the direct synthesis and purification of sodium iodide_2

8/20/2019 The Direct Synthesis and Purification of Sodium Iodide_2

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Iowa State University

Digital Repository @ Iowa State University

Re'%&ec+e ee a$d De'a%$

1965

Te direct synthesis and purication of sodiumiodide

James Russell Johnson Iowa State University

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ii

T A B L E O F C O N T E N T S

• ' Page

I N T R O D U C T I O N A N D

H I S T O R Y

1

Analysis o f

a

Harshaw Crystal 4

Single

Crystal

Growing 6

Methods o f P u r i f y i n g Alkali Halides 8

General methods

8

Specific methods 9

Synthesis o f S o d i u m Iodide 1 5

Indirect synthesis 1 5

Direct

synthesis

1 8

Methods

Used

for

Producing Other Halides 2 2

E X P E R I M E N T A L

P R O C E D U R E S A N D R E S U L T S

23

Direct Synthesis o f

S o d i u m

Iodide 2 3

R e v i e w o f previous w o r k

23

T h e

reaction between solid sodium

and solid iodine 23

T h e reaction between liquid sodium

and liquid iodine

2 4

T h e

reaction between

liquid

sodium

and

vapor iodine 25

T h e reaction between vapor sodium

and vapor iodine 3

5

Additional synthesis w o r k 3 6

T h e

reaction

between liquid sodium

and vapor iodine

3 6

T h e reaction between vapor sodium

and vapor iodine 6 1


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Please Note:

Figure

pages are

not

original

copy

and some

of

them

tend to

curl .

Filmed as received.

University Microfilms,

Inc.


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i ll

Page

Purification

o f

S o d i u m Iodide

•

. 8 2

Ion

exchange

8 2

Sublimation 9 1

Z o n e refining 1 0 1

D I S C U S S I O N 1 2 9

L I T E R A T U R E C I T E D 1 3 4

A C K N O W L E D G M E N T S

1 5 7


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1

I N T R O D U C T IO N A N D H I S T O R Y

T h e

preparation

and purification

o f

sodium

iodide

is o f great

interest

o w i n g

to

the use

o f large single

crystals

o f

t i i e

material in

optics and in radioactivity sensors.

Since the

beginning o f

this work, considerable interest has developed

in obtaining ultra-pure

alkali

halides. Such properties

as

nuclear mag

netic

resonance

(87),

ionic

conduction

and

diffusion ( 1 0 5 ) . .

electrical

conductivity

( 3 1 ,

100, 223), photoconductivity ( 1 0 2 ) ,

and

photolytic be

havior

( 1 4 3 )

are

all

affected b y

the

presence o f impurities.

Other

important physical behaviors o f Lhe alkali halides tnat are dependent on

the amount o f

impurity present

include electron spin

resonance

and re

laxation (63,

2 1 4 ) ,

Hall

mobility at low temperatures (34),

thermal con

ductivity ( 1 6 4 ) , optical absorption and fluorescence

( 1 8 1 ) ,

infrared and

ultraviolet spectra

(4),

and deposition o f thin

films

o f metals

(96).

D u e r i ç ? and Markham ( 6 0 )

conclude

for optical work,

that

commercial

cry

stals just

aren't

good enough, and

further,

that elemental impurities in

excess

o f

1 part per million, o r at most

1 0

parts per million, will interfere.

Color

centers in alkali halides

may

be

f o r m e d

b y

three

processes:

addition

o f

excess alkali metal, addition o f excess halogen, and b y

radiation. When an

alkali

halide crystal is heated

in an

alkali metal

vapor, metal atoms diffuse into the crystal and

ionize. T h e

electrons


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2

enter the anion

holes,

making the density less than the pure

crystal

{ 2 . 7 ) .

T h i s type o f

coloration produces F (Farbe-color)

centers

in the crystal,

and

is

o f

the

trapped-electron type. A trapped-hole

type

o f color center,

called

a V type, is f o r m e d when

the alkali halide

is heated with

b r o m i n e

or iodine

( 1 3 8 ) . T h e

pressure o f halogen

necessary

to accomplish

this

is o f

the o r d e r

o f

50.atmospheres,

and

i t

has

not been possible to f o r m

this

type

o f color

centers

with chlorine. T h e third

type

o f color center

is

f o r m e d

b y

ionizing

radiation,

especially soft x-radiation,

b o m b a r d i n g

the

alkali halide crystal. Trapped hole and trapped electron color

centers

m a y be

f o r m e d ( 1 9 2 ) . T h e

mechanism

o f

color

center

formation

due

to ionizing

radiation

is not well known, but experimental and

theoretical

w o r k is

currently

quite extensive. T h e basis for

the single

point

defects

( F

centers)

has

had

the

most

analysis:

the theories

o f

Seitz, Varley,

and

H o w a r d

have been

proposed ( 1 7 6 ) .

T h e

theoretical

foundation f o r

the

formation

o f

complex

color centers is not very well

advanced.

T h e use o f

the

above phenomenon to measure ionizing radiation came

before m a n y o f the studies mentioned above.

T h e technique

is

called

scintillation

counting. A s

high energy particles strike

the crystal,

electrons in the crystal are

excited

b y

photoelectric and

C o m p t o n effects.

These

excited

electrons strike fluorescent

centers

in

the

crystal. A


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3

fluorescent

center has electrons

which become

excited. A transition

occurs, then rearrangement to another excited

state,

and

emission

o f

luminescence

takes

place

(67).

C o m m o n l y ,

the

luminescence

is

de

tected with a photomultipler tube and the signal fed through cathode

follower circuit

into

a Geiger-Muller counter ( 1 2 ) . T h e

pulse-height

analyzer

usually used to record the

counter

output m a y b e

replaced

b y

digital recording with further

computing

to

separate the

background

count

using

a

m e t h o d

o f

moments

technique (76).

Alternately,

the

background

count m a y be separated b y a differential

coincidence

counter

using t w o electron photomultiplier tubes ( 1 4 1 ) .

S o d i u m iodide -thallium iodide is

the alkali halide

and

fluorescent

center

most used. F o r x-rays, this type o f crystal

appears

to be far

and away superior

(30). S o d i u m

iodide-thallium scintillation crystals

are far m o r e efficient than

a

Geiger-Muller counter f o r high energy

g a m m a

rays

( 5 5 times) ( 1 2 ) , and are

well

adapted to beta and

g a m m a

ray determinations

(64).

T h e theoretical

basis o f luminescence

is not well established, but

some

facts are k n o w n and

some

models have been advanced

(24, 108,

153). T h e luminescence near the

surface

o f

the

crystal

apparently

occurs

by

a different mechanism that

the

luminescence in .

the interior. T h e

presence

o f

defects

may provide

sites

for the

processes


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to

occur ( 1 0 8 ) .

Impurities other

than thallium ion must be excluded,

since

they.will

cause spurious

scintillations.

Analysis

o f

a

Harshaw

Crystal

K e e p i n g

in

m i n d the statement b y Duerig and M a r k h a m ( 6 0 ) that

commercial

crystals are

often

not

suitable f o r color

center

study,

the

following

table will illustrate the

problem.

T h e analyses were done b y

emission spectrographic analysis at the National B u r e a u o f Standards

(60).

A l t h o u g h

the

crystal

is

not

sodium

iodide,

a

qualitative

similarity

m a y

be

drawn. See Table 1 on page 5 f o r the

analyses..

Other

crystals for

which the

analysis

was given were potassium

chloride,

potassium bromide, and sodium fluoride.

These other

examples c o n f o r m e d

to the analysis

above

in general outline.

It

m a y

be seen that the

above crystal contains one element,

calcium,

which was

present

in the amount

1 0 0 0

- 10,000

parts

per

million,

and

six

elements,

silver,

aluminum,

iron,

lithium,

magnesium,

and silicon,

which were

present in the amount

1 0 0

- 1 0 0 0

parts per

million.

