Actinide Chemistry

17 The Solid-State Chemistry of Americium Oxides

Downloaded by MONASH UNIV on September 14, 2017 | http://pubs.acs.org Publication Date: June 1, 1967 | doi: 10.1021/ba-1967-0071.ch017

C. KELLER University of Karlsruhe and Nuclear Research Centre, Karlsruhe, Germany Ternary and polynary oxides of trivalent to hexavalent americium are obtained by solid-state reactions of Am O and AmO with the oxides of various elements. Compounds of pentavalent and hexavalent americium, which are isostructural with the corresponding ternary oxides of Pa, U, Np, and Pu, are formed only with the oxides of alkali metals and alkaline earth metals. By reaction of AmO with oxides of tetravalent elements—e.g., SiO , GeO , ZrO , HfO or ThO —ternary oxides or oxide phases with tetravalent americium are stabilized. The solid-state reaction of AmO with most group V elements yields compounds with trivalent americium which are isostructural with the analogous rare earth compounds. In the last types of reactions americium exhibits a typical actinide behavior. 2

3

2

2

2

2

2

2

2

2

T n a c c o r d a n c e w i t h its e l e c t r o n i c c o n f i g u r a t i o n a n d t h e r e s u l t i n g p o s i A

t i o n i n t h e p e r i o d i c system of elements t h e a c t i n i d e element a m e r i c i u m

is t h e h e a v y h o m o l o g of t h e rare e a r t h e l e m e n t e u r o p i u m (14) : Americium:

5s p d f

Europium :

4s pW f

2

2

Q

6s p ^( S )

10

2

c

6s p 7s> ( S

10

2

G

8

8

7 / 2

7/2

).

D e s p i t e this f o r m a l r e l a t i o n s h i p a c o m p a r i s o n of t h e c h e m i c a l p r o p erties of t h e t w o elements shows c o n s i d e r a b l e differences, n o t o n l y o f a q u a l i t a t i v e b u t also of a f u n d a m e n t a l n a t u r e . A l l experiments to d a t e h a v e f a i l e d to p r e p a r e b i v a l e n t a m e r i c i u m i n a n a l o g y w i t h ( C o m p o u n d s s u c h as A m O a n d A m H

2

E u (II).

contain bivalent americium only

i n a f o r m a l sense). I n contrast to t h e rare e a r t h elements, a m e r i c i u m is a b l e to exist i n s o l u t i o n as w e l l as i n s o l i d c o m p o u n d s i n t h e o x i d a t i o n states + 4 , + 5 , a n d -\-6. T h i s shows a close r e l a t i o n t o t h e elements 228

Fields and Moeller; Lanthanide/Actinide Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1967.

17.

K E L L E R

Americium

229

Oxides

p r e c e d i n g it i n the p e r i o d i c system of elements—i.e., u r a n i u m , n e p t u n i u m , and plutonium. T h e 3 + v a l e n c e of a m e r i c i u m is the most stable i n s o l u t i o n as w e l l as i n s o l i d c o m p o u n d s , element. Nd

(r =

3 +

as s h o w n b y its b e h a v i o r as a t y p i c a l a c t i n i d e

B e c a u s e of the s i m i l a r i o n i c r a d i i of A m

3 +

(r =

0.99 A . ) a n d

0.995 A . ), there is a close r e l a t i o n s h i p i n the c h e m i c a l b e h a v i o r

of these elements i n the 3 + v a l e n c e state. T w o oxides of a m e r i c i u m are k n o w n so f a r : A m 0 A m 0 , w h i c h crystallizes i n the fluorite l a t t i c e (a = 2

2

and A m 0

5.377 ±

2


is f o r m e d b y a n n e a l i n g the oxalate, h y d r o x i d e , or other easily posing compounds of A m 0

2

of a m e r i c i u m i n o x y g e n at 8 0 0 ° - 1 1 0 0 ° C .

decom

Reduction

w i t h h y d r o g e n at 6 0 0 ° C . y i e l d s the c u b i c m o d i f i c a t i o n of A m 0 2

( M n 0 - t y p e , rare e a r t h C - t y p e oxide, a = 2

(40).

3

0.001 Α . ) ,

3

11.03 Α . ) , at 8 0 0 ° C .

h e x a g o n a l m o d i f i c a t i o n ( L a 0 - t y p e , rare e a r t h A - t y p e oxide, a = 2

Α., c =

5.971 Α . ) .

3

the 3.817

3

T h e system A m - O has not b e e n i n v e s t i g a t e d sys

t e m a t i c a l l y as yet.

