- Email: [email protected]
The determination of oxidising and reducing cations in transition-metal oxides using vanadium sulphate solutions
314
Short communications Zusammenf~g-Eine Methode zur quantitativen Bestimmung des bei der Verbrenmmgsanalyse von Stahl erhaltenen Kohlendioxydes in einem Argon-Gaschromatographen wird beschrieben. O-0*3% C k&men auf etwa ho.01 % genau bestimmt werden. Die Genauigkeit fti hiihere Kohlenstoffgehalte ist geringer. Die Methode ist vorteilhaft fti kleine C-Mengen und kann mliglicherweise als Grundlage zu einer Automatisierung denen. Die MBglichkeit, Kohlenstoff und Schwefel in einer Probe zu bestimmen werden diskutiert. R&um&Description d’une m&hode de dosage de l’anhydride carbonique form& par la combustion de l’acier, au moyen de la chromatographie gazeuse dans l’argon. Les r&sultats indiquent que des quantitb inf&ieures & 0,3% de carbone peuvent &tre d&ermintes avec une pr&zision d’environ &0,01x, mais cette pr&zision est moindre pour les aciers g forte teneur en carbone. La m&hode eat utile pour d&erminer de faibles concentrations de carbone et elle peut &tre rendue automatique dans une large mesure. Discussions des possibilit6s d’estimation du carbone et du soufre dans un Cchantillon d’acier par les mCthodes de chromatographie gazeuse. REFERENCES
1 British Standard 1121: Purr 11: 1948. British Standards Institution, * A. K. Galwey, Tulanta, 1962.9, 1043.
London, 1949.
The determination of oxidising and reducing cations in transitiowmetal oxides using vanadium sulphate solutions (Received 27 August 1962. Accepted 22 October 1962) THE oxides and mixed oxides of the transition metals have been studied extensively in recent years. Much of this work has been stimulated by the technological importance of certain families of materials such as the ferrimagnetic mixed oxides containing iron (ferrites) ; those with the spine1 crystal structure of formula type (M’, Fe)BO1 and those with the garnet crystal structure, Ma(M’Fe)oO1r (M’ is usually a transition metal). An important aspect of these studies has been the finding of relationships between physical properties and chemical composition. It is routine to determine the total quantities of the metals present but a quantitative knowledge of the oxidation states of the various cations present is also important. It is not always possible to obtain this kind of information by chemical methods. One can discover, however, that the over-all stoichiometry is correct, allowing one to know, for example, the value of 1 if the formula for a spine1 is written M80r+~. A ferrite or other mixed oxide prepared by ignition at high temperature is very well crystallised and inert towards many reagents. Extended periods of digestion are often required to dissolve the sample. We have found that solutions of quinquevalent and quadrivalent vanadium sulphates in dilute sulphuric acid, because of their stability, are very satisfactory reagents for the determination of several reducing and oxidising cations, respectively, in solids. For the half-cell reaction VOa+ + 3Hz0 e V(OH),+ + 2H+ + ethe standard oxidation potential1 E0 is - 1NJO v while in 1M HISOl the potential is -1.02 v. Thus strongly oxidising cations like Co III, MnlI1, and MnIV will oxidise VIv in dilute HISO solutions and reducing cations such as Fe”, VII1 and T1‘II1 will reduce Vv in similar solutions.1s8 After the solid has dissolved the V’v which is left over from an excess of reagent by oxidising cations or that produced from Vv by reducing cations is titrated with a standard solution of KMnO,. The accuracy and precision obtainable is indicated by these results for the analyses of some pure oxides: OXIDATION (REDUCTION) EQIJWALENTS PER 1OOg OF MATERIAL
Oxide
Found
% of theoretical
Expected
v*o,
1.3319 & oNlO 1.267 zt 0.003 0.8297 f 0.0003
99.42 100.02 99.90
1.3342 1.2668 0.8305
MnBOI, Co@4
Short communications
315
