Thermal Behaviour of y-MnO, and Some Reduced Forms in Oxygen BY JOHN A. LEE, COLIN E. NEWNHAM" AND FRANK L. TYE Ever Ready Co. (Holdings) Ltd., Central Laboratories, St. Ann's Road, London N15 3TJ AND FRANK S. STONE School of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY Received 4th November, 1976 The products obtained by partial chemical reduction of an electrodeposited y-manganese dioxide have been studied by thermal analysis in an oxygen environment between room temperature and 725 K. Weight loss in the temperature range 430-520 K was independent of sample composition when up to 35 % of MnIv was replaced by MnIrI. Substitution of >50 % MnIv led to a dependence of weight loss on degree of reduction. With the aid of X-ray diffractometry and magnetic suscepti- bility measurements, these results could be explained by the formation of a single phase solid solution below -50 % reduction and a two-phase system when greater amounts of MnIII were incorporated into the solid.Weight loss in the neighbourhood of 630K could be resolved into two entities. The low temperature component was associated with the phase transition from y-Mn02 to j3-MnOz accom- panied by some loss of oxygen. The high temperature component was attributed to the loss of water resulting from the decomposition of Mn(OH),+ Previous thermal analysis studies on electrodeposited y-MnO, have identified three evolved entities designated I, II and 1II.l. Type I appeared at 390 K and was identified as the removal of molecular water reversibly adsorbed on the oxide surface.Type I1 was associated with the irreversible loss of water between 430 and 520 K. Experiments in static water vapour environments partially resolved type I1 into two components. The first component, IIa, appeared to arise from water held in the bulk of the oxide, and amounted to -20 mg g-l. The second type, IIb, was directly related in amount to the overall oxidation state of the oxide and was attributed to the removal of water by condensation of hydroxyls. Type I11 appeared at 590- 630K, but in near-vacuum, nitrogen or water vapour environments it was only poorly resolved and was not chemically assigned. The present paper reports t.g./d.t.g. studies of y-MnO, in an environment of oxygen. The first part focuses attention on the type I1 region and is especially concerned with the variations which arise with chemically-reduced y-MnO,. The t.g./d.t.g.technique has been exploited to throw light on the controversial question of whether y-MnO, and a-MnOOH form a complete range of solid solutions. This part is supplemented by X-ray diffraction and magnetic studies. The second part of the paper has been aimed at a better understanding of the type I11 region. The relevance of the oxygen environment is that it delays the onset of bulk oxide decom- position which otherwise obscures the type I11 feature. Earlier work had briefly 237238 THERMAL BEHAVIOUK OF ?t-MnG2 indicated that type I11 weight loss involved both water and oxygen. Hi' sc), the resulting oxide would either be a mixture of phases or be a highly non-stoichiometric dioxide, and this merited further investigation.EXPERIMENTAL MATERIALS The manganese dioxide used in this work was mainly the commercially electrodeposited y-phase Mn02 previously described.'. Chemical reduction of this dioxide was eEected by hydrazine sulphate or hydrazine h ~ d r a t e . ~ Hydrazine sulphate (0.24-1.47 g) was added to a suspension of y-Mn02 (9.5 g) in distilled water (100 cm3) and the whole stirred for 2 h at 24+0.2"C. The solid was separated by filtration and vacuum dried at ambient tempera- ture. Hydrazine sulphate could be replaced with hydrazine hydrate solution (6 % w/w) and an identical procedure carried out using aliquots in the range 0-19 cm3. Thermal behaviour and X-ray diffraction patterns of reduced samples of the same composition prepred by the two routes were identical.The level of reduction of y-Mn02, denoted by x in the following equivalent formulae ; MniV- Mn;" 0 2 - OH, ; (I - x) Mn02. xMnOOH ; MnOOH,, ranged from x = 0.1 1 to x = 0.95, where x = 1 .O signifies groutite, a-h,lnBOH. The commercially electrodeposited y-Mn02 used as starting material had a composition corresponding to x = 0.11, Chemically prepared y-Mn02 was used for certain experiments ; this was obtained from Mn304 by the method of Giovanoli, Maurer and Feitkne~ht.