Duerig and M a r k h a m stated above (60), that

1

part

per

million,

or perhaps 1 0

parts

per

million is all

that

is allowable f o r optical

work.

T h e emission spectrographic

analysis

doesn't approach

a

sensitivity o f

this level, and even as i t is,

detects

the

presence

o f seven elements

which

are

present

in

objectionable

quantities.


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5

Table

1.

Emission

spectrographic

analysis o f

a Harshaw

optical

sodium chloride

crystal

Element

Amount Element Amount Element Amount

A

g-(stiver) T

fl

A1

(aluminum) T

As (arsenic)

Au

(gold)

'

B

(boron)

Ba (barium)

Be

(beryllium)

Bi

(bismuth)

Ca (calcium)

V W

Cd (cadmium)

Ce

(cerium)

Co (cobalt)

Cr (chromium)

Cs

(cesium)

-?

Cu (copper)

-?

Fe ( iron) T

Ga

(gallium)

Ge

(

germanium) -

H f (hafnium)

Hg (mercury)

In (indium)

Ir (

iridium)

K

(potassium)

Li (lithium)

T

Mg

(magnesium) T

Mn (manganese)

Mo (molybdenum)

-

Na (sodium)

V S

Nb

(niobium)

Ni (nickel)

Os (osmium)

P

(phosphorus)

P b (lead) -?

Pd (palladium)

Pt

(platinum)

Ra (radium)

Rb (rubidium)

Rh

(rhodium)

•

Ru

(ruthenium)

Sb (

antimony)

•Sc

(scandium)

Si

(silicon)

Sn (tin)

Sr

(strontium)

Ta (tantalum)

Te

(tellurium)

Th

(thorium)

Ti (titanium)

T1

(thallium)

U (uranium)

V (vanadium)

W (tungsten)

Y

(yttrium)

Zn (zinc)

T

a

Key

to amounts: VS- very strong: greater than 1 0 % ;

M-medium: 0.1

-

.0% ; W -weak:

0.01 -0.1%

VW-very weak: 0.001 - ,

0.01%

(1000

-

10,000 p. p.m..); T

-

trace: 0.0001

-

0.001% ( 10 , 0 - 1000 p. p.m.)

-

not detected;

-? -probably

not

detected


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common, however, is the growth o f alkali halide crystals b y the

K y r o p o u l o s method ( 1 8 ) , and

the method has been applied

to transi

tion metal

fluorides

with

success

(37). Inert

atmospheres

are

u s e d "

in

m a n y

cases

(64,

1 5 4 ) as

the introduction o f oxygen o r

water

has

been shown

to cause the formation o f cloudy, colored crystals (205).

T h e

K y r o p o u l o s

method is

most

advantageous f o r growing large diameter

crystals,

b u t

the

thickness is limited due to

the

increasing distance

f r o m

the

cooled

chuck holding

the

seed crystal

( 1 3 3 ) .

O n

the other

hand, the Stober process i s best for growing crystals o f great length,

b u t the

thickness

i s limited by the temperature

gradient

that

can

be

maintained

across the

depth

o f the melt

( 1 3 3 ) .

In either case, i t is the

heat

conduction

problem that limits crystal size.

Industrially, the

crystals o f sodium iodide

are

grown by melting

sodium

iodide

and

letting the massive

melt cool at a very slow rate.

T h e

process

takes days and starts with

tne

purest

industrially

available

sodium

iodide.

I f the

crystal

is

to

be

a

scintillator crystal,

thallium

iodide

is added

to

make a mixed melt.

T h e salt is heated up prior'to melting

to

volatilize water which is

readily

picked up

by the

deliquescent

sodium

iodide. T h e n it is placed

in

a

sealed vessel, heated

above

i ts melting point, and

allowed

to cool

at

the

rate

o f

approximately

one

degree per hour.

Many

times,

when

the

sealed vessel is opened after solidification has

taken

place, a large


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amount o f iodine

gas is

given

off. When

all goes

well, a

clear

cylindrical crystal

with

height and diameter o f one

f o o t

is obtained.

Then

it

is

cut

u p

for

sale„

Impurities

present

in

the

starting material

are

incorporated

into

the crystal

with

this

technique. T h e heating o f

the

salt p r i o r to

crystal formation

also causes impurity problems

because

tne volatilized

water will react with iodide

ions

to produce

free

iodine

a n d .

hydroxide

ions. T h e overall reaction replaces

iodide ions

with

hydroxide

ions,

and

is

the

cause

o f

the

iodine

cloud

o n

opening

the

crystal g r o w i n g vessels. T h e

industrial

m e t h o d o f

g r o w i n g alkali

halide crystals is rather

ineffective

in preventing the addition

o f

m o r e

impurity, n o t to mention the retention o f the impurities already present.

Methods o f

Purifying

Alkali Halides

General

methods

High

purity metals, organic materials, a n d . salts have peen purified

in r e c e n t ,

years

by

a

wide

range

o f

processes.

some o f which are quite

new.

S o m e

o f

these methods

are zone

refining,

electron

beam

melting,

liquid-liquid extraction, ion . exchange,

chromatography, electrolysis,

and thermal diffusion.

In a discussion o f this

p r o b l e m

by Carlson and

Peterson

(36),

the

prerequisite conditions are

discussed.

A n equilibrium must be estab

lished between

two phases for

a segregation

to take place. There

are


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9

three possible

phases,

and hence six possible combinations. Gases

are miscible

in all proportions

, so no segregation can

take place

with

an

all

gaseous

system..

T h e

all

solid system

is

also

eliminated,

since

i t

is

impractical

to separate the

components

o f

a

solid solution. This

leaves

f o u r

useful phase

combinations: the solid-liquid, the liquid-

vapor,

the

solid-vapor, and the liquid-liquid.

Further, this discussion states' that

theoretical

distribution o f '

impurities

and thermodynamic

properties

m a y n o t

b e k n o w n

f o r

multi-

component

systems,

especially

i f

these

systems

are at very

low,

i.e.

ultrapure

concentrations. Phase diagrams are usually not available

f o r

this

concentration

region. N o t

the least

o f the

problems

is

the

con

tamination

f r o m the

vessel o r the atmosphere during the purification

work. Kinetically, purification

w o r k becomes ever slower and less

rewarding as

the

amount o f i m p u r i t y becomes smaller. Many

workers

who originate and

use

purification techniques are n o t interested in the

theoretical basis

o f a separation,

b u t merely want the process accom

plished.

This attitude does

not ease

the

burden on those who wish

to

repeat

o r extend purification work.

Specific

methods

Liquid-liquid extraction has provided the basis for

the

separation o f

several pairs o f

elements

that are

chemically quite

similar.

T h e

pairs,

tantalum-niobium

and

zirconium-hafnium," are particularly good

examples


16/165

10

o f

metals

that have

been

extremely difficult to separate b y ordinary

chemical

means such

as

crystallization,

b u t have

yielded

to techniques

f o r m i n g different complexes o f the metals under the same

set

o f con

ditions, followed

b y extraction with the

proper

solvent (80, p . 440).

Z i r c o n i u m , and h a f n i u m are

m o r e

alike in

the

tetravalent

state than any

other

t w o

elements,

b u t have been separated b y the

use

o f thenoyl-

trifluoracetone

to f o r m chelates followed

b y

extraction with an organic

solvent,

or

b y

nitric

acid

and tributylphosphate.

The

p e n . t a v a l . e n t

oxides o f tantalum and niobium m a y

be separated

b y treatment with a

solution

o f p o t a s s i u m ,

fluoride in

hydrogen fluoride, which converts the

oxides

to p o t a s s i u m , heptafluorotant.alate ( V ) and potassium p e n t a . f l u o r o -

monoxomobate ( V ) . T h e tantalum complex is m o r e

soluble

in the

organic

phase

o f

the

extraction

mixture.

I o n exchange

has

allowed spectacular separations

o f the rare

earth

elements when

complexed

with

citrate

and eluted

f r o m

an ion ex

change

resin.