Figure 1. Glove-box with thermomicrobalance (type Mettler) installât ed T h i s p a p e r b r i e f l y surveys the solid-state reactions of A m 0 Am 0 2

3

2

and

i n the presence of second or t h i r d m e t a l oxides at h i g h e r t e m p e r a -

tures. T h e m a i n interest is f o c u s e d u p o n three types of r e a c t i o n s :


230

LANTHANIDE/ACTINIDE

CHEMISTRY

( a ) R e a c t i o n w i t h t h e oxides of a l k a l i metals a n d a l k a l i n e e a r t h metals w i t h t h e a i m of p r o d u c i n g t e r n a r y oxides of p e n t a v a l e n t a n d hexavalent americium. ( b ) R e a c t i o n w i t h oxides of the g r o u p I V elements. It w a s to b e e x p e c t e d t h a t i n this r e a c t i o n t h e 4-f- v a l e n c e of a m e r i c i u m w o u l d b e m a i n t a i n e d w i t h c o m p o u n d s of t h e g e n e r a l t y p e A B 0 , a n d i n s o l i d solutions of t h e A 0 - B 0 t y p e . ( c ) T h e r m a l b e h a v i o r of A m 0 i n t h e presence of oxides of g r o u p I I I a n d V elements. It w a s to b e e x p e c t e d t h a t a m e r i c i u m w o u l d b e h a v e as a t y p i c a l a c t i n i d e element—i.e., that t h e m a j o r i t y of t h e t e r n a r y oxides to b e e x p e c t e d c o n t a i n A m ( I I I ) . T h i s a s s u m p t i o n is b a s e d u p o n t h e analogous b e h a v i o r of CeO >, P r O n , a n d T b 0 f o u n d i n reactions w i t h oxides of g r o u p V elements as w e l l as u p o n t h e excellent t h e r m a l s t a b i l i t y a n d t h e h i g h l a t t i c e s y m m e t r y of c o m p o u n d s l i k e M e X 0 3 a n d Me X 0 . I V

2

I V

4

2

2


L

6

4

7

m

l n

v

Methods

m

4

of

Investigation

A l l investigations w e r e c a r r i e d out i n g l o v e boxes w i t h q u a n t i t i e s of 5-20 mg. A m 0 . T h e e x p e r i m e n t a l results w e r e e v a l u a t e d m a i n l y b y x - r a y analysis. I n s p e c i a l cases, d i f f e r e n t i a l t h e r m a l analysis ( D T A ) a n d the t h e r m o g r a v i m e t r i c analysis ( T G A ) ( F i g u r e 1) w e r e e m p l o y e d , r e s p e c t i v e l y . T h e v a l e n c e of a m e r i c i u m i n t h e t e r n a r y oxides w i t h A m ( V ) a n d A m ( V I ) , after d i s s o l u t i o n of t h e r e a c t i o n p r o d u c t i n d i l u t e d H C 1 0 , w a s d e t e r m i n e d b y r e c o r d i n g a n a b s o r p t i o n s p e c t r u m of t h e s o l u t i o n obtained. 2 4 1

2

4

Table I .

System

T e r n a r y Oxides of T r i - to Hexavalent

Reaction

Composition

Li 0/Am0 2

Li 0/Am0 2

2

5

LiLi 0/Am0 2

Li 0/Am0 2

1

Na 0/Am0 2

Na 0/Am0 Na 0/Am0 2

2

2

AmO Am0 Am0 AmO,

5

2LUO + 2 A m O / 4 5 0 ° C . / O / 4 h r s . 2

f )

6

3

7

2

3

6

4

6

3

2

3

4

2

2

2

2

2

2

2

L i 0 + A m O / 6 0 0 ° C . / H / 3 0 hrs. 2

Am0 AmO, AmQ AmO

2

3

2

2 . 5 N a 0 + A m 0 / < 3 0 0 ° C . / O / 4 hrs. 3 . 5 N a 0 + A m O / 4 0 0 ° C . / O / 6 hrs. 2 N a 0 + A m O / 6 5 0 ° C . / O / 4 hrs. N a C 0 + A m O / 7 5 0 ° C . / N / 6 hrs.

5

6

4

2

2

s

2

2

2

2

2

2

2

2

2

2

3

2

2

2

BaOo + A m O / 1 1 0 0 ° C . / O / 8 hrs. 1.5BaO + A m O / 1 2 5 0 ° C . / O / 3 0 hrs.

6

2

3

2

2

BaO · A m 0 SrAm0 2

3

2

L i 0 + A m O / 6 0 0 ° C . / v a c u u m / 1 6 hrs. 4 L i 0 + A m 0 / 6 0 0 ° C . / v a c u u m / 1 6 hrs.

2

3

δ

2

2

6

8

Na Na Na Na

9

4

Li Am0 Li Am0

2

3 . 5 L i 0 + A m O / 3 6 0 ° G / O / 1 2 hrs. 1.5Li>0 + A m O / 7 0 0 ° C . / O / 6 hrs. L i A m 0 + L i O / 9 0 0 ° C . / N / 1 2 hrs.

6

Ba Am0 BaAm0

3

2

4

LiAm0

3

2

BaO/AmOi SrO/Am0

2

5

! 2

BaO/Am0 BaO/Am0

Li Li Li Li

3

Conditions

:

2

BaAmO /1250°G/H 1.5SrO + A m O / 1 2 5 0 ° C . / O / 3 0 hrs. 2

2

2

2


17.

