed at a rate SEPARATION of 500 ml/ min. When the pale yellow CI2 gas attacks the ferroniobium powder, a reaction takes place 3.1. Chlorination offerroniobium j7j rapidly as in eq. (1) and the temperature spikes due to exothermic reaction. Stability diagrams for the Fe-Ch and Nb-Ch sys- tems obtained from thermodynamical calculations are Fe-Nb(s) + 4Cl2(g) - FeCl3(g) + NbCls(g) (1) shown in Fig. 2 /8/. By controlling the partial pressure of chlorine gas, selective chlorination producing fer- The dark brown mixture of NbCls-FeCh was vapo- rous chloride and niobium pentachloride is possible. rized and condensed in the traps after producing lower

chlorides. When condensing, NbCl5 tends to deposit at Temperature (°C) lower temperatures, and rough separation obtaining 80 mole % NbCls of mixed chlorides by temperature 600 300200 100 gradient is possible. dimeaimer iFeCiJ 10 3.2. Separation of NbCh-FeCl-s mixed chlorides (s) Cfl 0 ®NbCI5 rn The different methods used for mutual separation of Q. NbCI, (g) Μ NbCls-FeCh are given below. -10 ο a) Simple distillation: CL -20 The vapor-liquid equilibrium for NbCls-FeCls is shown D) in Fig. 4. Mole fraction of NbCI, in vapor phase is Ο -30 always bigger than that of liquid phase. As the mole fraction ratio between both phases becomes close to -40 unity, separation by simple distillation becomes more difficult. Pure NbCl5 of 99.9 mole % is obtained from 987 6 5 4 3 ferroniobium chlorides (63 mole % NbCls) by 15 theo- Temperature (x100K) retical plate.

Fig. 2: Chemical potential diagram of Nb-Ch and Fe-Ch systems.

But low pressure chlorination is not practical from the aspect of productivity. Here, separation of NbCls from FeCh was tried after the ferroniobium chlorina- tion under Pci2 = 1 atm at 300° C. Fig. 3 shows chlori- nation apparatus made of pyrex glass. After flushing

Pyrex glass tube(25mm»)

oft gat ci. Ζ Fe-Nb alloy Condensate _ ^^ 7 II! ^ u Γ ι Ii ι 0 0.2 0.4 0.6 0.8 1.0 Mole fraction of NbCI5 in liquid,χ T.C. ΤΧ. T.C. T.C. T.C. \f7~m Trap

Κ Χ— A Fig. 4: Equilibrium compositions for NbClj-FeClj system.

30 CM IOCM Reaction part Condensation part b) Selective reduction by Iron powder: Fig. 3: Chlorination apparatus. It is better for separation to reduce FeCb to non-

41 Vol. 8, No. 1,1988 Ultra Fine Powder from Alloy Resources via Alkoxide

volatile FeCh by selective reduction, as shown in eq. NbCls is transferred to the "NaCl at 250° C by the (2). following reaction:

2FeCl3(g) + Fe(s) - 3FeCl2(s) (2) NbCl5-FeCl3(g) + NaCl(s) - NaNbCl6(s) +

FeCl3(s) (4) When the NbCls-FeCU mixture reacts with iron

powder, only FeCl3 reduces to FeCl2, producing a Separation by direct chlorination of ferroniobium in a NbCl5-FeCl2 binary system. From distillation after NaFeCU salt bath is also reported (eq. (5), (6)) /9/. selective reduction, the iron content was reduced to

0.07%. Fe-Nb(s) + NaCl(s) +7NaFeCl4(l) -NbCls(g) +

c) Organic solvent method: 8NaFeCl3(l) (5) The separation methods using organic solvent are very

interesting, having the advantages of low temperature, 2NaFeCl3(l) + Cl2(g) -2NaFeCl4(I) (6) homogeneity, easy handling, avoiding hydrolysis, etc.