These

procedures were developed at

the A m e s

L a b during

the period 1 9 4 1 - 1 9 4 5 b y S p e d d . v n g and

his

co-workers.

Lately, use o f

E D T A

and H E D T A have

made possible even

better

separations o f these

elements

in

large

amounts (45,

p.

882). Inorganic synthetic ion

ex

change materials have made

it

possible to do the following: to

remove

r u b i d i u m ,

f rom ,

cesium (7), to

distinguish

between

the alkali metals

(6, 189), and to separate the alkali

metals

f r o m

other

metals ( 1 5 1 ) .


17/165


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Differences

in

volatility

o f

materials

has

often

allowed

the

materials

to

be m a d e

purer.

Sublimation is a c o m m o n

technique

f o r organic

chemists,

and similar

use

can be

m a d e

o f

transport

reactions

f o r

the

purification

o f

salts such as

lithium fluoride

( 1 8 7 ) . In such a case,

there is a

very

definite distinction between the area where less

vola

tile

impurities are found, a pure material area,

and the

area where the

impurities

o f greater

volatility are found. Separations

f r o m such

c o m m o n

materials

in

lithium

fluoride

as

lithium

oxide

and

hydroxide

can

be made.

A n

added

refinement is

the

condensation onto

a heated

surface

to

make

m o r e

volatile impurities congregate in

another

section

o f the

apparatus

( 1 5 0 ) .

A n o t h e r example

o f tnis method is

the crystal-bar o r V a n

A r k e l

process, in which a metal is

purified b y

f o r m i n g an iodide in the

apparatus, 'and decomposing the iodide on

a

h o c wire ( 1 5 0 ) .

Diffusion t h r o u g h

membranes has been

the

basis

f o r

several

separa

tions o f

alkali

metal

halides. Passage through a porous

m e m b r a n e

takes place

b y means

o f alignment-type diffusion

f o r

those

materials

that can

f o r m

hydrogen bonds, while

other

materials are

transported

b y

hole-type

diffusion.

In

this

example,

definite diffusion

rankings

m a y

be

set u p

f o r positive

and

negative ions ( 1 9 1 ) . A porous

cellulose

filter

saturated with a nonpolar organic solvent can differentiate

between

s o d i u m

and

potassium

ions

with

a

permeability ratio o f potassium ion

to

s o d i u m ion

o f 30-40

(92).

Osmotic transfer

o f solvent

has

been used

to


19/165


20/165

14

Table

2. N e u t r o n activation analysis o f

zone refined potassium chloride

and

potassium

bromide

3

'

b,

c, d

( 9 )

Element

Concentration,

in

K O I (p.

p. m. )

Concentration

in K B r

(p.p.m.)

B r ( b r o m i n e )

Cs

(cesium)


21/165


22/165

16

went

o n

to

prepare sodium iodide in 1 8 1 3 by the action

o f

an

aqueous

solution

o f

h y d r o g e n "

iodide

on

potassium

carbonate

o r

potassium

hydroxide, followed by the concentration

o f

the solution b y evaporation

(74). This

method is still

preferred as the

most direct way

to

alkali

halides.

Dumas and

le R o y e r

( 1 7 7 ) set the pattern for

a

great n u m b e r o f

syntheses

o f

alkali halides

b y

dissolving

iodine in

the

alkali

hydroxide

to f o r m

a

mixture o f

the

iodide and

iodate. Then the

solution

is

evaporated to dryness and calcined until oxygen ceases to

be

evolved

to

reduce

tne iodate

to

iodide.

Liebig

( 1 2 4 ) showed

that

the above

pro

cess

f o r m e d

alkali hypohaiite

u p o n the

action

o f iodine o n the

alkali

hydroxide, and the

hypohaiite decomposed to halide and halate

u p o n

heating.

Other

investigators such

as

Preuss ( 1 6 6 ) , used the

same

reactions.

Pettenkofer ( 1 5 P )

f o r m e d

the hydriodic

acid

f r o m

the reaction

o f

iodine and phosphorus in

distilled water. Separation o f

the acid is

accomplished

b y

distillation.

Hydriodic

acid was

f o r m e d

by the r e a c t i o n ,

o f copper ( I ) iodide

on

h y d r o sulfuric

acid b y

Langbein

( 1 1 8 ) .

A n o t h e r method

o f

attack

involves

the formation

o f a

heavy metal

iodide. T h e heavy metal iodide

is

decomposed with water and

the

resulting hydrohalic

acid is

neutralized with a base.

Serulas

( 1 8 4 )

prepared

antimony

iodide

b y

heating

the

elements

together,

and

added water to f o r m

a

solution o f

hydriodic

acid and a precipitate o f

antimony


23/165


24/165

18

and

oxygen

( 1 2 8 ) „

Industrial purification steps often utilize the

addition

o f sodium

diethyldithiocarbamate (78,

1 2 8 )

to remove

heavy metal impurities„

Dithizone and 8-hydroxyquinoline ( 5 7 ) have been used to accomplish

the same e n d „ Dissolving an

iodide in

hot aqueous h y d r o g e n

iodide

results in purer materials u p o n

cooling

to 30° G. A t this

point the

purified crystals appear ( 9 7 ) „

Direct

synthesis

Synthesis o f

sodium

iodide f r o m

the

elements has not

met

with

much

success

I n summarizing attempted reactions between alkali

metals

and halogens, Merz and Weith ( 1 3 4 ) in 1 8 7 3 gave the data

which is shown on Table

3,

page 1 9 „ Other workers c o n f i r m their

conclusions

reached

with regard

to

the

action

o f

s o d i u m

on

chlorine

( 4 8 ) and b r o m i n e ( 1 9 3 ) „

A l l

the methods in

this section

for the production

o f

s o d i u m

iodide

utilize indirect

methods and Table 3 confirms

the reasons

f o r

this

emphasis

in

light o f the then-current knowledge regarding

direct

reactions

between sodium and iodine

E a r l y in

this century, T r a u t z

( 2 0 3 ) noted a chemiluminescence f r o m

the reaction o f sodium

or

potassium in

air

or

halogens,

and

Wilkinson

( 2 2 2 ) found luminescence occurred with

alkali metals

and halogens.


25/165

19

Table 3 . B e h a v i o r o f

alkali metals

and

haloqens

according to Merz

and Weith

Element pair B e h a v i o r

S o d i u m and chlorine

N o

reaction

when

dry

Sodium

and b r o m i n e

N o reaction, even

after

heating

S o d i u m and

iodine N o reaction,

even

when

melted

Potassium and

chlorine

Violent

reaction

even

in

the

cold

Potassium and b r o m i n e V e r y violent reaction;

explosion

Potassium and

iodine

Explosion, "welding flames"

This technique o f converging gas streams

led

to

a

whole

series

o f

papers

in

the 1 9 2 0 '

s

b y

a

group

o f German and

Russian physicists,

who

were investigating the energy spectrum o f elements

and conversions

between

these

states.

T h i s w o r k

followed

that

o f B o h r

and

was

done

concurrently with the development o f the quantum mechanics. These

workers sought

to explain

the mechanism o f

the reaction

between an

alkali

metal

with a halogen o r oxygen

ir i terms

: o f the

spectra


26/165

obtained,

o r

perhaps the reaction mechanism

was

to account

f o r the

spectra

According

to

Haber and Zisch

(85),

sodium atoms were

thought

to be excited b y the exothermic reaction between s o d i u m and

the halogen and

to produce

the sodium

D-iine spectra without m u c h

luminescence.

Investigators

used a

wide range

o f s o d i u m and

halogen

pressures,

f r o m

1 0

millimeters

( 2 1 ) to 1 5

millimeters

( 1 2 7 ) . In

all

cases, the sodium vapor and halogen

vapor were swept along with

a

nitrogen gas

stream„ T o

bring the gas streams together,

techniques o f

concentric tubes ( 1 9 , 88), opposing entrances into a reaction

vessel

( 2 2 ) „ or volatilization o f the vapors f r o m

adjacent

tubes ( 1 2 7 ) were '

employed.