The amount of Vrv and Vv reagents to be used, the quantity of sample, the concentration of HaSOd (maximum used equals 2.4M), etc., can be varied to accommodate a particular problem. Some materials are dissolved with such difficulty that only the finest available can be taken for samples; e.g., that passing through a 325-mesh screen or that obtained by making a suspension of the sample and collecting the slowest settling material. Among the most difficult substances to dissolve is yttriumiron garnet, YIFe5011. The finest material must be separated and boiled with the Vv reagent for several days under reflux to effect complete solution before determination of the Fen content can be done. We have used the Vrv and Vv reagents chiefly to check the stoichiometry of transition-metal mixed-oxide preparations in order to find suitable preparative methods before studying physical properties. We have thus been able to study, in addition to those already mentioned, the preparation of substances such as VOB, LiVO*, ColVOl and YgFe 60 Ix; solid solutions in the systems Fe*GeO,ZnFGO,, Co,GeO,-ZnMnpO,, LiMngOd-ZnMqOl, Fe,VO,--FeV,O,, C&O,-Mn,O,, NiMn,O,Mn,O,, and MgFe#-Mn,O,. Pure ferrites with compositions very close to that given by the formula, MFe&nO, have been found to exhibit physical properties different than those of slightly non-stoichiometric materials.s Observed electrical and magnetic properties, for example, can often be related to the presence of small amounts of FeII. The compounds MnlSnOl and Mn,TiO, were known to be instrinsicahy ferrimagnetic only after magnetic measurements had been made on samples known to be stoichiometric, i.e., containing no Mn1r1.4 In several of these systems the study of.physical properties of stoichiometric materials has yielded some evidence concerning specific oxidation states present in the solid. The oxidation states in CoprrVrvO, were discovered by analysis of magnetic susceptibility measurements.5 The constitution of substances in the C&O,-Mn,O, system has been deduced from studies of crystal symmetry and low-temperature magnetisation.a Ampex Computer Products Co. Culver City, Cali$ornia, U.S.A.
D. G. WICKHAM
MI. T. Lincoln Laboratory Lexington, Massachusetts, U.S.A.
E. R.
WHIPPLE
Summary-_Because vanadium sulphate solutions are very stable, they make useful analytical reagents. A solution of uinquevalent vanadium sulphate in dilute sulphuric acid can be used 8or the determination of Fe”, Tirrr and VrrI ions present in solid oxides. A similar solution of quadrivalent vanadium can be used for the determination of Corrr, Mnrrr and MnIv. The importance of the method in studies of mixed transition-metal oxides is briefly discussed. Zusammenfassung-Vanadinsulfatlijsungen sind wegen ihrer Stabilitlt niitzliche Massliisungen. Ftinfwertiges Vanadin in verdiinnter Schwefelsi&re kann zur Bestimmung von Fe(H), Ti(II1) V(II1) in festen Oxyden verwendet werden. Vierwertiges Vanadin in gleicher Losung dient zur Bestimmung von Co(III), Mn(III) und Mn(IV). Die Wichtigkeit der Verfahren zur Analyse von Mischungen von Ubergangsmetalloxyden wird kurz diskutiert. R&r&-I-es solutions de sulfate de vanadium constituent en raison de leur grande stabilite un reactif tres utile en analyse. Une solution de sulfate de vanadium(V) en milieu acide sulfurique dilue peut etre utilis& pour le dosage des ions Fe”, TPrr et Vrrl presents dam lea oxydes solides. Une solution de vanadium(IV) peut &tre utilisee pour le dosage de Corrr, Mnrrr et MnIV. L’importance de la methode pour l’ttude des oxydes mixtea des metaux de transition est brievement disc&e. REFERENCES 1 W. M. Latimer, The Oxidation States of the Elements and Their Potentials in Ayueous Solutions, Prentice-Hall, N.Y., 1938. p A. H. Webster and N. F. H. Bright, J. Amer. Chem. Sot., 1961,44, 110. 8 D. G. Wickham, E. R. Whipple and E. G. Larson, J. Znorg. Nucl. Chem., 1960,14,217. 4 D. G. Wickham, N. Menyuk and K. Dwight, J. Phys. Chem. Solids, 1961,20, 316. 5 N. Menyuk, K. Dwight and D. G. Wickham, Phys. Reu. Letters, 1960,4, 119. 6 D G. Wickham and W. J. Croft, J. Phys. Chem. Solids, 1958,7, 351.
