: O 646; TQ : A

Transcription

1 ELECTROCHEM ISTRY Vol. 11 No. 2 May 2005 : (2005) , 3 (, ) : 3 : 1) ; 2) Ag/AgCl ( ) ; 3). : ; ; ; ; : O 646; TQ : A [ 1 ].,, 2000, :, ;., 3. 1 [ 2, 3 ] ( 1).,,.,,, ;, ( ) ( ),.,,,, , Chen CaCl 2 [ 3 ],, [ 4 13 ]. 1998, (B ritish Titanium, BTi), Defense Evaluation and Research Agency(DERA),, ; , Defense Ad2 : , : , 3, Tel: ( , ) (862027) , E2mail: mel@whu. edu. cn

2 Fig. 1 Schematic diagram of the metal extraction by electrochem ical reduction of solid oxides in molten salts vanced Research Projects Agency ( DARPA ) 1230, Timet BTi, 4 3 [ 13 ].,,, [ ]?,,,,. [ 27 ]. ( ) ( ( SiO 2 + C = Si + CO 2 ). ).,,.,,, /,,,, ( ),,. 850 ( 2),., (13 kw h /kg Si), [ 27 ], [ ]., / / 2. 2,., ,, [ 26 ] [ 27 ].,,. 900 CaCl 2

3 2 : ( a) ( b) SEM [ 27 ] Fig. 2 SEM images of the Si powder ( b) by electrochem ical reduction of SiO 2 powder ( a) in molten CaCl 2 ( 2. 8 V, 850, 4 h) [ 27 ] 3 TiO 2 L itio 2 ( a) L iti 2 O 4 ( b) TEM [ 32 ] Fig. 3 B right field TEM images of the L itio 2 ( a) and L iti 2 O 4 ( b) with their electron diffraction patterns p repared by TiO 2 cathode in molten L icl at 700 [ 32 ] [ 31 ].,,., 700 L iti 2 O 4 L itio 2 [ 32 ] ( 3)., Ag/AgCl. Ag/AgCl, 800., Ag/AgCl [ 33, 34 ], 4., ( 48 h 8 mv),, ( 72 h ),, , SiO 2 [ 33, 34 ].

4 Ag/AgCl a) [ 33 ] ; b) [ 34 ] Fig. 4 Two kinds of the quartz sealed Ag/AgCl reference electrode a) with a p re2ionized salt bridge [ 33 ], b) with a thinned and sealed quartz at lower end functio2 ning as the ion conducting membrane [ 34 ] 3. 2 ( ), Cha ( ) [ 35 ].,. ( ),.,., TiO 2 [ 32 ] ;,,, ( 5),. CaCl 2, ( ) / /,. / /,., ( ) / ( ) / ( ),, ( ). 6. AgCl + e = Ag + Cl - SiO 2 + 4e = Si + 2O 2-5 N io ( SEM a ) 900 CaCl 2 ( a) ( b) 3 Fig. 5 CV s ofmo2cavity electrode with N io powder( inserted SEM image in a) in molten CaCl 2 at 900 ( a) and the Vari2 ation of peak current with potential scan rate ( b) 3 3 Q iu Guohong, Ma Meng, W ang D ihua, et al. Metallic cavity electrodes for Investigation of redox Active powders in molten salts [ J ]. J. Electrochem. Soc., ( subm itted).

