摘要:
1973 1517Reactions of Sodium Oxide with the Oxides V02, V203, VO, and VanadiumMetalBy Marten G. Barker ' and Alan J. Hooper, Department of Chemistry, University of Nottingham, UniversityPark, Nottingham NG7 2RDThe reactions of sodium oxide with vanadium metal and its lower oxides are described for different molar ratios ofreactants. All reaction products are identified by powder X-ray crystallography and the reaction temperaturedetermined by differential thermal analysis.No ternary oxides containing vanadium in the 4+ state were formed in the reactions of sodium oxide with vanadiumdioxide ; an equimolar mixture gave NaVO, and Na,VO,. The ternary oxide NaVO, was prepared by the reactionof vanadium(ll1) oxide with sodium oxide in equimolar proportions, but sodium orthovanadate Na3V04 was formedat higher sodium oxide concentrations. This product was also formed from reactions of the monoxide and vanad-ium metal with sodium oxide,THE sodium oxide-vanadium pentoxide system has beenstudied to some extent,lV4 but little is known about thereactivity of sodium oxide with the lower oxides of van-adium.Reactions of this type are of interest not onlybecause of the possibility of forming new ternary oxidescontaining vanadium in an oxidation state lower than+5, but also as a pointer towards the reactivity ofvanadium metal with sodium oxide in solution in liquidsodium.Three ternary oxides of vanadium have so far beenreported5 with vanadium in an oxidation state lowerthan 3-5: Na2V0,, prepared by the reaction of sodiumazide with sodium metavanadate at 320 "C in vacuum,Ka2V20, by the reaction of vanadium pentoxide andsodium azide, and NaVO, by the reaction of vanadiumdioxide and sodium azide at 500 "C.Chemical analysesof the last two compounds showed that only 72 and 97%of the vanadium was in the expected 4+ oxidation state.We describe here the reactions of sodium oxide withthe oxides VO,, V,03, and VO for different molar ratiosof reactants. All reaction products have been identifiedby powder X-ray diffraction methods and in certain reac-tions differential thermal analysis has been used todetermine the reaction temperature.RESULTS AND DISCUSSIONReactions of Sodium Oxide with Vanadium Dioxide.-The reaction products and their conditions of preparationare summaxised in Table 1.No ternary oxides containingvanadium in the +4 oxidation state were found asproducts of these reactions.38, 801.1 G. Canneri, Gazzetta, 1928, 58, 6.2 A. A. Fotiev and B. 1'. Slobodin, Zhur. priklad. Khiun., 1965,3 M. G. Barker and A. J. Hooper, preceding paper.4 G. Le Flem and K. Olazcuaga, Bzd. SOC. chim. Frame, 1968,2769.The product of experiment (1) consisted of a mixtureof NaVO, and Na,VO,. Pouchard reported that theproducts of a 1 : 1 mixture of sodium oxide and vanadiumTABLE 1Products and reaction conditions for sodium oxide-vanadium dioxide. All reactions were at 550 "C for24 h under argonExpt.(1)(2)(3)(4)(5)No. Na,O:VO, Products1 : 1 Na,VO, (IV), NaVO,I : 2 a-Na,VzO,, P-Na,V,O,, V2032 : 1 Na,VO, (111), Na,V04 (IV), Na1 : 3 Na,V30, (Na,.,V,O,)1 : 5 Na,V,O,, (Na,.,V,O,)dioxide heated at 500 "C in a sealed silica capsule gave anX-ray pattern in good agreement with that given byRudorff .