Using chlorobenzene, selective reduction of FeCl3 is The chlorination of ferroalloys is very easy and possible. The flow sheet for the organic reduction many chloride separation methods have been deve- process is shown in Fig. 5. The reaction of equation (3) loped. Impurities such as Al, Ta, Si, Ti must be inves- proceeds quantitatively at 130°C and the valuable tigated for ultra-high purities since these impurities byproduct of p-dichlorobenzene for insecticides is influence separation. obtained. 4. Nb-Ti SUPERCONDUCTING ALLOYS AS Nb SECONDARY RESOURCES ( Fe-Nb alloy) Recycle ->( HCl ) Γ Recovery of rare metals from Nb-Ti superconduc- Γ<§>— ( C.H.CI ) tor alloys as a secondary resource, and which could be -Κ C.II.CI, ) ( FeCl,-NbCI, ) an important Nb alloy, has been attempted. C404IO (447ΙΟ Solution Selective 1 st step 2nd step a) Characterization of Nb-Ti Alloy Scrap: Reduction Distillation >( NUCI, ) C403K3 ^Precipitate Nb-Ti superconductor is produced by 1) Assem- Fe,0, ) bling OFC pipe and Nb-Ti rod into a single core wire, 2) Wire drawing, 3) Assembling billet for multi-core

Fig. 5: Flowsheet for recovery of NbCI5 by chlorobenzene. wire, 4) Wire drawing, 5) Heat treatment, 6) Enamel insulation, 7) Inspection and testing /10/. But almost 90% of Nb-Ti scrap becomes multi-filament wire for testing. Fig. 6 shows the cross-section of multi-

2FeCl3 + C6H5C1 - 2FeCl2 + C6H4C12 + HCl (3) filament wire of 2.6mm diameter. Ultrafine wire of Nb-Ti alloy is· observed between the internal and Another NbCls does not react with chlorobenzene. external Cu. Stripping of Cu by anodic oxidation was Furthermore, large differences of chloride solubility in first tried as for electro-refining of Cu, after which chlorobenzene enable better separation (NbCls:460, separation of Nb and Ti using chloride was attempted.

FeCl5:5, 0, FeCl2:0.3mg per 100 g C6H5C1 at 30°C).

After the separation of selectively reduced FeCl2, b) Cu Stripping:

C6H5C1 and C6H4C12 are distilled at 130°and 180°C respectively, and pure NbCls of low ppm Fe content When the Nb-Ti wire was placed on both anode and

can be recovered. cathode sides in a H2SO4 and CuS04 electrolyte, disso- lution of anode Cu and Cu deposition on the cathode d) Separation with NaCl: was observed. The 6 steps of stripping Cu from alloy

Mutual separation of NbCls-FeCl3 is also possible by are shown in Fig. 7. They are I) Outside Cu dissolu- complex formation with NaCl. When ferroniobium tion, III) Dissolution of clad Cu on Nb-Ti wire, V) chlorides and NaCl are separated in a pyrex glass cell, Dissolution of centered Cu. After anodic dissolution,

42 Ν. Sato and Μ. Nanjo High Temperature Materials and Processes

OFC pipe Temp, CC) .70π—ι—0 50ι 0 r 300 100 Nb-Ti filament KbCli(s) NbCls(s)

Γτϊόί,Τϋ] , ite

Cladding OFC

OFC stabilizer

1 I mm

Fig. 6: Cross section of the multi-filament wire. Γ 700 500 300 Temp, (K)

Fig. 8: Chemical potential diagrams of Nb, Ti, Cu-Ch systems.

recommended because of the formation of non-volatile Cu chlorides. Chlorination of Nb-Ti wire was conducted in the same manner as for ferroniobium chlorination. After Cu separation the fine Nb-Ti wires were put in an inner quartz tube. After argon flushing and heating up to 300° C, chlorine gas was introduced into the tube. As the chlorine gas attacked the wire, a rapid and violent reaction occurred,

Nb-Ti(s) + 912Cl2(g) - NbCl5(s) + TiCU( 1) (7)

According to eq. (7), NbCls vapor condensed as solid in the trap maintained 135°C and TiCU vapor condensed as liquid in the ice-cooled trap, respectively. Fig. 7: Change of current and potential during anode oxidation. It is possible to recover pure chlorides from Nb-Ti alloy by chlorination. Though the chlorination of Nb-Ti only pure Nb-Ti wire was obtained as an anodic slime. wire has the advantages of low temperature and For industrial operation, improvements such as anode oxychloride-free chlorination, reaction control of compacting and wire recovering are necessary. chlorination in salt baths must be considered for industrial operation. c) Chlorination of Nb-Ti alloy: 5. SYNTHESIS AND SEPARATION OF ALK.OXIDES Chemical potential diagrams of Nb, Ti and Cu-Ch systems are shown in Fig. 8. Though niobium and It is very important to develop new processes to Titanium have many chlorides, only NbCls and TiCU produce valuable added material from cheap raw are produced under 1 atmospheric pressure of chlorine materials. The synthesis of alkoxides /ll/, which k gas at 300° C. Chlorination of Cu clad multiwire is not the key material for advanced material production,

