Purification and growth of succinonitrile crystals

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Purification and growth of succinonitrile crystals

A. Rivière, C. Marhic, M. Meyer, M. Lancin

To cite this version:

A. Rivière, C. Marhic, M. Meyer, M. Lancin. Purification and growth of succinonitrile crystals.

Revue de Physique Appliquée, Société française de physique / EDP, 1987, 22 (4), pp.221-225.

�10.1051/rphysap:01987002204022100�. �jpa-00245534�

Purification and growth of succinonitrile crystals

A.

Rivière,

^C.

Marhic,

^M.

Meyer

and M. Lancin

Laboratoire de

Physique

^des

Matériaux, C.N.R.S.,

1,

place

A.-Briand, 92195 Meudon

Principal

^Cedex,

France

(Reçu

^{le 9}

juin

1986, ^{révisé le 1 er}

décembre, accepté

^{le 6}

janvier 1987)

Résumé. ^- Des

polycristaux

de succinonitrile ayant ^une sous-structure stable et

reproductible

^{sont obtenus}

par

fluage

^en

compression

^à

température

^ambiante

d’éprouvettes

monocristallines. Les monocristaux sont

préparés

par la méthode de

Bridgman à partir

d’un matériau

purifié

par distillations successives ^et fusion de zone, ^contenant 50 ppm

d’impuretés.

^La

perfection

cristalline des échantillons était contrôlée par

diagrammes

de Laue en transmission obtenus dans une chambre conçue pour permettre la diffraction à basse

température.

La déformation par

fluage

^a

aussi permis

d’étudier le comportement

mécanique

du succinonitrile et de montrer

qu’il

^est

comparable

à celui des-autres solides.

Abstract. ^- Succinonitrile

samples

^{with a}

reproducible

and stable substructure are obtained

by compression

creep of

single crystals

^{at room} temperature. The succinonitrile

single crystals

^are

prepared using

^the

Bridgman

method. The

crystalline perfection

^{of the}

samples

is controlled with Laue patterns obtained in a camera

devised for low temperature diffraction. The material used for

crystal growth

contains 50 ppm of

impurities,

^it

has been

purified by

successive distillations followed

by

^zone

refining.

The creep deformation used ^to introduce the substructure allows also to

study

the mechanical behaviour of succinonitrile. The

experiments

result in mechanical

properties comparable

^to those of the other materials.

Classification

Physics

^Abstracts

81.10

1. Introduction.

This paper describes the

procedure

^{used to} prepare

polycrystalline samples

^of succinonitrile. The main achievement is the obtainement of pure

specimens

with a stable and

reproducible

substructure.

They

were

prepared

^to

study subgrain boundary

^diffusion.

Therefore

they

^{had to} fulfill the

following

^re-

quirements.

1)

^The relative misorientation between the

grains

must be smaller than 10

degrees.

^{In such a case, the}

subgrain

boundaries _{may be} assimilated to arrays ^of dislocations.

2)

^The

density

^{of the}

subgrain

boundaries must be

high enough

^{to allow the} measurement of the concentration of the

diffusing species

^{on reasonable}

depths.

3)

^The

impurity

content must be inferior to the concentration of

point

^{defects. It is difficult to}

evaluate this

quantity

^{since there is no} information available about

point

^defect concentration in the

case of

grain

boundaries. In these

conditions,

^the

only possibility

^{is to}

^take

^as

limiting

^{value the}

point

defect concentration in the bulk. The order of

REVUE DE PHYSIQUE APPLIQUÉE. - T. 22, ^N. 4, AVRIL 1987

magnitude

^{of this}

quantity,10- 4,

^{can be taken as an}

inferior limit of the

point

^defect concentration in the

grain

boundaries.

The

technicai procedure

^{used to} obtain the

plastic polycrystals

with such characteristics

depends strongly

^{on the}

specific properties

^{of the studied}

material i. e. the domain of

stability

^{of the}

plastic phase

^{and the chemical}

properties.

^The material is

hygroscopic

and may

polymerize

^at

high tempera-

ture. To avoid the contamination due to the chemical

reactivity

^of

succinonitrile,

^{most of the}

sample preparation

^is

performed

under neutral

atmosphere

or under vacuum.

The

purification

^method

using

distillation under

vacuum and zone

melting

refinement is described

iri

section 2. The

impurity

^{content of the}

resulting

material is measured

by liquid

gas

chromatography.

The details of the method used to grow

polycrystals

are

given

ⁱⁿ section 3. This

procedure

^{involves the}

preparation

^of

single crystals

^as intermediate

step.

Their

crystalline perfection

^is controlled with Laue diffraction

performed

^{at low}

temperature

^{as de-} scribed in section 4. The

polycrystals

^{are then ob-}

tained

by

creep deformation of the

single crystals.