Iodine

is present as atoms in flame

conditions

( 1 6 2 ) .

Examination

o f

the precipitate

and l ight

distribution

f r o m

the point

where the flame

occurred

by

Beutler

and

Polanyi

( 2 0 )

showed

p r i m a r y

and

secondary

reactions corresponding t o :

1 )

Na+ Ig

=

N a l + I

2 )

N a +

I + N a ~ Nsl

+

N a + .

h v

A

discussion o f

the vapor reaction between s o d i u m and iodine is the

topic

o f

a

paper b y Ootuka and

Schay

( 1 5 2 ) . Some difficulties arise

in

the

measurement,

in

that

i t

is

possible

for the nitrogen

gas,

used

as

a

carrier stream,

to

be

excited

also and to interfere

with

the results,

according

to Ljalikov and

Terenin ( 1 2 7 )

and

B e u t l e r

and Polanyi (20).

Hasche, Polanyi, and

V o g t

( 8 9 ) found that, due to self absorption, the

light

emission

f r o m

sodium vapor

alone is the same as that

f o r

sodium


27/165

21

vapor in reaction with iodine at low pressures .

Franz

and K a l l m a n n

( 6 5 ) used t h e excess

energy

o f reaction o f

sodium

and chlorine to

excite m e r c u r y atoms

to emission

and

determined

energies o f dissocia

tion o f

halogen

molecules

„

T o d a y this type

o f

reaction

is

called

a molecular

b e a m reaction

and is

described

in a reaction

between

potassium and alkali halides

b y N o r r i s ( 1 4 8 ) . A study o f

crossed

molecular beams o f cesium

and

b r o m i n e was m a d e by

Datz

and Minturn

( 5 1 ) , w h o

postulated a strip

ping mechanism

f o r the resulting reaction.

A l l o f the

w o r k described above

on the reactions o f sodium and

halogen

gas streams swept along with nitrogen illustrates

that

physicists

,

not

chemists,

were

doing

the

experimentation

N o w h e r e

is

a

chemical

test

done

to identify

the

products

o f

the

reaction

,

because these

scientists were primarily

interested in

the

energy

states o f s o d i u m and

the

transitions between these states T h e

possi

bility that

sodium

vapor

could react

with the nitrogen

carrier

gas

to f o r m

sodium nitride

was not discussed,

though

this

could certainly

happen.

T h e w o r k

is

c o m m o n l y

done

at

moderate

temperatures,

which

are

less

than

the

decomposition temperature o f

sodium

nitride, 300°

C.

T h e

reactions themselves seem

quite

possible under the conditions given,

but the

chemistry o f the processes is accorded

m i n o r

importance.


28/165

22

Methods Used f o r P r o d u c i n g Other Iodides

•

Direct

union

o f

elements

is

a

favored

means

o f

f o r m i n g

metal

iodides,

and

has been

successful f o r

such

iodides

as those

o f yttrium ( 1 1 2 ) , b o r o n

( 1 1 ) , and n i o b i u m in

the five ( 1 2 6 ) ,

four, and

three

( 4 3 ) valent states .

T i t a n i u m ( I V )

iodide

has been

prepared by

the reaction o f

aluminum,

iodine,

and titanium ( I V )

oxide

in a

sealed

and evacuated vessel (23).

This

reaction

t o o k

place

by

steps: first,

the

aluminum

and

iodine

reacted

violently at 1 0 0 - 1 1 0 ° C. and secondly, the reaction to

f o r m

the titanium

( I V )

iodide

t o o k place at 450° C. T h e iodides

o f a wide

variety o f

transition and

representative metals were

made by

the action o f

a l u m i n u m iodide on the

corresponding metal

oxide

( 3 9 )

„ T h e

driving

force f o r these

reactions is the

high heat

o f

formation

o f

a l u m i n u m

oxide.

A n o t h e r reaction process makes

use o f a

very high

pressure

b o m b

with

Hexogene giving pressures o f 50,000 kilograms

p e r square

centimeter and temperatures

o f 30,000

atmospheres f o r the

short

t i m e

-6

o f

4 x 1 0 seconds ( 1 3 6 ) „


29/165


30/165

T h e reaction between

liquid

s o d i u m and liquid iodine

This

possibility was

tried b y

means o f t w o

sets

o f conditions

;

one o f which

was planned

and

the

other

completely unplanned.

• T h e first m e t h o d used as

a

source o f

sodium

a dispersion

prepared

with a h i g h speed stirring m o t o r

in

a hydrocarbon

solvent. T h e

m e t h o d

m a d e i t possible to obtain very small particles

o f s o d i u m

in

the

m i c r o n

range

by

means

o f a 1 7 , 0 0 0

revolutions per

minute

stirrer

in a M o r t o n

designed

flask(139,

1 4 0 ) .

A

nitrogen

gas

p u r g e

o f

the

apparatus

was

used to

prevent

oxidation

b y air,

and

mineral

oil was chosen as the

hydrocarbon

solvent

to

p e r m i t

higher temperature operation

than the

m o r e

c o m m o n

dispersion solvents, A n

iodine

dispersion

in

the same

solvent was

'then added

to the

sodium

dispersion

in a

m a n n e r

similar

to

the

s o d i u m

hydride preparation by

Whaley(220).

V a r i o u s

conditions

o f

stirring speed. temperature, and length o f stirring

were tried.

With this method, separation o f the s o d i u m

iodide f r o m

the hydro

carbon solvent

was

the m a j o r

problem.

Positive tests f o r sodium ion

and iodide ion were obtained, b u t

the

reaction

6

was far f r o m quantitative.

T h e

second

m e t h o d o f reacting the two elements

in

the

liquid

state

occurred in

a vessel held at a temperature o f

150°

C which contained

molten s o d i u m

T h e attempted

reaction o f

sodium with iodine b u b b l i n g

through the

sodium

was n o t successful, so iodine was added to the

vessel and remained

on top o f the

sodium crust,

which had

farmed


31/165

even in presence o f

a

protective nitrogen purge. Six to twelve hours

later, during the night, the reaction

between

the elements occurred

with explosive

force.

T h e products gave strong s o d i u m and iodide ion

tests, which

represented approximately 25 % conversion to

sodium ior-

dide. T h i s method, though producing

an

appreciable amount o f desired

material,

was

not repeated due

to the

suddenness

o f the reaction.

T h e

reaction

between liquid sodium and

vapor

iodine This m e t h o d

was

tried

with

many different

approaches,

which will

b e

reviewed one

at

a

time.

O n e

trial

made

use o f

a

P y r e x tube,

which contained

the elements,

sealed in

a

dry box. T h e tube was heated until the sodium

melted

and

the

iodine

turned into a vapor.

Fairly

strong s o d i u m ,

ion

and iodide

ion

tests

were

obtained,

b u t

i t

was

n o t

possible

to

seal

uncontaminated

elements

in

a

tube, as

mentioned above.

A n extended series o f experiments was p e r f o r m e d using

the

b o m b

technique to

get

liquid sodium and vapor

iodine together.

T h e dry

b o x

and

gas-fired

furnace,

along with supplementary equipment,

was

made

available in

the

metals

reduction

laboratories o f A m e s

Lab. T h e

prac

t ical

experience o f the A m e s

Lab

workers was also p u t to

use.

The b o m b s used were fabricated

f r o m steel

pipe

with

a threaded or

flanged and

bolted

cap.

A magnesium

oxide jarred and sintered liner

was f o r m e d to fill the space between the b o m b and the charge,

as


32/165

shown

i n

Figure 1.

Samples

o f

sodium

and iodine were

weighed in the

helium-protected dry b o x and

placed

in the

bomb. A f t e r

removal

f r o m

the dry b o x , the b o m b s were placed in

a

steel

d r u m

furnace fired with

an ordinary h o m e gas

burner. I t was possible

to

insert

a thermocouple

lead in

a well o n

the

b o m b s

to

f o l l o w the

rate

o f temperature

increase.