43 Vol. 8, No. 1, 1988 Ultra Fine Powder from Alloy Resources via Alkoxide

was attempted, using cheap ferroniobium. Usually, Preparation of Metal alkoxides metal alkoxides are synthesized by the reaction between ml + nROH + nNH, metal chlorides and alcohol in benzene. Two types of Nb alkoxide synthesis from ferroniobium, as shown in V III Fig. 9 were tried. 1) Synthesis of mixed alkoxides from Η • Nb and Fe mixed chlorides, 2) Synthesis of alkoxides after chlo- R · i-Pr and n-Bu ride distillation.

Ferroniobium

Chlorination

NbCIs-FeCIa Ar CI] [Π] ROH.NH3

NHiCI • •lb(QR)i -Fe(OR); I Disti 11 at i on) > FeCli I Fe(0R)3 jI Distillation] NbCIs ROH.SH,

•MHiCl t NbfOR).

Hydrolysis I

UFP HbgOs Stirrer

Fig. 9: Production flowsheet from ferroniobium to NbiOs via Fig. 10: Experimental apparatus for alkoxide synthesis. alkoxide.

The experimental apparatus for alkoxides is shown Nb(OR)5. The analytical results for n-butoxide are in Fig. 10. The chlorides used are NbCl5-FeCl3 mixed shown in Table 1. chloride (Fe: 12.3%) from ferroniobium chlorination (I), crude NbCb Fe,680ppm) (II) and pure NbCIs Table; Removal of Fe and Ta using niobium butoxide. (Fe:92ppm) (II): from mixed chloride distillation. In Starting FNb 1chloride s Distilled Distilled an argon atmospheric glove box, chlorides were dis- chlorides (I) NbCIs (II) NbCIs (II) solved in benzene. Then an equal amount of alcohol was added slowly while stirring. When gaseous Fe Ta Fe Ta Fe Ta ammonium was bubbled into the benzene, white (%) (ppm) (ppm) (ppm) (ppm) (ppm) NH4CI was precipitated. The reactions are as follows.

Raw material 12.3 2900 680 670 92 510

NbCls(s) + 5ROH(l) + 5NH3(g) - Nb(OR)s(l) NH4CI ppt 7.5 36 420 160 52 130

+ 5NH4Cl(s) (8) Crude NtKOR)s 1.8 640 155 350 35 260 Distillate 0.7 460 4 250 6 220

FeCl3(s) + 3ROH(l) + 3NH3(g) - Fe(OR)3(s)

+ 3NH4C1(S) (9) Where mixed chlorides were employed (I), a dark (R = i-Pr, n-Bu) brown precipitate was observed during the flow of NHj gas. This product is an insoluble compound,

After filtration or centrifugal separation of the precipi- Fe(Bu")xCl3-x(NH3)y and iron was almost produced at tate, crude Nb (OR)s was obtained with recovering this stage. After the distillation of alkoxides under 0.04 benzene and alcohol by distillation. The pure Nb(OR)s torr at 187°C, little iron remains, so that system (I) is was recovered by sublimative purification of crude not suitable for economical processing.

44 Ν. Sato and Μ. Nanjo High Temperature Materials and Processes

n In the case of crude NbCls path (II), as the iron Nb(0Bu )s Hz0 content decreased very pure Nb (OR)j was obtained (0.2M in n-BuOH) (IM in n-BuOH) indicating the effectiveness of organic purification via distillation. When pure NbCls was used (II)', the same purification effect was obtained. FiItration Fi Itration On the other hand, effective separation of Ta was 0.2/im 0.2 At ra not observed even if the Ta content decreased slightly. The recovery rate of Nb was 87%, and further separa- tion from precipitate must be done on an industrial scale. When iso-propoxide was used, the same result was Hydrolysis obtained. The white solid of Nb (OPr')5 from the crude NbCls(Fe:680ppm) contained lOppm of Fe and 150 ppm of Ta, and purification by sublimation was also White ont effective.