Americium

K E L L E R

Oxides

231

Results and Discussion T h e r e a c t i o n c o n d i t i o n s a n d the lattice constants of the a m e r i c i u m compounds

d e s c r i b e d i n the f o l l o w i n g sections are l i s t e d i n T a b l e s

I

and II. Ternary Oxides of Trivalent to Hexavalent Americium with L i t h ium and Sodium. Solid-state reactions of A m 0

w i t h L i 0 i n o x y g e n at

2

2

3 5 0 ° - 4 5 0 ° C . , d e p e n d i n g o n the m o l a r r a t i o of L i 0 : A m 0 , result i n t h e 2

compounds

Li Am0 4

5

20).

6

The blackish-brown L i A m 0 4

d i s c o v e r e d b y K o v b a (26), Downloaded by MONASH UNIV on September 14, 2017 | http://pubs.acs.org Publication Date: June 1, 1967 | doi: 10.1021/ba-1967-0071.ch017

2

a n d L i o A m 0 w i t h h e x a v a l e n t a m e r i c i u m (4, has the t e t r a g o n a l s t r u c t u r e of

5

a n d H o e c k s t r a a n d S i e g e l (12),

w h i c h is a lattice d e r i v e d f r o m a - U F

Li U0 4

5

respectively,

closely r e l a t e d to the r o c k s a l t

5

structure. I n adherence to the h e x a g o n a l i n d e x i n g of x - r a y p o w d e r p a t terns of the c o m p o u n d s

Li Bi0 7

and L i P b 0

6

8

g i v e n b y Blasse ( 5 ) ,

6

and

S c h o l d e r a n d H u p p e r t ( 3 8 ) , r e s p e c t i v e l y , i t w a s also possible to deter m i n e the l a t t i c e constants Li Am

0 .

I V

8

of

Me Am 6

V I

0

6

(Li, Na), L i A m 0 , v

7

6

and

D e s p i t e the different A m : L i r a t i o a n d t h e different v a l e n c e

6

of a m e r i c i u m the c o m p o u n d s of the t y p e L i ^ A m O e ( χ •= 6, 7, 8 ) are isos t r u c t u r a l a m o n g e a c h other. T h e analogous solid-state r e a c t i o n of N a 0 2

2

with A m 0

2

i n oxygen

a l w a y s results i n «-Na AmO > of the rocksalt s t r u c t u r e b e l o w 3 0 0 ° C , 4

r

but

i n t h e t e m p e r a t u r e r a n g e b e t w e e n 300° a n d 5 0 0 ° C , one obtains N a A m 0 6

6

Americium with Alkaline and Alkaline E a r t h Elements Lattice Constants (A.) Type of Li Li Li Li

U0 ReO U0 Bi0

4

6

3

7

(12, 26), t e t r a g . (38), hexag. ( 5 ) , tetrag. ( 5 ) , hexag.

5

f )

4

6

L i P r 0 , unknown L i P b O (5), hexag. 2

a

Structure

c

, Isostructural Compounds

T

6.666 5.174 4.459 5.54

±0.001 ± 0.005 ± 0.005 ± 0.02

4.415 14.59 8.355 15.65

±0.002 ±0.05 ± 0.01 ± 0.05

Np, Pu Te, N p , P u Pa, U , Np, Pu Sb, N b , T a , Os, Pa, U , N p , P u

5.62

±0.02

15.96

±0.05

16.10

± 0.1

Sn, Zr, Ce, Pr, T b , Ir, P t , P u La, Pr, N d , Sm, Gd, E u U, Np, Pu Re, Te, N p , P u U, Ru Ti, Tc

3

8

e

«-LiEu0 a-Na UO Li ReO , Na U0 Li SnO 4

(3),

2

monoklin

, cubic hexag. (38), cubic (27), monoklin

r >

B a W O , cubic C a T i 0 , cubic

5.76 ± 0.03 4.757 ± 0.005 5.92 ± 0 . 0 1 b = 10.26 ± 0 . 0 2 8.81 ± 0 . 0 1 4.365 ± 0.005

C a F e 0 , orthorhomb. C a T i 0 , pseudocubic

4.23 ±

6

e

3

4

2

a

3

e

3

2

4

3

11.23 ± 0 . 0 2 β=100°7'

U , Np, Pu, Mo Pa, U , Np, Pu, Tc, Zr R . E . , Y , Sc

0.05


232

LANTHANIDE /ACTINIDE

Table l i a .