* The compound was poorly crystalline andwas not isostructural with the corresponding compoundsNa,TiO,, Na,SnO,, and Na,ZrO,.The X-ray patterngiven by Pouchard may also be interpreted on the basisof a mixture containing the compounds NaVO, andNa,V04, the latter being present entirely in the cubicmodification? Table 2 shows the X-ray powder patterngiven by the 1 : 1 reaction product together with thereported patterns of N+VO, and those of NaVO, andNa,VO,.There is excellent correlation of d values, but that ofthe relative intensities of diffraction lines is less good,particularly for the lines of NaVO,.This is almostcertainly due to the low crystallinity of the reactionproduct of experiment (1).6 W. Riidorff and H. Becker, 2. Naturforsch., 1954, 9b, 613.W. Riidorff and H. Becker, 2. Naturforsch., 1954, 9b, 614.7 M. Pouchard, Ph.D. Thesis, University of Bordeaux, 1967.8 W. Rudorff, G. Walter, and H. Becker, 2. anorg. Chem.,1956, 285, 2871518 J.C.S. DaltonThe differential thermal analysis (d.t.a.) trace given bythis product shows that two transitions take placebetween room temperature and 600 "C. An endothermicTABLE 2X-Ray diffraction data given by the product froin thereaction of Na,O : VO, ( 1 : 1)T'roduct Na,VO, a Na,VO, b NaVO, Na,VO, (IV) cd / A I I I , dlA I/Iod d / A I I I , d l A III, dlA I I I ,5.60 5 5-50 w 5.62 8 5.62 555.35 25 6-37 15 5-37 554.42 80 4.41 in 4.40 90 4.40 904.17 53.914 53.80 30 3-80 w 3-814 25 3-80 452.801 3 2.818 102.706 100 3-70 s 2-696 100 2.691 22 2-702 1002-571 5 2.561 5 2.574 102.461 15 2.466 12 2.475 252.383 42-290 5 2.305 8 2-304 152.186 70 2.18 s 2.279 40 2.186 100 2.199 62-149 1 2.159 152.118 102.099 32.080 11.912 20 1.916 111 1.909 20 1-914 251.721 2 1.728 101.698 2 1.707 1 1-705 21-593 15 1-591 10 1.595 251.557 20 1.574 1x7 1.560 15 1.564 181-498 10 1.505 m 1.501 121.748 1 1.743 4 1.757 81-239 in0 lief.8. Iicf. 7. c Ref. 3. d IV = TVeak, 111 = medium,s = strong.transition at 75", which was found to be reversible, mayreadily be assigned to the well known phase change of thedioxide VO,.A large exothermic peak represented thereaction of sodium oxide with vanadium dioxide at265 "C. An approximate heat of reaction may becalculated froin the ratio of the peak areas by use of theknown 9 heat of phase transition (AH 750 cal mol-l VO,)of vanadium dioxide. The value determined by thismethod was AH (265 "C) = -33.2 kcal mol-l VO,.The powder X-ray diffraction pattern of the product ofa reaction carried out in the d.t.a. apparatus, with amaximum temperature just above the reaction tempera-ture, was identical to that obtained from a reaction inwhich heating had been continued to GOO "C. There is,therefore, no experimental evidence to suggest that thecompound Na,VO, is formed in the reaction of sodiumoxide and vanadium dioxide.The compound Na,V,05 could not be prepared by thereaction of 1 niol of sodium oxide and 2 mol of vanadiumdioxide [experiment (2)].A previous attempt to prepareNa,V,O, by the reaction of an equimolar mixture ofsodium pyrovanadate Na4V20, and vanadium(I1r) oxideV,O,, at 500 "C in a sealed silica ampoule proved fruitlessas the reactants were found to be unchanged. Using asimilar type of reaction Pouchard 10 was however able toprepare three non-stoicheiometric compounds withstructures closely related t o vanadium bronzes of theT. Kawakubo and T. Nakagawa, J . Phys. Soc. Japan, 1964,19, 517.type NaZV2O5.. The direct reaction of sodium oxide andvanadium oxide [Table 1, experiments (4) and (5)] in themolar ratios 1 : 3 and 1 : 5 gave products identical to thosereported by Pouchard for the same sodium to vanadiumratios.The reaction of