2716
COMMUSICATIOSS TO THE
EDITOR
Vol. 66
gave the same e.p.r. spectra involved introducing manganese into pre-formed pyrophosphates by the same procedure and then firing at the above temperatures. The same method was used to introduce manganese into phosphor grade calcium fluoride and into calcium oxide prepared by ignition of phosphor grade calcium carbonate at 1000°. The manganese was fired into these samples at 1030". The Mn/Ca ratio was in CaFz and 10-3 in CaO. The e.p.r. spectra of Mn+2 in the two pyrophosphates and calcium fluoride are given in Fig. 1 and in calcium oxide in Fig. 2. Comparing these spectra with Kasai's, it is seen MnS04 is that (a) Kasai's spectrum of CaFz identical with our spectrum of P-CazPzO, : 2 X low3Mn, Fig. l(b); and (b) his spectrum of CazPz07 MnS04 resembles neither of our pyrophosphates, but rather it appears to be the spectrum of in CaO, Fig. 2(a). Our spectrum of in polycrystalline CaFz, a large number of sharp lines superimposed on six broad lines, Fig. l(a), appears to be consistent with the results of Baker, Bleaney, and Hayes3 for the e.p.r. of Mn+2 in a single crystal of CaFz. They found that each JIn+2 line, of which there are normally 30, is further split into nine components by hyperfine interaction between the Mn+2 ion and eight nearest-neighbor fluorine nuclei. A re-interpretation of Kasai's experiment investigating the behavior of manganese during the course of reaction to form fluorapatite based on our identification of his reactants follows. Manganese first diffuses into calcium oxide, which then reacts in formation of the apatite. I n support of our interpretation, we present in Fig. 2(b) a composite spectrum of calcium fluorapatite, C a 8 (PO& : 1.5 X Mn, and calcium oxide, CaO: 10-3 Mn, made by introducing both materials simultaneously into the resonant cavity. It matches exactly Kasai's curve for his fluorapatite mixture after 10 min. of firing at 1150". Further substantiation for our interpretation was obtained from time-temperature studies on the rate of manganese diffusion into calcium oxide and beta calcium pyrophosphate. We found that manganese diffused much more rapidly into CaO than into /3-CazP207at temperatures between 900 and 1150'.
+
+
C I IZW
I
I xyo
zoo0
m 1
I XKXl
.ooo
Fig. 1.-E.p.r. spectra of Mn+2 in polycrystalline substances: ( a ) CaF?, (b) P-Ca2P207,and ( c ) a-Ca2P207.
(3) J. M.Baker, B. Bleaney, and W. Hayes, Proc. Roy. Sor. (London), 8847, 141 (1958).
LAMPDIVISION R. I,. HICKOK GENERAL ELECTRIC COMPANY J. A. PARODI IACHTING RESEARCH -4ND DEVELOPMENT OPERATION W. C;. HEGELKEK LAMPRESEARCH LABORATORY CLEVELAND, OHIO RECEIVED OCTOBER 22, 1962
C
rrbo
3dao
I
1pm
T? WQI
I
3em
I
Ibw
Fig. 2.-E.p.r. spectra of Mn+2 in polycrystalline substances: (a) CaO, ( b ) mixture of CaO and CasF(POr)s, and (c) CaJTPOdh.