Temperature increase

rate

was difficult to control because

the furnace

was either

on

o r o f f

and

there was n o intermediate

position.

On

sev

eral

runs

the

temperature

increase was

slowed

manually

b y

switching

the furnace

on

and

off.

T h e first

attempt

using this

equipment

involved loading the two

elements directly into the jarred and sintered magnesium oxide

liner.

B y the

inflection

point o n the temperature

recorder chart, i t was est

imated that

the reaction

took

place

at

approximately 200-3

00°

C .

T h e

contents o f the b o m b ,

examined

in the dry

box,

were

a

fused mass o f

reactants and liner. T h e

fused material was insoluble in water,

and

showed that the liner

had

reacted with

both sodium

and iodine. Y i e l d

o f sodium iodide

was

7.79 % , which was determined gravimetrically

by precipitation

with silver nitrate.

A f t e r this run, all

succeeding

attempts were done

with

another

liner material inside the steel

b o m b and

magnesium oxide liner

mat

erial.

Most

metals

are

eliminated

as

possibilities because they

react

extensively with iodine to f o r m iodides.

Experience with

the crystal-


33/165

27

e-nrci

DtDC

SILICA O R

METAL

INNER LINER

JARRED AND

SINTERED

MgO

LINER

No

AND

U

CHARGE

F i g u r e

1.

B o m b

cross

section


34/165

28

bar

process o f refining refractory metals

has

shown

that

m o l y b d e n u m

is the only

metal that

remains

unaffected

b y

iodine vapors at

m o d e r a t e

to

high

temperatures,

with

nickel a relatively

p o o r

second

choice.

With this

in

mind,

a

run

was

made with a quartz (fused-silica)

liner inside the b o m b

and m a g n e s i u m

oxide

liner.

T h i s was the m o s t

successful run,

t h o u g h

the quartz liner cracked

and the

products s h o w e d

the

bluish tinge o f colloidal sodium. T h e

quartz

liner also showed

that

both

elements

h a d

been

adsorbed

on

the

inner

walls„ Analysis

o f

this

product follows i n

Table

4.

Table 4

„

Analysis

o f

a sodium-iodine b o m b

reaction; quartz liner

3

C o m p o u n d

-

Percent

y i e l d *

3

S o d i u m

iodide 6 9 . 7 6

S o d i u m h y d r o x i d e 2 5.30

Total

95„06

C

•

•

a

Sodium iodide determined b y

the

V o l h a r d m e t h o d ( 5

5 , p.

332),

s o d i u m

hydroxide

b y

nitric

acid

standardized with sodium carbonate(55, p, 202).

^ B a s ed o n

weight o f sodium.

c

Some

sodium lost b y

preliminary tests and

adsorption.


35/165

29

M o l y b d e n u m

i s

a difficult

metal

to fabricate, because i t loses its

ductility on

heating

and must be welded in

an

inert

atmosphere. Nev

ertheless , a liner

was

made f r o m m o l y b d e n u m

and

loaded with sodium

and

iodine in the

standard

manner,

and the b o m b fired.

O n

disass

embling

the

b o m b ,

i t was

f o u n d

that the welded seams had shattered

f r o m the pressure

increase

in the b o m b

and that the reactants

had fused

almost

b e y o n d recognition

with

the

magnesium

oxide

liner.

T h e

next

metal

tried

as

a b o m b

liner

was nickel.

T h o u g h

it

is

not

as resistant to

iodine

vapors as

is

m o l y b d e n u m ,

fabrication is consid

erably

easier. This b o m b using the

nickel

liner

was

loaded with

weighed amounts o f

the two

elements

in

the dry

b o x

and

fired

i n

the

furnace„ When the

recording potentiometer

reached 550° C (esti

mated

b o m b

temperature

was

200°

C

higher),

the

b o m b

exploded,

causing extensive

damage

to the furnace.

This

was the reaction noted

f o r

i ts

beauty

b y

those

in

the

r o o m s above in the

Metallurgy

Building.

T h e

contents o f the

b o m b were never found, and b o m b

reactions were

ceased b y c o m m o n consent.

O n a n e w tack, an apparatus was fabricated to allow iodine vapor

to pass over molten s o d i u m as shown i n

Figure

2 „ S o d i u m metal

was

placed in the

apparatus

in

the

dry box, as

was iodine. T h e

sodium

rested

on the horizontal

surface

between the vertical tubes, and the

iodine was placed in one

vertical

tube.

Sublimation o f iodine could


36/165

PYREX

APPARATUS

ALL JOINT

No

CHARGE IN BOAT

TO

VACUUM

O R

HELIUM

60mm

TO

AC

« S T 60-

mm

DRY

ICE

ACETONE

DEWAR

TRAP

CHARGE

VAR I A C

—

CONTROLLED

FURN CE

Figure

2.

U tube apparatus

cross section


37/165

be

carried

out at

one tube

with heat f r o m

a furnace,

and condensation

occurred at

the

other vertical tube with liquid nitrogen.

T h e main difficulty with

this

m e t h o d was that it was difficult t o

obtain a clean

sodium

surface

to

b e exposed to the iodine vapor, which

limited the reaction quite severely.

A t t e m p t s to

overcome

this

difficulty b y

designing a boat to contain

the

sodium and

heating

the sodium

to a

higher temperature with heating

tape

and

a

split

furnace

were not

successful„

A

two

level

boat with a

stainless steel wool filter

to remove

s o d i u m

oxide f r o m

the

sodium met

al as shown

in

Figure 3

did

not

operate as hoped, and washing s o d i u m

metal

in

various

organic

solvents to

remove

the

mineral oil

protectant

did not help.

T h e

sodium

oxide

crust

:

which

readily

formed,

prevented

signif

icant

contact between

the

iodine

vapor

and the sodium, though each

attempted reaction

run

produced a small quantity o f sodium iodide, as

shown b y

strong

sodium

and iodide

ion tests A quantitative determin-

t

ation

o f

the

percent iodide

in one such

run

gave

36,37 % .

I t

was f o u n d

during these experiments

that a

nitrogen gas

p u r g e

f o r m e d a gray deposit o n the

sodium

surface,

and

that this material

was

sodium

nitride. F o r

this

reason, helium was used

to

protect

the

reactants.

'

T h e last

traces o f

oxygen and nitrogen were r e m o v e d

f r o m

•

the helium b y passage

over

heated u r a n i u m

turnings (77). .


38/165

3 2

NICKEL

WIRE FORMING

F L O O R OF TOP LEVEL

F O R PLACEMENT

.OF METAL W O O L

FILLER

TOP

VIEW

i uu mm.

30mm

SIDE VIEW

50mm

-WIRE FLOOR

SOUD F L O O R

F i g u r e 3.

Two-level nickel

boat


39/165

33

Another

line o f attack on the liquid

sodium-vapor

iodine reaction

was

to bubble

iodine

gas through molten sodium.

A n apparatus m a d e

for

this attempt

used

a movable iodine

delivery tube

based

on stirrer

de

sign, and had

an inlet

and

outlet for h e l i u m p u r g e gas,

A

separate

iodine

generator

was the source o f iodine vapor, and the delivery tube

was

heated

with

heating

tape, as

shown

in

F i g u r e

4, Plugging o f the

'iodine delivery

tube u n d e r

the

surface

o f

the molten

sodium

kept

this

m e t h o d

f r o m

working,

even

though

the

sodium and

iodine were

well

above

the melting

point

and

sublimation

point,

respectively. A n

analysis o f

a

product obtained

b y

this m e t h o d was done

on

a portion

that

obviously-had reacted, and does not take into account the

large

amount

o f

completely

unreacted sodium. Most o f

the sodium

that

did

react

did

so

with

oxygen

and

water

vapor

to

f o r m

s o d i u m

hydroxide.

Table 5.

