Table 1. Tolerance Limits for Interfering Substances in Analysis of Rock Containing 0.50% TiOz4
Interfering Allowable Average yo Substance yo in Rock in Earth’s Crust 0.029 CrlOi 0.84 0.13 0.022 VzOa 0.06 0.013 CUO 0.010 W08 0.19 0.002 MoOa 0.01 US08 >0.60 >O ,0005 a This assumes a permissible error of iO.OlyoTiOt. Table
II. Precision of Absorbance Measurements
Absorbance
TiOz in Mean of 5 Sample, Measure- Mean Grams ments Deviation 0.0011 10 0.0874 0.0038 80 0.6718 0.0042 160 1.3312
Accuracy Limit Accepted for Rocks Analyzed According to Method Recommended ( i o .Ol% TiOzin rock)
0.017 0.017 0.017
With samples containing an amount of TiOz equivalent to 0.125% in a rock, the tolerance limits are the same as shown in Table I except for VzOs and CuO which must be decreased by a factor of about 1.5. In all cases the observed interference appeared to be proportional to the amount of interfer-
ing substance present, thus if the permissible error is taken to be =t0.02% Ti02 the above tolerances can be doubled. Interferences from CuO, VpOa, and MOO3 were approximately additive. I t can be seen from Table I that a very unusual enrichment of the interfering substances would have to occur before a serious error could be caused in a titanium determination. The analytical procedure detailed above is suitable for rocks containing up to 1.0% Ti02. If more than this is present either a smaller sample weight or smaller aliquot should be taken so that there is never more than 200 pg. of Ti02 in the 50-ml. flask. If this is done any interfering substances present will have an even smaller effect than when the standard procedure is used. If it is necessary to use larger samples or aliquots to determine accurately a very small content of TiOz, great care should be taken to keep the concentration of interfering elements below those corresponding to the standard case of a 5-ml. aliquot taken from a 0.4-gram sample in 100 ml. of solution. In difficult cases a preliminary separation may have to be made or compensating amounts of known interfering substances added to the reagent blank and standards. The precision and accuracy of the method is very good, as can be seen from the results shown in Tables I1 and 111. Yoe and Armstrong investigated the discrepancy between their determinations and the figures quoted by the National Bureau of Standards (Table 111). They found that a silica
Table 111. Comparison of Results from Various Sources for Analysis of National Bureau of Standards Argiilaceous Limestone Sample 1A
Ti02 Found Yoe and Present N. B. S. Armstrong Work“ 0.16 0.192 0,189 0 . I90 0.190 0.185 0.187 a Three separate rock samples.
separation, as recommended on the certificate analysis resulted in the loss of about 10% of the titanium present in the rock. The‘ discrepancy is exaggerated by the fact that the certificate value was based on a spread of figures ranging from 0.11 to 0.25’%, the higest figure being excluded from the mean. LITERATURE CITED
(1) Hillebrand, W. F., Lundell, G. E. F:, “Applied Inorganic Analyses,” 2nd ed., Wiley, New York, 1953. (2) M;son, B., “Principles of Geochemistry, Wiley, New York, 1952. (3) Nichols, P. N. R., Analyst 85, 452 (1960). (4) Shapiro, L., Brannock W. W., U. S. Geol. Survey Bull. ho. 1036-C, iv, 19 (1956). (5P.Yoe, J. H., Armstrong, A. R., ANAL. CHEM.19,100 (1947). (6) Yoe, J. H., Jones, A. L., IND.ENG. CHEM.,ANAL.ED. 16,111 (1944). RECEIVED for review February 2, 1961. Accepted June 13, 1961. Research Council of Alberta Contribution No. 153.