5 2 : V ( vs SCE ) AgCl Fig. 6 Op tical images of the reduced area on the AgCl coating at different times under constant potential electrolysis at V ( vs. SCE) by a p in2point contact electrode,. 3 4,. 3,,,.,,,,. :.. (R efe rence s) : [ 1 ] Cha Chuansin ( ), Lu Juntao ( ). Study of the electrochem istry of system s of p ractical importance [ J ]. Electrochem isty ( in Chinese), 1995, 1 (2) : 115. [ 2 ] Fray D J, Farthing TW, Chen G Z. Removal of oxygen from metal oxides and solid solutions by electrolysis in a fused salt [ P ]. 1WO Pat : , [ 3 ] Chen G Z, Fray D J, Farthing TW. D irect reduction of TiO 2 in molten calcium dichloride [ J ]. Nature, 2000, 407: 361. [ 4 ] Flower H M. A moving oxygen story [ J ]. Nature, 2000, 407: 305. [ 5 ] Mc Gowan P. Return to zero [ J ]. Chem istry in B ritain (2) : 21. [ 6 ] D r Chen and the philosopher s stone [ J ]. The Econo2 m ist, 2000, Sep t: 150. [ 7 ] Freemantle M ichael. Titanium extracted directly from TiO 2 [ J ]. C&E News, 2000, 25 ( Sep t) : 12. [ 8 ] H ill S. Get tough [ J ]. New Scientist, 2001, 170 (2297) : 47. [ 9 ] Rodriguez P, Mohandas K S. A paradigm shift in the e2 lectrowinning of metals [ J ]. Current Science, 2001, 81 (5) : 443. [ 10 ] Faller K, Froes F H. The use of titanium in fam ily au2 tomobiles: current trends [ J ]. Journal of the M inerals Metals & Materials Society, 2001, 53 ( 4) : 27. [ 11 ] Schauerte O. Titanium in automotive p roduction [ J ]. Advanced Engineering Materials, 2003, 5 (6) : 411. [ 12 ] Flower H M, Soutis C. Materials for airframes [ J ]. Aeronautical Journal, 2003, 107 ( 1072) : 331. [ 13 ] Martin J L. Low2cost titanium p rocess development [DB /CD ]. address pdf, [ 14 ] Chen G Z, Fray D J. Novel cathodic p rocesses in mol2 ten salts [A ]. Proceedings of 6 th International Sympo2 sium on Molten Salt Chem istry and Technology, eds. Chen N ianyi, Q iao Zhiyu [ C ]. Shanghai: Shanghai U2 niversity Press, 2001: 79. [ 15 ] Chen G Z, Fray D J. Voltammetric studies of the oxy2 gen2titanium binary system in molten calcium chloride [ J ]. Journal of the Electrochem istry Society, 2002, 149 (11) : E455 E467. [ 16 ] Ono K, Suzuki RO. A new concep t for p roducing Ti sponge: Calciotherm ic reduction [ J ]. JOM 2Journal of the M inerals Metals and Materials Society, 2002, 54 (2) : [ 17 ] Suzuki R O, Teranuma K, Ono K. Calciotherm ic re2 duction of titanium oxide and in2situ electrolysis in molten CaCl 2 [ J ]. Metallurgical and Materials Trans2 actions B2Process Metallurgy and Materials Processing Science, ( 3) : 287. [ 18 ] D ring K, Jackson M, Dashwood R, et al. Electro2 chem ical Deoxidation M echanism s of Titanium Oxides [A ]. in Cost2Affordable Titanium Symposium in Hon2 or of Professor Harvey Flower, Edited by F. H. Froes, M. A shraf Imam, and Derek Fray. P95. TM S ( The M inerals, Metals & Materials Society) [ C ]. Carolina, March 14 18, North 3 Deng Yuan, W ang D ihua, Xiao W ei, et al. Electrochem istry at conductor / insulator / electrolyte three2phase Interlines: a thin layer model [ J ]. J. Phys. Chem. B., ( subm itted).