Reaction

analysis;

iodine

bubbled through molten sodium

Substance

Percent

present

Sodium iodide; V o l h a r d

analysis

Sodium

hydroxide ; standard acid

S o d i u m ;

displacement

o f water in buret

3.12

7 7 . 6 7

19.21


40/165

34

V

X

2

INLET FROM GENERATOR

INLET

X

OUTLET

BALL JOINT^

1

TO AC

AND

VARIAC

PYREX

APPARATUS

SPLIT

FURNACE

MOLTEN

SODIUM

CHARGE

60mm

Figure 4. Cross section of apparatus

f o r bubbling

iodine into liquid sodium


41/165

35

. T h e

reaction between

vapor sodium and vapor

iodine

This set o f

conditions

put the elements in theif most reactive and difficult-to-han

dle-form.

A s a

first

trial, the c o m m o n lecture

demonstration

f o r the production

o f

sodium chloride f r o m the elements was adapted to substitute

iodine

f o r chlorine. I n this method, sodium which is b u r n i n g on a deflagrat

ing

spoon is thrust into

a

chlorine (iodine)

atmosphere. À

white

vapor

is

produced that upon

condensation

gives

strong

s o d i u m

and halide

tests.

Naturally

this

m e t h o d f o r m s

a

rather

appreciable

a m o u n t

o f

s o d i u m

hydroxide along with

the

desired product. T o avoid this, a nitrogen

gas

flow was directed into the

vessel

containing

the iodine,

but

the

situation was

n o t

improved very much.

In a determination

o f

the

purity o f

the s o d i u m iodide produced, a

quantitative

analysis

o f

the

product

was made. This

technique was

necessary because

the

sodium was not

weighed

prior to the reaction,

and some o f the sodium iodide

produced was

lost to the atmosphere and

was n o t

condensed. It was

therefore n o t

possible to calculate

the

yield.

T h e

results o f a typical run are shown

in Table

6.

A n o t h e r method

used

to test the vapor phase

reaction

utilized an

apparatus

made

f r o m

Pyrex

and

consisting o f a

vertical

a r m for sodium

and

a

horizontal a r m

for iodine. These vapor

generation

areas were


42/165

36

heated

with tube

furnaces,

and

the whole

apparatus

was evacuated to

-

5

a

pressure

o f

2

X

1 0 .

millimeters

o f

mercury.

Heating

above the

sublimation temperature

o f

iodine

caused transport o f tnat element, b u t

this

was

n o t successful with sodium.

Table 6. Analysis

o f

s o d i u m iodide p r o d u c e d b y

b u r n i n g sodium

in an

iodine atmosphere

3

C o m p o u n d Percent present

S o d i u m

iodide 97.02

S o d i u m h y d r o x i d e 2.98

Total

100.00

S o d i u m

iodide determined b y the

Fajans

m e t n o d ( 5 5 , p.

335),

and

s o d i u m hydroxide

determined

b y standardized nitr ic

acid.

A d d i t i o n a l synthesis

w o r k

T h e

reaction

between liquid

sodium

and

vapor

iodine

Maintenance

o f

a

clean s o d i u m surface was the aim o f

an

experiment utilizing the low-

density

properties

o f

helium gas. A n apparatus shown in Figure

5 was

constructed, set up and rotated 180° in the clamp. T h e n the helium

gas

purge,

which

passed

t h r o u g h a

heated tube o f u r a n i u m turnings as


43/165

»?

•s»

ç >

cw


44/165

described

above,

filled the

tube

b y displacing the air. . A f t e r fifteen

minutes o f

flushing with

helium, the bent tube

was rotated

to the pos

ition

shown in F i g u r e

5 ,

which retained a pocket

o f

h e l i u m

gas at

the

.closed

end

o f

the

tube,

even t h o u g h

this portion o f

the

tube

was n o

longer

the

hignest point

o f

the

apparatus. A

piece o f s o d i u m metal

was cleaned and

pushed

to the protected

e r : d

o f

the

bent

tube.

T h e

sodium

was

melted with a

Bunsen

flame, whereupon a black material

f o r m e d

on

the

surface and

it

was

n o t

possible

t o

keep

the surface

bright, even

b y shaking

the apparatus

to

try

to

clear the

film. Iodine

was added by

means

o f a polyethylene cup o n the

end

o f a wire.

N o

obvious

reaction

t o o k place, though the

iodine

did volatilize. T h e

p r o b l e m is that

the

sodium oxide and other impurities f o r m e d

should

b e

dense

enough

to

go

to

the

b o t t o m

o f

the

puddle

o f

s o d i u m

metal,

but

are

held

in place

b y

surface

tension.

In

another

trial with

the bent tube apparatus, the

tube

was evac

uated

before adding

the elements

and

refilled

with

helium

while

in the

inverted position d escribed

above,

This process was

repeated

three

times

and

the tube was rotated

back into the position shown in Figure

5.

When sodium was added and

melted,

the

surface stayed

m u c h

cleaner

than

in

the previous

trial.

Iodine was

added,

and the

tube

was

heated.

N o t

much apparent

reaction

occurred.

This m e t h o d using the

bent

tube

did

not

produce

satisfactory

results, and

was

abandoned.


45/165

T o

o v e r c o m e the chief p r o b l e m

o f the

m e t h o d

described

above, a

new rotating

double tube apparatus was designed and constructed, and

is

shown

in F i g u r e

6. This

apparatus

had

a reaction

chamber and

a

separate

chamber f o r melting sodium metal. When the molten s o d i u m

was

transferred to t h e

reaction

chamber, i t

was hoped that the oxide

film and

other

impurities

w o u l d b e left

behind.

T h e

m e t h o d o f operation f o r the new apparatus was to flush it

with

purified

helium,

then

to

add

a

cleaned

piece

o f

s o d i u m

metal

to

chamber

A , with the apparatus

rotated

so

that chamber

A

w o u l d b e

in

a

vertical

position.

. A f t e r melting the sodium with a B u n s e n flame, the

appartus

was rotated in a counterclockwise direction to

p u t

chamber B

in

a

ver

tical position.

When

this was done,

thé

molten s o d i u m

flowed t h r o u g h

the

connecting tube

to the reaction

chamber,

chamber

B .

T h e

addition

o f the iodine t o o k

place

in

a

similar manner, except that melting was

n o t

necessary.

Flushing

w i t h

purified helium t o o k place at all times,

and air

a n d water vapor

were

removed b y

evacuating the whole

apparatus

prior

to

use.

D u r i n g a

r u n with this apparatus, the sodium metal t u r n e d black

when

placed in chamber A. Melting

followed, which cleaned t h e

sur

face o f

the

sodium considerably. Transfer

to

chamber B was facilitated

b y wrapping heating

tape

around the connecting tube. When

iodine

was

added to the vessel, and the reaction chamber

heated, a

flame occurred


46/165

40

TO

VACUUM

He INLET

BALL

JOINTS

CHAMBER

PYREX

APPARATUS

.25_

mm

CHAMBER

Figure

6.

^ R o t a t e d double

tube

apparatus


47/165

and

small

deposits o f salt

f o r m e d o n the

walls

o f

t h e reaction chamber.

B u r n i n g pieces o f

s o d i u m devitrified and cracked

t h e

walls

o f this

cham

ber and consequently ruined the apparatus. T h e a m o u n t

o f

sodium

io

dide produced

b y this

reaction

was small, and

a large

a m o u n t o f sodium

hydroxide was

present

along with

unreacted

sodium.

T h e

chief

con

clusion

f r o m this w o r k

was

that P y r e x glass is n o t a suitable container

material f o r

the reaction

between s o d i u m

and iodine.

P y r e x will

not

contain b u r n i n g

sodium.

Still

another method which was used to

p r o m o t e the reaction

between

liquid

s o d i u m

and vapor iodine

was

that o f

adding

the elements to sod

ium

iodide

i tself.

S o d i u m

and iodine

were

placed in a nickel crucible.

S o d i u m iodide was placed

o n top

o f this mixture o f

the

t w o elements.