~ METHODS The t.g./d.t.g. apparatus has been described previously.' Prior to t.g./d.t.g. runs samples were evacuated at room temperature to pressures of 5-7x lo-' Torr and then oxygen was admitted. In most experiments 10Torr of oxygen was used to provide the static gas environment, although in certain circumstances pressures up to 450 Torr were employed. Characterization by X-ray diffractometry and chemical analysis was carried out on the starting materials, and also on the solids at intermediate stages of t.g./d.t.g.by arresting the linear heating programme and evacuating the oxygen. Analyses were made as soon as possible after cooling to room temperature. X-ray diffraction data of the powdered solids were recorded as diffractometer traces using a Philips PW 1130 unit with Ni-filtered Cu Kdl radiation and a goniometer scan rate normally 1" mi+. The procedure for chemical analysis of MnTV was based on methods employed by Vetter and Jaeger and Chapman and Freeman.6 The sample, typically 60mg, was refluxed in iron stabilised sodium oxalate solution (10 cm3, 0.025 mol dm-3) containing 2 cm3, 20 % v/v sulphuric acid for 30 min.This solution was diluted to 25 cm3, heated to 350 K and titrated with KMn04 (0.02 niol dm-3) ( Vl). To the same solution was added sodium pyrophosphate (-4g) which dissolved. The pM was adjusted to 6.5-7.0 by addition of sodium hydroxide pellets and the solution was titrated potentiometrically with 0.02 rnol ~ l m - ~ KMn04 (V2). Finally the volume of KMn04 required to standardise 10 cm3 of sodium oxalate solution was noted. x was calculated from the relationship x = 4[1-5( Vo- V1)/(24V2- SV,)]. Thermohygrometric analysis (THA) was performed with a Stanton Redcroft Thermo- balance TG750 and a differential d.t.g. unit using a linear heating rate of 15 K n1in-l and an oxygen flow (at atmospheric pressure) of 25 cm3 min-l, the gas being pre-dried with magnesium perchlorate and a molecular sieve.7 A commercial electrolytic hygrometer (Salford Electrical Instruments) coupled to the thermobalance was employed to andyse the evolved water.Magnetic susceptibility measurements were made using a Gouy balance constructed and described by Hagan.8 Temperature could be varied from 80 to 300 K and magnetic field from 3000 to 5500 G.J . A . LEE, C. E . NEWNHAM, F . L . TYE A N D F . S . STONE 239 RESULTS c HEMI c A L LY - RE D u CED y-MnO, T . G . / D . T . G . I N THE TYPE 11 REGION Oxygen environment t.g./d.t.g. curves for samples in the compositional range 0.11 6 x < 0.35 are given in fig. 1 .In parallel with the degree of chemical reduction of the manganese dioxides an associated increase in water loss in the region of 410 K was observed. This feature was also present in the previous water environment studies2 It reflects the presence of additional liydrogcn-bonded water adsorption following the increase in surface hydroxylation which accompanies chemical reduction. FIG. 1.-D.t.g. curves in 10Torr of oxygen for partially reduced oxides. Extent of reduction increases in the sequence (a) +. (e). x in (1 - x ) MnOa. xMnOOH is equal to (a) 0.11 (- - -1, (b) 0.14 (- -), (c) 0.18 (-), (d) 0.26 (--) and (e) 0.35 (- -). Chemical reduction appeared to induce a modification in the t.g./d.t.g. curve of the " as-received '' MnOz (x = 0.1 1) in the type I1 region.An initial reduction from x = 0.1 1 to x = 0.14 depressed the weight loss between 430 and 530 IS (fig. l), reflecting a decrease in the amount of type TI water. It is to be noted that the untreated unreduced y-MnO, differed in sample history from the other samples studied. The important observation however was made on the samples which had been reduced beyond x = 0.14 and especially those from x = 0.18 to x = 0.35. These showed no dependence of the type I1 feature upon the degree of reduction. The peak, however, shifted slightly to higher temperatures and is accordingly designated as type IIb., Brouillet et aL9 noted