6 [ 19 ] Yan X Y, Fray D J. Production of niobium powder by direct electrochem ical reduction of solid Nb 2 O 5 in a eutectic CaCl 2 2NaCl melt [ J ]. Metallurgical and Ma2 terials Transactions B2ProcessMetallurgy and Materials Processing Science, 2002, 33 ( 5) : 685. [ 20 ] Nohira T, Yasuda K, Ito Y. Pinpoint and bulk electro2 chem ical reduction of insulating silicon dioxide to sili2 con [ J ]. Nature Materials, 2003, 2 ( 6) : 397. [ 21 ] Yan X Y, Fray D J. U sing electro2deoxidation to syn2 thesize niobium sponge from solid Nb 2 O 5 in alkali2al2 kaline2earth metal chloride melts [ J ]. Journal of M a2 terials Research, 2003, 18 ( 2) : 346. [ 22 ] Chen G Z, Gordo E, Fray D J. D irect electrolytic p reparation of chrom ium powder [ J ]. Metallurgical and Materials Transactions B2Process Metallurgy and Materials Processing Science, 2004, 35 ( 2) : 223. [ 23 ] Gordo E, Chen G Z, Fray D J. Toward op tim isation of electrolytic reduction of solid chrom ium oxide to chro2 m ium powder in molten chloride salts [ J ]. Electro2 chim ica Acta, 2004, 49 ( 13) : [ 24 ] Fenn A J, Cooley G, Fray D, et al. Exp loiting FFC cambridge p rocess [ J ]. Advanced Materials & Proces2 ses, 2004, 162 : 51. [ 25 ] Glowacki B A, Yan X Y, Fray D J, et al. N iobium based intermetallics as a source of high2current/ high magnetic field superconductors[ J ]. Physica C, 2002, : [ 26 ] Ma Meng, W ang D ihua, Hu Xiaohong, et al. Pre2 pareation of titanium alloys by electrochem ical reduc2 tion of solid oxides [A ]. 12 th Proceeding of Chinese Electrochem istry Society[ C ]. Shanghai: H13. [ 27 ] J in Xianbo, Gao Pei, W ang D ihua, et al. Electro2 chem ical p reparation of silicon and its alloys from solid oxides in molten calcium chloride[ J ]. Angew. Chem. Int. Edit., 2004, 43: 733. [ 28 ] Greener route to pure silicon [ J ]. C&E News, 9 Feb. 2004, 24. [ 29 ] Electrochem ical extraction of silicon: new app roach for a more environmentally friendly large2scale p rocess [ DB ]. http: / /www. chem ie. de /news/e /34607 /? sort = 3, 30, January, [ 30 ] B radley David, Green silicon p roduction [ DB /CD ]. Elemental D iscoveries2sep termber 2004, Issue 73, ht2 tp: / /www. sciencebase. com / sep t042iss. htm l. [ 31 ] J iang Kai, Hu Xiaohong, W ang D ihua, et al. Prepara2 tion and p roperties study of sub2titanium oxide by elec2 tro2reduction of TiO 2 in moten CaCl 2 [ A ]. 12 th Pro2 ceeding of Chinese Electrochem istry Society [ C ]. Shanghai: G11. [ 32 ] J iang Kai, Hu Xiaohong, Sun Huijiao, et al. Electro2 chem ical synthesis of L itio 2 and L iti 2 O 4 in molten L icl[ J ]. Chem. Mater., 2004, 16: [ 33 ] Gao Pei( ), J in Xianbo ( ), W ang D ihua ( ), et al. Preparation of a novel reference e2 lectrode in molten electrode [ J ]. Electrochem istry ( in Chinese), 2005, 11 ( 1) : 8. [ 34 ] Gao Pei, J in Xianbo, W ang D ihua, Hu Xiaohong, Chen George Z., A Quartz Sealed Ag/Agcl Reference Electrode for CaCl 2 BasedMolten Salts [ J ], J. Elec2 troanal. Chem., 2005, 4. [ 35 ] Cha Chuansin, L i Changm ing, Yang Hanxi, et al. Powder m icroelectrode [ J ]. J. Electroanal. Chem., 1994, 368: 47. Innovation in Molten Salt Electrochem istry WANG D i2hua, CHEN Zheng 3 ( E lectrochem ical R esearch Cen tre, College of Chem istry and M olecu lar S cience, W uhan U niversity, W uhan , China) Ab s tra c t: Recent research developm ent in molten salt electrochem istry at the Electrochem ical Research Centre ofw uhan University is briefly reviewed. A ttention is first paid on the p reparation of silicon and its binary alloys, as well as oxide based functional materials. In addition, the quartz sealed Ag/AgC l reference electrodes suitable for high temperature molten salts are described. Focus is also given to two types of metal based cavity electrodes that are capable of loading m icrogram s of oxide powders and hence allow fast and rep roducible measurements for the electrochem ical behaviour of the powders in molten salts. The article finishes by highlighting the concep t of three2phase interline electrochem istry in conjunction with reporting the p relim inary results from the investiga2 tion of a simp le " thin layer model" for the electrochem ical reduction of solid AgCl in aqueous solution and solid SiO 2 in molten salts. Ke y wo rd s: Molten salt electrochem istry, Silicon, Reference electrode, Cavity electrode, Three2phase in2 terline electrochem istry