System Am 0 /B 0 Am 0 /Al 0 Am 0 /V 0 Am0 /Si0 Am0 /Ge0 BaO/AmOi BaO/AmOi TiOg/AmOi Ti0 /Am0 2

3

2

3

2

3

2

2


2

5

2

2

5

5

0 0 0 0

5

2

5

2

2

2

5

5

System

5

2

1 5

1 5

Am0 Am0

1 5

1 5

6

4

2

6

4

Ternary and Polynary Oxides of T e t r a Reaction

2

5

/As 0 2

Am(N0 )

7

Am0 .5/Ta 0 2

1

5

^-AmNb0 Am NbO o:-AmTa0

/Pa 0 2

Ta0

0

5

4

2

2

+

3

2

4

(NH ) HAsO /1000°C. 4

2

4

+ V O / 1 0 0 0 ° C . / 1 0 hrs. + N b O 5 / 1 2 0 0 ° C . / 2 4 hrs. 2

5

2

2

2

3

0

r >

2

i n d e p e n d e n t l y of the N a : A m ratio. to A m ( V I )

2

2

2

(Am ' ni, Pa . v)O

5

2

660°C. 2 A m 0 + 3 N b O / 1 2 0 0 ° C . / 2 4 hrs. 2 A m 0 + T a O / 1 2 0 0 ° C . / 2 4 hrs.

a

4

3 3

4

2Am0 2Am0

4

3 3

0

2

3

4

Am

2

2

2

4

AmV0 AmNb0

5

2

2

3 +

2

5

/V 0 /Nb 0 2

AmAs0

7

2

4

5

Conditions

A m 0 + ZrO /1200°C./20 h r s . / H A m 0 + HfO /1400°C./20 h r s . / H Am + H P O 7 8 0 ° C . / 4 hrs. A m 0 + ( N H ) H P O / 8 0 0 ° C . / 6 hrs.

2

9

4

1 5

4

2

Am Zr 0 Am Hf 0 A m P 0 · 0-0.5H O AmPO, 2

2

0

Am0

2

4

Composition

AmOi / Z r 0 Am0 /Hf0 Am0 /P 0

Am0

2

4

6

Table l i b .

3

2

4

4

/Nb /Ta /Nb /Ta

3

4

4

5

3

3

3

1

1 5

2

3

2

Conditions

A m 0 + H B O / 9 0 0 ° C . / 1 2 hrs. A m ( O H ) + A 1 ( O H ) / 1 2 5 0 ° C . / 1 6 hrs. A m V 0 + H / 1 2 0 0 ° C . / 8 hrs. A m ( O H ) + S i 0 · aq/230°C./7d A m ( O H ) + G e 0 · aq/230°C./7d B a O + A m N b O / 1 3 0 0 ° C . / 8 hrs. B a O + A m T a O / 1 3 0 0 ° C . / 8 hrs. T i 0 + A m N b O / 1 1 5 0 ° C . / 2 4 hrs. T i 0 + A m T a O / 1 1 5 0 ° C . / 2 4 hrs.

3

2

2

Reaction

AmB0 AmA10 AmV0 AmSi0 AmGe0 Ba AmNb0 Ba AmTa0 AmNbTiQe AmTaTi0

3

3

2

Ternary and Polynary Oxides of Tetra-

Composition

3

2

CHEMISTRY

2

5

5

2Am0

2

+ 3 T a O / 1 2 0 0 ° C . / 2 4 hrs.

2Am0

2

+

2

5

Pa 0 7ll00°C./8 2

Quantitative oxidation

of A m ( I V )

takes a surplus of a b o u t 0 . 3 - 0 . 5 moles N a 0 . 2

s o d i u m shortage, p a r t of the A m 0

2

hrs

5

I f t h e r e is a

2

is present after the r e a c t i o n

without

h a v i n g u n d e r g o n e c o n v e r s i o n to A m ( V I ) . T h e c o m p o u n d s of h e x a v a l e n t

americium

little thermal stability. A t 550°C. ( M e =

w i t h a l k a l i metals

have

L i ) and 700°C. ( M e =

Na)

t h e r e is a loss of o x y g e n , a n d c o m p o u n d s w i t h p e n t a v a l e n t are f o r m e d ( 3 1 ) . Li 0-Am0 -0 2

2

2

The continued

t h e r m a l d e c o m p o s i t i o n i n the

results d i r e c t l y i n A m 0

t h e d e c o m p o s i t i o n of N a A m 0 3

4

americium

2

system

above 900°-1000°C.; whereas

leads to A m 0

2

via N a A m 0 . 2

3

The indi-


17.

Americium

K E L L E R

233

Oxides

and Trivalent Americium w i t h Group III-V Elements Lattice Constants (A.) -

Type of Structure Aragonite, orthorhomb. L a A 1 0 , hexagonal G d V O g , orthorhomb. Z r S i 0 , tetragonal C a W 0 , tetragonal B a W O , cubic B a W 0 , cubic C a T a 0 , orthorhomb. C a T a O , orthorhomb.