vanadium dioxide with 2 mol of sodiumoxide [Table 1 experiment (3)] did not give the compoundNa,VO,. The loss of sodium was observed during reac-tion, and the final product gave an X-ray powder diffrac-tion corresponding to the orthovanadate Na,VO, :VO, + 2Na20 + Na,VO, + Na.In the sodium oxide-rich region no compounds may beprepared by the solid-state reaction of sodium oxide withvanadium dioxide, which contain vanadium in the 4+oxidation state.Disproportionation was observed withthe formation of either the 5+ state or mixtures of the5+ and 3+ states.This type of behaviour is fairlytypical of the 4+ oxidation state of vanadium, similardisproportionation reactions being found for some of thebinary halides.Reactions of Sodium Oxide with Vanadiim(m) Oxide.-The reactivity of sodium oxide with the oxide V,O, isconsiderably lower than with the other vanadium oxides.In order to achieve complete reaction experiments werecarried out at 810 "C in sealed silica ampoules under argon[experiments (1)-(4), Table 23.TABLE 2Reactions of sodium oxide with vanadium(111) oxideno. Reactants Products(1) Na,O + V,O, NaVO,(2) Na,O -+ V,O, NaVO,(3) 2Na,0 + VzO3 $NaVO, + iNa,VO, (IV) + Na(4) 3Na,0 + V20, NaVO, -/- Na,VO, (IV) -+ 2Na(5) Na,O + Na'i'O, NaVO,, Na,VO, (IV), Na,VO,(6) 2Na,0 + NaVO, Na,VO, (IV), Na,VO, (ITI), NaExpt.(HI), NaThe reactants in experiments (1) and (4) were used inthe form of compressed pellets and were in contact withthe silica ampoule.The powder X-ray diffractionpatterns of the products from these two reactions showedthe presence of an extra phase which is probably formedby the interaction of the reactants with silica. Thepowder X-ray diffraction patterns of the products fromthe remaining experiments (in which the sample was en-closed in platinum foil) did not show the presence of linesdue to this impurity.The compound NaVO, gave a powder X-ray diffrac-tion pattern, which closely resembled that of thehexagonal phase, a-NaFeO,. Line-splitting effects were,however, observed from all the preparations. The linescorresponding t o reflections from the 003, 006, 104, 107,and 113 Miller planes in a hexagonal structure wereclearly resolved into doublets. The effect was mostpronounced for the reflection from the 003 plane, whichgave two strong diffraction lines with the interplanarspacings i! 5.62 and 5.37 A.On heating the sample10 M. Pouchard, 12. Casalot, L. Rabardel, axid P. Hagtnmuller,Bull. SOC. chim. Fvance, 1968, 27421973 1519in a high temperature X-ray diffractometer attachment,the distorted form transformed, at ca. 200 "C, to regularhexagonal phase, giving a diffraction pattern exactlyanalogous to that of the compound a-NaFeO,. Oncooling to room temperature the distorted form wasobtained. The X-ray diffraction patterns of the twoforms of the compound NaVO, are given in Table 3.TABLE 3X-Ray diffraction patterns of NaVO, modificationsNaVO, (25 "C) NaVO, (200 "C)d l h5.626.372.8182-6912.6742.4752.4052.3832.1862.1592.1182.0992.0801.7431-7281.7071.5951.5011.4461.4351-4081.372IIIO55551022102554100151031410125125534d l A5-442.7142.5642.4652,1832.0251.7341.6031.4981.4451.378h k l0 0 30 0 61 0 11 0 31 0 41 0 61 0 71 0 81 1 01 1 31 0 10IIIO55151222100212201655a 3-00 A, G 16-30 AAn increase in the sodium oxide content [experiments(3) and (4), Table 21 gave Na3V04 as a reaction product.Sodium metal was evolved, and the silica capsule wastherefore severely attacked by the