6. PRODUCTION OF ULTRA-FINE Nb205 POWDER Centrifugal settl i ng Oxides, hydroxides and hydrates are easily pro- duced by hydrolysis of metal alkoxides /12-14/. As / alkoxides are easy soluble in alcohol, the alkoxide Wash i ng (HaG) method has the advantages of producing mixed, monodispersed oxides with high pruity. Production of ultrafine Nb20s powder from ferroniobium via Heating at 130"Ό,11ιγ Nb(OBu")5 was tried. The production flowsheet for Oryi ng or n Evacuation at R.T. Nb2Os from Nb (OBu )5 is shown in Fig. 11. After the filtration of both dehydrated n-BuOH solutions of Nb n (OBu )s and H2O with o.2 μπι membrane filter, UF? Nb?0s hydroxidation was produced by mixing two solutions. After centrifugal separation, washing, and drying, Fig. 11: Preparation of Nb20; powder from Nb (OBu°)5 homogenous, monodispersed UFP Nb205 with 0.2 μηι mean diameter was obtained. The SEM profile is shown in Photo 1.

7. PROPERTIES OF UFP Nb2Os > χ

Some properties of UFP Nb20s produced in section PZC = 3.3 5 were studied. From results of differential thermal V> analysis, a broad endothermic peak with weight decrease at 100° C corresponding to dehydration, and a sharp exothermic peak corresponding to transfor- mation, were observed. The structural results from <\ \o x-ray powder diffraction are amorphous at R.T., γ-

Nb205 (orthorhombic) after heating to 600° C and a-

Nb2Os (monoclinic) after the 1050°C heating. Fig. 12 shows the result of zeta potential measure- -3 1 1 1 1 2 3 4 ment. The point of zero charge is at pH 3.3, and this pH point is very important for avoiding agglomeration of ultra-fine powders on hydrolysis. Fig. 12: Electrophoretic mobility of Nb2Os powders obtained from Nb (OBu")5 vs pH.

45 Vol. 8, No. 1, 1988 Ultra Fine Powder from Alloy Resources via Alkoxide

development will be able to maintain the high techno- logical level against competition.

ACKNOWLEDGEMENTS

The authors are very thankful to the members of the electrometallurgy division for their support. The authors also wish to thank Mr. Y. Sato for technical support from ΕΡΜΑ.

REFERENCES

1. Min. Trade and Industry: "Rare Metal and High Technology", Nikkan Kogyo, (1982), 225. 2. Metal Mining Agency: "Rare Metal Data Book, Niob", (1985). 3. Kinzoku Jihyou: "New Metal Data Book", Format Ado, (1986), 445. 4. Μ AN JO, M. and SATO, N„ Senken Iho, 42: (1986), 204. 5. NANJO, M. and SATO, N., Kinzoku, (1987), 21. 6. METALLURGY Series, "Ferrous Metallurgy", (1980), 98. 7. SATO, N. and NANJO, M.; Mel. Trans, 16B: (1985), 639. 8. BARIN, L; KNACK, O. and KUBASCHEWSKI, O., Ther- modynamical Properties of Inorganic Substances, Supple- ment, Springer Verlag, (1976). 9. ROCKENBAUER, W„ Proceeding of the Int. Symp. on Nio- I 1 bium, (1983), 133. 0 1.50um 10. SAKAI, S., HITACHI CABLE REVIEWS, 4: (1985), 43. 11. BRADLEY, D.C., MEHROTRA, R.C. and GAUR, D P.,

Photo 1: SEM profile of Nb20, powder from NtyOBiOs. "Metal Alkoxides", Academic Press, (1978). 12. OZAKI, Y„ Ceramics, 16: (1981), 1570. 13. OZAKI, Y„ ibid., 21: (1986), 102. 14. OZAKI, Y„ Chem. Eng., 46: (1982), 46. 8. CONCLUDING REMARKS (Received September 16, 1987)

As mentioned above, metal alkoxides are very flexi- ble compounds involved in high technology progress. As for the new function of new materials, both shape and composition control are important. Organic puri- fication such as alkoxide distillation is also useful for separation. Extending the processes based on ferroniobium leads to 1) Nb-Ti alloy production by the Kroll method, 2) Carbon smelting reduction of homogene- ous oxide powder, 3) synthesis of binary, ternary or other mixed oxides, etc. When the ore which has been developed is consi- dered as a natural mixed ceramic, artificial minerals can be synthesized easily, with optional compositions and shapes, by the alkoxide method. Resources must be developed, not as technology from mining to waste, but as a cyclic system in a resource chain. When high- tech challenges our country severely, continuous innovation and technological revolution in resource

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