a similar invariance and proposed a reaction route involving dehydroxylation of the oxyhydroxide component of (1 - x ) MnO,. xMnOOM simultaneously with oxidation in accordance with the overall reaction : The net loss in weight resulting from reaction (1) is small, and therefore in oxygen in contrast to near-vacuum or water vapour environments, little dependence of type PIb upon x would be expected.Differential thermal analysis (d.t.a.) in oxygen, reported in an earlier paper,l indicated a net exothermic reaction at these temperatures (420-590K). Since the simple condensation of hydroxyls and removal as water is endothermic, this is further evidence for the presence of a simultaneous (exothermic) 4 MnOOH -!- Q2 + 4 MnO, + 2H20. (1)240 THERMAL BEHAVIOUR OF y-MnO, oxidation step. Finally, X-ray diffraction analyses on samples removed from the balance in the region of 500 K detected only y-MnO,. All the data are therefore consistent with reaction (1) for 0.14 < x < 0.35. Fig.2 shows the d.t.g. curves for the reduced oxides in the compositional range 0.54 < x < 0.91. Surprisingly, behaviour in the type I1 region is now dependent on chemical composition. Both the amount and the rate of weight loss increased with increase in the tervalent manganese content within the oxide. Fig. 3 shows the weight loss 0.1 6 - 0.14- 0.12- r( *k o.lo- M 0.08- 8 3 0.06- CI .- B 2 0.04- c 0 44 0.02 - sample temperaturelK FIG. 2.-D.t.g. curves in 10 Torr of oxygen for x equal to (a) 0.54 (- - -), (b) 0.70 (- .), (c) 0.76 (- -) and (d) 0.91 (-). I 100 - r( 8 0 - \ 8 6 0 - bo 0" v) - 0.2 0.4 0.6 0 . 8 1.0 X FIG. 3.-Weight loss up to 550 K as a function of degree of reduction. a, 10 Torr oxygen; 0, vacuum.J .A . LEE, C. E. NEWNHAM, F* L. TYE A N D F. S . STONE 241 associated with the type I and II features as a function of x, and the new behaviour at x > 0.5 is evident. First we should consider whether the dependence of type I1 on x arises from a buoyancy effect (volume change) or the poor accessibility of oxygen to samples as the extent of reduction is increased. The buoyancy effect was accordingly estimated for the particular experimental conditions; it was found to be too small to contribute. Accessibility of oxygen was examined by recourse to a specific set of experiments on the x = 0.91 sample where the oxygen pressure during t.g./d.t.g. was varied from 4 to 456 Torr (fig. 4). The results show that the type I1 feature is not an artefact caused by oxygen starvation.Since buoyancy and lack of oxygen accessibility are ruled out, we conclude that the increase in peak height for type I1 at x > 0.5 (fig. 2) indicates that the decomposition route in this range of x involves an intermediate which is less susceptible to oxidation than is the case for less-reduced oxide (x < 0.5) where the Brouiilet mechanism [reaction (1)J holds. 0.24- 1 I I 1 400 5 0 0 600 700 sample temperature/K Fig. 4.-D.t.g. curves for x = 0.91 at various oxygen pressures increasing in the sequence (a) -+ (e). (a) 4 (-), (b) 53 (- -), (c) 258 (- -), (d) 358 (- -) and (e) 456 Ton (- - -). 1 2 3 4 5 6 7 8 9 heating ratePC min-l FIG. 5.-Weight loss for x = 0.91 in 10 Torr of oxygen as a function of heating rate.242 THERMAL BEHAVIOUR OF y-MnO, A further important result in fig.2 is the evidence of an absorption process above the type 11 feature, clearly shown by traversal of the base line for the most reduced sample. The absorption process may well be present for the other samples but is masked by the type I1 evolution process. The total weight loss from a t.g./d.t.g. decomposition process should be independent of the linear heating rate.l O However, as fig. 5 shows, the weight loss corresponding with the decomposition of the x = 0.91 sample (MnOlSs4) in an oxygen environment up to the onset of the absorption region is a function of the heating rate. The occurrence of a dependence on heating rate is confirmatory evidence that two or more competing reactions are present.X-RAY DIFFRACTION The " as-received " y-MnO, and the chemically-reduced samples (0.1 1 < x < 0.95) were also studied by X-ray diffractometry. The diffraction data for samples with x between 0.1 1 and 0.46 showed five reflec- tions in the range 70" > 20 > lo", and these were assigned to the 110,021, 121,221 and 002 planes of the diaspore unit cell. In view of the relatively small number of observable reflections and also low intensity, it was more significant to examine the variations in individual d-spacings with x than to attempt to evaluate lattice para- meters. As shown in fig. 6, where the respective d-spacings for four of the above planes are plotted against x, the crystal lattice initially dilated uniformly as the mean I I 1 1.59 i- X 0.20.40.60.8 1.0 X 0.20.40.60.8 1.0 0.20.4 0.60.8 1.0 X X FIG.6.