T h e

first

t i m e

this

method

was used

a violent

reaction

t o o k

place and

sputtered sodium iodide out o f

the

crucible. This reaction,

however,

was

attributed

to the

presence o f

water

in

the

sodium iodide. F u r t h e r

runs utilized dried

s o d i u m

iodide which had

been

under

v a c u u m

f o r m o r e

than a day. Under these conditions, no reaction was

observed.

T h e

iodine

all

volatilized before

the

s o d i u m reached a reactive stage.

This difference

in

volatility had been

the

basic p r o b l e m with several

attempts,

and

is no doubt the

reason

f o r the

lack

o f success cited

in

the literature f o r the direct synthesis o f sodium iodide.

T h e

last method used

f o r

this

type

o f

liquid

sodium-vapor i odine


48/165

was

a modification to prevent occurrence o f the

problems

preventing

success

in

the

last two examples cited directly above. T h e apparatus

was

m a d e

o f

nickel

to overcome

the p r o b l e m

o f sodium attacking a

glass

container,

and

was sealed

to keep t h e

elements

together wnile

heating

them. Disadvantages o f this design are that nickel is n o t

entirely inert to the attack o f

iodine

vapor,

and

pressure built u p in

the apparatus due

to

volatilizing iodine. T h e pressure

is further

increased by the

h i g h heat

o f

reaction

o f

s o d i u m and iodine. This

piece o f equipment i s shown

in

F i g u r e 7. T h e lid contained a groove

to

accept

an "O" r i n g as a

seal, and

was held in place b y a bail fas

tened

to

the

sides o f

the nickel vessel.

T h e lid

could b e

tightened

d o w n b y

screwing

a

b o l t in the bail against the l id. ' A n

auxiliary lid

with

an

entrance tube

was

available

f o r

evacuating the

apparatus

o r

flushing with

helium.

T h e apparatus was loaded

with

iodine after

it

was evacuated and

flushed

with helium.

Next,

a piece

o f stainless steel

w o o l

was

stuffed

in the

container to

f o r m

a bed f o r the s o d i u m and to filter

out impurities

when the

sodium

was

melted.

Lastly, a piece

o f

s o d i u m

was added,

the

"O"

ring

lid put

in

place,

and

the lid tightened. A l l possible operations

were carried

out under the protection o f

à stream

o f purified

helium.

T o start

the reaction, a Fisher b u r n e r

was

used to

heat the

walls o f

the container.

This treatment melted

the sodium

and

allowed i t to r u n


49/165

43

ADJUSTING

BOLT

BAIL-

BAIL

SUPPORT-WELDED

BOLT

COPPER

COOLING

COILS

WATER

OUTLET

WATER

INLET

40m m.

NICKEL

VESSEL

No

AND lo

CHARGE

F i g u r e 7.

"O"

ring

sealed

nickel apparatus


50/165

44

down

t h r o u g h

the

stainless

steel wool filter

and

come into contact

with

the

iodine.

While

preparing to

heat

the resulting mixture o f the

elements, the

"O" ring

seal failed and released

a cloud o f

iodine vap

or. T h e seal was destroyed b y the action o f h o t iodine which m a d e it

hard and brittle.

A coil o f copper

tubing

was

soldered around

the t o p o f the

vessel

just below the "0" ring

seal

area

to

protect the seal

f r o m

heat.

In

the

next

trial,

the

vessel

w o r k e d

quite

well.

T h e

melting

o f

the

sod

ium to

allow i t

to pass

through the filter and

further

heating

o f the t w o

elements did

not

affect the seal. U p o n opening the container, it was

found

that

most

o f the

sodium and

iodine did

n o t

react.

A

greenish-

white

chalky

p o w d e r . , which

was in the b o t t o m o f the

vessel,

turned

into

a

mossy appearing

precipitate

when the products were

dissolved

in water.

T h e

solution was y e l l o w and the precipitate gradually

turned brown,

indicating that iodine

was dissolved in the solution.

A

test for

nickel

ion, p e r f o r m e d b y adding

a m m o n i a

and dimethylglyoxime,

showed

the

presence

o f

a moderate amount. P r i o r

to

this test ,

iodide

ion, which appeared

to

interfere, was

removed

with silver nitrate.

Silver

ion

w o u l d

also

interfere

b y

reacting

with ammonia, so silver

ions

were

removed with potassium

chloride

solution. A l l precipitates

were discarded

and

the

treatment-had the effect

o f

removing the iodine.

This trial added nickel

to

the product,

and

was n o t tried

again.

•


51/165

Analysis

o f

the

product

f r o m the above

reaction showed

i t was quite

impure.

The

m e t h o d

o f analysis

was used with

a

large n u m b e r o f prod

ucts obtained

and

is described in detail.

Each product was

dissolved

f r o m

the reaction

vessel with water.

This solution

was

gently boiled

over a

Fisher

b u r n e r until dryness.

Still

m o r e heating

often released a

small

amount o f

iodine,

and

in

m a n y

cases,

turned a

rather dark-appearing

product

into

a

brilliant white

mat

erial.

I t

must be

said

that

this

treatment

was

happened

o n

at

least

partially b y mistake, when a beaker containing a product inadvertently

was

boiled to dryness and n o t noticed unti l the material had been heat

ed

quite

strongly.

A f t e r a product material

cooled,

i t

was

placed in a

weighing bottle and further dried in

an

oven operating

at

1 1 0 °

G

f o r a

period

o f

at

least

twelve

hours.

Samples

o f

the

product were

titrated

with standardized solutions o f nitric acid and silver nitrate for the

determination

o f

sodium hydroxide and s o d i u m iodide.

The

nitric

acid was standardized against

p r i m a r y

standard tris-

hydroxymethylaminomethane

that

had

been dried in a v a c u u m desic

cator,

using metnyl purple

as

the indicator.

The

adsorption m e t h o d

was u s e d

1

t o

determine

iodide. T h e silver

nitrate solution

was stand

ardized

against

weighed

samples o f

oven-dried potassium

iodide. In

this case, 5 milliliters o f 1 % dextrin solution and 8 drops o f a 0.1 %

eosin

solution were added to each portion. Dextrin

was

used

as a


52/165

protective colloid to keep the

resulting silver

iodide

in a

finely

divided

state,

and eosin i s

highly

colored when silver

salts

are

present in ex

cess

in

a solution containing silver

iodide,

thus indicating the

end

point(55 , p. 335).

T w o samples o f

each

product were weighed, with b o t h hydroxide

and iodide determined o n the

same

sample. T h e h y d r o x i d e

is

titrated

first, using

phenolphthalein

as

an

indicator.

T h e n the

adsorption

method

m a y

be

used

to determine

iodide

content, because the

phenol

phthalein is new in the colorless f o r m

and

eosin works

as

the iodide

indicator

even in acidic solutions.

The

calculations

p e r f o r m e d

follow this

scheme:

the normality

and

volume o f

standardized

nitric acid used

allow

calculation o f

the weight

o f

sodium hydroxide

present

in

the

sample.

This

weight

o f

impurity

is

then subtracted f r o m

the

weight o f

the

sample to obtain a weight which

should b e

entirely

made u p b y

sodium iodide.

N e x t

normality

and

v o l u m e

o f

standardized silver nitrate

are used to

calculate the n u m b e r

o f

equivalents o f sodium

iodide that

are present. T h e

n u m b e r o f equiv

alents and the

corrected sample weight

are used to

calculate

the

cor

responding

equivalent w ô à g h t o f

the

sodium

iodide found.

This equiv

alent

weight, if the sample is pure sodium iodide, should equal the

equivalent weight o f

anhydrous

sodium iodide:

149.92. Sample cal

culations

follow f o r the

reaction o f sodium

and

iodine

in

the case o f


53/165

47

the reaction

o f s o d i u m

and iodine in

the nickel

apparatus

sealed with

an

"O"

ring,

which is described above

as the last

liquid

sodium-vapor

iodine

reaction.

.

Table 7.