alkali metal.Thecompound Na3h70, may be obtained as the sole productfrom the reaction at 550 "C of sodium oxide (2 mol) withNaVO, (1 mol) either in vacuum or argon [experiment (6)].I t is, therefore, this reaction, taking place after theformation of NaVO,, which gives rise to the formation ofthe orthovanadate in experiments (3)-(5) (Table 2).Pure NaVO, may readily be prepared by the hydrogenreduction of the metavanadate, NaVO,, at 600 "C. Thedistorted form is obtained from this reaction.Reaction of SodizGm Oxide with Vanadium Monoxide andVanadizcm Metal.-The reactants, in the form of inti-mately mixed powders, were heated under vacuum to575 "C, and the reaction products (Table 4) identified byX-ray powder diffraction.The quantity of Na,VO, increased from experiments(1)-(5) at the expense of the compound NaVO, and themonoxide VO.These observations, together with thepresence of unreacted vanadium monoxide, suggest thefollowing reaction mechanism. First, sodium oxidereacts with vanadium monoxide to give the compoundNaVO, [equation (l)]. The compound NaVO, is how-Na,O + VO + NaVO, + Na (1)TABLE 4Reactions of sodium oxide with vanadium inonoxide andvanadium metalReactants ProductsNa,O + 2VO VO + NaVO, + Na,VO, (IV) + NaNa,O + VO VO + NaVO, + Na,VO, (IV) + Na3Na20 + 2V0 VO + NaVO, + Na,VO, (IV)2Na20 + VO VO + NaVO, + Na,VO, (IV)5Na20 + 2V0 VO + Na,VO, (IV) + Na,VO, (111)3Na,0 + VONa,O + V2Sa,0 + V3Na,0 + V4Na20 + V+ Na,VO, (III)+ Na+ Na,VO, (III)+ Na+ Na+ Na,VO, (111) + Na+ Na+ NaNa,VO, (IV) + Na3V0, (111) $- Nap-V + NaVO, + Na3V0, (IV)8-V + Na,VO, (IV) + Na,VO, (111)p-V + Na,VO, (IV) + Na,VO, (111)Na,VO, (IV) + Na,VO, (111) + Naever unstable towards sodium oxide being oxidised to theorthovanadate Na,V04 [equation (a)].Reaction (2) is2Xa,0 + NaVO, -+ Na,V04 + 2Na (2)obviously favoured over reaction (1), but only in experi-ment (6) is the sodium oxide-vanadium monoxide ratiogreat enough for complete reaction [equation (3)],3Na20 + VO + Na,VO, + 3NaThe presencell of p-V in the products of experiments(7)-(9) suggests that, initially, sodium oxide reacts withvanadium metal in such a way that oxygen enters themetal lattice with the formation of a solid solution[equation (a)]. The behaviour of vanadium containingV + Na,O --t V(0) + Nadissolved oxygen may then be regarded as being analagousto that of the monoxide.The presence of two forms of Na3V04 in the reactionproducts is a consequence of the reaction conditions.The compound Na,VO, (111) will be slowly transformedto the compound Na,VO, (IV) at these temperaturesunder vacuum and hence both forms are observed in thereact ion products.(3)(4)EXPERIMENTALReagents.-Sodium oxide was prepared as describedpreviously.12 Vanadium dioxide was prepared by the solid-state reaction of the pentoxide V,O, with the sesquioxideV20, a t 650 "C under argon. Vanadium sesquioxide wasprepared by the hydrogen reduction of V,O, a t 650°, andthe monoxide, VO, by the solid-state reaction of vanadiummetal and the pentoxide at 1200 "C under vacuum.The methods used for the solid-state reactions of sodiumoxide with transition metal oxides is described in ref. 12.The d.t.a. apparatus used was described in ref. 3.[2/2384 Received, 17th October, 1972111 J. Henry, S. O'Hare, R. Mclune, and M. ICrug, J . Less-1% M. G. Barker and D. J. Wood, J.C.S. Daltopz, 1972, 9.Common Metats, 1970, 21, 115
ISSN:1477-9226
DOI:10.1039/DT9730001517
出版商:RSC
年代:1973
数据来源: RSC