16

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/rphysap:01987002204022100

222

This

procedure

^has

proved reproducible.

^Some

forty polycrystalline samples

have been

prepared using

this method.

They

follow the

requirements

^described

previously.

Part of them have been used for the diffusion

experiments

described in reference

[7].

2. Purification.

2.1 METHOD OF ANALYSIS. - The

purity

^{of suc-}

cinonitrile is controlled

by liquid

gas ^chromato-

graphy.

The succinonitrile

begin

^to

polymerize

^{in the}

range of

temperature

^{used for}

analysis.

^{As a}

^result,

the adits of the columns are

rapidly

contaminated

by

the

newly

^formed

polymer.

The columns are regener- ated after 12 to 15

experiments

^{in order to obtain a}

good sensitivity

^and

reproducibility

^{of the}

analysis.

The

analytical sensitivity

^{is within the} limit of 2 ppm for those

impurities

^{which are more} volatile than the

Fig. 1.

^{- Schematic}

drawing

of the distillation

apparatus

with a zone

melting

^{tube in}

filling position ;

the location would be the same for a

growth

^tube.

succinonitrile and of 25 ppm for those

impurities

which are less volatile.

2.2 METHODS OF PURIFICATION. ^- To eliminate the different

impurities

ⁱⁿ

succinonitrile,

^two

methods are

applied :

i)

Distillation under vacuum.

ii)

^Zone

melting

refinement.

Special

attention has been

paid

^for the removal of water

during

^the

purification

because succinonitrile is

hygroscopic. Besides,

^the water content has been controlled

during

^{all the}

following steps

^{of the}

sample preparation.

Succinonitrile is contaminated when it is heated in the presence of air. As recom-

mended

by

Glickman et al.

[1],

^the

filling

^{of the zone}

melting

^{tube or of the}

crystal growth

^tube is per- formed

directly

^{on the} distillation

apparatus (Fig. 1).

The commercial

product

^contains

approximately

1.5 % of

impurities,

^{of which 0.08 % is water. After}

four or five distillations under vacuum and sub-

sequent analysis,

the material contains

only

^{two or}

three hundred _{ppm of}

impurities.

It is then transfer- red

by

distillation under vacuum to a zone

refining

tube and then sealed under _argon

[2].

^The

product

^is

then

submitted to

melting

^zone

refining using

^the

apparatus

described elsewhere

[2].

After around one

hundred passages

^{of the}

melting

zone, the

impurity

concentration is measured

by chromatography.

^The

efficiency

^{of the}

purification

^is

clearly

^{visible in}

figure

^2.

The whole process, distillation ^{and zone}

refining

^is

repeated

until the total amount of

impurities

^{is less}

than 50 ppm.

Thus,

^the

purity

^{of the material}

satisfies condition 3 discussed in the introduction.

The pure succinonitrile is then used for

crystalline growth.

3.

Crystalline growth.

There are two distinct

steps

^{in the}

procedure,

^the

preparation

of the tubes

containing

^the

samples

^and

then the

growth

^itself.

3.1 GROWTH TUBES. ^- The distillation

apparatus

^is

used to fill under vacuum the

growth

^{tubes with} pure succinonitrile.

Prior to their

filling,

^{the tubes were}

placed

^{in a}

bath of silicone oil 200 and then dried at 573 K for an

hour. This is done to avoid too much adherence of succinonitrile to the tube wall and further facilitate the removal of the material.

Subsequent analyses

show that the silicone oil does not contaminate the

specimens.

3.2 POLYCRYSTAL PREPARATION. ^- Two different

approaches

^were

investigated

^{in order to} prepare

polycrystalline samples.

^The

polycrystals

^{were ob-}

tained either

by quenching liquid

succinonitrile or

by

creep deformation of

single crystals.

Fig.

^{2. -}

Impurity

concentration

profile

^{of a} succinonitrile

sample purified by

^zone

melting.

^{The curve}

gives

^the

relative concentration of the

impurities

less volatile than succinonitrile as a function of the

position along

^the

ingot.

3.2.1

Quenching.

^{- The}

growth tube,

^{filled with}

succinonitrile,

^{is heated to 366 K and then}

quenched

at 270 K. The

resulting samples

^are

polycrystals presenting only occasionally

^an

appropriate

^substruc-

ture. For this _reason, the creep process ^was

preferred

to introduce the substructure.

3.2.2

Creep.

^{- Under well defined} conditions the creep deformation of

single crystals

^{results in}

polyc- rystals

^{with a}

reproducible

substructure

correspond- ing

^{to our}

requirements (§ 1).

^This method has

already

^{been used to} prepare

pivalic

^acid

polycrystals [3],

^{it is now}

applied

^to succinonitrile.