-InterpIanar separation ( d ) as a function of composition for partially reduced y-Mn02. 0, Experimental points; 0, natural groutite.J . A . LEE, C. E . NEWNHAM, F . L . TYE AND F . S . STONE 243 valency of the manganese decreased, No new reflections appeared as x increased from 0.11 to 0.46, so the results are consistent with the formation of solid solution of MnOOH in y-MnO,. For x > 0.50, however, there was a marked change in the X-ray pattern. This can be seen in fig. 7, which shows a comparison of the diffractometer traces in the range 33" < 26 < 57" for six chemically reduced samples with x between 0.11 and 0.95. For the compositional range x = 0.46 to x = 0.70 the diffraction peaks decreased in intensity : the five reflections mentioned above could only be identified with difficulty, and the structure appeared to be reorganizing.Beyond x = 0.70, new reflections appeared and increased in intensity as x increased (those in the range 57 45 33 (b) " A FIG. 7.-X-ray diffraction traces (CuKor) of partially reduced y-Mn02. x in (1-x) Mn02. xMnOOH (a) 0.11, (b) 0.26, (c) 0.39, (4, 0.70, (e) 0.76 and (f) 0.91. 33" < 28 < 57" are shown in fig. 7). All the new reflections could be ascribed to the a-MnBOH structure, though the d-spacings were smaller than those of mineral groutite. There was no significant evidence for change in the unit cell size with x. Fig. 6 shows data for four d-spacings of four samples with x between 0.69 and 0.95 ; the values are almost constant.The correlation of these d-spacings with those of the 221, 021, 121 and 002 spacings of the diaspore structure, as implied in fig. 6, is arbitrary. To sum up, the results presented in fig. 6 and 7 are in accord with single-phase solid solution over only part of the range from y-MnO, to a-MnOOH. Attempts to isolate an intermediate by terminating t.g/.d.t.g. runs for x = 0.91 which had been heated in oxygen at selected temperatures up to 520 K and character- izing by X-ray diffraction were unsuccessful. Diffractometer traces showed only oxide with x = 0.91 or the oxidation product y-MnO,. However, in a corresponding experiment using synthetic groutite (a-MnOOH, x = 1 .O) as starting material, analysis244 THERMAL BEHAVIOUR OF y-Mn02 of material from a run terminated at 530 K showed the presence of corundum-phase Mn,O,.Structural details will be given elsewhere ; the result is of special interest since Mn20, ordinarily crystallises with the C-structure. MAGNETIC MEASUREMENTS Further information on the chemically-reduced samples was obtained from magnetic susceptibility measurements. Susceptibilities of seven samples were measured and the magnetic moment p was evaluated from the slopes of Curie-Weiss plots (x-l against T). These plots were linear over the range from 140 to 290 K. The variation of p with extent of reduction is shown in fig. 8. 3.5 - 0.2 0.4 0.6 0.8 1.0 X FIG. 8.-Magnetic moment as a function of sample composition for partially reduced y-MnOz. (-) Experimental, (- - -) calculated.p increased with reduction, as is to be expected for the change in valency from MnxV (pspin only = 3.87 B.M.) to Mn"' (,uspin only = 4.88 B.M.). In the range 0.1 < x < 0.4 the magnetic moments formed a consistent set, and no appreciable orbital contributions to the magnetic moment are indicated. This is entirely com- patible with the existence of a solid solution. At x - 0.5, however, where the X-ray data indicate a solid solution limit, the magnetic moment is anomalously high; an orbital contribution would be consistent with structural