5.053 5.336 5.45 6.87 5.04 8.520 8.518 5.34 5.33

3

4


4

3

e

3

6

2

6

2

e

Isostructural Compounds

c

5.85

5.738 12.91 7.76 6.20 11.03

11.00 10.95

7.53 7.49

8.092

R.E. Pr, N d , P u R.E., Pu Th-Pu Zr, C e , T h - P u R.E. R.E. L a - E u (-Lu) La-Dy

and Trivalent Americium with Group III-V Elements Type of

Structure

Lattice Constants

(A.)

b

c

a

Pyrochlor, cubic Pyrochlor, cubic C e P 0 · 0 - 0 . 5 H O , hexag. T h S i 0 , monoklin

10.565 10.650 6.99 6.73

6.93

T h S i 0 , monoklin

6.89

7.06

Z r S i Q , tetragonal Y T a 0 , monoklin

7.31 5.444

Z r S i 0 , tetragonal La NbO Y T a 0 , monoklin

5.30 3.819 5.489

La NbO Fluorite, cubic

3.889 5.458

4

2

4

4

4

4

4

0 3 3

3

4

0

3 3

3

Isostructural Compounds R.E. R.E. R.E., Cm, Ac R.E., Pu, C m

6.39 6.41 β = 103°50' 6.62 β = 105° 30' 6.42 5.141 β = 95°57' 11.34 7.835 5.115 β = 95°22' 7.820

11.25

11.21

La-Nd, Pu Ce-Lu R.E., Pu R.E. R.E. R.E. La-Nd, Cm La-Er, Y, C m

v i d u a l modes of d e c o m p o s i t i o n a n d the temperatures of

decomposition

are i n d i c a t e d i n F i g u r e s 2 a n d 3. The

simplest w a y

Li Am0 , 3

Li AmOo,

4

7

to

prepare

and N a A m 0 3

( N a 0 ) to react i n a stream of N 2

2

q u o t e d i n F i g u r e s 2 a n d 3.

4

lattice, L i A m 0 3

Li U0 3

Li

+

4

3

4

+

m e t a l americates

allowing A m 0

some 1 % 0

2

2

and

4

4

(37)

(V) Li 0 2

at t h e t e m p e r a t u r e s 7

3

3

alkali

is b y

T h e t h e r m a l s t a b i l i t y of L i A m 0

u p to some 1000 ° C ; via L i A m 0 W h i l e N a A m 0 , as N a U 0

2

the 4

6

extends

the d e c o m p o s i t i o n finally y i e l d s A m 0 . 2

c r y s t a l l i z e s i n the u n d i s t o r t e d N a C l -

has t h e t e t r a g o n a l l y d i s t o r t e d r o c k s a l t s t r u c t u r e of

( 5 ) , w h i c h is c a u s e d b y a l a r g e r difference i n the i o n i c r a d i i of

and A m . 5 +


234

LANTHANIDE/ACTINIDE

Li 0:Am0 2

, 3.5:1 0

2

LioO:Am0

360°C.

e

>-

LLAm0

Li AmO«

6

, 2.5:1

420°C. — L i

K

U

4

A m O

2

r

«.

8

450°-500°C. 0

CHEMISTRY

600°C. ^

2

4.5:1

800°C.

,

I 550°-900°C.

ο ι

550°C. —*-

u

Li Am0 3

1000°C. .

4

2

χ A

m

1000°C.

ί Λ

°

2

2


1000°C. w

900°C. ( N / ~jjT 0 )

4:1

2

Figure 2.

2

Li Am0 7

1000°C./O

6

Preparative

Li Am0

600°C. — —

3

1.5:1

2

LiAm0

2

600°C. ~* J J

1:1

conditions and thermal stability of compounds in the system Li-Am-0

Na 0:Am0 2

2

> 300°C.

2:1

-Na Am0 )

tt

4

5

350°C. 300°-50()°C.

3.5:1

Na Am0 e

6

6()0°-700°C. 600°-700°C.

2:1

Na Am0 3

4

700°-800°C. 700 -800°C. N o

1.5:1

Na Am0 2

3

2

900°C AmO.,

Figure 3. Preparative conditions and thermal stability of compounds in the system Na-Am-0 A l t h o u g h a b o v e 7 0 0 ° C . the t h e r m a l d e c o m p o s i t i o n of the A m ( V ) a n d A m ( V I ) c o m p o u n d s w i t h s o d i u m passes t h r o u g h N a A m 0 — o f the m o n o c l i n i c s t r u c t u r e of L i S n 0 ( 2 7 ) — i t w a s not possible to o b t a i n a n i n t e r m e d i a t e c o m p o u n d w i t h A m ( I V ) for L i - c o m p o u n d s . D o u b l e oxides i n the system L i 0 - A m 0 w e r e o b t a i n e d b y d i r e c t r e a c t i o n of L i 0 w i t h A m 0 i n a n e v a c u a t e d q u a r t z tube. A t 600 ° C . one obtains for L i 0 : A m 0 = 1.5:1 the substance L i A m 0 w h i c h is i s o s t r u c t u r a l w i t h L i P r 0 ( 3 6 ) ; i n t h e case of L i 0 : A m 0 = 4.5:1, t h e c o m p o u n d L i A m 0 . T h e L i 0 surplus is necessary to compensate for the v o l a t i l i z a t i o n of L i 0 . 2

2

2

3

3

2

2

2

2

2

2

2

3

2

8

2

3

6

2

2


17.