Short communications Zusammenf~g-Eine Methode zur quantitativen Bestimmung des bei der Verbrenmmgsanalyse von Stahl erhaltenen Kohlendioxydes in einem Argon-Gaschromatographen wird beschrieben. O-0*3% C k&men auf etwa ho.01 % genau bestimmt werden. Die Genauigkeit fti hiihere Kohlenstoffgehalte ist geringer. Die Methode ist vorteilhaft fti kleine C-Mengen und kann mliglicherweise als Grundlage zu einer Automatisierung denen. Die MBglichkeit, Kohlenstoff und Schwefel in einer Probe zu bestimmen werden diskutiert. R&um&Description d’une m&hode de dosage de l’anhydride carbonique form& par la combustion de l’acier, au moyen de la chromatographie gazeuse dans l’argon. Les r&sultats indiquent que des quantitb inf&ieures & 0,3% de carbone peuvent &tre d&ermintes avec une pr&zision d’environ &0,01x, mais cette pr&zision est moindre pour les aciers g forte teneur en carbone. La m&hode eat utile pour d&erminer de faibles concentrations de carbone et elle peut &tre rendue automatique dans une large mesure. Discussions des possibilit6s d’estimation du carbone et du soufre dans un Cchantillon d’acier par les mCthodes de chromatographie gazeuse. REFERENCES
1 British Standard 1121: Purr 11: 1948. British Standards Institution, * A. K. Galwey, Tulanta, 1962.9, 1043.
London, 1949.
The determination of oxidising and reducing cations in transitiowmetal oxides using vanadium sulphate solutions (Received 27 August 1962. Accepted 22 October 1962) THE oxides and mixed oxides of the transition metals have been studied extensively in recent years. Much of this work has been stimulated by the technological importance of certain families of materials such as the ferrimagnetic mixed oxides containing iron (ferrites) ; those with the spine1 crystal structure of formula type (M’, Fe)BO1 and those with the garnet crystal structure, Ma(M’Fe)oO1r (M’ is usually a transition metal). An important aspect of these studies has been the finding of relationships between physical properties and chemical composition. It is routine to determine the total quantities of the metals present but a quantitative knowledge of the oxidation states of the various cations present is also important. It is not always possible to obtain this kind of information by chemical methods. One can discover, however, that the over-all stoichiometry is correct, allowing one to know, for example, the value of 1 if the formula for a spine1 is written M80r+~. A ferrite or other mixed oxide prepared by ignition at high temperature is very well crystallised and inert towards many reagents. Extended periods of digestion are often required to dissolve the sample. We have found that solutions of quinquevalent and quadrivalent vanadium sulphates in dilute sulphuric acid, because of their stability, are very satisfactory reagents for the determination of several reducing and oxidising cations, respectively, in solids. For the half-cell reaction VOa+ + 3Hz0 e V(OH),+ + 2H+ + ethe standard oxidation potential1 E0 is - 1NJO v while in 1M HISOl the potential is -1.02 v. Thus strongly oxidising cations like Co III, MnlI1, and MnIV will oxidise VIv in dilute HISO solutions and reducing cations such as Fe”, VII1 and T1‘II1 will reduce Vv in similar solutions.1s8 After the solid has dissolved the V’v which is left over from an excess of reagent by oxidising cations or that produced from Vv by reducing cations is titrated with a standard solution of KMnO,. The accuracy and precision obtainable is indicated by these results for the analyses of some pure oxides: OXIDATION (REDUCTION) EQIJWALENTS PER 1OOg OF MATERIAL
Oxide
Found
% of theoretical
Expected
v*o,
1.3319 & oNlO 1.267 zt 0.003 0.8297 f 0.0003
99.42 100.02 99.90
1.3342 1.2668 0.8305
MnBOI, Co@4
Short communications
315