reorganisation and distortion of octahedral symmetry. Gabano and Labat l2 have also observed a similar effect on p at x = 0.5 for a sample of y-Mn02 reduced electrochemically. y-MnO, HEATED ABOVE 520 K T.G./D.T.G. AND THA IN THE TYPE 111 REGION that an oxygen environment at 10 Torr pressure enables type I11 weight loss to be resolved as a separate peak.The effect of increasing oxygen pressure has been studied, and fig. 9 shows results for x = 0.18. At high pressures of oxygen type 111 resolved into two components. Mass spectrometric analysis of the evolved species indicated that oxygen was liberated above 530 K and became the major product beyond 670 K.l Fig. 10 presents the simultaneously recorded differential thermogravimetric and thermohygrometric analyses for x = 0.11 under a dynamic flow of oxygen at atmospheric pressure. Results appertaining to the type I1 region fit the expected pattern. The evolved water vapour analysis fingerprinted the dehydroxylation It has already been notedJ .A . LEE, C. E. NEWNHAM, F . L . TYE AND F . S . STONE 245 rl 350 400 450 5 0 0 550 6 0 0 650 700 sample temperature/# FIG. 9.-D.t.g. curves for x = 0.18 at different oxygen pressures. (-) 4 Ton, (- - -) 190 Torr. 400 5 0 0 6 0 0 700 8 0 0 9 0 0 sample temperature/K FIG. 10.-Thermal hygrometric THA (- -) and d.t.g. (-) curve of y-MnOz in a dynamic oxygen environment. The ordinate for the d.t.g. curve is as indicated, that of the THA is arbitrary. process as registered by the largest rate peak. The two components comprising type I11 were present in the d.t.g. trace between 570 and 670 K. The first component of I11 yielded a specific water entity since a peak in the THA curve matches in position the d.t.g. hump at 590-600 K (fig. 10). The second component of type 111 is presumed to involve the loss of oxygen as the mass spectrometric analyses of the evolved gases detected principally oxygen at these temperatures and no THA signal is seen.This oxygen desorption process appeared to be divorced from the main dioxide lattice decomposition occurring later (i.e. 4 M n 0 , j 2Mn203 + 0,) and identified by the large d.t.g. peak at -870 K. It is possible that carbon present as an impurity in the commercially electrodeposited material might contribute to type 111. This, however, can be dismissed as the reason for the type I11 behaviour since a carbon-free synthetic y-MnO, produced by oxidation of Mn304 exhibited a type I11 component. Further- more an artificially increased carbon content within the dioxide failed to modify the t.g./d.t .g.behaviour.246 THERMAL IIEHAVIOUR OF y-MnO, The position maximum and value of rate of weight loss for type 111 was indepen- dent of the degree of reduction. However, the peak narrowed on the low temperature side and was more symmetrical for the reduced samples. Since it has been established that the thermal dehydroxylation in oxygen of a-MnBOH produces y-MnO,,l I this implies that the sample composition just prior to type I11 in t.g./d.t.g. runs corresponds to y-MnQ2 irrespective of the original degree of reduction. The oxygen contribution to type I11 does not then depend upon the initial oxidation state. The peak narrowing appeared to reflect a diminution of type TI1 water. X-RAY DIFFRACTION AND ANALYTICAL DATA X-ray diffraction measurements on samples withdrawn from d.t.g.experiments at the rate minima on either side of type I11 indicated a manganese dioxide phase transformation of y -+ P-MnO, during the type 111 process (fig. 11). For example the diffractometer line at 28 = 29" which is characteristic of the @ modification is present only after the loss of type 111. Significantly application of a linear heating programme to P-Mn02 resulted in the absence of a detectable weight loss in the region of type 111. 28 CU Kg FIG. 11.