acetone to which an aqueous solution of a manganous salt (acetate, nitrate, or sulfate) had been added, then drying. A second method which
THE EFFECT OF THE IONIZATION OF WATER ON DIFFUSIONAL BEHAT'IOR IS DILCTE AQTlEOUS ELECTROLYTES Sir: If one ion of a binary salt is radioactively tagged and an aqueous solution of the salt is allowed to
Dec., 1962
COMMUSICATIOSS TO THE EDITOR
diffuse into pure water, we would normally expect to obtain the binary salt diffusion coefficient by measuring the movement of radioactivity. The restriction of electroneutrality ensures that each tagged ion is accompanied by its oppositely charged counterpart. However, it has been pointed out recently‘ that if, in such a system, the salt concentration was reduced to the order of M ,then a different diffusional behavior might be observed. At this order of dilution, the concentration of salt and that of the ions resulting from the ionization of water become comparable. We now have an effective multicomponent system in which coupling can occur between the various species of ions so that the measured diffusion coefficients will contain contributions from cross-term coefficients. Due to the high mobilities of H + and OH- ions, the effect should be quite pronounced and may be detectable a t considerably higher concentrations than lo-’ M . If the concentration of salt is reduced to a sufficiently low value, we might also expect to measure the trace-ion diffusion coefficient of the tagged ion in the above system. In this case it is a trace species in a uniform electrolyte of H + and OH- ions of much higher concentration. In this Laboratory we have been calibrating open-ended capillaries by allowing fairly dilute tagged salt solutions to diffuse into pure water. It is imperative to know the concentration above which the assumption is valid that the binary salt diffusion coefficients are being measured. The effect also is of considerable interest for its own sake and therefore we have undertaken the exploratory studies reported below. The two salts used in these experiments were sodium chloride and magnesium bromide. “Carrierfree” W a c 1 was purified by selective elution through a cation ion-exchange column. JfgszBr2 was made by adding Analar HBr to “Specpure” MgO and then irradiating in the high neutron flux of the Lucas Heights Reactor, Sutherland, N.S.W. The specific activity obtained was of the order of 7 curies/g. of bromine. Solutions were made up approximately by weight and then successively diluted, all concentrations being checked by conductivity measurements. The water used in these studies was purified first by distillation and then by passage through an Elgastat de-ionizer at a rapid flow rate. Its specific conductance was 8.4 X 10-7 mho/cm. For the diffusion measurements a simple open-ended technique was used, the capillaries being of Perspex to minimize absorption. The diffusion coefficients obtained in this work are given in Table I. The measured coefficients are integral ones and for the purposes of this survey, the approximation has been made that they are equal to the differential coefficients at half the solution concentration. To demonstrate the incidence of the effect, these values are compared to salt diffusion coefficients calculated by the (1) L. A. Woolf, D. G. Miller, and L. J. Gosting, J. Am. Chem. SOC., 84, 317 (1962). (2) R. hlills. ibid.. 7 7 , GllG (195.5).
1.1
0
2717
I
I
1 103 1P
E
10-2
h/l1.
Figure 1.
Onsager and Fuoss limiting e q ~ a t i o n . ~The precision of the measurements is from 1 to 2%. TABLE I Dobsd.
x
Salt
NaCl
MgBr,
C , mole/l.
2 9 5 2 3 3 2
5 2 2.9 2.83
x x x x x x x x x x x
10-6 10-6 10-4 10-3 10-8 10-7 10-6 10-8 10-5 10-4 10-3
106.
crn.Q/seo.
1.51 1.54 1.58 1.58 2.13 2.16 2.10 1.75 1.62 1.30 1.14
&ld.
x 105. om. 2/sec. 1.61 1.60 1.59 1.58 1.26 1.26 1.25 1.25 1.24 1.21 1.15
From Table I, the change-over from binary to mixed diffusion is clearly seen for both salts. In the case of NaC1, the presence of some inactive carrier made it impracticable to use concentrations below M . Consequently only the beginnings of the transition to the trace-ion coefficient can be seen. For MgBrz, however, which was chosen because of the large numerical difference between the values of binary and trace coefficients and for the high specific activity obtainable, the changeover as illustrated in Fig. 1 is quite striking. In M both cases the effect commences at about and in the MgBrz case the rate of change is a maxiM . The surprisingly high mum at -4 X (3) L. Onsager and R. M. Fuoss, J. Phffs.Chem., 88, 2689 (1932).
2718
COMMUNICATIONS TO THE EDITOR
concentration a t which the effect becomes noticeable is undoubtedly related to the high mobilities of 11+ and OH- ions. Further studies would require greater control of water purity and a more refined diffusion technique to increase precision. It is of interest to speculate whetlicr tlic sliapc of thc curve in the transitional
Vol. 66
region would give information about the crossterm coefficients which are required to describe multicomponent diffusion. RESEARCH
OF
SCIENCES
A~~~~~~~~~ N~~~~~~~uNIVERsITY CANBERRA, A. C. T., AUSTRALIA RECEIVED NOVEMBER 9, 19G3
R. MILLS