Determination of Small Oxygen Deficiencies in Oxide Monocrystals HERBERT B. SACHSE and GORDON L. NICHOLS Keystone Carbon Co., St. Marys, Pa.
bA
direct method to determine small stoichiometric oxygen deficiencies of the order of 1 milliatom/mole in oxide monocrystals is described. The oxide is dissolved under vacuum either directly in H&Or in the presence of Fe+3 ions, or, if impossible [as in the case of rutile monocrystals (TiOz)] by a vacuum melting process in a mixed carbonate melt and subsequently also Fez(SO& solution. in H&Oa
+
T
HE DETERMINATION of small stoichiometric deviations was recently reported for oxide monocrystals with an oxygen excess, stressing their important, influence on the electrical
properties of semiconductors (4). Similar effects exist for oxygen-deficient oxides. Classic examples of the effect of oxygen deficiencies on electrical conductivity are Ti02 and ZnO. Between Ti02 and Ti01.995 the resistivity a t room temperature decreases by a factor 10’0. Simultaneously, the activation energy drops from 1.65 to 0.27 e.v. (6). Monocrystals of TiOz (rutile) make this transition a t 600” C. in pure hydrogen within minutes. By stoichiometric deficiency undetectable with normal chemical analysis, the dielectric loss can increase by a factor of 10 to 100, while simultaneously the apparent
dielectric constant increases from approximately 100 to more than 15,000 (7, 9). Further work with oxygen deficient TiOz monocrystals was done by Breckenridge and Hosler ( I ) and Cronemeyer ( 2 ) . When oxygen deficient synthetic crystals of pure ZnO with an initial resistivity of 0.3 to 0.7 ohm cm. and an activation energy of 0.01 e.v. are annealed for 30 hours a t 900” C. in oxygen, a final resistivity of 2.5 X lo6 ohm cm. and an activation energy of 0.04 e.v. is reached (S). This last figure is still far below the theoretical energy gap for intrinsic semiconduction in ZnO . VOI. 33, NO. 10, SEPTEMBER 1961
1349
In a number of other oxides the influence of the oxygen pressure on the electrical properties has been investigated without knowledge of their stoichiometric deviation. These few facts show the urgent need to determine the stoichiometric deviation of semiconducting compounds before electrical investigations are started. This holds true even more for monocrystals where grain boundary effects, which might overshadow non:toichiornetry, are absent. During recent years increasing emphasis has been laid on basic investigations of electrical and thermal properties of oxide monocrystals (6, 8). A strict comparison of results makes it not only desirable but imperative to know the degree of stoichiometry. CHEMICAL REACTIONS
It would be unrealistic to base the calculation of small stoichiometric oxygen deficiencies on the analytical determination of the bulk ratio of metal and oxygen. The possible deviation would be hidden in the usual precision level, as in the case of an oxygen surplus. Analytical methods, .which only respond to the deficiency, are normally based on oxidimetric analysis with permanganate or ceric sulfate as oxidizing agents. Small oxygen deficiencies in polycrystalline CuO, TiOz, and earth alkali titanates can be determined easily by dissolving these materials under vacuum
1.
Figure 1.
Vacuum melting apparatus
in HzSOd in the presence of a surplus of Fe+9. The following reactions take place: Cu+ Fe+a = Cu+* Fe+2 Ti+S + Fe+S = Ti+' + Fe+2
+
+
The Fe+2 product is titrated with
KMn04.