The first

step

^{consists in}

growing single crystals by

the

Bridgman

^method

using,

^the

apparatus

^described

in reference

[2].

^In the range of the

melting point,

the

temperature

is monitored with an accuracy of 0.1

K,

^the

gradient

^{is 12 K crri}

1.

The

crystals

^thus

obtained are flawless and

homogeneous.

^X ray Laue

patterns (cf. § 4.2)

^{further obtained on these}

samples

demonstrate that

they

^are

single crystals.

These

crystals

^{are cut with a solvent saw into}

cylinders

^{of 15 to 20 mm}

long.

^The

resulting samples

are then deformed

by compression

creep ^at T ⁼ 293 K

(0.89 T/Tm).

The load en the

crystal

^is

progressively

^increased

during

^{10 min} up ^to 120 KPa. The value of the deformation e thus obtained is

roughly equal

^{to 6 %.}

The

sample

^{is then} deformed under constant load.

Stress-changes

^{were realized in order to determine}

the influence of this

parameter

^{on the} deformation

rate. Each stress

change

^{is followed}

by

^a

quasi- steady

^{state which is sometimes}

preceded by

^{a short}

transitory stage (Fig. 3).

^{The values of the stress}

exponent n

^were calculated with the law

resulting

from

steady

^state creep models where é _{is pro-}

portional

^to

un [4].

The average value is n ⁼ 5.2 ± 1.8. After deformation the

samples

^{exhibit a}

polygonized

substructure as described

in §

4.

They

were maintained at 258 K to avoid _any evolution of the substructure

by grain boundary migration.

Fig.

^{3. -} Deformation rate è of a succinonitrile

sample plotted

^{on a}

logarithmic

^{scale as a} function of the deformation £. Several stress

changes

^are

realized, they

are sometimes followed

by

^short

transitory

stages. ^{A linear} variation of é versus e is then

observed ;

it is characteristic of

quasi steady

^state creep. The ^stress values and the stress

exponents n calculated for each stress

change

^{are also}

indicated.

In all the

experiments,

the variation of e versus e were

typical

^of creep under constant load. Such a

behaviour established from creep studies ^of

metals, oxides,

ionic and covalent

crystals,

^{has also been}

observed in

pivalic acid,

^{an other}

plastic

^molecular

crystal [9].

The value of the stress

exponent n

^is

comparable

to the one obtained

by

^{Hawthorne and} Sherwood for succinonitrile

[5]

^{and to}

experimental

^{values deter-}

mined for other solids

[4] including plastic crystals [6].

The

resulting polygonized

substructure is also

typical

^{of the} deformation of solids

by

creep. These characteristics show that the creep behaviour of succinonitrile is similar to the one observed in other solids.

224

4. Control of

crystalline perfection.

The

’use

_{of creep} to prepare the

polycrystalline samples requires

^as

starting

^material

single crystals

with a

good

^and

reproducible crystalline perfection.

Several methods are used to test the

quality

^{of the}

single crystals

i.e. Laue

patterns,

^thermal

etching

associated with direct observation

by optical

^micros-

copy.

4.1 THERMAL ETCHING. ^- Thermal

etching

is per- formed

by evaporating

^the

sample

^at 293 K. Within

one

hour,

^{it is}

possible

^{to obtain}

significant etching

due to a

preferential evaporation

^{at the}

grain

boundaries and at the dislocations.

For an amount of deformation

ranging

^{from 60 to}

70 % the size of the

grains

^is

equal

^{to a few microns}

as shown in

figure

^4. Since formation of etch

pits depends

^{on the} orientation of the

grains,

the thermal

etching

^{is not uniform in a}

polycrystal.

^The

density

of dislocations was measured on

grains

^{with an}

orientation suitable for the etch

pit

formation. The order of

magnitude

^{of the}

density

of dislocations is

104 cm- 2

in

quenched samples

^{and 8 x}

^{105 cm- 2}

^for

those obtained

by

creep deformation

(Figs.

^{7a and}

b).

4.2 LAUE METHOD. - The

plastic phase

^{of the}

molecular

crystals

^is characterized

by

^{the existence}

of a

dynamical

orientational disorder which

gives

rise to an

important

^diffuse

scattering

^{in the} X ray diffraction

patterns.

^{Of course, this} effect is more

pronounced

^at

high temperature. Moreover,

^{the X}

ray

scattering

^{factors of the atoms}

constituting

^the

succinonitrile molecule are low. Therefore the number of reflexions observed on a Laue

pattem

^is limited and their

intensity depend

^{on the}

tempera-

Fig.

^{4. -}

Optical micrograph

^{of a} succinonitrile

sample

deformed

by compression

creep. The

subgrain

^boundaries

were revealed on a

planar

^surface

by

^thermal

etching.