The amount of Vrv and Vv reagents to be used, the quantity of sample, the concentration of HaSOd (maximum used equals 2.4M), etc., can be varied to accommodate a particular problem. Some materials are dissolved with such difficulty that only the finest available can be taken for samples; e.g., that passing through a 325-mesh screen or that obtained by making a suspension of the sample and collecting the slowest settling material. Among the most difficult substances to dissolve is yttriumiron garnet, YIFe5011. The finest material must be separated and boiled with the Vv reagent for several days under reflux to effect complete solution before determination of the Fen content can be done. We have used the Vrv and Vv reagents chiefly to check the stoichiometry of transition-metal mixed-oxide preparations in order to find suitable preparative methods before studying physical properties. We have thus been able to study, in addition to those already mentioned, the preparation of substances such as VOB, LiVO*, ColVOl and YgFe 60 Ix; solid solutions in the systems Fe*GeO,ZnFGO,, Co,GeO,-ZnMnpO,, LiMngOd-ZnMqOl, Fe,VO,--FeV,O,, C&O,-Mn,O,, NiMn,O,Mn,O,, and MgFe#-Mn,O,. Pure ferrites with compositions very close to that given by the formula, MFe&nO, have been found to exhibit physical properties different than those of slightly non-stoichiometric materials.s Observed electrical and magnetic properties, for example, can often be related to the presence of small amounts of FeII. The compounds MnlSnOl and Mn,TiO, were known to be instrinsicahy ferrimagnetic only after magnetic measurements had been made on samples known to be stoichiometric, i.e., containing no Mn1r1.4 In several of these systems the study of.physical properties of stoichiometric materials has yielded some evidence concerning specific oxidation states present in the solid. The oxidation states in CoprrVrvO, were discovered by analysis of magnetic susceptibility measurements.5 The constitution of substances in the C&O,-Mn,O, system has been deduced from studies of crystal symmetry and low-temperature magnetisation.a Ampex Computer Products Co. Culver City, Cali$ornia, U.S.A.
D. G. WICKHAM
MI. T. Lincoln Laboratory Lexington, Massachusetts, U.S.A.
E. R.
WHIPPLE
Summary-_Because vanadium sulphate solutions are very stable, they make useful analytical reagents. A solution of uinquevalent vanadium sulphate in dilute sulphuric acid can be used 8or the determination of Fe”, Tirrr and VrrI ions present in solid oxides. A similar solution of quadrivalent vanadium can be used for the determination of Corrr, Mnrrr and MnIv. The importance of the method in studies of mixed transition-metal oxides is briefly discussed. Zusammenfassung-Vanadinsulfatlijsungen sind wegen ihrer Stabilitlt niitzliche Massliisungen. Ftinfwertiges Vanadin in verdiinnter Schwefelsi&re kann zur Bestimmung von Fe(H), Ti(II1) V(II1) in festen Oxyden verwendet werden. Vierwertiges Vanadin in gleicher Losung dient zur Bestimmung von Co(III), Mn(III) und Mn(IV). Die Wichtigkeit der Verfahren zur Analyse von Mischungen von Ubergangsmetalloxyden wird kurz diskutiert. R&r&-I-es solutions de sulfate de vanadium constituent en raison de leur grande stabilite un reactif tres utile en analyse. Une solution de sulfate de vanadium(V) en milieu acide sulfurique dilue peut etre utilis& pour le dosage des ions Fe”, TPrr et Vrrl presents dam lea oxydes solides. Une solution de vanadium(IV) peut &tre utilisee pour le dosage de Corrr, Mnrrr et MnIV. L’importance de la methode pour l’ttude des oxydes mixtea des metaux de transition est brievement disc&e. REFERENCES 1 W. M. Latimer, The Oxidation States of the Elements and Their Potentials in Ayueous Solutions, Prentice-Hall, N.Y., 1938. p A. H. Webster and N. F. H. Bright, J. Amer. Chem. Sot., 1961,44, 110. 8 D. G. Wickham, E. R. Whipple and E. G. Larson, J. Znorg. Nucl. Chem., 1960,14,217. 4 D. G. Wickham, N. Menyuk and K. Dwight, J. Phys. Chem. Solids, 1961,20, 316. 5 N. Menyuk, K. Dwight and D. G. Wickham, Phys. Reu. Letters, 1960,4, 119. 6 D G. Wickham and W. J. Croft, J. Phys. Chem. Solids, 1958,7, 351.