-X-ray diffractometer traces before (top) and after (bottom) type I11 weight loss. Table 1 contains analytical data for the electrodeposited and chemically prepared y-MnO, samples at the t.g./d.t.g. minimum before and after type 111 weight loss. The previous postulate of some oxygen loss is supported by the diminution in oxidation states after type 111.Column 4 of table 1 records the calculated weight loss due to oxygen removal based on the composition changes indicated by analysis and column 5 the experimental values calculated by dropping verticals from the minima on the rate curves to the temperature axis and integrating. Inaccuracies are inevitable in the extrapolation procedure and small errors in assessment of oxidation states are amplified in predictions of weight loss due to oxygen desorption. Never- theless it is considered that the values in columns 4 and 5 for the synthetic dioxideJ . A . LEE, C . E . NEWNHAM, F . L. TYE AND F . S . STONE 241 probably indicate only oxygen loss whereas with the electrodeposited material the duplex nature of type I11 is manifest and the considerably larger experimental weight loss reflects the additional removal of water as detected by THA.TABLE 1 .-ANALYTICAL DATA PERTAINING TO THE TYPE I11 REGION MnlO ratio MnlO ratio a t d.t.g. at.d.t.g. mnimum mrumum prior to after type I11 type I11 wt. loss wt. loss electro- deposited y-Mn02 MnO1.96 MnO1.93 chemically prepared y-Mn02 MnO1.98 Mn01.91 calculated weight loss Img g- 1 6 12 experimental weight loss Img g-l 20 9 DISCUSSION The distinctly different thermal characteristics in oxygen of materials in the two compositional ranges 0.11 < x < 0.35 and 0.54 4 x 4 0.91 described in this paper, together with the X-ray diffraction evidence (fig. 6 and 7), indicate the absence of a complete range of solid solution.It is concluded however that solid solution exists for solids with x between x = O(Mn0,) and x = 0.50 in agreement with electrode potential investigations performed by Bell and Huber and diffraction data reported by Giovanoli and Leuenberger.14 This is contrary to the work of others such as Bode and Schmier l 5 who claim the existence of a solid solution over the entire range from y-Mn02 to a-MnOOH. Critical examination of their data, however, suggests that their X-ray diffraction results are not consistent with a single homo- geneous phase. The solid solution limit of x - 0.50 established in this work may conform to a stabilized hydrogen bonded structure.16 The structural disordering beyond the homogeneous solution limit possibly reflects the effect of Jahn-Teller distortion at high MnlI1 contents.The structural implications of Jahn-Teller distortion in MnlI1 compounds are well authenticated. In the range 0.54 < x < 0.91 the solid may be either monophasic but different from that for x < 0.50 or may exist as two phases, with groutite forming at the expense of the stabilised, solid solution limit material. The invariance in the position of the X-ray diffraction lines and the increase in intensity in going from x = 0.70 to 0.91 supports the premise of two phases. The groutite phase should be more accurately described as near-groutite, as its d-spacings are slightly less than naturally occurring groutite. It is proposed that the modified groutite component decomposes under the t.g./ d.t.g.conditions to produce a corundum form of Mn,O, as an intermediate between MnOOH and y-MnO,. This proposal is made in view of the isolation of a corundum- structure sesquioxide by controlled decomposition of synthetic groutite to be reported elsewhere. Thus the steps are : 2MnOOH -+ Mn,O, (corundum) + H20 (2) 2Mn,O, +02 -+ 4Mn0,. (3) This corundum-structure intermediate probably suffers no immediate oxidation and allows reaction (2) to proceed to a reasonable extent before (3) begins. Distinctive evolution and absorption steps therefore result as can be seen in fig. 2. Giovandi and Leuenberger l4 thermally decomposed groutite to the monoclinic oxide Mn,08,248 THERMAL BEHAVIOUR OF y-MnO, at 470-550 K in a stream of dry oxygen. Additionally they reported that this oxide oxidized at temperatures in excess of 570 K to produce p-Mn0,.We were unable to detect Mn,08 as an intermediate in this work and in the latter stages of the absorption step only the y-phase manganese dioxide was apparent. Thus the forma- tion of Mn,08 is unlikely to be responsible for the observed weight loss and weight gain phenomena present in t.g./d.t.g. runs. The effect of increasing the pressure of the