STUDY OF RADIOLYSIS OF HYPOPHOSPHITE BY MEANS OF MÖSSBAUER SPECTROSCOPY

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STUDY OF RADIOLYSIS OF HYPOPHOSPHITE BY MEANS OF MÖSSBAUER SPECTROSCOPY

Y. Maeda, Y. Takashima

To cite this version:

Y. Maeda, Y. Takashima. STUDY OF RADIOLYSIS OF HYPOPHOSPHITE BY MEANS OF MÖSSBAUER SPECTROSCOPY. Journal de Physique Colloques, 1979, 40 (C2), pp.C2-553-C2-555.

�10.1051/jphyscol:19792192�. �jpa-00218570�

STUDY OF RADIOLYSIS OF HYPOPHOSPHITE BY MEANS OF MOSSBAUER SPECTROSCOPY

Y. Maeda and Y. Takashima

Department of Chemistry, Faculty of Science, Kyushu University, Fukuoka 812, Japan

Abstract.-y-ray and electron radiolysis of solid phosphinate have been studied. Ferric phosphinate is easily decomposed by y r a y s with the ferric ion being reduced to ferrous ion. Whereas, iron of ferrous phosphinate is insensitive to irradiation up to a dose of 1700 Mrad. The decomposition of anion ligand (i.e. phosphinic acid) decreased with increasing oxidation number of the metal ion except for ferric phosphinate. Some decomposition products are P2 - P2 precursor in solid material, The precursor is hydrolyzed on dissolving in water and changes to the compounds, P3 , P^-P2, P^-P1*, and P5.

1. Introduction.- It is known that the decomposition of the ligand molecule in metal compounds are affec- ted by the central metal ions IM. In this case phosphinic acid was selected as the ligand molecule.

Phosphinic acid is a monovalent lower oxo-acid.

Y~ray radiolysis of metal phosphinate has hardly been studied to date /2/, although there have been many studies about the radiolysis of trivalent metal phosphonate 13/. In Mg(H2P02) 2.6H20 and NH.,H2P02, HP02 and P02-H2P02 2~ have been reported as long lived radicals /4/. As the radicals produced in ra- diolysis play a major role in solid materials, metal- radical reactions are assumed to be significant.

2. Experimental.- Y- r aY a nd electron sources were used to irradiate the powdered compounds. A 3500 Ci cobalt 60 source provided the Y- r ay radiation for the material which was vacuum sealed in glass tubes.

For the electron bombardment a two meV resonance transformer generator was used with a conveyer sys- tem and in this case samples were contained in poly- ethylene bags. The dose rates were measured using Fr*icke dosimetry. For the Y~ray source the dose rate was 4x10 rad per hour and for electrons it was

lxlO6 rad per One pass. It takes one minute for the conveyor to make one pass. The chemical analysis was carried out as follows. The irradiated phosphinic metal compounds were dissolved in 0^2 ml of

six molar hydrochloric acid and immediately diluted with water to 50 or 100 ml. These solutions were then analyzed. The solutions of the compounds Fe(H2P02)2, Fe(H2P02)3, Co(H2P02)2, Mn(H2P02)2,

Ni(H2P02)2.6H20 and A1(H2P02)3 were analyzed after removing the metal ions using anion exchange resin (Dowex 1x8, 100-200 mesh). In order to determine the contents for phosphinic acid in hhe coexistence of orthophosphoric acid and phosphonic acid, we ana- lyzed for them using Anton's method /5/. The absorp- tion band at 400 nm was used for the determination of univalent phosphorus. Total phosphorus and penta- valent phosphorus produced in the radiolysis were determined according to the method reported by Lucena-Conde and Prat /6/, with the absorption band at 820 um measured with an Hitachi-101 spectropho- tometer. The Mossbauer spectrometer used was descri- bed elsewhere 111 with source being 57Co of 10 mCi activity in Pd foil. The parameters of the Mossbauer spectra were computed by fitting the Lorentzian line shapes to the experimental data using a least-squares method. Since the Mossbauer measurements were carried out after irradiation, only the stable changes in the investigated compounds were observed.

3. Results and Discussion.- Table I lists the per- centage decrease of phosphinate in the various metal phosphinates. Units used are percent of the decom- posed phosphinic molecule to total phosphorus. The values of the left column show the percentage de- crease of the phosphinic molecules by 400 Mrad Y-ray irradiati on. The values of the right side show the percentage decrease of the phosphinic molecules by 200 Mrad electron bombardment. The difference between Y~ray irradiation and electron bombardment is not observed except that the electron bombardment JOURNAL D E PHYSIQUE Colloque Cl, supplément au n° 3, Tome 40, mars 1979, page C2-553

Résumé.- Les effets de radiolyse aux électrons et aux rayons y sur des sels hypophosphites solides ont été étudiés par effet Mossbauer. L'hypophosphite de fer (III) se décompose sous l'influence des rayons y et le F e3 + est réduit en F e2 +. Par ailleurs, 1'hypophosphite ferreux (II) est stable sous des irradiations allant jusqu'à 1700 Mrad. La décomposition des anions diminue quand le nom- bre d'oxydation de l'ion métal augmente, à l'exception de 1'hypophosphite de fer. Plusieurs pro- duits de décomposition sont des précurseurs P2 - P2 dans les matériaux solides. Ces précurseurs se transforment par hydrolyse en des composés divers du type P3, P^-P2, P"-P" ou P5.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19792192

C2-554 ^JOURNAL DE PHYSIQUE

results in a higher yield in the decomposition of red with for some reason or other, the

H ~ O Z -

radical the phosphinic molecule. recombines with .H. If the - H radical diffuses rapid-

ly from the spool area, the decrease in phosphinate Table I

:

The decomposed fraction of HzPOZ- of the anion radical

proceeds

In

the nickel conr

sam~les.

pounds, hydrated water would have some effect on

I I

: y-ray irrad. : electron irrad.