Americium

K E L L E R

Oxides

235

B y solid-state reactions of A m 0 2

i t w a s p o s s i b l e to p r e p a r e L i A m 0 clinic « - L i E u 0

3

w i t h L i 0 i n h y d r o g e n at 6 0 0 ° C , 2

w h i c h is i s o s t r u c t u r a l w i t h t h e m o n o -

2

the l a t t i c e constant of w h i c h has b e e n d e t e r m i n e d

2

Barnighausen (3).

by

Probably, another h i g h temperature modification m a y

be e x p e c t e d for L i A m 0

w h i c h , as / 3 - L i E u 0

2

2

(2)

or L i G d 0 , has a n 2

orthorhombic structure. Most

of

the compounds

of

t e t r a v a l e n t to

hexavalent

americium

d e s c r i b e d here w e r e o b t a i n e d for u r a n i u m , n e p t u n i u m , a n d p l u t o n i u m (Table III).

T h e decomposition

t e m p e r a t u r e s of the a m e r i c i u m c o m -


p o u n d s are c o n s i d e r a b l y b e l o w ( 2 0 0 ° - 3 0 0 ° C . ) those of t h e c o r r e s p o n d i n g t e m p e r a t u r e s of the analogous neptunates a n d p l u t o n a t e s (4,

25).

Compounds of Americium with Alkaline Earths Metals. W h i l e the system a m e r i c i u m o x i d e — a l k a l i m e t a l o x i d e , at least for M e

1

= L i and

N a w e r e w o r k e d o n i n d e t a i l , o n l y a f e w attempts h a v e b e e n m a d e

to

c h a r a c t e r i z e the t e r n a r y oxides e x p e c t e d i n the system a m e r i c i u m o x i d e — a l k a l i n e e a r t h oxide. I n the solid-state r e a c t i o n of 3.5 B a O + compound B a ( B a . 5 , A m . 5 n

0

0

V I

)O

3

1 Am0

at 8 0 0 ° - 9 0 0 ° C . t h e

2

w i t h ordered perovskite structure

(17)

is f o r m e d . A t h i g h e r t e m p e r a t u r e s there is a loss of o x y g e n , t r a n s f o r m i n g Ba(Ba .5, A m , 5 ) O 0

0

3

into B a A m

I V

0

3

w i t h the c u b i c

perovskite lattice

i n s u c h a w a y t h a t no i n t e r m e d i a t e stages of this t r a n s i t i o n c a n b e r e c o g Table III.

Schematic Representation of L i t h i u m and Sodium Uranates (VI) and Transuranates (VI) U

Composition

Li

Me X O Me X 0 a-Me X0 £-Me X0 a-Me X0 £-Me XO Me XO

+ + +

2

3

1 0

2

2

7

2

2

4

+ = — =

+

—

e

Li

Pu Na

— — — —

+ + + + +

—

5

r>

6

Na

4

4

4

Np

+ + + + +

+ +

_

Li

—

_

— — + +

Am Na

Li

Na

__

_ _ _

__

+ +

—

— — + + +

—

—

+

+

existent none-existent

nized.

BaAm0

r e a c t i o n of B a 0

3

2

and S r A m 0

3

are o b t a i n e d i n a s i m p l e r w a y b y d i r e c t

(or B a C 0 ) and A m 0 3

2

( a i r , 30 hrs., 1 2 5 0 ° C . ) (4,

19).

T o a c h i e v e a q u a n t i t a t i v e r e a c t i o n of A m 0 , a m o l a r r a t i o of A m : M e 2

1 1

=

1:1.5 is r e q u i r e d ; there is n o s o l i d s o l u t i o n i n t h e system M e O - M e A m 0 i n contrast to t h e system B a U 0 / B a O . 3

SrAm0

3

The dark brown B a A m 0

3

3

and

are s o l u b l e i n s t r o n g acids a l o n g w i t h d i s p r o p o r t i o n a t i o n of

Am(IV).


236

L A N T H A N I D E / A C T I N I D E

T h e r e d u c t i o n of B a A m 0 compounds SrAm 0 2

which

3

and S r A m 0

probably

have

w i t h h y d r o g e n results i n

3

the

formula

BaAm 0 2

and

4

a n d the s t r u c t u r e of C a F e 0 . A m o r e d e t a i l e d i n v e s t i g a

(16)

4

most

C H E M I S T R Y

2

4

t i o n has not b e e n m a d e . The System A m 0 / B 0 2

t i o n of A m 0

a

2

with H B 0

2

3

3

3

2

2

m a t i o n w i t h i n 12 hours of A m B 0 of A m ( I V ) i n t o A m ( I I I ) .