Results on Oxygen Deficiency in Monocrystals of Ti02 M1. Error in Sam- KMnO, Gram0 . 0 2 0 7 ~ Deficient Oxygen Atom, Wt., Con- Micro- Micro- Atoms/ Oxygen/ Crystal Type Mg. sumed atoms grams mole Formula Mole Linden 130.5 1.77 18.30 293.0 0.0110 1.9890 f0.0005 72.7 1.20 12.43 199.0 0.0137 1.9863 iz0.0008 123.3 1.99 20.60 330.0 0.0134 1.9866 &0.0005 Linde, bluish transparent 176.0 1.38 14.30 229.0 0.0065 1.9935 A0 ,0007 207.5 1.62 16.80 269.0 0.0065 1.9935 A0.0006 Linde, bluish transparent, 216.0 1.37 14.20 227.0 0.0053 1.9947 f0,0007 after 36 hrs. 700' C. in 217.2 1.42 14.70 235 .O 0.0054 1.9946 f O ,0007 air Linde, oxidized 1000" C., 306.8 0.31 3.22 51.5 0.00084 1.9992 izO.0002 19 hrs. in air Linde, oxidized3 hrs., 190.7 1.09 11.30 181.0 0.0047 1.9953 f 0 . 0 0 0 3 vacuum 820" C. 42.4 0.83 8.60 137.5 0.0162 1.9838 &0.0011 Japanese I Japanese I, small chips 91.6 1.56 16.18 259.0 0.0143 1.9857 f0.0007 Japanese I, oxidized 3 142.6 0.74 7.64 122.2 0.0043 1.9957 f0.0005 hrs., vacuum, 820" C. Japanese I1 Opaque black 74.8 1.57 16.25 260.0 0.0174 1.9826 iz0.0006 97.0 1.72 17.85 286.0 0.0146 1.9854 f0.0006 Bluish transparent 149.0 1.57 16.25 260.0 0.0088 1.9912 iz0.0006 107.7 1.25 12.90 207.0 0.0095 1.9905 iz0.0008 No pumping 209.1 1.88 19.50 312.0 0.0075 1.9925 &0.0003 Continuous pumpingb 201.7 1.79 18.50 296.0 0.0073 1.9927 f0.0003 Large chips (3 hours)S 112.1 1.03 10.70 171.0 0.0076 1.9924
[email protected] a Inhomogeneous material. * During dissolution. e Partial dissolution to check homogeneity. Table
1350
ANALYTICAL CHEMISTRY
This method can naturally be extended to other oxides which tend t o oxygen deficiency, such as ZnO, VZO,, etc. One condition has to be met, that the ions with the highest valence are stable in aqueous solution. With Ti02 monocrystals, this method failed entirely because the dissolution rate was practically nil. Neither heating nor stirring nor the application of other acids than H,SOc accelerated the reaction. In cases where an electronegative element is involved, such as Ti, the usual approach is a caustic or carbonate melt which forms the titanate (zincate, vanadate). Since the melting process requires temperatures a t which the oxygen deficiency would disappear spontaneously by oxidation in air, a vacuum melting procedure was developed, which gave excellent results. PROCEDURE
A few chips of the Ti02 monocrystal were melted with 6 grams of 55 mole % in a platinum Na2C03 45% crucible, A (Figure l), of 20-ml. volume. This crucible was placed on a porous brick pad within a Vycor tube B, which was surrounded by a water-cooled fiveturn induction coil C energized with 400 kc. per second. After evacuation of the Vycor tube to less than loF3 mm. Hg, stopcock D was closed (Figure 1). Application of premelted carbonate lumps reduced the outgassing time considerably. For the following 4 hours, often overnight, permanence of vacuum was observed a t the manometer E, and if no leakage was found, the high frequency field was slowly built up following renewal of pumping until the entire batch of carbonate was melted
+
and reached a temperature of approximately 950' C. The program of the dissolution of the crystal chips could be observed visually through the clear melt and it required normally not more than 3 hours. According to the reacNazCOa = NaTiO, tion: Ti02 COz, the dissolution IS accompanied by a fine bubbling which ceases after the reaction is completed. The COZ pressure was held within 5 to 10 mm. For small deficiencies it is advisable to reduce the reaction temperature to 920' C. and to keep the COZ pressure below 0.6 mm. Thus, the oxygen dissociation pressure of COzis well matched to the oxygen equilibrium pressure of TiOz. After cooling and removing crucible A from the Vycor tube, the solid cone of frozen melt containing the titanate product could be easily taken out and was broken into a few large lumps, which were transferred into a Pyrex tube F , code Corning 6580. A surplus of diluted HzS04 FeZ(SO& was added to dissolve the salt cone and then the Pyrex tube was immediately closed with a stopcock fitted to the tube by a ground joint, (size 29/42). The dissolution process was sufficiently slow (2 hours), because of the relatively large lumps, that the evolved COz could be pumped off in a controlled manner, without losing any liquid. Although the applied liquids had been freed from oxygen by bubbling with nitrogen, the additional COz evolution helped to rinse out any traces of oxygen completely as shown by blank tests with known amounts of metallic Fe. After complete dissolution of the salt cone, the Fe+2 ion product was titrated with 0.0207N KMn04.