: ^{400 Mrad}

(%)

: ^{200 Mrad}

^(%)

I I

I

,

N~H~PO;HZO

I I

16

I I

17

I I

KH2P02

^I t

13

^I I

13

M ~ ( H ~ P o ~ ) ; ~ ~ o i ¹²

^{1 I I 1 1}

I

Ca(HzP02)z i

¹⁰ _I ^{I I 1 1}

Mn(HzP0z)z 6

I ^I

6.5

1

Fe (HzP02

12

j ⁵

^{I I}

^6.3

1

CO(H~POZ)Z I ⁶

^{I I} _I

^7.2

N~(HZPOZ);~HZO

i ⁵

^{1 I I 10}

I

~l(HzP02)3 i ²

^{1 t} 4 . 7

I

Fe(HzP02)

3 ¹ I 10 I ^I

2

1

1 I

In ferric phosphinate the coupled reduction of the central metal ions with the oxidative decomposition of the phosphinic molecules occurs at relative high G value. The phosphinates of manganese, iron(II), cobalt, and aluminium, show low G values. This re- sult suggests that the decomposition of the anion molecules in these compounds

is

affected by the cencral metal ion. The irradiation induced electron transfer from the anion to such central metal ions as ferric ion results in the high quantum yield of the decomposition of the anion molecule. Redox po- tential of the central metal ion affects the reac- tion mechanism of the anion molecule. The order of the G value of the decreased phosphinate decreases as follows; monovalent metal phosphinate

>

bivalent metal phosphinate > trivalent metal phosphinate.

&PO;

+ ~fi0~-

+ .H

(1)

HPo2-

+

H2PO;

+ ; 0 2 - ~ 2 ~ 0 2 ~ - +

- H (2) In equation

(2)

the radical reacts with a neighbo- ring ph~sphinic anion. If reaction (2) is interfe-

the radiolysis.

In iron(I1) phosphinate, the decomposition of the phosphinic molecules has a small G value. We were not able to recognized any additive peaks of oxidative iron in a Gssbauer spectrum of 1700 Mrad y-ray irradiated iron phosphinate, although y-ray irradiation brings about the decomposition of the phosphinic molecule.

In Mgssbauer spectra of the iron(II1) phos- phinate after T r a y irradiation (the dose of y-ray irradiation was 1200 Mrad), the ferric lines decrea- sed in intensity and the new absorption lines are characteristic of the bivalent iron doublet. Mixed crystals of Fe0.5A10.5(H2P02)3 and Fe0.12A10.88 (H2P02)) were prepared. X-ray powdered diffraction analysis shows that Feo.5A10.5(H2P02)3 has two type of patterns, that is, the crystal structure of iron phosphinate and aluminium phosphinate. Fe0.12Al~,e~

(H2P02)3 has only one pattern of aluminium phosphi- nate. In the Gssbauer spectrum of Fe0.12A10.88

(H2P02)3 iron(I1) component becomes dominant afcer 360 Mrad y-ray irradiation. Table I1 gives the yield of bivalent iron and the percentage of the decrease of phosphinic molecules per one mole per

100 Mrad y-ray irradiation. G values of iron(I1) produced in the raidolysis increase with decreasing amounts of iron. From the ratio of the yield of bi- valent iron to the decrease of phosphinic molecules, we are able to find that the decomposition of two or three phosphinic molecules brings about the reduc- tion of one iron atom. Larger G values of iron(I1) produced in Fe0.~zA10.e8(H2P02)3 than in Fe(H~P02)s show that an electron released from the decomposed H2P02- anion transfers to the central or neighboring iron(II1) atoms.

able I1

:

The Yield of ferrous species produced by y-irradiation, the decrease of the hypophosphite, and the c(Fe2+) value in y-radiolysis .

L

v I

: Yield of Fez+ j Decrease of P' i ^G(Fe~+)

Compound ; Dose(rad.) '

I

: (mol/molxl~'rad.) : (mol/molxl~'rad.):

I 1 I I

I I I 1

Fe(HzP02)3 :

¹

^{.1x109 0.057}

^{I I}

^0.12

^{I I}

I I I 1

I I I

: ^5.4~10' : ^0.078

^{1 I}

;

¹

^3.4

I I I 1

Fe0.~0Alo.ro(HzP02)3 j ^{4 . 0 j 0.070}

^I

^0.17

^I

^6.6

I I I

I I I 1

F ~ ~ . ~ ~ A ~ ~ . B B ( H z P O Z ) ~ 3.6~10' : ^{0.026 0.081}

^{I 1}

I I 1 I

1 I 1 1

References

/I/ Sugimori, A., B u l l . Chem. Soc. Japan,

39

(1966) 2583.

/ 2 / Kobayashi,

M.,

Takada, J., and Kiso, Y . , Radiochem.

Radioanal. L e t t .

9

(1972) 63, 67.

131 Haissinsky, M., J. Chim. Phys.

62

(1965) 1141, 1149.

/4/ KEksal, F. and Y i k s e l , H . , 2. Naturforsch.,

30A

0975) 1044; Morton, J . R . , Mol. Phys.

5

(1963) 193.

151

Anton, A., Anal. Chem.,

37

(1965) 1422.

/6/ Lucena-Conde, F. and P r a t , L . , Anal. Chim. Acta,

16

(1957) 473.

/ 7 / Takashima, Y . and Maeda, Y . , J. Inorg. Nucl. Chem.

2

(1969) 1337.