T h e solid-state r e a c

and A m 0 / A l 0 .

or B 0 3

3

3

2

(1:1)

3

at 900° C . results i n the for

a l o n g w i t h the t h e r m a l d e c o m p o s i t i o n

X - r a y analysis shows that A m B 0

t u r a l w i t h the l o w t e m p e r a t u r e modifications of L a B 0

is isostruc

3

and N d B 0

3

(29)

3


c r y s t a l l i z i n g i n the o r t h o r h o m b i c aragonite lattice. B y solid-state reactions of A m 0 compound

with A 1 0

2

2

f o r m a t i o n c o u l d be observed.

at 1 2 5 0 ° C . i n H

3

2

no

I n order not to increase the

r e a c t i o n t e m p e r a t u r e , a 1:1 m i x e d h y d r o x i d e p r e c i p i t a t i o n of a m e r i c i u m and a l u m i n i u m reacted i n H

2

for 2 - 8 hrs. at 1250 ° C . T h i s r e s u l t e d i n t h e

q u a n t i t a t i v e f o r m a t i o n of rose-colored

AmA10

h a v i n g the

3

hexagonal

d i s t o r t e d p e r o v s k i t e structure of the a l u m i n a t e s of L a , P r , N d (11),

and

Pu (17,35). T h e Reaction of A m G w i t h Oxides of the Group I V Elements.

The

2

d i o x i d e s of the elements

thorium, protactinium, uranium, neptunium,

a n d p l u t o n i u m react d i r e c t l y w i t h S i 0 h y d r o t h e r m a l l y to f o r m t e r n a r y oxides

2

and G e 0 of

either t h e r m a l l y o r

2

the t y p e A

I V

B

l v

0

4

which,

d e p e n d i n g u p o n the a c t i n i d e element a n d the c o n d i t i o n s of p r e p a r a t i o n , possess a z i r c o n ( Z r S i 0 ) , scheelite 4

s t r u c t u r e (16). Am0

2

(CaW0 ),

or h u t t o n i t e

4

(ThSi0 ) 4

Corresponding reaction products c o u l d be expected

e v e n if the l o w t h e r m a l s t a b i l i t y of A m 0

2

for

at the r e q u i r e d h i g h

r e a c t i o n temperatures causes difficulties. T h e solid-state r e a c t i o n of A m 0 with S i 0 Am0

2

2

2

at 1250 ° C . i n a l l cases r e s u l t e d i n a n extensive o x y g e n loss of

a l o n g w i t h the f o r m a t i o n of A m ( I I I ) .

T h e h o p e of f o r m i n g a n

A m ( I V ) s i l i c a t e b y a solid-state r e a c t i o n w a s p o o r because i n the series of tetravalent a c t i n i d e s o n l y silicates of T h ( I V )

a n d P a ( I V ) , b u t not of

U ( I V ) , N p ( I V ) , a n d P u ( I V ) could be obtained b y thermal methods. A n A m ( I V ) silicate, A m S i 0 , h a v i n g the structure of z i r c o n ( α-form 4

of the a c t i n i d e ( I V )

silicates) w a s o b t a i n e d b y h y d r o t h e r m a l synthesis

o u t of a m i x e d h y d r o x i d e p r e c i p i t a t i o n of A m ( O H )

+

4

Si0

2

* aq.

A m f r a c t i o n , after p r e c i p i t a t i o n b y the m e t h o d of P e n n e m a n n et al. w a s o x i d i z e d w i t h N a O C l i n a n a l k a l i n e s o l u t i o n to f o r m

The (31),

Am(OH) .

A f t e r 5 - 7 days at 2 3 0 ° C . a n d a p H of 8.2-8.6, the components

4

reacted

to f o r m c r y s t a l l i n e A m S i 0 , w h i c h is i s o s t r u c t u r a l w i t h the silicates of 4

the other tetravalent a c t i n i d e s p r e p a r e d the same w a y . A t t e m p t s to p r e p a r e A m G e 0 +

Ge0

2

4

b y a solid-state r e a c t i o n of

r e s u l t e d i n a p a r t i a l d e c o m p o s i t i o n of A m 0

1000°C. i n 0 . 2

T h e n o n d e c o m p o s e d p a r t of A m 0

2

2

Am0

2

i n a l l cases also at reacts b y f o r m i n g


17.

Americium

K E L L E R

AmGe0 nates).

w i t h scheelite s t r u c t u r e ( α - f o r m of the a c t i n i d e ( I V )

4

Pure A m G e 0

Am(OH)

+

4

2

4

a

u n d e r the same

experimental conditions

T h e t h e r m a l d e c o m p o s i t i o n of A m G e 0

as

starts at

4

1050°C.

(X) •


germa-

is o b t a i n e d a g a i n b y h y d r o t h e r m a l r e a c t i o n of

4

Ge0 (aq)

q u o t e d for A m S i 0 . about

237

Oxides

5.400 -

5.100

U

ι

Zr0 10 0

i

»

.

20

ι

30

,

40

•

1

Figure

4.

Lattice

50

ι

ι

I

ι

80

constants and extension of solid solutions

90 AmCL in the

system

Am0 -Zr0 2

O = 1200°C. X = 1400°C.