+
+
+
RESULTS
Table I compiles a number of representative data. Reliability and Ultimate Sensitiv-
ity. As already shown for oxides with oxygen surplus, the strict exclusion of parasitic oxygen is mandatory. For the vacuum melting phase this was accomplished by adjusting the COZ pressure between 5 and 10 mm. Separate experiments with oxygen deficient Ti02 crystals had shown t h a t under this condition neither oxidation nor reduction occurs. The fact that the same results were obtained with and without pumping during the dissolution process in the melt, as shown for bluish transparent Japanese I1 crystals, seemed to indicate that under these conditions the COzpressure is still less critical. The problem of parasitic oxygen was more critical during the wet phase of the dissolution. Since it was difficult to introduce welldefined oxygen deficiencies into Ti02 crystals, blank tests were made only for this phase of the process. Small portions of pure iron wire (0.002 inch in diameter) equivalent in reduction value to the observed oxygen deficiency were dissolved under the same conditions as the titanate containing melt cones and the produced Fe +2 concentration was titrated. The observed deviation was within k0.8 microatom of iron resulting in the same precision of measurement of oxygen deficiency.
With crystal samples of more than 100 mg., the deficiency value is accurate within *5%, for larger sample weights even better. The accuracy is finely limited by the blank; if larger crystal specimens are available for analysis, the sensitivity limit could easily be boosted by another order of magnitude. ACKNOWLEDGMENT
The authors thank Keystone Carbon Co. for the support of this work, and Eiso Yamaka of Nippon Telephone & Telegraph Public Corp. for supplying rutile crystals. LITERATURE CITED
(1) Breckenridge, R. G., Hosler, W. R.,
Phys. Rev. 91, 793 (1953).
(2)fCronemeyer, D. C., Ibid., 87, 876 (1952). (3) Fntsch, O., Ann. Phys. 22, 375 (1935). (4) Sachse, H. B., ANAL. CHEM.32, 529 (1960). (5) Slack, G. A., Newman, R., Phys. Rev. Letfen 1,59 (1958). (6) Verwey, E. J., Phil. Tech. Rd. 9, 47 (1947). (7) Ibid., 10, 232 (1949). (8) Yamaka, E., Sawamoto, K., Phys. Rev. 112, No. 6, 1861 (1959). (9) Zerfoss, A., Stokes, R. G., Moore, C. H.,Jr., J. Chem. Phys. 16, 1166 (1948).
RECEIVED for review March 24, 1961. Accepted June 29, 1961.
Rapid Chemical Determination of Aluminum, Calcium, and Magnesium in Raw Materials, Sinters, and Slags L. L. LEWIS, M. J. NARDOZZI, and L. M. MELNICK Applied Research laboratory, United States Steel Corp., Monroeville, Pa.
b A
chemical method has been developed for the determination of aluminum, calcium, and magnesium in raw materials, sinters, and slags. The method provides for a rapid group separation of these elements from mixtures, and for their subsequent direct determination. The separation is made by anion exchange chromatography with 1 OM hydrochloric acid as eluent. After the separation, the three metals are selectively titrated with (ethylenedinitri1o)tetraacetic acid. The method has the advantage of speed, yet retains the accuracy of the conventional methods used for determining these elements.
C
for the determination of aluminum, calcium, and magnesium in various materials are particularly time consuming and tedious because these elements have no selective and specific chemical reactions. Consequently, all procedures have required the isolation of these elements from mixtures. A procedure for a rapid group separation of these three elements and their subsequent rapid and direct determination would be useful. Numerous multistep procedures have been based on precipitation, extraction, and electrodeposition for the separation of aluminum, calcium, and magnesium from mixtures containing iron, HEMICAL PROCEDURES
manganese, and titanium. A onestep separation of aluminum, calcium, and magnesium as a group is possible, as indicated by the data of Kraus and Nelson (8), on the adsorption of metallic ions on anion exchange resins in 10M hydrochloric acid. The separation would be rapid because aluminum, calcium, and magnesium (in contrast with iron, manganese, and titanium) are not adsarbed on the resin and would thus be collected immediately. The separation scheme would also be useful for determining aluminum, calcium, and magnesium in nonferrous ores and alloys because copper, cobalt, zinc, tungsten, molybdenum, zirconium, and tin, in addition to iron, manVOL 33, NO. 10, SEPTEMBER 1961
* 1351