^The

parallel

^{scratches are due to the razor} blade of the microtome used to cut the

sample.

Fig.

^{5. -}

Photograph

^{of the Laue camera used to}

perform

diffraction patterns ^{at low} temperature :

a)

X ray film

holder ; b) collimator ; c) goniometric sample

holder ;

d) liquid N2

trap ;

e)

cooled gas

inlet ; f) thermocouple ; g) slide ; h)

X ray tube.

-f

Fig.

^{6. - Laue} diffraction patterns ^{obtained on} succinonit- rile

single crystals

^{at 293 K}

(a)

^{and 273 K}

(b).

ture

[8].

^{The Laue}

patterns

^{obtained at room}

temperature

^on succinonitrile exhibit a

large

^amount

of diffuse

scattering

^{and are not} convenient to

study

the

crystalline perfection (Fig. 6a).

^{A Laue camera}

has been

designed

^{in order to} realize the Laue

patterns

^{at a lower}

temperature.

^The

sample holder,

the collimator and the film camera are contained in a

device isolated from the outer

atmosphere

^{as shown}

in

figure

^{5. A} spray ^of inert gas, cooled

by liquid

nitrogen,

maintains the

specimen temperature

Fig.

^{7. -}

Optical micrographs showing

^etch

pits

^{on suc-}

cinonitrile

samples : a) quenched specimen ; b)

creep deformed

specimen.

around 273 K. The

temperature

^{of the}

diffracting sample

^is

continuously

^{recorded and} measured with

a

thermocouple.

^The

cooling

gas is dried before the

injection

^{in the} camera, in order to

prevent

^the formation of ice on the

sample.

^{When the}

tempera-

ture is lowered to 273

K,

the thermal

scattering

^is

sufficiently

^{reduced to}

improve significantly

^the

contrast. The Laue

patterns

^{thus obtained are suit-} able to characterize the

crystalline

^{state of the}

samples (Fig. 6b).

The

crystals

^were

systematically

controlled with the Laue diffraction method before creep defor- mation.

They

^were

always single crystals

^{with a}

relatively good crystalline perfection.

^{This method}

was then

applied

^{to the}

study

^of the substructure introduced

by

creep. The examination of the

shape

and size of the diffraction

spots

shows that the misorientation between the different

grains

^{is of the}

order of 3 to 4

degrees. Considering

the size and the misorientation between the

subgrains,

the substruc- tures

resulting

from creep deformation are suitable for diffusion studies

[7].

5. Conclusion.

The difficulties encountered in the

preparation

^of

pure

crystals

^{do not lie}

generally

in the choice of the methods but

mostly ^io

^their

application.

^{This is}

particularly

^{true in the case of} succinonitrile.

Exper-

imental

procedure,

which calls on classical technics of

purification, analysis

^and

growth, requires rigor-

ous

specimen preparation.

^The

single crystals

^which

are thus obtained are of

good crystalline perfection.

The deformation of succinonitrile

crystals by

creep introduces both a stable and

reproducible

^substruc-

ture in all the

specimens (40). Moreover,

^the pro- cedure used to prepare the

polycrystalline samples provided

^useful informations on the mechanical behaviour of the material.

References

[1] GLICKSMAN,

^M. E., SHAEFER, ^{R. I. and} AYERS, I. D., Metal. Trans. A 7A

(1976)

^1747.

[2]

BRISSAUD, M., DOLIN,

C.,

^LE DUIGOU, J., ^MCARDLE B. S. and SHERWOOD, J. N., ^J.

Cryst.

^{Growth 38}

(1977) 134.

[3]

^BRISSAUD, M., MARHIC, C., RIVIÈRE, ^{A. and}

PHILIBERT,

^{J., Philos.}

^Mag.

⁴⁴

(1981)

^815.

[4]

POIRIER, ^J. P., Plasticité à haute

température

^des

solides cristallins

(Ed. Eyrolles-Paris) 1976,

91 ff.

[5] HAWTHORNE,

^{H. M. and} SHERWOOD, J. N., ^Trans.

Farad. Soc. 60

(1970)

^1712.

[6]

^The

plastically crystalline

state, Ed. J. N. Sherwood

(Wiley) 1979,

p. 46.

[7] BRISSAUD-LANCIN,

M., MARHIC, ^{C. and} RIVIÈRE, A., ^Philos.

Mag.

^{A 53}

(1986)

^61.

[8]

FONTAINE, ^{H. and} BEE,

M.,

Bull. Soc. Fr.

Minéralog.

Cristallog.

⁹⁵

(1972)

^441.

[9] BRISSAUD-LANCIN,

M., RIVIÈRE, A.,

unpublished

results.