oxygen environment (fig. 4) can be qualitatively understood in terms of reaction (2) and (3). As the oxygen pressure increases, reaction (3) proceeds more quickly and the observed rate of weight loss will decrease. The phase transformation y -+ P-Mn02 as detected in the Type I11 region has been observed by other workers,17 but there are no reports in the literature of the transition being accompanied by a loss in weight (type 111).P-MnO, is also usually more stoichiometric than its y counterpart. The accommodation of such a large oxygen deficiency may indicate a crystallographic shear (CS)l structure. P-MnO, has the rutile structure. Rutile (Ti02) is well known to undergo crystallographic shear,lg* 2o and of the other first row transition metal oxides possessing the rutile structure CS plane formation has also been reported for VO, 21 and Cr02.22 It appears to be a requisite for formation of a CS structure that the metal concerned can form a corundum-phase trivalent oxide. With the recent confirmation of a corundum- phase Mn,O, l1 this requirement is met also by Mn, and although CS systems based on MnO, are not reported so far it is possible that MnOlSg1 (table 1) is an oxide containing CS planes.The sheared structure may form directly as an intermediate in the y -+ p transformation or result from a thermally induced shear defect in the newly formed pyrolusite lattice. As previously noted the loss of water in the type 111 region was peculiar to the electrodeposited y-Mn02. Fleischmann, Thirsk and Tordesillas 23 have studied the electrodeposition of y-MnO, and argue that the slow stage in crystal growth involves the dehydration of Mn(OH),. It is possible that at this lattice formation step the dehydration is not always complete and the water entity in type 111 reflects the reaction 0 2 Mn(OH)* + MnO, +2H,O. (4) The observed decrease in type 111 water with increasing levels of initial chemical reduction may mirror the reductions Mn(OH), + H+ + e -+ Mn00H + 2H,O ( 5 ) Mn(OH),+2H++2e --+ Mn(OH), +2H20.(6) The authors thank the Directors of Ever Ready Co. (Holdings) Ltd for permission to publish this paper and Mrs. J. L. Hitchcock for obtaining the thermohygrometric data. J. A. Lee, C. E. Newnham and F. L. Tye, J. Colloid Interface Sci., 1973, 42, 372. J. A. Lee, C. E. Newnham, F. S. Stone and F. L. Tye, J. Colloid Interface Sci., 1973, 45, 289. W. Feitknecht, H. R. Oswald and U. Feitknecht-Steinmann, Helv. Chim. Acta, 1960, 43, 239. R. Giovanoli, R. Mauer and W. Feitknecht, Helv. Chim. Acta, 1967, 50, 1072. K. J. Vetter and N. Jaeger, Electrochim. Acta, 1966, 11, 401. D. S. Freeman and W. G. Chapman, Analyst, 1971, 96, 865. A. Hagan, Ph.D. Thesis (University of Bristol, 1974). Ph. Brouillet, A. Grund, F. Jolas and R. Mellet, in Batteries 2, ed. D. H. Collins (Pergamon Press, 1965), p. 189. ' J. L. Hitchcock and P. F. Pelter, 4th h t . Conf. on Thermal Analysis (Budapest, 1974). lo G. Carter, Vacuum, 1962, 12,245.J . A . LEE, C . E. NEWNHAM, F. L. TYEANDF. S. STONE 249 l 1 J. A. Lee, C. E. Newnham, F. S. Stone and F. L. Tye, to be published. l2 J. P. Gabano and J. Labat, Compt. rend., 1967, 264, 164. l3 G. S. Bell and R. Huber, J. Electrochem. SOC., 1964, 1, 11 1. l4 R. Giovanoli and U. Leuenberger, Helv. Chim. Acta, 1969, 52, 2333. l5 M. Bode and A. Schmier, in Proceedings of the 3rd International Symposium on Batteries, ed. D. H. Collins (Pergamon Press, 1962), p. 329. S. Atlung, Manganese Dioxide Symposium (The Electrochemical SOC., Cleveland, U.S.A., 1975), paper no. 2. J. M. A. Laudy and P. M. de Wolff, J. Appl. Sci. Res., 1963, 10, 157. l8 J. S. Anderson, in Surface and Defect Properties of Solids (The Chemical Society, 1972), vol. I, p. 1. S. Andersson, B. Collen, U. Kuylenstierna and A. Magneli, Acta Chem. Scand., 1957,11,1641. 'O B. G. Hyde, Pruc. 7th Int. Symp. on Reactivity of Solids (Bristol, 1972) (Chapman and Hall, London, 1972), p. 23. " A. D. Wadsley, Rev. Pure Appl. Chem., 1955, 5, 165. '' M. A. Alario Franco, J. M. Thomas and R. D. Shannon, J. Solid State Chem., 1974, 9, 261. 23 M. Fleischmann, M. R. Thirsk and M. Tordesillas, Trans. Faraday SOC., 1962, 58, 1865. (PAPER 6/2044)