Sample

p u r i t y

calculations f o r

a

direct synthesis

p r o d u c t

V a l u e Sample

1 S a m p l e 2

Weight

o f product

taken

v

Milliliters

o f

nitric

acid used

Equivalents

o f nitric acid(N=

0.09631) used;

equal

to

equivalents o f

s o d i u m

hydroxide

present

Weight

o f sodium hydroxide f o u n d

0.2682 grams

12.53

0 . 0 0 1 2 1 4 3

0.0453 grams

Corrected weight o f

sample

( w e i g h t minus s o d i u m hydroxide)

0.2229

grams

Milliliters

o f

silver nitrate used Void-over

Equivalents

o f silver nitrate used

( N = 0 . 1 1 2 5 2 )

; equal to equiva

lents o f sodium

iodide

V o i d

Equivalent

weight

o f sodium

iodide -

V o i d

0.

2 2 0 1

grams

11 . 2 0

0 . 0 0 1 0 8 5 4

0.0405 grams

0.1796 grams

5.54

0 . 0 0 0 6 1 3 2 3

288.12


54/165

This table o f calculations shows that experimental titration tech

nique was

not o f the

best

order, due t o the p r o b l e m w i t h the first sample,

but

this

case is the

first

one described with regard to

synthesis

tech

niques

and

is

used for

that reason. T h e

equivalent

weight

obtained also

shows that the sodium iodide was quite impure, as already indicated

above in the description o f the method. T h e

impurities

included nickel

f r o m the vessel, and i t

can

be noted that

there

were m o r e equivalents o f

sodium hydroxide

present

than there

were

equivalents

o f

s o d i u m

iodide.

Checks

were m a d e

to

see i f the

above

technique o f determining b o t h

hydroxide

and iodide

in

the same sample was a valid

method. Solutions

o f sodium hydroxide and sodium iodide

were

m a d e up. T h e s o d i u m

hydroxide

solution was protected

f r o g i

carbon dioxide b y forcing air

entering

the

container to

pass

t h r o u g h

an Ascarite

drying

tube.

Sam

ples o f sodium hydroxide and sodium iodide were

taken

with a pipette

in a 1 : 5 ratio, and

phenolphthalein was added to exactly

duplicate

experimental

conditions. Results are

shown

in

Table 8.

T h e very

small

difference

between titrations

o f

reagents, separately

and

together,

ù.dicates

that

the procedure is

justified

and that the presence

o f phenol

phthalein does not affect the

result.

A

large n u m b e r

o f

trials

were m a d e to see if the method o f treatment

o f products o f direct synthesis was

a valid

one

and

to

check

the m e t h o d

o f calculation.


55/165

4 9

Table 8. Titration o f

sodium hydroxide

and sodium iodide on a k n o w n

sample

C o m p o u n d

f o u n d

Combined sample

3

Separate sample^

S o d i u m hydroxide; milliliters

o f

nitric

acid

required

#1-

2.

2 3

# 1-

2.

2 2

# 2-

2 . 2 4

# 2-

2

. 2 2

#

3-

2

. 1 6

S o d i u m iodide; milliliters

o f silver nitrate

required

#1-

9 .

5 0

#1-

9 . 44

# 2-

9, 45

# 2-

9,

50

#

3-

9.

50

# 3-

9. 46

^Containing

10.00

milliliters o f 0.099

8 8

N

sodium iodide, 2.00

milliliters

o f 0 . 1 1 1 1 N sodium

hydroxide,

and

two

drops

o f

phenol-

phthalein.

^ S o d i u m

hydroxide samples contain 2.00 milliliters o f

0 . 1 1 1 1

N

sodium hydroxide and

sodium iodide

samples contain 10.00 milliliters

o f

0.09988 N sodium

iodide.

Products were

crystallized

f r o m

ethanol

during

the

purity

trials,

but initial trials

indicated the presence

o f

the dihydrate

o f sodium io

dide.

Titrations were done

to

determine

the base

content

with

nitric

acid standardized as

described

above,

and

to

determine

iodide

content


56/165

with

silver iodide b y

the

Fajans or adsorption m e t h o d ( 5 5

,

p. 335). T h e

dihydrate

f o r m would cause great problems

in

crystal

growing,

because

dihydrate

decomposes

at

elevated temperatures.

This

in turn would

i-""

lead to the formation o f hydroxide in the crystal and

the

release

o f

ior

dine

gas.

Other

trials

were made to see i f the

weighing

technique was

ade

quate

to

obtain a condition o f constant

weight.

A preliminary investi

gation

showed

that

sodium

iodide

picks

u p

moisture

f r o m

the air

o n

long exposure, especially in h u m i d

weather

and in p o o r l y sealed con

tainers.

A sample o f

commercial

sodium iodide lost

approximately

2 0

%

o f i ts weight on oven drying, but then remained

at

constant

weight f o r f o u r

days even

though the seal on the weighing bottle was

n o t

air

tight.

Another

sample and

i ts

changes

in

weight

with

d i f y

ferent treatments is shown in Table

9 .

T h e next

set

o f

trials was to test

the

working

u p o f

the

products

obtained b y direct synthesis. One sample

o f

sodium iodide

was

treat

ed as shown in

Table 10.

Since the samples

shown

in

Tables 9 and

10did n o t contain

sodium

hydroxide, while

typical

products

did, a

product o f direct

synthesis

was

also

tested to determine the

effects

o f recrystallization. Tables 1 1 and

1 2 are similar in f o r m

to

Tables 9 and 10,

except

that sodium hydroxide

has

been added

to the

samples

in Tables 1 1 and 12.


57/165

5 1

Table

9. Testing

f o r constant

weight

with

a

s o d i u m

iodide

sample

3

•

Steps in treating s o d i u m iodide ' Weight o f sample

1.

Oven

and v a c u u m

dried

0

2. Exposed to air, then.vacuum

dried

3 .

Oven dried

c

a

Harshaw optical

grade

crystal.

^Weighing

bottle

previously treated in a similar fashion.

^Titrated with silver nitrate and shown to be 99.62

%

sodium iodide

with

g o o d

precision

on one sample,

and

to have an equivalent weight

o f

149.92

on

a second sample.

Table 10. Testing the effects o f recrystallizing sodium

iodide

3

Steps in

treating

s o d i u m iodide W e i g h t o f sample

1.

Oven

and vacuum dried

0.8273 grams

2.

Recrystallized f r o m absolute

ethanol

0.827

0 grams

3. A g a i n recrystallized f r o m absolute ethanol 0 . 8 1 9 1

grams

(transfer

loss)

1 . 1 7 7 8

grams

1 . 1 7 5 2 grams

1 . 1 7 7 8

grams

Equivalent weight o f the Harshaw optical grade

material

was

150.17.


58/165

52

Table 1 1 .

Testing

f o r constant

weight

with sodium

iodide-sodium

hydroxide

m i x e d

samples

Steps

in treating the sample Weight o f

sample

and weighing bottle

1 . P r i o r to treatment '

6.

7 8 6 2 grams

2. V a c u u m dried 6. 7 3 0 0 grams

3

Oven

dried

6.

7 1 0 0

grams

4. V a c u u m

and

oven dried

6

.

7098

grams

5 . T w e n ty h o u r exposure to air

6.

7 2 0 4

grams

^Product o f a

direct

synthesis run

which

was

titrated w i i ' h

silver

ni

trate

and shown to have an equivalent

weight

o f 170. 31 with

fair

preclu

sion. T h e amount o f s o d i u m hydroxide f o u n d b y

titration

with nitric

acid

was

subtracted

f r o m

the

sample

weight before

calculation

o f

the

equivalent weight.

T h e results on samples f r o m experimental

runs containing

s o d i u m

hydroxide were far

less

satisfactory than

those

without

sodium

hydrox

ide. This material with sodium

hydroxide

is

far m o r e hygroscopic, as

evidenced

b y

the weight increase

in

Table 11 and the

h i g h

equivalent

weight ih Table 12. D u r i n g

the

weighing processes, the sample mat

erial

the direct synthesis and purification of sodium iodide_2

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