2

It has b e e n k n o w n for a l o n g t i m e t h a t T h 0 series of m i x e d crystals w i t h Z r 0 fluorite

.

60 70 [mole 7·]

structure at l o w T h 0

and U 0

2

structure at h i g h e r content [e.g.

2

and U 0

2

f o r m extensive

a b o v e 1000 ° C . w h i c h h a v e a t e t r a g o n a l

2

2

content a n d a c u b i c

(6, 9, 26, 4 2 ) ] .

fluorite

F i g u r e 4 shows t h a t the

c o r r e s p o n d i n g series of m i x e d crystals exist also i n the system A m 0 - Z r 0 . 2

2

A one-phase s o l i d s o l u t i o n of fluorite structure extends a b o v e 18 m o l e % Am0

2

u p to p u r e A m 0 . T h e lattice constants of these o x i d e phases i n 2

crease p r o p o r t i o n a l l y w i t h the A m 0

2

content, w h i c h m u s t b e e x p l a i n e d

as a n i n d i c a t i o n of the presence of p u r e A m ( I V ) .

T h e corresponding

experiments i n the system A m 0 - H f 0 d i d not s h o w q u a n t i t a t i v e results, 2

2

b u t here too a fluorite phase of a large b u t u n d e t e r m i n e d extension is found. R e d u c t i o n of the A m 0 - Z r 0 a n d A m 0 - H f 0 2

2

2

2

fluorite phases results

i n the c o r r e s p o n d i n g t e r n a r y oxides a n d o x i d e phases of t r i v a l e n t a m e r i c i u m . I n the system A m O i - H f 0 5

2

there is a 1:1 c o m p o u n d A m H f 0

a p y r o c h l o r e s t r u c t u r e w h i c h has a n e a r l y s t o i c h i o m e t r i c

2

2

7

of

composition


238

LANTHANIDE/ACTINIDE CHEMISTRY

a/2(Â)

a(Â)

4

4

10.700

5.350 2 PHASES

10.600

tetrag. F. ss+

2 PHASES _o—

5.300

ss

ω ω

10.500 Downloaded by MONASH UNIV on September 14, 2017 | http://pubs.acs.org Publication Date: June 1, 1967 | doi: 10.1021/ba-1967-0071.ch017

1 PHASE

-I 5.250

πι

10.400

u

5.200

oR

-I

Zr0 10 2

Figure

5.

Lattice

i

L.

20

30

40

ss*

ss

h e x

50 60 70 -+ [mole%]

80

90 Am0

constants and extension of solid solutions Am0 -ZrO , 1200°C. 15

15

in the system

%

a(Â)|

10.700h -o

o

Q—°-

10.600 h

Hf0 10 2

Figure 6.

20 Lattice

30

40

*

50 60 70 [mole/o]

80

90 Am0

1R

e

constants in the system AmO

-Hf0 ,

t

5

2

1400°C.

( F i g u r e 5 ) . M o r e c o m p l i c a t e d are t h e results i n t h e system A m O i - Z r 0 . Besides t h e p u r e s t a r t i n g c o m p o n e n t s , t w o one-phase areas c a n b e o b s e r v e d at 1 2 0 0 ° C : a t e t r a g o n a l s o l i d s o l u t i o n of 0 - 6 m o l e % A m O i , a n d a c u b i c s o l i d s o l u t i o n of a b o u t 3 2 - 5 5 m o l e % A m O i . ( F i g u r e 6 ) . I n t h e c u b i c s o l i d s o l u t i o n , i n w h o s e r e g i o n exists A m Z r 0 w i t h t h e p y r o c h l o r e 5

r

5

2

2

7


2

17.

Americium

K E L L E R

Oxides

239

t y p e s t r u c t u r e , a c o n t i n u o u s t r a n s i t i o n f r o m the fluorite phase to t h e p y r o c h l o r e phase c a n b e observed.

I n this respect t h e system A m O i . - Z r 0 5

2

fits e x c e l l e n t l y i n t o the series o f rare e a r t h zirconates i n v e s t i g a t e d b y F r e n c h authors—e.g.,

(7, 8, 32); for t h e c o r r e s p o n d i n g H f systems there

are, as yet, n o c o m p r e h e n s i v e investigations r e p o r t e d i n the l i t e r a t u r e . T h e s t r i k i n g difference i n the systems A m O i - Z r 0 5

2

and

AmOi. -Hf0 5

2

cannot b e explained, however. A s expected, T h 0

2

forms a c o m p l e t e series o f m i x e d crystals w i t h

A m 0 , w h o s e l a t t i c e constants f o l l o w V e g a r d ' s r u l e ( F i g u r e 7 ) . Downloaded by MONASH UNIV on September 14, 2017 | http://pubs.acs.org Publication Date: June 1, 1967 | doi: 10.1021/ba-1967-0071.ch017

2

a(K)

Î Γ 5,800 5,700 5,600

Actinide Chemistry

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